Si etching with high aspect ratio and smooth side profile for mold fabrication

New optical devices can be obtained when finer patterns than the light wavelength are fabricated on an optical substrate surface. Imprint must be an important technology to fabricate the optical devices by replication. A silicon wafer is often used as a mold for an imprint. Fine and deep patterns have to be fabricated in the silicon surface. Bosh process is a process for Si deep etching. However, a sidewall undulation is usually observed because of an alternation of an etching and a deposition phases. The sidewall undulation is unacceptable to the imprint mold for optical devices. In this report a modified Bosh process is proposed in order to obtain very fine Si pattern without sidewall undulation.