CA1141695A - Magnetostrictive alloy thin film electroplating - Google Patents

Abstract

MAGNETOSTRICTIVE ALLOY THIN FILM ELECTROPLATING
METHOD
Abstract of the Disclosure A thin film of low magnetostriction Permalloy* 80%
nickel - 20% iron ? 1% is electroplated onto a substrate in a bath having a ratio of from 5.8:1 to 23:1 ratio of Ni to Fe ions with a plating current density from 10 ma/cm2 - 200 ma/cm2 when plating in sheet form or an Ni/Fe ratio of from 25:1 to 86:1 with a current density of from 2 ma/cm2 - 60 ma/cm2 when plating through a mask. The fluid in the system is constantly mixed, replenished with fresh iron, acid, and other reagents, is adjusted in temperature and subjected to a continuous laminar regime of mixing. The Fe++ ion concentration required is inverse to the circulation of bath fluid across the substrate.
Fresh solution is added to the bath from a reservoir where the above adjustments are made. The inlet for the fresh solution is at the lower end of the plating chamber and directed at a bath mixer which includes a slot through which the fresh solu-tion is directed to optimize mixing in the plating chamber.
Complexing agents are avoided. High speed plating is obtained with about 24.4 g/l of Ni++, 1.05 g/l of Fe ++, 25 g/l of H3BO3, 0.2 g/l of Na saccharin and a pH of 1.5 to 3.6.
* Trade Mark

Description

Background of the Invention : Field of the Invention The invention relates to chemistry, involving electrical energy and more particularly, electrolytic cell apparatus with an agitator and a solution controlling system.
Description of the Prior Art United States patent No. 3,652,442 of Powers et al entitled "Electroplating Cell Including Means to Agitate the Electrolyte in Laminar Flow" shows a bath container including .

'~, ~

. .

s 1 a reciprocating arm with a s~irring paddle composed of a

2 base portion triangular ln cross-section wlth sharp edges

3 facing forward and back to minimize turbulence and an apex

4 in the center pointing upwardly which is relat~vely blunt. A
transverse member is spaced above the base portion having an 6 inverted form of the same cross-section so the base member 7 and the transverse member define a slot through which the 8 fluid near the base of the bath container can pass as the 9 paddle is reciprocated back and forth across the base of the container to stir the electrolyte. However, this patent ll does not provide any means for circulating or replenishing 12 the bath. Tha patent descrlbes a bath with 109 g/l of NiC12 6H20, 13 3.88 g/l of FeC12 4H20, 12.5 g/l H3BO3, 0.4 g/l Na Lauryl 14 Sulfate, and 0.5 g/l saccharin, in a magnetic field of 40 Oe at a bath temperature of 20C by means of the continuous 16 plating technique with continuous agitation with the paddle, 17 for plating a flat sheet. With respect to the above formulation, 18 -for plating a flat sheet, the nickel-to-iron ratio of ions lg is believed to be excessive. On the other hand, the plating rate for deposition into photoresist mask defined patterns 21 is not defined at all.
22 United States patent No. 3,317,410 of Croll et al 23 for "Agitation System for Electrodeposition of Magnetic 24 Alloys" shows a plating system with continuous circulation of fluid and temperature control, where the solution impinges 26 at right angles onto the cathode, which is uniform or very 27 small areas only.
28 United States patent No. 3,649,509 of Morawetz et ~9 al for "Elect odeposition Systems" includes means for recycling fluid through a conduit in~o which heat, acid and specific 31 gravity additives are applied. The system ~ncludes no 32 paddle, the fluid is admitted far from the substrate to be 33 plated, no ions to be plated are added7 and no ~eaching Yo975-065 2 relative to Permalloy alloy is included. Measurernent is auto-matic and continuous, but adjustment is manual and intermittent.
Furthermore, manual adjustment i5 unreliable, requires labor and there may be a long response time in comparison to the plating time, and ~here may be resulting large fluctuations in solution temperature, pH and specific gravity. Also, specific gravity is not a correct measure of the rate of consumption of reagents comprising the alloy being plated and, in particular, of iron which is the most sensitive reagent in terms of main-taining a constant quantity level.
U.S. Patent No. 3,505,547 of Ambrosia et al teaches a bathfor depositing Permalloy alloys in which Fe ions are in a concentration in the range of 10 to 5 x 10 mole per liter and Ni ions are in a concentration of 10 to 5 x 10 mole per liter, such as 0.2 mole (52 grams) NiSo4, and 0.2 mole (55 grams) FeSO4 per liter. In another example, it teaches use of 0.4 mole (105 grams) NiSo4 and 0.1 mole 127.8 grams) FeSO4.
In still another case, 0.4 mole ~105 grams) NiSo4 and 0.2 mole (55 grams) FeSO4 are provided. In each case, 10 grams of H3BO3 were used along with metallic ion additives with negative deposition potentials such that they do not codeposit in an amount of 10 to 10 mole per liter. The pH is from 1.3 to 7.
U.S. Patent No. 3,716,464 of Kovac et al teaches a method of electrodepositing Ni-Fe (80-20) alloys. It also teaches use of a NiSO4 and FeSO4 solution with concentration levels such as 20/80 and 5/95 (1/19) of (Fe/Ni) sol. with about .3417 g/l of Fe and 6.72 g/l of Ni (based on NiSo4 6H2O = 30 g/l and FeSO4 7H2O = 1.7 g/l, with a peak current density of ma/cm and with a maximum plating rate of 125 A/min). The pH is 3.0 @ 25 C and 10 g/l of NaK-tartrate is used as a complexing agent.
* Trade Mark _ _ , . . .

s -- In a publication by Bartelson et al entitled '~lectro-deposltion o~ Ni-Fe Films," a solution of 25 60 g/l of Ni as nickel sulfamate, 1-3 g/l of Fe++ as ferrous ammonium sulfate, 25 g/l of boric acid, 1 g/l of saccharin, 0.5 g/l of sodium lauryl sulfate, pH 3.7-3.0, temperature 25-30 C, cathode current density 4.3~8.6 ma/cm is disclosed. However, the sulfamate ion is a complexing agent which complexes both nickel and iron.
Summary of the Invention A nickel-iron electroplating method for coating a sub-strate including means for electroplating nickel-iron alloy films onto a sheet substrate of a metallic material employing a plating current density of about 2 - 200 ma/cm2, and a plating bath fluid having an Fe++ ion concentration of about 0.3 g/l to about 14 g/l, an Ni + ion concentration of about 7 - 44 g/l, a pH of about 1 - 3.6, and maintained at a temperature of about 20 - 35C, wherein Fe++ ion concentration required for plating is inverse to circulation of said plating bath fluid across said substrate, wherein said bath fluid has a nickel-iron ratio of about 5.8:1 to 23.1 or 25:1 to 86:1.
In accordance with this invention a nickel-iron electro-plating system is provided including cell means for containing a plating bath, an anode, a cathode to be plated with a nickel-iron alloy comprising on the order of 20% iron, + about 1%.
The cell includes first and second vertical end walls, means for holding a wafer to be plated in the cathode of the cell with the surface to be plated supported facing the anode. A
reciprocable mixer is provided for agitation without substantial turbulence supported by bearing means for providing longitudinal stirring action by reciprocation between the end walls cyclical-ly over the surface of the cathode: The mixer includes a pair of parallel transverse blocks having a substantial slot there-_ . .

