U.S. patent application number 10/327996 was filed with the patent office on 2003-06-26 for semiconductor cleaner and method of cleaning semiconductor.
Invention is credited to Sasaki, Ken.
Application Number | 20030116175 10/327996 |
Document ID | / |
Family ID | 19188869 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030116175 |
Kind Code |
A1 |
Sasaki, Ken |
June 26, 2003 |
Semiconductor cleaner and method of cleaning semiconductor
Abstract
A semiconductor cleaner includes (a) an inner wet bath which is
filled with liquid and in which a wafer to be cleaned is soaked,
(b) an outer wet bath which is filled with liquid and in which the
inner wet bath is soaked, (c) a megasonic-wave irradiator located
outside the inner wet bath for irradiating megasonic waves to the
wafer to clean the wafer, and (d) a unit which moves the
megasonic-wave irradiator towards or away from the inner wet
bath.
Inventors: |
Sasaki, Ken; (Tokyo,
JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
1177 AVENUE OF THE AMERICAS (6TH AVENUE)
41 ST FL.
NEW YORK
NY
10036-2714
US
|
Family ID: |
19188869 |
Appl. No.: |
10/327996 |
Filed: |
December 26, 2002 |
Current U.S.
Class: |
134/1.3 ;
134/184 |
Current CPC
Class: |
H01L 21/67057
20130101 |
Class at
Publication: |
134/1.3 ;
134/184 |
International
Class: |
C25F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2001 |
JP |
2001-394439 |
Claims
What is claimed is:
1. A semiconductor cleaner comprising: (a) a wet bath which is
filled with liquid and in which a wafer to be cleaned is soaked;
(b) a megasonic-wave irradiator located outside said wet bath for
irradiating megasonic waves to said wafer to clean said wafer; and
(c) a unit which moves said megasonic wave irradiator towards or
away from said wet bath.
2. The semiconductor cleaner as set forth in claim 1, wherein said
unit moves said megasonic-wave irradiator by a distance in the
range of 2 mm to 20 mm both inclusive.
3. The semiconductor cleaner as set forth in claim 1, wherein said
megasonic-wave irradiator irradiates megasonic waves having a
frequency in the range of 750 KHz to 1 MHz both inclusive.
4. The semiconductor cleaner as set forth in claim 1, wherein said
wet bath is formed at an inner surface thereof with irregularity
having a surface roughness greater than a wavelength of said
megasonic waves.
5. The semiconductor cleaner as set forth in claim 1, wherein said
unit moves said megasonic-wave irradiator at a rate which is not
equal to multiples of a phase velocity of said megasonic waves and
multiples of a half of a phase velocity of said megasonic waves,
and said unit moves said megasonic-wave irradiator by a distance
which is not equal to multiples of a wavelength of said megasonic
waves and multiples of a half of a wavelength of said megasonic
waves.
6. A semiconductor cleaner comprising: (a) a wet bath which is
filled with liquid and in which first to N-th wafers to be cleaned
are soaked wherein N is an integer equal to or greater than two;
(b) first to N-th megasonic-wave irradiators located outside said
wet bath and associated with said first to N-th wafers,
respectively, for irradiating megasonic waves to said first to N-th
wafers to clean said first to N-th wafers; and (c) first to N-th
units which move said first to N-th megasonic-wave irradiators
towards or away from said wet bath, respectively.
7. The semiconductor cleaner as set forth in claim 6, wherein said
first to N-th units move said first to N-th megasonic-wave
irradiators, respectively, by a distance in the range of 2 mm to 20
mm both inclusive.
8. The semiconductor cleaner as set forth in claim 6, wherein said
first to N-th megasonic-wave irradiators irradiate megasonic waves
having a frequency in the range of 750 KHz to 1 MHz both
inclusive.
9. The semiconductor cleaner as set forth in claim 6, wherein said
wet bath is formed at an inner surface thereof with irregularity
having a surface roughness greater than a wavelength of said
megasonic waves.
10. The semiconductor cleaner as set forth in claim 6, wherein each
of said first to N-th units moves said megasonic-wave irradiator at
a rate which is not equal to multiples of a phase velocity of said
megasonic waves and multiples of a half of a phase velocity of said
megasonic waves, and each of said first to N-th units moves said
megasonic-wave irradiator by a distance which is not equal to
multiples of a wavelength of said megasonic waves and multiples of
a half of a wavelength of said megasonic waves.
11. A semiconductor cleaner comprising: (a) a wet bath which is
filled with liquid and in which a wafer to be cleaned is soaked;
and (b) a megasonic-wave irradiator located outside said wet bath
for irradiating megasonic waves to said wafer to clean said wafer,
said wet bath being formed at an inner surface thereof with
irregularity having a surface roughness greater than a wavelength
of said megasonic waves.
12. A semiconductor cleaner comprising: (a) an inner wet bath which
is filled with liquid and in which a wafer to be cleaned is soaked;
(b) an outer wet bath which is filled with liquid and in which said
inner wet bath is soaked; (c) a megasonic-wave irradiator located
outside said inner wet bath for irradiating megasonic waves to said
wafer to clean said wafer; and (d) a unit which moves said
megasonic-wave irradiator towards or away from said inner wet
bath.
13. The semiconductor cleaner as set forth in claim 12, wherein
said megasonic-wave irradiator is comprised of: (c1) a
megasonic-wave oscillation plate located in said outer wet bath and
below a bottom of said inner wet bath in parallel with said bottom
of said inner wet bath; and (c2) a megasonic-wave oscillator
connected at one end to said megasonic-wave oscillation plate and
at the other end to said unit, said megasonic-wave oscillator being
fit into an opening formed at a bottom of said outer wet bath for
slidable movement.
