U.S. patent application number 10/378628 was filed with the patent office on 2004-09-09 for plasma processing apparatus and method.
Invention is credited to Kanai, Saburou, Kanekiyo, Tadamitsu, Kihara, Hideki, Nishio, Ryoji, Okuda, Koji, Yoshioka, Ken.
Application Number | 20040173314 10/378628 |
Document ID | / |
Family ID | 32926524 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040173314 |
Kind Code |
A1 |
Nishio, Ryoji ; et
al. |
September 9, 2004 |
Plasma processing apparatus and method
Abstract
A plasma processing apparatus ands a plasma processing method of
excellent mass production stability by controlling deposition films
deposited on the wall of a vacuum vessel are provided. This
apparatus comprises a gas ring forming a portion of a vacuum
processing chamber and having a blowing port for a processing gas,
a bell jar covering a portion above the gas ring to define a vacuum
processing chamber, an antenna, disposed above the bell jar, for
supplying RF electric fields into the vacuum processing chamber to
form plasmas, a sample table for placing a sample in the vacuum
processing chamber, a Faraday shield disposed between the antenna
and the bell jar and applied with an RF bias voltage, and a
deposition preventive plate attached detachably to the inner
surface of the gas ring excluding the blowing port for the
processing gas. The area of the inner surface of the gas ring
including the deposition preventive plate that can be viewed from
the sample surface is set to about 1/2 or more of the area of the
sample.
Inventors: |
Nishio, Ryoji; (Kudamatsu,
JP) ; Yoshioka, Ken; (Hikari, JP) ; Kanai,
Saburou; (Hikari, JP) ; Kanekiyo, Tadamitsu;
(Kudamatsu, JP) ; Kihara, Hideki; (Kudamatsu,
JP) ; Okuda, Koji; (Kudamatsu, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
32926524 |
Appl. No.: |
10/378628 |
Filed: |
March 5, 2003 |
Current U.S.
Class: |
156/345.33 |
Current CPC
Class: |
C23C 16/45591 20130101;
C23C 16/4404 20130101; H01J 37/32495 20130101; C23C 16/4581
20130101; H01L 21/67069 20130101; H01J 37/3244 20130101; H01J
37/32477 20130101; H01J 37/321 20130101; C23C 16/4558 20130101;
H01J 37/32697 20130101; C23C 16/507 20130101 |
Class at
Publication: |
156/345.33 |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A plasma processing apparatus comprising: a gas ring forming a
portion of a vacuum processing chamber and having a blowing port
for a processing gas; a bell jar covering a portion above the gas
ring to define a vacuum processing chamber; an antenna, disposed
above the bell jar, for supplying a RF electric field into the
vacuum processing chamber to form plasmas; a sample table for
placing a sample in the vacuum processing chamber; a Faraday shield
disposed between the antenna and the bell jar and applied with an
RF bias voltage; and a deposition preventive plate attached
detachably to the inner surface of the gas ring excluding the
blowing port for the processing gas; wherein an area of the inner
surface of the gas ring including the deposition preventive plate
that can be viewed from the sample surface is set to about 1/2 or
more of the area of the sample.
2. A plasma processing apparatus as defined in claim 1, wherein the
deposition preventive plate has an opening for allowing the
processing gas introduced from the blowing port to pass
therethrough, and the opening is opened at a view angle of about
30.degree. at the blowing port of the processing gas.
3. A plasma processing apparatus as defined in claim 1, wherein the
deposition preventive plate is disposed at a portion, of the inner
surface of the bell jar, substantially corresponding to a Faraday
shield not-disposed surface of the outer surface of the bell
jar.
4. A plasma processing apparatus as defined in claim 1, wherein the
deposition preventive plate is made of an insulator and disposed at
a portion, of the inner surface of the bell jar, substantially
corresponding to a Faraday shield not-disposed surface of the outer
surface of the bell jar.
5. A plasma processing apparatus comprising: a gas ring forming a
portion of a vacuum processing chamber and having a blowing port
for a processing gas; a bell jar covering a portion above the gas
ring to define a vacuum processing chamber; an antenna, disposed
above the bell jar, for supplying an RF electric field into the
vacuum processing chamber to form plasmas; a sample table for
placing a sample in the vacuum processing chamber; a Faraday shield
disposed between the antenna and the bell jar and applied with an
RF bias voltage; and a deposition preventive plate attached
detachably at least to the inner surface of the gas ring excluding
the blowing port for the processing gas; wherein the area of the
inner surface of the gas ring including the deposition preventive
plate that can be viewed from the sample surface is set to about
1/2 or more of the area of the sample; and wherein the apparatus
further comprises a susceptor made of a dielectric material
covering the outer surface and the outer lateral side of the sample
table and a metal film disposed on the surface of the susceptor, in
which an RF voltage is applied to the metal film to provide the
surface of the susceptor with a bias voltage.
6. A plasma processing apparatus comprising: a gas ring forming a
portion of a vacuum processing chamber and having a blowing port
for a processing gas; a bell jar covering a portion above the gas
ring to define a vacuum processing chamber; an antenna, disposed
above the bell jar, for supplying an RF electric field into the
vacuum processing chamber to form plasmas; a sample table for
placing a sample in the vacuum processing chamber; a Faraday shield
disposed between the antenna and the bell jar and applied with an
RF bias voltage; and a deposition preventive plate attached
detachably at least to the inner surface of the gas ring excluding
the an antenna, disposed above the bell jar, for supplying an RF
electric field into the vacuum processing chamber to form plasmas;
a sample table for placing a sample in the vacuum processing
chamber; a Faraday shield disposed between the antenna and the bell
jar and applied with an RF bias voltage; and an RF power source
circuit for supplying a power source voltage to the antenna and the
Faraday shield, the RF power source circuit comprising an RF power
source, an antenna connected with the RF power source, a resonance
circuit connected in series with the antenna and supplying a
resonance voltage thereof as an RF bias voltage to the Faraday
shield, a detection circuit for detecting the resonance voltage of
the resonance circuit, and a comparator circuit for comparing the
resonance voltage detected by the detection circuit with a
predetermined set value; wherein a constant of the resonance
circuit is changed based on the result of comparison by the
comparison circuit.
10. A plasma processing method for a plasma processing apparatus
comprising: a gas ring forming a portion of a vacuum processing
chamber and having a blowing port for a processing gas; a bell jar
covering a portion above the gas ring to define a vacuum processing
chamber; an antenna, disposed above the bell jar, for supplying an
RF electric field into the vacuum processing chamber to form
plasmas; a sample table for placing a sample in the vacuum
processing chamber; a Faraday shield disposed between the antenna
and the bell jar and applied with an RF bias voltage; a deposition
preventive plate attached detachably at least to the inner surface
of the gas ring excluding the blowing port for the processing gas
and having an area at least 1/2 or more of the area of the sample;
a susceptor made of a dielectric material covering the outer
surface and the lateral side of the plating table, an electrode
disposed on the inner surface or on a side of the inner surface of
the susceptor and an RF bias power source circuit for applying the
RF voltage to the electrode to provide the surface of the susceptor
with a bias voltage, the RF bias power source circuit comprising a
circuit for supplying the RF voltage power source by way of a
variable capacitor to the electrode, a detection circuit for
detecting the electrode voltage, and a comparator circuit for
comparing the voltage detected by detection circuit with a
predetermined set value; wherein a constant of the variable
capacitor is changed based on the result of comparison by the
comparison circuit. blowing port for the processing gas; wherein
the area of the inner surface of the gas ring including the
deposition preventive plate that can be viewed from the sample
surface is set to about 1/2 or more of the area of the sample; and
wherein the apparatus further comprises a susceptor made of a
dielectric material covering the outer surface and the outer
lateral side of the sample table and a metal film disposed in the
inside of the susceptor, in which an RF voltage is applied to the
metal to provide the surface of the susceptor with a bias
voltage.
7. A plasma processing apparatus as defined in claim 5 or 6,
wherein the metal film is connected with a conductive portion of
the sample table.
8. A plasma processing apparatus as defined in claim 5 or 6,
wherein the sample table is made of an insulator and has, at the
inside thereof, an electrode for application of a susceptor bias
connected to a metal film with the susceptor is formed in the
inside thereof.
9. A plasma processing method for a plasma processing apparatus
comprising: a gas ring forming a portion of a vacuum processing
chamber and having a blowing port for a processing gas; a bell jar
covering a portion above the gas ring to define a vacuum processing
chamber;
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a plasma processing
apparatus and a plasma processing method and, more particularly, it
relates to a plasma processing apparatus and a plasma processing
method capable of suppressing occurrence of obstacles caused by
reaction products.
