CA2218392A1 - Method of electroplating a substrate, and products made thereby - Google Patents

Abstract

Disclosed is an electroplating method and products made therefrom, which in one embodiment includes using a current density J0, to form a conductive metal layer (30) having a surface roughness no greater than the surface roughness (20) of the underlying member (10). In another embodiment of electroplating a substrate surface having peaks and valleys, the method includes electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.

Description

TITLE METHOD OF ELECTROPLATING A SUBSI~ATE, ANP PRODUCTS MAPE THEREBY

BACKGROllND OF THE INVENTION

1. Field of the Invention The present invention relates to methods of electroplating and to products made thereby. In another aspect, the present invention relates to methods of electroplating a co~ e metal onto a ~ul~ le, and to products made thereby. In even another aspect, the present invention relates to methods of electroplating con~ ctors onto a seed layer supported by a substrate, and to products made thereby. In still another aspect, the present invention relates to mPthotle of clecL,oplating cc)n~ ctors onto a seed layer ~u~ol~ed by a diamond substrate, and to products made thereby.

2. Pescription of the Related A~t It is the physical and chernical properties of natural ~i~mon~ls which render o~ suitable for use in a wide range of applications. For example, natural diamonds are the hardest substance known and exhibit low friction and wear properties.
Specifically, a natural dialllond's thermal conductivity, thermal diffusivity properties, electrical resistivity and microhdl ~llle~ invite its substitution in various applications.
Specifically with respect to electronic applications, di~mon~, with a thermal conductivity four times that of copper and a dielectric con~L~lL less than alumina or ~IIlmimlm nitride, has long been recognized as a desirable m~tPri~l for electronic subsLl~es It is likewise believed that ~li~mon~1 films would find utility in a broad range of electronic uses.
UllrulL-IlldLely, diamond films are not naturally occurring, but rather must be m~nnf~c.tllred using any of a host of techniques. r Fortunately, however, the physical and ch~mi~ l plop~l~ies of synthetic di~mon-lfilms have been found to be co-llpal~ble to those of bulk tli~mon~
For ~ r, it has been reported that electron assisted chemical vapor deposition films have electrical resistivities greater than 10'3 Q-cm, microhardness of about 10,000 HV, thermal con~llctivity of about 1100 W m-l K-l, and thermal diffusivity of 200 to 300 mm2/s. These co"l~e favorably to those properties of natural diamond, i.e, resistivities in the range of 107 to 102~ Q-cm, microhardness in the range of 8,000 to 10,400 HV, thermal conductivity in the range of 900 to 2100 W m~l K-l, and thermal diffusivity of 490 to 1150 mm2/s. Thermal gravimetric analysis d~mn~ L~s the oxidation rates of diamond films in air are lower than those of natural diamond. Additionally, it is reported that the starting temperature of oxidation for microwave-assisted chemical vapor deposition .li,.".~ l film is about 800~C, as evidenced by weight loss, while the morphology shows visible oxidation etching pits at temperatures as low as 600~ C.
Thus, di~mc~n~l films also show promise for finding utility in a mllltit~l(le ofapplications, in~ lin~ electrical applications.
Currently, ~h~mic~l vapor deposition ~ n~l film has experienced limited market entry primarily as heat sinks for laser diodes. However, there are many other industrial uses planned for diamond film, virtually all of which require met~lli7~tion.
For example, diamond film substrates have been hailed as the only solution to many of the thermal management problems currently encoullL~;Ied in the electronic and optoelectronics par.k~ing area. As the packing density of electronic systems increases, this thermal m~n~gemP.nt problem is only going to exacerbate. Met~lli7~tion of diamond film s~tl~Les with highly con~ cting metals such as gold and copper is essPnti~l for these applications. Some of the applications which are in dire need of the development of a tenaciously adhering contluctinp~ metal film on a tli~monrl substrate include laser diodes and diode arrays for telecommunications, power modules for on-board s~tellite~, high powered microwave modules, MCMs, and especially 3-D MCMs.

