Atomic Layer Etching : Application to Nanoelectronic Device - - PowerPoint PPT Presentation

Atomic Layer Etching : Application to Nanoelectronic Device Processing

1

Yeom, Geun Young

Department of Advanced Materials Science and Engineering Sungkyunkwan University, Korea

15 Oct. 2013

The Tenth U.S.-Korea Forum on Nanotechnology

Contents

1

Concept

• f Atomic Layer Etching (ALET)

2

Various Application Study of ALET

3

Summary

2

Concept of Atomic Layer Etching (ALET)

3

① Etchant Feed ③ Neutral beam irradiation ④ Etch Products Purge

 Concept of ALET Ar Beam 1 cycle

① Etchant Adsorption ② Etchant Purge ③ Etching Products Desorption ④ Etching Products Purge

Ar neutral beam irradiation

Atomic layer etching technology

4

◈ Chemisorption of Cl2 on Material

Dissociative Langmuir isotherm chemisorption : PCl2 k1 k2 Sputtering of MCl by Ar neutral impact :

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

2 2

1

ad k ad g

MCl M Cl   

2 2

1 1

1

Cl Cl MCl

P k P k   

Coverage of the MCl precursor :

) ( , ) (

2

g Ar k ad

MCl MCl

neu

    

neu

Ar MCl MCl

f k f 

2



2

2 2 1

) 1 (

Cl MCl MCl

P k    

Etch mechanism of atomic layer etching

5

Experimental Equipment

Adsorption step Desorption step

6

Various Application Study of ALET

7

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) Etch Rate (/cycle) RMS Roughness ()

1.57 /cycle 1.36 /cycle

• Conditions :

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 neutral 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

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)

1 2 3 4 5 6 7 8 9

Ar Beam Irradiation Dose (×1015 atoms/cm2·cycle) Etch Rate (/cycle) RMS Roughness ()

1.57 /cycle 1.36/cycle

Si ALET as a function of etch parameters

8

• Conditions :

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 dose 2.402×1015 atoms/cm2·cycle Cl2 pressure 0.46 mTorr Cl2 supply time (tCl2) 20 sec Substrate temp. R.T.

1.0 1.2 1.4 1.6 1.8 2.0 40 60 80 100 120 140 160 180 200 0.6 0.9 1.2 1.5 1.8

(100) (100) (100) (111) (111) (111)

50 100 150 200 250 300

Number of Etch Cycles Etch Rate (/cycle) Etch Depth () RMS Roughness ()

Si ALET as a function of etch cycles

9

• ICP Etching : BCl3 (50 sccm)/Ar (50 sccm), 300 W, -60 V, 12 mTorr, 149 sec
• Atomic Layer Etching : Neutral beam irradiation dose (1.485×1017 atoms/cm2·cycle), BCl3 pressure (0.33 mTorr),

Etch cycle (217 cycle)

• Conditions :

Reference ICP ALET

185 190 195 200 205

Binding Energy (eV)

Cl 2p (199.03 eV) 189.2 eV 190.9 eV B 1s

Intensity (arb. Unit)

Etch residue remaining on the etched surface

10

• Conditions :

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·cycle Cl2 pressure 0~0.62 mTorr Cl2 supply time (tCl2) 10 sec

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 /cycle 1.47 /cycle

Cl2 Pressure (mTorr) Etch Rate (/cycle) RMS Roughness ()

2 4 6 8 10 12 0.0 0.5 1.0 1.5 2.0 2.5

(100) (100) (111) (111)

2 4 6 8 10

1.69 /cycle 1.47 /cycle

Ne Neutral Beam Irradiation Dose (×1015 atoms/cm2·cycle) Etch Rate (/cycle) RMS Roughness ()

InP ALET as a function of etch parameters

11

• ICP Etching : Cl2 (70 sccm)/Ar (30 sccm), 700 W, -100 V, 12 sec
• Atomic Layer Etching : Neutral beam irradiation dose (7.2×1015 atoms/cm2·cycle), Cl2 pressure (0.4 mTorr),

Etch cycle (100 cycle)

• Conditions :

20 30 40 50 60 70 80 90 100 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) Atomic Percent (%) P/In Ratio

Stoichiometry modification of InP surface

12

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 -doping plane I - InAlAs spacer layer (3 nm)

 Conventional gate recess process : Combination of wet & dry recess etching

• 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)

Application – InP HEMTs (Gate Recess Process)

