2017. 07. 15.
Geun Young Yeom
School of Advanced Materials Science and Engineering
Sungkyunkwan University (SKKU), Korea
Atomic Layer Etching with Ion/Neutral Beams
ALE 2017 Tutorial
2
Contents
ALE of Various Materials
(Si, III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
Introduction of Atomic Layer Etching with Ion/Neutral Beam
4
ALE Technology
1 Step
Etchant Adsorption
2 Step
Etchant Purge
Energetic Particle (photon/ion)
Irradiation
① Etchant Feed ③ Plasma Irradiation
④ Etch Products Purge
 Concept of ALET
Plasma
② Etchant Purge
3 Step
Etch Product Desorption
4 Step
Etch Product Purge
1 Cycle
Mechanism of ALE
4
 Chemisorption of Cl2 on materials
Dissociative Langmuir isotherm chemisorption :
PCl2
k1
k2
Sputtering of MCl by Ar bombardment:
where, k1 : adsorption rate constant (Pas)-1
k2 : desorption rate constant (s)-1
PCl2 : Cl2 pressure (Pa)
Sputtering rate of Cl-adsorbed Material (MCl) :
)()()(2 22 1
ad
k
adg MClMCl 
2
2
1
1
1 Cl
Cl
MCl
Pk
Pk


Coverage of the MCl precursor :
)(
,
)(
2
g
Ark
ad MClMCl neu
 
neuArMClMCl fkf 2
2
2
2
1
)1( ClMCl
MCl
P
k




 Desorption of chemisorbed materials by Ar+ bombardment
Adsorption Condition for ALE
 Irreversible saturation:
- Required for ALE
Surface saturates with a m
onolayer of precursor, stron
g chemisorption (=chemical
bonds formed)
 Reversible
saturation:
Physisorption only (weak bon
ds like van der Waals): once
precursor flux is stopped, surf
ace specie will desorb.
 Irreversible
non-saturation:
Physisorption multila
yers and continuous
deposition
Stop gas flow
5
Stop gas flow Stop gas flow
Adsorption and Reaction at Surfaces
6
Physisorption Chemisorption
weak, long range bonding
Van der Waals interactions
strong, short range bonding
Chemical bonding involving orbital overlap and
Charge transfer
Not surface specific Surface specific
ΔHads = 5~50 kJ/mol ΔHads = 50~500 kJ/mol
No surface reaction
Surface reactions may take place
Dissociation, reconstruction, catalysis
Multilayer adsorption
BET Isotherm used to model adsorption
equilibrium
Monolayer adsorption
Langmuir Isotherm used to model adsorption
equilibrium
First Principle Study of Al2O3 ALE
7
 Adsorption
Configuration Ah-EC Ah-TR At-EC AT-TR
Energy (Kcal/mol) -32.293 -32.142 -15.347 -17.574
Configuration Oh-EC Oh-TR Ot-EC Ot-TR
Energy (Kcal/mol) -32.633 -31.707 -45.617 -58.986
*: significant electron population change upon the
BCl3 adsorption
Cl B
Al
O
Ot-TR configuration led to the most stable BCl3 adsorption with an adsorption
energy of 58.99 Kcal/mol
“Understanding time-resolved processes in atomic-layer etching of ultra-thin Al2O3 film using BCl3 and Ar neutral beam”
Young I. Jhon, Kyung S. Min, G. Y. Yeom, and Young Min Jhon
Appl. Phys. Lett. 105, 093104 (2014)
Sputter Rate of Silicon in a Cl2 Environment
8
(8%)
(84%)
(8%)
“Near threshold sputtering of Si and SiO2 in a Cl2 environment”
D. J. Oostra, R. P. van Ingen, A. Haring, and A. E. de VriesG. N. A. van Veen
Appl. Phys. Lett. 50, 1506 (1987)
“Molecular dynamics simulation of atomic layer etching of silicon”
Satish D. Athavale and Demetre J. Economou
J. Vac. Sci. Technol. A 13 (2) (1995)
 Average product yield
Si ALE as a function of Ar Beam Energy
9
Below about 50 eV of energy, the chemical etching is found to be more dominant
than the physical sputtering. Etch rate increase by Ar energy (Threshold E < 50 eV)
Base pressure 2.0 × 10-6 Torr
Operating pressure 4.0 × 10-4 Torr
Cl2 partial pressure 10 mPa
tCl2 20 sec
tAr+ 5 sec
Ar flow rate 40 sccm
RF power 50 W
Ion acceleration
voltage
40 ~ 150 V
0 20 40 60 80 100 120 140 160
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
6
8
10
12
14
1/2 monolayer
EtchDepth(Å/halfcycle)
Ar Neutral Beam Energy (eV)
0.68
Si ALE as a function of Etch Parameters
10
 Use time domain to simplify
“Overview of atomic layer etching in the semiconductor industry”
Keren J. Kanarik, Thorsten Lill, Eric A. Hudson, Saravanapriyan Sriraman, Samantha Tan, Jeffrey Marks, Vahid Vahedi, and Richard A. Gottscho
J. Vac. Sci. Technol. A 33 (020802) (2015)
First Principle Study of Al2O3 ALE
11
 Desorption
“Understanding time-resolved processes in atomic-layer etching of ultra-thin Al2O3 film using BCl3 and Ar neutral beam”
