U.S. patent application number 09/808520 was filed with the patent office on 2001-11-01 for local etching apparatus and local etching method.
Invention is credited to Tanaka, Chikai, Yanagisawa, Michihiko.
Application Number | 20010036741 09/808520 |
Document ID | / |
Family ID | 11587494 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010036741 |
Kind Code |
A1 |
Tanaka, Chikai ; et
al. |
November 1, 2001 |
Local etching apparatus and local etching method
Abstract
A local etching apparatus and local etching method improving the
throughput of the local etching apparatus by preheating a discharge
tube before ignition of the plasma discharge. The local etching
apparatus is provided with a plasma generator 1, an alumina
discharge tube 2, and a heater 6. The heater 6 is constituted by a
heating wire 60, a power source 61 for supplying voltage to the
heating wire 60, and a voltage regulator 62 for controlling the
voltage supplied from the power source 61 to the heating wire 60.
Due to this, it is possible to heat the alumina discharge tube 2 to
the desired temperature by the heater 6 immediately before the
plasma discharge by the plasma generator 1. As a result, there is
no need to wait with the local etching work until the alumina
discharge tube 2 rises in temperature to the desired temperature
due to the heat by the plasma discharge, that is, it is possible to
perform the local etching work immediately after the plasma
discharge.
Inventors: |
Tanaka, Chikai; (Ayase-Shi,
JP) ; Yanagisawa, Michihiko; (Ayase-Shi, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Family ID: |
11587494 |
Appl. No.: |
09/808520 |
Filed: |
March 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09808520 |
Mar 14, 2001 |
|
|
|
09392113 |
Sep 8, 1999 |
|
|
|
Current U.S.
Class: |
438/710 |
Current CPC
Class: |
H01J 37/32366 20130101;
H01J 37/32192 20130101; H01L 21/6708 20130101; H01J 37/32357
20130101 |
Class at
Publication: |
438/710 |
International
Class: |
H01L 021/302; H01L
021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 1999 |
JP |
11-4562 |
Claims
What is claimed is:
1. A local etching apparatus comprising: a discharge tube with a
spray port of a nozzle portion facing an object to be etched in a
chamber; a plasma generator for causing plasma discharge of a
predetermined gas in said discharge tube so as to produce radicals
for locally etching a relatively thick portion present on a surface
of the object to be etched; and a heater for heating said discharge
tube to a predetermined temperature.
2. A local etching apparatus as set forth in claim 1, wherein said
heater is provided with: a heating member provided so as to
surround said discharge tube and capable of raising the temperature
in accordance with voltage applied thereto; and a voltage
controller for controlling the voltage applied to said heating
member.
3. A local etching apparatus as set forth in claim 2, wherein said
heating member of said heater is a heating wire wound around said
discharge tube.
4. A local etching apparatus as set forth in claim 1, wherein said
heater is an optical heater which emits infrared rays or a laser
beam to said discharge tube to heat said discharge tube.
5. A local etching apparatus as set forth in claim 1, wherein said
heater is provided with: a heating block arranged so as to surround
said discharge tube in a state contacting the outer side of said
discharge tube and has a fluid feed port and fluid exhaust port
communicating with a fluid storage portion at the inside; and a
fluid feeder for heating the fluid to a predetermined temperature
and feeding it to the fluid storage portion of said heating
block.
6. A local etching apparatus as set forth in claim 5, wherein said
heating block of said heater is comprised of a thin tube wound
around said discharge tube.
7. A local etching apparatus as set forth in any one of claims 1 to
6, wherein said discharge tube used is any one of an alumina
discharge tube, an aluminum nitride discharge tube, a sapphire
discharge tube, and a quartz discharge tube.
8. A local etching method comprising: a plasma generating step for
causing plasma discharge of a predetermined gas in a discharge tube
so as to produce radicals and spraying the radicals from a nozzle
portion of the discharge tube; a local etching step for locally
etching a relatively thick portion present on the surface of the
object to be etched by the radicals sprayed from the nozzle portion
while making the nozzle portion of the discharge tube move
relatively along the surface of the object to be etched; and a
heating step for heating the discharge tube at least to a time of
start of plasma discharge of said plasma generating step to at
least a temperature at which the etching depth of the object to be
etched at said local etching step becomes substantially
constant.
