U.S. patent application number 13/035159 was filed with the patent office on 2012-07-26 for plasma processing apparatus.
This patent application is currently assigned to HITACHI HIGH-TECHNOLOGIES CORPORATION. Invention is credited to Masaru Izawa, Go MIYA, Takumi Tandou.
Application Number | 20120186745 13/035159 |
Document ID | / |
Family ID | 46543269 |
Filed Date | 2012-07-26 |
United States Patent
Application |
20120186745 |
Kind Code |
A1 |
MIYA; Go ; et al. |
July 26, 2012 |
PLASMA PROCESSING APPARATUS
Abstract
Provided is a plasma processing apparatus in which accuracy or
reliability of processing is improved. This plasma processing
apparatus includes a sample stage in a processing chamber arranged
in a vacuum vessel and in which plasma is generated. The sample
stage has a cylindrical shape and operates as an evaporator through
which a refrigerant of a refrigerating cycle flows. Further, the
apparatus includes refrigerant passages which are concentrically
arranged inside of the sample stage, one or more detectors which
detect vibrations of the sample stage, and an control unit which
controls a temperature of the refrigerant flowing into the sample
stage based on detection results of a dryness of the refrigerant
flowing through the passages obtained from an output of the
detectors.
Inventors: |
MIYA; Go; (Hachioji, JP)
; Izawa; Masaru; (Hino, JP) ; Tandou; Takumi;
(Hachioji, JP) |
Assignee: |
HITACHI HIGH-TECHNOLOGIES
CORPORATION
|
Family ID: |
46543269 |
Appl. No.: |
13/035159 |
Filed: |
February 25, 2011 |
Current U.S.
Class: |
156/345.27 |
Current CPC
Class: |
H01J 37/32724 20130101;
H01L 21/67109 20130101; H01J 37/32715 20130101 |
Class at
Publication: |
156/345.27 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2011 |
JP |
2011-013565 |
Claims
1. A plasma processing apparatus comprising: a processing chamber
which is arranged in a vacuum vessel and in which plasma is
generated; a sample stage which is arranged inside toward the
bottom of said processing chamber, of which a sample is mounted on
an upper surface, which has a shape of a cylinder, and which
operates as an evaporator by flowing a refrigerant of a
refrigerating cycle through therein; a refrigerant passage which is
arranged in said sample stage and concentrically at a center of
said cylinder; one or more of detectors which are arranged under
said sample stage and detect vibrations of said sample stage; and
an control unit which controls an operation of a compressor or an
expansion valve configuring said refrigerating cycle based on a
detection result of a dryness of said refrigerant flowing through
said passage obtained from an output from said detector.
2. The plasma processing apparatus according to claim 1, wherein
one or more of said detectors are arranged on a bottom surface of
said sample stage and are connected to a position near an inlet of
said refrigerant to inside of said sample stage.
3. The plasma processing apparatus according to claim 2, wherein
additional one or more of said detectors are arranged on a bottom
surface of said sample stage and are connected to a position near
an outlet of said refrigerant from said sample stage.
4. The plasma processing apparatus according to claim 2, wherein
said refrigerant passage comprises a plurality of passages of
shapes of circular arcs which are concentrically arranged in a
multiple manner at different radial distances from said center in
said sample stage; and a connection passage connecting two passages
among said passages of shapes of circular arcs, and wherein
additional one or more of said detectors are arranged on the bottom
surface of said sample stage and near said connection passage.
5. The plasma processing apparatus according to claim 4, wherein
plan-view shape of said connection passage has a curvature radius
smaller than plan-view shape of said passages of shapes of circular
arcs.
6. The plasma processing apparatus according to claim 4, wherein
said passage in said sample stage is configured by joining two
upper and lower members, and a defect in the junction of said upper
and lower members is detected from an output from said one or more
detectors arranged to be connected to a position near said
connection passage on the bottom surface of said sample stage.
7. The plasma processing apparatus according to claim 1, further
comprising a member having electrical insulation arranged to be
contacted with the bottom surface of said sample stage, wherein
said one or more detectors are arranged to be contacted with said
member having the insulation.
8. A plasma processing apparatus comprising: a processing chamber
which is arranged in a vacuum vessel and in which plasma is
generated; a sample stage which is arranged inside toward the
bottom of said processing chamber, of which a sample is mounted on
an upper surface, which has a shape of a cylinder, and which
operates as an evaporator by flowing a refrigerant of a
refrigerating cycle through therein; a refrigerant passage which is
arranged in said sample stage and concentrically at a center of
said cylinder; one or more of detectors which are arranged under
said sample stage and detect vibrations of said sample stage; and a
control unit which is arranged between a compressor on said
refrigerating cycle and said sample stage and controls a
temperature of said refrigerant flowing into said sample stage
based on a detection result of a dryness of said refrigerant
flowing through said passage obtained from an output from said
detector.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a plasma processing
apparatus which processes a substrate-shaped sample such as a
semiconductor wafer mounted on a sample stage arranged in a
processing chamber in a vacuum vessel by using plasma formed in
this processing chamber and which processes the sample while
controlling a temperature of the sample stage including passages of
a refrigerant circulating through a refrigerating cycle in the
sample stage.
[0002] In a manufacturing process of a semiconductor device, a
plasma processing is conventionally performed to samples such as
semiconductor wafers by using a plasma etching apparatus or a
plasma CVD apparatus. In the above-described plasma processing, a
temperature of the sample has a significant impact on processing
results. Specifically, in the plasma etching processing, it has an
impact on a size of a processing pattern or processed profiles
formed on a sample surface by etching. On the other hand, in the
plasma CVD processing, it has an impact on quality of a film formed
on a sample surface or a deposition rate. Therefore, for the
purpose of improving quality of a processing performed on a surface
of a sample substrate in the above-described plasma processing, it
is extremely important to manage the sample temperature.
[0003] In the above-described plasma processing, there is adopted a
technology of controlling a temperature of an internal portion of
the sample stage and that of a sample holding surface to control a
sample temperature by using a temperature control unit arranged in
the sample stage for holding the sample. For example, an apparatus
system is used in which a passage of a refrigerant is formed in the
sample stage and a liquid refrigerant flows through this passage to
control a temperature of the sample stage by exchanging heat based
on a heat transfer between the refrigerant and a passage wall
surface contacted by it so that the sample is controlled to a
desired temperature. In this case, a refrigerant temperature
control unit (e.g., chiller unit) is connected to the sample stage
via piping, the refrigerant controlled to a predetermined
temperature by using a cooling device or a heating device in the
refrigerant temperature control unit is supplied to the passage in
the sample stage to exchange heat, and then is returned to the
refrigerant temperature control unit again.
[0004] The above-described refrigerant temperature control unit has
a configuration in which this liquid refrigerant is stored in a
tank for storage once to control its temperature and, then, the
refrigerant is supplied to the sample stage. In this configuration,
a heat capacity of the refrigerant becomes large since a large
amount of the refrigerant is used to control a temperature. As a
result, it is advantageous in keeping a sample temperature constant
even when the amount of heat entering the sample and the sample
stage changes. However, when a temperature of the sample and the
sample stage is intended to change notably and rapidly, on the
other hand, a rate of a temperature change fails to be increased
because of a large heat capacity of the refrigerant. Further, only
heat is transferred in the heat exchange between the liquid
refrigerant and the passage and, therefore, the amount of heat
transfer is small so that the temperature change of the sample
stage and the sample can not be quickened.
[0005] On the other hand, in the fabrication of semiconductor
devices, power applied to the sample during processing tends to
increase along with an increase in the diameter of a semiconductor
wafer as a sample in the above-described plasma processing. As a
result, the amount of heat entering the sample and the sample stage
is larger than before. Therefore, there is demanded a technology of
stably performing a temperature control of a semiconductor
substrate with high speed and high accuracy to this large heat
input. Further, due to a complication of a semiconductor device
structure and a multilayer film on a semiconductor substrate
surface, a temperature of the sample is expected to be controlled
speedily and appropriately according to each processing step for
processing each of a plurality of films.
[0006] Further, in the conventional refrigerant temperature control
unit, since a heat transfer between a passage wall and the liquid
refrigerant is performed while the liquid refrigerant flows through
the passage in the sample stage, a temperature of the liquid
refrigerant gradually rises up from entering an inlet of the
passage until exiting to an outlet thereof. There is a possibility
that an in-plane temperature distribution of sample stage surface
is deteriorated due to this temperature change of the refrigerant
since a surface temperature of the sample stage receives an
influence of the temperature of the refrigerant flowing through the
passage. As a result, the in-plane temperature distribution of the
sample may be deteriorated and deterioration of the in-plane
distribution of the plasma processing can be attributed.
