U.S. patent number 3,904,503 [Application Number 05/475,007] was granted by the patent office on 1975-09-09 for depositing material on a substrate using a shield.
This patent grant is currently assigned to Western Electric Company, Incorporated. Invention is credited to Alexander Maxim Hanfmann.
United States Patent |
3,904,503 |
Hanfmann |
September 9, 1975 |
Depositing material on a substrate using a shield
Abstract
The uniformity of the thickness of material, deposited on a
substrate by ion bombardment of a cathode, i.e., by sputtering, is
improved by shielding. A shield is shaped to conform with plots of
lines of constant thickness of the material deposited by a
sputtering machine. The shield is inserted between the cathode and
substrate during a preselected interval of the sputtering time to
shade a portion of the substrate and prevent excess deposition of
material thereon. Where characteristics of the sputtering machine
are such that deposition must be reduced in a wide swath along the
length of the substrate, a variable area shield is used.
Inventors: |
Hanfmann; Alexander Maxim
(Allentown, PA) |
Assignee: |
Western Electric Company,
Incorporated (New York, NY)
|
Family
ID: |
23885865 |
Appl.
No.: |
05/475,007 |
Filed: |
May 31, 1974 |
Current U.S.
Class: |
204/192.12;
118/50.1; 118/624; 118/720; 204/192.21; 204/192.25; 204/298.11;
204/298.25; 427/523 |
Current CPC
Class: |
C23C
14/044 (20130101); C23C 14/34 (20130101) |
Current International
Class: |
C23C
14/04 (20060101); C23C 14/34 (20060101); C23C
015/00 (); C23C 013/02 () |
Field of
Search: |
;204/192,298 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Weisstuch; Aaron
Attorney, Agent or Firm: Peters; R. Y.
Claims
What is claimed is:
1. An improved method for depositing material on a substrate
wherein a cathode acts as a source of material, and wherein a layer
of material is deposited on the substrate by ion bombardment of the
cathode in a chamber, wherein the improvement comprises:
inserting a shield between the cathode and the substrate to
selectively shade portions of the substrate from the material being
deposited thereon, the configuration of the shield being determined
by the variations in the deposit thickness which would occur in the
absence of said shield; and
withdrawing the shield after a predetermined interval, to increase
the uniformity of the layer of material deposited on the
substrate.
2. A method, as recited in claim 1, wherein the area of the shield
is variable and the steps include varying the area of the shield in
accordance with the size of the substrate portions selected to be
shaded.
3. A method, as recited in claim 1, wherein the substrate is moved
intermittently past the cathode in the chamber.
4. A method, as recited in claim 1, wherein the substrate is moved
continuously through the bombardment chamber.
5. A method, as recited in claim 3, wherein the chamber contains a
plurality of cathodes.
6. A method, as recited in claim 1, comprising the further steps
of:
determining the material thickness contours which are
characteristic of the deposition method in the absence of the
shield; and
configuring the shield accordingly to provide uniform
deposition.
7. An improved apparatus for depositing material on a moving
substrate, wherein a cathode acts as a source of material, and
wherein a layer of the material is deposited on the substrate by
ion bombardment of the cathode in a chamber, wherein the
improvement comprises:
a shield in the chamber for shading selected portions of the
substrate, the configuration of the shield being determined by the
variations in the deposit thickness which would occur in the
absence of said shield; and
means for positioning the shield between the cathode and the
substrate during selected intervals of bombardment, to increase the
uniformity of the layer of the material deposited on the
substrate.
8. An apparatus, as recited in claim 7, wherein the shield
comprises:
at least two portions positioned for overlapping relationship;
and
means for adjusting the amount of the overlap, and thereby the
effective area of the shield, to correspond to the portions of the
substrate selected for shading.
9. An apparatus, as recited in claim 7, wherein the positioning
means comprises:
a fluid power cylinder mounted on the sputtering chamber, said
cylinder having a piston rod extending therefrom into the
bombardment chamber for supporting the shield therein;
means for limiting the extent to which the piston rod is inserted
into the chamber to position the shield in relation to the
substrate; and
means for actuating the piston rod to insert and withdraw the
shield at preselected intervals from between the cathode and the
substrate so that the selected portions of the substrate are
shaded.
10. An apparatus, as recited in claim 9, wherein at least two fluid
power cylinders and shields are mounted in cooperating relationship
to permit adjusting the size of the area which will be shaded.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improved methods and apparatus for
depositing material on a substrate. More particularly, it relates
to shading portions of a substrate with a shield which may be
inserted and removed during the deposition of a thin film of
material to make the thickness of the deposited material more
uniform over the substrate.
