qiaolin(charlie) zhang, prof. kameshwar poolla, prof...

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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