Question

11.3. Consider the GaAs etch diagram (Figure 11.6). The left axis is for H,O, the right axis is for H2SO," and the bottom axis is for water. A solution of 30% H2Og 50% H2SO, and 20% water is made up and used for etching a GaAs wafer (a) Estimate the etch rate. (b) In practice it is found that the deposition rate slows with time. Suggest two possible mechanisms for this slowdown. (c) Would you expect this etch to be isotropic or anisotropic? Justify your answer. Remember that not all wet etches are isotropic 288 11 Etching H202 1.0 2.0 3.0 3.3 3.5 3.3 3.0 3.3 A2.0 1.5 1.0 3. 2.0 01. 0.5 um H20 H2S04 Figure 11.6 The etch rate of GaAs in H2SOs, H2O2 and H2O. The right leg is the concentration of H2SO4, the bottom leg is H2O, and the left leg is H202. All scales increase in the clockwise direction (after lida and Ito, reprinted by permission of the publisher, The Electrochemical Society Inc.).

Answer 1

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