14. The semiconductor cleaner as set forth in claim 12, wherein
said inner wet bath is composed of quartz.
15. The semiconductor cleaner as set forth in claim 12, wherein
said unit moves said megasonic-wave irradiator by a distance in the
range of 2 mm to 20 mm both inclusive.
16. The semiconductor cleaner as set forth in claim 12, wherein
said megasonic-wave irradiator irradiates megasonic waves having a
frequency in the range of 750 KHz to 1 MHz both inclusive.
17. The semiconductor cleaner as set forth in claim 12, wherein
said inner wet bath is formed at an inner surface thereof with
irregularity having a surface roughness greater than a wavelength
of said megasonic waves.
18. The semiconductor cleaner as set forth in claim 12, wherein
said unit moves said megasonic-wave irradiator at a rate which is
not equal to multiples of a phase velocity of said megasonic waves
and multiples of a half of a phase velocity of said megasonic
waves, and said unit moves said megasonic-wave irradiator by a
distance which is not equal to multiples of a wavelength of said
megasonic waves and multiples of a half of a wavelength of said
megasonic waves.
19. A semiconductor cleaner comprising: (a) an inner wet bath which
is filled with liquid and in which first to N-th wafers to be
cleaned are soaked wherein N is an integer equal to or greater than
two; (b) an outer wet bath which is filled with liquid and in which
said inner wet bath is soaked; (c) first to N-th megasonic-wave
irradiators located outside said inner wet bath and associated with
said first to N-th wafers, respectively, for irradiating megasonic
waves to said first to N-th wafers to clean said first to N-th
wafers; and (d) first to N-th units which move said first to N-th
megasonic-wave irradiators towards or away from said inner wet
bath, respectively.
20. The semiconductor cleaner as set forth in claim 19, wherein
each of said first to N-th megasonic-wave irradiators is comprised
of: (c1) a megasonic-wave oscillation plate located in said outer
wet bath and below a bottom of said inner wet bath in parallel with
said bottom of said inner wet bath; and (c2) a megasonic-wave
oscillator connected at one end to said megasonic-wave oscillation
plate and at the other end to each of said first to N-th units,
said megasonic-wave oscillator being fit into an opening formed at
a bottom of said outer wet bath for slidable movement.
21. The semiconductor cleaner as set forth in claim 19, wherein
said inner wet bath is composed of quartz.
22. The semiconductor cleaner as set forth in claim 19, wherein
said first to N-th units move said first to N-th megasonic-wave
irradiators, respectively, by a distance in the range of 2 mm to 20
mm both inclusive.
23. The semiconductor cleaner as set forth in claim 19, wherein
said first to N-th megasonic-wave irradiators irradiate megasonic
waves having a frequency in the range of 750 KHz to 1 MHz both
inclusive.
24. The semiconductor cleaner as set forth in claim 19, wherein
said wet bath is formed at an inner surface thereof with
irregularity having a surface roughness greater than a wavelength
of said megasonic waves.
25. The semiconductor cleaner as set forth in claim 19, wherein
each of said first to N-th units moves said megasonic-wave
irradiator at a rate which is not equal to multiples of a phase
velocity of said megasonic waves and multiples of a half of a phase
velocity of said megasonic waves, and each of said first to N-th
units moves said megasonic-wave irradiator by a distance which is
not equal to multiples of a wavelength of said megasonic waves and
multiples of a half of a wavelength of said megasonic waves.
26. A semiconductor cleaner comprising: (a) an inner wet bath which
is filled with liquid and in which a wafer to be cleaned is soaked;
(b) an outer wet bath which is filled with liquid and in which said
inner wet bath is soaked; and (c) a megasonic-wave irradiator
located outside said inner wet bath for irradiating megasonic waves
to said wafer to clean said wafer; said inner wet bath being formed
at an inner surface thereof with irregularity having a surface
roughness greater than a wavelength of said megasonic waves.
27. A method of cleaning a wafer soaked in liquid filled in a wet
bath, comprising the step of irradiating megasonic waves to said
wafer with a relative distance between said wafer and a
megasonic-wave irradiator being varied.
28. The method as set forth in claim 27, wherein said relative
distance is varied by reciprocating said megasonic-wave irradiator
relative to said wafer.
29. The method as set forth in claim 27, wherein said relative
distance is varied in the range of 2 mm to 20 mm both
inclusive.
30. The method as set forth in claim 27, wherein said megasonic
waves have a frequency in the range of 750 KHz to 1 MHz both
inclusive.
31. The method as set forth in claim 27, wherein relative distance
is varied by moving said megasonic-wave irradiator at a rate which
is not equal to multiples of a phase velocity of said megasonic
waves and multiples of a half of a phase velocity of said megasonic
waves, and by a distance which is not equal to multiples of a
wavelength of said megasonic waves and multiples of a half of a
wavelength of said megasonic waves.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a semiconductor wafer cleaner by
means of megasonic waves, and a method of cleaning a semiconductor
wafer by means of megasonic waves.
[0003] 2. Description of the Related Art
[0004] Supersonic waves such as megasonic waves are used in a lot
of fields for cleaning an object. For instance, megasonic waves are
used in a fabrication process of a semiconductor device for
cleaning a silicon wafer.
[0005] An example of a conventional silicon wafer cleaner for
cleaning a silicon wafer by means of megasonic waves is illustrated
in FIG. 1.
[0006] The illustrated silicon wafer cleaner 50 is comprised of a
cleaning bath 52 filled with cleaning solution 51 such as water, an
oscillation plate 53 adhered to an outer surface of a bottom of the
cleaning bath 52, and an oscillator 54 which oscillates the
oscillation plate 53.
