Sputtered W-Ti Film for X-Ray Mask Absorber

Abstract

Properties of DC-sputtered W-Ti absorber films such as internal stress, density and microstructure were systematically investigated for X-ray mask application. Smooth, stress-free amorphous W-Ti films with a comparatively high density of 16.5-17.0 g/cm3 were obtained by optimizing several conditions: gas pressure, N2 content in the working gas, DC power density and annealing temperature. The reproducibility of the film stress was about ±5×107 Pa. Reproducibility was found to be mainly determined by the degree to which the sputtering tool used could be controlled. Furthermore, it was confirmed that the optimized absorber films offered good stability under stress within 1×107 Pa when stored in an air atmosphere for more than 250 days.

Fabrication of high resolution x-ray masks using diamond membrane for second generation x-ray lithography

“…In order to make the W-Ti film amorphous, nitrogen (N 2 ) is added to the argon ͑Ar͒ working gas. 16 The stress of the amorphous W-Ti absorber is known to be stable against x-ray exposure 17 and in an air atmosphere. 18,19 We have investigated this material for a long time, and have developed some techniques to control its stress.…”

Development of x-ray mask fabrication process using w-sputtering

“…To meet 0.1 jam ULSI design role, the absorber should have a tensile stress less than 5• l0 s dyne/cm: and be stable within --+5 • 107 dyne/cm 2 [6]. Among the several candidate materials like Au [7,8], Ta [2,9,10], W [11,12] metals and their compounds [3,4,[13][14][15][16][17], W has long been studied as an absorber material for x-ray mask, due to its comparable thermal expansion with membrane materials, a relatively high Young's modulus and the possibility of dry etching. However, W film has a problem of stress instability due to oxygen diffusion along the grain boundary of columnar structure [6].…”

“…It is known that the density of film deposited by sputtering strongly depends on the sputtering pressure [6,15]. Fig.…”

Sputtered TaX film properties for x-ray mask absorbers

“…Recently, compounds of Ta or W, such as Ta 4 B, TaSiN, and WTi, have come into use as absorber materials because these materials are amorphous and their stress can be controlled more easily than that of Ta or W. [6][7][8] However, there have been no reports which have systematically investigated the characteristics of Ta or W compounds. For this reason, we have systematically investigated the characteristics of binary tantalum alloys and deposited selected materials by rf sputtering.…”