[0007] To solve the above-described problem, there is proposed a
technology in which the passage through which the refrigerant for
cooling the sample stage circulates is configured as a
refrigerating cycle including a compressor, a condenser, an
expansion valve, and an evaporator and the refrigerant is caused to
boil and evaporate in the refrigerant passage in the sample stage
to cool the sample stage; that is, the sample stage is operated as
an evaporator of the refrigerating cycle and a temperature of the
sample stage is controlled by using a refrigerant temperature
control unit of the so-called direct expansion system. As examples
of the above-described technology, those disclosed in JP-A-6-346256
and JP-A-2005-89864 are known.
[0008] As the above-described conventional technology, there is
disclosed a technology of configuring a refrigerating cycle for
introducing chlorofluorocarbon substitute R410a
(hydrofluorocarbon), for example, as the refrigerant to the
refrigerant passage in the sample stage and operating the sample
stage as an evaporator, using evaporative latent heat of the
refrigerant for heat exchange between the refrigerant and the
passage wall surface, and controlling the temperature with respect
to the large amount of heat entering the sample and the sample
stage. Further, there is disclosed a technology in which by
controlling a opening degree of the expansion valve a pressure of
the refrigerant in the passage is quickly controlled to thereby
change a refrigerant temperature quickly and, as a result, a
temperature of the sample stage and the sample is changed to a
desired temperature to thereby improve accuracy and reproducibility
of processing of the sample.
SUMMARY OF THE INVENTION
[0009] In a temperature control mechanism of a sample stage using a
refrigerant temperature control unit of a direct expansion system
disclosed in JP-A-6-346256 and JP-A-2005-89864, even though the
heat enters the sample stage from plasma, when refrigerant in a
passage is in a state of a gas-liquid mixed flow, a temperature of
the refrigerant becomes constant. On the other hand, when the
refrigerant is in a state referred to as dryout that a liquid
portion of the refrigerant completely evaporates and the entire
refrigerant changes into a gas, a temperature of the refrigerant
rises up.
[0010] Therefore, in the middle of entering a refrigerant inlet of
the sample stage, circulating through the passage in the sample
stage, and exiting from a refrigerant outlet, dryness gradually
rises up due to the heat transferred from the plasma and thus
dryout occurs in the sample stage. In this case, at the downstream
side further than a position in which the dryout occurs, the
refrigerant temperature becomes higher than that of the upstream
side. As a result, a temperature distribution of the sample stage
becomes inhomogeneous or a desired distribution cannot be
accomplished and, therefore, reproducibility and accuracy of the
sample processing are impaired. To prevent the problem, the
aforementioned dryout of the refrigerant or a sign of its
occurrence need to be detected. However, the above-described
problem is not considered in the conventional technology.
[0011] Further, in the refrigerant temperature control unit of the
direct expansion system disclosed in JP-A-6-346256 and
JP-A-2005-89864, a refrigerating cycle is configured in the sample
stage. Therefore, a pressure of the circulating refrigerant becomes
higher as compared with a case where a refrigerant of which a
temperature is controlled at the outside of the sample stage is
supplied and the sample stage is not used as a part of the
refrigerating cycle. In the configuration in which the liquid
refrigerant circulates by the above-described chiller unit, for
example, the refrigerant has a pressure of approximately 0.4 to 0.8
MPa (4 to 8 atmospheric pressure). On the other hand, in the
technology disclosed in JP-A-6-346256 and JP-A-2005-89864, when
using chlorofluorocarbon substitute R410a, for example, the
refrigerant has a high pressure of approximately 2.0 to 4.0 MPa (20
to 40 atmospheric pressure).
[0012] In addition, one metal disk whose surface is milled in a
groove shape to configure the refrigerant passage and another metal
disk are joined with each other, thereby generally manufacturing
the sample stage which mounts the sample. Accordingly, a force
applied to the refrigerant passage by a pressure of the refrigerant
acts on it so as to separate both of these metal disks. Therefore,
when the refrigerant has a pressure of approximately 0.4 to 0.8
MPa, strength of the junction can be easily secured. On the other
hand, when the refrigerant has a high pressure of approximately 2.0
to 4.0 MPa, there is a problem that a risk that the junction is
separated and the sample stage is broken becomes high. Further, as
described above, the refrigerant in the sample stage flows while
boiling. Since vibrations are generated in the sample stage along
with the boiling, the risk increases such that the separation in
the junction of two metal disks configuring the sample stage
occurs.
[0013] The plasma processing is generally performed in the
processing chamber decompressed to approximately several Pa; when
the junction of an peripheral portion of the sample stage arranged
in the processing chamber is separated and the refrigerant leaks
out of the sample stage, the refrigerant evaporates to raise a
pressure of the processing chamber and as a result a problem for
the plasma processing is posed. In addition, when a
chlorofluorocarbon substitute is used as the refrigerant, since it
is a compound of hydrogen, fluorine, and carbon, their components
diffuse in the plasma to thereby pose a problem for the plasma
processing. Moreover, even if the junction of the peripheral
portion of the sample stage is effectively joined and the
refrigerant is prevented from leaking out of the sample stage, the
refrigerant flows through an area except the provided passage when
the junction of an internal portion is separated and a short
circuit of the refrigerant passage occurs. Since the passage in the
sample stage is strictly designed, when the refrigerant flow
changes, a temperature distribution of the sample stage changes
into an originally unintended one. As a result, an in-plane
temperature distribution of the plasma processing on a sample
surface changes.
[0014] As can be seen, consideration is not made in the
above-described conventional technology with regard to a detection
unit for the dryout of the refrigerant while flowing through the
passage in the sample stage and a problem to detect separation in
the junction of the sample stage and breakage of the sample stage.
As a result, consideration is not made with regard to a problem
that accuracy, reproducibility, and reliability of the processing
by using the plasma processing apparatus are impaired.
[0015] It is an object of the present invention to provide the
plasma processing apparatus in which accuracy or reliability of the
processing is improved.
[0016] The above-described objects are accomplished by a plasma
processing apparatus including a processing chamber which is
arranged in a vacuum vessel and in which plasma is generated; a
sample stage which is arranged inside toward the bottom of this
processing chamber, of which a sample is mounted on an upper
surface, which has a shape of a cylinder, and which operates as an
evaporator by flowing a refrigerant of a refrigerating cycle
through therein; a refrigerant passage which is arranged in the
sample stage and concentrically at a center of the cylinder; one or
more of detectors which are arranged under the sample stage and
detect vibrations of this sample stage; and an control unit which
controls an operation of a compressor or an expansion valve
configuring the refrigerating cycle based on a detection result of
a dryness of the refrigerant flowing through the passage obtained
from an output from this detector.
[0017] Further, they are accomplished by a plasma processing
apparatus includes an control unit which is arranged between the
compressor on the refrigerating cycle and the sample stage and
controls a temperature of the refrigerant flowing into the sample
stage based on a detection result of a dryness of the refrigerant
flowing through the passage obtained from an output from this
detector.
[0018] Further, they are accomplished by the plasma processing
apparatus in which one or more of the detectors are arranged on a
bottom surface of the sample stage and are connected to a position
near an inlet of the refrigerant to inside of the sample stage.
[0019] Further, they are accomplished by the plasma processing
apparatus in which additional one or more of the detectors are
arranged on a bottom surface of the sample stage and are connected
to a position near an outlet of the refrigerant from the sample
stage.
[0020] Further, they are accomplished by the plasma processing
apparatus in which the refrigerant passage includes a plurality of
passages of shapes of circular arcs which are concentrically
arranged in a multiple manner at different radial distances from
the center in the sample stage; and a connection passage connecting
two passages among these passages of shapes of circular arcs and in
which additional one or more of the detectors are arranged on the
bottom surface of the sample stage and near the connection
passage.
[0021] Further, they are accomplished by the plasma processing
apparatus in which plan-view shape of the connection passage has a
curvature radius smaller than plan-view shape of the passages of
shapes of circular arcs.
[0022] Further, they are accomplished by the plasma processing
apparatus in which the passage in the sample stage is configured by
joining two upper and lower members, and a defect in the junction
of the upper and lower members is detected from an output from the
one or more detectors arranged to be connected to a position near
the connection passage on the bottom surface of the sample
stage.
[0023] Further, they are accomplished by the plasma processing
apparatus which further includes a member having electrical
insulation arranged to be contacted with the bottom surface of the
sample stage, in which the one or more detectors are arranged to be
contacted with the member having the insulation.