However, while the industry is in dire need of a tenaciously adhering (>lKpsi onpeel test) electroplated con-luctin~ metal film on a diamond substrate, the rhemir~1 inertness of rli~mond resists the formation of adherent co~ting~C on it. This is especially true for large area (>lmm x lmm) diamond film subsLI~les and thick metal films (>2 microns).
P~esell~ly, met~lli7~ti~n is accomp1i~hed through some form of physical vapor deposition. While this produces a high quality film, it also produces high m~tPri~l cost due to its extreme waste of metal. Ele.,LIùpl~ g is prt;r~l~ble because is allows metal to be deposited selectively, which would cut waste by over 90% from what is con~11med in a physical vapor deposition process.
Physical vapor deposition processes are ~iUI i ell~ly the industry standard because films deposited by such processes tend not to blister or peel at high temperatures. In a physical vapor deposition process, the substrate is mounted inside a high vacuum~'.1".",1,~.i . The ~.llnlllh~l is evacu~te-l, and metal is either evaporated or sputtered to form l 5 a coating on the sub~LI ~le. The ineffici~nr,y of the technique is due to the metal coating that is deposited onto the rest of the vacuum cl ~lll~el at the same time. Only a small xll~age of the metal that is consumed by the process lands on the substrate, with the rest being lost.
Ele.illupl~ g would seem to be the proper ~n~ e for mrt~11i7ing rli~mnnt1 film with gold. With cle~,llopl~Lillg, the plated metal is applied directly to the target, resulting in much less waste as colllp~ed to physical vapor deposition. However, even though cle~iLIopld~ has ~ nh1i~ d itself as a workhorse technology for cost effective thin film and foil f~hrir~tion in the ele.;ll~ ~s industry, only sputtering and evaporation of gold and copper have so far been collllnelcially s11r~ces~fi1lly utilized in m~t~lli7ing diamond film s~sLI~les (and only on small substrates and only to small thirl~n~ses).
"Met~11i7in~ CVD Diamond For Electronic Applications", Iacovangelo et aL
Tntf~.m~tional Journal of Microelectronics And Electronics p~r~ging, Vol. 17, No. 3, at 252-258 (1994), discloses a physical vapor deposition technique for depositing a gold layer onto a .1;, ~ film. As disclosed by Iacovangelo et al., thin gold films are applied to metal seed layers on diamond films by either a spulleling process or a rhemi~ l vapor deposition process.
As shown for coat numbers 11-13, the gold layers applied by the tearhings of Iacovangelo et al. exhibit ~he~ n to the diamond substrate on the order of 4 to 10 Kpsi.
Unfortunately, the gold layers produced by Iacovangelo et al were on the order of 0.5 microns thin, too thin for use in most applications.
Iacovangelo et al., further disclose the electroplating of a triple layer of copper, nickel and then gold onto a patterned thin film. However, as shown in Figure 4 of Iacovangelo et al., this ele~,LIoplated layer is on the order of 200,~bm wide, far too narrow for many applications. Electroplating onto diamond film substrates on the order of lcm x 1 cm or larger requires that the problems induced by thermal stress be solved.Iacovangelo et al. do not disclose or teach how to electroplate onto larger diamond film substrates in a manner sllfficiçnt to overcome the problems induced by thermal stress. Biaxial stresses increase with h~creasillg diamond film size.
,~1rlition~l p~ with applying metal layers to ~ ,o~ films include blistering, peeling and dçl~min~tion.
Therefore, there is a need in the art for a process for met~lli7in~ diamond and other types of substrates which does not suffer from one or more of the prior art limit~fion~
There is another need in the art for an ele-illoplating process for met~lli7in~
~ mnntl and other types of s~sLI ~Les which does not suffer from one or more of the prior art limitations.
There is even another need in the art for an electroplating process for met~lli7ing diamond and other types of substrates which provides a product with suitable adhesion between the gold layer and the diamond film.
There is still another need in the art for an electroplating process for met~lli7ing diamond and other types of subsL~Les which provides a product with suitable surface ro~lghn~
There is yet another a need in the art for met~lli7ed diamond and other types ofsubstrates which do not suffer from the prior art limit~tion~
There is even still another need in the art for a met~lli7ed diamond and other types WO 96/33298 PCT/US96/047~4 of substrates with suitable adhesion between the gold layer and the diamond film.
There is even yet another need in the art for a met~ 7ed diamond and other typesof substrates with suitable surface roughnPqq These and other needs in the art will become appalenl to those of skill in the art ~ 5upon review of this spe~ific.~tion.

SUMMARY OF THE INVENTION
It is one object of the present invention to provide a process for met~lli7ing mnn~1 and other types of sul,:,L, ~les which does not suffer from one or more of the prior 10art limitations.
It is another object to provide for an electroplating process for met~lli7.ing mnntl and other types of s~ Lt;S which does not suffer from one or more of the prior art limit~tiQnq.
It is even another object to provide for an electroplating process for met~lli7.ing 15diamond and other types of substrates which provides a product with suitable adhesion between the gold layer and the rli~montl film.
It is still another object to provide for an electroplating process for mP,t~lli7in~
diamond and other types of substrates which provides a product with suitable surface roughnPqq 20It is yet another object to provide for mets~lli7ed t1i~mon~1 and other tvpes of substrates which do not suffer from the prior art limit~tionc It is even still another object to provide for a met~lli7P,d diamond and other types of substrates with suitable ~tlhP.cion between the gold layer and the ~ monrl film.
It is even yet another object to provide for a met~lli7P,d diamond and other types 25of substrates with suitable surface roughnesq.
These and other objects ofthe present invention will become appalelll to those of skill in the art upon review of this specifiç~tion.
Accc l d;llg to one embodiment of the present invention there is provided a method of electroplating an article having a surface with peaks and valleys, and articles made theler.ol.. The method generally inc.llldçs electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.
According to another embodiment of the present invention there is provided a method of ele~;llupldlil~g an article having a surface with a surface rollghneee, and articles made Lllererlc,lll. The method generally inrllldes electroplating a conduct*e metal onto the surface utilizing a current density less than or equal to J0, to form a conductive metal layer having a surface ro~lghnees no greater than the article surface ro~lghnPeeAccording to even another embodiment of the present invention there is provided a method of electroplating an article compnsing a supporting member and a seed layer supl)c,l~ed by the sllp~ Lillg nlc;llllJt;l, with the seed layer having a surface with peaks and valleys, and articles made therefrom. The method generally in~.llldes electroplating a con-lllctive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.
Accold.l~ to still another embodiment of the present invention there is provideda method of electroplating an article comprising a supporting member and a seed layer supported by the diamond member, with the seed layer having a surface with a surface rou~hnPqe, and articles made therefrom. The method generally incllldee electroplating a conrluctive metal onto the seed layer surface utili7ing a current density less than or equal to J0, to form a con-luctive metal layer having a surface roughness no greater than the seed layer surface ro~lghness.
Accol ding to yet another embodiment of the present invention there is provided a method of met~lli7.ing a diamond film, and articles made therefrom. The methodgenerally in~.hldes a first step of applying a seed metal onto the diamond film to form a seed layer having a surface ro~lghn.oee, with the seed layer having a surface with peaks and valleys. The method further inrllldes ele~illoplalillg a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal.
According to even still another embodiment of the present invention these is provided a method of mP.t~lli7.ing a diamond film, and articles made therefrom. The method generally in~ ldes applying a seed metal onto the diamond film to form a seed layer, with the seed layer having a surface with a surface roughness. The method further inr~ es electroplating a conductive metal onto the seed layer surface uti~ ing a current density less than or equal to J0, to form a conductive metal layer having a surface roughness no greater than the seed layer surface roughness S According to even yet another embodiment of the present invention there is provided a method of electroplating an article to form an electroplated layer having a desired surface ro~1ghnçqc, and articles made thel~fiulll. The method generally inr.l1ld~c (a) electroplating at a current density, a conductive metal onto the article to form an electroplated layer. The method further inchlcles (b) detelllfilling the surface roughness ofthe ele.iL,uplaLed layer. The method still further int~111(1es increasing the current density of step (a) if the surface roughness determined in step (b) is less than the desired surface roughness, and decreasing the current density of step (a) if the surface roughness dt;~ e(l in step (b) is greater than the desired surface roughn~c~ This method may be operated interactively until the desired surface roughn~cc is obtained for the thi~l~nes.c required.