2. Description of the Prior Art
In the manufacture of semiconductor apparatus, thin films are
deposited on ceramic or glass substrates and various devices formed
therefrom. For example, a film of resistive material may be
deposited on a substrate and "thin-film" resistors formed; or
conductive material may be deposited and conductive paths formed;
or both materials may be deposited and resistors and
interconnecting conductors formed to produce a thin-film electrical
circuit.
One method used for depositing material on the substrate,
especially high melting-point materials such as tantalum, is ion
bombardment, i.e., sputtering, of the material in close proximity
to the subsstrate. The process may be carried out in bell jar,
in-line, or rotary types of sputtering chambers. Information
relative to carrying out the process may be had from two excellent
sources: R. W. Berry, P. M. Hall and M. T. Harris, Thin Film
Technology, D. VanNostrand Company, Inc., Princeton, New Jersey,
(1968); and L. J. Maissel and R. Glang, Handbook of Thin Film
Technology, McGraw-Hill Book Co., New York, N. Y. (1970).
Information relative to sputtering apparatus may be had from U.S.
patents: Charschan et al. 3,294,670; and Kauffman et al. 3,521,765,
both assigned to the assignee of record.
In the sputtering process, many factors, which involve the
particular apparatus being used, determine the distribution of
material over the surface of the substrate. That is, the thickness
varies somewhat in a pattern or contour peculiar to the apparatus
and configuration used. Typically, variations are from about .+-.4%
to about .+-.10% and about .+-.6% is a common experience.
As a result of the variations in the film thickness, the
characteristics of the devices, such as resistors made from the
material on the substrate by photolithographic processes must be
adjusted, usually by anodizing, to compensate for the variations.
The time required for anodizing may be substantially shortened by
depositing the material with a more uniform thickness
initially.
As noted, the thickness varies along contours peculiar to the
particular apparatus and deposition conditions. Consequently, in
order to make the thickness more uniform, the deposition must be
reduced, within the contours where the material would be thicker
(generally the center portions of the substrate), to the extent
that it is nearly the same as elsewhere on the substrate.
Some prior art apparatus (such as that disclosed in copending
application of C. H. George, Ser. No. 175,247, filed Aug. 26, 1971,
now U.S. Pat. No. 3,856,654 and assigned to the assignee of record)
has been able to improve uniformity by means of a fixed shield in
the sputtering chamber. However, a fixed shield cannot be adjusted
and, therefore is limited in its ability to compensate when
sputtering conditions change. In other prior art cases, moving
shields or controllable shields have been used to produce thin
films which increase in thickness at an approximately uniform rate,
or to prevent deposition until sputtering conditions reach
equilibrium conditions, i.e., stabilize sufficiently so that
deposition can proceed at the planned rate. But these shields are
not capable of producing a film of uniform thickness or improving
the uniformity of deposition.
What is needed is a shield which approximates the contour of the
area which would be overdeposited and which can be positioned to
shade that area of the substrate for just the necessary time to
prevent overdepositing. It is also desirable that the area of the
shield be capable of being increased or decreased to accommodate
changing conditions.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention resides in providing new
and improved methods and apparatus for depositing material on a
substrate. With this and other objects in view, the present
invention contemplates a new and improved method for depositing
material on a substrate which includes inserting a shield between
the cathode and the substrate during ion bombardment of the cathode
in a sputtering chamber to deposit the material. The shield shades
selected portions of the substrate and is withdrawn after a
predetermined interval so that the uniformity of the material on
the substrate is increased.
The present invention also contemplates a new and improved
apparatus of the kind wherein a cathode acts as a source of
material and is bombarded with ions to deposit the material on a
substrate. Mechanisms external to a sputtering chamber position a
shield between the cathode and substrate inside the chamber during
selected intervals of bombardment of the cathode to shade selected
portions of the substrate and reduce any variation in thickness of
material deposited over the surface of the substrate.
The thickness of material deposited during ion bombardment varies
over a substrate and is dependent on many factors indigenous to the
particular apparatus and sputtering process. However, the
variations are consistent and the thickness of the material on a
representative sample of substrates may be measured and contours of
constant thickness plotted. A shield of the general shape of the
contours is inserted between the cathode and the substrate just
long enough to reduce the thickness of what would be an
overdeposited area, usually the center of the substrate, to that of
the surrounding area.
