The Tenth U.S.-Korea Forum on Nanotechnology Atomic Layer Etching : Application to Nanoelectronic Device Processing 15 Oct. 2013 Yeom, Geun Young Department of Advanced Materials Science and Engineering Sungkyunkwan University, Korea 1
Contents Concept 1 of Atomic Layer Etching (ALET) Various Application Study of ALET 2 Summary 3 2
Concept of Atomic Layer Etching (ALET) 3
Atomic layer etching technology ① Etchant Adsorption ② Etchant Purge Concept of ALET ① Etchant Feed ③ Neutral beam irradiation ④ Etch Products Purge Ar Beam 1 cycle ④ Etching Products Purge ③ Etching Products Desorption Ar neutral beam irradiation 4
Etch mechanism of atomic layer etching ◈ Chemisorption of Cl 2 on Material Dissociative Langmuir isotherm chemisorption : 2 2 k Cl M 1 MCl P Cl2 2 ( ) ( ) ( ) g ad ad k 2 Coverage of the MCl precursor : k 1 2 k P 1 Cl 2 MCl k 1 2 MCl ( 1 ) 1 P k P 1 MCl Cl Cl 2 2 , Sputtering of MCl by Ar neutral impact : k Ar 2 MCl MCl neu ( ) ( ) ad g k 1 : adsorption rate constant (Pa s) -1 where, k 2 : desorption rate constant (s) -1 P Cl2 : Cl 2 pressure (Pa) Sputtering rate of Cl-adsorbed Material (MCl) : f k f 2 MCl MCl Ar neu 5
6 Desorption step Experimental Equipment Adsorption step
Various Application Study of ALET 7
Si ALET as a function of etch parameters Conditions : 2.0 × 10 -6 Torr Chamber pressure 2.5 × 10 -4 Torr Base pressure Inductive power 800 Watts 0~2.587 × 10 15 Ar neutral beam Ar flow rate Acceleration voltage 50 Volts 10 sccm atoms/cm 2 ·cycle irradiation dose Cl 2 supply time Cl 2 pressure 0~0.67 mTorr 20 sec Cycle 75 cycle (t Cl2 ) 2.0 9 2.0 5.5 8 5.0 1.57 � /cycle 1.57 � /cycle RMS Roughness ( � ) RMS Roughness ( � ) Etch Rate ( � /cycle) Etch Rate ( � /cycle) 1.6 1.6 7 4.5 1.36 � /cycle 6 4.0 1.36 � /cycle 1.2 1.2 5 3.5 (100) (111) (100) 4 3.0 (100) 0.8 0.8 (111) (111) (100) 3 2.5 (111) 0.4 2 2.0 0.4 1 1.5 0.0 0.0 0 1.0 0.0 0.4 0.8 1.2 1.6 2.0 2.4 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Ar Beam Irradiation Dose Cl 2 Pressure (mTorr) ( × 10 15 atoms/cm 2 ·cycle) 8
Si ALET as a function of etch cycles Conditions : 2.0 × 10 -6 Torr Chamber pressure 2.5 × 10 -4 Torr Base pressure Inductive power 800 Watts 2.402 × 10 15 Ar beam Ar flow rate Acceleration voltage 50 Volts 10 sccm dose atoms/cm 2 ·cycle Cl 2 supply time (t Cl2 ) Cl 2 pressure 0.46 mTorr 20 sec Substrate temp. R.T. 300 2.0 (100) (100) (100) (111) (111) (111) 1.8 RMS Roughness ( � ) 250 1.8 Etch Rate ( � /cycle) Etch Depth ( � ) 1.5 200 1.6 1.2 150 1.4 0.9 100 1.2 0.6 50 1.0 40 60 80 100 120 140 160 180 200 Number of Etch Cycles 9
