CORAL Name: | nitride | |||||||||||||||
Model Number: | -- | |||||||||||||||
Location: | ICL | |||||||||||||||
What it does: | wet station | |||||||||||||||
Introduction: | The ICL machine named "nitride" is a wet etch bench used to remove silicon nitride from 4" or 6" Si or SiGe whole wafers. Partial wafers, wafers that have seen gold or metal processes are not allowed. Also, due to the high boiling temperature of the etchant, photoresist is not effective and is not allowed. Patterning of silicon nitride should be done in a plasma etcher. The user transfers wafers to teflon cassettes and immerses
them in the liquid etchant for a predetermined time. Then
they are rinsed with DI water and dried. |
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Safety: | This processes uses boiling phosphoric acid at 165°C. Be very alert. DO NOT ASSUME AN UNKNOWN WET SUBSTANCE IS WATER. The Personal Protective Equipment (PPE) required to work at any wet etch sink includes:
The PPE is kept in the wet etch bay and is meant to be shared. However, do not use any equipment which is wet or ripped or stained or questionable or does not fit well. New PPE is available in the glove room or by asking a staff member. Face- shields should be changed whenever they become stained. Other Safety notes: Loss of cleanroom air movement or power failure may mean
loss of fume exhaust. Therefore all users should leave the
lab if this occurs. Unusual quiet or air whistling is a sign
of loss of air handling capability. |
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Procedure: | Note: We suggest that users perform a quick BOE etch in the oxide wet bench prior to nitride strip. A thin oxide or oxynitride layer will act as a barrier to the phosphoric etchant.
Sink Information The nitride etch vessel is a quartz bath enclosed by an insulated heating element. The Modutek controller applies power to the heater which drives up the bath temperature. DI water is injected at the process temperature setpoint to stop the rise in temperature and maintain it at setpoint. This system is equipped with a second temperature feedback loop to monitor steam temperature. This is a safety feature. Loss of proper steam temperature might mean the cool DI water has formed a layer over the (higher temp.) etchant. This is a danger because placing a cassette in the bath in this state will cause the cool water to be enveloped by the etchant and burst into steam and splash the area. Therefore variation from the steam setpoint will interlock the DI water inject. Process program:
Spin dryer program |
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Author: | Paul Tierney, 11/01 <ptierney@mtl.mit.edu> |