m330_01_gas_cabinet气柜.pdf.pdf - 第18页
GAS SYSTEM Figure 2-10 Cooling Spiral tube with Ammonium chloride (NH 4 Cl) deposit Frequent cleaning is required for process operation and is highly depe ndent on the customer s situation. A starti ng cleaning interval …
GAS SYSTEM
A Persys Pyrogenic External Torch can be used only on customers request. For more
information about the Persys Pyrogenic External Torch, refer to its user manual, see Vendor
documentation (M540.00).
Coldtrap
A coldtrap is necessary whenever a process produces condensable waste products, which can
contaminate vacuumlines and potentially cause particle problems. An example of such a
process is silicon-nitride (Si
3
N
4
) from SiH
2
Cl
2
and NH
3
.
The gasses should cool down on a cold surface so it is important to have that surface as close
to the entrance of the cold-trap as possible. A cooling water temperature of 15
o
C is required
for an optimized operation.
Specifically for the nitride deposition process two different forms of waste product can be
found in the coldtrap. A white powder form and a glassy solid form. The glassy form is what
occurs as the gasses are shock-cooled on any cold surface. This is the form that is wanted on
the coldtrap. The white powder form occurs from slow cooling and condensation in the gas-
phase, and will hardly be trapped by the coldtrap. Instead, most of it will be found at the inlet
filter and exhaust of the dry pump, or in the oil of a wet pump. A short connection between
tube and coldtrap should decrease the amount of powder form and increase the glassy form.
Special precautions are required to prevent O-ring damage or melting.
A coldtrap usually consists of two parts: the outer housing and the inner cooling element.
Waste products of the deposition process are rapidly cooled off on the inner element and
removed from the gas stream.
Figure 2-9 Coldtrap (small design)
Figure 2-10 shows a spiral tube with the incoming cooling line in the center, spiraling down
to the bottom. Some white NH
4
Cl deposit is visible which can be removed by rinsing into
hot water.
GAS CABINET REFERENCE MANUAL
2-12
GAS SYSTEM
Figure 2-10 Cooling Spiral tube with Ammonium chloride (NH
4
Cl) deposit
Frequent cleaning is required for process operation and is highly dependent on the customers
situation. A starting cleaning interval is 2 microns of accumulative nitride deposition on the
wafers. Further determination needs to be done by the customer.
Because the waste product of the nitride process is water-soluble the deposit can be removed
by rinsing with water. Hot water will speed up this cleaning procedure. Rinsing with
isopropanol afterwards will facilitate blow-drying before remounting.
Cooling water is connected with QuickConnects. Dirt or corrosion occuring inside the
quickconnect might hamper the connection. Forced air-drying with compressed air is usually
sufficient to clear the obstruction.
Vacuum pumps system
Vacuum pump systems are used for LPCVD processes to create under-pressure in de process
tube. The current industry standard is dry pump, although wet (oil lubricated) pumps are still
widely used. Refer to the vendor documentation
(M540.00) for detailed technical
information.
GAS CABINET REFERENCE MANUAL
2-13
GAS SYSTEM
2.2 Electronics
Interconnection Boards
The digital and analog interconnection boards for the gassystem are used as an
interconnection between the DPC, the safety boards and the gaspanel. The safety boards
allow the opening of valves for specific (dangerous) gases only if all safe conditions are
satisfied.
For a complete description of the interconnection and safety boards, see the DPC Reference
manual.
DPC
The Digital Process Controller together with the Digital Temperature Controller (DTC)
forms the heart of the system control. For detailed information refer to the DPC reference
manual (M410.00)
Safety board
A safety board is used to check the safety conditions when using hydrogen and oxygen in a
Tempress external torch. It is used as a hardware protection. This safety board works only in
combination with the Tempress DPC control system. It is not used in this configuration as a
“stand-alone” unit.
Pressure interface board
A pressure interface board is used in Low Pressure Chemical Vapour Deposition (LPCVD)
gassystems as safety component for the right gaspressure. The process gaspressure will be
compared with a safety setpoint of default 1.4 Torr. Specific valves can only be opened if the
process pressure is below this safety setpoint.
High/Low limit board
A high/low limit board is used as a safety component to prevent specific valves to be opened
if a required gasflow is out of range.
2.3 Processes
A variety of guaranteed processes are available on the Tempress Diffusion systems, including:
Atmospheric
• Anneal
• Dry Oxidation (with or without TransLC cleaning)
• Wet Oxidation (with or without TransLC cleaning)
• POCl
3
GAS CABINET REFERENCE MANUAL
2-14