Image reversal

Warning:

This page has not been released yet.

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

1. Standard exposure based on the Heidelberg µPG 501 Mask Maker
2. Run Recipe 2 on the Image Reversal Oven
3. Flood expose
   1. Use MA6/BA6
   2. Flood Exposure setting. Make sure is is set up before loading the mask
   3. 3s exposure
   4. A mask plate or the plate holder is not needed
   5. Load mask onto stage chrome and photoresist side up and hit load, it will cycle through and expose substrate
4. Develop shorter time than normal, typically half the normal time
5. Inspect

SPR 220

Steps:

1. Normal cleaning and HMDS
2. Spin normally to achieve the appropriate thickness
3. Standard softbake (for 3-5um 90s @ 115C)
4. Standard exposure based on thickness of the resist, substrate reflectivity, and the tool that is used
5. Standard Post Exposure Bake (for 3-5um 90s @ 115C)
6. Run Recipe 2 on the Image Reversal Oven
7. Flood expose
   1. Use MA6/BA6
   2. Flood Exposure setting. Make sure is is set up before loading the wafer
   3. Twice normal exposure for thickness of the resist, and substrate reflectivity
   4. A mask plate or the plate holder is not needed
   5. Load wafer onto stage and hit load, it will cycle through and expose substrate
8. Standard Post Exposure Bake (for 3-5um 90s @ 115C)
9. Develop shorter time than normal, typically half the normal time
10. Inspect

Shipley 1800 series

Steps:

1. Normal cleaning and HMDS
2. Spin normally to achieve the appropriate thickness
3. Standard softbake
4. Standard exposure based on thickness of the resist, substrate reflectivity, and the tool that is used
5. Run Recipe 2 on the Image Reversal Oven
6. Flood expose
   1. Use MA6/BA6
   2. Flood Exposure setting. Make sure is is set up before loading the wafer
   3. Twice normal exposure for thickness of the resist, and substrate reflectivity
   4. A mask plate or the plate holder is not needed
   5. Load wafer onto stage and hit load, it will cycle through and expose substrate
7. Develop shorter time than normal, typically half the normal time
8. Inspect

See also

• Image Reversal Oven
• Optical lithography
• Lithography processing