Robust sourcedrain

1
Goals
Approaches

• Robust source/drain
• Reduce/eliminate ohmic anneal
• Reduce access resistance
• Allow source metal set-back
• DC-to-RF Dispersion
• Reduce sensitivity of device performance to
  surface
• Epitaxial alternatives to all-SiN passivation for
  increased reliability and process control

• Implantation and n GaN cap
• n cap layers
• Implant technology optimized with transistor
  performance
• Reduce implant thermal budget
• Thick capped deeply recessed HEMTs
• Develop robust deep recess
• Hybridize epitaxial and conventional solutions

2
Issues / Risks
n Capping Channel/Cap communication Low
barrier to vertical current flow Solutions
Delta doping at Cap/Barrier interface
Implantation Risks Gate leakage Recess Etch
Need reliable etch stop/endpoint
detection Solutions RGA endpoint detection
SF6 etch chemistry ICP vs RIE Risks Gate
Leakage Threshold voltage uniformity Deep
Recess HEMT Structure Deep AlGaN Recess Graded
AlGaN cap requires end-point detection Solutions
RGA endpoint detection Risks Gate leakage
Threshold uniformity Ion Implantation AlN
Cap layer Need AlN cap to allow high
temperature anneal Solutions Reproducible AlN
capping technology Reduce anneal Temp Risks
difficulty in cap removal
3
Deeply Recessed GaN-based HEMTs

• Thick cap layer
• reduced modulation from surface states
  dispersion suppression
• Epitaxial field plate
• reduced electric field peak
• Current status
• 15.2 W//mm at drain bias of 70V

m
L
(
m)
FP
4
n-GaN Capped AlGaN/GaN HEMTs
Delta dopings
Graded
EF

• n-GaN cap layer
• reduced access resistance
• non-alloyed ohmic contact
• Communication between n GaN and channel
• lower the barrier graded GaN/AlGaN and
  delta-dopings
• Current status Rsh150 ?/?, Rc0.7 ?-mm

5
Implanted AlGaN/GaN HEMTS
Present AlGaN/GaN HEMT

• Advantages of implanted devices
• Unannealed contacts
• Gate aligned to implantation edge, not ohmic
  metal edge
• Lateral dopant engineering
• Implanted device isolation
• Reduced access resistance
• Technological hurdles
• AlN capping layer
• Reduce thermal budget

Drain
Gate
Source
AlGaN
GaNFe
Ion Implanted AlGaN/GaN HEMT
Gate
Drain
Source
Contact Implant
Contact Implant
AlGaN
Access Implant
Access Implant
GaNFe
6
Short term (6 months) goals

• Manufacturable GaN and AlGaN deep etch technology
• Endpoint Detection
• ICP with RGA for endpoint detection using
  epitaxial marker layers
• Uniform and accurate threshold voltage control
• Applicable to all deep recess devices, not
  limited to specific structures
• Potential etch chemistries
• BCl3 Remove Surface Oxide
• Cl2 GaN and AlGaN, ICP vs RIE
• SF6 large AlGaN/GaN selectivity
• Ion Implantation
• AlN capping technology
• Repeatable
• Optimized with device metrics