U.S. patent application number 09/863860 was filed with the patent office on 2001-10-11 for plasma treatment method and apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Komino, Mitsuaki, Sakamoto, Yoshio.
Application Number | 20010027843 09/863860 |
Document ID | / |
Family ID | 27469388 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010027843 |
Kind Code |
A1 |
Komino, Mitsuaki ; et
al. |
October 11, 2001 |
Plasma treatment method and apparatus
Abstract
A plasma treatment method comprising exhausting a process
chamber so as to decompress the process chamber, mounting a wafer
on a suscepter, supplying a process gas to the wafer through a
shower electrode, applying high frequency power, which has a first
frequency f.sub.1 lower than an inherent lower ion transit
frequencies of the process gas, to the suscepter, and applying high
frequency power, which has a second frequency f.sub.2 higher than
an inherent upper ion transit frequencies of the process gas,
whereby a plasma is generated in the process chamber and activated
species influence the wafer.
Inventors: |
Komino, Mitsuaki; (Tokyo,
JP) ; Sakamoto, Yoshio; (Tokyo, JP) |
Correspondence
Address: |
Edgar H. Haug, Esq.
Frommer Lawrence & Haug LLP
745 Fifth Avenue
New York
NY
10151
US
|
Assignee: |
TOKYO ELECTRON LIMITED
|
Family ID: |
27469388 |
Appl. No.: |
09/863860 |
Filed: |
May 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09863860 |
May 23, 2001 |
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09556133 |
Apr 20, 2000 |
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6264788 |
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09556133 |
Apr 20, 2000 |
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09094451 |
Jun 10, 1998 |
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6106737 |
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09094451 |
Jun 10, 1998 |
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08424127 |
Apr 19, 1995 |
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5900103 |
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Current U.S.
Class: |
156/345.44 |
Current CPC
Class: |
H01J 37/32082 20130101;
H01J 37/3244 20130101; C23C 16/4485 20130101; C23C 16/5096
20130101; Y10S 156/916 20130101; C23C 16/4405 20130101; H01J
37/32935 20130101; H01J 37/32963 20130101; C23C 16/45565 20130101;
H01J 37/32146 20130101; H01J 37/32155 20130101; H01J 37/32165
20130101; C23C 16/4483 20130101; C23C 16/4557 20130101; C23C 16/517
20130101; C23C 16/4407 20130101 |
Class at
Publication: |
156/345 |
International
Class: |
H01L 021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 1994 |
JP |
6-106045 |
Apr 28, 1994 |
JP |
6-113587 |
May 24, 1994 |
JP |
6-133638 |
Jun 1, 1994 |
JP |
6-142409 |
Mar 25, 1994 |
JP |
H06-079541 |
Claims
What is claimed is:
1. A plasma treatment method of plasma-treating a substrate, which
is to be treated, under decompressed atmosphere comprising, the
steps of: exhausting a process chamber so as to decompress the
process chamber; mounting the substrate, which is to be treated, on
a lower electrode; supplying a process gas to the substrate on the
lower electrode through an upper electrode; applying high frequency
power, which has a first frequency f.sub.1 lower than an inherent
lower ion transit frequencies of said process gas, to the lower
electrode; and applying high frequency power, which has a second
frequency f.sub.2 higher than an inherent upper ion transit
frequencies of said process gas, to the upper electrode, whereby a
plasma is generated in the process chamber and activated species
influence the substrate to be treated.
2. The plasma treatment method according to claim 1, wherein said
process gas is formed of a plurality of component gases, said first
frequency f.sub.1 is the lowest of the inherent lower ion transit
frequencies of said component gases, and said second frequency
f.sub.2 is the highest of the inherent higher ion transit
frequencies of said composite gases.
3. The plan treatment method according to claim 1, wherein the
first frequency f.sub.1 is lower that the second frequency
f.sub.2.
4. The plasma treatment method according to claim 1, wherein the
first frequency f.sub.1 is set lower than 1 MHz, and the second
frequency f.sub.2 is set higher than 10 MHz.
5. The plasma treatment method according to claim 4, wherein the
first frequency f.sub.1 is in a range of 100 kHZ-1 MHz, and the
second frequency f.sub.2 in a range of 10 MHz-100 MHz.
6. The plasma treatment method according to claim 1, wherein high
frequency components of said first frequency f.sub.1 are removed
from said high frequency power applied to the upper electrode.
7. The plasma treatment method according to claim 1, wherein high
frequency components of said second fluency f.sub.2 are removed
from high frequency power entering into a pr supply circuit through
plasma, a power supply circuit serving to apply said high frequency
power, which has the first frequency f.sub.1, to the lower
electrode.
8. The plasma treatment method according to claim 1, further
comprising the steps of, applying high frequency power, which has a
frequency same as the first frequency f.sub.1 and which is
amplitude-modulated, to the upper electrode.
9. The plasma treatment method according to claim 1, further
comprising the steps of, applying high frequency power, which has a
frequency same as the second frequency f.sub.2 and which is
amplitude-modulated, to the lower electrode.
10. The plasma treatment method according to claim 8, wherein
amplitude modulation is carried out to form one of sine,
triangular, rectangular and sawtooth waveforms or their composite
waveform.
11. The plasma treatment method according to claim 9, wherein
amplitude modulation is carried out to form one of sine,
triangular, rectangular and sawtooth waveforms or their composite
waveform.
12. The plasma treatment method according to claim 1, wherein one
or more gases selected from the group consisting of CF.sub.4,
C.sub.4F.sub.8, CHF.sub.3, Ar, O.sub.2 and CO gases are used as the
process gas.
13. The plasma treatment method according to claim 1, further
comprising the steps of, introducing one or more cleaning gases
selected from the group consisting of ClF.sub.3, CF.sub.4 and
NF.sub.3 gases into the process chamber while keeping a ring and/or
a baffle plate attached to the lower electrode when plasma is
stopped; and dry cleaning the ring and/or the baffle plate.
14. The plasma treatment method according to claim 1, further
comprising the steps of, detaching the ring and/or the baffle plate
from the lower electrode when plasma is stopped; and dry cleaning
the ring and/or the baffle plate using at least one or more
cleaning gases selected from the group consisting of ClF.sub.3,
CF.sub.4 and NF.sub.3.
15. The plasma treatment method according to claim 1, further
comprising the steps of, detaching the ring and/or the baffle plate
from the lower electrode when plasma is stopped; and wet cleaning
the ring and/or the baffle plate using at least one cleaning
solution selected from a group of isopropylalcohol, water and
fluorophosphoric acid.
16. The plasma treatment method according to claim 1, further
comprising the steps of counting the number of particles adhering
to the substrate which has been treated in the process chamber; and
cleaning the ring and/or the baffle plate while keeping plasma
stopped when the number of particles adhering becomes larger than a
predetermined value.
17. The plasma treatment method according to claim 1, further
comprising the steps of, counting the number of particles
scattering in atmosphere exhausted from a treatment apparatus
and/or at least in one or more areas in an exhaust pipe; and
cleaning the ring and/or the baffle plate while keeping plasma
stopped when the number of particles becomes larger than a
predetermined value.
18. A plasma treatment apparatus for plasma-treating a substrate,
which is to be treated, under decompressed atmosphere comprising: a
chamber earthed; means for exhausting the chamber; a lower
electrode on which the substrate to be treated is mounted; an upper
electrode arranged in the chamber to oppose to the lower electrode;
means for supplying process gas to the substrate on the lower
electrode through the upper electrode; a first power supply
connected to the lower electrode through a first matching circuit
to apply high frequency power, which has a first frequency f.sub.1
lower than an inherent lower ion transit frequency of the process
gas, to the lower electrode; a second power supply connected to the
upper electrode through a second matching circuit to apply high
frequency power, which has a second frequency f.sub.2 higher than
an inherent upper ion transit frequency of the process gas, to the
upper electrode; first filter means for removing high frequency
components of the second frequency f.sub.2 from the high frequency
power applied to the lower electrode; and second filter means for
removing high frequency components of the first frequency f.sub.1
from the high frequency power applied to the upper electrode.
19. The plasma treatment apparatus according to claim 18, wherein
the first filter means is connected to a first circuit, which
connects a first matching circuit to the lower electrode, at an end
thereof and the first circuit includes a first earthed capacitor at
the other end thereof; and the second filter means is connected to
a second circuit, which connects the first matching circuit to the
upper electrode, at an end thereof and the second circuit includes,
at the other end thereof, a second earthed capacitor and an
induction coil connected in series to the second capacitor.
20. The plasma treatment apparatus according to claim 18, wherein
said first filter means has an impedance larger than several
k.OMEGA. relative to the high frequency power having the first
frequency f.sub.1 and an impedance smaller than several .OMEGA.
relative to the high frequency power having the second frequency
f.sub.2; and said second filter means has an impedance smaller than
several .OMEGA. relative to the high frequency power having the
first frequency f.sub.1 and an impedance larger than several
k.OMEGA. relative to the high frequency power having the second
frequency f.sub.2.
