Method of forming a memory cell by reducing diffusion of dopants under a gate
View Patent ↗A method of forming a memory cell includes forming a conductive floating gate over the substrate, forming a conductive control gate over the floating gate, forming a conductive erase gate laterally to one side of the floating gate and forming a conductive select gate laterally to an opposite side of the one side of the floating gate. After the forming of the floating and select gates, the method includes implanting a dopant into a portion of a channel region underneath the select gate using an implant process that injects the dopant at an angle with respect to a surface of the substrate that is less than ninety degrees and greater than zero degrees.
1. A method of forming a memory cell, comprising:
providing a substrate of semiconductor material of a first conductivity type;
forming first and second spaced-apart regions in the substrate of a second conductivity type, with a channel region therebetween;
forming a conductive floating gate over and insulated from the substrate;
forming a conductive control gate over and insulated from the floating gate;
forming a conductive erase gate laterally to one side of, and insulated from, the floating gate;
forming a conductive select gate laterally to an opposite side of the one side of, and insulated from, the floating gate; and
implanting, after the forming of the floating gate and the select gate, a dopant into a portion of the channel region underneath the select gate using an implant process that injects the dopant at an angle with respect to a surface of the substrate that is less than ninety degrees and greater than zero degrees.
2. The method of claim 1 , wherein the dopant is not implanted into a portion of the channel region underneath the floating gate.
3. The method of claim 1 , wherein the dopant is of the first conductivity type.
4. The method of claim 1 , wherein the dopant includes boron.
5. The method of claim 1 , wherein the angle with respect to a normal N to the surface of the substrate is generally 30°.
6. The method of claim 1 , wherein the dopant is injected with an implant energy of 15 KeV.
7. The method of claim 1 , wherein the dopant is injected with a total dose of 4E13.
8. The method of claim 1 , further comprising:
horizontally rotating the substrate 90 degrees; and
repeating the implanting for a second time.
9. The method of claim 8 , further comprising:
after the implanting for a second time, horizontally rotating the substrate another 90 degrees; and
repeating the implanting for a third time.
10. The method of claim 9 , further comprising:
after the implanting for a third time, horizontally rotating the substrate another 90 degrees; and
repeating the implanting for a fourth time.