U.S. patent application number 12/405432 was filed with the patent office on 2009-10-15 for plasma processing apparatus and the upper electrode unit.
This patent application is currently assigned to Tokyo Electron Limited. Invention is credited to Tetsuji Sato.
Application Number | 20090255631 12/405432 |
Document ID | / |
Family ID | 33545073 |
Filed Date | 2009-10-15 |
United States Patent
Application |
20090255631 |
Kind Code |
A1 |
Sato; Tetsuji |
October 15, 2009 |
Plasma Processing Apparatus and the Upper Electrode Unit
Abstract
In a plasma processing apparatus that executes plasma processing
on a semiconductor wafer placed inside a processing chamber by
generating plasma with a processing gas supplied through a gas
supply hole at an upper electrode (shower head) disposed inside the
processing chamber, an interchangeable insert member is inserted at
a gas passing hole at a gas supply unit to prevent entry of charged
particles in the plasma generated in the processing chamber into
the gas supply unit. This structure makes it possible to fully
prevent the entry of charged particles in the plasma generated
inside the processing chamber into the gas supply unit.
Inventors: |
Sato; Tetsuji; (Yamanashi,
JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Assignee: |
Tokyo Electron Limited
|
Family ID: |
33545073 |
Appl. No.: |
12/405432 |
Filed: |
March 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10830355 |
Apr 23, 2004 |
|
|
|
12405432 |
|
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Current U.S.
Class: |
156/345.43 ;
118/723E |
Current CPC
Class: |
H01J 37/3244 20130101;
H01L 21/67069 20130101 |
Class at
Publication: |
156/345.43 ;
118/723.E |
International
Class: |
C23F 1/08 20060101
C23F001/08; C23C 16/50 20060101 C23C016/50 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2003 |
JP |
JP2003-121214 |
May 30, 2003 |
JP |
JP2003-154844 |
Sep 19, 2003 |
JP |
JP2003-327186 |
Claims
1. A plasma processing apparatus that executes plasma processing on
a workpiece placed inside a processing chamber by generating plasma
with a processing gas supplied through a gas supply hole at a gas
supply unit disposed within said processing chamber, wherein: an
interchangeable insert member that prevents entry of charged
particles in the plasma generated inside said processing chamber
into said gas supply unit is mounted at said gas supply hole in
said gas supply unit.
2. A plasma processing apparatus according to claim 1, wherein:
said insert member comprises a gas passage formed therein that
communicates between an entry side and an exit side of said gas
supply hole; and said gas passage comprises a passage that
regulates the flow along a central axis of said gas supply hole and
extends perpendicular to or at an angle to the central axis.
3. A plasma processing apparatus according to claim 1, wherein:
said insert member comprises a gas passage formed therein that
communicates between an entry side and an exit side of said gas
supply hole while regulating the flow along a central axis of said
gas supply hole at all times.
4. A plasma processing apparatus according to claim 3, wherein:
said gas passage is a spiral passage.
5. A plasma processing apparatus according to claim 4, wherein: a
section of said gas passage has a shape with a thickness along the
central axis of said gas supply hole set larger than a width
thereof.
6. A plasma processing apparatus according to claim 1, wherein:
insert members constituted of different materials are used in
correspondence to different types of gas used in said plasma
processing.
7. A plasma processing apparatus according to claim 1, wherein:
insert members with gas passages formed in different shapes are
used in correspondence to different density levels of the plasma
generated inside said processing chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plasma processing
apparatus, and more specifically, it relates to a plasma processing
apparatus that does not allow charged particles of plasma generated
in a processing chamber to enter a gas supply unit.
[0003] 2. Description of the Related Art
[0004] Plaza processing apparatuses in the known art include those
that execute plasma processing such as etching on the work surface
of a workpiece, e.g., a semiconductor wafer (hereafter simply
referred to as a "wafer") placed within a processing chamber by,
for instance, supplying a processing gas from a gas supply unit
into the processing chamber and generating plasma with the
processing gas.
[0005] The gas supply unit in such a plasma processing apparatus is
constituted as a shower head having numerous gas supply holes
through which the processing gas is supplied into the processing
chamber. The plasma processing apparatus may be, for instance, a
plane parallel plasma processing apparatus having a lower electrode
disposed within the processing chamber, on which the workpiece is
placed. The gas supply unit is constituted of a shower head also
functioning as an upper electrode which is disposed at the ceiling
of the processing chamber so as to face opposite the lower
electrode.
[0006] The gas supply unit includes an electrode plate that
constitutes the lower surface thereof, in which numerous gas supply
holes are formed and an electrode support body supporting the
electrode plate. Inside the electrode support body, a buffer
chamber is formed as a space located above the electrode plate and
communicating with a gas supply pipe, and the buffer chamber also
communicates with the gas supply holes at the electrode plate. The
gas flowing in through the gas supply pipe is first supplied into
the buffer chamber and is then guided from the buffer chamber into
the processing chamber via the gas supply holes at the electrode
plate.
[0007] However, charged particles such as electrons and ions in the
plasma generated with the processing gases inside the processing
chamber may enter the buffer chamber through the gas supply holes
at the gas supply unit in the plasma processing apparatus. If
charged particles in the plasma enter the gas supply unit (shower
head), a glow discharge occurs in the buffer chamber at the gas
supply unit, giving rise to problems such as reaction products
becoming adhered to the inner surfaces of the gas supply unit and
the inner surfaces of the gas supply unit becoming corroded.
[0008] These problems are addressed in, for instance, Japanese
Patent Laid-open Publication No. 9-275093, which discloses a
structure achieved by mounting a screw having a hole decentered
from the central axis at each gas outlet hole of the gas supply
means so that there is no clear passage from one opening end of the
gas supply hole through the other opening end to prevent entry of
electrons and ions in the plasma into the gas supply means. This
technology was developed in order to minimize the entry of charged
particles through the mean free path based upon the concept that
the charged particles in the plasma are allowed to enter the gas
supply means since the thickness of the electrode plate (the height
of the gas supply holes) is approximately equal to the length of
the mean free path of the charged particles in the plasma.
[0009] However, the charged particles in the plasma enter the gas
supply means not only through the mean free path but also because
of other factors. For instance, the potential (the ground
potential) at the electrode support body constituting the upper
wall of the buffer chamber in the gas supply unit may become lower
than the potential (ground potential) at the electrode plate
constituting the lower wall of the buffer chamber. In such an
event, the charged particles in the plasma are allowed to readily
enter the buffer chamber from the gas supply holes at the electrode
plate toward the electrode support body. In addition, while the gas
supply unit normally maintains a field free state inside, the
equipotential line will become skewed at an end of a gas supply
hole and shifts into the gas supply hole if the gas supply hole is
clear, thereby allowing a concentration of energy of the electrons
and the like and allowing the electrons and the like to readily
enter the gas supply hole.
[0010] For this reason, charged particles in the plasma cannot be
fully prevented from entering the gas supply means simply by
mounting a screw having a hole decentered from the central axis at
each gas outlet hole of the gas supply means as disclosed in
Japanese Patent Laid-open Publication No. 9-275093. For instance,
since high-frequency power causes charged particles such as
electrons to vibrate along a direction perpendicular to the
equipotential line, the oscillating direction of the charged
particles becomes tilted if the equipotential line becomes skewed
and shifts into the end portion of the gas supply hole. In such a
case, the entry of the charged particles cannot be fully prevented
simply by mounting a screw having a hole decentered from the
central axis.
[0011] Furthermore, entry of the charged particles in the plasma is
most likely to occur when various conditions such as a specific gas
supply hole diameter, a specific gas type and a specific plasma
density coincide. This leads to a concept that if the gas passage
at the gas supply hole can be altered in correspondence to
predetermined conditions, the entry of the charged particles in the
plasma into the gas supply unit can be prevented more
effectively.
[0012] Accordingly, an object of the present invention, which has
been completed by addressing the problems discussed above, is to
provide a plasma processing apparatus capable of fully preventing
charged particles in the plaza generated inside the processing
chamber from entering the gas supply unit.
SUMMARY OF THE INVENTION
[0013] In order to achieve the object described above, in an aspect
of the present invention, a plasma processing apparatus that
executes plasma processing on a workpiece placed inside a
processing chamber by generating plasma with a processing gas
supplied through gas supply holes of gas supply unit disposed
inside the processing chamber, characterized in that an
interchangeable insert member, which prevents charged particles in
the plasma generated inside the processing chamber from entering
the gas supply unit, as mounted at each gas supply hole at the gas
supply unit, is provided.
[0014] The insert member may include a gas passage communicating
between the entry side and the exit side of the gas supply hole,
and the gas passage may include a passage which extends along a
direction perpendicular to or at an angle to a central axis of the
gas supply hole so as to regulate the flow along the central
axis.
[0015] Alternately, the insert member may include a gas passage
formed, for instance, as a spiral gas passage, which communicates
between the entry side and the exit side of the gas supply hole
while constantly regulating the flow in the gas supply hole along
the central axis. Such a gas passage may be formed so that its
section has a width (groove depth) along the direction
perpendicular to the central axis of the gas supply hole larger
than the thickness of the passage along the central axis of the gas
supply hole.
[0016] In addition, an insert member constituted of a specific
material may be used in conjunction with a specific gas type used
for the plasma processing. Furthermore, the shape of the gas
passage in the insert member may be determined in correspondence to
the density of the plasma generated in the processing chamber.
[0017] Even if charged particles such as electrons in the plasma
enter through the gas supply hole the flow of the charged particles
inside the gas supply hole is regulated along the central axis and
the charged particles are thus caused to collide into the inner
wall or the like of the insert member and lose energy before they
reach the upper end of the insert member in the plasma processing
apparatus according to the present invention described above. In
particular, even if the equipotential line becomes skewed at the
end of the gas supply hole, the oscillating direction of the
charged particles such as electrons becomes tilted and, as a
result, the charged particles enter the gas supply hole, the
movement of the charged particles along the central axis is
regulated through the gas passage. Thus, the entry of the charged
particles in the plasma into the gas supply unit can be prevented
with a high degree of reliability. This, in turn, effectively
prevents any occurrence of a glow discharge in the gas supply unit
since no energy is transferred into the gas supply unit.
[0018] Moreover, since interchangeable insert members are used
according to the present invention, optimal insert members can be
mounted at the gas supply unit in correspondence to various
conditions such as the specific gas type and the specific plasma
density.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic sectional view of the structure
adopted in an etching apparatus in an embodiment of the present
invention;
[0020] FIG. 2 is a schematic sectional view of the structure
adopted in the upper electrode (shower head) in the embodiment;
[0021] FIG. 3 is a schematic a sectional view of the upper
electrode which does not include the insert members achieved in the
embodiment;
[0022] FIG. 4 presents a structural example that may be adopted in
the insert members in the embodiment, with FIG. 4A showing an
external view of an insert member and FIG. 4B showing a sectional
view of an insert member;
[0023] FIG. 5 presents another structural example that may be
adopted in the insert members in the embodiment, with FIG. 5A
showing an external view of an insert member and FIG. 5B showing a
sectional view of an insert member;
[0024] FIG. 6 is a perspective of another structural example that
may be adopted in the insert members in the embodiment;
[0025] FIG. 7 presents sectional views of the insert member in FIG.