[0007] A silicon wafer 55 to be cleaned is kept soaked in the
cleaning solution 51 in the cleaning bath 52. By activating the
oscillator 54, the oscillation plate 53 is oscillated by the
oscillator 54, resulting in that megasonic waves 56 are irradiated
towards the cleaning bath 52 from the oscillation plate 53. The
silicon wafer 55 is cleaned by the thus irradiated megasonic waves
56.
[0008] As illustrated in FIG. 1, the megasonic waves 56 are
irradiated from the oscillation plate 53 in all directions. Hence,
the megasonic waves 56 includes first megasonic waves 56a
irradiated upwardly from the oscillation plate 53, and second
megasonic waves 56b irradiated obliquely upwardly from the
oscillation plate 53.
[0009] A part of the second megasonic waves 56b is reflected at a
sidewall 52a of the cleaning bath 52, and is directed towards
inside of the cleaning bath 52 as reflected megasonic waves 56c. As
a result, the first megasonic waves 56a and the reflected megasonic
waves 56c interfere with each other at locations indicated with
solid circles 57 (.circle-solid.). This means that the silicon
wafer 55 locally receives the megasonic waves 56 having high
intensity.
[0010] As mentioned above, since the silicon wafer 55 receives the
megasonic waves 56 too much at the locations 57 at which the first
megasonic waves 56a and the reflected megasonic waves 56c interfere
with each other, there is caused a problem that wirings formed on
the silicon wafer 55 are partially broken.
[0011] Many attempts have been made so far in order to solve the
above-mentioned problem.
[0012] As an example of the solution to the above-mentioned
problem, Japanese Unexamined Patent Publication No. 11-221534 has
suggested a supersonic wave cleaner. FIG. 2 illustrates the
suggested supersonic wave cleaner.
[0013] The illustrated supersonic wave cleaner 60 is comprised of a
cleaning bath 62 filled with a cleaning solution 61, a first
supersonic wave oscillator 63 fixed onto an outer surface 62a of a
bottom of the cleaning bath 62, a first variable oscillator 64
which controls a frequency of supersonic waves emitted from the
first supersonic wave oscillator 63, a second supersonic wave
oscillator 65 designed to be movable upwardly and downwardly
relative to the cleaning bath 62, and a second variable oscillator
66 which controls a frequency of supersonic waves emitted from the
second supersonic wave oscillator 65.
[0014] A silicon wafer 67 to be cleaned is kept soaked in the
cleaning solution 61 with being fixed to the second supersonic wave
oscillator 65. The silicon wafer 67 moves upwardly and downwardly
in the cleaning solution 61 together with the second supersonic
wave oscillator 65. While the silicon wafer 67 moves upwardly and
downwardly in the cleaning solution 61, the first supersonic wave
oscillator 63 irradiates supersonic waves to the silicon wafer 67,
and thus, the silicon wafer 67 is cleaned.
[0015] It is said in the Publication that since the silicon wafer
67 is cleaned by supersonic waves propagated from both of the first
and second supersonic wave oscillators 63 and 65 in different
manners, the above-mentioned problem caused by applying only
supersonic waves irradiated from the first supersonic wave
oscillator 63 to the silicon wafer 67 can be solved.
[0016] Japanese Unexamined Patent Publication No. 61-194727 has
suggested a supersonic wave cleaner. FIG. 3 illustrates the
suggested supersonic wave cleaner 70.
[0017] The supersonic wave cleaner 70 includes a reflector 72
inclined by a predetermined angle .theta. in a cleaning bath 71.
The reflector 72 is formed at a surface thereof with slight
irregularity. Supersonic waves irradiated from a supersonic wave
oscillator 73 arranged on a sidewall of the cleaning bath 71 are
reflected at the reflector 72, and then, irradiated to a silicon
wafer 75 being kept soaked in cleaning solution 74 filling the
cleaning bath 71 therewith.
[0018] In accordance with the supersonic wave cleaner 70, since
supersonic waves are irregularly reflected by the slight
irregularity formed at a surface of the reflector 72, it would be
possible produce supersonic waves having no directivity, but having
a uniform density. Hence, it is said in the Publication that the
above-mentioned interference problem can be solved.
[0019] However, the supersonic wave cleaner 60 illustrated in FIG.
2 and the supersonic wave cleaner 70 illustrated in FIG. 3 are
accompanied with the following problems.
[0020] In the supersonic wave cleaner 60 illustrated in FIG. 2,
since it is necessary to attach the silicon wafer 67 to the second
supersonic wave oscillator 65, a cleanness of the silicon wafer 67
might be deteriorated in a step of attaching the silicon wafer 67
to the second supersonic wave oscillator 65, or by the second
supersonic wave oscillator 65 making contact with the silicon wafer
67.
[0021] In addition, since steps of attaching the silicon wafer 67
to the second supersonic wave oscillator 65 and separating the
second supersonic wave oscillator 65 from the silicon wafer 67 have
to be additionally carried out, the number of steps for fabricating
the supersonic wave cleaner 60 would be unavoidably increased.
[0022] Furthermore, since the supersonic wave cleaner 60 has to
include two oscillators, specifically, the first and second
supersonic wave oscillators 63 and 65, the number of parts for
constructing the supersonic wave cleaner 60 is unavoidably
increased, and hence, costs for fabricating the supersonic wave
cleaner 60 is also increased.
