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A source replenishment device for vacuum deposition
Vacuum/volume Printed in Great
37/number Britain
1 O/pages
769
0042-207X/%7 Pergamon
to 771 I1967
$3.00+ Journals
.OO Ltd
A source replenishment device for vacuum deposition* RAHill, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA received
5 August
1986
A device providing remotely controlled linear and intermittent rotational motion has been developed and applied to the task of adding successive pieces of source metal to the filament in a vacuum deposition apparatus.
1. Introduction A device designed to add successive pieces of source metal to the filament in a vacuum deposition apparatus has been developed. In the present application, two such devices are required to reload the two tungsten filaments used in the simultaneous evaporation of films on both sides of a sequence of substrates. The absence of vacuum ports in the immediate vicinity of the filament housings required gear-driven devices that would produce both linear and intermittent rotational motion. In particular, for a wand of the type shown in Figure 1 carrying four small inverted ‘U-shaped pieces of source metal, the desired motion consists of the following steps: (a) a linear (vertical) excursion past the filament; (b) a 45” rotation to orient the replacement metal over the filament; (c) a reversed linear excursion during which the replacement metal is ‘picked off’ the wand by the filament; (d) a 45” rotation; where the sequence can be carried out four times. The resulting device, described in the following sections, has performed at pressures < lo-” Pa and at temperatures > 100°C.
shaft (S). As shown in Figure 3(b), the four point Geneva follower provides an intermittent 90” rotation for each full rotation of the drive shaft. As shown in Figures 2 and 3(c), the Geneva follower/gear assembly drives the rotator (R) through a rotator gear (RG) with an RG/G gear ratio of two. Thus, each full rotation of the drive shaft results in a 45” rotation of the rotator. A plunger (P), carried axially by the cam and rotator assemblies, contains transverse pin and bearing assemblies that run on tracks (T) machined inside the rotator as shown in Figure 3(d). This bearing configuration provides for full axial motion of
(a)
2. Apparatus description
(b)
c
A schematic of the replenishment device is shown in Figure 2. The entire mechanism is carried between a top plate (TP) and a bottom plate (BP) separated by three pillar posts (PP). Rotary motion is applied to the device via the drive shaft (DS), which through a drive gear (DG) and intermediate.gear (G) produces a rotary motion of the cam (C). A top view of these components is shown in Figure 3(a), along with the bearing block (BB) that provides support for the upper and lower intermediate shafts (S). Four short pillar posts are used to mount the bearing block to the bottom plate. Motion of a Geneva driver (GD), also attached to the drive shaft, results in the intermittent rotation of a Geneva follower (GF) and gear (G) assembly attached to the upper intermediate
(cl * This work was supported Contract
by the US Department No DE-ACO4-76-DP00789.
of Energy
under
Figure 1. View of the wand loaded near the filament.
(d) with replenishment
metal positioned
769
R A Hi//: Source
replenishment
device
for vacuum
deposltton
BALL BEARING SILVER BUSHING
Figure 2. Schematic of the replenishment device. The views denoted by the callouts a. b, c, are shown in Figure 3. Dimensions of the bottom plate (BP) and top plate (TP) are 152.4mm x 50.8 mm.
