1. Developing Etching Process for Nanostructures on InGaP and AlInP Using OX-35 Etcher Jieyang Jia, Li Zhao Mentors: Mary Tang, James McVittie EE412 Final Presentaion, Spring 2014 6/6/2014

2. Accomplishments Systematic etching calibration on 4 materials with 2 series of recipes InGaP and AlInP nanostructures achieved Process insights that will help future users First time in SNF on Ox-35 First time in SNF with RIE?

3. Ox-35

4. Materials

5. Recipes Low ER High ER, 75W 4mT High ER, 25W 4mT High ER, 25W 2mT High ER, 25W 8mT Chamber Clean Chamber pressure(mT)10442820 DC power(W)1207525 70 ICP power(W)3502000 Cl2 flow(sccm)077770 CH4 flow(sccm)5088880 H2 flow(sccm)105.5 0 SF6 flow(sccm)0000020 O2 flow(sccm)00000100

6. MotivationMethodologyResults

7. Motivation Why nanostructures Why InGaP/AlInP Why ox-35 MethodologyResults

8. Nanostructures on III-V: PROS D. Liang, et al. Nano Letters 2013, 13 (10) Anti- reflection Better light management Better light extraction

9. Nanostructures on III-V: CONS D. Liang, et al. Nano Letters 2013, 13 (10) Better optical properties Larger surface recombination loss Solution: do it on materials with smaller surface recombination!

10. Why on InGaP and AlInP InGaP Smaller surface recombination rate Common top junction material for multi- juntion solar cells AlInP Large bandgap Common window layer material for PV and LED

11. Bonus materials: why InP and SiO2 InP Simpler material to etch, good starting material SiO2 Mask for nanostructure etching

12. Why Reactive-ion Etching (RIE) Low temperature (allows photoresist mask) Higher etching rate Better selectivity More controllable and repeatable Comparing to Inductive Coupled Plasma (ICP) and Electron Cyclotron Resonance (ECR) Etching

13. MotivationMethodology Design of experiments Process flow Results

14. Design of Experiments 4 materials: InP, InGaP, AlInP, SiO2 nanospheres 2 series of recipes: CH4/H2 and Cl2/CH4/H2 processes Etching rate, conformity, mask condition, etc. Tuning: RF power, pressure, chemical composition (imcomplete)

15. Process Flow: Nanostructure Formation Wafer cut & clean SiO 2 sphere mask coating SiO 2 sphere etch – “ball shrinking” Sample dry etch Sample wet etch Characterization

16. Process Flow: Process Calibration Bare materials Photoresist coating Photoresist developing Etching Characterization

17. Tools Ox-35 EtcherWet benches KarlsussHeadway

18. MotivationMethodologyResults Etching calibration Nanostructures

19. Results Overview MaterialRecipe Etch Rate (vertical/horizontal) (nm/min) Undercut (nm/min) Sidewall Angle (dec) Smoothness (bottom/sidewall) Photoresist Condition Comments InPLow ER 1548167.3Smooth/roughPolymer observed Significant polymer formation High ER, 75W 4mT 750NA>86Smooth/zigzagDegraded, porous High ER, 25W 4mT 404150051Rough/roughDegraded High ER, 25W 2mT NA Etching failed High ER, 25W 8mT 269<013.3Rough/roughWavy, locally peeled InGaPLow ER 70884Smooth/smoothPolymer observed Significant polymer formation High ER, 75W 4mT >300<0>80Smooth/zigzagDegradedEpi etched through High ER, 25W 4mT 240<078Rough/mild zigzagDegraded High ER, 25W 2mT 192NA75.3Smooth/smoothNASiO2 mask High ER, 25W 8mT 17830039Very rough/very roughWavy AlInPLow ER <5NA No etching observed High ER, 75W 4mT >300NA Smooth/zigzagPorousEpi etched through High ER, 25W 4mT 4281140varyingSmooth/roughPorous High ER, 25W 2mT 365NA82Smooth/smoothNASiO2 mask High ER, 25W 8mT 9013407.1Very rough/very roughWavy SiO2Low ER <5NA No etching observed High ER, 75W 4mT 70/2NA High ER, 25W 4mT <50/<50NA High ER, 25W 2mT <50/<50NA High ER, 25W 8mT <50/<50NA Chamber Clean 400/300NA

20. InP CH4/H2 recipe: ER=154.4nm/min SW angle=67.3˚ Significant polymer formation Cl2/CH4/H2 recipe: ER=750nm/min PR mask was etched porous

21. InGaP CH4/H2 recipe: ER=70nm/min SW angle~90˚ Very smooth sidewalls and bottom “Capping” effect Cl2/CH4/H2 25W, 8mT recipe: ER=178nm/min Undercut=300nm/min SW angle~39˚ Good conformity for nanostructure etching

22. AlInP CH4/H2 recipe: Doesn’t etch at all! Cl2/CH4/H2 75W, 8mT recipe: ER=90nm/min Undercut=1340nm/min SW angle~7.1˚ More chemical than physical

23. SiO2 Nanospheres CH4/H2 and Cl2/CH4/H2 recipes: Negligible etching rate = good selectivity O2/SF6 chamber clean recipe: L. ER=400nm/min V. ER=300nm/min Ideal for ball shrinking!

24. InGaP Nanostructures Cl2/CH4/H2 25W 4mT, 1min O2/SF6 70W 20mT, 1min + Cl2/CH4/H2 25W 8mT, 2min

25. AlInP Nanostructures Cl2/CH4/H2 25W 4mT, 1min O2/SF6 70W 20mT, 1min + Cl2/CH4/H2 25W 8mT, 2min

26. Conclusion on Experimental Results Both Cl2/CH4/H2 and CH4/H2 recipes etch well Cl2 recipe is faster but rougher InP CH4/H2: slow, smooth and straight Cl2/CH4/H2: ideal for nanostructure etching InGaP

27. Conclusion on Experimental Results CH4/H2: doesn’t work! Cl2/CH4/H2: very sensitive to Cl2, resulting in large undercut AlInP Survives both Cl2/CH4/H2 and CH4/H2 processes O2/SF6 chamber clean recipe is ideal for shrinking! Shrink more on InGaP than AlInP SiO2 nanospheres

28. Accomplishments Systematic etching calibration on 4 materials with 2 series of recipes InGaP and AlInP nanostructures achieved Process insights that will help future users

29. Additional Process Insights Process insights that will help future users CH4/H2 recipes generates a lot of polymer Accumulative process time should not exceed 20min before chamber clean (or very bad thing will happen) InGaP: 1min 1:6 dilute HCL dip recommended to remove oxide AlInP: Almost always comes with GaAs cap, 1min citric acid dip + 1 min HCL dip recommended

30. Motivation Why nanostructures Why ox-35 Methodology Design of experiments Process flow Results Etching calibration Nanostructures