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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to apparatus for the treatment of semiconductors
and, more particularly, to apparatus for the treatment of semiconductors
in which the undesired deposits formed within the reaction chamber during
the vapor phase reaction of semiconductor substrates can be removed
easily.
One conventional arrangement for vapor phase silicon, silicon dioxide,
silicon nitride, or the like on semiconductor substrates is composed of a
reaction chamber, means for heating the semiconductor substrates, and
means for introducing a reaction gas into the reaction chamber. With this
arrangement, the reaction material is deposited on the semiconductor
substrates through the reduction or thermal decomposition of the reaction
gas. However, the reaction material is not only deposited on the
semiconductor substrates, but also on the heating table, the inner walls
of the reaction chamber, and the like. The deposit formed on the heating
table must be removed prior to the next cycle of vapor phase, because the
semiconductor substrates will not be heated evenly unless the surface
bearing them is flat. Moreover, the reaction material deposited on the
inner walls of the reaction chamber may fall on the substrates during the
reaction so as to cause abnormal growth, or may cloud the inspection
window (namely, the window for looking into the reaction chamber) so as to
interfere with visual inspection. In order to remove these undesired
deposits, a method is available which involves heating the reaction
chamber to a high temperature of about 1,000.degree. C. and then
introducing a corrosive gas such as HCl into the reaction chamber.
However, since this method requires high temperatures of the order of
1,000.degree. C., it is impossible to remove the deposits from the parts
which cannot be heated to such high temperatures. Moreover, this method is
not applicable to low temperature vapor phase arrangements. Furthermore,
the parts which should not be exposed to HCl gas need be cleared of the
deposits either by disassembling the apparatus to pickle its components or
by using mechanical means to scrape off the deposit.
SUMMARY OF THE INVENTION
It is an object of this invention to provide novel apparatus for the
treatment of semiconductors in which the undesired deposits formed within
the reaction chamber during the vapor phase reaction of semiconductor
substrates can be easily removed without any trouble.
It is another object of this invention to provide novel apparatus for the
treatment of semiconductors which has improved durability.
It is still another object of this invention to provide novel apparatus for
the treatment of semiconductors in which the treatment reaction may be
effected at normal or elevated pressure.
In accordance with this invention, there is provided apparatus for the
treatment of semiconductors comprising a reaction chamber for effecting
the vapor phase reaction of semiconductor substrates, means for
introducing a vapor phase reaction gas into said reaction chamber, a
plasma generating section, means for introducing into said plasma
generating section a gas suitable for the plasma treatment of the inside
of said reaction chamber, microwave power applying means for activating
the gas contained in said plasma generating section, conduit means for
introducing the activated gas into said reaction chamber, and evacuation
means.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagrammatic representation of an apparatus for the treatment
of semiconductors in accordance with one embodiment of this invention;
FIG. 2a is a perspective view, on an enlarged scale, of the plasma
generating section of the apparatus of FIG. 1;
FIG. 2b is a sectional view of the plasma generating section of FIG. 2a;
and
FIGS. 3 and 4 are diagrammatic representations of apparatus for the
treatment of semiconductors in accordance with other embodiments of this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The apparatus for the treatment of semiconductors provided by this
invention is based on the combination of an arrangement for the vapor
phase reaction of semiconductors and an arrangement for plasma treatment,
whereby the deposits formed within the reaction chamber of the former
arrangement can be removed by plasma etching.
One preferred embodiment of this invention is described below by reference
to the accompanying drawings.
Referring first to FIG. 1, there is shown a reaction chamber 1 made of
quartz, for example, in which a heating table 1a having semiconductor
substrates 2 placed thereon is contained. In addition, reaction chamber 1
is connected to a vacuum device 3 for maintaining the inside of reaction
chamber 1 at reduced pressure. Preferably, vacuum device 3 is a rotary
type vacuum pump having a sufficient rate of evacuation and a sufficient
degree of vacuum to maintain the inside of reaction chamber 1 at a high
vacuum of, for example, 0.5 to 1.0 Torr. This vacuum device is used for
the purposes of chemical vapor deposition (CVD) and plasma etching, both
of which are carried out at reduced pressure. Further, reaction chamber 1
is also connected to a source 4 of vapor phase reaction gas which serves
to effect the vapor phase reaction of semiconductor substrates 2 and to a
source 5 of etching gas which serves to remove the undesired deposits
formed within reaction chamber 1 during the vapor phase reaction. The
source 4 of vapor phase reaction gas is composed of, for example, a source
4a of silane (SiH.sub.4) gas and a source 4b of oxygen (O.sub.2) gas, each
of which is provided with a flowmeter. The vapor phase reaction gas fed
from source 4 is introduced into reaction chamber 1 by way of a cut-off
valve 6 and a conduit 7. The source 5 of etching gas is composed of, for
example, a source 5a of Freon (CF.sub.4) gas and a source 5b of oxygen
gas, each of which is provided with a flowmeter. The etching gas
consisting of a mixture Freon and oxygen is led through a conduit 8 to a
plasma generating section 9, where it is activated and then introduced
into reaction chamber 1 by way of a cut-off valve 10 and conduit 7. To
plasma generating section 9, the microwave power originating from a
microwave oscillator 11 is applied by way of a waveguide 12. This
waveguide is provided with a microwave matching device 12a. Generally,
plasma generating section 9 is formed by using a quartz tube extending
through the end portion of waveguide 12. In such a configuration, however,
the quartz tube will be excessively worn out due to plasma discharge and
need be replaced whenever the number of treatment cycles reaches 300 or
so. In order to overcome this disadvantage, a barrier 12b composed of a
material, for example, a non-conductive material such as Teflon, glass,
plastics or the like, which is permeable to microwaves and impermeable to
gases, may be positioned in the end portion of waveguide 12, as shown more
fully in FIGS. 2a and 2b. In this case, plasma generating section 9 may be
composed of a conductive material such as stainless steel, aluminum,
copper or the like. Preferably, barrier 12b is composed of a material
having good resistance to etching or at least the surface thereof which
may come into contact with the etching gas is coated with such a material.