[0002] Materials to be etched which are used in the field of
semiconductor device production can include volatile materials such
as Si, Al and SiO.sub.2, for example, for DRAM (Dynamic Random
Access Memory) or logic circuit IC. Further, non-volatile materials
such as Fe have been adopted for FRAM (Ferroelectric Random Access
Memory) or MRAM (Magnetic Random Access Memory)
[0003] The non-volatile materials are difficult to be etched since
the melting point of reaction products formed during etching is
high. Further, since the vapor pressure of the reaction products
after etching is low and the deposition coefficient to the inner
walls of vacuum vessels (vacuum processing chamber) is high, the
inner walls of the vacuum vessels are covered with deposits of the
reaction products even after processing only a small amount of
samples (several to several hundred of sheets). Further, when
peeled and fallen, the deposits form obstacles.
[0004] When the reaction products are deposited, the coupling state
between induction antennas and plasmas in the reactor changes to
vary, with time, the etching rate or the uniformess thereof,
vertical etching property, deposition states of reaction products
on the etching side wall, etc.
[0005] Concrete examples of the non-volatile materials can include
Fe, NiFe, PtMn, and IrMn as ferromagnetic or anti-ferromagnetic
materials used for MRMA or magnetic heads, as well as Pt, Ir, Au,
Ta, and Ru as noble metal materials used for capacitor portions or
gate portions in DRAM, capacitor portions in MRAM and TMR
(Tunneling Magneto Resistive) elements in MRAM. In addition, they
can also include Al.sub.2O.sub.3, HfO.sub.3, and Ta.sub.2O.sub.3 as
highly dielectric materials, and PZT (Lead Titanate Zirconate), BST
(Barium Strontium Titanate) and SBT (Strontium Bismuth
tantalate).
[0006] Further, also in the field of semiconductor device
production, a technique of forming Si, SiO.sub.2 or SiN films by a
plasma CVD method has frequently been adopted as production steps
for semiconductor devices. In this technique, a polymerizable gas
such as monosilane is injected into plasmas to form films on a
wafer. In this process, a great amount of polymer films are
deposited on the inner wall of a reactor other than the wafers to
inhibit mass production stability. That is, when polymer film is
deposited to an excessive thickness on the inner wall of the
reactor, the polymer film is peeled and fallen from the surface of
the inner wall and adhered on the wafer as obstacles in the same
manner as described previously. Accordingly, it is necessary to
conduct plasma cleaning by using a violent special gas such as
NF.sub.3, or manual cleaning conducted after opening the
reactor.
[0007] In addition, in the field of semiconductor device
production, a SiO.sub.2 plasma dry etching step is used frequently.
In the etching, fluoro carbon such as C.sub.4F.sub.8,
C.sub.5F.sub.8, CO, CF.sub.4 and CHF.sub.3 is used as an etching
gas. Reaction products formed by reaction of such gas in the
plasmas contain a great amount of free radicals such as C, CF,
C.sub.2F.sub.2 and, when the free radicals are deposited on the
inner wall of the reactor, they cause occurrence of obstacles like
the case described previously. Further, when the free radicals are
evaporated again in the plasmas, they change the chemical
composition of the plasmas to vary the wafer etching rate with
time. Induction type plasma processing apparatus in which coiled
antennas are disposed on the outer circumference of a vacuum vessel
or plasma processing apparatus in which a microwaves are introduced
into the vacuum vessel have been known as existent plasma
processing apparatuses. In any of the processing apparatuses
described above, since countermeasures for the deposited matters on
the inner wall of the vacuum vessel in a case of etching the
non-volatile material is not completely effective, a manual
cleaning operation by opening the vacuum vessels to atmosphere is
conducted repeatedly. Since manual cleaning requires as much as 6
to 12 hours from the start of the cleaning to the start of the
processing for the succeeding sample, this lowers the operation
efficiency of the apparatus.
[0008] For example, Japanese Patent Laid-open Nos. 10-275694,
11-74098 and 2000-323298 disclose plasma processing apparatus in
which plasmas are generated by an induction method in a processing
vessel, a Faraday shield is formed between induction antennas
disposed on the outer circumference of a vacuum vessel and plasmas,
and an RF power source is connected to the Faraday shield to supply
electric power, thereby reducing deposition of reaction products to
the inner wall of the vacuum vessel, or enabling cleaning for the
inner wall of the vacuum vessel.
[0009] This apparatus is effective for, of the vacuum vessel, the
portions that formed of a non-conductive material such as ceramics
or quartzes and that effective electric fields due to the Faraday
shield can reach. However, the apparatus is not effective for other
portions formed of non-conductive material or conductive
materials.
[0010] As has been described above, when reaction products are
deposited excessively on the inner wall of the vacuum vessel,
deposited films are peeled and fallen from the surface of the inner
wall and adhered as obstacles on the wafer. Further, in the plasma
processing apparatus using the induction antennas, the coupling
state between the induction antennas and the plasmas in the
reaction vessel is changed to vary the etching rate and the
uniformess thereof, the vertical etching property, and the
deposition state of the reaction products to the etching side wall.
Further, when the inner wall of the vacuum vessel is cleaned, since
it takes much time till the start of the processing for the
succeeding sample, the operation efficiency of the apparatus is
lowered. Further, in the plasma processing apparatus intended to
decrease the adhesion of reaction products to the inner wall of the
vacuum vessel or enable cleaning for the inner wall of the vacuum
vessel by providing the Faraday shield between the induction
antennas disposed on the outer circumference of the vacuum vessel
and plasmas and connecting the RF power source to the Faraday
shield to supply electric power, the range of the aimed effect is
limited.
SUMMARY OF THE INVENTION
[0011] The present invention has been accomplished in view of the
foregoing situations and it is an object of the present invention
to provide a plasma processing apparatus of excellent mass
production stability by controlling deposition films deposited on
the inner wall of a vacuum vessel.
[0012] According to one aspect of the present invention, there is
provided a plasma processing apparatus comprising:
[0013] a gas ring forming a portion of a vacuum processing chamber
and having a blowing port for a processing gas;
[0014] a bell jar covering a portion above the gas ring to define a
vacuum processing chamber;
[0015] an antenna, disposed above the bell jar, for supplying RF
electric fields into the vacuum processing chamber to form
plasmas;
[0016] a sample table for placing a sample in the vacuum processing
chamber;
[0017] a Faraday shield disposed between the antenna and the bell
jar and applied with an RF bias voltage; and
[0018] a deposition preventive plate attached-detachably to the
inner surface of the gas ring excluding the blowing port for the
processing gas;
[0019] wherein the area of the inner surface of the gas ring
including the deposition preventive plate that can be viewed from
the sample surface is set to about 1/2 or more of the area of the
sample.
DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0020] Other objects and advantages of the invention will become
apparent from the following description of embodiments with
reference to the accompanying drawings in which:
[0021] FIG. 1 is a diagram of a plasma processing apparatus
according to a preferred embodiment of the present invention;
[0022] FIG. 2 is a schematic perspective view of a Faraday
shield;
[0023] FIG. 3 is a graph for explaining a method of optimizing
FSV;
[0024] FIG. 4 is a circuit diagram for explaining FSV feedback
control;
[0025] FIGS. 5A and 5B are side views showing examples of attaching
the Faraday shield to the bell jar;
[0026] FIGS. 6A, 6B and 6C are diagrams for explaining attaching
structures of a deposition preventive plate;
[0027] FIG. 7 is a graph showing an example of heat calculation for
the deposition preventive plate;
[0028] FIG. 8 is a diagram explaining a supporting structure for
the deposition preventive plate;
[0029] FIGS. 9A and 9B are views explaining a countermeasure for
deposit deposited on the bell jar inner wall;
[0030] FIG. 10 is a view explaining adhesion of deposit near the
deposition preventive plate;
[0031] FIG. 11 is a view showing an example of a structure of the
deposition preventive plate;
[0032] FIG. 12 is a view showing another example of a structure of
the deposition preventive plate;
[0033] FIG. 13 is a view showing a further example of a structure
of the deposition preventive plate;
[0034] FIG. 14 is a view showing a structure of a sample holding
portion including the sample table;
[0035] FIG. 15 is a diagram of a substrate bias circuit including a
susceptor surface;
[0036] FIG. 16 is a graph for explaining a relation between a
susceptor thickness and a bias voltage generated on the susceptor
surface;
[0037] FIG. 17 is a view explaining the state of adhesion of
deposit on a thin-walled susceptor;
[0038] FIG. 18 is a view explaining the state of adhesion of
deposit on a thin-walled susceptor;
[0039] FIG. 19 is a view showing an example of flame spraying a
metal film to the lower surface of the susceptor;
[0040] FIG. 20 is a view showing an example of flame spraying a
metal film to the lower surface of the susceptor;
[0041] FIG. 21 is a view showing an example of embedding a metal
film in the susceptor;
[0042] FIG. 22 is a view showing an example of embedding a metal
film in the susceptor;
[0043] FIG. 23 is a view showing an example of applying a susceptor
having a metal film to a sample table made of ceramic
dielectrics;
[0044] FIG. 24 is a view showing an example of applying a susceptor
having a metal film to a sample table made of ceramic
dielectrics;
[0045] FIG. 25 is a view showing a connection structure for bias
applying electrode;
[0046] FIG. 26 is a circuit diagram for explaining means for
controlling an RF bias voltage applied to a susceptor surface;
[0047] FIG. 27 is a view for explaining a structural example of a
means for controlling an RF bias voltage applied to a susceptor
surface;
[0048] FIG. 28 is a circuit diagram for explaining an example of
supplying RF bias to a susceptor by using a separate power
source;
[0049] FIG. 29 is a view for explaining an example of an electrode
structure in a case of supplying RF bias to a susceptor by using a
separate power source;
[0050] FIG. 30 is a graph for explaining a method of optimizing a
susceptor bias voltage;
[0051] FIG. 31 is a circuit diagram for explaining a susceptor bias
application circuit having a feedback circuit;
[0052] FIG. 32 is a circuit diagram for explaining a susceptor bias
application circuit having a feedback circuit; and
[0053] FIG. 33 is a view for explaining each of regions in the
inside of a vacuum processing chamber.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0054] A first embodiment of the present invention is to be
described with reference to the drawings. In the first embodiment,
a method of suppressing deposition of reaction products during
processing on the inner wall of a vacuum vessel is to be described
with reference to an example of an etching process in a case where
a sample put to plasma processing is a non-volatile material.
[0055] FIG. 1 is a cross sectional view of a plasma processing
apparatus according to this embodiment. A vacuum vessel 2 has a
bell jar 12 made of an insulative material (for example,
non-conductive material such as quartzes or ceramics) closing an
the upper portion of the vacuum vessel 2 to define a vacuum
processing chamber. A sample table 5 for placing a sample 13 to be
processed is provided inside the vacuum vessel and plasmas 6 are
formed in the processing chamber to process the sample. Further,
the sample table 5 is formed above a sample holding unit 9
including the sample table.
[0056] Coiled upper antenna 1a and lower antenna 1b are disposed on
the outer circumference of the bell jar 12. A disk-like Faraday
shield 8 put into capacitive coupling with the plasmas 6 is
disposed outside the bell jar 12. The antennas 1a and 1b and the
Faraday shield 8 are connected in series by way of a matching box
to an RF power source (first RF power source) 10 as will be
described later. Further, a serial resonance circuit (a variable
capacitor VC3 and a reactor L2) having variable impedance is
connected in parallel between the Faraday shield 8 and the
ground.
[0057] A processing gas is supplied by way of a gas supply pipe 4a
to the inside of the vacuum vessel 2 and the gas in the vacuum
vessel 2 is evacuated to a predetermined pressure by an exhausting
device 7. The processing gas is supplied from the gas supply pipe
4a to the inside of the vacuum vessel 2. In this state, the
processing gas is converted into plasmas by the effect of electric
fields generated by the antennas 1a and 1b. The placing electrode 5
is connected with a substrate bias power source (second RF power
source) 11. This can draw ions present in the plasmas onto the
sample 13.
[0058] An RF power source 10, an RF power with a HF band such as,
13.56 MHz, 27.12 MHz or 40.68 MHz, or an RF power source of higher
frequency such as of VHF band is used and plasma generating
electric fields can be obtained in the vacuum vessel 2 by supplying
the RF power to the induction coupled antennas 1a and 1b and the
Faraday shield 8. In this case, reflection of the electric power
can be suppressed by matching the impedance of the induction
coupled antennas 1a and 1b with the output impedance of the RF
power source 10 by use of the matching box 3. Variable capacitors
VC1 and VC2 connected in an inverted L-shape as shown, for example,
in the figure is used as the matching box 3.
[0059] The Faraday shield is made of a conductor formed with
longitudinal strip-shaped slits 14 as shown in FIG. 2 and disposed
in a manner overlapping the vacuum vessel (bell jar 12) made of
ceramics. The voltage applied to the Faraday shield 8 can be
controlled by a variable capacitor (VC3 shown in FIG. 1) The
voltage applied to the Faraday shield 8 (shield voltage) is
preferably set to an optional value corresponding to the processing
recipe or cleaning treatment recipe on every wafer.
[0060] The principle of the cleaning for the inner wall of the
vacuum vessel by the Faraday shield is as described below. That is,
a bias voltage is generated inside the vacuum vessel (inner wall of
the bell jar) by an RF voltage applied to the Faraday shield,
thereby drawing ions present in the plasmas toward the wall of the
vacuum vessel, and bombarding the vacuum vessel wail by the drawn
ions to cause physical and chemical sputtering and prevent
deposition of reaction products on the wall of the vacuum
vessel.
[0061] An optimal Faraday shield voltage (FSV) exists for the
cleaning of the inner wall by the Faraday shield. The optimal FSV
undergoes the effects of the RF power source frequency, materials
for the vacuum vessel wall, plasma density, plasma composition,
constitution for the entire vacuum vessel, materials for the sample
to be processed, processing rate and the processing area.
Accordingly, the optimal FSV value has to be changed on every
process.
[0062] FIG. 3 is a graph for explaining a method of optimizing FSV,
which shows a relation between FSV and a light emission intensity
(light amount) of a material for the vacuum vessel wall (aluminum
or oxygen constituting alumina in a case where the wall material is
made of alumina). As shown in the graph, light emission of the wall
material increases as the FSV is higher at a certain FSV value
(point b in FIG. 3) as a boundary. This shows that at FSV lower
than the point b, not only deposits are not deposited by sputtering
for the deposits but also the wall material itself is sputtered as
well at FSV not lower than the point b.
[0063] While the optimal FSV value is a voltage at the point b, a
point a is sometimes determined as the optimal value depending on
the process. For example, this is a case in which processing
reaction of the workpiece or reaction in the gas phase are made
different from intended conditions by the release of the wall
material into the gas phase due to the sputtering to the material
for the vacuum vessel wall, and the aimed process cannot be
executed. That is, by setting FSV to the point a, deposition of
deposits, is allowed though slightly, to the inner wall of the
vacuum vessel, so that the wall material is not sputtered at all.
This can prevent process troubles caused by the release of the wall
material. However, it is necessary to clean the inner wall of the
vacuum vessel by a process used exclusively for cleaning before
substantial deposition of deposits on the inner wall of the vacuum
vessel (the FSV is set higher than the point b in this case).
[0064] On the contrary, point c is sometimes set as an optimal
value depending on the process. For example, aimed process can not
sometimes be conducted stably when reaction products are deposited,
if little, on the inner wall of the vacuum vessel, obstacles are
generated or the RF power for generating the plasmas is absorbed to
the deposits to vary the plasma characteristics. In this case, FSV
is set to the point c as described above. That is, it is possible
to set the condition such that the inner wall may be scraped
somewhat but the reaction products are not deposited at all. In
this case, it results in a drawback that the vacuum vessel is
consumed greatly but the number of cleaning cycles for the inner
wall cal be decreased.
[0065] FSV is set to the point b in a case where neither the
scraping of the inner wall nor the deposition of the reaction
products is desirable. In this case, it is important to improve the
reproducibility for the FSV setting voltage. This is because change
with the lapse of time has to be suppressed in a case of conducting
the same process in different apparatus or conducting the same
process continuously even in the same apparatus. For this purpose,
feedback control for FSV is important.