Young I. Jhon, Kyung S. Min, G. Y. Yeom, and Young Min Jhon
Appl. Phys. Lett. 105, 093104 (2014)
Threshold Energy for Sputtering
12
Si
SiO2
 Ion energy control is essential to enable atomic
scale precision
 Energy threshold chosen specifically to enable reactant
activation and removal of one material selective to all others
“Atomic Layer Etching at the Tipping Point: An Overview”
G. S. Oehrlein, D. Metzler, and C. Li
ECS Journal of Solid State Science and Technology, 4 (6) N5041-N5053 (2015)
“Sputtering Yields at Very Low Bombarding Ion Energies”
R. V. Stuart and G. K. Wehner
Journal of Applied Physics, 7 (33) (1962)
Energy Control of Energetic Particles for Desorption
13
1) Ion mass
2) Frequency
 Energy distribution of the ions incident to the electrode by the above oscillation
500 eV Ar+ : velocity = 5 × 106 cm/sec
It takes 400 ns for the movement of 2 cm
Oscillation period at 13.56MHz
1
13.56 10
	 74	
∴ During the pass of sheath, the incident ions oscillate for a few times
+
2cm
maxmin
Energy Control of Energetic Particles for Desorption
14
 Novel plasma pulsing methods (waveforms) can be used to tailor ion energy
distribution function
“Control of ion energy distribution at substrates during plasma processing”
S.-B. Wang and A. E. Wendt
Journal of Applied Physics 88, 643 (2000)
“Atomic layer etching with pulsed plasmas”
Vincent M. DONNELLY, Demetre J, and ECONOMOU
US 20110139748A1, 2011
Formation of Energetic Neutral Beam
15
When the ion beam was reflected by a reflector at the angles lower than 15º,
most of the ions reflected were neutralized and the lower reflector angle showed
the higher degree of neutralization.
 Ion-surface neutralization
16
Contents
Introduction of Atomic Layer Etching (ALE) with Ion/Neutral Beam
ALE of Various Materials
(Si, III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
ALE using ECR Ion Source
17
CF4/O2
“Digital chemical vapor deposition and etching technologies for semiconductor processing”
Y. Horiike, T. Tanaka, M. Nakano, S. Iseda, H. Sakaue, A. Nagata, H. Shindo, S. Miyazaki, and M. Hirose
J. Vac. Sci. Techno!. A 8 (3) (1990)
ALE of Si using Low Energy Ion (ECR)
18
“Selflimited layerbylayer etching of Si by alternated chlorine adsorption and Ar+ ion irradiation”
Takashi Matsuura, Junichi Murota, Yasuji Sawada, and Tadahiro Ohmi
Appl. Phys. Lett. 63 (20) (1993)
ALE using Helical Plasma Source
19
“Realization of atomic layer etching of silicon”
Satish D. Athavale and Demetre J. Economou
J. Vac. Sci. Technol. B 14(6) (1996)
 Conditions :
Si ALE
20
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.0
0.4
0.8
1.2
1.6
2.0
(100)
(111)
(100)
(111)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Cl2 Pressure (mTorr)
EtchRate(Å/cycle)
RMSRoughness(Å)
1.57 Å/cycle
1.36 Å/cycle
0.0 0.4 0.8 1.2 1.6 2.0 2.4
0.0
0.4
0.8
1.2
1.6
2.0
(100)
(111)
(100)
(111)
0
1
2
3
4
5
6
7
8
9
Ar Beam Irradiation Dose
(×1015 atoms/cm2·cycle)
EtchRate(Å/cycle)
RMSRoughness(Å)
1.57 Å/cycle
1.36Å/cycle
Base pressure 2.0×10-6 Torr Chamber pressure 2.5×10-4 Torr Inductive power 800 Watts
Acceleration voltage 50 Volts Ar flow rate 10 sccm
Ar beam
irradiation dose
0~2.587×1015
atoms/cm2·cycle
Cl2 pressure 0~0.67 mTorr Cl2 supply time (tCl2) 20 sec Cycle 75 cycle
“Surface Roughness Variation during Si Atomic Layer Etching by Chlorine Adsorption Followed by an Ar Neutral Beam Irradiation”
S. D. Park, C. K. Oh, D. H. Lee, and G. Y. Yeom
Electrochemical and Solid-State Letters, 8 11 C177-C179 (2005)
Etch Residue
21
 Conditions :
 ICP Etching : BCl3 (50 sccm)/Ar (50 sccm), 300 W, -60 V, 12 mTorr, 149 sec
 Atomic Layer Etching : Ne beam irradiation dose (1.485×1017 atoms/cm2·cycle), BCl3 pressure (0.33 mTorr),
Etch cycle (217 cycle)
“Precise Depth Control and Low-Damage Atomic-Layer Etching of HfO2 using BCl3 and Ar Neutral Beam”
S. D. Park, W. S. Lim, B. J. Park, H. C. Lee, J. W. Bae, and G. Y. Yeom
Electrochemical and Solid-State Letters, 11 4 H71-H73 (2008)
22
Contents
Introduction of Atomic Layer Etching (ALE) with Ion/Neutral Beam
ALE of Various Materials
(Si, III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
GaAs ALE using ECR Source
23
Layer by layer etching with the etch rate in the range of 0.5 nm/cycle
has been achieved on GaAs.
