Figure 4

SEM images of the etching profile angles obtained with different mixture ratios of BCl₃ with (BCl₃ + N₂) labelled as (a) and (BCl₃ + Cl₂) labelled as (b), showing that etching angles can be controlled by adjusting the gas mixture ratio. (a₁) Mixture ratio of 20% results in the lowest etching angle, 41.11°; (a₂) mixture ratio of 40% results in an etching angle of 45.73°; (a₃) mixture ratio of 80% results in an etching angle of 61.67°; and (a₄) BCl₃ gas alone (100%) results in the largest etching angle of 78.04°. (b₁) Mixture ratio of 20% results in an etching angle of 76.45°; (b₂) mixture ratio of 40% results in an etching angle of 72.62°; (b₃) mixture ratio of 80% results in the lowest etching angle of 70.78°; and (b₄) BCl₃ gas alone (100%) results in the largest etching angle of 77.46°.