Trench MOSFET having drain-drift region comprising stack of implanted regions

• US 20060038223A1
• Filed: 08/23/2005
• Published: 02/23/2006
• Est. Priority Date: 07/03/2001
• Status: Abandoned Application

• Current Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Original Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Inventors: Darwish, Mohamed N.
• Application Number:
  US11/209,409
• Publication Number:
  US 20060038223A1
• Time in Patent Office: Days
• US Class Current: 257/330
• CPC Class Codes: H01L 29/0634 Multiple reduced surface field (multi-RESURF) structures, e.g. double RESURF, charge compensation, cool, superjunction (SJ), 3D-RESURF, composite buffer (CB) structures
• CPC Class Codes: H01L 29/0878 Impurity concentration or distribution
• CPC Class Codes: H01L 29/0886 Shape
• CPC Class Codes: H01L 29/1095 Body region, i.e. base region, of DMOS transistors or IGBTs cell layout H01L29/0696
• CPC Class Codes: H01L 29/66734 with a step of recessing the gate electrode, e.g. to form a trench gate electrode
• CPC Class Codes: H01L 29/7811 with an edge termination structure guard regions per se H01L29/0619; field plates per se H01L29/402
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

A trench MOSFET is formed in a structure which includes a P-type epitaxial layer overlying an N+ substrate. A trench is formed in the epitaxial layer. A drain-drift region is formed by implanting N-type dopant through the bottom of the trench at different energies, creating a stack of N-type regions that extend from the bottom of the trench to the substrate. The energy and implant dose of the regions are set such that doping concentration of the drain-drift region increases monotonically with increasing depth below the bottom of the trench.

Claims

1. A power MOSFET comprising:

a substrate of a first conductivity type;

an epitaxial layer on said substrate, said epitaxial layer generally being of a second conductivity type opposite to said first conductivity type, a trench being formed in said epitaxial layer, a bottom of said trench being located in said epitaxial layer;

an insulating layer lining said bottom and a sidewall of said trench;

a conductive gate in said trench;

a source region adjacent a surface of said epitaxial layer; and

a drain-drift region of said first conductivity type extending through said epitaxial layer from said bottom of said trench to said substrate, said drain-drift region forming a PN junction with a portion of said epitaxial layer of said second conductivity type,

wherein said drain-drift region comprises a vertical stack of overlapping implanted regions and wherein a doping concentration in a vertical cross-section of said drain-drift region starting at said bottom of said trench increases monotonically with increasing distance below said bottom of said trench over the entire distance to said substrate.

2. The power MOSFET of claim 1 wherein at least 75% of a cross-sectional area of said drain-drift region is located directly below said trench.

3. The power MOSFET of claim 2 wherein at least 90% of a cross-sectional area of said drain-drift region is located directly below said trench.

4. The power MOSFET of claim 1 wherein said PN junction intersects a sidewall of said trench.

5. The power MOSFET of claim 1 wherein a side edge of each of said implanted regions is concave towards an interior portion of said drain-drift region.

6. The power MOSFET of claim 1 wherein said implanted regions are made at different energies.

7. The power MOSFET of claim 1 wherein said epitaxial layer comprises two epitaxial sublayers having different doping concentrations.

8. The power MOSFET of claim 1 comprising a body region of said second conductivity type in said epitaxial layer.

9. The power MOSFET of claim 8 wherein a lower border of said body region is at a level below a bottom of said trench.

10. The power MOSFET of claim 9 wherein said body region extends to said substrate.

11. The power MOSFET of claim 1 wherein said drain-drift region comprises at least three of said overlapping implanted regions.