In some instances the factors influencing deposition cause a swath
of thicker material to be deposited along the centerline of the
substrate and, therefore, an adjustable shield is inserted between
the cathode and substrate which is adjusted to the width of the
swath. The width depends on the material and sputtering
conditions.
The invention further contemplates mechanisms which position
shields from outside the chamber either through sliding type vacuum
seals or hermetic seals.
DESCRIPTION OF THE DRAWINGS
Other objects and features of the invention will be more readily
understood from the following detailed description of the specific
embodiment thereof, when read in conjunction with the accompanying
drawings in which:
FIG. 1 is an isometric view of an "in-line" sputtering machine
showing an "in-line" sputtering chamber;
FIG. 2 is an isometric view of the "in-line" sputtering chamber of
FIG. 1;
FIG. 3 is a plan view along line 3--3 of the chamber of FIG. 2
showing the interior of the chamber;
FIG. 4 is a partial cross section showing the interior of a
"rotary" sputtering chamber;
FIG. 5 is an illustration of topographical contours of constant
thickness of material deposited on a substrate in an "open-end
in-line" type apparatus;
FIG. 6 is an illustration of topographical contours of constant
thickness of material deposited on a substrate in a "closed-end
in-line" prior art type apparatus;
FIG. 7 is an illustration of topographical thickness contours of
material deposited in "closed-end in-line" apparatus, the contours
of which are illustrated in FIG. 6, using rod cathodes and a.c.
sputtering;
FIG. 8 is an elevation showing the shape of a shield for the
topography of FIG. 5;
FIG. 9 is an elevation showing the shape of a shield for the
topography of FIG. 6;
FIG. 10 is an elevation showing the shape of a shield for the
topography of FIG. 7;
FIG. 11 is an elevation showing a variable-area shield for the
topography of FIG. 7;
FIG. 11a is an elevation showing an alternate arrangement for the
shield portion of FIG. 11;
FIG. 11b is an elevation showing another arrangement for the shield
portion of FIG. 11;
FIG. 12 is a cross sectional elevation of a pneumatic cylinder and
an evacuated seal arrangement for operating the shield of FIGS. 8
and 9;
FIG. 13 is a cross sectional elevation of a pneumatic cylinder and
bellows arrangement for operating the shields of FIGS. 8 and 9;
FIG. 14 is a partial cross sectional elevation of a pneumatic
cylinder arrangement for operating the shield of FIGS. 11 and 11a
or 11b;
FIG. 15 is a partial elevation showing a limit switch and cam for
coordinating the operation of a shield with the "open-end, in-line"
type sputtering apparatus;
FIG. 16 is a partial elevation showing the mounting of a limit
switch to coordinate the operation of a shield with the
"closed-end, in-line" type apparatus; and
FIG. 17 is a diagram of an electrical circuit for controlling the
operation of the shields in conjunction with a limit switch.
DETAILED DESCRIPTION OF THE INVENTION
Apparatus for Depositing Material
Referring now to FIG. 1, there is shown an "open-end, in-line"
sputtering machine 20 of the type having a sputtering chamber 22
and disclosed in U.S. Pat. No. 3,294,670 which issued to S. S.
Charschan et al. Dec. 27, 1966. Another apparatus having a similar
sputtering chamber 22, a "closed-end, in-line" sputtering machine
is disclosed by U.S. Pat. No. 3,521,765 which issued to R. D.
Kauffman et al. July 28, 1970. The subject matter of the U.S. Pat.
Nos. 3,294,670 and 3,521,765 patents is incorporated herein by
reference.
Substrates 24 on which material is to be deposited (refer to FIG.
2) may be transported through the chamber 22 in carriers 26 which
are pushed along a track 28. The motion of the carriers 26 may be
nearly constant or there may be a pause as carriers are added to
and removed from the column of carriers being pushed through the
chamber 22. In other cases, the substrates 24 may be carried
through the chamber 22 by a chain conveyer 29 (refer to FIG. 16) in
the bottom of the track 28 rather than a column of the carriers 26.
The conveyer 29 usually operates at a constant speed.
In addition to apparatus which transports the substrates 24 through
the chamber 22 in a staight line, such as sputtering machine 20,
there re other types which transport the substrates in steps in a
circular path around a cylindrical sputtering chamber 32 (refer to
FIG. 4). Such apparatus is described in the aforementioned
copending C. H. George application.