[0024] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a longitudinal sectional view illustrating a
schematic of a configuration of a plasma processing apparatus
according to a first embodiment of the present invention;
[0026] FIGS. 2A and 2B are enlarged lateral and longitudinal
sectional views illustrating a configuration of the sample stage
according to the first embodiment illustrated in FIG. 1;
[0027] FIGS. 3A to 3E are graphs illustrating outputs of detection
by each vibration sensor arranged on the sample stage according to
the first embodiment illustrated in FIG. 1;
[0028] FIGS. 4A and 4B are lateral and longitudinal sectional views
illustrating a schematic of a configuration of the sample stage
according to a second embodiment;
[0029] FIG. 5 is a longitudinal sectional view illustrating a
schematic of a configuration of the sample stage according to a
third embodiment;
[0030] FIG. 6 is a longitudinal sectional view illustrating a
schematic of a configuration of the sample stage according to a
fourth embodiment; and
[0031] FIGS. 7A and 7B are graphs illustrating time-series output
of detection by a pressure gauge according to the fourth embodiment
illustrated in FIG. 6.
DESCRIPTION OF THE EMBODIMENTS
[0032] Embodiments of the present invention will be described below
with reference to the accompanying drawings.
First Embodiment
[0033] A first embodiment of the present invention will be
described below with reference to FIGS. 1 to 3E.
[0034] FIG. 1 is a longitudinal sectional view illustrating a
schematic of a configuration of a plasma processing apparatus
according to the first embodiment of the present invention. In
particular, in the present embodiment, FIG. 1 illustrates a
configuration of the plasma processing apparatus which forms ECR
plasma by using an electric field by microwave and a magnetic field
and etches a substrate-shaped sample such as a semiconductor wafer
arranged in a processing chamber in a vacuum vessel.
[0035] In the present embodiment, there is arranged a processing
chamber lid 2 configuring an upper part of the vacuum vessel and
made of plate-shaped quartz for tightly sealing the inner and outer
parts of the processing chamber on a processing chamber wall 1
configuring the vacuum vessel and having a cylindrical shape,
thereby configuring the processing chamber 3 in which a pressure is
internally reduced. A sample stage 4 having a cylindrical shape is
provided inside toward the bottom of the processing chamber 3, and
a sample 5 (a semiconductor wafer in the present embodiment) is
held on a mounting surface, which is an upper surface of the sample
stage 4.
[0036] An opening of a gas-introducing tube 6 is provided on an
upper portion of the processing chamber 3 and a processing gas 7
being a highly reactive gas for performing etching processing is
introduced into the processing chamber 3 from the opening. An
evacuate port 8 is provided under the processing chamber 3 and the
processing gas 7 introduced into the processing chamber 3, plasma,
and particles of reaction products generated by the etching
processing are exhausted. Ahead of the evacuate port 8, a pressure
control valve 9 and a turbo molecular pump 12 as a type of a vacuum
pump are provided. When an opening degree of the pressure control
valve 9 is controlled, a pressure of the processing chamber 3 is
controlled to approximately several Pa.
[0037] Microwave 10 is applied via the processing chamber lid 2
being an upper part of the processing chamber 3 and generates
plasma 11 by the interaction with a magnetic field caused by a
solenoid coil (not illustrated) arranged around the processing
chamber wall 1. When the sample 5 is exposed to this plasma 11, a
plasma etching processing is performed.
[0038] Further, in the present embodiment, in order to control a
temperature of the sample 5, which is a circular semiconductor
wafer, a refrigerant passage 20 is provided in the sample stage 4.
To this refrigerant passage 20, a refrigerant temperature control
unit 21 using a refrigerating cycle of a direct expansion system is
connected and chlorofluorocarbon substitute as a refrigerant flows
through the passage 20.
[0039] The refrigerant temperature control unit 21 has a compressor
22, a condenser 23, expansion valves 24-1 and 24-2, and an
evaporator 26. The refrigerant fed from the sample stage 4 is
introduced to the evaporator 26 via the expansion valve 24-2 having
controlled therein an opening degree and is evaporated until a
dryness becomes equal to approximately zero therein. Thereafter,
the refrigerant is introduced to the compressor 22 and compressed
therein, and then is introduced to the condenser 23.
[0040] To the condenser 23 coolant water 25 is introduced and the
refrigerant introduced to the condenser 23 is cooled to be
condensed. The condensed refrigerant is introduced to the expansion
valve 24-1 having controlled therein an opening degree. After being
controlled to a desired pressure by the opening degree, the
refrigerant is introduced to the refrigerant passage 20 and
circulates while boiling and evaporating.
[0041] Based on the above-described configuration of the
refrigerating cycle, the sample stage 4 is controlled to a desired
temperature. Incidentally, the refrigerant introduced into the
sample stage 4 controls a temperature of the sample stage 4 while
boiling. Therefore, the sample stage 4 functions as a first
evaporator as it were and the evaporator 26 inside of the
refrigerant temperature control unit 21 functions as a second
evaporator.
[0042] Further, although not illustrated, piping between the
expansion valve 24-1 and the sample stage 4 and another piping
between the expansion valve 24-2 and the sample stage 4 are covered
with insulation, thereby insulating the piping.
[0043] Incidentally, when an opening degree of the expansion valve
24-1 is reduced, since the pressure of the refrigerant in the
refrigerant passage 20 is lowered, the temperature is lowered. On
the contrary, when an opening degree of the expansion valve 24-1 is
increased, since the pressure of the refrigerant is raised, the
temperature is raised. Besides, when an opening degree of the
expansion valve 24-2 is reduced, since the pressure of the
refrigerant in the refrigerant passage 20 is raised, the
temperature is raised. On the contrary, when an opening degree of
the expansion valve 24-2 is increased, since the pressure of the
refrigerant in the refrigerant passage 20 is lowered, the
temperature is lowered.
[0044] When the number of rotations of the compressor 22 is
increased, since a flow rate of the refrigerant introduced to the
sample stage 4 is increased, the pressure is increased and the
temperature is increased. When the opening degrees of these
expansion valves 24-1 and 24-2, and the number of rotations of the
compressor 22 are controlled, the sample stage 4 is controlled to a
desired temperature. As a result, the sample 5 is controlled to a
target temperature suitable for the plasma etching processing.
[0045] At a plurality of places on the bottom surface of the sample
stage 4 according to the present embodiment, vibration sensors 37-1
to 37-3 as detectors for detecting vibrations are arranged to
thereby detect vibrations near the arranged places. In addition, in
the present embodiment, as the vibration sensors, AE sensors
(acoustic emission sensors) are used.
[0046] FIGS. 2A and 2B are enlarged lateral and longitudinal
sectional views illustrating a configuration of the sample stage
according to the present embodiment illustrated in FIG. 1. FIG. 2A
illustrates a top view of a section of the sample stage 4.
[0047] In the sample stage 4 according to the present embodiment, a
planar shape in which the refrigerant passages are approximately
concentrically arranged in a multiple manner in a plurality of
positions with different radii as illustrated in this figure has a
plurality of circular arc portions. Here, there is arranged a
passage in which, in order to cause the refrigerant to flow from an
arbitrary circular arc passage in a certain radial position to a
circular arc passage in a different radial position in the outside
or in the inside, both the passages are connected and arranged and
having a circular arc planar shape with a smaller curvature radius.
This portion of the passage or that of the sample stage 4 having
arranged therein the passage is called as a bend section.
[0048] The refrigerant introduced from a refrigerant inlet 30
circulates through the refrigerant passage 20 while being divided
into two directions as indicated by arrows and further flows
through an inside passage via the bend sections 31. As described
above, the refrigerant circulates through via the approximately
concentric passages and the bend section 31 and then joins together
near the refrigerant outlet 32. The refrigerant is ejected from the
refrigerant outlet 32 to the outside of the sample stage 4 and
returned to the refrigerant temperature control unit 21 as
illustrated in FIG. 1. The above-described configuration makes it
possible to improve an azimuthal uniformity of a temperature of a
sample or a sample stage in different radial positions.
[0049] Further, FIG. 2B illustrates a configuration near the sample
stage 4. The sample stage 4 is composed of two metallic circular
plates 35-1 and 35-2 (e.g., made of aluminum base alloy). In a
bottom surface of the circular plate 35-1, rectangular grooves with
a section of the planar-shaped passage viewed from the upper side
as illustrated in FIG. 2A are arranged. Then, a surface in which
the groove is not formed in the bottom surface of the circular
plate 35-1 is joined with the upper surface of the circular plate
35-2, thereby configuring the refrigerant passage 20. Therefore, an
area in which the plates are joined is illustrated by using a
hatched portion in FIG. 2A.
[0050] In the present embodiment, the vibration sensors are
arranged on the bottom surface of the sample stage 4 and vibrations
caused by the refrigerant are measured, thereby detecting a state
of the refrigerant. Also, vibrations associated with separation
between the joined circular plates 35-1 and 35-2 are detected.
[0051] Hereinafter, arrangement places of the vibration sensors
will be described with reference to FIG. 2B. In addition, to assist
understanding the arrangement places, the arrangement places of the
vibration sensors 37-1 to 37-3 are illustrated also in FIG. 2A by
using a broken line.