[0023] In the supersonic wave cleaner 70 illustrated in FIG. 3, the
reflector 72 arranged in the cleaning bath 71 produces a useless
space 76 therebelow, resulting in an unnecessary increase in a size
of the cleaning bath 71 and hence the supersonic wave cleaner
70.
[0024] In addition, since the reflector 72 is inclined, supersonic
waves reflected at an upper portion of the reflector 72 and
supersonic waves reflected at a lower portion of the reflector 72
reach the silicon wafer 75 in different distances. Accordingly, the
supersonic waves reflected at an upper portion of the reflector 72
would have a greater attenuation factor than the supersonic waves
reflected at a lower portion of the reflector 72. Thus, it is not
always possible to produce supersonic waves having a uniform
density.
[0025] Japanese Unexamined Patent Publication No. 2001-120918 has
suggested a method of cleaning a filtering plane in a solid-liquid
separator, including the steps of producing supersonic waves by
means of a supersonic wave oscillator, applying the supersonic
waves to a movable oscillator, moving the oscillator relative to
the filtering plane, and applying the supersonic waves to the
filtering plane to thereby clean the filtering plane.
[0026] However, the above-mentioned problems remain unsolved even
in the suggested method.
SUMMARY OF THE INVENTION
[0027] In view of the above-mentioned problems in the conventional
supersonic wave cleaner, it is an object of the present invention
to provide a semiconductor cleaner which is capable of avoiding
megasonic waves from interfering with each other to thereby prevent
local concentration of megasonic waves to a semiconductor wafer to
be cleaned.
[0028] It is also an object of the present invention to provide a
method of doing the same.
[0029] In one aspect of the present invention, there is provided a
semiconductor cleaner including (a) a wet bath which is filled with
liquid and in which a wafer to be cleaned is soaked, (b) a
megasonic-wave irradiator located outside the wet bath for
irradiating megasonic waves to the wafer to clean the wafer, and
(c) a unit which moves the megasonic-wave irradiator towards or
away from the wet bath.
[0030] In the semiconductor cleaner in accordance with the present
invention, the megasonic-wave irradiator is moved upwardly and
downwardly relative to the wet bath with megasonic waves being
irradiated to a wafer from the megasonic-wave irradiator. As a
result, megasonic waves are deviated in phases from each other, and
thus, megasonic waves interfere with each other in broader areas.
Hence, it would be possible to prevent local concentration of
megasonic waves to a wafer.
[0031] It is preferable that the unit moves the megasonic-wave
irradiator by a distance in the range of 2 mm to 20 mm both
inclusive.
[0032] It is preferable that the megasonic-wave irradiator
irradiates megasonic waves having a frequency in the range of 750
KHz to 1 MHz both inclusive.
[0033] The wet bath may be formed at an inner surface thereof with
irregularity having a surface roughness greater than a wavelength
of the megasonic waves.
[0034] It is preferable that the unit moves the megasomicwave
irradiator at a rate which is not equal to multiples of a phase
velocity of the megasonic waves and multiples of a half of a phase
velocity of the megasonic waves, and the unit moves the
megasonic-wave irradiator by a distance which is not equal to
multiples of a wavelength of the megasonic waves and multiples of a
half of a wavelength of the megasonic waves.
[0035] There is further provided a semiconductor cleaner including
(a) a wet bath which is filled with liquid and in which first to
N-th wafers to be cleaned are soaked wherein N is an integer equal
to or greater than two, (b) first to N-th megasonic-wave
irradiators located outside the wet bath and associated with the
first to N-th wafers, respectively, for irradiating megasonic waves
to the first to N-th wafers to clean the first to N-th wafers, and
(c) first to N-th units which move the first to N-th megasonic-wave
irradiators towards or away from the wet bath, respectively.
[0036] It is preferable that the first to N-th units move the first
to N-th megasonic-wave irradiators, respectively, by a distance in
the range of 2 mm to 20 mm both inclusive.
[0037] It is preferable that the first to N-th megasonic-wave
irradiators irradiate megasonic waves having a frequency in the
range of 750 KHz to 1 MHz both inclusive.
[0038] It is preferable that each of the first to N-th units moves
the megasonic-wave irradiator at a rate which is not equal to
multiples of a phase velocity of the megasonic waves and multiples
of a half of a phase velocity of the megasonic waves, and each of
the first to N-th units moves the megasonic-wave irradiator by a
distance which is not equal to multiples of a wavelength of the
megasonic waves and multiples of a half of a wavelength of the
megasonic waves.
[0039] There is still further provided a semiconductor cleaner
including (a) a wet bath which is filled with liquid and in which a
wafer to be cleaned is soaked, and (b) a megasonic-wave irradiator
located outside the wet bath for irradiating megasonic waves to the
wafer to clean the wafer, the wet bath being formed at an inner
surface thereof with irregularity having a surface roughness
greater than a wavelength of the megasonic waves.
[0040] By forming irregularity having a surface roughness greater
than a wavelength of the megasonic waves, on an inner surface of a
sidewall of the wet bath, the megasonic waves are irregularly
reflected at the inner surface of a sidewall of the wet bath. As a
result, megasonic waves are deviated in phases from each other, and
thus, megasonic waves interfere with each other in broader areas.
Hence, it would be possible to prevent local concentration of
megasonic waves to a wafer.
[0041] There is yet further provided a semiconductor cleaner
including (a) an inner wet bath which is filled with liquid and in
which a wafer to be cleaned is soaked, (b) an outer wet bath which
is filled with liquid and in which the inner wet bath is soaked,
(c) a megasonic-wave irradiator located outside the inner wet bath
for irradiating megasonic waves to the wafer to clean the wafer,
and (d) a unit which moves the megasonic-wave irradiator towards or
away from the inner wet bath.