6, with FIG. 7A showing a sectional view of the insert member in
FIG. 6 taken along A-A and FIG. 7B showing a sectional view of the
insert member in FIG. 6 taken along B-B;
[0026] FIG. 8 schematically illustrates the overall structure of
another plasma processing apparatus in which the present invention
may be adopted;
[0027] FIG. 9 schematically illustrates the structure of an
essential portion of the plasma processing apparatus in FIG. 8;
[0028] FIG. 10 schematically illustrates the structure of an
essential portion of the plasma processing apparatus in FIG. 8;
[0029] FIG. 11 schematically illustrates the structure of an
essential portion of the plasma processing apparatus in FIG. 8;
[0030] FIG. 12 is a schematic sectional view of the structure
adopted in another plasma processing apparatus in which the present
invention may be adopted;
[0031] FIG. 13 is a sectional view of the plasma processing
apparatus in the embodiment shown in FIG. 12 with its upper
electrode set at a processing position;
[0032] FIG. 14 presents simplified views of the upper electrode
unit achieved in the embodiment, with FIG. 14A showing the upper
electrode unit with the upper electrode set at a retracted position
and
[0033] FIG. 14B showing the upper electrode unit with the upper
electrode set at the processing position;
[0034] FIG. 15 shows the structure adopted in the means for drive
control at the upper electrode drive mechanism in the
embodiment;
[0035] FIG. 16 is a block diagram of the upper electrode position
control executed by the CPU shown in FIG. 15;
[0036] FIG. 17 shows the structure adopted in the pneumatic circuit
in the embodiment;
[0037] FIG. 18 illustrates the functions of the pneumatic circuit
in the embodiment;
[0038] FIG. 19 illustrates the functions of the pneumatic circuit
in the embodiment;
[0039] FIG. 20 shows the results of position control achieved by
driving the upper electrode in the embodiment upward; and
[0040] FIG. 21 shows the results of position control achieved by
driving the upper electrode in the embodiment downward.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] The following is a detailed explanation of the preferred
embodiments of the present invention, given in reference to the
attached drawings. It is to be noted that the same reference
numerals are assigned to components having substantially identical
functions and structural features in the specification and drawings
to preclude the necessity for a repeated explanation thereof.
[0042] (Plasma Processing Apparatus Achieved in an Embodiment of
the Present Invention)
[0043] The structure adopted in the plasma processing apparatus
achieved in an embodiment of the present invention is now explained
in reference to FIG. 1. FIG. 1 is a sectional view of the structure
of a plasma processing apparatus achieved in the embodiment. A
plasma processing apparatus 100, which is an RIE plasma etching
apparatus, includes a cylindrical processing chamber (chamber) 110
constituted of a metal such as aluminum or stainless steel. The
processing chamber 110 is grounded for protection.
[0044] Inside the processing chamber 110, a disk-shaped lower
electrode (susceptor) 112, on which a workpiece such as a
semiconductor wafer (hereafter simply referred to as a wafer) is
placed, is disposed. The lower electrode 112 constituted of, for
instance, aluminum is supported by a barrel-shaped supporting unit
116 extending upward perpendicular to the bottom of the processing
chamber 110 via an insulating barrel-shaped holding unit 114. At
the upper surface of the barrel-shaped holding unit 114, a focus
ring 118 constituted of, for instance, quartz, which encircles the
upper surface of the lower electrode 112, is disposed.
[0045] An evacuating passage 120 is formed between the side wall of
the processing chamber 110 and the barrel-shaped supporting unit
116. An annular baffle plate 122 is mounted either at the entrance
to or in the middle of the evacuating passage 120, and an
evacuation port 124 is provided at the bottom of the evacuating
passage 120. An evacuation device 128 is connected to the
evacuation port 124 via an evacuation pipe 126. The evacuation
device 128, which includes a vacuum pump (not shown), is capable of
reducing the pressure in the processing space within the processing
chamber 110 to a predetermined degree of vacuum. A gate valve 130,
which opens/closes the delivery bay through which the wafer W is
carried in/out is mounted at the side wall of the processing
chamber 110.
[0046] A high-frequency source 132 for plasma generation and also
for RIE is electrically connected to the lower electrode 112 via a
matcher 134 and a power supply rod 136. High-frequency power with a
predetermined frequency, e.g., 60 MHz, is applied to the lower
electrode 112 from the high-frequency source 132. In addition, at
the ceiling of the processing chamber 110, a shower head (hereafter
referred an "upper electrode") 138 to be detailed later, which is
used to supply a processing gas and also functions as an upper
electrode, is disposed at a position facing opposite the lower
electrode 112. The potential at the upper electrode 138 is set to
ground level. Thus, the high-frequency voltage from the
high-frequency source 132 is capacitatively applied between the
lower electrode 112 and the upper electrode 138.
[0047] An electrostatic chuck 140 that holds the wafer W by
electrostatically attracting the wafer W is provided at the upper
surface of the lower electrode 112. The electrostatic chuck 140 is
constituted by enclosing an electrode 140a formed from a conductive
film between a pair of insulating films 140b and 140c. A DC source
142 is electrically connected with the electrode 140a via a switch
143. As a DC voltage is supplied from the DC source 142, the wafer
W is attracted and held onto the electrostatic chuck 140 with the
resulting coulomb force.
[0048] A coolant chamber 144, which may extend along, for instance,
the circumferential direction is provided inside the lower
electrode 112. A coolant such as cooling water sustaining a
predetermined temperature and supplied from a chiller unit 146 via
pipings 148 and 150 circulates through the coolant chamber 144. The
temperature of the wafer W on the lower electrode 112 can be
controlled in correspondence to the temperature of the coolant. In
addition, a heat transfer gas such as an He gas is supplied from a
heat transfer gas supply unit 152 via a gas supply line 154 to the
space between the upper surface of the electrostatic chuck 140 and
the back surface of the wafer W.
[0049] As FIG. 2 also shows, the upper electrode (shower head) 138
includes an electrode plate 156 located on the lower side, at which
numerous gas passing holes 156a are formed, an electrode support
body 158 which detachably supports the electrode plate 156 and an
intermediate member 157 disposed on top of the electrode plate 156
and having gas communicating holes 157a each communicating with one
of the gas passing holes 156a at the electrode plate 156. The gas
supply holes at the gas supply unit according to the present
invention are each constituted with a gas passing hole 156a and the
corresponding gas communicating hole 157a described above. Inside
the electrode support body 158, a buffer chamber 160 is formed and
a gas supply piping 164 extending from a processing gas supply unit
162 is connected to a gas supply port 160a at the buffer chamber
160.
[0050] The processing chamber 110 is enclosed by a dipole ring
magnet 166. The dipole ring magnet 166 is constituted with a pair
of annular or coaxial magnets disposed at an upper position and a
lower position over a distance from each other in the embodiment.
The magnets constituting the dipole ring magnet 166 are each
achieved by housing a plurality of anisotropic segment pole magnets
in a ring-shaped casing formed of a magnetic material so that they
form uniform horizontal magnetic fields that are oriented in a
single direction as a whole inside the processing chamber 110. As
the processing gas is supplied into the processing chamber 110, a
magnetron discharge is caused by an RF electric field along the
vertical direction attributable to the high-frequency source 132
and the horizontal magnetic field attributable to the dipole ring
magnet 166 in the space between the upper electrode 138 and the
lower electrode 112 in the processing chamber 110 and, as a result,
high-density plasma is generated near the surface of the lower
electrode 112.
[0051] The plasma processing apparatus includes a control unit 168
that controls the individual units in the apparatus. The control
unit 168 controls the operations of, for instance, the evacuation
device 128, the high-frequency source 132, the switch 143 for the
electrostatic chuck, the chiller unit 146, the heat transfer gas
supply unit 152 and the processing gas supply unit 162. The control
unit 168 may be connected to a host computer within the factory
(not shown) to enable control from the host computer.
[0052] When executing, for instance, an etching process with the
plasma processing apparatus 100 structured as described above, the
gate valve 130 is first set in an open state to allow the wafer W,
i.e., the workpiece, to be carried into the processing chamber 110
and placed on the lower electrode 112. At this time, a DC voltage
from the DC source 142 is applied to the electrode 140a of the
electrostatic chuck 140 to electrostatically attract the wafer W
onto the lower electrode 112. Then, a specific type of processing
gas such as NH3 is supplied from the processing gas supply unit 162
into the processing chamber 110 at a predetermined flow rate and a
predetermined flow rate ratio, and the pressure inside the
processing chamber 110 is set to a predetermined value via the
evacuation device 128. In addition, high-frequency power at a
specific frequency is applied from the high-frequency source 132 to
the lower electrode 112 at a predetermined power level. The
processing gas supplied into the processing chamber 110 via the
upper electrode 138 as described above is raised to plasma between
the two electrodes 112 and 138 through a high-frequency discharge
and the work surface of the wafer W is etched with radicals and
ions occurring in the plasma.
[0053] By applying high-frequency power at a frequency higher than
that in the related art, e.g., 50 MHz or higher, to the lower
electrode 112, a higher density can be achieved for the plasma in a
more desirable state of dissociation and high density plasma can be
formed at a lower pressure.
[0054] Next, the upper electrode (shower head) 138 representing an
example that may be adopted in the gas supply unit in the
embodiment is explained in further detail in reference to drawings.
FIG. 2 is a sectional view of the structure adopted in the upper
electrode in the embodiment, whereas FIG. 3 presents another
example of an upper electrode provided for comparison with the
upper electrode in the embodiment.
[0055] As shown in FIG. 2, insert members 200 are inserted at gas
passing holes 156a constituting part of the gas supply holes, which
are located at the electrode plate 156 in the upper electrode 138
in the embodiment. The insert members 200, which can be attached to
and detached from the electrode plate 156 freely, can be replaced
by insert members 200 with any of various structures featuring gas
passages formed in different shapes and constituted of different
materials, in correspondence to various conditions such as the gas
type and the plasma density level. The insert members 200 are used
to prevent charged particles such as electrons and ions in the
plasma generated within the processing chamber 110 from entering
the upper electrode through the gas passing holes 156a. The insert
members 200 each include a gas passage 212 through which the
processing gas flows. The gas passage 212 is formed so that entry
of charged particles in the plasma is disallowed while the
processing gas is allowed to flow through it. It is to be noted
that the structure of the insert members 200 is to be described in
detail later.
[0056] If the insert members 200 are not inserted at the gas
passing holes 156a of the upper electrode 138 as shown in FIG. 3,
charged particles in the plasma may enter the upper electrode 138
through the gas passing holes 156a at the electrode plate 156.
Electrons, which move particularly fast among charged particles,
can enter the gas supply unit with ease. If charged particles in
the plasma enter the upper electrode 138, a glow discharge occurs
in the buffer chamber 160 inside the upper electrode 138, which
results in reaction products becoming adhered to the inner surfaces
at the upper electrode 138 and corrosion inside the upper
electrode.
[0057] In addition, while the charged particles in the plasma are
allowed to enter the upper electrode 138 when the length of the
mean free path of the charged particles in the plasma is
substantially equal to or greater than the thickness of the
electrode plate 156 (the height of the gas supply holes), entry of
charged particles may be attributed to the following causes as
well. For instance, the potential (the ground potential) at the
electrode support body 158 constituting the upper wall of the
buffer chamber 160 in the upper electrode 138 may become lower than
the potential (the ground potential) at the electrode plate 156,
which is in electrical contact with the intermediate member 157
constituting a lower wall of the buffer chamber 160. In such an
event, charged particles in the plasma are allowed to enter the
buffer chamber 160 with greater ease from the gas passing holes
156a at the electrode plate 156 and flow toward the electrode
support body 158.
