Sputter enhanced ion implantation process

A sputter enhanced ion implantation process is disclosed that uses to advantage the ion beam sputtering phenomenon to deposit layers of coatings on surfaces of interest simultaneously with ion implanting that surface, and that without the use of a separate evaporation system. The process can be applied to almost any workpiece of varied geometries. The process can be used for the deposition of hard coatings as well as ion implanting soft solid lubricants into various substrates. The process is particularly suitable for improving the physical and chemical properties of workpieces exposed to excessive wear, erosion, corrosion and fatigue and workpieces benefitting from a reduced coefficient of friction, such as ball bearings, gears, toolings, orthopaedic surgical implants and the like.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to ion implantation and, more 
particularly, to a sputter enhanced ion implantation process that uses to 
advantage the ion beam sputtering phenomenon for forming layers of 
coatings on surfaces of interest simultaneously with ion implanting that 
surface. 
2. The Prior Art 
Ion implantation is a well known process. As known, ion implantation 
improves the physical and chemical properties of the surfaces of 
workpieces, such as razor blades and surgical instruments. See U.S. Pat. 
No. 3,900,636 entitled "Method of Treating Cutting Edges." See also U.S. 
Pat. No. 3,925,116 entitled "Superhard Martensite and Method of Making the 
Same." Of particular interest has been the ion implantation of workpieces, 
such as surgical orthopaedic implants, made from titanium and its alloys, 
see U.S. Pat. No. 4,465,524 entitled "Titanium and its Alloys." While 
effectively improving the wear performance of titanium-alloy surgical 
implants, ion implantation thereof has caused the surfaces of the implants 
to discolor at spots. In a recently granted U.S. Pat. No. 4,693,760 of 
mine entitled "Ion Implantation of Titanium Workpieces Without Surface 
Discoloration," it is noted that the discolorations on the ion implanted 
workpieces are sputter deposited thereon from parts located within the 
workpiece handling endstation due to sputtering by the ion beam. By 
preventing undesirable sputtering occasioned by ion implantation, the 
process of my U.S. Pat. No. 4,693,760 has achieved its stated objective. 
The disclosure and teachings of my said U.S. Pat. No. 4,693,760 are 
incorporated herein by reference. In a copending and related application 
Ser. No. 167,632, filed Mar. 11, 1988, entitled "Method and Apparatus for 
the Ion Implantation of Spherical Surfaces," Group Art Unit 111, and 
assigned to a common assignee with this application, to wit, Spire 
Corporation of Bedford, Mass., the adverse undesirable effects of 
sputtering during ion implantation also have been recognized and dealt 
with. Other workers in the field also have described the significance and 
adverse effects of sputtering experienced during the ion implantation of 
components for wear and corrosive protection. See F. A. Smidt et al, "U.S. 
Navy Manufacturing Technology Program on Ion Implantation," Materials 
Science and Engineering, 90(1987) pp. 385-397. These workers have noted, 
inter alia, that sputtering is an effect which must be taken into 
consideration for high fluence ion implantation. They have specifically 
noted that the "sputtering yield" depends on the energy deposition 
function, the escape depth for a sputtered ion, and the binding energy to 
the surface. They have also noted that the sputtering yield is a function 
of the angle of incidence of the ion beam on the sample. One of the 
consequences of this angular dependence of sputtering, these workers have 
observed, is the fact that the retained ion implanted dose at steady state 
is a function of the geometry of the part being ion implanted. 