[0052] The vibration sensor 37-1 is arranged on the bottom surface
of the sample stage 4 and near the refrigerant inlet 30 and the
vibration sensor 37-3 is arranged on the bottom surface of the
sample stage 4 and near the refrigerant outlet 32, respectively.
Further, the vibration sensors 37-2 are arranged on the bottom
surface of the sample stage 4 and near the bend sections 31. When
the vibration sensors are arranged at the above-described places,
respectively, vibrations near the respective places can be
detected. For example, since the vibration sensor 37-1 is arranged
near the refrigerant inlet 30, the vibrations near the refrigerant
inlet 30 can be detected. Further, signals of the vibrations
detected by these vibration sensors 37-1 to 37-3 are transmitted to
a signal processor 39 for processing.
[0053] Hereinafter, a specific evaluation and processing method for
the vibrations detected by the vibration sensors 37-1 to 37-3 will
be described. In the present embodiment, an object in which the
vibration sensors 37-1 to 37-3 are arranged on the bottom surface
of the sample stage 4 is to mainly detect the vibrations associated
with boiling of the refrigerant in a gas-liquid mixture phase.
However, vibrations detected on the bottom surface of the sample
stage 4 are present in addition to the above-described vibrations.
Examples of such vibrations include vibrations from a floor of a
place in which the plasma processing apparatus is arranged and
vibrations caused by the turbo molecular pump 12 attached to the
processing chamber wall 1. These vibrations are a noise component
in the detection according to the present embodiment.
[0054] Therefore, the vibrations associated with boiling of the
refrigerant and the noise component are separated; a spectral
analysis using a fast Fourier analysis generally used for the
analysis of data on vibrations such as sound is performed to
convert into a frequency of vibration data and a power spectrum
indicating intensity of the frequency. Further, by decibel
conversion of the acquired power spectrum, a sound pressure level
is acquired. The decibel conversion is a method which represents
the power spectrum by the common logarithm of a ratio to a
reference value and, in general, a sound pressure level Lp is
acquired from an intensity p at a certain frequency by using an
equation (1).
Lp=20.times.log.sub.10(p/p.sub.0) (1)
[0055] Here, p.sub.0=20.times.10.sup.-6 [Pa] (Pascal).
[0056] Since the acquired sound pressure level is data including
noise components, a component less than a certain threshold is
considered as noise. A component more than or equal to the certain
threshold is used for the analysis of the vibrations associated
with boiling of the refrigerant. In the present embodiment, the
threshold is set to zero. A weak component is eliminated from among
the noise components of the data acquired by the vibration sensors
by the above-described operation. For example, the vibrations from
a floor of the place in which the plasma processing apparatus is
arranged, which is one of the above-described noises is eliminated
by this operation.
[0057] Results detected by the vibration sensors 37-1 and 37-3 and
arranged by using the above-described method are illustrated in
FIGS. 3A and 3C, respectively. Further, detection results of one of
the plurality of vibration sensors 37-2 are illustrated in FIG. 3B.
FIGS. 3A to 3E are graphs illustrating outputs of detection by the
respective vibration sensors arranged on the sample stage 4
according to the first embodiment illustrated in FIG. 1. Moreover,
these graphs are acquired at a state in which plasma 11 is
generated in the processing chamber 3 and at a state in which the
refrigerant is supplied to the refrigerant passage 20 by the
refrigerant temperature control unit 21. The abscissa represents
the frequency and the ordinate represents the sound pressure
level.
[0058] Here, particularly, FIG. 3C illustrates detection results
acquired in the case where dryout does not occur at the refrigerant
outlet 32. In the graph of FIG. 3A, peaks 40-a appear at
frequencies of 450 Hz, 900 Hz, and 1350 Hz. These are matched with
a fundamental frequency of 450 Hz, its second harmonic of 900 Hz,
and its third harmonic of 1350 Hz with respect to the number of
rotation of 27000 rpm of the turbo molecular pump 12. Therefore,
the peaks are determined to be caused by the operation of the turbo
molecular pump 12.
[0059] Also, in the detection results of the vibration sensors 37-2
and 37-3 respectively illustrated in FIGS. 3B and 3C, the peaks
respectively illustrated in the peaks 40-b and 40-c appear at
exactly the same frequencies (namely, 450 Hz, 900 Hz, and 1350 Hz)
as those of the peak 40-a. Further, the sound pressure levels of
these peaks 40-a to 40-c are approximately the same as each other.
The reason is as follows. Since the sample stage 4 is mechanically
connected to the processing chamber wall 1, vibrations of the turbo
molecular pump 12 are propagated with approximately the same
intensity to the vibration sensors 37-1 to 37-3 arranged on the
bottom surface of the sample stage 4. As a result, the vibrations
are detected with approximately the same sound pressure levels.
[0060] Further, in FIGS. 3A to 3C, peaks 41-a to 41-c appear at
approximately 650 Hz in addition to the peaks 40-a to 40-c,
respectively. Here, in FIG. 3D, there are illustrated the detection
results of one of the vibration sensors 37-2 in a state in which
the turbo molecular pump 12 is operated, operations of the
refrigerant temperature control unit 21 is stopped, and supply of
the refrigerant to the refrigerant passage 20 is stopped. When the
refrigerant flows, the peak 41-b appears at approximately 650 Hz as
illustrated in FIG. 3B whereas, when the refrigerant does not flow,
there only appear peaks 40-d associated with the operation of turbo
molecular pump 12 and no peak appears at approximately 650 Hz as
illustrated in FIG. 3D. Further, although not illustrated here,
when the refrigerant does not flow, there appears no peak at
approximately 650 Hz also in the detection results of the vibration
sensors 37-1 and 37-3 in the same manner as in FIG. 3D. Therefore,
the peaks 41-a to 41-c are determined to appear only when the
refrigerant flows through.
[0061] Here, when comparing the peaks 41-a to 41-c at approximately
650 Hz of FIGS. 3A to 3C at a state in which the refrigerant flows,
differences between sizes of the peaks 41-a to 41-c arise. Here,
since a size of the peak 41-a detected by the vibration sensor 37-1
arranged near the refrigerant inlet 30 is extremely small, this
peak is generated due to the vibrations associated with boiling of
the refrigerant. The reason is as follows. Near the refrigerant
inlet 30, it is immediately after the introduction of the
refrigerant at a state in which dryness of the refrigerant is equal
to approximately zero to the refrigerant passage 20 and, therefore,
the refrigerant does not nearly receive heat from the plasma 11.
Accordingly, boiling does not nearly occur, and as a result,
vibrations are not nearly generated.
[0062] Further, based on the detection results of one of the
vibration sensors 37-2 arranged near the bend sections 31
illustrated in FIG. 3B, the refrigerant receives heat from the
plasma 11 in a process of flowing from the refrigerant inlet 30 to
the bend section 31. Accordingly, the vibrations become greater due
to the fact that boiling violently occurs and, as a result, the
peak 41-b at approximately 650 Hz becomes larger than the peak
41-a. Further, in the detection result (FIG. 3C) of the vibration
sensor 37-3 arranged near the refrigerant outlet 32, which is
further downstream than the bend sections 31, the peak 41-c is
lower than the peak 41-b in the sound pressure level. The reason is
as follows. When the refrigerant receives heat from the plasma 11
in a process of flowing from the bend section 31 to the refrigerant
outlet 32, boiling is continued and the dryness becomes high.
Specifically, since a ratio of the liquid is reduced in the
refrigerant in a gas-liquid mixture phase, a size of the vibrations
caused by the boiling becomes small.
[0063] As discussed above, the peaks 41-a to 41-c at approximately
650 Hz in FIGS. 3A to 3C are determined to depend on the vibrations
generated by the boiling.
[0064] Next, in FIG. 3E, there is illustrated the detection result
of the vibration sensor 37-3 at a state in which the dryout occurs
before the refrigerant reaches the refrigerant outlet 32 and, as a
result, all the refrigerant at the refrigerant outlet 32 turns into
a gas completely. Incidentally, the dryout at the refrigerant
outlet 32 occurs in the case where the amount of heat entering the
sample stage 4 from the plasma 11 is excessively large or a flow
rate of the refrigerant introduced to the refrigerant passage 20 is
excessively small. When the dryout occurs, as illustrated in FIG.
3E, the peak at approximately 650 Hz does not appear while there
appear peaks 40-e associated with the operation of turbo molecular
pump 12.
[0065] The vibrations due to the boiling indicated as the peaks
41-a to 41-c of FIGS. 3A to 3C are generated when bubbles are
generated in the liquid and the bubbles rise up to a gas-liquid
interface and burst. Therefore, as illustrated in FIG. 3E, when the
dryout occurs at the refrigerant outlet 32, since all the
refrigerant evaporates and only a gas is present, vibrations are
not generated and the peak at approximately 650 Hz does not
appear.
