This process reverses the action of positive resist so negative images can be formed with the same resolution and processing ease that a positive resist allows. What’s more, image reversal allows variations of the slope of the photoresist sidewall for higher resolution and/or lift off profiles.
For example, if the normal slope of approximately 68 degrees is altered to 90 degrees vertical, resolution is increased 20%. And, if an angle of 112 degrees is achieved, there is a strong overhang that makes metal deposition followed by liftoff controllable.
Positive resist offers far better resolution, and it doesn’t require solvents for development. In contrast, the resolution limit of negative resist is approximately 1 micron, and it requires solvents known to be carcinogens.
YES image reversal systems deliver anhydrous ammonia (NH3) into a vacuum oven. There are two advantages of an ammonia system: 1) easier control of vapor pressure, and 2) an absence of residual water vapor, which will react with the NH3 to produce NH3OH, a corrosive to the system that also creates contaminating particles.
For more information on achieving repeatable and usable reversals, visit the YES-58TA & 310TA product pages.