Resolution Enhancement Techniques in Optical Lithography Book

	Preface	xiii
	List of symbols	xv
	List of abbreviations	xvii
1	Introduction	1
1.1	Brief history of printing and lithography	1
1.2	Optical lithography and integrated circuits	2
1.3	Basics of optical lithography	6
1.3.1	Illumination	6
1.3.2	Reticle	8
1.3.3	Exposure	13
1.3.4	Photoresist	18
1.3.5	Optical lithography system parameters	23
1.4	Requirements of microlithography	24
1.5	Nonoptical microlithography techniques	26
1.6	Current challenges of optical microlithography	27
1.7	Three parameters affecting resolution	28
1.8	Scope of discussion	30
2	Optical Imaging and Resolution	31
2.1	Coherent imaging	31
2.1.1	Principle	31
2.1.2	Resolution	34
2.2	Mask spectrum	39
2.2.1	Pitch dependence	42
2.2.2	Dependence on dimension	42
2.2.3	Two-dimensional patterns	44
2.3	Partially coherent imaging	45
2.4	Complex degree of coherence	55
2.5	Rayleigh's resolution limit	58
2.6	Lithography resolution limit	59
2.7	Quantification of image quality	59
2.7.1	Modulation transfer function	60
2.7.2	Contrast	60
2.7.3	Exposure latitude	60
2.7.4	Normalized image log slope	61
2.7.5	Depth of focus	62
2.7.6	Exposure-defocus window	64
2.7.7	Total window	66
2.7.8	Common window	68
2.7.9	Linewidth variability	69
3	Modified Illumination	71
3.1	Partial coherence factor	71
3.1.1	Large [sigma]	71
3.1.2	Small [sigma]	79
3.1.3	Medium [sigma]	79
3.2	Off-axis illumination	80
3.2.1	Dipole	80
3.2.2	Quadrupole	84
3.2.3	Annular	85
3.2.4	Implementation issues	87
3.3	General guidelines	90
4	Optical Proximity Correction	91
4.1	Image distortion	91
4.2	Optical proximity correction approaches	92
4.2.1	Catastrophic OPC	93
4.2.2	Linewidth variation minimization	94
4.2.3	Line shortening	100
4.2.4	Corner rounding	100
4.3	Numerical techniques	101
4.3.1	Rule-based	102
4.3.2	Model-based	103
4.3.3	Hybrid	105
4.4	Implementation	106
4.4.1	Correction function derivation	106
4.4.2	CAD system	110
4.5	Discussion	115
5	Alternating Phase-Shifting Mask	117
5.1	Principle	117
5.2	Mask-making process	121
5.3	Issues	123
5.3.1	Intensity imbalance	123
5.3.2	Aberration sensitivity	126
5.3.3	Mask defect	128
5.4	Implementation	130
5.4.1	Dark-field application	131
5.4.2	Light-field application	133
5.5	Summary	138
6	Attenuated Phase-Shifting Mask	139
6.1	Principle	139
6.2	Mask making	147
6.2.1	Thin film	147
6.2.2	Opaque border	148
6.3	Discussion	151
7	Selecting Appropriate RETs	153
7.1	Critical levels	153
7.2	Methodology	154
7.2.1	Include applicable approaches	154
7.2.2	Select promising techniques	155
7.2.3	Experimental quantification	158
7.3	Optimization results	158
7.3.1	Storage	160
7.3.2	Isolation	163
7.3.3	Word line	164
7.3.4	Bit line contact	166
7.4	Summary and discussion	168
8	Second-Generation RETs	171
8.1	Multiple exposure	171
8.1.1	Forming sharp corners	172
8.1.2	Assembling patterns	172
8.2	Pupil filtering	175
8.3	Advanced illumination scheme	176
8.3.1	Concurrent reticle-illumination optimization	176
8.3.2	Dark-field illumination	177
8.4	Compensating process	180
8.5	Mask and photoresist tone	180
	Concluding Remarks	183
	k[subscript 1] Conversion Charts	187
	Bibliography	189
	Index	209