Polycrystalline silicon resistors for integrated circuits

The suitability of thin films of doped polycrystalline silicon on SiO2 substrates for the production of high value resistors for monolithic integrated circuits is considered. Resistors fabricated from this material posses the advantages of high sheet resistivity and dielectric isolation while still preserving an all silicon technology compatible with conventional production techniques.Relevant structural and electrical properties of doped polycrystalline films produced by both vacuum evaporation onto hot substrates with gas-doping and by diffusion-annealing of amorphous films have been investigated. Sheet resistivities and TCR values measured on 2500 Å polycrystalline films have proved superior to those encountered with conventional diffused resistors. Typically films with sheet resistivities of 1 kΩ/□ had TCR's of −1000 ppm/°C while conventional diffused resistors are generally made from material of 200 Ω/□ and +2000 ppm/°C TCR. Etched resistor line widths of 0·25 mil. have been obtained in the polycrystalline material employing conventional photolithographic techniques. The temperature stability and linearity of doped polycrystalline resistors have been investigated.