[0058] In addition, while the upper electrode 138 normally
maintains a field free state inside, the equipotential line will
become skewed at the ends of the gas supply holes (each constituted
with a gas passing hole 156a and the corresponding gas
communicating hole 157a) and shifts into any clear gas supply hole,
thereby allowing a concentration of the energy of the electrons and
the like in the gas supply hole. Namely, when charged particles
such as electrons are caused to oscillate by high-frequency power,
they oscillate along a direction perpendicular to the equipotential
line and thus, if the equipotential line becomes skewed and shifts
into the end of a gas supply hole, the oscillating direction of the
charged particles, too, becomes tilted, which causes the energy of
the charged particles such as electrons to readily concentrate at
the end portion of the gas supply hole. As a result, the charged
particles such as electrons are allowed to enter the gas supply
holes with ease. Under these circumstances, the charged particles
are more likely to enter the buffer chamber 160 while holding a
high level of energy.
[0059] Such entry of charged particles from the plasma can be
prevented by forming a passage extending along a direction
perpendicular to or at an angle to the central axis of each gas
supply hole so as to regulate the flow along the central axis. The
entry of the charged particles in the plasma can be prevented more
effectively as the length of the passage extending along the
direction perpendicular to or at an angle to the central axis
increases, since the charged particles in the plasma along the
vertical direction will more readily collide with the wall or the
like defining the gas passage as the length of the passage
extending along the direction perpendicular to or at an angle to
the central axis increases and thus, the energy level of the
charged particles in the plasma can be kept low. The presence of
such a passage at each gas supply hole prevents the charged
particles in the plasma from advancing to the buffer chamber 160 at
the upper electrode 138.
[0060] Furthermore, the charged particles in the plasma are likely
to enter the upper electrode 138 most readily when various
conditions such as a specific gas supply hole diameter, a specific
gas type and a specifics plasma density level coincide. This leads
to a concept that if the gas passage at the gas supply hole can be
altered in correspondence to predetermined conditions, the entry of
the charged particles from the plasma into the upper electrode 138
can be prevented more effectively.
[0061] Based upon this concept, an insert member 200 is inserted at
each of the gas supply holes at the upper electrode 138 and the
part of the gas passage formed at the insert member, which extends
vertically or at an angle is made to range over a sufficient
length, according to the present invention. In addition, insert
members 200 can be replaced with a different type of insert members
in conformance to various conditions such as the gas type and the
plasma density so as to alter the passage through the gas supply
hole to adjust to specific conditions.
[0062] Next, structural examples that may be adopted in the insert
members 200 inserted at the gas passing holes 156a constituting
part of the gas supply holes at the upper electrode 138 as
described above are explained in reference to drawings. FIG. 4
presents a structural example that may be adopted in the insert
members mounted at the gas supply holes of the upper electrode.
FIG. 4A presents an external view of an insert member, whereas FIG.
4B presents a sectional view of the insert member mounted at a gas
passing hole 156a.
[0063] As shown in FIGS. 2 and 4B, the gas passing holes 156a
formed at the electrode plate 156 of the upper electrode 138 are
each constituted with a hole 156b formed on the side toward the
intermediate member 157 and a hole 156c which communicates with the
hole 156b and has a diameter smaller than that of the hole 156b.
The insert members 200 are inserted at the hole 156b which
constitute part of the gas passing holes 156a and are formed on the
side toward the intermediate member 157.
[0064] The insert members according to the present invention each
include a gas passage formed to extend along a direction
perpendicular to or at an angle to the central axis of the gas
supply hole so as to regulate the flow along the central axis. For
instance, a gas passage 202 at the insert member 200 in FIG. 4 is
formed in a spiral shape so as to communicate between the upper end
and the lower end of the insert member 200 while constantly
regulating the flow along the central axis at the gas passing hole
156a. In more specific terms, such a gas passage may be achieved by
forming a spiral groove at the external circumferential surface of
the insert member 200, as shown in FIG. 4A, for instance. The gas
passage 202 is formed by this spiral groove and the inner wall of
the gas passing hole 156a as the insert member 200 is inserted at
the gas passing hole 156a. It is to be noted that although not
shown, the gas passage may instead be formed in a zigzag pattern at
the insert member.
[0065] In addition, as shown in FIG. 4B, the gas passage 202 may be
formed so that its section has a width (groove depth) along a
direction extending perpendicular to the central axis of the gas
passing hole, which is larger than the thickness of the gas passing
hole 156a along the central axis. As the number of turns of the
spiral gas passage 202 increases, the entry of charged particles
can be prevented with greater effectiveness. However, as the number
of turns of the spiral gas passage 202 increases, the gas passage
becomes narrower, resulting in a lowered flow rate of the
processing gas. Accordingly, the number of turns that the spiral
gas passage 202 makes should be determined so as to strike an
optimal balance between the desired level of charged particle entry
prevention and the desired processing gas flow rate. For instance,
it is desirable to form the spiral gas passage so that it makes 1.5
turns or more at the external side surface of the insert member
200.
[0066] When such insert members 200 are inserted at the individual
gas passing holes 156a, the gas passages 202 of the insert members
200 regulate the flow along the central axes of the individual gas
passing holes 156a at all times and thus, any charged particles in
the plasma that may enter through the gas passing holes 156a are
bound to collide into the inner walls or the like of the insert
members 200 and lose their energy before they reach the upper ends
of the insert members 200.
[0067] Furthermore, even if the equipotential line becomes skewed
at the end of a gas passing hole 156a and the direction along which
charged particles such as electrons oscillate becomes tilted as a
result to allow the charged particles to enter through the gas
passing hole 156a, the flow along the central axis of the gas
passing hole 156a is regulated by the gas passage 202 at all times.
Thus, the charged particles collide into the inner wall or the like
of the insert member 200 and their energy becomes dissipated before
they reach the upper end of the insert member 200.
[0068] Consequently, the charged particles in the plasma are
prevented from entering the buffer chamber 160 inside the upper
electrode 138 with a high degree of effectiveness. With no energy
transferred into the buffer chamber 160, it is ensured that a glow
discharge does not occur within the buffer chamber 160.
[0069] In addition, since the gas passage 202 of the insert member
200 is formed so that its thickness along the central axis of the
gas passing hole 156a is smaller than its width (groove depth)
along the direction perpendicular to the central axis, as shown in
FIG. 4B. The space inside the gas passing hole 156a along the axial
direction can be narrowed to cause charged particles such as
electrons to readily collide into the wall and the like of the
insert member 200 and to lose energy quickly. Furthermore, as the
flow rate of the processing gas can be increased, the occurrence of
a glow discharge inside the upper electrode 138 can be prevented
without having to greatly alter the gas outlet characteristics of
the upper electrode (shower head) 138.
[0070] It is to be noted that the insert members according to the
present invention may each be detachably mounted through the entire
length of the gas passing hole 156a at the electrode plate 156, as
in the case of an insert member 210 shown in FIG. 5. FIG. 5A
presents an external view of the insert member 210, whereas FIG. 5B
is a sectional view of the insert member 210 mounted at the gas
passing hole 156a. A gas passage 212 of this insert member 210 may
be formed over the entire insert member 210, as shown in FIG. 5A,
for instance.
[0071] In another specific example of the insert members according
to the present invention, the gas passage formed to regulate the
flow along the central axis of the gas supply hole and extends
along the direction perpendicular to or at an angle to the central
axis may be present along both the diameter and the circumference
of the insert member. More specifically, it may be provided as an
insert member 230 shown in FIGS. 6 and 7. FIG. 6 is a perspective
showing the structure adopted in the insert member 220, whereas
FIG. 7A and FIG. 7B are both sectional views taken along A-A and
B-B in FIG. 6 respectively.
[0072] The insert member 220 is detachably inserted at the hole
156b in the gas passing hole 156a at the electrode plate 156, as is
the insert member 200 shown in FIG. 4. As shown in FIGS. 6 and 7,
the insert member 220 has an overall shape of a substantially
circular column with a circumferential groove 224 formed at a
substantially middle portion of the outer side surface.
[0073] At a lower position relative to the circumferential groove
224 of the insert member 220, an axial hole 226 is formed along the
axis of the gas passing hole 156a and a diameter-direction hole 228
is formed along the diameter of the gas passing hole 156a to
communicate with the upper end of the axial hole 226, as shown in
FIG. 7A. The diameter-direction hole 228 is in communication with
the circumferential groove 224. The diameter-direction hole 228 and
the circumferential groove 224 together form a passage extending
perpendicular to or at an angle to the central axis of the gas
supply hole.
[0074] As shown in FIG. 7B, at a position upward relative to the
circumferential groove 224 of the insert member 220, axial grooves
229 are formed perpendicular to the direction along which the
diameter-direction hole 228 is formed so as to cut through to the
upper end of the insert member 220. The lower ends of the axial
grooves 229 are in communication with the circumferential groove
224.
[0075] As the insert member 220 is inserted at the gas passing hole
156a, a passage is formed by the individual grooves and the inner
wall of the gas passing hole 156a. A gas passage 222 of the insert
member 220 adopting the structure described above extends upward
from its lower end along the axial direction through the axial hole
226, passes along the diameter through the diameter-direction hole
228 from the upper end of the axial hole 226, makes a 90.degree.
turn along the circumferential groove 224 and then extends upward
through the axial grooves 229 to the upper end of the gas passage
222.
[0076] By inserting this insert member 220 at each gas passing hole
156a, it can be ensured that even if charged particles in the
plasma enter the gas passing hole 156a, they cannot reach the axial
grooves 229 without first advancing along the diameter through the
diameter-direction hole 228 and then making a 90.degree. turn at
the circumferential groove 224. Since the flow in the gas passing
hole 156a along its central axis is regulated with the passage
extending both along the diameter and along the circumference in
this manner, the charged particles are bound to collide into the
inner wall or the like of the insert member 220 and lose energy
before they reach the upper end of the insert member 220.
[0077] In addition, even if the equipotential line becomes skewed
at the end of a gas passing hole 156a causing a tilt in the
direction along which charged particles such as electrons oscillate
and the charged particles are allowed to enter the gas passing hole
156a, the flow in the gas passing hole 156a along the central axis
is regulated by the gas passage 222 at all times and thus, charged
particles are bound to collide into the inner wall or the like of
the insert member 220 to lose energy before they reach the upper
end of the insert member 220.
[0078] Such insert members 220, too, make it possible to
effectively prevent entry of charged particles in the plasma into
the buffer chamber 160 at the upper electrode 138. As a result, no
energy is transferred into the buffer chamber 160 and the
occurrence of a glow discharge inside the buffer chamber 160 can be
prevented with a high degree of reliability.
[0079] It is to be noted that the dimensions of the section of the
gas passage 222 at the insert member 220, too, should be determined
so as to strike an optimal balance between the desired level of
charged particle entry prevention and the desired processing gas
flow rate. More specifically, if the diameter of the gas passing
hole 156a is approximately 4 mm to 5 mm, it is desirable to set the
height of the gas passing hole 156a along the axial direction over
the diameter-direction hole 228 and the circumferential groove 224
in the gas passage 222 to 0.5 mm to 1.5 mm.
[0080] Next, materials that may be used to constitute the insert
members according to the present invention are explained. The
insert members 200, 210 and 220 described above may be constituted
of a fluororesin such as Teflon (registered trademark), a
tetrafluoroethylene resin (PTFE), a chlorine trifluoroethylene
resin (PCTFE), a tetrafluoroethylene parfluoroalkylvynylether
copolymer resin (PFA), a tetrafluoroethylene-hexafluoride propylene
copolymer resin (PFE) or a fluorovinyllidene resin (PVDF) instead
of quartz. These materials are desirable since they have low
dielectric constants, achieve a high level of voltage withstanding
performance against AC voltages and can be processed with ease,
which makes it possible to minimize production costs.
