U.S. patent application number 15/207495 was filed with the patent office on 2016-11-03 for icp source design for plasma uniformity and efficiency enhancement.
The applicant listed for this patent is Advanced Micro-Fabrication Equipment Inc, Shanghai. Invention is credited to Tuqiang NI, Gang SHI, Songlin XU.
Application Number | 20160322205 15/207495 |
Document ID | / |
Family ID | 50547641 |
Filed Date | 2016-11-03 |
United States Patent
Application |
20160322205 |
Kind Code |
A1 |
XU; Songlin ; et
al. |
November 3, 2016 |
ICP SOURCE DESIGN FOR PLASMA UNIFORMITY AND EFFICIENCY
ENHANCEMENT
Abstract
An ICP A plasma reactor having an enclosure wherein at least
part of the ceiling forms a dielectric window. A substrate support
is positioned within the enclosure below the dielectric window. An
RF power applicator is positioned above the dielectric window to
radiate RF power through the dielectric window and into the
enclosure. A plurality of gas injectors are distributed uniformly
above the substrate support to supply processing gas into the
enclosure. A circular baffle is situated inside the enclosure and
positioned above the substrate support but below the plurality of
gas injectors so as to redirect the flow of the processing gas.
Inventors: |
XU; Songlin; (Shanghai,
CN) ; SHI; Gang; (Shanghai, CN) ; NI;
Tuqiang; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Advanced Micro-Fabrication Equipment Inc, Shanghai |
Shanghai |
|
CN |
|
|
Family ID: |
50547641 |
Appl. No.: |
15/207495 |
Filed: |
July 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
14066631 |
Oct 29, 2013 |
9431216 |
|
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15207495 |
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13337248 |
Dec 26, 2011 |
9095038 |
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14066631 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/32119 20130101;
H01J 37/32449 20130101; H01J 37/32642 20130101; H01J 37/32633
20130101; H01L 21/31 20130101; H01L 21/3065 20130101; H01J 37/321
20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01L 21/31 20060101 H01L021/31; H01L 21/3065 20060101
H01L021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2011 |
CN |
201110319250.8 |
Oct 19, 2011 |
CN |
201110319252.7 |
Nov 1, 2012 |
CN |
201210431839.1 |
Claims
1. A plasma reactor comprising: an enclosure having a cylindrical
sidewall and a ceiling, wherein at least part of the ceiling forms
a dielectric window; a substrate support positioned within the
enclosure below the dielectric window; an RF power applicator
positioned above the dielectric window to radiate RF power through
the dielectric window and into the enclosure; a plurality of gas
injectors distributed uniformly above the substrate support to
supply processing gas into the enclosure; and, a circular baffle
situated inside the enclosure and positioned above the substrate
support but below the plurality of gas injectors so as to redirect
flow of the processing gas, wherein the baffle has a central
aperture having a variable diameter.
2. The plasma chamber of claim 1, wherein the central aperture
diameter can be varied from the outside of the chamber.
3. The plasma reactor of claim 1, wherein the baffle comprises one
of anodized aluminum, ceramic, or quartz.
4. The plasma reactor of claim 2, wherein the baffle comprises a
ring and a plurality of blades, wherein the blades are actuated by
the rotation of the ring to thereby vary the diameter of the
aperture.
5. The plasma reactor of claim 4, further comprising manual
mechanical means configured to rotate the ring.
6. The plasma reactor of claim 4, further comprising a stepper
motor configured to rotate the ring.
7. The plasma reactor of claim 1, further comprising a step motor
configured to move the baffle vertically so as to lower or raise
the baffle.
8. The plasma reactor of claim 1, wherein the baffle comprises a
dielectric material and further comprises a coil embedded within
the dielectric material.
9. A method of fabricating a semiconductor substrate, comprising:
placing the substrate on a substrate support positioned within a
plasma reactor, wherein the plasma reactor comprises an enclosure
having a cylindrical sidewall and a ceiling, wherein at least part
of the ceiling forms a dielectric window, an RF power applicator is
positioned above the dielectric window to radiate RF power through
the dielectric window and into the enclosure, and a plurality of
gas injectors are distributed uniformly above the substrate;
varying gas flow distribution by positioning a circular baffle
having an aperture inside the enclosure such that the baffle is
above the substrate support but below the plurality of gas
injectors so as to define a gap above the substrate; supplying
processing gas to the injectors; and, p1 applying an RF power to
the RF power applicator.
