US 3573098 A
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Description (OCR text may contain errors)
March 30, 1971 J w, BlEBER ET AL 3,573,098
ION BEAM DEPOSITION UNIT 2 Sheets-Sheet 1 Filed May 9. 1968 March 30, 1971 w, B|EBER ET AL 3,573,098
ION BEAM DEPOSITION UNIT Filed May 9, 1968 2 Sheets-Sheet 2 TEMPE FA Tl/AE GRAD/El) T BY DARRELL M- .5017
United States Patent lint. Cl. C230 13/00, 13/12 US. Cl. 1l72l2 4 Claims ABSTRACT 0F THE DISCLOSURE An ion beam deposition apparatus wherein a supply of ions is generated and purified in an ion source; extracted and accelerated from the ion source by a first pair of concentric hemispherical electrodes; focused into an ion beam by a second pair of concentric hemispherical electrodes and selectively deflected by a pair of planar electrostatic deflection plates to form a circuit pattern upon a substrate. The ions are generated in the ion source by heating a deposition material to a temperature sufiicient to initiate vaporization and by establishing a localized arc discharge between an electrode and the deposition material to increase vaporization and to ionize the vaporized atoms to create a uniformly charged species of ions.
CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of United States patent application Ser. No. 438,604, filed Mar. 10, 1965, now abandoned.
BACKGROUND OF THE INVENTION The present invention relates to deposition apparatus and more particularly to means in combination with apparatus for depositing ions on a substrate whereby ions having a high current are selectively produced so that the percentage of desired ions of the total ions produced is very high.
The manufacture of thin film and semiconductor integrated microelectronic circuits presently is accomplished by the condensation of metallic and insulating aggregates of atoms and molecules upon a suitable substrate. Areas upon which condensation occurs are selected by the use of masks, either in the form of thin stencil sheets or photographic emulsions. Deposits from the vapor are formed only on unmasked areas. These masks are costly and time-consuming to fabricate. They are difficult to align in the vacuum chamber where deposition occurs and they rapidly become so thickly coated with deposits that they must be discarded. If ditferent thicknesses of one material must be deposited on a substrate surface, a separate mask must be used for each thickness. Also, each different material must have its own set of masks. Large metal masks warp away from the substrate, thereby limiting the size of the circuit capable of being fabricated on a single surface. The ion beam deposition technique according to the teachings of this invention eliminates the need for masks. The material in the instant invention which forms the circuit elements is deposited from a collimated beam of ions. The charged nature of the ions allows the size, thickness and position of deposit to be regulated electrostatically and electromagnetically so that no masks are required. In the present state of art of microelectronic circuit production, several days may elapse between initial circuit design and the finished circuit. This is necessary because accurate mask layout must be made, the mask must be produced, and each production chamber must be equipped with the proper combination of masks, substrates, and source materials. With the ion beam deposition equipment, any circuit configuration can be produced with one apparatus; there are no special equipment requirements for any circuit. Beam current, particle energy, deposits thickness, and pattern definition, are controlled electronically either by manual control, semi-automatic control, or by a programmed computer. Thus, the time consumed for a completed circuit is only that time necessary to program the circuit parameters into a form acceptable to the computer or operator and the time required for actual deposition of materials.
When a deposit is made by atomic techniques now in use upon a surface, the adhesion of the deposit film to the substrate is often weak so that the film is unsuitable for use in microelectronic applications. Because the particles deposited by the instant invention are energetic, undesirable surface layers of atmospheric gases, which adhere to substrate surfaces in even very low vacuums, are removed. Also minute fissures in the substrate surface are created by the particles into which the film subsequently deposited can become locked. Both these efiects, which are the result of using the instant invention, insure the adhesion of a film to a substrate surface, insuring, in turn,
' the reliability of the film for microelectronic applications.
Active elements are produced in semiconducting substrates by introducing impurity elements to change the electrical conduction characteristics of the substrate. Diffusion oven supply heat which enhance the natural diffusion of the impurities into the semiconducting material. The fact that the ion beam can be energy regulated will allow artificial diffusion to take place; i.e., the depth of penetration and quantity of ions of a desired impurity can be regulated by the energy and density of the ion beam. Thus, semiconductor integrated circuits can be produced with the ion beam in a shorter time, with less expensive equipment and with carefully controlled electrical characteristics.
