U.S. patent application number 12/389828 was filed with the patent office on 2009-06-25 for polishing slurry, method of treating surface of gaxin1-xasyp1-y crystal and gaxin1-xasyp1-y crystal substrate.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Keiji ISHIBASHI, Takayuki NISHIURA.
Application Number | 20090159845 12/389828 |
Document ID | / |
Family ID | 37671390 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090159845 |
Kind Code |
A1 |
ISHIBASHI; Keiji ; et
al. |
June 25, 2009 |
POLISHING SLURRY, METHOD OF TREATING SURFACE OF GAXIN1-XASYP1-Y
CRYSTAL AND GAXIN1-XASYP1-Y CRYSTAL SUBSTRATE
Abstract
The present polishing slurry is a polishing slurry for
chemically mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1), characterized in that this polishing slurry
contains abrasive grains formed of SiO.sub.2, this abrasive grain
is a secondary particle in which a primary particle is associated,
and a ratio d.sub.2/d.sub.1 of an average particle diameter d.sub.2
of a secondary particle to an average particle diameter d.sub.1 of
a primary particle is not less than 1.6 and not more than 10.
According to such the polishing slurry, a crystal surface having a
small surface roughness can be formed on a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal at a high polishing
rate and effectively.
Inventors: |
ISHIBASHI; Keiji;
(Itami-shi, JP) ; NISHIURA; Takayuki; (Itami-shi,
JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
Osaka
JP
|
Family ID: |
37671390 |
Appl. No.: |
12/389828 |
Filed: |
February 20, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11527682 |
Sep 27, 2006 |
7507668 |
|
|
12389828 |
|
|
|
|
Current U.S.
Class: |
252/182.33 |
Current CPC
Class: |
C09K 3/1463 20130101;
C09G 1/02 20130101; H01L 33/0095 20130101; H01L 21/02024
20130101 |
Class at
Publication: |
252/182.33 |
International
Class: |
C09K 3/00 20060101
C09K003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2005 |
JP |
2005-288278 (P) |
Claims
1-13. (canceled)
14. A GaxIn1-xAsyP1-y crystal substrate obtained by a method of
treating a surface of a GaInx1-xAsyP1-y crystal, characterized in
that said surface treating method comprises the steps of: a
preparing a polishing slurry containing abrasive grains formed of
SiO2, wherein said abrasive grain is a secondary particle in which
a primary particle is associated, and a ratio d2/d1 of an average
particle diameter d2 of said secondary particle to an average
particle diameter d1 of said primary particle is not less than 1.6
and not more than 10, and chemically mechanically polishing a
surface of the GaxIn1-xAsyP1-y crystal using said polishing slurry.
Description
RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. application Ser.
No. 11/527,682, filed Sep. 27, 2006, claiming priority of Japanese
Patent Application No. 2005-288278, filed Sep. 30, 2005, the entire
contents of each of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a polishing slurry for
chemically mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal used in a substrate for
a semiconductor device such as a light emitting element, an
electronic element and a semiconductor sensor, a method of treating
a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using
the polishing slurry, and a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal substrate obtained by the surface treating method.
[0004] 2. Description of the Background Art
[0005] A Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1) such as a GaAs crystal
and an InP crystal is very useful as a material for forming a
substrate of a semiconductor device such as a light emitting
element, an electronic element and a semiconductor sensor.
[0006] The Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1) used as a substrate for
a semiconductor device is obtained by subjecting an external
circumference of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal to
shape forming processing, slicing the crystal to have a
predetermined thickness, and grinding or lapping a surface thereof
and, by such the slicing and, grinding or lapping, a procession
denatured layer (this refers to a layer in which crystal lattices
are disturbed, which is formed on a surface side region of a
crystal by processing a crystal surface; the same hereinafter) is
formed on a surface side region of the
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal, and a roughness of a
surface of the Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal becomes
great.
[0007] As a thickness of the procession denatured layer of this
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate becomes
greater, or as a surface roughness thereof becomes greater, quality
of a substrate surface is deteriorated, irregularities of a surface
of a Group III-V compound crystal layer which is epitaxial-grown on
this Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal become great, and
crystallizability of the surface is deteriorated. For this reason,
a semiconductor device of better quality cannot be formed.
[0008] For this reason, as a method of forming a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate from a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal, the following method
is widely performed: Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is
sliced to have a predetermined thickness, a surface thereof is
ground or lapped and, further, the surface is polished chemically
and mechanically, thereby, a procession denatured layer of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is removed, and a
surface roughness is reduced.
[0009] As a polishing slurry for chemically mechanically polishing
a surface of the Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal, a
polishing slurry containing spherical colloidal silica abrasive
grains, an inorganic salt, and alkali metal chlorinated
isocyanurate which is an oxidizing agent (e.g. see Japanese Patent
Publication No. 3077665 (hereinafter, referred to as Patent
Document 1)), and a polishing slurry containing spherical colloidal
silica abrasive grains, a mineral acid and persulfate which is an
oxidizing agent (e.g. see Japanese Patent Laying-Open No. 64-087147
(hereinafter, referred to as Patent Document 2)) are proposed. In
chemical mechanical polishing (hereinafter, referred to as CMP)
using these polishing slurries, a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is oxidized with an
oxidizing agent and a mineral acid to form an oxidized layer, and
this oxidized layer is removed with colloidal silica abrasive
grains.
[0010] However, in polishing slurries shown in Patent Document 1
and Patent Document 2, since spherical colloidal silica abrasive
grains are used as abrasive grains, a rate of polishing a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is low due to a low
rate of removing the oxidized layer, and an efficiency of CMP is
low. When a colloidal silica abrasive grain having a large particle
diameter is used, a polishing rate can be enhanced, but a surface
roughness is increased. In addition, also when an abrasive grain
having a higher hardness than that of a colloidal silica abrasive
grain, such as an Al.sub.2O.sub.3 abrasive grain is used, a
polishing rate can be enhanced, but since a new procession
denatured layer is formed due to this abrasive grain having a high
hardness, better surface quality can not be obtained.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to provide a polishing
slurry which can form a crystal surface having a small surface
roughness on a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal at a
high polishing rate and effectively, a method of treating a surface
of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using such the
polishing slurry, and a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
substrate obtained by such the surface treating method.
[0012] The present invention provides a polishing slurry for
chemically mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1), characterized in that this polishing slurry
contains abrasive grains formed of SiO.sub.2, this abrasive grain
is a secondary particle in which primary particles are associated,
and a ratio d.sub.2/d.sub.1 of an average particle diameter d.sub.2
of a secondary particle to an average particle diameter d.sub.1 of
a primary particle is not less than 1.6 and not more than 10.