[0042] For instance, the megasonic-wave irradiator may be comprised
of (c1) a megasonic-wave oscillation plate located in the outer wet
bath and below a bottom of the inner wet bath in parallel with the
bottom of the inner wet bath, and (c2) a megasonic-wave oscillator
connected at one end to the megasonic-wave oscillation plate and at
the other end to the. unit, the megasonic-wave oscillator being fit
into an opening formed at a bottom of the outer wet bath for
slidable movement.
[0043] It is preferable that the inner wet bath is composed of
quartz.
[0044] There is further provided a semiconductor cleaner including
(a) an inner wet bath which is filled with liquid and in which
first to N-th wafers to be cleaned are soaked wherein N is an
integer equal to or greater than two, (b) an outer wet bath which
is filled with liquid and in which the inner wet bath is soaked,
(c) first to N-th megasonic-wave irradiators located outside the
inner wet bath and associated with the first to N-th wafers,
respectively, for irradiating megasonic, waves to the first to N-th
wafers to clean the first to N-th wafers, and (d) first to N-th
units which move the first to N-th megasonic-wave irradiators
towards or away from the inner wet bath, respectively.
[0045] There is further provided a semiconductor cleaner including
(a) an inner wet bath which is filled with liquid and in which a
wafer to be cleaned is soaked, (b) an outer wet bath which is
filled with liquid and in which the inner wet bath is soaked, and
(c) a megasonic-wave irradiator located outside the inner wet bath
for irradiating megasonic waves to the wafer to clean the wafer,
the inner wet bath being formed at an inner surface thereof with
irregularity having a surface roughness greater than a wavelength
of the megasonic waves.
[0046] In another aspect of the present invention, there is
provided a method of cleaning a wafer soaked in liquid filled in a
wet bath, including the step of irradiating megasonic waves to the
wafer with a relative distance between the wafer and a
megasonic-wave irradiator being varied.
[0047] It is preferable that the relative distance is varied by
reciprocating the megasonic-wave irradiator relative to the
wafer.
[0048] It is preferable that the relative distance is varied in the
range of 2 mm to 20 mm both inclusive.
[0049] It is preferable that the megasonic waves have a frequency
in the range of 750 KHz to 1 MHz both inclusive.
[0050] It is preferable that relative distance is varied by moving
the megasonic-wave irradiator at a rate which is not equal to
multiples of a phase velocity of the megasonic waves and multiples
of a half of a phase velocity of the megasonic waves, and by a
distance which is not equal to multiples of a wavelength of the
megasonic waves and multiples of a half of a wavelength of the
megasonic waves.
[0051] The advantages obtained by the aforementioned present
invention will be described hereinbelow.
[0052] In accordance with the present invention, it would be
possible to increase the number of locations at which megasonic
waves interfere with one another, and scatter the locations in a
broader area. Hence, it would be possible to reduce an intensity of
megasonic waves locally concentrating to a wafer due to
interference of megasonic waves with one another. Thus, it would be
possible to prevent a wafer from being damaged due to interference
of megasonic waves with one another.
[0053] The above and other objects and advantageous features of the
present invention will be made apparent from the following
description made with reference to the accompanying drawings, in
which like reference characters designate the same or similar parts
throughout the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a schematic view illustrating a conventional
semiconductor cleaner.
[0055] FIG. 2 is a schematic view illustrating another conventional
semiconductor cleaner.
[0056] FIG. 3 is a schematic view illustrating still another
conventional semiconductor cleaner.
[0057] FIG. 4 is a schematic view of a semiconductor cleaner in
accordance with the first embodiment.
[0058] FIG. 5 illustrates irradiation of megasonic waves in the
semiconductor cleaner in accordance with the first embodiment.
[0059] FIG. 6 is a schematic view of a semiconductor cleaner in
accordance with the second embodiment.
[0060] FIG. 7 is a schematic view of a semiconductor cleaner in
accordance with the third embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0061] Preferred embodiments in accordance with the present
invention will be explained hereinbelow with reference to
drawings.
[0062] [First Embodiment]
[0063] FIG. 4 illustrates a semiconductor cleaner 10 in accordance
with the first embodiment.
[0064] The semiconductor cleaner 10 in accordance with the first
embodiment is comprised of an inner wet bath 18 which is filled
with cleaning solution 11 and in which a wafer 12 to be cleaned is
soaked, an outer wet bath 15 which is filled with water 14 and
which surrounds the inner wet bath 13, and a megasonic-wave
irradiator 16 arranged below a bottom of the inner wet bath 13 for
irradiating megasonic waves.
[0065] The megasonic-wave irradiator 16 is comprised of a
megasonic-wave oscillation plate 17 located in the outer wet bath
15 and below a bottom of the inner wet bath 13 in parallel with a
bottom of the inner wet bath 13, a megasonic-wave oscillator 18
connected at one end to the megasonic-wave oscillation plate 17 for
oscillating the megasonic-wave oscillation plate 17 to produce
megasonic waves, and at the other end to a later mentioned motor
19, and a motor 19 which moves the megasonic-wave oscillation plate
17 and the megasonic-wave oscillator 18 upwardly and downwardly
relative to the inner wet bath 13.
[0066] A wafer 12 is kept soaked in the cleaning solution 11 by
means of an appropriate holder (not illustrated).
[0067] The outer wet bath 15 may be composed of any material,
whereas the inner wet bath 13 is composed preferably of quartz.