21. A plasma treatment apparatus for plasma-treating a substrate,
which is to be treated, under decompressed atmosphere comprising: a
chamber earthed; exhaust means for exhausting the chamber; a lower
electrode on which the substrate is mounted; an upper electrode
arranged in the chamber to oppose to the lower electrode; means for
supplying process gas to the substrate on the lower electrode
through the upper electrode; a first power supply connected to the
lower electrode through a first matching circuit to apply high
frequency power, which has a first frequency f.sub.1 lower than an
inherent lower ion transit frequency of the process gas, to the
lower electrode; a second power supply connected to the upper
electrode through a second matching circuit to apply high frequency
power, which has a second frequency f.sub.2 is higher than an
inherent upper ion transit frequency of the process gas, to the
upper electrode; and an amplitude modulator circuit connected to
the first and second power supplies to modulate the amplitude of
the high frequency power having the first frequency f.sub.1 to
apply amplitude-modulated high frequency to the upper
electrode.
22. The plasma treatment apparatus according to claim 18, wherein
said exhaust means exhausts the chamber to an internal pressure of
10-250 mtorr.
23. The plasma treatment apparatus according to claim 18, further
comprising a ring freely detachably attached to the outer
circumference of the lower electrode to cause reaction products
created by heat or plasma to adhere not to the lower electrode but
to the ring.
24. The plasma treatment apparatus according to claim 18, further
comprising the ring freely detachably attached to the outer
circumference of the lower electrode to cause reaction products
created by heat or plasma to adhere not to the lower electrode but
to the ring; and lifter means for moving the lower electrode up and
down together with the ring.
25. The plasma treatment apparatus according to claim 18, wherein
the chamber has an opening through which the substrate to be
treated is carried in and out, and the ring is moved up and down
between the upper end and the lower and of said opening by the
lifter means.
26. The plasma treatment apparatus according to claim 25, further
comprising a baffle plate attached to the outer circumference of
the ring and positioned higher than the upper end of said chamber
opening, when the ring is lifted, to shield the chamber opening
from plasma atmosphere.
27. The plasma treatment apparatus according to claim 26, further
comprising an exhaust opening formed in that portion of the chamber
aide wall which is lower than the top of the lower electrode; and
holes formed in the baffle plate to adjust or rectify the flow of
the process gas, wherein each hole in the baffle plate is tilted
relative to the vertical axis to cause the process gas, which has
passed through the holes, to flow in a direction reverse to the
direction in which gas is exhausted by a rotary pump.
28. The plasma treatment apparatus according to claim 26, wherein
the baffle member comprises plural plates in which holes each
having a substantially same pitch are formed, and they are placed
one upon the others to shift their corresponding holes a little to
form a step-like hole.
29. The plasma treatment apparatus according to claim 18, further
comprising a cover member freely detachably attached to the upper
electrode to cover a peripheral portion thereof so as to prevent
reaction products from adhering to the upper electrode.
30. The plasma treatment apparatus according to claim 29, wherein
the upper electrode has first engaged recesses or projections
formed in or on the outer circumference thereof, the cover member
has second engaging projections or recesses formed on or in an
inner circumference thereof and the cover member is made of elastic
material, and the second engaging projections or recesses are
engaged with the first engaged recesses or projections while
elastically deforming the cover member.
31. The plasma treatment apparatus according to claim 29, wherein
said cover member includes a wall member to cover an upper inner
wall of the chamber.
32. The plasma treatment apparatus according to claim 18, wherein
an insulating layer, 3 mm or more thick, is formed at least on the
inner side wall of the chamber.
33. The plasma treatment apparatus according to claim 18, further
comprising a vaporizer for vaporizing liquid material from which
the process gas is created, wherein said vaporizer includes a
housing provided with a liquid material inlet communicated with a
liquid material supply supply and with a process gas outlet
communicated with the chamber, and a porous conductive heating unit
arranged in the housing.
34. The plasma treatment apparatus according to claim 33, wherein
said vaporizer includes vibrators to vibrate the porous conductive
heating unit.
35. The plasma treatment apparatus according to claim 33, wherein
said vaporizer in arranged adjacent to a process gas introducing
section of the chamber.
36. The plasma treatment apparatus according to claim 33, wherein
said vaporizer is made integral to the process gas introducing
section of the chamber.
37. The plasma treatment apparatus according to claim 33, further
comprising a bypass arranged between the vaporizer and the process
gas introducing section wherein the process gas outlet of the
vaporizer is selectively communicated with one of the bypass and
the process gas introducing section.
38. The plasma treatment apparatus according to claim 33, wherein
said porous conductive heating unit is a sintered ceramics.
39. The plasma treatment apparatus according to claim 33, wherein a
passage through which liquid material flows is formed in the porous
conductive heating unit.
40. The plasma treatment apparatus according to claim 33, wherein a
second gas introducing opening is formed downstream the vaporizer
and a gas mixing passage through which plural gases are mixed
extends downstream the second gas introducing opening.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plasma treatment method
by which substrates such as semiconductor wafers are etched or
sputtered under plasma atmosphere. It also relates to a plasma
treatment apparatus for the same.
[0003] 2. Description of the Related Art
[0004] Recently, semiconductor devices are more and more highly
integrated and the plasma treatment is therefore asked to have a
finer workability in their making course. In order to achieve such
a finer workability, the process chamber must be decompressed to a
greater extent, plasma density must be kept higher and the
treatment must have a higher selectivity. In the case of the
conventional plasma treatment methods, however, high frequency
voltage becomes higher as output is made larger, and ion energy,
therefore, becomes stronger than needed. The semiconductor wafer
becomes susceptible to damage, accordingly. Further, the process
chamber is kept about 250 mTorr in the case of the conventional
methods and when the degree of vacuum in the process chamber is
made higher (or the internal pressure in the chamber is made
smaller), plasma cannot be kept stable and its density cannot be
made high.
SUMMARY OF THE INVENTION
[0005] When gases are made plasma, the action of ions in the plasma
becomes different, depending upon frequencies of high frequency
power. In short, ion energy and plasma density can be controlled
independently of the other when high frequency power having two
different frequencies is applied to process gases. However, ions
(loaded particles) easily run from plasma to the wafer at a
frequency band, but it becomes difficult for them to run from the
plasma sheath to the wafer at another frequency band (or transit
frequency zone). The so-called follow-up of ions becomes
unstable.
[0006] Particularly molecular gases change their dissociation,
depending upon various conditions (such as kinds of gas, flow rate,
high frequency power applying conditions and internal pressure and
temperature in the process chamber), and the follow-up of ions in
the plasma sheath changes in response to this changing
dissociation. Further, the follow-up of ions at the transit
frequency zone also depends upon their volume (or mass).
Particularly in the case of molecular gases used in etching and
CVD, the dissociation of gas molecules progresses to an extent
greater than needed when electron temperature becomes high with a
little increase of high frequency power, and the behavior of ions
in the plasma sheath changes accordingly. Plasma properties such as
ion current density become thus unstable and the plasma treatment
becomes uneven, thereby causing the productivity to be lowered.
[0007] When the frequency of high frequency power is only made high
to increase plasma density, the dissociation of gas molecules
progresses to the extent greater than needed. It is therefore
desirable that the plasma density is raised not to depend upon
whether the frequency is high or low.
[0008] An object of the present invention is therefore to provide
plasma treatment method and apparatus capable of controlling both
of the dissociation of gas molecules and the follow-up of ions and
also capable of promoting the incidence of ions onto a substrate to
be treated.
[0009] Another object of the present invention is to provide plasma
treatment method and apparatus capable of raising the plasma
density with smaller high frequency power not to damage the
substrate to be treated. According to the present invention, there
can be provided a plasma treatment method of plasma-treating a
substrate to be treated under decompressed atmosphere comprising
exhausting a process chamber; mounting the substrate on a lower
electrode; supplying plasma generating gas to the substrate on the
lower electrode through an upper electrode; applying high frequency
power having a first frequency f.sub.1, lower than the lower limit
of ion transit frequencies characteristic of process gas, to the
lower electrode; and applying high frequency power having a second
frequency, higher than the upper limit of ion transit frequencies
characteristic of process gas, to the upper electrode, whereby a
plasma generates in the process chamber and activated species
influence the substrate to be treated. it is preferable that the
first frequency f.sub.1 is set lower than 5 MHz, more preferably in
a range of 100 kHz-1 MHz. It is also preferable that the second
frequency f.sub.2 is set higher than 10 MHz, more preferably in a
range of 10 MHz-100 MHz.
[0010] High frequency power having the frequency lower than the
lower lit of ion transit frequencies is applied to the lower
electrode. Therefore, the follow-up of ions becomes more excellent
and ions can be more efficiently accelerated with a smaller power.
In addition, both of ion and electron currents change more
smoothly. Further, the follow-up of ions does not depend upon kinds
of ion. The plasma treatment can be thus made more stable even when
the degree in the process chamber and the rate of gases mixed
change. On the other hand, high frequency power having the
frequency higher than the upper limit of ion transit frequencies is
applied to the upper electrode. Therefore, ions can be left free
from frequencies of their transit frequency zone to thereby enable
more stable plasma to be generated.
[0011] Ion transit frequency zones of process gases used by the
plasma treatment in the process, such as s etching, CVD and
sputtering, of making semiconductor devices are almost all in the
range of 1 MHz-10 MHz.
