U.S. patent number RE38,937 [Application Number 10/233,546] was granted by the patent office on 2006-01-24 for susceptor for vapor-phase growth apparatus.
This patent grant is currently assigned to Sumitomo Mitsubishi Silicon Corporation. Invention is credited to Osamu Nakamura.
United States Patent |
RE38,937 |
Nakamura |
January 24, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Susceptor for vapor-phase growth apparatus
Abstract
It was an objective of the present invention to provide a
susceptor which can prevent a increasing phenomenon of the dopant
concentration of the epitaxial layer at the peripheral portion of
the wafer. By providing a through-hole 7 passing through to a rear
side at the outer peripheral side of the wafer inside the wafer
pocket 6, a down flow of a reacting source gas from the upper
surface of the susceptor 5 is formed, so that the unwanted flow of
the dopant species being exhausted at the rear surface onto the
wafer surface can be avoided. As a result, a raise in the dopant
concentration at the outer peripheral portion of the epitaxial
layer 9 can be controlled.
Inventors: |
Nakamura; Osamu (Imari,
JP) |
Assignee: |
Sumitomo Mitsubishi Silicon
Corporation (Tokyo, JP)
|
Family
ID: |
35614202 |
Appl.
No.: |
10/233,546 |
Filed: |
September 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09122803 |
Jul 27, 1998 |
06129047 |
Oct 10, 2000 |
|
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Current U.S.
Class: |
117/102; 117/200;
117/84; 117/93; 118/725; 118/728; 118/500; 117/88; 117/2 |
Current CPC
Class: |
C30B
25/14 (20130101); C23C 16/4583 (20130101); C23C
16/4412 (20130101); C30B 25/12 (20130101) |
Current International
Class: |
C23C
16/00 (20060101) |
Field of
Search: |
;117/2,84,88,93,102,200
;438/758 ;428/248.1 ;118/725,728,500 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lund; Jeffrie R.
Attorney, Agent or Firm: Breiner & Breiner, L.L.C.
Claims
What is claimed is:
1. A susceptor for a vapor-phase growth apparatus comprising at
least one through hole passing through a rear side at an outer
peripheral portion of a wafer pocket which is formed as a concave
shape in order to mount said wafer.
2. The susceptor of claim 1, wherein the at least one through hole
is shaped as a groove and a plurality thereof is provided on a
periphery.
.Iadd.3. A method for growing an epitaxial layer having a lower
dopant concentration than the dopant concentration of a wafer, the
method comprising: positioning the wafer in relation to a
susceptor, the susceptor having a through hole; providing a
reacting source gas to the wafer; and forming a vapor flow through
said through-hole to provide vapor flowing from an upper surface of
the susceptor to a lower surface of the susceptor and thereby
preventing flow of a dopant species from a rear side of the wafer
to a surface of the wafer. .Iaddend.
.Iadd.4. A method in accordance with claim 3 wherein the susceptor
further comprises a wafer pocket having a concave surface for
mounting the wafer and wherein the through-hole passes-from the
concave surface to the rear side of the susceptor..Iaddend.
.Iadd.5. The method according to claim 3 further comprising
providing the through-hole on an outer peripheral side of the
wafer..Iaddend.
.Iadd.6. The method according to claim 4 further comprising
providing the through-hole on an outer peripheral side of the
wafer..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement of a susceptor
which is employed to a vapor-phase growth apparatus to grow an
epitaxial film onto the semiconductor wafer. More specifically, the
present invention relates directly to a vapor-phase growth
apparatus in which a through-hole portion extending to a rear side
of the susceptor is provided at the most outer peripheral portion
inside the wafer pocket in order to mount the wafer, and a raise in
dopant concentration at the outer periphery of the grown epitaxial
film can be controlled.
2. Description of the Prior Art
As to a vapor-phase growth apparatus in order to grow an epitaxial
film onto the semiconductor wafer, there have been several
conventional types of apparatus available; they may include (1) a
vertical-type vapor-phase growth apparatus in which the susceptor
being placed on a circular disc is heated from its bottom side, and
(2) a single wafer type vapor-phase growth apparatus with which a
good quality epitaxial film can be fabricated.
For example, inside the rectangular chamber being fabricated of
quartz in said single wafer type vapor-phase growth apparatus,
semiconductor wafer is mounted on the disc-shaped susceptor which
is a graphite being coated with SiC. The semiconductor wafer is
heated using a heater which is provided outside of the chamber in
order to react with various types of reacting source gases passing
through the chamber, resulting in growing the epitaxial film on the
semiconductor wafer.
As seen in FIG. 3, said susceptor 5 is composed of a high purity
graphite which is coated mainly by SiC. On the surface, a groove
called as a wafer pocket 6 is formed in order to accomodate the
silicon wafer. The size of said wafer pocket 6 is slightly larger
than the dimension of the wafer 8 and the depth is about 1 mm.
After placing the wafer 8 inside the wafer pocket 6, the susceptor
is held in the reacting source gaseous flow at a predetermined
temperature to generate the silicon epitaxial film layer 9 on the
wafer surface.