10. The method of claim 9, further comprising a varying diameter of
the aperture.
11. The method of claim 10, wherein varying diameter of the
aperture comprises activating a stepper motor.
12. The method of claim 10, wherein varying diameter of the
aperture comprises mechanically rotating a ring from outside the
plasma reactor.
13. The method of claim 9, wherein the step of varying gas flow
distribution comprises generating radially uneven gas flow.
14. The method of claim 9, further comprising moving the baffle
vertically so as to lower or raise the baffle.
15. The method of claim 9, wherein the baffle comprises a
dielectric material and the method further comprising energizing a
coil embedded within the dielectric material.
16. The method of claim 15, wherein energizing the coil comprises
applying to the coil RF power separately from the RF power applied
to the RF power applicator.
17. The method of claim 9, further comprising applying to the
baffle a vertical ring extension set to be orthogonal to the
baffle.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S. patent
application Ser. No. 14/066,631, filed on Oct. 29, 2013, which is a
Continuation-in-Part Application of U.S. patent application Ser.
No. 13/337,248, filed on Dec. 26, 2011, which claims priority to
Chinese Patent Application Nos. 201110319252.7 filed on Oct. 19,
2011 and 201110319250.8 filed on October 19, 2011. Application Ser.
No. 14/066,631 also claims priority to Chinese Patent Application
No. 201210431839.1 filed on Nov. 1, 2012, the entireties of which
are incorporated herein by reference.
FIELD
[0002] The subject invention relates to plasma reactors and,
especially to uniform gas distribution in inductively-coupled
plasma reactors.
RELATED ART
[0003] Plasma reactors or chambers are well known in the art and
are widely used in the fabrication of semiconductor integrated
circuits, flat panel displays, light emitting diodes, solar cells,
etc. In a plasma chamber it is conventional to apply an RF power to
ignite and sustain the plasma inside the vacuum chamber. There are
various manners in which the RF power can be applied, and each
manner has different characteristics, e.g., efficiency, plasma
dissociation, uniformity, etc. One technology that is relevant to
this disclosure is inductively-coupled plasma (ICP) chambers.
[0004] In inductively-coupled plasma processing chambers, an
antenna, usually in the form of a coil, is used to transmit the RF
power into the chamber. In order to couple the RF power from the
antenna into the chamber, a dielectric window is provided at the
location where the antenna is situated. In chambers for processing
substrates, e.g., silicon wafers, the substrate is situated on a
chuck and the plasma is generated above the substrate. Therefore,
the antenna is positioned over the ceiling of the chamber, such
that the ceiling is made of a dielectric material or includes a
dielectric window.
[0005] In the plasma processing chamber, various gasses are
injected into the chamber so that chemical and/or physical
interaction of ions with the substrate can be used to generate
various features on the substrate by, e.g., etching, depositing,
etc. In many such processes, one parameter of high importance is
within-wafer processing uniformity. That is, a process occurring at
the center of the substrate should be of identical or highly
similar characteristics as the process occurring at the edge of the
substrate. Thus, for example, when performing an etching process,
the etching rate at the center of the wafer should be the same as
that at the edge of the wafer.
[0006] One parameter that helps in achieving good processing
uniformity is even distribution of the processing gas within the
chamber. To achieve such uniformity, many chamber designs employ a
showerhead situated above the wafer to uniformly inject the
processing gas. However, as noted above, in ICP chambers, the
ceiling must include a window for the RF power transmitted by the
antenna. Consequently, such design does not lend itself to
showerhead implementation of gas injection.
[0007] FIG. 1 illustrates a cross-section of a prior art ICP
chamber design. An ICP chamber 100 has a generally cylindrical
metallic sidewall 105 and a dielectric ceiling 107, forming a tight
vacuum enclosure that is pumped by a vacuum pump 125. A pedestal
110 supports a chuck 115, which holds a wafer 120 to be processed.
The RF power from an RF power supplier 145 is applied to antennas
140, which is generally in the form of a coil. Processing gas is
supplied from a gas source 150 via pipelines 155 into the chamber
to ignite and sustain plasma, and thereby process the wafer 120. In
standard ICP chambers, the gas is supplied into the vacuum
enclosure either by circumference injectors/nozzles 130, by a
central nozzle 135, or both.