[0012] Impedances including such capacitive components that the
impedance relative to high frequency power becomes smaller than
several k.OMEGA. and that the impedance relative to relatively low
frequency power becomes larger than several a are arranged in
series between the upper electrode and its matching circuit and
between them and the ground. Current is thus made easier to flow to
raise the plasma density and ion control.
[0013] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention and, together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0015] FIG. 1 is a block diagram showing the plasma etching
apparatus according to an embodiment of the present invention;
[0016] FIG. 2 is a flow chart showing the plasma etching method
according to an embodiment of the present invention;
[0017] FIG. 3 shows a waveform of frequency applied to an upper (or
second) electrode;
[0018] FIG. 4 shows a waveform of frequency applied to a lower (or
first) electrode (or suscepter);
[0019] FIG. 5 is a graph showing transit frequency zones of various
gases;
[0020] FIG. 6 is a block diagram showing the plasma etching
apparatus according to another embodiment of the present
invention;
[0021] FIG. 7 is a block diagram showing the plasma etching
apparatus according to a further embodiment of the present
invention;
[0022] FIG. 8 is a block diagram showing the plasma etching
apparatus according to a still further embodiment of the present
invention;
[0023] FIG. 9 is a vertically-sectioned view showing a housing and
a ring member of the plasma etching apparatus;
[0024] FIG. 10 is a vertically-sectioned view showing the ring
member being cleaned;
[0025] FIG. 11 is a vertically-sectioned view showing the ring
member being cleaned;
[0026] FIG. 12 is a perspective view showing an upper shower
electrode and a semiconductor wafer dismantled;
[0027] FIG. 13 is a block diagram showing the plasma etching
apparatus according to a still further embodiment of the present
invention;
[0028] FIG. 14 is a vertically-sectioned view showing the plasma
etching apparatus when the suscepter is lowered;
[0029] FIG. 15 is a vertically-sectioned view showing the plasma
etching apparatus when the suscepter is lifted;
[0030] FIG. 16 is a partly-sectioned view showing a wafer carry-in
and -out gate and a baffle member;
[0031] FIG. 17 is a partly-sectioned view showing the wafer
carry-in and -out gate and another baffle member;
[0032] FIG. 18 is a block diagram showing the plasma etching
apparatus according to a still further embodiment of the present
invention;
[0033] FIG. 19 is a perspective view showing a cover for the upper
shower electrode;
[0034] FIG. 20 is a perspective view showing another cover for the
upper shower electrode;
[0035] FIG. 21 is a vertically-sectioned view showing the cover for
the upper shower electrode;
[0036] FIG. 22 is a plan view showing the cover for the upper
shower electrode;
[0037] FIG. 23 shows how the cover is attached to the upper shower
electrode;
[0038] FIG. 24 shows how the cover is detached from the upper
shower electrode;
[0039] FIG. 25 is a sectional view showing the cover being
cleaned;
[0040] FIG. 26 is a sectional view showing a further cover;
[0041] FIG. 27 is a sectional view showing a still further
cover;
[0042] FIG. 28 is a sectional view showing a still further
cover;
[0043] FIG. 29 is a block diagram showing a magnetron plasma
etching apparatus in which plasma is being generated;
[0044] FIG. 30 is a perspective view showing a baffle member
arranged on the side of the suscepter;
[0045] FIG. 31 is a vertically-sectioned view showing a hole formed
in the baffle member;
[0046] FIG. 32 is a vertically-sectioned view showing another hole
formed in the another baffle member;
[0047] FIG. 33 shows plasma generated in the conventional
apparatus;
[0048] FIG. 34 is in tended to explain the relation of the process
chamber to magnetic field generated by a permanent magnet;
[0049] FIG. 35 is a block diagram showing the plasma etching
apparatus according to a still further embodiment of the present
invention;
[0050] FIG. 36 is a block diagram showing the inside of a
vaporizer;
[0051] FIG. 37 is a sectional view showing another vaporizer;
[0052] FIG. 38 is a sectional view showing a further vaporizer;
[0053] FIG. 39 is a perspective view showing a still further
vaporizer;
[0054] FIG. 40 is a sectional view showing a pipe in which plural
kinds of gas axe mixed;
[0055] FIG. 41 is a block diagram showing a plasma CVD apparatus
provided with the vaporizer;
[0056] FIG. 42 is a sectional view showing the inside of the
conventional vaporizer; and
[0057] FIG. 43 is a graph showing the change of gas flow rate at
the initial stage of gas supply.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] Some embodiments of the present invention will be described
with reference to the accompanying drawings. Referring to FIGS. 1
through 5, a first embodiment will be described.
[0059] A process chamber 2 of an etching treatment apparatus 1 is
assembled by alumite-processed aluminium plates. It is earthed and
a suscepter 5 insulated by an insulating plate 3 is arranged in it.
The suscepter 5 is supported by its bottom through the insulating
plate 3 and a support 4.
[0060] A coolant chamber 6 is formed in the suscepter support 4. It
is communicated with a coolant supply supply (not shown) through
inlet and outlet pipes 7 and 8 and coolant such as liquid nitrogen
is circulated between it and the coolant supply supply.
[0061] An internal passage 9 is formed in a suscepter assembly
which comprises the insulating plate 3, the support 4, the
suscepter 5 and an electrostatic chuck 11, and heat exchanger gas
such as helium gas is supplied from a gas supply supply (not shown)
to the underside of a wafer W through it.
[0062] The top center portion of the suscepter 5 is swelled and the
electrostatic chuck 11, same in shape as the wafer W, is mounted on
the swelled portion of the suscepter 5. A conductive layer 12 of
the electrostatic chuck 11 is sandwiched between two sheets of high
molecular polyimide film. It in connected to a 1.5 kV DC high
voltage power supply 13 arranged outside the process chamber 2.
[0063] A focus ring 14 is arranged on the top of the suscepter 5
along the outer rim thereof, enclosing the wafer W. It is made of
insulating material not to draw reactive ions.
[0064] An upper electrode 21 is opposed to the top of the suscepter
assembly. Its electrode plate 24 is made of SiC or amorphous carbon
and its support member 25 is made by an alumite-process aluminium
plate. Its underside is separated from the wafer W an the suscepter
assembly by about 15-20 mm. It is supported by the top of the
process chamber 2 through an insulating member 22. A plurality of
apertures 23 are formed in its underside.
[0065] A gas inlet 26 is formed in the center of the support 25 and
a gas inlet pipe 27 is connected to it. A gas supply pipe 28 is
connected to the gas inlet pipe 27. The gas supply pipe 28 is
divided into three which are communicated with process gas supply
sources 35, 36 and 37, respectively. The first one is communicated
with the CF.sub.4 gas supply source 35 through a valve 29 and a
mass flow controller 32. The second one with the O.sub.2 gas supply
supply 36 through a valve 30 and a mass flow controller 33. The
third one with the N.sub.2 gas supply supply 37 through valve 31
and a mass flow controller 34.
[0066] An exhaust pipe 41 is connected to the bottom of the process
chamber 2. An exhaust pipe 44 is also connected to the bottom of an
adjacent load lock chamber 43. Both of them are communicated with a
common exhaust mechanism 45 which is provided with a turbo
molecular pump and the like. The load lock chamber 43 is connected
to the process chamber 2 through a gate valve 42. A carrier arm
mechanism 46 is arranged in the load lock chamber 43 to carry the
wafers W one by one between the process chamber 2 and the load lock
chamber 43.
[0067] A high frequency power applier means for generating plasma
in the process chamber 2 will be described.
[0068] A first oscillator 51 serves to oscillate high frequency
signal having a frequency of 800 kHz. A circuit extending from the
oscillator 51 to the lower electrode (or suscepter) 5 includes a
phase controller 52, an amplifier 53, a matching unit 54, a switch
SW.sub.1 and a feeder rod 55. The amplifier 53 is an RF generator
and the matching unit 54 includes a decoupling capacitor. The
switch SW.sub.1 is connected to the feeder rod 55. A capacitance 56
is arranged on an earthed circuit of the feeder rod 55. The phase
controller 52 houses a bypass circuit (not shown) and a changeover
switch (not shown) therein to enable signal to be sent from the
first oscillator 51 to the amplifier 53 through the bypass circuit.
High frequency signal oscillated is applied to the suscepter 5
through the phase controller 52, the amplifier 53, the matching
unit 54 and feeder rod 55.
[0069] On the other hand, a second oscillator 61 serves to
oscillate high frequency signal having a frequency of 27 MHz. A
circuit extending from the oscillator 61 to the upper (or shower)
electrode 21 includes an amplitude modulator 62, an amplifier 63, a
matching unit 64, a switch SW.sub.2 and a feeder rod 65. The
amplitude modulator 62 is connected to a signal circuit of the
second oscillator 61 and also to that of the first oscillator 51.
It houses a bypass circuit (not shown) and a changeover switch (not
shown) in it to enable signal to be sent from it to the amplifier
63 through the bypass circuit. The amplifier 63 is an RP generator
and the matching unit 64 includes a decoupling capacitor. The
switch SW.sub.2 is connected to the feeder rod 65. A capacitance 66
and an inductance 67 are arranged on an earthed circuit of the
feeder rod 65. High frequency signal oscillated is applied to the
upper electrode 21 through the amplitude modulator 62, the
amplifier 63, the matching unit 64 and the feeder rod 65. High
frequency signal having the frequency of 800 kHZ can also be
applied, as modulated wave, to the amplitude modulator 62.