[0013] In the polishing slurry of the present invention, an average
particle diameter d.sub.2 of a secondary particle of an abrasive
grain can be not less than 30 nm and not more than 300 nm. In
addition, a shape of an abrasive grain may be at least any shape of
a cocoon shape, a mass shape and a chain shape. In addition, the
abrasive grain content can be not less than 5 mass % and not more
than 40 mass %. In addition, an abrasive grain can be formed of
colloidal silica. In addition, a value X of a pH and a value Y (mV)
of a oxidation-reduction potential of the polishing slurry can
satisfy both relationships of the following equation (1) and
equation (2):
Y.gtoreq.-50X+1000 (1)
Y.ltoreq.-50X+1900 (2)
In addition, a pH of the polishing slurry can be not more than 5 or
not less than 8. In addition, the polishing slurry can contain the
aforementioned abrasive grains, an organic acid and/or a salt
thereof, and an oxidizing agent.
[0014] Also, the present invention provides a method of treating a
surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1) using a polishing
slurry, and this surface treating method is a method of treating a
surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal including
the steps of: preparing a polishing slurry characterized in that
the polishing slurry contains abrasive grains formed of SiO.sub.2,
this abrasive grain is a secondary particle in which primary
particles are associated, and a ratio d.sub.2/d.sub.1 of an average
particle diameter d.sub.2 of a secondary particle to an average
particle diameter d.sub.1 of a primary particle is not less than
1.6 and not more than 10; and chemically mechanically polishing a
surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using the
polishing slurry.
[0015] In the method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal of the present
invention, a step of chemically mechanically polishing a surface of
a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using the polishing
slurry can be performed by rotating a polishing pad and a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal on different rotation
axes at a rotation number of not less than 10/min and not more than
200/min and at a polishing pressure of not less than 4.9 kPa (50
gf/cm.sup.2) and not more than 98 kPa (1000 gf/cm.sup.2) by
interposing the polishing slurry between the polishing pad and the
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal.
[0016] The method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal of the present
invention can include a step of washing a surface of the chemically
mechanically polished Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
with pure water after the step of chemically mechanically
polishing. Alternatively, the step may include a step of polishing
a surface of the chemically mechanically polished
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using a polishing
solution formed of an acidic aqueous solution or a basic aqueous
solution after the step of chemical mechanical polishing. Further,
the method may include a step of washing a surface of the
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal which has been polished
using the polishing solution with pure water after the step of
polishing using the polishing solution.
[0017] Also, the present invention provides a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate obtained by a
method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal, in which the surface
treating method includes the steps of: preparing a polishing slurry
characterized in that the polishing slurry contains abrasive grains
formed of SiO.sub.2, this abrasive grain is a secondary particle in
which primary particles are associated, and a ratio d.sub.2/d.sub.1
of an average particle diameter d.sub.2 of a secondary particle to
an average particle diameter d.sub.1 of a primary particle is not
less than 1.6 and not more than 10; and chemically mechanically
polishing a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal using this polishing slurry.
[0018] According to the present invention, a polishing slurry which
can form a crystal surface having a small surface roughness on a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal at a high polishing
rate and effectively, a method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using such the
polishing slurry, and a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
substrate obtained by such the surface treating method can be
provided.
[0019] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic cross-sectional view showing a method
of chemically mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal in the present
invention.
[0021] FIG. 2A is a schematic view showing a cocoon-shaped abrasive
grain in the polishing slurry of the present invention.
[0022] FIG. 2B is a schematic view showing a mass-shaped abrasive
grain in the polishing slurry of the present invention.
[0023] FIG. 2C is a schematic view showing a chain-shaped abrasive
grain in the polishing slurry of the present invention.
[0024] FIG. 3 is a schematic cross-sectional view showing a method
of polishing a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal using a polishing solution in the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0025] One embodiment of a polishing slurry of the present
invention is a polishing slurry for chemically mechanically
polishing a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal (0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1), characterized
in that this polishing slurry contains abrasive grains formed of
SiO.sub.2, this abrasive grain is a secondary particle in which
primary particles are associated, and a ratio d.sub.2/d.sub.1 of an
average particle diameter d.sub.2 of a secondary particle to an
average particle diameter d.sub.1 of a primary particle is not less
than 1.6 and not more than 10.
[0026] Herein, chemical mechanical polishing refers to smoothing
chemically and mechanically a surface of a subject to be abraded,
using a polishing slurry. Referring to FIG. 1, for example, a
surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 can be
chemically mechanically polished by pressing
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 against a polishing
pad 18 while polishing pad 18 fixed on a platen 15 is rotated
around a rotation axis 15c, and while a polishing slurry 17 is
supplied on polishing pad 18 from a polishing slurry supply port
19, and a weight 14 is placed on a crystal holder 11 to which
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 is fixed, and this is
rotated around a rotation axis 11c of crystal holder 11.
[0027] Polishing slurry 17 of the present embodiment, by containing
abrasive grains 16 formed of SiO.sub.2, can remove a procession
denatured layer 1a of Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1
to reduce a surface roughness.
[0028] In addition, since abrasive grain 16 is a secondary particle
in which primary particles are associated, a polishing rate is
increased, and it becomes possible to effectively treat a surface
of Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1. By association of
primary particles to become a secondary particle, an abrasive grain
having an edgeless irregular shape on its surface is formed, and a
polishing rate can be enhanced without generating a scratch. When
an abrasive grain having a surface on which an edge is present is
used, a scratch is generated upon polishing, and it becomes
difficult to reduce a surface roughness. In addition, from a
viewpoint of formation of an edgeless irregular shape, it is
preferable that a primary particle is spherical or a shape of a
spheroid.
[0029] Herein, from a viewpoint that a primary particle is
spherical or a shape of a spheroid, and a secondary particle having
an edgeless irregular shape on its surface is easily formed, it is
preferable that an abrasive grain is formed of SiO.sub.2 such as
fumed silica and colloidal silica, particularly, colloidal silica.
As a method of synthesizing colloidal silica, there are a synthesis
method using a water glass (sodium silicate etc.) as a raw
material, and a synthesis method using alkoxysilane as a raw
material (sol-gel method). The former is low cost, and easily
produces colloidal silica in a large amount, and the latter affords
an abrasive grain having a high purity. By regulating the synthesis
condition, a particle diameter of a primary particle, an
association degree of a primary particle, and a particle diameter
of a secondary particle can be freely controlled.
[0030] In addition, an association degree of abrasive grain 16 is
not particularly limited, but from a viewpoint of easy formation of
an edgeless irregular shape on its surface, a ratio
(d.sub.2/d.sub.1 ratio) of an average particle diameter d.sub.2 of
a secondary particle to an average particle diameter d.sub.1 of a
primary particle is not less than 1.6 and not more than 10.