Alternatively, the insert members may be constituted of a porous
ceramic instead of a resin. Furthermore, the insert members 200
achieved in the embodiment, which are used in the field free upper
electrode 138, may instead be constituted of metal, e.g., aluminum,
instead of resin.
[0081] The insert members mounted at the gas supply holes in the
upper electrode 138 in the embodiment are interchangeable.
Accordingly, the optimal type of insert members should be selected
in correspondence to various conditions including the gas type and
the plasma density to be inserted at the gas supply holes in the
upper electrode 138. By using the optimal insert members, it is
possible to fully prevent charged particles in the plasma generated
in the processing chamber 110 from entering the upper electrode
138, which constitutes the gas supply unit.
[0082] More specifically, insert members constituted of different
materials may be mounted in correspondence to different types of
processing gases. For instance, insert members constituted of
polyimide may be used in conjunction with a CF gas, and insert
members constituted of PTFE with a high level of corruption
resistance may be used in conjunction with a corrosive gas such as
a NH3 gas, a HBR gas or a C12 gas.
[0083] In addition, insert members formed in different shapes may
be mounted in correspondence to different density levels of the
plasma generated inside the processing chamber 110. For instance,
as the plasma density rises, it becomes necessary to more
rigorously ensure that charged particles in the plasma cannot enter
the upper electrode readily and, accordingly, the insert members
200 or 210 having the spiral gas passages 202 or 212 as shown in
FIG. 4 or FIG. 5 should be used, whereas if the plasma density is
low, the insert members 220 having the gas passages 222 structured
as shown in FIGS. 6 and 7 formed therein are good enough.
[0084] As explained in detail above, the present invention provides
a plasma processing apparatus with which it is impossible to fully
prevent charged particles in plasma generated inside the processing
chamber from entering the gas supply unit.
[0085] While the invention has been particularly shown and
described with respect to a preferred embodiment thereof by
referring to the attached drawings, the present invention is not
limited to this example and it will be understood by those skilled
in the art that various changes in form and detail may be made
therein without departing from the spirit, scope and teaching of
the invention.
[0086] For instance, while high-frequency power is applied to the
lower electrode 112 alone and the upper electrode 138 is grounded
in the explanation given above on the plasma processing apparatus
100 achieved in the embodiment, the present invention may also be
adopted in a plasma processing apparatus in which high-frequency
power is also applied to the upper electrode 138 as well as to the
lower electrode 112. In such a case, too, a glow discharge inside
the upper electrode 138 can be prevented as effectively as in the
embodiment.
[0087] In addition, the present invention may be adopted in a
plasma processing apparatus other than a plane parallel plasma
etching apparatus, such as a helicon wave plasma etching apparatus
or an inductively coupled plasma etching apparatus. In more
specific terms, the present invention may be adopted in plasma
processing apparatuses such as those explained in reference to
FIGS. 8 to 11 and FIGS. 12 through 21.
[0088] (Another Example of Plasma Processing Apparatus in which the
Present Invention May be Adopted)
[0089] Next, another example of a plasma processing apparatus in
which the present invention may be adopted is explained in
reference to drawings. The plasma processing apparatus in this
example is employed to execute specific types of plasma processing
such as etching and film formation processing on work substrates,
e.g., semiconductor wafers or glass substrates for liquid crystal
display devices, by using plasma.
[0090] It is an established practice in the area of semiconductor
device production to process a work substrate such as a
semiconductor wafer or a glass substrate for a liquid crystal
display device in a desired manner by employing a plasma processing
apparatus that executes, for instance, etching processing or film
formation processing on the work substrate with plasma generated
inside a vacuum chamber and applied onto the work substrate.
[0091] In the plasma processing apparatus which may be a so-called
plane parallel plasma processing apparatus, a stage on which the
semiconductor wafer or the like is placed is provided inside the
vacuum chamber, a shower head is provided at the ceiling of the
vacuum chamber so as to face opposite the stage and a pair of plain
parallel electrodes are constituted with the stage and the shower
head.
[0092] A specific type of processing gas is supplied from the
shower head into the vacuum chamber and at the same time, the
vacuum chamber is evacuated through its bottom so as to fill the
vacuum chamber with a processing gas atmosphere achieving a
predetermined degree of vacuum. In this state, high-frequency power
with a predetermined frequency is supplied between the stage and
the shower head, thereby generating plasma with the processing gas,
and as the plasma is applied to the semiconductor wafer, the
semiconductor wafer is processed, e.g., etched.
[0093] The plasma processing apparatus in the related art as
described above include those having an evacuation ring formed as
an annular plate surrounding the stage with numerous permeating
hole or slit-shaped evacuating passages formed therein to achieve
an even flow of the processing gas around the semiconductor wafer
by uniformly evacuating the atmosphere around the stage and to
prevent a plasma leak from the processing space (see, for instance,
Japanese Utility Model Publication No. 5-8937 (FIGS. 1 through
3)).
[0094] While the evacuation ring has a function of preventing a
plasma leak from the processing space within the vacuum chamber, as
described above, it is necessary to ensure that electrons are not
allowed to pass through the evacuating passages readily by reducing
the opening area of the evacuating passages or increasing the
length of the evacuating passages in the evacuation ring in order
to further improve the plasma leak preventing effect. It is, to be
noted that if a plasma leak occurs, the plasma becomes unstable and
it becomes difficult to execute a specific type of plasma
processing on the semiconductor wafer or the like. For this reason,
the likelihood of a plasma leak needs to be minimized.
[0095] However, if the function of the evacuation ring for
preventing plasma leak is improved as described above, it becomes
more difficult to achieve a sufficient level of conductance of the
gas. This gives rise to a problem in that with the evacuation
performance becoming poor, the processes that can be executed
become limited. If, on the other hand, priority is given to high
evacuation performance in order to avoid the problem discussed
above, it becomes necessary to use a large high-performance vacuum
pump to result in an increase in the apparatus production
costs.
[0096] As described above, if the function of the evaluation ring
for preventing a plasma leak is improved, the conductance of the
gas becomes poor, and it is difficult to satisfy both the
requirements for the plasma leak preventing function and the
sufficient level of conductance of the gas in the plasma processing
apparatus in the related art. This leads to problems in that a
desired type of plasma processing cannot be executed due to the
occurrence of a plasma leak and in that the processes which can be
executed become limited due to poor conductance of the gas and the
like.
[0097] Accordingly, an object of the present invention, which has
been completed by addressing the problems discussed above, is to
provide a plasma processing apparatus having a high level of gas
conductance capacity to enable a wide range of processes without
increasing the production costs and also having an effective plasma
leak preventing function to allow plasma processing to be executed
in a desirable manner with stable plasma.
[0098] In order to achieve the object described above, in an aspect
of the present invention, a plasma processing apparatus comprising
a vacuum chamber in which a work substrate is placed, a stage
disposed within the vacuum chamber on which the work substrate is
placed, a plasma generating mechanism that generates plasma within
the vacuum chamber to be used to execute a specific type of
processing on the work substrate, an evacuation ring disposed so as
to surround the stage and having an evacuating passage formed
therein and an evacuation mechanism that evacuates the vacuum
chamber via the evacuating passage, characterized in that the
evacuation ring includes a side wall portion formed substantially
perpendicular to the surface of the stage on which the work
substrate is placed and a bottom portion ranging inward from the
lower end of the side wall portion and in that the evacuating
passage is formed at least at the side wall portion, is
provided.
[0099] The side wall portion of the evacuation ring is constituted
with an inner cylindrical member and an outer cylindrical member
disposed coaxially to each other over a predetermined distance from
each other, which should be positioned so as to offset an opening
at the inner cylindrical member and an opening at the outer
cylindrical member from each other.
[0100] In this structure, the opening at the inner cylindrical
member and the opening at the outer cylindrical member may be
formed in a longitudinally elongated rectangular shape, and the
inner cylindrical member and the outer cylindrical member may each
have a plurality of such openings set along the circumferential
direction over predetermined intervals.
[0101] In addition, the evacuating passage may be formed with the
opening formed at the inner cylindrical member, a clearance formed
between the inner cylindrical member and the outer cylindrical
member and the opening formed at the outer cylindrical member.
[0102] Also, the evacuating passage may be formed at the bottom
portion of the evacuation ring in the plasma processing
apparatus.
[0103] In another aspect of the present invention, the object
described above is achieved by providing a plasma processing
apparatus comprising a vacuum chamber in which a work substrate is
placed, a stage disposed within the vacuum chamber on which the
work substrate is placed, a plasma generating mechanism that
generates plasma inside the vacuum chamber to be used to execute a
specific type of processing on the work substrate, an evacuation
ring disposed so as to surround the stage and having an evacuating
passage formed therein and an evacuation mechanism that evacuates
the vacuum chamber from the bottom of the evacuation ring via the
evacuating passage, characterized in that the evacuation ring
includes a first member having a first opening and a second member
disposed over a distance with a clearance formed between the first
member and the second member and having a second opening formed at
a position offset from the first opening, in that the evacuating
passage is formed to extend from the first opening into the
clearance and pass through the clearance to be led out from the
second opening and in that the plasma is trapped inside the
clearance.
[0104] The present invention achieved in an embodiment is now
explained in detail in reference to drawings. FIG. 8 is a schematic
illustration of the structure adopted in the embodiment achieved by
adopting the present invention in a plane parallel plasma etching
apparatus used to etch semiconductor wafers. In FIG. 8, reference
numeral 301 indicates a cylindrical vacuum chamber constituted of,
for instance, aluminum and having an internal space that can be
closed off in an airtight state.
[0105] A stage 302 on which a semiconductor wafer W is placed is
provided inside the vacuum chamber 301, and the stage 302 also
functions as a lower electrode. At the ceiling inside the vacuum
chamber 301, a shower head 303 constituting an upper electrode is
disposed and a pair of plain parallel electrodes are constituted by
the stage 302 and the shower head 303.
[0106] A free space 304 in which the gas is diffused is formed at
the shower head 303 and numerous narrow holes 305 are formed on the
lower side relative to the free space 304 for gas diffusion. A
specific type of processing gas supplied from a processing gas
supply system 306 is diffused inside the free space 304 for gas
diffusion, and the diffused processing gas is then supplied in a
shower directed toward the semiconductor wafer W through the narrow
holes 305. While the potential at the shower head 303 is set to the
ground level in the embodiment, a high-frequency source may be
connected to the shower head 303 to apply high-frequency power both
to the stage 302 and to the shower head 303, instead.
[0107] Two high-frequency sources 309 and 310 are connected to the
stage 302 via two matchers 307 and 308 respectively and, as a
result, high-frequency power can be supplied to the stage 302 by
superimposing the high frequency power with one of the two
different specific frequencies (e.g., 100 MHz and 3.2 MHz) on the
high frequency power with the other frequency. It is to be noted
that a single high-frequency source may be used to supply
high-frequency power to the stage 302 so that high-frequency power
with a single frequency is supplied to the stage 302, instead.
[0108] In addition, an electrostatic chuck 311 which
electrostatically holds the semiconductor wafer W is provided at
the surface of the stage 302 on which the semiconductor wafer W is
placed. The electrostatic chuck 311 adopts a structure achieved by
disposing an electrostatic chuck electrode 311b inside an
insulating Layer 311a, with a DC source 312 connected to the
electrostatic chuck electrode 311b. A focus ring 313 is provided at
the upper surface of the stage 302 so as to surround the
semiconductor wafer W.