FIGs. lA-C, show respectively, substrate 10 with irregularity 20 without an ele~,LlùplaLed metal, substrate 10 with irregularity 20 ele~iLluplated over by electroplated metal 30, and substrate 10 with irregularity 20 electroplated s~sL~lially filled by electroplated metal 30.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a method for electroplating a conductive metal onto a target conductive metal layer surface, such that the formed electroplated metal layer will have a resulting surface roughn~sc less than the initial surface roughn~sc of the target layer.
~ The present invention also provides a method for ele~,LlùplaLillg a conductive metal onto a target conductive metal layer surface, such that the formed electroplated metal layer will have reduced likelihood of blistering away from the target layer at elevated temperatures, and will have good adhesion to the target layer.
The present invention generally in~ des a first step of met~lli7ing a supportingsubstrate to form a seed layer, followed by electroplating a conductive layer onto the seed layer. Alternatively, the present invention may also be utilized to ele.;LIoplale a conductive metal directly onto a conductive substrate even without a seed layer.
In the practice of the present invention, the substrate may comprise any material that will be suitable for the desired application. Non-limiting examples of supporting substrate m~t~.ri~l~ include metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.
Although much of the following description for the present invention makes reference to tli~m~ntl film as the substrate, it is to be understood that this invention finds applicability to any type of substrate.
The ~l;n~ films utilized in the practice of the present invention are well knownto those of skill in the art. The diamond films utilized in the present invention may be made by any suitable process. G~nel~lly, such suitable methods of making diamond films are generally ~h~ d as chemical vapor deposition techniques such as hot fil~m~ntDC arcjet, RF arcjet, microwave plasma, and microwave plasma jet methods.

Initial trç~tment of the supportin~ substrate In the practice of the present invention, the supi)ol ~h~g substrate must generally be cleaned to provide a proper surface for m~.t~lli7ing For example, with diamonds and many metals, such cle~ning generally includes degreasing, removal of residual carbon, and the removal of the cleaning solutions.
For 1 - n~ methods of cleaning a diamond film are well known to those of skill in the art, and any suitable method may be utilized. Degreasing is generally accomrli~hed by boiling the ~ mon~1 film in suitable chemical solvents, non limiting eY~mples of which include trichloroethylene, acetone and alcohols. The removal of residual carbon is generally accompli~h~od at slightly elevated temperatures ufili7ing an acid wash followed by a base wash. As a non limiting ~ - r lei, residual carbon may be removed using sulfuric acid/chromium trioxide at 160~C followed by ~,l.. ol-i~lm hydroxide/hydrogen peroxide at 70~C. P~c~ c of these cle~nin~ solutions are then removed by subjecting the diamond film to ultrasonic rlç~nin~ in deionized water.
In some applications, it will be necçcc~ry that the surface ro~ghnçss of the final ele.iLluplaled con~lctive layer be quite low. For c,~ lc, many electrical applications will S require the final electroplated conduct*e layer have a surface ro~lphnecc less than about 350 nm, ~ r~;~ly less than about 300 nm, and more pr~r~l~bly less than about 250 nm, and most preferably less than about 200 nm. Of course, it is to be understood that the present invention can be utilized to form a final electroplated conductive layer having almost any desired surface ro~lghnçss.
The surface rol-ghnPcc ofthe underlying ~ul~ Le will tend to infll-~.nre the surface rol-ghnrec ofthe final ele~illuplaLed conrl~ctive layer. It is generally plt;rt;;lled to start with a substrate having a surface roughness near that desired in the final electroplated con~ ctive layer. Likewise, the surface ro~-~hnecc of the seed layer on the substrate will also tend to inflllçnre the surface ro--ghnrcc of the final electroplated con~l-lctive layer.
Thus, if a seed layer is utilized it is generally plt;rt;lled to utilize one having a surface rol-ghnec.c near that desired in the final electroplated conductive layer.