[0070] The reason why the earthed circuit of the feeder rod 55
includes no inductance resides in that the electrostatic chuck 11,
the gas passage 9, the coolant chamber 6, lifter pins (not shown)
and the like are included in the lower electrode signal
transmission circuit, that the feeder rod 55 itself is long, and
that the suscepter 5 itself has large inductance accordingly.
[0071] The amplifiers 51 and 64 are arranged independently of the
other. Therefore, voltages applied to the upper electrode 21 and
the suscepter 5 can be changed independently of the other.
[0072] Referring to FIG. 2, it will be described how silicon oxide
film (SiO.sub.2) on the silicon wafer W is plasma-etched.
[0073] Both of the load lock chamber 43 and the process chamber 2
are exhausted to substantially same internal pressure. The gate
valve 42 is opened and the wafer W is carried from the load lock
chamber 43 into the process chamber 2 (step S1). The gate valve 42
is closed and the process chamber 2 is further exhausted to set its
internal pressure in a range of 10-250 mTorr (step S2).
[0074] The valves 29 and 30 are opened, and CF.sub.4 and O.sub.2
gases are introduced into the process chamber 2. Their flow rates
are controlled and they are mixed at a predetermined rate. The
(CF.sub.4+O.sub.2) mixed gases are supplied to the wafer W through
apertures 23 of the upper shower electrode 21 (step S3). When the
internal pressure in the chamber 2 becomes stable at about 1 Pa,
high frequency voltages are applied to the upper and lower
electrodes 21 and 5 to generate plasma between them.
[0075] Frequencies of high frequency power applied to the upper and
lower electrodes 21 and 5 to generate plasma are controlled as
follows (step S4).
[0076] The switches SW.sub.1 and SW.sub.2 are opened to disconnect
(OFF) the capacitance 56 from the feeder rod 55 and the capacitance
66 and the inductance 67 from the feeder rod 65. When the
oscillators 61, 51, the amplitude modulator 62 and the amplifiers
63, 53 are made operative under this state, high frequency power
having a certain waveform is applied to the upper electrode 21.
High frequency power having a frequency same as or higher than the
higher one of upper ion transit frequencies characteristic of
CP.sub.4 and O.sub.2 gases is applied to the upper electrode 21.
High frequency power having a waveform shown in FIG. 3, for
example, is applied to the upper electrode 21. Plasma is thus
generated.
[0077] On the other hand, high frequency power having a certain
waveform is applied to the lower electrode 5 by the oscillator 51.
High frequency power having a frequency same as or lower than the
lower one of ion transit frequencies characteristic of CF.sub.4 and
O.sub.2 gases is applied to the lower electrode S. High frequency
power having a waveform shown in FIG. 4, for example, is applied to
the lower electrode. Ions in plasma are thus accelerated and drawn
to the wafer W. passing through the plasma sheath, to thereby act
on the wafer W.
[0078] The high frequency by which plasma is generated has the
waveform shown in FIG. 3 in this case. Therefore, the dissociation
of gases introduced into the process chamber 2 is not advanced to
an extent greater than needed. In addition, the frequency of 800
kHz by which ions in plasma are accelerated and drawn to the wafer
W can be controlled in phase by the phase controller 52. Ions can
be thus drawn to the wafer W before the dissociation of gases
progresses to the extent greater than needed. When ions most
suitable for etching are generated, therefore, they can be made
incident onto the wafer W. When they are caused to act on the wafer
W while cooling it, therefore, anisotropic etching having a high
aspect rate can be realized.
[0079] The phase control of the high frequency power (frequency:
800 kHz) applied to the lower electrode may be based on a state
under which the dissociation of gases does not progress to the
extent greater than needed or a state under which the dissociation
of gases progresses to the final stage, they are then combined
again and become radicals suitable for etching.
[0080] Further, it may be arranged that a dummy wafer DW is used
and that the treatment is carried out while confirming the extent
to which the phase of the high frequency 800 kHz is shifted. The
timing at which the phase of the high frequency 800 kHz is shifted
may be previously set in this case, depending upon kinds of process
gases, etching, coating and the like.
[0081] When the end point of anisotropic etching is detected (step
S5), exhaust, process gas introducing and plasma control steps S6,
S7 and S8 are successively carried out to isotropically etch film
on the wafer W. The exhaust step S6 is substantially same as the
above-described one S2. At the process gas introducing step S7,
C.sub.4F.sub.8, CH3, Ar and CO gases, for example, different from
those at the above-described step S3, are supplied to the process
chamber 2.
[0082] At the plasma control step S8, plasma is controlled
substantially as seen at the above-described step S4. When the end
point of isotropic etching is detected (step S9), the applying of
the high frequency power is stopped and the process chamber 2 is
exhausted while supplying nitrogen gas into it (step S10). The gate
valve 42 is opened and the wafer W is carried from the process
chamber 2 into the load lock chamber 43 (step S11).
[0083] Referring to FIG. 5, the plasma control steps S4 and S8 will
be described in more detail.
[0084] FIG. 5 is a graph showing ion transit frequency zones
characteristic of three kinds of gases A, B and C, in which
frequencies are plotted on the vertical axis. An ion transit
frequency zone Az of gas A extends from an upper end Au to a lower
end Al, an ion transit frequency zone Bz of gas B from an upper end
Bu to a lower end Bl, and an ion transit frequency zone Cz of gas C
from an upper end Cu to a lower end Cl. CHF.sub.3 or CO gas is
cited as gas A. Ar gas is cited as gas B. CP.sub.4, C.sub.4F.sub.8
or O.sub.2 gas is cited as gas C. At least one or more gases
selected from the group consisting of CF.sub.4, C.sub.4F.sub.8,
CHF.sub.3, Ar, O.sub.2 and CO gases are used as process gas. In
short, process gas may be one of them or one of mixed gases
(CH.sub.3+Ar+O.sub.2), (CRF.sub.3+CO+O.sub.2),
(C.sub.4F.sub.8+Ar+O.sub.2- ), (C.sub.4F.sub.8+CO+Ar+O.sub.2) and
(CF.sub.4+CHF.sub.3).
[0085] When mixed gases of A, B and C are used as process gas, the
high frequency power applied to the upper electrode has a frequency
higher than the highest one Bu of upper ion transit frequencies Au,
Bu and Cu and the high frequency power applied to the lower
electrode has a frequency lover than the lowest one Cl of lower ion
transit frequencies Al, Bl and Cl.
[0086] Another etching treatment method conducted using the
above-described etching treatment apparatus 1 will be
described.
[0087] The switches SW.sub.1 and SW.sub.2 are closed or turned on
to connect the signal transmission circuits to their earthed
circuits. High frequency signal (frequency: 800 kHz) is amplified
directly by the amplifier 53, bypassing the phase controller 52,
and applied to the suscepter 5 through the matching unit 54. On the
other hand, high frequency signal (frequency: 27 MHz) is amplified
directly by the amplifier 63, bypassing the amplitude modulator 62,
and applied to the upper electrode 21 via the matching unit 64 and
the feeder rod 65.
[0088] Conventionally, the matching unit arranged on the side of
the suscepter is matched relative to the high frequency of 800 kHz
but it becomes high in impedance relative to the high frequency of
27 MHz applied from the upper electrode, thereby making it
difficult for the high frequency applied from the upper electrode
to flow to the suscepter. Plasma is thus scattered, so that the
plasma density decreases.
[0089] In the apparatus 1, however, the capacitance 56 is arranged
between the feeder rod and the ground. A DC resonance circuit can
be thus formed relative to the high frequency applied from the
upper electrode. When the value of the capacitance 56 is adjusted,
considering the constant of a distributed constant circuit,
therefore, composite impedance can be made smaller than several
.OMEGA. to thereby make it easy for the high frequency applied from
the upper electrode to flow to the suscepter 5. Therefore, current
density can be raised and plasma density thus attained can also be
raised.
[0090] On the other hand, the capacitance 66 and the inductance 67
are attached to the feeder rod 65 arranged on the side of the upper
electrode 21. Therefore, a DC resonance circuit is also provided
relative to the high frequency of 800 kHz, thereby making it easy
for the high frequency 800 kHz applied to the side of the suscepter
5 to flow to the upper electrode 21. The incidence of ions in
plasma onto the wafer W is promoted accordingly.
[0091] Although high frequency power having the frequency 27 MHz
has been applied to the upper electrode 21 and high frequency power
having the frequency 800 kHz to the lower electrode 5 in the
above-described embodiment, other frequencies may be set, depending
upon kinds of process gas.
[0092] It is desirable that high frequency power applied to the
lower electrode 5 has a frequency lower than the inherent lower ion
transit frequency or lower than 1 MHz and that high frequency power
applied to the upper electrode 21 has a frequency higher than the
inherent upper ion transit frequency or higher than 10 MHz. When so
arranged, ions are more efficiently accelerated with a smaller high
frequency power and the follow-up of ions in the plasma sheath to
bias frequencies becomes stable even when the rate of gases mixed
and the degree of vacuum in the process chamber are a little
changed. Therefore, ions can be made incident onto the wafer
without scattering in the plasma sheath, thereby enabling a finer
work to be achieved at high speed.
