Fully isolated dielectric memory cell structure for a dual bit nitride storage device and process for making same
View Patent ↗A method of fabricating a dual bit dielectric memory cell structure on a silicon substrate includes implanting buried bit lines within the substrate and fabricating a layered island on the surface of the substrate between the buried bit lines. The island has a perimeter defining a gate region, and comprises a tunnel dielectric layer on the surface of the silicon on insulator wafer, an isolation barrier dielectric layer on the surface of the tunnel dielectric layer, a top dielectric layer on the surface of the isolation barrier dielectric layer, and a polysilicon gate on the surface of the top dielectric layer. A portion of the isolation barrier dielectric layer is removed to form an undercut region within the gate region and a charge trapping material is deposited within the undercut region.
1. A method of storing data in a dual bit dielectric memory cell, the method comprising:
a) utilizing a source-to-drain bias in the presence of a control gate field to inject a charge into a source charge trapping region;
b) utilizing a drain-to-source bias in the presence of a control gate field to inject a charge into a drain charge trapping region;
c) providing an isolation barrier between the source charge trapping region and the drain charge trapping region, wherein the isolation barrier is substantially less conductive relative to the source charge trapping region and the drain charge trapping region, and functions to reduce charge spread between the source and drain charge trapping regions.
2. The method of claim 1 , wherein the step of providing an isolation barrier includes providing an isolation barrier comprised of oxide.
3. The method of claim 2 , wherein the step of providing an isolation barrier comprised of oxide includes providing an isolation barrier from about 50 Å to 100 Å in thickness, the step of utilizing a source-to-drain bias in the presence of a control gate field to inject a charge into a source charge trapping region includes injecting a charge into a source charge trapping region that is from about 50 Å to 100 Å in thickness, and the step of utilizing a drain-to-source bias in the presence of a control gate field to inject a charge into a drain charge trapping region includes injecting a charge into a drain charge trapping region that is from about 50 Å to 100 Å in thickness.
4. The method of claim 1 , wherein the step of utilizing a source-to-drain bias in the presence of a control gate field to inject a charge into a source charge trapping region includes injecting a charge into a source charge trapping region comprising a nitride compound, and the step of utilizing a drain-to-source bias in the presence of a control gate field to inject a charge into a drain charge trapping region includes injecting a charge into a drain charge trapping region comprising the nitride compound.
5. The method of claim 1 , wherein the step of utilizing a source-to-drain bias in the presence of a control gate field to inject a charge into a source charge trapping region includes injecting a charge into a source charge trapping region comprising a material selected from the group consisting of Si 2 N 4 and SiO x N 4 , and the step of utilizing a drain-to-source bias in the presence of a control gate field to inject a charge into a drain charge trapping region includes injecting a charge into a drain charge trapping region comprising the material.
6. The method of claim 1 , wherein the step of utilizing a source-to-drain bias in the presence of a control gate field to inject a charge into a source charge tapping region includes injecting a charge into a source charge trapping region that extends beneath a control gate for a length from about 300 Å to about 500 Å, and the step of utilizing a drain-to-source bias in the presence of a control gate field to inject a charge into a drain charge trapping region includes injecting a charge into a drain charge trapping region that extends beneath a control gate for a length from about 300 Å to about 500 Å.
7. The method of claim 1 , wherein the source and drain charge trapping regions comprise silicon nitride or silicon oxynitride, and the isolation barrier comprises silicon oxide.