U.S. patent application number 12/230565 was filed with the patent office on 2009-01-08 for plasma processing apparatus and a plasma processing method.
Invention is credited to Tetsunori Kaji, Toshio Masuda, Kazue Takahashi, Ken'etsu Yokogawa.
Application Number | 20090008363 12/230565 |
Document ID | / |
Family ID | 17746569 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090008363 |
Kind Code |
A1 |
Takahashi; Kazue ; et
al. |
January 8, 2009 |
Plasma processing apparatus and a plasma processing method
Abstract
In an oxide film etching process, a plasma having a suitable
ratio of CF.sub.3, CF.sub.2, CF, and F is necessary, and there is a
problem in that the etching characteristic fluctuates in accordance
with a temperature fluctuation of the etching chamber. Using a UHF
type ECR plasma etching apparatus having a low electron
temperature, a suitable dissociation can be obtained, and by
maintaining the temperature of a side wall of the etching chamber
in a range from 10.degree. C. and 120.degree. C., a stable etching
characteristic can be obtained. Since oxide film etching using a
low electron temperature and a high density plasma can be obtained,
an etching result having a superior characteristic can be obtained,
and, also, since the side wall temperature adjustment range is low,
a simplified apparatus structure and a heat resistant performance
countermeasure can be obtained easily.
Inventors: |
Takahashi; Kazue;
(Kudamatsu-shi, JP) ; Masuda; Toshio; (Toride-shi,
JP) ; Kaji; Tetsunori; (Tokuyama-shi, JP) ;
Yokogawa; Ken'etsu; (Tsurugashima-shi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
17746569 |
Appl. No.: |
12/230565 |
Filed: |
September 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11348300 |
Feb 7, 2006 |
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12230565 |
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09414520 |
Oct 8, 1999 |
7048869 |
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11348300 |
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Current U.S.
Class: |
216/69 ; 216/67;
257/E21.252 |
Current CPC
Class: |
H01L 21/31116 20130101;
H01J 37/32522 20130101; H01J 37/32192 20130101; H01J 37/32678
20130101 |
Class at
Publication: |
216/69 ;
216/67 |
International
Class: |
C23F 1/02 20060101
C23F001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 1998 |
JP |
10-289696 |
Claims
1. A plasma processing method of using a plasma processing
apparatus comprising a vacuum processing chamber, a sample table
for mounting a sample which is processed in said vacuum processing
chamber, a temperature adjustment side wall of said vacuum
processing chamber and a plasma generation means for generating a
plasma according to introduction of a gas which contains at least
carbon and fluorine, thereby forming a gas species which contains
carbon and fluorine by plasma dissociation and a plasma processing
is carried out using said plasma, the plasma processing method
comprising the steps of: generating a plasma which contains the
formed gas species, of a reduced amount of F and a greater amount
of CF.sub.3, CF.sub.2 or CF as a ratio of the gas species, by
controlling the electron temperature of said plasma generated to a
range of from 0.25 eV to 1 eV, so as to perform an etching with an
etching characteristic of a predetermined selection ratio and a
predetermined etching speed, etching said sample having an
insulating film as a film to be processed, using said plasma, and
controlling a temperature of said temperature adjustment side wall
to a range of 10.degree. C. to 120.degree. C., thereby adhering
deposits to the temperature adjustment side wall and controlling
the amount of the gas released from the deposits so as to restrain
a time lapse change of the etching characteristic.
2. A plasma processing method according to claim 1, wherein said
plasma generation means is an electron cyclotron resonance system
using a microwave at a frequency of from 300 MHz to 1 GHz.
3. A plasma processing method according to claim 2, wherein a
temperature-adjusted coolant medium is used as a means for
controlling the temperature of said temperature of said temperature
adjustment side wall so as to establish restraint of the time lapse
change.
4. A plasma processing method according to claim 3, wherein the
temperature of said temperature adjustment side wall is controlled
to a range of 30.degree. C. to 50.degree. C.
5. A plasma processing method according to claim 1, wherein a
temperature-adjusted coolant medium is used as a means for
controlling the temperature of said temperature adjustment side
wall so as to establish restraint of the time lapse change.
6. A plasma processing method according to claim 1, wherein the
temperature of said temperature adjustment side wall is controlled
to a range of 30.degree. C. to 50.degree. C. so as to establish
restraint of the time lapse change.
7. A plasma processing method according to claim 1, wherein said
temperature of said temperature adjustment side wall is controlled
so as to restrain a time lapse change of the amount of the gas
released from the deposits.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation application of
application Ser. No. 11/348,300, filed Feb. 7, 2006, which is a
Continuation application of application Ser. No. 09/414,520, filed
Oct. 8, 1999, the contents of which are incorporated herein by
reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus and a plasma processing method and in particularly to an
apparatus for etching an insulation film such as a silicon oxide
film of a wafer using a plasma and relates to a plasma etching
apparatus and a plasma etching method having a plasma generation
source which can be corresponded to a minute practicing of an
etching pattern and further enable for maintaining a stable etching
characteristic during a long period.
[0003] Among conventional plasma processing apparatuses, an oxide
film plasma etching apparatus is exemplified and techniques and
problems of this apparatus are shown. As the conventional plasma
source of an oxide film use etching apparatus, a type which is used
most widely is a narrow electrode type high frequency plasma
generation apparatus which is comprised of a pair of opposing
electrodes.
[0004] The systems of the narrow electrode type high frequency
plasma generation apparatus have known that 25 there is a system in
which a high frequency having from 13.56 MHZ to a several 10 MHZ
degree is applied to one electrode and to another electrode by
mounting a wafer a high frequency bias of about 1 MHZ is applied
separately to the electrode on which a wafer is mounted, and there
is another system in which a high frequency is applied to the pair
of electrodes.