[0066] FIG. 4 is a circuit diagram for explaining the FSV feedback
control. As shown in the figure, output of the RF power source 10
for plasma generation is applied by way of the impedance box (VC1,
VC2) and antennas 1a and 1b to the Faraday shield 8. FSV is divided
by the capacitors C2 and C3 into a small signal, which is passed
through a filter 15 to eliminate harmonic waves or other frequency
components, detected by a detector 16, converted into a DC voltage
and then amplified by an amplifier 17. Thus, a DC voltage signal in
proportion with FSV is obtained. The signal is compared with a
preset value or a setting value set by the recipe output of a main
body apparatus control unit 20 to control a motor by way of a motor
controller 19 and rotate a variable capacitor VC3 for determining
the FSV voltage. Thus, FSV can be controlled to a value set by the
main body apparatus control section 20. For example, the FSV value
can be controlled constant also in a case of conducting the same
processing in different apparatus or continuously in the same
apparatus. Further, difference between the apparatus or a change
with the lapse of time can be suppressed.
[0067] The Faraday shield is put to capacitive coupling with
plasmas through the wall (bell jar) of the dielectric vacuum
vessel. As a result, FSV is divided into static capacitance between
the Faraday shield and the plasmas and static capacitance due to
ionic sheath formed to the wall, and the voltage after division is
applied to the ionic sheath. This accelerates the ions and causes
ion sputtering to the inner wall of the vacuum vessel. For example,
in a case where the thickness of the wall of the alumina vacuum
vessel is 10 mm, the voltage applied to the ionic sheath is about
60 V for FSV of 500 V.
[0068] Increase of the voltage applied to the ion sheath with low
FSV is useful. This is because generation of high FSV makes the
handling difficult by the reason, for example, that this tends to
cause abnormal discharge. In order to increase the voltage applied
to the ionic sheath by low FSV, it is effective to make the static
capacitance as low as possible between the Faraday shield and the
plasmas since the static capacitance of the ionic sheath is
determined solely by the plasma characteristics of the process. In
order to attain this, it is necessary that the dielectric constant
of the material of the dielectric vacuum vessel is high and the
thickness of the wall of the dielectric vacuum vessel is as thin as
possible. As the material suitable to this purpose, an alumina can
be adopted as a typical material having high strength and high
dielectric constant.
[0069] When a vacuum vessel of thin wall thickness is manufactured
by a highly dielectric material such as alumina, it is necessary to
consider a gap between the Faraday shield and the wall (bell jar)
of the vacuum vessel. Since the dielectric constant of alumina is
about 8, the wall thickness of 10 mm is: 10/8=1.25 mm when
converted as the thickness of atmospheric air. Assuming a case
where the gap between the Faraday shield and the vacuum vessel is 0
to 1 mm, the gap between the Faraday shield and the plasma changes
nearly about one-half as 1.25 to 2.25 mm when converted as that for
atmospheric air. This means that the voltage applied on the ionic
sheath changes from about 33 to 60 V under the conditions described
above.
[0070] When the voltage applied on the ion sheath changes greatly
as described above, deposits are adhered to some portions while
deposits are not deposited to other portions on the inner wall of
the vacuum vessel to reduce the effect of suppressing adhesion of
deposits by the application of FSV. In order to prevent this, it is
necessary to make the gap between the Faraday shield and the vacuum
vessel constant or to prepare a Faraday shield with a thin film and
put it into intimate contact with the vacuum vessel.
[0071] While it is easy to manufacture the Faraday shield by
fabrication of a metal plate, it is not practical to manufacture
such that the gap relative to the wall (bell jar) of the vacuum
vessel is 0.5 mm or less. However, the gap between the Faraday
shield and the vacuum vessel can be filled by attaching a
conductive elastomeric material, for example, a conductive sponge
to a portion below the Faraday shield.
[0072] FIGS. 5A and 5B are views showing an example of attaching a
Faraday shield to a bell jar. FIG. 5A shows an example where a gap
is present between the Faraday shield 14 and the bell jar 12, in
which deposits are tend to deposit on the inner surface of a vacuum
vessel at a portion with gap. On the other hand, deposits are not
deposited near a skirt portion with no gap. FIG. 5B is a view
showing an example where the gap is filled with an elastomeric
conductor 12a, for example, conductive sponge. This can provide the
Faraday shield 14 with the same effect as that it is in close
contact with the bell jar 12. Since the conductive sponge is highly
shrinkable, it can bury gaps of different sizes flexibly.
[0073] FIGS. 6A and 6B are views explaining an attaching structure
of a deposition preventive plate. FIG. 6A shows a gas blowing port
23 formed at a skirt portion of the bell jar 12 and a gas ring
thereblow. In the constitution, when plasma processing is
continued, deposits are deposited at the portions indicated by A
and B of the figure. The deposits can be prevented from deposition
on the inside of the bell jar at a portion above B in the figure by
the ion sputtering effect of FSV. A consideration has to be taken
for the portions A and B. The portion A is the periphery of the gas
blowing port 23 and, when deposits are adhered there, the deposits
are liable to peel off by the effect of the gas stream, and the
peeled deposits are placed as obstacles on the wafer as a workpiece
to hinder the process. Further, the portion B is the inner wall of
the bell jar 12 but the Faraday shield 14 is far from the inner
wall of the bell jar. Accordingly, the ionic sheath voltage due to
FSV is lowered and the effect of suppressing the adhesion of the
deposits by ion sputtering is not so effective for the portion
B.
[0074] FIG. 6B is a view for explaining a structure covering the
gas blowing port 23 with a deposition preventive plate 22. The
portion A is the periphery of the gas blowing port and adhesion of
the deposits to the portion has to be decreased as much as
possible. In order to decrease the adhesion of deposits to the gas
blowing port 23, it is necessary to decrease the region of the
plasmas 6 which can be seen from the gas blowing port 23 through
the hole of the deposition preventive plate 22, that is, to
decrease the view angle relative to the plasmas, and it is also
necessary that the gas blowing port 23 does not directly view the
wafer, that is, the central axis of the gas blowing port 23 is set
in the direction of the plasma forming space above the sample such
that the sample is contained in a region out of the view angle.
[0075] FIG. 6C is a view showing a detailed example of a relation
between the deposition preventive plate and the gas blowing port.
In this example, the view angle is decreased to about 30.degree.
and the wafer cannot be viewed directly through the gas blowing
port.
[0076] It is effective to make a gap between the deposition
preventive plate 22 and the gas jetting port 23. The size of the
gap is preferably 0.5 mm or more. The gap provides several
advantageous. At first, even with the hole of the same size formed
in the deposition preventive plate for passing the gas, the view
angle to the plasmas can be made smaller by providing the gap and
the amount of deposits adhered to the gas blowing port 23 can be
decreased. Further, when a gas is blown from the gas jetting port
23 into the vacuum vessel, a large lowering of pressure occurs and
the gas is formed from a viscous flow into a intermediate flow and
finally formed into a molecular stream. In this case, at the
periphery of the gas glowing port 23, the pressure of the gas is
still relatively high and the gas is in a state of the intermediate
flow and, the deposits adhered at the periphery of the port
undergoes the effect from the gas stream tending to be peeled. By
the provision of the gap, the gas flow near the deposition
preventive plate 22 is formed into the molecular stream and the gas
stream has less effect of peeling the deposits adhered on the
deposition preventive plate to decrease the peeling of the
deposits. Further, as will be described later, the temperature of
the deposition preventive plate 22 can be elevated efficiently to
decrease the amount of deposits adhered to the deposition
preventive plate 22.
[0077] FIG. 7 is a graph showing an example of heat calculation of
the deposition preventive plate. The result of process has provided
a finding that a material such as Fe or Pt is less adhered to a
member at a temperature of 250.degree. C. or higher. Then, the
deposition preventive plate was designed such that the temperature
of the deposition preventive plate is 250.degree. C. or higher. In
the heat design, heat balance was calculated for the input heat
from the plasmas, heat dissipation from the supporting portion or
the deposition preventive plate and the dissipation of radiation
heat from the entire deposition preventive plates. FIG. 7 shows the
result of the heat calculation.
[0078] In a case of a deposition preventing plate made of SUS
(stainless steel), it can be seen that the equilibrium temperature
exceeds 250.degree. C. at RF input to plasmas of about 500 W. In a
case of a deposition preventive plate made of Al (alumite finished
surface), the equilibrium temperature of the deposition preventive
plate is 250.degree. C. or higher at an RF input of 1000 W. The
structural features for each of the portions are to be described
upon calculation.
[0079] Since plasma input heat is diffused isometrically in a
reactor, it is calculated as RF input plasma x area of deposition
preventive plate/entire plasma contact area. In the deposition
preventive plate designed now, input heat to the deposition
preventive plate is 260 W at a RF input to plasmas of 1200 W.
