Takashi Onose

Development of high coherence, 200mW, 193nm solid-state laser at 6 kHz

The high coherent, high power 193-nm ArF lasers are useful for interference lithography and microprosessing applications. In order to achieve high coherence ArF lasers, we have been developing a high coherence 193 nm solid state laser for the seeding to a high power ArF laser. We used the sum frequency mixing of the fourth harmonic (FH) of a 904-nm Ti:sapphire laser with a Nd:YVO4 laser (1342 nm) to generate 193-nm light. The laser system consists of a single-mode Ti:sapphire oscillator seeded by a 904-nm external cavity laser diode, a Pockels cell, a 6-pass amplifier, a 4-pass amplifier, a 2-pass amplifier and a wavelength conversion stage. The required repetition rate of 6 kHz corresponding to the ArF laser, along with a low gain at 904 nm induces serious thermal lens effects; extremely short focal lengths of the order of cm and bi-foci in the vertical and horizontal directions. From the analysis of thermal lens depending on pump intensity, we successfully compensated the thermal lens by dividing a 527-nm pump power with 15, 25 and 28 W to 3-stage amplifiers with even passes, resulting in the output power above 10W with a nearly diffraction limited beam. This 904-nm output was converted to 3.8 W in the second harmonic by LBO, 0.5 W in FH by BBO sequentially. Finally the output power of 230 mW was obtained at 193 nm by mixing the FH with a 1342-nm light in CLBO.

Development of high-power, 6 kHz, single-mode Ti:sapphire laser at 904 nm for generating 193 nm light

A high power, 6 kHz, single-mode Ti:sapphire laser operating at 904 nm has been developed to produce a 193 nm light source. The output power was above 10 W with a bandwidth of 160 MHz. The Hansch–Couillaud locking scheme was successfully applied to stabilize the frequency of the pulse laser. The thermal lens in the Ti:sapphire crystal having a focal length down to 10 mm along with strong astigmatism was compensated by distributing thermal load to three amplifiers with an even number of passes, resulting in a nearly diffraction limited beam. This Ti:sapphire laser contributed to the generation of 193 nm light with an output power above 200 mW.

A Sub-Watt, Line-narrowing, 193-nm Solid State Laser Operating at 6 kHz with KBBF for Injection-locking ArF excimer laser systems

We present a line-narrowing 193-nm solid state laser with a KBBF prism-coupled device. This laser delivers an output power of 0.2 W at a repetition rate of 6 kHz.

Amplification of DUV solid-state laser pulse using ArF laser

Deep ultra violet (DUV) lasers are actively used for material micro processing and semiconductor lithography. Argon fluoride excimer laser (ArF excimer laser) is the typical light source which can generate above 100-W optical power at the wavelength of below 200-nm. Using all-solid-state DUV light source as a seed laser and amplifying by ArF excimer, both high average power and high beam quality can be realized in the DUV region [1]. In this paper, we report on the output characteristics of hybrid ArF excimer laser.