U.S. patent application number 10/486207 was filed with the patent office on 2005-07-14 for semiconductor manufacturing method and apparatus.
Invention is credited to Fujii, Toshiaki, Yokoyama, Shin.
Application Number | 20050150516 10/486207 |
Document ID | / |
Family ID | 18990311 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050150516 |
Kind Code |
A1 |
Fujii, Toshiaki ; et
al. |
July 14, 2005 |
Semiconductor manufacturing method and apparatus
Abstract
The present invention aims to provide processes and equipments
for manufacturing semiconductors, according to which oxidation of
wafer surfaces can be controlled by simple means and contaminants
promoting oxidation and contaminants inviting a decreased yield of
wafers can also be totally controlled. To achieve the object above,
the present invention provides a process for manufacturing a
semiconductor, characterized in that a substrate is treated while
exposing the surface of the substrate with a negative ion-enriched
gas; and an equipment for manufacturing a semiconductor comprising
a gas channel through which a gas to be treated is passed; a
negative ion-enriched gas generator consisting of a gas cleaner
located at an upstream part of said gas channel and a negative ion
generator located at a downstream part thereof: and means for
supplying the resulting negative ion-enriched gas to the surface of
each substrate.
Inventors: |
Fujii, Toshiaki; (Kanagawa,
JP) ; Yokoyama, Shin; (Hiroshima, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
18990311 |
Appl. No.: |
10/486207 |
Filed: |
August 10, 2004 |
PCT Filed: |
May 14, 2002 |
PCT NO: |
PCT/JP02/04656 |
Current U.S.
Class: |
134/1.3 ;
134/1.2; 134/902; 257/E21.256; 257/E21.284 |
Current CPC
Class: |
H01L 21/31138 20130101;
H01L 21/02238 20130101; H01L 21/31658 20130101 |
Class at
Publication: |
134/001.3 ;
134/001.2; 134/902 |
International
Class: |
C25F 001/00; C25F
003/30 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2001 |
JP |
2001-144350 |
Claims
1-8. (canceled)
9. A process for manufacturing a semiconductor, comprising:
treating a substrate while exposing a surface of the substrate with
a negative ion-enriched gas.
10. The process of claim 9, wherein said negative ion-enriched gas
is prepared by passing a clean gas freed of microparticles and/or
chemical contaminant through a negative ion generator.
11. The process of claim 10, wherein said chemical contaminant is
one or more selected from the group consisting of ionic components,
inorganic matters, and organic matters.
12. The process of claim 10, wherein said negative ion-enriched gas
is prepared by passing a gas having a microparticle concentration
of class 100 or less, an ionic component concentration of 10
.mu.g/m.sup.3 or less, and an organic matter concentration of 10
.mu.g/m.sup.3 or less through a negative ion generator.
13. The process of claim 9, wherein the concentration of negative
ions in said negative ion-enriched gas is 1,000 negative ions/mL or
more.
14. The process of claim 9, wherein the concentration of negative
ions in said negative ion-enriched gas is 5,000 negative ions/mL or
more.
15. The process of claim 9, wherein the concentration of negative
ions in said negative ion-enriched gas is 10,000 negative ions/mL
or more.
16. The process of claim 9, wherein the concentration of negative
ions in said negative ion-enriched gas is 50,000 negative ions/mL
or more.
17. An equipment for manufacturing a semiconductor comprising: a
gas channel through which a gas to be treated is passed; a negative
ion-enriched gas generator including a gas cleaner located at an
upstream part of said gas channel and a negative ion generator
located at a downstream part of said gas channel; and means for
supplying resulting negative ion-enriched gas to a surface of a
substrate.
18. The equipment of claim 17, wherein said gas cleaner prepares a
gas having a microparticle concentration of class 100 or less, an
ionic component concentration of 10 .mu.g/m.sup.3 or less, and an
organic matter concentration of 10 .mu.g/m.sup.3 or less.
19. The equipment of claim 17, wherein said negative ion-enriched
gas generator prepares a negative ion-enriched gas having a
negative ion concentration of 1,000 negative ions/mL or more.
20. The process of claim 17, wherein the concentration of negative
ions in said negative ion-enriched gas is 5,000 negative ions/mL or
more.
21. The process of claim 17, wherein the concentration of negative
ions in said negative ion-enriched gas is 10,000 negative ions/mL
or more.
22. The process of claim 17, wherein the concentration of negative
ions in said negative ion-enriched gas is 50,000 negative ions/mL
or more.
Description
TECHNICAL FIELD
[0001] The present invention relates the manufacture of
semiconductors, particularly processes and equipments for
manufacturing semiconductors in leading-edge industries such as
semiconductors and liquid crystals.
BACKGROUND ART
[0002] Air cleaning in the working environment Is very important
for the manufacture of semiconductors, which normally takes place
in an air-conditioned space called clean room. A conventional air
cleaning technique in a semiconductor factory (clean room) is
explained with reference to FIG. 8.
[0003] In FIG. 8, ambient air 1 first passes through a prefilter 2
where coarse particles are eliminated and then the temperature and
humidity are conditioned in an air conditioner 3 and then dusts are
collected by a medium-performance filter 4. Then, fine particles
are collected by an HEPA filter 6 at the ceiling of a clean room 5.
Such an air cleaning system maintains a microparticle concentration
of class 10,000 in the-clean room. In FIG. 8, references 7-1 and
7-2 represent fans and arrows indicate air streams.
[0004] The air cleaning system in conventional clean rooms for the
purpose of removing microparticles is designed as shown in FIG. 8
and effective for removing microparticles but not effective for
removing gaseous hazardous components.
[0005] As improvements in the quality and precision of products
increasingly advance in the recent semiconductor industry, not only
microparticles (particulate substances) but also gaseous substances
have come to participate in contamination of semiconductors.
[0006] However, conventional dust filters for clean rooms (e.g.,
HEPA filters, ULPA filters, etc.) as shown in FIG. 8 can collect
only microparticles, but gaseous hazardous components from ambient
air are not collected and but introduced into clean rooms. Such
gaseous hazardous components include e.g. gases called hydrocarbons
(HCs) derived from automobile emissions and outgassing (gas
release) from polymer resin products widely used as consumer
products; and basic (alkaline) gases such as NH.sub.3 and
amine.
[0007] Among them, hydrocarbons (HCs) must be completely eliminated
because they cause pollution even at very low concentrations as
gaseous hazardous components in normal air (indoor and outdoor
air). Recently, outgassing from the materials of clean rooms or
polymer resins of manufacturing equipments or appliances used has
become a problem as a source of hydrocarbons (HCs).
[0008] These gaseous substances in question also include those
generated during operations in clean rooms. That is, typical clean
rooms contain gaseous substances not only introduced from ambient
air (those having passed through microparticle-collecting filters
for clean rooms to enter the clean rooms) but also generated in the
clean rooms so that they contain higher concentrations of gaseous
substances than ambient air, which increase the possibility of
contaminating semiconductor substrates.
[0009] When microparticulate contaminants are deposited on the
surfaces of semiconductor substrates, they cause breakage or short
in circuits (patterns) on the substrate surfaces, resulting in
failure. When gaseous hazardous components, especially hydrocarbons
(HCs) are deposited on the surfaces of semiconductor substrates,
they increase the contact angle to adversely affect e.g.
substrate-resist affinity (compatibility). The lowered
substrate-resist affinity adversely affects the film thickness of
the resist or adhesion of the resist to the substrate. Hydrocarbons
(HCs) also have the disadvantage that they deteriorate the pressure
resistance of oxide films on the surfaces of semiconductor
substrates (lowered reliability). The contact angle here means the
contact angle of wetting with water and indicates the degree of
contamination on substrate surfaces. That is, substrate surfaces
stained with hydrophilic (oily) contaminants repel water and resist
wetting. This increases the contact angle between the substrate
surfaces and water drops. Thus, contamination is more serious at
larger contact angles, while contamination is weaker at smaller
contact angles. NH.sub.3 causes production of ammonium salts or the
like to invite haze (resolution failure) in semiconductor
substrates.
[0010] For these reasons, the productivity (yield) of semiconductor
products Is lowered by not only microparticles but also gaseous
contaminants as described above.
[0011] Especially, the above gaseous substances as gaseous
hazardous components are generated from the sources described above
and more concentrated in clean rooms than ambient air so that they
are deposited on substrates to contaminate their surfaces because
air circulation is recently increased in clean rooms for saving
energy.
[0012] To address these contamination problems, we have previously
proposed various space cleaning methods using photoelectrons or
photocatalysts.
[0013] For example, methods for removing microparticulate
substances using photoelectrons are described in JP-B-HEI-3-5859,
JP-B-HEI-6-74909, JP-B-HEI-8-211 and JP-B-HEI-7-121367. Methods for
removing gaseous hazardous components using photocatalysts are
described in Japanese Patent No. 2863419 and Japanese Patent No.
