Gas Panels

CR Yellow Alert Gas leak in MSM Audible alarm, yellow flashing light on fire gas panel Uncertain could be real 1. Accept alarm 2. Cz area technician 3. Make PA announcement 4. Determine which gas detector is in alarm (its location) Suspend current operation. Scan panels for flashing yellow or red light. Turn around to MSM Fire Gas panel. Press "accept" button CCR Layout MSM Fire Gas panel Visual and audible Whatever op is doing when alarm occurs Initially disorientating because MSM does not have its own sound source. Alarm could be missed if second simultaneous alarm occurs on main bank of Fire Gas panels... 

Make PA announcement for personnel to stop hotwork and stay away from MSM PA systems This message takes up time and distracts operator from watching Fire Gas panel. Consider taped messages. 

The molecular sieve module fire and gas panel should be given its own alarm sound source and alarm accept control, since there is currently a risk of an alarm being missed. 

It is important to recognize that a production reactor is not simply a reaction chamber. If it is a low pressure unit, there will be a vacuum system which can be quite complex. There will be a gas panel which regulates gas mass flow into the chamber. The method of heating the wafers and/or the entire chamber has to be chosen carefully. Wafer transport involves many tradeoffs, and for batch systems if any degree of automation is required, will be quite involved. Finally, most production reactors these days operate under microprocessor control, and quite a lot of software must be developed. 

Gas enters at the center of the electrode along the axis of rotation from the gas panel. It was found that if the gas were allowed to flow in directly and impinge normally to the upper electrode, that excessive deposits built up rapidly at the center of this upper electrode, and poor deposition uniformities were observed. Therefore, a gas injection shield was placed at the center of the lower electrode to provide some radial momentum to the incoming gas flow. This shield is illustrated in Figure 19. 

The hot wall approach to the plasma-enhanced CVD system has been described in Chapter 3. A schematic of a typical system is shown in Figure 21. The elements of this system are similar to that of the cold-wall system just described. There is a gas panel, vacuum system, and an RF power supply to create the discharge. The RF frequency typically used is 400 kHz. The reaction chamber of such a system is shown in Figure 22. The electrodes are a set of several long narrow rectangular slabs of graphite with pockets cut into them. The graphite electrodes lead to some problems with particulate contamination, but attempts to use aluminum have not been successful. 

Figure 4-12 shows a gas panel schematic of what might be encountered in a typical... 

Figure 4-12. Schematic of a gas panel showing typical major components.

Restrietive CGA orifiees and eleetronic excess flow sensors mandatory in all gas panels. 

Loss of power All gas panels shut down (normal valve positions) and remain off until reset by the user. All monitors and associated equipment (904,917,959) boot upon restoration of power and become totally functional without user interaction. Before toxic gas can flow, the 904 wall units must be reset manually by the user. 

When using extremely hazardous gases, it is advised that a separate cylinder purge gas source be employed, not the same inert source as used elsewhere in the plant, since only one cylinder would be affected if process gas should accidentally backfill a cylinder. The most convenient designs have the process gas panels and their associated purge gas panel all in the same cabinet. 

There are many different designs of gas panels, with some of the features that follow. 

On panels having these features, the panel can be purged on the high pressure side only, by closing the isolation valve before purging. For safety reasons it is often recommended that the low pressure side also be purged to insure there is no gas inside the panel when the operator exchanges the cylinder, and to help remove moisture from corrosive gas panels. 

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