Referring now to FIG. 3, which is a plan view along line 3--3 of
FIG. 2 looking down into the chamber 22, the track 28 is partially
cut away to show the carrier 26 transporting one of the substrates
24 from left to right past a cathode 30.
In a rotary version of the sputtering chamber (refer to the partial
cross-section FIG. 4) the substrates 24 are carried
counter-clockwise around the chamber 32 past either a cylindrical
cathode 34 or rod cathodes 36 (shown in phantom) which are easy to
cool.
As disclosed in the various reference cited, the cathodes 30 34 and
36 are highly negative with respect to the chambers 22 and 32 and
substrates 24; and an inert gas, such as argon, is maintained at
less than atmospheric pressure in the chambers. However, the
cathodes 30, 34 and 36 may be operated with an a.c. potential so
that they are alternately highly positive and then highly negative
with respect to the chambers 22 and 32. In either case, the gas is
ionized, the cathodes 30, 34 and 36 are bombarded by the ions,
particles of cathode material are dislodged, and the particles are
deposited on the substrate 24. Thus, the cathodes 30, 34 and 36
must be composed of the material to be deposited on the substrates
24.
The transfer of material from the cathodes to the substrates 24 is
a result of particle collisions and influenced by many factors
which depend on the sputtering machine 20 and process conditions.
These give rise to variations in the thickness of the material
across the substrates 24. However, the variations are essentially
the same for each of the substrates 24 once the sputtering
conditions have been established.
Uniformity of the Deposited Material
The thickness of the material deposited on the substrates 24 may be
measured in a number of ways; but where a resistive material, such
as tantalum or tantalum nitride, is deposited, a four-point probe
resistance measurement in ohms per square may be made. The
resistance of the material deposited on the substrates 24 is
measured at regular intervals over the area of the substrates.
Although the resistance in ohms per square may be converted to
thickness in angstroms or other linear measure it is usually more
convenient to leave it in the form of ohms per square. Measurement
of a representative sample of substrates permits plotting the
general topographical contours (in terms of ohms per square) of the
material deposited on the substrate.
For example, FIG. 5 is representative of the distribution of
tantalum material deposited on substrates 24 by the "open-end,
in-line" type apparatus which transports the substrates 24 through
the sputtering chamber in the carriers 26. Here the topographical
contours 38 of constant thickness have roughly an octagon shape and
the material on the substrates 24 within the solid contour 38a is
thicker than the material outside the contour. The variation
between the thickest, midrange, and thinest portions of the
sputtered layer is approximately .+-.6%. By shielding the area
within the contour 38a for a portion of the sputtering time, using
applicant's invention for shading or shielding the substrates 24,
the variation may be reduced to about .+-.3%.
Another example, refer to FIG. 6, is representative of the
distribution of tantalum material deposited on a substrate 24 by
the "closed-end, in-line" type apparatus which transports the
substrates 24 through the sputtering chamber 22 and on a conveyor
29 rather than the carriers 26. Here contours 40 of constant
thickness are truncated and the material within (above) the solid
contour 40a is thicker than the material outside (below) the
contour 40a. The variation in this case is about .+-.4.5% of the
midrange thickness. By shading or shielding the area within the
contour 40a for a portion of the sputtering time in accordance with
applicant's invention, the variation may be reduced to about
.+-.3%.
In the "closed-end, in-line" apparatus, the plate cathode 30, refer
to FIG. 3, may be replaced by a cathod (not shown) constructed of
horizontal rods and the sputtering performed with alternating
current. Under these conditions, topographical contours 42, refer
to FIG. 7, are obtained wherein the material deposited along a
horizontal centerline is thicker than elsewhere. Thus, a swath of
material between the solid contours 42a is thicker than the
material between the contours and the edges of the substrates 24.
The variation here may be as much as .+-.10% of midrange and this
may be reduced to about half by use of applicant's invention.
Shading or Shielding the Substrate
Referring again to FIGS. 3 and 4, a shield 44 is placed between the
substrate 24 and cathodes 30, 34 or 36 depending on which apparatus
and type of cathode is used. Typically, the shield is positioned
approximately 1 inch away from the substrate 24.
