U.S. patent application number 10/266769 was filed with the patent office on 2003-05-01 for fabrication method of semiconductor integrated circuit device.
Invention is credited to Ogasawara, Kunio, Takahashi, Osamu.
Application Number | 20030082865 10/266769 |
Document ID | / |
Family ID | 19150365 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030082865 |
Kind Code |
A1 |
Takahashi, Osamu ; et
al. |
May 1, 2003 |
Fabrication method of semiconductor integrated circuit device
Abstract
Provided is a fabrication method of a semiconductor integrated
circuit device, which comprises disposing, in a ultrapure water
preparing system, UF equipment having therein a UF module which has
been manufactured by disposing, in a body thereof, a plurality of
capillary hollow fiber membranes composed of a polysulfone membrane
or polyimide membrane, bonding the plurality of hollow fiber
membranes at end portions thereof by hot welding, and by this hot
welding, simultaneously adhering the hollow fiber membranes to the
body. Upon preparation of ultrapure water to be used for the
fabrication of the semiconductor integrated circuit device, the
present invention makes it possible to prevent run-off of ionized
amine into the ultrapure water.
Inventors: |
Takahashi, Osamu; (Eniwa,
JP) ; Ogasawara, Kunio; (Chitose, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
19150365 |
Appl. No.: |
10/266769 |
Filed: |
October 9, 2002 |
Current U.S.
Class: |
438/200 ;
257/E21.228; 257/E21.625 |
Current CPC
Class: |
H01L 29/40114 20190801;
H01L 27/11526 20130101; C02F 1/444 20130101; H01L 21/02057
20130101; C02F 1/42 20130101; C02F 1/441 20130101; H01L 21/823462
20130101; H01L 27/105 20130101; C02F 1/001 20130101; H01L 27/11546
20130101; H01L 21/28238 20130101; C02F 9/00 20130101; C02F 1/32
20130101; H01L 21/02063 20130101; C02F 2103/04 20130101 |
Class at
Publication: |
438/200 |
International
Class: |
H01L 021/8238 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2001 |
JP |
2001-335371 |
Claims
What is claimed is:
1. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) introducing, as first raw
material water, indifferent water into a primary pure water system
having a primary purifying system; (b) introducing, as second raw
material water, primary water, which has been obtained by the
purification through said primary purifying system, into a
secondary pure water circulating system having a secondary
purifying system; and (c) feeding a first wetting treatment
apparatus with secondary pure water, which has been obtained by the
purification through said secondary purifying system, thereby
subjecting a semiconductor integrated circuit wafer to first
wetting treatment; said step (c) including the sub-steps of: (C1)
removing ions through an ion removing filter; (c2) removing foreign
particles through an ultrafiltration filter; and (c3) feeding said
first wetting treatment apparatus with the pure water, which has
passed through said ion removing filter and said ultrafiltration
filter, wherein, from said secondary pure water fed to said first
wetting treatment apparatus, an ionized amine or ionized amine
substance has been removed to such an extent as not to affect the
characteristics of the semiconductor integrated circuit device to
be fabricated using said secondary pure water.
2. A fabrication method according to claim 1, wherein said ion
removing filter and said ultrafiltration filter are disposed within
said secondary purification system.
3. A fabrication method according to claim 2, wherein said
ultrafiltration filter is a heat welded type.
4. A fabrication method according to claim 3, wherein said ion
removing filter is a membrane type.
5. A fabrication method according to claim 3, wherein said first
wetting treatment is cleaning treatment.
6. A fabrication method according to claim 5, wherein said
semiconductor integrated circuit device comprises a flash memory
portion.
7. A fabrication method according to claim 6, wherein the
characteristics of said semiconductor integrated circuit device are
write or erase characteristics of the flash memory portion.
8. A fabrication method according to claim 3, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 20 nm or less.
9. A fabrication method according to claim 3, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 10 nm or less.
10. A fabrication method according to claim 3, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 5 nm or less.
11. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) introducing, as first raw
material water, indifferent water into a primary pure water system
having a primary purifying system; (b) introducing, as second raw
material water, primary water, which has been obtained by the
purification through said primary purifying system, into a
secondary pure water circulating system having a secondary
purifying system; and (c) feeding a first wetting treatment
apparatus with secondary pure water, which has been obtained by the
purification through said secondary purifying system, thereby
subjecting a semiconductor integrated circuit wafer to first
wetting treatment; said step (c) including the sub-steps of: (c1)
removing foreign particles from the pure water through an
ultrafiltration filter; (c2) removing ions from said pure water,
which has passed through said ultrafiltration filter, by a membrane
type ion removing filter; and (c3) feeding said first wetting
treatment apparatus with said pure water which has passed through
said ion removing filter.
12. A fabrication method according to claim 11, wherein said ion
removing filter and said ultrafiltration filter are disposed in
said secondary purifying system.
13. A fabrication method according to claim 12, wherein said
ultrafiltration filter is a heat welded type.
14. A fabrication method according to claim 13, wherein said first
wetting treatment is cleaning treatment.
15. A fabrication method according to claim 14, wherein said
semiconductor integrated circuit device has a flash memory
portion.
16. A fabrication method according to claim 15, wherein the
characteristics of said semiconductor integrated circuit device are
write or erase characteristics of the flash memory portion.
17. A fabrication method according to claim 11, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 20 nm or less.
18. A fabrication method according to claim 11, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 10 nm or less.
19. A fabrication method according to claim 11, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 5 nm or less.
20. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) introducing, as first raw
material water, indifferent water into a primary pure water system
having a primary purifying system; (b) introducing, as second raw
material water, primary water, which has been obtained by the
purification through said primary purifying system, into a
secondary pure water circulating system having a secondary
purifying system; and (c) feeding a first wetting treatment
apparatus with secondary pure water, which has been obtained by the
purification through said secondary purifying system, thereby
subjecting a semiconductor integrated circuit wafer to first
wetting treatment; said step (c) including the sub-steps of: (c1)
removing foreign particles from the pure water through an
ultrafiltration filter disposed in said secondary purifying system;
(c2) removing ions from said pure water, which has passed through
said ultrafiltration filter, by a membrane type ion removing filter
disposed outside of said secondary pure water circulating system;
and (c3) feeding said first wetting treatment apparatus with said
pure water, which has passed through said ion removing filter.
21. A fabrication method according to claim 20, wherein said first
wetting treatment is cleaning treatment.
22. A fabrication method according to claim 21, wherein said
semiconductor integrated circuit device has a flash memory
portion.
23. A fabrication method according to claim 22, wherein the
characteristics of said semiconductor integrated circuit device are
write or erase characteristics of the flash memory portion.
24. A fabrication method according to claim 20, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 20 nm or less.
25. A fabrication method according to claim 20, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 10 nm or less.
26. A fabrication method according to claim 20, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 5 nm or less.
27. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) introducing, as first raw
material water, indifferent water into a primary pure water system
having a primary purifying system; (b) introducing, as second raw
material water, primary water, which has been obtained by the
purification through said primary purifying system, into a
secondary pure water circulating system having a secondary
purifying system; and (c) feeding a first wetting treatment
apparatus with secondary pure water, which has been obtained by the
purification through said secondary purifying system, thereby
subjecting a semiconductor integrated circuit wafer to first
wetting treatment; said step (c) including the sub-steps of: (c1)
removing ions from the pure water through an ion removing filter
disposed inside of said secondary purifying system, (c2) causing
pure water, which has passed through said ion removing filter, to
pass through a heat welded type ultrafiltration filter disposed
inside of said secondary purifying system, thereby removing foreign
particles, and (c3) feeding said first wetting treatment apparatus
with said pure water which has passed through said ultrafiltration
filter.
28. A fabrication method according to claim 27, wherein said ion
removing filter is a membrane type.
29. A fabrication method according to claim 27, wherein said first
wetting treatment is cleaning treatment.
30. A fabrication method according to claim 29, wherein said
semiconductor integrated circuit device has a flash memory
portion.
31. A fabrication method according to claim 30, wherein the
characteristics of said semiconductor integrated circuit device are
write or erase characteristics of the flash memory portion.
32. A fabrication method according to claim 29, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 20 nm or less.
33. A fabrication method according to claim 29, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 10 nm or less.
34. A fabrication method according to claim 29, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 5 nm or less.
35. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) introducing, as first raw
material water, indifferent water into a primary pure water system
having a primary purifying system; (b) introducing, as second raw
material water, primary water, which has been obtained by the
purification through said primary purifying system, into a
secondary pure water circulating system having a secondary
purifying system; and (c) feeding a first wetting treatment
apparatus with secondary pure water, which has been obtained by the
purification through said secondary purifying system, thereby
subjecting a semiconductor integrated circuit wafer to first
wetting treatment; said step (c) including the sub-steps of: (c1)
removing ions by an ion removing filter; (c2) removing foreign
particles through an ultrafiltration filter; and (c3) feeding said
first wetting treatment apparatus with said pure water, which has
passed through said ion removing filter and said ultrafiltration
filter, wherein said ultrafiltration filter is disposed at a
position permitting self cleaning.
36. A fabrication method according to claim 35, wherein said ion
removing filter and said ultrafiltration filter are disposed in
said secondary purifying system.
37. A fabrication method according to claim 35, wherein said first
wetting treatment is cleaning treatment.
38. A fabrication method according to claim 37, wherein said
semiconductor integrated circuit device has a flash memory
portion.
39. A fabrication method according to claim 38, wherein the
characteristics of said semiconductor integrated circuit device are
write or erase characteristics of the flash memory portion.
40. A fabrication method according to claim 37, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 20 nm or less.
41. A fabrication method according to claim 37, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 10 nm or less.
42. A fabrication method according to claim 37, wherein said
semiconductor integrated circuit device has an MISFET whose gate
insulating film or a tunnel oxide film has a thickness, in terms of
a silicon oxide film, of 5 nm or less.
43. A fabrication method of a semiconductor integrated circuit
device, comprising the steps of: (a) feeding a cleaning apparatus
with ultrapure water through a filter having a cation removing
property; and (b) cleaning, with the ultrapure water fed through
said filter, a main surface of a wafer on which a device is to be
formed and which includes a portion from which a single crystal
region having silicon as a principal component is exposed.
44. A fabrication method according to claim 43, wherein said filter
is a cation removing filter.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a fabrication method of a
semiconductor integrated circuit device, particularly to a
technique effective when adapted to a method of improving the
quality of pure water to be used for the fabrication of the
semiconductor integrated circuit device.
[0002] Upon fabrication of a semiconductor device including
microfabrication of an integrated circuit, it is required to remove
impurities from the surface or interface of a semiconductor wafer
(which will hereinafter be called "wafer" simply) by cleaning,
thereby maintaining cleanness. Foreign matters on a wafer may cause
disconnection or short-circuit of wiring. In particular, heavy
metal components must be removed completely, because they have a
serious influence on electric properties of the device.