Application of seed layer Once the substrate is degreased and r.le~netl, the optional seed layer may be applied. Methods of applying a seed layer to a substrate, especially a diamond film are well known to those of skill in the art. In the practice of the present invention, the seed layer may be applied using any suitable technique. In general, physical vapor deposition methods are utilized to create the seed layers. Such techniques include sputtering techniques, thermal evaporation, and electron-beam evaporation, and are well known to those of skill in the art.
Apparatus for accomplishing physical vapor deposition are well known, and any suitable appal~L~Is may be utilized in the practice of the present invention. Suitable eql-ipmrnt inrl.ldrc a ~L~da--l thermal evaporator such as the Edwards E306A (Edwards Colllpally, Great Britain) coating system.
According to the present invention, the seed layer may include one or more subsurface layers. Optionally, the seed layer may further include a top surface layer of the same metal as the metal to be electroplated onto the seed layer. Of course, any metal or material that will adhere to the SI1IJ~O1 Liilg substrate, and provide a suitable surface for the electroplated metal may be utilized. Non-limiting examples of materials suitable for use as the seed layer(s) include ~ mimlm, copper, chromium, gold, nickel, niobium, p~ll~tlillm, pl~timlm, silicon, t~nt~lllm~ il "." t~ln~t~n, and collll,illalions of any of the rOI~goll~g Titanium will tend to diffuse into gold. Therefore, if th~ni--m is utilized as asubsurface seed layer, a layer of pl~timlm or tlmg~t~n is generally utilized between the tit~nil-m and gold layers.
With some metals, the seed layer will tend to be susceptible to de1~"il-,.l;on unless the substrate is heated prior to and during the physical vapor deposition process. The temperature is generally great enough to discourage del~min~tion of the final seed layer but less than the degradation telll~el~L~Ire of the ~ mt)nfl film or the metal melting point, whichever is less. For example, generally during the physical vapor deposition process of depositing a chromium seed layer onto diamond film, the diamond film is heated to a le,ll~ L~lre in the range of about 150~C to about 400~C. Preferably, the physical vapor deposition process is carried out at a telll~el~L~Ire in the range of about 175~C to about 300~C, and most plerel~ly at a t~lllp~ L,lre in the range of about 1 85~C to about 225~C.
While various opc;l~ling pressures may be utilized, it is plt;r~;;ll ~;d that the physica vapor deposition process for applying the seed layer is generally carried out at near vacuum, on the order of about 6X10~ millibar or less, preferably on the order of about lX10~ millibar or less. It is important that the vaporized chemical be thermally driven to the target in a relatively unimpeded manner. Thus, it is n~cess~ry to create proper conditions so that the vaporized çh~mic~l will have a high mean free path, on the order of a m~ nihlde greater than the f~iet~nce between the ~hlomic~l target and the supporting substrate.
Generally, the vacuum chamber is purged with nitrogen prior to obtaining the vacuum, to remove substantially all oxidants.
In the practice of the present invention, the seed layer must have a relatively perfect crystal structure, which structure can be infl~enced by the application rate. Low seed layer application rates are utilized to provide a seed layer with the proper crystal structure. Suitable application rates are on the order of 5-10~/sec or lower.
Electroplating a conductive layer S Once the seed layer is in place, the cQn~1u~tive layer is applied onto the seed layers ili7.ing an electroplating technique.
The inventors have determined that electroplating at low electroplating rates, RL~
utilizing low ele~ opla~ g current df~ne~ip~J JL~ will result in an ele-,~,ol)la~ed layer having a surface roughnPcc less than that of the underlying layer upon which it is electroplated, with roughness declc;a~illg with de~ ;d~illg RH and JH The inventors have also determined that electroplating at high electroplating rates, RH~ utili7ing high electroplating current dP.nCh;PC, JH~ will result in an electroplated layer having a surface roughnP,ss greater than that of the underlying layer upon which it is electroplated, with roughn~ss increasing with increasing RH and JH- An interme~ te electroplating rate R;" utili~ing an intermediate current density J0, such that RL<RO<RH~ and JL<JO<JH~ will result in an electroplated layer having a surface roughnP,,cs equal to that of the underlying layer upon which it is electroplated.
The present invention thus provides a method of forming an electroplated layer having a surface ro lghn~cc less than or equal to the surface roughness of the target layer, by utilizing an electroplating rate less than or equal to RO, at interme~ te current density less than or equal to JO.
The present invention also provides a method of forming an electroplated layer having a target surface roughnPcc by monitoring the rou~hn.occ of the forming el~,~,LIoplaled layer, and ,ll~lt;a~ing the elc~Lluplalillg rate and current density above RO and JO, if the lllolllLoled roughn~cc is less than the target rou~hnesc, and by decreasing the electroplating rate and current density below RO and ~ if the monitored roughn~cc is greater than the target roughness.
The particular deposition rate or current density which will result in an ele.,LIopldled layer having a roughn~cc greater than, less than or equal to that of the layer upon which it is ele~illupldLed~ will vary accolding to the type of metal being electroplated, = =

the type of cle~iLI~lJlaLillg solution utilized, pH, solution density, bath te",pc;,~u,t:, anode-to-cathode ratio, type of agitation, as well as other factors. It is generally nece~ ry to conduct a simple test over a range of deposition rates or current densities to determine RO
and JO, and the ranges for RL~ JL~ RH and JH
For; r1~ when utilizing a certain colllllwl~ilally available gold plating solution, it is generally nece.~ry to provide a current density at the anode of less than 1 mA/cm2 to provide an ele~iLI opla~ed layer having a surface ro~l~hn~e~ less than the roughness of the underlying layer. Pl~:rt:l~bly, the current density at the anode will be in the range of about 0.001 to about 0.95 mA/cm2, more plert;l~bly in the range of about 0.01 to about 0.7 1 0 mA/cm2, even more preferably in the range of about 0.1 to about 0. 5 mA/cm2, and most preferably in the range of about 0.1 to about 0.2 mA/cm2, to provide an electroplated layer having a surface ro~ghnes.c less than the roughness of the underlying layer.
The surface of a substrate is not regular and may contain many irregularities, which may be naturally occurring, an unwanted result of processing or h~n~11ing, or may intentionally m~mlf~ tllred into the substrate (such as vias). As used herein, the irregularity will be characterized as having a valley or low region, and peaks or high regions.
An alternative electroplating embodiment of the present invention in~ ldes electroplating a surface having surface irregularities such as crevices, cracks, grooves, exposed microcavities, sc, ~lches, slits, slots, openings, hollow portions, cavities, chambers, notches, pits, holes, vias, and/or voids. According to this alternative embodiment, the electroplating is con~ cted such that the surface irregularity is substantially filled by the electroplating process.
Rt;rt;,t;"ce is now made to FIGs. lA-C, which show It;~e-;Li~rely, substrate 10 with irregularity 20 without an electroplated metal, substrate 10 with irregularity 20 electroplated over by electroplated metal 30, and substrate 10 with irregularity 20 substantially filled by electroplated metal 30.
While not wishing to be limited by theory the inventors believe that electroplating over irregularities, as shown in FIG. lB will result in lower adhesion, and will provide trapped electroplating solvents which will boil at elevated temperatures and blister the article. The inventors also believe that the prior art electroplating methods generally would ele~ opldLe over any surface irregularities, because at higher current d~.n~itie.~ the electroplating charge would acc~-m~ te at the surface ofthe substrate, at peaks, and be depleted at the bottom, or valley, of the irregularity. The inventors further believe that lower current d~on~ities allow for the metal to substantially fill the irregularity, resulting in better adhesion Thus, the present invention in~ (ies electroplating a surface having surface irregularities such as crevices, cracks, grooves, exposed microcavities, scratches, slits, slots, openings, hollow portions, cavities, chambers, notches, pits, holes, vias, and/or voids, to s~bst~nti~lly fill S~L~ILi~r all of the irregularities with the electroplated metal.
Plcrel~ly the volume of an irregularity is at least 50 percent, more plcrtlably at least 80 percent, even more preferably at least 90 percent and even more preferably at least 95 percent, still more preferably at least 98 percent, and most preferably at least 99 percent filled. Preferably at least 50 percent, more preferably at least 80 percent, even more pl e rt;l ably at least 90 percent and even more ~1 ercl al)ly at least 95 percent, still more ~Icrcl~bly at least 98 percent, and most plere,~bly at least 99 percent ofthe irregularities on the surface will be filled.
The proper ele-,lloplàLillg rate can be easily determined by varying the electroplating rate over a range and analyzing the filling of the irregularities.
In the practice ofthe present invention, the electroplating is generally carried out as follows. The supporting Illclllbcl with seed layer is co~ e~iled to a cathode and a pl~tin--m plate connected to the anode. With the supporting member and platinum plate submerged in an electroplating solution, a current is applied to drive the electroplating process.
The process ofthe present invention finds utility in providing useful products for use in electronic appli. ~linn~ The products ofthe present invention have utility in a broad range of elecLI. ~, applicaLiolls, in~ ing sre~ifi~lly as diodes, flat panel displays, power ~mrlifi~rs, and as m--ltir.hir modules in general.