Further, a d.sub.2/d.sub.1 ratio is preferably not less than 2.0
and not more than 8. Herein, an average particle diameter d.sub.1
of a primary particle of abrasive grain 16 is calculated by the
following equation (4):
d.sub.1=6/(.rho..times.S) (4)
from measurement of an adhesion specific surface area (referred to
as BET specific surface area; the same hereinafter) by a gas
adsorption method. In the equation (4), .rho. represents a density
of a particle, and S represents a BET specific surface area. In
addition, an average particle diameter d.sub.2 of a secondary
particle of an abrasive grain is calculated by the following
equation (5):
d.sub.2=(k.times.T)/(3.times..pi..times..eta..sub.0.times.D)
(5)
from measurement of a diffusion coefficient in Brownian movement of
a particle by a dynamic light scattering method. In the equation
(5), k represents a Boltzmann constant, T represents an absolute
temperature, a represents a ratio of a circumference of a circle to
its diameter, .eta..sub.0 represents a viscosity of a solvent, and
D represents a diffusion coefficient.
[0031] An average particle diameter d.sub.2 of a secondary particle
of abrasion grain 16 is not particularly limited, but from a
viewpoint of enhancement of a polishing rate, the diameter is
preferably 30 nm or more and, from a viewpoint of reduction in a
surface roughness, the diameter is preferably 300 nm or less. From
such the viewpoint, an average particle diameter d.sub.2 of a
secondary particle of abrasive grain 16 is more preferably 60 nm or
more, and preferably 250 nm or less.
[0032] In addition, a shape of abrasive grain 16 is not
particularly limited. Referring to FIG. 2A to FIG. 2C, the shape
is, however, from a viewpoint that the particle forms an edgeless
irregular shape, at least any shape of a cocoon shape shown in FIG.
2A, a mass shape shown in (B1) and (B2) of FIG. 2B, and a chain
shape shown in (C1) and (C2) of FIG. 2C is preferable. Further,
from a viewpoint of enhancement of a polishing rate, it is more
preferable that a shape of abrasive grain 16 is a mass shape or a
chain shape rather than a cocoon shape. Since the polishing slurry
of the present embodiment contains abrasive grains having the
aforementioned edgeless irregular shape on their surface,
mechanical polishing effect is increased, and it becomes possible
to enhance a polishing rate without increasing a thickness of
procession denatured layer 1a. Herein, a shape of abrasive grain 16
can be observed with SEM (scanning electron microscope) and the
like.
[0033] Polishing slurry 17 of the present embodiment is
specifically such that abrasive grains 16 (preferably, colloidal
silica abrasive grains) formed of SiO.sub.2 are dispersed in water
which is a dispersing medium. The abrasive grain content in
polishing slurry 17 is not particularly limited, but from a
viewpoint of enhancement of a polishing rate, the content is
preferably 2 mass % or more and, from a viewpoint of reduction in a
surface roughness and enhancement of surface quality, the content
is preferably 40 mass % or less. From such the point of view, the
abrasive grain content in polishing slurry 17 is more preferably 5
mass % or more, and more preferably 20 mass % or less.
[0034] In addition, it is preferable that a value X of a pH and a
value Y (mV) of oxidation-reduction potential (referred to as ORP;
the same hereinafter) of the polishing slurry of the present
embodiment satisfy both relationships of the following equation (1)
and equation (2):
Y.gtoreq.-50X+1000 (1)
Y.ltoreq.-50X+1900 (2)
Herein, ORP means an energy level (potential) determined by the
equilibrium state between an oxidized entity and a reduced entity
which are present together in a solution. ORP obtained by
measurement is a value relative to a reference electrode and, when
a kind of a reference electrode is different, a measured value of
the same solution is apparently different. In general academic
articles, as a reference electrode, a normal hydrogen electrode
(N.H.E) is used in many cases. ORP in the present application is
expressed as a value using a normal hydrogen electrode (N.H.E) as a
reference electrode.
[0035] When a value X of a pH and a value Y (mV) of ORP of
polishing slurry 17 of the present embodiment are:
Y.gtoreq.-50X+1000, an oxidizing power of polishing slurry 17 is
weak, and a rate of polishing a surface of
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 is lowered. On the
other hand, when Y.gtoreq.-50X+1900, an oxidizing power of
polishing slurry 17 becomes too strong, the corroding action on
polishing facilities such as a polishing pad and a platen becomes
too strong, and stable CMP becomes difficult.
[0036] In addition, from a viewpoint of more enhancement of a
polishing rate, further, Y.gtoreq.-50X+1300 is preferable. That is,
it is preferable that a value X of a pH and a value Y (mV) of ORP
of polishing slurry 17 satisfy both relationships of the following
equation (2) and equation (3):
Y.ltoreq.-50X+1900 (2)
Y.gtoreq.-50X+1300 (3)
[0037] An acid such as hydrochloric acid and sulfuric acid, and a
base such as KOH and NaOH which are contained in a conventional
polishing slurry are weak in a force of oxidizing a surface of
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal. For this reason, it is
preferable that an oxidizing agent is added to the polishing slurry
of the present embodiment to enhance ORP, that is, enhance an
oxidizing power. An amount of an oxidizing agent to be added is
adjusted so that a value X of a pH and a value Y (mV) of ORP of
polishing slurry 17 satisfy both relationships of
Y.gtoreq.-50X+1000 (equation (1)) and Y.ltoreq.-50X+1900 (equation
(2)).
[0038] Herein, an oxidizing agent to be added to a polishing slurry
is not particularly limited, but from a viewpoint of enhancement of
a polishing rate, chlorinated isocyanuric acid such as
trichloroisocyanuric acid, chlorinated isocyanurate such as sodium
dichloroisocyanurate, permanganate such as sodium permanganate,
dichromate such as potassium dichromate, bromate such as potassium
bromate, thiosulfate such as sodium thiosulfate, persulfate such as
ammonium persulfate and potassium persulfate, hypochlorous acid,
nitric acid, aqueous hydrogen peroxide, ozone, and the like are
preferably used. These oxidizing agents may be used alone, or two
or more may be used together.
[0039] In addition, it is preferable that a pH of polishing slurry
17 of the present embodiment is not more than 5 or not less than 8.
By contacting an acidic polishing slurry having a pH of 5 or less
or a basic polishing slurry having a pH of 8 or more with a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal to oxidize procession
denatured layer 1a of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal, a polishing rate can be enhanced. From a viewpoint of
further enhancement of a polishing rate, a pH of polishing slurry
17 is more preferably not more than 4 or not less than 9, further
preferably not more than 3 or not less than 10.
[0040] Herein, an acid, a base and a salt which are used for
adjusting a pH are not particularly limited, but an inorganic acid
such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric
acid and carbonic acid, an organic acid such as formic acid, acetic
acid, citric acid, malic acid, tartaric acid, succinic acid,
phthalic acid and fumaric acid, a base such as KOH, NaOH,
NH.sub.4OH and amine, and salts containing these acids or bases can
be used. Alternatively, the aforementioned oxidizing agent may be
added to adjust a pH.
