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Ion beam system for implanting industrial products of various shapes
Nuclear Instruments and Methods in Physics Research B6 (1985) 88-93 North-Holland. Amsterdam
88
ION BEAM SYSTEM FOR IMPLANTING INDUSTRIAL A.S. DENHOLM
PRODUCTS OF VARIOUS SHAPES
and A.B. WITTKOWER
Zymet, Inc., 33 Cherryhill Dr., Danvers, Ma 01923, USA Implantation of metals and ceramics with ions of nitrogen and other species has improved surface properties such as friction, wear and corrosion in numerous industrial applications. Zymet has built a production machine to take advantage of this process which can implant a 2 x 10” ions/cm* dose of nitrogen ions into a 20 cm X 20 cm area in about 30 min using a 100 keV beam. Treatment is accomplished by mounting the product on a cooled, tiltable, turntable which rotates continuously, or is indexed in 15” steps to expose different surfaces in fixed position. Product cooling is accomplished by using a chilled eutectic metal to mount and grip the variously shaped objects. A high voltage supply capable of 10 mA at 100 kV is used, and the equipment is microcomputer controlled via serial light links. All important machine parameters are presented in sequenced displays on a CRT. Uniformity of treatment and accumulated dose are monitored by a Faraday cup system which provides the microprocessor with data for display of time to completion on the process screen. For routine implants the operator requires only two buttons; one for chamber vacuum control, and the other for process start and stop.
1. Introduction Ion implantation of non-semiconductor surfaces has been studied over the past ten years, and improvements in numerous areas have been demonstrated; notably reductions in friction and wear, and increased corrosion resistance [l]. Nitrogen is the species usually implanted
and achievements have progressed from laboratory experiments to a number of successful practical applications, particularly in the UK [2]. The mechanisms which account for the observed effects are qualitatively understood, at best, and are discussed elsewhere in these proceedings [3]. A dose range seems well established at (2-5) x 1017 ions/cm’; one or two orders of magnitude above that required for semiconductor implants, and numerous successful treatments have been performed with nitrogen at energies below 100 keV. This corresponds to a penetration range of about 1000 A in steel. The high dose levels, currents and voltages required for expeditious processing involve high beam powers; beams which can significantly raise the temperature of the implanted product. For most materials, process temperature must be restricted and special cooling techniques, often complicated by the great variety of product shapes, are required. Geometries can be rectalinear, cylindrical, sometimes completely non regular, or simply flat, and they must be gripped, cooled and manipulated to present various faces to the beam. The nature of the metal treatment market is decidedly different from that of the semiconductor market. In particular, the value added by implantation var0168-583X/85/$03.30 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
ies over several orders of magnitude, depending on the particular product; and most applications could not bear the cost of a high priced machine. It follows that the design criteria for the equipment must also be quite different from those for a semiconductor implanter. The specific reasoning behind the Z-100 format is discussed in the next section.
2. Design criteria 2.1. Size It is axiomatic that large objects cannot be implanted in a small vacuum chamber, but less obvious that small objects cannot usually be implanted economically in a large implanter. As an example, consider the case of printed circuit board drills. These come in various sizes; a typical drill might have a shaft diameter of 0.2 cm, and compact mounting results in a packing density of 5 drills/cm*. A standard batch size is rarely over 2000 drills, and would cover an area of only 400 cm’; to use a machine with a substantially larger implant area would be inefficient, Machine cost is a second criterion, and cost is related to machine size. Since ion implantation into metals has yet to achieve large scale industrial usage, it would seem unwise to produce, at least initially, a machine rivaling semiconductor implanters in size, cost, or complexity. For these reasons, a modestly sized machine with an implant field 20 cm by 20 cm (400 cm2) was defined. If
AS. Denholm. A. B. WittkowerI Implanting industrialproducts
the product needs to be rotated about a central axis, the implant field area is reduced to 250 cm2. 2.2. Species Ion implantation is a nonequilibrium process. Therefore opportunity exists to implant any of the 100 or so elements into any conceivable material having a tolerable vapor pressure. Fortunately, normally used engineering metals are restricted to a few dozen materials. Even so, the number of possible implant/product permutations is overwhelming. However, research over the past ten years has shown that nitrogen implantation can beneficially affect the wear and friction properties of numerous metals under mild abrasive and adhesive conditions. These metals include many steels, tungsten carbide, some titanium compounds and chromium. In addition, corrosion of copper, for example, can be inhibited by nitrogen implantation. Nitrogen’s effect upon aluminium alloys has not yet been fully established. Though by no means a panacea, it was appropriate to direct the first metals implanter design towards nitrogen implantation in particular; although as noted later the equipment has much broader capability. 