U.S. patent number 3,868,924 [Application Number 05/295,173] was granted by the patent office on 1975-03-04 for apparatus for indiffusing dopants into semiconductor material.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Reimer Emeis, Wolfgang Keller, Arno Kersting, Konrad Reuschel.
United States Patent |
3,868,924 |
Reuschel , et al. |
March 4, 1975 |
Apparatus for indiffusing dopants into semiconductor material
Abstract
Apparatus for indiffusing dopant into a semiconductor material.
The apparatus comprises a heatable tube of the same semiconductor
material, the wall of which is from 0.5 to 20 mm thick and is
gas-tight under reaction conditions. Heating means include an
induction coil spaced from the heatable tube and a relatively
narrow graphite ring fixed about the tube to accelerate such
heating.
Inventors: |
Reuschel; Konrad (Vaterstetten,
DT), Keller; Wolfgang (Pretzfeld, DT),
Kersting; Arno (Erlangen, DT), Emeis; Reimer
(Ebermannstadt, DT) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin/Munich, DT)
|
Family
ID: |
27182016 |
Appl.
No.: |
05/295,173 |
Filed: |
October 5, 1972 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
50087 |
Jun 26, 1970 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Jun 30, 1969 [DT] |
|
|
1933128 |
|
Current U.S.
Class: |
118/715; 118/900;
219/638 |
Current CPC
Class: |
C30B
31/12 (20130101); C30B 31/10 (20130101); C23C
16/44 (20130101); Y10S 118/90 (20130101) |
Current International
Class: |
C30B
31/10 (20060101); C23C 16/44 (20060101); C30B
31/12 (20060101); C30B 31/00 (20060101); C23c
013/08 () |
Field of
Search: |
;118/48-49.5
;117/106-107.2 ;219/1 ;13/26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kaplan; Morris
Attorney, Agent or Firm: Lerner; Herbert L.
Parent Case Text
A known apparatus for indiffusing dopants into a semiconductor
material comprises a sealable graphite tube wherein both wafers of
the semiconductor material to be coated, and the dopant substance
are accommodated. To effect diffusion, the graphite tube is
connected to voltage and heated to diffusion temperature. The
heated graphite tube is surrounded by a quartz tube, through which
an inert gas is passed. This inert gas cools the quartz tube and
thus prevents impurities in the atmosphere from contacting the
semiconductor material to be coated.
The construction of this apparatus is relatively expensive,
however. Moreover, the semiconductor material must not come into
contact with the graphite tube since, at the diffusion temperatures
the carbon reacts undesirably with the semiconductor material.
Hence, the graphite tube is provided with special holders, which
prevent the semiconductor wafers and the graphite tube from
contacting each other.
It is also known to diffuse dopants into a semiconductor material
by utilization of quartz tubes or quartz ampules which are heated
in a diffusion furnace. The use of quartz tubes or ampules entails
similarly, the problem of preventing the semiconductor wafers from
contacting the quartz. To this end, a support disc is usually
provided between 10 to 20 semiconductor wafers in such a quartz
tube. The semiconductor wafers are so pressed in between the
support disc that they do not contact the quartz tube at any point
along its circumference. The use of a plurality of such support
discs naturally results in less semiconductor wafers being doped
during one operating process. The use of quartz tubes also has the
disadvantage that the diffusion temperature is limited to
approximately 1,200.degree. C. since at this temperature, quartz
softens. The supporting discs prevent the quartz tube from
compressing the wafers to be diffused and from damaging them when
the quartz tube, following diffusion, is removed. The diffusion
speed is relatively low at 1,200.degree. C. The use of quartz
tubes, moreover, demands special diffusion furnaces, since neither
direct heating nor induction heating is applicable.
It had also been suggested to provide a heatable tube of the same
semiconductor material, instead of a quartz or graphite tube, for
diffusion to take place. This type of tube can withstand higher
temperatures than a tube of quartz or graphite for example, thus
allowing the diffusion process to be accelerated. Furthermore, the
material to be coated may come into contact with the tubular wall
without producing adverse results. The semiconductor tube of the
prior art, is installed into a vacuum chamber, wherein the tube is
heated to effect diffusion.
