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)