[0005] In this narrow electrode type of plasma source etching
apparatus, since the distance between the electrodes is narrow, for
example, from 20 mm to 30 mm, it is known as a narrow electrode
type plasma source and a parallel flat plate type plasma source.
Further, in the narrow electrode type plasma source, it is
difficult to generate a plasma in a region where the pressure is
low, however, by the addition of a magnetic field, an apparatus is
obtained in which a lowering of the discharge pressure can be
achieved.
[0006] In addition to the above-stated narrow electrode type of
apparatus, other plasma etching apparatuses have been known. These
apparatuses include a plasma etching apparatus having an induction
type plasma source in which an induction coil is used and another
plasma etching apparatus in which a plasma etching microwave is
introduced. In these apparatuses having an induction type etching
source and a microwave type plasma source, it is possible to
generate and maintain the plasma under a low pressure; and, since
the plasma density is high, such a plasma source is known as a low
pressure and a high density plasma source.
[0007] In silicon oxide film etching, as an etching gas, a mixture
gas, in which argon (Ar), a gas including carbon (C) and fluorine
(F), such as C.sub.4F.sub.8, and a gas including hydrogen (H), such
as CHF.sub.3, are mixed, is used; and, further, another mixture
gas, in which oxygen (O.sub.2) and carbon monoxide (CO) and
hydrogen (H.sub.2) etc. are added to the above-stated mixture gas,
is used. These gases are dissociated by the plasma and are
dissolved to form CF.sub.3, CF.sub.2, CF, and F. The amount and the
ratio of this gas molecule species exerts a large influence on the
etching characteristic of the silicon oxide film (hereinafter, it
will be referred to merely as an "oxide film").
[0008] In particular, in the case of a high density plasma source,
since the electron temperature in the plasma is high, plasma
dissociation progresses, and the plasma comes to have many fluorine
gas molecules F. Further, as the ionization progresses, the ratio
of neutral gas molecule species (radicals) becomes low. For these
reasons, in oxide film etching with a high electron temperature and
a high density plasma, since the amount of CFx (CF.sub.3, CF.sub.2,
CF) which adheres to a silicon surface, which is a foundation of
the oxide film, is lowered, there are problems in that the
etching-speed of the silicon (Si) is large and the selection ratio
is small.
[0009] As means for solving the above stated problems, a method for
increasing the CFx radical amount in the plasma has been known, in
which the temperature of the wall face of the etching chamber is
raised to about 200.degree. C., in an effort to discharge the
deposition film which has adhered to the wall face by reducing the
adhesion of the deposition film to the wall face of the etching
chamber. As a result, in an apparatus in which a high density
plasma is used, to obtain the desired selection ratio, a high
temperature performance of the wall face of the etching chamber
becomes indispensable.
[0010] An oxide film etching apparatus described in Japanese
application patent laid-open publication No. Hei 7-183283 is an
example of an apparatus in which a wall face of an etching chamber
is formed to have a high temperature performance.
[0011] As a countermeasure for obtaining the high selection ratio
in addition to the above technique, there is a known method in
which the electron temperature in the plasma is lowered and plasma
dissociation is restrained. More specifically, in this method the
plasma application is carried out intermittently, and so this
method is called a pulse plasma method.
[0012] As another one example of obtaining a high selection ratio,
there is a method in which materials for consuming fluorine (F) are
installed in an etching 25, chamber in advance. In Japanese
application patent laid-open publication No. Hei 9-283494, such a
method is described, in which a side wall of an etching chamber is
constituted by silicon (Si), and a heating means for heating the
side wall and a bias application means are provided, so that the
fluorine (F) in the plasma is consumed.
[0013] In oxide film etching in which narrow electrode type of
plasma generation is used, in correspondence with the fine
patterning in which a device pattern size is less than 0.25 .mu.m,
it is necessary to make the scattering of the ion incident angle at
a portion to be subjected to the etching extremely small. Since the
scattering of the ion incident angle causes an abnormality of the
etching shape and a decrease in the number of ions reaching the
bottom of a deep hole, problems are caused including a lowering of
the etching speed and a premature stopping of the etching in the
formation of holes. This scattering of the ion incident angle is
caused by the incident angle distribution having a spread angle
because the ions collide with radicals in the plasma.
[0014] To solve the above-stated problems, it is effective to
decrease the number of collisions between ions and radicals; more
particularly, it is necessary to lower the pressure. As a result,
in the narrow electrode type of plasma generation apparatus,
because it is difficult to carry out the plasma discharge under low
pressure conditions, even under a low pressure sufficient to
generate a plasma, it is proposed that the frequency of the plasma
generation source be made high and that a magnetic field be
applied.
[0015] Further, in the narrow electrode type of plasma source in
which the distance between the electrodes is narrow, in a case
where a low pressure is used, since the average free path distance
of the gas molecules becomes long, the collision frequency of the
gas molecules is decreased, and, in place of this, the collision
between the gas molecules and the electrode becomes dominant.
[0016] This is not a preferable condition, since, in the etching
apparatus, according to the collision of the gas molecules in the
plasma, it is necessary to control the maintenance and the reaction
of the plasma; and, as a result, in order to accommodate a low
pressurization, it is necessary to provide a large electrode
interval.
[0017] When the electrode interval is wide, the surface area of the
side wall in the etching chamber becomes large. Here, the surface
of the etching chamber is the surface which is subjected to the
plasma, and the surface does not include a surface of the top plate
(ceiling), a surface of the floor, and a surface of the electrode
(the wafer).
[0018] Until now, in the narrow electrode type plasma source, from
the aspect of the plasma and a wafer, since the side wall area is
narrow, the deposition and the gas discharge at the side wall have
almost no influence on the etching characteristic; however, in the
narrow electrode type plasma apparatus in which a low
pressurization is used, it is necessary to take a new
countermeasure.
