Silicon epitaxial wafer and production method therefor

Details Silicon epitaxial wafer and production method therefor Silicon epitaxial wafer and production method therefor

2001-07-10

2003-05-27

Utech, Benjamin L. (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

Reexamination Certificate

active

06569239

ABSTRACT:

RELATED APPLICATION
This application claims the priority of Japanese Patent Application No. 10-228665 filed on Jul. 29, 1998, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a silicon epitaxial wafer and a production method therefor and particularly, to high precision control of surface roughness of a silicon epitaxial layer through realization of uniform temperature distribution in a surface of a silicon wafer.
2. Description of the Prior Art
A design rule of a semiconductor device has already been reached to a subquarter micron level in a practical aspect. As an electric charge handled in a semiconductor device is decreased with progress in miniaturization, even a small number of minute defects in the vicinity of a surface of a silicon single crystal substrate have a possibility of giving a fatal influence on device characteristics larger than in the past: deterioration in performances of a bipolar circuit and a CMOS circuit has especially been problematic.
Therefore, it is expected that, hereinafter, a silicon epitaxial wafer produced by growing a silicon epitaxial layer on a silicon single crystal substrate in a vapor phase will increasingly be used instead of the silicon single crystal substrate, which is produced in a process in which a silicon single crystal ingot pulled from a melt is sliced and a slice is mirror-polished. In the following description, a silicon single crystal substrate and a silicon epitaxial wafer are generically called as a silicon wafer.
High level uniformity of thickness distribution is required for a silicon epitaxial wafer. The thickness distribution uniformity may alternatively be expressed by a flatness of a silicon epitaxial layer which is grown on a silicon single crystal substrate since the silicon single crystal substrate is originally high in flatness. The reason why the high level flatness is required is that a wavelength of exposure light which has been used in photolithography in recent years is shorter down to the far-ultra violet region and a depth of focus has greatly been reduced, so that there arises a necessity to earn any amount of a process margin. Such a requirement for high level flatness is strengthened more and more as a diameter of a silicon wafer is increased from a current 200 mm to 300 mm or more.
A structure of a single wafer type vapor phase thin film growth apparatus
20
is shown as an example in FIG.
8
. In the apparatus, a silicon wafer W is singly disposed in a process vessel
21
made of transparent quartz and vapor phase growth of a thin film is performed while the silicon wafer W is heated from above and under by radiation of infrared lamps
29
a
,
29
b
. The infrared lamps
29
a
are an outside group and the infrared lamps
29
b
are an inside group.
The interior of the process vessel
21
is partitioned into an upper space
21
a
and a lower space
21
b
by a susceptor
25
on which a silicon wafer is disposed. A raw material gas which is introduced together with H
2
gas, a carrier gas, through a gas supply port
22
into the upper space
21
a
flows in a direction of an arrow A in the figure while forming a near laminar flow along a surface of the silicon wafer W and then discharged from an exhaust port on the other side. A purge gas which is H
2
gas under higher pressure than that of the raw material gas is supplied into the lower space
21
b
. The reason why the purge gas is under the higher pressure is to prevent the raw material gas from flowing into the lower space
21
b
through a gap between the process vessel
21
and the susceptor
25
.
The lower space
21
b
contains support means made of quartz for supporting the susceptor
25
by the rear surface and lift pins
28
for loading and unloading of a silicon wafer W on the susceptor
25
.
The support means is constructed from a rotary shaft
26
and a plurality of spokes
27
which radially branch away from the rotary shaft
26
. Vertical pins
27
b
,
27
c
are provided to the far end of each spoke
27
and the top end of the rotary shaft
26
and the fore ends of the vertical pins
27
b
,
27
c
are respectively engaged in recesses
25
c
,
25
d
formed in the rear surface of the susceptor
25
for supporting the susceptor
25
. The rotary shaft
26
is rotatable by drive means, not shown, in a direction of an arrow C in the figure.
The head of each of the lift pins
28
is enlarged in diameter and is rested while hanging on a tapered side wall of a through-hole
25
b
formed in the bottom surface of a pocket
25
a
of the susceptor
25
for disposing a silicon wafer W therein. The shaft portion of each lift pin
28
is inserted through a through-hole
27
a
which is formed by boring the middle portion between both ends of a spoke
27
and each lift pin
28
is designed to be vertically hung down in a stable manner.
A silicon wafer W is loaded on and unloaded from the susceptor
25
by vertical movement of the support means. For example, when the silicon wafer W is unloaded from the susceptor
25
, the support means is moved downward and the tail ends of the lift pins
28
are directly put into contact with the inner surface of the lower space
21
b
of the process vessel
21
as shown in FIG.
9
. With such encouraged conditions, the lift pins
28
push up the rear surface of the silicon wafer W with the heads, thereby floating the silicon wafer W upward from the pocket
25
a
. Thereafter, a handler, not shown, is inserted in a space between the susceptor
25
and the silicon wafer W and the silicon wafer W is handed over or received and further transported.
A susceptor
25
is usually made from graphite base material coated with a thin film of SiC (silicon carbide). The reason why graphite is chosen as base material is that though it is related with the fact that heating for vapor phase thin film growth apparatuses in the early stage in development was mainly conducted by high frequency induction heating, in addition graphite has merits such as a high purity product being easy to be obtained, being easy to be machined, a thermal conductivity being excellent, being hard to be broken and the like. However, graphite is a porous material mass and therefore has problems such as there being a possibility to release occluded gas during process, the surface of a susceptor being changed into SiC through a reaction between graphite and a raw material gas in the course of vapor phase thin film growth and the like. From such reasons, it is generalized that the surface of graphite is covered by a SiC film before use. A SiC thin film is usually formed by CVD (a chemical vapor deposition method).
A material of the lift pins
28
is also graphite as base material coated with SiC as in the case of the susceptor
25
.
While a requirement for a flatness of a silicon epitaxial wafer has increasingly been severer every year, there has been found that even with a single wafer vapor phase thin film growth apparatus having a structure mentioned above, whose structural materials are improved, differences in thickness between positions in the surface of an epitaxial layer are not avoided according to a specific area in the surface. Especially when a thickness of a silicon epitaxial layer exceeds about 8 &mgr;m, there is a trend that differences in thickness between positions in the surface of a silicon epitaxial layer are increased to a level which is unfavorable for practical use.
A film thickness distribution of a silicon epitaxial layer observed by the inventors is shown in
FIGS. 10A
to
10
C, wherein the silicon epitaxial layer with p type conductivity and a resistivity of 10 &OHgr;·cm was grown on a p
+
type silicon single crystal substrate with a diameter of 200 mm, a main surface of a (100) plane and a resistivity of 0.01 &OHgr;·cm to 0.02 &OHgr;·cm to a target thickness 15 &mgr;m.
FIG. 10A
shows a measurement direction for a thickness distribution; a direction which faces to a notch N which show a crystallographic orientation is called a vertical direction and a direction whi

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