[0066] As can be seen from the above, in the detection result of
the vibration sensor 37-3 arranged near the refrigerant outlet 32,
in the case where the peak 41-c indicating boiling of the
refrigerant appears, the dryout is considered not to occur. On the
other hand, in the case where the peak 41-c does not appear, the
dryout is considered to occur.
[0067] As described above, the signal processor 39 performs
processings in which respective vibration data detected by the
vibration sensors 37-1 to 37-3 is subjected to spectrum analysis
using fast Fourier analysis to convert to a power spectrum, a sound
pressure level is calculated by decibel conversion, peaks having
the sound pressure levels of zero or more are extracted, a peak
indicating boiling of the refrigerant is identified, and the
presence or absence of the dryout is determined based on a height
of the peak.
[0068] In the present embodiment, operations in the case where the
signal processor 39 determines that a sign of the dryout is
detected will be here described. In the present embodiment, when a
sound pressure level of the peak 41-c indicating boiling of the
refrigerant is lower than a certain threshold (e.g., three decibel)
in the detection result of the vibration sensor 37-3, a flow rate
of the refrigerant is increased. As a result, since a flow rate of
the refrigerant is increased and the refrigerant is ejected from
the refrigerant outlet 32 before it completely evaporates, the
dryout is avoided.
[0069] To cope with the above-described problem, the number of
rotation of the compressor 22 in the refrigerant temperature
control unit 21 is increased. Note that, when the number of
rotation of the compressor 22 is increased, a temperature of the
refrigerant in the refrigerant passage 20 is raised and
temperatures of the sample stage 4 and the sample 5 are raised. As
a result, since the temperature of the sample 5 rises up above the
target temperature, a harmful influence is exerted on the etching
processing.
[0070] To prevent this phenomenon, in the refrigerant temperature
control unit 21 while the number of rotation of the compressor 22
is increased, at the same time, an opening degree of the expansion
valve 24-1 is decreased or an opening degree of the expansion valve
24-2 is increased. By this operation, increase of the temperature
of the refrigerant is prevented while increasing a flow rate of the
refrigerant. Further, by performing the above-described operation,
in the case where the dryness at the refrigerant outlet 32 is
lowered and a sound pressure level of the peak 41-c of the
detection result of the vibration sensor 37-3 becomes larger than a
certain threshold, it can be determined that the dryout is
suppressed and the number of rotation of the compressor 22 and
opening degrees of the expansion valves 24-1 and 24-2 may be
maintained. By the above-described operation, a temperature of the
sample 5 is controlled and maintained in the desired range while
the dryout is suppressed; accuracy and reliability of the
processing of the sample are improved.
[0071] When performing the above-described control of the flow rate
and temperature of the refrigerant, it is preferred to find out
correlations among the number of rotation of the compressor 22, the
opening degrees of the expansion valves 24-1 and 24-2, and either
the temperature of the refrigerant or that of the sample stage 4 by
using experiments and the like and records data on the correlations
in advance. In the present embodiment, the refrigerant temperature
control unit controller 33 transmit command signals to the
refrigerant temperature control unit 21 via an input and output
interface so as to cause a computing unit to read out data
memorized in an not-illustrated, internal memory device, to select
a value of the temperature of the refrigerant to be set using the
above-described data according to a program similarly memorized in
the memory device, and to control to the set value of the
temperature of the refrigerant.
[0072] The number of rotation of the compressor 22 and the opening
degrees of the expansion valves 24-1 and 24-2 of the refrigerating
cycle, which receives the command signals, are controlled by their
drive units, which are not illustrated, and the temperature of the
refrigerant is controlled to a desired value. Further, the
refrigerant temperature control unit controller 33 may transmit
above-described commands of operating the compressor 22 and the
like so as to keep the temperature of the refrigerant measured by
using a thermometer arranged on the sample stage 4 or a thermometer
27 arranged in the refrigerant temperature control unit 21 in the
predetermined range.
[0073] Moreover, in the present embodiment, the peak of the
vibrations associated with boiling of the refrigerant appears at
approximately 650 Hz; however, it does not necessarily appear at
the above-described frequency. The vibrations are caused by
generation and disappearance of the bubbles as described above and,
therefore, are influenced by dryness and physical properties of the
refrigerant such as viscosity, density, and surface tension.
Further, since the physical properties are influenced by a type of
the refrigerant and the temperature, it is difficult to predict in
advance at which frequency the peak of the vibrations due to
boiling of the refrigerant appears. However, the vibrations of the
turbo molecular pump 12 having the possibility of confusing its
vibrations with those due to boiling of the refrigerant can be
determined because their sound pressure levels are very high as
described above and the frequency of the peaks appear at integral
multiplies of the number of rotation.
[0074] Consequently, in the present embodiment, the vibrations
associated with boiling of the refrigerant and the vibrations of
the turbo molecular pump 12 are distinguished and a spectrum of the
vibrations associated with boiling of the refrigerant is detected.
Further, as described above, by comparing the detection result
(FIG. 3B) at a position in which boiling of the refrigerant occurs
and the detection result (FIG. 3D) in the case where the operation
of the refrigerant temperature control unit 21-1 is stopped and the
supply of the refrigerant to the refrigerant passage 20 is stopped,
it becomes easy to determine the frequency of the peak indicating
the vibrations associated with boiling of the refrigerant.
[0075] Incidentally, in the sample stage 4 according to the present
embodiment, a total of 8 vibration sensors 37-1 to 37-3 are
arranged as one each at the refrigerant inlet 30, at the
refrigerant outlet 32, and near the bend sections 31 of six places,
respectively; however, the number of the arrangement is not limited
thereto. In the configuration of the refrigerant passage 20
according to the present embodiment, the refrigerant is not cooled
and flows through while receiving heat from a wall surface of the
refrigerant passage 20 and boiling. Therefore, as a distance in
which the refrigerant flows is longer, namely, it is nearer the
refrigerant outlet, the dryness becomes higher in general.
Accordingly, when the vibration sensor 37-3 is arranged at only one
position near the refrigerant outlet 32 and the vibrations
associated with boiling of the refrigerant are detected, a minimum
of dryout can be detected.
[0076] Further, by using the vibration sensors 37-2 arranged near
the bend sections 31 to detect vibrations at the relevant bend
sections 31, it can be determined with high accuracy whether the
refrigerant evaporates properly while the refrigerant flows through
or whether the sample stage 4 is cooled or in an abnormal state.
Further, by detecting the vibrations near the refrigerant inlet 30
with the vibration sensor 37-1, it can be determined with high
accuracy whether the dryness of the refrigerant near the
refrigerant inlet 30 is equal to zero (0%) or a value close to zero
(the refrigerant is laid in a saturated liquid state). Then,
necessity and accuracy of the control in the temperature of the
refrigerant with the refrigerant temperature control unit 21 can be
improved.
[0077] Further, when the heat amount received from the plasma 11 by
the sample 5 or the sample stage 4 is extremely large and the flow
rate of the refrigerant is low, the dryout might occur before the
refrigerant introduced from the refrigerant inlet 30 reaches the
bend sections 31. In that case, the peak indicating the vibrations
associated with boiling of the refrigerant is detected not by the
vibration sensors 37-2 and 37-3 but by only the vibration sensor
37-1. In that case, the flow rate of the refrigerant need to be
increased more compared with the case where the dryout occurs
between the bend sections 31 and the refrigerant outlet 32 as
described above. Therefore, the number of rotation of the
compressor 22 is increased further along with the opening degree of
the expansion valve 24-1 is lowered or the opening degree of the
expansion valve 24-2 is raised so that the refrigerant is
maintained at the target temperature while raising the flow rate of
the refrigerant. As seen above, by determining at which position of
the refrigerant passage 20 the dryout occurs, reliability in the
control of the flow rate of the refrigerant is improved. Therefore,
the plurality of vibration sensors are preferably arranged as shown
in the present embodiment.
[0078] Further, the vibration sensors are arranged at positions
under the passage as described above and between the refrigerant
inlet 30 and the refrigerant outlet 32 so that a detection accuracy
of a sign of the occurrence of the dryout and its position and the
effects of reduction in standing of bubbles generated by
evaporation with the supply control of the refrigerant performed
based on these detection results and suppression of the dryout are
improved. In addition, these detection units are preferably
arranged near the bend sections 31 and the like.
[0079] The reason is that in the refrigerant passage 20, since the
curvature radii of each passage become smallest at the bend
sections 31, concentrations of stress to separate the circular
plates 35-1 and 35-2 from each other due to an internal pressure of
the refrigerant are easy to occur at the junction near the bend
section 31 and there is a high possibility that junction defects
such as separation and crack are generated. Therefore, by arranging
the vibration sensors 37-2 near the bend sections 31, not only the
vibrations due to boiling of the refrigerant but also those
associated with the separation of the junction when it occurs are
detected and, therefore, the occurrence of the separation can be
detected.
