### 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 |

© H. Föll (Semiconductor Technology - Script)