“Controllable layerbylayer etching of III–V compound semiconductors with an electron cyclotron resonance source”
K. K. Ko and S. W. Pang
J. Vac. Sci. Techno!. B 11(6) (1993)
GaAs ALE
24
 Conditions :
Base pressure 3.0×10-7
Torr 1st
grid voltage 10 Volts Cl2 pressure 0~0.62 mTorr
Chamber pressure 2.0×10-4
Torr 2nd
grid voltage -250 Volts
Ne beam
Irradiation dose
0 ~ 4.55×1016
atoms/cm2·cycle
Inductive power 300 Watts Ne flow rate 70 sccm Cl2 supply time (tCl2) 10 sec
Cl2 gas pressure (mTorr)
Etchrate(Å/cycle)
RMSroughness(Å)
1.63 Å/cycle
1.41 Å/cycle
0.0 0.1 0.2 0.3 0.4 0.5 0.6
0.0
0.5
1.0
1.5
2.0
2.5
GaAs (100)
GaAs (111)
1
2
3
4
5
6
7
8
9
“Atomic layer etching of (100)/(111) GaAs with chlorine and low angle forward reflected Ne neutral beam”
Woong Sun Lim, Sang Duk Park, Byoung Jae Park, Geun Young Yeom
Surface & Coatings Technology 202, 5701–5704 (2008)
Stoichiometry Modification of GaAs Surface
25
 Conditions :
Base pressure 3.0×10-7
Torr 1st
grid voltage 10 Volts Cl2 pressure 0.4 mTorr
Chamber pressure 2.0×10-4
Torr 2nd
grid voltage -250 Volts
Ne neutral beam
Irradiation dose
3.03×1016
atoms/cm2·cycle
Inductive power 300 Watts Ne flow rate 70 sccm Cl2 supply time (tCl2) 10 sec
Inductive power 700 Watts Etch time 12sec
D.C bias voltage -100 Volts Gas pressure 12 mTorr [Cl2(70sccm)/Ar(30sccm)]
ALET
ICP
0
20
40
60
80
0.4
0.6
0.8
1.0
Atomicpercent(%)
As/Garatio
Ga
As
Reference ALET ICP
As/Ga ratio
XPS take off angle: 50°
40 60 80 100 120 140 160 180 200
0
50
100
150
200
250
300
350
GaAs (100)
GaAs (111)
0.0
0.5
1.0
1.5
2.0
2.5
1
2
3
4
5
6
7
Number of etch cycle
Etchrate(Å/cycle)
RMSroughness(Å)
Etchdepth(Å)
“Atomic layer etching of (100)/(111) GaAs with chlorine and low angle forward reflected Ne neutral beam”
Woong Sun Lim, Sang Duk Park, Byoung Jae Park, Geun Young Yeom
Surface & Coatings Technology 202, 5701–5704 (2008)
InP ALE
26
 Conditions :
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
0.0
0.5
1.0
1.5
2.0
2.5
(100) (100)
(111) (111)
1
2
3
4
5
1.69 Å/cycle
1.47 Å/cycle
Cl2 Pressure (mTorr)
EtchRate(Å/cycle)
RMSRoughness(Å)
0 2 4 6 8 10 12
0.0
0.5
1.0
1.5
2.0
2.5
(100) (100)
(111) (111)
0
2
4
6
8
10
1.69 Å/cycle
1.47 Å/cycle
Ne Beam Irradiation Dose
(×1015 atoms/cm2·cycle)
EtchRate(Å/cycle)
RMSRoughness(Å)
Base pressure 3.0×10-7 Torr Chamber pressure 8.9×10-5 Torr Inductive power 300 Watts
1st grid voltage 5 Volts 2nd grid voltage -250 Volts Ne flow rate 70 sccm
Ne neutral beam
irradiation dose
0~10.6×1015
atoms/cm2·cycl
e
Cl2 pressure 0~0.62 mTorr
Cl2 supply time
(tCl2)
10 sec
“Atomic layer etching of InP using a low angle forward reflected Ne neutral beam”
S. D. Park, C. K. Oh, J. W. Bae, G. Y. Yeom, T. W. Kim
Appl. Phys. Lett. 89, 043109 (2006)
Stoichiometry Modification of InP Surface
27
 Conditions :
 ICP Etching : Cl2 (70 sccm)/Ar (30 sccm), 700 W, -100 V, 12 sec
 Atomic Layer Etching : Ne beam irradiation dose (7.2×1015 atoms/cm2·cycle), Cl2 pressure (0.4 mTorr),
Etch cycle (100 cycle)
20 30 40 50 60 70 80 90 100
0
10
20
30
40
50
60
70
80
90
100
P peak As-is
In peak Atomic Layer Etching
C peak Conventional ICP Etching