3~

1 between. Each block has a symmetrical wedye shape with sub-stantial opening defined between the blocks. The blocks have sharp edges facing the directions towards which the blade is adapted to reciprocate. An inlet YO9-75-065 4a '~
.,~

1 to the cell exists in one of said end wall~s aligned with the 2 cathode surface whereby the lnlet is adapted to pass fluid 3 through the slot dlrectly onto the surface of one end of the 4 cathode. A reservoir for electrolyte is provided having an outlet connected by conduit means to the inlet, and there is-6 means for pumping fluid up from the reservoir into the inlet 7 via the conduit means. An outlet from the cell at an upper 8 portion thereof high above the base of the cell has a second 9 conduit means for carrying electrolyte into the reservoir.
Preferably, a thermostatic control, a temperature sensor and 11 heating means are connected to the reservoir for maintaining 12 the reservoir substantially at 25C. A pH sensor and a 13 dispenser for dilute acid and an Fe~+ ion are provided for 14 dispensing the acid and the ion through a valve into the reservoir. Stirring means is provided in the reservoir for 16 maintaining a unifor~ set of temperature, pH, iron ion and 17 related conditions. For high speed plating,the electrolyte 18 comprises about 24.4 g/l of Ni , 1.05 g/l of Fe , 2.5 g/l 19 of H3B03, 0.2 g/l of Na Saccharin, and a pH of 1.5 - 3.6 with a current density from about 2 - 200 ma/cm . Further in 21 accordance with this invention, a thin film of low oagneto-22 striction Permalloy alloy 80% nickel - 20% iron + 1% is 23 electroplated in a bath ha~ing a ratio of about25:1 to 24 86:1 g/liter ratio of Ni to Fe ions with an overall plating ~5 current density of about 2 - 110 ma/cm when plating through 26 a mask. Complexing agents are avoided.
27 In prior practice in which a Permalloy alloy film 28 is plated over a cathode which has recesses and raised areas, 29 or when it is neces~ary to plate a Permalloy all~y film through a resist mask, the strong composition dependence upon small ,~' `I

s 1 rrent density variation is e~tremely undesirable. For instance, U.S. patent No. 3,853,715 tries to minimize this problem by in-tro-ducing narrow nonplated frames around each pattern. While useful for large dimension patterns, the solution given in the above-mentioned patent is impractical in the case of very small patterns such as the T and I bars in a bubble memory. Heretofore in gen-eral, the nickel:iro~ratio in baths has been 80:1, and the film composition has been strongly dependent on the current density.
In addition, the plating rate was so high that it became diffi-cult to control. Prior baths are very sensitive to small varia-tions in temperature, pH, iron concentration as well as small variations in the conditions used for agitation.

Brief Description of the Drawings . _ . . _ .
FIG. 1 shows a schematic diagram of a plating system in accordance with this invention.
FIG. 2 shows a partially cut away perspective view of the plating cell of FIG. 1.
FIG. 3 shows a perspective view of the reservoir of FIG. 1, partially cut away.
FIG. 4A shows a graph of percentage of iron by wt. vs. pH.
FIG. 4B shows a graph of percentage of iron by wt. vs.
temperature. `
FIG. 5 shows a graph of percentage of Fe in a film by weight vs. plating current per unit area relatlve to the limits of the tolerance band for producing Permalloy films of 19-21%
Fe by weight.
FIG. 6 shows a graph of the coercive force Hc, of the anisotrophy field Hk and the anisotrophy field dispersion vs. weight percent of Fe.

1 FIG. 7 sllows a graph of permeabLlity vs. frequency 2 for the sheet films plated from thls bath in ~wo di~erent 3 states of annealing.
4 FIG. 8 is a graph of isocomposition lines of FeC12 7H2O in grams per liter vs. the overall curren~ density 6 in ma/cm for plating through a mask.
7 FIG. 9 is a graph of percentage of iron in the 8 film vs. overall current when plating T and I bar patterns 9 through a mask.

Description of a Preferred Embodiment ll FIG. l shows apparatus adapted for practising this 12 invention. The plating of nickel-iron alloys is performed 13 in container 12. The walls are composed oF a dielectric 14 material such as glass or a plastic such as polymethacrylate.
A cathode 14 is composed of a metal p-late having platers 16 tape composed of an insoluble polymer adhesively secured to 17 the exterior thereof on the edges and lower surface to 18 protect it from the electroplating bath and thus giving a l9 very ill defined current density and current density distri-bution. Cathode 14 includes apertures 15 having countersinks 2-1 not exceeding 0.025" and preferably only 0.010" thickness on 22 the tops and counterbores on the bottom into which discs of 23 a substrate 17 to be plated are inserted and supported on 24 elastomertc discs 19. Discs 19 hold discs 17 in firm contact with cathode 14 to permit electrical current to flo~
26 through the contact between them. Substrate materials 17 27 which have been found appropriate include 1 1/4 inch diameter 28 sapphire, garnet, various ceramics or Si wafers covered with O O O
29 thermal SiO2 and metallized with 50A to 200A of Ti and lOOA
to lOOOA of Cu, Permalloy, Au, etc.
31 Cathode 14 is secured by screws to a dielectric 32 material base 18 which holds discs 19 in place, recessed not 1 more than 0.0025 in. from the top sur~ace of the cathode.
2 Base 18 rests upon the bottom of container 12. Electrical 3 contact to cathode 14 is provided by brass support post 20 4 which is fastened to cathode 14. Post 20 is covered with platers tape to insulate it wherever it is immersed in the 6 electroplating bath, when container 12 is filled. Post 20 7 is connected at terminal 22 to a source of electrical current, 8 not shown.
9 Anode 24 is composed of wire mesh screening, and it is supported by an insulated frame including upright 11 polymethacrylate block 40, horizontal block 41, bolts 42, 12 and polymethacrylate block 43. Anode 24 is composed of 13 inert platinum, solid nickel or of a combination of an inert 14 Pt sheet and a Ni wire mesh. Terminal metal strip 28 is connected at one end to anode 24.
16 The bath level during plating is above anode 24, 17 so anode 24 is immersed in the bath during plating. The 18 bath is constantly replenished and its temperature is controlled 19 by recirculation from a reservoir 39 where it is refreshed by dispensing acid, iron and preferably also Na Saccharin, 21 Na lauryl sulfa~e and/or [Ni ] if needed and constantly 22 stirred by a reciprocating mixer 35 otherwise referred to 23 herein as a paddle, which travels back and forth above the 24 surface of cathode 14 at an approximate distance of 1/32 ~5 to 1/8 inch for providing agitation of the bath with mlnimal 26 turbulence. The mixer 35 is carried by upright arms 34 27 which are secured at their top ends to transverse member 33 28 (FIG. 2) which is secured at the center to link arm 36 which 29 is secured by pin 37 to crank 38 which is secured to rotate about the shaft of the electric motor 32. When motor 32 is 31 energized, the arm 36 drives mixer 35 back and forth with 32 simple harmonic reciprocal motion at a substantially uniform .
- . ; . - ~