Artificial diffusion can be practiced by the instant invention for a variety of microelectronic applications Where it is advantageous to penetrate a previously deposited material with a material diiferent than that which is previously deposited. For example, the electrical characteristics of semiconductor or dielectric films can be altered by artificially diiiusing small quantities of material, commonly called impurities, into the material, or the characteristics of metal films can be altered by artificially diifusing small quantities of metal different than the previously deposited metal film, a process commonly called alloying. The in stant invention can, in addition, be used to directly form films having the characteristics of those films made by the artificial diffusion procedure just described. By precisely controlling the purity of the ion beam, that is, by precisely controlling the composition of the beam, deposits with small impurity concentrations or specified alloy characteristics can be formed directly.
The concept of a collimated ion beam, whose current, energy and purity is adjustable, is applicable to any process in which material is to be deposited in atomic form into or on a surface, or where energy is to be delivered to a target in a controlled manner. Examples of these processes arc: welding or cutting of metals and nonmetals; sensitization of metal and nonmetal surfaces; plating of surfaces; deposition of inorganic and organic materials; creation of microminiature relief maps or other analogs; creation of patterns, either microminiature or full size, which represent stored information such as braille writing or any other process of information storage; any process in which an ionizable material is to be deposited into or on a sur face; and any process in which energy is to be delivered to a collector or target.
If ions rather than neutral atoms are utilized in making the deposits, the velocity and trajectories of the ions may be controlled.
A description of an attempt to create an ion beam deposition unit can be found in the proceedings of the third symposium on electron beam technology (given Mar. 23, 24, 1961, edited by R. Bakish and published by Alloyed Electronics Corporation, Cambridge, Mass). Two recent patents, to George A. Bronson, No. 3,117,022, and Robert W. Morris, No. 3,133,874, provide apparatus which illustrate embodiments of ion deposition apparatus. Certain unique and improved characteristics are presented by the instant invention which are not disclosed or taught by any of the aforementioned prior art.
SUMMARY OF THE INVENTION It is therefore an object of this invention to produce a source of ions of a deposition material that can be accurately deposited in a preselected configuration by ion beam deposition.
It is another object of this invention to produce a source of ions of a uniform charge species.
It is another object of this invention to provide a source of ions having a narrow spread of kinetic energy.
It is another object of this invention to provide a source of ions relatively free of contamination by unionized atoms.
These and other objects of this invention are accomplished by first vaporizing atoms from a deposition material in an ionization source. This vaporization is accomplished preferably by first heating the deposition material to a temperature sufiicient to initiate vaporization of the deposition material and then maintaining a low potential localized arc of energetic particles between an electrode and the deposition material. The localized arc imparts additional energy to the deposition material causing increased vaporization of atoms in the locale of the arc discharge. The vaporized atoms are then singly ionized by bombardment of the energetic particles of the arc. Single ionization is insured by maintaining the potential of the localized are at a level between the first and second ionization potentials of the vaporized atoms. Extraction of only ions from the ionization source is facilitated by maintaining the localized are perpendicular to the direction of ion extraction so that the unionized atoms will not enter the ion extraction path.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the over-all components of the instant invention including interconnecting electrical controls and power sources diagrammatically shown by arrows.
FIG. 2a is a cross-section schematic view illustrating the instant invention;
FIG. 2b and FIG. are detail perspective of the vapor source and ionizer assembly which forms the means for selectively producing pure ions, and forming in part the over-all combination of FIG. 2a, minus interconnecting electrical circuitry for purposes of illustration and drawing convenience.