2.3. Beam energy Experiments have shown that nitrogen implantation is effective against wear and friction at energies as low as 50 keV for treatment at normal incidence. Unfortunately, most products or tools are not flat; implants will occur at a variety of angles on a single object (such as along the flutes of a drill). This feature dictates a beam energy somewhat higher to attain an average penetration equivalent to a 50 keV implant at normal incidence angle. Consequently, 100 keV was chosen as a machine energy which would allow some margin. 2.4. Beam power A critical issue in the design of any ion implanter is the ability to remove heat, generated by the ion beam, from the product. Using concepts which have been treated by various authors, for example, Grabowski and Kant [4], one can calculate the temperature rise if the beam power density, product emissivity, thermal capacity, and product shape are known under various conditions of radiative or conductive cooling. Although certain implants into metals may benefit from higher temperatures, most nitrogen implants lose their effectiveness above about 200°C through the “out diffusion” of nitrogen. Thus, it is desirable to restrict the temperature at the product mounting position to less than lOO”C, bearing in mind that the actual temperature under the beam area may be substantially higher. The temperature at the treatment surface, of course, de-
89
pends upon the specific product geometry, and must be estimated in each case. The Z-100 machine has a maximum beam power of 800 W distributed over 400 cm’, i.e., 2 W/cm’. For many products a beam power ten times higher would not cause deleterious effects, but parts having geometries of low heat conductivity, such as a small diameter protrusion on an injection mold, may restrict the average beam power density to substantially lower values. 2.5. Product handling A versatile metal products implanter requires that a large variety of objects be held, cooled, and presented to the beam with many orientations. After considering the most likely types of product to be treated, it was concluded that a holder was required which would rotate the product continuously or in steps to present different faces to the beam; and further that a tilt feature was needed which could set the angle to the beam direction between + 90”. A concept for inexpensively jigging, or fixturing, a broad range of shapes was also desired; this led to the “Cool Grip”TM holder, a lowmelting-point metal grip method, described in detail in the body of this paper. “Cool GriIPM firmly holds irregularly shaped objects and keeps their temperature at the mounting site below 100°C. 2.6. Automation To allow operation of the Z-100 by relatively unskilled personnel, it was desirable that processing should be automatic; from the closing of the product chamber door on a loaded machine, to the opening at the end of an implant. However, due to the diversity of product mountings, loading and unloading remains manual. As the technology advances, automatic handling, specific to the product, will evolve as it has in the past ten years for semiconductor wafers.
3. System description Accelerator layout, dictated by the criteria just discussed, is shown in outline in fig. 1. A horizontal, rather than vertical, design simplifies extension of the beam line and provides floor level access to all components for easy maintenance. The profile of the equipment permits passage through a standard double doorway. High voltage power is provided from a simple, linear, 100 kV, 10 mA supply positioned below the high voltage terminal. Alongside it is an isolation transformer providing 3 kVA to the terminal electronics (fig. 1). The terminal contains power supplies for the source filament, arc voltage, and vaporizer (where reI. IMPLANTATION SYSTEMS
90
A.S. Denholm,
A. B. Wirtkower I Implanting industrial products
quired); and also houses one or more gas bottles with controlled leak valves to provide gases used by the source. The controlling and monitoring of components in the high voltage terminal is accomplished via a serial fibre optic loop to the ground level of the machine. The ion source is cooled by a closed loop water heat exchanger completely within the terminal. The terminal, with its power supplies, slides out of the machine on rails to provide convenient servicing of the ion source and its supplies. The ion source is of a standard Freeman geometry [5], but utilizing a.c. rather than d.c. filament current for reasons related to spreading the beam uniformly, as discussed in a companion paper describing the beam optics [6]. Ions from the source are emitted from a 5 cm long vertical slit into the acceleration gap, where the electric field is shaped to expand the beam radially in the vertical dimension (fig. 1). The geometry is designed to provide a beam cross section 20 cm high by 2 cm wide at the target plane 90 cm from the slit, i.e., in the center of the product chamber. A process area (target plane) which is 20 cm wide as well as 20 cm high is desired, and is obtained by scanning in the horizontal dimension. Rapid movement of the beam is not required, therefore it is attractive to use a mechanical scanning technique. Two methods have been used. One approach, as described in ref. [6], maintains the source in a fixed position and oscillates the ground acceleration electrode about a vertical axis, thus developing a time changing wedge-shaped, electric field in the horizontal dimension; which deflects the beam to left and right of the beam line. The other is mechanically more complex, but it is also more precise and flexible. Both the source and acceleration electrodes are moved, essentially as one, to direct the beam at a controlled angle about the beam line axis in the horizontal plane. In this case the source at high voltage and the acceleration electrode at ground potential pivot about a point 30 cm behind the source slit. The geometry of the acceleration gap remains fixed; thus the beam deflection corresponds precisely to the rota-
Fig. 1. Z-100 outline.