The shape of the shield 44 is chosen with due regard to the
movement, or lack thereof, of the substrates 24 through the
sputtering chamber 22. Referring now to FIG. 8, the contour 38a of
FIG. 5 is shown in phantom. The shield 44 is made narrower than the
contour 38a because the substrates 24 move through the sputtering
chamber 22 in the direction of the arrow. The shield 44 is
interposed between the cathode 30 and one of the substrates 24 when
what would be the right-hand edge of the contour 38a is in line
with the right-hand edge of the shield, and the shield is removed
when that one of the substrates 24 has moved to the point where
what would be the left-hand edge of the contour is in line with the
left-hand edge of the shield.
Similarly, referring to FIG. 9, the contour 40a is shown in phantom
and a triangular shield 46 for this contour is shown narrower than
the area to be shielded because of the movement of substrates 24 in
the direction of the arrow.
Where the area to be shaded is a swath (refer to FIG. 10) between
the contours 42a (shown in phantom), a roughly oval-shaped shield
48 may be used. This shield is aligned with the swath to be shaded.
Since the swath would be thickest at the center and fall off toward
the edges, the shield 48 is made wider at the center to provide
more shading there.
In order to avoid having to make another shield 48 when the width
of the swath between contours 42a changes because of changes made
in the process and/or equipment, the shield 48 may be made in two
overlapping portions 48a and 48b (refer to FIG. 11) such that the
portions 48a and 48b may be moved in the directions of the arrows
50 to increase or decrease the width of the swath which is shaded.
In essence this is a shield which may be varied in area or size.
However, the portions 48a and 48b are operated from opposite sides
of the sputtering chamber 22. Alternatives, in which the portions
may be operated from the same side of the chamber 22, are shown for
a side-by-side arrangement in FIG. 11a and with an offset piston
rod in an overlapping arrangement in FIG. 11b. The shield portions
48a and 48c are moved from the same side of the sputtering chamaber
22 in the direction of the arrows 50 to change the width of the
area shaded.
Referring now to FIG. 12, which is a view of the sputtering chamber
22 along the line 12--12 of FIG. 3, the shield 44 may be positioned
between the substrates 24 and the cathode 30 by a pneumatic
cylinder 52. A piston rod 54 is moved by a piston 56, fixed
thereto, when air is admitted to the cylinder. The distance the rod
54 moves and, therefore, the distance the shield 44 is inserted
into the chamber 22, is determined by the position of a split
collar 58 on the rod 54. The collar 58 is positioned on the rod 54
and clamped by a screw (not shown) so that, when the collar strikes
the end of the cylinder 52, the shield 44 will be in the desired
position. The piston 56 itself acts as the stop for the retracted
position.
The chamber 22 is at a pressure below atmospheric. In order to keep
ambient air or any gas leaking past the seals of the cylinder 52
from entering the chamber 22, an evacuated seal 60 is interposed
between the cylinder and the chamber. The seal 60 includes O-ring
seals 62 above and below a vacuum port 64. A pressure, slightly
below the pressure of chamber 22, is maintained at the port 64 to
evacuate the seal 60 and prevent leakage of gas into the
chamber.
The mechanism of FIG. 12 is a simple and directly operating one.
However, it has seals which will wear, require continuous
application of a vacuum, and must be replaced occasionally. This
may be avoided by the bellows mechanism shown schematically in FIG.
13 which is an elevation of the interior of the sputtering chamber
22. A flexible bellows 66 seals the chamber 22 from the outside
atmosphere. A pneumatic cylinder 68 is supported on a bridge 70 and
connected to a yoke 72 which is fastened externally to the bellows
66. Internally a stem 74, guided in a cylindrical support 76,
connects the bellows 66, through a link 78 to a support arm 80 for
the shield 44. An O-ring 81 provides a seal between the support 76
and the chamber 22 so that, together, the bellows 66, support 76
and O-ring 81 seal the chamber 22 from the atmosphere. The arm 80
is hinged to the inside of the chamber 22 by means of a leaf spring
82. In order to reduce the length of the stroke and, therefore, the
amount of flexing the bellows 66 must do, the length of the arm 80
from the link 78 to the shield 44 is made much greater than from
the link 78 to the end of the spring 52 which is fastened to the
chamber 22. As in the direct acting cylinder 52, a stop 58 is
clamped on an extension 84 of the piston rod to permit adjusting
the distance the shield 44 is inserted into the chamber 22 (as
shown in phantom) and the piston 56 acts as the stop for the
retracted position.