[0093] According to the present invention, the follow-up of ions is
more excellent due to the high frequency power applied to he first
electrode and they can be more efficiently accelerated with a
smaller power. In addition, plasma itself can be kept stable. A
more stable treatment can be thus realized even when the degree of
vacuum in the process chamber and the rate of gases mixed
change.
[0094] Further, when the dissociation is controlled not to progress
to the extent greater than needed and the phase of the high
frequency power applied to the first electrode is also controlled,
ions or radicals needed for the treatment can be created at a
desired timing and they can be made incident onto the wafer.
Anisotropic etching treatment having a high aspect rate can be thus
attained. In addition, damage applied to the wafers can be reduced.
Further, plasma density can be made high without raising the high
frequency power and its frequency, and ion control can be made
easier.
[0095] A second embodiment will be described referring to FIG. 6.
Same components as those in the above-described first embodiment
will be mentioned only when needed.
[0096] An etching treatment apparatus 100 has, as high frequency
power applier mans, two high frequency power supplies 141, 151 and
a transformer 142. The primary side of the transformer 142 is
connected to the first power supply 141 and then earthed. Its
secondary side is connected to both of the upper and lower
electrodes 21 and 105. A first low pass filter 144 is arranged
between the secondary side and the upper electrode 21 and a second
low pass filter 145 between the secondary side and the lower
electrode 105. The first power supply 141 serves to apply high
frequency power having the relatively low frequency such as 380 kHz
to the electrodes 105 and 21. When silicon oxide (SiO.sub.2) film
is to be etched, it is optimum that a frequency f.sub.0 of high
frequency power applied from the first power supply 141 is 380 kHz
and when polysilicon (poly-Si) film is to be etched, it is
preferably in a range of 10 kHz-5 MHz.
[0097] The transformer 142 has a controller 143, by which the power
of the first power supply 141 is distributed to both electrodes 105
and 21 at an optional rate. For example, 400 W of full power 1000 W
can be applied to the suscepter 105 and 600 W to the upper
electrode 21. In addition, high frequency powers whose phases are
shifted from each otter by 180.degree. are applied to the suscepter
105 and the upper electrode 21.
[0098] The second power supply 151 serves to apply high frequency
power having the high frequency such as 13.56, for example, to the
upper electrode 21. It in connected to the upper electrode 21 via a
capacitor 152 and then earthed. This plasma generating circuit is
called P mode one. It is optimum that a frequency f.sub.1 of high
frequency power applied from it is 13.56 MHz, preferably in a range
of 10-100 MHz.
[0099] It will be described how silicon oxide film (SiO.sub.2) on
the silicon wafer W is etched by the above-described etching
apparatus 100.
[0100] The wafer W is mounted on the suscepter 105 and sucked and
held there by the electrostatic chuck 11. The process chamber 102
in exhausted while introducing CF.sub.4 gas into it. After its
internal pressure reaches about 10 mTorr, high frequency power of
13.56 MHz is applied from the second power supply 151 to the upper
electrode 21 to make CF.sub.4 gas into plasma and dissociate gas
molecules between the upper electrode 21 and the suscepter 105. On
the other hand, high frequency power of 380 kHz is applied from the
first power supply 141 to the upper and lower electrodes 21 and
105. Ions and radicals such as fluoric ones in plasma-like gas
molecules are thus drawn to the suscepter 105, thereby enabling
silicon oxide film on the wafer to be etched.
[0101] The generating and keeping of plasma itself are attained in
this case by the high frequency power having a higher frequency and
applied from the second power supply 151. Stable and high density
plasma can be thus created. In addition, activated species in this
plasma are controlled by the high frequency power of 380 kHz
applied to the upper and lower electrodes 21 and 105. Therefore, a
more highly selective etching can be applied to the wafer W. Ions
cannot follow up to the high frequency power which has the
frequency of 13.56 MHz and by which plasma is generated. Even when
the output of the power supply 131 is made large to generate high
density plasma, however, the wafers w cannot be damaged.
[0102] The first and second low pass filters 144 and 145 are
arranged on the secondary circuit of the transformer 142. This
prevents the high frequency power having the frequency of 13.56 MHz
and applied from the second power supply 151 from entering into the
secondary circuit of the transformer 142. Therefore, the high
frequency power having the frequency of 13.56 MHz does not
interfere with the one having the frequency of 380 kHz, thereby
making plasma stable. Blocking capacitors may be used instead of
the low pass filters 144 and 145. Although high frequency powers
have been continuously applied to the electrodes in the above case,
modulation power which becomes strong and weak periodically may be
applied to the electrodes 21 and 105.
[0103] A third apparatus 200 will be described with reference to
FIG. 7. Same components as those in the above-described first and
second embodiments will be mentioned only when needed.
[0104] A high frequency power circuit of this apparatus 200 is
different from that of the second embodiment in the following
points: A suscepter 205 of the apparatus 200 is not earthed; no low
pass filter is arranged on the secondary circuit of a transformer
275; and a second transformer 282 is arranged on the circuit of a
second power supply 281.
[0105] The second power supply 281 serves to generate high
frequency power of 3 MHz. It is connected to the primary side of
the transformer 282, whose secondary side are connected to upper
and lower electrodes 21 and 205. A controller 293 which controls
the distribution of power is also attached to the secondary side of
the transformer 282.
[0106] It will be described how the etching treatment is carried
out by the apparatus 200.
[0107] High frequency powers of 3 MHz whose phases are shifted from
each other by 180.degree. are applied from the power supply 281 to
the suscepter 205 and the upper electrode 21 to generate plasma
between them. At the same time, high frequency powers of 380 kHz
whose phases are shifted from each other by 180.degree. are applied
from a power supply 274 to them. Ions in plasma generated are thus
accelerated to enter into the wafer W.
[0108] Further, the two high frequency power supplies 274 and 281
in the third apparatus are arranged independently of the other. In
short, they are of the power split type. Therefore, they do not
interfere with each other, thereby enabling a more stable etching
treatment to be realized.
[0109] Furthermore, high frequency powers are supplied from the two
power supplies 274 and 281 to both of upper and lower electrodes 21
and 205, respectively. The flow of current can be thus concentrated
on a narrow area between the upper 21 and the lower electrode 205.
As the result, a high density plasma can be generated and the
efficiency of controlling ions in plasma can be raised.
[0110] A fourth embodiment will be described, referring to FIGS. 8
through 12. Same components as those in the above-described
embodiments will be mentioned only when needed.
[0111] As shown in FIG. 8, an etching apparatus 300 has a
cylindrical or rectangular column-like air-tight chamber 302. A top
lid 303 is connected to the side wall of the process chamber 302 by
hinges 304. Temperature adjuster means such as a heater 306 is
arranged in a suscepter 305 to adjust the treated face of a treated
substrate W to a desired temperature. The heater 306 is made, for
example, by inserting a conductive resistance heating unit such as
tungsten into an insulating sintered body made of aluminium
nitride. Current is supplied to this resistant heating unit through
a filter 310 to control the temperature of the wafer W in such a
way that the treated face of the wafer W is raised to a
predetermined temperature.
[0112] A high frequency power supply 319 is connected to the
suscepter 305 through a blocking capacitor 318.
[0113] When the wafer W is to be etched, the high frequency power
of 13.56 MHz is applied from the power supply 319 to the suscepter
305.
[0114] The suscepter 305 is supported by a shaft 321 of a lifter
mechanism 320. When the shaft 321 of the lifter mechanism 320 is
extended and retreated, the suscepter 305 is moved up and down. A
bellows 322 is attached to the lower end of the suscepter 305 not
to leak gases in the process chamber 302 outside.
[0115] Reaction products deposit in the process chamber 302. A ring
325 is freely detachably attached to the outer circumference of the
suscepter 305. It is made preferably of PTFE (teflon), PFA,
polyimide or PBI (polybenzorimdazole). It may also be made of such
a resin that has insulation in a temperature range of common
temperature--500.degree. C. or of such a metal like aluminium that
has insulating film on its surface. A baffle plate 326 is made
integral to it. A plurality of holes 328 are formed in the baffle
plate 326. They are intended to adjust the flow of gases in the
process chamber 302, to make its exhaust uniform, and to make a
pressure difference between the treatment space and a space
downstream the flow of gases. A top portion 327 of the ring 325 is
bent inwards, extending adjacent to the electro-static chuck 11, to
make the top of the suscepter 305 exposed as small as possible.
[0116] An upper electrode 330 is arranged above the suscepter 305.
when the etching treatment is to be carried out, the suscepter 305
is lifted to adjust the interval between the suscepter 305 and the
upper electrode 330. The upper electrode 330 is made hollow and a
gas supply pipe 332 is connected to this hollow portion 331 to
introduce CH.sub.4 gas and others from a process gas supply supply
333 into the hollow portion 331 through a mass flow controller
(MFC) 334. A diffusion plate 335 is arranged in the hollow portion
331 to promote the uniform diffusion or scattering of process
gases. Further, a process gas introducing section 337 having a
plurality of apertures 336 is arranged under the diffusion plate
335. An exhaust opening 340 which is communicated with an exhaust
system provided with a vacuum pump and others is formed in the side
wall of the process chamber 302 at the lower portion thereof to
exhaust the process chamber 302 to an internal pressure of 0.5
Torr, for example.
