Method of making a three-dimensional memory array with etch stop

A method of making a semiconductor device, comprising:

• forming a sacrificial feature over a substrate;
• forming a plurality of etch through regions comprising an etch through material and an etch stop region comprising an etch stop material over the sacrificial feature;
• forming a stack of alternating layers of a first material and a second material over the plurality of the etch through regions and the etch stop region;
• etching the stack to form a plurality of openings through the stack and through the etch through regions to expose the sacrificial feature, such that the etch through material is etched preferentially compared to the first and the second materials of the stack;
• removing the sacrificial feature through the plurality of openings;
• and etching the stack to form a slit trench up to or only partially through the etch stop region, such that the first and the second materials of the stack are etched preferentially compared to the etch stop material,
• wherein:
• the plurality of etch through regions comprise a plurality of portions of a layer of the etch through material and the etch stop region comprises a substantially rail shaped region of the etch stop material embedded between the portions of the layer oft he etch through material;
• and
• forming the plurality of etch through regions and the etch stop region comprises one of:
• (a) forming a substantially rail shaped region of the etch stop material over the sacrificial feature, and forming the layer of the etch through material around the substantially rail shaped region;
• (b) forming the layer of the etch through material over the sacrificial feature, forming a substantially rail shaped trench in the layer of the etch through material, and filling the trench with a substantially rail shaped region of the etch stop material;
• and
• (c) forming the layer of the etch through material over the sacrificial feature, forming mask over the layer of the etch through material such that a substantially rail shaped region in the layer is exposed in the mask, and on implanting the exposed substantially rail shaped region in the layer of the etch through material to convert the etch through material to the etch stop material in the substantially rail shaped region.