<title>Compact debris shutter design of a laser-produced plasma source for high-NA application</title>

Abstract

ABSTRACT A compact debris shutter for use with a laser produced plasma source is designed for installation to our EUV interferometer. The shutter is for operation under vacuum based on a gyroscope design for space satellites. It is of a hollow cylinder shape of 20cm diameter enabling to stop debris of the plasma source traveling at a speed below 260m/s at a spinning speed of 6000rpm. Keywords : debris shutter, laser produced plasma source, extreme ultraviolet light, high n umerical aperture 1. INTRODUCTION In the extreme ultraviolet (EUV) wavelength region, multilayer mirrors have been used to develop normal incidence optics superior in brightness and resolution to the conventional grazing incidence optics. The superiority comes from a simple reason that the multilayer mirrors can be large enough to realize bright optics with a laboratory source such as a laser-produced plasma (LPP). In other words, a large numerical aperture NA is expected for the EUV multilayer optics. For practical uses of the LPP for these high NA optics applications, it is essential to solve the particle debris problem, i.e., the target material ejected by the plasma production should be stopped before depositing to precise optics. The EUV multilayer mirrors comprising the optics are delicate and expensive since these are needed to be prepared by super-polishing realizing high precision figures and extreme smoothness, then applied with precise deposition of EUV multilayers for high reflectance, which can be deteriorated very easily by the deposition of the debris contamination. This problem is common to the EUV optics with a LPP source typically in the next generation lithography cameras under a laboratory condition. In the case of this EUVL, the LPP source is very specialized in a specific wavelength for high throughput and performance. This is mainly due to the high throughput requirements of the wa fer exposures w ith high repetition rate laser of a kHz order and a long target lifetime requirement. Consequently, the permissible amount of debris in this camera is extremely small