Method of making embedded memory device with silicon-on-insulator substrate
A method of forming a semiconductor device where memory cells and some logic devices are formed on bulk silicon while other logic devices are formed on a thin silicon layer over insulation over the bulk silicon of the same substrate. The memory cell stacks, select gate poly, and source regions for the memory devices are formed in the memory area before the logic devices are formed in the logic areas. The various oxide, nitride and poly layers used to form the gate stacks in the memory area are formed in the logic areas as well. Only after the memory cell stacks and select gate poly are formed, and the memory area protected by one or more protective layers, are the oxide, nitride and poly layers used to form the memory cell stacks removed from the logic areas, and the logic devices are then formed.
1. A semiconductor device, comprising:
a substrate having:
a first area of bulk silicon,
a second area with a first insulation layer directly over bulk silicon and a silicon layer directly over the first insulation layer, and
a third area of bulk silicon,
wherein the first and third areas of the substrate lack any silicon layer disposed over insulation material;
memory cells formed in the first area, wherein each of the memory cells includes:
spaced apart first source and first drain regions formed in the bulk silicon and defining a first channel region of the bulk silicon extending there between,
a floating gate disposed over and insulated from a first portion of the first channel region,
a select gate disposed over and insulated from a second portion of the first channel region,
a control gate disposed over and insulated from the floating gate, and
an erase gate disposed over and insulated from the first source region;
first logic devices formed in the second area, wherein each of the first logic devices includes:
spaced apart second source and second drain regions formed in the silicon layer and defining a second channel region of the silicon layer extending there between, and
a first conductive gate disposed over and insulated from the second channel region;
second logic devices formed in the third area, wherein each of the second logic devices includes:
spaced apart third source and third drain regions formed in the bulk silicon and defining a third channel region of the bulk silicon extending there between, and
a second conductive gate disposed over and insulated from the third channel region.
2. The semiconductor device of claim 1 , wherein:
the floating gates, the select gates, the control gates and the erase gates are formed of polysilicon; and
the first conductive gates and the second conductive gates are formed of a metal material.
3. The semiconductor device of claim 2 , wherein:
the first conductive gates are insulated from the silicon layer by a high K insulation material; and
the second conductive gates are insulated from the bulk silicon by a high K insulation material.
4. The semiconductor device of claim 1 , wherein the first source and first drain regions extend deeper into the bulk silicon than do the second source and second drain regions into the silicon layer.
5. The semiconductor device of claim 1 , wherein the first source and first drain regions extend deeper into the bulk silicon than a thickness of the silicon layer.
6. The semiconductor device of claim 1 , wherein the third source and third drain regions extend deeper into the bulk silicon than do the second source and second drain regions into the silicon layer.