[0019] Further, to accommodate a large diameter wafer, it is
necessary to make the gas pressure distribution across the wafer
face and the reaction product distribution uniform; and, for this
purpose, it is necessary to provide a wide electrode interval, and
so the area ratio of the side wall becomes more and more
important.
[0020] The influence of the affects of the reaction products which
adhere to the side wall on the etching characteristic is discussed
above, however, when the etching is continued over a long period of
time, a change of the influence becomes a problem. For example, by
repeatedly carrying out etching operation, the temperature of the
side wall will rise gradually. When the temperature of the side
wall has risen sufficiently, the characteristic of the adhesion and
adsorption of the reaction products on the side wall is changed,
and, as a result, the etching characteristic fluctuates.
[0021] Further, in a case where the amount of the deposition film
on the side wall accompanying the etching is increased gradually,
in accordance with the dependence on the amount of the deposition
film, it is possible to change the desorption and adsorption
characteristic of the reaction products at the side wall
surface.
[0022] A phenomenon in which the etching characteristic is
influenced by the time lapse change stated above is known
particularly in the case of oxide film etching. As a result, the
temperature change of the side wall in the oxide film etching
apparatus represents an important problem.
[0023] In particular, in a high electron temperature and high
density plasma source, it is necessary to establish a high side
wall temperature. In the case of a high side. wall temperature,
even the side wall temperature fluctuates a little, and so the
adsorption and desorption characteristic of the deposition film is
changed largely. For these reasons, it is necessary to restrain the
side wall temperature fluctuation to a small range, and a high
accuracy temperature adjustment, such as 200.degree.
C..+-.2.degree. C. needs to be carried out.
[0024] As stated above, in any of the plasma sources, to satisfy
the requirement for oxide film etching, namely. for obtaining a
high etching speed, while attaining a high selection ratio, low
micro loading, and the passing-through of a deep hole, there still
remain problems to be solved.
[0025] The important problem in an oxide film etching apparatus
involves the dissociation of the gas molecules as the plasma is
being formed under the most suitable conditions for the etching of
the oxide film. To address this problem, a new plasma generation
source producing a high density plasma under a low electron
temperature has been proposed. For example, Japanese application
patent laid-open publication No. Hei 8-300039, discloses a UHF type
ECR apparatus having a plasma excitation frequency in the UHF band
from 300 MHZ to 1 GHz. The electron temperature of the plasma which
is excited in the frequency band in the above stated range is low,
for example, from 0.25 eV to 1 eV, and the plasma dissociation of
C.sub.4F.sub.8 is at a level suitable to oxide film etching.
Further, since it is an ECR.(Electron Cyclotron Resonance) system,
even under a low pressure, it is possible to generate a high
density plasma.
[0026] As stated above, for achieving fine patterning on a wafer of
large diameter, it is necessary to make the electron temperature
low and to prevent an excessive dissociation of the etching gas,
and further to make the plasma density high. Further, it is
necessary to make the plasma density, the gas pressure and the
reaction product distribution on the wafer uniform; and, as a
result, it is necessary to provide an apparatus in which the oxide
film etching characteristic is not changed over a long period of
operation.
SUMMARY OF THE INVENTION
[0027] It is an object of the present invention to provide a plasma
processing apparatus and a plasma processing method, wherein, using
a UHF type ECR plasma etching apparatus to generate a high density
plasma under a low electron temperature necessary for oxide film
etching etc., a premature stopping of the etching does not occur,
and in which a stable operation or a stable processing can be
carried out.
[0028] The characteristic feature according to the present
invention resides in a plasma processing apparatus and in a plasma
processing method using a vacuum processing chamber, a sample table
for mounting a sample which is processed in said vacuum processing
chamber, and a plasma generation means, wherein, when plasma
processing is carried out by generating a plasma by introduction of
a gas which contains at least carbon and fluorine into the
processing chamber, and by which a gas species is generated which
contains carbon and fluorine according to a plasma dissociation,
said plasma generation means being a plasma generation means in
which the degree of plasma dissociation is in a middle range and
said gas species containing carbon and fluorine is generated fully
in the plasma, and wherein the temperature of a region which forms
a side wall of said vacuum processing chamber is controlled to have
a range of 10.degree. C. to 120.degree. C.
[0029] In a UHF type ECR plasma etching apparatus having a UHF band
microwave radiation antenna disposed at a position opposite to the
wafer, an etching gas is supplied from a gas supply portion
provided on an antenna portion. The UHF band microwave is radiated
directly to the plasma from the antenna and is radiated in the
plasma through a dielectric body which is provided at a periphery
of the antenna.
[0030] In an electrode for mounting the wafer (a wafer mount
electrode or a lower electrode), an etching position and a wafer
delivery position are located at separate locations, and an
electrode raising and lowering function is provided. A distance
(called an "electrode interval") between the wafer mount electrode
and the antenna or the gas supply plate is established as 50 mm to
100 mm taking into consideration re-association of the reaction
products.
[0031] According to the plasma processing apparatus, a side wall
temperature at a periphery of the electrode is temperature adjusted
within a range of 10.degree. C. to 120.degree. C., preferably a
range of 30.degree. C. to 50.degree. C. As the side wall
temperature fluctuates, a gas species is discharged from a
deposition film on the side wall, and this has an influence on the
etching characteristic.
[0032] In accordance with the present invention, to restrain the
above-stated influence, the temperature control accuracy of the
side wall is controlled to .+-.5.degree. C. Since the side wall
temperature is low, even when the temperature of the side wall
fluctuates by 5.degree. C. degree, the fluctuation of a discharge
gas amount which is discharged from the side wall will be small, so
that the influence on the etching characteristic can be
neglected.
