Generally, the semiconductor backside trench fill structures 73 (e.g., the portions of the semiconductor backside trench fill structures 73 as formed at the processing steps of FIGS. 17A and 17B that are not implanted by the boron atoms) can be removed selective to the sets of at least one bridge structure 73B by performing a selective isotropic etch process. The backside cavities 79′ are formed in volumes from which the portions of the semiconductor backside trench fill structures 73 are removed. In one embodiment, the selective isotropic etch process comprises a wet etch process employing trimethyl-2 hydroxyethyl ammonium hydroxide (TMY). Generally, the set of at least one bridge structure 73B can overlie a respective backside cavity 79′ within each of the backside trenches 79. Each backside cavity 79′ comprises a volume of a void within a respective one of the backside trenches 79.
