Microsoft PowerPoint - Nanoforum2009_JHJangHigh Mesa Waveguide Dong-Hyun Kim
Nano-HEMTs Fabricated by utilizing Ne- based Atomic Layer Etching
Gwangju Institute of Science & Technology
Department of Information & Communications
S.H. Shin1, T.W. Kim1, J.I. Song1, G.Y. Yeom2, and J.H. Jang1
Department of Materials Science and Engineering
SKKU
Outline
Introduction
2. Key fabrication processes for Nano-HEMTs
3. Two step recess technology employing atomic layer etching
Atomic Layer Etching
Characteristics of Vertical Schottky Diodes
DC and RF Characteristics of Nano-HEMTs
Depletion-mode InAs Composite Channel p-HEMTs
Enhancement-mode InAs Composite Channel p- HEMTs
Conclusions
Overview of UltraOverview of Ultra--fast Electronic fast Electronic DevicesDevices
Record High fT of III-V HEMTs
< Ref. : Shinohara et al. (IPRM 2004) >
State of the Art
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InP-based HEMT
C ut
610 GHz for 15-nm p-HEMTs IEEE IEDM, 2007
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 4
Gate Recess: Critical Process for NanoGate Recess: Critical Process for Nano-- HEMTHEMT
Buffer
Channel
Insulator
Cap
ZEP
Buffer
Channel
Insulator
Cap
ZEP
InP InP
Wet etching
Two-step recess for HEMT fabrication • 1st step: wet etch n+ InGaAs/InAlAs multi-layer cap removal • 2nd step: dry etch InP etch stop layer removal:
• Ar-based RIE (Conventional) • or Ne-based atomic layer etching (ALET)
<Ref: Suemitsu et al. (IEDM 98)>
• Problems of Conventional Ar-based RIE • Low etch selectivity • Electrical & physical damage: Ion bombardment
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 5
Atomic Layer Etching Technique Atomic Layer Etching Technique (ALET)(ALET)
Reactant Feed
Reactant molecules adsorb onto a substrate surface. The etchant does not spontaneously etch the substrate.
Reactant Purge
Beam Irradiation
An energetic beam irradiates the surface, and surface atoms bonded with reactant are etched off owing to beam- induced chemical etching.
Product Purge
Etching products are purged after which one cycle of digital etching is completed
InP layer
Cl2 gas
Ne neutron-beam
The expected advantages of Ne-based ALET over Ar-based RIE • The higher etch selectivity (ALET) • The lower electrical & physical damage Low energy neutral beam
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 6
Etching Property of ALETEtching Property of ALET
Composition of In0.52Al0.48As surface
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20 40 60 80 100 0.0
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, Reference , Atomic Layer Etching , Reactive Ion Etching
Very high selectivity of InP over InAlAs (~70) cf) Ar-based RIE (~20)
Minimal surface modification
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 7
Surface RoughnessSurface Roughness
The smallest rms roughness achieved by ALET process
AFM image
Vertical Schottky DiodeVertical Schottky Diode
-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 10-12
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GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 9
The Fabricated DevicesThe Fabricated Devices
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 10
6060--nm Depletionnm Depletion--Mode pMode p--HEMTsHEMTs
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VGS [ V ]
ALET RIE
VDS=0.5V
DC Characteristics
•GM,Max of the p-HEMTs fabricated by the ALET process was larger than that of the p-HEMT fabricated by the Ar-based RIE by 21% →much lower plasma-induced damage characteristics of the ALET process
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 11
6060--nm Depletionnm Depletion--Mode HEMTsMode HEMTs
1E8 1E9 1E10 1E11 1E12 0
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EnhancementEnhancement--mode HEMT (Emode HEMT (E-- HEMTs)HEMTs)
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VDS = 0.5V
E-HEMTs were fabricated by utilizing buried-Pt gate • Gate metal stack: Pt(6 nm)/Ti/Pt/Au • Post-annealing was carried out to drive Pt into InAlAs
•ALET: gM,max = 1.38 S/mm •RIE: gM,max = 1.1 S/mm
•VT = 0.07 V
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•FT of 403 GHz •Higher fT than D-HEMTs
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 13
ConclusionsConclusions
The effect of ALET in the two-step gate recess process • Higher InP etch selectivity against the underlying
In0.52Al0.48As barrier layer Better uniformity of device characteristics
Less plasma-induced damage compared to conventional Ar- based RIE process The smoother etched surface
Better gate diode characteristics The higher transconductance The lower subthreshold slope
Buried Pt gate • The thinner effective Schottky layer thickness
Alleviation of short channel effect Better gate modulation characteristics
• The higher Schottky barrier height due to the annealed Pt Positive shift of threshold voltage The smaller gate leakage current
GGwangjuwangju IInstitute ofnstitute of SScience andcience and TTechnologyechnology Department of Information and CommunicationsDepartment of Information and Communications 14
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Thank You!!
Department of Information & Communications