9. A local etching method as set forth in claim 8, wherein said
heating step is comprised of heating the discharge tube to the
temperature at all times.
10. A local etching method as set forth in claim 8, wherein said
heating step is comprised of heating the discharge tube to the
temperature until the start of plasma discharge of said plasma
generating step.
11. A local etching method as set forth in any one of claims 8 to
10, wherein said heating step is comprised of heating a location of
the discharge tube between the plasma discharge location and the
spray port of the discharge tube to the temperature.
12. A local etching method as set forth in any one of claims 8 to
11, wherein said heating step is comprised of raising a temperature
of a heating member surrounding the discharge tube by application
of voltage so as to heat the discharge tube to the temperature.
13. A local etching method as set forth in any one of claims 8 to
11, wherein said heating step is comprised of emitting infrared
rays or a laser beam to the discharge tube to heat the discharge
tube to the temperature.
14. A local etching method as set forth in any of claims 8 to 11,
wherein said heating step is comprised of feeding a heated fluid
into a heating block arranged so as to surround the discharge tube
in a state contacting the outer side of the discharge tube so as to
heat the discharge tube to the temperature.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a local etching apparatus
and a local etching method for locally etching a protrusion on a
surface of a wafer by radicals or locally etching a relatively
thick portion of a wafer so as to make the distribution of
thickness of the wafer uniform.
[0003] 2. Description of the Related Art
[0004] FIG. 10 is a schematic sectional view of an example of a
local etching apparatus of the related art.
[0005] This local etching apparatus is provided with a discharge
tube 100, a gas feed device 110, a plasma generator 120, and a
stage 130.
[0006] Due to this configuration, it is possible to feed gas from
the gas feed device 110 to the discharge tube 100, generate
microwaves M from a microwave generator 121 of the plasma generator
120 to the inside of a waveguide 122 to cause plasma discharge of
the gas in the discharge tube 100, and spray the radicals G
produced by the plasma discharge from a nozzle portion 101 of the
discharge tube 100 on to a wafer W on the stage 130.
[0007] By making the stage 130 move in the horizontal direction, a
portion Wa relatively thicker than a defined thickness on the
surface of the wafer W (hereinafter referred to as a "relatively
thick portion") is guided directly under the nozzle 101 where the
radicals G are sprayed from the nozzle 101 to the relatively thick
portion Wa to locally etch the relatively thick portion Wa. By
locally etching the entire surface of the wafer W in this way, it
is possible to make the distribution of surface thickness of the
wafer W uniform and flatten the surface of the wafer W as a
whole.
[0008] The above local etching apparatus of the related art,
however, had the following problems.
[0009] The depth of local etching of the wafer W by the radicals G
depends on the temperature of the discharge tube 100.
[0010] FIG. 11 is a view of the correlation between the surface
temperature of the discharge tube 100 and the etching depth.
[0011] As shown in FIG. 11, the etching depth by the radicals G
becomes larger along with a rise of the surface temperature of the
discharge tube 100. When the surface temperature of the discharge
tube 100 reaches a certain value T.sub.0, the etching depth at a
temperature above the temperature T.sub.0 becomes substantially
constant.
[0012] At the time of ignition of the plasma discharge in the
discharge tube 100, the discharge tube 100 is cold. The temperature
of the discharge tube 100 rises along with time due to the heat of
the plasma. Therefore, the etching depth of the wafer W by the
radicals G will not stabilize until the surface temperature of the
discharge tube 100 reaches the above temperature T.sub.0.
Accordingly, if the etching work is commenced before the surface
temperature of the discharge tube 100 reaches T.sub.0, the etching
rate of the wafer W becomes unstable and it is not possible to
flatten the wafer W to a high precision. In view of this, in the
local etching apparatuses of the related art, it was necessary to
allow for a long standby time until the surface temperature of the
discharge tube 100 reaches T.sub.0. It was not possible to start
the etching work during that period. As a result, the throughput of
the flattening of the wafer W was low and the mass producibility
was poor.
