Trench MOSFET having implanted drain-drift region

• US 6,600,193 B2
• Filed: 08/02/2002
• Issued: 07/29/2003
• Est. Priority Date: 07/03/2001
• Status: Expired due to Term

• Current Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Original Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Inventors: Darwish, Mohamed N.
• Primary Examiner(s): Ho, Hoai
• Assistant Examiner(s): HOANG, QUOC DINH
• Application Number:
  US10/211,438
• Publication Number:
  US 20030008460A1
• Time in Patent Office: 361 Days
• Field of Search: 257/330, 257/341, 257/331, 257/332
• US Class Current: 257/330
• CPC Class Codes: H01L 21/2253 by ion implantation
• 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 29/0847 of field-effect transistors with insulated gate H01L29/0653 takes precedence; with a passive supplementary region between source or drain and substrate related to punch-through, capacity or isolation phenomena H01L29/1079; with LDD or DDD structure H01L29/7833; for thin film transistors H01L29/78618
• CPC Class Codes: H01L 29/0878 Impurity concentration or distribution
• 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 29/7811 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. An N-type dopant is implanted through the bottom of the trench into the P-epitaxial layer to form a buried layer below the trench, and after a up-diffusion step a N drain-drift region extends between the N+ substrate and the bottom of the trench. The result is a more controllable doping profile of the N-type dopant below the trench. The body region may also be formed by implanting P-type dopant into the epitaxial layer, in which case the background doping of the epitaxial layer may be either lightly doped P- or N-type. A MOSFET constructed in accordance with this invention can have a reduced threshold voltage and on-resistance and an increased punchthrough breakdown voltage.

Claims

1. A power MOSFET comprising:

a semiconductor substrate of a first conductivity type;

an epitaxial layer overlying the substrate, a trench being formed in the epitaxial layer; and

a gate positioned in the trench and electrically isolated from the epitaxial layer by an insulating layer which extends along a bottom and a sidewall of the trench;

the epitaxial layer comprising;

a source region of the first conductivity type, the source region being located adjacent a top surface of the epitaxial layer and the sidewall of the trench;

a body of the second conductivity type; and

a drain-drift region of the first conductivity type extending between the substrate and the bottom of the trench, the doping concentration of the drain-drift region increasing monotonically with increasing distance below the trench.

2. The power MOSFET of claim 1, wherein the first conductivity type is N and the second conductivity type is P.

3. The power MOSFET of claim 1, wherein a junction between the drain-drift region and the body extends from near the bottom of the trench down to the substrate.

4. The power MOSFET of claim 1, wherein the junction is curved in a plane orthogonal to that defined by the top surface of the epitaxial layer.

6. The power MOSFET of claim 1, further comprising a body contact region of the second conductivity type in the body and extending to the top surface of the epitaxial layer.

7. The power MOSFET of claim 1, wherein the drain-drift region has doping levels in the range of 5×

10¹⁵/cm³ to 5×

10¹⁷/cm³.

5. The power of claim wherein 1, a portion of the body is in direct contact with the substrate.