tion of the source/acceleration electrodes, i.e., +5” provides +10.3 cm deflection at the target plane 90 cm from the source slit. During set-up, the beam is directed, “gated”, into cooled monitor cups at the flag. Fig. 2 shows the horizontal profile of the beam at the target and Faraday flag planes recorded as it scanned across small diameter (3 mm) Faraday cups. The source housing and work chamber are separately evacuated by diffusion pump systems which are automatically controlled by the microprocessor. A 6” gate valve isolates the source housing when the work chamber is vented to remove the treated product. This valve marks the division between the accelerator section, and the work chamber section. The design configuration is such that large variations in work chamber geometry and size can be made without affecting the accelerator system. For example, larger treatment fields can be obtained by extending the beam line to permit the beam to expand and deflect further, and larger or multiple chambers can be accommodated. In one form, an electron beam evaporation source has been incorporated below the work chamber to provide coincident ion implantation and thin film deposition; allowing enhanced deposition and mixing applications. 3.1. Product handling system As already discussed, the ion beam projects a cross section of 20 cm x 20 cm at the target plane in the center of the work chamber when full scan is used. The implant can also be achieved with a reduced beam scan or with the beam fixed in position. Although the beam is diverging slightly, for all practical purposes it crosses the vertical plane YY (fig. 1) at 90”. If only flat surfaces were to be treated, holding the work piece would be relatively simple. However, shapes such as those shown
Fig. 2. Horizontal beam profile from beam scan (dimensions at half amplitude are in flag and target planes respectively).
A.S. Denholm, A. B. Wittkower I Implanting industrial products
in fig. 3 are more typical. In the case of the rectangular which could be a precision punch for example, it may be required to implant faces a, b, c, d, and e; and in the case of the hollow cylinder, treatment of the outside and inside surfaces may be specified. To enable processing of a variety of shapes, the work chamber is fitted with a manipulator which grips, cools, and positions the product at various angles with respect to the beam. The concept, shown in fig. 4, consists of a turntable that can be rotated continuously or indexed in increments of 15”, and also tilted through 180”. To achieve the tilt function, the turntable is carried on an arm which rotates about the axis of the work chamber; the effective radius of the arm is variable to adjust for differing heights of product. Referring to fig. 3, the rectangular shape would be treated (faces a, b, c, and d) with the turntable horizontal and the object mounted on it (face e uppermost). The four faces would be implanted separately, each at normal incidence, by indexing in 90” steps. The turntable then would be tilted 90” from horizontal, to implant the uppermost surface (face e). In the case of the body,
low cylinder, rotation of the turntable in the horizontal position provides outside circumferential treatment only; rotation with 45” table tilt provides beam access to the ends of the inner surface as well. Fig. 5 shows various applications of the turntable. The significance of treatment in these various modes with regard to “dose factors” and retained dose are discussed in a companion paper [3]. The various objects mounted on the turntable usually require cooling. This is generally accomplished by using a eutectic metal which melts just above 100°C. The turntable, in the form of a water cooled disk (fig. 6), is designed for quick demounting from the work chamber. Products after preparation are inserted into the heated eutectic metal with the surfaces to be treated suitably exposed. The metal is then allowed to solidify around them. This technique, called Cool GripTM, provides both convenience in fixturing and good thermal conduction for heat flow out of the product. Turntable rotation, indexing and tilt are all con-
-
Beam
Beam
B
-
0
Beam
/
Beam
91
Beam
ii--
a) Flat
e )’
b) Cylindrical
c) Llnelr Edge
Outside
d) Rectangular Tip
Fig. 3. Manipulator requirements for rectalinear and cylindrical shapes. \ Process Chamber 50 cm Diameter
I
-&
30cmDeep
e) Cyllndrlc~l
Variable Radius Arm
spin On Work Holder (Hz0 Cooled)
/ ’ Rotary
Gate Valve Diftusion
Pump 1
Fig. 4. Product manipulator.