Recently, certain unexpected advantages have been obtained using a hybrid 
process designated as ion-beam-assisted deposition (IAD), also referred to 
as ion-beam-enhanced deposition (IBED). See R. A. Kant et al, "Ion Beam 
Modification of TiN Films During Vapor Deposition," Materials Science and 
Engineering, 90(1987), pp. 357-365. In this hybrid process, a sample is 
provided with layers of coatings by reactive vapor deposition while at the 
same time the deposited layers are also exposed to bombardment by 
energetic ions of an ion beam. Some of these unexpected advantages have 
included a reduced oxygen contamination in the deposited layers of 
coatings, a broader coating-substrate interface, larger grains and 
increased lattice constants in the deposited layers of coatings, with the 
coatings being both denser and more adherent than conventionally prepared 
coatings without simultaneous ion bombardment. Additionally, the hybrid 
process allows for the production of considerably thicker layers of 
similar composition and structure to those obtained by direct ion 
implantation. The hybrid process also permits the fabrication of deposited 
coatings of unique microstructures, such as amorphous or metastable 
phases, it extends the range of allowable processing conditions, including 
deposition at room temperature, and it also provides for ion beam mixing 
of the coating-substrate interface. The hybrid process also is believed to 
reduce some of the problems encountered during conventional vapor 
deposition, namely poor adherence, high porosity and high internal stress 
prevalent in the vapor deposited layers. The hybrid process requires, 
however, the concurrent utilization of an ion beam implanter and of a 
reactive evaporation system, both designed to impact on a sample in a 
specially designed deposition chamber. The process is thus both expensive 
and cumbersome. 
SUMMARY OF THE INVENTION 
It is a principal object of the present invention to overcome the above 
disadvantages by providing a simplified process that achieves all of the 
advantages of the abovedescribed hybrid process but without the need for a 
separate evaporation system. 
More specifically, it is an object of the present invention to provide a 
sputter enhanced ion implantation process that uses to advantage the 
heretofore undesirable by-product of ion beam implantation, to wit, 
sputtering, to deposit layers of coatings on surfaces of interest 
simultaneously with ion implanting that surface and employing but an ion 
beam for accomplishing both tasks. The process essentially includes 
providing a fixture formed of a material intended for forming the coating 
on a workpiece presented by the fixture to an ion beam for simultaneous 
ion implantation. The coating is formed on the workpiece by sputtering of 
the fixture material upon being exposed to the ion beam, while the ion 
beam directly striking the workpiece and the thereon forming layers of 
coating is responsible for effecting the ion implantation of the surface 
of the workpiece. The process of the invention is applicable to almost any 
workpiece of whatever geometry. The process is useful for the deposition 
of hard coatings as well as ion implanting soft solid lubricants into 
various materials serving as substrates. The process of the invention is 
particularly suitable for improving, at reduced expense, the physical and 
chemical properties of workpieces designed to be exposed to excessive 
wear, erosion, corrosion and fatigue and workpieces benefitting from 
exhibiting a lower coefficient of friction at their surfaces. Some of such 
workpieces include ball bearings, industrial gears and toolings, and 
orthopaedic surgical implants and the like. 
Other objects of the present invention will in part be obvious and will in 
part appear hereinafter. 
The invention accordingly comprises the process of the present disclosure, 
its components, parts and their interrelationships, the scope of which 
will be indicated in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In general, the present invention pertains to a sputter enhanced ion 
implantation process that uses to advantage the ion beam sputtering 
phenomenon for depositing layers of coatings on surfaces of interest 
simultaneously with ion implanting that surface. 
Ion implantation to improve the physical and chemical properties of the 
surfaces of workpieces is well known. It also is known that the wear 
resistance of certain metals, such as titanium and its alloys, can be 
markedly improved by first providing their surfaces with a layer of metal 
coating by electron beam evaporation and then subjecting the coated 
surfaces to bombardment with light ions of an ion beam, causing part of 
the metal coating to embed into the titanium surface. See U.S. Pat. No. 
4,465,524, above mentioned. This patent, in also recognizing and 
mitigating the harmful effects of sputtering of the surface during ion 
implantation, employs light ions the mass of which is insufficient to 
cause such sputtering. One of the noted harmful effects of sputtering, in 
particular as applicable to orthpaedic surgical implants formed of Ti 
and/or its alloys, has manifested itself as surface discoloration. Its 
elimination during ion implantation represents the salient purpose of my 
said prior U.S. Pat. No. 4,693,760. The disclosure and teachings of this 
Patent No. 4,693,760 have been incorporated herein by reference. Others 
also have recognized the harmful effects of sputtering during ion 
implantation, see the article by F. A. Smidt et al. mentioned above. 