EXAMPLES
The following non-l~miting ~ l l~s are provided to further illustrate the invention and are not meant to limit the invention in any manner. The following Procedures I-III
di.~c--cses the general method of preparing mP.t~lli7etl diamond film.
Procedure I
General Sample Pl epal ~lion The r1i~mon-1 samples utilized in the Examples were lcm x lcm di~mon-l film, produced by standard çhlo.mic.~l vapor deposition ("CVD").

De~l ~asillg the diamond film The first step in sample pl~pal~Lion is degreasing, in which the diamond sample is sequentially boiled in trichloroethylene, acetone and then mçth~nol.
The diamond sample is placed in 400 ml of trichloroethylene in a 600 ml Pyrex beaker. Next, the beaker is placed on a standard hot plate inside a fume hood. By means ofthe hot plate, the trichloroethylene is brought to a boil. A~er 15 mimltes, the ~i~mon~
film is removed from the boiling trichloroethylene. Unless otherwise specified, the diamond sample is always handled ~ltili7in3~ metal tweezers and holding the diamond by the edges.
The above procedures are next repeated with acetone. The diamond sample is placed in 400 ml of acetone in a 600 ml Pyrex beaker. Next, the beaker is placed on a standard hot plate inside a fume hood. By means of the hot plate, the acetone is brought to a boil. After 15 mimltçs, the diamond film is removed from the boiling acetone.
The above procedures are next repeated with meth~nol. The diamond sample is placed in 400 ml of mP.th~n~l in a 600 ml Pyrex beaker. Next, the beaker is placed on a ~L~da~d hot plate inside a fume hood. By means ofthe hot plate, the meth~nol is brought to a boil. After 15 minllte~, the diamond film is removed from the boiling m.eth~nol.

Removal of residual carbon from the diamond film 3 0 1 gram of chromium trioxide powder is stirred into 400 ml of semiconductor grade CA 022l8392 l997- l0- l6 sulfuric acid in a 600 rnl Pyrex beaker. Next, the beaker is placed on a standard hot plate inside a fume hood. By means of the hot plate, the mixture of sulfuric acid/.,hloll-iu trioxide powder is heated to 160~C. The diamond film is placed in the mixture for 30 min-ltes and then removed.
A similar procedure is repeated with a mixture of 200 ml of semiconductor grade ~"""o~ m hydroxide and 200 ml of hydrogen peroxide in a 600 ml Pyrex beaker. This beaker is placed on a sL~ndald hot plate inside a fume hood. By means ofthe hot plate, the mixture is heated to 70~C. The fli~monfl film is placed in the mixture for 30 minutes and then removed.

Removal of residual cleaning solution The diamond sample is placed in 600 ml of deionized water in a 600 ml Pyrex beaker. The beaker is then placed inside a standard ultrasonic cleaner, with the fli~monrl sample subjected to ultrasonic cleaning for at least three hours.
Procedure II
Pl e~al dlion of the seed layer A seed layer was applied to the cleaned diamond film samples of Procedure I
utilizing an Edwards E306A coating system. The Edwards E306A is a standard thermal evaporator, the operation of which is known to those of skill in the art, and which was operated generally as follows.

Mounting of the diamond film samples After venting the vacuum f~.h~mh.or with nitrogen gas, the bell jar is removed.
Removal ofthe bell jar provides access to and permits subsequent removal of the sample holder, i.e. the metal plate at the top of the appal~lus under the jar. Next, one of the screws in the sample holder metal plate is loosened, and a corner of the diamond film sample is placed under the screw. The .li~ .i sample is oriented such that the substrate side of the sample is against the plate, with the growth side of the sample facing out. The ~ 30 screw is then tight- nPd until the washer is snug against the holder, sufficiently tight to WO 96/33298 PCT/US96/047~54 secure the sample when the plate is held upside down. The sample holder is then placed in the evaporator. The piezoelectric holder is then placed in its standard position.

Mounting the chromium and gold targets First, the center target holder, and two of the ~elipl~ l target holders on the target holding appa~ s are loosened. Next, a standard ~hermal evaporation chromium stick, commercially available from R.D. Mathis Company, is positioned with one end in the center target holder, and the other end in one of the peripheral target holders. A
standard thermal evaporation molybdenum boat, also commercially available from R.D.
Mathis Company, is positioned with one end in the center target holder, and the other end in the other peripheral target holder. To encourage good electrical connections, a small metal shim is inserted between the molybdenum boat and washer of the center target holder, and the chromium holder is rotated until the chromium target is in electrical contact with the side electrode. Next, all the target holders are ti~htened to secure the chroll~lll stick and the molybdenum boat. Finally, a small 2mm x 2mm x 2mm nugget of gold of at least 99.99% purity is placed in the molybdenum boat.