2991963. A method for removing microparticles and gaseous
substances at the same time by combining photoelectrons and
photocatalysts is described in Japanese Patent No. 2623290.
[0014] It is thought that current Al wirings will not suffice for
patterns on wafer surfaces of semiconductor products with higher
quality (microfabricated products) in future and will be replaced
by Cu wirings. Thus, it will be necessary in future to use Cu
wirings and interlayer dielectrics with low dielectric constant
(low-k) to shorten the delay because the combination of current Al
wirings and SiO.sub.2 dielectrics requires a long wiring delay
under compact wiring-and design rules for future ultra large scale
Integrated circuits (ULSIs). However, Cu materials are more
susceptible to oxidation than conventional Al or W. Thus, it will
be also important in future to controls gaseous substances,
especially those oxidizing wafer surfaces (wiring surfaces and
interfaces) though it was sufficient in the past to pay attention
to removal of only microparticles in semiconductor manufacturing
environments.
[0015] Possible materials promoting oxidation of wafer surfaces
include water (moisture) and organic matters (HCs) in clean room
air, but it is difficult to control moisture present at about
45-50% (RH) in clean room air. This is because excessive reduction
of moisture in the air adversely affects the health of operators
working in the clean room.
[0016] Thus, it would be desirable to provide a novel method for
controlling (inhibiting) oxidation of wafer surfaces by controlling
materials in clean rooms including moisture and HCs.
[0017] In view of the circumstances described above, the present
invention aims to provide processes and equipments for
manufacturing semiconductors, according to which oxidation of wafer
surfaces can be controlled by simple means and contaminants
promoting oxidation and contaminants inviting a decreased yield of
wafers can also be totally controlled.
DISCLOSURE OF THE INVENTION
[0018] To solve the problems described above, the present invention
provides processes for manufacturing semiconductors, characterized
in that semiconductor substrates are treated while using a negative
ion-enriched gas obtained by a negative ion generator to inhibit
oxidation of the surfaces of the substrate during semiconductor
manufacturing steps.
[0019] Accordingly, an embodiment of the present invention relates
to a process for manufacturing a semiconductor, characterized in
that a substrate is treated while exposing the surface of the
substrate with a negative ion-enriched gas. In the present
invention, the negative ion-enriched gas is preferably prepared by
passing a clean gas preliminarily freed of microparticles and/or
chemical contaminants through a negative ion generator. The
chemical contaminants here include one or more selected from the
group consisting of ionic components. Inorganic matters and organic
matters. In the present invention, the negative ion-enriched gas is
preferably prepared by passing a gas having a microparticle
concentration of class 100 or less, an ionic component
concentration of 10 .mu.g/m.sup.3 or less and an organic matter
concentration of 10 .mu.g/m.sup.3 or less through a negative ion
generator.
[0020] Another embodiment of the present invention provides an
equipment for manufacturing a semiconductor comprising a gas
channel through which a gas to be treated is passed; a negative
ion-enriched gas generator consisting of a gas cleaner located at
an upstream part of said gas channel and a negative ion generator
located at a downstream part thereof; and means for supplying the
resulting negative ion-enriched gas to the surface of each
substrate.
BRIEF EXPLANATION OF THE DRAWINGS
[0021] FIG. 1 is a flow chart showing specific processing steps on
a semiconductor substrate in a semiconductor factory (clean
room).
[0022] FIG. 2 is a schematic view showing an example of an
apparatus for obtaining a negative ion-enriched gas used In the
present invention.
[0023] FIG. 3 is a schematic view showing another example of an
apparatus for obtaining a negative ion-enriched gas used in the
present invention.
[0024] FIG. 4 is a schematic view showing another example of an
apparatus for obtaining a negative ion-enriched gas used in the
present invention.
[0025] FIG. 5 is a schematic view showing another example of an
apparatus for obtaining a negative ion-enriched gas used in the
present invention.
[0026] FIG. 6 is a schematic view showing another example of an
apparatus for obtaining a negative ion-enriched gas used in the
present invention.
[0027] FIG. 7 is a schematic view showing another example of an
apparatus for obtaining a negative ion-enriched gas used in the
present invention.
[0028] FIG. 8 is a schematic view showing an air cleaning system
commonly used in conventional semiconductor factories (clean
rooms).
THE MOST PREFERRED EMBODIMENTS OF THE INVENTION
[0029] The present invention was accomplished on the basis of the
finding that semiconductor products suitable for the needs for high
performance can be prepared by treating substrates while exposing
them to a gas having a high level of cleanliness (i.e. very low
microparticle concentration and chemical contaminant concentration)
and rich in negative ions (i.e. negative ion-enriched gas) to
inhibit oxidation of the substrates during various substrate
processing steps at a given stage of semiconductor manufacturing
processes in a clean room and thereby improve the yield of the
semiconductor products.
[0030] The method for preparing a negative Ion-enriched gas used in
the processes of the present invention is divided into a negative
ion generating stage and a gas cleaning stage before generating
negative ions. Each stage is explained below.
[0031] A. Negative Ion Generating Methods
[0032] Our studies showed that oxidation of substrate surfaces is
inhibited by exposing substrates to a negative ion-enriched gas.
The "negative ion" (also called as "minus ion") here refers to a
substance formed by attaching n electron to an electrophilic
substance such as oxygen, e.g. small ions (hydrate ions) such as
O.sub.2.sup.-(H.sub.2O).su- b.n formed by attaching one or more
water molecules to a negatively charged oxygen molecule. Ions
having CO.sub.x.sup.- or NO.sub.x.sup.- as a core such as
CO.sub.3.sup.-(H.sub.2O).sub.n and NO.sub.2.sup.-(H.sub.2O- ).sub.n
can also be taken as "negative ions" according to the present
invention. The concentration of negative ions sufficient for
inhibiting oxidation of substrate surfaces varies with the
purpose/type of the semiconductor, the desired performance for the
semiconductor, coexisting materials and other factors, but normally
1,000 negative ions/mL or more, preferably 5,000 negative ions/mL
or more, more preferably 10,000 negative ions/mL or more, still
more preferably 50,000 negative ions/mL or more. Preferred negative
ion concentrations can be determined by appropriate pretests
depending on the purpose/type of the semiconductor, the desired
performance, coexisting materials and other factors. The reason why
oxidation of substrate surfaces is inhibited by negative
ion-enriched gases has not been unknown well, but it is supposed
that negative ions have a reducing effect on the surfaces of
substrates.
[0033] The concentration of negative ions in a gas can be
determined by measuring the electrical mobility of the ions under
electric field. Such instruments for measuring the concentration of
negative ions in a gas are commercially available e.g. under trade
name Air Ion Counter Model 83-1001B from Dan Science.
[0034] Means for generating negative ions include methods using
photoelectrons as proposed by us (JP-B-HEI-8-10616, Japanese Patent
No. 3139591), discharge, water spray, irradiation, etc. Various
methods for generating negative ions are explained below.
[0035] A-1: Negative Ion Generating Method Using Photoelectrons
[0036] The negative ion generating method using photoelectrons
involves irradiating a photoelectron emitting member with UV rays
from a UV source such as a UV lamp optionally in the presence of an
electric field to generate photoelectrons, thereby forming negative
ions. Here, an electric field can be formed by placing an electrode
(positive electrode) on the side opposite to the photoelectron
emitting member (negative electrode) to accelerate photoelectron
emission from the photoelectron emitting member. Thus, negative ion
generators using photoelectrons comprise a photoelectron emitting
member and a UV source such as a UV lamp, and optionally an
electrode for establishing an electric field. Inert gases such as
N.sub.2 can also be used as feed gases other than air.
[0037] The photoelectron emitting member is not limited so far as
it can emit photoelectrons upon UV irradiation and preferably has a
smaller photoelectric work function. From the viewpoint of the
effect and economical efficiency, the member is preferably any one
of Ba, Sr, Ca, Y, Gd, La, Ce, Nd, Th, Pr, Be, Zr, Fe, Ni, Zn, Cu,
Ag, Pt, Cd, Pb, Al, C, Mg, Au, In, Bi, Nb, Si, Ti, Ta, U, B, Eu,
Sn, P and W or compounds or alloys or mixtures thereof. These can
be used alone or in combination of two or more. Suitable composite
materials include physically composite materials such as
amalgam.
