JFET structure for integrated circuit and fabrication method

• US 6,861,303 B2
• Filed: 05/09/2003
• Issued: 03/01/2005
• Est. Priority Date: 05/09/2003
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hao, Pinghai, Khan, Imran, Hou, Fan-Chi
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): LINDSAY JR, WALTER LEE
• Application Number:
  US10/434,642
• Publication Number:
  US 20040222475A1
• Time in Patent Office: 662 Days
• Field of Search: 438/189, 438/188, 438/196, 438/194, 438/200, 438/202, 438/137, 438/217, 438/218, 438/745
• US Class Current: 438/189
• CPC Class Codes: G11C 2211/4068 Voltage or leakage in refresh operations
• CPC Class Codes: H01L 21/8232 Field-effect technology
• CPC Class Codes: H01L 27/085 including field-effect components only
• CPC Class Codes: H01L 29/0692 Surface layout
• CPC Class Codes: H01L 29/1066 Gate region of field-effect devices with PN junction gate
• CPC Class Codes: H01L 29/66901 with a PN homojunction gate
• CPC Class Codes: H01L 29/808 with a PN junction gate , e.g. PN homojunction gate H01L29/7725, H01L29/775, H01L29/778, H01L29/806 take precedence

Abstract

Junction field effect transistors (JFETs) can be fabricated with an epitaxial layer that forms a sufficiently thick channel region to enable the JFET for use in high voltage applications (e.g., having a breakdown voltage greater than about 20V). Additionally or alternatively, threshold voltage (VT) implants can be introduced at one or more of the gate, source and drain regions to improve noise performance of the JFET. Additionally, fabrication of such a JFET can be facilitated forming the entire JFET structure concurrently with a CMOS fabrication process and/or with a BiCMOS fabrication process.

Claims

1. A method of fabricating a Junction Field Effect Transistor comprising:

introducing at least one threshold voltage implant at an implant location associated with at least one of a gate region, a source region and a drain region;

forming the source and drain regions with one of a p-type and n-type dopant; and

forming the gate region between the source and drain regions to have one of a n-type or p-type dopant that is a different type of dopant from that used to form the source and drain regions, whereby the at least one threshold voltage implant mitigates noise associated with operation of the JFET.

2. The method of claim 1, wherein each of the process steps of introducing and forming is performed concurrently with an associated process step in one of a CMOS process and a BiCMOS process.

3. The method of claim 1, the at least one threshold voltage implant being introduced at the gate region only.

4. The method of claim 1, the at least one threshold voltage implant being introduced at the source and the drain regions only.

5. The method of claim 1, the introduction of the at least one threshold voltage implant further comprising introducing one of a NMOS threshold voltage (VTN) implant and a PMOS threshold voltage (VTP) implant at the gate region and introducing another of a VTP implant and a VTN implant at the source and drain regions.

6. The method of claim 1, the introduction of the at least one threshold voltage implant further comprising introducing a partial threshold voltage implant at a selected portion of the implant location.

7. The method of claim 1, the introduction of the at least one threshold voltage implant further comprising introducing one of a NMOS threshold voltage (VTN) implant and a PMOS threshold voltage (VTP) implant at the implant location selected according to the type of dopant used to form the at least one of the gate region, source region and drain region associated with the implant location, the introduced one of a VTN and VTP implant being provided at an energy level that is greater than the energy level employed to form the at least one of the gate region, source region and drain region associated with the implant location.

8. The method of claim 1, further comprising:

forming a buried layer in a substrate to define a backgate region of the JFET;

forming an epitaxial layer over the buried layer; and

forming an isolation region in the epitaxial layer to surround the gate, source and drain regions, the isolation region connecting with the buried layer, the isolation region and the buried layer comprising one of an n-type and p-type dopant, which type is different from the epitaxial layer.

9. The method of claim 8, the epitaxial layer being formed to have a thickness sufficient to provide the JFET with a breakdown voltage that is greater than about 20 volts, the epitaxial layer being formed for the JFET concurrently an epitaxial layer of at least one of a bipolar transistor during a Bi-CMOS process and an epitaxial layer of a metal oxide field effect transistor during one of a Bi-OMOS and CMOS process.