Etch residue remaining on the etched surface Conditions : - ICP Etching : BCl 3 (50 sccm)/Ar (50 sccm), 300 W, -60 V, 12 mTorr, 149 sec - Atomic Layer Etching : Neutral beam irradiation dose ( 1.485 × 10 17 atoms/cm 2 ·cycle), B Cl 3 pressure (0.33 mTorr), Etch cycle (217 cycle) B 1s Cl 2p (199.03 eV) 189.2 eV 190.9 eV Intensity (arb. Unit) ALET ICP Reference 185 190 195 200 205 Binding Energy (eV) 10
InP ALET as a function of etch parameters Conditions : 3.0 × 10 -7 Torr Chamber pressure 8.9 × 10 -5 Torr Base pressure Inductive power 300 Watts 2 nd grid voltage 1 st grid voltage 5 Volts -250 Volts Ne flow rate 70 sccm 0~10.6 × 10 15 Ne neutral beam Cl 2 pressure 0~0.62 mTorr Cl 2 supply time (t Cl2 ) 10 sec atoms/cm 2 ·cycle irradiation dose 2.5 10 2.5 5 (100) (100) (100) (100) (111) (111) (111) (111) RMS Roughness ( � ) RMS Roughness ( � ) Etch Rate ( � /cycle) Etch Rate ( � /cycle) 2.0 1.69 � /cycle 2.0 8 1.69 � /cycle 4 1.5 1.5 6 1.47 � /cycle 3 1.47 � /cycle 1.0 1.0 4 2 0.5 0.5 2 1 0.0 0.0 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 2 4 6 8 10 12 Ne Neutral Beam Irradiation Dose Cl 2 Pressure (mTorr) ( × 10 15 atoms/cm 2 ·cycle) 11
Stoichiometry modification of InP surface Conditions : - ICP Etching : Cl 2 (70 sccm)/Ar (30 sccm), 700 W, -100 V, 12 sec - Atomic Layer Etching : Neutral beam irradiation dose (7.2 × 10 15 atoms/cm 2 ·cycle), Cl 2 pressure (0.4 mTorr), Etch cycle (100 cycle) 100 1.4 P peak As-is 90 In peak Atomic Layer Etching Atomic Percent (%) C peak Conventional ICP Etching 1.2 80 70 P/In Ratio 1.0 60 50 0.8 40 0.6 30 20 0.4 10 0 0.2 20 30 40 50 60 70 80 90 100 Θ (take-off angle) 12
Application – InP HEMTs (Gate Recess Process) Ohmic contact : Ti/PtAu n + InGaAs cap layer (30 nm) InP etch stop layer (6 nm) InGaAs Channel I - InAlAs Schottky layer (8 nm) InAlAs Buffer Si -doping plane S.I. InP Substrate I - InAlAs spacer layer (3 nm) Conventional gate recess process : Combination of wet & dry recess etching - Wet recess : InGaAs cap layer; Citric Acid + H 2 O 2 = 7:1 - Dry recess : InP etch stop layer; Ar RIE (Ar (50 sccm), 7 W, -65 V, 20 mTorr) 13
InP HEMTs (Gate Recess Process) Schottky Diode Characteristics Conditions : - Plasma Etching : Ar (50 sccm), 7 W, -65 V, 20 mTorr, 20 min - Atomic Layer Etching : Neutral beam irradiation dose (7.2 × 10 15 atoms/cm 2 ·cycle), Cl 2 pressure (0.4 mTorr), Etch cycle (62 cycle) 0.01 Plasma Etching 1E-3 Atomic Layer Etching 1E-4 I Schottky [mA/mm 2 ] 1E-5 Ideality factor Schottky barrier height ( B ) ( ) 1E-6 1E-7 1.25 0.56 eV Plasma Etching 1E-8 1E-9 Atomic Layer 1.17 0.64 eV Etching 1E-10 1E-11 1E-12 1E-13 1E-14 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 V schottky [V] 14
60-nm depletion mode InP HEMT Conditions : - Plasma Etching : Ar (50 sccm), 7 W, -65 V, 20 mTorr, 15 min - Atomic Layer Etching : Neutral beam irradiation dose (7.2 × 10 15 atoms/cm 2 ·cycle), Cl 2 pressure (0.4 mTorr), Etch cycle (41 cycle) DC Characteristics RF characteristics G M,Max of the p-HEMTs fabricated by the ALET process was larger than that using Ar-based RIE by 21% 15
