Reduced Anisotropy in Tetramethylammonium Hydroxide Based Silicon Etchants

At sub-10 nm technology nodes, silicon etching is critical to FEOL processes. One of the keys to developing solutions for these applications is being able to control the anisotropy of the Si etch, or the etch selectivity between , , and . We have focused on the impact of modifications to tetramethylammonium hydroxide (TMAH) on Si etch selectivity, with the ultimate goal of developing an isotropic Si etchant based on TMAH. As expected, aqueous TMAH solutions showed a high level of anisotropy ( : : = 1:5.5:5.1) and significant level of surface roughening. In contrast, some of the modified TMAH etch solutions tested had decreased surface roughening and a decreased level of anisotropy ( : : = 1:1.6:1.1). Pattern etching on implanted pSi wafers is used to highlight the differences in anisotropy between TMAH and the modifications.