[0109] An evacuation port 314 is provided at the bottom of the
vacuum chamber 301, and an evacuation system 315 constituted of a
vacuum pump and the like is connected to the evacuation port
314.
[0110] An evacuation ring 316 formed in an annular shape is
provided around the stage 302. As shown in FIG. 9, the evacuation
ring 316 includes a side wall portion 317 formed to range downward
almost perpendicularly and a bottom portion 318 ranging inward
perpendicular to the bottom end of the side wall portion 317.
[0111] As shown in FIG. 10, the side wall portion 317 is
constituted with an inner cylindrical member 319 and an outer
cylindrical member 320 disposed, coaxially to each other over a
predetermined distance from each other. The inner cylindrical
member 319 includes a plurality of openings 319a formed in a
vertically elongated rectangular shape and set over specific
intervals along the circumferential direction to constitute
evacuating passages. In addition, as shown in FIGS. 10 and 14, the
outer cylindrical member 320, too, includes a plurality of openings
320a formed in a vertically elongated rectangular shape to
constitute the evacuating passages. The openings 319a and the
openings 320a are disposed so that they are offset from each other
by a predetermined extent (by the distance C in FIG. 11) along the
circumferential direction.
[0112] The evacuating passages are thus each formed so that the gas
passes through the openings 319a at the inner cylindrical member
319, then passes through a clearance 321 formed between the inner
cylindrical member 319 and the outer cylindrical member 320 and
subsequently is discharged through the openings 320a at the outer
cylindrical member 320, as the arrows in FIG. 11 indicate.
[0113] The dimensions A to D in FIG. 11, i.e., the width A of the
clearance 321, the width B of the openings 319a, the width C over
which the openings 319a are offset relative to the corresponding
openings 320a and the thickness D of the inner cylindrical member
319 satisfy the following conditions:
C/A>1
B>2A
B/D>1
[0114] Namely, the evacuation ring 316 achieves a structure that
traps plasma in the clearance 321, and in order to assure this, the
width A of the clearance 321 is set relatively small, whereas the
offset width C of the openings 319a and the openings 320a is set
large enough to trap the plasma.
[0115] In addition, the width B of the openings 319a, which are not
used to trap the plasma, is set to a large value to ensure a high
enough conductance level with a large opening area, and for the
same reason, the thickness D of the inner cylindrical member 319 is
set to a small value. The thickness of the outer cylindrical member
320 and the width of the openings 320a, too, are set to similar
values based upon the same principle.
[0116] It is to be noted that FIG. 11 schematically illustrates the
structure of the evacuation ring 316 and it does not indicate the
actual dimensions accurately. In the actual application, the width
B of the openings 319a is set greater than 2 mm, e.g.,
approximately several millimeters if, for instance, the width A of
the clearance 321 is set to 1 mm. The offset width C of the
openings 319a and the openings 320a and the thickness D of the
inner cylindrical member 319 are also set to values conforming to
the conditions presented earlier and taking machinability into
consideration.
[0117] The length of the side wall portion 317 along the vertical
direction, too, is set to a value that will allow the openings 319a
and the openings 320a to range over large enough areas and assures
a satisfactory level of conductance.
[0118] By forming evacuating passages at the side wall portion 317
of the evacuation ring 316 and setting the length of the side wall
portion 317 along the vertical direction to a relatively large
value, as described above, the openings are allowed to range over
large enough areas and thus a satisfactory level of conductance is
assured. In addition, since the diameter of the evacuation ring 316
does not need to be increased even though the openings range over
great areas, the diameter of the vacuum chamber 301 itself does not
need to increase, and thus, the footprint of the apparatus remains
unchanged.
[0119] Furthermore, by forming the evacuating passages at the side
wall portion 317 with the openings 319a, the clearance 321 and the
openings 320a as described above, the openings are allowed to range
over large areas to assure a satisfactory level of conductance
while assuring the required plasma leak preventing function, as
well.
[0120] In other words, while electrons in the plasma are allowed to
pass through the openings 319a ranging over large areas in the gas
flow indicated by the arrows in FIG. 11, the outer cylindrical
member 320 is present ahead as the electrons advance and thus, the
likelihood of the electrons further passing through the clearance
321 and being led out to the outside through the openings 320a is
greatly lowered. Namely, since the plasma is highly unlikely to
leak to the outside of the openings 320a, a satisfactory level of
plasma leak preventing function can be assured even when the
openings range over large areas to achieve a high level of
conductance.
[0121] Moreover, numerous openings 318a each constituted as a
circular hole are formed at the bottom portion 318 of the
evacuation ring 316 as well, and these openings 318a, too, form
evacuating passages in the embodiment. By forming evacuating
passages at the bottom portion 318 in this manner, the conductance
can be further improved.
[0122] Instead of forming the evacuating passages at the bottom
portion 318 of the evacuation ring 316 with openings such as
circular holes as described above, the evacuating passage at the
bottom portion 318, may adopt a structure identical to that of the
evacuating passages at the side wall portion 317. However, since
the bottom portion 318 is located at a considerable distance from
the area in which plasma is formed, the evacuating passage at the
bottom portion 318 can be formed with simple circular holes or the
like without having to consider the plasma leak preventing function
as a crucial factor. In addition, if a sufficiently high level of
conductance can be assured with the evacuating passages formed at
the side wall portion 317 alone, no evacuating passages need to be
formed at the bottom portion 318.
[0123] The evacuation ring 316 described above may be formed by
using any material as long as it is electrically conductive and may
be constituted of, for instance, stainless steel or aluminum with
an alumite film or a sprayed coating deposited on the surface
thereof. The evacuation ring 316 constituted of a conductive
material is electrically connected to the ground potential.
[0124] As the vacuum chamber 301 is evacuated through the
evacuation port 314 via the evacuation ring 316 adopting the
structure described above by utilizing the evacuation system 315,
the atmosphere inside the vacuum chamber 301 achieves a
predetermined degree of vacuum.
[0125] Furthermore, a magnetic field forming mechanism 322 is
provided around the vacuum chamber 301 so as to form a desired
magnetic field in the processing space inside the vacuum chamber
301. The magnetic field forming mechanism 322 includes a rotating
mechanism 323, and as the magnetic field forming mechanism 322 is
rotated around the vacuum chamber 301, the magnetic field inside
the vacuum chamber 301, too, is allowed to rotate.
[0126] Next, an etching process executed in the plasma etching
apparatus structured as described above is explained. First, a gate
valve (not shown) at a transfer port (not shown) is opened, and a
semiconductor wafer W carried into the vacuum chamber 301 with a
transfer mechanism or the like is set on the stage 302. The
semiconductor wafer W placed on the stage 302 is then
electrostatically held onto the electrostatic chuck 311 by applying
a predetermined level of a DC voltage to the electrostatic chuck
electrode 311b of the electrostatic chuck 311 from the D.C. source
312.
[0127] Next, after moving the transfer mechanism out of the vacuum
chamber 301, the gate valve is closed, the vacuum chamber 301 is
evacuated with the vacuum pump or the like of the evacuation system
315, and then, after a specific degree of vacuum is achieved inside
the vacuum chamber 301, the processing gas to be used to execute a
specific type of etching process is supplied from the processing
gas supply system 306 into the vacuum chamber 301 via the free
space 304 for gas diffusion and the narrow holes 305 at a flow rate
of, for instance, 100 to 1000 sccm. Thus, the pressure inside the
vacuum chamber 301 is sustained at, for instance, approximately
1.33 to 133 Pa (10 to 100 mTorr).
[0128] In this state, high-frequency power with specific
frequencies (e.g., 100 MHz and 3.2 MHz) is supplied to the stage
302 from the high-frequency sources 309 and 310.
[0129] As the high-frequency power is applied to the stage 302 as
described above, a high-frequency electric field is formed in the
processing space between the shower head 303 and the stage 302. In
addition, a specific magnetic field is formed in the processing
space by the magnetic field forming mechanism 322. Thus, a plasma
with specific characteristics is generated from the processing gas
supplied into the processing space, and a specific film on the
semiconductor wafer W becomes etched with the plasma.
[0130] During this process, the high conductance at the evacuation
ring 316 makes it possible to evacuate the vacuum chamber with a
high degree of efficiency and, as a result, the atmosphere inside
the vacuum chamber easily achieves a high degree of vacuum without
having to employ a large, high performance vacuum pump or the like.
In addition, since a plasma leak can be prevented with a high
degree of reliability at the evacuation ring 316, the desired
etching process can be executed with a high level of accuracy with
stable plasma.
[0131] After the specific etching process is executed, the supply
of the high-frequency power from the high-frequency sources 309 and
310 is stopped, thereby ending the etching process, and then, the
semiconductor wafer W is carried out of the vacuum chamber 301 by
reversing the procedure described earlier.
[0132] It is to be noted that while the present invention is
adopted in a plasma etching apparatus that etches semiconductor
wafers in the embodiment described above, the present invention is
not limited to this example. For instance, it may be adopted in an
apparatus that processes substrates other than semiconductor
wafers, or in an apparatus that executes processing other than
etching, e.g., a film formation processing apparatus that executes
CVD or the like.
[0133] The plasma processing apparatus described above achieving a
high level of gas conductance capability supports a wide range of
processes without necessitating an increase in the production costs
and enables the plasma processing to be executed in a desirable
manner with stable plasma achieved through its high level of plasma
leak preventing function.
[0134] (Another Example of a Plasma Processing Apparatus in which
the Present Invention May be Adopted)
[0135] Next, yet another example of the plasma processing apparatus
in which the present invention may be adopted is explained. The
present invention is adopted in a plasma processing apparatus that
executes plasma processing on workpieces that may be glass
substrates for flat displays (FPD) such as liquid crystal displays
(LCD), i.e., FPD substrates such as LCD substrates, as well as
semiconductor wafers in this example. More specifically, an
explanation is given in reference to the example on a plasma
processing apparatus capable of implementing control so as to drive
a member such as an electrode disposed within the plasma processing
apparatus to a desired position and its upper electrode unit.
[0136] In a plasma processing apparatus that executes plasma
processing on a workpiece such as a semiconductor wafer (hereafter
simply referred to as a wafer) or an LCD substrate during various
processes of semiconductor devices or LCD substrate production,
follow-up control is normally implemented by utilizing a
servomotor, a stepping motor or the like as an actuator to
implement control so as to linearly drive a member such as an a
electrode disposed within the processing apparatus to a desired
position.
[0137] In such a structure having a motor utilized as an actuator,
a sturdy structural body is required to form a motive force
communicating mechanism constituted of a pulley, gears, a belt or a
chain to be used to convert the motor rotation to a linear motion,
and thus, the processing apparatus itself is bound to be large in
size. In addition, there is also a problem in that vibration and
noise caused by the rotational motion of the motor and the motive
force communicating mechanism adversely affect the results of the
wafer processing. Furthermore, it requires a regular maintenance
since the gears and the chain constituting the motive force
communicating mechanism are consumables.
[0138] While it is conceivable to utilize an actuator constituted
of a pneumatic actuator instead of a motor, the piping connection
for a pneumatic actuator is bound to be complex and there is also
the concern that an oil leak may cause contamination in the clean
room. For these reasons, a pneumatic actuator is not suitable for
an application in a plasma processing apparatus.