[0080] In such a configuration, the respective vibration sensors
37-1 and 37-2 and the like transmit the detection result of the
vibrations to the signal processor 39. When the computing unit of
this signal processor 39 determines the vibrations are associated
with the separation of the junction, the processing result is
transmitted to an apparatus controller 43 via a communication unit.
Then, according to a program memorized in advance in an internal
memory unit the apparatus controller 43 informs of occurrence of an
abnormality using an information unit equipped on the plasma
processing apparatus or displays it on the monitor of a command
input unit of the user. For example, a warning is displayed on a
control screen which is displayed in a CRT monitor for the command
input and the user can be notified.
[0081] As described above, an output is received from the detection
unit arranged on the bottom surface of the sample stage 4 and the
dryness of the refrigerant flowing or the occurrence of the dryout
is detected; by controlling operations of the refrigerating cycle,
flow of the refrigerant, and the temperature of the refrigerant
introduced to the refrigerant passage 20 in the sample stage 4 to a
desired value based on the result the refrigerant temperature
control unit 21 suppresses the occurrence of the dryout and
maintains the temperature of the sample 5 during the processing in
the desired range so that accuracy, yield, and reproducibility of
the processing are improved. Further, by early detection of the
occurrence of the separation at the bend sections 31 in which the
separation in the junction of the sample stage 4 is easy to occur,
the amount and the time of work required for maintenance/inspection
is reduced and reliability of the plasma processing apparatus and
efficiency of the processing with it are improved.
Second Embodiment
[0082] In the above-described embodiment, it is configured so that
the refrigerant passage 20 in the sample stage 4 has one system;
that is, the refrigerant to be supplied to the refrigerant passage
20 is controlled to one condition and the sample stage 4 is
substantially controlled to one temperature. In that case, the
temperature of the surface of the sample stage 4 or that of the
sample 5 is approximately uniform in the surface.
[0083] In contrast, when a plurality of systems, for example, two
systems of the refrigerant passages are formed in the sample stage
4 and the refrigerant with temperature higher than that of an outer
system is introduced to an inner system, the sample stage 4 or the
sample 5 can be made into a convex-shaped temperature distribution
which is higher in the inner side.
[0084] In an etching processing for forming a gate electrode, a
density in a reaction product generated in the processing becomes
high in an inner portion. Therefore, by setting the temperature of
the sample 5 higher in the inner side and lowering an attachment
coefficient of the reaction product to the gate, the processing is
generally conducted so as to make dimensions of the gate electrode
be uniform in the plane of the sample 5. A configuration in which
for controlling temperature distributions of the sample 5 and the
sample stage 4 as described above the plurality of systems of the
refrigerant passages are formed in the sample stage 4 will be
described as a second embodiment with reference to FIGS. 4A and
4B.
[0085] Hereinafter, FIGS. 4A and 4B illustrate lateral and
longitudinal sectional views illustrating a schematic of a
configuration of the sample stage according to the second
embodiment. FIG. 4A illustrates a plan view of the section of the
sample stage 4. In order to have a temperature distribution in a
radial direction, an inner refrigerant passage 20-1 and an outer
refrigerant passage 20-2 are provided in the sample stage 4, each
of which has approximately concentric passages and bend sections in
the similar manner as in the first embodiment. Further, to the
inner refrigerant passage 20-1 and the outer refrigerant passage
20-2, the refrigerant temperature control units 21-1 and 21-2 of
the direct expansion system described in the first embodiment are
connected, respectively.
[0086] In the inner refrigerant passage 20-1, the refrigerant
introduced from an inner refrigerant inlet 30-1 is divided into two
directions, circulates through the inner refrigerant passage 20-1,
and further flows through the passage on the outside via a bend
section 31-1. The above-described refrigerant which flows as being
divided into two directions joins together near an inner
refrigerant outlet 32-1, is ejected from the inner refrigerant
outlet 32-1 to the outside of the sample stage 4, and returns to
the refrigerant temperature control unit 21-1 as illustrated in
FIG. 4B.
[0087] Similarly, also in the outer refrigerant passage 20-2, the
refrigerant introduced from an outer refrigerant inlet 30-2 is
divided into two directions, circulates through the outer
refrigerant passage 20-2, and further flows through the passage on
the inside via a bend section 31-2. The above-described refrigerant
which flows as being divided into two directions joins together
near an outer refrigerant outlet 32-2 and is ejected from the outer
refrigerant outlet 32-2 to the outside of the sample stage 4.
[0088] Further, FIG. 4B illustrates a configuration near the sample
stage 4. In the same manner as in the first embodiment, the
vibration sensor 37-1 is arranged on the bottom surface of the
sample stage 4 and near the inner refrigerant inlet 30-1, the
vibration sensor 37-3 is arranged on the bottom surface of the
sample stage 4 and near the inner refrigerant outlet 32-1, a
vibration sensor 37-4 is arranged on the bottom surface of the
sample stage 4 and near the outer refrigerant inlet 30-2, and a
vibration sensor 37-6 is arranged on the bottom surface of the
sample stage 4 and near the outer refrigerant outlet 32-2. Further,
the vibration sensors 37-2 are arranged on the bottom surface of
the sample stage 4 and near the bend sections 31-1 and vibration
sensors 37-5 are arranged on the bottom surface of the sample stage
4 and near the bend sections 31-2.
[0089] The vibration sensors are arranged at these places,
respectively, thereby detecting vibrations near them in the same
manner as in the first embodiment. Then, signals of the vibrations
detected by these vibration sensors 37-1 to 37-6 are transmitted to
the signal processor 39 for processing.
[0090] A detection method using these vibration sensors 37-1 to
37-6 is the same as in the first embodiment. That is, vibrations of
the refrigerant at the inner refrigerant inlet 30-1, the bend
sections 31-1, the inner refrigerant outlet 32-1, the outer
refrigerant inlet 30-2, the bend sections 31-2, and the outer
refrigerant outlet 32-2 are detected using the vibration sensors
37-1 to 37-6. Further, the signal processor 39 performs processings
in which respective vibrations data detected by the vibration
sensors 37-1 to 37-6 are subjected to spectrum analysis using the
fast Fourier analysis, sound pressure levels are calculated using
power spectrum conversion and decibel conversion, the peaks having
the sound pressure levels of zero or more are extracted, the peak
indicating boiling of the refrigerant is identified, and the
presence or absence of the dryout is determined based on a height
of the peak. Further, it is determined whether the dryout of the
refrigerant occurs at the inner refrigerant outlet 32-1 or the
outer refrigerant outlet 32-2.
[0091] Also, when the signal processor 39 determines that a sign of
the dryout is detected, the refrigerant temperature control unit
controller 33 controls the number of rotation of the compressor 22
and the opening degrees of the expansion valves 24-1 and 24-2 in
the refrigerant temperature control units 21-1 or 21-2 in the same
manner as in the first embodiment. So, while preventing the dryout,
the refrigerant temperatures in the inner refrigerant passage 20-1
and the outer refrigerant passage 20-2 can be controlled to desired
values. Further, when the separation in the junction of the sample
stage 4 is detected using the vibration sensors 37-1 to 37-6, the
apparatus controller 43 issues a warning indicating that an
abnormality occurs to a plasma etching apparatus.
[0092] When configuring the apparatus and performing the operations
as described above, the temperatures of the refrigerants to be
introduced, respectively, are controlled to desired values while
preventing the dryout and, as a result, a temperature distribution
of the sample 5 can be controlled to perform preferable etching
processing in the same manner as in the first embodiment even when
a plurality of systems of the refrigerant passages, namely, the
inner refrigerant passage 20-1 and the outer refrigerant passage
20-2 are provided on the sample stage 4. Also in the same manner as
in the first embodiment, occurrence of the separation at the bend
sections 31-1 and 31-2 in which the separation of the junction in
the sample stage 4 is easy to occur can be detected.
[0093] Here, a positional relationship between the inner
refrigerant inlet 30-1 and the inner refrigerant outlet 32-1
according to the present embodiment will be described. In the
present embodiment, the inner refrigerant inlet 30-1 is arranged on
the inner circumference than the inner refrigerant outlet 32-1.
[0094] Also in the present embodiment, in order for the temperature
of the sample 5 to be made into a convex-shaped distribution that a
central part is higher than an outer periphery, the temperature of
the refrigerant to be introduced to the inner refrigerant passage
20-1 is made higher than that of the outer refrigerant passage
20-2. Then, the refrigerant with the dryness of approximately zero
introduced from the inner refrigerant inlet 30-1 boils by receiving
heat from the plasma 11. It circulates through the passage on the
inner circumference of the inner refrigerant passage 20-1 with the
dryness rising up. After the bend sections 31-1, the refrigerant
circulates through the passage on the outer circumference of the
inner refrigerant passage 20-1 while being heated by the plasma 11
and cooled by the outer refrigerant passage 20-2 adjacent to the
passage on the outer circumference to be ejected from the inner
refrigerant outlet 32-1.
