Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of...
Reexamination Certificate
1999-12-03
2001-09-11
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
C118S715000, C118S719000, C118S724000, C118S725000, C414S935000, C414S937000, C414S939000
Reexamination Certificate
active
06287984
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing a semiconductor device, and particularly to an apparatus and a method for accurately forming a silicon oxide film on the surface of a semiconductor substrate.
2. Description of the Background Art
A silicon oxide film formed by oxidizing a polysilicon film (hereinafter, referred to as “polyoxide film”) has been used, for example, as an insulating film between a floating electrode and a control electrode of a flash memory. A known method of forming a polyoxide film includes the steps of disposing a polysilicon film in a vertical batch type oxidizing furnace and supplying an oxidizing gas to the surroundings of the polysilicon film, to oxide the surface of the polysilicon film.
FIG. 3
is a configuration diagram of a related art vertical batch type oxidizing furnace for forming a polyoxide film. The related art vertical batch type oxidizing furnace includes gas flow rate control units
10
,
12
and
14
for controlling flow rates of nitrogen gas, oxygen gas and hydrogen gas, respectively. The gas flow rate control units
10
,
12
and
14
are communicated to an external burning pipe
16
. A burning heater
18
for burning hydrogen gas and oxygen gas to generate steam is provided around the burning pipe
16
.
A reaction chamber
22
is connected to the external burning pipe
16
via a gas inlet pipe
20
. A heater
24
for heating the gas inlet pipe
20
and the reaction chamber
22
is provided around the gas inlet pipe
20
and the reaction chamber
22
. An exhaust passage
26
is provided in the reaction chamber
22
. A shutter plate
28
for sealing the inner space of the reaction chamber
22
is provided at the bottom portion of the reaction chamber
22
.
The related art vertical batch type oxidizing furnace further includes a wafer boat
32
for holding a plurality of semiconductor wafers
30
. The wafer boat
32
is fixed on a boat lifter
36
by means of a boat holder
34
. The boat lifter
36
is adapted to carry the wafer boat
32
in the reaction chamber
22
in a condition where the shutter plate
28
is opened, and to seal the inner space of the reaction chamber
22
from the external atmosphere, that is, the atmosphere of a clean room.
A related art method for forming a polyoxide film will be described below with reference to FIG.
4
.
FIG. 4
is a flow chart showing sequential processing steps carried out for forming a polyoxide film using the related art vertical batch type oxidizing furnace.
In accordance with the related art method, at Step S
100
, the semiconductor wafers
30
held on the wafer boat
32
are inserted in the reaction chamber
22
by the boat lifter
36
. At this time, the reaction chamber
22
has been already heated at about 700° C. by the heater
24
. In the insertion stage of the semiconductor wafers
30
, a mixed gas of oxygen and nitrogen or an oxygen gas is supplied in the reaction chamber
22
while the flow rate of the gas is controlled at a specific value by the gas flow rate control units
10
and
12
or the single gas flow rate control
12
.
By supplying the oxygen containing gas in the reaction chamber
22
in the insertion stage of the semiconductor wafers
30
as described above, organic matters adhering on the surfaces of the wafers can be removed by oxidation. Accordingly, with the above-described insertion treatment, it is possible to enhance uniformity of the thickness of the polyoxide film over the entire surface of each wafer.
After insertion of the semiconductor wafers
30
in the reaction chamber
22
, at Step S
102
, the state in which the above gas is supplied in the reaction chamber
22
is kept for a specific period of time for stabilizing the wafer temperature.
The process goes on to Step S
104
, at which the reaction chamber
22
is heated to an oxidizing temperature, specifically, about 900° C. by the heater
24
.
After the temperature of the reaction chamber
22
reaches the oxidizing temperature, at Step S
106
, an oxidizing gas is supplied in the reaction chamber
22
via the gas inlet pipe
20
, to oxidize the semiconductor wafers
30
. At this moment, the flow rate of the oxidizing gas is controlled by the gas flow rate control units
10
,
12
and
14
, and also the oxidizing gas is heated by the external burning pipe
16
. The oxidizing gas may include steam gas produced by reaction of oxygen with hydrogen in the external burning pipe
16
, or oxygen gas.
After completion of the oxidizing step, at Step S
108
, the gas to be supplied in the reaction chamber
22
is changed from the oxidizing gas to nitrogen gas, so that the atmosphere in the reaction chamber
22
is substituted for the nitrogen gas.
At Step S
110
, the semiconductor wafers
30
are held in the reaction chamber
22
until the temperature of the semiconductor wafers
30
is lowered to a specific value.
After the temperature of the semiconductor wafers
30
is sufficiently lowered, at Step S
112
, the semiconductor wafers
30
on the wafer boat
32
are taken out from the reaction chamber
22
by the boat lifter
36
.
In accordance with the above-described related art method, since the surfaces of the semiconductor wafers
30
are exposed to atmospheric air in the clean room during the period in which the semiconductor wafers
30
are placed outside the reaction chamber
22
, organic matters and the like in atmospheric air may adhere on the surfaces of the semiconductor wafers
30
. As described above, the organic matters can be removed to some extent by supplying oxygen into the reaction chamber
22
in the insertion stage of the semiconductor wafers
30
.
In accordance with the related art method using the related art vertical batch type oxidizing furnace, however, the semiconductor wafers
30
are inserted in the reaction chamber
22
in the state in which the interior of the reaction chamber
22
is opened to atmospheric air in the clean room. In the insertion stage of the semiconductor wafers
30
, the concentration of oxygen gas to be supplied in the reaction chamber
22
is generally different from the concentration of oxygen in atmospheric air. As a result, according to the related art method, it is difficult to accurately control the oxygen concentration in the reaction chamber
22
, more specifically, to equalize the oxygen concentration in the reaction chamber over the entire region in the insertion stage of the semiconductor wafers
30
.
When the semiconductor wafers
30
held on the wafer boat
32
are inserted in the reaction chamber
22
, those held near the top portion of the wafer boat
32
pass through the interior of the reaction chamber
22
for a longer distance as compared with those held near the bottom portion of the wafer boat
32
. Accordingly, if there occurs a variation in oxygen concentration in the reaction chamber
22
in the insertion stage of the semiconductor wafers
30
, the oxidizing rate and the ability of removing organic matters adhering on the semiconductor wafers
30
in the insertion stage of the semiconductor wafers
30
are dependent on the positions of the semiconductor wafers
30
. Such dependence on the positions of the semiconductor wafers
30
causes deterioration of uniformity of the polyoxide film. In this way, the related art method has a problem that it is difficult to stably manufacture polyoxide films having uniform qualities over the entire surfaces of the semiconductor wafers
30
.
Also in accordance with the related art method, the semiconductor wafers
30
are heated to the oxidizing temperature in the oxygen containing atmosphere. To be more specific, since the temperature rise of the semiconductor wafers
30
is performed in a high temperature region of 700° C. or more in the oxygen containing atomosphere, a slight oxide film is formed on the surface of each semiconductor wafer
30
before the oxidizing treatment performed at the oxidizing temperature of about 900° C As a result, in accordance with the related art method, it is difficult to form an extrem
Elms Richard
Luu Pho
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
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