[0003] Pure water is used for washing away, from a wafer surface, a
chemical solution after cleaning therewith or wet etching
therewith, thereby making it clean; or for preparing a chemical
solution used in a cleaning or wet etching step. Pure water used in
such a step is prepared by removing, from raw water, fine
particles, organic matters and high molecular ions by an RO
(reverse osmosis) unit equipped with an RO (Reverse Osmosis)
membrane, removing the other ions by using an ion exchange resin,
and then removing fine particles and living bacteria, which are
still in the raw water after removal by the RO unit and ion
exchange resin, by UF equipment (ultrafiltration equipment). A
preparation process of such pure water is disclosed, for example,
in Japanese Unexamined Patent Application No. Hei 4(1992)-78483. In
Japanese Unexamined Patent Application No. Hei 10(1998)-216721,
disclosed is a technique of removing anions, which are too small to
pass through UF equipment, by an anion adsorption membrane
apparatus disposed downstream of the UF equipment.
SUMMARY OF THE INVENTION
[0004] The present inventors have investigated to construct a
system for obtaining pure water having high purity (which will
hereinafter be called "ultrapure water") to be used for the
fabrication of a semiconductor integrated circuit device. During
investigation, they found that the problems as described below
occur.
[0005] The UF equipment is used in the final step of the
preparation of ultrapure water. The UF equipment has a moduled
filter obtained by bundling a plurality of capillary hollow fiber
membranes with an adhesive which contains an epoxy resin as a raw
material. This filter needs periodical replacement with a new one
owing to the life of its material. The adhesive used for bundling
of the hollow fiber membranes contains an amine and a portion of
this amine has been ionized. When water is caused to pass through
this UF equipment after replacement of the filter, this ionized
amine is hydrolyzed and is transferred into ultrapure water. If
ultrapure water containing this ionized amine is used, for example,
for cleaning of a wafer just before the formation of a gate oxide
film of MISFET (Metal Insulator Semiconductor Field Effect
Transistor), Si (silicon) which constitutes the wafer is inevitably
etched by this ionized amine, resulting in the formation of
unevenness on the interface between the gate insulating film and
wafer after formation of the gate insulating film. When the MISFET
formed under such a state forms a memory cell of an electric
erasable programmable read only memory (EEPROM; which will
hereinafter be called "flash memory"), the breakdown voltage of the
gate insulating film lowers, leading to the problem of a
deterioration in write characteristics to the memory cell and erase
characteristics. Even if the above-described MISFET is used for
semiconductor devices other than the memory cell of a flash memory,
an electric current between source and drain is disturbed, causing
a failure in the characteristics.
[0006] The test made by the present inventors has revealed that the
ionized amine comes also from the RO unit and ion exchange resin.
There is a possibility that such ionized amine from the place other
than the UF equipment flows into ultrapure water.
[0007] An object of the present invention is to prevent run-off of
ionized amine into ultrapure water upon preparation of ultrapure
water to be used for the fabrication of a semiconductor integrated
circuit device.
[0008] The above-described and the other objects and novel features
of the present invention will be apparent from the description
herein and accompanying drawings.
[0009] Typical inventions, among those disclosed by the present
application, will next be summarized briefly.
[0010] In one aspect of the present invention, there is thus
provided a fabrication method of a semiconductor integrated circuit
device, which comprises introducing indifferent water, as first raw
material water, into a primary pure water system having a primary
purifying system; introducing, as second raw material water,
primary pure water, which has been obtained by purification through
the primary purifying system, into a secondary pure water
circulating system having a secondary purifying system; and feeding
a first wet treatment apparatus with secondary pure water which has
been obtained by purification through the secondary purifying
system, thereby subjecting a semiconductor integrated circuit wafer
to first wetting treatment,
[0011] wherein, in the secondary purifying system, conducted are an
ion removing step through an ion removing filter, a foreign
particle removing step through an ultrafiltration filter, and a
step of feeding the first wetting treatment apparatus with pure
water which has passed through the ion removing filter and the
ultrafiltration filter, and
[0012] at the time when fed to the first wetting treatment
apparatus, ionized amines or ionized amine substances have been
removed from the secondary pure water to such an extent as not to
affect the characteristics of the semiconductor integrated circuit
device.
[0013] In another aspect of the present invention, there is also
provided a fabrication method of a semiconductor integrated circuit
device, which comprises introducing, as first raw material water,
indifferent water into a primary pure water system having a primary
purifying system, introducing, as second raw material water,
primary water, which has been obtained through the primary
purifying system, into a secondary pure water circulating system
having a secondary purifying system, and feeding a first wetting
treatment apparatus with secondary pure water which has been
obtained by purification of the second raw material water through
the secondary purifying system, thereby subjecting a semiconductor
integrated circuit wafer to first wetting treatment,
[0014] wherein, in the secondary purifying system, carried out are
a step of removing foreign particles from pure water through a
ultrafiltration filter, a step of removing ions from the pure
water, which has passed through the ultrafiltration filter, by a
membrane type ion removing filter, and a step of feeding the first
wetting treatment apparatus with the pure water which has passed
through the ion removing filter.
[0015] In a further aspect of the present invention, there is also
provided a fabrication method of a semiconductor integrated circuit
device, which comprises introducing, as first raw material water,
indifferent water into a primary pure water system having a primary
purifying system, introducing, as second raw material water,
primary water, which has been obtained through the primary
purifying system, into a secondary pure water circulating system
having a secondary purifying system; and feeding a first wetting
treatment apparatus with secondary pure water which has been
obtained by purification through the secondary purifying system,
thereby subjecting a semiconductor integrated circuit wafer to
first wetting treatment,
[0016] wherein, in the secondary purifying system, carried out are
a step of removing foreign particles from pure water through a
ultrafiltration filter disposed in the secondary purifying system,
a step of removing ions from the pure water, which has passed
through the ultrafiltration filter, by a membrane type ion removing
filter disposed outside of the secondary pure water circulating
system, and a step of feeding the first wetting treatment apparatus
with the pure water which has passed through the ion removing
filter.
[0017] In a still further aspect of the present invention, there is
also provided a fabrication method of a semiconductor integrated
circuit device, which comprises introducing, as first raw material
water, indifferent water into a primary pure water system having a
primary purifying system, introducing, as second raw material
water, primary water, which has been obtained through the primary
purifying system, into a secondary pure water circulating system
having a secondary purifying system, and feeding a first wetting
treatment apparatus with secondary pure water which has been
obtained by purification through the secondary purifying system,
thereby subjecting a semiconductor integrated circuit wafer to
first wetting treatment, wherein:
[0018] in the secondary purifying system, carried out are a step of
removing ions from pure water through an ion removing filter
disposed inside of the secondary purifying system, a step of
causing the pure water, which has passed through the ion removing
filter, to pass through a heat welding type ultrafiltration filter
disposed inside of the secondary purifying system, thereby removing
foreign particles from the pure water, and a step of feeding the
first wetting treatment apparatus with the pure water which has
passed through the ultrafiltration filter.
[0019] In a still further aspect of the present invention, there is
also provided a fabrication method of a semiconductor integrated
circuit device, which comprises introducing, as first raw material
water, indifferent water into a primary pure water system having a
primary purifying system, introducing, as second raw material
water, primary water, which has been obtained through the primary
purifying system, into a secondary pure water circulating system
having a secondary purifying system, and feeding a first wetting
treatment apparatus with secondary pure water which has been
obtained by purification through the secondary purifying system,
thereby subjecting a semiconductor integrated circuit wafer to
first wetting treatment,
[0020] wherein, in the secondary purifying system, carried out are
a step of removing ions by an ion removing filter, a step of
removing foreign particles through a ultrafiltration filter, and a
step of feeding the first wetting treatment apparatus with the pure
water which has passed through the ion removing filter and the
ultrafiltration filter, and
[0021] the ultrafiltration filter is disposed at a position
permitting self cleaning.
[0022] The outline of the other inventions described in the present
application will next be described:
[0023] Item 1: A fabrication method of a semiconductor integrated
circuit device, which comprises cleaning a semiconductor substrate
or preparing a chemical solution with pure water prepared by a pure
water preparation step having sub-steps of:
[0024] (a) removing a first foreign matter from raw water
containing foreign matters, and
[0025] (b) removing, after the sub-step (a), foreign matters other
than the first foreign matter from the raw water by using a first
apparatus equipped with a filter formed by bonding a plurality of
hollow fiber membranes at the end portions thereof,
[0026] wherein the hollow fiber membranes permit passage of only
substances having a molecular weight not greater than a
predetermined value, the plurality of hollow fiber membranes are
heat welded or bonded with an amine-free material, and the first
apparatus removes the foreign matters other than the first foreign
matter from the raw water by causing the raw water to pass through
the filter.
[0027] Item 2: The fabrication method of a semiconductor integrated
circuit device according to Item 1, wherein the hollow fiber state
membranes are each composed mainly of polysulfone or polyimide.
[0028] Item 3: The fabrication method of a semiconductor integrated
circuit device according to Item 1, further comprising heat
treating the semiconductor substrate after the cleaning step,
thereby forming a gate insulating film.
[0029] Item 4: The fabrication method of a semiconductor integrated
circuit device according to Item 3, wherein the gate insulating
film is formed to have a film thickness of 20 nm or less.
[0030] Item 5: The fabrication method of a semiconductor integrated
circuit device according to Item 1, further comprising, after the
cleaning step, forming a nonvolatile memory cell, the nonvolatile
memory cell forming step having the following sub-steps:
[0031] (c) heat treating the semiconductor substrate, thereby
forming a gate insulating film,
[0032] (d) forming thereover a first conductive film,
[0033] (e) forming thereover a first insulating film,
[0034] (f) forming thereover a second conductive film,
[0035] (g) patterning the second conductive film, thereby forming a
control gate electrode made thereof, and
[0036] (h) patterning the first insulating film and the first
conductive film, thereby forming a floating gate electrode made of
the first conductive film.
[0037] Item 6: The fabrication method of a semiconductor integrated
circuit device according to Item 5, wherein the gate insulating
film is formed to have a thickness of 10 nm or less.
[0038] Item 7: The fabrication method of a semiconductor integrated
circuit device, which comprises:
[0039] (a) removing a first foreign matter from raw water
containing foreign matters,
[0040] (b) after the step (a), removing foreign matters other than
the first foreign matter from the raw water by using a first
apparatus equipped with a filter formed bonding a plurality of
hollow fiber membranes at end portions thereof, and
[0041] (c) after the step (b), cleaning a semiconductor substrate
or preparing a chemical solution with pure water prepared by
causing the raw water through a first filter made of a
hollow-fiber-type filter membrane having an ion exchange radical,
thereby removing ionized amines from the raw water, wherein:
[0042] the first apparatus is capable of removing foreign matters
other than the first foreign matter from the raw water by causing
the raw water to pass through the filter.
[0043] Item 8: The fabrication method of a semiconductor integrated
circuit device according to Item 7, wherein:
[0044] the step (a) includes a sub-step of removing ions from the
raw water through a second filter made of an ion exchange resin
having an ion exchange radical or a hollow-fiber-type filter
membrane having an ion exchange radical.
[0045] Item 9: The manufacturing method of a semiconductor
integrated circuit device according to Item 7, which further
comprises forming a gate insulating film by heat treating the
semiconductor substrate after cleaning.
[0046] Item 10: The manufacturing method of a semiconductor
integrated circuit device according to Item 9, wherein the gate
insulating film is formed to have a film thickness of 20 nm or
less.