[0080] The dissipation of heat irradiation from the deposition
preventive plate can be suppressed low since the surface radiation
rate can be decreased to about 0.2 by applying mirror finishing to
the surface. In a case of using Al (alumite finished surface) for
the deposition preventive plate, the diffusion of heat radiation is
somewhat increased since the radiation ratio of the alumite surface
is about 0.6.
[0081] FIG. 8 is a diagram for explaining a supporting structure of
the deposition preventive plate. The heat conduction surface is
decreased by supporting the deposition preventive plate for the
entire circumference at three points so as to decrease the heat
transfer from the supporting portion and bringing the area of
contact with the gas ring main body into a substantially
point-to-point contact. In a concrete example, the radial length
for the portion of contact is defined as 3 mm and the
circumferential length for the portion of contact is defined as 1
mm. Even when the contact heat resistance is assumed to an excess
value of about 3000 [W/(m.sup.2.multidot.K)], heat transfer from
the supporting portion of the deposition preventive plate
calculated according to: area of contact.times.contact heat
transmission ration.times.(temperature at the inner surface of
deposition preventive plate-temperature of gas ring) is only about
10 W.
[0082] A deposition preventive plate was actually manufactured
trially to measure the surface temperature actually. The material
of the deposition preventive plate used is Al (alumite finished
surface). At an RF input of 1200 W, it was confirmed that the
surface temperature was about 250.degree. C. which was
substantially the designed value.
[0083] As described above, adhesion of the deposits can not be
eliminated completely even when the deposition preventive plate is
kept at a high temperature. Therefore, it is important to stably
adhere the deposits adhered to the deposition preventive plate. For
this purpose, it is desirable that the surface of the deposition
preventive plate has unevenness to some extent in order to
mechanically improve the adhesion of the deposits. According to the
experiment made by the inventors, it has been found that the
surface roughness is preferably 10 .mu.m or more.
[0084] However, when adhesion of the deposits is started, the
thickness of the adhered deposits is gradually increased from the
thin film state. For example, unevenness of 10 .mu.m formed in the
deposition preventive plate has an anchoring effect for deposits
with a film thickness of about 10 .mu.m. However, as the thickness
of the adhered deposits increases, the anchoring effect is reduced.
Accordingly, in order to effectively provide the anchoring effect
from the initial state where the adhesion amount of the deposits is
small to a state where the amount of the deposits increases to some
extent, it is preferred that two types of unevenness for example,
10 .mu.m unevenness and 100 .mu.m unevenness are formed
simultaneously on the surface. The fabrication method for forming
such unevenness includes knurling for the formation of 100 .mu.m
unevenness and blasting fabrication for formation of 10 .mu.m
unevenness.
[0085] As has been described above, in order to elevate the
temperature of the deposition preventive plate, it is preferred to
apply mirror finishing to the surface of the deposition preventive
plate and apply unevenness formation to the surface for stably
adhering the deposits. Accordingly, in practice, unevenness can be
formed, in the deposition preventive plate, on the surface where
the deposits are adhered (plasma facing surface) and mirror
finishing can be applied to the surface not adhered with the
deposits (for example, surface facing the gap between the
deposition preventive plate and the gas blowing port). Further, to
reflect heat irradiated from the deposition preventive plate,
mirror finishing is preferably applied to the surface of the
portion not adhered with the deposits in the surface of the gas
ring with the gas blowing port.
[0086] The size of the deposition preventive plate is preferably a
minimum size capable of covering the gas blowing port. This is
because deposition of the deposits to some extent on the deposition
preventive plates is inevitable and thermal hysteresis is caused in
the deposition preventive plate in view of elevating the
temperature to decrease the adhesion amount of the deposits, and
the deposits are liable to peel off due to the difference between
the thermal expansion and shrinking amounts of the deposits and the
deposition preventive plate material.
[0087] Further, the deposition preventive plate is preferably
manufactured with an electroconductive material and it is
preferably grounded to the earth. This is because electric
discharge is stabilized as the grounding area relative to the radio
frequency waves for the generation of plasmas is increased.
Further, since the deposits are liable to peel off due to the
repulsion between the deposits by the coulomb effect when the
deposits are electrostatically charged, and this is provided for
the purpose of preventing electrostatic charging on the deposits as
much as possible.
[0088] The structural design and the heat design described above
were conducted, a deposition preventive plate with the surface
roughness of 10 .mu.m and 100 .mu.m was manufactured and platinum
Pt was continuously etched for 500 sheets to examine the
performance. As a result, adhesion of the deposits to the gas
blowing port was scarcely observed. Further, deposits adhered to
the deposition preventive plate were stable and peeling of the
deposits did not occur.
[0089] FIGS. 9A and 9B are views for explaining the countermeasure
for the deposits adhered to the portion B in FIG. 6A (the portion
on the inner wall of the bell jar 12 where the Faraday shield is
far from the inner wall of the bell jar and accordingly, a portion
where the ionic sheath voltage by FSV is lowered and the effect of
suppressing the adherance of deposits by the ion sputtering does
not exert effectively).
[0090] The portion B in FIG. 6A is a region where the ion sputter
by FSV is less effective since the distance between the inner wall
of the bell jar 12 and the Faraday shield 14 is large. Then, when
the deposition preventive plate 2 is extended to cover the portion,
the adhesion amount of the deposits can be decreased and the
deposits can be stabilized. FIG. 9A shows the structure. When a
test was conducted on the adhesion of deposits by using the
structure, it was found that deposits were adhered to a region of
about 15 mm in width of the bell jar of the inner wall around point
C in FIG. 9A as a center.
[0091] FIG. 9B is a modified example of FIG. 9A. As shown in the
figure, the bell jar 12 is formed such that the inner surface
thereof is substantially in contiguous with the inner surface of
the gas ring 4 and the bell jar 12 was disposed on the gas ring 4
to form the vacuum processing chamber.
[0092] With this constitution, the deposition preventive plates can
be formed continuously with the inner surface of the bell jar and
the inner surface of the gas ring. Thus, the region where the ion
sputtering by FSV is less effective can be protected effectively by
the deposition preventive plate.
[0093] FIG. 10 is a view for explaining adhesion of deposits near
the deposition preventive plate. At first, a dotted line shows an
equi-density line of plasmas. Referring to the point .degree. C.,
the point C corresponds to a corner for the deposition preventive
plate and the bell jar and the density of plasmas is slightly lower
at the portion compared with that for the periphery.
[0094] This is because plasmas are less turned behind the point C
due to the thickness of the deposition preventive plate.
Accordingly, it is probable that the deposits are less detached
since the number of ion sputtering per unit area on the inner wall
of the bell jar is smaller at the point C. There may be another
reason. This is, because the deposition preventive plate is
electroconductive and FSV is not effective to the ionic sheath
formed in the deposition preventive plate and a DC voltage of about
15 to 20 V determined by plasma characteristics is applied to the
ion sheath. On the contrary, in a region where FSV is effective, an
RF voltage, for example, of about 60-V is further applied in
addition to the DC voltage determined by the plasma characteristics
onto the ionic sheath formed on an inner wall of the bell jar,
which effectively accelerates ions to sputter the inner wall of the
bell jar. That is, the periphery of the point C corresponds to a
transition region from the ionic sheath at a low voltage formed in
the deposition preventive plate to the ionic sheath at high voltage
formed in the inner wall of the bell jar, and the periphery for the
point C is a region where the ionic sheath voltage is increased and
the ion sputtering becomes more effective gradually as it aparts
form the vicinity of the deposition preventive plate.
[0095] It is probable that a weak sputter, region by FSV is formed
near the point C as shown in FIG. 10 by the two reasons described
above. It is probable that the deposits are adhered in the region
since adhesion of the deposits is predominant over the sputtering
by FSV.
[0096] FIGS. 11, 12 and 13 are views showing, respectively,
structural examples of the deposition preventive plates. As shown
in FIG. 11, a knife edge-shaped deposition preventive plate was
manufactured in order to remove the cause for the lowering of the
plasma density which is one of the reason of forming the weak
sputter region and a test was conducted. As a result, as shown in
FIG. 11, it was confirmed that the weak sputter region is
contracted and the deposit adhesion region is contracted. Then, to
remove another cause, when an upper portion 22a of the deposition
preventive plate is changed to an insulator (alumina in this case),
the strong sputter region and the deposition region can be allowed
to coincide with each other with scarce adhesion of the deposits as
shown in FIG. 12. Since knurling is impossible for the surface of
alumina, unevenness was fabricated on the surface by a blast
treatment. Further, for the material of the insulator, quartz or
aluminum nitride can also be used.
