Lithography Flashcards
How many fully enclosed layers are needed for freely moving parts?
At least 2
Types of lithography
- electron beam
- laser
- proton beam
- x-ray
- soft
- stereo
negative resist
deposited soluble, responds to exposure by becoming insoluble (stays where the light shines, negative material height where mask is)
positive resist
deposited insoluble, responds to exposure by becoming soluble. (leaves where the light shines - positive material height where mask is)
serial process
carried out in series one step at a time
parallel process
all steps (or parts) are undertaken at the same time
aspect ratio
height : width
spin casting thickness is based on:
viscosity of resist and spin speed
Photo litho basic steps
1) resist applied on substrate, and prebaked to remove solvents
2) masks are aligned to substrate
3) exposure
4) post exposure bake
5) development washes away soluble material
6) resist can be used as a mask to pattern the underlying layer
7) resist is stripped to reveal the patterned underlying film
bright field mask
features are opaque
dark field mask
features are transparent
exposure system types
- contact aligner
- proximity aligner
- projection aligner
contact aligner
- mask and wafer in direct contact
- 1:1
- contact can damage mask
- high resolution
proximity aligner
- mask and wafer separated by a few micron gap
- 1:1
- lowered resolution due to increased diffraction
- better mask lifetime due to no contact
projection aligner
mask projected using high presicion options
5:1, - 10:1
lower mask tolerance and defect requirements