Patent ID: 9552991
Date: 2017-01-24
CPC Classifications: H01L

Claim:
1. A method of making a monolithic three dimensional NAND string, comprising: providing a stack of alternating first material layers and second material layers different from the first material layer over a substrate; etching the stack to form at least one trench in the stack; forming a blocking dielectric over a side wall of the at least one trench; forming a charge storage layer over the blocking dielectric in the at least one trench; forming a tunnel dielectric over the charge storage layer in the at least one trench; and forming a semiconductor channel over the tunnel dielectric in the at least one trench; wherein: etching the stack to form the at least one trench comprises etching the stack to form a plurality of trenches extending in a first direction; the plurality of trenches are separated by a plurality of rails extending in the first direction; each of the plurality of rails is located between two adjacent trenches; each of the plurality of rails comprises the stacked alternating first material layers and second material layers; and the semiconductor channel extends continuously over an upper surface of the plurality of rails and over a bottom surface and side walls of the plurality of trenches; and further comprising: etching the semiconductor channel to form a plurality of strips extending in a second direction which is substantially perpendicular to the first direction; filling the plurality of trenches with a sacrificial material after the step of forming the semiconductor channel and before the step of etching which forms the plurality of strips; forming a mask comprising a plurality of strips extending in the second direction over the sacrificial layer; and etching the sacrificial material using the mask to form a plurality of sacrificial strips, wherein the step of etching to form the plurality of strips comprises etching the semiconductor channel using at least one of the mask and the sacrificial strips to form the plurality of strips; and removing the mask and the sacrificial strips.