[0097] To further prevent adhesion of deposits more thoroughly, it
may suffice that the strong sputter region is wider, even slightly,
than the deposit adhesion region as shown in FIG. 13. Then, a gap
was made between the deposition preventive plate and the bell jar
such that plasmas could intrude between the deposition preventive
plate and the bell jar. To allow entrance of plasmas, it is
necessary that the distance of the gap be substantially lager than
the ionic sheath and be 5 mm or more. On the contrary, if it is
excessively large, since the deposits turned behind by diffusion,
the effect is reduced. Since the maximum value for the gap to
inhibit the deposits from being turned behind by the diffusion is
determined depending on the material of the deposits, and species
and pressure of gas, it is about 15 mm as a result of a test while
it is different depending on the processing process. As a result of
manufacturing a deposition preventive plate of the structure shown
in FIG. 13 and conducting a test, adhesion of deposits to the bell
jar could completely be suppressed. In this structure, it is not
necessary that the upper portion of the deposition preventive plate
is an insulative material but the same performance can be obtained
even when it is made of an electroconductive material.
[0098] An upper portion of the susceptor as a cover for the sample
table 5 also causes obstacles formed on the wafer when the deposits
are adhered. Then, an RF bias was applied also to the susceptor to
cause physical and chemical ion sputtering, so that the deposits
were not adhered.
[0099] FIG. 14 is a view showing a structure of a sample holding
portion 9 including a sample table. As shown in the drawing, the
sample table 5 connected with a substrate bias voltage 11 is
mounted on a ground base 36 and an insulation base 35. As the
material for the sample table, aluminum or titanium alloy is used
generally. A dielectric film is formed in an upper portion of the
sample table but at a portion for mounting a workpiece (sample 13)
such that the workpiece can be electrostatically attracted. While
the dielectric film is made of a flame sprayed film in the drawing,
it is sometimes formed of a polymeric material such as epoxy,
polyimide or silicone rubber. Further, the ceramic materials
formed, for example, by flame spraying can include alumina, alumina
nitride, and PBN (Pyrolitic Boron Nitride). Further, FIG. 14 shows
a structure of providing shielding using the ground base 36 and the
insulation cover 37 in order that the RF power passes through the
lateral side of the sample table 5 to the plasmas. Further, the
susceptor is generally made of a material such as quartz or alumina
so that it covers an electrode portion of the sample table except
for the surface where the sample is mounted, to prevent
plasma-induced injury.
[0100] FIG. 15 is a view showing a substrate bias circuit
(equivalent circuit) including a surface of the susceptor. The
output from the substrate bias power source 11 is mixed with a DC
voltage for electrostatic attraction supplied from an electrostatic
attraction power source in an impedance matching box (MB) 32 and
then supplied to the sample table 5. In this case, radio frequency
waves from the substrate bias power source 11 are supplied also to
the upper surface of the susceptor while passing from the sample
table 5 to the susceptor 34. The susceptor 34 forms in this
embodiment a capacitor using the susceptor material as a dielectric
material. The thus formed capacitor is represented as a capacitor C
(33) in FIG. 15.
[0101] The present inventors, at first, experimentally examined
adhesion of the deposits when the susceptor thickness was set to 5
mm as shown in FIG. 14. As a result, it has been found that a great
amount of deposits was adhered on the upper surface of the
susceptor.
[0102] Then, the relation between the thickness of the susceptor 34
and the bias voltage formed on the surface of the susceptor was
theoretically examined. The result is shown in FIG. 16. It is known
that adhesion of deposits can be suppressed when the voltage formed
on the bell jar inner wall is about 60 V or more. Further,
according to the test conducted by the inventors, since the bias
voltage (peak-to-peak) Vpp was often set in a range about from 400
to 500 V in the test, the susceptor was selected to have a
thickness of 4 mm so that a voltage of 60 V or higher could be
generated on the surface of the susceptor within the range of the
bias voltage Vpp.
[0103] FIGS. 17 and 18 are views for explaining the adhesion state
of deposits to the susceptor of a thin-wall thickness (for example,
4 mm thickness). As shown in FIG. 17, the deposits was experimented
for the adhesion state thereof with the entire thickness of the
upper surface of the susceptor being set to 4 mm. As a result, it
was confirmed that deposits were not adhered in a range shown by
arrows in the drawing (deposition restriction region). Thus, it was
found that adhesion of the deposits could be suppressed for the
portion in direct contact with the sample table. However, in the
constitution of FIG. 17, since deposits are adhered to the outer
circumference of the upper surface of the susceptor, they may
hinder the processing as obstacles to the workpiece. Then, the
insulation cover 37 disposed on the side of the sample table was
removed so that the sample table and the susceptor were in contact
with each other entirely for the upper surface of the susceptor and
the upper portion of the side of the susceptor. The constitution is
shown in FIG. 18. The adhesion state of the deposits was examined
experimentally in the same manner as above by using the structure
shown in FIG. 18. As a result, deposits were not adhered on the
upper surface of the susceptor and the upper portion for the side
of the susceptor in contact with the sample table. However, it was
found that when the susceptor was attached and detached repeatedly,
the deposits could not be removed sufficiently even under the same
condition. Further, it was found that when the deposits were not
removed completely, the deposits were deposited with a localized
distribution and, the deposits tended to remain on the surface of
the susceptor particularly.
[0104] The reason why the deposits were deposited with the
localized distribution and the deposits could not be removed
sufficiently was estimated as below. That is, since the susceptor
is made of alumina, the thickness is 4 mm, and the dielectric
constant is about 8, it corresponds to about 0.5 mm when converted
as an air layer. Assuming the gap as 0.1 mm between the susceptor
and the sample table for example, the thickness of the dielectric
material forming the capacitor C in FIG. 15 is a total of 0.5 mm
for the susceptor and 0.1 mm for the gap, which varies in the range
from 0.5 to 0.6 mm (20%). The variation causes localization of the
RF voltage generated on the surface of the susceptor to cause
localization in the removal of the deposits. However, it is
difficult and not practical to manufacture the susceptor and the
sample table such that they are in close contact with an accuracy
of the gap of 0.1 mm or less.
[0105] In order to overcome the problem, as shown in FIG. 19, a
flame sprayed metal film 39 was formed by flame spraying a metal
film to the lower surface of a susceptor 34. Tungsten was used for
the flame sprayed metal because it was known that tungsten has good
bondability with alumina. The metal film is not necessarily
tungsten so long as the film has an electroconductivity and good
bondability with the susceptor, and gold, silver, aluminum or
copper may also be used. Further, the preparation method for the
metal film is not necessarily restricted to the flame spraying but
any of methods capable of forming a thin film such as plating,
sputtering, vapor deposition, printing, coating and adhesion of
thin film may also be used. When this structure is adopted, since
the same voltage as that for the sample table is generated for the
entire metal film so long as the metal film and the sample table 5
are in contact with each other at one position, the problem caused
by the gap between the susceptor and the sample table can be
avoided.
[0106] As a result of examining the adhesion state of the deposits
by an experiment using the apparatus of the constitution shown in
FIG. 19, adhesion of deposits in the deposition restriction region
for the deposits shown by arrows could be eliminated with good
reproducibility. The advantage of this method is that the same
voltage as that for the sample table 5 is generated over the entire
metal film so long as the metal film and the sample table are in
contact with each other even at least at one point to generate a
uniform RF voltage on the surface of the susceptor 34. Accordingly,
as shown in FIG. 20, even in a state where other structures such as
the insulation cover 37 are present, a uniform RF voltage can be
generated on the surface of the susceptor for any range by
extending the flame spraying range of the flame sprayed metal film.
In the constitution in FIG. 20, it was experimentally confirmed
that adhesion of the deposits could be eliminated with good
reproducibility in the deposition restriction region for deposits
shown by arrows.
[0107] From the results described above, it has been found that the
RF voltage can be generated uniformly on the surface of the
susceptor to make the restriction for the adhesion of the deposits
uniform by using the metal film as formed by flame spraying. By the
use of the technique, also in a case where the thickness of the
susceptor has to be increased in view of the structure, the same
effect can be obtained by embedding the metal film in the
susceptor. FIGS. 21 and 22 show the structure.
[0108] As shown in the drawings, a flame sprayed metal film 39 is
embedded at a position of a predetermined depth from the surface of
the susceptor 34 (about 4 mm in the drawing), a contact is led from
the flame sprayed metal film 39 to the sample table 5 to ensure the
electric conduction, and the same RF voltage as that for the sample
table 5 is generated to the flame sprayed metal film 39.