[0047] Item 11: The manufacturing method of a semiconductor
integrated circuit device according to Item 7, which further
comprises forming a nonvolatile memory cell after the cleaning
step, the nonvolatile memory cell forming step having the following
sub-steps:
[0048] (c) heat treating the semiconductor substrate, thereby
forming a gate insulating film,
[0049] (d) forming thereover a first conductive film,
[0050] (e) forming thereover a first insulating film,
[0051] (f) forming thereover a second conductive film,
[0052] (g) patterning the second conductive film to form a control
gate electrode made of the second conductive film, and
[0053] (h) patterning the first insulating film and first
conductive film to form a floating gate electrode made of the first
conductive film.
[0054] Item 12: The manufacturing method of a semiconductor
integrated circuit device according to Item 11, wherein the gate
insulating film is formed to have a thickness of 10 nm or less.
[0055] Item 13: A fabrication method of a semiconductor integrated
circuit device, which comprises cleaning a semiconductor substrate
or preparing a chemical solution with pure water prepared through a
pure water preparing step comprising sub-steps of:
[0056] (a) removing a first foreign matter from raw water
containing foreign matters, and
[0057] (b) after the step (a), removing foreign matters other than
the first foreign matter by a first apparatus equipped with a
filter formed by bonding a plurality of hollow fiber membranes at
end portions thereof, wherein:
[0058] the sub-step (a) further comprises ions from the raw water
through a second filter made of a hollow-fiber-type filter membrane
having an ion exchange radical.
[0059] Item 14: The manufacturing method of a semiconductor
integrated circuit device according to Item 13, wherein the
semiconductor substrate is heat treated after the cleaning step,
thereby forming a gate insulating film.
[0060] Item 15: The manufacturing method of a semiconductor
integrated circuit device according to Item 14, wherein the gate
insulating film is formed to have a thickness of 20 nm or less.
[0061] Item 16: The manufacturing method of a semiconductor
integrated circuit device according to Item 13, which further
comprises forming a nonvolatile memory cell after the cleaning
step, the non-volatile-memory-cell forming step including the
following sub-steps:
[0062] (c) heat treating the semiconductor substrate, thereby
forming a gate insulating film,
[0063] (d) forming thereover a first conductive film,
[0064] (e) forming thereover a first insulating film,
[0065] (f) forming thereover a second conductive film,
[0066] (g) patterning the second conductive film to form a control
gate electrode made of the second conductive film, and
[0067] (h) patterning the first insulating film and first
conductive film to form a floating gate electrode made of the first
conductive film.
[0068] Item 17: The fabrication method of a semiconductor
integrated circuit device according to Item 16, wherein the gate
insulating film is formed to have a film thickness of 10 nm or
less.
[0069] Item 18: A fabrication method of a semiconductor integrated
circuit device, which comprises cleaning a semiconductor substrate
or preparing a chemical solution with pure water prepared through a
pure water preparing step comprising sub-steps of:
[0070] (a) removing a first foreign matter from raw water
containing foreign matters, and
[0071] (b) after the step (a), removing foreign matters other than
the first foreign matter by a first apparatus equipped with a
filter formed by bonding a plurality of hollow fiber membranes at
end portions thereof, wherein:
[0072] in a pathway for sending the pure water from the first
apparatus to an apparatus in which the cleaning step or chemical
solution preparing step is conducted, a first filter made of a
hollow-yarn type filter membrane having an ion exchange radical or
an ion exchange resin having an ion exchange radical is disposed;
and
[0073] ionized amines are removed from the pure water through the
first filter.
[0074] Item 19: The fabrication method of a semiconductor
integrated circuit device according to Item 18, further comprising
heat treating the semiconductor substrate after the cleaning step,
thereby forming a gate insulating film.
[0075] Item 20: The fabrication method of a semiconductor
integrated circuit device according to Item 19, wherein the gate
insulating film is formed to have a film thickness of 20 nm or
less.
[0076] Item 21: The fabrication method of a semiconductor
integrated circuit device according to Item 18, which further
comprises forming a nonvolatile memory cell after the cleaning
step, the non-volatile-memory-cell forming step including:
[0077] (c) heat treating the semiconductor substrate, thereby
forming a gate insulating film,
[0078] (d) forming thereover a first conductive film,
[0079] (e) forming thereover a first insulating film,
[0080] (f) forming thereover a second conductive film,
[0081] (g) patterning the second conductive film to form a control
gate electrode made of the second conductive film, and
[0082] (h) patterning the first insulating film and first
conductive film to form a floating gate electrode made of the first
conductive film.
[0083] Item 22: The fabrication method of a semiconductor
integrated circuit device according to Item 21, wherein the gate
insulating film is formed to have a film thickness of 10 nm or
less.
[0084] Item 23: A fabrication method of a semiconductor integrated
circuit device, which comprises cleaning a semiconductor substrate
or preparing a chemical solution with pure water prepared through a
pure water preparing step comprising sub-steps of:
[0085] (a) removing a first foreign matter from raw water
containing foreign matters, and
[0086] (b) after the step (a), removing foreign matters other than
the first foreign matter by a plurality of first apparatuses each
equipped with a filter formed by bonding a plurality of hollow
fiber membranes at end portions thereof, wherein:
[0087] the step (a) further comprises:
[0088] (a1) removing ions from the raw water by a second filter
made of an ion exchange resin having an ion exchange radical or a
hollow-fiber-type filtration membrane having an ion exchange
radical;
[0089] the step (a) is followed by at least one of the sub-steps
of:
[0090] (c) causing a portion of the raw water, which has passed
through the second filter, to pass through new one of the first
apparatus or new one of the second filter and then feeding the
resulting purified water to the second filter, and
[0091] (d) causing the residue of the pure water after the cleaning
step or chemical-solution-preparing step to pass through at least
one of new one of the first apparatus or new one of the second
filter and then feeding to the second filter; and
[0092] the steps (c) and/or (d) are carried out for a predetermined
term.
[0093] 24. The fabrication method of a semiconductor integrated
circuit device according to Item 23, further comprising forming a
gate insulating film by heat treating the semiconductor substrate
after the cleaning step.
[0094] 25. The fabrication method of a semiconductor integrated
circuit device according to Item 24, wherein the gate insulating
film is formed to have a film thickness of 20 nm or less.
[0095] 26. The fabrication method of a semiconductor integrated
circuit device according to Item 23, which further comprises
forming a nonvolatile memory cell after the cleaning step, the
non-volatile-memory-cell forming step including:
[0096] (c) heat treating the semiconductor substrate, thereby
forming a gate insulating film,
[0097] (d) forming thereover a first conductive film,
[0098] (e) forming thereover a first insulating film,
[0099] (f) forming thereover a second conductive film,
[0100] (g) patterning the second conductive film to form a control
gate electrode made of the second conductive film, and
[0101] (h) patterning the first insulating film and first
conductive film to form a floating gate electrode made of the first
conductive film.
[0102] Item 27: The fabrication method of a semiconductor
integrated circuit device according to Item 26, wherein the gate
insulating film is formed to have a film thickness of 10 nm or
less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0103] FIG. 1 is a fragmentary cross-sectional view illustrating a
fabrication method of a semiconductor integrated circuit device
according to one embodiment of the present invention;
[0104] FIG. 2 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 1;
[0105] FIG. 3 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 2;
[0106] FIG. 4 is a schematic view illustrating the preparing system
of ultrapure water to be used for the fabrication of the
semiconductor integrated circuit device according to the one
embodiment of the present invention;
[0107] FIG. 5 is a schematic view illustrating the details of the
ultrapure water preparing system illustrated in FIG. 4;
[0108] FIG. 6 is a schematic view of a UF module of UF equipment
included in the preparation system of ultrapure water to be used
for the fabrication of the semiconductor integrated circuit device
according to the one embodiment of the present invention;
[0109] FIG. 7 is a fragmentary cross-sectional view of the UF
module illustrated in FIG. 6;
[0110] FIG. 8 is a schematic view of a hollow fiber membrane
constituting the UF module illustrated in FIG. 6;
[0111] FIG. 9 is a schematic view of an ion filter to be disposed
downstream of the UF equipment included in the preparing system of
ultrapure water to be used for the fabrication of the semiconductor
integrated circuit device according to the one embodiment of the
present invention;
[0112] FIG. 10 is a fragmentary cross-sectional view for explaining
trapping of ions by the ion filter illustrated in FIG. 9;
[0113] FIG. 11 illustrates one disposal example of the ion filter
illustrated in FIG. 9;
[0114] FIG. 12 illustrates one disposal example of the ion filter
illustrated in FIG. 9;
[0115] FIG. 13 illustrates another disposal example of the ion
filter illustrated in FIG. 9;
[0116] FIG. 14 illustrates a further disposal example of the ion
filter illustrated in FIG. 9;
[0117] FIG. 15 is a schematic view illustrating the constitution of
the UF equipment included in the preparing system of ultrapure
water to be used for the fabrication of the semiconductor
integrated circuit device according to the one embodiment of the
present invention;
[0118] FIG. 16 is a schematic view for explaining an anion deminer
and a cation deminer included in the preparing system of ultrapure
water to be used for the fabrication of the semiconductor
integrated circuit device according to the one embodiment of the
present invention;
[0119] FIG. 17 is a schematic view for explaining ion adsorption by
an ion exchange resin shown in FIG. 16;
[0120] FIG. 18 is a schematic view of one example of a cleaning and
drafting apparatus to be used for the fabrication of the
semiconductor integrated circuit device according to the one
embodiment of the present invention;
[0121] FIG. 19 is a schematic view of a dilute hydrofluoric acid
preparing apparatus for preparing dilute hydrofluoric acid to be
fed to the cleaning and drafting apparatus shown in FIG. 18;
[0122] FIG. 20 is a schematic view of one example of a wet etching
apparatus to be used for the fabrication of the semiconductor
integrated circuit device according to the one embodiment of the
present invention;
[0123] FIG. 21 is a schematic view of one example of a cleaning and
drafting apparatus to be used for the fabrication of the
semiconductor integrated circuit device according to the one
embodiment of the present invention;
[0124] FIG. 22 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 3;
[0125] FIG. 23 is a fragmentary cross-sectional view for explaining
the shape of the interface between the semiconductor substrate and
the gate insulating film formed thereover after cleaning with
ultrapure water having ionized amines mixed therein;
[0126] FIG. 24 is a fragmentary cross-sectional view for explaining
the shape of the interface between the semiconductor substrate and
the gate insulating film formed thereover after cleaning with
ultrapure water free of ionized amines;
[0127] FIG. 25 is a schematic view illustrating the measuring
method of the breakdown voltage of the gate insulating film of
MISFET of the semiconductor integrated circuit device according to
the one embodiment of the present invention;
[0128] FIG. 26 is a schematic view illustrating the measurement
results of the breakdown voltage of the gate insulating film when
the semiconductor substrate is cleaned with ultrapure water
prepared just after replacement of UF of the UF equipment with a
new one;
[0129] FIG. 27 is a schematic view illustrating the measurement
results of the breakdown voltage of the gate insulating film when
the semiconductor substrate is cleaned with ultrapure water
prepared just after replacement, with new ones, of an ion exchange
resin type anion removing filter and an ion exchange resin type
cation removing filter each included in the preparing system of
ultrapure water to be used for the fabrication of the semiconductor
integrated circuit device according to the one embodiment of the
present invention;
[0130] FIG. 28 is a schematic view illustrating the measurement
results of the breakdown voltage of the gate insulating film when
the semiconductor substrate is cleaned with ultrapure water
prepared using UF of the UF equipment which UF has been used
long;
[0131] FIG. 29 is a schematic view illustrating the measurement
results of the breakdown voltage of the gate insulating film when
the semiconductor substrate is cleaned with ultrapure water
prepared using UF equipment having a UF replaced with a new one and
having a mix deminer disposed downstream of the equipment;
[0132] FIG. 30 is a schematic view illustrating the measurement
results of the breakdown voltage of the gate insulating film when
the semiconductor substrate is cleaned with ultrapure water
prepared using UF equipment having a UF replaced with a new one and
having, downstream of the equipment, an ion filter with a membrane
film;
[0133] FIG. 31 is a schematic view illustrating the relationship
between the amount of ionized amines attached to the semiconductor
substrate by cleaning with ultrapure water and existence or absence
of a defective gate insulating film;
[0134] FIG. 32 is a schematic view illustrating the relationship
between the cleaning date of the semiconductor substrate with
ultrapure water and percent defective of the gate insulating
film;
[0135] FIG. 33 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 22;
[0136] FIG. 34 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 33;
[0137] FIG. 35 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 34;
[0138] FIG. 36 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 35;
[0139] FIG. 37 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 36;
[0140] FIG. 38 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 39;
[0141] FIG. 39 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 38; and
[0142] FIG. 40 is a fragmentary cross-sectional view of the
semiconductor integrated circuit device during the fabrication step
following the step of FIG. 39.