SUMMARY OF THE INVENTION
[0013] The present invention was made to solve the above problem
and has as its object the provision of a local etching apparatus
and local etching method improving the throughput of the local
etching apparatus by preheating the discharge tube before ignition
of the plasma discharge.
[0014] To achieve the above object, according to a first aspect of
the present invention, there is provided a local etching apparatus
comprising: a discharge tube with a spray port of a nozzle portion
facing an object to be etched in a chamber; a plasma generator for
causing plasma discharge of a predetermined gas in the discharge
tube so as to produce radicals for locally etching a relatively
thick portion present on a surface of the object to be etched; and
a heater for heating the discharge tube to a predetermined
temperature.
[0015] Due to this configuration, it is possible to use the heater
to heat the discharge tube to a predetermined temperature,
specifically at least a temperature at which the etching depth of
the object to be etched becomes substantially constant. Suitably
thereafter, the plasma generator is used to cause plasma discharge
of a predetermined gas in the discharge tube to produce radicals
for locally etching a relatively thick portion present on the
surface of the object to be etched. Further, by making a nozzle
portion of the discharge tube move along the surface of the object
to be etched, it is possible to locally etch a relatively thick
portion present on the surface of the object to be etched by the
radicals sprayed from the nozzle portion. In this way, since it is
possible to preheat the discharge tube to at least a temperature at
which the etching depth of the object to be etched becomes
substantially constant, there is no need to wait with the local
etching work until the discharge tube rises to that temperature by
the heat due to the plasma discharge such as with the local etching
apparatus of the related art and it is possible to immediately
perform local etching at a stable etching depth by performing the
local etching work.
[0016] Various heaters may be considered for heating the discharge
tube, but giving a preferable example of a heater, according to an
embodiment of the invention, the heater is provided with: a heating
member provided so as to surround the discharge tube and capable of
raising the temperature in accordance with voltage applied thereto;
and a voltage controller for controlling the voltage applied to the
heating member. In particular, according to an embodiment of the
invention, the heating member of the heater is a heating wire wound
around the discharge tube. Further, as another preferable example
of the heater, according to an embodiment of the invention, the
heater is an optical heater which emits infrared rays or a laser
beam to the discharge tube to heat the discharge tube. Further, as
another example, according to an embodiment of the invention, the
heater is provided with: a heating block arranged so as to surround
the discharge tube in a state contacting the outer side of the
discharge tube and has a fluid feed port and fluid exhaust port
communicating with a fluid storage portion at the inside; and a
fluid feeder for heating the fluid to a predetermined temperature
and feeding it to the fluid storage portion of the heating block.
In particular, according to an embodiment of the invention, the
heating block of the heater is comprised of a thin tube wound
around the discharge tube.
[0017] Note that it is possible to use various types of discharge
tubes as the discharge tube for the local etching apparatus.
Therefore, according to an embodiment of the invention, the
discharge tube used is any one of an alumina discharge tube, an
aluminum nitride discharge tube, a sapphire discharge tube, and a
quartz discharge tube.
[0018] Note that the steps executed by the local etching
apparatuses in their operation also stand as method inventions.
[0019] Therefore, according to a second aspect of the present
invention, there is provided a local etching method comprising: a
plasma generating step for causing plasma discharge of a
predetermined gas in a discharge tube so as to produce radicals and
spraying the radicals from a nozzle portion of the discharge tube;
a local etching step for locally etching a relatively thick portion
present on the surface of the object to be etched by the radicals
sprayed from the nozzle portion while making the nozzle portion of
the discharge tube move relatively along the surface of the object
to be etched; and a heating step for heating the discharge tube at
least to a time of start of plasma discharge of the plasma
generating step to at least a temperature at which the etching
depth of the object to be etched at the local etching step becomes
substantially constant.
[0020] In the heating step, the discharge tube may be heated at
least until the time of the start of the plasma discharge of the
plasma generating step and a heating time is arbitrary.
[0021] Therefore, according to an embodiment of the invention, the
heating step is comprised of heating the discharge tube to the
above temperature at all times. Further, according to an embodiment
of the invention, the heating step is comprised of heating the
discharge tube to the temperature until the start of plasma
discharge of the plasma generating step.
