Variable dispersion compensator is essential to realize wavelength division multiplexing (WDM) for next,generation (40-Gbit/s) ultrahigh speed optical communication. As one of core components, etalon made of ultrathin,single crystal silicon is highly required. A novel single step ultra-precision machining process with diamond,grinding and chemo-mechanical grinding (CMG) has been recently developed for the fabrication of ultra-thin,silicon-based etalon. An encountered issue in the process is breakage of ultra-thin etalon during diamond,grinding and/or after ground etalon being demounted from chuck table. The influence of grinding conditions on,the breakage of ultra-thin etalon can be categorized in two cases. Indicated in this report was that the breakage,of etalon during grinding was mainly attributed to large grinding force (motor current) while the breakage of,etalon after demounting was mostly dominated by damage degree in the subsurface of ground etalon. The proper,grinding conditions were finally suggested to avoid the breakage in the fabrication process of ultra-thin siliconbased,etalon.