[0033] Further, since the plasma source is a UHF type ECR system,
the plasma dissociation is in a middle range and a CFx species
exists fully to a level necessary for the oxide film etching. Since
the problem of a shortage of CFx species and an excess F, which is
inherent in a high density plasma source, can be solved, to
increase the selection ratio, it is unnecessary to increase the
side wall temperature.
[0034] Herein, when the dissociation is excessive, F or C becomes
rich, and when the dissociation is insufficient, there is a
shortage of F, CF.sub.2, CF.sub.3, etc; accordingly, it is
desirable to have a plasma dissociation fall in middle range.
Further, since the side wall temperature is controlled to a low
temperature, with a side wall temperature control accuracy of
.+-.5.degree. C., the fluctuation of the etching characteristic can
be restrained for a long period of operation.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 is a schematic sectional diagram showing an etching
apparatus of a plasma processing system representing one embodiment
according to the present invention;
[0036] FIG. 2 is a graph showing a size relationship of various
kinds of plasma sources of a plasma processing apparatus and a
plasma processing method according to the present invention;
[0037] FIG. 3 is a graph showing a characteristic of a gas
discharge from a deposition film of a plasma source of a plasma
processing apparatus and a plasma processing method according to
the present invention;
[0038] FIG. 4 is a graph showing the influence of a side wall
temperature on a time lapse change of a plasma source of a plasma
processing apparatus and a plasma processing method according to
the present invention;
[0039] FIG. 5 is a graph showing an etching speed change in a case
where a temperature adjustment of a side wall is not performed;
and
[0040] FIG. 6 is a graph showing an etching speed change in a case
where a temperature adjustment of a side wall is performed
according to the present invention.
DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
[0041] Hereinafter, a plasma processing apparatus and a plasma
processing method representing one embodiment according to the
present invention will be explained.
[0042] FIG. 1 is an example of a UHF type ECR plasma etching
apparatus. At a peripheral portion of an etching chamber 1 (a
vacuum processing chamber), which is operated as a vacuum vessel, a
coil 2 is installed, and this coil 2 generates an electron
cyclotron resonance (ECR) field. An etching gas is supplied from a
gas supply pipe 3 and is introduced via a gas supply plate 4 to the
etching chamber 1. The gas supply plate 4 is comprised of a plate
made of silicon or a glass form carbon in which about 100 fine
holes having a diameter of from 0.4 mm to 0.5 mm degree are
provided.
[0043] At an upper portion of the gas supply plate 4, a disc-shaped
antenna 5 is provided, and this antenna 5 radiates microwave energy
in the UHF band. The microwave energy is supplied to the antenna 5
from a power supply 6 through an induction shaft 7. When the
microwave energy is radiated from a periphery of the antenna 5, an
oscillating electric field in a space above the antenna 5 is
introduced into the etching chamber 1 through a dielectric body 8.
Further, between the antenna 5 and an electrode 9, a volume
combination electric field is generated, and this electric field
becomes an effective plasma generation source. The frequency of the
microwave energy is set to a range of from 300 MHZ to 1 GHz and has
a band area in which the electron temperature of the plasma is a
low temperature of from 0.25 eV to 1 eV.
[0044] In this embodiment according to the present invention, a
frequency band in the vicinity of 450 MHZ can be employed. Further,
as the dielectric body 8, a quartz or an alumina material can be
employed. Further, a heat resistant polymer having a small
dielectric loss, such as a polyimide etc., can be employed as
well.
[0045] The electrode for mounting a wafer (the wafer mount
electrode or sample table) 9 is provided below the gas supply plate
4, and a wafer 10 representing a sample is supported on the sample
table through a electrostatic adsorption. To draw the ions in the
plasma to the wafer 10, a high frequency bias is applied to the
wafer mount electrode 9 from a high frequency power supply 11.
[0046] Further, the temperature control of an inner wall of the
etching chamber 1, representing the vacuum processing chamber,
which is an essential feature according to the present invention,
is carried out at a temperature adjustment side wall 12 of the
etching chamber 1. To the temperature adjustment side wall 12,
although not shown in the figure, a coolant medium which is
temperature controlled is introduced, so that the temperature
adjustment side wall 12 is maintained at a constant temperature. In
this embodiment according to the present invention, the constant
temperature in the temperature adjustment side wall 12 is set to
30.degree. C.
[0047] The etching gas and reaction products are deposited on the
inner wall of the etching chamber 1 and they are also deposited at
the periphery and in a downstream area of the wafer mount electrode
9, so that a deposition film is generated which is the origin of
the foreign matter in the etching chamber 1. Accordingly, it is
necessary to periodically remove the deposition film, however, it
is not always easy to remove a strongly adhered deposition film.
Herein, in this embodiment according to the present invention, the
cleaning of the deposition film is carried out using an exclusive
cleaning apparatus.
[0048] The time used for establishing a vacuum state by evacuation
of the etching chamber 1, which has been opened to the air for
cleaning, is important from an aspect of the non-operation time of
the apparatus and further from an aspect of an improvement of the
productivity of the apparatus. Accordingly, it is desirable to
prevent the deposition film from adhering on a portion where a
component exchange-over is not carried out easily, and to try to
provide the component to which the deposition film has adhered as a
component which can be easily replaced by another clean component.
In this way, the opening time for cleaning in the etching chamber 1
can be shortened, and a reduction of the cleaning and evacuation
time can be achieved.
