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Symbol Glossary / x

The Lithography Process / 1

Definition: Semiconductor Lithography / 1

Overview of the Lithography Process / 2

Processing: Substrate Preparation / 3

Processing: Photoresist Spin Coating / 4

Processing: Post-Apply Bake / 5

Processing: Alignment and Exposure / 6

Processing: Post-Exposure Bake / 7

Processing: Development / 8

Processing: Pattern Transfer / 9

Image Formation / 11

Maxwell's Equations: The Mathematics of Light / 11

The Plane Wave and the Phasor / 12

Basic Imaging Theory / 13

Diffraction / 14

Fraunhoffer Diffraction: Examples / 15

The Numerical Aperture / 16

Fourier Optics / 17

Spatial Coherence and Oblique Illumination / 18

Partial Coherence / 19

Aberrations / 20

Aberrations: The Zernike Polynomial / 21

Aberrations: Zernike Examples / 22

Chromatic Aberration / 23

Horizontal-Vertical (H-V) Bias / 24

Defocus / 25

Flare / 26

Vector Nature of Light / 27

Polarization / 29

The Optical Invariant / 30

Immersion Lithography: Resolution / 31

Immersion Lithography: Depth of Focus / 32

Imaging into a Photoresist / 33

Standing Waves: Definition / 33

Standing Waves: Mathematics / 34

Fresnel Reflectivity / 35

Swing Curves / 36

Top Antireflective Coatings (TARC) / 37

Bottom Antireflective Coatings (BARC) / 38

Photoresist Chemistry / 39

Novolak/DNQ Resists 39

Chemically Amplified Resists 40

Absorption of Light / 41

Photoresist Bleaching and the Dill Parameters /42

Exposure Kinetics / 43

Measuring the Dill ABC Parameters / 44

Chemically Amplified Resist Kinetics / 45

Diffusion in Chemically Amplified Resists / 46

Acid Loss Mechanisms / 47

Post-Apply Bake Effects / 48

Photoresist Development Kinetics / 49

Surface Inhibition / 50

Developer Temperature and Concentration / 51

The Development Path / 52

Lithography Control and Optimization / 53

NILS: The Normalized Image Log-Slope / 53

NILS: The Log-slope Defocus Curve / 54

NILS: Image Optimization / 55

NILS: Exposure Optimization / 56

NILS: PEB Optimization / 57

NILS: Development Optimization / 59

NILS: Total Process Optimization / 60

Defining Photoresist Linewidth / 61

Critical Dimension Control / 62

Critical Dimension Control: Effect on Devices / 64

Overlay Control / 65

Line Edge Roughness / 66

Metrology: Critical Dimension / 67

Metrology: Overlay / 68

The Process Window / 69

Depth of Focus / 71

Resolution / 73

Rayleigh Criteria: Resolution / 74

Rayleigh Criteria: Depth of Focus / 75

Mask Error Enhancement Factor (MEEF) / 76

Resolution Enhancement Technologies / 77

Phase Shift Masks / 78

Phase Shift Masks: Alternating / 79

Phase Shift Masks: Attenuated / 80

Optical Proximity Effects / 81

Optical Proximity Correction (OPC) / 82

Off-Axis Illumination / 83

Lithography Simulation / 85

Moore's Law / 86

Next Generation Lithography (NGL) / 87

Equation Summary / 88

Glossary / 92

Index / 117

Preface

The material in this Field Guide to Optical Lithography is a distillation of material I have been putting together for the last 20 years or so. I have been subjecting students in my graduate level lithography course at the University of Texas at Austin to my disorganized notes for 14 years, and have published some similar material in my first book, Inside PROLITH, and my column in Microlithography World called "The Lithography Expert." However, the challenge here was not in creating the material for the book but rather deciding what material to leave out and how to make what remained as condensed as possible. As people who know me can attest, I am rarely lacking for words and brevity is not my strong suit (I am a lousy poet). I hope, however, that the kind reader will forgive me when one page on a topic of interest does not satisfy - it is an unavoidable consequence of the Field Guide format, and my own limitations as an overly verbose writer.

I thank Jeff Byers, William Howard, and Rob Jones for their help in reviewing the draft manuscript of this Field Guide. My many mistakes kept them quite busy.

This Field Guide is dedicated to my wife Susan and our daughter Sarah, who have taught me that there is indeed something more fun in this world than lithography.

Chris Mack