### 6.2.4 Summary to: 6.2 Chemical Vapor Deposition

| Chemical Vapor Deposition (CVD) is simple in principle |  |
Epitaxial Si layer
SiCl4 + 2 H2 | Þ | Si + 4 HCl
| (1000 oC - 1200 oC) |
Polycrystalline Si layer
| 60 Pa |
SiH4 | Þ | Si + 2 H2
| 630oC |
SiO2 layer ("TEOS process)
Si(C2H5O)4 | Þ | SiO2 + 2H2O + C2H4
| (720 oC) |
Si3N4 layer
3 SiH2Cl2 + 4NH3 | Þ | Si3N4 + 2HCl + 1,5 H2
| (» 700 oC)) |
W layer
| 104 Pa |
WF6 + H2 | Þ | W + (nasty) gases
| 470oC |
|  | Find to gases that react ot the desired material at elevated temperatures |
|  | Put your wafer(s) into some machine, evacuate, heat to the desired temperature (preferably only the wafers) and admit the gases (and remove undesired reaction products). |
|  | There are many quute different technical ways (all of them expensive) to realize a CVD apparatus |
| Major CVD process are |
| Deposition of epitaxial Si layers - obviously always on (atomically clean) Si substrates. By admitteing some gases carrying doping atoms (e.g. AsH3, AsH3) the layer can be doped in-situ. |
| Depositon of poly crystalline Si layers. |
|  | Chemically similar to epitaxial layers, in reality quite different because the CVD reactos can be simpler. |
|  | Poly-Si is needed for many uses: Gate electrode, interconnect, filling of holes, sacrifical layer. |
|  | Its great advantage is its full compatibility with Si and SiO2; its great disadvantage is its mediocre conductivity (for heavy doping). |
| Deposition of Si3N4 |
|  | Very important. Always prone to produce mechanical stress (Si3N4 is an unyielding ceramic!). |
| W (and Silicides, and ...) |
|  | Not "good" processes, but sometimes unavoidable! |
Questionaire
Multiple Choice questions to all of 6.2

© H. Föll (Semiconductor Technology - Script)