DETAILED DESCRIPTION OF THE INVENTION
[0143] Prior to detailed description of the invention according to
the present application, meanings of some terms used in this
application will be explained below.
[0144] The term "wafer" means a single crystalline Si substrate
(generally, a nearly flat and circular shape), a sapphire
substrate, a glass substrate or any other insulating,
semi-insulating or semiconductor substrate and a composite
substrate thereof used for fabricating semiconductor integrated
circuit devices. Further, the term "semiconductor integrated
circuit device" as used herein means not only those fabricated on a
semiconductor or insulating substrate such as silicon wafer or
sapphire substrate but also those fabricated on another insulating
substrate such as glass, for example, TFT (Thin-Film-Transistor) or
STN (Super-Twisted-Nematic) liquid crystals unless otherwise
specifically indicated.
[0145] The term "device surface" means a main surface of a
substrate on which device patterns corresponding to a plurality of
chip regions are formed by lithography.
[0146] The term "resist pattern" means a film pattern obtained by
patterning a photosensitive resin film (resist film) by
photolithography. This pattern includes a simple resist film free
of openings at such a portion.
[0147] The term "UF equipment" (Ultrafiltration Equipment) means
pressure filtration equipment for separating molecules by their
size through a ultra filter (UF). In this equipment, separation is
carried out at a molecular cutoff range of about thousands to
hundreds of thousands. The term "ultra filter" embraces hollow
fiber type ultra filter and spiral type ultra filter.
[0148] The term "ion exchange resin" means a synthetic resin having
a capacity of adsorbing thereto ions existing in water, thereby
removing them from water. It can be classified into two types, that
is, a cation exchange resin for adsorbing and removing cations
(Na.sup.+, Ca.sup.2-, Mg.sup.2+, etc.) and an anion exchange resin
for adsorbing and removing anions (CI.sup.-, SO.sub.4.sup.2-,
SiO.sub.2, etc.). The term "ion exchange resin type ion removing
filter" embraces a cation removing filter for removing cations, an
anion removing filter for removing anions and a mixed ion removing
filter for removing both cations and anions.
[0149] The term "RO unit" (Reverse Osmosis unit) means an apparatus
for removing ions, organic matters, fine particles and living
bacteria in water through an RO film which is a filter membrane to
which reverse osmosis has been applied.
[0150] The term "vacuum degasifier" means an apparatus for spraying
water in a vacuum atmosphere, thereby removing a dissolved gas in
water.
[0151] The term "indifferent water" means water which will serve as
a raw material for obtaining high purity water to be used for the
fabrication of a semiconductor integrated circuit device. River
water, ground water (including well water) or the like is employed
as it.
[0152] The term "primary pure water" means high purity water from
which almost all the impurities such as ions, fine particles,
microorganisms and organic matters have been removed from treatment
water (indifferent water).
[0153] The term "ultrapure water" means water which is obtained by
removing trace of impurities such as fine particles, living
bacteria, TOC (total organic carbon), ions and dissolved oxygen
remaining in primary water, thereby having a markedly high purity
and is to be used, for example, for cleaning of a wafer.
[0154] The term "primary pure water unit" means one of a unit
constituting a ultrapure water preparing system. It is formed of a
reverse osmosis unit, ion exchanging apparatus and degasifier and
prepares primary pure water by removing almost all the impurities
such as fine particles, ions, microorganisms and organic matters
from water passing through a pretreatment apparatus.
[0155] The term "pretreatment system" means a system including
apparatuses for removing colloidal matters, particulate matters and
bacteria from raw water by physical and chemical treatments prior
to feeding of the raw water to a primary pure water unit.
[0156] The term "subsystem" means a system which is disposed in the
vicinity of a point of use and prepares ultrapure water by using,
as raw water, primary pure water. It comprises a UV sterilizer, a
cartridge polisher and a pressure filter.
[0157] The term "ultrapure water preparing system" means a system
for preparing high purity water by separating impurities from raw
water such as tap water, industrial water, well water or river
water through an ion exchange resin membrane or a filter membrane,
thereby purifying it. The system comprises a pretreatment unit, a
primary pure water unit and a subsystem.
[0158] The term "point of use" means a site at which ultrapure
water fed from a subsystem is taken out for the purpose of wafer
cleaning and provided for use.
[0159] The term "TOC (total organic carbon)" means an organic
carbon contained in ultrapure water and it embraces that from raw
water (natural water or recovered water) or that escaped from used
members such as ion exchange resin or pipe.
[0160] The term "ultrafiltration membrane" means a plastic porous
thin-film filter having numerous uniform pores and made of
cellulose nitrate, cellulose acetate, acetyl cellulose,
nitrocellulose, nylon, Teflon, polyvinyl chloride or ethylene
tetrafluoride resin.
[0161] The term "new" means an apparatus or member which has not
been used and it embraces that used for a predetermined term. With
regards to UF in the below-described embodiment, this predetermined
term corresponds to the term until discharge of ionized amine
outside the UF equipment terminates in the case where the UF is
made of an amine-containing material. This predetermined term
varies, depending on the specification of UF or amount of water fed
to the UF. In the below-described embodiment, the predetermined
term is about 1 month, preferably about 2 months, more preferably
about 3 months, each after its use is started.
[0162] In the below-described embodiment, when a reference is made
to the number of elements (including the number, value, amount and
range), the number of elements is not limited to a specific number
but can be not greater than or less than the specific number unless
otherwise specifically indicated or in the case it is principally
apparent that the number is limited to the specific number.
[0163] Moreover in the below-described embodiment, it is needless
to say that the constituting elements (including element steps) are
not always essential unless otherwise specifically indicated or in
the case where it is principally apparent that they are
essential.
[0164] Similarly, in the below-described embodiment, when a
reference is made to the shape or positional relationship of the
constituting elements, that substantially analogous or similar to
it is also embraced unless otherwise specifically indicated or in
the case where it is utterly different in principle. This also
applies to the above-described value and range.
[0165] In all the drawings for describing the below-described
embodiment, members having like function will be identified by like
reference numerals and overlapping descriptions will be omitted
[0166] In the below-described embodiments, MISFET (Metal Insulator
Semiconductor Field Effect Transistor) representing an electric
field transistor will be abbreviated as MIS, while a p-channel type
MISFET and an n-channel type MISFET will be abbreviated as pMIS and
nMIS, respectively.
[0167] The embodiments of the present invention will hereinafter be
described specifically based on accompanying drawings.
[0168] In this embodiment, the present invention is applied to a
fabrication method of a flash memory (semiconductor integrated
circuit device). This fabrication method of a flash memory will
next be described in the order of steps in accordance with FIGS. 1
to 41.
[0169] As illustrated in FIG. 1, a semiconductor substrate
(semiconductor integrated circuit wafer) 1 on which the flash
memory of this embodiment is to be formed has, for example, a
region 1A in which 5V type nMIS is formed, a region 1B in which 5V
type pMIS is formed, a region 1C in which MIS to be a memory cell
of a flash memory is formed, a region 1D in which a high
breakdown-voltage one-side offset nMIS is formed, a region 1E2 in
which a high breakdown-voltage loading nMIS is formed and a region
1F in which a high breakdown-voltage one-side offset pMIS is
formed.
[0170] First, the semiconductor substrate 1 made of p type single
crystal silicon Si is cleaned with dilute hydrofluoric acid (HF)
and ultrapure water, followed by oxidizing treatment on the surface
of the substrate to form a silicon oxide film 2A thereover. After
deposition of a silicon nitride film (not illustrated) over the
silicon oxide film 2A, the silicon nitride film is etched to
selectively leave the silicon nitride film over the silicon oxide
film 2A.
[0171] With the resulting silicon nitride film as a mask, an
impurity (for example, P (phosphorus)) having an n type
conductivity is introduced into the semiconductor substrate 1 by
ion implantation. After selectively thickening, by oxidizing
treatment, a portion of the silicon oxide film 2A in a region
having no silicon nitride film formed thereover, the silicon
nitride film is removed using, for example, hot phosphoric acid.
The semiconductor substrate 1 is then cleaned with NH.sub.4OH
(ammonium hydroxide)/H.sub.2O.sub.2 (hydrogen peroxide)/H.sub.2O,
dilute hydrofluoric acid and ultrapure water. The substrate 1 is
heat treated to diffuse the above-described impurity, whereby an n
type isolation region NiSO is formed.
[0172] As illustrated in FIG. 2, after cleaning the semiconductor
substrate 1 with dilute hydrofluoric acid and ultrapure water,
oxidizing treatment is conducted on the surface of the substrate to
form a silicon oxide film 2 thereover. With a photoresist film (not
illustrated) patterned by photolithography as a mask, an impurity
(for example, P) having an n type conductivity is introduced into
the semiconductor substrate 1 by ion implantation. After removal of
the photoresist film, with another photoresist film (not
illustrated) patterned by photolithography as a mask, an impurity
(for example, BF.sub.2 (boron difluoride) having a p type
conductivity is introduced into the semiconductor substrate 1 by
ion implantation. The semiconductor substrate 1 is then cleaned
with NH.sub.4OH/H.sub.2O.sub.2/H.sub.2O, hydrofluoric acid and
ultrapure water, followed by heat treatment to diffuse these
impurities, whereby an n type well 3 and a p type well 4 are
formed.
[0173] As illustrated in FIG. 3, the surface of the semiconductor
substrate 1 is oxidized to form a silicon oxide film (not
illustrated) thereover. After deposition of a silicon nitride film
(not illustrated) over the silicon oxide film, the silicon nitride
film is etched with a photoresist film (not illustrated) as a mask
to selectively leave the silicon nitride film over the silicon
oxide film. The photoresist film is removed. The semiconductor
substrate 1 is then cleaned with
NH.sub.4OH/H.sub.2O.sub.2/H.sub.2O, followed by further cleaning
with HCl/H.sub.2O.sub.2/H.sub.2O. By selective oxidization method,
a field insulating film 6 for element isolation is formed over the
surface of the semiconductor substrate 1.
