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348 IDT MICROSENSOR FABRICATION
Figure 12.1 Overview of process required to fabricate Rayleigh wave and Love wave IDT
microsensors
computer-aided design (CAD) system (e.g. L-Edit from Tanner Tools Inc.) and then
the electronic design files are exported in a standard format (e.g. GDS II) that offers
compatibility with the E-beam writer. The IDT structures are thus written on a positive
resist material that coats the mask plate on which a thin chromium layer has already
been deposited. The resist is developed and the chrome is etched away to leave the
desired IDT structures. It is common practice to make an inverse mask, or negative, from
the master positive mask plates using a quicker and more inexpensive ultraviolet (UV)
optical lithographic process. It is these copies that are then used in the silicon run and,
if damaged, can be replaced immediately. Figure 12.2 shows a typical IDT design that
would be written onto the positive and negative mask plates.
12.2.2 Wafer Preparation
Effective cleaning of the quartz wafers is a vital procedure, which is an essential require-
ment for the successful fabrication of IDT microsensors. In order to obtain good adhesion
and a uniform coating of the metallic film used to make the IDTs, a thorough cleaning of
