1 Silicon WaferManufacture Packaging Epitaxial Growth Oxidation Photo- lithography Etching Diffusion (Ion Implantation) Metallization Fabricati on Processes for VLSI Devices Chip Fabrication Processes 2 Silicon Wafer Preparation 3 Silicon Wafer Preparation 4 Czochralski (CZ) Growth Method • CZ is more co mmon method to grow silicon crystal today because it is capable of producing large diameter crystals, from which large diameter wafer can be cut. Lecture # 4
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• The raw Si used for crystalgrowth is purified from SiO2
(sand) through refining, fractionaldistillation and CVD.
• The raw material contains < 1 ppbimpurities except for O (» 1018
cm-3) and C (» 1016 cm-3)
• Essentially all Si wafers used forICs today come from Czochralskigrown crystals. Polysilicon materialis melted, held at close to 1415°C, and a single crystal seed isused to start the crystal growth.
• Pull rate, melt temperature androtation rate are all importantcontrol parameters.
• The only significant drawbackto the CZ method is that thesilicon is contained in liquidform in a crucible duringgrowth and as a result,impurities from the crucibleare incorporated.
• in the growing crystal. Oxygenand carbon are the two mostsignificant contaminants.
• These impurities are notalways a drawback, however.
Oxygen in particular can bevery useful in mechanicallystrengthening the siliconcrystal and in providing ameans for gettering otherunwanted impurities duringdevice fabrication.
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Modeling Crystal Growth: relationship between pull