ALD Nucleation and Area-Selective Deposition

ALD Nucleation and Area-Selective Deposition Prof Gregory N. Parsons Department of Chemical and Biomolecular Engineering North Carolina State University Raleigh North Carolina USA 1

Outline 1. Nucleation during ALD Inhibited, Island Growth 2. New model for Island Growth Use Growth Rate, Fit to starting defect density Definition of Selectivity Approach for Selective Deposition Comparison 3. Area Selective Deposition Motivation Methods to achieve selectivity Examples comparing selectivity data 4. Atomic Layer Etching 2

Shapes of Thin Film Nuclei vapor Three surface tensions: v1, v2, 12 phase 1 phase 2 Force Balance Equation: v1 12 v2 cos Wetting condition: v 1 12 v 2 equilibrium contact angle 3

Common Growth Modes Weber Volmer (WV) Frank Van der Merwe (FM) Stranski Krastanov (SK) v1 12 v2 v1 12 v2 balance of forces; 1 st layer wets surface, subsequent layers do not Strain 4

2D vs 3D Nucleation 2D: ALD TiO2 on ITO W Song et al. JACS (2014) 3D: ALD Pt on TiO2 Goulas et al. J.Mat.Chem.A (2012) 2D small nuclei coalesce 3D larger nuclei coalesce 5

ALD Thermochemistry OH + Al(CH 3 ) 3 O Al(CH 3 ) 2 + CH 4 First Half Reaction TMA (g) OH (s) Transition State 0 E(eV) 1 CH 4(g) 2 Lewis Acid/Base Product [ O Al(CH 3 ) 2 ] (s) C. Musgrave 6

What do we see experimentally? 7

Inhibited Growth Nuclei form via deposition on Defects present on starting surface? Defects generated during deposition? Both? What are the defects? 8

Controlling Nucleation ALD Island Growth Models 2003 Alum & Green 2004 Puurunen & Vandervorst 2007 O. Nilsen et al. ALD Blocking Layers ZnO: Yan, Marks, Chang et al. 2001 CVD Selectivity W, Si: Many authors Co: Yang et al. 2013 Improve Understanding of Nucleation and Selectivity Metals Metals Dielectrics Dielectrics 9

Island Growth Expected from Chemistry Steady State ALD: Brønsted Lowry acid/base reaction OH (acid) H + + CH 3 ligand (base). O : conjugate base; CH 4 is conjugate acid Surface maintains oxidation state A: Si OH + Al(CH 3 ) 3 Si O Al(CH 3 ) 2 + CH 4 B: Si O Al(CH 3 ) 2 + H 2 O Si O Al(OH) 2 + 2 CH 4 CH 4 purg ALD Nucleation: on metal (Si) Surface changes oxidation state Si H + H 2 O Si OH (Si 0 Si +1 ) 10

Outline 1. Nucleation during ALD Inhibited, Island Growth 2. New model for Island Growth Use Growth Rate, Fit to starting defect density Definition of Selectivity Approach for Selective Deposition Comparison 3. Area Selective Deposition Motivation Methods to achieve selectivity Examples comparing selectivity data 4. Atomic Layer Etching 11

We can Fit Curve Using Island Growth Model Geometric Island Distribution: Puurunen and Vandervorst JAP (2004) Multi regional equation for surface coverage: 12

We can Fit Curve Using Island Growth Model Geometric Island Distribution: O. Nilsen et al. JAP (2007) Multi regional equation for thickness: 13

Random Model More Realistic than Geometric Geometric Distribution: Random Distribution: 14

Growth Defect Sites: Present and Created On starting surface or passivation layer Created during ALD Defects on starting surface: 0.0 Generated during ALD: 0 15

Shape of Curve Determined by Defect Density Fewer Defect Nucleation Sites (present or created) 16

Avrami Equation: Surface coverage vs time A extended = same size, no overlap > A film > A 0 (large t) easy to find vs t Growth Rate: ; and Starting Nuclei Density: During 0 : Avrami Equation: 1 17

Avrami Equation: Thickness vs time Surface Coverage 1 exp Film thickness vs time one equation: Need only: and to find Measure, fit 18

Measure, fit Data: HfO 2 ALD on SiO 2 and a C:H Stevens et al. Chem Mat (2018) 19