I
Drive
-*
Inslda
1) Cyllndrlcal
Groove
Fig. 5. Turntable applications. (a) Flat - 0” implantation angle, no rotation. (b) Cylindrical outside (e.g., drill tips) - 80“ implantation angle, rotation. (c) Linear edge (e.g., flat blades) - 80” implant angle, no rotation, two implants indexed 180”. (d) Rectangular tip (e.g., punch) - 45” implant angle, no rotation, four implants indexed 90”. (e) Cylindrical inside (e.g., wire drawing die) - 45” implant angle, rotation. (f) Cylindrical groove (e.g., split shaft bushing) - varying implant angle, no rotation, azimuthal cycle. I. IMPLANTATION
SYSTEMS
92
A.S. Denholm, A. B. Wittkower I Implanting industrial products Customized coverPlate
Fig. 6. Cool Gripm techniques and cooled disk.
trolled by a microprocessor. This, plus the facilities for presetting a specified dose and measuring the dose delivered, as discussed in the next section, make it possible to program the machine for a complex implant. 3.2. Control and monitoring Control and monitoring utilizes a 280 based microprocessor to communicate with stations around the machine via a serial optical loop. Interrogation and command of each subsystem occurs twice per second. The status of all elements significant to operation are displayed on a CRT, using several roll-over type screens. The first screen provides a graphic representation of the vacuum system, showing the condition of all valves, vacuum readings, and the overall system interlock information. Vacuum in the equipment is automatically controlled. A subsequent screen displays the accelerator status, e.g., high voltage, source filament and arc current, and leak valve position. Additional screens present information on beam scanning parameters, ion density, product manipulator rotation, indexing, and tilt, the dose required, and accumulated dose delivered. Ion density in the beam is measured in small Faraday cups situated on the flag shown in fig. 1. The current signals are fed, via an integrator, to the microprocessor for accumulation of the dose. The integrated current density required in a specific processing cycle is called the “dose factor” and “dialed” into the microprocessor. The “dose factor” is derived from the actual dose desired at the surface, the product geometry, and the manipulator program (discussed in ref. [3]). Using this value, and the information provided by the Faraday cups, the microprocessor can determine implant percentage of completion, and time to complete. This information is displayed on the CRT (operator) screen.
4. Conclusion A physically small (262 cm x 147 cm x 193 cm high), relatively inexpensive but sophisticated ion beam system has been developed for the implantation of in-
Fig. 7. Z-100 ion implantation system for industrial products.
dustrial products of varied shape (fig. 7). In its initial form, it has a relatively small treatment field, but this can readily be expanded by extension of the beam line. Programmed manipulation of the product position in the target chamber provides control of beam angle of incidence during an implant process cycle. The accelerator implants flat surfaces to a dose level of 2 x 1017ions/cm’ in 30 min. Replacement of a preloaded turntable and automatic pump-down to processing pressure is accomplished in about 4 min. Although largely used for nitrogen implantation, the standard system can also implant all elemental materials which exist in gaseous form by attaching the appropriate gas bottle in the high voltage terminal. A vaporizer and vaporizer power supply [5], can extend the species range to 24 additional elements with evaporation temperatures less than 900°C. The system does not provide or require mass analysis. A data logger is provided for batch identification and automatic documentation of treatment parameters. A particularly sophisticated addition exists which adds 8 kW of 4 turret e-beam evaporation capability for ion beam mixing and ion beam enhanced deposition. The deposition rate is slaved to the ion current density by microprocessor control. The authors gratefully acknowledge the collaboration of their colleagues D. Berrian, E. Mears, and J. Vanderpot, who were largely responsible for the engineering and design of the Z-100. We also thank M. Kanter, on leave from Soreq Nuclear Research Center, Yavne, Israel, for his studies in ion optics which were a significant controbution to the development; and the ready availability of Eaton/Nova technology, particularly in the source area, was of major assistance.
A.S. Denholm, A. B. Wittkower I Implanting industrial products
References [l]
[2] [3]
J.K. Hirvonen and CR. Clayton, in Surface modification and alloying by laser, ion and electron beams, eds., J.M. Poate, G. Foti and D.C. Jacobson (Plenum, New York, 1983) p. 323. S.J.B. Charter, L.R. Thomson and Cl. Dearnaley, Thin Solid Films 84 (1981) 355. A. Wittkower and J.K. Hirvonen, these Proceedings
[4]
[5] [6]
93
(Ion Implantation Equip. & Tech. ‘84) Nucl. Instr. and Meth. B6 (1985) 78. K.S. Grabowski and R.A. Kant, Ion Implantation equipment and techniques, eds., H. Ryssel and H. Glawischnig (Springer, Berlin, 1983) p. 364. Eaton Corporation, Ion Beam Systems Division, Beverly, Ma. M. Kanter and A. Wittkower, these Proceedings (Ion Implantation Equip. & Tech. ‘84) Nucl. Instr. and Meth. B6 (1985) 116.