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Θ (take-off angle)
AtomicPercent(%)
P/InRatio
“Atomic layer etching of InP using a low angle forward reflected Ne neutral beam”
S. D. Park, C. K. Oh, J. W. Bae, G. Y. Yeom, T. W. Kim
Appl. Phys. Lett. 89, 043109 (2006)
InGaAs ALE
28
Pristine 2.5 5 7.5 10 12.5 15 17.5 20
0
10
20
30
40
50
Cl Adsorption Time (sec)
In:Ga:AsAtomicPercentage(%)
Saturated Cl At% about 16%
In
Ga
As
Cl
0
5
10
15
20
25
30
ClAtomicPercentage(%)
0 10 30 50
0
20
40
60
80
100
(a)Ar
+
Ion Exposure Time :
50 (sec/cycle) × 100 Cycles
Acceleration Grid Voltage (V)
EtchDepth(Å)
“Atomic layer etching of InGaAs by controlled ion beam”
Jin Woo Park, Doo San Kim, Mu Kyeom Mun, Won Oh Lee, Ki Seok Kim amd Geun Young Yeom
Accepted by Journal of Physics D: Applied Physics
 Conditions :
Base pressure 2.0×10-6 Torr Chamber pressure 2.0×10-4 Torr
Inductive power 200 Watts
1st grid voltage 10 Volts 2nd grid voltage -100 Volts
Cl2 pressure 1.0 mTorr Ar pressure 3.0 mTorr
Cl supply time 10 sec Ar Irradiation time 50 sccm
InGaAs ALE
29
 Conditions :
Base pressure 2.0×10-6 Torr Chamber pressure 2.0×10-4 Torr Inductive power 200 Watts
1st grid voltage 10 Volts 2nd grid voltage -100 Volts Ar pressure 3.0 mTorr
Ar Irradiation time 50 sccm Cl2 pressure 1.0 mTorr Cl supply time 10 sec
0 10 20 30 40 50 60 70 80 90 100
0
50
100
150
200 InGaAs
Si
SiO2
HfO2
PR
ACL
Ar
+
Ion Exposure Time (sec/cycle)
EtchDepth(Å)
0.0
0.5
1.0
1.5
2.0
EtchRate(Å/Cycle)
100 200 300 400
100
200
300
400
500
EtchRate(Å/Cycle)
No. of ALE Cycles
EtchDepth(Å)
0.6
0.8
1.0
1.2
1.4
1.6
“Atomic layer etching of InGaAs by controlled ion beam”
Jin Woo Park, Doo San Kim, Mu Kyeom Mun, Won Oh Lee, Ki Seok Kim amd Geun Young Yeom
Accepted by Journal of Physics D: Applied Physics
Application – InP HEMTs (Gate Recess Process)
30
 Wet recess : InGaAs cap layer; Citric Acid + H2O2 = 7:1
 Dry recess : InP etch stop layer; Ar RIE [Ar (50 sccm), 7 W, -65 V, 20 mTorr]
“30 nm gate InAlAs/InGaAs HEMTs lattice-matched to InP substrates”
Tetsuya Suemitsu, Tetsuyoshi Ishii, Haruki Yokoyama, Yohatro Umeda, Takatomo Enoki, Yasunobu Ishii, Toshiaki Tamamura
Electron Devices Meeting, (1998). IEDM'98
 Conventional gate recess process : Combination of wet & dry recess etching
InAlAs Buffer
S.I. InP Substrate
InGaAs Channel
Ohmic contact : Ti/PtAu
n+ InGaAs cap layer (30 nm)
InP etch stop layer (6 nm)
I - InAlAs Schottky layer (8 nm)
Si d-doping plane
I - InAlAs spacer layer (3 nm)
InP HEMTs (Gate Recess Process)
31
 Conditions :
Base pressure 3.0×10-7 Torr Chamber pressure 2.0×10-4 Torr Inductive power 300 Watts
1st grid voltage 5 Volts 2nd grid voltage -250 Volts Ne flow rate 70 sccm
Ne neutral beam
Irradiation dose
7.2×1015
atoms/cm2·cycle
Cl2 pressure 0.4 mTorr
Cl2 supply time
(tCl2)
10 sec
EtchDepth(Å)
0 50 100 150 200
0
50
100
150
200
250
300
350
Number of Etch Cycles
InP Bulk
InP (80Å)/InAlAs Structure
AEPSE 2013
“A Two-Step-Recess Process Based on Atomic-Layer Etching for High-Performance In0.52Al0.48As/In0.53Ga0.47As p-HEMTs”
Tae-Woo Kim, Geun-Young Yeom, Jae-Hyung Jang, Jong-In Song