Our invention is to devise an arrangement of the aforedescribed
type, which makes such a vacuum chamber superfluous, thus
simplifying the apparatus. Our invention starts with apparatus for
the indiffusion of dopants into a semiconductor material provided
with a heatable tube consisting of the same semiconductor material.
The invention is characterized by the fact that the wall of the
tube is 0.5 to 20 mm thick and therefore virtually gas-tight under
the indiffusion conditions. The tube is preferably a bored out rod
of a crystalline semiconductor material. It may also consist,
however, of semiconductor material precipitated through thermal
dissociation of a gaseous compound of the semiconductor material,
on a heated carrier body, with the carrier body being removed
following precipitation of the semiconductor material.
Preferably, the tube itself constitutes the heating body. For this
purpose, its ends may be provided with electrodes or they may be
enclosed by an induction coil. To facilitate the heating up of the
tube, during induction heating, a ring of material with good
conductance properties may be placed upon the tube. The tube may be
sealed on both sides for carrying out the diffusion process. The
dopant and the semiconductor material are placed into the interior
of the tube, prior to the sealing thereof, However, the tube may
also be open on both sides, and the dopant together with an inert
carrier gas, traversing the tube.
Claims
We claim:
1. Apparatus for indiffusing dopants into a semiconductor material
which comprises a heatable tube of the same semiconductor material
in which the semiconductor material is accommodated and in which
the doping substance is found, the wall of the tube is from 0.5 to
20 mm thick, is virtually gas-tight under diffusion conditions, a
relatively narrow high conductivity ring is on said heatable tube,
and an induction coil surrounds the circumference of said heatable
tube.
2. The apparatus of claim 1, wherein the tube is of a semiconductor
material selected from silicon, germanium, silicon carbide,
tungsten carbide, titanium carbide, indium phosphide, gallium
arsenide and boron nitride.
3. The apparatus of claim 2, wherein each end of said tube is
covered with a lid of the same semiconductor material as said
tube.
4. The apparatus of claim 2 including stopper closing each end of
said tube, each of said stoppers, being formed with an opening, the
opening in one of said stoppers serving for the introduction of
doping substance.
Description
The invention further illustrated by the drawing, in which:
FIG. 1 shows a longitudinal section through a first embodiment of
the invention; and
FIG. 2 shows a longitudinal section through another embodiment of
the invention.
The arrangement of FIG. 1 has, primarily, a tube 1 of a crystalline
semiconductor material, for example silicon which may have a wall
thickness of about 0.5 to 20 mm. A ground section 2 is provided at
its left end, of the tube 1 with ground stopper 3, e.g., of quartz
fitted thereinto. The stopper 3 has an opening 4 to the interior 5
of the tube 1. The right side of the tube 1 has a ground section 7
with a stopper 6 hermetically fitted thereinto. The stopper 6 has
an opening 8, which connects to the interior 5 of the tube. The
interior 5 of the tube 1 contains semiconductor wafers 11, e.g., of
silicon, which are held in their position by two support discs 9
and 10. The support discs are preferably of the same semiconductor
material as discs 11, but may be of another material such as
ceramic. The tube 1 is provided in the vicinity of its ends, with
two annular electrodes 12 and 13, which have leads 14 or 15
connected to a voltage source (not shown in detail).
The diffusion process is effected by first of all arranging the
semiconductor wafers 11 between support discs 9 and 10, in the
interior of the tube 1. Thereafter, stoppers 3 and 6 are
gas-tightly placed in the tube and the nipples 4 or 8 of stoppers 3
and 6 respectively are connected to the dopant source. The other
nipple serves as the waste outlet. The doping substance is
preferably carried by an inert gas, e.g., argon, through the
interior of the tube. If n-doping is desired, a preferred substance
is phosphorus in the form of P.sub.2 O.sub.5, PCl.sub.3 or
(PNCl.sub.2).sub.3. PH.sub.3 is also a suitable dopant. The carrier
gas may be a noble gas such as argon or helium or another inert
gas.
To obtain required diffusion temperature, a voltage source is
applied to the tube 1 via both electrodes 12 and 13 and both leads
14 and 15. The voltage is such that the current required for
heating-up tube 1 flows. In addition to being dependent upon the
dimensions of the tube, the voltage also depends on the
conductivity of the semiconductor material.