[0038] Compounds of the elements above include oxides such as BaO,
SrO, CaO, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, Nd.sub.2O.sub.3,
ThO.sub.2, ZrO.sub.2, Fe.sub.2O.sub.3, ZnO, CuO, Ag.sub.2O,
La.sub.2O.sub.3, PtO, PbO, Al.sub.2O.sub.3, MgO, In.sub.2O.sub.3,
BiO, NbO and BeO; borides such as YB.sub.6, GdB.sub.6, LaB.sub.5,
CeB.sub.6, EuB.sub.6, PrB.sub.6 and ZrB.sub.2; and carbides such as
UC, ZrC, TaC, TiC, NbC and WC. Suitable alloys of the elements
above include brass, bronze, phosphor bronze, Ag--Mg alloys
(Mg=2-20 wt %), Cu--Be alloys (Be=1-10 wt %) and Ba--Al alloys,
among which Ag--Mg alloys, Cu--Be alloys and Ba--Al alloys can be
preferably used. Oxides of the elements above can be obtained by
heating only the surface of a metal in the air or chemically
oxidizing it. Alternatively, a metal or alloy material of any one
of the elements above can be heated before use to form an oxide
layer with prolonged stability on its surface and this oxide layer
can be used as a photoelectron emitting member. For example, an
Mg--Ag alloy can be treated at a temperature of 300-400.degree. C.
in water vapor to form an oxide film on its surface, and such an
oxide film can be used as a photoelectron emitting member over a
long period because it has prolonged stability.
[0039] Photoelectron emitting materials can be used in combination
with other materials. As an example, a UV transparent material such
as glass can be combined with a material capable of emitting
photoelectrons (JP-B-HEI-7-93098, JP-A-HEI-4-243540).
[0040] The photoelectron emitting member can also be incorporated
into a photocatalyst such as TiO.sub.2 (JP-A-HEI-9-294919). This
form is preferred for some types of equipments or desired
performances because the photocatalyst can eliminate any substance
adversely affecting the photoelectron emitting member to stabilize
It over a long period while coexisting gaseous contaminants can
also be eliminated.
[0041] The shape of the photoelectron emitting member can be
appropriately selected from plates, pleated sheets, grids and
others depending on the permeation mode of the negative ion
generating gas or the type of the equipments. Among them, grid-type
photoelectron emitting members are preferred for some types of
equipments applied because negative ions can be generated without
forming an electric field when a gas is passed from the bottom to
the top of the photoelectron emitting member. The photoelectron
emitting member can be preferably incorporated into the irradiation
source described below for some types of equipments applied because
the size of the photoelectron emitter is reduced. This can be
accomplished by e.g. affixing a photoelectron emitting member to
the surface of a UV lamp.
[0042] The irradiation source for emitting photoelectrons from the
photoelectron emitting member is not limited so far as it
irradiates the photoelectron emitting member to emit
photoelectrons, but normally UV rays or radiation are preferred
(Japanese Patent No. 2623290, JP-B-HEI-6-74910), and UV rays are
especially preferred because they can be used simply and
safely.
[0043] The type of the UV source that can be used is not limited so
far as it irradiates the photoelectron emitting member to emit
photoelectrons, preferably a mercury lamp such as a germicidal lamp
in terms of size reduction.
[0044] The optional electric field under which photoelectrons are
emitted is preferably 0.1 V/cm to 1 kV/cm, and can be appropriately
determined by pretests depending on the configuration and structure
of the equipments. The electrode member used for forming the
electric field is not limited so far as it produces no impurities
and allows the photoelectron emitting member to effectively emit
photoelectrons, and it may be in the form of a line, bar, grid or
plate made from SUS, Cn--Zn or W. These electrode members are
placed to create an electric field near the photoelectron emitting
member so that photoelectrons can be emitted under the electric
field.
[0045] A-2: Negative Ion Generating Method Using Discharge
[0046] The discharge-based method involves emitting electrons by a
discharge in a gas to generate negative ions using an apparatus
comprising a discharge electrode and a counter electrode.
[0047] Suitable discharges for generating negative Ions include
those well-known in the art such as corona, glow, arc, spark,
surface creepage, pulse, high-frequency, laser, trigger and plasma
discharges. Among them, surface creepage and pulse discharges are
preferred for some purposes in terms of the size reduction of the
equipments because of high concentrations of negative ions
generated. Corona discharge is preferred in terms of simplicity,
operability and effect.
[0048] A-3: Negative Ion Generating Method Using Water Spray
[0049] The negative ion generating method using water spray
involves generating negative ions via Lenard effect by atomizing
water, e.g. negative ions can be generated by spray charging of
droplets when water is atomized in the air. The mechanism by which
negative ions are generated via Lenard effect can be supposed as
follows. Water molecules are polar molecules having electrically
positive and negative charges and their positive sides are
outwardly oriented on the water surface (oriented dipoles). These
oriented dipoles attract many negative ions to form an electric
bilayer, which produces a negatively charged air when an energy
such as a high pressure is applied. That is, when water is atomized
under high pressure, negatively ionized air is produced because the
water surface is positive and the adjacent air becomes negative.
Then, this air is vaporized to remove coexisting excess water if
desired, whereby a negative ion-enriched air is formed.
[0050] A-4: Negative Ion Generating Method Using Irradiation
[0051] The irradiation-based method involves exposing air to a
radiation to generate negative ions. Radiations that can be used in
this method are not limited so far as they generate ions from
radiation sources, such as X-rays, .alpha.-rays, .gamma.-rays and
.beta.-rays. Among them, X-rays, .alpha.-rays and .gamma.-rays are
preferred in terms of operability or the like, with X-rays being
especially preferred. X-ray irradiation uses ions obtained by
exposing gas molecules to X-rays, and normally gas molecules are
bombarded with X-rays obtained by irradiating a metal target with
accelerated electron beams to ionize air molecules.
[0052] The mechanism of the ionization by soft X-rays that are
especially preferred for use in the processes of the present
invention is explained as follows. Air molecules absorb irradiating
X-rays or photons (wavelength 0.2-0.3 nm) to become ionized or
photoionized. Ionized electrons collide with neutral electrons and
molecules to ionize them because of their high kinetic energy.
These ionizations continuously occur by electron avalanche to
generate large amounts of ions. The ions generated here include
both positive and negative ions, of which only positive ions are
removed by suitable well-known means such as an electrode plate to
give a gas enriched in only negative ions.
[0053] The photon energy of soft X-rays preferred for use in the
present method is several KeVs to 10 KeV or less. i.e. about
{fraction (1/10)} times or less of the energy of hard X-rays used
for radiography, but a shield is required if irradiation takes
place in a region which operators may enter. The shield can be e.g.
a metal plate having a thickness of about 1 mm or a plastic (e.g.
vinyl chloride) plate having a thickness of about 2-3 mm.
[0054] A gas enriched in only negative ions can also be obtained by
the same procedure as described above using .alpha.-rays or
.gamma.-rays, which also produce large amounts of ions because of
their high kinetic energy. Suitable .gamma.-ray sources are
radioactive substances such as Cobalt 60 and Cesium 137.
[0055] When negative ions are generated by the above method using
discharge or irradiation, especially X-ray irradiation, ozone
(O.sub.3) may also be generated. This ozone must be removed from
the gas because it promotes oxidation of substrate surfaces. For
the purpose of the present invention, the ozone concentration in a
gas should desirably be 0.1 ppm or less, preferably 0.01 ppm or
less, more preferably 1 ppb or less. Thus, it is preferable e.g. to
use an inert gas free from the ozone source O.sub.2 such as N.sub.2
or to subject the product negative ion-enriched gas to an ozone
removal treatment in the discharge- or irradiation-based method.
Humidification of the gas after generation of negative ions may be
preferred for some purposes or desired specifications because
humidification promotes decomposition of ozone.
[0056] A means for removing generated ozone from the negative
ion-enriched gas is to treat the gas with a well-known
O.sub.3-treating agent after negative ions have been generated.
Well-known O.sub.3-treating agents that can be used for this
purpose include e.g. Mn-based catalysts. The materials and forms of
O.sub.3-treating agents that can be used in the present invention
should preferably consume little negative ions generated and
coexisting in the gas, e.g. manganese dioxide-based honeycomb or
mesh catalysts such as MnO.sub.2/TiO.sub.2--C and
MnO.sub.2/ZrO--C.
[0057] Characteristics of each of the negative ion generating
methods described above are shown in Table 1 below, wherein various
methods are relatively evaluated as follows: .smallcircle. means
good and .DELTA. means slightly poor.
1TABLE 1 Characteristics of various negative ion generating methods
Amount/ Large- Small- concen- Antioxidant scale scale tration of
effect/ appli- appli- negative ions purity of cability cability
generated negative ions Safety Photoelectron .DELTA.
.DELTA.-.largecircle. .DELTA. .largecircle. .largecircle. Discharge
.largecircle. .largecircle. .largecircle. .DELTA.-.largecircle.
.largecircle. Water spray .largecircle. .DELTA. .largecircle.
.DELTA.-.largecircle. .largecircle. Irradiation .largecircle.
.largecircle. .largecircle. .DELTA.-.largecircle. .DELTA.
[0058] As shown from the table above, the photoelectron-based
method is poor in large-scale applicability but good in antioxidant
effect because ozone-free clean negative ions are generated, while
the irradiation-based method is good in large-scale and small-scale
applicabilities and the amount of negative ions generated but
insufficient in safety. In the present invention, desirable
negative ion generating methods can be appropriately selected
depending on the purpose and desired performance or other factors,
taking into account advantages and disadvantages of various
negative ion generating methods described above.