IEEE TRANSACTIONS ON ELECTRON DEVICES, 55, 7, (2008)
60 nm Depletion Mode InP HEMT
32
 Conditions :
 Plasma Etching : Ar (50 sccm), 7 W, -65 V, 20 mTorr, 15 min
 Atomic Layer Etching : Ne beam irradiation dose (7.2×1015 atoms/cm2·cycle), Cl2 pressure (0.4 mTorr),
Etch cycle (41 cycle)
GM,Max of the p-HEMTs fabricated by the ALET process was larger than that
using Ar-based RIE by 21%
DC Characteristics RF Characteristics
“A Two-Step-Recess Process Based on Atomic-Layer Etching for High-Performance In0.52Al0.48As/In0.53Ga0.47As p-HEMTs”
Tae-Woo Kim, Geun-Young Yeom, Jae-Hyung Jang, Jong-In Song
IEEE TRANSACTIONS ON ELECTRON DEVICES, 55, 7, (2008)
33
Contents
Introduction of Atomic Layer Etching (ALE) with Ion/Neutral Beam
ALE of Various Materials
(Si, III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
HfO2 ALE
34
 Conditions :
Base pressure 3.0×10-7 Torr Chamber pressure 2.0×10-4 Torr Inductive power 300 Watts
1st grid voltage 60 Volts 2nd grid voltage -250 Volts Ar flow rate 30 sccm
Ar beam
Irradiation dose
0~2.67×1017
atoms/cm2·cycle
BCl3 pressure 0~0.33 mTorr
BCl3 supply time
(tCl2)
20 sec
BCl3 Pressure (mTorr)
EtchRate(Å/cycle)
RMSRoughness(Å)
1. 2 Å/cycle
-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
0.0
0.3
0.6
0.9
1.2
1.5
1.8
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25 30
0.0
0.3
0.6
0.9
1.2
1.5
1.8
10
20
30
40
50
60
70
80
EtchRate(Å/cycle)
RMSRoughness(Å)
1.2 Å/cycle
Ar Beam Irradiation Dose
(×1016 atoms/cm2·cycle)
“Precise Depth Control and Low-Damage Atomic-Layer Etching of HfO2 using BCl3 and Ar Neutral Beam”
S. D. Park, W. S. Lim, B. J. Park, H. C. Lee, J. W. Bae, and G. Y. Yeom
Electrochemical and Solid-State Letters, 11 4 H71-H73 (2008)
HfO2 ALE
35
 Conditions :
Base pressure 3.0×10-7 Torr Chamber pressure 2.0×10-4 Torr Inductive power 300 Watts
1st grid voltage 60 Volts 2nd grid voltage -250 Volts Ar flow rate 30 sccm
Ar neutral beam
Irradiation dose
1.485×1017
atoms/cm2·cycle
BCl3 pressure 0.33 mTorr
BCl3 supply time
(tCl2)
20 sec
Number of Etch Cycles
EtchDepth(Å)
EtchRate(Å/cycle)
RMSRoughness(Å)
50 100 150 200 250 300
0.0
0.3
0.6
0.9
1.2
1.5
1.8
50
100
150
200
250
300
350
400
10
15
20
25
30
35
40
45
50
“Precise Depth Control and Low-Damage Atomic-Layer Etching of HfO2 using BCl3 and Ar Neutral Beam”
S. D. Park, W. S. Lim, B. J. Park, H. C. Lee, J. W. Bae, and G. Y. Yeom
Electrochemical and Solid-State Letters, 11 4 H71-H73 (2008)
Al2O3 ALE
36
 Conditions :
Base pressure 5.0×10-7 Torr Chamber pressure 2.5×10-4 Torr Inductive power 300 Watts
1st grid voltage 100 Volts 2nd grid voltage -250 Volts Ar flow rate 50 sccm
BCl3 gas flow rate 0~100 scmm BCl3 supply time (tCl2) 30 s
Ar neutral beam
Irradiation time
125 sec
50 75 100 125 150
0.0
0.5
1.0
1.5
2.0 Region 3Region 2Region 1
SuputterRate(Å/cycle)
1
st
Grid Voltage (V)
0.0
0.5
1.0
1.5
2.0
EtchRate(Å/cycle)
0 25 50 75 100
0.00
0.25
0.50
0.75
1.00
1.25
One monolayer (0.95 - 1.05 Å / cycle)
EtchRate(Å/cycle)
Gas Flow Rate (sccm)
10
20
30
40
50
SurfaceRoughness(Å)