I. IMPLANTATION
SYSTEMS
88
ION BEAM SYSTEM FOR IMPLANTING INDUSTRIAL A.S. DENHOLM
PRODUCTS OF VARIOUS SHAPES
and A.B. WITTKOWER
Zymet, Inc., 33 Cherryhill Dr., Danvers, Ma 01923, USA Implantation of metals and ceramics with ions of nitrogen and other species has improved surface properties such as friction, wear and corrosion in numerous industrial applications. Zymet has built a production machine to take advantage of this process which can implant a 2 x 10” ions/cm* dose of nitrogen ions into a 20 cm X 20 cm area in about 30 min using a 100 keV beam. Treatment is accomplished by mounting the product on a cooled, tiltable, turntable which rotates continuously, or is indexed in 15” steps to expose different surfaces in fixed position. Product cooling is accomplished by using a chilled eutectic metal to mount and grip the variously shaped objects. A high voltage supply capable of 10 mA at 100 kV is used, and the equipment is microcomputer controlled via serial light links. All important machine parameters are presented in sequenced displays on a CRT. Uniformity of treatment and accumulated dose are monitored by a Faraday cup system which provides the microprocessor with data for display of time to completion on the process screen. For routine implants the operator requires only two buttons; one for chamber vacuum control, and the other for process start and stop.
1. Introduction Ion implantation of non-semiconductor surfaces has been studied over the past ten years, and improvements in numerous areas have been demonstrated; notably reductions in friction and wear, and increased corrosion resistance [l]. Nitrogen is the species usually implanted
and achievements have progressed from laboratory experiments to a number of successful practical applications, particularly in the UK [2]. The mechanisms which account for the observed effects are qualitatively understood, at best, and are discussed elsewhere in these proceedings [3]. A dose range seems well established at (2-5) x 1017 ions/cm’; one or two orders of magnitude above that required for semiconductor implants, and numerous successful treatments have been performed with nitrogen at energies below 100 keV. This corresponds to a penetration range of about 1000 A in steel. The high dose levels, currents and voltages required for expeditious processing involve high beam powers; beams which can significantly raise the temperature of the implanted product. For most materials, process temperature must be restricted and special cooling techniques, often complicated by the great variety of product shapes, are required. Geometries can be rectalinear, cylindrical, sometimes completely non regular, or simply flat, and they must be gripped, cooled and manipulated to present various faces to the beam. The nature of the metal treatment market is decidedly different from that of the semiconductor market. In particular, the value added by implantation var0168-583X/85/$03.30 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
ies over several orders of magnitude, depending on the particular product; and most applications could not bear the cost of a high priced machine. It follows that the design criteria for the equipment must also be quite different from those for a semiconductor implanter. The specific reasoning behind the Z-100 format is discussed in the next section.
2. Design criteria 2.1. Size It is axiomatic that large objects cannot be implanted in a small vacuum chamber, but less obvious that small objects cannot usually be implanted economically in a large implanter. As an example, consider the case of printed circuit board drills. These come in various sizes; a typical drill might have a shaft diameter of 0.2 cm, and compact mounting results in a packing density of 5 drills/cm*. A standard batch size is rarely over 2000 drills, and would cover an area of only 400 cm’; to use a machine with a substantially larger implant area would be inefficient, Machine cost is a second criterion, and cost is related to machine size. Since ion implantation into metals has yet to achieve large scale industrial usage, it would seem unwise to produce, at least initially, a machine rivaling semiconductor implanters in size, cost, or complexity. For these reasons, a modestly sized machine with an implant field 20 cm by 20 cm (400 cm2) was defined. If
AS. Denholm. A. B. WittkowerI Implanting industrialproducts
the product needs to be rotated about a central axis, the implant field area is reduced to 250 cm2. 2.2. Species Ion implantation is a nonequilibrium process. Therefore opportunity exists to implant any of the 100 or so elements into any conceivable material having a tolerable vapor pressure. Fortunately, normally used engineering metals are restricted to a few dozen materials. Even so, the number of possible implant/product permutations is overwhelming. However, research over the past ten years has shown that nitrogen implantation can beneficially affect the wear and friction properties of numerous metals under mild abrasive and adhesive conditions. These metals include many steels, tungsten carbide, some titanium compounds and chromium. In addition, corrosion of copper, for example, can be inhibited by nitrogen implantation. Nitrogen’s effect upon aluminium alloys has not yet been fully established. Though by no means a panacea, it was appropriate to direct the first metals implanter design towards nitrogen implantation in particular; although as noted later the equipment has much broader capability. 2.3. Beam energy Experiments have shown that nitrogen implantation is effective against wear and friction at energies as low as 50 keV for treatment at normal incidence. Unfortunately, most products or tools are not flat; implants will occur at a variety of angles on a single object (such as along the flutes of a drill). This feature dictates a beam energy somewhat higher to attain an average penetration equivalent to a 50 keV implant at normal incidence angle. Consequently, 100 keV was chosen as a machine energy which would allow some margin. 