FIG. 3 is a perspective view showing the instant invention in combination with multiple ion sources and multiple substrates available so that many circuits of the same or different design or pattern can be produced using any desired combination of materials without replacing or reloading the vapor sources, or replacing or reloading the system with new substrates.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to figures, like components of the instant invention have been given like numeral designations. In FIG. 1, a block diagram represents the major components of the instant invention. A means for producing selective ions 1 provides a vapor or gas composed of atoms or molecules of the material to be deposited. The means 1 includes a vaporizer 1a which produces vapor from a solid or liquid atomic form, or provides vapor from a gaseous atomic form of a material to be deposited, and an ionizer 1b which forms ions from some or all of the atomic or molecular vapor or gas which has been formed in the vaporizer In. An ion extractor 5 removes ions from the ionizer 1b, leaving neutral atoms and excluding particles whose electrical charge is different from the ions desired in the collimated beam. A beam purifier 7 removes from the ions formed by means 1 those ions which are not desirable; e.g., unwanted residual gas ions formed in the ionizer 11) or other element ions or compound ions. A velocity control means 9 accelerates or decelerates the ions from the extractor 5 electrostatically to be desired velocity. A beam focuser or momentum selection means 11 electrostatically and/ or electromagnetically selects and forms the ions into a fine beam of circular, ellipsoidal, or rectangular cross-section. The beam, a collimated beam, is electrically controlled by the beam focuser 11 so that largeor small-beam sizes are obtainable when desired. A second purifier, beam positioner 13, forms means to control the ion beam direction to a position on the collecting substrate surface at which deposition is desired. This control is accomplished by mechanical movement of the collecting substrate surface and electrostatic and/ or electromagnetic deflection of the ion beam. A beam neutralizer or means for neutralizing an ion beam 15 forms neutral atoms or molecules from the ions in the collimated beam. A collecting substrate surface 17 is the surface on or into which the material is deposited. Electronic control means 19 and 21 are electrically connected with the means 1 through 17. The electronic control means 19 and 21 control: quality and type of material vaporized in the vaporizer means 1a; the quantity of vapor ionized in the ionizer 1b; the magnitude of beam current; the purity of the beam realizable in beam purifier 7; the geometric ion beam cross-section; the velocity of ions in the beam determined by 9; the position, geometry, and quantity of the deposit; and the degree of vacuum established in the partial vacuum chamber. The electronic control means 19 and 21 are capable of preprograrnming to allow the entire procedure to proceed automatically to complete the desired deposit. The entire procedure is also capable of manual or semi-automatic control. Electronic control is capable of accepting from an operator instructions for controlling different deposit geometries, different ion energies, different beam purity and composition, and different deposit electrical characteristics.
The functions outlined and defined in general terms above need not be separate and distinct. One or many functions may be accomplished in one single operation in a device using the ion beam principle. Also, the functions of an ion beam device need not be in the order of the above description.
Referring now to FIGS. 2a through 2c, the configuration of the over-all combination of the instant invention is shown. Several different types of vapor source means 2 can be used to supply atomic vapor: an alumina or other refractory crucible wrapped with resistively heated tungsten wire; a tantalum boat resistively heated; an alumina or other refractory crucible heated with an electron gun or other means of electron or ion discharge; and direct electron bombardment of refractory materials in an alumina or other refractory crucible are a few examples. Means 4 disposed to direct a discharge of energetic particles such as electrons at said vapor source means may for example comprise an ionizing filament 4 made of 20 mil tantalum wire wound in a bi-filar spiral of approximately one-quarter inch diameter or any electron emitting filament which is sufliciently small to be contained in the space provided, such as a rectangular grid, or a circular coil formed from one or many turns of wire, or a point filament formed by a single bend in a single wire, is separated during operation approximately one-quarter inch above deposition material 6 in vapor source 2 and approximately one-half inch below a heat reflecting cover hood 8. The ionizing filament 4 is given a negative potential with respect to the deposition material 6 and the plasma cover hood 8 by connecting a lead from filament support 30 with a unrpotential voltage source 18. Porcelain insulators 32, attached to frame 34 by bolts 36, support filament support 30 and hood 8. Frame 34 is welded to heavy support frame 38. When the vapor source means 2 is not heated, a current of ten amperes through the ionizing filament 4 produces a pure electron flow toward the deposition material 6 of approximately ten milliamperes. Circuit means 28a connect vapor source means 2 with a voltage source 28; as the vapor source means 2 is heated using current from source 28, the deposition material 6 begins to vaporize. As will be taught below, the circuit means and voltage source 28 associated with vapor source means 2 comprise means disposed to confine the discharge of electrons from filament 4 to a desired area on the surface of deposition material 6. Deposition material vapor is directed upward toward the ionizing filament 4. Ionization of deposition material atoms in the vapor is accomplished by collision with electrons flowing from the ionizing filament 4. The device will now produce ions which can be extracted by the ion extractor and used in the instant invention. The rate of ionization is increased by the addition of a magnetic field about the plasma which forms between filament 4 and vapor source means 2. As seen in FIG. 2b such a magnetic field is generated by magnetic field means 3 (for example, a solenoid) disposed (by supports not shown) around the means for selectively producing pure ions 1. The magnetic field means 3 is energized by any voltage source (not shown) sufficient to provide a magnetic field within means 1, about the plasma as noted above, strong enough to cause spiralling of the electrons but not the ions. The spiralling effect allows the electrons to travel a greater distance between filament 4 and vapor source means 2 than otherwise is the case. The magnetic field also produces a pinch etfect upon the plasma, thereby increasing the density of the plasma in which ionization occurs due to energetic particles from filament colliding with atoms, within the plasma, from vapor source means 2. The total effect, as noted above, increases the rate of ionization.