1 - rate near the center of container 12 where the substrates 17 2 are located. In addition, fresh electroplating bath fluid is 3 pumped into container 12 from reservoir 39 by means of tubes 4 67 and 68, self-primlng, positive displacement pump 66, filter 84, and tube 44. Filter g4 filters out particles of 6 1 micron size and above, preferably. When fresh bath enters 7 container 1~, it is introduced into weir 45 containing a 8 baffle 46 for diverting the bath fluid down towards elongated 9 transverse inlet 49 through wall 51 separating weir 45 and plating cell 47~ The mixer 35 is composed of two horizontal 11 transverse blades forming a slot 48 between them which is 12 close to horizontal alignment with inlet 49. The inlet 49 is 13 preferably aligned to direct fluid directly onto the upper 14 surface of cathode 14 to supply the fresh solution directly lS to the substrates 17. Each of the two transverse blades 16 has a symmetrical wedge shape with sharp opposing edges 17 facing towards end walls 51 and 52 of plating cell 47.
18 There are also two confronting points of the blades which 19 define the slot 48. As a result of reciprocation of the blades of mixer 35, the bath solution near the cathode is 21 mixed thoroughly with a substantially laminar flow having ~2 little turbulence to avoid nonuniform polarization, while 23 minimizing the formation of a depletion zone which could 24 lead to formation of an iron hydroxide precipitate with too ~5 high a pH and hydrogen evolution at the cathode and avoids 26 [Fe+ ] depletion near the cathode since the solubility 27 product of [Fe+ ]-[OH ]2 has much lower solubility than the 28 solubility product [Ni ]-[OH ]2. In addition, it is necessa~y ~9 to mix the solution to minimize pitting caused by the formatlon 30 - of H2 bubbles in identically the same spots on the surface 31 of the cathode at all times during electrolysis. The sharp 32 edges of the transverse blocks facing end walls 51 and 52 of 33 cell chamber 47 reduce turbulence by providing minimal 34 resistance to flow. The triangular cross~section of the 1 blades of mixer 35 provides the set of confronting blunted 2 apexes over which fluid Elows with a flat base. In stirring, 3 the fluid is forced to flow through slot 48 between the two 4 blocks and over the upper block to mix with the bulk of the solution in cell 47. As the mixture passes through slot 48, laminar flow at the cathode surface is restored. The fluid 7 entering via inlet 49 passes immediately through slot 48 8 when mixer 35 is near end wall 51, and then the fresh fluid 9 is carried alGng with mixer 35 as it moves towards end wall 52.
11 The current path through the plating bath has a 12 cross-sectional area substantially equal to the cross-13 sectional area of cathode 14 and anode 24, i.e., the current 14 across the electrodes 14 and 24 is confined to the boundaries thereof and is not allowed to diverge or spread in its path 16 between said electrodes 14 and 24. As a result, the current 17 density is relatively constant throughout the whole cathode 18 area 14. The current density is found to be relatively 19 uniform and well defined; and the current density value can be predicted at any point on the cathode 14, since they are 21 the same at any given point thereon. Consequently, films 22 produced in the electroplating cell of this invention are 23 uniformly thick throughout, and where metal alloys are being 24 plated, the metal compositions which are normally a very strong function of the local current density will also be 26 uniform over the entire film.
27 When the bath leaves plating cell 47, it passes 28 into outlet weirbox 54 through slot 53 in wall 52 up above 29 anode 24. A fluid level sensor 70 in weirbox 54 is con-nected by wires 71 to the operational controller portion of 31 pump 66. Weirbox 54 is connected via outlet tube 55 to 32 return the fluid by gravity from weirbox 54 to reservoir 39 33 for treatment, (see FIG. 3).

The temperature is controlled by an expanded scale mercury thermometer 56 read by a capacitive sensor 57 such as a ~her-mowatch unit made by I2R company which signals temperature control 58 via wires 11 to operate a quartz encapsulated heat-ing element 60 il~mersed in fluid in reservoir 39 and connected electrically to control 58 via wires 10. In addition, p~
meter 61 is connected by wires 26 to sensors 62 which sense the pH in the solution. The pH meter 61 is connected by wires 27 to comparator 70 which is connected to operate a valve 63 to permit a solution of Fe++ ions and dilute HCl contained in burette 65 to flow through tubes 64 into reservoir 39, as required. A stirring mechanism is included within the reser-voir 39 in the form of a magnetically driven propeller or stirrer 75 connected by magnetic drive comprising a set of permanent bar magnets 77 and 78 located respectively above and below the base 79 of reservoir 39. Magnet 78 is located within control unit 76 which provides variable speed control of turn-ing of magnet 78. Alternatively a non-contaminating mechanical stirrer can be used.
The temperature in reservoir 39 is maintained preferably at from 25 - 30C. Fluid jacket walls 80 and chamber inner walls 81 form a space filled with fluid which is further temp--erature controlled ~y pumping fluid through tubing 82 wrapped about walls 81 by means of a circulator pump, not shown, in order to maximize temperature uniformity. The cooling coils can also be inserted directly into the reservoir tank provid-ing they are noncontaminating and provided they do not interfere with regular agitation of the bath. The precise temperature used is less important than uniformity in temperature in order that the yield of the films produced will be quite uniform.

A ~ .

1 A flowm~ter 83 is connected in series with tube 44 2 to monitor the rate of flow from pump 66 into weir 45 because 3 the rate of recirculation is in part a measure of the rate 4 of agitation resulting from the solution being forced into the cell via the thin, wide, slot-shaped inlet 49.

6 Bath and Process 7 Batch-fabricated,magnetic bubble devices and 8 magnetic recording thin film heads utilize Permalloy films 9 which are in the range of 2000A to lO,OOOA thick for bubble devices and 5000A to 50,000A ~0.5 to 5 ~m ) thick for recording 11 heads. Most of these fabrica~ion processes require for the 12 films to be plated in 2000A to lO,OOOA steps in bub~le 13 devices and up to 2 to 8 ~m high steps in recording head 14 devices. Films must also be plated over cathodes in which some areas are bloc~ed off wi~h photoresist. The ver,ical 16 steps and blocked-off areas with resist introduce local 17 current density variations. Such local current density 18 variations result in local composition and thickness differences.
19 For the electroplating process to be commercially useful in fabrication of magnetic bubble devices and magnetic 21 recording heads, the plating rate of the film should be 22 reasonably high, but not uncontrollably high (local current 23 density equivalent to 5 ma/cm to 120 ma/cm ). For practical 24 and economical reasons, it should be possible to plate a ~5 500A to 5 ~m thick film in 2 to 30 minutes. The film com-26 position should vary much less as a function of current 27 density than it does for prior art baths used for plating of O O
28 200 A to 2,000 A films, used for plated random access thin 29 film memories such as flat film or coupled magnetic film memories-1 High plating rate batlls have been developed for 2 fabrication of plated magnetic wire memories. The Permallo~y 3 film thickness on the wires is typically 5, 000 ~ to 10,000 4 A thick. The prior art form agitation used has been forced S flow agitation with impingment which is usually very highly 6 turbulent. Due to the nature of the wire fabrication process, 7 these films have to be plated in 1 to 8 minutes of the wire 3 residence time in the plating cell. Although some of these 9 baths are known, the literature available lacks important details about the baths, cell design or the exact plating 11 conditions.
12 The high plating rate Permalloy bath described 13 below is adapted for the purpose of fabrication of thin film 14 magnetic bubble devices and recording heads. Optimum plating condItions are described. The described plating bath satisfies 16 the current magnetic film property requirements for fabrication 17 of such products. Despite this, certain fuzther improvements 18 in control of various plating parameters and in magnetic 19 - properties are being sought.

Magnetic Film Property Requirements for Fabrication of ~1 Thin Film Bubble Devices and Recording Heads 22 It is necessary that the films used in fabrication 23 of recording heads are magnetically anisotropic. Magnetic 24 anisotropy permits use of rotational switching to improve the frequency response of the devices. Although it is desired 26 to have a square easy axis loop with a low remanence, the 27~ exact value of the coercive force Hc is not critically 2~ important. It is preferred, however, that Hc be below 0.8 29 Oe. The exact value of the easy ax-ls dispersion a, and skew B, are also not critically important for the proper operation 31 of the device. The important magnetic parameters af~ecting 32 the signal output of the device are: hard direction remanence, 33 saturation magnetization M , initial permeability ~, and 34 electrical resistivity of the film p.

_ .. . .. _ 1 High resistivity ls particularly important for.
2 heads to be operated at high frequencies. Since the read 3 signal depends on all four quantities enumerated above, it 4 is desired to minimize the hard direction remanence and LO
maximize each of the last three quantities. Furthermore, 6 since ~i is proportional to M /Hk, in order to maximize ~i' 7 it is desired to minimize the anisotropy field Hk, while 8 retaining the magnetic orien~ation of the film.

