Excimer laser microlithography at 193 NM

As integrated circuit devices are pushed toward higher speeds, higher packing densities, and lower power consumption, the requirements of high resolution optical lithography increase. Research into lithography at the 193 nm wavelength of an ArF excimer laser has been conducted. Using a variable numerical aperture refractive imaging system and a spectrally narrowed excimer laser, lithographic resolution to 0.25 p.m has been obtained in a new 193 nm resist material based on a copolymerization of a silylated methacrylate with a halogenated styrene. Specifics on the imaging system as well as the formulation and optimization of this resist material are presented. TABLE OF CONTENTS Page Chapter 1 . Introduction and summary 1 Chapter 2. Background Optical microlithography 4 2.1 Excimer lasers 6 2.2 Deep-UV lithographywith excimer lasers 8 2.3 ArF excimer laser lithography 9 2.4 Photosensitive resist materials for 193 nm 11 Chapter 3. ArF excimer laser for 193 nm lithography 16 3 . 1 UV laser systems 1 6 3.1. 1 Excimer laser systems 1 9 3.1. 2 Rare gas halogen excimers 22 3.1.3. Excitation schemes 25 3.1. 4 Excimer lasers for IC lithography 27 3 . 2 Spectral narrowing ofArF excimer laser 3 1 3.3 Laser characteristics 35 Chapter 4. Optics for 193 nm lithography 46 4.1 Optical materials for 193 nm 46 4.1. 1 UV properties of fused silica 48 4. 1 . 2 UV induced damage to fused silica 50 4. 1.3 Damage testing of fused silica with 193 nm radiation 53 4.2 193 nm refractive optics 58 4.2.1 Lens requirements and design 60 4.2.2 Illumination system for 193 nm 61 4.2.3 Refractive objective lens for 193 nm 65 4.2.4 Scalar diffraction modeling 74 4.2.4. 1 Scalar and vector diffraction models 74 4.2.4.2 Verification of scalar diffraction models 76 4.2. 5 Simulated 193 nm lens performance 77 4.2. 6 193 nm imaging performance 84 Chapter 5. Phase-shift masks for 193 nm projection lithography 91 5.1 193 nm resists for mask evaluation 98 5.2 Subtractive phase-shift mask process 99 5.3 Phase errors at 193 nm 100 5.4 Alternating 193 nm phase-shift mask 102 5.5 Attenuated 193 nm phase-shift mask 105 Chapter 6. Optimization, synthesis, and characterization ofP(SI-CMS) 109 as a crosslinking negative resist for 193 nm lithography 6. 1 Trimethylsilylmethyl methacrylate and poly(trimethylsilylmethyl 110 methacrylate as 193 nm materials 6.2 Crosslinking resists via chloromethyl styrene 114 6.3 Optimization of the 193 nm response of a crosslinking resist 117 6.4 Preparation ofP(SI-CMS) for 193 nm exposure 120 6.5 Physical chemistry ofP(SI-CMS) for 193 nm exposure 122 6.6 P(SI-CMS) formulations for maximum response at 131 various thicknesses 6.6. 1 Absorption properties ofP(SI-CMS) formulations 133 6.6.2 Gel point and physical properties ofP(SI-CMS) 134 formulations 6.7 Lithographic characterization ofP(SI-CMS) materials 138 6.7. 1 Evaluation of2000 A to 5000 A P(SI-CMS) 143 films 6.7. 2 P(SI-CMS) imaging at 193 nm 144 6.8 Oxygen plasma RTE behavior ofP(SI-CMS) 148 6.9 P(SI-CMS) summary 152 Chapter 7. Conclusions and recommendations 154 Appendix! Comparison of scalar and vector diffraction modelling 157 for deep-UV lithography ALL Scalar simulations 158 A1.2. Vector simulations 161 Experimental run data for scalar simulations 162 Experimenatl run data for vector simulations 174 Appendix II. Simulation code for 193 nm lens performance 178 References 186