[0117] When the wafer W is etched in the process chamber 302,
reaction products are caused and they adhere to the ring 325 and
the baffle plate 326, leaving the outer circumference of the
suscepter 305 substantially free from them. When the etching
treatment is finished, the wafer W is carried out of the process
chamber 302 into the load lock chamber 43. A next new wafer W is
then carried from the load lock chamber 43 into the process chamber
302 and etched in it. When this etching treatment is repeated many
times, a lot of reaction products adhere to the ring 325.
[0118] As shown in FIG. 9, the top lid 303 of the process char 302
is opened and the ring 325 is detached from the suscepter 305.
Reaction products are then removed from the ring 325 by
cleaning.
[0119] The time at which the ring 325 must be cleaned is determined
as follows:
[0120] the number of particles adhering to the wafer W which has
been treated by the apparatus 300 is counted and when it becomes
larger than a predetermined value;
[0121] the number of particles scattering in the atmosphere
exhausted from the apparatus 300 and/or at least in one or more
areas in the exhaust pipe is counted and when it becomes larger
than a predetermined value;
[0122] when predetermined sheets of the wafer W have been treated
in the apparatus 300; and
[0123] when the total of hours during which plasma has been
generated or the plasma treatment has been carried out reaches a
predetermined value.
[0124] Dry or wet cleaning is used. The dry cleaning is carried out
in such a way that ClF.sub.3, CF.sub.4 or NF.sub.3 gas is blown to
the ring 325 which is left attached to the suscepter 305 or which
is detached from the suscepter 305 and left outside the process
chamber 302, as shown in FIG. 10.
[0125] On the other hand, the wet cleaning is carried out in such a
way that the ring 325 to which reaction products have adhered is
immersed in cleaning liquid 351 in a container 350, as shown in
FIG. 11. IPA (isopropyl alcohol), water or fluorophosphoric acid is
used as cleaning liquid 351. The ring 325 from which reaction
products have been removed by the dry or wet cleaning is again
attached to the suscepter 305 and the plasma treatment is then
repeated.
[0126] When the wafers W are to be etched, plural rings 325 are
previously prepared relative to one suscepter 305. If so, cleaned
one can be attached to the suscepter 305 while cleaning the
other.
[0127] The dry or wet cleaning can be appropriately used to remove
reaction products from the ring 325. When the dry cleaning is
compared with the wet one, however, the former is easier in
carrying out it but its cleaning is more incomplete. To the
contrary, the latter is more excellent in cleaning the ring 325 but
its work is relatively more troublesome. Therefore, it is desirable
that the wet cleaning is periodically inserted while regularly
carrying out the dry cleaning.
[0128] The baffle plate will be described referring to FIGS. 12 and
13.
[0129] As shown in FIG. 12, it is preferable that an effective
diameter D.sub.1 is set not larger than a diameter D.sub.2. The
effective diameter D.sub.1 represents a diameter of that area where
the process gas jetting apertures 336 are present, and the diameter
D.sub.2 denotes that of the wafer W in this case. When the
effective diameter D.sub.1 is set in this manner, a high efficient
etching can be attained in the process chamber 302. It is the most
preferable that the effective diameter D.sub.1 is set to occupy
about 90g of the diameter D.sub.2.
[0130] Providing that the underside 338 of the upper electrode has
a diameter D.sub.3, the effective diameter D.sub.1, the diameter
D.sub.2 and the diameter D.sub.3 meet the following inequality
(1).
D.sub.1<D.sub.2<D.sub.3 (1)
[0131] When the ring the whole of which is made of insulating
material is used as it is, the effective area of the lower
electrode becomes substantially smaller than that of the upper
electrode, thereby making plasma uneven. This problem can be solved
when the effective area of the lower electrode is made same as that
of the upper electrode or when it is made larger than that of the
upper electrode.
[0132] As shown in FIG. 13, the baffle plate 326 is made integral
to the ring 325. It is divided into a portion 360 equal to the
diameter D.sub.4 and another portion 361 larger than it, and the
inner portion 360 is made of metal such as aluminium and stainless
steel while the outer portion 361 of PTFE (teflon), PPA, polyimide,
PBI (polybenzoimidazole), other insulating resin or
alumite-processed aluminium.
[0133] The diameter D.sub.4 is made same as or larger than the
diameter D.sub.3. At least the inner portion 360 of the baffle
plate 326 is positioned just under the upper electrode 330. The
ring 326 is divided into an upper half 363 and a lower half 364,
sandwiching an insulator 362 between them. The upper half 363 is
made of metal such as aluminium and stainless steel and it is made
integral to the inner portion 360 of the baffle plate 326. A power
supply 319 which serves to apply high frequency power to the
suscepter 305 is connected to these inner portion 360 of the baffle
plate 326 and upper half 363 of the ring 325 by a lead 367 via a
blocking capacitor 318. At least those portions (the inner portion
360 of the baffle plate and the upper half 363 of the ring) which
are positioned just under the upper electrode 330 are made same in
potential. In order to make it easy to exchange the ring 325, it is
preferable that the lead 367 is connected to the upper half 363 of
the ring or the inner portion 360 of the baffle plate 326 by an
easily-detached socket 368. A lower suscepter 365 is insulated from
the upper one 305 by an insulating layer 366. The lower half 364 of
the ring is also therefore insulated from the upper half 363
thereof by the insulator 362.
[0134] When at least that portion of the baffle plate 326 which is
positioned just under the upper electrode 330 is made same in
potential as the suscepter 305, as described above, plasma can be
made uniform.
[0135] Referring to FIGS. 14 and 15, it will be described how the
side opening 41 of the process chamber 302 through which the wafer
W is carried in and out is opened and closed as the suscepter is
moved up and down.
[0136] The ring 325 provided with the baffle plate 326 encloses the
suscepter 305. The lifter means 320 is arranged under the process
car 302 and the suscepter 305 is supported by the shaft 321 of the
lifter means 320.
[0137] When the suscepter 305 is moved down, as shown in FIG. 14,
the baffle plate 326 is positioned lower than the side opening 41.
When it is moved up, as shown in FIG. 15, the baffle plate 326 is
positioned higher than the side opening 41.
[0138] When the suscepter 305 is moved down and the baffle plate
326 is positioned lower than the side opening 41, therefore, the
wafer W can be freely carried in and out of the process chamber 302
through the side opening 41. When the baffle plate 326 is
positioned higher than the side opening 41 at the time of etching
treatment, however, the side opening 41 is shielded from the
process space between the upper and the lower electrode, thereby
preventing plasma from entering into the side opening 41.
[0139] As shown in FIG. 16, it may be arranged that a shielding
plate 370 is attached to the outer circumference of the baffle
plate 326 and that the side opening 41 is closed by the shielding
plate 370 when the suscepter 305 is moved up. Particularly, the
side opening 41 is too narrow for hands to be inserted. Therefore,
inert gas may be supplied, as purge gas, into a clearance 371
between the shielding plate 370 and the inner face of the process
chamber 302 not to cause process gases to enter into the side
opening 41. Similarly, purge gas may also be supplied into a
clearance 372 between the wafer-mounted stage 305 and the upper
half 363 of the ring 325.
[0140] The side opening 41 may be closed by a shielding plate 373
attached to the outer circumference of the baffle plate 326, as
shown in FIG. 17, when the baffle plate 326 is lifted half the side
opening 41.
[0141] Referring to FIGS. 18 through 28, the cleaning of a fifth
CVD apparatus will be described. Same components an those in the
above-described embodiments will be mentioned only when needed.
[0142] A CVD apparatus 500 has a process chamber 502 which can be
exhausted vacuum. A top lid 503 is connected to the side wall of
the process chamber 502 by hinges 505. A shower head 506 is formed
in the center portion of the top lid 503 at the underside thereof.
A process gas supply pipe 507 is connected to the top of the shower
head 506 to introduce mixed gases (SiH.sub.4+H.sub.2) from a
process gas supply 508 into the shower head 506 through a mass flow
controller (MFC) 510. A plurality of gas jetting apertures 511 are
formed in the bottom of the shower head 506 and process gases are
supplied to the wafer W through these apertures 511.
[0143] An exhaust pipe 516 which is communicated with a vacuum pump
515 is connected to the side wall of the process chamber at the
lower portion thereof. A laser counter 517 which serves to count
the number of particles contained in the gas exhausted from the
process chamber 502 is attached to the exhaust pipe 516. The
process chamber 502 is decompressed to about 10.sup.-6 Torr by the
exhaust means 515.
[0144] The process chamber 502 has a bottom plate 521 supported by
a substantially cylindrical support 520 and cooling water chambers
522 are formed in the bottom plate 521 to circulate cooling water
supplied through a cooling water pipe 523 through them.
[0145] A suscepter 525 is mounted on the bottom plate 521 through a
beater 526 and these heater 526 and the wafer-mounted stage 525 are
enclosed by a heat insulating wall 527. The heat insulating wail
527 has a mirror-finished surface to reflect heat radiated from
around. The heater 526 is heated to a predetermined temperature or
400-2000.degree. C. by voltage applied from an AC power supply (not
shown). The wafer W on the stage 525 is heated to 800.degree. C. or
more by the heater 526.