Some workers in the field have recently begun studying the role and effect 
of bombarding by energetic ions thin films during their reactive vapor 
deposition. See the R. A. Kant et al article referred to above. The study 
described therein pertains to an experimental system based on the 
concurrent use of an ion beam implanter together with an electron beam 
evaporation system. This hybrid technique has come to be known as 
ion-beam-enhanced deposition (IBED). FIG. 1 herein is a schematic 
representation of such an IBED system and has been reproduced in fact 
directly from said R. A. Kant article, specifically from page 358 thereof. 
As stated in said article, the IBED system of simultaneous ion 
implantation and thin film deposition is thought to offer many potential 
benefits. The IBED system allows for the fabrication of thicker layers of 
similar composition and structure to those obtained by ion implantation 
only. The IBED system also allows for the fabrication of unique 
microstructures, such as amorphous or metastable phases. The IBED system 
also allows for the extension in the range of allowable processing 
parameters, including deposition at room temperatures. The IBED system 
also allows for ion beam mixing of the film-substrate interface. The IBED 
system, according to the authors of said article, may also allow for the 
reduction and/or potential elimination of many of the problems encountered 
in thin film deposition, namely, poor adherence of the deposited film, and 
high porosity and high internal stress found in the deposited thin film. 
The IBED system represents, therefore, a most promising advance in the ion 
implantation art. 
The present invention is designed to achieve most, if not all, of the 
advantages of the IBED system without the need of employing a separate 
electron beam evaporation system. The process of the present invention is 
based on harnessing to advantage the ion beam sputtering phenomenon rather 
than suppressing it. The inventive process essentially comprises providing 
a fixture formed of a material intended for forming the layers of coatings 
on a workpiece presented by the fixture to an incoming ion beam for 
simultaneous ion implantation. The layers of coatings are formed on the 
surface of the particular workpiece by sputtering of the fixture material 
upon it being exposed to the ion beam. Simultaneously with the workpiece 
being sputter coated by the fixture material, the workpiece and the 
thereon forming coating are both being ion implanted by the energetic ions 
directly striking the surface of the workpiece. 
The process of the invention can be used practically on any workpiece with 
varied geometries. The process will now be described in more detail with 
reference to the drawing figures designed to illustrate, but not to limit, 
the applicability of the inventive process to various and variously shaped 
workpieces. 
As mentioned, the disclosure and teachings of my U.S. Pat. No. 4,693,760, 
granted Sept. 15, 1987, have been incorporated herein by reference. In 
particular, reference is made to FIG. 6 of said U.S. Pat. No. 4,693,760, 
which depicts a schematic view of an ion beam implanter with a workpiece 
handling endstation. The respective representative fixtures and workpieces 
illustrated in FIGS. 2-7 herein are all designed to be operatively mounted 
for cooling and/or rotation in the implantation chamber (i.e., the 
workpiece handling endstation) of such an ion beam implanter as shown and 
disclosed in said U.S. Pat. No. 4,693,760. 
In FIGS. 2-3, there is illustrated a fixture 10, which essentially is a 
plate formed with a plurality of cavities 12 in its front surface 14. 
Fixture 10 is removably mounted, for both rotation and cooling, on a base 
plate disposed within the implantation chamber of the ion beam implanter, 
see said U.S. Pat. No. 4,693,760. The cavities 12 are designed to 
accomodate a plurality of workpieces 16, herein being ball bearings, and 
to present these workpieces 16 to energetic ions 18 of an ion beam 
generated by said ion beam implanter. It will be noted that the fixture 10 
is presented to the ion beam at an angle, as indicated by an arrow 20, 
from the vertical. This angle can vary from about 10.degree. to about 
80.degree., and preferably is about 45.degree.. The selection of a 
specific angle is tailored to the task at hand, since it critically 
affects the implantation parameters and the resultant product of the 
sputter enhanced ion implantation process of the invention. 
