Abstract: A method of forming a planarized dielectric filled wide shallow trench in a semi-conductor substrate is provided. A layer of etch stop such as Si.sub.3 N.sub.4 is deposited onto the semi-conductor substrate, and wide trenches are formed through the Si.sub.3 N.sub.4 into the substrate by conventional RIE. The surface of the substrate including the trenches have formed thereon a SiO.sub.2 coating, conforming to the surface of the substrater. A layer of etch resistant material such as polysilicon is deposited onto the SiO.sub.2 material. The polysilicon outside the width of the trenches is then removed by chemical-mechanical polishing to expose the SiO.sub.2 there below, while leaving the SiO.sub.2 above the trenches covered with polysilicon. The exposed SiO.sub.2 is then RIE etched down to the Si.sub.3 N.sub.4, leaving a plug of SiO.sub.2 capped with the etch resistant polysilicon over each trench. These plugs are then removed by mechanical polishing down to the Si.sub.3 N.sub.