6.4.4 Summary to: 6.4 Etching Techniques

Structuring means selective removal of material (through a mask) by etching. There are three main conditions for etching:

1. Must attack material to be etched Þ etching rate.

2. Must not attack everything else Þ selectivity.

3. Must conserve structure of mask (good on left side of picture, not so good on right side).

Chemical etching:

Can be near perfect for points 1. and 2.. Example: HF attacks only SiO₂ but not Si and most other materials.

Fails miserably on point 3.

Underetching is unavoidable. Can't be used for lateral structure sizes < » 2 µm

Plasma etching ("Dry" etching)

In a plasma quite unusual reactions can take place - including reactions never seen in normal chemistry. Many materials can be etched in a suitable plasma

Etching might preserve the lateral mask dimensions - for reasons not always entirely clear

There is tremendous potential in plasma etching because of the tremendously large parameter space - and tremendous problems and costs for the same reasons

Allmost all "small" structures in semiconductor technology are obtained by plasma etching