[0022] The heated location of the discharge tube is arbitrary. As
one example, according to an embodiment of the invention, the
heating step is comprised of heating a location of the discharge
tube between the plasma discharge location and the spray port of
the discharge tube to the temperature.
[0023] Further, according to an embodiment of the invention, the
heating step is comprised of raising the temperature of a heating
member surrounding the discharge tube by application of voltage so
as to heat the discharge tube to the temperature. Further,
according to an embodiment of the invention, the heating step is
comprised of emitting infrared rays or a laser beam to the
discharge tube to heat the discharge tube to the temperature.
Further, according to an embodiment of the invention, the heating
step is comprised of feeding a heated fluid into a heating block
arranged so as to surround the discharge tube in a state contacting
the outer side of the discharge tube so as to heat the discharge
tube to the temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other objects, features, and advantages of the
present invention will become more readily apparent from the
following detailed description of a presently preferred embodiment
of the invention taken in conjunction with the accompanying
drawings, in which:
[0025] FIG. 1 is a partially cutaway schematic view of the
configuration of a local etching apparatus according to a first
embodiment of the present invention;
[0026] FIG. 2 is a partial enlarged sectional view for showing the
heater;
[0027] FIG. 3 is a schematic plan view of the state of the nozzle
portion scanning a silicon wafer;
[0028] FIG. 4 is a partial enlarged sectional view of a silicon
wafer for showing a local etching process;
[0029] FIG. 5 is a graph of the correspondence between the time
when performing flattening work without preheating an alumina
discharge tube and the temperature of the alumina discharge
tube;
[0030] FIG. 6 is a graph of the correspondence between the time
when performing flattening work with preheating of an alumina
discharge tube and the temperature of the alumina discharge
tube;
[0031] FIG. 7 is a sectional view of the essential portions of a
local etching apparatus according to a second embodiment of the
present invention;
[0032] FIG. 8 is a sectional view of the essential portions of a
local etching apparatus according to a third embodiment of the
present invention;
[0033] FIG. 9 is a sectional view of a modification of a local
etching apparatus;
[0034] FIG. 10 is a schematic sectional view of an example of a
local etching apparatus of the related art; and
[0035] FIG. 11 is a view of the correspondence between a surface
temperature of a discharge tube and an etching rate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Preferred embodiments of the present invention will be
explained next with reference to the drawings.
[0037] (First Embodiment)
[0038] FIG. 1 is a partially cutaway schematic view of the
configuration of a local etching apparatus according to a first
embodiment of the present invention.
[0039] As shown in FIG. 1, the local etching apparatus is provided
with a plasma generator 1, an alumina discharge tube 2, a gas
feeder 3, an X-Y drive 4, a Z-drive 5, and a heater 6.
[0040] The plasma generator 1 is a device for causing plasma
discharge of gas inside the alumina discharge tube 2 to produce
radicals G and is comprised of a microwave generator 10 and a
waveguide 11.
[0041] The microwave generator 10 is a magnetron and can generate a
microwave M of a predetermined frequency.
[0042] The waveguide 11 is for guiding the microwave M generated by
the microwave generator 10 and is fit over the alumina discharge
tube 2.
[0043] At the inside of the left end of the waveguide 11 is
attached a reflection plate (short plunger) for reflecting the
microwave M to form a standing wave. Further, in the middle of the
waveguide 11 are attached a 3-stub tuner 13 for phase alignment of
the microwave M and an isolator 14 for bending the reflected
microwave M heading toward the microwave generator 10 90.degree. in
direction (surface direction of FIG. 1) to prevent the reflected
wave from returning to the generator.
[0044] The alumina discharge tube 2 is a cylinder having a nozzle
portion 20 at its lower end and is connected at its upper end to a
feed pipe 30 of the gas feeder 3.
[0045] The gas feeder 3 is a device for feeding gas into the
alumina discharge tube 2 and has a SF.sub.6 (sulfur hexafluoride)
gas cylinder 31. The gas cylinder 31 is connected to the feed pipe
30 through a valve 32 and flow control device 33.