[0068] As illustrated in FIG. 4, the megasonic-wave oscillation
plate 17 is soaked in the wafer 14 filling the outer wet bath 15
therewith. The outer wet bath 15 is formed centrally at a bottom
thereof with an opening through which the megasonic-wave oscillator
18 is fit for slidable movement. A waterproof seal 20 is sandwiched
between the megasonic-wave oscillator 18 and the opening for
preventing leakage of the water 14.
[0069] The motor 19 is mechanically connected to the megasonic-wave
oscillator 18 through a converter 19a which converts rotational
motion into linear motion, such as rack and pinion. Accordingly
rotational motion output from the motor 19 is converted to linear
motion by the converter 19a, and then, the linear motion is
transferred to the megasonic-wave oscillator 18. Hence, if the
motor 19 rotates in a first direction (for instance, a clockwise
direction), the megasonic-wave oscillation plate 17 and the
megasonic-wave oscillator 18 move upwardly, whereas if the motor 19
rotates in a second direction (for instance, a counterclockwise
direction), the megasonic-wave oscillation plate 17 and the
megasonic-wave oscillator 18 move downwardly.
[0070] An operation of the semiconductor cleaner 10 in accordance
with the first embodiment is explained hereinbelow.
[0071] The motor 19 moves the megasonic-wave oscillation plate 17
and the megasonic-wave oscillator 18 upwardly or downwardly below a
bottom of the inner wet bath 13 with the wafer 12 being kept soaked
in the cleaning solution 11. While moving together with the
megasonic-wave oscillation plate 17, the megasonic-wave oscillator
18 oscillates the megasonic-wave oscillation plate 17 to thereby
emit megasonic waves from the megasonic-wave oscillation plate 17.
The thus emitted megasonic waves are irradiated to the wafer 12,
and resultingly, the wafer 12 is cleaned.
[0072] FIG. 5 illustrates that megasonic waves 21 emitted from the
megasonic-wave oscillation plate 17 are irradiated to the wafer 12.
In FIG. 5, only the wafer 12, the inner wet bath 13, the
megasonic-wave oscillation plate 17 and the megasonic-wave
oscillator 18 are illustrated, and other parts are omitted for
simplification of FIG. 5.
[0073] The megasonic waves 21 emitted from the megasonic-wave
oscillation plate 17 include first megasonic waves 21a emitted
upwardly from the megasonic-wave oscillation plate 17, and second
megasonic waves 21b emitted obliquely upwardly from the
megasonic-wave oscillation plate 17.
[0074] A part of the second megasonic waves 21b is reflected at a
sidewall 13a of the inner wet bath 13, and is directed towards
inside of the inner wet bath 13 as reflected megasonic waves 21c.
As a result, the first megasonic waves 56a and the reflected
megasonic waves 56c interfere with each other at locations
indicated with solid circles 57. This means that the silicon wafer
55 locally receives the megasonic waves 56 having high
intensity.
[0075] In the conventional semiconductor cleaner 50 illustrated in
FIG. 1, the first megasonic waves 56a irradiated upwardly from the
oscillation plate 53 and the reflected megasonic waves 56c
interfere with each other at the solid circles 57, and resultingly,
the silicon wafer 55 is damaged at the solid circles 57.
[0076] This is because the oscillation plate 53 and the cleaning
bath 52 are kept stationary relative to each other, and hence, an
intensity of megasonic waves is increased at uniform locations due
to interference of megasonic waves with each other.
[0077] In contrast, the megasonic-wave oscillation plate 17 from
which megasonic waves are irradiated is always made to move
upwardly or downwardly in the semiconductor cleaner 10 in
accordance with the first embodiment. Accordingly, since a relative
distance between the megasonic-wave oscillation plate 17 and the
inner wet bath 13 (exactly, between the megasonic-wave oscillation
plate 17 and the wafer 12 kept soaked in the inner wet bath 13) is
varied, locations at which an intensity of megasonic waves is
increased due to interference of megasonic waves with each other
are not uniform unlike the conventional semiconductor cleaner 50.
Hence, it is possible to prevent megasonic waves from locally
concentrating to the wafer 12, and thus, it is possible to protect
the wafer 12 from being damaged due to interference of megasonic
waves.
[0078] The reason is explained in detail hereinbelow.
[0079] In FIG. 5, phases of first megasonic waves 22a irradiated
from the megasonic-wave oscillation plate 17 when the
megasonic-wave oscillation plate 17 reaches its uppermost point are
illustrated in broken lines, and phases of second megasonic waves
22b irradiated from the megasonic-wave oscillation plate 17 when
the megasonic-wave oscillation plate 17 reaches its lowermost point
are illustrated in solid lines.
[0080] In FIG. 5, locations at which the reflected megasonic waves
21a and the first megasonic waves 22a interfere with each other are
indicated with hollow circles (.largecircle.), and locations at
which the reflected megasonic waves 21a and the second megasonic
waves 22b interfere with each other are indicated with star marks
(). It is understood that locations at which megasonic waves
interfere with each other are scattered relative to the solid
circles 57 illustrated in FIG. 1.
[0081] As mentioned above, the semiconductor cleaner 10 in
accordance with the first embodiment makes it possible to scatter
locations at which megasonic waves interfere with each other, and
hence, reduce an intensity of megasonic waves locally concentrating
to the wafer 12 due to interference of megasonic waves with each
other. As a result, it is possible to prevent the wafer 12 from
being damaged due to interference of megasonic waves with each
other.
[0082] A distance by which the megasonic-wave oscillation plate 17
and the megasonic-wave oscillator 18 move upwardly and downwardly
is dependent on a size of the wafer and/or a size of the inner wet
bath 13. According to the experiments having been conducted by the
inventor, the above-mentioned advantageous effects can be ensured
regardless of sizes of the wafer 12 and the inner wet bath 13, if
the distance is set equal to or greater than 2 mm, and equal to or
smaller than 20 mm.