the plunger, while limiting its rotation to that provided by the rotator. Both linear and rotational motion of the plunger with respect to the cam are afforded by a silver bushing in the bottom of the cam assembly. Linear motion ofthe plunger is provided by a control arm (CA) clamped to the plunger that is driven via a
VIEW
roller bearing in contact with the cam. A compression spring (not shown), positioned axially between the control arm and rotator gear, provides a necessary restoring force. A wand (W), an easily adjustable extension of the plunger, carries the spoke assembly shown in Figures 2 and 3(e). A slot has been machined in each spoke to provide a receptacle or holder for the replenishment metal. Since one full rotation of the drive shaft results in a 45 rotation of the plunger, it is necessary that the cam rotate I X0’ to provide the plunger with its full extension plus an additional 45 to maintain the phase relationship between control arm and cam. Thus, the cam gear-to-drive gear ratio, CG/DG, must be I .60 so that eachfullturnofthedriveshaft resultsina 5.;Xturnofthecam. In operation, then, two full turns of the drive shaft are required for one cycle of operation. Properly phased, the control arm is at the lowest point of the cam with the Geneva driver at its fully engaged position. As the drive shaft is rotated, cam and control arm will rotate together (22.5 ‘) until the Geneva driver disengages from the follower, locking the rotator from further rotation. As the cam continues to rotate, the plunger begins its linear excursion, which is essentially completed at the moment the Geneva driver re-engages the follower. Once again, the cam and control arm rotate together. while the plunger is at maximum extension. After the 45 ’ rotation ofthe plunger, the Geneva driver again disengages from the follower, locking the rotator. and the plunger begins its linear retreat. controlled by continued rotation of the cam. By appropriate orientation of the spoke assembly shown in Figure 3(e) with the filament. an inverted ‘U.-shaped piece of replenishment metal can be ‘picked off’ one spoke by the filament, as shown in Figure I. Completion of the operation occurs with the control arm at the lowest point on the cam with the Geneva driver fully engaged and the plungerwand assembly at the halfway point in its second 45 rotation.
VIEW
(c)
(b)
(a)
Figure 3. Cross-sectional views of the replenishment device. Views (a),(b),(c), _, are at the positions a. b,c, denoted in Figure 2. Diameter of the rotator (R) shown in (d) is 19.05 mm; diameter of the ball bearings pinned to the plunger (P) is 6.35 mm.
770
(d)
R A Hill: Source
replenishment
device for vacuum
deposition -2.5
3. Vacuum considerations
The requirement that the mechanism described above must work in a high vacuum environment without seizing and without contaminating the system is formidable and paramount. First, all components (except the plunger) were machined from type 304 stainless steel. This includes the plates, pillars, bearing block, control arm, rotator, and cam. Shafting, gears, gear clamps, and Geneva mechanism were supplied in 304 stainless steel by Berg*. Kovar was used for the plunger so that an alumina insulator could be brazed between plunger and wand. This provides electrical insulation of the wand from the plunger so that, if desired, source replenishment can take place by melting the metal pieces from the wand. The return spring was formed from 302 stainless steel. Precision (ABEC-7) 440C stainless steel ball bearings were used for all shafting and rollers. Precision (ABEC5) 44OC stainless steel ball bearings were used for the rotator and cam bearings. It was necessary to machine copper beryllium keepers for the latter bearings as they are commonly provided with fibre keepers. All bearings were disassembled, the balls silver-plated (1.3 pm thickness), and reassembled before they were pressed into their respective housings. The Geneva follower and the gears situated on intermediate shafts were gold-plated. The last two steps ensure that gears and ball bearings do not stick or gall during operation. While the cam has a sinusoidal configuration, it is necessary to provide a flat on its peak extending about k 20”. This ensures that the control arm reaches the top of the cam before the Geneva mechanism unlocks. Without this provision, the Geneva mechanism has a tendency to bind just as it unlocks because ofthe torque produced on the control arm by the sloping part of the cam when the return spring is under maximum compression. The rotator assembly was designed with internal tracks because of the desire to use ball bearings between the plunger and rotator. A sliding bearing, located between the plunger and rotator, could stick or gall during vacuum operation because ofthe considerable torque exerted on the rotator by the plunger. This torque, caused by the restoring force ofthe compression spring, occurs during the axial motion of the plunger when the control arm roller is in contact with the sioping part of the cam. The internal profile of the rotator was contoured with a wirecut electrical discharge machine (WEDM). This is a simple, inexpensive process with an intrinsic accuracy better than kO.025 mm. As an alternate procedure, this part could be fabricated as two half-cylinders, which are subsequently joined by a vacuum braze or. more simply, by a press-fit into gear RG. A clamp at the top end would provide additional structural integrity. It should be noted that assembly of ultraclean piece parts is difficult, i.e., these parts can easily stick and gall. Thus it is * Winfred
M Berg Inc.