[0008] As can be appreciated from FIG. 1, the gas from the
circumference injectors 130 is largely pumped out and is not
effectively dissociated to reach the surface of the wafer 120.
Thus, much of the gas from the circumference injectors 130 may be
processed at the edge of the wafer, but little reaches the center
of the wafer 120, leading to non-uniformity. Conversely, the gas
provided from the central nozzle 135 is concentrated at the center
of the wafer and is not used at the edge of the wafer, also leading
to non-uniformity.
[0009] Accordingly, there is a need in the art for an improved ICP
chamber design that improves the gas distribution within the
chamber to provide enhanced processing uniformity.
SUMMARY
[0010] The following summary of the invention is included in order
to provide a basic understanding of some aspects and features of
the invention. This summary is not an extensive overview of the
invention and as such it is not intended to particularly identify
key or critical elements of the invention or to delineate the scope
of the invention. Its sole purpose is to present some concepts of
the invention in a simplified form as a prelude to more detailed
description that is presented below.
[0011] According to an aspect of the invention, a plasma reactor is
provided that includes an enclosure, a dielectric window, an RF
antenna provided over the dielectric window, a plurality of gas
injectors to supply gas into the enclosure, and a baffle situated
within the enclosure to constrict and/or redirect the flow of the
gas exiting form the injectors.
[0012] According to another aspect of the invention an ICP plasma
reactor is provided, having an enclosure wherein at least part of
the ceiling forms a dielectric window. A substrate support is
positioned within the enclosure below the dielectric window. An RF
power applicator is positioned above the dielectric window to
radiate RF power through the dielectric window and into the
enclosure. A plurality of gas injectors are distributed uniformly
above the substrate support to supply processing gas into the
enclosure. A circular baffle is situated inside the enclosure and
positioned above the substrate support but below the plurality of
gas injectors so as to redirect the flow of the processing gas.
[0013] According to another aspect of the invention, the baffle may
be formed of a conductive or dielectric material. For example, the
baffle may be fabricated of anodized aluminum, of ceramic, of
quartz, etc.
[0014] According to yet another aspect of the invention, the baffle
may be formed as a circular disk with a central opening. The baffle
may also have secondary openings distributed around the central
opening. The baffle may have an extension extending from the
central opening. The extension may be formed as a cylindrical
section, a conical section, etc. The baffle may incorporate an RF
antenna therein. The baffle may be vertically movable so as to be
raised or lowered over the substrate support, thereby varying the
gap over the substrate.
[0015] According to a further aspect of the invention, a method of
fabricating a semiconductor device on a substrate is provided,
including placing the substrate on a substrate support positioned
within a plasma reactor, wherein the plasma reactor comprises an
enclosure having a cylindrical sidewall and a ceiling, wherein at
least part of the ceiling forms a dielectric window, an RF power
applicator is positioned above the dielectric window to radiate RF
power through the dielectric window and into the enclosure, and a
plurality of gas injectors are distributed uniformly above the
substrate; positioning a circular baffle inside the enclosure such
that the baffle is above the substrate support but below the
plurality of gas injectors so as to define a gap above the
substrate; supplying the processing gas to the injectors; and,
applying RF power to the RF power applicator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The accompanying drawings, which are incorporated in and
constitute a part of this specification, exemplify embodiments of
the present invention and, together with the description, serve to
explain and illustrate principles of the invention. The drawings
are intended to illustrate major features of exemplary embodiments
in a diagrammatic manner. The drawings are not intended to depict
every feature of actual embodiments nor relative dimensions of
depicted elements, and are not drawn to scale.
[0017] FIG. 1 is a schematic cross-section of a prior art ICP
processing chamber.
[0018] FIG. 2 is a schematic cross-section of an ICP processing
chamber according to an embodiment of the invention.
[0019] FIG. 3 is a schematic cross-section of an ICP processing
chamber according to another embodiment of the invention.
[0020] FIG. 4 is a schematic cross-section of an ICP processing
chamber according to another embodiment of the invention.
[0021] FIG. 5 is a schematic cross-section of an ICP processing
chamber according to another embodiment of the invention.
