Cover wafer with protective layer of sio2 oxide

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Cover wafer with protective layer of SiO2 (oxide) Remove layer where n-well should be built Implant or diffuse n dopants into exposed wafer Strip off SiO2 p substrate 30/111 0: Introduction
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Digital IC Oxidation Grow SiO2 on top of Si wafer 900 1200 ºC with Si and O 2 in oxidation furnace p substrate SiO 2 31/111 0: Introduction
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Digital IC Photoresist Spin on photoresist Photoresist is a light-sensitive organic polymer Softens where exposed to light p substrate SiO 2 Photoresist 32/111 0: Introduction
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Digital IC Lithography Expose photoresist through n-well mask Strip off exposed photoresist p substrate SiO 2 Photoresist 33/111 0: Introduction
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Digital IC Etch Etch oxide with hydrofluoric acid (HF) Only attacks oxide where resist has been exposed p substrate SiO 2 Photoresist 34/111 0: Introduction
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Digital IC Strip Photoresist Strip off remaining photoresist Use mixture of acids called piranah etch Necessary so resist doesn’t melt in next step p substrate SiO 2 35/111 0: Introduction
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Digital IC n-well n-well is formed with diffusion or ion implantation Diffusion Place wafer in furnace with arsenic gas Heat until As atoms diffuse into exposed Si Ion Implanatation Blast wafer with beam of As ions Ions blocked by SiO2, only enter exposed Si n well SiO 2 36/111 0: Introduction
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Digital IC Strip Oxide Strip off the remaining oxide using HF Back to bare wafer with n-well Subsequent steps involve similar series of steps p substrate n well 37/111 0: Introduction
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