qiaolin(charlie) zhang, prof. kameshwar poolla, prof...
TRANSCRIPT
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FLCC
WorkshopApril 6, 2005
AcknowledgmentFunded by Advanced Micro Devices, Applied Materials, ASML, Atmel, Cadence, Canon, Cymer, Cypress, DuPont, Ebara, Hitachi Global Storage Technologies, Intel, KLA-Tencor, Mentor Graphics, Nikon Research, NovellusSystems, Panoramic Technologies, Photronics, Synopsys, Tokyo Electron, and the UC Discovery Grant.
• Minimax finds optimal offsets
• Wi is the weighting factor for CD target i
CD Uniformity Control Across Litho-etch SequenceQiaolin(Charlie) Zhang, Prof. Kameshwar Poolla, Prof. Costas Spanos, UC Berkeley
Motivation
Multi-zone PEB Bake Plate
2005 Main Objectives
Develop Inspection (DI) CDU ControlOur Approach
The Problem
Simulation Results of DI CDU Control FI CDU Control Simulation - Bowl Plasma Signature
Final Inspection (FI) CDU Control
Simultaneous CDU Control for Multiple CD Targets Future GoalsSimultaneous CDU Control for
Multiple CD TargetsGoal
• Across-wafer CD uniformity (CDU) is critical for:– Advanced logic devices, MPU and memory– Yield improvement
• Etch tool sets have limited control authority to address spatial non-uniformity.– Dual-zone He chuck is often the only knob
• Litho tool sets have much more control authority to address spatial non-uniformity.– Multi-zone PEB bake plate– Variable dose settings at exposure How can we improve the across-wafer CDU and what
is the maximum CDU we can achieve?
Poor Across-Wafer CD Uniformity
Processing Tool
EtchEtch
Wafer
LithoLitho
• Compensate for systematic across-wafer CD variation sources across the litho-etch sequence using all available control authority:– Exposure step: die to die dose– PEB step: temperature of multi-zone bake plate– Etch: backside pressure of dual-zone He chuck
Exposure PEB /Develop Etch
Wafer-levelCD MetrologyOptimizer
Scatterometry/CDSEM
dose temperature He pressure
• PEB step is critical due to chemically amplifiedresist
• Spatially programmable bake plate is introduced into PEB to enable PEB temperature uniformity
Initial modeling studies for CD Uniformity control (done)Assess controllability of various actuator settings in the litho-etch sequence for reduction of CD non-uniformity. Select processing sequence.Building sensitivity model.
Assess potential DI & FI CDU improvement (done)Based on CD offset modelBased on temperature offset model
• Complete preliminary experimental study for CD non-uniformity reducing across the litho-etch sequence (ongoing)• Assess predictive capability of mode, and build optimizing
software to compute optimal changes in control parameters.• Provide proof of concept test of CD non-uniformity reduction
scheme based on direct CD metrology.
• Official milestone: Complete preliminary experimental study for CD non-uniformity reducing across the litho-etch sequence.– Assess predictive capability of mode, and build optimizing
software to compute optimal changes in control parameters.– Provide proof of concept test of CD non-uniformity reduction
scheme based on direct CD metrology.
Schematic setup of multi-zone bake plate
(approximate)
24
36
5 71
• DI CD is a function of zone offsets
baselineresistDI CDSTCD→→→
+∆=
( )
( )⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡=
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡=
→
721
72111
...,...
...,...
OOOg
OOOg
T
TT
mm
baselineTTT→→→
−=∆
( )
( )⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡=
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡=
→
721
72111
...,...
...,...
OOOf
OOOf
CD
CDCD
nn
DI
• Seen as a constrained nonlinear programming problem• Minimize• Subject to: Up
iLow OOO ≤≤
⎟⎠⎞
⎜⎝⎛ −⎟
⎠⎞
⎜⎝⎛ −
→→→→
ettDI
T
ettDI CDCDCDCD argarg
7...2,1=i
69%61%72%CDU ImprovementIsolated LineSemi-isolated LineDense Line
Optimal DI CD
Dense Line Semi-isolated Line Isolated Line
Optimal DI CDOptimal DI CD
Experimentally extracted
baseline DI CDU
Simulated optimal DI CDU after applying
PEB tuning
• Across-wafer FI CD is function of zone offsets
• Minimize: ⎟⎠⎞
⎜⎝⎛ −⎟
⎠⎞
⎜⎝⎛ −
→→→→
ettFI
T
ettFI CDCDCDCD argarg
DIFIsp CDCDCD→→∆→
−=∆ _
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡=∆+=
→→→
)...,(...
)...,(
721
7211
_
OOOg
OOOgCDCDCD
n
spDIFI
• Plasma etch signature:
Upi
Low OOO ≤≤• Subject to: 7...2,1=i
-5
-4
-3
-2
-1
Assumed bowl shape plasma etch signature
Dense Semi-isolated Isolated
Simulated baseline FI CD
Simulated corrected DI CD after PEB tuning
Simulated optimal FI CD after PEB
tuning
65%57%68%FI CDU ImprovementIsolatedSemi-isolated Dense
Note that DI CDU may actually worsen!
62.6%32.4%60.1%Wd = 0.05; Ws =0.05 ; Wi =0.90
54.1%54.7%48.2%Wd = 0.05; Ws =0.90 ; Wi =0.05
61.8%15.9%66.8%Wd = 0.90; Ws =0.05 ; Wi =0.05
58.4%44.7%62.9% Wd =0.36; Ws =0.33 ; Wi =0.31 Iso LineSemi-iso LineDense Line
Simulation of simultaneous CDU control for dense, semi-iso and iso lines
Dense Semi-isolated Isolated
Simulated baseline FI CD
Simulated optimal FI CD after PEB
tuning
)))((max(minarg OFWO iiiO
opt =
2_ iii TCDCDF −=
• It is good to have simultaneous CDU control for multiple CD targets
• Formulated as a minimax optimization problem