Source of soft x-rays with an x-ray optical system for submicron lithography

摘要

Abstract: A system for X-ray lithography has been developed at the Institute for X-Ray Optical Systems (Moscow) which utilizes a powerful plasma pulse source of VUV and soft rays together with an X-ray optical system (XOS) of the Kumakhov lens type. The XOS provides the opportunity to control the distribution and divergence of the X-ray emission. The source of X-rays is a micropinch narrowing of a plasma pulse electric discharge of the low-inductive 'vacuum spark' type in the vapors of the electrode material. Typical parameters of the source are: energy stored in the capacitors, 500 Joules; emitted energy of X-rays in a band near 1 Kev, 8 - 10 J (efficiency to 2%); energy of VUV emission (20 - 1000 A), about 50 J; emission pulse time, 10 ns, frequency of discharges up to 15 Hz. The dimensions of the micropinch spot is 50 - 100 micrometers but the position of the pulse varies up to 3 mm. The capillary optic system contains about 3000 glass capillaries with variable cross-section and is 600 mm in length. The diameter of the output cross-section of the 'semilens' is 60 mm which provides uniform illumination of a 40 $MUL 40 mm$+2$/ mask. The distance between the source and the XOS input is 100 mm. The density of X-rays at the XOS input is 200 mW/cm$+2$/. With a 50% transmission efficiency and a relative input-to-output cross-section of 0.2, the density of X-ray emission on the wafer is expected to be about 10 mW/cm$+2$/. Using a negative resist with a sensitivity of 20 mJ/cm$+2$/, this leads to an exposure time of about 2 seconds per field. With the use of a capillary lens, the angular divergence is not controlled by the c position jitter but by the lens and is about 3 milliradians. The current status of this system will be described.!4