[0095] In that case, by making the dryness of the refrigerant
sufficiently high at the bend sections 31-1, even if the heat
quantity to the outer refrigerant passage 20-2 is larger than the
heat quantity from the plasma 11 and the refrigerant circulates
through the passage on the outer circumference of the inner
refrigerant passage 20-1 with the dryness being lowered, the
dryness is suppressed from being reduced to zero before the
refrigerant reaches the inner refrigerant outlet 32-1. Therefore,
before the refrigerant introduced to the inner refrigerant passage
20-1 is ejected from the inner refrigerant outlet 32-1, the dryness
will not become equal to zero. When the dryness of the refrigerant
in a gas-liquid mixture phase is not equal to zero as described
above, the temperature of the refrigerant does not change; the
refrigerant temperature does not change at a process in which the
refrigerant flows through the inner refrigerant passage 20-1. As a
result, a temperature distribution which is even in an azimuthal
direction can be realized in the sample stage 4 and the sample
5.
[0096] On the other hand, in opposition to the present embodiment,
when the inner refrigerant inlet 30-1 is arranged on the outer
circumference than the inner refrigerant outlet 32-1, in the
example of FIG. 4A the refrigerant is introduced from the inner
refrigerant outlet 32-1 and is ejected from the inner refrigerant
inlet 30-1. When the temperature of the refrigerant to be
introduced to the inner refrigerant passage 20-1 is made higher
than that of the refrigerant to be introduced to the outer
refrigerant passage 20-2, the refrigerant with the dryness of
approximately zero introduced from the inner refrigerant outlet
32-1 receives heat from the plasma 11 and simultaneously circulates
while being cooled from the passage of the innermost circumference
of the outer refrigerant passage 20-2 adjacent to the outer
circumference to reach the bend sections 31-1.
[0097] In this case, when the heat quantity to the outer
refrigerant passage 20-2 is larger than the heat quantity from the
plasma 11, the refrigerant circulates through the passage on the
outer circumference of the inner refrigerant passage 20-1 with the
dryness remaining to be zero and the refrigerant temperature being
dropped and reaches the bend sections 31-1. Therefore, the
temperature distribution in the azimuthal direction in the inner
refrigerant passage 20-1 becomes non-uniform so that the
temperature distribution in the azimuthal direction of the sample
stage 4 and the sample 5 becomes non-uniform. As a result,
uniformity in an in-plane distribution of the plasma processing of
the sample 5 is remarkably impaired.
[0098] Incidentally, when the inner refrigerant inlet 30-1 is
arranged on the inner circumference than the inner refrigerant
outlet 32-1 as in the present embodiment, an optimal value of the
dryness of the refrigerant in the bend sections 31-1 is influenced
by both of the heat quantity to the outer refrigerant passage 20-2
and the heat quantity from the plasma 11. If the former is larger
than the latter, for example, while the refrigerant after the bend
sections 31-1 circulates through the passage on the outer
circumference of the inner refrigerant passage, the dryness is
gradually lowered. Therefore, the dryness at the bend sections 31-1
needs to be made sufficiently high such that the dryness of the
refrigerant will not be equal to zero before it is ejected from the
inner refrigerant outlet 32-1.
[0099] On the contrary, if the heat quantity to the outer
refrigerant passage 20-2 is smaller than the heat quantity from the
plasma 11, while the refrigerant after the bend sections 31-1
circulates through the passage on the outer circumference of the
inner refrigerant passage, the dryness gradually rises. Therefore,
the dryness at the bend sections 31-1 needs to be sufficiently low
such that the dryness of the refrigerant is prevented from becoming
equal to one, that is, the dryout is prevented from occurring
before the refrigerant is ejected from the inner refrigerant outlet
32-1. When the amount of heat entering from the plasma 11 and the
amount exiting to the adjacent refrigerant passage as described
above are found out in advance by calculations or experiments and,
further, the optimal dryness at the bend sections 31-1 is found
out, it can be checked whether the dryness is the optimal value by
the vibration sensor 37-2 during the plasma processing.
Specifically, when the optimal value of the dryness at the bend
sections 31-1 is high and close to unity (100%), a liquid portion
of the refrigerant ought to be small and the peak 41-b illustrated
in FIG. 3B ought to be low.
[0100] On the other hand, when the optimal value of the dryness at
the bend sections 31-1 is small, since the liquid portion of the
refrigerant is large and boils violently, the peak 41-b illustrated
in FIG. 3B ought to be high. As described above, during the plasma
processing, the vibrations at the inner refrigerant inlet 30-1 and
the inner refrigerant outlet 32-1 are detected using the vibration
sensors 37-1 and 37-3 and at the same time the vibrations at the
bend section 31-1 are detected using the vibration sensor 37-2 to
prevent the dryness from becoming equal to zero or to prevent the
dryout from occurring in the entire area of the inner refrigerant
passage 20-1.
[0101] Moreover, with regard to the arrangement of the refrigerant
passages, when the plurality of systems of the refrigerant passages
are provided in the sample stage 4 and the refrigerants with
different temperatures are introduced to the respective systems, as
described in the present embodiment, it is preferable that the
dryness is raised by heating from the plasma 11 before the
refrigerant reaches the passage adjacent to the refrigerant passage
through which the refrigerant with lower temperature circulates.
With this non-uniformity of the temperature distribution in the
azimuthal direction of the sample stage 4 and the sample 5 is
eliminated, and as a result, an in-plane distribution of the plasma
etching processing of the sample 5 can be made uniform.
Third Embodiment
[0102] A third embodiment of the present invention will be
described below with reference to FIG. 5. In the second embodiment,
the vibration sensors 37-1 to 37-6 are arranged directly on the
bottom surface of the sample stage 4. However, in the etching
processing, in order that ions in the plasma 11 are pulled in
toward the sample 5 as a workpiece, a radio-frequency power source
53 is connected to the sample stage 4 to apply a radio frequency
power in many cases. In that case, since a radio frequency power
exerts a harmful influence on the vibration sensors 37-1 to 37-6,
they cannot be arranged directly on the bottom surface of the
sample stage 4. The third embodiment of the present invention copes
with the above-described problem. In the same manner as in the
first embodiment, the vibrations due to boiling of the refrigerant
introduced to the sample stage 4 are detected using the vibration
sensors and the dryout of the refrigerant is detected. Unlike the
first embodiment, piping made of electrically insulating materials
(e.g., alumina ceramics) is arranged under the sample stage 4 and
the vibration sensors are arranged on the insulating piping to
thereby detect vibrations.
[0103] FIG. 5 illustrates a vicinity of the sample stage used in
the present embodiment and components connected to it. Here,
although a top view of the cross section of the sample stage 4 is
not illustrated, a sample stage same as the sample stage 4
illustrated in the second embodiment of the present invention is
used. Circular holes are formed at portions in which the circular
plate 35-2 configuring the lower side of the sample stage 4 is
connected to the inner refrigerant inlet 30-1, the inner
refrigerant outlet 32-1, the outer refrigerant inlet 30-2, and the
outer refrigerant outlet 32-2 and electrically insulating piping
51-1 to 51-4 are inserted into and connected to the holes,
respectively. 0 rings 57 are installed at respective upper parts of
these insulating piping 51-1 to 51-4 to form a shaft sealing
structure so that the refrigerant introduced to or ejected from the
inner refrigerant passage 20-1 is sealed so as not to leak.
Further, the vibration sensors 37-1, 37-3, 37-4, and 37-6 are
arranged directly at the insulating piping 51-1 to 51-4,
respectively. Also, although not illustrated, areas of the
insulating piping 51-1 to 51-4 in which the vibration sensors 37-1,
37-3, 37-4, and 37-6 are not arranged are covered with thermally
insulating materials, thereby performing heat insulation.
[0104] The above-described insulating piping 51-1 to 51-4 is
tightly contacted with and fixed on the bottom surface of the
sample stage 4 and the vibrations due to the refrigerant at the
inner refrigerant inlet 30-1, the inner refrigerant outlet 32-1,
the outer refrigerant inlet 30-2, and the outer refrigerant outlet
32-2 can be detected using the vibration sensors 37-1, 37-3, 37-4,
and 37-6 through the insulting piping 51-1 to 51-4,
respectively.
[0105] Further, electrically insulating members 55-1 and 55-2 made
of electrically insulating materials are tightly contacted with and
fixed on the bottom surface of the sample stage 4 under the bend
sections 31-1 of the inner refrigerant passage 20-1 and the bend
sections 31-2 of the outer refrigerant passage 20-2, respectively.
Vibration sensors 37-2 and 37-5 are tightly contacted with and
fixed on the insulating members 55-1 and 55-2, respectively. By
this, the vibrations of the refrigerant at the bend sections 31-1
and 31-2 can be detected with the vibration sensors 37-2 and 37-5.