Heater Adjllstment For proper operation, it is nPcç~ry that the radiant heater is pointed at the ~ mnn~l film s~mpl~ that the thermnco-lple is close to the di~montl film samples, but not shadowing any of them from the evaporating metal, and that the window on the radiant heater is clear and not covered with metal.

Pumpdown The rotary pump is Png~ged to pump down the vacuum chal,lbel until the Piranni gauge reads 0.06 mbar. Next, the diffusion pump is ~ng~ged and filled with liquid nitrogen. To protect the operator from exposure to the radiant heater, a cover is placed over the bell jar. The radiant heater is set to 200~C and ~ng~ed Over the next few hours, the diffusion pump is operated to take the pressure in the vacuum chamber down to 6E-6 mbar.

Thermal evaporation of the seed layer The thermal e~/~ol~lor is first operated to form a chro~ lll layer directly on the diamond film, and then operated to form a gold layer on the clll on~iulll layer.First utili~in~ the chromium stick as the target, the current is increased until a chromium deposition rate of 0.5 to 1.0 nm/sec is achieved, to form a chromium layer from 17.5 nm to 22.5 nm thick. Subsequently, the target holding ap~ L~Is is rotated so that the gold nugget in the molybdenum boat is now the target. The current is increased until a gold deposition rate of 0.5 to 1.0 nrn/sec is achieved, to form a gold layer from 275 nm to 325 nm thick.
Once the clll~llliulll and gold layers are formed, the current is stopped, the SU~ e heater is turned off, the tliffil~ion pump is ~ Png~ge~l, and the chamber is vented once. The chamber is pumped down again, but with the roughing pump instead of with the rlifl;l~ir~n pump. The apparatus is then allowed to cool at room te;llllJel~Lule for about an hour, at which time the chamber is again vented, and the seed layer coated diamond film removed.

Procedure III
Plepal~lion of gold layer Diamond film samples from Procedure II having a chromium and gold seed layer are utilized in this Example.
800 ml of a sulfite-based, non-toxic gold electroplating solution, available from r,.~Pl~ d is utilized in a 1500 ml Pyrex beaker. The solution must be tested to make sure its operational pal~llelt;l~ are within tolerances. The pH, which must be between 10.5 and 11, is ill,l~ased with KOH and dew~ased with DI water. The density, which must be between 12~ Baume ("Be") and 16~Be, is increased with gold concentrate from Englehard, and decreased with DI water.
During the electroplating operation, the solution is ~git~ted by means of a m~gnP,tir. stirbar, and the solution temperature is ~ ;..Pd between 55~C and 60~C by means of an electrical hot plate.
The ~l;~,.. ~n~ sarnple is ~tt~-~hed to the cathode ~llig~tor clip, and a pl~tim-m plate WO 96/33298 PCT/US961047~4 (2" x 2") is ~tt~rhrd to the anode alligator clip. Only about S cm2 of the anode is placed into the solution. A standard HP power supply which provides current measurable to a tenth of a milli~mp is utilized.
The electroplating is cnn~lucted at a current of 0.5mA, which sets the current density at the cathode to 0.5 mA/cm2, to provide a deposition rate of about 0.4 microns gold/hr. The electroplating is continued until the desired thiçL-nrs~ of gold is obtained.

Procedure IV
Peel Test Procedure The plated diamond films from Procedure III are tested using the "Peel Test"
procedure of ASTM B-571 (11), except that an ~lllmimlm test strip is substituted for the steel or brass strip. The equipment utilized was a Seb~ti~n III tester.
The non ele~ uplaLed (back) side of the diamond film is secured to an ~lllmimlm b~.kpl~te using J.B. Weld epoxy. An alllminllm pull strip is secured to the electroplated (front) side of the ~ monll film using J.B. Weld Epoxy. A metal clip is utilized to press the pull strip against the sample. The sample is then allowed to cure at 1 50~C for 3 hours, and at room Lel..~ L~Ire for 21 hours. The Sebaefi~n III tester is then utilized to provide a pulling force at a pulling angle 90~ to the surface of the film, to pull the ~lnmimlm pull strip off of the diamond film. The digital display will indicate the force with which the m~rhine was pulling when the pull strip was removed. By dividing this force value by the area of the pull strip, it can be reported in pounds per square inch.

Example 1 Control At Hi~h Deposit Rate A lcm x lcm diamond sample was coated with a seed layer of 200A chromium and 3000A gold by Procedures I and II as shown above. Seven gold layers were then applied at various current densities utili~ing Procedure III above at the parameters as shown in Table 1 below.

Table 1 Layer No. Current Density Ek,~ u~Jlal;llg Layer Thickness Total Thickness Deposit (mA/cm~) time (min) (~m) (!lm) Rate (llm/hr) " I 5.6 0.5 0.3 0.3 36 2 5 1 0.4 0.7 24 3 10 2 0.8 1.5 24 4 10 2 0.5 2.0 15 4 1.0 3.0 15 6 10 2 0.5 3.5 15 0 7 10 2 0.5 4.0 15 Peel Test of Procedure IV was con~ cted on the above 7 layer sample: sample peeled at 20 pounds (350psi).

Examl~le 2 Control At High Deposit Rate A l cm x l cm diamond sample was coated with a seed layer of 200A chromium and 3000A gold by Procedures I and II as shown above. A 4.5 ~lm gold layer was applied at a deposition rate of 18 ~m/hr utili7ing Procedure III. Peel Test results utili~ing Procedure IV was as follows: peeled at 251bs (440 psi).

Example 3 Rou~hnçss vs. Deposit Rate Two lcm x lcm 11;," ". ~ samples "A" an "B" were each coated with a seed layer of 200A chlo1l~-1 and 3000A gold by Procedures I and II as shown above. Eight layers of gold were then deposited on each seed layer by Procedure III above, with surface rol l~nP.~ measured initially and af[er deposition of each gold layer. Results are presented in Table 2.

