Ta/SiN-Structure X-Ray Masks for Sub-Half-Micron LSIs

Abstract

In the subtractive X-ray mask fabrication process, suppressing distortions introduced in the bulk-Si etching step is of the utmost importance. Influences of absorber and membrane stresses on mask distortions were investigated in order to obtain good position accuracy. The required stress conditions in order to suppress absorber- and membrane-stress-induced distortions are <2×108 dyn/cm2 for Ta, and <5×108 dyn/cm2 for SiN with a thickness of 2 µm. A five-level mask-to-mask overlay accuracy of <0.085 µm (3σ) was obtained by applying these conditions to actual device mask fabrication. Distortions induced in the bulk-Si etching step were drastically suppressed below 0.058 µm (3σ) in these masks. Absorber patterns with linewidths down to 0.14 µm were successfully fabricated. Pattern position shifts occurring in the frame-mounting step are dominant in our X-ray mask fabrication process.

Defect-free x-ray masks for 0.2-μm large-scale integrated circuits

“…2,3 For application of the x-ray mask to device fabrication, the number of defects must be reduced to zero. 2,3 For application of the x-ray mask to device fabrication, the number of defects must be reduced to zero.…”

X-ray mask distortion correction technology using pattern displacement simulator

“…[1][2][3][4][5][6][7][8][9][10][11] For example, use of a thick silicon substrate, 9 backetching after rigid frame mounting, 10 and reducing the absorber stress gradient 11 can all reduce the distortion caused during mask fabrication. Pattern placement is affected by many factors, such as electron beam writing accuracy, membrane and absorber stresses, and mask fabrication method.…”

Fabrication of 0.2 μm large scale integrated circuits using synchrotron radiation x-ray lithography

“…[1][2][3][4][5][6][7][8][9][10] The 512 kilobit static random access memory ͑SRAM͒ fabrication with 100% bit yield by IBM's group in 1993, for example, demonstrated that SR lithography was a viable candidate for sub-0.25 m device fabrication. 9 As the result of the development of SR rings, [11][12][13] x-ray steppers, 14 -18 high-quality x-ray masks, 19,20 and mask inspection 21 and repair 22 systems over the last decade, an infrastructure for SR lithography is now complete.…”