[0059] It was found that when negative ions generated by the
discharge-based method were then humidified or they are generated
by the water spray-based method, the resulting negative ions had
larger particle diameters than obtained by the others negative ion
generating methods described above. For example, negative ions
formed by the photoelectron-based method or the discharge-based
method without humidification have a particle diameter of about 1
nm, but negative ions formed by the discharge-based method followed
by humidification or generated by the water spray-based method have
a particle diameter of about 3-5 nm. Our studies revealed that
negative ions of larger particle diameters are more effective for
inhibiting oxidation of substrates according to the present
invention. The detailed reason for this is unknown, but supposed as
follows. Negative ions consist of a negatively charged core
molecule (e.g. oxygen molecule) to which water molecules are
adsorbed (attached), and a somewhat large number of the water
molecules adsorbed are more effective for inhibiting oxidation of
substrates. Thus, the negative ion generating method using
discharge followed by humidification or using water spray is
preferably used for some purposes, scales of equipments and desired
specifications.
[0060] When a substrate is treated in the presence of thus prepared
negative ion-enriched gas in the present invention, it is more
effective for inhibiting oxidation of the substrate if a positive
electrode is placed in the direction of the site where the negative
ion-enriched gas is applied, i.e. the substrate-processing site to
attract negative ions in an electric field. This is because
negative ions slowly move so that they are much consumed with some
shapes or structures of equipments.
[0061] Negative ions generated to form a negative ion-enriched gas
in the present invention as described above may be consumed by
contaminants if they are contained in the gas. If micropartioulate
substances exist in the gas for example, the charges of generated
negative ions are transferred to these microparticles to form
charged particles so that the negative ions are consumed. This
lowers the concentration of negative ions to be effectively used
for inhibiting oxidation of substrates. It is known that
semiconductor substrates are significantly contaminated by the
presence of microparticles and chemical contaminants, which results
in a significant decrease in yield. When negative ions are
generated in a gas containing acidic gases such as Cl.sub.2,
negative ions having Cl.sub.2 as a core are also formed and such
negative ions do not suit the purpose of the present invention,
i.e. "inhibiting oxidation of substrates" because they are thought
to be oxidative. Therefore, it is desirable to sufficiently
eliminate such chemical contaminants before entering into the
negative ion generating stage.
[0062] From this point of view, a gas preliminarily freed of
microparticles and chemical contaminants such as ionic components
and inorganic and organic matters are preferably passed through the
negative ton generator described above to generate negative ions in
the present invention. Specifically, the gas supplied to the
negative ion generator in the present invention preferably has a
microparticle concentration of class (the number of particles
having a standard particle diameter of 0.1 .mu.m in 1 ft.sup.3 of a
gas) 100 or less, preferably 10 or less, more preferably 1 or less;
an ionic component concentration of 10 .mu.g/m.sup.3 or less,
preferably 5 .mu.g/m.sup.3 or less, more preferably 2 .mu.g/m.sup.3
or less; and an organic matter concentration of 10 .mu.g/m.sup.3 or
less, preferably 5 .mu.g/m.sup.3 or less, more preferably 2
.mu.g/m.sup.3 or less. The "ionic components" here refer to acidic
gases such as NO.sub.x, SO.sub.x, HCl, HF, Cl.sub.2, F.sub.2, HBr
and Br.sub.2; and basic gases such as ammonia and amine.
[0063] As described above, the gas supplied to the negative ion
generator should preferably have preliminarily undergone
contaminant removal treatments. The contaminant removal treatments
that can be performed before generating negative ions in the
present invention are mainly classified into removal of
microparticles and removal of chemical contaminants specifically
explained below.
[0064] B. Removal of Microparticles
[0065] The gas to be treated to generate negative ions in the
present invention should preferably be preliminarily freed of
microparticles to class 100 or less, preferably 10 or less, more
preferably 1 or less, and any microparticle removing means known in
the art can be used so far as this cleanliness can be achieved.
Microparticle removing means that can be used in the present
invention include e.g. the use of a filter or photoelectrons as
proposed by us elsewhere.
[0066] B-1: Microparticle Removing Means Using Filters
[0067] Filters that can be used as microparticle removing means in
the present invention include those well-known in the art such as
ULPA filters, HEPA filters, medium performance filters and
electrostatic filters, which can be used alone or combined.
[0068] B-2: Microparticle Removing Means Using Photoelectrons
[0069] This means removes microparticles using photoelectrons
proposed by us in JP-B-HEI-6-74909, JP-B-HEI-7-121369,
JP-B-HEI-8-211, JP-B-HEI-8-22393, Japanese Patent No. 2623290, etc.
This method involves generating negative ions in the same manner as
described above for the negative ion generating method using
photoelectrons, charging microparticles with the negative ions
generated and collecting/removing the charged microparticles using
an electrode or the like. Thus, the photoelectron-based
microparticle removing means that can be used in the present
invention comprises a photoelectron emitting member, a UV source,
an electrode member and a charged microparticle collecting member.
The photoelectron emitting member, UV source and electrode member
can be those described above for the negative ton generating method
using photoelectrons.
[0070] Suitable charged microparticle collecting members typically
include various electrode members such as dust collecting plates
and dust collecting electrodes or electrostatic filters used in
conventional particle charging devices, but wool structures such as
steel wool electrodes and tungsten wool electrodes can also be
effectively used. Electret members can also be suitably used.
[0071] Preferred combinations of the photoelectron emitting member,
electrode member and charged microparticle collecting member can be
appropriately selected depending on the shape and structure of the
space to be cleaned, desired performance and economical efficiency.
For example, the locations and shapes of the photoelectron emitting
member and electrode can be appropriately determined taking into
account the shape of the space, effect, economical efficiency and
other factors in such a manner that they can surround a UV source
to combine the UV source, photoelectron emitting member, electrode
member and charged microparticle collecting member into a unit,
which can effectively use UV rays emitted from the UV source and
efficiently emit photoelectrons and charge/collect microparticle by
the photoelectrons. When a rod-like or cylindrical UV lamp is used
as a UV source, for example, UV rays are radially emitted around
the circumference of the lamp and the amount of photoelectrons
emitted increases by irradiating the photoelectron emitting member
with the circumferential radial UV rays as much as possible. Thus,
it is preferred that the photoelectron emitting member is
circumferentially located opposite the UV lamp and the
photoelectron emitting electrode is located on the opposed
face.
[0072] C. Removal of Ionic Components and Chemical Contaminants
[0073] As described above, the gas to be treated to generate
negative ions in the present invention should preferably be
preliminarily freed of ionic components such as acidic gases
including Cl.sub.2, NO.sub.x and SO.sub.x and basic gases including
ammonia; and chemical contaminants such as inorganic and organic
matters, specifically to an ionic component concentration of 10
.mu.g/m.sup.3 or less, preferably 5 .mu.g/m.sup.3 or less, more
preferably 2 .mu.g/m.sup.3 or less; and an organic matter
concentration of 10 .mu.g/m.sup.3 or less, preferably 5
.mu.g/m.sup.3 or less, more preferably 2 .mu.g/m.sup.2 or less.
Suitable means for removing such contaminants can be any methods
well-known in the art, e.g. using adsorbents or photocatalysts, as
specifically explained below.
[0074] C-1: Means for Removing Chemical Contaminants Using
Adsorbents
[0075] In the present invention, the means for removing chemical
contaminants using adsorbents consists in collecting/removing
acidic gases such as NO.sub.x, SO.sub.x, HCl, HF, Cl.sub.2,
F.sub.2, HBr and Br.sub.2; and basic gases such as ammonia and
amine in a gas to be treated during generation of a negative
ion-enriched gas, and any adsorbents can be used so far as they
efficiently adsorb various acidic/basic gases mentioned above to
low concentrations. Such known adsorbents include silica gel,
zeolite, alumina, activated carbon and ion exchange fibers, among
which activated carbon and ion exchange fibers are effective and
therefore can be preferably used in the present invention.
Especially, ion exchange fibers can be preferably used for some
purposes because they can collect contaminants to low
concentrations via chemical reactions and high cleanliness can be
achieved. Activated carbon can be appropriately used as those
impregnated with an acid or alkali depending on the component to be
collected.
[0076] The adsorbents described above can be used in any shape, but
generally fibrous and honeycomb shapes are preferred because of
small pressure loss.
[0077] Ion exchange fibers comprise a cation exchanger or an anion
exchanger or an ion exchanger having both cation and anion exchange
groups supported on the surface of a carrier such as a natural or
synthetic fiber or a mixture thereof, and the ion exchanger may be
directly supported on a fibrous carrier or the ion exchanger may be
supported on a woven or knitted or flocked base formed of fibers.
Ion exchange fibers that can be used in the present invention are
preferably those prepared by graft polymerization, especially
radiation-induced graft polymerization. This is because
radiation-induced graft polymerization allows ion exchange fibers
to be formed using various types and shapes of materials.