[0046] By adopting this configuration for the plasma generator 1,
when a gas is fed from the gas feeder 3 to the alumina discharge
tube 2 and a microwave M is generated from the microwave generator
10, plasma discharge is caused in the alumina discharge tube 2 and
activated species gases G produced by the plasma discharge are
sprayed from the spray port 21 of the nozzle portion 20.
[0047] An object to be etched, here a silicon wafer W, is designed
to be held by the electrostatic force of a chuck 90 in a chamber 9
when placed on the chuck 90. The chamber 9 is provided with a
vacuum pump 91. The vacuum pump 91 may be used to make the inside
of the chamber 9 a vacuum. Further, a hole 92 is formed in the
center of the top surface of the chamber 9. The nozzle portion 20
of the alumina discharge tube 2 is inserted through this hole 92
into the chamber 9. An O-ring 93 is attached between the hole 92
and the alumina discharge tube 2 so as to hold the space between
the hole 92 and the alumina discharge tube 2 air-tight.
[0048] A duct 94 is provided around the nozzle portion 20 inserted
into the hole 92. By driving the vacuum pump 95, the reaction
product gas at the time of etching is exhausted to the outside of
the chamber 9.
[0049] The X-Y drive 4 is arranged inside the chamber 9 and
supports the chuck 90 from below.
[0050] The X-Y drive 4 makes the chuck 90 move in the lateral
direction in FIG. 1 by an X-drive motor 40 and makes the chuck 90
and the X-drive motor 40 move together in the direction
perpendicular to the surface of the paper on which FIG. 1 is drawn
by a Y-drive motor 41. That is, it is possible to make the nozzle
portion 20 move in the X-Y direction relative to the silicon wafer
W by the X-Y drive 4.
[0051] A Z-drive 5 supports the X-Y drive 4 in the chamber 9 from
below. The Z-drive 5 makes the X-Y drive 4 move in the vertical
direction by a Z-drive motor 50 and enables the distance between
the spray port 21 of the nozzle portion 20 facing the silicon wafer
W side and the surface of the silicon wafer W to be adjusted.
[0052] The drive operations of the X-drive motor 40 and Y-drive
motor 41 of the X-Y drive 4 and the Z-drive motor 50 of the Z-drive
5 are controlled by a control computer 45 based on a predetermined
program.
[0053] The heater 6 is a heating device for heating the alumina
discharge tube 2 to a desired temperature and is provided with a
heating wire 60 as a heating member, a power source 61 for
supplying voltage to the heating wire 60, and a voltage regulator
62 for controlling the voltage supplied from the power source 61 to
the heating wire 60 and constituting a voltage controller together
with the power source 61.
[0054] The heating wire 60 is a nichrome wire and, as shown in FIG.
2, is wound around the outer circumference of the alumina discharge
tube 2 so as to surround a predetermined location of the alumina
discharge tube 2. Specifically, the heating wire 60 is wound around
a location below a discharge location where the waveguide 11 and
the alumina discharge tube 2 intersect. Further, the two ends of
the heating wire 60 are electrically connected to the voltage
regulator 62 outside the chamber 9. The voltage regulator 62 is
electrically connected to the power source 61.
[0055] Due to this, by turning the power source 61 on and adjusting
the voltage regulator 62 so as to control the voltage supplied to
the heating wire 60, the heating wire 60 will rise to a temperature
corresponding to the supplied voltage and the alumina discharge
tube 2 will be heated to the desired temperature.
[0056] Note that in FIG. 1, reference numeral 7 is an etching
region limiter which is provided with a nozzle 70 attached to the
chamber 9 in a state with its opening facing the inside of the
chamber 9 and an N.sub.2 (nitrogen) gas storage cylinder 73
connected to this nozzle 70 through a valve 71 and a flow rate
controller 72.
[0057] Next, an explanation will be given of the operation of the
local etching apparatus of this embodiment. Note that since it is
possible to execute the local etching method according to the
aspect of the present invention by operating the local etching
apparatus, the explanation will be given along with the steps of
that method.
[0058] First, the plasma generation step is executed.
