Dual-counterdoped channel field effect transistor and method

• US 6,960,499 B2
• Filed: 06/14/2004
• Issued: 11/01/2005
• Est. Priority Date: 02/24/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Chen, Ih-Chin, Vasanth, Karthik, Nandakumar, Mahalingam
• Primary Examiner(s): Le, Thao P.
• Application Number:
  US10/866,469
• Publication Number:
  US 20040224457A1
• Time in Patent Office: 505 Days
• Field of Search: 438/197, 438/289
• US Class Current: 438/197
• CPC Class Codes: H01L 21/2652 Through-implantation
• CPC Class Codes: H01L 21/2658 of a molecular ion, e.g. decaborane
• CPC Class Codes: H01L 29/1033 with insulated gate, e.g. characterised by the length, the width, the geometric contour or the doping structure with channel and gate aligned in the lengthwise direction H01L29/42376; with buried channel H01L29/7838

Abstract

A field effect transistor with a dual-counterdoped channel is disclosed. The transistor features a channel comprising a first doped region (28) and a second doped region (26) underlying the first doped region. A source and drain (32) are formed adjacent to the channel. In one embodiment of the present invention, the first doped region (28) is doped with arsenic, while the second doped region (26) is doped with phosphorus. The high charge-carrier mobility of the subsurface channel layer (28) allowing a lower channel dopant concentration to be used, which in turn allows lower source/drain pocket doping. This reduces the capacitance and response time of the transistor.

Claims

1. A method for forming a field effect transistor, comprising the steps of:

providing a region of semiconductor material doped a first conductivity type;

forming spaced apart source/drain pockets of said first conductivity type in said region of semiconductor material and counterdoped regions of opposite conductivity type disposed within each of said source/drain pockets forming source/drains; and

forming a channel region disposed in said region of semiconductor material between said source/drain pockets, said channel region having a first region of one of undoped or doped opposite conductivity type and a second doped region underlying the first region of said opposite conductivity type and having a greater charge-carrier mobility than said first region, said second doped region being the primary conduction channel between said source and said drain.

2. The method of claim 1, further comprising the step of implanting a third dopant in a channel region overlying the first region.

3. The method of claim 1, further comprising the step of implanting a fourth dopant in a pocket surrounding the source/drain region.

4. The method of claim 2, wherein the first dopant comprises phosphorus, and wherein the second dopant comprises a p-type dopant, and wherein the third dopant comprises arsenic.

5. A method for forming a field effect transistor, comprising the steps of:

providing a region of semiconductor material doped a first conductivity type;

forming a source region of said first conductivity type and a drain region of said first conductivity type, both said source region and said drain region disposed in said region of semiconductor material and separated by a channel region disposed in said region of semiconductor material;

providing said channel region by forming a first region in said channel region of one of undoped or opposite conductivity counterdoped type; and

doping said channel region with a dopant to form a second counterdoped region underlying the first region of said opposite conductivity type, said second doped region having a greater charge-carrier mobility than said first region, said second doped region being the primary conduction channel between said source region and said drain region.

6. The method of claim 5, wherein the counterdopants are an n-type dopants.

7. The method of claim 5, wherein the first doped region comprises a first dopant, and wherein the second doped region comprises a second dopant different from the first dopant.

8. The method of claim 7, wherein the first dopant comprises arsenic, and wherein the second dopant comprises phosphorus.

9. The method of claim 5, further comprising a first pocket surrounding the source, and a second pocket surround the drain, the first and second pockets each having a higher dopant concentration than the source and drain regions.