Metal contact via structure surrounded by an air gap and method of making thereof

A method of forming a three-dimensional memory device, comprising:

• forming a metal interconnect structure embedded in a lower interconnect level dielectric layer over a substrate;
• forming at least one material layer and a first contact level dielectric layer over the at least one material layer;
• replacing an upper portion of the first contact level dielectric layer overlying the metal interconnect structure with a sacrificial material plate including a first sacrificial material;
• forming a via cavity extending through the sacrificial material plate, a lower portion of the first contact level dielectric layer, and the at least one material layer to a top surface of the metal interconnect structure;
• forming a sacrificial spacer comprising a second sacrificial material on a sidewall of the via cavity;
• forming a metal contact via structure in a remaining volume of the via cavity inside the sacrificial spacer, wherein the metal contact via structure contacts an upper portion of the sidewall of the remaining portion of the sacrificial material plate;
• and
• removing the remaining portion of the sacrificial material plate and the sacrificial spacer to provide a tubular cavity free of any solid material around a lower portion of the metal contact via structure.

A structure comprising:

• a metal interconnect structure embedded in a lower interconnect level dielectric layer overlying a substrate;
• at least one material layer overlying the metal interconnect structure;
• a first contact level dielectric layer overlying the at least one material layer;
• a metal contact via structure vertically extending through the first contact level dielectric layer and the at least one material layer and contacting a top surface of the metal interconnect structure;
• and
• an encapsulated tubular cavity free of any solid material therein, laterally surrounding at least lower portion of the metal contact via structure, and vertically extending through each of the at least one material layer,
• wherein the structure comprises at least one feature selected from:
• a first feature in which the metal contact via structure comprises a concave surface that continuous extends azimuthally by 360 degrees over the encapsulated tubular cavity and connects a sidewall of the lower portion of the metal contact via structure to a sidewall of an upper portion of the metal contact via structure that overlies the encapsulated tubular cavity;
• a second feature in which the metal contact via structure comprises a metallic liner including a planar bottom portion that contacts the top surface of the metal interconnect structure and a vertically extending portion that extends from the planar bottom portion to a periphery of a top surface of the metal contact via structure inside an inner boundary of the encapsulated tubular cavity, and a metal fill portion located inside the metallic liner and extending from a top surface of the planar bottom portion to the top surface of the metal contact via structure;
• or
• a third feature in which the structure further comprises a tubular dielectric spacer laterally surrounding the lower portion of the metal contact via structure and laterally surrounded by the encapsulated tubular cavity.