For example, a quartz plate having a Teflon coating formed thereon may be
used as barrier 12b. Preferably, at least the inner walls of plasma
generating section 9 is also resistant to etching. If plasma generating
section 9 is constructed in this manner, the apparatus will have improved
durability and will enable one to carry out the etching treatment thereof
with safety.
In the operation of the above-described apparatus for the treatment of
semiconductors in accordance with this invention, semiconductor substrates
2 are placed on the heating table 1a positioned within reaction chamber 1
and the vapor phase reaction gas, such as a mixture of silane and oxygen,
fed from source 4 is introduced into reaction chamber 1 with cut-off valve
6 in the open position and cut-off valve 10 in the closed position,
whereby the heated semiconductor substrates 2 are subjected to vapor phase
reaction. On this occasion, silicon, silicon nitride (Si.sub.3 N.sub.4),
silicon dioxide (SiO.sub.2) and the like are undesirably deposited on
heating table 1a and the side walls of reaction chamber 1. After the vapor
phase reaction of semiconductor substrates 2 has been completed, the
inside of reaction chamber 1 is subjected to plasma etching treatment for
the purpose of removing the undesired deposits. With cut-off valve 6 in
the closed position and cut-off valve 10 in the open position, an etching
gas, such as a mixture of Freon and oxygen, is led from source 5 to plasma
generating section 9, where it is activated by means of a microwave and
then introduced into reaction chamber 1. The etching species produced in
plasma generating section 9 have a very long life and accordingly enable
one to remove easily the deposits formed on heating table 1a and the side
walls of reaction chamber 1.
In the above-described apparatus for the treatment of semiconductors,
vacuum device 3 is positioned on the outlet side of reaction chamber 1, as
shown in FIG. 1. That is, the treatment reaction is effected at reduced
pressure. As shown in FIG. 3, however, vacuum device 3 may be positioned
on the inlet side of reaction chamber 1. In this case, the treatment
reaction is effected at normal or elevated pressure. While etching
treatment was possible only at reduced pressure according to the
conventional plasma etching process, this invention permits etching
treatment to be carried out at normal pressure simply by using a mixture
of Freon and oxygen as the etching gas and a microwave as the power
applying means. Thus, the apparatus for the treatment of semiconductors
having vacuum device 3 positioned on the inlet side of reaction chamber 1
is suitable for the purpose of subjecting semiconductor substrates to CVD
at normal pressure. In addition, it is particularly suitable for the
purpose of treating samples whose properties may be changed at reduced
pressure. Furthermore, in cases where CVD and etching treatment are
carried out at normal pressure, a reaction chamber 21 which is open to the
atmosphere as shown in FIG. 4 may be used instead of the reaction chamber
which is sealed off as shown in FIG. 3.
A single example is given below in which an apparatus of this invention was
used to carry out the treatment of semiconductors.
EXAMPLE
At first, sample wafers 2 were subjected to chemical vapor deposition by
using an apparatus as shown in FIG. 1. More specifically, with cut-off
valve 10 in the closed position and cut-off valve 6 in the open position,
a mixture of silane and oxygen was let flow through reaction chamber 1
containing simple wafers 2 placed on heating table 1a, whereby a SiO.sub.2
film was formed on the surfaces of sample wafers 2 to a thickness of about
1.mu.. Heating table 1a was kept at a temperature of 500.degree. C. On
this occasion, an SiO.sub.2 film was not only formed on the surfaces of
sample wafers 2, but also on the exposed portion of heating table 2, the
side walls of reaction chamber 1, and the like.
After sample wafers 2 were withdrawn from reaction chamber 1, cut-off valve
6 was closed and cut-off valve 10 was opened. Then, rotary pump 3 was
operated to evacuate reaction chamber 1. Thereafter, a mixture of Freon 14
and oxygen was introduced into reaction chamber 1. The partial pressures
of Freon 14 and oxygen were 0.3 Torr and 0.15 Torr, respectively.
Subsequently, microwave oscillator 11 was actuated to apply microwave
power through waveguide 12 to plasma generating section 9 and thereby
start a plasma discharge within plasma generating section 9. The etching
gas activated by means of the plasma discharge was led through conduit 7
to reaction chamber 1, whereby the SiO.sub.2 film deposited on heating
table 1a, the side walls of reaction chamber 1, and the like was etched
away. When the microwave power was 1KW, the SiO.sub.2 film formed within
reaction chamber 1 was removed in about 10 minutes.
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