Etching various materials
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Key ingredients in wet etchants:
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Oxidizer: H2O2, HNO3
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Acid or Alkali to dissolve oxidized surface: H2SO4, NH4OH
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Diluent media to transport reactants and products through: H2O, CH3COOH
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Below are given a few etchants used for different materials; as it can be seen, the etchant must be well chosen, and also the conditions such as temperature, concentration should be precise
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to etch SiO2: HF + NH4F + H2O (called buffered HF, written as: BHF)
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to etch Si3N4:
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buffered HF, but very small etching rate
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with H3PO4, rate for Si3N4: SiO2 - 10 : 1, 140oC
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to etch Si: HF + HNO3
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to etch Al: H3PO4 +HNO3
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to etch Au and Pt: HCl + HNO3
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to etch W: KH2PO4 + KOH + K3Fe(CN)6 + H2O |
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Substrate preparation