Moreover, several improvements have been proposed in order to
minimize the surface contact between the inner surface of the
pocket and the wafer rear surface. These proposed improvements may
include (1) a structure to contact-hold the wafer to a plurality of
convex portions by forming a mesh-shaped shallow fine groove
so-called a roulette, (2) making a tapered surface in order to
confine the contact of the wafer at its outer periphery, or (3)
using much coarser surface roughness of coated SiC surface than the
surface roughness of the wafer.
As to a reacting source gas, a dopant source gas such as diborane
(P type) or phosphine (N type) is added to a chloro-silane gas
which is hydrogen diluted. Hence the silicon epitaxy as well as a
bi-product of HCl are produced on the wafer surface through a heat
CVD (chemical vapor deposition) reaction. As a result, although the
silicon epitaxial growth on the wafer surface can proceed, the rear
surface of said wafer is also exposed to diffusion reaction gas to
create a Si--H--Cl atmosphere, which might furthermore lead to a
precipitation/etching reaction in a microscopic scale.
For instance when the epitaxial growth having lower concentration
than the dopant concentration of the wafer is conducted such as an
epitaxial growth of P type film (specific resistance is 1
.OMEGA.cm) against the wafer with the dopant concentration P ++
type (specific resistance is 5 m.OMEGA.cm), the dopant
concentration in the epitaxial layer tends to increase at the outer
peripheral portion of the wafer, as demonstrated in FIG. 4 which
shows a change in dopant concentration from the center of the wafer
and as a function of a distance from the center to the most outer
periphery.
The above phenomenon might be due to the fact that the dopant
species of the wafer 8 might be exhausted in Si--H--Cl atmosphere
at the rear surface of wafer 8, and the exhausted dopant species
might migrate to the front surface through the gaseous diffusion
flow 11, resulting in increasing the dopant gaseous concentration
locally. As a result, a particular region of the epitaxial layer
where the dopant concentration is out of the range defined by the
specification, leading to a poor production efficiency of the
device.
SUMMARY OF THE INVENTION
Objective of the Invention
All of the forgoing have resulted in a requirement for improvement
of the apparatus of the present invention in which it is an
objective of the present invention to provide a susceptor which can
prevent the increasing phenomenon of the dopant concentration in
the epitaxial layer at its peripheral portion, as it would be
obvious when the epitaxial growth proceeds at lower concentration
than the dopant concentration of the wafer. It is, accordingly,
another objective to provide a susceptor for the vapor-phase growth
apparatus which can avoid the unwanted flow of the dopant species
being exhausted at the rear side to the wafer surface.
Disclosure of the Invention
The present inventors found that, in a suscpetor for the
vapor-phase growth apparatus, the aforementioned localized
nonuniform distribution of the dopant concentration can be
minimized by forming a vapor flow in order to prevent the unwanted
flow of the dopant species being exhausted at the rear side to the
wafer surface. After investigating various designs for the
susceptor to achieve said objectives, the following design was
evaluated to perform the best efficiency. By providing a
through-hole passing through to the rear side at the outer
peripheral portion of the wafer inside the wafer pocket, the
down-flow from the upper surface of the susceptor is generated, so
that the unwanted flow of the dopant species being exhausted toward
the wafer surface can be prevented. As a result, the raise in the
dopant concentration can be controlled at the outer peripheral
portion of the epitaxial layer.
Namely, according to the present invention, a susceptor can be
provided which is characterized by providing a through-hole passing
through to the rear side at the most outer peripheral portion
inside the wafer pocket which is a concave portion for mounting the
wafer.
According to the present invention, the localized raise of the
dopant concentration at the most outer peripheral portion of the
grown epitaxial layer can be prevented by providing a through-hole
passing through to the rear side of the susceptor at the outer
periphery inside the wafer pocket which is used for mounting the
wafer. Specifically, the raise in the dopant concentration in the
epitaxial layer can be avoided when the epitaxial growth with a
lower concentration than the dopant concentration of the wafer is
progressing.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and many other objectives, features and advantages of the
present invention will be more fully understood from the ensuing
detailed description of the preferred embodiment of the invention,
which description should be read in conjunction with the
accompanying drawings.
FIG. 1a is a view explaining a vapor-phase growth apparatus
employing a susceptor, according to the present invention.
FIG. 1b is another view describing the cross-sectional view of the
susceptor along its radius direction.
FIGS. 2a and 2b are upper half views of the susceptor, according to
the present invention.
FIG. 3 shows a cross-sectional view of the conventional type of
susceptor along its radius direction.
FIG. 4 shows changes in a dopant concentration as a function of a
distance from the center of the wafer along its radius
direction.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A vapor-phase growth apparatus seen in FIG. 1a has a rectangular
chamber 1 made of quartz, in which the semiconductor wafer 8 is
mounted on the circular disc-shaped susceptor 5 which is a graphite
substrate being coated with SiC. The semiconductor wafer 8 is
heated by a heater (not shown) which is placed outside of the
chamber 1 to react with the reacting source gas flowing
horizontally inside the chamber 1 in order to generate the
epitaxial film 9 on the semiconductor wafer surface 8.