NY 11518. USA.
499
Ocean Avenue, East Rockaway, Long Island.
mm rad
l.Omm die
I /
jk0.60mm
8.40mm
t---t-
(b)
(a) Figure 4. Schematic
important employed
of wand and replenishment
that press-fits and sliding-fits in conventional applications.
metal with dimensions.
are not as tight as those
4. Operation As mentioned in Section 2, proper phasing of the replenishment device requires that the control arm be positioned at the lowest point on the cam when the Geneva driver is fully engaged. This phase relationship can be easily adjusted without unclamping the control arm from the plunger. It is accomplished by moving the rotator assembly along the plunger towards the control arm until the rotator gear is disengaged from its drive gear. With the Geneva driver fully engaged in the follower, the rotator assembly is then rotated to position the control arm at the lowest point of the cam, at which position the rotator gear and its drive gear are re-engaged Source metal, in this case 1.Omm diameter gold wire, is cut into 15 mm lengths and formed into a ‘U’ shape as shown in Figure 4(b). One end of the ‘U’ is flattened (using a vice having polished faces) so that it may be inserted into a slot machined in the spokes shown in Figures 3(e) and 4(a). In this fashion, the shoulder at the end of the flattened portion of the replacement metal rests on the top surface of the spoke, while the flattened portion maintains the proper orientation of the replacement metal with the spoke. In operation, the replenishment device has been subjected to a vacuum bake at 150°C for 8 h. The device was subsequently tested at an elevated temperature (lOOC), at room temperature, and after residing motionless in a vacuum at 10mh Pa for three weeks. Operated with a Huntington Model VF-166-C rotary motion feedthrough, the replenishment device has worked flawlessly.
771
37/number Britain
1 O/pages
769
0042-207X/%7 Pergamon
to 771 I1967
$3.00+ Journals
.OO Ltd
A source replenishment device for vacuum deposition* RAHill, Sandia National Laboratories, Albuquerque, New Mexico 87185, USA received
5 August
1986
A device providing remotely controlled linear and intermittent rotational motion has been developed and applied to the task of adding successive pieces of source metal to the filament in a vacuum deposition apparatus.
1. Introduction A device designed to add successive pieces of source metal to the filament in a vacuum deposition apparatus has been developed. In the present application, two such devices are required to reload the two tungsten filaments used in the simultaneous evaporation of films on both sides of a sequence of substrates. The absence of vacuum ports in the immediate vicinity of the filament housings required gear-driven devices that would produce both linear and intermittent rotational motion. In particular, for a wand of the type shown in Figure 1 carrying four small inverted ‘U-shaped pieces of source metal, the desired motion consists of the following steps: (a) a linear (vertical) excursion past the filament; (b) a 45” rotation to orient the replacement metal over the filament; (c) a reversed linear excursion during which the replacement metal is ‘picked off’ the wand by the filament; (d) a 45” rotation; where the sequence can be carried out four times. The resulting device, described in the following sections, has performed at pressures < lo-” Pa and at temperatures > 100°C.
