Investigation of masking materials for high-ion-density plasma etching of GaAs

Abstract

One of the most important steps in achieving good pattern transfer using dry etching of semiconductors is to find the best masking materials for the process. In particular, for high-ion-density plasma etching the high ion currents incident on the sample can provide a severe test of mask stability. For electron cyclotron resonance (ECR) etching of GaAs with Cl 2 /Ar plasmas, both microwave power and rf power are found to have significant effects on mask degradation while the Cl to Ar ratio and process pressure have a relatively constant effect over the given regions investigated (total flow rate for Cl 2 and Ar is 15 sccm, 1.5-10 mTorr). Of the potential masking materials of photoresist, SiO 2 , SiN X and W, SiN X is found to be the most stable under ECR conditions. The surface morphology of the photoresist and SiO 2 was significantly changed during Cl 2 /Ar ECR etching while sputtering of W creates micromasking on the GaAs.

Dry etching of III-V semiconductors in IBr/Ar electron cyclotron resonance plasmas

“…Another weak point of this plasma chemistry (CH4/ H 2) is mask erosion because of the high dc self bias needed to obtain practical etch rates, which may cause sidewall roughness after pattern transfer. 22 This will decrease performance of devices like optical wave guides for communication or ridge waveguide lasers because of scattering of light from the rough sidewalls . 23 Other candidates studied include C12-, BCI~-, HBr, and ICl-based plasmas.…”