Coating apparatus – Control means responsive to a randomly occurring sensed... – Temperature responsive
Reexamination Certificate
2000-01-18
2001-06-05
Lund, Jeffrie R. (Department: 1734)
Coating apparatus
Control means responsive to a randomly occurring sensed...
Temperature responsive
C118S715000, C118S724000, C118S725000, C118S712000, C118S713000
Reexamination Certificate
active
06241822
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a vertical heat treatment apparatus for forming an oxide film on a surface of each semiconductor wafer of a batch of the semiconductor wafers, and, more particularly, to such vertical heat treatment apparatus in which thickness of the oxide films formed on the plurality of semiconductor wafers can be precisely detected.
BACKGROUND OF THE INVENTION
Conventionally, as a heat treatment apparatus used in a manufacturing process of a semiconductor device, a lateral or horizontal heat treatment apparatus is used in which a reaction tube and a heater are laterally disposed. However, recently, a vertical heat treatment apparatus are increasingly used in which the reaction tube and the heater are vertically disposed. This is because, in the vertical heat treatment apparatus, possibility of incorporation of external air into the reaction tube is reduced, uniformity of thickness and homogeneity of films formed are superior to those of the lateral type heat treatment apparatus, and the like. The heat treatment apparatus is used for forming a field oxide film for element isolation, a gate oxide film and the like of a semiconductor device, and, according to recent miniaturization and increase in an integration degree of a semiconductor device, more strict control of a thickness of an oxide film formed is required.
FIG. 6
illustrates a schematic cross section of a vertical heat treatment apparatus as a first prior art example.
The vertical heat treatment apparatus of
FIG. 6
comprises a reaction tube
102
, a gas supply tube
103
for introducing a predetermined gas into the reaction tube
102
, a heater
104
for heating inside of the reaction tube
102
, and a quartz boat
105
for loading semiconductor wafers
101
. Approximately 50 through 100 sheets of semiconductor wafers
101
are loaded on the quartz boat
105
as one set (hereafter referred to as a “batch”).
Next, an explanation will be made on a method of forming an oxide film on each of the semiconductor wafers by using the prior art vertical heat treatment apparatus mentioned above.
First, into the reaction tube
102
heated to a high temperature of 800 degrees Celsius through 1000 degrees Celsius by the heater
104
, the quartz boat
105
on which a batch of semiconductor wafers
101
are loaded is inserted. Then, a predetermined gas such as oxygen, steam, water vapor and the like is introduced into the heated reaction tube
102
from the gas supply tube
103
at a predetermined flow rate. Thereby, chemical reaction occurs at the surface of each of the semiconductor wafers
101
with the introduced gas, and a desired oxide film is formed on the surface of each of the semiconductor wafers
101
. In this case, it is necessary to confirm that each of the oxide films formed on the surface of the semiconductor wafers
101
has a desired film thickness. For this purpose, the quartz boat
105
on which the semiconductor wafers
101
are loaded is taken out from the reaction tube
102
, and the thickness of the oxide film formed on each of the semiconductor wafers
101
is measured by using a film thickness measurement apparatus not shown in the drawing.
In order to fabricate an oxide film having a predetermined film thickness on each of the semiconductor wafers
101
by using the prior art vertical heat treatment apparatus, it is necessary to perform condition determining operations in which relations of a rate of forming an oxide film on a semiconductor wafer and a formed film thickness, with respect to a heat treatment temperature of the semiconductor wafer, a heat treatment time of the semiconductor wafer and a flow rate of various gases introduced into the reaction tube
102
are previously clarified. However, in the conventional vertical heat treatment apparatus, a flow rate of a reaction gas introduced into the reaction tube
102
and a temperature inside the reaction tube
102
vary delicately depending on an individual difference of an apparatus, variation of environment of the apparatus and the like. Thus, it becomes difficult to form an oxide film having a desired film thickness on a semiconductor wafer
101
, by using the conditions such as the heat treatment time and the like determined based on the above-mentioned condition determining operations. As a result, it was difficult to stably and uniformly form oxide films each having a desired film thickness on a batch of semiconductor wafers.
If, as a result of the above-mentioned measurement of film thickness, there are semiconductor wafers having oxide films whose thickness is smaller than a predetermined film thickness, heat treatment is again performed for such semiconductor wafers until the oxide films each having a predetermined film thickness are fabricated. In case the heat treatment is performed again, process steps increase by such additional heat treatment, so that time loss and cost in the manufacturing process increase.
On the other hand, if there are semiconductor wafers having oxide films whose thickness is out of specification, for example, whose film thickness is too thick, such semiconductor wafers are discarded. In such case, there occur an increase in manufacturing cost and deterioration of manufacturing yield of a semiconductor device.
In order to solve the above-mentioned problems, there is proposed a lateral reduced pressure vapor phase growth system in Japanese patent laid-open publication No. 3-82017. In this system, a thickness of a film formed on each of semiconductor wafers disposed in a reaction tube is measured regularly, and, by using the result of the measurement, a heating temperature within the reaction tube and a flow rate of gas introduced into the reaction tube are feedback-controlled, thereby a film having a desired film thickness is formed on each of the semiconductor wafers.
An explanation will be made on the lateral reduced pressure vapor phase growth system disclosed in the above-cited Japanese publication as a second prior art apparatus.
FIG. 7
is a block diagram illustrating a structure of the lateral reduced pressure vapor phase growth apparatus including various control system, as the second prior art apparatus.
The prior art apparatus shown in
FIG. 7
comprises a reaction tube
201
, halogen lamps
202
for heating inside of the reaction tube
201
, and a quartz boat
203
for loading semiconductor wafers
204
. The reaction tube
201
comprises a gas inlet
205
and a gas outlet
206
. The prior art apparatus of
FIG. 7
also comprises a laser light emitting potion
216
which is composed of a laser source
207
, a polarizer
208
and a compensator
209
, and a laser light detecting portion
217
which is composed of an analyzer
210
and a photo-detector
211
. The laser light emitting portion
216
and the laser light detecting portion
217
are disposed outside the reaction tube
201
as a pair, and compose an ellipsometer. The prior art apparatus of
FIG. 7
further comprises, as a portion constituting a control system, a data processing portion
212
for processing an output signal from the photo-detector
211
, a central processing portion
213
, a temperature control portion
214
for controlling a heating temperature by the halogen lamps
202
, and a gas flow rate control portion
215
for controlling a flow rate of a gas introduced into the reaction tube
201
from the gas inlet
205
.
Next, an explanation will be made on a method of forming a film by using the lateral reduced pressure vapor phase growth apparatus shown in FIG.
7
. First, the reaction tube
201
is previously heated to a high temperature of 100through 1000 degrees Celsius by the halogen lamps
202
. Then, a batch of 50 through 100 sheets of semiconductor wafers
204
are loaded on the quartz boat
203
such that each of these semiconductor wafers
204
is stood vertically thereon. The quartz boat
203
thus loaded with the semiconductor wafers
204
is inserted into the reaction tube
201
.
The reaction tube
201
is vacuated from the gas outlet
206
to a pressure of approximately 0
Hayes, Soloway, Hennessey Grossman & Hage, P.C.
Lund Jeffrie R.
NEC Corporation
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