2003-10-14 Using RF measurements and simple, empirical...

C O N F I D E N T I A L

Etch Product Business Group

Using RF measurements and simple, empirical plasma models to enhance the performance of dielectric etch systems

Steven Shannon, Daniel Hoffman, Jang-Gyoo Yang, Alex Paterson, Theodoros Panagopoulos, John Holland, Dog Buchberger, Brad Mays, Allen Fox, Mike Chafin, Troy Detrick22 October 200356th Gaseous Electronics Conference


A more appropriate title slide

Need quick turn-around analysis of plasma processes – especially when customers are involvedNeed simple calculations for results for incorporation into process control algorithmsKey is to not get lost in more complicated details until necessary –start with a simple model and build off of itUsed for customer explanation and simple calculation for process control in etch processes

Focus for this talk – analysis of capacitive coupled plasma etch reactors – RF distributions and simple plasma models


Abstract

A simple plasma model determines plasma parameters from RF measurements made inside the cathode matchbox– Electron Density– Sheath Thickness– DC Bias Potential– Power Delivery Efficiency

Model combines rigorous RF characterization of the process chamber, measurement of voltage and current during processing, and a high frequency plasma equivalent circuit model to obtain these parametersThis model has been implemented on the eMax and Enabler platforms to enhance equipment operation, in particular, enhanced control of ΔV chucking and implementation of a standard de-chucking “Best Known Method”


Methodology Used

1. Proper electrical characterization of the chamber Lump elements and transmission line theoryRF impedance measurement of components

2. Experimental measurement of plasma impedance window that adequately represents process window of the chamber.

3. Calculation of plasma parameters based on voltage and current measurement combined with equivalent circuit analysis of the process chamber

4. Construction of simple scaling laws that can quickly approximateplasma parameters based on RF measurement

Build ParameterModels

CalculateParameters

Obtain PlasmaImpedance Matrix

CharacterizeChamber


Electrical Characterization

RF Generator

Matchbox with VI ProbeMeasure VI for

Process Window

1-Port Impedence Sweepand

Time Domain Reflectometry

NO PLASMA Solve for Plasma Impedences

Calculate Plasma Parameters

Develop Empirical Models Basedon RF measurements (V, I)

RF Generator

Matchbox with VI ProbeControl Plasma ParametersBased on Empirical Models

and VI Measurements


Equivalent Circuit

V-gen

Z-gen

Z-mesh

Z-plasma

Z-isoZ-kit

Z-series

Z-shunt

Generator Match Cathode Plasma


Plasma Model Problem – Leiberman High Frequency Model with Vacuum Capacitor Sheaths

Cathode

GroundedElectrode

Bulk PlasmaSheaths

Grounded Sheath

Powered Sheath

Z-bulk

Zbulk i C01

i Lp Rp

1−

s0Irf

e ne A.

Cpowered0 A

s0 .

Equivalent ImpedanceMeasured through VI Probe

Need to Solve forne and s0


Determination of Sheath Thickness and Electron Density:

este

ebulkesheathcalc

AenIs

nZnsZZ

ω=

+=

0

0 )())((

From V,I data at fixed point in the system (along with pressure and power considerations), solve for the current through the total discharge impedance

Solve for ne

Plug in ne and solve for sheaththickness

Break up sheath components into grounded and powered sheathsbased on system asymmetry and x5/2 voltage scaling

Result: electron density and powered sheath thickness profilesas functions of measured RF voltage for constant power


Electron Density Analysis

1000W2000W3000W

0 500 1000 1500 20001 .108

1 .109

1 .1010

1 .1011 Plasma Density Vs. Wafer Voltage

Wafer Voltage Amplitude (V)

Plas

ma

Den

sity

(cm

-3)

.

0 500 1000 1500 20001 .108

1 .109

1 .1010



Plas

ma

Den

sity

(cm

-3)

.

0 500 1000 1500 20001 .108

1 .109

1 .1010



Plas

ma

Den

sity

(cm

-3)

.