[0049] In this embodiment according to the present invention, to
prevent the deposition film from-adhering to the downstream region
of the etching chamber 1, a deposition film cover 13 is provided in
the downstream region of the temperature adjustment side wall 12 of
the etching chamber 1. To the cover 13, a vacuum evacuation and
wafer delivery opening portion is provided. Since the deposition
film can be removed with this cover 13, the adhesion of the
deposition film in the downstream region of the temperature
adjustment side wall 12 can be reduced.
[0050] A vacuum chamber 15 is connected directly to the etching
chamber 1, and a turbo molecular pump 14 having an evacuation speed
of from 2000 L/s to 3000 L/s is installed in the vacuum chamber 15.
Further, although not shown in the figure, to an opening portion of
the turbo molecular pump 14, a vacuum evacuation speed adjustment
conductance valve 16 is installed, and this evacuation speed
adjustment conductance valve 16 is used for separating the turbo
molecular pump 14 during the chamber open time, or the evacuation
speed adjustment conductance valve 16 is used for not opening the
chamber to the air.
[0051] Next, an example of oxide film etching using the plasma
processing apparatus of this embodiment according to the present
invention will be explained.
[0052] To the etching chamber 1 which is evacuated to a high vacuum
condition, although not shown in the figure, the wafer 10 is
carried in from a transfer chamber by a transfer arm, and the wafer
10 is delivered onto the wafer mount electrode 9. The transfer arm
is then retracted, and, after a valve arranged between the etching
chamber 1 and a transfer chamber has been closed, the wafer mount
electrode 9 is raised to a position where the etching is to be
carried out. In the case of this embodiment according to the
present invention, the distance between the wafer 10 and the gas
introduction plate 4 (an electrode interval) is set to from 50 mm
to 100 mm.
[0053] As the etching gas, a mixture gas comprised of Ar, and
C.sub.4F.sub.8, and O.sub.2 is used, and the respective flow
amounts are 500 sccm, 10 sccm and 5 sccm. The pressure of the
etching gas is 2 Pa. The output of the UHF microwave power supply 6
is 1 kW, and the output of a bias power supply 11 to the wafer 10
is 600 W.
[0054] A current is applied to the coil 2 and a resonance magnetic
field having 0.016 T of UHF energy at 450 MHZ is generated between
the gas supply plate 4 and the wafer mount electrode 9 (namely the
wafer 10). Next, the microwave power supply 6 is operated. Due to
the electron cyclotron resonance phenomenon, a strong plasma is
generated in the ECR area having a resonance magnetic field
strength of 0.016 T.
[0055] To improve the uniformity of the etching characteristic, it
is necessary to ensure that the incident ion density on the surface
of the wafer 10 is uniform, and, when the ECR is positioned as
stated above and the shape of the ECR area is formed with a raised
portion extending toward the wafer 10, the required uniformity of
the ion current density can be attained.
[0056] After a spark of the plasma, not shown in-the figure, from a
direct current power supply which is connected directly in parallel
with the high frequency power supply 11, a high voltage is applied
to the wafer mount electrode 9, and then the wafer 10 is
electrostatically attracted to and held on the wafer mount
electrode 9.
[0057] At a rear face of the wafer 10, helium (He) gas is
introduced, and the temperature adjustment of the wafer 10 is
carried out between the wafer mounting face of the wafer mount
electrode 9, which is temperature controlled by a coolant medium,
and the wafer 10, through the helium (He) gas.
[0058] Next, the high frequency power supply 11 is operated, and a
high frequency bias is applied to the wafer mount electrode 9.
Accordingly, ions are incident vertically from the plasma onto the
wafer 10. In oxide film etching, it is necessary to carry out a
processing with high energy ions.
[0059] In this embodiment, according to the present invention, a
high frequency bias voltage Vpp (the voltage between the maximum
peak and the minimum peak) has a value of from 1000 V to 2000 V. In
response to the impact of high energy ions with the wafer surface,
the temperature of the wafer 10 rises. In oxide film etching, since
the selection ratio is high at higher temperature values, the
etching characteristic has a superior characteristic, and so the
wafer temperature is adjusted to a value of several 10.degree. C.
However, since it is necessary to carry out the processing with
high energy ions, the heat input amount to the wafer 10 is large,
and so the coolant medium temperature of the wafer mount electrode
9 is set in the vicinity of -20.degree. C.
[0060] At this time, when the bias voltage is applied to the wafer
10, the etching is started, and the etching is finished within a
predetermined etching time. Or, though not shown in the figure, by
monitoring the plasma luminescence strength change of the reaction
products and further judging the finish point of the etching, an
etching finish time can be determined, and, after a suitable over
etching has been performed, then the etching is finished. The
etching is completed at a time when the application of the high
frequency bias voltage is stopped. Simultaneously with this, the
supply of the etching gas is stopped.
[0061] However, it is necessary to provide a process in which the
electrostatically held wafer 10 is released from the wafer mount
electrode 9, and, for this purpose, an electric adsorption gas,
such as Ar etc., is supplied. By stopping the supply of the
electrostatic adsorption voltage, and then connecting the electric
supply line to an earth ground, while maintaining the discharge of
the microwave energy, an electric adsorption time of 10 seconds is
allocated. Accordingly, the electric charges on the wafer 10 are
adsorbed by the earth ground through the plasma, and, as a result,
the wafer 10 can be removed easily.
[0062] When the electric adsorption process is ended, the supply of
the electric adsorption gas is stopped, and also the supply of the
microwave energy is stopped. Further, the current supply to the
coil 2 is stopped. Further, the wafer mount electrode 9 is lowered
until the surface thereof reaches the wafer delivery position.
[0063] After that, for some time, the etching chamber 1 is
evacuated until high vacuum is achieved. At a time point when the
high vacuum state has been reached, the valve between the etching
chamber 1 and the transfer chamber is opened, the transfer arm is
inserted therein and then the waver 10 is carried out. In case
there is to be a next etching process, a new wafer is carried in
and the etching is performed again according to the above-stated
procedures.