HfO 2 ALET Conditions : 3.0 × 10 -7 Torr Chamber pressure 2.0 × 10 -4 Torr Base pressure Inductive power 300 Watts 2 nd grid voltage 1 st grid voltage 60 Volts -250 Volts Ar flow rate 30 sccm 0~2.67 × 10 17 Ar neutral beam BCl 3 pressure 0~0.33 mTorr BCl 3 supply time (t Cl2 ) 20 sec atoms/cm 2 ·cycle Irradiation dose 1.8 80 1.8 90 80 70 1.5 RMS Roughness ( � ) 1.5 Etch Rate ( � /cycle) RMS Roughness ( � ) Etch Rate ( � /cycle) 1. 2 � /cycle 1.2 � /cycle 70 60 1.2 1.2 60 50 0.9 0.9 50 40 0.6 0.6 40 30 0.3 0.3 30 20 20 0.0 0.0 10 10 0 5 10 15 20 25 30 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 Ar Neutral Beam Irradiation Dose BCl 3 Pressure (mTorr) ( × 10 16 atoms/cm 2 ·cycle) 16
HfO 2 ALET Conditions : 3.0 × 10 -7 Torr Chamber pressure 2.0 × 10 -4 Torr Base pressure Inductive power 300 Watts 2 nd grid voltage 1 st grid voltage 60 Volts -250 Volts Ar flow rate 30 sccm 1.485 × 10 17 Ar neutral beam BCl 3 pressure atoms/cm 2 ·cycl 0.33 mTorr BCl 3 supply time (t Cl2 ) 20 sec Irradiation dose e 1.8 400 50 45 350 1.5 RMS Roughness ( � ) Etch Rate ( � /cycle) 40 Etch Depth ( � ) 300 1.2 35 250 0.9 30 200 0.6 25 150 0.3 20 100 15 0.0 50 10 50 100 150 200 250 300 Number of Etch Cycles 17
MOSFET fabrication with HfO 2 ALET <Main etch challenges> Gate dimensions down to Mask Mask (TEOS) (TEOS) less than 30 nm CD control better than After Etch Poly-Si Poly-Si 2 nm required Metal (TiN) Low silicon recess (~ 1 nm) Metal (TiN) Metal Gate oxide (HfO2) Gate oxide (HfO2) Si Si <Convention RIE etcher> <Atomic layer etcher> No Charging Damage No Etch Charge trap Residue TiN TiN In oxide layer HfO2 HfO2 Over etching Precise depth control Etch Residue 18
TEM Image of HfO 2 etched by ALET Precise Etching of HfO 2 on SiO 2 using ALET : Blank wafer (HfO 2 on SiO 2 ] etching Glue Glue HfO 2 3.5 nm 1.7 nm SiO 2 SiO 2 1.6 nm Si Si Before ALET Process After 30 Cycle of ALET 19
20 MOSFET device results
MOSFET device as a function of gate length 21
Condition for atomic layer etching of graphene 1. O 2 Plasma Condition 1. O 2 Plasma Condition Base Pressure 3.0×10 -7 Torr Working Pressure 8.9×10 -5 Torr Inductive Power 300 Watts 1 st Grid Voltage No Bias 2 nd Grid Voltage No Bias O 2 Gas Flow Rate 20 sccm 5 min O 2 radical exposure time 2. Ar Plasma Condition 2. Ar Plasma Condition Base Pressure 3.0×10 -7 Torr Working Pressure 4.2×10 -5 Torr Inductive Power 300 Watts 1 st Grid Voltage 30 V 2 nd Grid Voltage -150 V Ar Gas Flow Rate 30 sccm 1 min Ar neutral beam Irradiation time 22
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