Uniform field oxidation for locos isolation

DETAILED DESCRIPTION A principal object of the invention is to provide an effective and very manufacturable method to locally oxidize the silicon in an integrated circuit.
Another object of the present invention is to provide a method of local oxidation of silicon that will provide nearly the same field oxide thicknesses in the different sized nitride openings.
Yet another object is to provide a method of local oxidation which can be used in the fabrication of ULSI active isolation.
In accordance with the objects of this invention, a new method of local oxidation using a nitrogen implant through a spin-on-glass film is achieved.
A thin silicon oxide layer is formed over the surface of a silicon substrate.
A layer of silicon nitride is deposited overlying the silicon oxide layer.
The silicon oxide and silicon nitride layers are patterned to provide openings of various sizes exposing portions of the silicon substrate to be oxidized.
Ions are selectively implanted into said silicon substrate through the openings.
The patterned surface of the substrate is covered with a spin-on-glass material.
The spin-on-glass material is thicker within the smaller openings and thinner within the larger openings.
The spin-on-glass material is soft-baked.
Nitrogen ions are selectively implanted into the silicon substrate through the spin-on-glass material within the openings wherein fewer nitrogen ions are implanted through the thicker spin-on-glass material within the smaller openings and more nitrogen ions are implanted through the thinner spin-on-glass material within the larger openings.
The spin-on-glass material is removed.
Field oxide regions are grown within the openings wherein the rate of field oxidation is inhibited most within the openings through which a larger concentration of nitrogen ions were implanted and inhibited to a lesser extent in openings through which smaller concentrations of nitrogen ions were implanted resulting in nearly equal thicknesses of field oxide regions in all openings of various sizes