State any four materials used in fabrication of semiconductor device and describe its need.
For fabrication of semiconductor devices like transistors diode, solar cell etc. we have to make use of following types of materials
1. Substrate: o It is used for deposition of thin film layers, Substrate can be plastic, glass or ceramic. o Plastic substrate are used only for thin film solar cells, Glass or Ceramic are high temperature substrates. They are used for deposition of metals for resistors and capacitors.
2. Metals: o The fabrication of the passive part of integrated silicon and thin film circuits involves use of different metals. o The metals usually act as capacitor plate, as heat dissipater as a mechanical support.
3. Capacitance Material: o They should have high dielectric constant, pin-hole free continuous layer, ability to withstand thermal stress, o Commonly used capacitance material are SiO, ZnS, SiO2.
4. Junction coating: o The junction protected by using resins as coating material are called junction coating. o The material generally used are high purity silicon resin and silicon modified polyester resin, because of the satisfactory performance and long life.
5. Device potting: o It is process of filling a complete electronic device with Gelatinous compound for resistance of shock and vibrations, exclusion of moisture and corrosive agents o Silicon fluids dielectric gels and flexible potting resins are some of the potting materials
6. Packaging: o A suitable enclosure or packaging is needed for ensure safety of solid state devices. o Metal cans and sealed glass containers satisfy the extreme requirements of space and military users.