[0109] The sample table for placing the sample 13 can include, in
addition to those types of forming electrostatic attraction film on
the metal sample table, for example, by flame spraying, those types
of embedding a metal electrode into the sample table made of
ceramic dielectrics such as aluminum nitride or alumina, and
conducting electrostatic attraction or applying RF bias by the
metal electrode. Also in the case of the substrate of this type, it
is possible to manufacture a susceptor having the quite same
function by forming the metal film to the susceptor.
[0110] FIGS. 23 and 24 show the example described above. FIG. 23
show a case of forming a metal film to the rear face of the
susceptor 34. An electrostatically attracting and RF bias applying
electrode 40 made of tungsten is embedded in the sample table 5
made of aluminum nitride. A conduction patterns (flange conduction
patterns 41, 42, 43) are embedded from the electrode to the flame
sprayed metal film 39 to make electric conduction between the
electrode 40 and the flame sprayed film 39. This can generate the
same RF voltage as that for the tungsten electrode to the flame
sprayed metal film 39 at the rear face of the susceptor. Naturally,
the deposition restriction performance of the deposits to the
surface of the susceptor by the structure is the quite same as that
described previously.
[0111] FIG. 24 is an example of embedding a flame sprayed metal
film 39 in the inside of a susceptor 34, in which quite the same
effect can be provided in function as in the embodiment of FIG. 23
by extending the conduction patterns described for FIG. 23 (flange
conduction patterns 41, 42, 43) and connecting the electrode 40
embedded in the sample table 5 to the flame sprayed metal film 39
embedded in the susceptor 34 by contact.
[0112] In the case of the placing electrode 5 shown in FIG. 23 or
FIG. 24, it is necessary to prepare a pattern for supplying radio
frequency waves from the electrostatically attracting and RF bias
applying electrode 40 embedded in the electrode 5 to the flame
sprayed metal film 39, and FIG. 25 shows such an example.
[0113] In FIG. 25, a flange conduction pattern 41 in parallel with
the electrostatically attracting and RF bias applying electrode 40
made of tungsten is formed by embedding a tungsten thin film like
the tungsten electrode in the placing electrode. The embedded
tungsten thin films can be connected with each other by a method of
extending through a hole at a necessary portion after forming the
placing electrode and brazing a perforation terminal.
[0114] With the bias application method to the susceptor described
so far, adhesion of deposits on the upper surface of the susceptor
are just suppressed when the RF voltage for the sample table is at
a certain value (400 V in this embodiment). However, if the voltage
for the sample table is higher, the RF voltage on the surface of
the susceptor is increased excessively to result in a problem that
susceptor is scraped to shorten the part life. This drawback can be
overcome as shown in FIG. 26 by using means for controlling the RF
bias voltage applied to the surface of the susceptor from the
outside. FIG. 26 shows a circuit for controlling the voltage for
the susceptor metal film by a variable capacitor VC attached
externally. FIG. 27 is an actual structure thereof.
[0115] A ceramic cover 50 is formed, for example, by flame spraying
on the surface of the sample table at a portion in contact with the
susceptor such that the susceptor flame sprayed metal film 51 and
the sample table 5 are not in direct contact with each other. The
ceramic cover 50 has a function of forming a capacitor C' shown in
FIG. 26 and transmitting a portion of the RF voltage applied to the
sample table 5 to the susceptor flame sprayed metal film 51. Then,
the RF voltage applied to the sample table 5 is transmitted to the
susceptor flame sprayed metal film 51 by another external variable
capacitor VC. Since the RF voltages transmitted by the two
capacitors are at the same phase, they are simply added, and an RF
voltage generated on the surface of the susceptor is determined
depending on the voltage. For example, assuming the susceptor
thickness as 4 mm, the surface area of the susceptor flame sprayed
metal film as 400 cm.sup.2, the thickness of the ceramic cover made
of alumina as 300 .mu.m and the maximum capacitance of the variable
capacitor VC as 8000 pF, the voltage on the surface of the
susceptor is variable within a range from about 30 to 100 V by
varying the capacitance of the variable capacitor VC at a bias RF
voltage of the sample table of 400 V. As described above, proper
selection of the susceptor thickness, the ceramic cover, the
surface area of the flame sprayed metal film and the variable
capacitor VC allows to control the RF voltage generated on the
surface of the susceptor. Further, although not illustrated, the
susceptor flame sprayed metal film may also be incorporated in the
inside of the susceptor so long as this can be connected with the
variable capacitor VC.
[0116] It is also possible to make the bias voltage applied to the
susceptor variable also by using a separate RF power source from
the RF power source for supplying an RF power to the sample table,
which is shown in FIG. 28. In this embodiment, a susceptor bias
power source 11a for supplying the RF power to the susceptor metal
film is used separately from the substrate bias power source 11 for
supplying bias to the sample table. FIG. 29 shows an electrode
structure in this case. It is important that insulation and
grounding shield (grounding base 36) are incorporated between the
sample table 5 and the susceptor flame sprayed metal film 51 such
that the RF voltage applied to the susceptor flame sprayed metal
film 51 undergoes no effect by the RF voltage. With this
constitution, although there is a drawback of requiring the
susceptor bias power source 11a, the bias applied to the susceptor
can be controlled quite independently of the RF voltage applied to
the sample 13. Further, the susceptor flame sprayed metal film 51
in this embodiment can be incorporated into the inside of the
susceptor although not illustrated so long as it can be connected
with the susceptor bias power source 11a.
[0117] FIG. 30 is a graph for explaining the method of optimizing
the susceptor bias voltage. Like FSV described previously, there
also exists an optimal value for the susceptor bias voltage. The
voltage is influenced by the frequency of the bias power source,
material and the thickness of the susceptor, plasma density, plasma
composition, constitution for the entire vacuum reactor, and the
material, processing rate and processing area of the sample.
Accordingly, the optimal voltage of the susceptor bias voltage has
to be changed for every process. Similarly to the embodiment in
FIG. 3, light emission from the susceptor material is increased as
the susceptor bias voltage is higher at a certain value of the
susceptor bias voltage (point b in FIG. 3) as a boundary. It shows
that the susceptor bias voltage at the point b or lower is
associated with the state where deposits are deposited on the
susceptor, while the susceptor bias voltage at the point b or
higher is associated with the state where the deposits are
sputtered and not deposited, as well as the susceptor material
itself is sputtered.
[0118] While the optimal voltage for the susceptor bias voltage is
at the point b, a point a is sometimes determined as the optimal
value depending on the process. For example, this corresponds to a
case in which processing reaction for the workpiece or reaction in
the gas phase is made different from intended conditions by the
release of the material into the gas phase by the sputtering to the
material for the susceptor, and the aimed process can not be
executed. That is, by setting the susceptor bias voltage to the
point a, deposition of deposits is allowed, though slightly, to the
susceptor material, by which the susceptor material is not
sputtered at all. This can prevent process troubles caused by the
release of the susceptor material. Instead, it is necessary to
conduct cleaning for the susceptor by a process used exclusively
for cleaning (in which the susceptor bias voltage is set higher
than the point b) before substantial deposition of deposits on the
susceptor.
[0119] On the contrary, aimed process can not sometimes be
conducted stably when deposits are deposited, if little, on the
susceptor due to the reason such as generation of obstacles or the
like. In this case, the optimal susceptor bias voltage is set to
the point c, and the condition can be set such that the susceptor
may be scraped to some extent but the reaction products are not
deposited at all. In this case, it results in a drawback that the
susceptor is consumed greatly but can provide an advantage that
cleaning for the susceptor can be decreased.
[0120] On the contrary, there is a case where aimed process can not
be conducted stably when the deposits are adhered, even little, on
the susceptor by the reason such as occurrence of obstacles and the
like. In this case, it is possible to set the optimal point of the
susceptor bias voltage to point c and set to such conditions that
the susceptor may be allowed to be scraped somewhat but deposits
are not deposited at all. In this case, a drawback of increasing
the susceptor consumption is present but it can provide a merit
capable of reducing susceptor cleaning.
[0121] The susceptor bias voltage is set to the point b in a case
neither the scraping of the susceptor nor the adhesion of the
reaction products is desirable. In this case, it is important to
improve the reproducibility for the bias setting voltage of the
susceptor. This is because change with lapse of time has to be
suppressed in a case of conducting the same process in different
apparatus or conducting the same process continuously even in the
same apparatus. For this purpose, feedback control for the
susceptor bias voltage is important.
