Nano-HEMTs Fabricated by utilizing Ne- based Atomic Layer Etching Dong-Hyun Kim S.H. Shin 1 , T.W. Kim 1 , J.I. Song 1 , G.Y. Yeom 2 , and J.H. Jang 1 High Mesa Waveguide Gwangju Institute of Science & Technology Department of Information & Communications Department of Materials Science and Engineering SKKU Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 1 Department of Information and Communications Department of Information and Communications
Outline � Introduction 1. High speed electronic devices 2. Key fabrication processes for Nano-HEMTs 3. Two step recess technology employing atomic layer etching � Atomic Layer Etching � Properties of the etched surface (Selectivity, XPS, and AFM) � 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 Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 2 Department of Information and Communications Department of Information and Communications
Overview of Ultra- -fast Electronic fast Electronic Overview of Ultra Devices Devices State of the Art Record High f T of III-V HEMTs Electronic Devices 700 628 GHz for 30-nm p-HEMTs InP-based HEMT IEEE EDL, 2008 800 800 800 800 610 GHz for 15-nm p-HEMTs III-V HBTs Cutoff frequency f T (GHz) IEEE IEDM, 2007 600 562 GHz for 25-nm P-HEMTs IEEE EDL, 23, 573 Cutoff Frequency [GHz] Cutoff Frequency [GHz] Cutoff Frequency [GHz] Cutoff Frequency [GHz] 600 600 600 600 III-V HEMTs 547 GHz for 30-nm P-HEMTs IEEE EDL, 25, 241 500 400 400 400 400 472 GHz for 30-nm LM-HEMTs JJAP, 41, 4B, 437 400 GHz for 45-nm P-HEMT IEEE EDL, 22, 507 400 200 200 200 200 SiGe HBTs Si CMOS 0 0 0 0 300 1985 1985 1985 1985 1990 1990 1990 1990 1995 1995 1995 1995 2000 2000 2000 2000 2005 2005 2005 2005 2010 2010 2010 2010 1998 2000 2002 2004 2006 2008 Year Year Year Year Year < Ref. : Shinohara et al. (IPRM 2004) > Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 3 Department of Information and Communications Department of Information and Communications
Gate Recess: Critical Process for Nano- - Gate Recess: Critical Process for Nano HEMT HEMT � Two-step recess for HEMT fabrication • 1 st step: wet etch � n + InGaAs/InAlAs multi-layer cap removal • 2 nd step: dry etch � InP etch stop layer removal: • Ar-based RIE (Conventional) • or Ne-based atomic layer etching (ALET) Ar-based plasma Wet etching & ALET ZEP ZEP Cap Cap InP InP Insulator Insulator Channel Channel Buffer Buffer <Ref: Suemitsu et al. (IEDM 98)> • Problems of Conventional Ar-based RIE • Low etch selectivity • Electrical & physical damage: � Ion bombardment Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 4 Department of Information and Communications Department of Information and Communications
Atomic Layer Etching Technique Atomic Layer Etching Technique (ALET) (ALET) Cl 2 gas InP layer Ne neutron-beam Reactant Feed Reactant Purge Beam Irradiation Product Purge Reactant molecules Excess reactant is An energetic beam Etching products are adsorb onto a substrate purged irradiates the surface, purged after which surface. The etchant and surface atoms one cycle of digital does not spontaneously bonded with reactant are etching is completed etch the substrate. etched off owing to beam- induced chemical etching. � 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 Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 5 Department of Information and Communications Department of Information and Communications
Etching Property of ALET Etching Property of ALET Composition of Selectivity of In 0.52 Al 0.48 As surface InP over In 0.52 Al 0.48 As 1.5 1.5 300 InP Bulk , Reference InP (80 Å )/InAlAs Epitaxial Structure , Atomic Layer Etching 250 1.2 1.2 , Reactive Ion Etching Etch Depth ( Å ) 200 As/InAl ratio 0.9 0.9 Al/In ratio 150 0.6 0.6 100 50 0.3 0.3 0 0.0 0.0 0 50 100 150 200 20 40 60 80 100 Number of Etch Cycles take-off angle � Very high selectivity of InP over InAlAs (~70) cf) Ar-based RIE (~20) � Minimal surface modification Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 6 Department of Information and Communications Department of Information and Communications