“Atomic layer etching of Al2O3 using BCl3/Ar for the interface passivation layer of III–V MOS devices”
K.S. Min a, S.H. Kang a, J.K. Kim a,c, Y.I. Jhon b, M.S. Jhon b, G.Y. Yeom
Microelectronic Engineering 110, 457–460 (2013)
BeO ALE
37
 Conditions :
Base pressure 5.0×10-7 Torr Chamber pressure 2.5×10-4 Torr Inductive power 300 Watts
1st grid voltage 125 Volts 2nd grid voltage -250 Volts Ar flow rate 50 sccm
BCl3 gas flow rate 0~100 scmm BCl3 supply time (tCl2) 30 s
Ar neutral beam
Irradiation time
125 sec
50 100 150 200 250
50
100
150
200
EtchRate(Å/min)
EtchRate(Å/cycles)
Number of Atomic Layer Etch Cycles
0.25
0.50
0.75
1.00
1.25
1.50
1.75
0 25 50 75 100
0.00
0.25
0.50
0.75
1.00 Ar 125(v) 250(s)
One monolayer (0.7 - 0.8 Å / cycle)
EtchRate(Å/cycle)
Gas Flow Rate (sccm)
“Atomic layer etching of BeO using BCl3/Ar for the interface passivation layer of III–V MOS devices”
K.S. Min, S.H. Kang, J.K. Kim, J.H. Yumg, Y.I. Jhon, Todd W. Hudnall, C.W. Bielawski, S.K. Banerjee, G. Bersuker, M.S. Jhon, G.Y. Yeom
Microelectronic Engineering 114, 121–125 (2014)
MOSFET Fabrication with HfO2 ALE
38
 Main etch challenges
 Gate dimensions down to
less than 30 nm
 CD control better than
2 nm required
 Low silicon recess (~ 1 nm)
HfO2
TiN
Over etching Etch residue
Charge trap
in oxide layer
HfO2
TiN
Precise depth control
No etch
residue
No charging
damage
Convention RIE etcher Atomic layer etcher
“Atomic layer etching of ultra-thin HfO2 film for gate oxide in MOSFET devices”
Jae Beom Park, Woong Sun Lim, Byoung Jae Park, Ih Ho Park, Young Woon Kim and Geun Young Yeom
J. Phys. D: Appl. Phys. 42, 055202 (2009)
Silicon
Gate Oxide (HfO2)
Metal (TiN)
Poly-Si
Mask
(TEOS)
Silicon
Gate Oxide (HfO2)
Metal (TiN)
Poly-Si
Mask
(TEOS)
After etch
TEM Image of HfO2 Etched by ALE
39
HfO2
SiO2
Si
Glue
Before ALE process
3.5 nm
1.7 nm
Si
SiO2
Glue
After 30 cycles of ALE
1.6 nm
 Precise etching of HfO2 on SiO2 using ALE
: Blank wafer (HfO2 on SiO2) etching
“Atomic layer etching of ultra-thin HfO2 film for gate oxide in MOSFET devices”
Jae Beom Park, Woong Sun Lim, Byoung Jae Park, Ih Ho Park, Young Woon Kim and Geun Young Yeom
J. Phys. D: Appl. Phys. 42, 055202 (2009)
MOSFET IG-VG
40
However, there are differences in MOSFET (without S/D active region) due to
gate oxide edge damage which could be the leakage path in the heterogeneous
interface between the high-k dielectric and the capping nitride layer
“Atomic layer etching of ultra-thin HfO2 film for gate oxide in MOSFET devices”
Jae Beom Park, Woong Sun Lim, Byoung Jae Park, Ih Ho Park, Young Woon Kim and Geun Young Yeom
J. Phys. D: Appl. Phys. 42, 055202 (2009)
MOSFET IG-VG
41
JG
(A/cm
2
)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
10
-7
10
-5
10
-3
10
-1
10
1
G
(a)NMOSCAP
Area = 2x10
-5
cm
2
WE
RIE
ALE
PMOSCAP
Area = 2x10
-5
cm
2
VG
(V)
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
10
-7
10
-5
10
-3
10
-1
10
1
(b) NMOSFET W / L = 10m / 1.0m
G
S D
WE
RIE
ALEJ(A/cm
2
)
VG
(V)
IG-VG characteristics of STI edge transistor
IG-VG characteristics of S/D edge transistor
The ALET can minimize the plasma etching
damage at the edge of gate oxide.
