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State & Explain Different Silicon compounds?

Mumbai University > Electronics Engineering > Sem 8 > MEMS Technology

Marks: 5M

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There 3 principal silicon compounds in MEMS & microsystem: Silicon dioxide (SiO2), Silicon Carbide (SiC) & Silicon nitride ($Si_3N_4$) – each has distinct characteristic & unique applications.

Silicon dioxide ($SiO_2$)

  • It is least expensive material to offer good thermal & electrical insulation.
  • Also used a low – cost material for “mask” in micro fabrication processes such as etching, deposition & diffusion.
  • Used as sacrificial material in “surface micromachining”.
    • By dry heating of silicon : $Si+O_2→ SiO_2$
    • Or by oxide silicon in wet steam $Si+2H_2O→SiO_2+2H_2$
  • Silicon Dioxide ($SiO_2$) is used in MEMS due to following reasons,
    • as a thermal & electric insulator.
    • as a mask & etching of silicon substrate.
    • sacrificial layer in surface micromachining
    • It offer stronger resistance as compared to silicon in etching process.

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Silicon Carbide (SiC)

Its very high melting point and resistance to chemical reactions make it ideal candidate material for being masks in micro fabrication processes.

  • Silicon carbide is used in MEMS as it offers very strong resistance to the oxidation at very high temperature.
  • SiC is product which is obtained while producing the silicon from the row silicon.

Silicon nitride (Si3N4)

  • Produced by chemical reaction $3SiCl_2H_2+4NH_3→Si_3N_4+6HCL+6H_2$
  • Used as excellent barrier to diffusion to water and icons.
  • Its ultra strong resistance to oxidation & many etchants make it a superior material for masks in deep etching.
  • Also used as high strength electric insulators.
  • Selected properties SiIts ultra strong resistance to oxidation & many etchants make it a superior material for masks in deep etching.
  • Also used as high strength electric insulators.
  • Selected properties Si3N4films are as follows:

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Polycrystalline silicon

  • It is usually called “polysilicon”.
  • It is an aggregation of pure silicon crystals with randomly orientations deposited on the top of silicon substrates:

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  • These polysilicon usually are highly doped silicon.
  • They are deposited to the substrate surfaces to produce localized “resistors” & “gates for transistors”
  • Being randomly oriented, polysilicon is even stronger than single silicon crystals.
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