[0139] As an alternative, a pneumatic actuator may be utilized as
the actuator. A pneumatic actuator is advantageous in that there is
no risk of an oil leak or contamination of the clean room. There is
another advantage to the pneumatic actuator in that it can be
provided as a light weight, compact unit capable of achieving a
high output. For these reasons, pneumatic actuators are used in
plasma processing apparatus applications, in a wafer cassette
elevator mechanism (see, for instance, the Japanese Patent
Laid-open Publication No. 2001-35897) and in a gate switching
mechanism (see, for instance, Japanese Patent Laid-open Publication
No. 10-209245 (U.S. Pat. No. 6,113,734)) provided at the wafer
transfer port in the processing chamber.
[0140] However, when a pneumatic actuator is used as the actuator
to implement control on the drive of a member disposed inside the
plasma processing apparatus, the compressibility due to the
material characteristics inherent to air such as the viscosity and
density, and the nonlinearity attributable to the communication
delay compromise the control performance. In addition, the control
performance is also affected by external factors such as the
temperature. Thus, highly accurate positional control, in
particular, cannot easily be achieved with a pneumatic
actuator.
[0141] For this reason, a pneumatic actuator is primarily utilized
in simple tasks such as a constant repetitive operation and is not
deemed suitable for drive control of, for instance, an electrode,
in which highly accurate positional control must be achieved in the
related art.
[0142] Accordingly, an object of the present invention, which has
been completed by addressing the problems discussed above, is to
provide a plasma processing apparatus and an upper electrode unit
with which highly accurate positional control can be implemented by
using a pneumatic actuator.
[0143] In order to achieve the object described above, in a first
aspect of the present invention, a plasma processing apparatus that
executes plasma processing on a workpiece with plasma generated by
using an electrode disposed inside a processing container,
comprising a sliding support member that slidably supports the
electrode with a slide mechanism so that the electrode is allowed
to slide freely along one direction, a pneumatic cylinder having a
rod disposed continuous with the sliding support member, a
pneumatic circuit that drives the pneumatic cylinder and a means
for control that implements positional control of the electrode by
controlling the pneumatic circuit, is provided.
[0144] A second aspect of the present invention achieves the object
by providing an upper electrode unit of a plasma processing
apparatus that executes plasma processing on a workpiece with
plasma generated by using an upper electrode disposed inside a
processing container, comprising the upper electrode disposed
inside the processing container, a sliding support member that
slidably supports the upper electrode with a slide mechanism so as
to allow the upper electrode to slide freely along the vertical
direction, a pneumatic cylinder having a rod disposed continuous to
the sliding support member, a pneumatic circuit that drives the
pneumatic cylinder and a means for control that implements
positional control of the upper electrode by controlling the
pneumatic circuit.
[0145] According to the invention achieved in the first aspect and
the second aspect by adopting the structure described above, the
sliding support member provided independently of the pneumatic
cylinder slidably supports the electrode so as to allow the
electrode to slide freely along one direction (e.g., the vertical
direction) and, as a result, any load (external disturbance) that
would otherwise be applied to the pneumatic cylinder along a
direction other than the one direction is eliminated to engage the
pneumatic cylinder in movement along one direction exclusively.
Consequently, highly accurate positional control of the electrode
is achieved with the pneumatic cylinder.
[0146] In addition, by providing the upper electrode, the drive
mechanism of the upper electrode and the means for its control as
an integrated unit as in the second aspect, the upper electrode
unit can be installed into an existing plasma processing apparatus
with ease to achieve positional control for the upper electrode
with a pneumatic cylinder.
[0147] The slide mechanism used in the first and second aspects may
include a rail disposed at the external circumference of the
sliding support member along the direction in which electrode
slides and a guide member that guides the rail along the sliding
direction while supporting the rail slidably and is fixed to the
processing container. By adopting such a slide mechanism, the
electrode can be slidably supported through a simple structure. The
guide member in this slide mechanism may be fixed to the processing
container via a horizontal adjustment member of the electrode. In
such a case, a fine adjustment of the electrode along the
horizontal direction can be achieved readily by adjusting the
inclination of the guide member with the horizontal adjustment
member.
[0148] Also, the rod of the pneumatic cylinder used in the first
and second aspects may be disposed at an approximate center of the
electrode. This structure is effective in preventing decentering of
a load applied to the rod of the pneumatic cylinder and suppressing
an occurrence of moment, and thus, even more accurate positional
control of the electrode is achieved.
[0149] Furthermore, the pneumatic circuit used in the first and
second aspects may include a switching valve provided at a position
between a pneumatic source and the pneumatic cylinder, which enable
drive of the rod of the pneumatic cylinder by switching the flow of
compressed air supplied to the pneumatic cylinder based upon a
control signal provided by the means for control and a drive stop
valve disposed at a position between the switching valve and the
pneumatic cylinder, which allows the rod of the pneumatic cylinder
to stop and be held by cutting off the compressed air supplied to
the pneumatic cylinder based upon a stop signal provided by the
means for control. By adopting such a structure in the pneumatic
circuit, it becomes possible to control the position to which the
electrode moves and the direction along which the electrode moves
with the means for control, and thus, if an abnormality occurs in
the plasma processing apparatus, the movement of the electrode can
be stopped and the electrode can be held at the stop position.
[0150] In addition, a means for positional detection that detects
the position of the electrode by detecting the movement of the rod
at the pneumatic cylinder used in the first and second aspects may
be provided to allow the means for control to implement the
positional control of the electrode based upon a deviation
determined by subtracting the current position of the electrode
detected with the means for positional detection from a target
position set for the electrode. In such a case, the target position
may be set over a plurality of stages leading to the position to
which the electrode is to be ultimately moved, so as to drive the
electrode gradually. By driving the electrode gradually in this
manner, the occurrence of abrupt drive and vibration caused by
material characteristics inherent to the air used to drive the
pneumatic cylinder such as the viscosity and the density can be
minimized. Thus, while the upper electrode is driven with the
pneumatic cylinder, problems such as attracting particles and the
like in the processing container, for instance, can be
prevented.
[0151] It is to be noted that the electrode referred to in the
description of the first aspect is one of a pair of electrodes
disposed parallel to each other inside the processing container,
and the workpiece may be placed on the other electrode.
[0152] The following is a detailed explanation of a preferred
embodiment of the present invention, given in reference to attached
drawings. It is to be noted that in the specification and the
drawings, the same reference numerals are assigned to components
having substantially identical functions and structural features to
preclude the necessity for a repeated explanation thereof.
[0153] FIGS. 12 and 13 schematically illustrates the structure
adopted in a plane parallel plasma processing apparatus 400, Which
is a typical example of the plasma processing apparatus achieved in
the embodiment of the present invention. FIG. 12 shows the upper
electrode set at the retracted position, whereas FIG. 13 shows the
upper electrode set at the processing position. FIG. 14
schematically illustrates the mechanism used to drive the upper
electrode shown in FIGS. 12 and 13 to facilitate an explanation of
its functions, with FIG. 14A showing a state in which the upper
electrode is set at the retracted position and FIG. 14B showing a
state in which the upper electrode is set at the processing
position.
[0154] The plasma processing apparatus 400 achieved in the
embodiment includes a cylindrical chamber (processing container)
402 constituted of aluminum with a surface thereof having undergone
anodization (alumite processing), and the chamber 402 is
grounded.
[0155] A susceptor stage 404 formed in a substantially columnar
shape, on which a workpiece such as a semiconductor wafer (a
hereafter simply referred to as a "wafer") W is placed is provided
at the bottom inside the chamber 402 via an insulating plate 403
constituted of ceramic or the like. A susceptor 405 constituting a
lower electrode is set on the susceptor stage 404. A high pass
filter (HPF) 106 is connected to the susceptor 405.
[0156] Inside the susceptor stage 404, a temperature adjustment
medium chamber 407 is formed. A temperature adjustment medium which
is guided into the temperature adjustment medium chamber 407 via a
supply pipe 408 is made to circulate within the temperature
adjustment medium chamber 407 and then is discharged through a
discharge pipe 409. With the temperature adjustment medium
circulating in this manner, the temperature of the susceptor 405 is
adjusted to a desired level.
[0157] An electrostatic chuck 411 assuming a shape substantially
identical to that of the wafer W is disposed on the central portion
of the susceptor 405 on the upper side, which is formed as a
projecting disk. The electrostatic chuck 411 is achieved by setting
an electrode 412 between insulating members. A DC voltage at, for
instance, 1.5 kV is applied to the electrostatic chuck 411 from a
DC electrode 413 connected to the electrode 412. As a result, the
wafer W becomes electrostatically held onto the electrostatic chuck
411.
[0158] At the insulating plate 403, the susceptor stage 404, the
susceptor 405 and the electrostatic chuck 411, a gas passage 414
through which a heat transfer medium (e.g., a back side gas such as
an He gas) is supplied to the rear surface of the workpiece i.e.,
the wafer W, is formed. The heat is transferred between the
susceptor 405 and the wafer W via the heat transfer medium, thereby
sustaining the temperature of the wafer W at a predetermined
level.
[0159] An annular focus ring 415 is disposed at the edge of the
susceptor 405 at its upper end so as to surround the wafer W placed
on the electrostatic chuck 411. The focus ring 415 is constituted
of an insulating material such as ceramic or quartz, or an
electrically conductive material. The presence of the focus ring
415 improves the etching uniformity.
[0160] An evacuation pipe 431 is connected at the bottom of the
chamber 402, and an evacuation device 435 is connected to the
evacuation pipe 431. The evacuation device 435, which includes a
vacuum pump such as a turbo molecular pump, adjusts the pressure of
the atmosphere inside the chamber 402 to a predetermined lower
level (e.g., 0.67 Pa or lower). In addition, a gate valve 432 is
provided at the side wall of the chamber 402. As the gate valve 432
opens, a transfer of the wafer W into/out of the chamber 402 is
enabled. It is to be noted that the wafer W is transferred with,
for instance, a transfer arm.
[0161] In addition, an upper electrode 420 is disposed above the
susceptor 405 to run parallel to the susceptor 405 and to face
opposite the susceptor 405. The upper electrode 420 can be driven
along one direction, e.g., the vertical direction, by an upper
electrode drive mechanism 500. Thus, the distance between the
susceptor 405 and the upper electrode 420 can be adjusted. It is to
be noted that the upper electrode drive mechanism 500 is to be
described in detail later.
[0162] The upper electrode 420 is supported at the inner wall of
the ceiling of the chamber 402 via a bellows 422. The bellows 422
is mounted at the inner wall at the ceiling of the chamber 402 with
a fastening means such as a bolt via an annular upper flange 422a
and is also attached to the upper surface of the upper electrode
420 with a fastening means such as a bolt via an down flange
422b.
[0163] The upper electrode 420 includes an electrode plate 424
constituting a surface facing opposite the susceptor 405 and having
numerous outlet holes 423 and an electrode support member 425 that
supports the electrode plate 424. The electrode plate 424 is
constituted of, for instance, quartz, whereas the electrode support
member 425 is constituted of an electrically conductive material
such as aluminum with a surface thereof having undergone alumite
processing.
[0164] A gas supply port 426 is provided at the electrode support
member 425 of the upper electrode 420. A gas supply pipe 427 is
connected to the gas supply port 426. In addition, a processing gas
supply source 430 is connected to the gas supply pipe 427 via a
valve 428 and a mass flow controller 429.
[0165] An etching gas, for instance, to be used to execute plasma
etching is supplied from the processing gas supply source 430. It
is to be noted that while FIG. 12 shows a single processing gas
supply system comprising the gas supply pipe 427, the valve 428,
the mass flow controller 429, the processing gas supply source 430
and the like, the plasma processing apparatus 400 includes a
plurality of processing gas supply systems in reality. Namely,
CHF8, Ar and He, for instance, to constitute to the processing gas,
the flow rates of which are controlled independently of one
another, are individually supplied into the chamber 402.