[0174] With a photoresist film patterned by photolithography as a
mask, an impurity (for example, BF.sub.2) having a p type
conductivity is introduced by ion implantation. The impurity is
diffused by heat treatment, whereby a p type channel stopper region
7 is formed. The silicon nitride film remaining on the
semiconductor substrate 1 is then removed using, for example, hot
phosphoric acid.
[0175] The semiconductor substrate 1 is then cleaned with dilute
hydrofluoric acid and ultrapure water. The ultrapure water used in
this Embodiment is prepared by a system as illustrated in FIGS. 4
and 5. FIG. 4 is a schematic view illustrating the outline of the
ultrapure water preparing system of this Embodiment, while FIG. 5
is a schematic view illustrating one example of the details of the
ultrapure water preparing system illustrated in FIG. 4. A technique
relating to such a ultrapure water preparing system is also
described in Japanese Patent Application No. 2001-314813 already
applied by the present inventors.
[0176] As illustrated in FIGS. 4 and 5, by the pretreatment system
(primary purifying system) PTS, groundwater (indifferent water
(first raw material water) which will hereinafter be called "raw
water") pumped up from a well is subjected to chemical and physical
treatments to remove colloidal matters (first foreign matter),
particulate matters (first foreign matter) and bacteria (first
foreign matter) from the raw water. By an RO unit (primary
purifying system) RO1, fine particles (first foreign matter),
organic matters (first foreign matter), bacteria (first foreign
matter) and high molecular ions (first foreign matter) are removed
from the raw water. By an ion exchange resin type cation removing
filter (primary purifying system) CED1, cations (first foreign
matter) are removed from the raw water, followed by removal of a
dissolved gas in the raw water by a vacuum degasifier (VD). By an
ion exchange resin type anion removing filter (primary purifying
system) AED1, anions (first foreign matter) are removed from the
raw water. After removal of cations (first foreign matter) from the
raw water by an ion exchange resin type cation removing filter
(primary purifying system), anions are removed from the raw water
by an ion exchange resin type anion removing filter (primary
purifying system) AED2. Downstream thereof, an RO unit RO2 (not
illustrated in FIG. 5) may be disposed to remove, from the raw
water, fine particles generated from the anion and cation removing
filters. Through the above-described steps, primary pure water can
be prepared from the raw water. The primary pure water system
(pretreatment system) here is made of units used for preparing
primary pure water from the raw water.
[0177] The primary pure water (second raw material water) thus
prepared is then fed to an intermediate storage tank (secondary
purifying system) MIDT, followed by delivery to a heat exchanger
(secondary purifying system) HEXC by a pump (secondary purifying
system) PUMP. While the primary pure water is kept at a fixed
temperature by the heat exchanger HEXC, it is fed to an UV
sterilizer (secondary purifying system) UV01 or a low-pressure UV
oxidizer (secondary purifying system) UVO2, in which the primary
pure water is oxidized or sterilized by exposure to UV rays. The
primary pure water sterilized by the UV sterilizer UVO1 is caused
to pass through an ion exchange resin type mixed ion removing
filter (secondary purifying system) MED to remove cations and
anions, and then delivered to UF equipment (first equipment) UFE.
Fine particles and the like, which cannot be removed by the RO unit
and ion removing filter, can be removed by the UF equipment UFE,
making it possible to prepare ultrapure water (secondary pure
water) to be used for the fabrication of the semiconductor
integrated circuit device of this Embodiment and to feed the thus
prepared ultrapure water to a point of use USEP. The secondary pure
water system (subsystem (secondary pure water circulating system))
is formed of each equipment for preparing ultrapure water from
primary pure water and point of use USEP.
[0178] Of the ultrapure water sent to the point of use USEP, a
portion of it which has not been used up at the point of use USEP
can be returned to the intermediate storage tank MIDT for recycling
use. Of the ultrapure water used at the point of use USEP (which
water will hereinafter be called "wastewater"), that re-usable as
ultrapure water is subjected to ion exchange to remove cations and
anions. The wastewater is then subjected to sterilizing treatment
and removing treatment of impurities such as fine particles,
organic matters, bacteria and high molecular ions by using an RO
unit RO3 having sterilizing capacity by exposure to ultraviolet
rays and fine-particle removing capacity through an RO membrane.
After various treatments as described above, the wastewater,
together with the raw material treated by the RO unit RO1, is sent
to the cation removing filter CED1. After these steps, a portion of
the wastewater becomes re-usable as ultrapure water.
[0179] FIG. 6 is a schematic view of a UF module of the UF
equipment UFE illustrated in FIGS. 4 and 5. FIG. 7 is a
cross-sectional view taken along a line A-A of FIG. 6. The UF
module in this Embodiment is made by disposing, in a body KOT, a
plurality of capillary hollow fiber membranes TYM formed from a
polysulfone membrane or polyimide membrane, bonding these plurality
of hollow fiber membranes TYM at end portions thereof by hot
welding and by this hot welding, adhering these hollow fiber
membranes TYM to the body. As illustrated in FIG. 8, the hollow
fiber membranes are each made of a polysulfone membrane or
polyimide membrane so that water, ion molecules and low molecules
can penetrate inside of the hollow fiber membranes TYM, but high
molecules cannot. Since the plurality of hollow fiber membranes TYM
are hot welded each other at end portions thereof in the body KOT
and the hollow fiber membranes TYM are adhered to the body,
discharged from the UF module is only primary pure water which has
penetrated inside of the hollow fiber membranes TYM and thereby
deprived of high molecules, that is, ultrapure water.
[0180] When the plurality of hollow fiber membranes TYM are bonded
each other at end portions thereof by an adhesive containing an
epoxy resin as its raw material, the adhesive contains an amine and
a portion of this amine exists as ionized form. In this Embodiment,
on the other hand, the plurality of hollow fiber membranes TYM are
hot welded at end portions thereof so that the adhered portions do
not contain amine. Use of the UF module of this Embodiment
therefore makes it possible to prevent discharge of ionized amine
which will otherwise occur when primary pure water is fed to the UF
module and ionized amine is hydrophilized and then, discharged as a
mixture with ultrapure water. Even if ultrapure water prepared by
the ultrapure water preparing system according to this Embodiment
is used for a cleaning step of the semiconductor substrate 1 just
before the formation of a gate oxide film of MISFET which will be a
memory cell of a flash memory, it is possible to prevent an
inconvenience such as formation of unevenness on the interface
between a gate oxide film and semiconductor substrate 1 after
formation of the gate oxide film, which will otherwise be caused by
etching of the semiconductor substrate by ionized amine. This
results in the prevention of lowering in the breakdown voltage of
the gate oxide film, thereby making it possible to prevent
deterioration in write characteristics and erase characteristics.
Lowering in the breakdown voltage of the gate oxide film can be
prevented so that even in MISFET other than memory cell, smooth
flow of electric current between source and drain is not disturbed.
In this Embodiment, the plurality of hollow fiber membranes TYM are
bonded each other by hot welding, but hot welding may be replaced
with bonding via an amine-free urethane material.
[0181] Downstream of the UF equipment UFE (refer to FIGS. 4 and 5),
an ion filter (first filter) having a membrane film MBF in the
circular sheet form may be disposed as illustrated in FIG. 9. The
ultrapure water passing through the UF equipment UFE is supplied to
its ion filter and then, enters into the membrane film MBF from a
membrane hole MBH of the membrane film MBF. As illustrated in FIG.
10, an ion exchange radical IER has been formed in the membrane
hole MBH. Ions in the ultrapure water are adsorbed to this ion
exchange radical IER and thus can be removed. In other words, even
if a plurality of hollow fiber membranes TYM disposed in the UF
module of the UF equipment UFE (refer to FIGS. 4 and 5) are bonded
each other at end portions thereof by an amine-containing adhesive
(for example, an epoxy resin) and ionized amine is discharged
together with ultrapure water, it can be removed from the ultrapure
water by causing the water to pass through the above-described ion
filter.
[0182] As illustrated in FIG. 11, it is possible to omit the anion
removing filter AED3 and mixed ion removing filter MED from the
ultrapure preparing system of this Embodiment illustrated in FIGS.
4 and 5 and dispose an ion filter as illustrated in FIG. 9
downstream of the UF equipment. In FIG. 11, the heat exchanger HEXS
is not illustrated. When the system does not include these filters,
an ion filter IFA having an ion exchange radical capable of
adsorbing thereto anions and an ion filter IFC having an ion
exchange radical capable of adsorbing thereto cations are disposed
as the ion filter. Without using the anion removing filter AED3 and
mixed ion removing filter MED, anions and cations can be removed
from the primary pure water by the ion filter IFA and ion filter
IFC. Moreover, even when the ionized amine runs off from the UF
module, it can be removed by the ion filters IFA and IFC. In such a
ultrapure water preparing system of this Embodiment, the anion
removing filter AED3 and mixed ion removing filter MED can be
omitted, which contributes to simplification of this system. This
makes it possible to facilitate the maintenance of the ultrapure
water preparing system of this Embodiment.
[0183] As illustrated in FIG. 12, the anion removing filter AED3
and mixed ion removing filter MED in the ultrapure water preparing
system of this Embodiment illustrated in FIGS. 4 and 5 may be
replaced with the above-described ion filter (second filter) IFA
and ion filter (second filter) IFC. In FIG. 12, the heat exchanger
HEXC is not illustrated. Since the ion exchange resin constituting
the anion removing filter AED3 and mixed ion removing filter MED
contains an amine, there is a possibility of ionized amine leaking
from the anion removing filter AED3 and mixed ion removing filter
MED when primary pure water is caused to pass through these
filters. The test made by the present inventors has revealed that
ionized amine is leaked from the anion removing filter AED3 and
mixed ion removing filter MED and a leak amount from the anion
removing filter AED3 is greater. It is therefore possible to be
free from inconvenience such as leakage of ionized amine when the
anion removing filter AED3 and mixed ion removing filter MED are
replaced with the ion filters IFA and IFC.
[0184] As illustrated in FIG. 13, the ion filter IFC may be
installed in the pipe line (pathway) PL for delivering ultrapure
water to the point of use USED from the UF equipment UFE. The point
of use USEP embraces not only cleaning and drafting equipment
(first wet treating equipment) to be used for cleaning (first wet
treatment) of the semiconductor substrate 1 but also
chemical-solution preparing equipment (first wet treating
equipment) in which a chemical solution such as dilute hydrofluoric
acid is prepared using ultrapure water. Ionized amine is cation so
that installment of the ion filter IFC in the pipe line PL makes it
possible to remove, by the filter IFC, ionized amine from ultrapure
water to be fed to the point of use USEP even if ionized amine
flows out from the UF equipment UFE as a mixture in ultrapure
water. In this Embodiment, the ion filter IFC is installed in the
pipe line PL. Instead of the ion filter IFC, a mixed ion removing
filter may be used for the removal of ionized amine from ultrapure
water.
[0185] The UF equipment UFE is made of a plurality of UF modules
UFM as illustrated in FIG. 14. Similar to the UF modules as
described with reference to FIG. 6, these UF modules UFM have,
disposed in the body thereof, a plurality of capillary hollow fiber
membranes made of a polysulfone membrane or polyimide membrane.
