Trench-gate semiconductor devices and their manufacture

• US 6,541,817 B1
• Filed: 11/29/1999
• Issued: 04/01/2003
• Est. Priority Date: 11/28/1998
• Status: Expired due to Term

• Current Assignee: Nexperia B.V. (Wingtech Technology Co., Ltd.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Hueting, Raymond J. E., Hurkx, Godefridus A. M.
• Primary Examiner(s): Fahmy, Wael
• Assistant Examiner(s): LOUIE, WAI SING
• Application Number:
  US09/450,229
• Time in Patent Office: 1,219 Days
• Field of Search: 257/135, 257/328, 257/329, 257/330, 257/331, 257/335, 257/339, 257/341, 438/212, 438/259, 438/268, 438/270, 438/271
• US Class Current: 257/330
• CPC Class Codes: H01L 21/2255 the applied layer comprising oxides only, e.g. P2O5, PSG, H3BO3, doped oxides
• 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 29/42368 the thickness being non-uniform
• CPC Class Codes: H01L 29/7813 with trench gate electrode, e.g. UMOS transistors trench gate electrodes per se H01L29/4236

Abstract

In a trench-gate semiconductor device, for example a cellular power MOSFET, the gate (11) is present in a trench (20) that extends through the channel-accommodating region (15) of the device. An underlying body portion (16) that carries a high voltage in an off state of the device is present adjacent to a side wall of a lower part (20b) of the trench (20). Instead of being a single high-resistivity region, this body portion (16) comprises first regions (61) of a first conductivity type interposed with second regions (62) of the opposite second conductivity type. In the conducting state of the device, the first regions (61) provide parallel current paths through the thick body portion (16), from the conduction channel (12) in the channel-accommodating region (15). In an off-state of the device, the body portion (16) carries a depletion layer (50). The first region (61) of this body portion (16) is present between the second region (62) and the side wall (22) of the lower part (20b) of the trench (20) and has a doping concentration (Nd) of the first conductivity type that is higher than the doping concentration (Na) of the second conductivity type of the second region (62). A balanced space charge is nonetheless obtained by depletion of the first and second regions (61, 62), because the width (W1) of the first region (61) is made smaller than the width (W2) of the lower-doped second region (62). This device structure can have a low on-resistance and high breakdown voltage, while also permitting its commercial manufacture using dopant out-diffusion from the lower trench part (20b) into the lower-doped second region (62) to form the first region (61).

Claims

1. A trench-gate semiconductor device comprising in a semiconductor body:

a channel-accommodating region of a second conductivity type between source and drain regions of an opposite first conductivity type, the source region being adjacent to a major surface of the body;

a trench that extends from the source region at the said major surface, through the channel-accommodating region and into an underlying body portion between the channel-accommodating region and the drain region;

a gate that is present in an upper part of the trench and that is capacitively coupled to the channel-accommodating region adjacent to a side wall of the upper part of the trench for inducing a conduction channel in the channel-accommodating region in an on-state of the device;

the said body portion being present adjacent to a lower part of the trench and comprising first regions of the first conductivity type that are interposed with second regions of the second conductivity type to carry a depletion layer from the drain region to the channel-accommodating region in an off-state of the device and to provide parallel current paths along the first regions in the on-state of the device;

the current-path first region being located adjacent to the side wall of the lower part of the trench and thereby present between the second region and the lower part of the trench, and having a width measured perpendicular to said side wall that is less than the width of the second region, and having a doping concentration of the first conductivity type that is higher than the doping concentration of the second conductivity type of the second region; and

wherein the improvement comprises an insulating layer of the second region that separates the current-path first region of the first conductivity type from the channel-accommodating region of the second conductivity type by extending downwardly and laterally to the side wall of the upper part of the trench where the gate is present;

the insulating layer of the second region having a doping concentration of the second conductivity type that is lower than that of the channel-accommodating region and lower than the doping concentration of the first conductivity type of the current-path first region and that thereby provides field-relief between the channel-accommodating region and the current-path first region in the off state of the device.

2. A device as claimed in claim 1, wherein the said insulating layer of the second region extends laterally over the current-path first region and thereby provides a vertical spacing, at the side wall of the trench, of the channel-accommodating region of the second conductivity type from the underlying current-path first region of the first conductivity type.

3. A device as claimed in claim 1, wherein the gate is capacitively coupled to the channel-accommodating region and to the said spacer part of the second region via a gate insulating layer at the side wall of the trench, and wherein both the gate and the gate insulating layer extend into the lower part of the trench, with the gate insulating layer being thicker in the lower part of the trench than in the upper part so as to reduce the capacitive coupling between the gate and the current-path first region of the body portion.

4. A device as claimed in claim 1, wherein the upper part of the trench is wider than the lower part of the trench and extends laterally over the current-path first region that is located adjacent to the side wall of the lower part of the trench.

5. A device as claimed in claim 1, wherein the lower part of the trench is filled with insulating material.

6. A device as claimed in claim 1, wherein the lower part of the trench comprises a semiconductor region of the second conductivity type that forms a p-n junction with the current-path first region.

7. A device as claimed in claim 1, wherein, in the depth direction of the trench, the current-path first region has a length adjacent to the lower part of the trench that is longer (for example an order of magnitude longer) than that of the channel-accommodating region adjacent to the upper part of the trench.

8. A device as claimed in claim 1, wherein the current-path first region has a doping concentration of the order of 10¹⁶ cm⁻

3, and wherein the second region has a doping concentration of the order of 10¹⁵ cm<sup>−

3</sup>.

9. A device as claimed in claim 1, wherein the current-path first region has a doping concentration that corresponds to a dopant diffusion profile from the lower part of the trench and which is formed by etching the trench into a body portion of the second conductivity type having a doping concentration for providing the second region, and dopant of the first conductivity type is out-diffused from the trench into the body portion, through at least a side wall of a lower part of the trench, so as to form the first region adjacent to the side wall of the lower part of the trench with a doping concentration of the first conductivity type that is higher than the doping concentration of the second conductivity type of the body portion and with a diffusion depth measured perpendicular to said side wall that is less than the remaining width of the body portion measured perpendicular to said side wall.

10. A device as claimed in claim 1, wherein the second regions of the second conductivity type are regions of an epitaxial layer having a uniform doping concentration of the second conductivity type.