Reactive ion beam etching of PLZT electrooptic substrates with repeated self-aligned masking

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Abstract
Deep channels in electrooptic substrates are often desired for optical fiber coupling and the fabrication of embedded electrodes in waveguides and spatial light modulators. While ion beam etching can be used to form channels with vertical wall profiles, the achievable etch depth is often rate-limited by the substrate/mask etch ratio. In this paper we compare etch rates of the electrooptic material (Pb,La)(Zr,Ti)O3 under argon-ion beam etching and CF4 and C2F6 reactive ion beam etching (RIBE). Then, as an alternative to the use of thick or multilayered masks, of limited resolution, we present a method using backside exposure to apply repetitively a self-aligned photoresist mask for multiple RIBE runs. This procedure has been used to fabricate channels of 7-μm depth in the electrooptic material.