The susceptor 5 of the present invention has an arc-shaped
groove-type through-hole portion 7 at the most outer peripheral
portion inside the wafer pocket 6 for mounting the semiconductor
wafer 8. The inner plain portion of the wafer pocket is a coated
SiC layer.
In FIG. 1a, although the reacting source gas 10 is introduced
horizontally from the gas inlet opening 2 of the chamber 1 to the
gas exhaust opening 3, the source gas is supplied and heated
particularly to the wafer surface 8 and the bi-product gas is
generated during the epitaxial reaction, so that the gas can be
subjected to the volumetric expansion. By providing a through-hole
portion 7 at the outer peripheral portion inside the wafer pocket
of the susceptor 5, a localized gas flow is generated from the
wafer surface 8, and the boron species being exhausted from the
rear surface of the wafer 8 can be exhausted without the unwanted
flow-back to the front surface of the wafer 8.
Furthermore, by blowing the source gas directly toward the front
surface of the wafer 8, the gas flow 12 passing from the front
surface to the rear surface of the wafer 8 through the through-hole
can be promoted, so that the growth efficiency can be enhanced.
Moreover, by providing an exhaust opening 4 at the rear side of the
susceptor 5 in the chamber 1, the gas flow passing from the front
surface to the rear surface of the wafer 8 through the through-hole
portion 7 can also be promoted, resulting in that the epitaxial
growth efficiency can be improved.
In the above, although the single wafer type vapor-phase growth
apparatus has been described, the type of the apparatus to which
the present invention is applicable includes any prior art types
including a vertical-type vapor-phase growth apparatus or a
barrel-type vapor-phase growth apparatus. With any one of these
types of growth apparatus, according to the present invention, the
reacting source gas can flow in parallel to the wafer surface being
placed in the susceptor.
The through-hole portion of the susceptor in this invention can be
various types including an arc-shaped groove-type through-hole
portion as mentioned previously, an ovalshaped through-hole
portion, or a plurality of small size of holes. Moreover, with the
single wafer type of vapor-phase growth apparatus supporting wafers
at the central portion of the susceptor, if through-holes as many
as possible can be provided, the exhausting efficiency of the boron
species from the rear surface of the wafer could be enhanced in
such a way that said many through-holes are designed and fabricated
with relatively large connecting area left, so that the area can be
strong enough to withstand the weight of the outer peripheral
portion area by the wafer pocket. Similarly, with any other
susceptor types than the single wafer type, it is recommended to
provide through-holes as many as possible if there is an enough
connecting portion left to withstand the structural strength under
considering the wafer weight. Furthermore, it is preferable to
define the diameter (or width) of the through-hole along the wafer
direction to be, at most, equal to the wafer's outer periphery
under taking the heating effect into account.
EMBODIMENTS
Using the horizontal single wafer type vapor-phase growth apparatus
with a lamp-heating method as seen in FIG. 1, an epitaxial film
with the film thickness of about 10 pm was formed at a reaction
temperature of 1,150.degree. C. onto the P++ type (100) plane
silicon semiconductor base plate (with 200 mm diameter) having the
specific resistance of 5 m.OMEGA.cm using SiHCl.sub.3 diluted with
hydrogen as the silicon supplying source gas. Two tests were
conducted; one was with susceptor having the through-hole of the
present invention and the other was with the conventional type of
susceptor without any through-holes as seen in FIG. 3.
As seen in FIGS. 2a and 2b, the suscpetor according to the present
invention has an arcshaped groove-type through-hole portion 7 at
the most outer peripheral portion of the wafer pocket 6. In FIG.
2a, four locations are installed with the through-hole portions 7
leaving the connecting area of 75 mm on its peripheral portion. On
the other hand, in FIG. 2b, four locations are provided with
through-hole portions 7 leaving 5 mm connecting area on its
peripheral portion. The length fractions of said each through-hole
portion per the total peripheral length was approximately 50% and
90%, respectively.
The raise in the dopant concentration of the outer peripheral
portion of the grown epitaxial film was listed in Table 1 and
presented in FIG. 4. By comparing with the conventional type as
seen in FIG. 3, it was found that the longer the through-hole
portion in both FIG. 2a and FIG. 2b, the lesser the dopant
concentration increase. Table I. Comparison of dopant concentration
at center and 3 mm from the edge for conventional type susceptor
and the susceptor of the present invention.
TABLE-US-00001 TABLE I 3 mm from center location the edge increment
(.times. 10.sup.16 atoms/ (.times. 10.sup.16 atoms/ (.times.
10.sup.15 atoms/ susceptor cm.sup.3) cm.sup.3) cm.sup.3)
conventional type 1.00 1.20 2.0 (FIG. 3) Example 1 1.00 1.10 1.0
(FIG. 2a) Example 2 1.00 1.05 0.5 (FIG. 2b)
While the invention has been explained with reference to the
structure disclosed herein, it is not confined to the details as
set forth, and this application is intended to cover modifications
and changes as may come within the scope of the following
claims.
* * * * *