9 Experimental Apparatus and Procedures The basic composition of the plating bath and the 11 plating conditions are shown in Table I. The electroplating 12 cell used in developing and optimizing this bath consists of 13 the rectangular Lucite (polymethacrylate)container enclosing 14 the cell of FIGS. 1 and 2 in which the bottom of the cell represents the cathode and the top of the cell represents 16 the anode. The anode-cathode arrangement can be reversed or 17 placed on its side so long as the mixer or paddle agitator 18 35 and the inlet slot 49 facilitating the mixing and entry 19 of the fresh solution respectively are also suitably rotated (such that agitation and refreshing of the cathode surface 21 is continuously maintained). Both the anode 24 and the 22 cathode 14 fill the cell 47 substantially from wall to wall 23 in each directlon. This arrangment results in a uniform 24 primary current distribution over the whole cathode area.
All films for recording head devices are plated in a 40 Oe 26 magnetic field provided by permanent magnets 25 shown in 27 phantom in FIG. 2. After plating, all films are annealed 28 for 2 hours at 200C in a 40 Oe easy axis field. Subsequently, 29 they can be additionally annealed for 2 hours at 200C in Yo975-065 14 . _ . _ . ... . . .. .. . _ . _ _ _ ~ 43 ~
1 - the absence of a magnet:Lc fiel~ or for 2 hours at 200C in a 2 cross-field or both. The static magnetic properties 3 of the films are measured before annealing, after easy-axis 4 annealing and after the annealing in absence of the field and/or the cross-field when it is used.
6 The static magnetic properties of the films, 7 coercive force H , anisotropy field Hk~ easy axis dispersion 8 plus skew, + ~, and magnetostrlction ~ are measured using 9 a 60-cycle inductive B-H loop tester. The magnetic moment, Ms, of several films was measured using a force magnetometer.
11 Currently, each sample is compared on a B-H loop tester with 12 a standard sample. The initial permeability ~i of each 13 sample is measured. The electrical resistivity p of the 14 films is measured using a four-point probe.
The film thickness is evaluated from tlle weight 16 gain of the sample during plating and from a profilometer 17 measurement. The film thickness is subsequently verified 18 using an X-ray fluorescence and/or a wet chemical technique.
19 The film composition is also de~ermined using the X-ray 2n fluorescence technique or a wet chemical technique.

~3 Discussion of Plating Parameters and Their Effect on Film ~4 Composition and Magnetic Properties ~5 The following plating parameters were investigated:
26 a. Current density.
27 b. pH and the rate of change of pH during plating.
28 c. Temperature and the rate of change of temperature 29 during plating.

1 - d. Agitation (heigllt of the paddle over the 2 cathode at a fixed rate of travel of the paddle).
3 e. Operation of the apparatus with recirculation 4 agitation only and no paddle movement and operatlon of the cell with no recirculation and 6 with paddle agitation only. Operation wlth 7 both paddle movement and recirculation.
8 f. Speed of movement of the paddle in presence and 9 in absence of recirculation.
g. Change of [Fe ] ion content of the bath and 11 the rate of consumption of the [FE ] ion 12 during plating.
13 h. Partial and/or complete substitution o~ chloride 14 ion by sulfate and by fluoride ions.
i. Change ln sodium saccharin content.
16 j. Type of anode (inert Pt, soluble Ni, and mixed 17 Ni-Pt).
18 k. Addition of cobalt sulfate to the bath.
19 Because of the preferential electrodeposition of iron in presence of nickel, most of the commercial (~0/20) Permalloy 21 electroplating baths are operated with a high nickel-to-iron 22 ratio in solution. (I. W. Wolf, Electrochem. Technology, pp.
23 164-7, 1, No. 5-6, 1963; W. O. Freitag, J. S. Mathias, 24 Electroplating and Metal Finishing, pp. 42-47, February, 1964;
and T. R. Long, J. Appl. Physics, 31, Suppl. 5, 1960.) 26 In the baths described in the first two references 27 immediately preceding, the films are plated at very low 28 current densities ~~5 ma/cm ) and therefore it takes 20 to 29 30 minutes to deposit a 0.5 to 1 ~m film. In addition, the composition of the films deposited from Yo975-065 16 .

3s 1 these baths is extremely sensitive to- minute current density 2 variations (see FIG. 5 curve labeled Wolf's~bath). These films 3 exhibit a tensile stress, with a nonuniform stress gradient 4 through the thickness of the film (the films curl when removed from the substrate).
6 FIGS. 4A , 4B and 5 and Table II summarize the effect 7 of the more important plating parameters on the film composition 8 and on magnetic properties of sheet films. The reader is 9 referred to these FIGS. 4A, 4B, and 5 and in particular to Table II. FIG. 5 gives a comparlson of the rate of change 11 of the iron content in the film with current density for the 12 present bath and for a Wolf's type bath.
13 The well known Wolf's bath gives an iron composition 14 vs. current density curve shown in dotted line form in FIG.

5. This curve shows a very sharp essentially vertical line 16 with the tolerance band lines marking a 19 - 21% Fe tolerable 17 spread of the metal composition required for Permalloy Ni-Fe 18 alloy corresponding to a current range of 7-8 ma/cm2, which 19 means that a slight 1 ma/cm shift in current can throw the bath out of the Permalloy 19 -21% Fe alloy range. In the 21 case of curve A, the corresponding current range is 55 - 65 22 ma/cm2, which is a far wider range in absolute terms and as 23 a percentage of the current than that for the Wolf's bath.
2~4 Curve A is based upon 2~ thick films with weak agitation.
The pH is allowed to change from 2.5 to 2.9 while plating, 26 and the iron content of about 1.35 g/l is allowed to drop.
27 Curve B shows the result of intense agitation and adjustment 28 of pH at 2.5 and iron at 1.41 g/l. Note that for Curve B, 29 above 80 ma/cm2 and for Curve A, between 5 and 20 ma/cm2, s 1 rhe result is practically independent of current density.
2 The films plated from the present bàth at current densities 3 anywhere between 5 and about 100 ma/cm2 show very sma:Ll 4 internal stress gradient. The stress gradient is uniform throughout the thickness of the film, and when the film is

6 lifted off the substrate, it does not curl.

7 Films plated at low current densities, i.e., ~ 30

8 ma/cm2 initially, when only ~ 0.5 ~m thick, have an extremely

9 pronounced texture orientation. The 110 plane is in the plane of the film. As the thickness increases, orientation 11 diminishes. The orientation diminishes more rapidly in films 12 plated at higher current densities. Films plated at ~ 60 13 ma/cm2 show very little grain orientation. All films are 14 under a tensile stress. The stress has a uniform gradient through the thickness of the film. Upon heating to 200C
16 for 2 to 4 hours, the tensile stress increases.
17 FIG. 6 is a plot of static magnetic properties Hc, 18 Hk, and ~ + ~ for the 2 ~m thick films as a function of the 19 weight % of Fe in the film. All solid lines in FIG. 6 represent films which were annealed in an easy axis field.
21 The dashed curve represents values of Hk for the 2 ~m 22 thick films after they have been annealed in a cross-field.
23 The hard axis (cross-field) annealing results in lowering of 24 the Hk value by about 50% to 80% based on the original Hk value in a plated form. The Hc, and ~ + ~ values are not 26 shown for the films after hard axis annealing because Hc in 27 the 2 ~m thick films changes oniy very slightly during the 28 hard axis annealing. The ~ ~ B increased during the hard 2g axis anneal by about 25%.

Yo975-065 18 1 FIG. 7 summari~es the results of the measurement 2 of the initial permeabillty ~i as a functlon o frequency 3 for various thicknesses of films after the easy axis annealing 4 and also for the same films after a subsequent hard axis annealing. The ~i value of the easy axis annealed fil~s at 6 - low frequencies is about 2,000. This value is in good 7 agreement with the initial permeability reported for Permalloy 8 alloy in bulk form. After hard axis annealing, the initial 9 permeability ~i of these films is approximately 4,0~0. This is again in good agreement wlth the ~i ~ M iHk relat~on, 11 since the hard axis annealing result is a 50% to 80%
12 decrease of the Hk value.
13 From the shape of the curves in FIG. 7, it can be 14 concluded that in films thinner than 2 ~m, during switching, eddy current damping does not play a major role. This is 16 as predicted on the basis of 20 micro Q - cm resistivity and 17 of the resulting calculated skin depth.
18 For the purpose of fabrication of the high frequency 19 heads for disc file applications, it is desired to maintain the high initial permeability of the films at 2,000 or 4,000 21 to much higher frequencies than is presently the case. The 22 high initial permeability, at high frequencies, can be 23 maintained by increasing the electrical resistivity of the 24 films. This bath is quite amenable to addition of a third element for deposition of ternary alloys of higher resistivity.
26 Based on the investigation of the effect of different 27 plating variables on the Permalloy composition reported in 28 FIGS. 4A and 4B and Table II, it is concluded that in order 29 to plate 80/20 nickel-iron films reproducibly on a commercial ~0975-065 19 ... .