[0041] In particular, in a polishing slurry using the
aforementioned organic acid and/or a salt thereof for adjusting a
pH, a rate of polishing a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal is enhanced as compared with a polishing slurry using the
aforementioned inorganic acid and/or a salt thereof to realize the
same pH. From a viewpoint of enhancement of a polishing rate, it is
preferable that the organic acid and a salt thereof are carboxylic
acid containing 2 or more carboxyl groups in one molecule and a
salt thereof, respectively. Herein, preferable examples of
dicarboxylic acid include malic acid, succinic acid, phthalic acid
and tartaric acid. Preferable examples of tricarboxylic acid
include citric acid. Therefore, it is preferable that a polishing
slurry contains the abrasive grains, the oxidizing agent, the
organic acid and/or a salt thereof.
Embodiment 2
[0042] Referring to FIG. 1, a method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal (0.ltoreq.x.ltoreq.1,
0.ltoreq.y.ltoreq.1) of the present invention is a method of
treating a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
1 using the polishing slurry 17 of the embodiment 1, and includes
the steps of: preparing the polishing slurry 17; and chemically
mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 using this polishing
slurry 17. By such the chemical mechanical polishing, a crystal
surface having a low surface roughness is obtained at a high
polishing rate and effectively.
[0043] In the method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal of the present
embodiment, it is preferable that the step of chemically
mechanically polishing a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using the polishing
slurry is performed by rotating a polishing pad and a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal on different rotating
axes at a rotation number of 10/min or more and 200/min or less and
at a polishing pressure (corresponding to a pressure applied to
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 by pressing against
polishing pad 18 in FIG. 1) of not less than 4.9 kPa (50
gf/cm.sup.2) and not more than 98 kPa (1000 gf/cm.sup.2) by
interposing the polishing slurry between the polishing pad and the
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal.
[0044] When a polishing pressure is less than 4.9 kPa (50
gf/cm.sup.2) or a rotation number is less than 10/min, a polishing
rate is lowered and, when a polishing pressure is more than 98 kPa
(1000 gf/cm.sup.2) or a rotation number is more than 2000/min,
surface quality of a crystal is deteriorated. From such the
viewpoint, in CMP of a GaAs crystal, it is preferable that a
polishing pressure is not less than 9.8 kPa (100 gf/cm.sup.2) and
not more than 49 kPa (500 gf/cm.sup.2), and a rotation number of a
polishing pad and a GaAs crystal is not less than 30/min and not
more than 70/min. In addition, in a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal (0x.ltoreq.1,
0.ltoreq.y.ltoreq.1), as x and y are nearer 1, a hardness of a
crystal is lowered, and it is further preferable that a polishing
pressure of a GaAs crystal is not less than 9.8 kPa (100
gf/cm.sup.2) and not more than 29.4 kPa (300 gf/cm.sup.2), and a
polishing pressure of an InP crystal is not less than 14.7 kPa (150
gf/cm.sup.2) and not more than 49 kPa (500 gf/cm.sup.2).
[0045] It is preferable that the method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal of the present
embodiment includes a step of washing a surface of the chemically
mechanically polished Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
with pure water after the step of chemical mechanical polishing.
Impurities such as a polishing slurry (abrasive grains and a
polishing solution) attached to a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal during a step of
chemical mechanical polishing can be removed by washing a surface
of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal with pure water. A
method of washing a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is
not particularly limited, but from a viewpoint of that impurities
are effectively removed by mechanical action, an ultrasound washing
method, and a scrub washing method are preferably used.
[0046] Referring to FIG. 3, it is also preferable that the method
of treating a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal of the present embodiment includes a step of polishing a
surface of the chemically mechanically polished
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using a polishing
solution formed of an acidic aqueous solution or a basic aqueous
solution after the step of chemical mechanical polishing.
[0047] Herein, a step of polishing using a polishing solution
refers to a step which is performed for removing the impurities
attached to a surface of a subject to be abraded using a polishing
solution not containing a solid matter such as abrasive grains,
like an acidic aqueous solution or a basic aqueous solution.
Referring to FIG. 3, for example, impurities on a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 can be removed by
pressing Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 against a
polishing pad 38 while a polishing pad 38 fixed on a platen 35 is
rotated around a rotation axis 35c, and while a polishing solution
37 is supplied on a polishing pad 38 from a polishing solution
supply port 39, and a weight 34 is placed on a crystal holder 31 to
which Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 is fixed, and
this is rotated around a rotation axis 31c of crystal holder
31.
[0048] By polishing a surface of
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1 using polishing
solution 37 of the present embodiment formed of an acidic aqueous
solution or a basic aqueous solution, impurities such as a
polishing slurry (abrasive grains and a polishing solution)
attached to a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal during the step of chemical mechanical polishing can be
effectively removed. From a viewpoint of removal of impurities
attached to a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal, it is
preferable that a polishing solution is an acidic aqueous solution
having a pH of 5 or lower, or a basic aqueous solution having a pH
of 9 or higher. Herein, an acidic aqueous solution is not
particularly limited, but an aqueous solution of an inorganic acid
such as hydrochloric acid, nitric acid, sulfuric acid and
phosphoric acid, an aqueous solution of an organic acid such as
formic acid, acetic acid, citric acid, malic acid, tartaric acid,
succinic acid, phthalic acid and fumaric acid, or an aqueous
solution containing 2 or more of acids from the inorganic acids and
organic acids are preferably used. In addition, a basic aqueous
solution is not particularly limited, an aqueous solution of a base
such as KOH, NaOH, NH.sub.4OH and amine is preferably used.
[0049] Further, it is preferable that the method of treating a
surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal of the
present embodiment includes a step of washing a surface of the
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal which has been polished
using a polishing solution with pure water after the step of
polishing using the polishing solution. A metal ion and an ion
containing a light element of an atomic number of 1 to 18 in an
acidic aqueous solution or a basic aqueous solution which are
impurities attached to a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal during a step of
polishing using a polishing solution can be effectively removed by
washing a surface of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
with pure water. A method of washing a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal is not particularly
limited, but from a viewpoint that the impurities are effectively
removed by mechanical action, an ultrasound washing method and a
scrub washing method are preferably used.
Embodiment 3
[0050] A Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1) of the present invention
is obtained by the surface treating method of the embodiment 2. By
the surface treatment method of the embodiment 2, a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate having a low
surface roughness is effectively obtained. Herein, as an index
expressing a surface roughness, there are a surface roughness Ry
and a surface roughness Ra. A surface roughness Ry refers to a sum
obtained by extracting only a 10 .mu.m square (10 .mu.m.times.10
.mu.m=100 .mu.m.sup.2; hereinafter the same) as a standard area of
a rough curved surface in its average plane direction, and summing
a height from an average plane from this extracted part to a
highest summit and a depth from the average plane to a lowest
valley bottom. In addition, a surface roughness Ra refers to a
value obtained by extracting only a 10 .mu.m square as a standard
area from a rough curved surface in its average plane direction,
summing an absolute value of a deviation from an average plane of
this extracted part to a measurement curved surface and averaging
it by a standard area. Herein, measurement of surface roughnesses
Ry and Ra can be performed by using AFM (by an atomic force
microscope; hereinafter the same).