Avrami Model Fits Most Data Sets Green et al. JAP 2002 HfO 2 ALD: HfCl 4 /H 2 O on SiO 2 and Si H Ġ = 0.052 nm/cycle N = 0.07 nm 2 R. Puurunen JAP 2004 HfO 2 ALD: HfCl 4 /H 2 O on SiO 2 and Si H Ġ = 0.047 nm/cycle N = 0.020 nm 2 20

Exception: Dynamic Coalescence Observed for Pt ALD Grillo et al. Chem Mat (2017) 21

Selectivity in Chemical Reactions A Chemical Reaction: 1 2 1 2 Definitions of Chemical Selectivity: Deposition Reaction: Desired Undesired Selectivity S = Thickness on 1 θ θ θ θ Selectivity S = 1 Thickness on 1 θ = Surface coverage Gladfelter, ChemMat (1993) changes with thickness 22

Definitions of Selectivity in Deposition 1. Thermodynamics: Selectivity, R G = ratio of driving force of the reaction on the desired surface to that on the undesired surface What is reaction with defects? 2. Elemental Counts: From the ratio of elemental counts, selectivity is 2000 to 1 : Depends on thickness 3. Film Thickness: Selectivity is 6 nm before substantial nucleation on nongrowth surface : Substantial? Selectivity is the amount of film we can grow in the desired region before nucleation in the non growth region sets on. Depends on measurement method 4. Film Growth Rate: These deposition rates indicate a selectivity of >185 : Depends on thickness Reinke et al. ACS AMI (2015) 23 Singh et al. Chem Mat (2018) Kalanyan et al. Chem Mat (2016) McDonnell et al. JPCC (2013) Carlsson & Boman JVSTA (1985)

Empirical Definition of Selectivity Gladfelter, Chem. Mat. 1993: Selectivity: θ θ θ θ S ranges from 0 to 1 θ S1, θ S2 : Coverage on growth and non growth surfaces θ s from SEM, TEM, AFM, STM, etc. Atomic %: from XPS, AES, RBS, etc. Problem: Selectivity value changes with thickness, growth time 24

Nucleation Model and Definition of Selectivity Fewer nucleation sites Improved Selectivity θ θ θ θ 0.9; 0.052. 25

Example: S = 0.9; t S=0.9 = 1.3 nm θ θ θ θ. Data from: Stevens et al. Chem Mat (2018) 26

Outline 1. Nucleation during ALD Inhibited, Island Growth 2. New model for Island Growth Use Growth Rate, Fit to starting defect density Definition of Selectivity Approach for Selective Deposition Comparison 3. Area Selective Deposition Motivation Methods to achieve selectivity Examples comparing selectivity data 4. Atomic Layer Etching 27

FIN FET Transistor

Self Aligned Via Used Now

Fully Aligned Via Needs Area Selective Deposition

Approaches to Area Selective Deposition Inherent Activated Passivated 31

Inherent 1. Pattern Si/SiO 2 2. ALD W: WF 6 + Si (s) W + SiF 4 : G<<0 WF 6 + SiO 2 : G>>0 0.62 5.0 10. 6.5 Kalanyan et al. Chem Mat (2016) 32

Activated 1. Electron/ion beam + MeCpPtMe 3 P O2 = 2 mtorr 2. ALD Pt: MeCpPtMe 3 /O 2 at 300 C 0.04 0.05.. Mackus et al. JPPC (2013) 0.04 0.0005.. P O2 = 800 mtorr 33

Activated 1. Pattern Pt 2. ALD Fe 2 O 3 : O 2 / t butyl ferrocene at 250 C 20 nm Singh et al. Chem Mat (2018) 34

Passivated Hydrophobic Hydrophilic Precursor Pulse No adsorption on SAM Argon Purge Reactant Pulse Argon Purge KJ Park et al. APL (2005) 35

Passivated 1. Solution coating of octadecyl trichlorosilane (ODTS) monolayer on patterned SiO 2 2. HfO 2 ALD:Tetrakis(dimethyl amido)hafnium Hf(N(CH 3 ) 2 ) 4 + H 2 O Deposition only on Si H regions Auger No growth on oxide/odts regions R.Chen et al. APL (2005) 36

Renew surface and extend selectivity Etching, Removal, Cleaning add third step. Single step Multiple steps Deposition: Etch/Renew: Repeat 37

