III V Semiconductor Etching Process Quality Rather Than Quantity Alan Webb (formally of Plessey, GEC, Marconi, Bookham, Oclaro etc... ) Wednesday 12 th October 2016 Ricoh Arena, Coventry, UK Part of The 7 th Vacuum Symposium UK
Caswell, Northamptonshire
Caswell Science and Technology Park
Optoelectronics Lasers Modulators Amplifiers Detectors
Laser Fabrication 3 wafer: ~2500 die Plan view of chip Completed Laser Chip Bar Cleave / Facet coating Wafer Thinning Metal Deposition Etch & Dep Tools Cross section of Ridge Photolithography Dielectric Deposition & Etch Bare Wafer Gratings fabrication MOVPE Overgrowth MOVPE Reactor Photolithography Tracks MOVPE Growth (2stages) Purchased bare wafer
A Bonded Chip
III V Dry Etching GaInAsP material system grown on InP Halogens : eg. Cl Br I or CH 4 / H 2
Developing the Process It is difficult to develop a process progressing through several different material structures and maintain complete control. It is even more difficult with the restraint of the peripheral architecture on the rest of the wafer. However, it can be done.
HBr Test Structure
HBr Ridge Etch
Cl 2 / N 2 Etch
Grating Fabrication Low power oxygen RIE to de-scum AFM used to assess mark space ratio prior to etch Target mark/space is 1±0.3
TEM micrograph showing an overgrown DFB laser grating (grating period ~240nm)
Dry Etch Requirements Gentle Precise Controllable Physical + chemical Methane (CH 4 ) + Hydrogen (H 2 )
Etch Mechanism Etching and Deposition Polymer formation Polymer removal Gas mixture critical Elimination of residuals Vacuum quality
CH 4 + H 2 Large amount of H 2 to initiate breakdown Cracking of CH 4 results in polymer Contamination control Vacuum quality Low power plasma dimension control
Processes to Consider Simplified with no other interference!!! O 2 RIE 4C + 3O 2 2CO 2 + 2CO CH 3 + 2C + 3O 2 H 2 O + OH + 2CO 2 + 2CO The III V semiconductor reaction : InP + CH 4 + H 2 methyl / ethyl (Gp III) + PH 3 InP + 3CH 4 + H 2 In(CH 3 ) 3 + PH 3 + H 2 GaAs etc
Residual Gases The number of unwanted atoms and molecules within the environment can have a detrimental effect on dry processing. Both gas phase and surface effects can occur, which produce unwanted results. Poor quality etching could be the result.
Contamination Control Unwanted Reactions OH H 2 O O O 2 CO Monitor N 2 and Ar
In Situ Monitoring
Mass Spectrometry Raw Data High resolution Mass Scan High Resolution Mass Scan 1.00E-06 residual gases - air leak 1.00E-07 pp 1.00E-08 1.00E-09 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 m / q
Species to Monitor? Species Mass H H 2 CH 4 1 2 16 O O 2 16 32 CH 3 COH SiH 15 29 OH H 2 O 17 18 CO CO 2 SiO 28 44 Ar 40
Species to Monitor? Dominant species from etchant or reactions or important species to realise precise control? Are they the same?
In-situ Process Monitoring 1.00E-05 Polymer removal B412 #20 1.00E-06 mtorr 1.00E-07 1.00E-08 H H2 He CH3 O OH H2O CO COH O2 Ar CO2 1.00E-09 14 15 16 17 18 19 20 21 22 23 24 25 26 27 Time (mins)
In Situ Plasma Monitoring 1.00E-05 Polymer Removal (O2 RIE) 1.00E-06 Signal 1.00E-07 1 2 4 15 16 17 18 28 29 32 40 44 1.00E-08 1.00E-09 31 32 33 34 35 36 37 38 Time (mins)
A Methane (CH4) Hydrogen (H2) Etch Process In - situ Process Monitoring 1.00E-05 1.00E-06 H2 O2 H H2 P H He CH3 CH4 / O 1.00E-07 CH4 CH3 O OH H2O N2 / CO 1.00E-08 N2 CO CO2 H2 H COH / SiH O2 Ar / SiC CO2 / SiO 1.00E-09 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 time (mins)
HBr Ridge Etch
High resolution Mass Scan HBr chemistry 1.00E-06 H H2 Bromine has 2 stable isotopes: 79Br (50.69 %) and 81Br (49.31%). single scan 1.00E-07 Br HBr I He 1.00E-08 PH PHx Br2+ HBr2+ 1.00E-09 1.00E-10 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 m / q
High resolution Mass Scan 1.00E-06 Mass scan Thurs 14th Oct 2010 H2 He j = 6 sccm 1.00E-07 Br + HBr P 1.00E-08 P (Br + HBr)2+ P2 1.00E-09 PO 1.00E-10 0 2 4 6 8 1012141618202224262830323436384042444648505254565860626466687072747678808284868890 m / q
HBr scan during process HBr chemistry - ridge etch 1.00E-06 Bromine has 2 stable isotopes: 79Br (50.69 %) and 81Br (49.31%). 1.00E-07 p single scan 1.00E-08 1.00E-09 1.00E-10 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 m / q
Developing the Process for Manufacture Developing a process is even more difficult for reproducibility and repeatability, such that it is the same for wafer to wafer, for batch to batch, hour by hour, day by day, because that is what manufacturing demands!!!
HBr Batch Processing Etch process stablisation 1.00E-05 1.00E-06 P 1.00E-07 1.00E-08 H H2 He CH3 CH4 / O OH H2O CO/ N2 O2 / PH Ar Br HBr 1.00E-09 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 time
Complex Features Realised
Requirements Precise control of the vacuum, residual gas and the plasma environment are all important in being able to reliably reproduce complex features within optoelectronic devices. These are the fundamental building blocks of many types of integrated chips.
Chip-on-tile for angled waveguide output
Questions?