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

Abstract

We present a mask-aligner lithographic system operated with a frequency-quadrupled continuous-wave diode laser emitting at 193 nm. For this purpose, a 772 nm diode laser is amplified by a tapered amplifier in the master-oscillator power-amplifier configuration. The emission wavelength is upconverted twice, using LBO and KBBF nonlinear crystals in second-harmonic generation enhancement cavities. An optical output power of 10 mW is achieved. As uniform exposure field illumination is crucial in mask-aligner lithography, beam shaping is realized with optical elements made from fused silica and CaF featuring a diffractive non-imaging homogenizer. A tandem setup of shaped random diffusers, one static and one rotating, is used to control speckle formation. We demonstrate first experimental soft contact and proximity prints for a field size of 1 cm with a standard binary photomask and proximity prints with a two-level phase mask, both printed into 120 nm layers of photoresist on unstructured silicon substrates.

Semiconductor-based narrow-line and high-brilliance 193-nm laser system for industrial applications

“…4 demonstrate a minimum feature size smaller than 375 nm for amplitude masks. Using phase masks, the full potential of the new laser source will become even more prominent and a further extension using concepts of Advanced Mask Aligner Lithography (AMALITH) [4,18] for resolution enhancement is feasible.…”

“…Introducing such improvements, also optical lithography relying on CW DUV lasers might be within reach. However, the full potential of the laser system will become visible for modern lithography using not only amplitude but phase masks [18]. Increasing the power level to 100 mW and beyond will require more complex frequency mixing processes using different crystals and high-power pump fiber lasers to achieve an efficient frequency conversion process.…”

Printing sub-micron structures using Talbot mask-aligner lithography with a 193 nm CW laser light source

“…By rotating the diffuser during the exposure, the irradiance of various statistically independent speckle patterns is integrated in the resist during exposure. The superposition of these patterns reduces the visibility of speckle, as demonstrated later in this section [9,[31][32][33].…”

“…Uniform irradiance in the mask plane is achieved using an imaging microlens array (MLA) homogenizer as a Köhler integrator, i.e., a combination of two MLAs and a Fourier lens [34]. In comparison to a previous approach using a diffractive non-imaging homogenizer [9], we demonstrate here a clear improvement with regard to field uniformity and light efficiency [33]. Though the results of this publication are limited to small print fields of about 15 mm x 15 mm to maintain reasonable exposure times for the proof-of-principle experiments, the demonstrated principles can be directly adapted to full-field mask-aligner illumination.…”

“…The integration of LED and diode laser light sources into mask-aligner lithography has been demonstrated [6][7][8], solving the task of beam shaping for uniform mask illumination in various ways. Recently, we reported on the implementation of a novel deep ultraviolet (DUV) frequencyquadrupled continuous wave (CW) light source emitting at λ = 193 nm in a mask-aligner and demonstrated test exposures [9].…”