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14 Etch 10 - Etching This lecture covers how materials are...

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Wafers must be cleaned prior to use and at various points in the process wet chemical etching is the low-cost method of choice for cleaning and layer removal. Dry etching is a vital part of the pattern transfer process in VLSI and ULSI glow discharge or “plasma” is used to give a high degree of control over etch. Etching This lecture covers how materials are etched using wet and dry processes…
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Ion energy Low Ion density High Physical reactions Some Chemical reactions Strong By-products Volatile + Ion source Wafer Dry etching involves a source of low energy ions which strike the wafer to physically remove material Dry etch basics
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Cleaning Redeposition Unstick Particulates Redeposition React or unstick Metallics Oxidize surface Oxidizing agent Organics Remove functional oxide Etch (HF) Native oxide Risk Cleaning action Contaminant Wafer cleaning is a vital yield issue but may not be given much attention in textbooks.
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Cleaning examples Blank wafer Boiling H 2 SO 4 + H 2 O 2 HF dip Water wash or HF vapor Surface removal DZ growth Oxide growth Oxide etch RCA clean 80 ° C NH 4 OH:H 2 O 2 :H 2 O 10% HF dip Water wash Resist strip Oxidizing agent, e.g. plasma or boiling HNO 3 NH 4 F:HF dip Water wash Water spec is 18 M .cm
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Dry etch principles Wet etching has many drawbacks - Contamination -
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