When the plurality of hollow fiber membranes are bundled using an
amine-containing adhesive, ionized amine presumably comes to be
mixed in ultrapure water discharged from the UF modules UFM. In
this Embodiment, the above-described ion filter IFC is therefore
disposed upstream of each of the UF modules UFM. This makes it
possible to remove ionized amine by the ion filter IFC even if
ionized amine is mixed in ultrapure water discharged from the UF
modules UFM. Upon disposal, the capacity of allowing the passage of
water is set greater in the ion filter IFC than in the UF module
UFM. When the ion filter IFC is inferior in this capacity to the UF
module UFM, a plurality of the ion filters IFC are disposed per UF
module UFM so that the total capacity of the plurality of ion
filters IFC would exceed that of one UF module UFM.
[0186] When a plurality of hollow fiber membranes are bundled by an
amine-containing adhesive as the above-described UF modules UFM,
the amount of ionized amine is small relative to the whole amine
amount. Of the whole amine, only ionized amine is hydrophilized and
flows out from the UF modules UFM, passing through the hollow fiber
membranes. Most of the amine existing in the ionized form is
discharged from the UF modules together with ultrapure water after
an elapse of a predetermined term after disposal of new UF modules
in the UF equipment UFE which term varies depending on the amount
of water caused to pass through the UF modules. An area for
installing new UF modules UFMN is established in the UF equipment
UFE as illustrated in FIG. 15. To new UF modules UFMN installed in
this area as well as to the other UF modules UFM, primary pure
water which has passed through the anion removing filter AED3 and
mixed ion removing filter MED is fed. The primary pure water fed to
the new UF modules UFMN is discharged, from the new UF modules
UFMN, as ultrapure water containing ionized amine existing in the
new UF modules UFMN, fed to the upstream of the anion removing
filter AED3 and mixed ion removing filter MED, and then unites with
the primary pure water upstream thereof. The ultrapure water,
together with the primary pure water, is then fed to the anion
removing filter AED3 and mixed ion removing filter MED. The anion
removing filter AED3 and mixed ion removing filter MED used here
each has, in the body KOT1 thereof, a plurality of ion exchange
resins IEJ disposed as illustrated in FIG. 16. As illustrated in
FIG. 17, the ion exchange resins IEF each has an ion exchange
radical IER1 which adsorbs thereto ions in the primary pure water
fed to the body KOT1. Ionized amine contained in the ultrapure
water is a cation so that it can be adsorbed to and removed by the
mixed ion removing filter MED. The ultrapure water from which
ionized amine has been removed is fed again to the UF equipment UFE
together with the primary pure water. The above-described steps are
then repeated. By these steps, new UF modules UFMN can be cleaned
to remove ionized amine existing therein, whereby primary pure
water used for the removal of ionized amine can be provided for
recycling use without being discarded. The test made by the present
inventors has revealed that when a column having a diameter of
about 106 mm and a height of 1150 mm was used as a new UF module
UFMN, run-off of ionized amine from the new UF module UFMN stopped
about two or three months (preferably about 3 months) after about 3
m.sup.3 per hour of the primary pure water was caused to pass
through the new UF module UFMN. Such a new UF module UFMN which
becomes free from leakage of ionized amine after such a step can be
used as a substitute for an old UF module UFM. The number of such
new UF modules UFMN to be disposed must be equal or greater than
that of UF modules which are worn and need replacement. The number
of new modules can be set freely depending on whether the old UF
modules UFM are replaced wholly or partially.
[0187] Alternatively, new UF modules UFMN as described above may be
installed in a pathway (refer to FIGS. 4 and 5) for returning, to
an intermediate storage tank MIDT, a nonused portion of ultrapure
water at the point of use USEP. Ultrapure water fed to the new UF
module UFMN is discharged therefrom as ultrapure water containing
ionized amine existing in the new UF module UFMN. This
ionized-amine-containing ultrapure water is sent to the
intermediate storage tank MIDT (refer to FIGS. 4 and 5) and there,
unites with primary pure water. The ionized amine can be removed
when the primary pure water passes through the mixed ion removing
filter MED (refer to FIGS. 4 and 5). The ultrapure water from which
ionized amine has been removed is fed again to the UF equipment UFE
together with the primary water. The above-described steps are then
repeated. By such steps, ionized amine existing in the new UF
module UFMN can be removed. Moreover, ultrapure water used for the
removal of ionized amine can be provided for recycling use without
being discarded.
[0188] As described above, the ion exchange resin IEJ (refer to
FIGS. 16 and 17) constituting the anion removing filter AED3 and
mixed ion removing filter MED contains an amine. The amine in the
ion exchange resin does not contain so much ionized amine. As in
the UF module UFM, the ionized amine is hydrophilized and
inevitably flows out from the anion removing filter AED3 and mixed
ion removing filter MED. It is therefore possible to remove ionized
amine contained in the ion exchange resin IEJ by disposing new
anion removing filters AED3 and mixed ion removing filters MED in
an area similar to the area in which the new UF modules UFMN are
disposed. The ionized amine contained in the ion exchange resin IEJ
may be removed, as in the case of the new UF modules UFMN, by
disposing new anion removing filters AED3 and mixed ion removing
filters MED in a pathway (refer to FIGS. 4 and 5) for returning a
nonused portion of the ultrapure water at the point of use USEP to
an intermediate storage tank MIDT.
[0189] When the ultrapure water prepared through the
above-described steps is used in a cleaning step of the
semiconductor substrate 1 from which a silicon nitride film used
for the formation of the above-described field insulating film 6
(refer to FIG. 3) has been removed, a cleaning and drafting
apparatus as illustrated in FIG. 18 can be used. The ultrapure
water prepared by the ultrapure water preparing system of this
Embodiment which has been described with reference to FIGS. 4 to 17
is fed to each of a treatment tank SC1 and pure water tanks QDR1,
QDR2, OF1 and OF2 which are points of use USED of ultrapure water
(refer to FIGS. 4 and 5). As described above using FIG. 13, an ion
filter IFC having an ion exchange radical capable of adsorbing
thereto cations or a mixed ion removing filter MED may be installed
in respective pipe lines for feeding ultrapure water to the
treatment tank SC1 and pure water tanks QDR1, QDR2, OF1 and OF2.
The treatment tank SC1 is fed with H.sub.2O.sub.2 and NH.sub.4OH,
while the treatment tank HF is fed with dilute hydrofluoric acid
prepared using the ultrapure water of this Embodiment. The
semiconductor substrate 1 is cleaned as described below by such a
cleaning and drafting apparatus. First, cleaning with
NH.sub.4OH/H.sub.2O.sub.2/H.sub.2O is conducted in the treatment
tank SC1, followed by cleaning with ultrapure water in the pure
water tanks QDR1 and OF1. After cleaning with dilute hydrofluoric
acid in the treatment tank HF, cleaning with pure water is
conducted in the pure water tanks QDR2 and OF2. The semiconductor
substrate 1 is then dried by IPA (isopropyl alcohol) vapor drying
method, by which the cleaning step of the semiconductor substrate 1
by the cleaning and drafting apparatus as illustrated in FIG. 18 is
completed. When the cleaning and drafting apparatus as illustrated
in FIG. 18 is applied to another cleaning step which does not need
the treatment in the treatment tank SC1 and pure water tanks QDR1
and OF1, the cleaning step may be started from the treatment in the
treatment tank HF.
[0190] FIG. 19 is a schematic view of a dilute hydrofluoric acid
preparing apparatus. This dilute hydrofluoric acid preparing
apparatus is one of the points of use USEP of ultrapure water
(refer to FIGS. 4 and 5). The ultrapure water prepared by the
ultrapure water preparing system of this Embodiment described using
FIGS. 4 to 17 is first fed in a predetermined amount to a pure
water weighing tank TANK 1. As described above with reference to
FIG. 13, an ion filter IFC having an ion exchange radical capable
of adsorbing thereto cations or a mixed ion removing filter MED is
installed in the pipe line for feeding ultrapure water to the pure
water weighing tank TANK 1. Undiluted hydrofluoric acid fed from a
hydrofluoric acid canister CAN1 to an undiluted hydrofluoric acid
tank TANK 2 is weighed by being transferred from the undiluted
hydrofluoric acid tank TANK2 to a hydrofluoric acid weighing tank
TANK 3. From the pure water weighting tank TANK 1 and the
hydrofluoric acid weighing tank TANK 3, ultrapure water and
undiluted hydrofluoric acid are then fed respectively to a blending
tank TANK4, in which ultrapure water and the undiluted hydrofluoric
acid are blended at a predetermined ratio to prepare dilute
hydrofluoric acid. In this Embodiment, shown as an example is an
about 1:99 or 1:19 mixture of undiluted hydrofluoric acid and
ultrapure water. The dilute hydrofluoric acid is then transferred
from the blending tank TANK4 to a feeding tank TANK5, whereby it
can be provided for a cleaning and drafting apparatus.
[0191] After removal of the silicon nitride film used for the
formation of the field insulating film 6 (refer to FIG. 3) and
cleaning of the semiconductor substrate 1, the surface thereof is
oxidized to form thereover a gate insulating film 8 having a film
thickness of about 20 nm. By wet etching with a photoresist film
(not illustrated) patterned by photolithography, the gate
insulating film 9 in a region 1C is selectively removed. In this
Embodiment, wet etching can be carried out by a wet etching
apparatus (refer to FIG. 20) which uses ultrapure water prepared by
the ultrapure water preparing system of this Embodiment described
above using FIGS. 4 to 17. The ultrapure water is fed to each of
the pure water tanks QDR3, OF3 and OF4 which are points of use USEP
(refer to FIGS. 4 and 5) of the ultrapure water. As described above
using FIG. 13, an ion filter IFC having an ion exchange radical
capable of adsorbing thereto cations or a mixed ion removing filter
MED may be installed in each of the pipe lines for feeding the pure
water tanks QDR3, OF3 and OF4 with ultrapure water. An etching tank
ETCH contains an etching solution for etching of the silicon oxide
film. In such a wet etching step of the gate insulating film 8 by
the wet etching apparatus, the gate insulating film 8 is wet etched
by immersing the semiconductor substrate 1 in the etching tank
ETCH. After cleaning the semiconductor substrate 1 by ultrapure
water in the pure water tanks OF3 and OF4, the semiconductor
substrate 1 is dried by spin drying, whereby the wet etching step
of the gate insulating film 8 by the wet etching apparatus as
illustrated in FIG. 20 is completed.
[0192] After removal of the photoresist film, the semiconductor
substrate 1 is cleaned, for example, by a cleaning and drafting
apparatus as illustrated in FIG. 21. The ultrapure water prepared
by the ultrapure water preparing system of this Embodiment
described based on FIGS. 4 to 17 is fed to each of treatment tanks
SC2 and SC3, and pure water tanks QDR3, QDR4, OF5 and OF6 which are
each a point of use USEP of the ultrapure water (refer to FIGS. 4
and 5). As described above using FIG. 13, an ion filter IFC having
an ion exchange radical capable of adsorbing thereto cations or a
mixed ion removing filter MED may be installed in respective pipe
lines for feeding the treatment tanks SC2 and SC3, and pure water
tanks QDR3, QDR4, OF5 and OF6. The treatment tank SC2 is fed with
H.sub.2O.sub.2 and NH.sub.4OH, while the treatment tank SC3 is fed
with H.sub.2O.sub.2 and HC1 (hydrochloric acid). Cleaning of the
semiconductor substrate 1 by such a cleaning and drafting apparatus
is carried out in the following manner. First, cleaning with
NH.sub.4OH/H.sub.2O.sub.2/H.sub.2O is conducted in the treatment
tank SC2, followed by cleaning with the ultrapure water in the pure
water tanks QDR3 and OF5. After cleaning with
HCl/H.sub.2O.sub.2/H.sub.2O in the treatment tank SC3, cleaning
with ultrapure water is conducted in the pure water tanks QDR4 and
OF6. The semiconductor substrate 1 is dried by IPA vapor drying
method, whereby a cleaning step of the semiconductor substrate 1 by
the cleaning and drafting apparatus as illustrated in FIG. 21 is
completed.
