Isotropic etching
– Same etch rate in all directions
– Lateral etch rate is about the same as vertical etch rate
– Etch rate does not depend upon the orientation of the mask edge
• Anisotropic etching
– Etch rate depends upon orientation to crystalline planes
– Lateral etch rate can be much larger or smaller than vertical etch
rate, depending upon orientation of mask edge to crystalline axes
– Orientation of mask edge and the details of the mask pattern
determine the final etched shape
• Can be very useful for making complex shapes
• Can be very surprising if not carefully thought out
• Only certain “standard” shapes are routinely used