[0051] By reducing surface roughnesses Ry and/or Ra of a main plane
of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate, an
epitaxial layer having better morphology and crystallizability can
be formed on a main plane of a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal, and a semiconductor device having better property can be
manufactured. In order to obtain a device having better property,
it is preferable that, in a main surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal substrate, a surface
roughness Ry is 10 nm or lower, and a surface roughness Ra is 1 nm
or lower.
[0052] A polishing slurry, a method of treating a surface of a
Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal using such the
polishing slurry, and a Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
obtained by such the surface treating method regarding the present
invention will be further specifically explained based on the
following Examples and Comparative Examples.
EXAMPLE 1
[0053] (A-1) Lapping of GaAs crystal
[0054] A GaAs crystal grown by a VB (Vertical Bridgeman) method was
sliced with a plane parallel with a (100) plane to obtain a GaAs
crystal substrate of diameter 50 mm.times.thickness 0.5 mm. A (100)
plane of this GaAs crystal substrate was lapped as follows: a
lapping pad was disposed on a platen of a diameter of 300 mm
arranged on a lapping apparatus, and a platen and a GaAs crystal
substrate were rotated to each other with rotation axes shifted
while a lapping slurry with Al.sub.2O.sub.3 abrasive grains
dispersed therein was supplied to a lapping pad, and a (100) plane
of a GaAs crystal substrate fixed to a crystal holder was pressed
against a platen. Herein, as a lapping pad, a non-woven pad
(Suba800 manufactured by Nitta Haas Incorporated) was used and, as
a platen, a stainless platen was used. As an Al.sub.2O.sub.3
abrasive grain, three kinds having an abrasive grain diameter of 10
.mu.m, 5 .mu.m and 2 .mu.m were prepared and, as lapping
progresses, an abrasive grain diameter was lowered stepwisely. An
abrading pressure was 4.9 kPa (50 gf/cm.sup.2) to 98 kPa (1000
gf/cm.sup.2), and rotation numbers of a GaAs crystal substrate and
a platen were 10/min to 200/min. By such the lapping, a surface of
a GaAs crystal substrate became specular. In a GaAs crystal
substrate after this lapping, a surface roughness Ry was 8.4 nm,
and a surface roughness Ra was 0.86 nm. An abrading time in this
lapping was 20 min. An average lapping rate was 1.6 .mu.m/min.
(A-2) Chemical mechanical polishing (CMP) of GaAs crystal
[0055] A (100) plane of a GaAs crystal substrate after the lapping
was chemically mechanically polished as follows. Referring to FIG.
1, that is, a back ((-100)plane) of a GaAs crystal substrate
(Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1) after the lapping
was adhered to a ceramic crystal holder 11 with a wax. A polishing
pad 18 was disposed on a platen 15 of a diameter of 380 mm arranged
on a CMP apparatus (not shown), and a surface ((100) plane) of a
GaAs crystal was chemically mechanically polished by rotating a
GaAs crystal substrate (Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal
1) around a rotation axis 11c of crystal holder 11 while a
polishing slurry 17 with abrasive grains 16 dispersed therein was
supplied to polishing pad 18 from a polishing slurry supply port
19, and polishing pad 18 was rotated around a rotation axis 15c,
and a GaAs crystal substrate (Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y
crystal 1) was pressed against polishing pad 18 by placing a weight
14 on crystal holder 11.
[0056] Herein, polishing slurry 17 was prepared by dispersing and
diluting colloidal silica (SiO.sub.2) (Quotron PL-10H manufactured
by Fuso Chemical Co., Ltd.) (SiO.sub.2 solid matter 24 mass %)
having an average particle diameter of a primary particle of 90 nm
and an average particle diameter of a secondary particle of 220 nm
as abrasive grain 16 in water to a SiO.sub.2 solid matter of 15
mass %, and sodium carbonate (Na.sub.2CO.sub.3), sodium sulfate
(Na.sub.2SO.sub.4), sodium tripolyphosphate (Na-TPP), and sodium
dichloroisocyanurate (Na-DCIA) as an oxidizing agent were
appropriately added to adjust a pH to 9.0, and ORP to 1050 mV. In
addition, as polishing pad 18, a suede pad of polyurethane (Supreme
RN-R manufactured by Nitta Haas Incorporated) was used and, as
platen 15, a stainless platen was used. A polishing pressure was
19.6 kPa (200 gf/cm.sup.2), and both of rotation numbers of a GaAs
crystal substrate (Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1)
and polishing pad 18 were 40/min.
[0057] A polishing rate in this CMP was 1.5 .mu.m/min. In addition,
when surface roughnesses Ry and Ra of a GaAs crystal substrate
after CMP were measured using AFM, they were 2.4 nm and 0.25 nm,
respectively. The results are summarized in Table 1.
EXAMPLES 2 to 4, COMPARATIVE EXAMPLES 1 TO 3
[0058] According to the same manner as that of Example 1 except
that a polishing slurry containing colloidal silica abrasive grains
having an average particle diameter d.sub.1 of a primary particle,
an average particle diameter d.sub.2 of a secondary particle, and a
d.sub.2/d.sub.1 ratio shown in Table 1 as the abrasive grains were
used in the (A-2), lapping and CMP of a GaAs crystal substrate were
performed. Surface roughnesses Ry and Ra of the resulting GaAs
crystal substrate were measured. The results are summarized in
Table 1.
[0059] In a polishing slurry of each Example, as an abrasive grain
material, Quotron PL-3H (SiO.sub.2 solid matter 20 mass %)
manufactured by Fuso Chemical Co., Ltd. having d.sub.1 of 30 nm,
d.sub.2 of 80 nm and a d.sub.2/d.sub.1 ratio of 2.7 was used in
Example 2, Quotron PL-7 (SiO.sub.2 solid matter 20 mass %)
manufactured by Fuso Chemical Co., Ltd. having d.sub.1 of 70 nm,
d.sub.2 of 130 nm and a d.sub.2/d.sub.1 ratio of 1.9 was used in
Example 3, Snowtex PS-MO (SiO.sub.2 solid matter 18 to 19 mass %)
manufactured by Nissan Chemical Industries, Ltd. having d.sub.1 of
20 nm, d.sub.2 of 150 nm and a d.sub.2/d.sub.1 ratio of 7.5 was
used in Example 4, and unassociated colloidal silica (SiO.sub.2)
was used in Comparative Examples 1 to 3, and abrasive grains
material were diluted in water to a SiO.sub.2 solid matter of 15
mass % in all cases. A pH and ORP of polishing slurries of each
Example and each Comparative Example were adjusted as in Example 1.
