Effects of ultrasonic agitation and surfactant additive on surface roughness of Si (1 1 1) crystal plane in alkaline KOH solution

Abstract

In the silicon wet etching process, the “pseudo-mask” formed by the hydrogen bubbles generated during the etching process is the reason causing high surface roughness and poor surface quality. Based upon the ultrasonic mechanical effect and wettability enhanced by isopropyl alcohol (IPA), ultrasonic agitation and IPA were used to improve surface quality of Si (111) crystal plane during silicon wet etching process. The surface roughness Rq is smaller than 15nm when using ultrasonic agitation and Rq is smaller than 7nm when using IPA. When the range of IPA concentration (mass fraction, wt%) is 5–20%, the ultrasonic frequency is 100kHz and the ultrasound intensity is 30–50W/L, the surface roughness Rq is smaller than 2nm when combining ultrasonic agitation and IPA. The surface roughness Rq is equal to 1nm when the mass fraction of IPA, ultrasound intensity and the ultrasonic frequency is 20%, 50W and 100kHz respectively. The experimental results indicated that the combination of ultrasonic agitation and IPA could obtain a lower surface roughness of Si (111) crystal plane in silicon wet etching process.