Although pneumatic cylinders 52 and 68 were chosen to illustrate
operation of the shield 44 in FIGS. 12 and 13 respectively, other
means of operation may be used. For example, in the direct acting
apparatus of FIG. 12, the pneumatic cylinder may be replaced by a
linear electric motor. Or, in the case of the short-stroke, bellows
mechanism of FIG. 13, the pneumatic cylinder 68 may be replaced by
a single revolution motor and adjustable-stroke, crank mechanism
arranged to lower the shield 44 on one revolution and raise it on
the next revolution.
Again, using pneumatic cylinders to illustrate (refer to FIG. 14)
the shield portions 48a and 48b of FIG. 11 may be positioned from
opposite sides of the chamber 22 by two pneumatic cylinders 52, one
of which is shown in phantom on the opposite side of the chamber,
or the shield portions 48a and 48c may be positioned from the same
side of the chamber by means of the side-by-side pneumatic
cylinders 52 in either the side-by-side arrangement of FIG. 11a or
the overlapping arrangement using the offset piston rod 54 of FIG.
11b.
Operation of the Shields
The shields, such as shield 44, are inserted between cathodes and
substrates to shade predetermined portions of the substrates for
predetermined periods of time. This requires coordinating the
insertion of any of the shields with the movement of the substrate
24 and timing the duration of the shielding. This may be done by
means of a limit switch 86 and cam 88 (refer to FIG. 15) for the
"open-end, in-line" type apparatus; or by means of the limit switch
86 (refer to FIG. 16) mounted to engage lug 90 for the "closed-end,
in-line" type apparatus.
Once the insertion of a shield, such as shield 44, has been
coordinated with the movement of the substrates 24 through the
sputtering apparatus by the limit switch 86, actuation of solenoid
valves to operate pneumatic cylinders, or relays to operate
electric motors, or the equivalent of these, may be achieved
through the control circuit of FIG. 17.
When the limit switch 86, refer now to FIG. 17, is moved to its
normally open position and allowed to close again; for example, by
one of the cam lobes 92 on cam 88 (refer to FIG. 15) or by the lug
90 (refer to FIG. 16), the coil of a relay 94 is energized and its
normally open contact 96 is closed. The closed contact 96 applies
energy to the relay 94 through a normally closed contact 98 of a
timer 100. Thus, the relay 94 will remain energized until contact
98 is opened after a preset time delay to open (TDO). The timer 100
preferably should have a range of from 0.1 to about 400 secs.
When relay 94 is energized, it also closes a normally open contact
102, which energizes a clutch 104 of a delay timer 106, preferably
having a range of 0.1 to 400 secs., and starts timing a delay,
which is preset on the timer 106, after which the shield is
inserted. At the end of its delay period, timer 106 opens a
normally closed contact 108 to de-energize a drive motor 110 and
closes normally open contact 112 to energize a clutch 114 of timer
100. The timer 100 starts timing the duration of shielding, which
has been preset on that timer, and immediately closes normally open
contact 116 to energize a spring-return solenoid valve 118 through
a normally closed contact 120.
Referring now to FIG. 12 for illustration, the closed contact 116
and energized solenoid 118 actuate the pneumatic cylinder 52 so
that it inserts the shield 44 between the cathode (not shown) and
one of the substrates 24 in the chamber 22. At the end of the
preset time, the timer 100 momentarily: opens a normally closed
contact 120, to de-energize a timer motor 122; opens the contact
116 to de-energize the solenoid valve 118 so that the spring
returns the valve and the cylinder 52 withdraws the shield 44 from
between the cathode and substrate in the chamber 22; and
momentarily opens the contact 98 to de-energize the relay 94 and
reset the circuit. The shield 44 may also be manually operated
independently of the timers 100 and 106 by operation of the switch
124. This is helpful for initial set up and positioning.
Applicant's method and apparatus provides distinct advantages over
the prior art in increased uniformity of the deposited material by
shielding the substrate for only a portion of the deposition time.
Further advantage and improved uniformity is achieved by shaping
the shield to thickness contours and shielding only predetermined
portions of the substrate. Still further advantage is gained, in
certain cases, by making the shield variable in size.
While there has been described and illustrated herein practical
embodiments of the present invention, it is to be understood that
various modifications and refinements, which may depart from the
disclosed embodiment, may be adopted without departing from the
spirit and scope of the invention. For example, shields, such as
the shield 44, may be perforated or slotted, particularly adjacent
the periphery, soften the shading and improve the thickness
uniformity in specific instances. As another example, if the
shields are actuated by a linear motor or similar magnetic device,
the motor or device may be enclosed by the chamber 22 to eliminate
the need for the evacuated seal 60.
* * * * *