[0083] The megasonic waves 21 irradiated from the megasonic-wave
oscillation plate 17 may have any frequency. However, according to
the experiments having been conducted by the inventor, the
megasonic waves 21 having a frequency in the range of 750 KHz to 1
MHz both inclusive could clean the wafer 12 to the best degree.
Accordingly, it would be preferable that the megasonic-wave
oscillator 18 oscillates the megasonic-wave oscillation plate 17
such that the megasonic waves 21 having a frequency in the range of
750 KHz to 1 MHz both inclusive are irradiated from the
megasonic-wave oscillation plate 17.
[0084] [Second Embodiment]
[0085] FIG. 6 is a top view of a semiconductor cleaner 30 in
accordance with the second embodiment, when viewed from upward.
[0086] In the semiconductor cleaner 30 in accordance with the
second embodiment, eight wafers (not illustrated) are arranged in
the inner wet bath 13 in parallel with one another. The
semiconductor cleaner 30 is designed to include first to eighth
megasonic-wave oscillation plates 17a to 17h and first. to eighth
megasonic-wave oscillators 18a to 18h in association with eight
wafers.
[0087] Each of the first to eighth megasonic-wave oscillation
plates 17a to 17h is identical in structure with the megasonic-wave
oscillation plate 17 in the first embodiment, and each of the first
to eighth megasonic-wave oscillators 18a to 18h is identical in
structure with the megasonic-wave oscillator 18 in the first
embodiment.
[0088] Accordingly, a distance by which each of the eight wafers
moves upwardly and downwardly can be controlled for each of the
eight wafers.
[0089] A single megasonic-wave oscillation plate may be used in
place of the first to eighth megasonic-wave oscillation plates 17a
to 17h. However, by using the first to eighth megasonic-wave
oscillation plates 17a to 17h in place of a single megasonic-wave
oscillation plate, it would be easier to control each of the
megasonic-wave oscillation plates.
[0090] [Third Embodiment]
[0091] FIG. 7 illustrates a semiconductor cleaner 40 in accordance
with the third embodiment.
[0092] The semiconductor cleaner 40 in accordance with the third
embodiment is comprised of an inner wet bath 43 which is filled
with cleaning solution 41 and in which a wafer 42 to be cleaned is
soaked, an outer wet bath 45 which is filled with water 44 and
which surrounds the inner wet bath 43, and a megasonic-wave
irradiator 46 arranged below a bottom of the inner wet bath 43 for
irradiating megasonic waves.
[0093] The megasonic-wave irradiator 46 is comprised of a
megasonic-wave oscillation plate 47 located in the outer wet bath
45 and below a bottom of the inner wet bath 43 in parallel with a
bottom of the inner wet bath 43, and a megasonic-wave oscillator 48
connected to the megasonic-wave oscillation plate 47 for
oscillating the megasonic-wave oscillation plate 47 to produce
megasonic waves.
[0094] The wafer 42 is kept soaked in the cleaning solution 41 by
means of an appropriate holder (not illustrated).
[0095] The inner wet bath 43 is formed at an inner surface 43a of a
sidewall thereof with irregularity having a surface roughness
greater than a wavelength of megasonic waves irradiated from the
megasonic-wave oscillation plate 47.
[0096] In general, if a wave had a wavelength smaller than a
surface roughness of a wall at which the wave is reflected, the
wave would be irregularly reflected. In the semiconductor cleaner
40 in accordance with the third embodiment, megasonic waves
irradiated obliquely upwardly from the megasonic-wave oscillation
plate 47 are reflected at the inner surface 43a of the sidewall of
the inner wet bath 43, and then, interfere with megasonic waves
irradiated upwardly from the megasonic-wave oscillation plate 47.
Since the megasonic waves irradiated obliquely upwardly from the
megasonic-wave oscillation plate 47 are irregularly reflected at
the inner surface 43a, locations at which those megasonic waves
interfere with each other are in a broader area than the
conventional semiconductor cleaner 50 illustrated in FIG. 1.
[0097] Hence, it is possible to reduce an intensity of the
megasonic waves from locally concentrating to the wafer 42 due to
interference of megasonic waves with each other, and thus, it is
possible to protect the wafer 42 from being damaged.
[0098] It should be noted that the inner wet bath 13 in the
semiconductor cleaner 10 in accordance with the first embodiment
may be designed to have slight irregularity at an inner surface of
a sidewall thereof.
[0099] Hereinbelow is explained an example of the semiconductor
cleaners 10 and 40 in accordance with the first and third
embodiments.
[0100] In theory, if the cleaning solution 11 and 41 is comprised
of water, supersonic waves such as megasonic waves are reflected at
a surface of the water 11 or 41 by 99.9%, and the thus reflected
supersonic waves are directed to inside of the inner wet bath 13 or
43. The supersonic waves directed to inside of the inner wet bath
13 or 43 interferes with supersonic waves directed to a surface of
the water 11 or 41, resulting in that sound pressure is locally
strengthened every pitch of a standing wave. This is explained in
detail hereinbelow.
[0101] It is assumed that megasonic waves irradiated from the
megasonic-wave oscillation plate 17 or 47 have a frequency of 950
KHz.
[0102] A phase velocity of supersonic waves in pure water is equal
to 1483 m/s at 20 degrees centigrade. A wavelength .lambda. is
calculated as follows. 1 Wavelength = Phase velocity C [ m / s ] /
Frequency F [ Hz ] = 1483 / 950 = 1.56 mm
[0103] Accordingly, a pitch of a standing wave is calculated as
follows.