1 production basis, it is necessary to control pH within 2 approximately + 0.1, temperature ~rithin approximately 3 0.5C, and iron content of the bath within approximately 4 5% of the initial value. It is also necessary to control the current density within about ~ 5% and the agitation rate 6 withln certain prescribed limits. The last two can be 7 easily controlled by using a well-regulated power supply, a 8 reproducibly fixed distance of the agitation paddle 35 above g the cathode, a fixed recirculation rate, and a substan~ially fixed rate of travel of paddle 35. The first three variables 11 require constant adjustment during each plating run because 12 they tend to change continuously during deposition. Constant 13 recirculation of the solution during plating remo~es the 14 partially altered solution from the plating tank and continuously introduces from a large reservoir freshly adjusted solution 16 The filter constantly removes any precipitate or sediment 17 formed during the electrolysis. Thus, recirculation serves 18 a dual function: a) removal of partially spent solution for 19 its adjustment in the reservoir and removal of the residues, and b) assistance in obtaining unifor~ agitation of the 21 plating solution in the tank.

22 ~ Example I
23 During deposition of 2 ~m of film out of a typical 24 800 ml bath, the pH of the bath increased by approximately 0.3 to 0.5 pH units (from 2.5 to approximately 2.9), the 26 temperature increased by approximately 0.5C and the iron 27 content decreased by approximately 2% (while the nickel 28 content remained nearly constant). When an inert, large 29 area Pt screen anode was used, the pH ins~ead o~ increasing, decreased by approximately 0.2 to 0.4 pH units (from 2.5 to 31 about 2.1).

.

1 The reproducibility can be improved and the useful 2 life of the bath can be extended by preparing a large volume 3 of bath and recirculatlng a portion of it through the plating 4 cell 47, while at the same time constan~ly monitoring the pH, temperature and intermittently measuring ths iron content 6 of the bath in the reservoir and suitably adjusting all 7 three quantities within the limits shown above.
8 Referring to the arrangement of FIG. 1, the reservoir 9 plating tank and a suitable reci~culation system provided excellent results. The pH was controlled only within + 0.2 11 units, the temperature within + 0.4C, snd automatic con~rol was 12 provided for the iron content. This resulted in greatly 13 improved reproducibility of the plated films. Later a ~4 system was employed which permitted the pH control to within ~ 0.05 pH unit, temperature to within + 0.3C and the iron 16 content of the bath to within approximately 4%.
17 The high plating rate bath of Table I permits 18 plating of films at a rate as high as 1 ~m/min. and also 19 plating of films at a rate as low as 500 A/min. The plated film composition is relatively insensitive to small current 21 density variations. Magnetic properties of the plated films 22 are quite acceptable for use in thin film magnetic recording 23 heads.

Yo975-065 21 1 TA~LE L
2 Preferred Plating Bath Conditions 3 Optimum Ranges 4NiCl 6H 0* 109 g/l 30 to 150 g/l C 2 4H20 5.25 g/l 4.5 to 5.77 g/l 6H3B03 25 g/l 12.5 to 25 g/l 7~a Saccharin 0.8 g/l 0 to 2 g/l 8 Na Lauryl Sulfate (Maprofix)***0.2 g/l Fixed value 9 p}l 2.5 + 0.1 1.5 to 3.6 Current Density 60 ma/cm 10 to 120 ma/cm2 11 Na Citrate, tartrate, 10 to 80 g/l 10 to 80 g/l 12 oxalate, phosphate**

13 * In addition to chloride salts, sulfate and fluoride salts 14 may be used. The chloride ion can be completely or partially substituted by a sulfate ion. Alternatively, ammonium sulfate 16 salt can be added to the bath in amounts of 50 to 150 g/l.
17 ** Addition of complexing agents is optional. _ 18 Plating rate About 10,000 A/min (2~ per 2 min) 19 at 60 ma/cm2 Agitation Continuous laminar flow 21 Rate of travel of the paddle about 22 8"/sec in a reciprocating fashion at 23 about 1/32" spacing above the cathod~
24 with a range of spacing of 0 - 1/4"
Anode Pt sheet wrapped with Ni wire mesh 26 Temperature 25 + 0.5C 20 to 35C
27 Cathode Current Efficiency About 80% - 90%
***Trade Mark 3~

1 In Table I the ratios of Ni:Fe are as follows:
2 Conversion 3 LowFactor 2 6H20 30 g/l x.247 Ni 704 g/l FeC12'4H2 4.5 g/l x.2815 Fe+ 1.27 g/l Ni:Fe ion weight ratio 5c8:1 7 Optimum 8 NiC126H20 109 g/l x.247 Ni+ 26.92 g/l 2 2 S.25 g/l x.2815 Fe 1.48 g/l Ni:Fe ion weight ratio 1802:1 ll High 12 2 2 150 g/l x.247 Ni 37.05 g/l 13 FeCl 4H 0 5.72 g/l x.2815 Fe 1.61 g/l 14 Ni:Fe ion weight ratlo 23.0:1 2 Summary of the Effect of Various Plating 3 Parameters on the Film Composition_and on the 4 Magnetic Properties S Current Density id As current density increases, the 6 iron content decreases. (FIG. 5) 7 The rate of change is 0.4% Fe/ma/cm 8 for most of Curve A and part of 9 Curve B in FIG.. 5.

10 pH As pH increases in the 1.5 to 3.5 pH

11 range, the iron content dPcreases.

12 (FIGS. 4A, 4B and 5) The rate of change

13 is 5.55% Fe/pH unit.

14 Temperature As temperature increases in the lS 20 to 35C range, iron content in 16 t~e film decreases. (FIGS. 3A, 3B i:
17 and 4) The rate of change is 18 0.75% Fe/C.
19 Agitation As the mixer distance increases from near contact with the cathode to 21 about 1/4" above the cathode at a 22 fixed id of about 60 ma/cm2, the 23 iron content increases. The deposit 24 acquires a "burned" appearance~
~ eventually passivates complete-ly 26 when the limiting current is reached 27 at which metal ions cannot be supplied 28 any faster.
29 Change of Iron Content A 10% change in iron content in the bath results in about 3 to 4% change 31 ~n lron content in the film.

1 TABLE II (continued) 2 Rate of Depletion of Iron When using 800 ml of solution in 3 connection with the Pt inert 4 electrode, approximately 1.85~ of iron and 0.45% of nickel are used 6 per 1 ~m of deposited film. When 7 using a soluble nickel electrode or 8 a mixed Pt-Ni electrode, nickel in 9 the bath remains unchanged. After plating 5 ~m of film out of an 11 800 ml bath, about 9.3% of the 12 original iron in the bath is depleted.
13 Type of Anode (1) When using an inert Pt anode, pH of 14 the 800 ml bath decreases from 2.5 to about 2.1 during the course of 16 deposition of .Q 2 ~m film.
17 (2) When using a soluble nickel anode, 18 the pH increases rapidly. When using 19 a mixed Pt-Ni anode, the pH of the 800 ml bath increases from 2.5 to 21 about 2.9 much more slowly.
22 Substitution of Cl by When Cl is substitut2d by S04 , 23 SO4 and by F slightly lower ~ , a + ~ and Hk are 24 obtained. I~hen Cl is substituted by F , there are no major changes 26 in film composition or magnetic 27 properties.
28 Change in Na Saccharin When Na Saccharin is completely 29 absent, films are highly stressed and lift off the substrate after 31 about 1 to 1.5 ~m of film is deposited.