2.4. Beam power A critical issue in the design of any ion implanter is the ability to remove heat, generated by the ion beam, from the product. Using concepts which have been treated by various authors, for example, Grabowski and Kant [4], one can calculate the temperature rise if the beam power density, product emissivity, thermal capacity, and product shape are known under various conditions of radiative or conductive cooling. Although certain implants into metals may benefit from higher temperatures, most nitrogen implants lose their effectiveness above about 200°C through the “out diffusion” of nitrogen. Thus, it is desirable to restrict the temperature at the product mounting position to less than lOO”C, bearing in mind that the actual temperature under the beam area may be substantially higher. The temperature at the treatment surface, of course, de-
89
pends upon the specific product geometry, and must be estimated in each case. The Z-100 machine has a maximum beam power of 800 W distributed over 400 cm’, i.e., 2 W/cm’. For many products a beam power ten times higher would not cause deleterious effects, but parts having geometries of low heat conductivity, such as a small diameter protrusion on an injection mold, may restrict the average beam power density to substantially lower values. 2.5. Product handling A versatile metal products implanter requires that a large variety of objects be held, cooled, and presented to the beam with many orientations. After considering the most likely types of product to be treated, it was concluded that a holder was required which would rotate the product continuously or in steps to present different faces to the beam; and further that a tilt feature was needed which could set the angle to the beam direction between + 90”. A concept for inexpensively jigging, or fixturing, a broad range of shapes was also desired; this led to the “Cool Grip”TM holder, a lowmelting-point metal grip method, described in detail in the body of this paper. “Cool GriIPM firmly holds irregularly shaped objects and keeps their temperature at the mounting site below 100°C. 2.6. Automation To allow operation of the Z-100 by relatively unskilled personnel, it was desirable that processing should be automatic; from the closing of the product chamber door on a loaded machine, to the opening at the end of an implant. However, due to the diversity of product mountings, loading and unloading remains manual. As the technology advances, automatic handling, specific to the product, will evolve as it has in the past ten years for semiconductor wafers.
3. System description Accelerator layout, dictated by the criteria just discussed, is shown in outline in fig. 1. A horizontal, rather than vertical, design simplifies extension of the beam line and provides floor level access to all components for easy maintenance. The profile of the equipment permits passage through a standard double doorway. High voltage power is provided from a simple, linear, 100 kV, 10 mA supply positioned below the high voltage terminal. Alongside it is an isolation transformer providing 3 kVA to the terminal electronics (fig. 1). The terminal contains power supplies for the source filament, arc voltage, and vaporizer (where reI. IMPLANTATION SYSTEMS
90
A.S. Denholm,
A. B. Wirtkower I Implanting industrial products
quired); and also houses one or more gas bottles with controlled leak valves to provide gases used by the source. The controlling and monitoring of components in the high voltage terminal is accomplished via a serial fibre optic loop to the ground level of the machine. The ion source is cooled by a closed loop water heat exchanger completely within the terminal. The terminal, with its power supplies, slides out of the machine on rails to provide convenient servicing of the ion source and its supplies. The ion source is of a standard Freeman geometry [5], but utilizing a.c. rather than d.c. filament current for reasons related to spreading the beam uniformly, as discussed in a companion paper describing the beam optics [6]. Ions from the source are emitted from a 5 cm long vertical slit into the acceleration gap, where the electric field is shaped to expand the beam radially in the vertical dimension (fig. 1). The geometry is designed to provide a beam cross section 20 cm high by 2 cm wide at the target plane 90 cm from the slit, i.e., in the center of the product chamber. A process area (target plane) which is 20 cm wide as well as 20 cm high is desired, and is obtained by scanning in the horizontal dimension. Rapid movement of the beam is not required, therefore it is attractive to use a mechanical scanning technique. Two methods have been used. One approach, as described in ref. [6], maintains the source in a fixed position and oscillates the ground acceleration electrode about a vertical axis, thus developing a time changing wedge-shaped, electric field in the horizontal dimension; which deflects the beam to left and right of the beam line. The other is mechanically more complex, but it is also more precise and flexible. Both the source and acceleration electrodes are moved, essentially as one, to direct the beam at a controlled angle about the beam line axis in the horizontal plane. In this case the source at high voltage and the acceleration electrode at ground potential pivot about a point 30 cm behind the source slit. The geometry of the acceleration gap remains fixed; thus the beam deflection corresponds precisely to the rota-
Fig. 1. Z-100 outline.