shaft (S). As shown in Figure 3(b), the four point Geneva follower provides an intermittent 90” rotation for each full rotation of the drive shaft. As shown in Figures 2 and 3(c), the Geneva follower/gear assembly drives the rotator (R) through a rotator gear (RG) with an RG/G gear ratio of two. Thus, each full rotation of the drive shaft results in a 45” rotation of the rotator. A plunger (P), carried axially by the cam and rotator assemblies, contains transverse pin and bearing assemblies that run on tracks (T) machined inside the rotator as shown in Figure 3(d). This bearing configuration provides for full axial motion of
(a)
2. Apparatus description
(b)
c
A schematic of the replenishment device is shown in Figure 2. The entire mechanism is carried between a top plate (TP) and a bottom plate (BP) separated by three pillar posts (PP). Rotary motion is applied to the device via the drive shaft (DS), which through a drive gear (DG) and intermediate.gear (G) produces a rotary motion of the cam (C). A top view of these components is shown in Figure 3(a), along with the bearing block (BB) that provides support for the upper and lower intermediate shafts (S). Four short pillar posts are used to mount the bearing block to the bottom plate. Motion of a Geneva driver (GD), also attached to the drive shaft, results in the intermittent rotation of a Geneva follower (GF) and gear (G) assembly attached to the upper intermediate
(cl * This work was supported Contract
by the US Department No DE-ACO4-76-DP00789.
of Energy
under
Figure 1. View of the wand loaded near the filament.
(d) with replenishment
metal positioned
769
R A Hi//: Source
replenishment
device
for vacuum
deposltton
BALL BEARING SILVER BUSHING
Figure 2. Schematic of the replenishment device. The views denoted by the callouts a. b, c, are shown in Figure 3. Dimensions of the bottom plate (BP) and top plate (TP) are 152.4mm x 50.8 mm.
the plunger, while limiting its rotation to that provided by the rotator. Both linear and rotational motion of the plunger with respect to the cam are afforded by a silver bushing in the bottom of the cam assembly. Linear motion ofthe plunger is provided by a control arm (CA) clamped to the plunger that is driven via a
VIEW
roller bearing in contact with the cam. A compression spring (not shown), positioned axially between the control arm and rotator gear, provides a necessary restoring force. A wand (W), an easily adjustable extension of the plunger, carries the spoke assembly shown in Figures 2 and 3(e). A slot has been machined in each spoke to provide a receptacle or holder for the replenishment metal. Since one full rotation of the drive shaft results in a 45 rotation of the plunger, it is necessary that the cam rotate I X0’ to provide the plunger with its full extension plus an additional 45 to maintain the phase relationship between control arm and cam. Thus, the cam gear-to-drive gear ratio, CG/DG, must be I .60 so that eachfullturnofthedriveshaft resultsina 5.;Xturnofthecam. In operation, then, two full turns of the drive shaft are required for one cycle of operation. Properly phased, the control arm is at the lowest point of the cam with the Geneva driver at its fully engaged position. As the drive shaft is rotated, cam and control arm will rotate together (22.5 ‘) until the Geneva driver disengages from the follower, locking the rotator from further rotation. As the cam continues to rotate, the plunger begins its linear excursion, which is essentially completed at the moment the Geneva driver re-engages the follower. Once again, the cam and control arm rotate together. while the plunger is at maximum extension. After the 45 ’ rotation ofthe plunger, the Geneva driver again disengages from the follower, locking the rotator. and the plunger begins its linear retreat. controlled by continued rotation of the cam. By appropriate orientation of the spoke assembly shown in Figure 3(e) with the filament. an inverted ‘U.-shaped piece of replenishment metal can be ‘picked off’ one spoke by the filament, as shown in Figure I. Completion of the operation occurs with the control arm at the lowest point on the cam with the Geneva driver fully engaged and the plungerwand assembly at the halfway point in its second 45 rotation.
VIEW
(c)
(b)
(a)
Figure 3. Cross-sectional views of the replenishment device. Views (a),(b),(c), _, are at the positions a. b,c, denoted in Figure 2. Diameter of the rotator (R) shown in (d) is 19.05 mm; diameter of the ball bearings pinned to the plunger (P) is 6.35 mm.
