Self-aligned back-side gate vias

An apparatus, comprising:

• first and second metallization layers;
• and
• a transistor structure between the first and second metallization layers, the transistor structure comprising a gate electrode between source and drain regions, wherein:
• a first of the source and drain regions is coupled to the first metallization layer;
• a second of the source and drain regions is coupled to the second metallization layer by a first metal structure in contact with the second of the source and drain regions;
• the gate electrode is coupled to a metal line in the second metallization layer by a second metal structure in contact with the gate electrode;
• a first dielectric structure is between and in contact with the metal line and the first of the source and drain regions;
• a second dielectric structure is between and in contact with the metal line and the second of the source and drain regions;
• and
• the first dielectric structure has a first composition different than a second composition of the second dielectric structure.

A method, comprising:

• forming alternating first and second rows of first and second sacrificial materials on a first side of a substrate, wherein the substrate comprises a first array of transistor structures coupled to a metallization network on a second side opposite the first side, and a second array of sacrificial structures is between and in contact with the first array and the first rows;
• replacing the first sacrificial material in the first rows with a dielectric material;
• removing the second rows of the second sacrificial material;
• exposing first portions of a first set of the transistor structures by etching between the first rows;
• forming first contacts on the first side to the first set of the transistor structures;
• removing the first rows of the dielectric material;
• and
• replacing the sacrificial structures with dielectric plugs and with second contacts on the first side to second portions of a second set of the transistor structures.