It also will be noted that certain of the incoming energetic ions 18 strike 
the workpieces 16 directly, certain other energetic ions 18 strike the 
front surface 14 of the fixture 10 directly, and certain other energetic 
ions 18 strike the walls of the plurality of cavities 12 directly. The 
energetic ions 18 striking directly the plurality of workpieces 16 effect 
ion implantation of the surfaces thereof. The energetic ions 18 striking 
the front surface 14 directly do not appreciably affect the process of the 
invention. However, the energetic ions 18 striking the walls of the 
plurality of cavities 12 cause sputtering of the material thereof, 
depending on its sputtering coefficient and the energy level of the ion 
beam. It is this sputtering of the fixture 10, specifically of its 
component material, heretofore to be suppressed as undesirable, that the 
inventive process employs to advantage. It is the component material of 
the fixture 10 that serves as the material for forming the layers of 
coatings, by sputtering, on the surfaces of the workpieces 16 
simultaneously as these workpieces 16 are being ion implanted by the 
directly impinging energetic ions 18 thereon. Consequently, the energetic 
ions 18 directly striking the surfaces of the workpieces 16 not only 
penetrate these surfaces themselves, but in addition also serve to nail 
down the layers of sputter coatings simultaneously formed on the surfaces. 
Furthermore, the energetic ions 18 striking these surfaces, as they are 
being coated by sputtering, also propel some portions of the thereon 
sputtered layers of fixture material into the surfaces of the workpieces 
16 themselves. Further and depending on the choices of the component 
material for the fixture 10 and of the specific energetic ions 18 
generated by the ion implanter to impact on that specific fixture 
material, various advantageous chemical compositions and/or precipitates 
can be formed on the surfaces of the workpieces 16 or being implanted into 
those surfaces. The distances of implantation below the surfaces are 
largely influenced by: the level of energy of the ion beam, its current 
density, the ion dose on the surfaces of the workpieces 16 and of the 
fixture 10, its geometry factor, the maximum allowed temperature of the 
fixture 10 and of the workpieces 16, and the time duration of the ion 
implantation. 
It will be appreciated that the fixture 10 is both rotated, as indicated by 
an arrow, and cooled to a certain maximum temperature. As the fixture 10 
is rotated, the workpieces 16, i.e., the ball bearings herein, also rotate 
in their respective cavities 12, exposing thereby different surface areas 
thereof to the incoming energetic ions 18, as well as to the indirect 
actions of those energetic ions 18 striking the internal containing walls 
of the cavities 12. As a consequence, the entire surface of the workpieces 
16 is uniformly coated by the fixture material and is uniformly implanted 
by the energetic ions 18 of the ion beam. The varied combinations of 
fixture materials and choice of energetic ions to subject the workpieces 
16 to the process of the invention is limited only by the experimenter's 
imagination and/or the compatibility of the materials forming the 
workpieces 16 themselves. 
A further obtained advantageous result of the invention process resides in 
that the ion implantation yield, heretofore often less than 20 atomic 
percent due to sputtering, does not reach saturation levels until it well 
exceeds 20 atomic percent, and being about 100 atomic percent. 
During the sputter enhanced ion implantation, the relative exposure of the 
workpieces 16 to the direct impact of the energetic ions 18 versus the 
impact of the sputtering from the fixture 10 can be held constant by 
keeping the angle 20 constant. This relative exposure also can be varied, 
however, by changing the angle of incidence of the ion beam impacting on 
the fixture 10 and the therein contained workpieces 16. This change can be 
simply effected, even during the ion implantation process itself, by 
changing the angle 20 of the fixture 10, or more precisely its cooled 
mounting plate, with respect to the ion beam. This relative exposure is 
further influenced by the specific composition of the fixture material and 
by the configuration and location of the fixture with respect to the 
workpieces contained therein or associated therewith. 
