IGBT with waved floating P-Well electron injection

• US 10,367,085 B2
• Filed: 09/24/2015
• Issued: 07/30/2019
• Est. Priority Date: 08/31/2015
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Seok, Kyoung Wook
• Primary Examiner(s): Swanson, Walter H
• Assistant Examiner(s): Ly, Kien C
• Application Number:
  US14/864,317
• Publication Number:
  US 20170062596A1
• Time in Patent Office: 1,405 Days
• Field of Search: None
• CPC Class Codes: H01L 21/266 using masks H01L21/26586 takes precedence
• CPC Class Codes: H01L 29/0619 with a supplementary region doped oppositely to or in rectifying contact with the semiconductor containing or contacting region, e.g. guard rings with PN or Schottky junction
• CPC Class Codes: H01L 29/0696 of cellular field-effect devices, e.g. multicellular DMOS transistors or IGBTs
• 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 29/4238 characterised by the surface lay-out
• CPC Class Codes: H01L 29/66333 Vertical insulated gate bipolar transistors
• CPC Class Codes: H01L 29/7395 Vertical transistors, e.g. vertical IGBT

Abstract

An IGBT includes a floating P well and a floating N+ well that extends down into the floating P well. A bottom surface of the floating P well has a waved contour with thinner portions and thicker portions. When the device is on, electrons flow laterally from an N+ emitter and through a channel region. Some electrons pass downward, but others pass laterally through the floating N+ well to one of the thinner portions of the floating P type well. The electrons then pass down from the thinner portions into the N− drift layer. Other electrons pass farther through the floating N+ well to subsequent, thinner electron injector portions of the floating P type well and then into the N− drift layer. The extra electron injection afforded by the waved floating well structure reduces V_CE(SAT). The waved contour is made without adding any masking step to the IGBT manufacturing process.

Claims

1. An Insulated Gate Bipolar Transistor (IGBT) die structure comprising:

a P type collector layer;

an N−

type drift layer disposed over the P type collector layer;

a P type body region that extends into the N−

type drift layer;

an N+ type emitter region, wherein the N+ type emitter region extends into the P type body region from an upper semiconductor surface;

a floating P type well region that extends into the N−

type drift layer from the upper semiconductor surface and that is laterally separated from the P type body region, wherein the floating P type well region forms a waved bottom interface with the underlying N−

type drift layer, and wherein the floating P type well region has a thinner portion disposed between two of a plurality of thicker portions;

a floating N+ type well region that extends into the floating P type well region from the upper semiconductor surface, wherein the floating N+ type well region extends over the thinner portion;

a gate disposed above a channel, wherein the channel extends from the N+ type emitter region, across a part of the P type body region, across a portion of the N−

type drift layer, and across a part of the floating P type well region, to the floating N+ type well region, wherein in an IGBT transistor on state electrons flow in a current path from the N+ type emitter region, through the channel and into the floating N+ type well region, to the thinner portion and then down into the N−

type drift layer;

a first metal terminal, wherein the first metal terminal is coupled to the P type body region and to the N+ type emitter region;

a second metal terminal, wherein the second metal terminal is coupled to the gate; and

a third metal terminal that is coupled to the P type collector layer.

2. The IGBT die structure of claim 1, wherein the thinner portion of the floating P type well region is less than half as thick as the thicker portions of the floating P type well region.

3. The IGBT die structure of claim 1, further comprising:

an N+ type buffer layer disposed between the P type collector layer and the N−

type drift layer.

4. The IGBT die structure of claim 1, wherein the gate extends over some but not all of the floating N+ type well region.

5. The IGBT die structure of claim 1, wherein the floating P type body region is surrounded by one or more of the N+ type emitter regions when the IGBT die structure is considered from a top-down perspective.

6. The IGBT die structure of claim 1, wherein the N+ type emitter region and a plurality of other N+ type emitter regions together substantially surround the floating P type well region when the IGBT die structure is considered from the top-down perspective.

7. The IGBT die structure of claim 1, wherein the N+ type emitter region is a single N+ type emitter region that by itself substantially surrounds the floating P type well region when the IGBT die structure is considered from the top-down perspective.

10. The IGBT die structure of claim 1, wherein the channel includes a first inversion layer portion, an accumulation layer portion, and a second inversion layer portion, wherein the first inversion layer portion extends from the N+ type emitter region and across part of the P type body region, wherein the accumulation layer portion extends from the first inversion layer portion to the second inversion layer portion, and wherein the second inversion layer portion extends from the accumulation layer portion, across part of the floating P type well region, and to the floating N+ type well region.

11. The IGBT die structure of claim 1, wherein the floating P type well region has multiple separate thinner portions, wherein each of the multiple separate thinner portions is disposed between two of the plurality of thicker portions, and wherein the floating N+ type well region extends over every one of the multiple separate thinner portions.

