Three-dimensional memory devices having a shaped epitaxial channel portion and method of making thereof

A method of manufacturing a device, comprising:

• forming an alternating stack comprising insulating layers and spacer material layers over a substrate;
• forming a memory opening through the alternating stack;
• forming an epitaxial channel portion on a semiconductor surface underneath the memory opening, the epitaxial channel portion including at least one crystallographic facet that is at an angle with respect to a horizontal plane;
• removing an upper portion of the epitaxial channel portion;
• and
• forming a memory stack structure on a remaining portion of the epitaxial channel portion, wherein removal of the upper portion of the epitaxial channel portion is performed by:
• oxidizing the upper portion of the epitaxial channel portion into a semiconductor oxide portion;
• and
• removing the semiconductor oxide portion selective to the remaining portion of the epitaxial channel portion employing an anisotropic etch.

A method of manufacturing a device, comprising:

• forming an alternating stack comprising insulating layers and spacer material layers over a substrate;
• forming a memory opening through the alternating stack;
• forming an epitaxial channel portion on a semiconductor surface underneath the memory opening;
• removing an upper portion of the epitaxial channel portion, wherein a remaining portion of the epitaxial channel portion comprises a chamfer;
• and
• forming a memory stack structure on the remaining portion of the epitaxial channel portion, wherein:
• the chamfer is located in a peripheral portion of the epitaxial channel portion;
• the chamfer has an upper edge that adjoins a periphery of a horizontal top surface located in a center portion of the epitaxial channel portion and a lower edge that adjoins a sidewall of the memory opening;
• the chamfer comprises an inner periphery and an outer periphery;
• the inner periphery of the chamfer comprises the upper edge of the chamfer;
• the outer periphery of the chamfer comprises the lower edge of the chamfer;
• removal of the upper portion of the epitaxial channel portion is performed through a recess etch process that comprises a wet etch process that removes a semiconductor material of the epitaxial channel portion selective to materials of the alternating stack;
• and
• the wet etch process employs a buffered etching solution comprising trimethyl-2 hydroxyethyl ammonium hydroxide and ammonium hydroxide, wherein a volume ratio of the trimethyl-2 hydroxyethyl ammonium hydroxide to ammonium hydroxide is in a range from 1:10 to 1:1,000.