[0022] FIG. 6 is a schematic cross-section of an ICP processing
chamber according to another embodiment of the invention.
[0023] FIG. 7 is a schematic cross-section of an ICP processing
chamber according to another embodiment, designed to overcome
radial-asymmetry.
[0024] FIG. 8 is a schematic of a baffle according to an embodiment
having a variable opening diameter.
DETAILED DESCRIPTION
[0025] Embodiments of the invention relate to an
inductively-coupled plasma chamber having improved uniformity,
especially gas distribution uniformity. Within-wafer uniformity is
improved by the embodiments of the invention wherein provisions are
made to redirect gas injected by injectors and/or nozzles so as to
improve the gas distribution within the chamber.
[0026] Here an embodiment of the invention is described in detail
with reference to FIG. 2. FIG. 2 illustrates a plasma processing
apparatus 200 according to one embodiment of the invention.
Elements illustrated in FIG. 2 which correspond to the elements
illustrated in FIG. 1 are given with the same reference numbers,
except that they are in the 2xx series. It will be appreciated that
the apparatus 200 is merely exemplary and that the apparatus 200
may include fewer or additional components and the arrangement of
the components may differ from that illustrated in FIG. 2.
[0027] FIG. 2 illustrates a cross-section of an ICP chamber design
implementing a gas diversion feature according to one embodiment of
the invention. ICP chamber 200 has a metallic sidewall 205 and a
dielectric ceiling 207, forming a tight vacuum enclosure that is
pumped by a vacuum pump 225. The dielectric ceiling 207 is provided
only as one example, but other ceilings can be used, e.g., a dome
ceiling, a metallic ceiling with a dielectric window, etc. A
pedestal 210 supports a chuck 215, which holds a substrate 220 to
be processed. A bias power is generally applied to the chuck 215,
but is not shown in FIG. 2, as it is not pertinent to the disclosed
embodiment. The RF power from an RF power supplier 245 is applied
to antennas 240, which is generally in the form of a coil.
[0028] Processing gas is supplied from a gas source 250 via
pipelines 255 into the chamber to ignite and sustain plasma, and
thereby process the substrate 220. In this embodiment, the gas is
supplied into the vacuum enclosure by circumference injectors or
nozzles 230, but additional gas may optionally injected via a
central nozzle 235. If the gas is supplied from both the injectors
230 and the nozzle 235, the amount of the gas supplied from each
may be arranged to be independently controlled. Any of these
arrangements for injecting the gas may be referred to as plasma gas
injector arrangement. In FIG. 2, a baffle 270 is situated within
the chamber so as to restrict and/or redirect the flow of the gas
emanating from the injectors 230. As shown in the callout, in this
embodiment the baffle is generally in the form of a disk with a
central hole or opening. The baffle is positioned below a gas
injection point, but above the level of the substrate. In this
manner, the gas is restricted to flow further towards the center of
the chamber before it can flow downwards towards the substrate, as
shown by dotted-line arrows.
[0029] In general, the baffle 270 may be made of a metallic
material, such as anodized aluminum. Fabricating the baffle from
metallic material may be advantageously employed to restrict the
plasma to the area above the baffle, as the RF from a coil will be
blocked by the baffle. On the other hand, the baffle 270 may be
fabricated of a dielectric material, such as ceramic or quartz. In
an embodiment using a dielectric baffle the RF from the coil may
pass through the baffle, such that plasma may be maintained below
the baffle (illustrated in broken-lines), depending on the amount
of the gas reaching below the baffle.
[0030] In some circumstances it may be needed to further restrict
the gas flow and cause the gas to spend more time over the center
of the wafer to ensure full dissociation over the wafer. An
embodiment beneficial for such applications is illustrated in FIG.
3. The elements of FIG. 3 that are similar to those of FIG. 2 are
noted with the same reference numbers, except in the 3xx series. As
shown in FIG. 3 and the callout of FIG. 3, the baffle 372 of this
embodiment is made in the shape of a disk having a vertical ring
extension 373, generally in the shape of a cylindrical section. The
vertical extension creates a gap 374 through which the gas can flow
to the side, i.e., to the area of the chamber beyond the
circumference of the substrate. The size of the gap 374 determines
the flow of the gas above the substrate and the time the gas spends
above the substrate so as to be dissociated by the plasma.
