Recessed gate silicon-on-insulator floating body device with self-aligned lateral isolation
View Patent ↗Embodiments of a manufacturing process for recessed gate devices on silicon-on-insulator (SOI) substrate with self-aligned lateral isolation are described. This allows the creation of true in-pitch recessed gate devices without requiring an extra isolation dimension. A lateral isolation trench is formed between pairs of recessed gate devices by etching the silicon-on-insulator area down to a buried oxide layer on which the silicon-on-insulator layer is formed. The position of the trench is self-aligned and defined by the gate width and the dimension of spacers disposed on either side of the gate. The isolation trench is filled with a dielectric material and then etched back to the middle of the SOI body and the remaining volume is filled with a doped conductive material. The doped conductor is subject to a thermal cycle to create source and drain regions of the device through out-diffusion of the doped material.
1. A method of fabricating semiconductor memory cells comprising:
forming a plurality of recessed gate devices on a silicon-on-insulator substrate formed over a buried oxide layer, each recessed gate device comprising a floating body region and spacers disposed on opposite sides of a gate region;
etching the silicon-on-insulator substrate until the buried oxide layer is reached to form a lateral isolation trench aligned to the gate by the spacer width;
partially filling the lateral isolation trench with a dielectric fill material;
filling a remaining portion of the lateral isolation trench with doped polysilicon; and
thermally cycling the doped polysilicon to create source and drain regions proximate the floating body region.
2. The method of claim 1 further comprising placing a defined mask pattern over the silicon-on-insulator substrate to allow partial removal of material to form the recess region of each recessed gate device.
3. The method of claim 2 wherein the spacer comprises a silicon nitride material, and wherein dielectric fill material comprises silicon oxide.
4. The method of claim 1 wherein the source and drain regions extend from the lateral isolation trench to the gate region.
5. The method of claim 1 wherein the source and drain regions extend from the lateral isolation trench and do not contact the gate region.
6. The method of claim 1 wherein the lateral isolation trench defines a self-aligned contact area for each device adjacent the lateral isolation trench.
7. The method of claim 6 wherein the lateral isolation trench is configured to have substantially vertical sides extending from a top surface to the buried oxide layer.
8. The method of claim 6 wherein the lateral isolation trench is configured to have tapered sides extending inwardly from a top surface to the buried oxide layer.