Chamber Matchingof ICP etch chambers

using RF equipment model

R. Wagner1), M. Klick2), M. Bauer1), L. Eichhorn2), T. Zwack1)

Texas Instruments Deutschland GmbH1), Plasmetrex GmbH2)

Overview

• Motivation

• Project Goal• Measurement Method• RF Equipment Models• Measurement Results: detected HW failures

• Corrective Actions (HW)

• Results Etch Rate matching• Summary / Conclusion

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Motivation

• Texas Instruments Germany, WFAB Freising (FFAB) has 3similar Applied Materials Centura DPS Shallow Trench etch chambers

• All STI chambers run the same kind of etch processes

• But the etch chambers show dissimilar etch results (e.g. etch rate) - despite the same process settings and hardware

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STI silicon etch time while the start situation of the project

Si e

tch tim

e

Project Goal

• The project target: Optimization of the chamber matching (same hardware / same process / same results)

• Therefore a cooperation with Plasmetrex was started.

• The focus of the project:RF Power components impact on process results– Check all RF power components

– Detect & fix power hardware failures

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RF Equipment Model and Conclusions - ICP Etcher

Surface, Contacts

Overheating

Geometry

Bended coil wires

ESC

Pollution, Aging

Z bias =1

jω C+Rloss

Z source = jωL+RlossPlasma density variation:Can be often compensated by R2Rthough process timeor endpoint control

Ion energy variation& higher temperature of ESC:Compensation by R2R difficultbecause influence toω- DC, - resist stability, - mask erosion, - uniformity

Impedance of Coil and ESC

RF Equipment Model

• Method for RF hardware characterization of production tools, developed by Plasmetrex.

• RF equipment model– Tool/chamber-specific– Parameterization of HW components by off-line results with

network analyzer• Real time measurement (during process)

– VI probe

• Provides finally real plasma power and voltage (ion energy).

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Plasmetrex’ RF Equipment Model DPS

RF Equipment Model contains• ICP (DTCU / Source) parameters as L, R, fres

• Cable damping (power loss) and length, partially characteristic impedance Z0• Electrode parameters incl. ESC as C*, R*, and design and loss parameters

RF Model forPower Cable

RF Model forCoil (DTCU)

RF Model forESC / Electrode

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Design and loss parameters- Length l of electrode system- Capacitance of electrodeLoss parameter- Damping constant α for distributed losses

Design parameter- L @ operating frequency- Resonance frequency fres

Loss parameters- Rloss @ operating frequency → State of coil wires and contacts

Design parameter- Length lLoss parameters- Damping constant α for distributed RF losses

Offline results: Coil failure

– Chamber 1: Black wires → Overheating

– Chamber 2 & Chamber 6: Ok

– Chamber 3: Bad contact from pin to coil found from measurement,

→ repaired → Ok, Measurement results shown here after repair

– Chamber 4: Black wires → Overheating

– Chamber 5: Partially darker wires, center part is new one8

Offline results: Coil failure II

• Power Cable:– Different cable lengths used

Different losses Chamber matching issue

– Damaged cable plug

– Connectors damaged by overheating

• DTCU/Coil:– Coil of one chamber damaged by

overheating – Loose / eroded contacts in DTCU

lead to instable states;

Large RF power loss causedby ohmic resistance heating

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Offline results: Electrode / Bias power

• No large difference in design parameters and ESC impact• Different RF losses (resistance) cause different real bias

power

Different loss @ one chamberthrough reassembling of electrode

Different losses indifferent chambers

Chamber : #3 #4 #4 #1 #2#5#6

• Real bias power in plasma has large impact on CD

• Real Time Measurement for bias power coupling– RF Voltage and Current

• RF Losses RF equipment model

• Real RF power → Chamber Comparison

Real Time Measurement – Bias power

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Real Time Measurement ResultsRF Power - From Generator to Wafer

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Based on RF Equipment Model and real-time measurement.

60% Bias RF power loss between generator and plasma

•20% loss in matchbox– Can change if matchbox

replaced•40% loss in electrode system

– Causes also heating in electrode system

– Wafer temperature ↑

Equipment 2

Real Time Measurement Results IIRF Power - From Generator to Wafer

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RF voltage scales ion energy:• Damage potential• Mask erosion• Selectivity• The real RF voltage at the electrode is often much higher than at the matchbox measured.

RF current scales bulk power in plasma:

• Uniformity• Ion flux

Equipment 2

Equipment 2

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Real Time Measurement Results IIIRF Power - From Generator to Wafer

• Power variations between chambers are about 20% here. Impact on:– CD– Selectivity– Etch rate

• Root cause: Different RF power losses.

• The repeated measurementshows a very goodreproducibility.

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Excellent candidate for tool and process indicator, in particular for impact on CD !

RF Current – Explanation and Verification

• At different Measurement Points Plasma current is ten times smaller than matchbox current !

• The directly measured RF current at chamber wall (Hercules)– Same behavior as the

plasma current– Deviation from non-constant

current at chamber wall

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Corrective Actions

• Establish same source power cable types (length) to all chambers (replace wrong / too short cables)

• Replace all damaged RF Adapter 7/16 (bias power)

• Replace damaged DTCU (with overheated coil)

• Replace damaged Bias power cable

• Adjust RF Harmonic filter (max. transmission frequency)• Fix the connector issues (loose screws, …)

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Results: Etchrate matching: Si-ER

After the corrective actions have been implemented, the STI etch rates harmonized significantly. This effect is clearly visible in the endpoint charts and process etch time charts.

STI pure Silicon Etch time (Process Works controlled)during Project progress

Box Plot of Silicon Etch timewhile the start situationof the Project

Box Plot of theSilicon Etch time after completing all corrective actions of the Project

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Chb.#1 Chb.#2 Chb.#3 Chb.#1 Chb.#2 Chb.#3

Ch. #1Ch. #2Ch. #3

Results: Etchrate matching Barc-ER

The improved etch rate matching is visible at all process etch steps.

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STI BARC Etch time (Endpoint controlled)during Project progress

Box Plot of theBARC Etch timewhile the start situationof the Project

Box Plot of theBARC Etch time after completing all corrective actions of the Project

Chb.#1 Chb.#2 Chb.#3 Chb.#1 Chb.#2 Chb.#3

Ch. #1Ch. #2Ch. #3

Results: Etchrate matching Nitr.-ER

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STI Nitride Etch time (Endpoint controlled)during Project progress

Box Plot of theNitride Etch timewhile the start situationof the Project

Box Plot of theNitride Etch time after completing all corrective actions of the Project

Chb.#1 Chb.#2 Chb.#3 Chb.#1 Chb.#2 Chb.#3

Ch. #1Ch. #2Ch. #3

Conclusion

• Chamber HW differences were found and classified by RF Equipment Model:– Cable lengths and losses

– Coil resistances and losses

• Major reason of the chamber differences: Variation in power loss in power supply and electrode system

• The detected faults were removed and fixed.

• After the corrective actions have been implemented, the STI etch rates harmonized significantly.

• Corrective actions for bias power (CD) are scheduled.

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