1.56/2=0.78 mm
[0104] This is small enough to be canceled by a wave generated at a
surface of the water 11 or 41 by supersonic waves. Accordingly, it
is possible to ignore non-uniformity in cleaning the wafer 12 or
42, caused by a pitch of a standing wave, that is, damages of the
wafer 12 or 42 caused by megasonic waves locally having a high
intensity due to interference of megasonic waves with each
other.
[0105] Accordingly, reflected megasonic waves which may
interference with non-reflected megasonic waves are limited to
megasonic waves reflected from either the inner wet bath 13, 43 or
the wafer 12, 42.
[0106] In order to prevent cancellation of cleaning effects of
megasonic waves and/or interference of megasonic waves with each
other while the megasonic-wave oscillation plate 17 moves upwardly
or downwardly, it would be necessary for the megasonic-wave
oscillation plate 17 to move at a rate which is not equal to
multiples of a phase velocity of megasonic waves and multiples of a
half of a phase velocity of megasonic waves, and by a distance
which is not equal to multiples of a wavelength of megasonic waves
and multiples of a half of a wavelength of megasonic waves.
[0107] Herein, there is considered a specific example having the
following specification.
[0108] Frequency of megasonic waves: 950 KHz
[0109] Cleaning solution: Water
[0110] Temperature of cleaning solution: 20 degrees centigrade
[0111] Revolution speed of the motor 19: 10,000 per second
[0112] Gear ratio of the motor 19: 1:4
[0113] Material of which the inner wet bath 13 and 43 is composed:
Quartz
[0114] In order to avoid a rate Ca of the megasonic-wave
oscillation plate 17 from being equal to multiples of a phase
velocity of megasonic waves and multiples of a half of a phase
velocity of megasonic waves, it is assumed that the rate Ca is
equal to one-third ({fraction (1/3)}) of a phase velocity C.
Ca=C/3=1483/3=494.33 [m/s]=4943.3 [cm/s]
[0115] A distance L which ensures the rate Ca of 4943.3 [cm/s]
under the above-mentioned conditions is calculated as follows.
L=Ca[cm/s]/the number of reciprocation=4943.3/2500=1.977 cm
[0116] Herein, the number of reciprocation is calculated as 2500,
because the motor 19 rotates at a revolution speed of 10000/s and
has a gear ratio of 1/4.
[0117] Accordingly, a distance La by which the megasonic-wave
oscillation plate 17 moves upwardly or downwardly is calculated as
a half of the distance L.
La=L/2=1.977/2=0.989 [cm]
[0118] Since the distance La of 0.989 cm is not equal to multiples
of a wavelength of megasonic waves and multiples of a half of a
wavelength of megasonic waves, the megasonic waves do not interfere
with each other.
[0119] When the inner wet bath 13 or 43 is composed of quartz, the
inner wet bath 13 or 43 is frequently dealt with hydrofluoric acid
at an inner surface thereof in order to reduce a surface roughness
thereof. After being dealt with hydrofluoric acid, the inner wet
bath 13 or 43 usually has a surface roughness of about 0.5 mm,
which is smaller than a wavelength of megasonic waves. Accordingly,
megasonic waves are mirror-reflected at an inner surface of the
inner wet bath 13 or 43, or pass through the inner wet bath 13 or
43.
[0120] Since the megasonic-wave oscillation plate 17 or 47 is
arranged below a bottom of the inner wet bath 13 or 43, it is
necessary for a bottom of the inner wet bath 13 or 43 to have such
a surface roughness as mentioned above.
[0121] As having been explained in the third embodiment, it is
necessary for the inner surface 43a of a sidewall of the inner wet
bath 13 or 43 to have a structure for preventing megasonic waves
from mirror-reflecting in order to avoid interference of megasonic
waves with each other. As mentioned earlier, if a wave had a
wavelength smaller than a surface roughness of a wall at which the
wave is reflected, the wave would be irregularly reflected. In
order to utilize this phenomenon, the inner wet bath 13 or 43 is
designed to have a sidewall having the inner surface 43a having a
surface roughness of 3 mm. Since the inner wet bath 13 or 43 is
composed of quartz, it is sufficiently possible to design the inner
wet bath 13 or 43 to have a sidewall having the inner surface 43a
having a surface roughness of 3 mm.
[0122] In summary, the example of the semiconductor cleaners 10 and
40 in accordance with the first and third embodiments has the
following dimensions.
[0123] Frequency of megasonic waves: 950 KHz
[0124] Cleaning solution: Water
[0125] Temperature of cleaning solution: 20 degrees centigrade
[0126] Revolution speed of the motor 19: 10,000 per second
[0127] Gear ratio of the motor 19: 1:4
[0128] Material of which the inner wet bath 13 and 43 is composed:
Quartz
[0129] Portion of the inner wet bath 13 and 43 to be dealt with
hydrofluoric acid: only bottom
[0130] Surface processing of the inner wet bath 13 and 43: only
sidewall (surface roughness of 3 mm)
[0131] Distance by which the megasonic-wave oscillation plate 17 or
47 moves: 0.989 cm
[0132] While the present invention has been described in connection
with certain preferred embodiments, it is to be understood that the
subject matter encompassed by way of the present invention is not
to be limited to those specific embodiments. On the contrary, it is
intended for the subject matter of the invention to include all
alternatives, modifications and equivalents as can be included
within the spirit and scope of the following claims.
[0133] The entire disclosure of Japanese Patent Application No.
2001-394489 filed on Dec. 26, 2001 including specification, claims,
drawings and summary is incorporated herein by reference in its
entirety.
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