Oven, YES, Image Reversal/HMDS - Status: Available
||YES Oven - Image Reversal or HMDS application
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The YES oven can be used as a image reversal oven or and HMDS oven. In image reversal mode, it uses NH3 (ammonia) gas to reverse the tone of positive photoresist. This can be used to create an undercut profile in the photoresist for lift-off processing. In the reversal process, the chamber is purged of oxygen using vacuum and heat. It is then filled with NH3 (ammonia) vapor. The NH3 reacts with the acid in the exposed resist rendering it insoluble in developer. The proceeding flood exposure causes acid to form in the previously unexposed areas allowing them to be removed in development, leaving behind the negative image of the first exposure.
The HMDS process involves chamber evacuation and heating which drives off water. HMDS vapor is introduced which creates a mono layer of silicon. This hydrophobic monolayer promotes good photoresist adhesion.