In-situ Monitoring of Thin-Film Formation Processes by Spectroscopic Ellipsometry

In-situ Monitoring of Thin-Film Formation Processes by Spectroscopic Ellipsometry Alexey Kovalgin Chair of Semiconductor Components MESA+ Institute for Nanotechnology

Motivation Advantages of in-situ over ex-situ: Real-time monitoring incubation time process kinetics transition effects accurate wafer loading/unloading effects are excluded Possible to observe features not seeable by exsitu techniques Precise control of film thickness Non-destructive method (both in- and ex-situ) 2

The group s science Today s Talk CMOS Add functionality More than Moore Downsizing More CMOS Metal-semi junctions Thin silicon Matching, reliability Low-temp fabrication Radiation/gas detectors Light from silicon Tunable components Nanotech Beyond Moore Nano-electronics: Thin films & devices 3

SC Members Contributing to This Work Bui Van Hao Arjen Boogaard Tom Aarnink Alfons Groenland Ihor Brunets Rob Wolters Jurriaan Schmitz 4

Outline Cluster Deposition System Real-Time Monitoring by SE Thermal Atomic Layer Deposition of TiN In-situ Thermal Oxidation of TiN Ex-situ Thermal Oxidation of TiN (a comparison) Plasma Oxidation of TiN Plasma Oxidation of Si ICPECVD of SiO 2 Percolation Effects by SE Conclusions 5

Home-Built Cluster Deposition System Reactor 1 CVD plasma mode Low temp SiO 2 Reactor 2 ALD (CVD) WN x C y TiN a-si Reactor 3 1 2 3 ALD (CVD) Loadlock High-K Al 2 O 3 7

Thermal ALD of TiN Step 1: Heat up the reactor and the wafer Ambient: N 2 Pressure: 1 mbar Time: 3 min Step 2: Deposition Precursors TiCl 4 NH 3 Temperature 25-425 o C ALD cycle [1]: TiCl 4 : 2 sec [2]: N 2 : 4 sec [3]: NH 3 : 2 sec [4]: N 2 : 4 sec 9

RBS and XRD analysis XRD:cubic crystal structure, main corresponds to (2), high stress (shift to the right) RBS: Ti 1 N 1 Cl.2 H.5 grown at 425 o C 1

Optical model for SE TiN SiO 2 Si Optical model for insitu monitoring by SE n k n k Optical constants of SiO 2 [Cauchy] Optical constants of TiN [Gen-Osc Drude-Lorentz] 11

Thickness measurements: SE = SEM Solid lines = measured Dotted lines = modeled 12

Real-Time Monitoring Thickness [nm] 45 4 35 3 25 2 15 1 5 ALD of TiN at 35 o C, 16 cycles Zooming in 5 1 15 2 25 3 35 Time [min] 13

Zooming in Growth of TiN during 2 minutes (1 cycles) Thickness [nm] 1,45 1,38 1,31 1,24 1,17 1 cycle 1,1 1, 1,5 11, 11,5 12, Time [min] 14

Deposition Rate versus Temperature Dep. rate [Å/cycle] 1,,8,6,4,2,,67,21,25,16,19,2 275 325 375 425 Temperature [ o C] 15

Optical model for SE TiO x TiN SiO 2 1 2 3 Si Optical model for in-situ monitoring Loadlock n k Purpose: Oxidation behavior of ALD TiN in dry O 2 at 3-425 o C Optical constants (n,k) of TiO x layer 17

Thickness measurements by SE 5-nm TiN fully oxidized at 35 o C and 1 mbar of dry O 2 18

Verification by X-ray Reflectivity 5-nm TiN fully oxidized at 35 o C and 1 mbar of dry O 2 Material Density Thickness Roughness Intensity (counts/s) (Counts/s) 1,, 1,, 1, 1, 1, 1 1 Silicon 2.328 Substrate SiO 2 1.99 17.5 nm.5 nm TiO x 3.74 9.7 nm I: Simulated data I: Measured data 1.1 nm 1.2.6 1 1.4 1.8 2 2.2 2.6 3 3.4 3.8 Incident angle (deg).4.8 1.2 1.6 2. 2.4 2.8 3.2 3.6 4. Incident angle (deg) 19

Composition by XRD and XPS 3 TiO 2 Si Intensity [counts] 2 1 TiO TiO TiO 1 8 x1 4 Ti2p3 6 1 3 5 7 9 2 Theta [deg] c/s 4 2 Ti2p1 XRD pattern: crystalline titanium monoxide (TiO) 475 47 465 46 455 Binding Energy (ev) 45 XPS analysis: the oxide mainly consists of titanium dioxide (TiO 2 ) 2

Real-Time Monitoring of TiN Oxidation Oxidation behavior of 5-nm TiN in dry O 2 at 3, 35 and 4 o C 21

ALD Temperature Effect 5 nm TiN grown at 35 o C 5 nm TiN grown at 425 o C Oxidation at 4 o C Oxidation at 425 o C Oxide thickness [nm] TiO x thickness 12 12 1 8 6 4 2 Time, min 6 2 4 6 Time [min] Faster TiO x thickness 1 Time, min 7 Slower 22

Thickness TiN Thickness Effect 1 6 2 5 nm TiN 2 4 6 min 4 TiO x thickness 16 nm TiN 3 2 1 1 min 2 min 3 min 23

Thicker TiN => Better Agreement 24 TiOx thickness TiN thickness Start of oxidation 15 12 9 6 3 3 2 1 1 min 2 min 3 min

