2. An etch engineer has only a high pressure plasma etch and an ion mill availab

Question

2. An etch engineer has only a high pressure plasma etch and an ion mill available. Select which you would use in the following applications. Justify your answer.

a. Etching 5000Å of polysilicon that serves as the upper electrode of a large square capacitor. The capacitor dielectric is 50Å of SiO2. The polysilicon is deposited on top of the dielectric.

b. Recessing the channel of a GaAs Field Effect Transistor. For this application, the residual etch damage must be minimized.

c. Anisotropic patterning of a thin layer of platinum on a thick insulating layer.

Explanation / Answer

(a):

High pressure plasma.
-selectivity of poly vs. SiO2 (ion beams are inherently non selective)

(b):

High pressure plasma
-ion mill can cause electrical damage to substrate from ion bombardment

(c):

Ion mill
-anisotropy can be achieved
-film is thin with a thick insulator

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