Method for integrating DMOS into sub-micron CMOS process
This invention is forming the DMOS channel after CMOS active layer before gate poly layer to make the modular DMOS process step easily adding into the sub-micron CMOS or BiCMOS process. And DMOS source is formed by implant which is separated by a spacer self-aligned to the window for DMOS body. By this method, the performance of CMOS and bipolar devices formed original CMOS or BiCMOS process keeps no change. The product design kit, such as standard cell library of CMOS and BiCMOS, can be used continuously with no change.
1. A method for integrating double diffused metal oxide semiconductor (DMOS) into sub-micron complementary metal oxide semiconductor (CMOS) process, comprising the following steps:
burying buried layers of a required conductivity type into a semiconductor substrate, and forming tub and well structures needed in the succeeding steps, said well being formed in said tub;
defining active regions, and performing a thermal oxidation process to form required field oxide layers at ends of said well structures;
sequentially forming a first polysilicon layer and a silicon nitride layer, and patterning said first polysilicon layer and said silicon nitride layer to form a pattern required by DMOS bodies, and performing a body ion implant process and a drive-in process to form required DMOS bodies;
utilizing a plasma enhanced chemical vapor deposition (PECVD) process to form a silicon oxide (SiO 2 ) film, and utilizing a dry-etching process to selectively etch said silicon oxide (SiO 2 ) film in order to form given-size openings on the silicon oxide (SiO 2 ) films above said DMOS bodies, and utilizing said openings to perform a DMOS source implant process to form required DMOS sources; and
performing the standard CMOS process, and sequentially forming DMOS gates, drains and pad electrodes.
2. The method according to claim 1 , wherein the dose and the number of said body ion implant depend on required punchthrough voltage and threshold voltage.
3. The method according to claim 1 , wherein said body ion implant and said DMOS source implant are separated by self-aligned spacers, and the dose of said DMOS source implant may be more than ten times the dose of said body ion implant.
4. The method according to claim 1 , wherein after having formed said DMOS sources, a capacitor mask is used to selectively etch said first polysilicon layer and said silicon nitride layer so that said silicon nitride layer can function as a dielectric layer of a capacitor, and said first polysilicon layer can function as a lower electrode of said capacitor; a second polysilicon layer formed in said standard CMOS process is used as an upper electrode of said capacitor; thus, a capacitor structure is completed.
5. The method according to claim 1 , wherein said tub structure and said well structure can be simultaneously one of N-type and P-type.
6. The method according to claim 1 , wherein said DMOS bodies can be one of N-type and P-type, and the conductivity type of said DMOS bodies is different from that of said tub structure and said well structure.
7. The method according to claim 1 , wherein said DMOS sources can be one of N-type and P-type, and the conductivity type of said DMOS sources is different from that of said DMOS bodies.