.

s l TABLE II (continued) 2 At about 0.4 g/l of Na Saccharin, 3 the internal stress is sufficiently 4 reduced that 5 to 8 ~ thick films can be readily plated. Beyond 0.4 g/l 6 and up to 2 g/l of Na Saccharin, only 7 very sli~ght changes in magnetic 8 properties are observed.
g Addition of Cobalt Sulfate In amounts up to 2.3 g/l, Hc decreases, ~ + ~ decreases, however, Hk nearly ll doubles. The film contains about 12 10% Co.

14 Iron and ~ydrogen Ion Make-up Solution for Burette 65 FeCl 4H O 20 g/l or equivalent amount of 16 FeSO
17 HCl Enough to produce pH 0.5 solution l~ In cases in which a Permalloy film is plated over l9 a cathode which has recesses and raised areas or when it is necessary to plate a Permalloy film through a resist mask ~l tboth of which situations occur in fabricating magnetic thin 22 film heads and bubble memory overlays), the strong composition dependen~ce upon small current density variation is extremely ~4 undesirable and, indeed, makes it impossible to electroplate usable films. In connection with wire memory abrication, 26 other baths were developed which permit electroplating 27 Permalloy films at very high rates. (T. R. Long, J. Appl.
28 Physics, 31, Suppl. (5) 1960; E. Toledo, R. ~lo, Plating, 57, 29 P. 43, 1970.) Yo975-065 26 s The present bath, plating technique and apparatus for electrodeposition of Permalloy films permit reproducible dep-osition of ~0i20 films from low nickel:iron ratio baths at rates which are both practical and easy to control when plating films anywhere fxom 1,000 A to 5 microns thick. This bath has an excellent throwing power. At low, moderately high, and high current densities and in presence of strong agitation, it gives deposits whose composition is nearly independent of the current density (see FIG. 5 curves A and B, FIG. 9 curves AA and BB
and FIG. 8, curves A, B, C, D, and E~. These features make the bath unique and particularly useful for plating various magnetic devices in which it is necessary to deposit the film through a resist mask.
Below are given the key features of the bath, plating apparatus and technique and properties of the resulting films:
1. The film composition is only slightly dep~ndent on current density of 20 to ~5 ma/cm2 and is even completely independent of the current density variation over a wide range of currents below 20 ma/cm and above 80 ma/cm . ~At high agitation rates and moderately high current densities, the composition is substantially independent of the current density.) 2. The films are relatively stress free even when plated up to 25 ~ thick. The films do not curl when lifted off the substrate, which indicates that the stress gradient through the thickness of the film is linear. The features described in (1) and (2) permit electroplating very narrow (down to 2.5~) lines and patterns through a mask without lifting or peeling of the pattern.

1 3. The films deposited from this bath possess a 2 high initial permeability. The permeability of these films 3 can be increased further by hard axis annealing. The high 4 initial permeabili.y, substantially closed hard axis loops, and easy magnetic switching, wit'nout hard axis 6 locking and/or without excessive remanance, make the 7 films particularly useful for fabricating magnetic thin 8 film recording devi-ces.
9 - 4. The films plated from this bath, when using the disclosed pH, temperature control, and iron 11 addition and control, are uniform with respect to 12 composition throughout their thickness except for the 13 first 100 to 300A in which there is a composition 14 gradient.
5. The film deposition rate, while it can be 16 relatively high (up to about l~m/min), is slow enough 17 to allow accurate thickness control in films which are 18 only 500 A thick.
19 6. The bath is relatively insensitive to variations in temperature.
21 7. The plating apparatus is designed so as 22 to permit controlling pH at 2.5 + 0.05, temperature at 25 + 0.5C, and iron in the bath at 1.41 + 0.02 g/l.
24 The pH is controlled using a pH stat composed of meter 61 and comparator 76 coupled with solenoid valve 63 and 26 the burette 65 containing HCl solution and Fe ions 27 described above in Table III.

1 8. Since the rate of loss of iron is directly 2 proportional to the rate of change of the pH, iron is 3 added simultaneously ~rom burette 65 while ad~usting 4 the pH. The rate of Fe consumption can be observed during plotting without any adjustment to produce a 6 calibration curve. It has been found that the rate of 7 [Fe++] consumption is proportional to the change of the pH. BasPd on the calibration curve, a suitable make up 9 solution is prepared, as will be obvious to those skilled in the art. Up to lO0 ~m of Permalloy is ll plated onto a 4.5" x 4.5" substra~e with iron [Fe ]
12 ions in the bath being maintained at 1.41 g/l and pH at 13 2.5 ~ 0.05. The bath composition is shown in Table I.
14 Composition of the HCl-Iron make-up solution is shown in Table III.
16 9. The bath is normally operated under 17 conditions (pH and total iron in the bath) under which 18 erric ion in excess of about 0.01 g/l precipitates out 19 and is filtered out prior to entering the plating cell.
10. The ferric ion formation can be further 21 reduced by addition of complexing ions such as citrate, 22 tartrate, oxaiate, phosphate, isoascorbic acid, and the 23 li~ke. All of the above 9 when added in small quantities, 24 do not substantially alter the plating conditions under which an 80/20 composition is obtained. In addition, 26 the ferrous to ferric ion oxidation can also be diminished 27 by preparing the iron make-up solution using FeS04-4H20-HCl 28 solution (rather than FeC12'4H20) and by adding ammonium 29 sulfate salt to the bath.

2 Bath Plating Conditions for Plating Through Masks 3 Optimum Ranges 4 NiCl 6H O 109 g/l 70 - 180 g/l 2 4 2 1.5 g/l 1.1 to 3.8 g/l 6 H3Bo3 25 g/l 12.5 to 25 g/l 7 Na Saccharin 0.8 g/l 0.4 to 0.8 g/l 8 Na Lauryl Sulfate 0.2 g/l 0.2 g/l to 0.4 g/l 9 H20 make up to 1 liter make up to 1 liter id ~ 5 ma/cm2 5 to 40 ma/cm2 11 Plating rate 500A/min 500 - 30,000A/min 12 pH 2.5 1.5 to 3.6 13 Na Citrate, tartrate 14 oxalate, phosphate** 10 to 30 g/l 10 to 30 g/l [Ni +] 26.9 g/l 17 to 44 g/l 16 [Fe ] .42 g/l ~.31 to 1.07 g/l 17 Ni:Fe ratio in g/l 64:1 86:1 to 25.1:1 g/l .
18 **Addition oE complexing agents is optional.
19 One of the unique feature~s of this bath, when used in connection with the plating apparatus discussed, is the 21 extremely broad range of current densities under which it can ~2 be used to plate sound, usable NiFe deposits in sheet film 23 form.
24 Even more unique is the capability of the same bath with only minor adjustmsnt of the [Fe++] concentration to be 26 used for plating discrete patterns through masks with 27 excellent thickness and compositional uniformity.
28 In particular, f ilms were plated in 2.5~m and 29 25~m wide lines ~slots] in resist with varying spaces and into 2.5~m T and I bar patte-rns. FIG. 9 shows the 31 relationshlp between the percentage of Fe in the film and Yo975-065 30 1 the current density for both the 2.5~m pattern on varying spaces from 2 0.25~m through 500~m. While in this case no attempt was made to obtain 3 a 20/80:Fe/Ni composition from FIG. 9, it is obvious that excellent 4 compositional uniformity was obtained when overall current density of 5ma/cm2 through 25 ma/cm2 was used. From curve AA and the bars around 6 each point showing the spread of data in the 50 points examined, it is 7 clear that smallest deviation from the mean takes place at an overall 8 current density of 5 ma/cm (equivalent to a 1545A/min plating rate 9 Table V). As the current density is increased to an overall value of 10 ,, O " O
ma/cm (5,000A/min plating rate Table V) to 20 ma/cm~ (9,OOOA/min plating 11 rate), the deviation from the mean increases (long vertical bars in FIG.
12 9). At an overall current density of 40 malcm equivalent to a plating 13 rate of 30,000A/min, the mean value is shifted considerably downward to 14 a lower %Fe and the spread of %Fe over isolated 2.5~m patterns is very large. The deviation of the film thickness is very large compared to 16 the deviation for 5 and 10 ma/cm average current densities. Table V
17 shows examples of mean thickness and thickness spread for the 5, 10, 20, 18 40 and 60 ma/cm overall current density. A similar situation exists in 1~ the case of plating of 25~m bars at varying spaces on curve B-B, except the absolute value of the mean %Fe is slightly lower at 5 ma/cm2, 10 21 ma/cm2 and 25 ma/cm2.
~2 FIG. ô represents the relationship between the iron [Fe ~ ion 23 content of the bath and the overall current density for the plating of 24 2.5~m lines and T and I bar patterns for bubble memory devices through masks. The curves marked A through E are isocomposition lines, with 26 curve E representing 20% Fe, D about 22% Fe, C about 25% Fe, B about , 1 40% Fe, and A about 50~ Fe in the film. This figure points to the key 2 part of the invention showing the fact that while plating through masks, 3 the film composition does not vary over relatively broad range of current 4 densities (namely, 5 ma/cm2 through almost 20 ma/cm2 of the overall current density). Such behavior is most unique and unexpected in electro-6 plating baths which are known to have anomalous codeposition of Fe with 7 the host metal. It permits the dimensions of the patterns and the 8 spacing of the patterns to vary over a rather large range without adversely 9 affecting the film composition or thickness from a spottospot on the `10 cathode plated through a mask.
11 Plating Thro_gh_a Mask 12 In plating from the bath of this invention onto a metallic 13 film coated with a mask of a photoresist or the like, results have been 14 obtained using the bath compositions outlined below in E~amples II - V
for providing 80/20 compositions of nickel and iron.
16 Example II
17 The bath included the constituents as follows:
18 NiC12 6H2 109 g/l 26.9 g/l [Ni ]
19 FeCl 4H 0 1.85 g/l .521 g/l [Fe ]
H3B03 12.5 g/l 21 Na Saccharin 0.4 g/l 22 Na Lauryl Sulfate 0.4 g/l 23 2 make up to 1 liter 2 24 The overall plating cur~ent de~sity was 20 ma/cm 9 and a pH level of 2.5 was maintained. An excellent film was produced. The Ni:Fe ratio in the 26 bath was 51.6:1 in g/l.