[0078] The natural fibers can be wool, silk and the like, and the
synthetic fibers can be those derived from hydrocarbon polymers or
fluorine-containing polymers or polyvinyl alcohol, polyamide,
polyester, polyacrylonitrile, cellulose or cellulose acetate. The
hydrocarbon polymers include aliphatic polymers such as
polyethylene, polypropylene, polyisobutylene and polybutene;
aromatic polymers such as polystyrene and poly
.alpha.-methylstyrene; alicyclic polymers such as polyvinyl
cyclohexane; or copolymers thereof. The fluorine-containing
polymers include polyethylene tetrafluoride, polyvinylidene
fluoride, ethylene-ethylene tetrafluoride copolymers, ethylene
tetrafluoride-propylene hexafluoride copolymers, vinylidene
fluoride-propylene hexafluoride copolymers, etc. Any of these
materials are preferred as carriers for ion exchanges so far as
they have a large area in contact with gas stream, a shape with low
resistance for easy grafting and a high mechanical strength with
less waste fibers dropping and produced, and are less susceptible
to heat, and they can be appropriately selected by those skilled in
the art taking into account the intended use, economical
efficiency, effect and other factors, but normally polyethylene or
composite materials of polyethylene and polypropylene are
preferably used.
[0079] Ion exchangers that can be introduced into these materials
are not specifically limited, but include various cation exchangers
or anion exchangers. For example, suitable ion exchangers contain
cation exchange groups such as carboxyl, sulfonate, phosphate and
phenolic hydroxyl; or anion exchange groups such as primary to
tertiary amino groups and quaternary ammonium group; or both of the
cation and anion exchange groups mentioned above. Specifically,
fibrous ion exchangers having a cation exchange group or an anion
exchange group can be obtained by graft-polymerizing e.g. acrylic
acid, methacrylic acid, vinyl benzene sulfonic acid, a styrene
compound such as styrene, halomethylstyrene, acyloxystyrene,
hydroxystyrene or aminostyrene; vinyl pyridine, 2-methyl-5-vinyl
pyridine, 2-methyl-5-vinylimidazole or acrylonitrile onto the
fibrous base described above optionally followed by reaction with
sulfuric acid, chlorosulfonic acid or sulfonic acid. Alternatively,
the above monomers may be graft-polymerized onto the fiber in the
presence of a monomer having two or more double bonds such as
divinylbenzene, trivinylbenzene, butadiene, ethylene glycol,
divinyl ether or ethylene glycol dimethacrylate.
[0080] The diameter of the ion exchange fiber preferred for use as
a chemical contaminant adsorbent in the present invention is 1-1000
.mu.m, preferably 5-200 .mu.m and can be appropriately determined
depending on the type of the fiber, purpose, etc. The type and
amount of the cation exchange group and anion exchange group
introduced into the ion exchange fiber can be determined depending
on the type and concentration of the component to be removed in the
gas to be treated. For example, the type and amount of the ion
exchange group can be determined on the basis of preliminary
measurement/evaluation of the component to be removed in a gas. For
example, fibers having a cation exchange group or an anion exchange
group or both cation and anion exchange groups can be used
depending on whether the gas to be removed is basic or acidic or a
mixture of both.
[0081] The gas is effectively supplied to the ion exchange fiber at
right angle to the ion exchange fiber in the form of a filter. The
flow rate of the gas supplied to the ion exchange fiber can be
appropriately determined by pretests, but the gas can be normally
supplied at about 1,000-100,000 (h.sup.-1) expressed as SV (spatial
velocity) in view of the high removal rate of ion exchange fibers
for gaseous components. Ion exchange fibers prepared by
radiation-induced graft polymerization as previously proposed by us
can be preferably used as appropriate because they are especially
effective (JP-B-HEI-5-9123, JP-B-HEI-5-67235, JP-B-HEI-5-43422,
JP-B-HEI-6-24626, etc.). When ion exchange groups are introduced
into fiber materials (carriers) by radiation-induced graft
polymerization, the ion exchange capacity increases because the
carriers are homogeneously irradiated to depth so that ion
exchangers are firmly fixed at high density over a large area. As a
result, even low concentrations of gaseous components can be
rapidly and efficiently removed. The preparation of ion exchange
fibers by radiation-induced graft polymerization also has the
following advantages. The preparation can be performed with a
material having a shape close to that of the target product at room
temperature in a gas phase with high grafting degree to give an
adsorption filter containing low levels of impurities. Thus, ion
exchange fibers prepared by radiation-induced graft polymerization
rapidly adsorb much gaseous components because ion exchangers
having the function of adsorbing gaseous components are
homogeneously fixed in large quantity at high density. Moreover,
filter materials with small pressure loss can be formed.
[0082] For some specifications desired, adsorbents formed from
glass and fluorine resins such as a glass fiber filter having a
fluorine resin as a binder can also be preferably used as chemical
contaminant removing adsorbents in the present invention. Such
filters are effective for removing gaseous organic matters and
particulate materials at the same time (Japanese Patent No.
2582806).
[0083] C-2: Means for Removing Chemical Contaminants Using
Photocatalysts
[0084] Means for removing chemical contaminants in a gas using
photocatalysts are preferred when gaseous components to be removed
contain organic matters (HCs) such as phthalate esters. High
molecular weight HCs including phthalate esters such as DOP must be
removed because they cause lowered productivity and yield such as
deteriorated pressure resistance of oxide films and lowered
reliability once they are adsorbed to substrate surfaces.
[0085] Any photocatalysts can be used so far as they can be exited
by irradiation to decompose HCs into inert forms for substrates
such as CO.sub.2 and H.sub.2O. Normally, semiconductor materials
are preferably used as photocatalysts in the present invention
because they are effective and readily available with good
workability. In view of the effect and economical efficiency, any
one of Se, Ge, Si, Ti, Zn, Cu, Al, Sn, Ga, In, P, As, Sb, C, Cd, S,
Te, Ni, Fe, Co, Ag, Mo, Sr, W, Cr, Ba and Pb or compounds or alloys
or oxides thereof are preferred and can be used alone or in
combination of two or more.
[0086] Examples are elements such as Si, Ge and Se; compounds such
as AlP, AlAg, GaP, AlSb, GaAs, InP, GaSb, InAs, InSb, CdS, CdSe,
ZnS, MoS.sub.2, WTe.sub.2, Cr.sub.2Te.sub.3, MoTe, Cu.sub.2S, and
WS.sub.2; and oxides such as TiO.sub.2, Bi.sub.2O.sub.3, CuO,
Cu.sub.2O, ZnO, MoO.sub.3, InO.sub.3, Ag.sub.2O, PbO, SrTiO.sub.3,
BaTio.sub.3, Co.sub.3O.sub.4, Fe.sub.2O.sub.3 and NiO. For some
applications, a metal member can be baked to form a photocatalyst
on the surface of the metal member. For example, a photocatalyst
can be prepared by baking a Ti member at 1000.degree. C. to form
TiO.sub.2 on its surface (JP-A-HEI-11-90236). The above
photocatalyst materials are preferably used with additives such as
Pt, Ag, Pd, RuO.sub.2 and Co.sub.3O.sub.4 to promote the
HC-decomposing effect of the photocatalysts. These additives can be
used alone or in combination. The dose is normally 0.01-10% by
weight relative to the photocatalyst and optimal concentrations can
be appropriately selected by preliminary experiments depending on
the type of the additive and desired performance or the like.
Additives can be added by well-known techniques such as immersion,
photoreduction, sputter deposition and kneading.
[0087] The photocatalysts can be used by immobilizing them in a
space where the gas to be treated circulates or on the wall face of
a channel through which the gas flows or suspending them in a space
where the gas circulates. The photocatalysts can be immobilized in
a unit by coating the photocatalysts on an appropriate material in
the form of a plate, flocculent, line, fiber, mesh, honeycomb,
membrane, sheet or fabric or wrapping or inserting them in or
between these materials. For example, any one of photocatalyst
materials can be immobilized on a ceramic, metal, fluorine resin or
glass material by appropriately using a well-known fixing means
such as sol-gel process, sintering, vapor deposition or sputtering.
Preferred materials on which photocatalysts are immobilized are
normally in the form of a fiber, mesh or honeycomb because of the
small pressure loss. For example, TiO.sub.2 fixed on a glass fiber
by sol-gel process or a photocatalyst fixed on the surface of a
transparent linear article (JP-A-HEI-7-256089) can be used as a
means for removing chemical contaminants in a gas in the present
invention.
[0088] In the present invention, the light source for irradiating
photocatalysts can be any one of well-known light sources that can
irradiate the photocatalysts to produce a photocatalytic effect.
Thus, photocatalytic decomposition of HCs can be accomplished by
bringing a gas to be treated with a photocatalyst while irradiating
the photocatalyst with light beams having an absorbance wavelength
range determined by the type of the photocatalyst.