Surface Roughness Surface Roughness AFM image ALET RIE Wet etching 1.37 Å 2.97 Å 7.77 Å The smallest rms roughness achieved by ALET process Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 7 Department of Information and Communications Department of Information and Communications
Vertical Schottky Diode Vertical Schottky Diode 0 10 ALET RIE Ti/Pt/Au -2 10 2 ] -4 10 I [ mA/mm In 0.52 Al 0.48 As 3000Å -6 10 N-type InP sub. -8 10 -10 10 Ni/Ge/Au -12 10 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 V [V] RIE: Φ B = 0.56 eV, η = 1.25 � ALET: Φ B = 0.64 eV, η = 1.17 Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 8 Department of Information and Communications Department of Information and Communications
The Fabricated Devices The Fabricated Devices Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 9 Department of Information and Communications Department of Information and Communications
60- -nm Depletion nm Depletion- -Mode p Mode p- -HEMTs HEMTs 60 DC Characteristics 500 500 1200 0.4V ALET ALET 400 400 RIE RIE 0.3V 1000 I DS [ mA / mm ] I DS [ mA / mm ] 0.2V G M [ mS / mm ] 300 800 300 600 0.1V 200 200 400 0V 100 100 200 VDS=0.5V -0.1V -0.2V 0 0 0 0.0 0.1 0.2 0.3 0.4 0.5 -0.8 -0.6 -0.4 -0.2 0.0 0.2 V DS [ V ] V GS [ V ] • G M,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 Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 10 Department of Information and Communications Department of Information and Communications
60- -nm Depletion nm Depletion- -Mode HEMTs Mode HEMTs 60 RF Characteristics 60 50 ALET RIE 40 H 21 [ dB ] 30 20 10 VGS=0.05V,VDS=0.5V 398GHz f T =355GHz 0 1E8 1E9 1E10 1E11 1E12 Frequency [ Hz ] Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 11 Department of Information and Communications Department of Information and Communications
Enhancement- -mode HEMT (E mode HEMT (E- - Enhancement HEMTs) HEMTs) � 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 40 1.0 500 1600 Current gain H 21 E-HEMT Unilateral gain U g 0.8 400 MAG/MSG 30 1200 Stability factor K I DS [ mA / mm ] G M [ mS / mm ] 0.6 300 Gain [dB] 20 K 800 0.4 200 fmax = 470 GHz 10 400 0.2 100 fT = 403 GHz V DS = 0.5V V GS =0.4 V, V DS = 0.6 V 0 0.0 0 0 1 10 100 1000 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 Frequency [GHz] V GS [ V ] • V T = 0.07 V • F T of 403 GHz • Higher f T than D-HEMTs • ALET: g M,max = 1.38 S/mm • RIE: g M,max = 1.1 S/mm Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 12 Department of Information and Communications Department of Information and Communications
Conclusions Conclusions � The effect of ALET in the two-step gate recess process • Higher InP etch selectivity against the underlying In 0.52 Al 0.48 As 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 Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 13 Department of Information and Communications Department of Information and Communications
Other Interesting Stuffs !!! Other Interesting Stuffs !!! � Ring resonator based Optical Filters and Biosensors � Oxide Thin Film Transistors � Single Photon Detectors Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 14 Department of Information and Communications Department of Information and Communications
Thank You!! Gwangju Institute of Science & Technology Department of Information & Communications Gwangju wangju I Institute of nstitute of S Science and cience and T Technology echnology G 15 Department of Information and Communications Department of Information and Communications
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