770
(d)
R A Hill: Source
replenishment
device for vacuum
deposition -2.5
3. Vacuum considerations
The requirement that the mechanism described above must work in a high vacuum environment without seizing and without contaminating the system is formidable and paramount. First, all components (except the plunger) were machined from type 304 stainless steel. This includes the plates, pillars, bearing block, control arm, rotator, and cam. Shafting, gears, gear clamps, and Geneva mechanism were supplied in 304 stainless steel by Berg*. Kovar was used for the plunger so that an alumina insulator could be brazed between plunger and wand. This provides electrical insulation of the wand from the plunger so that, if desired, source replenishment can take place by melting the metal pieces from the wand. The return spring was formed from 302 stainless steel. Precision (ABEC-7) 440C stainless steel ball bearings were used for all shafting and rollers. Precision (ABEC5) 44OC stainless steel ball bearings were used for the rotator and cam bearings. It was necessary to machine copper beryllium keepers for the latter bearings as they are commonly provided with fibre keepers. All bearings were disassembled, the balls silver-plated (1.3 pm thickness), and reassembled before they were pressed into their respective housings. The Geneva follower and the gears situated on intermediate shafts were gold-plated. The last two steps ensure that gears and ball bearings do not stick or gall during operation. While the cam has a sinusoidal configuration, it is necessary to provide a flat on its peak extending about k 20”. This ensures that the control arm reaches the top of the cam before the Geneva mechanism unlocks. Without this provision, the Geneva mechanism has a tendency to bind just as it unlocks because ofthe torque produced on the control arm by the sloping part of the cam when the return spring is under maximum compression. The rotator assembly was designed with internal tracks because of the desire to use ball bearings between the plunger and rotator. A sliding bearing, located between the plunger and rotator, could stick or gall during vacuum operation because ofthe considerable torque exerted on the rotator by the plunger. This torque, caused by the restoring force ofthe compression spring, occurs during the axial motion of the plunger when the control arm roller is in contact with the sioping part of the cam. The internal profile of the rotator was contoured with a wirecut electrical discharge machine (WEDM). This is a simple, inexpensive process with an intrinsic accuracy better than kO.025 mm. As an alternate procedure, this part could be fabricated as two half-cylinders, which are subsequently joined by a vacuum braze or. more simply, by a press-fit into gear RG. A clamp at the top end would provide additional structural integrity. It should be noted that assembly of ultraclean piece parts is difficult, i.e., these parts can easily stick and gall. Thus it is * Winfred
M Berg Inc.
NY 11518. USA.
499
Ocean Avenue, East Rockaway, Long Island.
mm rad
l.Omm die
I /
jk0.60mm
8.40mm
t---t-
(b)
(a) Figure 4. Schematic
important employed
of wand and replenishment
that press-fits and sliding-fits in conventional applications.
metal with dimensions.
are not as tight as those
4. Operation As mentioned in Section 2, proper phasing of the replenishment device requires that the control arm be positioned at the lowest point on the cam when the Geneva driver is fully engaged. This phase relationship can be easily adjusted without unclamping the control arm from the plunger. It is accomplished by moving the rotator assembly along the plunger towards the control arm until the rotator gear is disengaged from its drive gear. With the Geneva driver fully engaged in the follower, the rotator assembly is then rotated to position the control arm at the lowest point of the cam, at which position the rotator gear and its drive gear are re-engaged Source metal, in this case 1.Omm diameter gold wire, is cut into 15 mm lengths and formed into a ‘U’ shape as shown in Figure 4(b). One end of the ‘U’ is flattened (using a vice having polished faces) so that it may be inserted into a slot machined in the spokes shown in Figures 3(e) and 4(a). In this fashion, the shoulder at the end of the flattened portion of the replacement metal rests on the top surface of the spoke, while the flattened portion maintains the proper orientation of the replacement metal with the spoke. In operation, the replenishment device has been subjected to a vacuum bake at 150°C for 8 h. The device was subsequently tested at an elevated temperature (lOOC), at room temperature, and after residing motionless in a vacuum at 10mh Pa for three weeks. Operated with a Huntington Model VF-166-C rotary motion feedthrough, the replenishment device has worked flawlessly.
771