1. Etching of patterned SiO2 film by diluted HF
26/07/2016

2. Input from ANU
d0: 70, 100, 150 nm
a: 300, 600, 900 nm

3. 20 sec etch
1st batch
50 sec etch
SiO2 by PECVD

4. 1st batch
AFM measurements after the growth (+ HCl treatment)
Hole depth ~15 nm
(SiO2 thickness ~28 nm by PECVD)

5. 30 sec etch
2nd batch
35 sec etch
SiO2 by sputtering

6. 2nd batch
Ellipsometry measurements
PMMA A2 495, 4000 rpm
56.1 +/- 0.3
After 25 sec of etch
SiO2, sputtering at RT
26.5 +/- 0.3
GaAs
R2=0.99
SiO2, sputtering at RT
27.9 +/- 0.3
After 35 sec of etch and remove PMMA
GaAs
R2=0.96

7. 2nd batch
D70P300_1
25 sec etch
~ 62 nm

8. 2nd batch
D70P300_1
30 sec etch
~ 63.5 nm

9. 2nd batch
D70P300_1
35 sec etch
~ 64 nm

10. 2nd batch
D70P300_1
35 sec etch + remove PMMA (rinse in acetone)
~ 5-10 nm

11. Very low etch rate + peeling of the PMMA during etching
Conclusions:
Total thickness – 82.6 nm
Depth of the holes – 62 nm
Thickness of the SiO2 – 26.5 nm
~ 6 nm holes inside SiO2 – confirmed by previous slide
Very low etch rate + peeling of the PMMA during etching
Possible ways to improve:
Improve PMMA – resist peeling due to poor adhesion and low thickness
O2 plasma (Zone 2)
Increase PMMA thickness by factor 2
Change resist to ZEP (same as ANU)
Increase etching rate by increasing HF concentration
Change etch type from wet etch to plasma etch