[0064] In the above description, the representative flow of the
etching process was explained.
[0065] The electron temperature of the UHF band microwave ECR
plasma is in a range of from 0.25 eV to 1 eV and the dissociation
of C.sub.4F.sub.8, which is the etching gas, does not progress
much. The dissociation of C.sub.4F.sub.8 is a complicated process,
in which the gas species which contributes to the etching is first
dissociated from CF.sub.3 to CF.sub.2, then CF is generated, and
finally F is generated. As a result, the higher the electron
temperature, the more the plasma becomes rich in F.
[0066] As stated in the Background of the Invention, to ensure the
proper selection ratio in the oxide film etching, in the deposition
of a film on the foundation silicon, it is necessary to restrain
the etching according to the high incident ion energy. Namely,
since high energy ions are incident on the wafer, when there is no
deposition film, there is a possibility that the etching will
progress according to a physical sputter.
[0067] As a result, for the etching to progress, it is necessary to
supply high energy ions to the bottom of a hole, however to ensure
the required selection ratio, it is necessary to supply radicals
which form a deposition film. It is said that the radicals for
forming the deposition film are CF.sub.3 and CF.sub.2.
[0068] On the other hand, F radicals form SiF.sub.4 etc. and the
foundation silicon is caused to be etched. As a result, to perform
high selection ratio etching, it is necessary to make CF.sub.2/F
(CF.sub.2-F ratio) large. In the case of UHF band microwave ECR
plasma, since the electron temperature is low, the generation
amount of F is small, and a plasma having a plentiful amount of
CF.sub.3, CF.sub.2 and CF is formed.
[0069] Accordingly, as shown in the case of a high electron
temperature and a high density plasma, to supply CF.sub.2 and
CF.sub.3, which become insufficient due to the excessive progress
of the dissociation of the plasma, it is unnecessary to heat the
inner wall of the etching chamber 1 to more than 200.degree. C.
[0070] As the necessary points for achieving a fine processing
correspondence etching, the following points are stated, namely (1)
under a low electron temperature, the plasma dissociation is
restrained suitably and a plasma having a large CF.sub.2/CF
(CF.sub.2-CF ratio) is generated; (2) the discrepancy between a
90.degree. angle and the ion incident angle is restrained to a
small value and a tapering formation of the etching shape; and (3)
even when the etching is repeated many times, the fluctuation of
the etching characteristic is small.
[0071] In addition to the above, an item relating to the etching
characteristics is an important development problem, however, in
the present specification, such an item is not mentioned.
[0072] The above-stated item (1) for the necessary points for the
fine processing correspondence etching is solved by the use of the
UHF band microwave plasma etching apparatus according to the
present invention.
[0073] As to the above-stated item (2) for the necessary points for
the fine practicing correspondence etching, a main cause is that
the orbit of the ions is displaced with the collision of the ions
and a gas molecule in the vapor phase, and so it is effective to
lower the pressure to lessen the occurrence of such collisions.
Since the UHF band microwave plasma etching apparatus according to
the present invention cases electron cyclotron resonance, it is
possible to generate the plasma under a low pressure.
[0074] As to the above-stated item (3) for the necessary points for
the fine processing correspondence etching, it is necessary to
prevent fluctuation of the etching characteristic even when the
number of etching operations which are repeated is in the order of
several hundred; namely, it is necessary to restrain the time lapse
change. A main cause of the time lapse change is the time
fluctuation of the kinds of gas which are discharged from the
deposition film which adheres to the inner wall (the side wall, the
ceiling, etc) and the other components of the etching chamber 1.
More specifically, the temperature fluctuation of the members to be
subjected to the processing, such as the side wall, represents a
large cause of the problem.
[0075] As a countermeasure against the restraint of the time lapse
change, basically the apparatus is formed so as to prevent
fluctuation of the desorption and adsorption phenomenon of the
deposition film on the wall face using temperature control;
however, in various plasma generation systems, the wall face area
used to form the apparatus differs.
[0076] The relationship between the etching chamber height and the
side face area is shown in FIG. 2. In the narrow electrode plasma
type apparatus, the height of the etching chamber is low, and also
the area of the side wall face is narrow. On the other hand, in the
high density plasma apparatus, the height of the etching chamber
is-high, and also the area of the side wall face is wide.
[0077] In the UHF type ECR apparatus according to the present
invention, the height of the etching chamber (the electrode
interval) and the area of the side wall are positioned
intermediately relative to the other types of apparatus, and the
apparatus occupies a region which is suitable for oxide film
etching. Namely, according to the present invention, the height of
the etching chamber (the electrode interval) and the area of the
side wall has a middle value in the 30 mm -100 mm range of the
narrow electrode (about 30 mm) and the microwave ECR induction type
(more than 100 mm). The height of the etching chamber, namely the
electrode interval, is a distance of from 50 mm to 100 mm, and the
reaction products generated by the etching are re-dissociated and
re-incident on the wafer 10.
[0078] For the above stated reasons, the etching characteristic of
the oxide film is influenced, however, this is caused by making the
most suitable performance to the influence degree, such as the
re-dissociation and the incidence of the reaction products etc.
with the etching characteristic of the oxide film. Namely, in this
embodiment according to the present invention, the electrode
interval is set to a predetermined distance which is determined by
a relative relationship of the mean free ion path in the vicinity
at a pressure of 2 Pa.
[0079] Since the electrode interval is set to the above stated
distance, the pressure distribution on the face of the wafer 10 can
be made uniform. In a case where the wafer diameter is large,
such-as from 200 mm to 300 mm, the difference in pressure between
the center and the periphery of the wafer 10 can be small. Further,
since the conductance, which depends on the electrode interval, is
large, a high speed of evacuation of the chamber 1 to a high vacuum
can be attained, and, as a result, the time during which the
etching gas and the reaction products remain in the chamber.