“Atomic layer etching of ultra-thin HfO2 film for gate oxide in MOSFET devices”
Jae Beom Park, Woong Sun Lim, Byoung Jae Park, Ih Ho Park, Young Woon Kim and Geun Young Yeom
J. Phys. D: Appl. Phys. 42, 055202 (2009)
Silicon
Gate Oxide
Metal Gate
Poly-Si
Gate Stack
Reference Antenna Structure MOSFET
No Antenna
Plate Type Comb Type
MOSFET Device as a function of Gate Length
42
 MOS Parameter - IG
As gate length decrease from 1 um to 100 nm, the gate leakage current is as
low as wet etching compared that of plasma etching
“Atomic layer etching of ultra-thin HfO2 film for gate oxide in MOSFET devices”
Jae Beom Park, Woong Sun Lim, Byoung Jae Park, Ih Ho Park, Young Woon Kim and Geun Young Yeom
J. Phys. D: Appl. Phys. 42, 055202 (2009)
43
Contents
Introduction of Atomic Layer Etching (ALE) with Ion/Neutral Beam
ALE of Various Materials
(III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
Need for ALE
44
 Films getting thinner: slow etch rate is not a problem
 High etch selectivity
∙ Negligible etching into underlayer
 Low etch damage and contamination
 Precise control of etch depth in atomic scale
“Atomic Level Etching of Poly-Si in a Microwave Electron Cyclotron Resonance Plasma Etcher”
Yasushi Sonoda (HITACHI)
Possible Application of Anistropic ALE
45
Gate etch Contact etch Dummy/Sacrificial
layer removal
2D-materials
46
“Fluorocarbon-based Atomic Layer Etching of Silicon Dioxide for Self-aligned Contact”
Eric Hudson (Lam Reserach)
Logic Challenges for 10 nm Node and Beyond
 Self-aligned contact
ALE of SiO2 using ICP with Pulsing Gases
47
“Fluorocarbon assisted atomic layer etching of SiO2 using cyclic Ar/C4F8 plasma”
Dominik MetzlerRobert L. Bruce, Sebastian Engelmann, and Eric A. Joseph Gottlieb S. Oehrlein
J. Vac. Sci. Technol. A 32, 020603 (2014)
SEMATECH ALET Workshop
April 21, 2014
ALE Tool by Lam Research Inc.
48
“Fluorocarbon-based Atomic Layer Etching of Silicon Dioxide for Self-aligned Contact”
Eric Hudson (Lam Research)
 Oxide ALE for SAC etch
: Better selectivity and loading
ALE Tool by Lam Research Inc.
