Method for forming a flash memory device with straight word lines
View Patent ↗Embodiments of the present invention disclose a memory device having an array of flash memory cells with source contacts that facilitate straight word lines, and a method for producing the same. The array is comprised of a plurality of non-intersecting shallow trench isolation (STI) regions that isolate a plurality of memory cell columns. A source column is implanted with n-type dopants after the formation of a tunnel oxide layer and a first polysilicon layer. The implanted source column is coupled to a plurality of common source lines that are coupled to a plurality of source regions associated with memory cells in the array. A source contact is coupled to the implanted source column for providing electrical coupling with the plurality of source regions. The source contact is collinear with a row of drain contacts that are coupled to drain regions associated with a row of memory cells. The arrangement of source contacts collinear with the row of drain contacts allows for straight word line formation.
1. A method for forming a semiconductor memory device with an implanted source column in a silicon substrate comprising:
forming a layer of tunnel oxide over a silicon substrate having shallow trench isolation (STI) regions filled with an oxide material;
forming a first layer of polysilicon over the layer of tunnel oxide;
forming a first mask over the first layer of polysilicon to isolate a column parallel to the STI regions in the silicon substrate;
forming a source column by implanting dopants into the column in the silicon substrate through the first layer of polysilicon and the layer of tunnel oxide;
forming a common source line in the silicon substrate, wherein the common source line is perpendicular to the implanted source column, the common source line is coupled to a source region in the silicon substrate, the source region is associated with a memory cell and the common source line is permanently coupled to the implanted source column; and
forming a source contact along a row of drain contacts associated with a row of memory cells perpendicular to the implanted source column, wherein the source contact is coupled to the implanted source column.
2. The method of claim 1 wherein the layer of tunnel oxide is formed over the silicon substrate after a formation of the STI regions in the silicon substrate.
3. The method of claim 1 wherein the dopants comprise n-type dopants.
4. The method of claim 1 further comprising forming source and drain regions in the silicon substrate, wherein the source and drain regions are formed before the common source line is formed in the silicon substrate.
5. The method of claim 1 further comprising:
removing the first mask after implanting the dopants into an isolated region in the silicon substrate to form the source column wherein the first layer of polysilicon is defined.
6. The method of claim 1 further comprising:
forming an interpoly dielectric layer over the first layer of polysilicon; and
forming a second layer of polysilicon over the interpoly dielectric layer.
7. The method of claim 1 wherein further comprising:
performing stack gate definition to form a plurality of memory cells on the silicon substrate.
8. The method of claim 1 wherein the stack gate definition is accomplished using mask and etch processes.
9. The method of claim 1 further comprising:
forming a plurality of word lines that are non-intersecting in the silicon substrate, wherein the plurality of word lines are coupled to a plurality of control gates in the silicon substrate; and wherein the plurality of word lines intersect the source column adjacent to the source contact in a straight formation.