[0166] A first high-frequency source 440 is connected to the upper
electrode 420, with a first matcher 441 inserted at the power
supply line. In addition, a low pass filter (LPF) 442 is connected
to the upper electrode 420. The first high-frequency source 440 is
capable of outputting power at a frequency in the range of 50 to
150 MHz. As the power at such a high-frequency is applied to the
upper electrode 420, high-density plasma can be formed in a desired
state of dissociation inside the chamber 402 and plasma processing
can be executed at a lower pressure compared to the related art.
Ideally, the frequency of the power output from the first
high-frequency source 440 should be 50 to 80 MHz, and typically, it
is adjusted to 60 MHz as shown in the figure or to a value close to
60 MHz.
[0167] A second high-frequency source 450 is connected to the
susceptor 405 constituting the lower electrode, with a second
matcher 451 inserted at the power supply line. The second
high-frequency source 450 is capable of outputting power at a
frequency in the range of several hundred kHz to several tens of
MHz. As the power at a frequency in this range is applied to the
susceptor 405, a desired ionization effect can be achieved without
damaging the workpiece, i.e., the wafer W. Typically, the frequency
of the power output from the second high-frequency source 450 is
adjusted to 2 MHz, as shown in the figure, or to 13.56 MHz.
[0168] Next, the upper electrode drive mechanism 500 is explained
in detail. The upper electrode drive mechanism 500 includes a
substantially cylindrical sliding support member 504 that slidably
supports the upper electrode 420 so as to allow the upper electrode
420 to slide relative to the chamber 402. The sliding support
member 504 is mounted at an approximate center of the top surface
of the upper electrode 420 with a bolt or the like.
[0169] The sliding support member 504 is disposed so that it is
allowed to freely enter and withdraw from a hole 402a formed at an
approximate center of the upper wall of the chamber 402. More
specifically, the external circumferential surface of the sliding
support member 504 is slidably supported at the edge of the hole
402a at the chamber 402 via a slide mechanism 510.
[0170] The slide mechanism 510 includes a guide member 516 retained
at a vertical portion of a retaining member 514 having an L-shaped
section and disposed, for instance, at the top of the chamber 402
and a rail portion 512 slidably supported by the guide member 516
and formed to extend along one direction (the vertical direction in
the embodiment) at the external circumferential surface of the
sliding support member 504.
[0171] The retaining member 514, which securely retains the guide
member 516 of the slide mechanism 510 includes a horizontal portion
fixed to the top of the chamber 402 via an annular horizontal
adjustment plate 518. The horizontal adjustment plate 518 is used
to adjust the horizontal position of the upper electrode 420. The
horizontal adjustment plate 518 may be secured onto the chamber 402
with a plurality of bolts or the like set over uniform intervals
along the circumferential direction so as to adjust the extent of
inclination of the horizontal adjustment plate 518 along the
horizontal direction in correspondence to the extents to which the
individual bolts protrude. As the inclination of the guide member
516 at the slide mechanism 510 along the vertical direction is
adjusted by adjusting the inclination of the horizontal adjustment
plate 518 along the horizontal direction, the inclination of the
upper electrode 420 supported via the guide member 516 is adjusted
along the horizontal direction. As a result, it is possible to
retain the upper electrode 420 at the correct horizontal position
at all times through a simple operation.
[0172] A pneumatic cylinder 520 used to drive the upper electrode
420 is mounted on the upper side of the chamber 402 via a barrel
body 501. Namely, the lower end of the barrel body 501 is mounted
by assuring air tightness with a bolt or the like so as to cover
the hole 402a at the chamber 402 and the upper end of the barrel
body 501 is mounted by assuring air tightness at the lower end of
the pneumatic cylinder 520.
[0173] The pneumatic cylinder 520 includes a rod 502 that can be
driven along one direction, and the lower end of the rod 502 is
disposed continuous to an approximate center area on the upper side
of the sliding support member 504 with a bolt or the like. Thus, as
the rod 502 of the pneumatic cylinder 520 is driven, the upper
electrode 420, too, is driven by the sliding support member 504
along the slide mechanism in one direction. As the inner space of
the rod 502 assuming a cylindrical shape comes into communication
with a central hole formed at an approximate center of the sliding
support member 504, the rod is set in a state of communication with
the atmosphere. Thus, the power supply line from the matcher 441 or
the like can be connected to the upper electrode 420 through the
inner space of the rod 502 via the central hole at the sliding
support member 504.
[0174] In addition, a means for positional detection such as a
linear encoder 505 that detects the position of the upper electrode
420 is provided to the side of the pneumatic cylinder 520. An upper
end member 507 having an extension 507a extending sideways from the
rod 502 is provided at the upper end of the rod 502 of the
pneumatic cylinder 520, and a detection portion 505a of the linear
encoder 505 is in contact with the extension 507a of the upper end
member 507. Since the upper end member 507 interlocks with the
movement of the upper electrode 420, the position of the upper
electrode 420 can be detected with the linear encoder 505.
[0175] The pneumatic cylinder 520 is constituted by enclosing a
tubular cylinder main body 522 with an upper support plate 524 and
a lower support plate 526. An annular partitioning member 508 that
partitions the inner space of the pneumatic cylinder 520 into an
upper space 532 and a lower space 534 is disposed on the external
circumferential surface of the rod 502.
[0176] As shown in FIG. 14, compressed air is supplied into the
upper space 532 of the pneumatic cylinder 520 from an upper port
536 at the upper support plate 524. Compressed air is also supplied
into the lower space 534 of the pneumatic cylinder 520 from a lower
port 538 at the lower support plate 526. By controlling the
quantities of air supplied into the upper space 532 and the lower
space 534 from the upper port 536 and the lower port 538
respectively, the drive of the rod 502 along the one direction (the
vertical direction in this example) can be controlled. The
quantities of air supplied into the pneumatic cylinder 520 are
controlled at a pneumatic circuit 610 provided near the pneumatic
cylinder 520.
[0177] Next, a means for drive control 600 provided in the plasma
processing apparatus in the embodiment as part of the upper
electrode drive mechanism 500 is explained. FIG. 15 is a circuit
diagram of the means for drive control 600 provided as part of the
upper electrode drive mechanism 500 and FIG. 16 is a block diagram
of the pneumatic circuit 610.
[0178] As shown in FIG. 15, the means for drive control 600 is
constituted with the pneumatic circuit 610 and a means for control
700 that controls the pneumatic circuit 610. The means for control
700 includes a CPU (central processing unit) 720 constituting the
main body of the means for control 700, an interface 740 that
exchanges various signals with the external apparatuses, an
interlock circuit 760 used to execute a self diagnosis of the
pneumatic circuit 610 and the like. The interface 740 exchanges
control signals with a control device (not shown) that controls the
plasma processing apparatus 400 and also receives sensor signals
from various sensors. The signals input to the interface 740
include an upper electrode drive control signal containing target
position information used to drive the upper electrode 420 to a
specific target position and the like, a gate valve control signal
used to control the gate valve and sensor signals from the various
sensors. In addition, the signals output from the interface 740
include an upper electrode position stable signal indicating
whether or not the position of the upper electrode 420 has
stabilized and whether or not the movement of the upper electrode
420 has been completed and a wafer transfer signal indicating
whether or not the upper electrode 420 is set at a position out of
the transfer path of the transfer arm transferring a wafer and thus
the wafer can be safely transferred into the chamber 402.
[0179] The sensor signals include a signal from an origin point
sensor that detects whether or not the upper electrode 420 is
positioned at the origin point. The origin point as referred to in
this context is the origin point of the means for upper electrode
positional detection such as the linear encoder 505. In more
specific terms, the origin point sensor may be constituted with,
for instance, a contact sensor or an optical sensor. In such a
case, the origin point sensor may be disposed on the inner side of
the upper wall constituting the barrel body 501 on the chamber 402,
and the position at which the origin point sensor detects the upper
end of the sliding support member 504, i.e., the uppermost position
of the upper electrode 420, may be set as the origin point. Another
sensor signal input to the interface 740 is a transfer verification
position sensor signal inquiring whether or not the upper electrode
420 is set at a position that allows a wafer transfer. In response
to the transfer verification position sensor signal input to the
interface 740, the CPU 720 detects whether or not the upper
electrode 420 is currently set at a position, i.e., a retracted
position, at which the upper electrode 420 is out of the way of the
transfer arm transferring the wafer based upon the detection signal
provided by the linear encoder 505 and outputs a wafer transfer
signal via the interface 740.
[0180] The interlock circuit 760, to which a signal from a switch
620 that detects whether or not compressed air is output from a
pneumatic source 605 in the pneumatic circuit 610 to drive the
upper electrode 420 is input, outputs a drive enabled signal to the
pneumatic circuit 610 if compressed air is output from the
pneumatic source 605, i.e., if the signal from the switch 620
indicates an ON state. If, on the other hand, no compressed air is
output from the pneumatic source 605, i.e., if the signal from the
switch 620 indicates an OFF state, it stops the output of the drive
enabled signal to the pneumatic circuit 610.
[0181] In addition, the interlock circuit 760 stops the output of
the drive enabled signal to the pneumatic circuit 610 if an
external interlock signal is input even when the signal from the
switch 620 indicates an ON state. The interlock signal is input
from the control device (not shown) to the means for control 700
when, for instance, an abnormality necessitating the drive of the
upper electrode 420 to be stopped occurs in the plasma processing
apparatus 400.
[0182] The CPU 720 controls the pneumatic circuit 610 based upon
the signals from the interface 740. It controls the movement of the
upper electrode 420 so as to position the upper electrode 420 at
the target position through feedback control achieved by
implementing PID control (control executed by combining a
proportional operation, a differential operation and an integration
operation) as indicated in the block diagram in FIG. 16, for
instance. In the block diagram shown in FIG. 16, Ref (s) is the
target position for the upper electrode 420 and Y(s) is the current
position. G(s) is the transfer function, and K.sub.P, K.sub.I,
K.sub.D, K.sub.A and K.sub.V respectively indicate the proportional
gain, the integral gain, the differential gain, the acceleration
feedback gain and the velocity feedback gain.
[0183] More specifically, the deviation is determined by
subtracting the current position from the target position set for
the upper electrode 420, and PID control is implemented based upon
an output (which can be adjusted in correspondence to the integral
gain K.sub.I) in proportion to the time integral of the deviation
and used to correct the steady state deviation, an output (which
can be adjusted in correspondence to the differential gain K.sub.D)
in proportion to the time-varying change in the deviation and used
to minimize the change rate and an output (which can be adjusted in
correspondence to the proportional gain K.sub.P) in proportion to
the deviation. Namely, in this PID control, a function of
predicting the movement which is in proportion to the current
deviation (a proportional operation), a function of eliminating the
offset by holding the integral of the previous deviation (an
integration operation) and a function of predicting future movement
(a differential operation) are incorporated.
[0184] In addition, the pneumatic circuit 610 is controlled in the
embodiment through the acceleration feedback control, implemented
based upon outputs from pressure sensors (not shown) disposed at
the ports 536 and 538 of the pneumatic cylinder 520 in order to
control the external disturbance, as shown in FIG. 16, and the
velocity feedback control implemented based upon the output of the
linear encoder 505 taken into the means for control 700, as shown
in FIG. 15.