[0146] An electrostatic chuck 530 is arranged on the top of the
wafer-mounted stage 525. It comprises polyimide resin films 531,
532 and a conductive film 533. A variable DC voltage supply (not
shown) is connected to the conductive film 533.
[0147] A detector section 538 of a temperature sensor 537 is
embedded in the suscepter 525 to successively detect temperature in
the wafer-mounted stage 525. The power of the AC power supply which
is Supplied to the heater 526 is controlled responsive to signal
applied from the temperature sensor 537. A lifter 541 is connected
to the suscepter 525 through a member 543 to move it up and down.
Those portions of a support plate 546 through which support poles
544 and 545 are passed are provided with bellows 547 and 548 to
keep the process chamber 502 air-tight.
[0148] A cover 560 is freely detachably attached to the shower head
506. It is made of material of the PTFE (teflon) group, PFA,
polyimide, PEI (polybenzoimidazole) or polybenzoazole, which are
insulators and heat resistant. In the case of the plasma CVD
apparatus, the wafer-mounted stage 525 is heated to about
350-400.degree. C. at the time of plasma process and in the case of
the heat CVD apparatus, it is usually heated higher than
650.degree. C. or to about 800.degree. C. The cover 560 is
therefore made of such a material that can resist this radiation
heat.
[0149] As shown in FIG. 19, a large-diameter opening 563 is formed
in a bottom 561 of the cover 560. When the cover 560 is attached to
the shower head 506, the gas jetting apertures 511 of the shower
head 506 appear in the opening 563.
[0150] As shown in FIG. 20, a plurality of apertures 565 may also
be formed in the cover 560. These apertures 565 are aligned with
those of the shower head 506 in this case.
[0151] As shown in FIG. 21, recesses 570 may be formed in the outer
circumference of the shower head 506 while claws 571 are formed on
an inner circumference 562 of the cover 506, as shown in FIG. 22.
The claws 571 are fitted into recesses 570 in this case while
elastically deforming the cover 560. The three claws 571 are
arranged on the inner circumference 562 of the cover 560 at a same
interval, as shown in FIG. 22.
[0152] As shown in FIG. 23, the cover 560 may be attached to the
shower head 506 in such a way that bolts 575 are screwed into
recesses 573 of the shower head 506 through a cover side 562.
[0153] It will be described how upper electrode cover is
cleaned.
[0154] When mixed gases (SiH.sub.4+H.sub.2), for example, are
introduced into the process chamber 502 to form film on the wafer
W, reaction products adhere to the upper electrode cover 560. As
shown in FIG. 24, the top lid 503 is opened and the cover 560 is
detached from the shower head 506. The cover 560 is then immersed
in cleaning liquid 581 in a container 580 (wet cleaning). Or the
dry cleaning may be conducted in such a way that cleaning gas such
as ClF.sub.3, CP.sub.4 or NF.sub.3 gas is introduced into the
process chamber 502 while keeping the cover 560 attached to the
shower head 506.
[0155] The time at which the cleaning must be conducted is
determined as follows. The number of particles contained in the gas
exhausted through the exhaust pipe 516 is counted by the counter
517 and when it becomes larger than a limit value, the cleaning of
the cover 560 must be started.
[0156] As shown in FIG. 26, the underside of the top lid 503 may be
covered by a cover 585, in addition to the shower head 506. Or the
inner face of the process chamber 502 may be covered by a cover
586, in addition to the shower head 506, as shown in FIG. 27. An
opening 587 is formed in the cover 586 in this case, corresponding
to the side opening 41 of the process chamber 502. Or a cover 590
having a curved bottom 591 may be used, as shown in FIG. 28.
[0157] A sixth embodiment will be described referring to FIGS. 29
through 34. Same components as those in the above-described
embodiments will be mentioned only when needed.
[0158] As shown in FIG. 29, a magnetron type plasma etching
apparatus 600 has a rotary magnet 627 above a process chamber 602.
Upper and lower electrodes 624 and 603 are opposed in the process
chamber 602.
[0159] Process gases are introduced from a gas supply supply 629 to
the space between the upper and the lower electrode through an MFC
630. The rotary magnet 627 serves to stir plasma generated between
both of the electrodes 603 and 624.
[0160] A suscepter assembly comprises an insulating plate 604, a
cooling block 605, a heater block 606, an electrostatic chuck 608
and a focus ring 612. A conductive film 608c of the electrostatic
chuck 608 is connected to a filter 610 and a variable DC high
voltage supply 611 by a lead 609. The filter 610 is intended to cut
high frequencies. An internal passage 613 is formed in the cooling
block 605 and liquid nitrogen is circulated between it and a
coolant supply supply (not shown) through pipes 614 and 615. A gas
passage 616 is opened at tops of the suscepter 603, the heater 617
and the cooling block 605, passing through the suscepter assembly.
The base end of the gas passage 616 is communicated with a heat
exchanger gas supply supply (not shown) to supply heat exchanger
gas such as helium gas to the underside of the wafer W through it.
The heater block 606 is arranged between the suscepter 603 and the
cooling block 605. It is shaped like a band-like ring and it is
several mm thick. It is a resistant heating unit. It is connected
to a filter 619 and a power supply 620.
[0161] Inner and outer pipes 621a and 521b are connected to the
suscepter 603 and the process chamber 602. They are conductive
double pipes, the outer one 621a of which is earthed and the inner
one 621b of which is connected to a high frequency power supply 623
via a blocking capacitor 622. The high frequency power supply 623
has an oscillator for oscillating the high frequency of 13.56 MHz.
Inert gas is introduced from a gas supply supply (not shown) into a
clearance between the inner 621a and the outer pipe 621b and also
into the inner pipe 621b.
[0162] Except the upper electrode, the inner faces of the top of
the process car 602 is covered by an insulating protection layer
625, 3 mm or more thick. similarly, the inner face of its side wall
is covered by an insulating protection layer 626, 3 mm or more
thick.
[0163] In the conventional magnetron type plasma etching apparatus,
the flow of electrons tends to gather near the inner wall of the
process chamber, as shown in FIG. 34. The flow of plasma is thus
irradiated in a direction W. that is, to the side wall of the
process chamber, thereby damaging it. In the above-described
apparatus 600, however, the side wail of the process chamber 602 is
covered by the insulating protection layer 626 so that it can be
protected.
[0164] Process gas supply and exhaust lines or systems of the
apparatus 600 will be described.
[0165] A process gas supply pipe 628 is connected to the side wall
of the process chamber 602 at the upper portion thereof and
CF.sub.4 gas is introduced from a process gas supply 629 into the
process chamber 602 through it. An exhaust pipe 633 is also
connected to the side wall of the process chamber 602 at the lower
portion thereof to adjust the process chamber 602 by an exhaust
means 631, which is provided with a vacuum pump. A valve 632 is
attached to the exhaust pipe 633.
[0166] As shown in FIG. 30, a baffle plate 635 is arranged between
the outer circumference of the suscepter 603 and the inner wall of
the process chamber 602. Plural holes 634 are formed in the baffle
plate 635 to adjust the flow of exhausted air or gas.
[0167] As shown in FIG. 31, each hole 634 is tilted. Therefore, the
conductance of gas rises when it passes through the holes 634 and
the gradient of electric field becomes gentle accordingly. This
prevents discharge from being caused in the holes 634 and plasma
from flowing inward under the baffle plate 635.
[0168] As shown in FIG. 32, holes 634a, 634b, 634c and 634d each
having a same pitch may be formed in plural baffle plates 635a,
635b, 635c and 635d to form a step-like exhaust hole 634A. This
exhaust hole 634A can be formed when the baffle plates 635a, 635b,
635c and 635d are placed one upon the others in such a way that the
holes 634a, 634b, 634c and 634d are a little shifted from their
adjacent ones. When these exhaust holes 634A are formed, abnormal
discharges in plasma generation can be more effectively prevented
In the conventional apparatus, each hole 692 in the baffle plate
extends only vertical, as shown in FIG. 33. Those holes 692 allow
plasma to flow inward under the baffle plate and abnormal
discharges such as sparkles to be caused in them, thereby causing
metal contamination and particles. In the apparatus 600, however,
the holes 634 are directed toward the exhaust opening 633. The
reduction of exhaust speed can be thus prevented. When the
direction in which the turbo-pump 631 is driven is made reverse to
the flow of exhausted gas, that is, when it is made anticlockwise
in a case where exhausted gas flows clockwise, the speed of
exhausted gas can be raise to a further extent.
[0169] A seventh embodiment will be described ref erring to FIGS.
35 through 43. TEOS gas is used to form film on the wafer W in this
seventh plasma CVD apparatus. Same components as those in the
above-described embodiments will be mentioned only when needed.
[0170] The plasma CVD apparatus 700 has a cylindrical or
rectangular process chamber 710, in which a suscepter 712 is
arranged to hold a wafer W on it. It is made of conductive material
such as aluminium and it is insulated from the wall of the process
chamber 710 by an insulating member 714. A heater 716 which is
connected to a power supply 718 is embedded in it. The wafer W on
it is heated to about 300.degree. C. (or film forming temperature)
by the heater 716. The process chamber is of the cold wall type in
this case, but it may be of the hot wall type. The process chamber
of the hot wall type can prevent gas from being condensed and
stuck.
