Multi-level contact to a 3D memory array and method of making

1. A multilevel device, comprising:

at least one device region and at least one contact region having a plurality of stacked electrically conductive layers, wherein the electrically conductive layers form a stepped pattern in the contact region;

a conformal etch stop layer located over the electrically conductive layers;

a first electrically insulating layer located over the etch stop layer;

a conformal sacrificial layer located over the first electrically insulating layer;

a second electrically insulating layer located over the sacrificial layer;

a plurality of contact openings extending through the etch stop layer, the first electrically insulating layer, the sacrificial layer and the second electrically insulating layer in the contact region to the plurality of electrically conductive layers; and

a plurality of electrically conductive contacts, wherein each respective one of the plurality of electrically conductive contacts is located in a respective one of the plurality of contact openings, and each electrically conductive contacts is in electrical contact with a respective one of the plurality of electrically conductive layers;

wherein:

the plurality of electrically conductive layers comprise at least a first conductive layer in a first device level located over a substrate and a second conductive layer in a second device level located higher than the first device level over the substrate;

the first conductive layer comprises a first portion which laterally extends past the second conductive layer to form at least a portion of the step pattern;

the plurality of contact openings comprises a first contact opening which extends to the first portion of the first conductive layer and a second contact opening which extends to an upper surface of the second conductive layer;

a first electrically conductive contact of the plurality of electrically conductive contacts is located in the first contact opening;

a second electrically conductive contact of the plurality of electrically conductive contacts is located in the second contact opening;

in the first electrically conductive contact extends deeper than the second electrically conductive contact;

each of the conformal etch stop layer, the first electrically insulating layer and the sacrificial layer has a substantially uniform thickness and each is arranged in the step pattern over the plurality of electrically conductive layers in the contact region;

the second electrically insulating layer has a variable thickness and a substantially planar upper surface; and

the second electrically insulating layer is thicker over the first portion of the first conductive layer than over the second conductive layer.

2. The device of claim 1 , wherein:

the conformal etch stop layer and the conformal sacrificial layer comprise the same material;

the first and the second electrically insulating layers comprise the same material; and

the conformal sacrificial layer comprises a different material from that of the first electrically insulating layer.

3. The device of claim 2 , wherein:

the conformal etch stop layer and the conformal sacrificial layer comprise the same nitride material; and

the first and the second electrically insulating layers comprise the same oxide material.

4. The device of claim 3 , wherein the etch stop layer comprises silicon nitride, the first electrically insulating layer comprises silicon oxide, the sacrificial layer comprises silicon nitride, and the second electrically insulating layer comprises silicon oxide.

5. The method of claim 1 , wherein:

the device comprises a vertical NAND device;

the device region comprises:

a plurality of semiconductor channels, wherein at least one end portion of each of the plurality of semiconductor channels extends substantially perpendicular to a major surface of the substrate;

a plurality of charge storage regions, each charge storage region located adjacent to a respective one of the plurality of semiconductor channels; and

a plurality of control gate electrodes having a strip shape extending substantially parallel to the major surface of the substrate, wherein the plurality of control gate electrodes comprise at least a first control gate electrode located in the first device level and a second control gate electrode located in the second device level;

the first conductive layer comprises a portion of the first control gate electrode which extends from the device region to the contact region; and

the second conductive layer comprises a portion of the second control gate electrode which extends from the device region to the contact region.

6. The device of claim 1 , wherein:

the vertical NAND device comprises an array of monolithic three dimensional NAND strings located over a silicon substrate;

at least one memory cell in the first device level of the three dimensional array of NAND strings is located over another memory cell in the second device level of the three dimensional array of NAND strings; and

the silicon substrate contains an integrated circuit comprising a driver circuit for the memory device located thereon.