Formation of high voltage transistor with high breakdown voltage
View Patent ↗A high voltage transistor exhibiting an improved breakdown voltage and related methods are provided. For example, a method of manufacturing an integrated circuit includes etching a poly silicon layer to provide a gate stacked above a floating gate of a flash memory cell. A source and a drain of the flash memory cell are implanted in a substrate. The poly silicon layer is etched to provide a gate of a high voltage transistor. Lightly doped drain (LDD) implants are provided in source/drain regions of the high voltage transistor in the substrate. An annealing operation is performed on the integrated circuit, wherein the annealing causes each of the LDD implants to form a graded junction in relation to a channel in the substrate between the LDD regions, and further causes sidewalls to oxidize on the gates of the flash memory cell and on the gate of the high voltage transistor.
1. A method of manufacturing an integrated circuit, the method comprising:
forming a flash memory cell on a substrate, the flash memory cell having a gate stacked above a floating gate;
forming a high voltage transistor on the substrate, the high voltage transistor having a gate and source/drain regions;
providing lightly doped drain (LDD) implants in the source/drain regions of the high voltage transistor in the substrate; and
annealing the integrated circuit, wherein the annealing is sufficient to concurrently cause:
each of the LDD implants to form a graded junction in relation to a channel in the substrate between the source/drain regions;
oxidized sidewalls to form on the gate of the flash memory cell, and
oxidized sidewalls to form on the gate of the high voltage transistor.
2. The method of claim 1 , wherein forming the flash memory cell on a substrate comprises:
etching a poly silicon layer to provide the gate stacked above the floating gate of the flash memory cell; and
implanting a source and a drain of the flash memory cell in the substrate.
3. The method of claim 1 , wherein forming the high voltage transistor on the substrate comprises etching a poly silicon layer to provide the gate of the high voltage transistor.
4. The method of claim 1 , wherein the high voltage transistor is adapted to sustain a programming voltage provided to the flash memory cell.
5. The method of claim 1 , wherein the high voltage transistor is adapted to sustain a programming voltage greater than approximately 9.5 volts provided to the flash memory cell.
6. The method of claim 1 , wherein the annealing comprises heating the integrated circuit to approximately 900 degrees C.
7. The method of claim 1 , further comprising implanting a source and a drain of the high voltage transistor adjacent to the LDD implants in the source/drain regions, wherein the source and drain of the high voltage transistor have a dopant concentration higher than the LDD implants.
8. The method of claim 1 , further comprising after annealing the integrated circuit, providing LDD implants in source/drain regions of a low voltage transistor in the substrate.
9. The method of claim 1 , wherein the integrated circuit has a nominal feature size less than approximately 130 nm.
10. The method of claim 1 , wherein the integrated circuit is a programmable logic device.
11. A method of manufacturing an integrated circuit, the method comprising in order:
etching a poly silicon layer to provide a gate stacked above a floating gate of a flash memory cell;
implanting a source and a drain of the flash memory cell in a substrate;
etching the poly silicon layer to provide a gate of a high voltage transistor;
providing lightly doped drain (LDD) implants in source/drain regions of the high voltage transistor in the substrate;
annealing the integrated circuit, wherein the annealing is sufficient to concurrently cause:
each of the LDD implants to form a graded junction in relation to a channel in the substrate between the source/drain regions;
oxidized sidewalls to form on the gate of the flash memory cell, and
oxidized sidewalls to form on the gate of the high voltage transistor; and
providing LDD implants in source/drain regions of a low voltage transistor in the substrate.
12. A method of manufacturing an integrated circuit, the method comprising in order:
etching a poly silicon layer to provide a gate stacked above a floating gate of a flash memory cell and a gate of a high voltage transistor;
implanting a source and a drain of the flash memory cell in a substrate;
providing lightly doped drain (LDD) implants in source/drain regions of the high voltage transistor in the substrate;
annealing the integrated circuit, wherein the annealing is sufficient to concurrently cause:
each of the LDD implants to form a graded junction in relation to a channel in the substrate between the source/drain regions;
oxidized sidewalls to form on the gate of the flash memory cell, and
oxidized sidewalls to form on the gate of the high voltage transistor; and
providing LDD implants in source/drain regions of a low voltage transistor in the substrate.