Semiconductor device structure with composite interconnect structure and method for preparing the same

A semiconductor device structure, comprising:

• a first lower semiconductor structure disposed over a semiconductor substrate, wherein the first lower semiconductor structure has a first sidewall and a second sidewall opposite to the first sidewall;
• a first upper semiconductor structure covering a top surface and the first sidewall of the first lower semiconductor structure, wherein the first lower semiconductor structure and the first upper semiconductor structure comprise different materials;
• a first oxide portion disposed over the semiconductor substrate and extending along the second sidewall of the first lower semiconductor structure;
• a dielectric layer disposed over the first oxide portion, wherein the first oxide portion separates the dielectric layer from the semiconductor substrate;
• a second lower semiconductor structure disposed over the semiconductor substrate, wherein the second lower semiconductor structure has a third sidewall facing the second sidewall of the first lower semiconductor structure and a fourth sidewall opposite to the third sidewall;
• a second upper semiconductor structure covering a top surface and the third sidewall of the second lower semiconductor structure;
• and
• a second oxide portion disposed over the semiconductor substrate and extending along the fourth sidewall of the second lower semiconductor structure, wherein the second oxide portion is covered by the dielectric layer;
• wherein the first oxide portion is in direct contact with a sidewall of the second upper semiconductor structure;
• wherein a material of the first oxide portion is the same as a material of the second oxide portion.