[0031] In the embodiment shown in FIG. 3, the diameter of the ring
opening, d, may be sized to equal the diameter of the substrate, or
be larger or smaller than the diameter of the substrate. The
diameter of the opening can be set depending on a desired flow
restriction. Also, since the vertical ring extension is set to be
orthogonal to the disk, the diameter at the opening of the ring
extension 373 is the same as the diameter at the opening of the
ring 372 itself.
[0032] On the other hand, sometimes it is desirable to restrict the
exit of the gas from the ring towards the substrate, but once the
gas flows towards the substrate it is sometimes desirable to
enhance the flow in the horizontal direction towards the periphery
of the chamber. An arrangement beneficial for such situations is
illustrated in FIG. 4. In FIG. 4 a baffle 475 is structured of a
ring with a conical-section extension 476. The conical-section 476
has an upper opening diameter d, which is smaller than a lower
opening diameter d', wherein the lower opening is in close
proximity to the substrate. The lower opening is positioned so as
to define gap 477, through which gas flows horizontally towards the
wall of the chamber. The sidewall of the conical section makes an
angle .phi. with the ring, the angle .phi. being less than 90
degrees.
[0033] In any of the above embodiments it may be desirable to let
some gas flow out prior to it reaching the central opening of the
baffle. FIG. 5 illustrates an embodiment that is somewhat of a
modification of the embodiment of FIG. 2. As shown in FIG. 5, a
baffle 578 is in the shape of a disk with a central opening,
somewhat similar to the baffle 272 of FIG. 2. The central opening
may be of the same or different diameter as that of FIG. 2. In
addition, auxiliary or secondary openings 579 are provided about
the central opening, so as to enable some gas to escape prior to
reaching the central opening. The secondary openings may be of
smaller diameters than the central opening. The auxiliary openings
can be applied to any of the embodiments shown above, and may be
distributed evenly around the central opening. For example, the
second callout in FIG. 5 illustrates a modified baffle 580 that is
similar to that illustrated in FIG. 3, except that the auxiliary
openings have been added around the extension to enable some gas to
flow out prior to reaching the central opening and flowing into the
extension.
[0034] In the embodiments disclosed above, the baffle is used to
control the flow of the processing gas. Additionally, the baffle
can be used to passively control the plasma. In general, the plasma
can diffuse through the holes on the baffle to the lower portion of
the chamber. The larger the holes, the higher the plasma density
becomes. By changing the number and locations of the holes, the
plasma density distribution within the chamber can also be changed.
The baffle can also be used to actively control the plasma. Such an
example is illustrated in FIG. 6.
[0035] In the embodiment of FIG. 6, a baffle 680 is used to
actively control the plasma. As illustrated, a secondary antenna
682 is embedded within the baffle 680. The secondary antenna may be
in the form of a coil. In the example shown in the callout the
antenna is in the form of a single loop (shown in broken line), but
other designs may be employed. The secondary antenna may be
energized using a same power supplier 645 as a main antenna
(illustrated as broken-line arrow), or it may be energized from a
different RF power supplier 647. Regardless of the power supplier
used, the amplitude of the power applied to the secondary antenna
or coil 682 may be controlled independently of the power applied to
the main antenna 640.
[0036] According to one embodiment, the baffle 680 is made of a
dielectric material and the coil is embedded within the dielectric.
For example, the baffle 680 may be made by sintering a ceramic
material with a metallic coil embedded within the ceramic. In this
manner, the power from the secondary coil is applied to the plasma
above the baffle and to the plasma below the baffle. On the other
hand, according to another embodiment, the baffle 680 is made with
a dielectric on one side and a conductor on the other side, such
that the RF power applies only to one side of the baffle. For
example, the top of the baffle 680 may be made of a conductive
material, so that the RF power from the secondary coil 682 is
applied only to the plasma below the baffle. Such an arrangement is
illustrated in the second callout of FIG. 6, wherein the coil 682
is embedded within a ceramic disk 685 such that the RF energy from
the coil can be applied to the plasma below the baffle, but a
conductive disk 683 is provided on top of the ceramic disk 685,
such that the energy from the coil 682 cannot be applied to the
plasma above the baffle. Additionally, in such an arrangement the
baffle also blocks the RF power from the main antenna 640 from
being applied to the plasma below the baffle 680. Consequently, the
RF power to the main antenna 640 can be tailored (e.g., frequency,
power, etc.) to control the plasma above the baffle 680, while the
RF power to the secondary antenna 680 can be tailored to control
the plasma below the baffle.