The energy level of the ion beam can vary from about 500 eV to about 400 
keV, and is typically about 50 keV to about 180 keV, depending on other 
process variables and the desired specifications for the ion implanted 
workpieces. The fixture 10 can be formed of one or more of the group 
consisting of Pb, Ag, Sn, In, Au, Mo, W, Ta, Ti, U, Be, Mn, Fe, Co, Cu, 
Cr, Al, V, Ni, Zn, Si, C, B, Hf, Y, Zr, Nb, Pd, Pt, Ir and Os. The 
energetic ions 18 of the ion beam, on the other hand, can contain one or 
more of the group including H, N, B, C, Ne, S, Pb, 0, Si, Ar, Xe, Kr, Ag, 
Cr, Ti, Fe V, Co, Cu, Mn, Ni, Y, Zr, Nb, Mo, Hf, Ta, and W. The ball 
bearings 16 themselves can be formed of hardened steel, including 
austenite steel or martensite steel, or any other suitable metal. 
In FIGS. 4 and 5, the sputter enhanced ion implantation process of the 
invention is illustrated as being applied to a cylindrical industrial 
tooling 24. The cylindrical tooling 24 is rotatably mounted in operative 
association with its stationary fixture 26, which is shaped as one half of 
a hollow cylinder. Preferably, the longitudinal axis of the cylindrical 
tooling 24 is disposed concentric with the longitudinal axis of the 
fixture 26. Both the fixture 26 and the cylindrical tooling 24 are 
operatively mounted on a stationary cooled base plate disposed within the 
implant chamber of the ion beam implanter, see my said U.S. Pat. No. 
4,693,760. It will be appreciated that, as in the previous example 
illustrated in FIGS. 2-3, certain energetic ions 28 will impinge on the 
rotating surface of the cylindrical tooling 24 while certain other 
energetic ions 28 will strike the inner concave surface 25 of the fixture 
26, causing sputtering thereof. Some of this sputtering reaches the 
rotating surface of the cylindrical tool 24 and causes the formation of 
layers of coatings thereon. As these sputter formed layers of coatings are 
accumulated on the rotating surface of the cylindrical tooling 24, both 
the layers of coatings and the surface of the tooling 24 are ion implanted 
by the energetic ions 28 striking the cylindrical tooling 24 itself. The 
relative compositions of the component materials forming the cylindrical 
tooling 24, the fixture 26 and the energetic ions 28 of the ion beam can 
be as described in detail above with respect to the example shown in FIGS. 
2 and 3. 
The sputter enhanced ion implantation process of the invention is 
illustrated in FIGS. 6 and 7 as being applied to a toothed gear 30, 
commonly encountered in various industrial products, more specifically, to 
the teeth 32 thereof. Gear 30 is rotatably mounted in operative 
association with a pair of stationary fixtures 34. Both the gear 30 and 
the pair of fixtures 34 are operatively mounted within the implant chamber 
of the said ion implanter. Although the pair of fixtures 34 are depicted 
as having a triangular cross section, such need not be the case. The 
operative side of the pair of fixtures 34 is the one side 35 currently 
exposed to the energetic ions 36 during ion implantation. Of course, the 
triangular shape of the pair of fixtures 34 allows for the presentation of 
the other two sides thereof in future implantations, would that become 
necessary or desirable. Such rotation of the surfaces of the pair of 
fixtures 34 may be called for when the originally exposed surfaces 35 
become unusable for purposes of the invention process by extensive wear, 
as for example due to the effects of self-sputtering. As in the previous 
examples, certain of the energetic ions 36 strike the teeth 32 of the gear 
30 directly, while other energetic ions 36 strike the surfaces 35 of the 
pair of fixtures 34 disposed at angle thereto. The latter cause sputtering 
of the fixture material to be deposited as layers of coatings on the teeth 
32 of the gear 30, simultaneously with those teeth 32 being ion implanted 
by the directly impinging ions 36 thereon. The gear 30 is both rotated 
with respect to the pair of fixtures 34 and is cooled so as not to exceed 
a maximum predetermined level of temperature, which preferable is about 
300.degree. F. (or about 100.degree. C.). The selection of the maximum 
temperature is influenced, among others, by the materials of the 
implantation target, of the fixtures and of the specific ions applied 
thereto. 
