XR-1541

6% solution

Spin-speed vs. resist thickness:

1000 rpm – 1900 Ang

2000 rpm – 1337 Ang

3000 rpm – 1108 Ang

4000 rpm – 972 Ang

5000 rpm – 883 Ang

2% solution

Spin-speed vs. resist thickness:

velocity------acceleration-------time-------thickness

2000 rpm----1000 rpm/s-------60s-------450 A

3000 rpm----1500 rpm/s-------60s-------390 A

4000 rpm----2000 rpm/s-------60s-------353 A

5000 rpm----3000 rpm/s-------60s-------323 A

5000 rpm----5000 rpm/s-------90s-------287 A

1% solution on 1" pieces

Spin-speed vs. resist thickness:

velocity------acceleration-------time-------thickness

1000 rpm----500 rpm/s--------60s-------278 A

2000 rpm----1000 rpm/s-------60s-------196 A

3000 rpm----1500 rpm/s-------60s-------178 A

4000 rpm----2000 rpm/s-------60s-------151 A

5000 rpm----2500 rpm/s-------60s-------139 A

1% solution on 4" wafer

Spin-speed vs. resist thickness:

velocity------acceleration-------time-------thickness

3000 rpm----1500 rpm/s-------60s-------165 A

5000 rpm----2500 rpm/s-------60s-------116 A

Important Note:

HSQ is sensitive to the time between coating and exposure. It is best to expose immmediately after coating samples.

Develop process:

We currently use two develop processes. One is a "normal" process and the other is a "high contrast" process.

"Normal" process:
1. after spin coat, hot plate bake at 250C for 2min
2. EBL expose, base dose ~1000uC/cm2
3. develop 70sec, with 2.3% TMAH (MF-319) at room temperature
4. rinse with gently flowing DI water from tap for ~30 sec (it is important to use the flowing DI water to reduce residue)

"High contrast" process:
1. after spin coat, hot plate bake at 80C for 4min
2. EBL expose, base dose ~2000uC/cm2
3. develop 30 sec, with 25% TMAH at 80C
4. rinse with gently flowing DI water from tap for ~30 sec (it is important to use the flowing DI water to reduce residue)

Pros/cons:
1. "normal" process needs a lower dose than "high contrast" process, so "normal" process will have faster EBL write time.
2. "normal" process only needs room temperature developer.
3. "high contrast" process is needed for thick HSQ (6% solution, >100nm thickness) to prevent resist exposure in backscattered areas near large features.
4. "high contrast" process also of course needed for minimum size features that are densly packed (for example 10nm dots on 40nm pitch).
5. "high contrast" process also gives straighter sidewalls in resist.

Also, adding NaCl to the developer has been shown to improve contrast.

Removing HSQ:

After exposing HSQ it turns into silicon dioxide. Therefore, HSQ can be removed with the same chemical that removes silicon dioxide which is HF or BOE.
The removal rate of thermal silicon dioxide with 5:1 BOE is approximately 100 nm/min, while for unannealed PECVD oxide the removal rate is ~490 nm/min [1]. But with HSQ that has been exposed by EBL, or baked at temperatures at 250 C or lower, it has been observed that the removal rate of HSQ is much faster, possibly as fast as removing 100 nm in a few seconds. Also, please consider that BOE will etch any other oxide which is present on your sample.

[1] Kirt R. Williams, Kishan Gupta, Matthew Wasilik, "Etch Rates for Micromachining Processing - Part II", Journal of Microelectromechanical Systems, Vol. 12, No. 6, December 2003