[0037] Any of the above embodiments can be further modified by
making the baffle movable. Such an arrangement is schematically
illustrated in FIG. 6. In FIG. 6 a step motor 690 is coupled to the
baffle 680 by, e.g., rack and pinion arrangement, such that the
step motor 690 can be energized to move the baffle vertically so as
to lower or raise the baffle 680, such that the gap between the
baffle 680 and a substrate 620 can be changed.
[0038] FIG. 7 is a schematic cross-section of an ICP processing
chamber according to another embodiment, designed to overcome
radial-asymmetry. For example, in some designs the interior space
of a chamber is not symmetric with respect to the central axis of a
wafer that is being processed. Such designs may lead to asymmetric
distribution of charged or neutral species, or both, in the plasma.
Ion distribution may be controlled via RF power coupling; however,
neutral species distribution is not affected by an RF power and is
dependent more on the gas flow within the chamber. Therefore,
according to embodiments of the invention, illustrated in FIG. 7, a
baffle 772 is designed to alter the gas flow so as to control the
flow of the neutral species.
[0039] As illustrated in FIG. 7, the baffle 772 is provided with a
wall 773, which extends upwards from a baffle plate 771. That is,
the wall 773 extends from the plate 771 in a direction away from
the wafer and towards the ceiling of the chamber. The gas is
injected between the ceiling and the baffle 772, such that the wall
773 forms a barrier to the gas flow. However, as shown by the
examples provided in callouts A-C, the barrier is radially uneven,
such that it enables higher gas flow at some radial location than
in other radial locations. This may be achieved in various manners,
but specific examples are provided in callouts A-C.
[0040] In the example illustrated in callout A, the wall 773 is
made uneven. That is, a height h.sub.1 is shown to be higher than a
height h.sub.2 at the opposite side of the wall. Of course, the
minimum and maximum heights need not necessarily be on opposite
sides. Rather, at the area where higher flow is needed, the height
should be lower. Also, while in callout A the height is changed
gradually, this is not a requirement. Rather, the height can be
changed abruptly such as, e.g., using a step-wise design.
[0041] Alternatively, as illustrated in callout B, holes may be
provided on wall 773 to allow the control of the flow. In callout B
the distribution of the holes is made uneven to generate uneven gas
flow. Specifically, in callout B more holes are made on the left
side than the right side. However, alternatively or in addition,
the sizes or shapes of the holes can be changed to cause uneven
distribution, as illustrated in callout C.
[0042] In the embodiments described above the resulting gas
distribution is static, i.e., once the baffle is placed within the
chamber it provides a specific gas distribution that cannot be
changed without disassembling the chamber or replacing the baffle.
However, at times it is desirable to change the flow
characteristics of the chamber without having to disassemble the
chamber. Therefore, according to other embodiments the aperture of
the baffle is made variable without having to disassemble the
chamber. This can be achieved in different ways, but one example is
provided in FIG. 8. The baffle of FIG. 8 has a rotatable ring 871
which may be rotated from the outside of the chamber either
manually or mechanically using, e.g. stepper motors. When the ring
871 is rotated it activates leafs or blades 874, which act like a
camera iris to vary the size of the aperture 876.
[0043] It should be understood that processes and techniques
described herein are not inherently related to any particular
apparatus and may be implemented by any suitable combination of
components. Further, various types of general purpose devices may
be used in accordance with the techniques described herein. The
present invention has been described in relation to particular
examples, which are intended in all respects to be illustrative
rather than restrictive. Those skilled in the art will appreciate
that many different combinations will be suitable for practicing
the present invention.
[0044] Moreover, other implementations of the invention will be
apparent to those skilled in the art from consideration of the
specification and practice of the invention disclosed herein.
Various aspects and/or components of the described embodiments may
be used singly or in any combination. It is intended that the
specification and examples are considered as exemplary only, with a
true scope and spirit of the invention to be indicated by the
following claims.
* * * * *