[0122] FIGS. 31 and 32 show susceptor bias application circuits
each with a feed back control circuit corresponding, respectively,
to FIGS. 26 to 28. In both of the circuits, the voltage for the
susceptor flame sprayed metal film is detected by way of an
attenuator and filter 52 and then converted into a dc voltage.
Thus, a DC voltage signal is in proportion to the susceptor bias
voltage. The signal is compared with a preset value set by the
recipe of the main body apparatus control section 57 or the setting
value to control a motor for rotating a variable capacitor VC that
determines the susceptor bias voltage in the case of FIG. 31.
Further, the output of the susceptor bias power source 11a is
controlled in the case of FIG. 32. By using the method, the
susceptor bias voltage can be controlled to a value set in the main
body apparatus, and the value of the susceptor bias voltage can be
controlled at a constant level in a case of processing by the same
process in different apparatus or in the same apparatus
continuously, to suppress the difference between the apparatuses
and the change with time.
[0123] Methods and structures for the region to control such that
the deposits are not deposited or adhered, that is, the bell jar
12, the gas blowing port 23 and the susceptor 34 have been
described above. So long as the reaction products from the sample
13 or the materials synthesized in the gas phase are volatile
ingredient of high vapor pressure, the materials are exhausted by
the exhaustion device from the discharging portion or the periphery
of the materials to be processed and most of them are exhausted
although deposited to some extant to a lower portion of the
electrode or the exhaustion dust.
[0124] However, when highly depositing materials, that is,
materials having a low vapor pressure and adhesion coefficient to
solid of about 1 (almost captured when in contact with solid) are
formed as reaction products from the sample or synthesized in the
gas phase, the materials are deposited on the bell jar, susceptor
disposed at the periphery of the sample or vacuum reactor wall
including the gas blowing port and are scarcely exhausted.
[0125] In the situation described above, when it is controlled such
that the deposits are not adhered to any portion in the vacuum
reactor, such highly depositing materials have no place for
deposition. Accordingly, the density of the highly depositing
material in the gas phase is increased to increase depositing
motive force and, as a result, they are compulsorily deposited on
the bell jar or the susceptor.
[0126] That is, such control not to adhere the deposits on the bell
jar or the susceptor can be attained by providing a place for
depositing the great amount of deposits. Then, by increasing the
amount of the deposits that can be deposited, or rapidly depositing
them from the gas phase, performance for controlling the amount of
deposits on the bell jar or the susceptor can be enhanced.
[0127] That is, it is necessary to provide a region for depositing
deposits rapidly and in a great amount from the gas phase
(deposition trap region) near the periphery of the workpiece where
highly depositing reaction products are formed, or periphery of
plasma regions. The deposition preventive plate functions as a
cover for suppressing the adhesion of deposits to the gas blowing
port, since it is premise that deposits are deposited to the
preventive plate itself, this is also a sort of traps.
[0128] FIG. 33 shows the inside of a vacuum reactor being divided
into regions including deposits trap. At first, the bell jar region
and the wafer (sample)/susceptor region are regions controlled so
as not to adhere deposits. All other regions in contact with the
plasmas are deposition trap regions, in which deposition trap
region {circle over (1)} is a region including the deposition
preventive plate and a lower portion of the gar ring. The region
{circle over (1)} can be directly observed (viewed) from the wafer.
The bell jar region, the wafer/susceptor region and the deposition
trap region {circle over (1)} constitute all the region that can be
observed (viewed) directly from the wafer, which are regions for
generating plasmas and also regions where or highly depositing
materials formed from the wafer in plasma gas phase are most likely
to adhere. When the deposits are deposited in the regions under not
controlled state, they cause obstacles to the wafer or vary the
plasmas with time. Accordingly, in the region that can be observed
directly from the wafer, adhesion of the deposits have to be
controlled as completely as possible.
[0129] In accordance with the invention, in a case of using the
structure shown in FIGS. 12 and 13 for the deposition preventive
plate, 100% of the regions that can be observed from the wafer are
in the deposition-controlled state. Further, also in a case of
using the structures shown in FIG. 6, FIG. 9, FIG. 11, it is
necessary that 90% or more of the surface area of the regions that
can be observed from the wafer is in the deposition-controlled
state.
[0130] Further, since the suppressing function of the bell jar
region or the wafer/susceptor region can be enhanced when the
deposition trap region provides a sufficient function as described
above, it is preferred that the surface areas for the bell jar
region and the susceptor region are as small as possible and the
surface area for the deposition trap region {circle over (1)} is as
large as possible. In a case where highly depositing reaction
products are formed from the wafer, it has been found by the
experiment conducted by the inventors that the deposition
suppressing function in the bell jar region and the wafer/susceptor
region is lowered when the surface area S1 for the deposition trap
region {circle over (1)} is defined as: S1<0.55 SW (where SW is
a wafer surface area). Accordingly, to rapidly deposit the reaction
products to the deposition trap, a relation is defined as:
S1.gtoreq.0.5 S1 and, preferably, as: S1.gtoreq.S1.
[0131] The deposition trap region {circle over (2)} is referred to
as a ring cover which is present below the deposition trap region
{circle over (1)}. While the region can not be observed directly
from the wafer, highly depositing materials are transported through
diffusion and a great amount of deposits are adhered on the upper
surface thereof. The deposition trap region {circle over (3)} is a
side cover for the electrode which can neither be observed directly
from the wafer, but a great amount of deposits are adhered to the
upper portion thereof like the deposition trap region {circle over
(2)}. Since the deposition trap regions {circle over (2)} and
{circle over (3)} are not directly observed from the wafer, there
is less possibility that the deposits adhered thereto form
obstacles to the wafer or cause change with time of plasmas.
However, the deposition traps are important in order to conduct
cleaning operation efficiently when the apparatus is opened to
atmospheric air. That is, since the reaction products are highly
depositing, 90% or more of them can be adhered and recovered in the
deposition trap regions {circle over (1)}, {circle over (2)} and
{circle over (3)}. Accordingly, the inside of the vacuum reactor
can be cleaned efficiently by arranging the deposition trap regions
{circle over (1)}, {circle over (2)} and {circle over (3)} each
into a swap kit (made exchangeable) and entirely replacing them
with already cleaned parts after opening to the atmospheric air.
For this purpose, there are two necessary conditions that the
deposit trap is light in weight and easy to be detached/attached.
To make the weight of the trap reduced, it is important that the
material for the deposition trap is made of a light weight
material, for example, aluminum
[0132] After opening to an atmospheric air, the deposition traps
are detached successively in the order of {circle over (1)},
{circle over (2)} and {circle over (3)} from the vacuum reactor and
a minimal required cleaning operation is conducted. The minimal
required cleaning place is, for example, the periphery of the
opening for wafer transportation. Then, swap kits for deposition
traps after cleaning are attached in the order opposite to the
above and the evacuation can be conducted immediately. As a result,
the cleaning operation can be performed at a minimal time. The
cleaning operation in the procedures described above can not only
shorten the cleaning time but also shorten the time required for
evacuation. This is because moistures in the atmospheric air
adsorbed to parts in the non-vacuum state can be minimized by
opening the reactor to the atmospheric air only for the minimal
required time, and the amount of the solvent remaining in the
vacuum reactor can be minimized by using a cleaning solvent (pure
water or alcohol) by a minimal required amount. After cleaning, the
detached deposition traps {circle over (1)}, {circle over (2)} and
{circle over (3)} are cleaned and then utilized again as the swap
kits for atmospheric opening/cleaning operation in the next time.
The regions to be arranged into the swap kits as the deposition
traps are not necessarily be restricted only to the regions shown
in FIG. 33. While differing depending on the process or the
material to be handled, it is effective to make the entire regions
to be adhered with deposits as the deposition traps. For example,
in a case where deposits are adhered only in one-half or more of
the region for the electrode cover, the upper-half of the electrode
cover is arranged into the swap kit. On the contrary, under the
conditions where the deposits are adhered as far as the exhaustion
duct, it is effective to also arrange the inner wall of the
exhaustion duct as the deposition trap region and arrange the same
into the swap kit.
[0133] As has been described above according to the present
invention, since the deposited films deposited on the inner wall of
the vacuum reactor are controlled, it can provide a plasma
processing apparatus and a plasma processing method of satisfactory
mass production stability.
[0134] While the invention has been described in its preferred
embodiments, it is to be understood that the words which have been
used are words of description rather than limitation and that
changes within the purview of the appended claims may be made
without departing from the true scope and spirit of the invention
in its broader aspects.
* * * * *