High gain transistor for analog applications
An analog high gain transistor is disclosed. The formation of the analog high gain transistor is highly compatible with existing CMOS processes. The analog high gain transistor includes a double well, which includes the well implants of the low voltage (LV) and intermediate voltage (IV) transistors. In addition, the analog high gain transistor includes light doped extension regions of IV transistor and a thin gate dielectric of the LV transistor.
1. A method comprising:
forming a first device region, a second device region, and a third device region on a substrate;
forming a first device well in the first device region using a first masked ion implantation process and a second masked ion implantation process;
forming an analog high gain transistor using the first device region;
forming a low voltage transistor using the second device region; and
forming an intermediate voltage transistor using the third device region,
wherein the analog high gain transistor includes a first gate with a first gate dielectric on the first device region and a first gate electrode over the first gate dielectric, the low voltage transistor includes a second gate with a second gate dielectric on the second device region and a second gate electrode over the second gate dielectric, the intermediate voltage transistor includes a third gate with a third gate dielectric on the third device region and a third gate electrode over the third gate dielectric, the first gate dielectric of the analog high gain transistor is a first section of a gate dielectric material, the second gate dielectric of the low voltage transistor is a second section of the gate dielectric material, the first gate dielectric of the analog high gain transistor and the second gate dielectric of the low voltage transistor are thinner than the third gate dielectric of the intermediate voltage transistor, the intermediate voltage transistor and the analog high gain transistor have respective lightly doped extension regions with equal dopant concentrations, the low voltage transistor has a lightly doped extension region with a higher dopant concentration than the lightly doped extension regions of the intermediate voltage transistor and the analog high gain transistor, the first device well has a dopant concentration that is greater than a dopant concentration of a second device well in the second device region, and the dopant concentration of the first device well is greater than a dopant concentration of a third device well in the third device region.
2. The method of claim 1 wherein the gate dielectric material is formed by oxidation.
3. The method of claim 1 wherein the respective lightly doped extension regions of the intermediate voltage transistor and the analog high gain transistor are formed by a third implantation process.
4. The method of claim 1 wherein the first gate dielectric and the second gate dielectric are about 20 angstroms thick.
5. The method of claim 1 wherein the third gate dielectric is about 60 angstroms thick.
6. The method of claim 1 wherein the first gate electrode, the second gate electrode, and the third gate electrode comprise polysilicon, and the first gate dielectric, the second gate dielectric, and the third gate dielectric comprise silicon oxide.
7. The method of claim 1 wherein the first gate electrode, the second gate electrode, and the third gate electrode comprise a metal, and the first gate dielectric, the second gate dielectric, and the third gate dielectric comprise a high-k gate dielectric.
8. The method of claim 1 wherein the low voltage transistor has a smaller channel length than the analog high gain transistor.
9. The method of claim 1 wherein the dopant concentration of the first device well is about 1.5E16/cm 3 .