Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-03-29
2002-10-29
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S405000, C219S411000, C392S416000, C118S724000, C118S050100
Reexamination Certificate
active
06472639
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a heat treatment method and a heat treatment apparatus for substrate heating, and more particularly to a heat treatment method and a heat treatment apparatus that allow a substrate to be heated to the desired temperature at a high rate and with good uniformity.
2. Description of the Related Art
As wafers have increased in diameter due to the need to achieve higher semiconductor integration and lower manufacturing costs, it has become difficult to form films with high precision across the surfaces of all the wafers of a batch inside a conventional batch-type vertical CVD apparatus. In view of this, single or dual substrate processing CVD apparatus in which each wafer is individually treated are being mostly used at the moment. A single or dual substrate processing CVD apparatus may be a cold-wall type or a hot-wall type.
(1) Cold-Wall Type
In a cold-wall apparatus, a wafer placed in a cooled reactor furnace body is directly heated by a lamp, or the wafer is heated after being placed on a susceptor heated by a heater, a lamp. or the like, and a film is deposited by feeding a starting material gas. This type of apparatus differs from the batch type in that fluctuations among wafers can be reduced because the film can be deposited under the same heating conditions each time, but the wafers must be rotated in order to obtain a uniform film thickness distribution across the wafer surface, or various measures must be taken in order to create uniform conditions in which gas is fed above the wafers through a shower plate. Another approach is to render the wafer temperature uniform by adjusting the shape or arrangement of heating lamps, as described in Japanese Unexamined Patent Application (Kokai) 4-255214.
(2) Hot-Wall Type
In a hot-wall apparatus, on the other hand, it is possible to dispense with complicated means for creating uniformity such as those found in cold-wall CVD apparatus, and the wafer temperature can be readily rendered uniform in the manner disclosed, for example, in Japanese Unexamined Patent Application 7-94419.
FIG. 10
is a schematic cross section of such a hot-wall CVD apparatus. A reactor furnace body
3
itself is heated by resistance heater
4
disposed outside the reactor furnace body
3
, and wafers W inside the reactor furnace body
3
are heated. A wafer W supported by tweezers
8
and transported from a transfer chamber
1
into the reactor furnace body
3
through a gate valve
5
is heated at a fairly high rate in the initial period of heating because of the temperature difference (400 to 700° C.) with the hot-wall system, but because the heat-up rate is proportional to the fourth power of the temperature difference, the heat-up rate decreases as the wafer temperature approaches the temperature of the hot-wall system, and ultimately a period of 5 minutes or greater is required for preheating, as shown in FIG.
11
. By contrast, lamp heating markedly reduces the preheating time without appreciably lowering the heat-up rate due to the fact that because the filament temperature is high (2500 to 3000 K). the difference in temperature between the wafer and the filament is about 2000° C. even as the wafer approaches the desired temperature (400 to 700° C.).
As referred to herein, “preheating time” is the time elapsed between the moment a wafer W has been transferred to the reactor furnace body
3
and the moment the wafer W has reached the desired temperature and the desired uniformity has been achieved. The aforementioned hot-wall system is a system heated by a resistance heater
4
and composed of the reactor furnace body
3
itself and the atmosphere and objects inside the reactor furnace body
3
.
A distinctive feature of the aforementioned hot-wall CVD apparatus is that because the wafer W and the interior walls of the reactor furnace body
3
are in a state of thermal equilibrium in which the temperatures of the two are equal to each other, the wafer temperature can be kept constant irrespective of the film type, providing excellent temperature uniformity and temperature stability. Another distinctive feature is that an additional gas introduction port (not shown) and an additional gas exhaust port (not shown) are provided at positions facing a CVD gas introduction port
6
connected to a flange
13
and an exhaust port
7
connected to a flange
14
across the wafers W, and a highly uniform film thickness is achieved by switching these ports during film formation and reversing the direction of gas flow.
Hot-wall CVD apparatus are disadvantageous, however, in that their throughput is low because the temperature of the wafers W is close to room temperature, and considerable preheating time which is about 5 minutes or longer (see
FIG. 11
) elapses between the moment the wafers are introduced into the reactor furnace body
3
and the moment the desired temperature is reached, resulting in an extended overall treatment time (tact time), including the film forming time.
In addition, this phenomenon becomes more pronounced with lower heating temperatures (furnace body temperatures). This occurs for the following reasons. The lower the temperature (under about 500° C.) of the reactor furnace body
3
, the lower the spectral radiant intensity (radiation intensity) and the farther the shift of the blackbody radiation wavelength distribution (radiation wavelength distribution) toward longer wavelengths, as shown in
FIG. 12. A
silicon wafer, on the other hand, has a very low absorption coefficient at wavelengths longer than 1.2 &mgr;m, resulting in poor heating efficiency and minimal absorption of heat from the furnace body, as shown in FIG.
13
. At &lgr;=3 &mgr;m, for example, the absorption efficiency is 3% and 15% at a wafer temperature of 400° C. and 500° C., respectively. consequently, the heating efficiency decreases with a reduction in the temperature of the reactor furnace body
3
. This causes considerable time to be expended when wafers are heated in a hot-wall CVD apparatus.
In addition, the temperature of the furnace body itself decreases due to the introduction of cold wafers W into the reactor furnace body, and time is needed for this temperature to recover. A feed-forward control (FFC) technique and a rapid heating technique have been proposed as means aimed at addressing this problem.
(1) FFC Technique
As noted above, the hot-wall system, in addition to being disadvantageous in the sense that the wafer heat-up rate is slow, is also disadvantageous in the sense that the temperature of the system is lowered by the introduction of wafers into the system. FFC is a technique in which the second drawback is dealt with by presetting the temperature of the system somewhat higher in view of the reduction in the temperature of the reaction furnace body. According to FFC results, however, setting the system temperature (FFC set temperature) somewhat higher (in the absence of a cooling means, the temperature cannot be set high, and it is no more than several tens of degrees Centigrade) merely improves the preheating time somewhat, failing to produce a depreciable reduction, as shown in FIG.
14
.
(2) Rapid Heating Technique
As shown by the schematic cross section in
FIG. 15
, the technique envisages providing a rapid heater
9
in which the heat capacity of the heater for heating a reactor furnace body
3
is reduced to allow for rapid heating, and installing a forced air cooling mechanism (not shown) in which cooling air is forced through an excessively heated reactor furnace body
3
to allow the reactor furnace body
3
to be cooled at a high rate. According to this technique, the system temperature (FFC set temperature) during the loading of a wafer W can be set higher, making it possible to reduce the initial heating time needed to achieve the set temperature, as shown in FIG.
16
. It is still impossible, however, to reduce the control period that needs to elapse before the set temperature can be stably sustained, so the resulting effect is small despite
Kasanami Katsuhisa
Matsuyama Naoko
Nishitani Eisuke
Sasaki Shinya
Fuqua Shawntina T.
Kokusai Electric Co. Ltd.
LandOfFree
Heat treatment method and heat treatment apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat treatment method and heat treatment apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat treatment method and heat treatment apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2920625