Photolithography process

Before spin resist it is necessary:
· Clean GaAs wafer piece in NPM hot, ID water, 2-Propanol, ID water.
· Dehydration bake @ 110° C for 5 minutes

Positive Photoresist

Negative reversal process for resist AZ 5214E

Spin-coat resist 5000rpm for 60s
Soft bake at 110° C for 60s
Expose at 10mW/cm2 with UV light for 1.8s (maskaligner MA6 or MJB3)
Bake at 110° C for 60s
Flood expose without mask for 4s
Develop in MF319 developer for 25s and rinse with ID water

Negative Photoresist

Photoresist	Spin Speed/Time	Soft bake Temp/Time	Exposure Time (assuming 10mW/cm2)	Develop Time (Developer MF 319)	Post-Exposure Bake Temp/Time	Thickness
AZ 5214E	5000rpm/60s	110° C/60s	3s	20s	115° C/60s	1.3um
AZ 1818	5000rpm/60s	110° C/60s	4s	22s	115° C/60s	1.6um
AZ 4533	5000rpm/60s	110° C/60s	10s	35-40s	115° C/60s	3.5um
AZ 4562	5000rpm/60s	110° C/60s	15-20s	50-60s	115° C/60s	5um

Photolitography process with positive resists.

A typical positive resist (such AZ 4533 and AZ 4562) is composed of three major components: a photoactive compound (inhibitor), a base resin, and a suitable organic solvent systems. All or most of the solvent is lost afterspin and bake. The base resin alone is moderately soluble in the aqueous alkaline developer. Resist is appied to the wafer by spinning. The thickness of the resist film is a function of the spin speed. Final thickness is also affected by subsequent heating steps.
Resist films are usually chosen to be between 0.3 and 2.5 µm thick, depending on the application.


Lithography consists of six basic steps:

• Wafer Preparation
  
• Photoresist coating
  
• Softbake
  
• Exposure
  
• Development
  
• Post-Exposure Bake