tion of the source/acceleration electrodes, i.e., +5” provides +10.3 cm deflection at the target plane 90 cm from the source slit. During set-up, the beam is directed, “gated”, into cooled monitor cups at the flag. Fig. 2 shows the horizontal profile of the beam at the target and Faraday flag planes recorded as it scanned across small diameter (3 mm) Faraday cups. The source housing and work chamber are separately evacuated by diffusion pump systems which are automatically controlled by the microprocessor. A 6” gate valve isolates the source housing when the work chamber is vented to remove the treated product. This valve marks the division between the accelerator section, and the work chamber section. The design configuration is such that large variations in work chamber geometry and size can be made without affecting the accelerator system. For example, larger treatment fields can be obtained by extending the beam line to permit the beam to expand and deflect further, and larger or multiple chambers can be accommodated. In one form, an electron beam evaporation source has been incorporated below the work chamber to provide coincident ion implantation and thin film deposition; allowing enhanced deposition and mixing applications. 3.1. Product handling system As already discussed, the ion beam projects a cross section of 20 cm x 20 cm at the target plane in the center of the work chamber when full scan is used. The implant can also be achieved with a reduced beam scan or with the beam fixed in position. Although the beam is diverging slightly, for all practical purposes it crosses the vertical plane YY (fig. 1) at 90”. If only flat surfaces were to be treated, holding the work piece would be relatively simple. However, shapes such as those shown
Fig. 2. Horizontal beam profile from beam scan (dimensions at half amplitude are in flag and target planes respectively).
A.S. Denholm, A. B. Wittkower I Implanting industrial products
in fig. 3 are more typical. In the case of the rectangular which could be a precision punch for example, it may be required to implant faces a, b, c, d, and e; and in the case of the hollow cylinder, treatment of the outside and inside surfaces may be specified. To enable processing of a variety of shapes, the work chamber is fitted with a manipulator which grips, cools, and positions the product at various angles with respect to the beam. The concept, shown in fig. 4, consists of a turntable that can be rotated continuously or indexed in increments of 15”, and also tilted through 180”. To achieve the tilt function, the turntable is carried on an arm which rotates about the axis of the work chamber; the effective radius of the arm is variable to adjust for differing heights of product. Referring to fig. 3, the rectangular shape would be treated (faces a, b, c, and d) with the turntable horizontal and the object mounted on it (face e uppermost). The four faces would be implanted separately, each at normal incidence, by indexing in 90” steps. The turntable then would be tilted 90” from horizontal, to implant the uppermost surface (face e). In the case of the body,
low cylinder, rotation of the turntable in the horizontal position provides outside circumferential treatment only; rotation with 45” table tilt provides beam access to the ends of the inner surface as well. Fig. 5 shows various applications of the turntable. The significance of treatment in these various modes with regard to “dose factors” and retained dose are discussed in a companion paper [3]. The various objects mounted on the turntable usually require cooling. This is generally accomplished by using a eutectic metal which melts just above 100°C. The turntable, in the form of a water cooled disk (fig. 6), is designed for quick demounting from the work chamber. Products after preparation are inserted into the heated eutectic metal with the surfaces to be treated suitably exposed. The metal is then allowed to solidify around them. This technique, called Cool GripTM, provides both convenience in fixturing and good thermal conduction for heat flow out of the product. Turntable rotation, indexing and tilt are all con-
-
Beam
Beam
B
-
0
Beam
/
Beam
91
Beam
ii--
a) Flat
e )’
b) Cylindrical
c) Llnelr Edge
Outside
d) Rectangular Tip
Fig. 3. Manipulator requirements for rectalinear and cylindrical shapes. \ Process Chamber 50 cm Diameter
I
-&
30cmDeep
e) Cyllndrlc~l
Variable Radius Arm
spin On Work Holder (Hz0 Cooled)
/ ’ Rotary
Gate Valve Diftusion
Pump 1
Fig. 4. Product manipulator.