In this configuration, since the insulating members 55-1 to 55-4
are tightly contacted with and fixed on the sample stage 4,
respectively, even if the vibration sensors 37-1, 37-3, 37-4, and
37-6 are arranged at any position of the insulating members 55-1 to
55-4, vibrations can be detected. However, when the respective
vibration sensors are arranged away from the sample stage 4 and in
a position near the refrigerant temperature control unit 21-1 or
21-2, since vibrations of driving components such as the expansion
valves 24-1 and 24-2 and the compressor 22 are also detected, an
S/N ratio is lowered. Therefore, the respective vibration sensors
are preferably arranged at areas of the respective insulating
members near the sample stage 4.
[0106] The detection method using the vibration sensors 37-1 to
37-6 is the same as in the first embodiment. That is, the vibration
sensors 37-1 to 37-6 detect the vibrations of the refrigerant at
the inner refrigerant inlet 30-1, the bend sections 31-1, the inner
refrigerant outlet 32-1, the outer refrigerant inlet 30-2, the bend
sections 31-2, and the outer refrigerant outlet 32-2. With the data
processed by the signal processor 39 it is determined whether the
dryout of the refrigerant occurs at the inner refrigerant outlet
32-1 or the outer refrigerant outlet 32-2. Also, when the signal
processor 39 determines that a sign of the dryout is detected, by
controlling the number of rotation of the compressor 22 and the
opening degrees of the expansion valves 24-1 and 24-2 in the
refrigerant temperature control unit 21-1 or 21-2 in the same
manner as in the first embodiment, the refrigerant temperature in
the inner refrigerant passage 20-1 and the outer refrigerant
passage 20-2 can be controlled to a desired value while preventing
the dryout.
[0107] When configuring the apparatus and performing the operations
as described above, also in the case of applying radio frequency
power to the sample stage 4, the temperatures of the refrigerants
to be introduced to the inner refrigerant passage 20-1 and the
outer refrigerant passage 20-2 are controlled to desired values
while preventing the dryout and, as a result, a temperature
distribution of the sample 5 can be controlled to perform
preferable etching processing in the same manner as in the first
embodiment. Also in the same manner as in the first embodiment,
occurrence of the separation at the bend sections 31-1 and 31-2 in
which the separation of the junction in the sample stage 4 is easy
to occur can be detected.
Fourth Embodiment
[0108] In the first and second embodiments, it is configured so
that the separation in the junction of the sample stage 4 is
detected by using the vibration sensors 37-1 to 37-6. In contrast,
in the fourth embodiment, a pressure gauge is arranged on the
piping between the refrigerant temperature control unit 21-1 or
21-2 and the sample stage 4 to detect pressure of the refrigerant
and the separation of the junction of the sample stage 4 and the
occurrence of the refrigerant leakage are detected. A fourth
embodiment will be described below with reference to FIGS. 6, 7A,
and 7B.
[0109] FIG. 6 illustrates a vicinity of the sample stage 4 used in
the present embodiment and components connected to it. Further, a
configuration of this sample stage 4 is the same as that of the one
of which the top-view section is shown in FIG. 2A and the same
reference numerals as in FIG. 2A are used to explain.
[0110] To the inner refrigerant passage 20-1 and the outer
refrigerant passage 20-2, the refrigerant temperature control units
21-1 and 21-2 are connected, respectively, and the refrigerants are
supplied to the respective passages. Here, a pressure gauge 60-1 is
connected to the piping at a downstream of the expansion valve 24-1
in the refrigerant temperature control unit 21-1 and between the
expansion valve 24-1 and the inner refrigerant inlet 30-1;
approximately the same pressure as that of the refrigerant in the
inner refrigerant passage 20-1 can be measured.
[0111] In the above-described configuration, a time change of the
refrigerant pressure detected by the pressure gauge 60-1 is
illustrated in FIG. 7A. When a preset temperature of the
refrigerant is not changed up or down and the amount of heat
entering the sample 5 and the sample stage 4 from the plasma 11 is
not changed, the refrigerant pressure does not change and constant
with time as in a stable-pressure region 72-1. When the separation
occurs in the junction of the sample stage 4 under such a state,
since a volume of the refrigerant passage suddenly increases, the
refrigerant pressure drops and a pressure change 72-2 arises. Then,
when a progress of the separation stops, a change in the volume
stops so that the pressure change 72-2 of the refrigerant also
stops and the pressure becomes constant again as in a
stable-pressure region 72-3. This phenomenon appears as a
time-series pressure change such that a pressure is reduced and
recovered within a specific time or a pressure suddenly drops from
a stable value and then recovers to the same value as or a value
close to that of the previous pressure. The above-described
detection result of the refrigerant pressure is transmitted to the
signal processor 39.
[0112] When the pressure change 72-2 appears between the
stable-pressure regions 72-1 and 72-3 as illustrated in FIG. 7A and
its size is larger than or equal to a predetermined threshold, the
signal processor 39 judges that the separation occurs and the
processing result is transmitted to the apparatus controller 43.
Alternatively, based on a signal from the signal processor 39,
which receives signals of the pressure change, the computing unit
of the apparatus controller 43 judges. Based on this, a warning
indicating that an abnormality occurs is issued to the plasma
etching apparatus. For example, the warning is displayed on a
control screen of the plasma etching apparatus and is informed to
an operator.
[0113] Further, since in a plasma etching apparatus a plurality of
wafer processings are generally repeated using the same processing
conditions, the detection results of the refrigerant pressure are
saved at the processings and a change in the refrigerant pressure
may be detected by comparison with the past detection result of the
refrigerant pressure at the processing of the same type. The
detection result 75-1 of the refrigerant pressure in the case where
the plasma etching processing is properly performed as illustrated
by a broken line in FIG. 7B and the detection result 75-2 in the
case where the pressure change 72-2 appears as illustrated by a
solid line in the same figure are compared and thereby the pressure
change associated with the separation of the junction of the sample
stage 4 can be detected more certainly.
[0114] Incidentally, in the present embodiment, the pressure gauge
60-1 is arranged downstream of the expansion valve 24-1 and between
the expansion valve 24-1 and the inner refrigerant inlet 30-1;
however, a place for the arrangement is not limited thereto. Since
an object of the arrangement of the pressure gauge 60-1 is to
detect the refrigerant pressure in the refrigerant passage 20-1, a
place in which the pressure can be measured as close to that in the
passage as possible is preferable. Therefore, it is necessary there
is no component with low conductance such as a valve like between
the expansion valve 24-1 and the inner refrigerant inlet 30-1.
Accordingly, the pressure gauge 60-1 may be arranged downstream of
the inner refrigerant outlet 32-1 and between the inner refrigerant
outlet 32-1 and the expansion valve 24-2.
[0115] Further, in the present embodiment, in order to detect the
pressure of the refrigerant flowing through the inner refrigerant
passage 20-1, the pressure gauge 60-1 is arranged between the inner
refrigerant inlet 30-1 and the refrigerant temperature control unit
21-1; in the same manner, when the pressure gauge 60-2 is arranged
between the outer refrigerant inlet 30-2 and the refrigerant
temperature control unit 21-2, the pressure of the refrigerant
flowing through the outer refrigerant passage 20-2 can be detected
and the separation in the junction of the sample stage 4 can be
detected to inform an operator of the abnormality with the signal
processor 39 and the apparatus controller 43. Moreover, when there
are the plurality of systems (two systems in the present
embodiment) of the refrigerant passages of the inner refrigerant
passage 20-1 and the outer refrigerant passage 20-2 in the sample
stage 4 as in the present embodiment, it is preferable that all the
systems have the pressure gauges arranged between the refrigerant
passages and the refrigerant temperature control units.
[0116] As seen above, by arranging the pressure gauges between the
sample stage 4 and each of the refrigerant temperature control
units 21-1 and 21-2, detecting the refrigerant pressure, and
capturing the time change, the separation of the junction in the
sample stage 4 can be detected and an operator can be notified of
the abnormality.
[0117] When the first to fourth embodiments as described above are
applied, the dryout and the separation of the junction in the
sample stage 4 both of which are possible when a temperature
control unit of the direct expansion system is used in a plasma
processing apparatus.
[0118] According to the above-described embodiments, the dryness of
the refrigerant in the sample stage can be detected with high
accuracy and a flow of the refrigerant is controlled so that a
temperature value of the sample or sample stage during the
processing or a temperature distribution in the azimuthal direction
or in the radial direction of the sample can be made close to a
desired temperature value or distribution. In addition, separation
in portions in which members configuring the passage in the sample
stage are joined can be detected early with high accuracy. Through
the above-described effects, accuracy, reproducibility, and
reliability of the processing of the sample in a plasma processing
apparatus can be improved.
[0119] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
* * * * *