Increasing Densitywith

Increasing Power


Comparison to Langmuir Probe Measurement

13.56MHz and 60MHz power sweep matrix run at two separate pressuresLangmuir probe with passive RF compensation (Scientific Systems Smart Probe)Sufficient ground reference in chamberMeasurements taken at the center of the dischargeResults compared with density obtained at calculated on wafer RF voltage for 13.56MHz power curve

ENIVI Probe

13MHzMatch

13MHzDrive

60MHzDrive


Measured Density Vs. Calculated Density

1.00E+08

1.00E+09

1.00E+10

1.00E+11

0 5 10 15 20

Run Number

Den

sity

(cm

-3)

Langmuir ProbeRF Model


Sheath Thickness Analysis

1000W2000W3000W

0 500 1000 1500 20000

0.5

1

Dark Space Thickness Vs. Wafer Voltage

Wafer Voltage Magnitude (V)

Dar

kSp

ace

Thic

knes

s(c

m)

.

0 500 1000 1500 20000

0.5

1



Dar

kSp

ace

Thic

knes

s(c

m)

.

0 500 1000 1500 20000

0.5

1



Dar

kSp

ace

Thic

knes

s(c

m)

.A

tConstantW

aferVoltageIncreasing

Pow

erDecreases

Sheath

Thickness


What this gives us – separation of sheath and bulk electrical characteristics

Both grounded sheath and powered sheath impedances can be determinedVoltages and currents through each component can be calculated – system power delivery efficiency can be approximatedVdc on the wafer can be approximated using a simple plasma model

Grounded Sheath

Powered Sheath

Z-bulk

Vbias34

e n e

ε 0s 0

2 A aA b

⎛⎜⎝

⎞⎟⎠

5

2

1−

⎡⎢⎢⎢⎣

⎤⎥⎥⎥⎦

=Vbias34

e n e

ε 0s 0

2 A aA b

⎛⎜⎝

⎞⎟⎠

5

2

1−

⎡⎢⎢⎢⎣

⎤⎥⎥⎥⎦

=


Allows for more accurate calculation of on wafer RF and DC voltages – captures non-linearity between DC voltage and RF voltage at matchbox

0 200 400 600 800 1000 1200 140030

40

50

60

70

80Old Vs. New Wafer Voltage Difference

"Old" Vrf Measurement (V)

Erro

r in

Old

Mea

sure

men

t (V

)

.


Application - ΔV electrostatic chucking

DC voltage applied causes charge separation induced force to hold wafer to work pieceInduced DC potential from plasma has to be corrected for to provide consistent force chucking from process to processInaccurate representation of induced plasma potential results in variable chucking force from process to process

Monopolar Electrostatic Chuck

Embedded mesh with appliedDC voltage V

Plasma Discharge

Wafer

V Generatedby Plasma


Experimental Assessment of Vdc Prediction

Tested on eMax CT’ MERIE chamber over large pressure, power, and B-Field window for numerous dielectric etch processesΔV is controlled across electrostatic chuck (presumably referenced from DC plasma potentialIf reference potential is correct, all processes should have identical VI characteristics as ΔV is varied

ENIVI Probe

13MHzMatch

13MHzDrive

Monopolar Electrostatic Chuck

Embedded mesh with appliedDC voltage V

Plasma Discharge

Wafer

V Generatedby Plasma


Accurate representation of DC potential results in more consistent tool performance

Using Vrf CompensationUsing Vdc Obtained from Model

0 200 400 600 800 1000 1200 140030

40

50

60

70

80Old Vs. New W afer Voltage Difference

"Old" Vrf Measurement (V)

Erro

rin

Old

Mea

sure

men

t(V

) .

Iesc Vs V Setting

-160

-140

-120

-100

-80

-60

-40

-20

0

20

-500 -450 -400 -350 -300 -250 -200 -150 -100

V (Volts)

More Consistant Chucking RealizedUsing Simple Plasma Model

Same chucking voltage can nowbe used on ALL eMax CT’ Processes

Process Dependent Chucking Voltagewas a TOP concern at several

customer sites - NOW RESOLVED


Conclusions

Rigorous RF characterization of process chambers, combined with simple plasma models, can provide good first estimates of plasma parameters, including electron density, sheath thickness, and DC potentialsUsing these simple models, Applied Materials dielectric etch chambers have been able to standardize chucking and de-chucking of wafers for all processes and use non-evasive, low cost techniques to characterize their plasma discharges


RF Input

Ground Isolation

RF HotElectrode

Process Kit

Coaxial Delivery


Iesc Vs KVSP

-160

-140

-120

-100

-80

-60

-40

-20

0

20

-600 -500 -400 -300 -200 -100 0

KVSP (Volts)

Iesc

(mic

roam

ps)

Blue = Empirical ModelRed = Vrf Scaling

2003-10-14 Using RF measurements and simple, empirical...

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