In FIG. 8 is illustrated, in schematic section and on an enlarged scale, 
one of the plurality of workpieces 16 shown in FIGS. 2 and 3 after these 
workpieces 16 have been subjected to the sputter enhanced ion implantation 
process of the invention. The original surface 40 of the workpiece 16, a 
ball bearing, is shown enveloped by a plurality of layers 42, 44 and 46 of 
sputter induced coatings formed thereon. These plurality of layers 42, 44 
and 46 are intentionally exaggerated in size and thickness for the 
purposes of illustration only. It will be recalled that these plurality of 
layers 42, 44 and 46 of coatings are primarily formed of the material 
comprising the fixture 10 and are interlaced by some of the energetic ions 
18, shown as dots 48. It will also be recalled that certain of these 
energetic ions 18 directly impinging on the surface 40 of the ball bearing 
16 have penetrated a certain distance into and below the surface 40. In so 
doing, some of these penetrating ions also have caused some of the 
sputtered ions of the fixture material also to be implanted onto and below 
the surface 40 of the ball bearing 16. It will also be understood that the 
thickness of these layers 42, 44 and 46 of sputter coatings depends on the 
implant parameters, in particular, the time duration of the sputter 
enhanced ion implantation process. 
EXAMPLE I 
Spherical workpieces 16 formed of 52100 steel, with a diameter size of 
5/32", were subjected to the sputter enhanced ion implantation process of 
the invention in an ion implanter with the following implant parameters: 
Ion beam current density: 2.0 uA/cm.sup.2 
Time duration of ion implantation: 10.5 hours 
Ion species employed: N.sup.+ 
Angle of incidence of the ion beam: Was varied between about 40.degree. and 
about 70.degree. 
Energy of ion implantation: 80 Kev 
Maximum temperature of the workpieces 16: Less than 120.degree. C. 
Ion dose on workpieces 16: 1.5.times.10.sup.17 ions/cm.sup.2 
Composition of fixture 10: Pb 
Sputtering coefficient of the fixture 10: Ranges between about 8-15 
atoms/ion 
Ion dose on fixture 10: 4.5.times.10.sup.17 ions/cm.sup.2 
Depth of ion implantation below the surface: About 2000 Angstroms 
##EQU1## 
EXAMPLE II A cylindrical tooling 24 formed of sapphire, with a diameter 
size of 3/8", was exposed to the sputter enhanced ion implantation in the 
ion implanter, with the following implant parameters: 
Ion beam current density: 23 uA/cm.sup.2 
Time duration of ion implantation: 1.2 hours 
Ion species employed: Ta 
Energy of ion implantation: 120 Kev 
Ion dose on the workpiece 24: 2.times.10.sup.17 ions/cm.sup.2 
Composition of fixture 26: Ta 
Sputtering coefficient of the fixture 26: Ranges from about 3 to about 10 
atoms/ion 
Ion dose on fixture 26: 6.times.10.sup.17 ions/cm.sup.2 
Depth of ion implantation below the surface: About 200 Angstroms 
Geometry factor: 3 
EXAMPLE III 
A toothed gear 30 formed of 9310 steel, with a diameter size of 3", was 
exposed to the sputter enhanced ion implantation in the ion implanter with 
the following implant parameters: 
Ion beam current density: 4.0 uA/cm.sup.2 
Time duration of ion implantation: 4.4 hours 
Ion species employed: Ar 
Energy of ion implantation: 120 Kev 
Ion dose on workpiece 30: 2.times.17 ions/cm.sup.2 
Composition of pair of fixtures 34: Ag 
Sputtering coefficient of the fixtures 34: Ranges from about 6-12 atoms/ion 
Ion dose on pair of fixtures 34: 4.times.10.sup.17 ions/cm.sup.2 
Depth of ion implantation below the surface: About 1000 Angstroms 
Geometry factor: 2 
Thus it has been shown and described a sputter enhanced ion implantation 
process for the ion implantation and simultaneous sputter coating of 
workpieces, which process satisfies the objects and advantages set forth 
above. 
Since certain changes may be made in the present disclosure without 
departing from the scope of the present invention, it is intended that all 
matter described in the foregoing specification or shown in the 
accompanying drawings, be interpreted in an illustrative and not in a 
limiting sense.