Compact source ballast trench MOSFET and method of manufacturing

• US 10,325,908 B2
• Filed: 04/26/2017
• Issued: 06/18/2019
• Est. Priority Date: 04/26/2017
• Status: Active Grant

• Current Assignee: Alpha & Omega Semiconductor, Ltd.
• Original Assignee: Alpha & Omega Semiconductor, Ltd.
• Inventors: Lui, Sik, Bobde, Madhur, Pan, Ji
• Primary Examiner(s): Prenty, Mark V
• Application Number:
  US15/498,289
• Publication Number:
  US 20180315749A1
• Time in Patent Office: 783 Days
• CPC Class Codes: H01L 27/0629 in combination with diodes, or resistors, or capacitors
• CPC Class Codes: H01L 27/0727 in combination with diodes, or capacitors or resistors
• CPC Class Codes: H01L 29/086 Impurity concentration or distribution
• CPC Class Codes: H01L 29/0865 Disposition
• 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 29/167 further characterised by the doping material H01L29/1604 takes precedence
• CPC Class Codes: H01L 29/41741 for vertical or pseudo-vertical devices
• CPC Class Codes: H01L 29/41766 with at least part of the source or drain electrode having contact below the semiconductor surface, e.g. the source or drain electrode formed at least partially in a groove or with inclusions of conductor inside the semiconductor H01L29/41733 - H01L29/41758 take precedence
• CPC Class Codes: H01L 29/66727 with a step of recessing the source electrode
• 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 29/7803 structurally associated with at least one other device assemblies H01L25/00; integrated circuits H01L27/00
• CPC Class Codes: H01L 29/7806 the other device being a Schottky barrier diode
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

A trench metal-oxide-semiconductor field-effect transistor (MOSFET) device, comprising a substrate of a first conductivity type, a body region of a second conductivity type, a gate electrode formed in a gate trench extending in the body region and substrate, a lightly doped source region and a heavily doped source region formed in the body region, and a source contact extending to the body region formed in a source contact trench next to the gate trench. The lightly doped source region is extended deeper in the body region than the heavily doped source region. The lightly doped source region is adjacent to the source contact trench. A ballast resistor is formed at the lightly doped source region between the heavily doped source region and the body region and a Schottky diode is formed at a contact between the source contact and the lightly doped source region.

Claims

1. A trench metal-oxide-semiconductor field-effect transistor (MOSFET) device, comprising:

a) a substrate of a first conductivity type, the substrate comprising an epitaxial layer of the first conductivity type provided on top of a heavily doped silicon wafer of the same conductivity type;

b) a body region of a second conductivity type that is opposite to the first conductivity type formed above the substrate;

c) a gate trench formed in the body region and substrate, wherein the gate trench is lined with a dielectric layer and a gate electrode is formed in the gate trench;

d) a lightly doped source region and a heavily doped source region formed in the body region, wherein the lightly doped source region is extended deeper in the body region than the heavily doped source region; and

e) a source contact extending to the body region formed in a source contact trench next to the gate trench, wherein the lightly doped source region is adjacent to the source contact trench and wherein a Schottky diode is formed at a contact between the source contact and the lightly doped source region, wherein the heavily doped source region extends fully between the gate trench and the source contact trench.

2. The device of claim 1, wherein a ballast resistor is formed at the lightly doped source region between the heavily doped source region and the body region.

3. The device of claim 2, wherein the ballast resistor has a length, wherein the length of the ballast resistor is adjusted by changing a depth of the heavily doped source region.

4. The device of claim 2, wherein the ballast resistor has a width, wherein the width of the ballast resistor is adjusted by a width of the source contact trench.

5. The device of claim 2, wherein the ballast resistor has a resistance value, wherein the resistance value is adjusted by a doping concentration of the lightly-doped source region.

6. The device of claim 1, wherein a depth D of the body region is between 0.5 T and 0.8 T, where T is the depth of the gate trench;

wherein a depth d of the lightly doped source region is between 0.25 D and 0.5 D; and

wherein a depth of the heavily doped source region is between 0.25 d and 0.5 d.

7. The device of claim 1, wherein the source contact trench has a width, wherein the width ranges from 0.5 μ

m to 1.5 μ

m.

8. The device of claim 1, wherein a doping concentration of the lightly doped source region ranges from about 1×

10¹⁵/cm³ to about 1×

10¹⁸/cm³ and a doping concentration of the heavily doped source region ranges from about 8×

10¹⁹/cm³ to about 8×

10²⁰/cm³.