SOI trench DRAM cell for 256 MB DRAM and beyond

Claim 2

A trench structure, comprising: a substrate; a storage node of polysilicon in the substrate; an annular oxide band including diffused oxygen wherein the oxygen is diffused radially outward from within the trench into the substrate beneath a surface of the substrate and surrounding the storage node, the annular oxide band being tapered wherein a gradual increase in thickness of the annular oxide band toward the walls of the trench.

Claim 3

The trench structure of claim 1, further comprising: a nitride collar in the trench in contact with the annular oxide band.

Claim 4

An SOI DRAM comprising a plurality of the trench structures of claim 1, the trench structures being arranged such that the annular oxide bands surrounding adjacent trench structures intersect.

Claim 5

The trench structure as recited in claim 1, wherein the annular oxide band has a thickness between about 200 Å to about 500 Å.

Claim 6

An SOI trench DRAM cell prepared by a process comprising providing a substrate; etching a trench in the substrate; forming an oxide layer on the walls of the trench; forming a masking layer on the oxide layer on the walls of the trench; removing the masking layer from an upper portion of the trench; forming a masking collar on the upper portion of the trench and leaving an exposed section of the oxide layer on the trench walls about the trench below the masking collar; oxidizing the exposed section of the oxide layer in the trench to form an annular oxide region in the substrate below a surface of the substrate, the annular oxide region being tapered wherein a gradual increase in thickness of the annular oxide region towards the walls of the trench.

Claim 7

An SOI trench DRAM cell prepared by a process comprising providing a substrate; etching a trench in the substrate; forming an oxide layer on the walls of the trench; forming a masking layer on the oxide layer on the walls of the trench; removing the masking layer from an upper portion of the trench; forming a masking collar on the upper portion of the trench and leaving an exposed section of the oxide layer on the trench walls about the trench below the masking collar; oxidizing the exposed section of the oxide layer in the trench to form an annular oxide region in the substrate below a surface of the substrate, the annular oxide region being tapered wherein a gradual increase in thickness of the annular oxide region towards the walls of the trench.

Claim 8

An SOI trench DRAM cell prepared by a process comprising: providing a substrate; etching a trench in the substrate; forming an oxide layer on the walls of the trench; forming a nitride masking layer on the oxide layer in the trench; removing the nitride masking layer from an upper portion of the trench; forming a nitride masking collar on the upper portion of the trench and leaving an exposed section of the oxide layer on the trench walls about the trench below the masking collar; oxidizing the exposed section of the oxide layer in the trench to form an annular oxide region in the substrate below a surface of the substrate, the annular oxide region being tapered wherein a gradual incraese in thickness of the annular oxide region toward the walls of the trench; removing the masking collar and any remaining masking layer; forming a thin nitride layer on trench wall surfaces; and extending the depth of the trench by etching.

Claim 9

An SOI trench DRAM cell prepared by a process comprising: providing a substrate; etching a trench in the substrate; forming an oxide layer on the walls of the trench; forming a nitride masking layer on the oxide layer in the trench; removing the nitride masking layer from an upper portion of the trench; forming a nitride masking collar on the upper portion of the trench and leaving an exposed section of the oxide layer on the trench walls about the trench below the masking collar; oxidizing the exposed section of the oxide layer in the trench to form an annular oxide region in the substrate below a surface of the substrate, the annular oxide region being tapered wherein a gradual incraese in thickness of the annular oxide region toward the walls of the trench; removing the masking collar and any remaining masking layer; forming a thin nitride layer on trench wall surfaces; and extending the depth of the trench by etching.