The magnetic field means 3 is not illustrated in FIG. 2a in order to reduce the complexity of FIG. 2a. In construction of the means 3 about the means 1, however, certain requirements must be met that can be considered with reference to FIG. 2a even though means 3 is not illustrated therein. The coil of the means 3 is of such geometrical configuration that the apertures; e.g., vapor source and ionizer assembly opening 26 and the immediately opposed opening 40 in hemisphere 10, are not obstructed, and that the mechanical function of the means 1 and extractor assembly 5a is not interfered with. In addition, the axis of the coil of means 3 is oriented parallel to the direction of the discharge from filament 4 to deposition material 6; i.e., the coils of means 3 must be so oriented with respect to means 1 that the direction of the magnetic field is oriented parallel to the direction of the discharge from filament 4 to deposition material 6.
The operation of vaporizer 1a, ionizer lb, and purifier 7 is greatly improved in the instant invention, both in the quantity of desired ions produced compared to the total ions produced and in the quality of the ions produced, by carefully controlling the temperature of deposition material 6 in vapor source 2, the potential of the discharge are between filament 4 and vapor source 2, and the orientation of the discharge are with respect to the direction of extraction of the ions from ionizer assembly 1 as defined by openings 2d and 40. As used here, the quality of the ions produced, and hence the quality of the ion beam, denotes the absence of ions with a wide range of kinetic energies, the absence of ions of more than one charge species, and the absence of contaminants such as an ionized atoms or vapor in the ion beam. In the fabrication of microelectronic elements by ion beam deposition, an extremcly high quality ion beam is a necessity in order for the ion beam to be precisely focused and deflected to deposit circuit geometries of high definition.
In particular, it has been found desirable when generating ions in ionizer assembly 1 to heat deposition material 6 in vapor source 2 to a temperature such that vaporization of atoms for deposition material 6 is just ini tiated and that a relatively small quantity of atoms congregate above the surface of vapor source 2. This temperature is approximately 1100 C. to 1300 C. depending upon the composition of the deposition material d in vapor source 2.
A relatively low voltage potential is then applied between filament 4 and vapor source 2 to establish an arc discharge between filament 4 and deposition material 6 in vapor source 2. This are discharge will be localized in nature and will fix upon a nucleating point in vapor source 2 usually defined by a hot spot on the surface of deposition material 5, where there is an abundance of vaporized atoms. Once the arc discharge is established, additional energy is supplied to the surface of deposition material 6 by the impingement of the electrons of the are. This increased application of energy to the localized surface of deposition material 6 causes the vaporization of increased numbers of atoms resulting in a dense population of atoms of the deposition material in the region of the arc discharge between filament 4 and vapor source 2. Because vapor source 2. is heated to a temperature to just initiate the vaporization of atoms, and because of the low potential of the arc discharge, the vaporized atoms will possess relatively low and substantially uniform kinetic energies. This characteristic is important to insure a high quality ion beam in this invention. This mode of operation is to be contrasted with prior art devices where a high potential of 1000 volts or more is applied across a filament and a vapor source to produce a general discharge known as a glow discharge; or where the vapor source is heated to such a high temperature that massive vaporization of the deposition material occurs. In the practice of the instant invention, the vapor source 2 is heated only to the point where the atoms of the deposition material 6 in vapor source 2 begin to vaporize to form a nucleating point for the arc discharge between filament 4 and vapor source 2. The potential between the filament 4 and vapor source 2 is then maintained at a low level, to be more particularly set forth below, so that the arc discharge remains localized causing the evaporization of additional atoms from a particular area on the surface of vapor source 2. In this manner only sufficient atoms that can be efficiently ionized are vaporized from vapor source 2 and these vaporized atoms all possess nearly uniform kinetic energy thus insuring efficient utilization of the deposition material and a high quality ion beam.