13

• 1.0
• 0.8
• 0.6
• 0.4
• 0.2

0.0 0.2 0.4 0.6 0.8 1E-14 1E-13 1E-12 1E-11 1E-10 1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01

Plasma Etching Atomic Layer Etching

Vschottky [V] ISchottky [mA/mm2]

Ideality factor ( ) Schottky barrier height (B ) Plasma Etching

1.25 0.56 eV

Atomic Layer Etching

1.17 0.64 eV

• Plasma Etching : Ar (50 sccm), 7 W, -65 V, 20 mTorr, 20 min
• Atomic Layer Etching : Neutral beam irradiation dose (7.2×1015 atoms/cm2·cycle), Cl2 pressure (0.4 mTorr),

Etch cycle (62 cycle)

• Conditions :

InP HEMTs (Gate Recess Process)

Schottky Diode Characteristics

14

• Plasma Etching : Ar (50 sccm), 7 W, -65 V, 20 mTorr, 15 min
• Atomic Layer Etching : Neutral beam irradiation dose (7.2×1015 atoms/cm2·cycle), Cl2 pressure (0.4 mTorr),

Etch cycle (41 cycle)

• Conditions :

60-nm depletion mode InP HEMT

RF characteristics

GM,Max of the p-HEMTs fabricated by the ALET process was larger than that using Ar-based RIE by 21%

DC Characteristics

15

• 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 0~2.67×1017 atoms/cm2·cycle BCl3 pressure 0~0.33 mTorr BCl3 supply time (tCl2) 20 sec

BCl3 Pressure (mTorr) Etch Rate (/cycle) RMS Roughness ()

• 1. 2 /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 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

Etch Rate (/cycle) RMS Roughness ()

1.2 /cycle

Ar Neutral Beam Irradiation Dose (×1016 atoms/cm2·cycle)

HfO2 ALET

16

• 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·cycl e BCl3 pressure 0.33 mTorr BCl3 supply time (tCl2) 20 sec

Number of Etch Cycles Etch Depth () Etch Rate (/cycle) RMS Roughness ()

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

HfO2 ALET

17

MOSFET fabrication with HfO2 ALET

<Main etch challenges>

• Gate dimensions down to

less than 30 nm

• CD control better than

2 nm required

• Low silicon recess (~ 1 nm)

Si

Gate oxide (HfO2) Metal (TiN) Poly-Si

Si

Metal Gate oxide (HfO2) Mask (TEOS) Metal (TiN) Poly-Si Mask (TEOS)

After Etch

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>

18

HfO2

SiO2

Si Glue Before ALET Process

3.5 nm 1.7 nm

Si

SiO2

Glue After 30 Cycle of ALET

1.6 nm

TEM Image of HfO2 etched by ALET

 Precise Etching of HfO2 on SiO2 using ALET : Blank wafer (HfO2 on SiO2] etching

19

MOSFET device results

20

MOSFET device as a function of gate length

21

Condition for atomic layer etching of graphene

Base Pressure 3.0×10-7 Torr Working Pressure 8.9×10-5 Torr Inductive Power 300 Watts 1st Grid Voltage No Bias 2nd Grid Voltage No Bias O2 Gas Flow Rate 20 sccm O2 radical exposure time 5 min Base Pressure 3.0×10-7 Torr Working Pressure 4.2×10-5 Torr Inductive Power 300 Watts 1st Grid Voltage 30 V 2nd Grid Voltage

• 150 V

Ar Gas Flow Rate 30 sccm Ar neutral beam Irradiation time 1 min

• 1. O2 Plasma Condition
• 1. O2 Plasma Condition
• 2. Ar Plasma Condition
• 2. Ar Plasma Condition

