Methods and structures for three-dimensional dynamic random-access memory

A method for forming a three-dimensional dynamic random-access memory (3D DRAM) structure, comprising:

• depositing alternating layers of crystalline silicon (c-Si) material and crystalline silicon germanium (c-SiGe) material using an heteroepitaxy process on a substrate;
• etching of a pattern of holes with at least one high aspect ratio (HAR) hole into the substrate, the pattern of holes configured to provide chemistry access to the alternating layers of c-Si material and c-SiGe material to laterally etch or deposit materials to form 3D DRAM features of the 3D DRAM structure without subsequent HAR etching of holes in the substrate to form the 3D DRAM features;
• merging a portion of the pattern of holes formed by etching material between the portion of the pattern of holes to form slot features of the 3D DRAM structure;
• forming an isolation slot from at least one slot feature which has a liner of a first dielectric material which is removable by exposure to hydrogen fluoride (HF) and which has ends filled with a second dielectric material impervious to HF, the isolation slot configured to provide lateral cell isolation and give structure support to the 3D DRAM structure;
• forming a lower electrode of a capacitor of the 3D DRAM structure that is supported at one or more ends of the isolation slot that are filled with the second dielectric material;
• and
• removing the liner of the first dielectric material of the isolation slot to provide space to fill with a high-k top electrode material for increased 3D DRAM cell capacitance while maintaining structural support of the lower electrode.