[0059] That is, by turning the power source 61 of the heater 6
shown in FIG. 1 on and controlling the voltage supplied to the
heater wire 60 by the voltage regulator 62, the heating wire 60
wound around the alumina discharge tube 2 is heated and the
temperature of the alumina discharge tube 2 is made to rise to a
predetermined temperature T.sub.0 by that heat. The temperature
T.sub.0 is the temperature shown in FIG. 11. With an alumina
discharge tube 2, it is for example 100.degree. C. If the alumina
discharge tube 2 is raised to over this temperature T.sub.0, the
etching depth of the wafer W in the later explained local etching
step becomes substantially constant.
[0060] When the surface temperature of the alumina discharge tube 2
reaches the above mentioned T.sub.0.degree. C. by the execution of
this heating step, the power source 61 is turned off and the plasma
generation step is executed.
[0061] That is, the vacuum pump 91 is driven to make the inside of
the chamber 9 a predetermined low atmospheric pressure state and
the Z-drive 5 is operated to raise the X-Y drive 4 as a whole and
bring the silicon wafer W close to the opening 21 of the nozzle
portion 20.
[0062] Further, the valve 32 of the gas feeder 3 is opened to feed
the SF.sub.6 gas in the gas cylinder 31 through the feed pipe 30 to
the inside of the alumina discharge tube 2. At this time, the
opening degree of the valve 32 and the flow rate controller 33 are
adjusted to adjust the flow rate of the SF.sub.6 gas to for example
300 sccm.
[0063] In parallel with the above operation of feeding the SF.sub.6
gas, the microwave generator 10 is driven. The microwave M causes
plasma discharge of the SF.sub.6 gas and production of radicals G
including F (fluorine) radicals. Due to this, the radicals G are
guided into the nozzle portion 20 of the alumina discharge tube 2
and sprayed from the spray port 21 of the nozzle portion 20 to the
silicon wafer W side. Suitably thereafter, the opening degree of
the valve 71 of the etching region limiter 7 and the flow rate
controller 72 are adjusted to adjust the flow rate of the N.sub.2
gas from the nozzle portion 20 to for example 500 sccm, the
pressure of the SF.sub.6 gas inside the nozzle portion 20 is made
1.5 Torr, and diameter of the flow of the radicals G sprayed from
the nozzle portion 20 is reduced to limit the etching region to the
desired size.
[0064] The local etching step is executed in this state.
[0065] That is, the control computer 45 is used to drive the X-Y
drive 4 and make the chuck 90 holding the silicon wafer W move
zigzag in the X-Y direction.
[0066] Specifically, as shown in FIG. 3, the nozzle portion 20 is
made to scan the silicon wafer W relatively in a zigzag pattern. At
this time, the relative speed of the nozzle portion 20 with respect
to the silicon wafer W is set so as to be substantially inversely
proportional to the thickness of the relatively thick portion. Due
to this, as shown in FIG. 4, the nozzle portion 20 moves directly
over the non-relatively thick portion Wb at a high speed and falls
in speed in accordance with the thickness of the relatively thick
portion Wa when coming above the relatively thick portion Wa. As a
result, the etching time of the relatively thick portion Wa becomes
longer and the relatively thick portion Wa is shaved flat. The
entire surface of the silicon wafer W is locally etched in this
way.
[0067] At this time, due to the heat of the plasma discharge, the
temperature of the alumina discharge tube 2 becomes higher than the
above mentioned temperature T.sub.0, so the etching depth with
respect to the entire surface of the silicon wafer W becomes
substantially constant. As a result, the surface of the silicon
wafer W is flattened by a substantially uniform etching depth.
[0068] After the processing for flattening one wafer W in this way
is finished, the microwave generator 10 of the plasma generator 1
shown in FIG. 1 is turned off to stop the plasma discharge and the
power source 61 of the heater 6 is turned on to execute the heating
step. Due to this, it is possible to maintain the lowest value of
the falling temperature of the alumina discharge tube 2 after the
plasma discharge is stopped at the above temperature T.sub.0.
[0069] In this state, a robot etc. is used and the gate valve 96 is
opened to take out the silicon wafer W on the chuck 90, convey the
processed silicon wafer W to a predetermined location, and set the
second silicon wafer W on the chuck 90.