If a highly-doped semiconductor material, which is relatively easy
to produce, is used for the tube, the voltage required for starting
the heating-up process, can be relatively low. When a certain
heating-up temperature is attained, the conductivity of the tube
then becomes independent of the doping of the semiconductor
material and is essentially determined by the dimensions of the
tube.
The tube is preferably of the same semiconductor material, as
wafers 11. For example, when the wafers 11 comprise silicon, a tube
of crystalline silicon is employed. Such a tube can be created by
drilling out a rod of crystalline silicon. The tube may also
comprise silicon which is precipitated through thermal dissociation
of a gaseous compound of the silicon, on a heated carrier body,
with the carrier body being removed following the precipitation of
the silicon. Contrary to layers of sintered silicon, this
precipitated layer of crystalline silicon, is highly
gas-impermeable, at an appropriate wall thickness. Thus, for
example, in a tube having a wall thickness of 2 mm, a tubular
length of 150 mm and an inner diameter of 20 mm, a leakage rate of
only 3.sup.. 10.sup.-.sup.5 Torr liter/s, was established.
Satisfactory results were obtained even at a wall thickness of
about 0.5 mm. The upper limit is about 20 mm since no further
improvements can be obtained above this limit.
The use of a silicon tube has the further advantage that it is
heatable to much higher temperatures than quartz, without the
resulting loss of its mechanical stability and its gas
impermeability, as in the case of the former. In practice this
means that the diffusion process may be fundamentally accelerated
compared to a diffusion in a quartz tube or a quartz ampule. Since
the semiconductor wafers 1, in this instance the silicon wafers, do
not enter into a chemical reaction with the silicon of the tube 1,
the latter may be seated directly on the wall of the tube 1. It is
sufficient, therefore, to provide only two support discs, as
holders for the wafers.
FIG. 2 shows another embodiment according to the invention. This
arrangement is essentially a tube 18, consisting of an homogenous,
crystalline semiconductor material, for example silicon. The tube
18 is gas-tightly sealed with two lids 19 and 20, which consist of
the same semiconductor material. The tube 18 is surrounded by
induction coil 21. A ring 22 of a material with good conductance
properties, such as graphite, is seated upon the tube 18. The
interior of the tube 18 is provided with two support discs 23 and
24, with semiconductor wafers 25, for example of silicon arranged
therebetween. A boat 26 holding the dopant is in the interior of
the tube. This boat consists preferably of the same material as the
tube 18.
Firstly, the lid 20 is placed upon the tube and welded gas-tightly
to the tube 18, in a vacuum or protective gas, with the aid of
high-frequency energy. Thereafter, the boat 26, the support discs
23 and 24 and the semiconductor wafers 25, are placed into the tube
interior. Finally, lid 19 is placed upon the tube and is welded
gas-tightly with the tube 18 in a vacuum or in protective gas with
the aid of high-frequency energy. Thereafter, a high-frequency
voltage is applied to the induction coil 21. This high-frequency
voltage results in a current in the graphite ring 22, which heats
the graphite ring 22 and thereby also the left part of the tube 18.
The temperature increase reduces the specific resistance in that
part of the tube 18 so that the current necessary for heating up
the tube, can now flow in said part. The heating zone, starting
from the zone of the tube adjacent to the graphite ring, expands
across the entire length of the tube. The temperature of the tube
is determined thereby, by the high-frequency current.
The same advantage as for embodiment according to FIG. 1 therefore
applies for the embodiment according to FIG. 2. Here too, a
considerably higher diffusion temperature and thus a higher
diffusion speed can be obtained than for example, in a quartz
ampule. The semiconductor wafers 25, for example of silicon, may be
seated without difficulty on the wall of the tube 18 when the tube
also consists of silicon, for instance. No chemical reaction occurs
then between the silicon wafers and the tubular wall.
Embodiments other than those shown in FIGS. 1 and 2 are feasible.
It is possible, for example, to use the resistance heat shown in
FIG. 1 in a completely closed tube according to FIG. 2. Conversely,
an open tube of a compound of the dopant, passed by a carrier gas,
according to FIG. 1, may also be heated by an induction heat,
according to FIG. 2. The invention is not limited to a device for
the diffusion of wafers comprising silicon, with tubes made of
silicon. It is also possible to use tubes of for example, silicon
carbide, tungsten carbide, titanium carbide, indium phosphide,
gallium arsenide, boron nitride of germanium.
* * * * *