1 Example III
2 The same bath as in Example II was used with the only exceptions as 3 follows:
2 4 2 1.1 g/l .31 g/l [Fe ]
Na Lauryl Sulfate 0.2 g/l 6 The overall plating current density was ~0 ma/cm with a pH of 2.5.
7 Similar results were achieved.
8 In this case, the nickel-iron ion g/l ratio in the bath was 9 84.3:1 Example IV
11 The same bath as in Example III was used with the only exceptions as 12 follows:
13 FeC12 3.8 g/l 1.07 g/l [Fe ]
14 H3B03 25 g/l Na Saccharin 0.8 g/l 16 Na Lauryl Sulfate 0.4 g/l 17 The overall plating current density was 40 ma/cm2 and pH ~as held at 18 2.5. The nickel-iron g/l ratio in the bath was 25:1. No recirculation 19 was used other than paddle agitation and bath volume was 200cc. This bath was used for plating a single 2~m film.
21 Example V
22 The same bath as in Example IV was used with the only exceptiorl as 23 follows:
~24 FeC12 1.5 g/l 0.472 g/l [Fe ]
The overall plating current density was 5 ma/cm for a plating rate of O O
26 1545A/min and 10 ma/cm2 for a plating rate oE 5000A/min (Table V). The 27 pH was held at 2.5. The nickel-iron g/l ratio in the bath was 63.74:1.
28 Plating Non-80/20 Ran~e Ni/Fe Composition: Sheet Form 29 In plating from the bath of this invention of a metallic film in sheet form, favorable results have been obtained using the bath Y0975-065 _33_ 3~

l compositions outlined below in Examples VI to X for providing nickel~
2 iron films.
3 Example VI
4 The bath included the constituents as follows:
2 2 109 g/l 26.9 g/l [Ni ]
2 2 5.0 g/l 1.4 g/l [Fe ]
3 3 Z5 g/l 8 Na Saccharin 0.8 g/l 9 Na Lauryl Sulfate 0.5 g/l pH 2.5 ll The plating current density was 5 ma/cm2 at a plating rate of 1545A/min.
12 The film produced was 50% Fe. The Ni:Fe ratio in the bath was 19.2:1 in 13 g/l.
14 Example VII
The same bath as in Example VI was~ used with the only differences as 16 follows:
17 The plating current density was lO ma/cm2, the plating rate 18 was about 5000A/min, and the percentage of Fe was about 52.
19 Example VIII
The same bath as in Example VI was used with the only differences as 21 follo~s:
22 The platin~ current density was 20 ma/cm , the plating rate 23 was lO,OOOA/min and the percentage of Fe was about 50.
24 Example IX
The same bath as in Example VI was used with the only differences as 26 follows:
27 The plating current density was 40 ma/cm , the plating rate 28 was 30,000A/min, and the percentage of Fe was about 30.

Y0975-065 _34_ lb~5 1 Example X
2 The same bath as in ~xample VI was used wlth the only differences 3 as follows:
4 The plating current density was 60 ma/cm2, the plating rate was 55,000A/min, and the percentage of Fe was about 20.
6 Plating 80/20 Ni/Fe ComPOsition - Sheet Form 7 In plating from the bath of this invention to form a metallic 8 film in sheet form, favorable results have been obtained using the bath 9 compositions outlined below in the Examples XI and XII for providing 80/20 Ni/Fe films.
11 ExamPle XI
12 NiC12 6H2 109 g/l 26.9 g/l [Ni ]
13 FeCl 4H O 5.25 g/l 1.45 g/l ~Fe ]
14 H3B03 25 g/l Na Saccharin 0.8 g/l 16 Na Lauryl Sulfate 0.2 g/l 17 p~, 2.5 + 0.1 18 The plating current density was 60 ma/cm2, Na citrate, tartrate, oxalate, 19 or phosphate was included to 10 to 30 g/l. The percentage of iron in the films produced was 20 + 2. The pla~ing rate was about 10,000A/min. The 21 Wi:Fe ratio was 18.55:1 in the bath in g/l.
22 Example XII
23 C 2 6 2 40 g/l 10 g/l [Ni ]

24 4 2 20 g/l 4.5 g/l [Ni ]
FeCl '4H O 4.5 g/l 1.25 g/l [Fe ]
26 Na Saccharin 0.8 g/l 27 Na Lauryl Sulfate 0.2 g/l 28 pH 2.5 ~ 0.1 29 Temperature 25C + 0.5C