[0185] The positional control of the upper electrode 420 may be
achieved by setting the target position over a plurality of stages
preceding the ultimate position to which the upper electrode 420 is
to be moved and by driving the upper electrode 420 gradually. In
this case, abrupt drive or abrupt vibration attributable to
material properties such as the viscosity and the density of the
air used to drive the pneumatic cylinder can be minimized. As a
result, problems of attracting particles inside the chamber 402 and
the like while driving the upper electrode with a pneumatic
cylinder do not occur.
[0186] A structural example that may be adopted in the pneumatic
circuit 610 is now explained. FIG. 17 is a circuit diagram of a
structure that may be adopted in the pneumatic circuit 610. FIGS.
18 and 19 are functional diagrams illustrating the operation of the
pneumatic circuit 610. The pneumatic circuit 610 is in a neutral
state in FIG. 17, is engaged in the drive control of the upper
electrode 420 in FIG. 18 and is in a state of emergency stop in
FIG. 19.
[0187] As shown in FIGS. 15 and 17, the pneumatic circuit 610
includes a 5-port electromagnetic valve 630 constituting a
switching valve capable of switching the flow path to a neutral
state or a drive control state in response to a valve control
signal provided by the CPU 720. A 5-port switching valve 640 is
disposed in a pipeline extending from the 5-port electromagnetic
valve 630 and communicating with the upper port 536 of the
pneumatic cylinder 520, and a 5-port switching valve 650 is
disposed in the pipeline extending from the 5-port electromagnetic
valve 630 and communicating with the lower port 538 of the
pneumatic cylinder 520. These 5-port switching valves 640 and 650,
each used as a drive stop valve when effecting an emergency stop of
the pneumatic cylinder 520, can be controlled with a 3-port
electromagnetic valve 660.
[0188] Now, the specific relationship with which the individual
valves are connected with each other is explained. The pneumatic
source 605 is connected to a p-port of the 5-port electromagnetic
valve 630; and an a-port of the 5-port electromagnetic valve 630 is
connected to a p-port of the 5-port switching valve 640. In
addition, a b-port of the 5-port electromagnetic valve 630 is
connected to a p-port of the 5-port switching valve 650. A c-port
and a d-port of the 5-port electromagnetic valve 630 are used as
discharge ports.
[0189] With the 5-port electromagnetic valve 630, the flow path can
be switched to an N state, an L state or an R state. A force
applying member such as a spring is disposed on each side of the
5-port electromagnetic valve 630, and a force is applied to the
5-port electromagnetic valve 630 to set it in the N state unless
power is supplied in response to a valve control signal provided by
the means for control 700. Then, if positive power is supplied in
response to the valve control signal, for instance, the 5-port
electromagnetic valve 630 is set in the L state against the force
applied by the force applying members, whereas if negative power is
applied in response to the valve control signal, the 5-port
electromagnetic valve 630 is set in the R state against the force
applied by the force applying members. When the 5-port
electromagnetic valve 630 is in the N state, each port at the
5-port electromagnetic valve 630 is in a cut-off state. When the
5-port electromagnetic valve 630 is in the L state, its p-port and
a-port are connected with each other and its d-port and b-port are
connected with each other, whereas when the 5-port electromagnetic
valve 630 is in the R state, its p-port and b-port are connected
with each other and its c-port and a-port are connected with each
other.
[0190] The upper port 536 of the pneumatic cylinder 520 is
connected to an a-port of the 5-port switching valve 640 whereas
the lower port 538 is connected to an a-port of the 5-port
switching valve 650. With both the 5-port switching valve 640 and
the 5-port switching valve 650, the flow path can be switched to
either the N state or the L state. At each of the 5-port switching
valves 640 and 650, a force applying members such as a spring is
provided on one side thereof to apply a force to the 5-port
switching valve to set it in the N state unless compressed air is
supplied through the 3-port electromagnetic valve 660. As
compressed air is supplied through the 3-port electromagnetic valve
660, the 5-port switching valves enter the L state against the
force applied by the force applying members. At each of the 5-port
switching valves 640 and 650, the p-port and a b-port are connected
with each other and a c-port and the a-port are connected with each
other in the N state, and the p-port and the a-port are connected
with each other and the d-port and the b-port are connected with
each other in the L state.
[0191] The pneumatic source 605 is connected to a p-port of the
3-port electromagnetic valve 660, and a b-port and an a-port at the
3-port electromagnetic valve 660 are connected with each other. It
is to be noted that the b-port at the 3-port electromagnetic valve
660 is used as a discharge port. As shown in FIG. 15, the flow path
is switched to either the N state or the L state at the 3-port
electromagnetic valve 660 based upon the drive enabled signal
provided by the interlock circuit 760. A force applying member such
as a spring is provided on one side of the 3-port electromagnetic
valve 660 and a force is applied to set the 3-port electromagnetic
valve 660 in the N state unless power is supplied in response to
the drive enabled signal provided by the means for control 700.
Then, as the drive enabled signal is output, it enters the L state
against the force applied by the force applying member. At the
3-port electromagnetic valve 660, the p-port is cut off and the
b-port and the a-port are connected with each other in the N state,
whereas the p-port and the a-port are connected with each other and
the b-port is cut off in the L state.
[0192] When the switch 620 of the pneumatic source 605 is in an OFF
state, as shown in FIG. 17, the output of the drive enabled signal
from the interlock circuit 760 is stopped and thus, the flow path
at the 3-port electromagnetic valve 660 is in the N state and the
flow path at the 5-port electromagnetic valve 630, too, is in the N
state in the pneumatic circuit 610 adopting the structure described
above. In this neutral state, the ports 536 and 538 at the
pneumatic cylinder 520 are cut off from the pneumatic source 605 by
the 5-port electromagnetic valve 630, and, as a result, the upper
electrode 420 is held in a stopped state.
[0193] As the switch 620 of the pneumatic source 605 is turned on,
the drive enabled signal is output from the interlock circuit 760,
thereby setting the flow path at the 3-port electromagnetic valve
660 in the L state. As a result, the flow path at the 5-port
switching valves 640 and 650 each enter the L state. Consequently,
drive of the upper electrode 420 is enabled with the compressed air
supplied to the pneumatic cylinder 520 by switching the flow path
at the 5-port electromagnetic valve 630.
[0194] When the upper electrode 420 is to move downward, for
instance, from this state, the flow path at the 5-port
electromagnetic valve 630 is set in the L state, as shown in FIG.
18. In response, the compressed air from the pneumatic source 605
is guided in through the upper port 536 at the pneumatic cylinder
520 and is discharged through the lower port 538, causing the
sliding support member 504 to move downward and ultimately causing
the upper electrode 420 to move downward.
[0195] When the upper electrode 420 is to move upward, for
instance, from the neutral state shown in FIG. 17, the flow path at
the 5-port electromagnetic valve 630 is set in the N state unlike
in the operation shown in FIG. 18. As the stop signal from the
interlock circuit 760 enters the OFF state, the flow path at the
3-port electromagnetic valve 660 is set in the L state under these
circumstances as well. As a result, the flow paths at both the
5-port switching valve 640 and the 5-port switching valve 650 are
set in the L state. In response, the compressed air from the
pneumatic source 605 is guided in through the lower port 538 at the
pneumatic cylinder 520 and then discharged through the upper port
536, causing the sliding support member 504 to move upward and
ultimately causing the upper electrode 420 to move upward.
[0196] FIG. 19 shows the state of the pneumatic circuit 610 when an
emergency stop is applied while driving the upper electrode. As the
stop signal from the interlock circuit 760 is turned on, the flow
path at the 3-port electromagnetic valve 660 enters the N state. As
a result, the flow paths at the 5-port switching valves 640 and 650
both enter the N state. In response, the compressed air from the
pneumatic source 605 is guided through the lower port 538 at the
pneumatic cylinder 520, and the compressed air from the pneumatic
source 605 is cut off from both the upper part 536 and the lower
port 538 at the pneumatic cylinder 520, thereby stopping the
sliding support member 504 and stopping the upper electrode
420.
[0197] FIGS. 20 and 21 present the results of tests conducted by
implementing the specific control shown in FIG. 16 with the
pneumatic circuit 610 achieved in the embodiment as described above
with the target position set over a plurality of stages preceding
the ultimate position to which the upper electrode 420 was to move.
FIG. 20 is a graph of the relationship between the position of the
upper electrode 420 and the time observed by gradually driving the
upper electrode 420 upward, whereas FIG. 21 is a graph of the
relationship between the position of the upper electrode 420 and
the time, observed by gradually driving the upper electrode 420
downward. FIGS. 20 and 21 indicate that stable and accurate
follow-up control was achieved to drive the upper electrode 420
upward or downward to set the target position.
[0198] Various indices measured based upon these test results,
which include approximately .+-.0.15 mm representing the accuracy
with which the upper electrode was stopped and approximately 60
mm/sec representing the operating speed, indicate that the
structure adopted in the embodiment is highly viable in practical
application. In other words, highly accurate positional control is
enabled by employing the plasma processing apparatus 400
[0199] In the plasma processing apparatus in the embodiment
described in detail above, the sliding support member 504 is
provided independently of the pneumatic cylinder 520 to slidably
support the upper electrode 420 along one direction (e.g., the
vertical direction), and thus, any load (external disturbance) that
would be applied to the pneumatic cylinder 520 along a direction
other than the one direction is eliminated to allow the pneumatic
cylinder 520 to move only along the one direction. Consequently,
the positional control for the upper electrode 420 can be
implemented with a high degree of accuracy with the pneumatic
cylinder 520.
[0200] The rod 502 at the pneumatic cylinder 520 is disposed at an
approximate center of the upper electrode 420 to prevent
decentering of the load applied to the rod 502 at the pneumatic
cylinder 520 and the occurrence of a moment and, as a result, the
position of the electrode can be controlled with an even higher
degree of accuracy.
[0201] It is to be noted that while the upper electrode 420 is
driven by using the pneumatic cylinder 520 in the embodiment
described above, the lower electrode may instead be slidably
supported and be driven with the pneumatic cylinder 520. However,
at the lower electrode on which the workpiece such as a wafer or a
liquid crystal substrate is placed, various additional mechanisms
including a workpiece holding mechanism, a workpiece back side gas
mechanism and an electrode temperature adjustment mechanism must be
mounted, whereas the upper electrode does not need such additional
mechanisms. For this reason, a higher degree of positional control
accuracy can be achieved for the upper electrode 420 by driving the
upper electrode 420 with the pneumatic cylinder and thus minimizing
the load applied to the rod 502 at the pneumatic cylinder 520.
[0202] In addition, the components such as the upper electrode 420,
the upper electrode drive mechanism 500 for the upper electrode
420, the pneumatic circuit 610 and the means for control 700 may be
provided as an integrated upper electrode unit, as shown in FIG.
14, to facilitate positional control to be implemented with a
pneumatic cylinder on an upper electrode 420 in an existing plasma
processing apparatus simply by installing the upper electrode
unit.
[0203] In conjunction with the plasma processing apparatus and the
upper electrode unit described above, highly accurate positional
control can be achieved with a pneumatic cylinder functioning as a
pneumatic actuator by minimizing the load applied to the pneumatic
cylinder.
[0204] It is to be noted that while an explanation is given above
in reference to the embodiment on an example in which the present
invention is adopted in a plasma etching apparatus, the present
invention may instead be adopted in a different type of processing
apparatus such as a film forming apparatus or an ashing apparatus.
In addition, while the workpiece processed in the embodiment
described above is a semiconductor wafer, the present invention is
not limited to this example, and the present invention may be
adopted to process a workpiece such as a glass substrate for a flat
display (FPD) in a liquid crystal display (LCD) device, i.e., an
FPD substrate which may be an LCD substrate.
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