chamber matching of icp etch chambers using rf...
TRANSCRIPT
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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