After the atoms of deposition material are vaporized from vapor source 2, they are ionized by the repeated collisions with the electrons in the discarge arc. It is important to the functioning of the ion beam apparatus that substantially all of the vaporized atoms of the deposition material be ionized to the same degree and thus constitute a uniform charge species. This is accomplished by removing the same number of electrons from each of the vaporized atoms so that all atoms are either singly ionized, doubly ionized, etc. Since the ionization potential for each level of ionization is distinct and increases for each higher degree of ionization, the degree of ionization of the vaporized atoms can be controlled by controlling the potential of the arc discharge between filament 4- and vapor source 2. It has been found preferable to generate a population of atoms ionized to a single charge species by maintaining the potential of arc discharge at a level greater than the first ionization potential of the vaporized atoms but less than the second ionization potential. In this manner, the vaporized atoms in the vicinity of the arc discharge: will be singly ionized and the statistical probability for the occurrence of doubly or higher charged ions is extremely small.
Thus, the maintenance of a low vapor source temperature and a selected low discharge are potential not only makes possible the eflicient use of the deposition material in vapor source 2 and a narrow spread of ion kinetic energies as set forth above, but it also insures that the ions will all be of the same charge species. The desired arc discharge potential is dependent upon the composition of deposition material 6 in the vapor source. The first and second ionization potentials, designated V and V respectively, for three commonly employed deposition materials are set forth in the following table along with the temperatures to which the materials have Additional refinement of the quality of the ion beam, in the nature of preventing the entrapment of unionized atoms in the stream of ions extracted from the ionizer assembly, can be achieved by properly orienting the discharge arc between filament 4- and vapor source 2 with respect to the direction of extraction as defined by openings 26 and 40. After establishment of the discharge are between filament 4 and vapor source 2, nearly all of the atoms of deposition material 6 vaporized will be vaporized in the area where the discharge are impinges upon the surface of vapor source 2. These vaporized atoms will remain in the vicinity of the discharge arc and Will move in directions generally parallel to the dischargearc. By positioning the are substantially perpendicular to the direction of ion extraction as defined by openings 26 and 40 very few, if any, of the unionized atoms will enter the ion extraction path. This configuration further insures the quality of the ion beam by reducing the incidence of unionized atoms, or vapor, in the ion beam.
The ion source assembly comprising vaporizer 1a; ionizer 1b and beam purifier 7 is useful in many other applications in which a high current of pure heavy ions is either essential to or improves the operating characteristics of the application. For example, in ion accelerator applications requiring a source of heavy ions; in vacuum tube applications in which a filament or other electrode deteriorates and requires re-plating to return the tube to normal operation, or in any sealed chamber in which it is desired to produce a coating on some or all parts of the enclosure.
The plasma hood 8 serves to increase further the efliciency of the ion source assembly of FIGS. 2b and 2c and prevents the vacuum chamber 23, as seen in FIG. 3, which surrounds the entire apparatus from becoming coated with condensed vapor. The plasma hood 8 is made of tantalum, or any refractory metal, and heat generated by the plasma is usually suflicient to revaporize most of the material condensed on it. The plasma hood 8 reflects radiant heat, maintaining the temperature in the region of vapor ionization at a higher level than without the hood. It is this combination of a plasma cover hood with an ionizing filament in the ionizer assembly 1b which establishes aportion of the novelty of the instant invention.
Continuing with refrence to FIG. 2a, an ion extractor assembly m consists of two tantalum hemispheres 10 and 12, with radii of curvature one and one-half inches and one-half inches, respectively. Holes of .234 and .125 inch, respectively, were bored in the center of the curvature of the hemispheres 10 and 12. The larger hemisphere 10 was placed with its .234 hole 40 just above the ionizing filament 4 and one-quarter inch in front of the vapor source and ionizer assembly opening 26. The hemisphere 10 is electrically grounded, or at a voltage nearer zero than hemisphere 12, by means of a lead connecting hemisphere 10 to a voltage source 28. The smaller hemisphere 12, placed concentric to the larger hemisphere 10, is operated at a high negative potential, also derived from voltage source 28, ranging from 1000 to l5,000 volts with respect to the larger hemisphere 10. Approximately 5,000 volts are usually used, since at this voltage sufiicient ions are extracted and no breakdown problems are encountered. The electric fields thus set up by the ion extractor assembly 5a (hemispheres 10 and 12) extract ions from the plasma existing inside the vaporizer and ionizer assembly 1 and accelerates them toward the smaller hemisphere 12 due to the high negative potential existing there with respect to hemisphere 10. The electric field configuration is such that the ions partially focus and a large portion of them pass through the hole in the small hemisphere 12 of the ion extractor assembly 5a.