Passivation + Removal 1. Solution deposit octadecylphosphonic acid (ODPA) SAM on Copper 2. Al 2 O 3 ALD: TMA/H 2 O at 150C 3. Acetic acid wet etch removes SAM and nuclei After wet etch: 5 10. 20 2 10. 100 0.12 Fit Quality? Hashemi et al. ACS Nano (2015) 38

Passivation + Regeneration SAM Vapor 1. Vapor deposit dodecanethiol (DDT) SAM on Copper 2. ZnO ALD: DEZ/H 2 O at 150C 3. Repeat 5 10. 200 0.18 Fit Quality? Hashemi et al. ACS AMI (2016) 39

In situ Cleaning 1. Pattern Cu/SiO 2 2. ZrO 2 ALD: ZyALD/Ethanol at 200C 3. Ethanol reduces CuO, inhibits ALD 2 3nm Selvaraj et al. JVST (2014) 40

In situ Gas Phase Inhibition 1. Expose Hacac (vapor inhibitor) to patterned SiO 2 /Al 2 O 3, adsorbs on SiO 2 2. One cycle of SiO 2 Plasma ALD: BDEAS (H 2 Si[N(C 2 H 5 ) 2 ] 2 ) & O 2 plasma 3. Repeat Mameli et al. ACS Nano (2017) 41

ALD + Etching 1. ~4 cycles Ta 2 O 5 Plasma ALD: TBTDET & O 2 on pattern TiN/SiO 2 surface 2. NF 3 plasma etch 3. Repeat Deposition 0.10 0.05. 1.0 Deposition + Etch 0.04 0.0002.. Vallat et al. JVSTA (2017) 42

Tungsten ALD: W on Al 2 O 3 ALD Cycle Number 43

WF 6 etches TiO 2 but not Al 2 O 3 Not Self limiting Ti + W + O + F at Equilibrium: < 100C: WO 3(s) + TiF 4(s) 220C: WO 2 F 2(g) + TiF 4(g) W, Ti volatile Al + W + O + F at Equilibrium: < 100C: WO 3(s) + AlF 3(s) 220C: WO 2 F 2(g) + AlF 3(s) Solid Equilibrium Concentration (mol) 1.0 0.8 0.6 0.4 0.2 0.0 TiF 4(s) WO 3(s) WF 6(g) TiF 4(g) HSC Chemistry 7.1 WF 2 O 2(g) Equilibrium Thermo Calculation 0 100 200 300 400 No Etching Etching 220C Temperature ( C) 44

Outline 1. Nucleation during ALD Inhibited, Island Growth 2. New model for Island Growth Use Growth Rate, Fit to starting defect density Definition of Selectivity Approach for Selective Deposition Comparison 3. Area Selective Deposition Motivation Methods to achieve selectivity Examples comparing selectivity data 4. Atomic Layer Etching 45

Self Limiting Plasma/Ion Atomic Layer Etching C.T. Carver et al. ECS J. Sol. St. Sci. and Tech. (2015) 46

Self Limiting Thermal Atomic Layer Etching Younghee Lee and S.M. George, ACS Nano (2015) 47

Self Limiting Thermal Atomic Layer Etching Younghee Lee, C. Huffman, S.M. George, Chem Mat (2016) 48

Self Limiting Thermal Atomic Layer Etching Younghee Lee, C. Huffman, S.M. George, Chem Mat (2016) 49

Self Limiting ALE: TiO 2 + WF 6 /BCl 3 190C: WF 6 + TiO 2 WO 3(s) + TiF 4(s) BCl 3 + WO 3(s) + TiF 4(s) BF 3(g) + WOCl 4(g) + TiCl 4(g) + B 2 O 3(s) Quartz Crystal Microbalance 170C W species volatile HSC Chemistry 7.1 Atomic Layer Etching Lemaire & Parsons, Chem Mat (2017)

Selective Area CVD of Cobalt CVD chemistry currently ahead of ALD for selective deposition Selective Co CVD Up to 9 nm C. C.Yang et al. Microelectronic Engineering (2013) 51

Summary 1. Nucleation during ALD Inhibited, Island Growth 2. New model for Island Growth Use Growth Rate, Fit to starting defect density Definition of Selectivity Approach for Selective Deposition Comparison 3. Area Selective Deposition Motivation Methods to achieve selectivity Examples comparing selectivity data 4. Atomic Layer Etching 52