PROCESS DESCRIPTION
P
ROCESS
M
ANUAL
4.1.2.4 Typicalities
Due to the low vapor pressure condensation may occur at any cold spot in the supply line.
Condensation leads to droplets formation, which cause MFC blockage. Heat tracing the
supply line strongly depends on the customer situation. A long distance between the bottle
cabinet and tube necessitates heating. This includes the bottle and lines supplied by the
customer, and the lines in the gas cabinet up to the MFC.
On the other hand, a small distance may not require heating and simple insulation may be
sufficient. Therefore, insulation and heating of the supply lines needs to be addressed at each
location. If it is a necessity apply an increased temperature from bottle to tube.
Due to the lower pressure downstream the MFC heating is not required from the MFC to the
tube and insulation is sufficient.
As DCS reacts with NH
3
the residual product is NH
4
Cl. That must be trapped using a
coldtrap. These gasses should be cooled down with a shock, not with a gradual decrease.
A cooled flange is required to extent O-ring lifetime, due to the high temperature of 770-800-
830
o
C. Especially at unloading conditions, the door O-ring is likely to burn. Also, the balljoint
O-ring receives a lot of heat, especially at pumping down conditions.
However, a too cold flange will cause NH
4
Cl condensation, which shows as a white powder
deposit on the flange.
To improve cross-wafer uniformity in the first few wafers it is necessary to apply a set of
dummy wafers at the gas inlet side of the load. An extra boat might be necessary.
4.1.3
Process result indication
Nitride results (2)
pressure effect
0
10
20
30
40
50
60
70
0
50
100
150
200
250
300
350
deposition pressure [mtor]
th
ick
n
es
s [
A
]
high flow
medium flow
low flow
4.1.4
Startup parameters for processing
The optical properties of a new and/or cleaned quartz tube change most dramatically after
the first deposition of foreign (=different refractive index) material. For accurate temperature
control a new and/or cleaned tube needs therefore to be coated before any (automatic)
profiling is performed. Use the default process settings for 1 hour to obtain a reasonable
coating.
Type Wafer
Size
[mm]
Process
Time
[min]
Pressure
[mtor]
Thickness
[Å]
Temp.
[
o
C]
SiH
2
Cl
2
[sccm]
NH
3
[sccm]
4.1-2