In addition, in a polishing slurry of each Comparative Example, as
an abrasive grain material, unassociated colloidal silica having
d.sub.1 of 40 nm was used in Comparative Example 1, unassociated
colloidal silica having d.sub.1 of 100 nm was used in Comparative
Example 2, and unassociated colloidal silica (SiO.sub.2) having
d.sub.1 of 200 nm was used in Comparative Example 3, and any silica
was diluted in water to a SiO.sub.2 solid matter of 15 mass %. A pH
and ORP of polishing slurries of each Example and each Comparative
Example were adjusted as in Example 1.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example
1 Example 2 Example 3 Example 4 Example 1 Example 2 Example 3
Crystal composition GaAs GaAs GaAs GaAs GaAs GaAs GaAs CMP Abrasive
Average secondary particle 220 80 130 150 -- -- -- grain diameter
d.sub.2 (nm) Average primary particle 90 30 70 20 40 100 200
diameter d.sub.1 (nm) d.sub.2/d.sub.1 ratio 2.4 2.7 1.9 7.5 -- --
-- Content of abrasive grain (mass %) 15 15 15 15 15 15 15
Oxidizing agent Na-DCIA Na-DCIA Na-DCIA Na-DCIA Na-DCIA Na-DCIA
Na-DCIA Acid, base, salt (pH adjusting agent) Na.sub.2CO.sub.3,
Na.sub.2CO.sub.3, Na.sub.2CO.sub.3, Na.sub.2CO.sub.3,
Na.sub.2CO.sub.3, Na.sub.2CO.sub.3, Na.sub.2CO.sub.3,
Na.sub.2SO.sub.4, Na.sub.2SO.sub.4, Na.sub.2SO.sub.4,
Na.sub.2SO.sub.4, Na.sub.2SO.sub.4, Na.sub.2SO.sub.4,
Na.sub.2SO.sub.4, Na-TPP Na-TPP Na-TPP Na-TPP Na-TPP Na-TPP Na-TPP
pH of polishing slurry 9 9 9 9 9 9 9 ORP of polishing slurry (mV)
1050 1050 1050 1050 1050 1050 1050 Polishing pressure (kPa) 19.6
19.6 19.6 19.6 19.6 19.6 19.6 Polishing pad rotation number (/min)
40 40 40 40 40 40 40 Crystal rotation number (/min) 40 40 40 40 40
40 40 Polishing rate (.mu.m/min) 1.5 0.81 1.0 1.1 0.32 0.52 1.0
Surface Surface roughness Ry (nm) 2.4 1.3 2.3 1.9 2.3 3.5 6.0
assessment after Surface roughness Ra (nm) 0.25 0.12 0.22 0.18 0.21
0.32 0.51 CMP Note) Na-DClA: sodium dichloroisocyanurate,
Na.sub.2CO.sub.3: sodium carbonate, Na.sub.2SO.sub.4: sodium
sulfate Na-TPP: sodium tripolyphosphate
[0060] As shown in Comparative Examples 1 to 3, when polishing is
performed using a polishing slurry containing unassociated
spherical colloidal silica abrasive grains, as a particle diameter
of an abrasive grain grows larger, a polishing rate is enhanced,
but both of surface roughnesses Ry and Ra are increased, and
surface quality is deteriorated.
[0061] To the contrary, as shown in Examples 1 to 4, by performing
CMP using a polishing slurry containing colloidal silica abrasive
grains in which the grains are a secondary particle (average
particle diameter d.sub.2) obtained by association of primary
particles (average particle diameter d.sub.1), a d.sub.2/d.sub.1
ratio is not less than 1.6 and not more than 10, and d.sub.2 is not
less than 30 nm and not more than 300 nm, and in which a value X of
a pH and a value Y (mV) of ORP satisfy a relationship of
-50X+1000.ltoreq.Y.ltoreq.-50X+1900, and a pH is 8 or more, under
the condition of a polishing pressure of 19.6 Pa (200 gf/cm.sup.2),
and a rotation number of a polishing pad and a GaAs crystal of
40/min, a GaAs crystal substrate having a surface having small
surface roughnesses Ry and Ra was obtained at a high polishing
rate.
EXAMPLE 5 TO EXAMPLE 7
[0062] According to the same manner as that of Example 1 except
that a polishing slurry having a pH and ORP shown in Table 2 was
used, lapping and CMP of a GaAs crystal substrate were performed.
Surface roughnesses Ry and Ra of the resulting GaAs crystal
substrate were measured. The results are summarized in Table 2.
[0063] In addition, in a polishing slurry of each Example, a pH and
ORP were adjusted to each pH and each ORP shown in Table 2 using
the same colloidal silica abrasive grain as that of Example 2,
using malic acid, sodium malate, and trichloroisocyanuric acid
(TCIA) which is an oxidizing agent in Example 5, and using sodium
carbonate (Na.sub.2CO.sub.3), sodium sulfate (Na.sub.2SO.sub.4),
sodium tripolyphosphate (Na-TPP), and sodium dichloroisocyanurate
(Na-DCIA) which is an oxidizing agent in Example 6. In Example 7,
all of an acid, a base, a salt and an oxidizing agent were not
added.
TABLE-US-00002 TABLE 2 Example 5 Example 6 Example 7 Crystal
composition GaAs GaAs GaAs CMP Abrasive Average secondary particle
diameter d.sub.2 (nm) 80 80 80 grain Average primary particle
diameter d.sub.1 (nm) 30 30 30 d.sub.2/d.sub.1 ratio 2.7 2.7 2.7
Content of abrasive grain (mass %) 15 15 15 Oxidizing agent TCIA
Na-DCIA -- Acid, base, salt (pH adjusting agent) Malic acid
Na.sub.2CO.sub.3, -- Na malate Na.sub.2SO.sub.4, Na-TPP pH of
polishing slurry 4 9 7.5 ORP of polishing slurry(mV) 1200 1000 600
Polishing pressure (kPa) 19.6 19.6 19.6 Polishing pad rotation
number (/min) 40 40 40 Crystal rotation number (/min) 40 40 40
Polishing rate (.mu.m/min) 0.98 0.79 0.22 Surface assessment after
Surface roughness Ry (nm) 1.6 1.3 3.2 CMP Surface roughness Ra (nm)
0.15 0.12 0.28 Note) TClA: trichloroisocyanuric acid, Na-DClA:
sodium dichloroisocyanurate Na.sub.2CO.sub.3: sodium carbonate,
Na.sub.2SO.sub.4: sodium sulfate, Na malate: sodium malate Na-TPP:
sodium tripolyphosphate
[0064] As shown in Examples 5 and 6, by performing CMP using a
polishing slurry containing colloidal silica abrasive grains in
which primary particles (average particle diameter d.sub.1) are
associated to be a secondary particle (average particle diameter
d.sub.2), a ratio d.sub.2/d.sub.1 is not less than 1.6 and not more
than 10, and d.sub.2 is not less than 30 nm and not more than 300
nm, and in which a value X of a pH and a value Y (mV) of ORP
satisfy a relationship of -50X+1000.ltoreq.Y.ltoreq.-50x+1900, and
a pH is not higher than 5 or not lower than 8, a GaAs crystal
substrate having small surface roughnesses Ry and Ra was obtained
at a high polishing rate. In Example 7, a relationship between a
value X of a pH and a value Y (mV) of ORP of a polishing slurry is
Y.ltoreq.-50X+1000, a polishing rate was lowered, and both of
surface roughnesses Ry and Ra of a GaAs crystal substrate after CMP
were increased.
