High-range laser bandwidth tuning for focus drilling

193nm ArF immersion microlithography has been used widely in high-volume manufacturing, and it is considered to be the main solution below 32 nm node until extreme ultraviolet (EUV) lithography becomes ready. Laser systems are now enlarging its function and capability to meet various applications. In this paper we report a newly developed solution for focus drilling technique applied to increase the depth of focus (DoF) for patterning contacts, vias and trenches. The laser light is stabilized at any E95 in the range from 0.3 pm to 2.5 pm, where E95 is defined as the width of the spectral range that contains 95% of the integrated spectral intensity. The high-range bandwidth is realized by introducing a newly developed line narrowing module (LNM) in the oscillator resonator. The bandwidth is measured with the on-board Fabry-Perot etalon and well controlled. This technique is easy upgradable to Gigaphoton latest GT62A-1SxE with the flexible output power (60W - 90W) and stabilized spectrum (E95=0.3pm). In comparison to another focus drilling technique where the large DoF is achieved by tilting a wafer stage during scan, the increase of the bandwidth of light source has much smaller impact on the required performance of the scanner such as productivity, overlay and critical dimension uniformity (CDU). In the paper we present the data that indicate the increases in DoF with broadening of the laser spectrum as well as imaging and overlay results obtained at high bandwidth.