22

Atomic layer etching of HOPG (highly

• riented pyrolytic graphite) graphene
• 1. HOPG graphene

Reference

1000 1500 2000 2500 3000

Intensity Raman Shift

Reference

1 cycle

1000 1500 2000 2500 3000

1 Cycle

Intensity Raman Shift

Reference

1000 1500 2000 2500 3000

2 Cycle 1 Cycle

Intensity Raman Shift

Reference

2 cycle

1000 1500 2000 2500 3000

3 Cycle 2 Cycle 1 Cycle

Intensity Raman Shift

Reference

3 cycle

1000 1500 2000 2500 3000

4 Cycle 3 Cycle 2 Cycle 1 Cycle

Intensity Raman Shift

Reference

4 cycle

1000 1500 2000 2500 3000

5 Cycle 4 Cycle 3 Cycle 2 Cycle 1 Cycle

Intensity Raman Shift

Reference

5 cycle 6 cycle

1000 1500 2000 2500 3000

6 Cycle 5 Cycle 4 Cycle 3 Cycle 2 Cycle 1 Cycle

Intensity Raman Shift

Reference

23

LOGO Atomic layer etching of CVD graphene

CVD graphene

CVD graphene on SiO2 wafer Transmittance (%) Bilayer graphene 94.7 % Monolayer graphene (1 cycle ALET) 97.0 % No graphene (2 cycle ALET) 99.4 %

2.3 % 2.4 %

• 1. Transmittance differences: 2.3-2.4%

 Layer by Layer etching

• 2. 2D peak is recovered with annealing

process

• 3. D peak is generated because of high

energy of Ar beam (48 eV)

24

282 284 286 288 290

Binding Energy (eV) Intensity (count / s)

sp2 (284.6 eV) sp3 (286.7 eV) CO (289.1 eV) as-is graphene (n=2) O2 radical chemicsorbtion (n=2) 1 cycle ALET (n=1) Annealing (n=1)

5 10 20 30 40 60 70 80 90

as-is graphene O2 radical chemicsorbtion 1 cycle ALET Annealing

sp2 sp3 CO

Atomic percentage (%)

Carbon binding E change : Atomic layer etching of graphene

• 2. CVD graphene

C1s n : CVD graphene layer

Decrease 18.37 % Increase 12.77 % Increase 5.6 % Increase 7.72 % Decrease 1.85 % Decrease 5.6 % Increase 7.1 % Decrease 7.1 % 83.42 % 79.7 % 16.58 % 20.3 % 0 % 0 % 25

Restructure of graphene surface damage

2500 2600 2700 2800 2900

Intensity (a.u.) Raman Shift (cm

• 1)

Increase G` peak

H2:He Gas ratio: 42:1 Working pressure: 130 mTorr Temperature: 1000 oC Time: 30 min

Annealing

282 284 286 288 290

72.6 % 27.3 %

Binding energy (eV) Intensity (count / s)

C1s

282 284 286 288 290

79.7 % 20.3 %

Intensity (count / s) Binding energy (eV)

C1s

1500 2000 2500 3000

n = 2 n = 1 n = 1 n = 0 # 2 + Annealing # 3 + 1 cycle etching # 1 + 1 cycle etching Reference # 4 # 3 # 2 # 1

Intensity (a.u.) Raman Shift (cm

• 1)

# :experiment number n: graphene layer

before ALET #1+ 1 cycle ALET #3+ 1 cycle ALET

26

LOGO

Inductively coupled plasma (ICP) source - 13.56 Mhz Gas : Ar 25 - 125 sccm Power : 100 – 500 w 1st Grid voltage : 0 v 2nd Grid voltage : G

• Mass spectroscopy

10 20 30 40 50 0.00 2.50x10

5

5.00x10

5

7.50x10

5

1.00x10

6

Base pressure 1.0x10

• 6 Torr

Power : 250(w) 1st Grid : 0(v) 2nd Gird : G 25 (sccm) 50 (sccm) 75 (sccm) 100 (sccm) 125 (sccm) IEDF (c/s) Ion Energy (eV) 10 20 30 40 50 0.00 2.50x10

4

5.00x10

4

7.50x10

4

1.00x10

5

1.25x10

5

IEDF (c/s) 100 (w) 200 (w) 300 (w) 400 (w) 500 (w) Base pressure 1.0x10

• 6 Torr

Ar : 50(sccm) 1st Grid : 0(v) 2nd Gird : G Ion Energy (eV)

Ar beam energy modification

20 40 60 80 Intensity Ion Energy (eV)

27

LOGO

BN - insulator

Materials for future 2-D devices

MoS2, WS2, etc - semicondutor

28

Properties of ALET

The max-min non-uniformity : 2.56 % Wide process window

29

• Atomic layer etching has been successfully applied to

the fabrication of various nanoscale devices to nanoscale Si and III-V devices.

• Using the ALET, not only the precise etching depth

control but also the decrease of etch damage could be

• bserved.
• It is believed that ALET could be more successfully

applied to future 2-D device applications.

Summary

30

Thank you for your attention!

31