[0089] Main absorbance wavelength ranges of various photocatalysts
are as follows. Si:<1,100(nm); Ge:<1,825(nm): Se:<590(nm);
AlAs:<517(nm); AlSb:<827(nm); GaAs:<886(nm);
InP:<992(nm); InSb:<6,888(nm); InAs:<3,757(nm);
CdS:<520(nm); CdSe:<730(nm); MoS.sub.2:<585(nm);
ZnS:<335(nm); TiO.sub.2:<415(nm); Zno:<400(nm);
Cu.sub.2O:<625(nm); PbO:<540(nm);
Bi.sub.2O.sub.3:<390(nm).
[0090] The light source used for irradiating the photocatalysts can
be appropriately selected from any well-known light sources having
a wavelength in the absorbance range of the photocatalysts such as
sunlight and UV lamps. Suitable UV sources normally include mercury
lamps, hydrogen discharge tubes, xenon discharge tubes and Lyman
discharge tubes and they can be appropriately used. Specific forms
of suitable light sources include germicidal lamps, black light
lamps, fluorescent chemical lamps, UVB lamps and xenon lamps. Among
them, germicidal lamps (main wavelength 254 nm) can be especially
preferably used for the following reasons. They can increase the
effective irradiation dose to photocatalysts to increase
photocatalytic effect; they are free from ozone; they can be easily
installed; they are inexpensive and easy to maintain and manage;
and they have high performance. The irradiation dose to
photocatalysts is generally 0.05-50-mW/cm.sup.2, preferably
0.1-10-mW/cm.sup.2.
[0091] HCs can also be collected by using adsorbents such as
activated carbon, but the use of adsorbents has problems with
adsorption capacity and breakthrough. That is, the adsorption
capacity becomes rapidly saturated at high concentrations of the
gas generated, which requires additional operations such as
replacement, while breakthrough invites the problem of secondary
pollution due to the spill of collected matters. In contrast,
photocatalysts can be very preferably used as means for removing
chemical contaminants such as HCs in the present invention because
they are free from accumulation of HCs and can stably decompose HCs
for a long period.
[0092] Next, the water content that is important for generating
negative ions in the present invention is explained.
[0093] Water in a gas plays an important role in the mechanism by
which negative ions are generated in the present invention. Thus,
negative ions that are effective for inhibiting oxidation of
substrates can be efficiently obtained by controlling the water
content in the gas.
[0094] Especially, the mechanism by which negative ions are
generated using the photoelectron-based method and the
discharge-based method is thought to be explained as follows.
Electrons generated may form negative ion clusters such as
O.sub.2.sup.-(H.sub.2O).sub.n, O.sup.-(H.sub.2O).sub.n and
OH.sup.-(H.sub.2O).sub.n by the electron attachment or clustering
to molecules having high electron affinity such as water molecules
and oxygen molecules. These reactions are shown below. 1 O 2 + e -
-> O 2 - O 2 - + H 2 O -> O 2 - ( H 2 O ) O 2 - ( H 2 O ) n -
1 + H 2 O -> O 2 - ( H 2 O ) n
[0095] As shown from the formulae above, water charged with
electrons becomes negative ions. Thus, it is not necessary to
control the water content when electrons are supplied to correspond
to the water content in the gas. If the concentration of generated
electrons is low, however, water having the so-called oxidative
effect harmful to wafers is liberated to adversely affect the
wafers. The presence of such harmful water can be known by testing
the oxidation state of the wafer surface exposed to the atmosphere,
e.g. the state of formation of natural oxide films. If the presence
of harmful water is detected in this manner, dehumidification to an
appropriate content is preferred. For the purpose of removing
harmful water, dehumidification is preferred to a relative humidity
in a gas of about 45.+-.5%, preferably 30% or less, more preferably
20% or less. Dehumidification of the gas can be accomplished by
appropriately using a well-known method preferably before negative
ions are generated normally in the present invention.
[0096] Dehumidifying means that can be used in the present
invention include well-known methods such as cooling, adsorption,
absorption, compression and membrane separation, and one or more of
the above means can be used in combination after appropriate
pretests depending on the field to which the present invention is
to be applied and the scale, configuration and operation conditions
of the equipments, e.g. whether it is applied under atmospheric or
pressurized condition. The dehumidifying means preferably keeps
stable dehumidification performance over a long period, normally
several to six months or longer, and especially the means based on
cooling, adsorption or membrane separation are simple and
effective. Preferred dehumidifying means based on cooling are
electronic dehumidification and cooling coils because of the
compact structure and effectiveness and preferred dehumidifying
means based on adsorption are systems in which the dehumidifier per
se is regenerated for continuous long dehumidification (fixed or
rotary system) because of the simplicity and effectiveness.
Dehumidifying materials that can be used in the adsorption-based
dehumidifying means include silica gel, zeolite, activated carbon,
activated alumina, magnesium perchlorate, calcium chloride,
alumina-pillared clay porous materials, bound activated carbon and
porous aluminum phosphate. The alumina pillared clay porous
materials here refer to materials obtained by exchanging
exchangeable cations between layers of a layered silicate with
multinuclear metal hydroxide ions including aluminum and
dehydrating the ion exchanged silicate by heating. The bound
activated carbon is obtained by carbonizing polyvinyl formal and
activating it at a temperature of 850.degree. C. or less. Porous
aluminum phosphate is also called molecular sieve and obtained by
reacting an alumina hydrate such as aluminum hydroxide, boehmite or
pseudoboehmite with phosphoric acid using a heat-dissociable
template such as an organic base, e.g. tripropylamine.
[0097] In the negative ton generating method using water spray, it
is necessary to remove harmful water using well-known dehumidifying
means such as eliminators or heating coils because the so-called
water mist is generated by water spray (atomization).
[0098] Dehumidification described above is applied when the amount
of electrons in a gas is 0.1 PA or less expressed as the current
value measured in a space, but reversely the gas is preferably
humidified to generate negative ions to which more water molecules
are attached when this value is 0.1 PA or more. Humidification can
be accomplished by means well-known In the art, e.g. by heating
water with a heater or vaporizing or ultrasonically spraying or
supplying water through a membrane. When water is added to the gas
by humidification, excess water not having participated in
generating negative ions is preferably removed by using a
dehumidifying means such as an eliminator or heating coil.
[0099] As described above, effective negative ion-enriched gases
for inhibiting oxidation at proper water contents can be formed by
appropriately using humidifying means and dehumidifying means.
Thus, a proper amount of water can be effectively used as a
negative ion source by properly controlling water contents.
[0100] Inert gases such as N.sub.2 and Ar can be used as gases for
generating negative ions to form a negative ion-enriched gas and
such inert gases are preferably hydrated by the humidifying means
described above because they are normally dry and cannot
efficiently generate negative ions as such. The amount of water to
be added can be determined after appropriate pretests depending on
the negative ion generating method, desired specification and other
factors.
[0101] Next, several specific embodiments of semiconductor
manufacturing equipments according to the present invention are
explained with reference to the attached drawings.
[0102] FIG. 1 shows specific processing steps on a semiconductor
substrate in a semiconductor factory (clean room, class 10,000).
The present invention can be applied to each specific processing
step shown in FIG. 1. That is, a semiconductor manufacturing
equipment of the present invention comprises a negative
ion-enriched gas generator as explained below and a means for
supplying the negative ion-enriched gas prepared by said generator
to the surface of a substrate in a semiconductor processing
equipment at various specific processing steps shown in FIG. 1. For
example, a substrate can be cleaned/dried while inhibiting
oxidation of the substrate by combining an apparatus comprising a
"negative ion-enriched gas generator" and a "means for supplying
the resulting negative ion-enriched gas to the surface of a
substrate" explained below with an "apparatus for spraying a gas to
a substrate to wash and dry the surface of the substrate with air",
which can be used during the step "clean and dry the substrate"
shown in FIG. 1.
[0103] FIG. 2 shows a schematic view of a negative ion-enriched gas
generator according to an embodiment of the present invention
comprising a clean gas generator consisting of an adsorbent-based
chemical contaminant removing means and a filter-based
microparticle removing means; and a discharge-based negative ion
generator. Such an apparatus generates a negative ion-enriched air
at class 10 or less free from chemical contaminants (100,000
negative ions/mL or more). Semiconductor substrates can be
prevented from contamination by performing each specific processing
step shown in FIG. 1 while exposing the surfaces of the
semiconductor substrate to the negative ion-enriched air generated
in the present example.
[0104] Negative ion-enriched air generator A shown in FIG. 2
comprises a fan 20 for supplying a clean room air, an adsorbent
(ion exchange fiber and activated carbon) 21 for removing chemical
contaminants in the clean room air, a dust filter (ULPA filter) 22
for removing microparticles in the clean room air (class 10,000)
and microparticles. generated from fan 20, a discharging member
(corona discharge) 23 for generating negative ions, and an O.sub.3
decomposing/removing member 24 for removing O.sub.3 generated from
discharging member 23. In the figure, 25-1 indicates the flow of
the air introduced by fan 20 into negative ion-enriched gas
generator A, 25-2 indicates the flow of the negative ion-enriched
gas generated by negative ion-enriched gas generator A, and 26
represents negative ions. In discharging member 23 In FIG. 2, 23-1
represents a needle-like discharge electrode and 23-2 represents a
counter electrode.