Continuing with reference to FIG. 2a, an electrostatic beam focus 11a, which also functions as a decelerator and velocity control unit, is composed of two hemispheres 14 and 16 identical in size and shape to the hemispheres 12 and 10, respectively, of ion extractor assembly 5. In the beam focus 11a, the smaller hemisphere 1a is placed in electrical contact with a smaller hemisphere 12 of the ion extractor 5a and is thus at the same negative voltage. The large hemisphere 16 of the beam focus 11a is connected by a lead to the voltage source 28 and acts both as a decelerator and a final focusing element. The velocity of the ions can be controlled by the potential derived from voltage source 28 on the large hemisphere 16. The velocity, in turn, determines the position at which the ion beam reaches its minimum focal diameter. Zero, negative, and small positive potentials from source 28 on this large hemisphere 16, with respect to ground, have used successfully. The voltages applied to the ion extraction hemisphere 12, and the ion decelerator or velocity control ion focus hemisphere 16 relative to the ion source and vaporizer assembly 1 are established by the unidirectional voltage source 28.
The position of ion impingement as a collimated beam upon a substrate collecting surface 17 is regulated by electrostatic deflection and by mechanical movement of the substrate 17. Electrostatic deflection is accomplished by the use of parallel metallic plates which comprise in part beam positioner or third beam purifier, deflection plates 13. By applying electric potentials to the deflection plates 13, an electric field is created which deflects the ions from their normal path. This is accomplished by applying to both deflection plates 13, a unipotential voltage from voltage source 18 while applying a variable directional voltage to plate 13 also from voltage source 18. The unipotential voltage on 13 from voltage source 18 is usually identical to that placed upon large hemisphere 16 by the voltage source 28, since distortion of the beam crosssection is less but any electrostatic field created between plates 13 will have the desired effect of deflecting the ions from their normal path. Since some impure ions are of different energy than the desired ions while also being of a different mass than the desired ions which are to be deposited on substrate 17 (that is, those ions not generated within means 1), they are deflected away from the position of the deposition; that is, the more massive particles are deflected less than the deposit ions; less massive particles are deflected more than the deposit ions. Thus, electrostatic deflection accomplishes two functions: beam deflection and further beam purification.
Continuing with reference to FIG. 2a, mechanical movement of the substrate 17 is achieved by conversion of a jewelers lathe compound 25 (that unit to which the cutting tool is normally attached and which controls the motion of a tool by means of two Vernier knobs). All standard lubricants are removed from the lathe 25 and replaced with vacuum lubricants. The movement knobs (shown only diagrammatically in FIG. 2a as 22) are removed and two stepping switches (not shown) are 9 mounted face-to-face on each movement shaft. Thus, the collector surface of the substrate 17 can be moved by external (not shown) electrical activation of the stepping switches (not shown) or by manual activation.
The ion beam should be neutralized immediately before or during impact with the collecting surface 17 so that succeeding ions will not be repelled by charge buildup. This is accomplished by bathing the collecting surface 17 with electrons from an incandescent filament a having a power source 18. This neutralizing filament 15a forms the beam neutralizer of the instant invention and can be made from mil tantalum wire bent into the shape of a circle about the same diameter as hole in the decelerator hemisphere 16, for example. With this neutralizing filament 15a placed about one-eighth of an inch away from the collecting surface of substrate 17 and concentric to the collimated ion beam, it is possible to deposit a nonconducting layer on nonconducting substrate surfaces 17.
As discussed above and presented here in summary, the ion beam current (collimated beam) is capable of control by several means: an increase in source heat by vapor source 2 results in increased vapor density which, in turn, will result in a more dense plasma at the ionizing filament 4; a higher negative voltage on the small hemispheres 12 and 14- results in more ions being removed from the plasma with concomitant stronger focusing so that more ions pass through the holes in the small hemispheres 12 and 14; a greater negative voltage on the large hemisphere 16 of the decelerator and focusing assembly 11a, which minimizes ion loss, results in more deposition on substrate 17. An operator has the option of choosing which control he will carry in order to change the ion current. The most convenient means to do this is by regulation of the source heat to the vapor source means 2, and as pointed out above such regulation comprises a feature of the instant invention.
