High-voltage transistor and fabrication process
View Patent ↗A high-voltage transistor and fabrication process in which the fabrication of the high-voltage transistor can be readily integrated into a conventional CMOS fabrication process. The high-voltage transistor of the invention includes a channel region formed beneath a portion of the gate electrode after the gate electrode has been formed on the surface of a semiconductor substrate. In a preferred embodiment, the channel region is formed by the angled ion implantation of dopant atoms using an edge of the gate electrode as a doping mask. The high-voltage transistor of the invention further includes a drain region that is spaced apart from the channel region by a portion of a well region and by an isolation region residing in the semiconductor substrate. By utilizing the process of the invention to fabricate the high-voltage transistor, the transistor can be integrated into an existing CMOS device with minimal allocation of additional substrate surface area.
1. A process for fabricating a high-voltage transistor comprising the steps of:
providing a substrate having a principal surface and having a first region and a second region therein,
wherein an isolation region resides within the first region;
forming a gate dielectric layer overlying the principal surface;
forming a gate electrode overlying a portion of the first region, a portion of the second region and a portion of the isolation region;
implanting ions at an angle of incidence of more than 30° to about 55° with respect to the normal into the substrate to form a channel region in the second region and beneath the gate electrode using the gate electrode as an implant mask, wherein the ions are implanted at an angle of incidence offset from a normal of the principal surface, and wherein the ions are implanted with an implantation dose of about 1.0×10 13 to about 2.0×10 13 ions/cm 2 ; and
doping the substrate to form a source region and a drain contact region in the substrate,
wherein the source region resides in the second region and the drain contact region resides in the first region, and
wherein the drain contact region is separated from the channel region by the isolation region and a portion of the first region.
2. The process of claim 1 , wherein the step of forming a channel region further comprises annealing the substrate at a temperature of about 800° C. to about 900° C.
3. The process of claim 1 , wherein the step of implanting comprises implanting boron at an implant energy of about 30 keV to about 60 keV.
4. The process of claim 1 further comprising the step of forming a lightly-doped source region in the second well region intermediate to the channel region and the source region.
5. The process of claim 1 , wherein the step of providing an isolation region comprises forming a trench in the first well region and filling the trench with a material selected from the group consisting of an insulator material and a dielectric material.
6. The process of claim 5 , wherein the step of forming a trench comprises forming a trench having a depth of about 0.25 to about 0.5 microns.
7. The process of claim 1 , wherein the step of forming source and drain regions comprises ion implantation ofphosphorus at an implant dose of about 2×10 15 to about 4×10 15 ions/cm 2 .
8. A process for fabricating a high-voltage transistor comprising the steps of:
providing a substrate having substrate surface;
forming a well region in the substrate;
forming a trench in the well region and filling the trench with an insulator material to form an isolation region;
forming a gate dielectric layer overlying the substrate surface;
forming a gate electrode overlying a portion of the well region and a portion of the isolation region in the trench and separated from the substrate surface by the gate dielectric layer; and
forming a channel region in the substrate after forming the gate electrode,
wherein the channel region underlies at least a portion of the gate electrode.
9. The process of claim 8 further comprising the step of forming a drain region in the well region, wherein the drain region is spaced apart from the channel region by the isolation region and a portion of the well region.
10. The process of claim 8 , wherein the step of forming a channel region comprises angled ion implantation using a implant angle of about 30° to about 55° with respect to a normal to the substrate surface.
11. The process of claim 8 , wherein the step of filling the trench with an insulator material comprises depositing silicon oxide.
12. The process of claim 11 further comprising the step of planarizing the silicon oxide.
13. The process of claim 8 further comprising the step of forming a source region in the substrate spaced apart from the gate electrode and separated from the isolation region by the channel region and a portion of the well region.
14. The process of claim 13 further comprising the step of forming a lightly-doped source region in the substrate intermediate to the source region and the channel region.
15. A process for fabricating a high-voltage transistor comprising the steps of:
providing a substrate having a principal surface and having a first region and a second region therein,
wherein an isolation region resides within the first region;
forming a gate dielectric layer overlying the principal surface;
forming a gate electrode overlying at least a portion of the first region, a portion of the second region and a portion of the isolation region;
implanting ions into the substrate to form a channel region in the second region and beneath the gate electrode using the gate electrode as an implant mask, wherein the ions are implanted at an angle of incidence of more than 30° to about 55° with respect to a normal of the principal surface, and wherein the ions are implanted with an implantation dose of about 1.0×10 13 to about 2.0×10 13 ions/cm 2 ; and
forming an electrical contact to the first region, wherein the electrical contact is separated from the channel region by the isolation region.
16. The process of claim 15 , wherein the step of providing a substrate having a second region comprises providing an undoped substrate.
17. The process of claim 15 , wherein the step of providing a substrate having a second region comprises providing a substrate having a second well region.
18. The process of claim 17 , wherein the step of providing a first well region comprises doping the substrate with a conductivity-determining dopant of a first conductivity type.
19. The process of claim 17 , wherein the step of providing a substrate having a second well region comprises doping the substrate with a conductivity-determining dopant of a second conductivity type.
20. The process of claim 17 , wherein the step of implanting ions to form a channel region comprises implanting ions of a second conductivity type.
21. A process for fabricating a high-voltage transistor comprising the steps of:
providing a substrate having a principal surface and having a first region and a second region therein,
wherein an isolation region resides within the first region;
forming a gate dielectric layer overlying the principal surface;
forming a gate electrode overlying a portion of the first region, a portion of the second region and a portion of the isolation region;
implanting ions into the substrate to form a channel region in the second region and beneath the gate electrode using the gate electrode as an implant mask, wherein the ions are implanted at an angle of incidence offset from a normal of the principal surface; and
doping the substrate to form a source region and a drain contact region in the substrate,
wherein the source region resides in the second region and the drain contact region resides in the first region, and
wherein the drain contact region is separated from the channel region by the isolation region and a portion of the first region;
wherein the isolation region is formed by forming a trench and filling the trench with an insulator material, and wherein the gate electrode is formed overlying the portion of the isolation region in the trench.
22. A process for fabricating a high-voltage transistor comprising the steps of:
providing a substrate having a principal surface and having a first region and a second region therein,
wherein an isolation region resides within the first region;
forming a gate dielectric layer overlying the principal surface;
forming a gate electrode overlying at least a portion of the first region, a portion of the second region and a portion of the isolation region;
implanting ions into the substrate to form a channel region in the second region and beneath the gate electrode using the gate electrode as an implant mask, wherein the ions are implanted at a angle of incidence offset from a normal of the principal surface; and
forming an electrical contact to the first region, wherein the electrical contact is separated from the channel region by the isolation region;
wherein the isolation region is formed by forming a trench and filling the trench with an insulator material, and wherein the gate electrode is formed overlying the portion of the isolation region in the trench.