Outline Cluster Deposition System Real-Time Monitoring by SE Thermal Atomic Layer Deposition of TiN In-situ Oxidation of TiN Ex-situ Oxidation of TiN (a comparison) Plasma oxidation of TiN Plasma oxidation of Si ICPECVD of SiO 2 Percolation effects by SE Conclusions 25

Dry Oxidation of TiN at 4 o C Oxidation in a furnace followed by ex-situ SE measurements 8-nm thick initial ALD TiN film grown at 425 o C Thickness, nm 16 12 8 4 TiOx TiN 1 2 3 4 Time, min 1. ALD of TiN (reactor 2) 2. Removing 3. Furnace oxidation 4. Removing 5. SE measurements 26

Is Ex-situ Monitoring Reliable? 16 Oxide Thickness [nm] 12 8 4 1 2 3 4 Time, min In-situ: 5 nm TiN grown at 35 o C & oxidized at 4 o C Oxide thickness [nm] 12 1 8 6 4 2 Ex-situ: 8 nm TiN grown at 425 o C & oxidized at 4 o C 2 4 6 Time [min] 27

Loading Effect Oxide Thickness [nm] 2 16 12 8 4 5 1 15 2 Time, min 2 The same deposition and oxidation conditions except exposure time to N 2 ambient: 1. Opening the furnace, N 2 flow 2. Loading the wafers, N 2 flow 3. Closing the furnace, 4. Waiting to stabilize temperature, 5. Introducing O 2 Equal exposure time of 15 min for each point Non-equal (longer) exposure time Oxide Thickness [nm] 16 12 8 4 5 1 15 2 Time, min 28

ALD in Reactor 2 + Plasma in Reactor 1 a) Growth in Reactor 2 b) Transfer via Loadlock c) Oxidation in Reactor 1 1 2 3 Loadlock 3

TiN in N 2 O-Ar Plasma at 25 o C 2 regimes: Slow regime (.8 nm in 175 min) 5 Oxide Thickness [nm] 4 3 2 1 Sharp transition in between Very fast regime (3.5 nm in 5 min) 5 1 15 2 Time, min 31

TiN in N 2 O-Ar Plasma: 25 o C vs 3 o C Dependence on temperature: Fast regime similar slope Slow regime higher slope 8 Oxide Thickness [nm] 7 6 5 4 3 2 1 3 o C 25 o C 5 1 15 2 Time, min 32

Kinetics of Si Oxidation in N 2 O-Ar Plasma Fast regime (2.2-2.5 nm in 5 min) Slow regime (1.3-1.4 nm in 9 min) Transition fast => slow less sharp than for TiN Oxide Thickness [nm] 5 4 3 2 1 35 o C 4 o C 15 o C 5 1 15 Time, min 34

Plasma Oxidation: TiN vs. Si Initial oxidation (1 st regime) occurs faster for TiN Further oxidation (2 nd regime) occurs faster for Si (better O diffusion?) T-dependence is more pronounced for TiN compared to Si 5 TiN oxidation at 25 o C Oxide Thickness [nm] 4 3 2 1 Si oxidation at 35 o C 5 1 15 2 Time, min 35

Kinetics of SiO 2 Deposition in Plasma SiO 2 films by Inductively Coupled (IC) plasma (Reactor 1) Plasma: SiH 4 (.8% ) + N 2 O (18% ) + Ar (81.92% ) Deposition temperature: 35-15 o C SiO2 thickness (nm) 4 3.5 3 2.5 2 1.5 1.5 Oxidation + CVD G.R. (nm/min) 1 1.1.1 1 2 3 4 Time (min) Oxidation 2 4 Time (min) Two components 1. Plasma oxidation: unavoidable first seconds - very fast dominant for thin films 2. Deposition: constant rate dominant for thick films Influence on film properties? A. Boogaard, A.Y. Kovalgin, R.A.M. Wolters, Micr. Eng., 86, p. 177 (29) 37

Negative Charge in Plasma SiO 2 Films 7 6 (1b) Net Effective Charge (cm -2 ) Negative charge 1E+12-1E+12-2E+12 Plasma-oxidation component (3b) Capacitance (pf) 5 4 3 2 1-6 -4-2 2 4 6 Positive charge Applied Voltage (V) Deposition component QS HF -3E+12 1 2 3 4 5 6 7 Tox (nm) A. Boogaard, A.Y. Kovalgin, R.A.M. Wolters, Micr. Eng., 86, p. 177 (29) 38

Real-Time Monitoring of TiN ALD We observe: 6, Transition from discontinuous to continuous layer Thickness [nm] 5 4 3 2 1 Incubation time 2 4 6 8 1 Time [min] 4

Conclusions In-situ SE technique is a powerful tool to observe features not seeable or affected by ex-situ techniques Real-Time monitoring enables accurate measurements of process kinetics In this work in-situ SE was successfully used to study: ALD of TiN films at temperatures 25-425 o C Thermal oxidation of ALD TiN films in the range 35-425 o C Plasma oxidation of TiN films and Si at 35-3 o C Plasma-Enhanced oxidation & deposition of SiO 2 films Verification of film thickness by other methods is needed 41

Acknowledgements This work is financially supported by the Dutch Technology Foundation (STW), project 117 Mark Smithers (MESA+) for SEM measurements. Gerard Kip (MESA+) for XPS analyses. Minh (IMS, MESA+) for AFM measurements. H.J. Wondergem (Philips Eindhoven) for XRR and XRD analyses. 42