The entire apparatus as described in FIG. 1 and FIGS. 2a, 2b and 2c excepting certain circuitry (not shown) is mounted in a partial vacuum chamber 23, having a vacuum pump 24, defined by dashed lines and shown in FIG. 3. A pressure within the vacuum chamber 23 of 10 mm. Hg is maintained during most operations of the device. The apparatus has an approximately eight cubic foot volume and is evacuated by a six-inch oil diffusion pump 24 having a liquid nitrogen cold trap backed by a l5-cubic-foot-per-minute holding pump (not shown).
The ultimate design of the device will take many different forms depending upon the specific application. For production of microcircuits, an embodiment of the ultimate design is shown in the FIG. 3 to be described below.
Referring to FIG. 3, since any thin film or semiconductor integrated circuit is generally made from several different deposited materials, means must be provided for several different ion source assemblies 1, as shown in FIGS. 1, 2a, and 2b. Multiple ion source assemblies 1 can be made available to the ion beam device by several different means. One example would be to place several separate and distinct ion source assemblies 1 upon a table 20 which can be rotated mechanically. Each ion source assembly 1 could produce ions of a type different from all the remaining, or several ion source assemblies 1 could produce the same type of ions so that the ion beam device would be long lived for any initial setup. A second example (not shown) of providing multiple ion source assemblies 1 would be to use a single source of energetic particles while a rotatable table disposes several different vapor sources and vapor source materials into proper position with respect to the source of energetic particles. Many other means by which the vapor source means 2, vapor source material 6, ionizer filament 4 and cover hood 8, as shown in FIG. 2b, can be combined so as to form the ion source assembly 1, whether as separate and distinct parts or as parts of assemblies, can be devised. Ionization will be accomplished using the arc discharge 1t) principle as described above. The type of vapor source means 2 will be dictated by the type of vapor material 6 to be vaporized.
Continuing with reference to FIG. 3, the ion extractor 5a removes ions from the ionizer .and vaporizer assembly 1; the beam focuser and decelerator velocity control unit a brings the ions to a desired velocity and forms them into a collimated beam. The deflection plates 13 act as a final beam positioner (and as a last ion beam purifier) to direct selected ions toward a focus in the plane of the substrate surface 17. As seen with reference to FIG. 2a, the plates 13 are operated as electrostatic deflectors. Other means such as electromagnetic coils can also be used.
In the embodiment of FIG. 3, many different substrates 17 are conveniently disposed to receive ion deposition. Several substrates 17 are placed circumferentially upon a turntable 20a, which is rotated by mechanical drive means (not shown). The desired substrate 17 can thus easily be disposed to receive ion deposition.
The requirements which must be fulfilled by the neutralizer 15a is that it supply to the substrates 17, large quantities of low energy electrons to efficiently neutralize the ions being deposited while at the same time not inter fering with the ion beam definition. This can be accomplished by using as neutralizer 15a a flood electron gun which indiscriminately sprays the entire substrate surface 17 with large quantities of electrons. Other means (not shown) will also suflice: by an electron filament located near the substrate, or by an electrically grounded conductive layer deposited on the substrate prior to use of the instant invention, or by starting deposition at a point which is grounded so that as deposition proceeds, the deposit itself neutralizes the charge. The substrate material or collective surface 17 can be any material useful in the microelectronic art. For example, silicon wafers are often used for producing integrated circuitry, while insulating or metal substrates are often used for thin film circuit production. To enable more than one circuit to be made during one chamber evacuation, a multiple substrates changer and storage mechanism may be included. This device would be capable of placing the substrate 17 into the desired position for deposit, removing the completed circuit from the deposit region and reloading the device with a new substrate. As mentioned in the discussion of FIG. 2a, the vacuum chamber 23 will be evacuated by a vacuum facility 24, such as a mechanical pump ganged with oil or mercury diffusion pumps or by any other vacuum pumping apparatus. The vacuum chamber 23 will be large enough to contain the device components, be equipped With pressure sensing devices (not shown), such as an ionization pressure gage, and possess sufficient electrical feed-throughs to external controlling mechanisms (not shown).
