Image reversal

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About this Process
Process Details
Equipment Image reversal
Technology Lithography
Chemicals Used Photoresist
Gases Used NH3



Image reversal is a process to reverse the tone of positive photoresists. Similar to a negative photoresist, areas that are exposed become "protected", while the unexposed areas will be developed away. After exposure, the sample is exposed to ammonia, which reacts with the exposed areas making them impervious to the developer solution. The sample is then flood exposed, which allows the areas that were not exposed initially (and therefore not affected by the ammonia) to be developed. This process is commonly used to create clear field masks but can also be used with most standard photoresists on any sample.

Procedure

The image reversal procedure includes the standard lithography steps with the addition of the ammonia exposure and flood exposure. Please see the section below for specifics with certain photoresists.

  1. Photoresist application and softbake
  2. Sample exposure
  3. Ammonia treatment
  4. Flood exposure
  5. Photoresist development

Ammonia treatment

The sample is heated and exposed to ammonia using the Image Reversal Oven. Details about how the ammonia works

Flood exposure

...

Common applications

Some sort of intro

Mask reversal

SPR 220

Shipley 1800 series

Limitations?

Minimum feature size

Profile control

See also