[0171] The electrostatic chuck 11 is arranged on the suscepter 712.
Its conductive film 12 is sandwiched between two sheets of film
made of polybensoimidazole resin. A variable DC high voltage power
supply 722 is connected to the conductive film 12. A focus ring 724
is arranged on the suscepter 712 along the outer rim thereof.
[0172] A high frequency power supply 728 is connected to the
suscepter 712 via a matching capacitor 726 to apply high frequency
power having a frequency of 13.56 MHz or 40.68 MHz to the suscepter
712.
[0173] An upper electrode 730 serves as a plasma generator
electrode and also as a process gas introducing passage. It is a
hollow aluminium-made electrode and a plurality of apertures 730a
are formed in its bottom. It has a heater (not shown) connected to
a power supply 731. It can be thus heated to about 150.degree. C.
by the heater.
[0174] A process gas supply line or system provided with a
vaporizer (VAPO) 732 will be described referring to FIGS. 35 and
36.
[0175] Liquid TEOS is stored in a container 734. At the film
forming process, a liquid mass flow controller (LMFC) 736 is
controlled by a controller 758 to control the flow rate of liquid
TEOS supplied from the container 734 to the vaporizer 732.
[0176] As shown in FIG. 36, a porous and conductive heating unit
744 is housed in a housing 742 of the vaporizer 732. The housing
742 has an inlet 738 and an outlet 740. The inlet 738 is
communicated with the liquid supply side of the container 734. The
outlet 740 is communicated with the hollow portion of the upper
electrode 730.
[0177] The heating unit 744 is made of sintered ceramics in which
conductive material such as carbon is contained, and it is porous.
It is preferably excellent in workability and in heat and chemical
resistance. Terminals 747 are attached to it and current is
supplied from a power supply 746 to it through them. When current
is supplied to it, it is resistance-heated to about 150.degree. C.
Further, vibrators 748 are embedded in the housing 742, sandwiching
the heating unit 744 between them. It is preferable that they are
supersonic ones. The power supply 746 for the heating unit 744 and
a power supply (not shown) for the vibrators 748 are controlled by
the controller 758.
[0178] It will be described how the vaporizer 732 is operated.
[0179] When liquid TEOS is supplied from the container 734 to the
vaporizer 732, it enters into holes in the porous heating unit 744
and it is heated and vaporized. Because its contact area with the
porous heating unit 744 becomes extremely large, its vaporized
efficiency becomes remarkably higher, as compared with the
conventional vaporizers.
[0180] Further, vibration is transmitted from vibrators 748 to
liquid TEOS caught by the heating unit 744 and in its holes. Heat
transfer face and liquid vibrations are thus caused. Therefore, the
border layer between the heat transfer face of each hole in the
heating unit 744 and liquid TEOS, that is, the heat resistance
layer is made thinner. As the result, convection heat transmission
is promoted to further raise the vaporized efficiency of liquid
TEOS.
[0181] According to the vaporizer in this case, gas-like TEOS is
moved by pressure difference caused between the inlet 738 and the
outlet 740 and thus introduced into the process chamber 710 without
using any carrier gas.
[0182] A bypass 750 and a stop valve 752 may be attached to the
passage extending from the outlet 740 of the vaporizer, as shown in
FIG. 35. The bypass 750 is communicated with a clean-up unit (not
shown) via a bypass valve 754. The clean-up unit has a burner and
others to remove unnecessary gas components. Further, a sensor 756
is also attached to the passage extending from the outlet 740 to
detect whether or not liquid TEOS is completely vaporized and
whether or not gases are mixed at a correct rate. Detection signal
is sent from the sensor 756 to the controller 758.
[0183] The operation of the above-described CVD apparatus 700 will
be described.
[0184] The wafer w is carried into the process chamber 710 which
has been decompressed to about 1.times.10.sup.-4 several Torr, and
it is mounted on the suscepter 712. It is then heated to
300.degree. C., for example, by the heater 716. While preparing the
process chamber 710 in this manner, liquid TEOS is vaporized by the
vaporizer 732. High frequency power is applied from the high
frequency power supply 728 to the lower electrode 712 to generate
reactive plasma in the process chamber. Activated species in plasma
reach the treated face of the wafer W to thereby form P-TEOS
(plasma-tetraethylorthosilicate) film, for example, on it.
[0185] Other vaporizers will be described referring to FIGS. 37
through 41.
[0186] As shown in FIG. 37, a vaporizer 732A may be made integral
to an upper electrode 730A of a process chamber 710A. It is
attached integral to the upper electrode 730A at the upper portion
thereof with an intermediate chamber 770 formed under it. Its
housing 742A has a gas outlet side 774 in which a plurality of
apertures 772 are formed.
[0187] A gas pipe 776 is communicated with the intermediate chamber
770 in the upper electrode 730A to introduce second gas such as
oven and inert gases into it. A bypass 750A extends from that
portion of the upper electrode 730A which is opposed to the gas
pipe 776 to exhaust unnecessary gas from the upper electrode 730A.
Further, plates 780a, 780b and 780c in which a plurality of
apertures 778a, 778b and 778c are formed are arranged in the lower
portion of the intermediate chamber 770 with an interval interposed
between them.
[0188] As shown in FIGS. 38 and 39, a liquid passage 782 is formed
in a heating unit 744B in the case of a vaporizer 732B. It includes
a center passage 782a and passages 782b radically branching from
the center passage 782a. When it is formed in the heating unit 744B
in this manner, it enables liquid to be uniformly distributed in
the whole of the porous heating unit 744B, thereby raising gas
vaporized efficiency to a further extent.
[0189] After liquid is vaporized by a vaporizer 738C, two or more
gases may be mixed, as shown in FIG. 40. A second gas supply
opening 784 is arranged downstream the vaporizer 738C and second
gas component such as oxygen and inert gases is supplied through
it. A gas mixing duct 786 extends downstream it and a bypass 750C
having a bypass valve 754C, and a stop valve 752C are further
arranged in the lower portion of the gas mixing duct 786. A
strip-like mer 788 is housed in the gas mixing duct 786 to form a
spiral passage 790 in it. First and second gas components are fully
mixed, while passing through the spiral passage 790, and they reach
a point at which the bypass 750 branches from the passage extending
to the side of the process chamber.
[0190] In addition to TEOS (tetraethylorthosilicate),
trichlorsilane (SiRC1.sub.3), silicon tetrachloride (SiCl.sub.4),
pentaethoxytantalum (PEOTE: Ta(OC.sub.2H.sub.5).sub.5),
pentamethoxytantalum (PNOTa: Ta(OCH.sub.3).sub.5),
tetrasopropoxytitanium (Ti(i-OC.sub.3H.sub.7).sub.4- ),
tetradimethylaminotitanium (TDMAT: Ti(N(CH.sub.3).sub.2).sub.4),
tatraxisdiethylazinotitanium (TDEAT:
Ti(N(C.sub.2H.sub.5).sub.2).sub.4), titanium tetrachloride
(TiCl.sub.4), Cu(HFA).sub.2 and Cu(DPM).sub.2 may be used as liquid
material to be vaporized. Further, Ba(DPX).sub.2/THF and
Sr(DPX).sub.2/THF may be used as thin ferroelectric film foring
material. Water (H.sub.2O), ethanol (C.sub.2H.sub.5OH),
tetrahydrfuran (THF: C.sub.4H.sub.8O) and dirmethylaluminiumhydride
(DMAH: (CH.sub.3).sub.2AlH) may also be used.
[0191] A vaporizer 819 may be attached to a batch type horizontal
plasma CVD apparatus 800, as shown in FIG. 41. This CVD apparatus
800 includes a process chamber 814 provided with an exhaust opening
810 and a process gas supply section 812, a wafer boat 816 and a
heater means 818. Connected to the process gas supply section 812
are a process gas supply line or system having a liquid container
815, a liquid mass flow controller 817 and a vaporizer 819. This
vaporizer 819 is substantially same in arrangement as the
above-described one 732.
[0192] As shown in FIG. 42, a conventional vaporizer 701 has a
housing 702 which is kept under atmospheric pressure and which is
filled with a plurality of heat transmitting balls 703 each being
made of material, excellent in heat transmission. These heat
transmitting balls 703 are heated higher than the boiling point of
liquid material by an external heater means (not shown) to vaporize
liquid material introduced from below. Carrier gas is introduced
into the vaporizer 701 to carry vaporized process gases.
[0193] In the conventional vaporizer 701, however, gas flow rate
becomes excessive at the initial stage of gas supply, that is,
overshooting is caused. FIG. 43 is a graph showing how gas flow
rates attained by the conventional and our vaporizers change at the
initial stage of gas supply, in which time lapse is plotted on the
horizontal axis and gas flow rates on the vertical axis. A curve P
represents results obtained by the conventional vaporizer and
another curve Q those obtained by our present vaporizer. As
apparent from FIG. 43, gas flow rate overshoots a predetermined one
v.sub.1, in the case of the conventional vaporizer, after the lapse
of 10-20 seconds since the supply of gas is started. In the
above-described vaporizer used by the present invention, however,
it reaches the predetermined flow rate V.sub.1 without overshooting
it.
[0194] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details,
representative devices, and illustrated examples shown and
described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their
equivalents.
* * * * *