WO 96133298 PCT/US96/047~;4 Table 2 Cumulative layer Current Density at Deposition rate F~nn~hn.~.cg ;. L ,.~ c~ (~m) anode (mA/cm2) (~bm~r) (nm) SAMPLE"A"

1.3 5 20 350 1.6 0.5 0.1 232 1.9 0.5 0.1 200 2.0 0.5 0.05 187 2.2 0.5 0.07 162 2.3 0.5 0.05 140 4.0 1.8 0.6 221 SAMPLE "B"

1.3 5 20 350 1.6 0.5 0.1 240 1.9 0.5 0.1 246 2.0 0.5 0.05 212 2.2 0.5 0.07 180 2.3 0.5 0.05 190 4.0 1.8 0.6 230 Example 4 Annealing of seed layer 3 lcm x l cm diamond samples "C" were each coated with a seed layer of 200A
chromium and 3000A gold by Procedures I and II as shown above. 3 l cm x l cm rii~mnn~l samples "D" were each coated with a seed layer of 200A chromium and lOOOA gold by Procedures I and II as shown above, and an additional 2000A gold by Procedures I and WO 96133298 PCT/US96/047~i4 II as shown above, except that an deposition temperature of 50~C was utilized.
For samples C-l and D-1, the seed layer was not ~nn~le~l, for sample C-2 and D-~, 2, the seed layer was ~nn~le~l at 300~C, and for s~mrles C-3 and D-3, the seed layer was ~nn~led at 400~C. All samples were then electroplated with a 5A thick gold layer at 0.8 J' SmA/cm2 by Procedure III above.
These six ele.,l,~?laLed samples were all subjected to anns~lin~ at 350~C. Finally, all samples were subjected to the Peel Test of Procedure IV. Results are shown in the following Tables 3-6.

10 Table 3 Surface Rol-~hness Of Seed Layer Before Electroplating (nm) SAMPLES C SAMPLES D
1 (SEEDLAYERNOT 250 250 ANNEALED) 2 (SEED LAYER 254 269 ANNEALED AT 300~C) 3 (SEED LAYER 262 288 ANNEALED AT 400~C) Table 4 Surface Roughness 25Of Electroplated Gold Layer (nm) SAMPLES C SAMPLES D
1 (SEED LAYERNOT 181 206 ANNEALED) 2 (SEED LAYER 183 233 ANNEALED AT 300~C) 3 (SEED LAYER 150 207 ANNEALED AT 400~C) Wo 96/33298 PCT/US96/047S4 Table 5 Surface Roughness Of Electroplated Gold Layer - After Annç~lin~ At 350~C (nm) SAMPLES C SAMPLES D
1 (SEED LAYER NOT 180 213 ANNEALED) 2 (SEED LAYER 180 230 ANNEALED AT 300~C) 3 (SEED LAYER 250 450 ANNEALED AT 400~C) Samples in the bottom row blistered, accounting for the high surface ro-lghn~es Tablç 6 Peel Test Results (PSI) SAMPLES C SAMPLES D
1 (SEED LAYER NOT 2400 (epoxy broke) 2900 ANNEALED) 2 (SEED LAYER ANNEALED 2900 (limit of peel tester) 2900 AT 300~C) 3 (SEED LAYER ANNEALED 33 0 AT 400~C) Example 5 Thermal Stress and Thermal Cycling Of Large Samples (21mm x 21mm) 21mm x 21mm samples were each coated with a seed layer of 200A chrol"iu"l and 3000A gold by Procedures I and II as shown above. Seed layers were subjected to no ~nn~lin~, ~nn~ling at 350~C, or ~nn~linF~ at 400~C. A gold layer of 5A was then deposited on the seed layer of each sample by Procedure III above. One set of samples was then subjected to thermal stress (~nn~lin3~) at 350~C or 400~C for 30 mim-t~

Another set of samples was then subjected to thermal cycling from 150~C to -65~C, in close agreemt;l~l with military standards. The samples were subjected to 16 cycles, with a cycle as follows: climbing to 150~C in 15 mimltc~, dwell for 15 mimlte.~, down to -65~
in 15 minlltes, dwell for 15 mimltes This procedure varied from standard military sperifir,~tion~ in that 15 minute L~ re ine~ llLs were utilized instead of 10 minute in.,l~",e"L~.

Table 7 Peel Testin~ After Thermal Cyclin~ (PSI) SAMPLES For Thermal SAMPLES For The~nal Stress Cycling l(SEEDLAYERNOT 350~C:3600 3600 ANNEALED) 400~C:2000 2 (SEED LAYER ANNEALED 350~C: 3600 3600 AT300~C) 400~C: 1800 3 (SEEDLAYERANNEALED 350~C:0 0 AT400~C) Example 6 21mm x 21mm s~mples of tli~montl were degreased and cleaned according to Procedure I above. The teaching~ of Procedure II were followed to deposit the seed layer, except that the thickness of chromium was always 300 ang~L,~J",s, and copper was deposited instead of gold. The copper was deposited to a thic.1~n~ of 2000 angstroms, but at varying substrate temperatures. Also, the base pressure in the thermal evaporator cl~"l~el was varied. Also, the te"lpe,~L.lre ofthe seed layer anneal step was varied. All of the samples were then electroplated with cooper to a thic~ness of 8-10 microns. All ofthe samples were then anne~le~ at 350~C. All ofthe samples were then observed for blisters.

