28-03-2014, 12:18 PM
Photolithography
[attachment=60576]
Temporarily coat photoresist on wafer
Transfers designed pattern to photoresist
Most important process in IC fabrication
40 to 50% total wafer process time
Determines the minimum feature size
Applications of Photolithography
Main application: IC patterning process
Other applications: Printed electronic board, nameplate, printer plate, and et al.
Basic Steps of Photolithography
Photoresist coating
Alignment and exposure
Development
Photolithography Process, Primer
Promotes adhesion of PR to wafer surface
Wildly used: Hexamethyldisilazane (HMDS)
HMDS vapor coating prior to PR spin coating
Usually performed in-situ with pre-bake
Chill plate to cool down wafer before PR coating
Spin Coating
Wafer sit on a vacuum chuck
Slow spin ~ 500 rpm
Liquid photoresist applied at center of wafer
Ramp up to ~ 3000 - 7000 rpm
Photoresist spread by centrifugal force
Evenly coat on wafer surface
Purpose of Soft Bake
Evaporating most of solvents in PR
Solvents help to make a thin PR but absorb radiation and affect adhesion
Soft baking time and temperature are determined by the matrix evaluations
Over bake: polymerized, less photo-sensitivity
Under bake: affect adhesion and exposure
Wafer Cooling before Development
After PEB the wafer is put on a chill plate to cool down to the ambient temperature before sent to the development process
High temperature can accelerate chemical reaction and cause over-development and PR CD loss
[attachment=60576]
Temporarily coat photoresist on wafer
Transfers designed pattern to photoresist
Most important process in IC fabrication
40 to 50% total wafer process time
Determines the minimum feature size
Applications of Photolithography
Main application: IC patterning process
Other applications: Printed electronic board, nameplate, printer plate, and et al.
Basic Steps of Photolithography
Photoresist coating
Alignment and exposure
Development
Photolithography Process, Primer
Promotes adhesion of PR to wafer surface
Wildly used: Hexamethyldisilazane (HMDS)
HMDS vapor coating prior to PR spin coating
Usually performed in-situ with pre-bake
Chill plate to cool down wafer before PR coating
Spin Coating
Wafer sit on a vacuum chuck
Slow spin ~ 500 rpm
Liquid photoresist applied at center of wafer
Ramp up to ~ 3000 - 7000 rpm
Photoresist spread by centrifugal force
Evenly coat on wafer surface
Purpose of Soft Bake
Evaporating most of solvents in PR
Solvents help to make a thin PR but absorb radiation and affect adhesion
Soft baking time and temperature are determined by the matrix evaluations
Over bake: polymerized, less photo-sensitivity
Under bake: affect adhesion and exposure
Wafer Cooling before Development
After PEB the wafer is put on a chill plate to cool down to the ambient temperature before sent to the development process
High temperature can accelerate chemical reaction and cause over-development and PR CD loss