10/9/2003 1

W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Influence of Gas Composition on Wafer Temperaturein a W CVD Reactor: Experimental Measurements,Model Development, and Parameter Identification

H. -Y. Chang* and R. A. AdomaitisISR and Department of Chemical Engineering

J. N. Kidder, Jr. and G. W. RubloffISR and Materials and Nuclear Engineering

University of Maryland

Contact information:www.isr.umd.edu/~adomaitiadomaiti@umd.edu

*Currently at Novellus Systems

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Overview

ULVAC Tw

True Wafer Temperature

•Research motivation: significant mismatch between single available temperature measurement and true wafer temperature;

• Experimental observations of strong influence of gas composition on wafer temperature;

• Gas phase simulations and assessing the applicability of global eigenfunction expansion methods and other OO-MWR;

• Process recipe developmentusing a validated dynamic process model; parameter ID issues.

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Tungsten CVD

Reactor chamber details

ULVAC cluster tool

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

ULVAC W CVD Operating and Control Structure

•Look-up table: static and not always activated

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Data Acquisition and Experiment Setup

• Signals captured synchronously

• Hardware and software integration

• Challenges: – Signals are of different types and different ranges

– Noise reduction of TC signal

•Offset wafer to assess gas/susceptor thermal conduction effects

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Experimental Results at 0.5 Torr

• Constant lamp powerΤemp change due to gas composition change

• Temp increased as N2increased κH2 ≈ 6κN2 at 0.5 Torr

• TC5 had the largest temp change Both sides of wafer contact gas mixture

– System TC is outside reactor chamber

– Look-up table is inactive in I/O mode

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Gas Flow and Heat Transfer Model

Assumptions

• Fully-developed, laminar gas flow

• Transport and gas thermodynamic properties in bulk gas phase are constant

• No buoyancy or wafer rotation induced flow (Gr = 1.99; Ra = 1.35)

• Heat generated by viscous dissipation and gas and surface reactions are negligible

(Chang & Adomaitis, 1999 Int. J. Heat & Fluid Flow)

Gas velocity, temperature

Gas temp BCs

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Wafer/Susceptor Thermal Dynamics Model

Estimated parameters: Qlp,0, βwf , hwf,0, α0 (steady state/Gauss-Newton)

γ0 , ∆w,∆s (colloc int/G-N, physical arguments)

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Gas Phase Model Solution

Global (eigenfunction) expansion

•vx by Galerkin’s method•Iterative solution procedure

•Projection operations carried out by quadrature•Object-oriented version of MWRtools (www.ench.umd.edu/software/MWRtools)

•Trial function objects for 3D temperature field•SD objects to represent modeling equations/solution; collocation time integrator•PARAM objects to facilitate Gauss-Newton procedure

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Model Solution / Parameter Identification Procedure

Simulation Approach

Main script[rhs, J, drdp] = ulvac_fun(t,s,p)

•unpack state s and parameter p objects•evaluate diff-eq “rhs”, Jacobian, and derivatives w.r.t parameters to be identified; define in terms of SD objects

•Set initial state s and parameter p objects•s = newtraph(s,p)•S = odaepc(s,p)•p = gnstep(s,p)

MWRtools: www.ench/umd.edu/software/MWRtools

Parameter Estimation Sequence1) Using TC5 data estimate Qlp,0 and βwf; steady-state model and data

2) Identify hwf,0 and α0 with TC1-3 measurements; steady-state model/data

3) Identify γ0 , ∆w,∆s with TC1-3 measurements; transient model/data

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Representative Gauss-Newton Iterations

Identify hwf,0 andα0 with TC1-3

measurements:

Results: hwf,0=3.0 W/m2/K α0= -0.03 W/m2/K Qlp,0=30.3 kW/m2 βwf=17.8

Physically reasonable values: Chang et. al. (2001), JVST B, to appear

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Model Prediction for Temperature vs Gas Composition

Inte

rior R

egio

nO

utsi

de R

egio

n•Mean model prediction error is less than 3 K for each data set

•Significant model nonlinearities

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Experimental Results at 0.5 Torr (cont.)

• Temp differences were less than 5 K at corresponding s.s. pointsrepeat gas composition change in reverse order

• TC5 responded to the initial ramping faster than other TCs

• Insignificant temp changes for N2 100 → 60 sccm and H2 40 → 100 sccm

Gas convective heat transfer modeling term relatively unimportant in the low pressure condition of the ULVAC system

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Heat Flux Across Wafer Top/Gas Boundary

∆q = q N2=100 - q N2=60N2 = 100 sccm and 0.5 Torr

• The difference of energy flux ∆q < 7 W/(m2K) is small compared to heat transfer rate q itself; convective heat transfer is negligible compared to gas conduction.

• Relative insensitivity of the wafer temp to gas velocity field justifies omission of combined side inlet and showerhead inlet streams in flow simulation.

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Parameter Estimation and Dynamic Simulation

1) Three different temperature setpoints

2) Collocation-based time integration

γ0 = 12 kW/m2

∆w = 0.8 mm (cf. 0.5 mm wafer)

∆s = 0.65 cm (cf. 2 cm showerhead)

Initial mismatch due to initial u(t) spike

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Dynamic Simulation and Model Validation

Model validation

•Re-check dynamic model validity with final set of parameter values;•Tsh(0) depends on time since previous reactor operating cycle.

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Deposition Process Recipe

Time(sec.)

Ion

curr

ent f

or H

2(A

mp)

Ion

curr

ent f

or H

F(A

mp)

H2

HF

H2 depletion

HF generation

0 400 800 1200 16000.00E+000

2.00E-011

4.00E-011

6.00E-011

8.00E-011

0.00E+000

3.00E-012

6.00E-012

9.00E-012

1.20E-011

Temperature.Step 1 Step 2 Step 3 Step 4 Step 5

H2 flush Cold wafer cycle Hot wafer cycleHeating Cooling

H2 flushing Cold waferbackground

Heating Hot wafer deposition

Quadrupole Mass Spectrometer data by Dr. Yiheng Xu

Process Prep.

Dep.H2 40sccm 40sccm 40sccm 40sccm 200sccmWF6 0sccm 10sccm 0sccm 10sccm 0sccmPressure 0.5Torr 0.5Torr 0.5Torr 0.5Torr 0.5Torr

Cool down

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W CVD Simulation Chang, Adomaitis, Kidder, and Rubloff, 2000 Annual AIChE Meeting

Conclusions and Current Work

•Simulator validation: excellent agreement between model predictions and measured wafer temperature;

• Extrapolation of wafer temperature predictions to true process operating gas composition;

•Current simulation research to investigate wafer temperature nonuniformity, gas phase reduced-basis discretization methods; validation of blanket W deposition model;

•Extension of simulation methods to CVD reactor design and other semiconductor manufacturing processes.

Process Prep.

Dep.