Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING ICP ETCHING TALK 6 1

Equipment and technological processes for manufacturing GaAs MMICs 2 PLASMA ETCHING - 2 The limitations of RIE etching are:-  Low etch rates  High substrate damage in some cases  Potential low selectivity's especially to resist

3 The limitations in etch rate are often due to the relatively low concentration of ions in the plasma  This can be solved by having a more efficient plasma excitation method The damage is due tot eh high energy ions accelerated across the dark space in an RIE plasma. This is due to the RF generating the plasma and the two are linked to one RF supply  The answer is to remove the generation of the plasma from the energy RF source which forms the dark space above the wafer – thus gaining independent control of the two ICP etching systems achieve these two desirable goals Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2

4 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP advantages An ICP etching system decouples the power supply providing the plasma from that causing the bias on the substrate wafer This way both parameters can be optimised independently with much enhanced process results and much more flexible processes

5 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP advantages

Equipment and technological processes for manufacturing GaAs MMICs 6 PLASMA ETCHING - 2 Enclosure removed

7 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP advantages Electrostatic shield -eliminates capacitive coupling -reduces electrical damage to devices -reduces chamber particles Separate RF generators for ICP and electrode -provides separate control over ion energy and ion density High conductance pumping port

8 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP Principle of Operation High ion density (>10 12 cm -3 ) Low ion energy Separate control provides high process flexibility Chemical and ion-induced etching. Anisotropy and isotropy control

9 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 “True ICP” Performance Grounded slotted antennae design Inserted between RF coil and dielectric tube Located on atmospheric side of tube Eliminates generator beating (capacitive cross talk) and eliminates capacitive currents which can cause device damage

10 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 GaAs/AlGaAs etching Process Overview

11 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP GaAs/AlGaAs etch SiCl 4 /Ar Based recipe GaAs e/r > 0.35 µm/min Sel to Oxide >10:1 Sel to resist > 5:1 Sel GaAs:AlGaAs 1:1 Uniformity: <  3% (4” wafer) <  5% (6” wafer) Anisotropic profile, Smooth sidewalls Requires active cooling Pictures courtesy of Oxford Instruments

12 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP GaAs Via Etch BCl 3 /Cl 2 Based recipe Etch rate µm/min. Sel. GaAs:PR - 5  15:1 Uniformity: <  5% (4”wafer) Vertical or sloped profile can be controlled. Active cooling required Pictures courtesy of Oxford Instruments

13 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP selective GaAs/AlGaAs etch BCl 3 /SF 6 Based recipe Etch rate: ~30nm/min. Sel. > GaAs:AlGaAs 50:1 GaAs:PMMA 3:1 Uniformity: <  3% (3” wafer) Low damage process Active cooling required Pictures courtesy of Oxford Instruments

14 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP BCl 3 /Cl 2 chemistry etch results Chemistry: BCl 3 /Cl 2 Etch rate: >100nm/min. Selectivity: >1:1 (PR mask) Uniformity: <  2% (2” wafer) <  5% (Batch 20 x 2”) Low damage process

15 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP BCl 3 /Cl 2 with active cooling etch Chemistry: BCl 3 /Cl 2 Etch rate: >500nm/min. Selectivity: >7:1 (SiO 2 mask) >18:1 (Ni mask) ~1:1 Uniformity: <  4% (2” wafer) Profile control: >85° (requiring mask profile >80 ° and hard mask) >70degree(PR mask, requiring profile >70 °) Low damage process With PR mask Pictures courtesy of Oxford Instruments

16 Equipment and technological processes for manufacturing GaAs MMICs PLASMA ETCHING - 2 ICP Etch Cl 2 /Ar chemistry etch results Etch rate: >1000nm/min. Selectivity: >7:1 (SiO 2 mask) >18:1 (Ni mask) Uniformity: <  2% (2” wafer) <  5% (batch 4 x 2”) <  5% (batch 20 x 2” Profile control: >85° Low damage process