[0193] As illustrated in FIG. 22, the surface of the semiconductor
substrate 1 is oxidized to form a gate insulating film (tunnel
oxide film) 9 having a film thickness of about 10 nm over the
surface of the p type well 4 in a region 1C. The gate insulating
film 9 may have a film thickness not greater than 10 nm, for
example, about 5 nm.
[0194] By CVD, a polycrystalline Si film (first conductive film) 10
of about 200 nm thick is deposited over the main surface (device
surface) of the semiconductor substrate 1. This polycrystalline Si
film 10 may be formed by depositing amorphous Si over the
semiconductor substrate 1 by CVD and then heat treating this
amorphous Si to convert amorphous Si to polycrystalline Si.
[0195] After deposition of a phosphate glass film (not illustrated)
over the surface of the polycrystalline Si film 10, for example, by
the coating method, the semiconductor substrate 1 is heat treated
to introduce P into the polycrystalline Si film 10. After removal
of the phosphate glass film, the polycrystalline Si film 10 is
patterned with a photoresist film (not illustrated) patterned by
photolithography as a mask. This makes it possible to leave the
polycrystalline Si film 10 in the region 1C, and to form gate
electrodes 10D, 10E2 and 10F in the regions 1D, 1E2 and 1F,
respectively. After removal of the photoresist film used for
patterning of the polycrystalline Si film 10, heat treatment at
about 950.degree. C. is conducted to form a silicon oxide film
(first insulating film) 11 over the surface of the polycrystalline
Si film 10 (including gate electrodes 10D, 10E2 and 10F).
[0196] In the cleaning step of the semiconductor substrate 1 with
ultrapure water, the ultrapure water, if it contains ionized amine,
inevitably etches Si constituting the semiconductor substrate 1. As
illustrated in FIG. 23, which is an enlarged view of the region IC,
the interface between the gate insulating film 9 and the
semiconductor substrate 1 (p type well 4) becomes uneven. This
unevenness adversely affects the shape of a thin film formed over
the gate insulating film 9 and the interface between the gate
insulating film 9 and polycrystalline Si film 10 or the interface
between the polycrystalline Si film 10 and silicon oxide film 11
sometimes becomes uneven.
[0197] By using the ultrapure water preparing system of this
Embodiment described based on FIGS. 4 to 17, inclusion of ionized
amine in the ultrapure water can be prevented. Use of the ultrapure
water prepared according to this Embodiment can therefore prevent
the formation of unevenness on the interface between the gate
insulating film 9 and semiconductor substrate 1 (p type well 4)
(refer to FIG. 24). This makes it possible to prevent lowering in
the breakdown voltage of the gate insulating film so that when
MISFET which will be a memory cell of a flash memory is formed in
the region IC, deteriorations in the write characteristics to the
memory cell and erase characteristics can be prevented.
[0198] The present inventors measured the breakdown voltage of the
gate insulating film 9 in a manner as shown in FIG. 25. Described
specifically, the applied voltage when an electric current of about
1.times.10.sup.-11 is sent between the semiconductor substrate 1
and polycrystalline Si film 10 was measured by a probe. In FIG. 25,
members other than the semiconductor substrate 1, field insulating
film 6, gate insulating film 9 and polycrystalline Si film 10 are
omitted. FIGS. 26 to 30 are the measuring results of the breakdown
voltage of the gate insulating film 9 at plural sites on the whole
surface of the semiconductor wafer (semiconductor substrate 1). The
gate insulating films 9 at sites showing a voltage less than 8V are
regarded defective because of a decline in breakdown voltage.
[0199] FIG. 26 shows the measuring results of the breakdown voltage
of the gate insulating film 9 formed after cleaning the
semiconductor substrate 1 with the ultrapure water which has been
prepared just after replacement of the UF modules UFM (refer to
FIG. 14) of the UF equipment UFE with new ones. In FIG. 26, shown
are the results in the case where the UF equipment is not equipped
with the ion filter IFC as illustrated in FIG. 14. As described
above using FIG. 14, the UF modules UFM each has, in the body of
thereof, a plurality of hollow fiber membranes bundled with an
amine-containing adhesive. In a novel UF module UFM, a portion of
an amine exists as ions. The ionized amine is hydrophilized and
flows out from the UF module as a mixture with the ultrapure water.
In the cleaning step of the semiconductor substrate 1 with the
ultrapure water, this ionized amine inevitably etches Si
constituting the semiconductor substrate 1, thereby forming an
unevenness on the interface between the surface and the gate
insulating film 9 formed thereover. It has been confirmed from the
test results shown in FIG. 26 that this unevenness lowers the
breakdown voltage of the gate insulating film 9.
[0200] FIG. 27 shows the measuring results of the breakdown voltage
of the gate insulating film 9 formed after cleaning the
semiconductor substrate 1 with the ultrapure water which has
prepared just after the replacement of the anion removing filter
AED3 and mixed ion removing filter MED (refer to FIGS. 4 and 5)
with new ones. Similar to the results shown in FIG. 26, in FIG. 27
shown are results in the case where the ion filter IFC as
illustrated in FIG. 14 is not installed. As described above in FIG.
12, the ion exchange resin constituting the anion removing filter
AED3 and mixed ion removing filter MED contains amines so that when
the primary water passes through these filters, ionized amine runs
out from them. This ionized amine is hydrophilized and discharged
from the UF equipment UFE as a mixture with the ultrapure water.
Similar to the results shown in FIG. 26, this ionized amine
inevitably etches Si constituting the semiconductor substrate 1,
thereby forming an unevenness on the interface between its surface
and the gate insulating film 9 formed thereover. It has been
confirmed from the test results shown in FIG. 27 that this
unevenness lowers the breakdown voltage of the gate insulating film
9.
[0201] FIG. 28 shows the measuring results of the breakdown voltage
of the gate insulating film 9 formed after cleaning of the
semiconductor substrate 1 with ultrapure water prepared using the
UF modules UFM of the UFE equipment UFE which have been used long
(for example, at least about 3 months). Similar to the results
shown in FIG. 26 or 27, in FIG. 28 shown are results in the case
where the ion filter IFC as illustrated in FIG. 14 is not
installed. As described above in FIG. 15, most of the amines
existing in the ionized form are discharged, together with the
ultrapure water, from the UF modules after an elapse of a
predetermined term which varies depending on the amount of water
caused to pass through the UF modules UFM. There is no possibility
of the ionized amine flowing out from the UF modules UFM if they
have been used long so that unevenness on the interface between the
semiconductor substrate 1 and the gate insulating film 9 which will
otherwise be formed as a result of etching, by ionized amine, of Si
constituting the semiconductor substrate 1 does not occur. It can
be confirmed also from the test results shown in FIG. 28 that the
gate insulating film 9 is free from a reduction in the breakdown
voltage because such an inconvenience is inhibited.
[0202] FIG. 29 shows the measuring results of the breakdown voltage
of the gate insulating film 9 formed after cleaning the
semiconductor substrate 1 (refer to FIG. 13) with the ultrapure
water prepared by replacing the UF modules UFM with new ones and
disposing a mixed ion removing filter MED downstream of the UF
equipment UFE. In this case, the ionized amine flowing out from the
new UF modules UFM can be removed by the mixed ion removing filter
MED so that unevenness on the interface between the semiconductor
substrate 1 and the gate insulating film 9, which will otherwise be
formed as a result of etching, by ionized amine, of Si constituting
the semiconductor substrate 1, does not occur. It can be confirmed
also from the test results shown in FIG. 29 that the gate
insulating film 9 is free from a reduction in the breakdown voltage
because such an inconvenience is inhibited.
[0203] FIG. 30 shows the measuring results of the breakdown voltage
of the gate insulating film 9 formed after cleaning the
semiconductor substrate 1 (refer to FIG. 13) with the ultrapure
water prepared by replacing the UF modules UFM with new ones and
disposing an ion filter IFC (refer to FIG. 11) downstream of the UF
equipment UFE. In this case, the ionized amine flowing out from the
new UF modules UFM can be removed by the ion filter IFC so that
unevenness on the interface between the semiconductor substrate 1
and the gate insulating film 9, which otherwise be formed as a
result of etching, by ionized amine, of Si constituting the
semiconductor substrate 1, does not occur. It can be confirmed also
from the test results shown in FIG. 30 that the gate insulating
film 9 is free from a reduction in the breakdown voltage because
such an inconvenience is inhibited.
[0204] FIG. 31 illustrates the relationship, classified by
specification, between the amount of ionized amine attached to the
semiconductor substrate 1 as a result of cleaning with ultrapure
water and existence or absence of defective gate insulating film 9
studied by the testing method as illustrated in FIG. 25. At this
time, the ultrapure water is fed to a cleaning and drafting
apparatus (refer to FIG. 18) at a rate of 15 liter/minute. The
cleaning step is started with the treatment in the treatment tank
HF. After removal of the gate insulating film 8 formed in the
region 1C to expose Si constituting the semiconductor substrate 1,
treatment is conducted in the pure water tanks QDR2 and OF2. Since
the amount of ionized amine mixed in the ultrapure water was trace,
the treatment time in the pure water tank OF2 was adjusted to about
100 minutes so that the amount of ionized amine attached to the
semiconductor substrate 1 is clearly different among the
specifications of the ultrapure water preparing system. The item
indicated as "P test" shows the test results by the testing method
(which will hereinafter be called "probe test") illustrated in FIG.
25. Among the specifications of the ultrapure water preparing
system to be tested, the specification indicated by "ReF" has UF
modules UFM of the UF equipment UFE which modules have been used
for a long period of time (for example, about three months or
greater). The specification indicated by "new UF" has new UF
modules as the modules of the UF equipment UFE. The specification 1
indicates UF equipment UFE installed with new UF modules UFM after
cleaning for about 2 weeks in a similar manner to that described
above using FIG. 15. The specification 2 indicates UF equipment UFE
installed with new UF modules after cleaning for about 6 weeks in a
similar manner to that described above using FIG. 15. The
specification 3 indicates UF equipment UFE which is installed with
new UF modules and has a cation deminer and an anion deminer
disposed downstream of the UF equipment UFE (between the UF
equipment UFE and point of use USEP). The specification 4 indicates
UF equipment UFE (FIG. 11) which is installed with new UF modules
UFM and has an ion filter IFA and an ion filter IFC disposed
downstream of the UF equipment UFE (between the UF equipment UFE
and point of use USEP). As a result of comparison in the attached
amount of ionized amine among these specifications, supposing that
the attached amount of ionized amine in ReF is 100, the amount is
greater in the new UF, Specification 1, Specification 2 and
Specification 3 than in ReF. According to the results of the probe
test, the new UF and specification 1 are judged defective. Although
the specification 2 is judged defective as a result of the probe
test, its defectiveness is lighter than that of the new UF or
specification 1. From these results, confirmed are effectiveness of
the ultrapure water preparing system of this Embodiment
characterized in that ionized amine is removed by UF equipment and
an ion exchange resin type ion removing filter (ion filter IFA and
ion filter IFC) or deminer (cation removing filter and anion
removing filter) disposed downstream of the UF equipment UFE
(between the UF equipment and the point of use USEP) and
effectiveness of the use of new UF modules UFM as illustrated in
FIG. 15 after cleaning for a predetermined term.