s 1 The current density was 30 ma/cm , and the plating rate was 2 about 5,000A/min. The percentage of Fe in the films produced was 20 3 2. There were 14.5 g/l of [Ni ~ and 1.25 g/l of ~Fe ] for an Ni:Fe 4 ratio of 11.6:1 in ~he bath in g/l.
S Plating W_th Prior Art Bath 6 Example XIII
7 A plating bath of the composition shown in U.S. patent 3,652,442 was 8 prepared to consist of:
2 6 2 109 g/l 26.9 g/l Ni FeCl 4H 0 3.9 g/l 1.10 g/l Fe 11 H3B03 12.5 g/l 12 Na Lauryl Sulfate 0.2 g/l 13 Na Saccharin 0.4 g/l 14 Temperature 25C
Current density 20 ma/cm2 16 Films were plated from this bath as prepared without adjusting 17 the pH to 2.5 through a 2.5 ~m aperture mask.
18 The films had very highly modular surfaces with some "burning"
19 around the edges and showed very large thickness variations over the surfaces of the wafers, and showed signs of severe internal stresses and 21 flaking. The nickel:iron ra~io in the bath was 24.4:1.
22 Even though the bath shown above is similar to the bath in 23 Example IVI it gives "burned" (black: rough and oxidized which are also 24 too high in iron) deposits which also are too high in iron content to be useful in magnetic bubble memory devices.
26 Example XIV
27 When plating bath #3 from U.S. patent 3,652,442 was used 28 without adjustment of pH in connection with the present apparatus and 29 plated at 25C with a~itation as described in Table 1 and at the 1 preferred current density of 60 ma/cm , the films had high Hc values, partially open B-H loops, and showed distinctly less that 15% Fe. This range thus shows itself to be too low to produce 80:20 magnetic films.
We have found that automatic and continuous measurement with automatic adjustment avoids long response times and large fluctuations in solution temperature, pH, and specific gravity.
The large storage reservoir tank permits holding fluctuations low, and provides automatic quick response to any changes. It has been found also that specific gravity is not a satisfac-tory measure of the rate of consumption of reagents, particu~
larly ~Fe++ 3 which is the most sensitive quantity (reagent).
The change of [Fe++3 is proportional to p~I as taught herein, and hence it is necessary to measure pH only on a continuous basis and to predetermine the rFe+~ ion consumption in order to make an appropriate adjustment in the ~Fe++~ content of the bath along with adding acid. rFe++] is lost through plating out and through oxidation to ~Fe + ] . At a pH above 3.5, [Fe ~ will tend to precipitate to a small degree, which is then taken out by the filter in the line. Measurements have yielded a calibration curve not included herein which shows the close relationship of the change of pH due to Fe++ consump-tion. This data has been used to precalculate the ratio of Hc to ~Fe ~ added while adjusting pH as shown in Table III
above.

YO9-7ri~065 -37-B

s 1 Table V
2Plating Through the Mask with Long Line Openi~s 3Varying from 2.5 ~m to 25 ~m with Varying Spaces 4Plating Rate Average Spread of Data 5 for a W_fer 6 5 ma/cm2 1545A/min 1540 1550 7 spread of composition 47 to 52%-Fe (FIG. 9) 8 10 ma/cm2 5000A/min 4375 5333 9 spread of composition 48 to 53% Fe 20 ma/cm2 9000A/min 8700 12,167 11 spread of composition 45 to 54% Fe 12 40 ma/cm2 25 9 OOOA/min 18,000 30,000 13 deposits very nodular and "burned"
14 spread of composition 22 to 52% Fe 60 ma/cm2 50,000A/min 35,000 57,000 16 deposits very nodular and "burned"
17 spread of composition 11 to 23% Fe 18 Table VI
19 Pr~ _ r Ni-Fe Platin~ Without .
20"Burnin&", with Sound, Bright Deposi~s and Good Adhesion 21 - Sheet Form 2 Through a ~ask 22 Platin~ Current Density 10-200 maJcm 2-60 ma cm 23 [Fe ] 1 - 14 g/l 0.3 - 1.0 g/l 24 [Ni ] 7 - 37 g/l 17- 44 g/l Agitation none to ultrasonic mechanical agitation 26 pH 1 - 3.o 1 - 3.6 27 Temperature 20 - 35C 20 - 35C

3~

2Limits ~or Plating Ni-Fe, 20;o Fe +l'Ç

3Sheet Form 2 Through a ~ask 4Plating Current Density 10-200 ma/cm 2-60 mafcm [Fe J l.l - 1.7 g/l 0.3 - 0.7 g/l 6[Ni J . 7 - 37 g/l 17 - 44 g/l 7 Agitation, pH and temperature ranges were the sa.-e as in 8 TABLE VI.

Y0975-065 ~39~

.~ ' .
..

.

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A nickel-iron electroplating method for coating a substrate having a mask deposited thereon including means for electroplating nickel-iron allow films containing about 20% iron onto a sheet substrate of a metallic material having said mask thereon, said method including employing a plating current density of about 2 - 60 ma/cm2, a plating bath fluid having an Fe++ ion concentration of about 0.3 g/l t-o about 0.7 g/l, an Ni++ ion concentration of about 17 - 44 g/l, a pH of about 1 - 3.6, and maintaining said bath at a temperature of about 20° -35° C, wherein Fet++ ion concentration required for placing 20%
iron is inverse to circulation of said plating bath fluid across said substrate.

2. An electroplating method in accordance with claim 1 including containing said plating bath in a cell having an anode, and a cathode including said substrate to be plated with an Nine metallic film, holding said cathode with the surface to be plated facing the anode of said cell, passing plating bath fluid directly onto the surface of said cathode by means of an inlet to said cell aligned with the surface of said cathode, pumping plating bath fluid up from a reservoir into said inlet via conduit means, returning plating bath fluid to said reservoir, sensing the chemical concentration present in said system, and automatically dispensing a reagent including at least Fe++ ions by means of a reagent dispenser into said reser-voir in response to the chemical concentration present in said system.

3. A method in accordance with claim 1 wherein said bath fluid has a nickel-iron ratio of from about 25:1 to about 85:1.

4. A method in accordance with claim 2 including providing agitation without substantial turbulence.

5. A method in accordance with claim 2 wherein said chemical concentration is sensed by a pH sensor, and said reagent dispenser dispenses acid and Fe++ ions.

6. A method in accordance with claim 2 wherein the temperature of said bath is maintained automatically by a temperature sensor, a thermostatic control, and heating means in said reservoir.

7. A nickel-iron electroplating method for coating a substrate having a mask deposited thereon including means for electroplating a nickel-iron film onto a sheet substrate of a metallic material.
said method including employing a plating current density of about 2 - 60 ma/cm2, a plating bath fluid having an Fe++ ion concentration of about 0.3 g/l to about 1.0 g/l, an Ni++ ion concentration of about 17-44 g/l, a pH of about 1 - 3.6, and maintaining said fluid at a temperature of about 20° - 35° C, wherein Fe++ ion concentration required for plating is inverse to circulation of said plating bath fluid across said substrate.

8. An electroplating method in accordance with claim 7 including containing said plating bath fluid in a cell having an anode and a cathode including said substrate to be plated with said nickel-iron film, holding said cathode with the surface to be plated facing the anode of said cell, passing plating bath fluid directly onto the surface of said cathode by means of an inlet to said cell aligned with the surface of said cathode, pumping said fluid up from a reservoir into said inlet via conduit means, returning plating bath fluid to said reservoir, sensing the chemical concentration present in said system, and automatically dispensing a reagent including at least Fe++ ions into said reservoir in response to the chemical concentration present in said system.

9. A method in accordance with claim 7 wherein said bath fluid has a nickel-iron ion ratio of about 25:1 to about 86:1.

10. An electroplating method in accordance with claim 8 including providing agitation without substantial tur-bulence.

11. An electroplating method in accordance with claim 8 wherein said chemical concentration is sensed by a pH
sensor, and said reagent dispenser dispenses acid and Fe++
ions.

12. A method in accordance with claim 8 wherein the temperature of said bath is maintained automatically by a temperature sensor, a thermostatic control, and heating means for said reservoir.

13. Electroplating apparatus including:
cell means for containing a plating bath, an anode and a cathode including a substrate to be plated with an NiFe metallic film, said cell including means for holding said cathode with the surface to be plated facing the anode of said cell, an inlet to said cell aligned with the surface of said cathode whereby said inlet is adapted to pass plating bath fluid directly onto the surface of said cathode, a reservoir for plating bath fluid having an outlet connected by conduit means to said inlet, means for pumping said plating bath fluid up from said reservoir into said inlet via said conduit means, an outlet from said cell for carrying said plating bath fluid into said reservoir, a chemical sensor for producing an electrical signal as a function of a chemical concentration present in said system and a reagent dispenser for automatically dispensing a reagent including at least Fe++ ions through a valve into said reservoir in response to said signal from said sensor.

14. Apparatus in accordance with claim 13 wherein said cell includes a mixer for providing agitation without sub-stantial turbulence.

15. A method in accordance with claim 13 wherein said chemical sensor comprises a pH sensor, and said reagent dispenser dispenses acid and Fe++ ions.

16. Apparatus in accordance with claim 13 wherein said reservoir includes a temperature sensor, a thermostatic control, and heating means for automatically maintaining the temperature of said plating bath.