EXAMPLE 8
[0065] (B-1) Lapping of InP crystal
[0066] An InP crystal which had been grown by a LEC (liquid
Encapsulated Czochralski) method was sliced with a plane parallel
with a (100) plane to obtain an InP crystal substrate of diameter
50 mm.times.thickness 0.5 mm. A (100) plane of this InP crystal
substrate was lapped like (A-1) of Example 1.
(B-2) Chemical mechanical polishing (CMP) of InP crystal
[0067] According to the same manner as that of Example 1 except
that a polishing slurry obtained by diluting colloidal silica
(SiO.sub.2) (Quotron PL10H manufactured by Fuso Chemical Co., Ltd.)
(SiO.sub.2 solid matter 24 mass %) having an average particle
diameter d.sub.1 of a primary particle of 90 nm, and an average
particle diameter d.sub.2 of a secondary particle of 220 nm, and a
d.sub.2/d.sub.1 ratio of 2.4 in water to a SiO.sub.2 solid matter
of 10 mass %, and adjusting a pH of a polishing slurry to 4, and
ORP of a polishing slurry to 1200 mV using citric acid and
triochloroisocyanuric acid (TCIA) which is an oxidizing agent was
used, a polishing pressure was 29.4 kPa (300 gf/cm.sup.2), and a
rotation number of a polishing pad and an InP crystal was 50/min,
CMP of a (100) plane of InP crystal substrate after lapping was
performed. Surface roughnesses Ry and Ra of the resulting InP
crystal substrate were measured. The results are summarized in
Table 3.
EXAMPLES 9 TO 11, COMPARATIVE EXAMPLES 4 TO 6
[0068] According to the same manner as that of Example 8 except
that a polishing slurry containing colloidal silica abrasive grains
having an average particle diameter d.sub.1 of a primary particle,
an average particle diameter d.sub.2 of a secondary particle and a
d.sub.2/d.sub.1 ratio shown in Table 2 as the abrasive grains were
used in the (B-2), lapping and CMP of an InP crystal substrate were
performed. Surface roughnesses Ry and Ra of the resulting InP
crystal substrate were measured. The results are summarized in
Table 3.
[0069] In addition, in a polishing slurry of each Example, as
abrasive grain material, Quotron PL-3H (SiO.sub.2 solid matter 20
mass %) manufactured by Fuso Chemical Co., Ltd. having d.sub.1 of
30 nm, d.sub.2 of 80 nm and a d.sub.2/d.sub.1 ratio of 2.7 was used
in Example 9, Quotron PL-7 (SiO.sub.2 solid matter 20 mass %)
manufactured by Fuso Chemical Co., Ltd. having d.sub.1 of 70 nm,
d.sub.2 of 130 nm, and a d.sub.2/d.sub.1 ratio of 1.9 was used in
Example 10, Snowtex PS-MO (SiO.sub.2 solid matter 18 to 19 mass %)
manufactured by Nissan Chemical Industries, Ltd. having d.sub.1 of
20 nm, d.sub.2 of 150 nm, and a d.sub.2/d.sub.1 ratio of 7.5 was
used in Example 11, and unassociated colloidal silica (SiO.sub.2)
was used in Comparative Examples 4 to 6, and any of them was
diluted in water to a SiO.sub.2 solid matter of 10 mass %. In
addition, in a polishing slurry of each Comparative Example, as an
abrasive grain material, unassociated colloidal silica having
d.sub.1 of 40 nm was used in Comparative Example 4, unassociated
colloidal silica of d.sub.1 of 100 nm was used in Comparative
Example 5, and unassociated colloidal silica having d.sub.1 of 200
nm was used in Comparative Example 6, and any of them was diluted
in water to a SiO.sub.2 solid matter of 10 mass %. A pH and ORP of
polishing slurries of each Example and each Comparative Example
were adjusted as in Example 8.
TABLE-US-00003 TABLE 3 Example Example Comparative Comparative
Comparative Example 8 Example 9 10 11 Example 4 Example 5 Example 6
Crystal composition InP InP InP InP InP InP InP CMP Abrasive
Average secondary particle 220 80 130 150 -- -- -- grain diameter
d.sub.2 (nm) Average primary particle 90 30 70 20 40 100 200
diameter d.sub.1 (nm) d.sub.2/d.sub.1 ratio 2.4 2.7 1.9 7.5 -- --
-- Content of abrasive grain (mass %) 10 10 10 10 10 10 10
Oxidizing agent TCIA TCIA TCIA TCIA TCIA TCIA TCIA Acid, base, salt
(pH adjusting agent) Citric acid Citric acid Citric acid Citric
acid Citric acid Citric acid Citric acid pH of polishing slurry 4 4
4 4 4 4 4 ORP of polishing slurry (mV) 1200 1200 1200 1200 1200
1200 1200 Polishing pressure (kPa) 29.4 29.4 29.4 29.4 29.4 29.4
29.4 Polishing pad rotation number (/min) 50 50 50 50 50 50 50
Crystal rotation number (/min) 50 50 50 50 50 50 50 Polishing rate
(.mu.m/hr) 20 13 16 18 4.2 7.0 14 Surface Surface roughness Ry (nm)
2.7 1.5 2.5 2.3 2.6 3.9 6.9 assessment after Surface roughness Ra
(nm) 0.28 0.14 0.25 0.21 0.24 0.37 0.62 CMP Note) TCIA:
trichloroisocyanuric acid
[0070] As shown in Comparative Examples 4 to 6, when polishing is
performed using a polishing slurry containing unassociated
spherical colloidal silica abrasive grains, as a particle diameter
of the abrasive grain grows larger, a polishing rate is enhanced,
but both of surface roughnesses Ry and Ra are increased, and
surface quality of an InP crystal substrate is deteriorated.
[0071] To the contrary, as shown in Examples 8 to 11, by performing
CMP using a polishing slurry containing colloidal silica abrasive
grains in which primary particles (average particle diameter
d.sub.1) are associated to be a secondary particle (average
particle diameter d.sub.2), a d.sub.2/d.sub.1 ratio is not less
than 1.6 and not more than 10, and d.sub.2 is not less than 30 nm
and not more than 300 nm, and in which a value X of a pH and a
value Y (mV) of ORP satisfy a relationship of
-50X+1000.ltoreq.Y.ltoreq.-50X+1900, and a pH is 5 or lower, under
the condition of a polishing pressure of 29.4 kPa (300
gf/cm.sup.2), and a rotation number of a polishing part and an InP
crystal of 50/min, an InP crystal substrate having a surface having
small surface roughnesses Ry and Ra was obtained at a high
polishing rate.