49
 Deposition + Activation cyclic process
: Concept vs. Experiment
“Fluorocarbon-based Atomic Layer Etching of Silicon Dioxide for Self-aligned Contact”
Eric Hudson (Lam Research)
SiO2 ALE using O2 as Desorption Gas
50
“A novel atomic layer etching of SiO2 with alternating O2 plasma with fluorocarbon film deposition”
Takayoshi Tsutsumi (Nagoya Uni.), Masaru Zaitsu, Akiko Kobayashi, Hiroki Kondo,
Toshihisa Nozawa, Nobuyoshi Kobayashi, Masaru Hori
CxFy film
SiO2
Substrate
Fluorocarbon
plasma
Ar plasma
C-C
Ar+ COy
SiF2 or SiF4
CxFy film
SiO2
Substrate
Ar/C4F8
plasma
O2 plasma
Ox
+ COy
SiF2 or SiF4
 Advantage
 To remove extra carbon such as CO or CO2, COFx during ALE
 To maintain clean chamber by O2 plasma process
Step 1 Step 2 Step 1 Step 2
Low Energy E-beam Etch Tool of Applied Materials for ALE
51
 Electron beam-generated plasma etch tool
“Low Damage Etch Chamber for Atomic Precision Etching”
L. Dorf, S. Rauf, A. Agarwal, G. Monroy, K. Ramaswamy, K. Collins (Applied Materials)
Low Energy E-beam Etch Tool of Applied Materials for ALE
52
“Low Damage Etch Chamber for Atomic Precision Etching”
L. Dorf, S. Rauf, A. Agarwal, G. Monroy, K. Ramaswamy, K. Collins (Applied Materials)
 Si ALE in chlorine at different ion energies
53
Cyclic Etch Tool by TEL
“Modeling and simulation for rapid advanced cyclic etch processes”
Peter Ventzek (TEL)
 One way
: Spatial pulsing with microwave plasma processes
 Allows access to an energy range where
chemistry can be done on a surface and
the sub-surface left pristine
ECS
Bias 13.56 MHz
Plasma diffusion region
Plasma generation region
Microwave (2.45 GHz)
Z
54
ALE Tool by Hitachi
“Atomic Level Etching of Poly-Si in a Microwave Electron Cyclotron Resonance Plasma Etcher”
Yasushi Sonoda (HITACHI)
 Gas pulsing process
: Tri-time modulation
A: Etch
B: Depo C: Purge
Si
Cl2-based
plasma
O2-based
plasma
Ar plasma
SiN Mask
Depo film
A: Etch
 Cl2-based
Si etch step
 Bias & Plasma
pulsing
B: Depo
 O2-based
passivation
step
C: Purge
 Ar purge
step
 Tri-TM is triadic combination of pulsing techniques, bias plasma and gas pulsing
 Tri-TM process is demonstrated for Fin etching of Si
55
ALE Tool by Hitachi
“Atomic Level Etching of Poly-Si in a Microwave Electron Cyclotron Resonance Plasma Etcher”
Yasushi Sonoda (HITACHI)
 Results: Gas pulsing process
: Gas pulsing enables to realize the vertical profile and higher selectivity
Single step process Gas pulsing process
A: Etch
A: Etch
B: Depo C: Purge
Continuous process:
 Tapered profile
 Lower selectivity
 Rounding etch front
Gas pulsing process achieves:
 Vertical profile
 Higher selectivity
 Flat etch front
*Specification of etching sample
- L/S 1:1 32 nmDP
- SiN-HM (60 nm)/Si
Possible Advantage of Neutral Beam instead of Ar Ion Beam?
56
50 100 150 200
100
150
200
250
300
350
0 to 50
50 to 100
100 to 150
150 to 200
EtchDepth(Å)
Number of Cycles
(b)
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
EtchRate(Å/cycle)per50cycle
Ref Damaged CF₄ CF₄
+5cy
CF₄
+10cy
100cy
1.1
1.2
1.3
1.4
1.5
1.6 (b)
1.27
1.29
1.31
1.37
1.42
SheetResistance(x100Ω/□)
Experimental Condition
1.24
ALE condition
“Damaged silicon contact layer removal using atomic layer etching for deep-nanoscale semiconductor devices”
Jong Kyu Kim, Sung Il Cho, Sung Ho Lee, Chan Kyu Kim, Kyung Suk Min, Seung Hyun Kang, and Geun Young Yeom
Journal of Vacuum Science & Technology A 31, 061310 (2013)
“Atomic layer etching removal of damaged layers in a contact hole for low sheet resistance”
Jong Kyu Kim, Sung Il Cho, Sung Ho Lee, Chan Kyu Kim, Kyung Suk Min, and Geun Young Yeom
Journal of Vacuum Science & Technology A 31, 061302 (2013)
Possible Advantage of Neutral Beam instead of Ar Ion Beam?
Etch selectivity improved by over 60 %
with low-damage plasma source
57
58
Contents
Introduction of Atomic Layer Etching (ALE) with Ion/Neutral Beam
ALE of Various Materials
(III-V Compounds, High-k Dielectirics)
Recent Research Trends
Summary
Summary
59
Gas
Gas
Gas
Power
Power
Power
Continuous etch
RF Bias Pulsing
Cycle time ~0.1-10 ms
Gas Pulsing (ALE)
Cycle time ~0.1-10 sec
Time
 Continuous Etch
 Maintain constant gas and RF power
 Recipe steps typically >10 sec
 RF Pulsing
 Rapid variation in RF power to plasma
 Many different process benefits
 Bias pulsing modulates ion energy,
effectively decouples ion energy control
from gas neutral chemistry
 Gas Pulsing
 Rapid variation of gas mixture delivered to reactor
 Generally slower than RF pulsing
 Synchronize gases to RF power (bias)
to enable processes of atomic layer etching
 Neutral Beam ? What else ?
Properties of ALE
60
Theoretical Uniformity : 0.0 %Wide process window