Image Reversal

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.

image reversal process

Why not just use a negative resist?

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-8TA & 10TA product pages.