[0105] According to negative ion-enriched gas generator A shown in
FIG. 2. a clean room air (having a microparticle concentration of
class 10,000 and a negative ion concentration of 100 ions/mL or
less) introduced by the fan first passes through adsorbent 21 for
collecting chemical contaminants and filter 22 for collecting
microparticles, whereby it is cleaned to a microparticle
concentration of class 10 or less and both ionic component
concentration and organic matter concentration of 2 .mu.g/m.sup.3
or less. Then, negative ions are generated by discharge-based
negative ion generator 23, and generated ozone is removed by ozone
decomposing/removing member 24, whereby a clean negative
ion-enriched gas is provided having a concentration of 100,000
negative ions/mL or more, a microparticle concentration of class 10
or less, both ionic component concentration and organic matter
concentration of 2 .mu.g/m.sup.3 or less, and an ozone
concentration of 0.01 ppm or less. This negative ion-enriched gas
can be used as a substrate-exposing gas in various processing steps
shown in FIG. 1 to achieve a semiconductor manufacturing process in
which substrates are inhibited from oxidation and both
microparticle contamination and chemical contamination are
prevented.
[0106] FIG. 3 shows a schematic view of a negative ion-enriched gas
generator according to another embodiment of the present invention,
comprising a clean gas generator using adsorbent/microparticle
collecting filter and a photoelectron-based negative ion generator.
In FIG. 3, similar elements to those shown in FIG. 2 are designated
with the same references and not explained.
[0107] Negative ion-enriched air generator A shown in FIG. 3
comprises a cleaner consisting of a chemical contaminant-collecting
adsorbent 21 and a microparticle-collecting filter 22; and a
negative ion generator consisting of a photoelectron emitting
member 27, a UV lamp 28 and an electric field-forming electrode 29.
According to negative ion-enriched gas generator A shown in FIG. 3,
a clean room air introduced by the fan is cleaned through chemical
contaminant-collecting adsorbent 21 and microparticle-collecting
filter 22 to a microparticle concentration of class 10 or less and
both ionic component concentration and organic matter concentration
of 2 .mu.g/m.sup.3 or less, then introduced into the negative ion
generator where photoelectron emitting member 27 is irradiated with
UV rays to emit photoelectrons. Thus, a clean negative ion-enriched
gas is provided having a concentration of 10,000 negative ions/mL
or more, a microparticle concentration of class 10 or less, and
both ionic component concentration and organic matter concentration
of 2 .mu.g/m.sup.3 or less. According to the photoelectron-based
method, the ozone removing member as shown in FIG. 2 is normally
unnecessary because ozone is not generated. The negative
ion-enriched gas generated by negative ion-enriched gas generator A
shown in FIG. 3 can be used as a substrate-exposing gas in various
processing steps shown in FIG. 1 to achieve a semiconductor
manufacturing process In which substrates are inhibited from
oxidation and both microparticle contamination and chemical
contamination are prevented.
[0108] FIG. 4 shows a schematic view of a negative ion-enriched gas
generator according to another embodiment of the present invention,
comprising a clean gas generator consisting of an adsorbent-based
chemical contaminant-removing means and a microparticle-removing
means; and a photoelectron-based negative ion generator as shown in
FIG. 3. In FIG. 4, similar elements to those shown in FIG. 3 are
designated with the same references.
[0109] Negative ion-enriched air generator A shown in FIG. 4
comprises a clean gas generator consisting of a chemical
contaminant-collecting adsorbent 21 and a microparticle removing
means formed of a photoelectron emitting member 41, a UV lamp 42,
an electric field-forming electrode 43 and a charged microparticle
collecting member 44; and a negative ion generator consisting of a
photoelectron emitting member 27, a UV lamp 28 and an electric
field-forming electrode 29. According to negative ion-enriched gas
generator A shown in FIG. 4, a clean room air introduced by the fan
first passes through chemical contaminant-collecting adsorbent 21
where chemical contaminants in the gas are removed. Then, the gas
is introduced into the photoelectron-based microparticle removing
means where photoelectron emitting member 41 is irradiated with UV
rays to emit photoelectrons, which generate negative ions. Then,
microparticles in the gas are charged with the negative ions
generated. The charged microparticles are collected/removed by
charged microparticle collecting member 44 at the subsequent stage.
As a result, a gas cleaned to a microparticle concentration of
class 100 or less and both ionic component concentration and
organic matter concentration of 2 .mu.g/m.sup.3 or less is formed,
and this clean gas is introduced into the negative ion generator,
where photoelectron emitting member 27 is irradiated with UV rays
to emit photoelectrons. Thus, a clean negative ion-enriched gas is
provided having a concentration of 5,000 negative ions/mL or more,
a microparticle concentration of class 100 or less, and both ionic
component concentration and organic matter concentration of 2
.mu.g/m.sup.3 or less. The negative ion-enriched gas generated by
negative ion-enriched gas generator A shown in FIG. 4 can be used
as a substrate-exposing gas in various processing steps shown in
FIG. 1 to achieve a semiconductor manufacturing process in which
substrates are inhibited from oxidation and both microparticle
contamination and chemical contamination are prevented.
[0110] FIG. 5 shows a schematic view of a negative ion-enriched gas
generator according to another embodiment of the present invention,
comprising a clean gas generator using
adsorbent/microparticle-collecting filter, and a negative ion
generator using water spray. In FIG. 5, similar elements to those
shown in FIG. 2 are designated with the same references and not
explained.
[0111] Negative ion-enriched air generator A shown in FIG. 5
comprises a cleaner consisting of a chemical contaminant-collecting
adsorbent 21 and a microparticle-collecting filter 22; and a
negative ion generator consisting of a water-spray nozzle 33, an
excess water eliminator 34 and a water supply tank 31. According to
negative ion-enriched gas generator A shown in FIG. 5, a clean room
air introduced by the fan is cleaned through chemical
contaminant-collecting adsorbent 21 and microparticle-collecting
filter 22 to a microparticle concentration of class 10 or less and
both ionic component concentration and organic matter concentration
of 2 .mu.g/m.sup.3 or less, then introduced into the negative ion
generator where water from water supply tank 31 is sprayed at a
high pressure from water spray nozzle 33 through heat exchanger 32
to form negative ions. The resulting negative ion-enriched gas is
freed of excess water by eliminator 34 and heated to a desired
temperature by a reheater 35. Thus, a clean negative ion-enriched
gas is provided having a concentration of 200,000-300,000 negative
ions/mL or more, a microparticle concentration of class 10 or less,
and both ionic component concentration and organic matter
concentration of 2 .mu.g/m.sup.3 or less. Excess water collected by
eliminator 34 is received in water supply tank 31 and recycled to
water spray nozzle 33. As described above, the ozone removing
member as shown in FIG. 2 is normally unnecessary because ozone is
not generated according to the photoelectron-based method. The
negative ion-enriched gas generated by negative ion-enriched gas
generator A shown in FIG. 5 can be used as a substrate-exposing gas
in various processing steps shown in FIG. 1 to achieve a
semiconductor manufacturing process in which substrates are
inhibited from oxidation and both microparticle contamination and
chemical contamination are prevented.
[0112] In the water spray-based negative ion generating method,
about 10-20% of positive ions may be generated simultaneously with
negative ions under some conditions. Normally, any special means
for removing positive ions is not necessary because large amounts
of negative ions are generated and as low as 20% of positive ions
are neutralized by negative ions according to the water spray-based
method if they are generated, but it may be sometimes desirable to
collect/remove positive ions by placing a negative electrode
further downstream of reheater 35.
[0113] FIG. 6 shows a schematic view of a negative ion-enriched gas
generator according to another embodiment of the present invention,
comprising a clean gas generator using
adsorbent/microparticle-collecting filter and a negative ion
generator using X-ray irradiation. In FIG. 6, similar elements to
those shown in FIG. 2 are designated with the same references and
not explained.