10. The method of claim 8, the gate region being formed to connect with the isolation region, thereby providing a connection between the gate region with the backgate region of the JFET, the gate region being spaced apart from the source and drain regions by field oxide.

11. The method of claim 10, the gate region having spaced apart end portions that connect with substantially opposed side edges of the isolation region, the gate region being interposed between the source and drain regions.

12. The method of claim 1, prior to forming the gate, source and drain regions the method further comprising forming a field oxide layer that defines separate moat regions for each of the gate, source and drain regions of the JFET.

13. A method of fabricating a Junction Field Effect Transistor (JFET) in a Complementary Metal Oxide Semiconductor (CMOS) or Bipolar CMOS (BiCMOS) process, the method comprising the steps of:

concurrently forming an epitaxial layer that defines a channel region of the JFET and associated regions of at least one of a bipolar transistor and a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), the epitaxial layer having a thickness sufficient to provide the JFET with a breakdown voltage that is greater than about 20 volts;

concurrently forming source and drain regions of the JFET with source and drain regions of a corresponding first type of MOSFET; and

concurrently forming at least one gate region of the JFET with source and drain regions of a corresponding second type of MOSFET, which is different from the first type of MOSFET.

14. The method of claim 13, the epitaxial layer having a thickness greater than about 3 μ

m.

15. The method of claim 13, further comprising:

concurrently forming a buried layer in a substrate that defines a backgate region of the JFET and a buried layer of at least one MOSFET formed with the at least one gate region of the JFET; and

forming an isolation region in the epitaxial layer of the JFET to surround the gate, source and drain regions thereof, and to connect with the buried layer, the isolation region of the JFET being formed concurrently with one of an n-well region and a p-well region of at least one MOSFET.

16. The method of claim 13, prior to forming the gate, source and drain regions of the JFET, the method further comprising forming a field oxide layer that defines separate moat regions for each of the gate, source and drain regions of the JFET.

17. The method of claim 13, prior to forming the gate, source and drain regions of the JFET, the method further comprises introducing threshold voltage implants to form a VT implant region associated with at least one of the gate region, the source region and the drain region, the threshold voltage implants comprising one of a NMOS threshold voltage (VTN) implant and a PMOS threshold voltage (VTP) implant selected according to where the VT implant region is formed, whereby the at least one threshold voltage implant mitigates noise associated with operation of the JFET.

18. The method of claim 17, the introduction of the threshold voltage implants further comprising introducing threshold voltage implants at the gate region of the JFET, which threshold voltage implants are a type of dopant selected according to the type of dopant to be used to form the gate region of the JFET.

19. The method of claim 17, the introduction of the threshold voltage implants further comprising introducing the threshold voltage implants at the source region and the drain region of the JFET, which threshold voltage implants are a type of dopant selected according to the type of dopant to be used to form the source region and the drain region of the JFET.

20. The method of claim 17, the introduction of the threshold voltage implants further comprising introducing one of VTN implants and VTP implants at the gate region of the JFET and introducing a different one of VTP implants and VTN implants at the source and drain regions of the JFET, the type of threshold voltage implant introduced at each implant location depending on the type of JFET.

21. The method of claim 17, the introduction of the threshold voltage implants further comprising introducing the threshold voltage implants to form a partial VT implant region associated with a desired portion of the at least one of the gate region, the source region and the drain region.

22. The method of claim 17, the threshold voltage implants being introduced at an energy level that is greater than the energy level employed to form the at least one of the gate region, source region and drain region associated with the VT implant region.

23. The method of claim 13, further comprising:

forming a buried layer in a substrate that defines a backgate region of the JFET;

forming an isolation region in the epitaxial layer to surround the gate, source and drain regions of the JFET and to connect with the buried layer, the isolation region being formed concurrently with one of a n-well and a p-well of a respective n-type or p-type MOSFET, the isolation region and the buried layer comprising one of n-type and p-type dopants, which are different from that of the epitaxial layer.

24. The method of claim 23, the gate region of the JFET being formed to connect with the isolation region to provide a connection between the gate region of the JFET and the backgate region of the JFET, the gate region of the JFET being separated from the source and drain regions by field oxide.

25. The method of claim 24, the gate region of the JFET having spaced apart end portions that connect with substantially opposed side edges of the isolation region, such that the gate region is interposed between the source and drain regions of the JFET.