Using LPCVD silicon nitride cap as a barrier to reduce resistance variations from hydrogen intrusion of high-value polysilicon resistor

摘要

A new method of forming a polysilicon resistor having reduced resistance variations by using an LPCVD silicon nitride cap over the polysilicon resistor is described. A field oxide layer is provided overlying a semiconductor substrate. A polysilicon layer is deposited overlying the field oxide layer and etched away where it is not covered by a mask to form a polysilicon resistor. The polysilicon resistor is oxidized to form an oxide layer on all surfaces of the polysilicon resistor. A silicon nitride barrier layer is deposited overlying the oxide layer. An interlevel dielectric layer is dpeosited overlying the silicon nitride barrier layer. Contact openings are etched through the interlevel dielectric layer, silicon nitride barrier layer, and oxide layer to the polysilicon resistor. The contact openings are filled with a metal layer which is patterned. The patterned metal layer is covered with a passivation layer wherein the passivation layer contains hydrogen atoms and wherein the silicon nitride barrier layer prevents the hydrogen atoms from penetrating the polysilicon resistor.