[0114] Negative ion-enriched air generator A shown in FIG. 6
comprises a cleaner consisting of a chemical contaminant-collecting
adsorbent 21 and a microparticle-collecting filter 22; and a
negative ion generator consisting of a very weak X-ray (soft
X-rays: wavelength 0.2-0.3 nm) generator 36. According to negative
ion-enriched gas generator A shown in FIG. 6, a clean room air
introduced by the fan is cleaned through chemical
contaminant-collecting adsorbent 21 and microparticle-collecting
filter 22 to a microparticle concentration of class 10 or less and
both ionic component concentration and organic matter concentration
of 2 .mu.g/m.sup.3 or less, then introduced into the negative ion
generator where the gas is irradiated with X-rays so that gas
molecules are ionized to generate negative ions. In FIG. 6, B
represents an ionization zone of gas molecules with X-rays. When
the gas is irradiated with X-rays, negative ions and positive ions
are generated but positive ions are removed by negative electrode
37. Thus, a clean negative ion-enriched gas is provided having a
concentration of 100,000 negative ions/mL or more, a microparticle
concentration of class 10 or less, and both ionic component
concentration and organic matter concentration of 2 .mu.g/m.sup.3
or less. The negative ion-enriched gas generated by negative
ion-enriched gas generator A shown in FIG. 6 can be used as a
substrate-exposing gas in various processing steps shown in FIG. 1
to achieve a semiconductor manufacturing process in which
substrates are inhibited from oxidation and both microparticle
contamination and chemical contamination are prevented.
[0115] During irradiation of the gas with X-rays to generate
negative ions, a slight amount of ozone may be generated under some
irradiation conditions. If there is a possibility that ozone is
generated, an ozone decomposing/removing member 24 is preferably
placed further downstream of negative electrode 37 for removing
positive ions as shown in FIG. 7 so that even a minor amount of
ozone can be decomposed/removed if it is generated. Thus, a clean
negative ion-enriched gas is provided having a concentration of
100,000 negative ions/mL or more, a microparticle concentration of
class 10 or less, both ionic component concentration and organic
matter concentration of 2 .mu.g/m.sup.3 or less, and an ozone
concentration of 0.01 ppm or less, and this gas can be used as a
substrate-exposing gas in various processing steps shown in FIG. 1
to achieve a semiconductor manufacturing process in which
substrates are inhibited from oxidation and both microparticle
contamination and chemical contamination are prevented.
EXAMPLES
[0116] Negative ion-enriched gas generators according to various
embodiments of the present invention shown in FIGS. 2 to 7 were
used to prepare negative ion-enriched gases. The apparatuses used
have the following structures.
[0117] 1) Negative ion-enriched gas generator 1: the apparatus
having the structure shown in FIG. 2 (capacity: about 30 L)
[0118] Adsorbent 20: a mixed bed of an ion exchange fiber:
activated carbon (1:1);
[0119] Dust filter 21: ULPA filter;
[0120] Discharging member: 30 kV applied across the electrodes;
[0121] O.sub.3 decomposing/removing member;
MnO.sub.2/TiO.sub.2--C.
[0122] 2) Negative ion-enriched gas generator 2: the apparatus
having the structure shown in FIG. 3 (capacity; about 30 L)
[0123] Adsorbent 20 and dust filter 21: the same as described above
in 1):
[0124] UV lamp 28: a germicidal lamp (4 W);
[0125] Photoelectron emitting member 27: a thin film of Au coated
on TiO.sub.2;
[0126] Electrode 29: a grid electrode made from SUS was placed
above the lamp as shown in FIG. 3: electric field 10 V/cm.
[0127] 3) Negative ion-enriched gas generator 3: the apparatus
having the structure shown In FIG. 4 (capacity: about 40 L)
[0128] Adsorbent 20: the same as described above in 1);
[0129] Photoelectron emitting members 27 and 41, UV lamps 28 and
42, electrodes 29 and 43; the same as described above in 2);
[0130] Charged microparticle collecting member: a Cu--Zn plate.
[0131] 4) Negative ion-enriched gas generator 4: the apparatus
having the structure shown in FIG. 5 (capacity: about 200 L)
[0132] Adsorbent 20 and filter 21: the same as described above in
1):.
[0133] Water sprayer: atomization with water-spray nozzle 33
supplied with 3 L/min of ion exchange water at a water pressure of
350 kPa and a water/air ratio (L/G)=1;
[0134] Reheater: produced water drops were vaporized using a
reheating coil.
[0135] 5) Negative ion-enriched gas generator 5: the apparatus
having the structure shown in FIG. 6 (capacity: about 30 L)
[0136] Adsorbent 20 and filter 21: the same as described above in
1);
[0137] X-ray generator 36: wavelength 0.2-0.3 nm;
[0138] Negative electrode 37; a Ca--Zn plate.
[0139] Negative ion-enriched gas generators 1 to 3 and 5 described
above were supplied with a clean room air (microparticle
concentration class 10,000, organic matter concentration 100-120
.mu.g/m.sup.3, NH.sub.3 concentration 15-20 .mu.g/m.sup.3) at a
flow rate of 3 L/min. Negative ion-enriched gas generator 4
described above was supplied with the same clean room air at a flow
rate of 30 L/min. The properties of the air obtained from negative
ion-enriched gas generators 1 to 5 are shown in Table 2 below.
2TABLE 2 Properties of negative ion-enriched gases Negative
Negative ion Micro- Organic ion conc. particle matter Ammonia
Cleaning generating (number/mL) conc. conc. conc. Apparatus method
method Inlet Outlet number/ft.sup.3 .mu.g/m.sup.3 .mu.g/m.sup.3 1)
FIG. 2 Adsorption/ Discharge .ltoreq.100 100,000.ltoreq. <10
<2 <1 ULPA 2) FIG. 3 Adsorption/ Photoelectron .ltoreq.100
10,000.ltoreq. <10 <2 <1 ULPA 3) FIG. 4 Adsorption/
Photoelectron .ltoreq.100 8,000-10,000 <100 <2 <1
photoelectron 4) FIG. 5 Adsorption/ Water .ltoreq.100
200,000-300,000 <10 <1 <1 ULPA spray 5) FIG. 6 Adsorption/
X-ray .ltoreq.100 100,000.ltoreq. <10 <1 <1 ULPA
irradiation
[0140] The concentration of O.sub.3 in the negative ion-enriched
gas obtained by apparatus 1) was 0.01 ppm or less.
[0141] The surface of an Si wafer was exposed to the negative
ion-enriched gases obtained from negative ion-enriched gas
generators 1 to 5 described above and the production state of oxide
films was observed. An Si wafer high resolution XPS made by Scienta
type ESCA300 was used as the wafer sample after washed with RCA and
then treated with HF (0.05%) and rinsed with pure water and dried,
Negative ion-enriched gases obtained from negative ion-enriched gas
generators 1 to 5 above were sprayed on the surface of this wafer
sample at a flow rate of 3 L/min and the thickness of the oxide
film formed on the sample surface was measured after given periods
of time. The results are shown in Table 3 below. As a comparative
example, the surface of the same wafer sample was exposed to the
clean room air directly used. The results are also shown in Table 3
below.
3TABLE 3 Si wafer oxidation test Thickness of oxide Ap- Negative
ion film (angstroms) pa- Cleaning generating After exposure After
exposure ratus method method for 3 hours for 12 hours 1)
Adsorption/ Discharge <0.02 <0.02 ULPA 2) Adsorption/
Photoelectron <0.02 <0.02 ULPA 3) Adsorption/ Photoelectron
<0.02 <0.02 photoelectron 4) Adsorption/ Water spray <0.02
<0.02 ULPA 5) Adsorption/ X-ray <0.02 <0.02 ULPA
irradiation Comparative example: 0.3 5 exposed to clean room
air
[0142] Then, the wafer sample surface was exposed (exposure period:
12 h) to gases containing about 500, about 1,000, about 3,000,
about 5,000, about 10,000, about 30,000 and about 50,000 negative
ions/mL prepared under varying treatment conditions using negative
ion-enriched gas generator 1 to determine effective negative ion
concentrations for inhibiting the production of oxide films. An
effect was shown at concentrations of 1,000 negative ion s/mL or
more as proved by oxide film thicknesses of <0.1 angstrom, and a
remarkable effect was shown at 5,000 negative ions/mL or more as
proved by <0.05 angstroms. An especially remarkable effect was
shown at 10,000 negative ions/mL or more as proved by <0.02
angstroms.
[0143] Industrial Applicability
[0144] It was concluded from the foregoing findings that the
present invention could have the following advantages.
[0145] (1) Substrates can be subjected to various processing steps
while inhibiting them from oxidation by supplying a negative
ion-enriched gas into the spaces of semiconductor manufacturing
processes.
[0146] (2) Gases stable against pollution (having an antipollution
function) can be prepared because clean negative ion-enriched gases
free from microparticles and chemical components are obtained by
removing microparticles and chemical contaminants.
[0147] (3) Generated negative ions can be prevented from being
consumed by contaminants such as microparticles by using a gas
freed of microparticles and chemical contaminants to prepare
negative ion-enriched gases.
[0148] (4) It will be important in future to prevent substrate
surfaces from oxidation, in addition to current pollution sources
such as microparticles and chemical contaminants. According to the
present invention, clean gases can be obtained that also have an
antioxidant effect for substrate surfaces.
[0149] (5) More practical antipollution gases can be provided
because preferable negative ion generating methods can be selected
(see Table 1) depending on the preferred specifications such as the
scale of the equipment to which the present invention is to be
applied, the amount of negative ions to be generated and the
desired antioxidant effect.
* * * * *