The over-all control unit shown in FIG. 1 as 19 and 21 is an input device which reduces idea to form; i.e., the various constants necessary to deposit the required amounts of material at predesignated locations on the substrate 17 and in the proper sequence originate from this unit. The control unit 19 and 21 may consist of manual, semi-automatic, or automatic control. The con trol can be connected to several independent ion beam deposition devices to increase the number of microelectronic circuits which are produced for any sequence of input commands.
Other ion beam control means well known in the art can be conveniently used in combination with the above apparatus. For example, a mass filter could be used to further purify and remove ions of mass different from the mass of the desired deposit ions, instead of using the described electrostatic means of the embodiments of FIGS. 2a and 3. The filter might be one of many mass spectrometer types such as the quadruple or magnetic sector.
Also, the ion beam focusing means 11a of FIGS. 2a and 3 is not unique as described but may include other 1 1 well known means such as a magnetic lens or other electrostatic lens configurations.
Once a pure beam of monoenergetic particles is obtained, one of many known focusing lens systems could be used to reduce the beam diameter to a desired value in place of the electrostatic beam focuser 11a in FIG. 2a. Such a lens system takes the high velocity beam, decelerates it to a low enough velocity for etficient deposit upon a collecting surface and directs the particles toward a focus in the plane of a substrate surface such as a surface 17 in the instant invention. Either magnetic or electrostatic lens systems can be used to fulfill the focusing requirements of such a beam focuser.
Instead of the parallel deflection plates 13, plates similar to those used in deflecting the electron beam in some cathode ray tubes, or as in electromagnetic focusing used in magnetic type cathode ray tubes or magnetic spectrometers, or by mechanical movement of the substrate, or by a combination of these methods, would equally well provide the necessary beam positioning just before the beam impinges on substrate 17. Space-charge dispersion of a charged ion beam becomes more severe for low velocity ions. This can be partially compensated for by focusing the beam with the beam focuser and decelerator velocity control unit 11a in a short distance. Thus, for deposition of thin film circuit elements which require a very small final beam diameter, mechanical movement of the substrates 17 to position the surface of substrate 17 is preferred.
'What is claimed is:
11. In a process for ion beam deposition in a partial vacuum which includes the step of generating a supply of ions of a deposition material by vaporizing atoms of the deposition material and ionizing said atoms by low potential arc discharge, an improved method of generating said ions comprising:
(a) initially heating the deposition material to a temperature just sufficient to initiate the vaporization of atoms from a nucleating point in the deposition material; then (b) establishing the low potential are discharge from an electrode terminating only at said nucleating point to vaporize additional atoms of the deposition material and to ionize said atoms; and
(c) deflecting said ionized atoms at a substrate to form a circuit thereon.
2. In a process for ion beam deposition in a partial vacuum which includes the steps of:
(a) generating a supply of ions of a deposition material in a vapor source;
(b) directionally extracting the ions from the vapor source; and
(c) deflecting the ions to a substrate; an improvement in step (a) comprising:
(d) heating the deposition material to a temperature no greater than that required to initiate the vaporization of a portion of the deposition material to form a nucleating point for the establishment of an arc discharge; then (e) establishing a directional localized low potential are discharge of energetic particles between an electrode and the nucleating point in the deposition material to increase the vaporization of the deposition material and to create a dense localized population of atoms between the deposition material and the electrode;
(f) maintaining the arc discharge at a limited potential to confine the arc discharge to a localized region and to ionize essentially all of the vaporized atoms to a uniform charge species; and
(g) deflecting said ionized atoms at a substrate to form a circuit thereon.
3. The process as claimed in claim 2 wherein the directionality of the arc discharge between the electrode and the deposition material is approximately perpendicular to the direction of extraction of the ions from the vapor source.
4. The process as claimed in claim 2 wherein the potential of the arc discharge is maintained at a level between the first and second ionization potentials of the deposition material.
References Cited UNITED STATES PATENTS 2,600,151 6/1952 Backus 313-63X 2,677,060 4/1954 Woodward et al. 313-63X 3,117,022 1/1964 Bronson et al 117212 3,245,895 4/1966 Baker et al. 11793.3X 3,341,352 9/1967 Ehlers 117-93.3 3,371,649 3/1968 Gowcn 204-192X RALPH S. KENDALL, Primary Examiner US. Cl. X.R.