[0070] Suitably thereafter, when the plasma generation step is
executed, the temperature of the alumina discharge tube 2 rises
from a temperature of an initial value of the temperature T.sub.0.
Therefore, it is possible to perform the local etching step on the
second silicon wafer W immediately without waiting for the
temperature of the alumina discharge tube 2 to rise to the
temperature T.sub.0. Similarly, it is possible to perform the local
etching step on a third and later silicon wafers W immediately.
[0071] In this way, according to the local etching apparatus of
this embodiment, since it is possible to execute the local etching
step immediately without waiting for the temperature of the alumina
discharge tube 2 to rise to the temperature T.sub.0 due to the
preheating effect of the heater 6, it is possible to greatly
increase the number of silicon wafers W processed per unit time,
that is, the throughput.
[0072] The present inventors conducted the following experiments to
provide evidence of this point.
[0073] FIG. 5 is a graph of the correspondence between the time in
the case of performing the flattening work without preheating the
alumina discharge tube 2 and the temperature of the alumina
discharge tube 2. FIG. 6 is a graph of the correspondence between
the time in the case of performing the flattening work with
preheating of the alumina discharge tube 2 and the temperature of
the alumina discharge tube 2.
[0074] As shown in FIG. 5, during the work for flattening the first
silicon wafer W, it takes 15 minutes for the temperature of the
alumina discharge tube 2 to reach the temperature T.sub.0 when
executing the plasma generation step to cause plasma discharge at
minute 0. Further, the 5-minute local etching step was performed by
minute 20, then the plasma discharge was stopped and the transfer
step executed. It took approximately 2 minutes for the transfer of
the silicon wafer W.
[0075] Suitably thereafter, the work for flattening the second
silicon wafer W was started at minute 22. At the time of this work,
residual heat due to the plasma discharge at the work for
flattening the first silicon wafer W remained. It therefore took 10
minutes for the temperature of the alumina discharge tube 2 to
reach the temperature T.sub.0. Further, the 5-minute local etching
step was executed by minute 37, then the plasma discharge was
stopped and the 2-minute transfer step was executed by minute
39.
[0076] Further, in the work for flattening the third and later
silicon wafers W, the same time as the work for flattening the
second silicon wafer W was required.
[0077] That is, as shown in FIG. 5, the flattening work for five
silicon wafers W can be completed in 85 minutes.
[0078] As opposed to this, when preheating the alumina discharge
tube 2 before the flattening work, as shown in FIG. 6, since the
alumina discharge tube 2 was preheated, during the work for
flattening the first silicon wafer W, the temperature of the
alumina discharge tube 2 reached the temperature T.sub.0 when
executing the plasma generation step at minute 0. It was therefore
possible to execute the 5-minute local etching step by minute 5.
Further, when the plasma discharge was stopped and the heating step
executed and the step for transferring the second silicon wafer W
was performed in 2 minutes before minute 7, the temperature of the
alumina discharge tube 2 was held at the temperature T.sub.0 by the
effect of the heating step. The 5-minute local etching step for the
second silicon wafer W could therefore be immediately performed by
minute 12. Further, in the work for flattening the third and later
silicon wafers W, the same time as the work for flattening the
second silicon wafer W was required.
[0079] That is, according to the local etching apparatus of this
embodiment, as shown in FIG. 6, the time by which it was possible
to complete the flattening work for five silicon wafers W was just
33 minutes. The throughput reached as much as about 2.6 times that
of the case of no preheating.
[0080] (Second Embodiment)
[0081] FIG. 7 is a sectional view of the essential portions of a
local etching apparatus according to a second embodiment of the
present invention. Note that parts the same as those shown in FIG.
1 to FIG. 6 are explained given the same reference numerals.
[0082] This embodiment differs from the first embodiment in the
point that use is made of an optical heater which heats the alumina
discharge tube 2 by emitting infrared rays to the alumina discharge
tube 2.
[0083] The optical heater 80, as shown in FIG. 7, is provided with
a known halogen heater 81 and a power source 82. At the time of
operation, it is possible to specifically work the local etching
method according to the aspect of the invention.
