Fabrication of 0.25 μm surface acoustic wave devices by ion beam proximity printing

The electrodes of surface acoustic wave (SAW) devices cannot be represented in a stencil mask as cantilevered beams because the high aspect ratio makes them unstable. Therefore a complementary exposure technique has been developed. The mask pattern is formed by segmenting the electrodes into equal length open and closed areas. The wafer is then exposed twice with an offset equal to the segment length, thus forming a continuous electrode image. This approach has two advantages: (1) the high process latitude of ion beam proximity printing (IBPP) is preserved since, in contrast to the grid-support approach, no areas are doubly exposed; and (2) only precision translation is required to register the exposures, preserving the single level nature of SAW patterns. Linewidth is shown to change by less than ±15% for ±20% changes in exposure at a 0.25 μm nominal linewidth.