We fabricated 2.6 GHz surface acoustic wave (SAW) filters using an electron beam exposure system. The filter consists of an interdigital transducer of aluminum on piezoelectric material (LiTaO3). Since the LiTaO3 density was high, a large number of electrons were backscattered from the material when exposed by electron beams. When a conventional negative resist was used, the backscattered electrons degraded the image contrast so that resist residue remained on unexposed areas after development. The process margin, which indicates exposure tolerance, was calculated. The process margin was small for LiTaO3, indicating that it is difficult to suppress resist residue when negative resist is used and that a positive resist should be used. To obtain vertical walls of positive resist, we used a 0.4-micrometers double-layer configuration in which the upper layer had a lower sensitivity than the bottom layer. To prevent the piezoelectric substrate from breaking due to the pyroelectric effect, the resist pre- and post-baking temperature was raised gradually at a rate of 5 degrees/minute. The 0.4-micrometers line and space patterns required for a 2.6 GHz filter could be produced accurately. The fabricated SAW filter had a 2.58 GHz center frequency and an insertion loss of 5.0 dB.

Date Published: 9 July 1992
PDF: 8 pages
Proc. SPIE 1671, Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing II, (9 July 1992); doi: 10.1117/12.136021

Published in SPIE Proceedings Vol. 1671:
Electron-Beam, X-Ray, and Ion-Beam Submicrometer Lithographies for Manufacturing II
Martin C. Peckerar, Editor(s)