EXAMPLES 12 TO 15
[0072] According to the same manner as that of Example 8 except
that a polishing slurry having a pH and ORP shown in Table 4, and
the condition of a polishing pressure and a rotation number of a
polishing pad and an InP crystal shown in Table 4 were used,
lapping and CMP of an InP crystal substrate were performed. Surface
roughnesses Ry and Ra of the resulting InP crystal substrate were
measured. The results are summarized in Table 4.
[0073] In addition, in a polishing slurry of each Example, a pH and
ORP were adjusted to each pH and each ORP shown in Table 4 using
the same colloidal silica abrasive grain as that of Example 9,
using malic acid and trichloroisocyanuric acid (TCIA) which is an
oxidizing agent in Example 12, using sodium malate and
trichloroisocyanuric acid (TCIA) which is an oxidizing agent in
Example 13, and using nitric acid and trichloroisocyanuric acid
(TCIA) which is an oxidizing agent in Example 14. In Example 15,
all of an acid, a base, a salt and an oxidizing agent were not
added.
TABLE-US-00004 TABLE 4 Example 12 Example 13 Example 14 Example 15
Crystal composition InP InP InP InP CMP Abrasive Average secondary
particle diameter d.sub.2 (nm) 80 80 80 80 grain Average primary
particle diameter d.sub.1 (nm) 30 30 30 30 d.sub.2/d.sub.1 ratio
2.7 2.7 2.7 2.7 Content of abrasive grain (mass %) 10 10 10 10
Oxidizing agent TCIA TCIA TCIA -- Acid, base, salt (pH adjusting
agent) Malic acid Na malate HNO.sub.3 -- pH of polishing slurry 2.5
3.8 1.8 7.5 ORP of polishing slurry (mV) 1400 1250 1450 600
Polishing pressure (kPa) 29.4 29.4 29.4 29.4 Polishing pad rotation
number (/min) 50 50 50 50 Crystal rotation number (/min) 50 50 50
50 Polishing rate (.mu.m/hr) 17 12 10 5 Surface assessment after
Surface roughness Ry (nm) 1.8 1.7 2.0 3.9 CMP Surface roughness Ra
(nm) 0.15 0.14 0.17 0.32 Note) TCIA: trichloroisocyanuric acid, Na
malate: sodium malate, HNO.sub.3: nitric acid
[0074] As shown in Examples 12 to 14, by performing CMP using a
polishing slurry containing colloidal silica abrasive grains in
which primary particles (average particle diameter d.sub.1) are
associated to be a secondary particle (average particle diameter
d.sub.2), a ratio d.sub.2/d.sub.1 is not less than 1.6 and not more
than 10, and d.sub.2 is not less than 30 nm and not more than 300
nm, and in which a value X of a pH and a value Y (mV) of ORP
satisfy a relationship of -50X+1000.ltoreq.Y.ltoreq.-50X+1900, and
a pH is 5 or lower, an InP crystal substrate having small surface
roughnesses Ry and Ra was obtained at a high polishing rate.
Further, as shown in Examples 12 and 13, by using a polishing
slurry containing malic acid or sodium malate which is dicarboxylic
acid or a salt thereof as a pH adjusting agent, a rate of polishing
an InP crystal substrate was further enhanced.
EXAMPLES 16 TO 18
[0075] In Example 1, a step of polishing a GaAs crystal substrate
after a CMP step using a KOH aqueous solution having a
concentration of 2 normal (referred to as 2N; the same hereinafter)
as a basic aqueous solution as shown in Table 5, and/or a step of
washing with an ultrasound of 1 MHz (1.times.10.sup.6 Hz using pure
water were performed.
[0076] Referring to FIG. 3, in the above polishing step, that is, a
back ((-100) plane) of the GaAs crystal substrate
(Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1) after CMP was
adhered to a ceramic crystal holder 31 with a wax. A surface ((100)
plane) of a GaAs crystal was chemically polished by disposing a
polishing pad 38 on a platen 35 of a diameter of 380 mm arranged on
a polishing apparatus (not shown), and rotating a GaAs crystal
substrate (Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1) around a
rotation axis 31c of crystal holder 31 while a polishing solution
37 was supplied to polishing pad 38 from a polishing solution
supply port 39, polishing pad 38 was rotated around a rotation axis
35c, and a GaAs crystal substrate
(Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1) was pressed against
polishing pad 38 by placing a weight 34 on a crystal holder 31.
Herein, as polishing pad 38, a suede pad of polyurethane (Supreme
RN-R manufactured by Nitta Haas Incorporated) was used and, as
platen 35, a stainless platen was used. A polishing pressure was
9.8 Pa (100 gf/cm.sup.2), a rotation number of a GaAs crystal
substrate (Ga.sub.xIn.sub.1-xAs.sub.yP.sub.1-y crystal 1) and
polishing pad 38 was 30/min, and a polishing time was 10 min.
[0077] In addition, an ultrasound washing step with pure water was
performed by immersing a GaAs crystal substrate after the CMP step
or after a chemical polishing step in pure water, and applying an
ultrasound of 1 MHz to this pure water. A washing time was 10
min.
[0078] Elemental analysis of impurities remaining on a surface of
the GaAs crystal substrate after a chemical polishing step or after
a pure water washing step was performed using TXRF (total
reflection fluorescent X-ray analysis method). The results are
summarized in Table 5. As a reference, the results of analysis of
impurities remaining on a surface of a GaAs crystal substrate after
a CMP step in Example 1 are also described in Table 5.
TABLE-US-00005 TABLE 5 Exam- Exam- Exam- Exam- ple ple ple ple 1 16
17 18 Crystal composition GaAs GaAs GaAs GaAs Surface Polishing
step -- KOH(2N) -- KOH(2N) treating using step polishing after CMP
solution Pure water -- -- Ultra- Ultra- washing step sound sound
Amount of impurities Si 4100 50 540 40 on crystal surface K 110 420
40 30 (.times.10.sup.10 atoms/cm.sup.2) S 620 420 300 180 Cu 400
110 80 50 Ca 2800 30 20 10 Note) KOH: potassium hydroxide
[0079] As shown in Example 17, by providing a pure water washing
step after a CMP step, impurities on a GaAs crystal substrate
surface could be reduced. In addition, as shown in Example 16, by
providing a chemical polishing step after a CMP step, impurities on
a GaAs crystal substrate surface, particularly, a Si
atom-containing substance derived from a colloidal silica abrasive
grain upon CMP could be remarkably reduced. Further, as shown in
Example 18, by providing a pure water washing step after a chemical
polishing step, impurities on a GaAs crystal substrate surface,
particularly, a K atom-containing substance derived from a
polishing solution upon a chemical polishing step could be
remarkably reduced.
[0080] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *