Lift-off resist

About this Process
Process Details
Equipment	Lift-off resist
Technology	Lithography

LOR or lift off resist process is a method of getting better definition of structures while using liftoff. By using 2 layers of material you are able to create a negative profile and are able to get better definition of the features. You can purchase tubes of LOR 10B through the LNF store.

Procedure

Steps for LOR 10B process on a 4" or 6" silicon substrate

1. Clean substrate
   • O₂ Plasma
   • Nanostrip
   • Acetone/IPA
2. Dehydration bake 110-115C 1-2 min
3. Spin LOR for 30s
   1. Speed and thereby thickness will depend on thickness of metal
   2. Thickness should be at least 1.5x the thickness of the metal
   3. Thickness should be < 1/3 minimum space between structures
   4. For thickness vs. spin speed see LOR data sheet
4. Bake at 190C 5 min
5. Spin 1813 @ 4krpm 30s
6. Bake at 110C for 4 min
7. Expose 6-8.5s on MA6 (approximately 0.25s on stepper)
8. Develop for 20 - 30s MF300. Check for double line around feature
9. If it needs more develop time develop additional 5s
10. Evaporate or sputter metal
11. Soak in 65-80C remover PG for 15 - 30min, ultrasonic is usually not be necessary
12. Rinse

PMGI SF 6 can be used for thinner and smaller features and it can be purchased from the LNF Store. Characterization and process information.

For thicker Metal and larger features LOR 20B and 30B can be used.

General LOR thickness table in µm

Product	1krpm thickness	4krpm thickness
LOR 1A	0.2	0.1
PMGI SF5	0.3	0.15
PMGI SF 6	0.4	0.24
LOR 3A	0.6	0.3
LOR 5A	1.0	0.5
LOR 10B	1.8	0.9
LOR 20B	3.9	1.9
LOR 30B	5.9	2.8

Additional information

• When baked at 190C LOR will be somewhat conformal
• When baked at 275C LOR will flow and become planar
• LOR is compatible with most resists including Ebeam resist

Limitations

• LOR is soluble in developers so it will continue to undercut the top photoresits for as long as it is developing. Therefore develop time is critical to achieve small features.
• Exposure will vary depending on substrate
• Develop time will vary depending on thickness of the LOR
• Bake times for glass are longer and higher temperature