Mask-aligner lithography using a continuous-wave diode laser frequency-quadrupled to 193 nm

Area of Science:

• Optics and Photonics
• Materials Science
• Microfabrication Technology

Background:

• Mask-aligner lithography is a key technique in microelectronics manufacturing.
• The development of advanced light sources is crucial for improving lithographic resolution and efficiency.
• Ultraviolet (UV) lithography, particularly at 193 nm, offers significant advantages for high-resolution patterning.

Purpose of the Study:

• To present a novel mask-aligner lithographic system operating at 193 nm.
• To demonstrate the feasibility of using a diode laser source with nonlinear frequency upconversion for deep UV lithography.
• To achieve uniform illumination and control speckle for high-quality printing.

Main Methods:

• Utilized a 772 nm diode laser amplified in a master-oscillator power-amplifier (MOPA) configuration.
• Employed a two-stage second-harmonic generation (SHG) process using LBO and KBBF nonlinear crystals to reach 193 nm.
• Implemented beam shaping with diffractive non-imaging homogenizers made of fused silica and CaF2.
• Used a tandem setup of static and rotating diffusers to manage speckle noise.

Main Results:

• Achieved an optical output power of 10 mW at 193 nm.
• Demonstrated successful soft contact and proximity printing over a 1 cm^2 field size.
• Printed 120 nm photoresist layers on silicon substrates using both binary and phase masks.
• Successfully controlled speckle formation through the diffuser tandem setup.

Conclusions:

• The developed 193 nm mask-aligner system is capable of high-quality lithographic printing.
• Nonlinear frequency conversion of diode lasers presents a viable pathway for deep UV lithography.
• The beam shaping and speckle control techniques are effective for uniform illumination in mask aligners.