Processing of III-Nitride (I) (Courtesy of Grace Xing at Notre Dame)

Transcription

1 Processing of III-Nitride (I) (Courtesy of Grace Xing at Notre Dame) Outline: 1. Introduction 2. Dry etching Slide # 1

2 Introduction Hynix semiconductor Slide # 2

3 Introduction Hynix semiconductor Slide # 3

4 Plasma Etching Basic method of plasma etching Chemical etching Energetic ion enhanced etching Sputtering etching Protective ion enhanced etching Hynix semiconductor Slide # 4

5 Plasma etching Hynix semiconductor Slide # 5

6 Plasma etching Hynix semiconductor Slide # 6

7 GaN dry etch stop technology and its application to Gate Recessing in AlGaN/GaN HEMTs Dario Buttari et al, UCSB Problem: Obtain a reproducible etch depth Possible Approaches Timed Etch Etch Stop Layer Low Power Plasma Etching on AlGaN Low power Cl 2 dry etch: Poor Reproducibility Influence of surface oxides and residual oxygen in the chamber Solution: BCl 3 chemistry Selectively etch of GaN over AlGaN Advantages Optimization Etch characterization results Slide # 7

8 Time controlled etch Timed Controlled Etch minor variations in etching power and gas composition cause major variation in etch rate therefore etch depth Slide # 8

9 Selectively etch Etch Stopper Minor variations in etching power and gas composition cause variations in etch rate but minor variation in etch depth Slide # 9

10 HEMT Output Characteristics (timed etch) Depletion mode Gate leakage Tolerable (has to be improved) Enhancement mode Plasma power: 15W 200s 230A etch depth Original AlGaN x=0.35 thickness 280A Slide # 10

11 Transconductance and linearity Device dimensions: Lg:0.8um Wg:75um Lgs:0.7um Lgd:1.0um 80% Criteria Slide # 11

12 Poor Etch Repeatability (timed etch) Same conditions Nominally identical samples Slide # 12

13 Etch Depth Dead Time Original AlGaN x=0.3 thickness: 250A on SiC substrate Etch Depths determined by AFM Slide # 13

14 Oxidizers on Silicon Technics Planar Etch PEIIA Plasma System 300mT Electrode frequency: 30kHz Slide # 14

15 Surface Oxide Dead Time Thinner.oxide Thicker Plasma power: 15W 200s 10sccm Cl 2 10mTorr Original AlGaN x=0.35 thickness 290A Slide # 15

16 Boron Tetrachloride No Dead Time Thinner.oxide Thicker Plasma power: 15W 200s 10sccm BCl 3 10mTorr Original AlGaN x=0.35 thickness 290AA Slide # 16

17 Oxide Etching Way to check oxide removal GaN in Cl 2 Incomplete oxide removal by wet etch? AlGaN in Cl 2 Plasma power: 15W 200s 10sccm Cl 2 10mTorr 3um Semi-insulating GaN buffer Plasma power: 15W 200s 10sccm Cl 2 10mTorr Original AlGaN x=0.35 thickness 290A Slide # 17

18 Residual Oxygen Dramatic Sensitivity Reduced Sensitivity GaN in Cl 2 AlGaN in Cl 2 Plasma power: 15W 200s 10sccm Cl 2 10mTorr Original AlGaN x=0.35 thickness 290AA Plasma power: 15W 200s 10sccm Cl 2 10mTorr 3um Semi-insulating GaN buffer Slide # 18

19 Oxygen Scavenger AlGaN in BCl 3 GaN in BCl 3 Plasma power: 15W 200s 10sccm BCl 3 10mTorr Original AlGaN x=0.35 thickness 290A Plasma power: 15W 200s 10sccm BCl 3 10mTorr 3um Semi-insulating GaN buffer Slide # 19

20 Surface Morphology Cl 2 BCl 3 9.6Å rms 2.8Å rms Plasma power: 15W 200s 10sccm 10mTorr Original AlGaN x=0.35 thickness 290A Slide # 20

21 Summary and AlGaN etch stop Problem: Reproducible recess depth on AlGaN Source of irreproducibility: Oxides on the surface of AlGaN Cl 2 : poor deoxidation characteristics BCl 3 : deoxidizer and oxygen scavenger Etch stopper AlGaN Pretreatment chemistry BCl 3 Etching chemistry Cl-based (GaCl 3 and AlCl 3 are volatile) BCl 3 /SF 6 Etch-inhibition chemistry F-based (AlF 3 is not volatile) Slide # 21

22 Overview of selective etch of GaN/AlGaN by ICP UCSB facility Determination of selectivity Selectivity and its dependence on RF power (and ICP power) Pressure Damange? Slide # 22

23 Selectivity: laser interferometry Slide # 23

24 Dependence on power RF power does not have strong control on selectivity, similar results hold for ICP power Selectivity should be affected at low power levels, but at the expense of etch rate Etch rate increases linearly with RF power, which controls damage Slide # 24

25 Dependence on pressure Selectivity improves with increasing chamber pressure Etch rate is almost constant Slide # 25

26 Evaluation of etch damage Z scale is 7 nm for both AFM as grown rms = 0.14 nm after BCl3, rms = 0.21 nm No or very little interaction Sample GaN on sapphire BCl 3 treatment does not change morphology: AFM of surface before (left) and after (right) the treatment Slide # 26

27 Etch damage after a deep etch Sample: GaN on sapphire Same etch depth: 500 nm Different etch conditions correspond to different tested selectivity 20% SF 6 is the best choice Slide # 27

28 Surface roughness is function of etch rate Slide # 28