[0084] Specifically, the halogen heater 81 is arranged in a state
with its front facing a location lower than the discharge location
where the waveguide 11 and alumina discharge tube 2 intersect. The
infrared rays S from the not shown lamp of this halogen heater 81
are directed toward the above location of the alumina discharge
tube 2 so as to heat the alumina discharge tube 2 to the above
temperature T.sub.0.
[0085] The rest of the configuration, mode of operation, and
advantageous effects are similar to those of the above first
embodiment, so descriptions thereof will be omitted.
[0086] (Third Embodiment)
[0087] FIG. 8 is a sectional view of the essential portions of a
local etching apparatus according to a third embodiment of the
present invention. Note that parts the same as those shown in FIG.
1 to FIG. 6 are explained given the same reference numerals.
[0088] This embodiment differs from the first and second
embodiments in the point that the heater is comprised of a thin
tube wound around the alumina discharge tube 2 and fed with a fluid
of a predetermined temperature so as to heat the alumina discharge
tube 2.
[0089] The heater 83 is provided with a thin tube 84 as a heating
block, a temperature control unit 85, and a fluid circulation pump
86. At the time of operation, it is possible to specifically work
the local etching method according to the aspect of the
invention.
[0090] The thin tube 84 is wound around the alumina discharge tube
2 in a state contacting its outside. The inside constitutes a fluid
storage portion. The thin tube 84 passes through the inside of the
temperature control unit 85 to reach the pump 86. The fluid feed
port and fluid exhaust port of the thin tube 84 are connected to
the exhaust side and intake side of the pump 86.
[0091] Due to this configuration, the fluid R inside the thin tube
84 is made to circulate by the pump 86, is heated by the
temperature control unit 85, and heats the alumina discharge tube 2
to the above temperature T.sub.0.
[0092] The rest of the configuration, mode of operation, and
advantageous effects are similar to those of the above first and
second embodiments, so descriptions thereof will be omitted.
[0093] Note that the invention is not limited to the above
embodiments. Various modifications and changes may be made within
the scope of the gist of the invention.
[0094] In the first embodiment, the heater 6 was turned off
substantially simultaneously with the execution of the plasma
discharge step and was turned on substantially simultaneously with
the end of the local etching step, but it is also possible to leave
the heater 6 on at all times to keep the temperature of the alumina
discharge tube above the temperature T.sub.0 at all times.
[0095] Further, in the first embodiment, a heating wire 60 was used
as the heating member, but it is also possible to use a heating
plate instead of the heating wire 60 and make the heating plate
abut against the outside of the alumina discharge tube 2.
[0096] In the second embodiment, infrared rays S were used to heat
the alumina discharge tube 2, but it is also possible to use a
laser beam etc. to heat it.
[0097] In the third embodiment, a thin tube 84 was used as the
heating block, but as shown in FIG. 9 it is also possible to bring
a hollow body 87 having a fluid storage portion 87a inside it into
contact with the outside of the alumina discharge tube 2, connect
the thin tube 84 to a fluid feed port 87b and fluid exhaust port
87c of the hollow body 87, and communicate the thin tube 84 to the
fluid storage portion 87a.
[0098] In the above embodiments, an alumina discharge tube 2 was
used as the discharge tube, but any of an aluminum nitride
discharge tube, sapphire discharge tube, and quartz discharge tube
may be used instead of the alumina discharge tube 2.
[0099] For example, in the above embodiments, SF.sub.6 gas was used
as the radical R producing gas, but CF.sub.4 (carbon tetrafluoride)
or NF.sub.3 (nitrogen trifluoride) gas may also be used. Further,
it is also possible to feed not a single SF.sub.6 gas, but a mixed
gas of SF.sub.6 gas and O.sub.2 gas or other gas to the alumina
discharge tube 2.
[0100] As explained in detail above, according to the present
invention, since the discharge tube is preheated to at least a
temperature at which the etching depth of the object to be etched
becomes substantially constant, there is no need to wait with the
local etching work until the discharge tube rises to that
temperature by the heat resulting from the plasma discharge as in
the conventional local etching apparatus. Therefore, it is possible
to perform the local etching work immediately. As a result, there
is the superior effect that it is possible to improve the
throughput of the flattening of the object to be etched.
* * * * *