Note: Descriptions are shown in the official language in which they were submitted.
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1~32S9
PHN 9578 1 1~19~0
Method of cleaning a reactor.
The invention relates to a method of cleaning
a reactor after a-t least one layer has been provided
therein from a gaseous phase on substrates and the
substrates have been removed from the reactor.
Methods of depositing layers from a gaseous phase
on substrates are used, for example in semiconductor -tech-
: nology, to obtain, for example, insulating, masking or
passivating layers consisting, for example, of silicon
nitride or silicon dioxide. Such layers may be deposited
from a gaseous phase in metal or quartz reactors, for
example, under reduced pressure and if desired while
using a gas plasma.
In practice it is difficult to avoid depositing
the material of which the layers consist on the reactor
wall and, either when removing the substrates from the
reactor or when placing a new batch of substrates in the
reactor, particles of the deposit from the reactor wall
fall on to the substrates, which gives rise to irregular
deposits and other undesired results.
One method of cleaning reactors consists in
rinsing the reactor with a solution which removes the
deposit. Such a treatment is time-consuming and often
requires the reac-tor to be dismantled.
It has also been tried to clean reactors using
a tetrafluoromethane plasma. This process also requires
much time and does not al1~ays give a clean reac-tor.
The object of the inven-tion is to provide a
simpler, less time-consuming method of cleaning these
reactors.
The invention is inter alia based on the recog-
nition of the fact that in certain circumstances cleaning
of reactors from a gaseous phase can still give particu-
larly good results.
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1143Z59
PHN 9578 2 1.8.1980
.
According to the invention, the method
;~ mentioned in the opening paragraph is therefore
characterized in that the cleaning is carried out with a
dry hydrogenfluoride-containing ga~seous phase.
It has been found that reactors can be cleaned
rapidly and completely by means of the method according to
the inventiQn. Further advantages of dry h ydrogen
fluoride are that it is not corrosive and yields volatile
reaction products.
It is not objection for the method according to
the invention if the material to be removed during the
cleaning has previously been deposited in the presence of
a plasma.
For cleaning, the pressure in the reactor is
preferably reduced and the dry hydrogen fluoride is then
introduced into the reactor. This embodiment of the method
according to the invention has proved particularly con-
venient in practice.
Depending, for example, on the thickness of the
layer to be removed from the reactor wall, the reduction
of the pressure and the supply of dry hydrogen fluoride
is repeated until the reactor wall is clean.
It is an advantage to monitor the pressure du-
ring the performance of the method in the reactor, since
when the pressure becomes constant, either the hydrogen
fluoride content of gaseous phase has become exhausted,
or the cleaning process has been completed.
Particularly good results are obtained when
silicon nitride or silicon dioxide-containing layers, for
example deposited in a plasma, have to be removed. The
temperature of the wall of the reactor -then is at least
160C.
An embodiment of the invention will now be
described with reference ~o the following E~ample.
Example
A cylindrical reactor made o~ aluminium or of
stainless steel, having a diameter of approximately 0.75 m
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11~3Z59
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PHN 9578 3 1.8.1980
and a height of approximately 0.10 m is used for thedeposition, by means of a plasma from the gaseous phase~
of a silicon nitride layer on each of a number of
substrates used for the manufacture of semiconductor de-
vices.
A gaseous phase consisting of a mixture of
silane and ammonia is passed through the reactor over
juxtaposed substrates in a conventional manner, the
temperature inside the reactor being 300C. A 1/um thick
layer of silicon nitride is formed on each substrate, a
l/um thick silicon nitride layer is also deposited on the
wall of the reactor.
~ fter removing the coated substrates from the
reactor, the silicon nitride layer is removed from the
reactor wall by means of a gaseous phase containing dry
hydrogen fluoride.
The pressure in the reactor is reduced to
approximately 1500 Pa and dry hydrogen fluoride is then
introduced into the reactor until a pressure of approxi-
mately 2500 Pa has been reached. The reactor wall is heated
to a temperature of 200 to 300C by means of a resistance
furnace surrounding the reactor, and a clean reactor is
obtained in approximately 3 minutes.
The termination of ~he etching process is indica-
ted by the pressure inside the reactor becoming constant at
a value of approximately 1500 Pa.
In this case dry hydrogen fluoride need only be
supplied to the reactor once.
Similar results are obtained in the case of
layers other than silicon nitride for example, those
containing silicon dioxide or several substances.
The invention is no-t restricted to the example
described. Many variations are possible to those skilled
in the art without departing from the scope of this inven-
tion.
For example, instead of a metal reactor a quartz
reactor may be used.
~143Z59
PHN 9578 4 1.8.1980
In a~dition to semiconductor devices, other
devices, for example, integrated magnetic heads for
writing and reading information, can be manufac-tured.
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