[0080] In a case where the area of the side wall is further
widened, there is a possibility that the adhesion amount of the
deposition film becomes large, with the result that the degree of
influence on the etching characteristic becomes large. In an
apparatus for maintaining a high density plasma, according to the
requirements of the plasma generation method, it is necessary to
form the height of the etching chamber to fall in a range from 100
mm to 200 mm. Accordingly, the ratio of the area of the side wall
to the whole area of the etching chamber is high, and so the
influence on the fluctuation of the etching characteristic by the
etching gas and the deposition of the reaction products on the side
wall will be large.
[0081] As methods for restraining this influence, there are methods
in which the temperature fluctuation of the side wall is reduced or
the side wall is heated to a high temperature to prevent a
deposition film from adhering thereto.
[0082] Further, as stated above, in an apparatus using a high
density plasma source, since the electron temperature is high, an
F-rich plasma is generated. Therefore, to ensure a proper selection
ratio, it is necessary to reduce the gas species which adheres to
the side wall, or it is necessary to promote a gas discharge from
the deposition film. As a result, it is necessary to raise the side
wall to a high temperature.
[0083] For the above stated reasons, in a high electron temperature
and high density plasma etching apparatus, the side wall is heated
to 200.degree. C. degree and the temperature fluctuation is
maintained within a range of .+-.2.degree. C. However, it is
difficult technically to heat the side wall to a high temperature
of more than 200.degree. C., and it is also difficult technically
to restrain, with high accuracy, the temperature fluctuation to as
little as .+-.2.degree. C. Further, such a technique invites a
complicated structure for the apparatus and a problem in
reliability, as well as an increase in cost. Further, the side wall
comprises the entire inner wall of the etching chamber, and
includes the top plate and other portions which contact the
plasma.
[0084] In a portion where the deposition film adheres, but which is
not contacted directly by the plasma, since this portion has a
possibility for affecting the etching characteristic, it is
necessary to take such portion fully into consideration. Further,
in the apparatus according to the present invention, since the side
wall is from 5.0 mm to 100 mm, the downstream region therefore can
hardly comprise a region where the deposition film is adhered. As a
result, for oxide film plasma etching, it is desirable to provide
an apparatus in which fluctuation of the etching characteristic is
not generated, even when the temperature adjustment accuracy in the
control of the side wall temperature is mitigated.
[0085] In the UHF type ECR plasma apparatus according to the
present invention, it is unnecessary to increase the side wall
temperature to improve the selection ratio. There is the advantage
that the side wall temperature can be established from the view
point of the restraint of the time lapse change.
[0086] FIG. 3 shows the results in a case in which the temperature
of the deposition film was changed 1.degree. C., and the gas
discharge amounts from the deposition film were measured. It is
seen from these results that when the temperature of the deposition
film is high, a large amount of gas is discharged with a
temperature fluctuation of 1.degree. C. It is supposed that when
the gas which corresponds to the flow amount of 0.01 sccm by the
conversion calculation of the flow amount of the etching gas, there
is a possibility that the etching characteristic is influenced, and
the temperature adjustment range of the side wall temperature at
this time is shown on the right side in FIG. 3.
[0087] In the case of a wall temperature of 200.degree. C., when
the side wall is not controlled to .+-.2.degree. C., the
fluctuation of the gas discharge amount becomes less than 0.01
sccm. On the other hand, when the side wall temperature is
controlled to less than 120.degree. C., even the side wall
temperature changes cause a small change in the gas discharge
amount. Namely, it is understood that even when the control
accuracy of the side wall temperature .+-.5.degree. C. and
.+-.10.degree. C., the gas discharge for giving an influence to the
etching characteristic does not occur.
[0088] In the etching apparatus according to the present invention,
the side wall temperature is established within a range of from
10.degree. C. to 120.degree. C. Preferably, it is controlled from
the room temperature 20.degree. C. to 50.degree. C. With this
temperature range, since the etching chamber is not heated to a
high temperature, there is the advantage that the size of the
apparatus is small, and the materials used for the vacuum sealing
and materials having a different thermal expansion coefficient can
be used freely, and the temperature control can be performed
easily.
[0089] According to the present invention, system is provided in
which a coolant medium which is connected to the temperature
adjustment means is introduced to the side wall. By the employment
of such a system, the temperature control can be carried out to
less than .+-.10.degree. C.
[0090] Further, FIG. 3 shows the results in which the discharge
amounts from the deposition film were measured. When the side wall
temperature reaches a high temperature of more than 200.degree. C.,
since the adhesion amounts of the deposition film themselves become
small, in an apparatus having a high temperature control in which a
deposition film does not adhere, as shown in the example of FIG. 3,
substantial gas discharge amounts become small.
[0091] The stability of the gas discharge amounts and the magnitude
of the fluctuation amounts into which the consideration of the
adhesion amounts is taken are shown in FIG. 4. In FIG. 4, the
horizontal axis indicates the side wall temperature of the etching
chamber, and the vertical axis indicates the relative magnitude of
the deposition film amount, the degree of influence on the time
lapse change and the gas discharge amount.
[0092] The gas discharge amount from the deposition film increases
abruptly for side wall temperatures which exceed 200.degree. C. On
the other hand, the amount of the deposition film which adheres to
the side wall (the deposition speed) reduces gradually in
proportion to an increase in the temperature and decreases abruptly
for temperatures in excess of 200.degree. C. The reason for this is
that when the temperature exceeds 200.degree. C., and further when
the temperature exceeds 300.degree. C., the deposition film does
not adhere to the side wall.