8. An Insulated Gate Bipolar Transistor (IGBT) die structure comprising:

a P type collector layer;

an N−

type drift layer disposed over the P type collector layer;

a P type body region that extends into the N−

type drift layer;

an N+ type emitter region, wherein the N+ type emitter region extends into the P type body region from an upper semiconductor surface;

a floating P type well region that extends into the N−

type drift layer from the upper semiconductor surface and that is laterally separated from the P type body region, wherein the floating P type well region forms a waved bottom interface with the underlying N−

type drift layer, wherein the floating P type well region has a thinner portion and a plurality of thicker portions, and wherein the floating P type well region has a substantially octagonal outer periphery when the IGBT die structure is considered from the top-down perspective;

a floating N+ type well region that extends into the floating P type well region from the upper semiconductor surface, wherein the floating N+ type well region extends over the thinner portion, and wherein the floating P type well region surrounds a substantially octagonal area of the floating N+ type well region;

a gate disposed above a channel, wherein the channel extends from the N+ type emitter region, across a part of the P type body region, across a portion of the N−

type drift layer, and across a part of the floating P type well region, to the floating N+ type well region, wherein in an IGBT transistor on state electrons flow in a current path from the N+ type emitter region, through the channel and into the floating N+ type well region, to the thinner portion and then down into the N−

type drift layer;

a first metal terminal, wherein the first metal terminal is coupled to the P type body region and to the N+ type emitter region;

a second metal terminal, wherein the second metal terminal is coupled to the gate; and

a third metal terminal that is coupled to the P type collector layer.

9. The IGBT die structure of claim 8, wherein the substantially octagonal outer periphery of the floating P type well region has rounded corners.

12. A semiconductor device comprising:

a P type collector layer;

an N−

type drift layer disposed over the P type collector layer;

a P type body region that extends into the N−

type drift layer;

an N+ type emitter region, wherein the N+ type emitter region extends into the P type body region from an upper semiconductor surface;

a floating P type well region that extends into the semiconductor device from the upper semiconductor surface and that is laterally separated from the P type body region, wherein the floating P type well region has a concentric thinner portion between concentric thicker portions;

a floating N+ type well region that extends into the floating P type well region from the upper semiconductor surface;

a gate that extends over a channel, wherein the channel extends from the N+ type emitter region and to the floating N+ type well region, wherein in a device on state electrons flow from the N+ type emitter region, through the channel, into the floating N+ type well region, to the thinner portion and then down into the N−

type drift layer;

a first metal terminal coupled to the P type body region and to the N+ type emitter region;

a second metal terminal coupled to the gate; and

a third metal terminal coupled to the P type collector layer.

13. The semiconductor device of claim 12, wherein the concentric thinner portion of the floating P type well region is less than half as thick as the concentric thicker portions of the floating P type well region.

14. The semiconductor device of claim 12, wherein the floating P type well region when considered from a top-down perspective has an outer periphery, wherein the outer periphery has a shape taken from the group consisting of:

an octagon, a square with rounded corners, a rectangle with rounded corners, a circle, and a ring.

15. The semiconductor device of claim 12, further comprising:

an N+ type buffer layer disposed between the P type collector layer and the N−

type drift layer.

16. An Insulated Gate Bipolar Transistor (IGBT) die structure comprising:

a P type collector layer;

an N−

type drift layer disposed over the P type collector layer;

a P type body region that extends into the N−

type drift layer;

an N+ type emitter region, wherein the N+ type emitter region extends into the P type body region;

a floating P type well region that extends into the N−

type drift layer, wherein the floating P type well region is laterally separated from the P type body region, wherein the floating P type well region has a plurality of concentric thicker bands, and wherein thinner rings are disposed between the thicker bands;

a floating N+ type well region that extends into the floating P type well region;

a gate that extends over a channel, wherein the channel extends from the N+ type emitter region, across a first part of the P type body region, across a part of the N−

type drift layer, across a part of the floating P type well region, and to the floating N+ type well region, and wherein the gate has a ring shape;

a first metal terminal, wherein the first metal terminal is coupled to the P type body region and to the N+ type emitter region;

a second metal terminal, wherein the second metal terminal is coupled to the gate; and

a third metal terminal that is coupled to the P type collector layer.

17. The IGBT die structure of claim 16, wherein the ring shape of the gate is an octagonal shape, and wherein each thinner rings has an octagonal shape.

18. The IGBT die structure of claim 16, wherein the floating P type well region forms a waved bottom interface with the underlying N−

type drift layer.

19. The IGBT die structure of claim 16, wherein each of the thinner rings less than half as thick as each of the thicker bands, wherein a portion of the floating N+ type well region is an emitter of a local electron-injecting NPN bipolar transistor, wherein a portion of the floating P type well region at each of the thinner rings is a base of the local electron-injecting NPN bipolar transistor, and wherein a portion of the N−

type drift layer adjacent each of the thinner rings is a collector of the local electron-injecting NPN bipolar transistor.

20. The IGBT die structure of claim 16, wherein the floating N+ type well region extends over every one of the thinner rings of the floating P type well region.