Methods of forming materials within openings, and method of forming isolation regions

A method of forming a material within an opening in a substrate, comprising:

• forming a nitride-containing layer over a substrate and overlying a pad oxide layer, the nitride-containing layer comprising at least two portions, one of the at least two portions being an upper portion and the other of the at least two portions being a lower portion, the upper portion etching faster when exposed to subsequent etching conditions than does the lower portion, the nitride-containing layer having an opening extending therethrough exposing a portion of the underlying substrate, the exposed portion of the substrate etched to further extend the opening into the substrate, the nitride-containing layer comprising an upper corner at a periphery of the opening, the upper corner having a corner angle with a first degree of sharpness, the forming the nitride-containing layer comprises:
• forming the lower portion of a first silicon nitride comprising a first stoichiometric amount of silicon;
• and
• forming the upper portion of a second silicon nitride comprising a second stoichiometric amount of silicon, the second amount being greater than the first stoichiometric amount;
• prior to the subsequent etching, forming a first silicon oxide layer within the opening extended into the substrate, the first layer contiguous with the pad oxide layer and not filling the opening, wherein the first layer and pad oxide layer define essentially square corners of the opening extended into the substrate;
• removing a portion of the upper corner by the subsequent etching to reduce the sharpness of the corner angle to a second degree while not changing the essentially square corners of the opening extended into the substrate;
• forming a second layer of material within the opening and over the nitride-containing layer, the second layer filling the opening;
• and
• planarizing the material to remove the material from over the nitride-containing layer while leaving the material within the opening in the nitride-containing layer wherein the subsequent etching conditions comprise planarizing the material.