[0205] FIG. 32 illustrates the relationship between the percent
defectives of the gate insulating film 9 and the cleaning date of
the semiconductor substrate 1 with ultrapure water reckoned from
the date on which the UF modules UFM of the UF equipment UFE are
replaced with new ones. At the time when mass production (cleaning
step) of the flash memory of this Embodiment is started again after
replacement of the UF modules UFM with new ones, a TOC content in
the ultrapure water, its specific resistance and concentration of
dissolved oxygen in the ultrapure water have recovered their normal
values, more specifically, approximately 1.0.+-.0.2 ppb, 18.25
M.OMEGA. and 20.+-.3.0 ppb, respectively. Although the mass
production is restarted when these TOC content, specific resistance
and concentration of dissolved oxygen become normal values, some
gate insulating films 9 are defective, suggesting that these
elements have no relationship with the percent defectives of the
gate insulating film 9. The TOC content, specific resistance and
dissolved oxygen concentration, each of the ultrapure water, become
the above-described values about 1.5 days, about 0.5 day and about
0.5 day after replacement of the UF modules UFM with the new ones,
so that for about three days after replacement with the UF modules
UFM with new ones, the cleaning step is not conducted even though
the ultrapure water is prepared. The percent defectives of the gate
insulating film 9 increases just after the replacement day of the
UF modules UFM with new ones, followed by gradual decrease day by
day. This occurs because as the primary pure water passes through
the new UF modules UFM, the ionized amine existing in the new UF
modules UFM flows out and its amount decreases. From the
above-described results, the effectiveness of the cleaning step of
new UF modules UFM for a predetermined term as illustrated in FIG.
15 can be confirmed.
[0206] As illustrated in FIG. 33, a silicon nitride film 13, a
silicon oxide film 14 and a silicon nitride film 15 are
successively stacked over the semiconductor substrate 1. These
silicon nitride films 13,15 are formed, for example, by deposition
by CVD, while the silicon oxide film 14 is formed, for example, by
heat treating the semiconductor substrate 1. The silicon oxide
films 11,14 and silicon nitride films 13,15 are called interlayer
capacitor film 16 collectively. With a photoresist film (not
illustrated) patterned by photolithography as a mask, the
interlayer capacitor film 16 is dry etched to remove the interlayer
capacitor film 16 from the regions 1A,1B.
[0207] Over the surface of the p type well 4 in the region 1A and
the surface of the n type well 3 in the region 1B, a silicon oxide
film (not illustrated) is formed by oxidizing treatment. Then, into
the p type well 4 in the region 1A and n type well 3 in the region
1B, BF.sub.2 is introduced.
[0208] After removal of the photoresist film used for dry etching
of the interlayer capacitor film 16, the surface of the
semiconductor substrate 1 is oxidized to form, for example, a gate
insulating film 17 of about 13.5 nm thick over the surface of the p
type well 4 in the region 1A and the surface of the n type well 3
in the region 1B as illustrated in FIG. 34.
[0209] Over the main surface of the semiconductor substrate 1, a
polycrystalline Si film (second conductive film) 18, WSi.sub.x film
(second conductive film) 19 and silicon oxide film 20 are stacked
successively. After the deposition of the polycrystalline Si film
18, a phosphate glass film (not illustrated) may be deposited by
the coating method, followed by heat treatment of the semiconductor
substrate 1 to introduce P into the polycrystalline Si film 18.
[0210] As illustrated in FIG. 35, with a photoresist film (not
illustrated) patterned by photolithography as a mask, the silicon
oxide film 20 is patterned. After removal of the photoresist film,
the WSi.sub.x film 19 and the polycrystalline Si film 18 are dry
etched with the silicon oxide film 20 as a mask. By this step, in
the regions 1A and 1B, gate electrodes 29A,29B made of the
WSi.sub.x film 19 and the polycrystalline Si film 18 can be formed
respectively, while in the region 1C, a control gate electrode 22
made of the WSi.sub.x film 19 and the polycrystalline Si film 18
can be formed. In the regions 1E2,1D,1F, the interlayer capacitor
film 16 is etched while leaving the silicon nitride film 13.
[0211] As illustrated in FIG. 36, the polycrystalline Si film 10 is
dry etched with the silicon oxide film 20 as a mask in the region
1C, whereby a floating gate electrode 24 can be formed. A region
other than the region 1C is covered with the photoresist film so
that exposure to etching atmosphere can be prevented. Here, the
floating gate electrode 24, interlayer capacitor film 16 and
control gate electrode 22 are called gate electrode 25
collectively. Oxidizing treatment is then conducted to form a thin
silicon oxide film 30 on the side walls and upper surfaces of the
gate electrodes 25, 29A and 29B.
[0212] As illustrated in FIG. 37, with a photoresist film (not
illustrated) patterned by photolithography as a mask, an n type
impurity (for example, P) is introduced into the p type well 4 on
one side of the gate electrode 25 by ion implantation, followed by
heat treatment.
[0213] After removal of the photoresist film, a new photoresist
film (not illustrated) is formed over the regions 1A, 1C, 1E2 and
1D. With this photoresist film as a mask, a p type impurity (for
example, BF.sub.2) is introduced into the n type well 3 by ion
implantation, whereby a p.sup.- type semiconductor region 31 is
formed.
[0214] After removal of the photoresist film from the regions 1A,
1C, 1E2 and 1D, another photoresist film (not illustrated) is
formed over the regions 1B and 1F. With the photoresist film as a
mask, an n type impurity (for example, P) is introduced into the p
type well 4 by ion implantation to form an n.sup.- type
semiconductor region 32. Then, the photoresist film is removed from
the regions 1B and 1F.
[0215] As illustrated in FIG. 38, a silicon oxide film is then
deposited over the semiconductor substrate 1 by CVD. By anisotropic
etching of the silicon oxide film, side wall spacers 33 are formed
by leaving the silicon oxide film on the side walls of the gate
electrodes 29A, 29B, 25, 10E2, 10D and 10F.
[0216] A photoresist film (not illustrated) is then formed over the
regions 1B and 1F and over the gate electrodes 29A, 25, 10E2 and
10D so as to cover, with the photoresist film, a predetermined
range of the n type semiconductor region 32 on one side of the gate
electrode 10D. With the photoresist film as a mask, an n type
impurity (for example, P) is then introduced into the p type well 4
by ion implantation.
[0217] After removal of the photoresist film, another photoresist
film (not illustrated) is formed over the regions 1A, 1C, 1E2 and
1D and over the gate electrodes 29B and 10F so as to cover, with
the photoresist film, a predetermined range of the p.sup.- type
semiconductor region 31 on one side of the gate electrode 10D. With
the photoresist film as a mask, a p type impurity (for example,
BF.sub.2) is then introduced into the n type well 3 by ion
implantation. After removal of the photoresist film, the
semiconductor substrate 1 is heat treated at about 900.degree. C.,
whereby p.sup.+ type semiconductor region 34 and n.sup.+ type
semiconductor regions 35 and 35A are formed. By these steps, 5V
type nMISQA, 5V type pMISQB, MISQC which will be a memory cell of a
flash memory, a high-breakdown-voltage loading nMISQE2, a
high-breakdown-voltage one-side offset nMISQD and a
high-breakdown-voltage one-side offset pMISQF can be formed in the
regions 1A, 1B, 1C, 1E2, 1D and 1F, respectively.
[0218] As illustrated in FIG. 39, a silicon oxide film 36 of about
150 nm thick is then deposited over the semiconductor substrate 1
by CVD. The silicon oxide film 36 is then dry etched with a
photoresist film (not illustrated) patterned by photolithography as
a mask, whereby a contact hole 38A reaching the n.sup.+ type
semiconductor region 35A is formed in the silicon oxide film
36.
[0219] After removal of the photoresist film, an amorphous Si film
is deposited over the semiconductor substrate 1 by CVD, thereby
embedding the contact hole 38A with the amorphous Si film. A
polycrystalline Si film is then formed by heat treatment of this
amorphous Si film. By dry etching with a photoresist film (not
illustrated) patterned by photolithography as a mask, the
polycrystalline Si film is patterned to form an interconnect TG.
The semiconductor substrate 1 is then heat treated, whereby a
silicon oxide film 36A is formed over the surface of the
interconnect TG.
[0220] As illustrated in FIG. 40, a BPSG film 37 is deposited over
the semiconductor substrate 1 by CVD, followed by heat treatment of
the semiconductor substrate at about 900.degree. C. in an N.sub.2
atmosphere to planarize the surface of the BPSG film 37.
[0221] Through a photoresist film (not illustrated) patterned by
photolithography, the BPSG film 37, silicon oxide film 36 and gate
insulating films 8,17 are dry etched, whereby a contact hole 38 is
formed.
[0222] After removal of the photoresist film used for perforation
of the contact hole 38, an MoSi (molybdenum silicide) film of about
30 nm thick is deposited in the contact hole 38 and over the BPSG
film by sputtering to form a barrier conductor film. Over the
barrier conductor film, a metal film to embed therewith the contact
hole 38 is deposited by sputtering. This metal film is composed
mainly of Al (aluminum) and contains Cu (copper). An antireflective
film is then formed by depositing an MoSi film over the metal film.
The barrier conductor film has a function of preventing diffusion
of the A1 in the metal film into the BPSG film 37 and silicon oxide
film 36, while the antireflective film serves to prevent irregular
reflection upon formation of a photoresist film over the
antireflective film in the subsequent step.
[0223] By dry etching through a photoresist film (not illustrated)
patterned by photolithography, the antireflective film, metal film
and barrier conductor film are patterned to form an interconnect
39, whereby the flash memory of this Embodiment is fabricated.
[0224] The present invention made by the present inventors was so
far described specifically based on the embodiment of the
invention. It is needless to say that the present invention is
however not limited to the embodiment, but can be modified to an
extent not departing from the gist of the invention.
[0225] For example, use of ultrapure water prepared in the
above-described embodiment for a cleaning step of a semiconductor
substrate during fabrication of a flash memory was described, but
it can be applied to a cleaning step during the fabrication of a
semiconductor integrated circuit device (for example, logic
circuit) other than the flash memory.
[0226] Of the inventions disclosed by the present application,
effects available by the representative ones will next be described
simply.
[0227] It is possible to prevent run-off of ionized amine into the
ultrapure water in the step of preparing ultra pure water to be
used for the fabrication of a semiconductor integrated circuit
device, making it possible to prevent lowering in breakdown voltage
of a gate insulating film which will otherwise occur due to the
formation of unevenness at the interface between the gate
insulating film and semiconductor substrate.
* * * * *