[0093] Accordingly, in the temperature range of the AREA 1 in FIG.
4, since the side wall temperature is low, the influence for
referring to the etching characteristic to the deposition film of
the side wall is small. Further, in the AREA 3 in FIG. 4, since the
temperature is high, the gas discharge amount from the unit
deposition film is large, however a deposition film will hardly
adhere, and, as a result, the gas discharge amount is small and the
influence on the etching characteristic is small.
[0094] However, in the AREA 2 in FIG. 4, which represents an
intermediate temperature range between AREA 1 and AREA 3, the
deposition film is comparatively large and the gas discharge amount
is large, and, as a result, the temperature fluctuation of the side
wall has a large influence on the etching characteristic.
[0095] Taking into consideration the above-stated points, to
restrain the time lapse change, the side wall temperature is set to
the AREA 1 or the AREA 3. The temperature range of the AREA 1 is
less than 120.degree. C., and in the AREA 3, the temperature range
is more than 200.degree. C., while in the AREA 2 the temperature
range is from 120.degree. C. to 200.degree. C.
[0096] According to this embodiment of the present invention, the
temperature of the side wall is established in the temperature
range of the AREA 1 in FIG. 4. Further, from the above-described
principle, the side wall temperature may be established in the low
temperature range, however, taking into consideration the ease in
establishing the temperature and providing a coolant medium without
creating condensation, the lower limitation temperature is set to
10.degree. C.
[0097] FIG. 5 shows the etching speed fluctuation in a UHF type ECR
plasma etching apparatus in a case of using a mixture gas
containing Ar and C.sub.4F.sub.8, and in which continuous etching
is carried out. In this case, the temperature adjustment of the
side wall is not carried out, and so the temperature fluctuation
rises with the discharge time of the plasma to 60.degree. C. degree
from room temperature. The temperature fluctuation is
.+-.20.degree. C. The etching speed of the silicon nitride at the
etching starting time is high, as a result of the fluctuation of
the etching characteristic.
[0098] On the other hand, FIG. 6 shows the etching characteristic
in a case where the temperature adjustment of the side wall is
carried out. After the etching chamber is opened to the air and
evacuation of the chamber is carried out, but without covering the
inner portion of the etching chamber by the deposition film and
also the process for presenting the regular state, immediately
after the etching is started, the etching characteristic is stable
from the starting time of the etching, and the fluctuation after
that is not hardly in evidence. Further, the side wall temperature
fluctuation at this time is within .+-.5.degree. C.
[0099] As understood from the above-stated results, in a UHF type
ECR plasma etching apparatus, by performing a temperature
adjustment of the side wall, an extremely stable etching
characteristic can be obtained. Further, in this embodiment
according to the present invention, it is assumed that a UHF type
ECR plasma etching apparatus is used, however, when the plasma
source is-suited for the etching of an oxide film, it is not
limited to a UHF type ECR plasma etching apparatus. Namely, when
the electron temperature in the plasma is the low, for example, an
electron temperature of less than 1 eV, and when a high density
plasma is used, for example, it is possible to employ an apparatus
using a pulse plasma source in which the application of the
microwave is carried out intermittedly.
[0100] Further, it is possible to employ an apparatus using a
plasma source in which an induction type plasma, except for the
fact that the microwave is pulse driven. When the side wall of the
etching chamber of these plasma sources is established at a range
of 10.degree. C. to 120.degree. C., it is possible to obtain a
superior oxide film etching characteristic, and, further, it is
possible to exhibit a stable characteristic during a long period of
operation.
[0101] Further, the temperature adjustment of the side wall is
exemplified by using a coolant medium, however the invention is not
limited to the use of a coolant medium, since it can employ any one
of the various types of compulsory cooling using water cooling and
vapor cooling, a heater, or lamp heating using infrared rays.
[0102] To summarize, the temperature must be formed within the
range of 10.degree. C. to 120.degree. C. With the above stated
temperature range, even when the temperature adjustment range of
the side wall is .+-.5.degree. C. degree, a fully stable etching
characteristic can be obtained.
[0103] According to the etching characteristic, even when the
temperature adjustment range of the side wall is .+-.10.degree. C.,
a stable etching characteristic can be obtained, and the
temperature adjustment can be carried out extremely easily.
[0104] According to the present invention, since a superior oxide
film etching characteristic can be obtained and a stable
characteristic can be obtained during a long period of operation,
the following advantages can be expected.
[0105] Namely, the yield can be improved and the throughput can be
improved. Further, since the temperature adjustment is established
in a low temperature range of from 10.degree. C. to 120.degree. C.,
the inconvenience in which the size of the etching chamber is made
large due to thermal expansion can be avoided. For example, the
line expansion coefficient of the aluminum alloy which is largely
used in the etching chamber is 24.times.10.sup.-6K.sup.-1; on the
other hand, for alumina and quartz, the respective line expansion
coefficients are 6.times.10.sup.-6K.sup.-1 and
0.41.times.10.sup.-6K.sup.-1. Since the line expansion coefficients
differ so much, when the etching chamber is heated to produce the
plasma discharge or the etching chamber is temperature controlled
compulsively at a high temperature, the differences in the sizes
between the materials become large, making it necessary to
structurally design the chamber to avoid thermal expansion.
[0106] Further, the change in size of the vacuum sealing portion
exerts an influence on the sealing characteristic, and the heat
resistant performance of the elastomer which forms the seal
material also becomes a problem. When the temperature reduces a
level of more than 150.degree. C., the possibility that the life of
the seal material will be short becomes high.
[0107] As stated above, various problems are caused due to high
temperature, and the addition of heat resistant performance
structurally causes the cost of the apparatus to increase.
* * * * *