Table 8 SAMPLE EVAPORATION EVAPORATION SEED LAYER BLISTER
SUBSTRATE BASE PRESSURE ANNEAL RATING
TEMPERATURE (MBAR) TEMPERATURE
(~C) (~C) 1 200 1.3E-6 AMBIENT MEDIUM
2 200 1.3E-6 300 MEDIUM
3 200 1.3E-6 400 MEDIUM
4 Cr: 200 1.3E-6 AMBIENT LOW
Cu: 50 1 .SE-7 Cr: 200 1.3E-6 300 LOW
Cu: 50 1 .5E-7 6 Cr: 200 1.3E-6 400 VERY LOW
Cu: 50 1 .SE-7 7 Cr: 200 1.3E-6 AMBENT HIGH
Cu: 50 1 .SE-7 8 Cr: 200 1.3E-6 300 HIGH
Cu: 50 1.5E-7 9 Cr: 200 1.3E-6 400 N/A (etched Cu: 50 1.5E-7 off) While the illustrative embodiments of the invention have been described with particularity, it will be understood that various other modifications will be appalelll to and can be readily made by those skilled in the art without departing from the spirit and scope of the invention. Acc~ldillgly, it is not intP.nrled that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompa~ing all the features of p~tent~hle novelty which reside in the present invention, in~ tlin~ all features which would be treated as equivalents thereof by those skilled the art to which this invention pertains.

Claims (30)

I CLAIM

1. A method of electroplating an article having a surface with peaks and valleys of initial surface roughness RO, the method comprising:
cleaning the conductive surface; and electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal to form an electroplated article having a surface roughness RE, wherein the electroplating, wherein the electroplating is carried out at a current density less than or equal to JO;
wherein JO is a current density which will result in the electroplated article having a surface roughness RE equal to RO.

2. The method of claim 1 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.

3. The method of claim 1 wherein the article comprises a supporting member and a seed layer forming the conductive surface.

4. The method of claim 3 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.

5. The method of claim 3 wherein the supporting member comprises diamond, and the seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.

6. A method of electroplating an article having a conductive surface with a surface roughness RO, the method comprising:
cleaning the conductive surface, and electroplating a conductive metal onto the surface utilizing a current density less than or equal to JO, to form a conductive metal layer having a surface roughness RE no greater than the article surface roughness RO;
wherein JO is a current density which will result in the conductive metal layer having a surface roughness RE equal to RO.

7. The method of claim 6 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets.

8. The method of claim 6 wherein the article comprises a supporting member and a seed layer.

9. The method of claim 8 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.

10. The method of claim 8 wherein the supporting member comprises diamond, and the seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.

11. A method of electroplating an article comprising a supporting member and a seed layer supported by the supporting member, with the seed layer having a conductive surface with peaks and valleys, the method comprising:
cleaning the conductive surface; and electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal wherein the electroplating is carried out at a current density less than or equal to JO
wherein JO is a current density which will result in the conductive metal layer having a surface roughness RE equal to RO.

12. The method of claim 11 wherein the article comprises metals, diamond, semiconductors, ceramics, thermoplastics or thermosets

13. The mahod of claim 11 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.

14. The method of claim 11 wherein the supporting member comprises diamond, andthe seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.

15. A method of electroplating an article comprising a diamond member and a seed layer supported by the diamond member, with the seed layer having a conductive surface with a surface roughness, the method comprising:
cleaning the conductive surface; and electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to JO, to form a conductive metal layer having a surface roughness no greater than the seed layer surface roughness

16. The method of claim 15 wherein the seed layer comprises aluminum, copper, chromium, gold, nickel, niobium, palladium, platinum, silicon, tantalum, titanium, tungsten, or combinations of any of the foregoing.

17. The method of claim 15 wherein the supporting member comprises diamond, andthe seed layer comprises chromium and gold, and the conducting metal comprises gold, wherein the chromium is adhered to the diamond.

18. A method of metallizing a diamond film comprising:
(a) applying a seed metal onto the diamond film to form a seed layer having a surface roughness RO, with the seed layer having a conductive surface with peaks and valleys;
(b) cleaning the conductive surface; and (c) electroplating a conductive metal onto the peaks to cover the peaks with the conductive metal, and into the valleys to substantially fill the valleys with the conductive metal, to form an electroplated article having a surface roughness RE, wherein the electroplating is carried out at a current density less than or equal to JO;wherein JO is a current density which will result in the electroplated article having a surface roughness RE equal to RO.

19. The method of claim 18 wherein in step (a) the diamond film is heated prior to applying the seed metal

20. The method of claim 18 wherein the seed metal comprises chromium, and the substrate is heated to a temperature in the range of about 150°C to about 400°C prior to applying the chromium.

21. The method of claim 20 wherein the seed metal further comprises gold.

22. The method of claim 21 wherein the conductive metal comprises gold.

23. The method of claim 22 wherein the electroplating is conducted at a currentdensity in the range of about 0.001 to about 0.95 mA/cm2

24. A method of metallizing a diamond film comprising:
(a) applying a seed metal onto the diamond film to form a seed layer, with the seed layer having a conductive surface with a surface roughness RO;

(b) electroplating a conductive metal onto the seed layer surface utilizing a current density less than or equal to JO, to form a conductive metal layer having a surface roughness RE no greater than the seed layer surface roughness RO;
wherein JO is a current density which will result in the electroplated article having a surface roughness RE equal to RO.

25. The method of claim 4 wherein in step (a) the diamond film is heated prior to applying the seed metal.

26. The method of claim 24 wherein the seed metal comprises chromium, and the diamond film is heated to a temperature in the range of about 150°C to about 400°C prior to applying the chromium.

27. The method of claim 26 wherein the seed metal further comprises gold.

28. The method of claim 27 wherein the conductive metal comprises gold.

29. The method of claim 28 wherein the electroplating is conducted at a current density in the range of about 0.001 to about 0.45 mA/cm2.

30. A method of electroplating onto a conductive surface of an article to form an electroplated layer having a desired surface roughness RD, the method comprising:
(a) electroplating at a current density, a conductive metal onto the conductive surface of the article to form an electroplated layer of surface roughness RE;
(b) determining the surface roughness RE of the electroplated layer;
(c) increasing the current density of step (a) if the surface roughness RE
determined in step (b) is less than the desired surface roughness RO, and decreasing the current density of step (a) if the surface roughness RE determined in step (b) is greater than the desired surface roughness RO.