Heating – Processes of heating or heater operation – Including apparatus purging – cleaning or accretion preventing
Reexamination Certificate
2000-08-21
2001-09-04
Wilson, Gregory (Department: 3749)
Heating
Processes of heating or heater operation
Including apparatus purging, cleaning or accretion preventing
C134S022110, C034S437000
Reexamination Certificate
active
06283746
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a furnace process, and more particularly to a method for purging furnace to decrease particle pollution in baking process.
2. Description of the Prior Art
Conventional furnace process takes advantage of heat convection and heat conduction principles to make the silicon wafer to reach heat balance with circumstances around the furnace so the temperature on control wafer can be exactly controlled, and the furnace can heat a great quantity of wafers at a time. It is able to reach the objective that reduce process time and cost for batch process.
However, conventional furnace process has some defect of itself. Because the furnace wall need to be heated to reach high temperature condition for long so the impurities are easy to deposit in the furnace and to pollute the wafers so that conventional furnace process is difficult to apply in the deep sub-micro process. Therefore, the pending problem that is the residual impurities are produced during the furnace process requires to be solved. Conventional method is used to wash the furnace, but the purge material is remained during the purge process, that result in the particle problem. Hence, conventional furnace process is becoming more and more difficult to control the pollutant source when the dimension of device is shrink gradually.
Cross-sectional view of the known prior art of the furnace process is illustrated in FIG.
1
A. First of all, a wafer
110
is placed into a furnace boat
100
to perform a baking process, wherein the furnace boat
100
includes an external tube
130
having a material of quartz and an inside tube
140
having a material of silicon carbide-silicon (SIC—Si). The cap
120
makes the wafer
110
to rise into the furnace boat
100
and proceed with the baking process at the high temperature and the low pressure.
Referring to
FIG. 1B
, an oxide layer
160
of impurities is formed on the wall of the inside tube
140
during the baking process, wherein the oxide layer
160
will increase thickness of itself to follow the process. It is necessary to perform a purge step to eliminate the oxide layer
160
which form on the wall of the inside tube
140
when the thickness of the oxide layer
160
increase to be standard value which is set in the apparatus, such as 400 K Å. The purge step of above is performed by level-style washing using the water and hydrofluoric acid (HF), and using gas such as NH
2
to dry the inside tube
140
, then, the inside tube
140
which has been purged is set into furnace boat
100
. For avoiding inside tube wall
150
to be damaged by oxide layer
160
at high temperature thermo-oxide process, hence it is necessary to perform a pre-coating process so as to form a silicon nitride layer (SiN)
170
over the inside tube wall
150
of furnace
100
in advance before the furnace
100
enter into the baking process of the wafer. The pre-coating process of above performs to transport a mixing gas which consists of SiH
2
Cl
2
(DCS) and ammonia (NH
3
) into the furnace
100
at the environment of high temperature and low pressure, and it proceeds to deposit a silicon nitride layer
170
on the inside tube wall
150
by low pressure chemical vapor deposition (LPCVD), wherein the pre-coating process is operated for about 14 to 16 hours at the surroundings which is about 800° C. and 0.3 torr pressure. Wafer's baking process begins proceeding after the pre-coating process has been finished.
In according with the furnace purge process of above, it will result in follow problems. Referring to
FIG. 2A
, there are issues about remained acid after the inside tube has been cleaned, that is acid
220
will adhere to the silicon nitride coating layer
210
of the inside tube wall
200
, wherein the remained acid
220
consists of water, hydrofluoric acid (HF) and OH
−
. The remained acid
220
will etch and damage the silicon nitride coating layer
210
at about 800° C. during the pre-coating process of the inside tube is baked, as shown in FIG.
2
B. If the silicon nitride coating layer
210
is etched over depth, the silicon nitride coating layer
210
of the inside tube
200
will produce slight breakages, and it will result in the silicon substrate (such as SIC—Si) of the inside tube
200
leak out, as shown in FIG.
2
C. The hole
240
is formed when the silicon substrate of the inside tube wall
200
leak out for long, hence, the structure of the inside tube will be destroyed this issue, as shown in FIG.
2
D.
In accordance with remained acid issues in the foregoing, two causes of the polluter for forming in the furnace process have been known: one of the particles
250
of pollution in the furnace process are chips which flakes off the silicon nitride coating layer
210
during the process; another of the particles
250
of pollution in the furnace process is silicon dioxide (SiO
2
) which is formed by leaking out the silicon substrate of the inside tube at high temperature. Moreover, when a pre-coating process is performed in the inside tube at high temperature, a silicon nitride layer having holes which contains nitrogen is due to nitrogen which is transported into the furnace remains in the hole which is formed by leakage of the silicon substrate, wherein the silicon nitride layer
270
which contains nitrogen is not the silicon nitride layer
210
of process. Hence, there are difference two silicon nitride layers to form, and in consequence the silicon nitride layer
210
of process is not able to coat completely on the inside tube wall, as shown in FIG.
2
E. Up to now there has been no effective method in the semiconductor industry to overcome issues of foregoing conventional process.
In accordance with the above description, a method for purging furnace to decrease particle polluter in baking process is therefore necessary, so as to raise the yield and quality of the follow-up process.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method is provided for purging furnace to decrease particle polluter in baking process that substantially overcomes drawbacks of above mentioned problems arised from the conventional methods.
Accordingly, it is a main object of the present invention to provide a method for purging furnace to decrease particle polluter during baking process. This present invention performs a treatment of the furnace for eliminating remained acid to avoid destroying the inside tube during furnace process. Hence, particle issue of the foregoing can be solved by this method.
Another object of the present invention is to provide a method for avoiding adhering remained acid on the inside tube when the furnace is purged. This present invention takes advantage of improved method for washing furnace to decrease the remained acid that has adhered to inside tube. Hence, this present invention can effectively raise quality of the process.
Still another object of the present invention is to provide a method for avoiding adhering remained acid on the inside tube when the furnace is purged. This present invention performs a treatment with low temperature and low pressure to eliminate remained acid that adhered to inside tube before the pre-coating of baking process so 2-in-1 processes which have pre-coating and baking process with high temperature and low pressure can be substituted for this method.
In accordance with the present invention, a new method for purging furnace to decrease particle pollution in baking process is disclosed. First of all, a pre-purged inside tube whose wall has oxide layer of impurities is provided, wherein the oxide layer is about 400K Å. The inside tube is washed with pure water by level-style washing. Then, taking the inside tube out and soaking it with hydrofluoric acid (HF). Next, the inside tube is taken out from hydrofluoric acid (HF) and it is soaked with pure water. It is dried with ammonia gas (NH
3
) after the inside tube is taken out from pure water. The inside tube is then washed with pure water by vertical-style
Chung Colin
Han Bruce
Hwang Paul
Wu Eddy
United Microelectronics Corp.
Wilson Gregory
LandOfFree
Method for purging furnace to decrease particle pollution in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for purging furnace to decrease particle pollution in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for purging furnace to decrease particle pollution in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2486410