Dry etching of Si field emitters and high aspect ratio resonators using an inductively coupled plasma source

Abstract

An inductively coupled plasma (ICP) source has been used to generate a Cl2 plasma for the etching of Si field emitters and resonators. An optimized etch condition was used to etch Si field emission devices with controllable sidewall angles as well as good uniformity for large arrays of emitters. A mask erosion technique was used to control the Si emitter profile. The sidewall angle of Si emitters increased from 55° to 75° as plasma pressure was increased from 0.1 to 5.0 mTorr. Sharp tips with good uniformity and a high packing density of 6.25×106 tips/cm2 were fabricated using 200 W ICP source power, 100 W stage power at 1 mTorr with 20 sccm of Cl2 flowing and an ICP source to sample distance of 8 cm. Released Si mechanical resonators were also fabricated with a vertical etch profile and smooth surfaces. An optimized etch condition of 250 W ICP source power and 70 W stage power at 5 mTorr with 20 sccm of Cl2 flow and an ICP source to sample distance of 6 cm provided an etch rate of 219 nm/min and a selectivity to a Ni–Ti mask of 26. Due to the high selectivity and etch rate, resonators and cantilevered beams as thick as 40 μm were fabricated giving improved device performance compared to thinner devices. Submicrometer Si resonators were also fabricated that were 3.1 μm thick with 1.7 μm wide comb drive fingers and 0.2 μm gaps between them.