I
Drive
-*
Inslda
1) Cyllndrlcal
Groove
Fig. 5. Turntable applications. (a) Flat - 0” implantation angle, no rotation. (b) Cylindrical outside (e.g., drill tips) - 80“ implantation angle, rotation. (c) Linear edge (e.g., flat blades) - 80” implant angle, no rotation, two implants indexed 180”. (d) Rectangular tip (e.g., punch) - 45” implant angle, no rotation, four implants indexed 90”. (e) Cylindrical inside (e.g., wire drawing die) - 45” implant angle, rotation. (f) Cylindrical groove (e.g., split shaft bushing) - varying implant angle, no rotation, azimuthal cycle. I. IMPLANTATION
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A.S. Denholm, A. B. Wittkower I Implanting industrial products Customized coverPlate
Fig. 6. Cool Gripm techniques and cooled disk.
trolled by a microprocessor. This, plus the facilities for presetting a specified dose and measuring the dose delivered, as discussed in the next section, make it possible to program the machine for a complex implant. 3.2. Control and monitoring Control and monitoring utilizes a 280 based microprocessor to communicate with stations around the machine via a serial optical loop. Interrogation and command of each subsystem occurs twice per second. The status of all elements significant to operation are displayed on a CRT, using several roll-over type screens. The first screen provides a graphic representation of the vacuum system, showing the condition of all valves, vacuum readings, and the overall system interlock information. Vacuum in the equipment is automatically controlled. A subsequent screen displays the accelerator status, e.g., high voltage, source filament and arc current, and leak valve position. Additional screens present information on beam scanning parameters, ion density, product manipulator rotation, indexing, and tilt, the dose required, and accumulated dose delivered. Ion density in the beam is measured in small Faraday cups situated on the flag shown in fig. 1. The current signals are fed, via an integrator, to the microprocessor for accumulation of the dose. The integrated current density required in a specific processing cycle is called the “dose factor” and “dialed” into the microprocessor. The “dose factor” is derived from the actual dose desired at the surface, the product geometry, and the manipulator program (discussed in ref. [3]). Using this value, and the information provided by the Faraday cups, the microprocessor can determine implant percentage of completion, and time to complete. This information is displayed on the CRT (operator) screen.
4. Conclusion A physically small (262 cm x 147 cm x 193 cm high), relatively inexpensive but sophisticated ion beam system has been developed for the implantation of in-
Fig. 7. Z-100 ion implantation system for industrial products.
dustrial products of varied shape (fig. 7). In its initial form, it has a relatively small treatment field, but this can readily be expanded by extension of the beam line. Programmed manipulation of the product position in the target chamber provides control of beam angle of incidence during an implant process cycle. The accelerator implants flat surfaces to a dose level of 2 x 1017ions/cm’ in 30 min. Replacement of a preloaded turntable and automatic pump-down to processing pressure is accomplished in about 4 min. Although largely used for nitrogen implantation, the standard system can also implant all elemental materials which exist in gaseous form by attaching the appropriate gas bottle in the high voltage terminal. A vaporizer and vaporizer power supply [5], can extend the species range to 24 additional elements with evaporation temperatures less than 900°C. The system does not provide or require mass analysis. A data logger is provided for batch identification and automatic documentation of treatment parameters. A particularly sophisticated addition exists which adds 8 kW of 4 turret e-beam evaporation capability for ion beam mixing and ion beam enhanced deposition. The deposition rate is slaved to the ion current density by microprocessor control. The authors gratefully acknowledge the collaboration of their colleagues D. Berrian, E. Mears, and J. Vanderpot, who were largely responsible for the engineering and design of the Z-100. We also thank M. Kanter, on leave from Soreq Nuclear Research Center, Yavne, Israel, for his studies in ion optics which were a significant controbution to the development; and the ready availability of Eaton/Nova technology, particularly in the source area, was of major assistance.
A.S. Denholm, A. B. Wittkower I Implanting industrial products
References [l]
[2] [3]
J.K. Hirvonen and CR. Clayton, in Surface modification and alloying by laser, ion and electron beams, eds., J.M. Poate, G. Foti and D.C. Jacobson (Plenum, New York, 1983) p. 323. S.J.B. Charter, L.R. Thomson and Cl. Dearnaley, Thin Solid Films 84 (1981) 355. A. Wittkower and J.K. Hirvonen, these Proceedings
[4]
[5] [6]
93
(Ion Implantation Equip. & Tech. ‘84) Nucl. Instr. and Meth. B6 (1985) 78. K.S. Grabowski and R.A. Kant, Ion Implantation equipment and techniques, eds., H. Ryssel and H. Glawischnig (Springer, Berlin, 1983) p. 364. Eaton Corporation, Ion Beam Systems Division, Beverly, Ma. M. Kanter and A. Wittkower, these Proceedings (Ion Implantation Equip. & Tech. ‘84) Nucl. Instr. and Meth. B6 (1985) 116.
I. IMPLANTATION
SYSTEMS