Process for manufacturing trench MIS device having implanted drain-drift region and thick bottom oxide

• US 7,435,650 B2
• Filed: 06/21/2004
• Issued: 10/14/2008
• 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., Qi, Jainhai, Terrill, Kyle W.
• Primary Examiner(s): Malsawma; Lex
• Assistant Examiner(s): Kraig; William F
• Application Number:
  US10/872,931
• Publication Number:
  US 20040227182A1
• Time in Patent Office: 1,576 Days
• Field of Search: 438/231, 438/232, 438/259, 438/270, 438/305, 438/306, 438/530, 438/546, 438/549, 438/545, 257/529, 257328-333, 257/E29.131, 257/E29.257, 257/E29.26, 257/E29.262, 257/E21.418
• US Class Current: 438/270
• CPC Class Codes: H01L 21/2253 by ion implantation
• CPC Class Codes: H01L 21/28185 with a treatment, e.g. annealing, after the formation of the gate insulator and before the formation of the definitive gate conductor
• CPC Class Codes: H01L 21/28194 by deposition, e.g. evaporation, ALD, CVD, sputtering, laser deposition H01L21/28202 takes precedence
• CPC Class Codes: H01L 21/28211 in a gaseous ambient using an oxygen or a water vapour, e.g. RTO, possibly through a layer H01L21/28194 and H01L21/28202 take precedence
• CPC Class Codes: H01L 21/823487 with a particular manufacturing method of vertical transistor structures, i.e. with channel vertical to the substrate surface with a current flow parallel to the substrate surface H01L21/823431
• 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 29/086 Impurity concentration or distribution
• 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 29/42368 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

A trench MIS device is formed in a P-epitaxial layer that overlies an N-epitaxial layer and an N+ substrate. In one embodiment, the device includes a thick oxide layer at the bottom of the trench and an N-type drain-drift region that extends from the bottom of the trench to the N-epitaxial layer. The thick insulating layer reduces the capacitance between the gate and the drain and therefore improves the ability of the device to operate at high frequencies. Preferably, the drain-drift region is formed at least in part by fabricating spacers on the sidewalls of the trench and implanting an N-type dopant between the sidewall spacers and through the bottom of the trench. The thick bottom oxide layer is formed on the bottom of the trench while the sidewall spacers are still in place. The drain-drift region can be doped more heavily than the conventional “drift region” that is formed in an N-epitaxial layer. Thus, the device has a low on-resistance. The N-epitaxial layer increases the breakdown voltage of the MIS device. In alternative embodiments, the thick bottom oxide layer can be omitted.

Claims

1. A process of fabricating a trench MIS device comprising;

providing a substrate of a first conductivity type;

forming a first epitaxial layer on the substrate, the first epitaxial layer being doped with a dopant of the first conductivity type to a doping concentration that is less than the doping concentration of the substrate;

forming a second epitaxial layer on the first epitaxial layer, the second epitaxial layer being generally of a second conductivity type;

forming a trench in the second epitaxial layer, the trench having sidewalls and a bottom;

depositing an insulating layer conformally in the trench and directionally etching the insulating layer so as to remove a portion of the insulating layer from the bottom of the trench, leaving the bottom of the trench intact and leaving sidewall spacers adjacent the sidewalls of the trench;

implanting a dopant of the first conductivity type between the sidewall spacers and through the intact bottom of the trench at a dose and energy such that following the implant the dopant forms a deep layer substantially separated from the trench;

heating the first epitaxial layer so as to diffuse the dopant upward, thereby forming a drain-drift region extending between the bottom of the trench and the first epitaxial layer;

forming a bottom insulating layer on the intact bottom of the trench between the sidewall spacers;

removing the sidewall spacers;

forming a gate insulating layer on a sidewall of the trench, the gate insulating layer being thinner than the bottom insulating layer;

introducing a conductive material into the trench;

implanting dopant of the first conductivity type into the second epitaxial layer to form a source region adjacent the sidewall of the trench and a top surface of the second epitaxial layer;

implanting dopant of the second conductivity type into the second epitaxial layer to form a body contact region adjacent the top surface of the second epitaxial layer;

forming a third insulating layer over the conductive material in the trench; and

depositing a metal layer, the metal layer being in electrical contact with the source region and the body contact region, the metal layer being electrically insulated from the conductive material in the trench by the third insulating layer.

2. The process of claim 1 wherein forming a trench comprises etching the second epitaxial layer and forming a pad oxide layer.

3. The process of claim 1 wherein the insulating layer comprises nitride.

4. The process of claim 1 wherein forming a bottom insulating layer comprises depositing a layer and etching the layer to form the bottom insulating layer.

5. The process of claim 4 wherein depositing a layer comprises depositing an oxide layer.

6. The process of claim 5 wherein depositing a layer comprises depositing a layer by chemical vapor deposition.

7. The process of claim 4 wherein the bottom insulating layer is a low-temperature oxide layer.

8. The process of claim 4 wherein depositing a layer comprises depositing a glass layer.

9. The process of claim 1 wherein forming a bottom insulating layer comprises thermally growing an oxide layer on the bottom of the trench.

10. The process of claim 1 wherein forming a bottom insulating layer comprises depositing a material that deposits preferentially on the bottom of the trench as compared with the sidewall spacers.

11. A process of fabricating a trench MIS device comprising:

providing a substrate of a first conductivity type;

forming a first epitaxial layer on the substrate, the first epitaxial layer being doped with a dopant of the first conductivity type to a doping concentration that is less than the doping concentration of the substrate;

forming a second epitaxial layer on the first epitaxial layer, the second epitaxial layer being generally of a second conductivity type;

forming a trench in the second epitaxial layer, the trench having sidewalls and a bottom;

depositing an insulating layer conformally in the trench and directionally etching the insulating layer so as to remove a portion of the insulating layer from the bottom of the trench, leaving the bottom of the trench intact and leaving sidewall spacers adjacent the sidewalls of the trench;

implanting a first portion of a dopant of the first conductivity type between the sidewall spacers and through the intact bottom of the trench at a dose and energy such that following the implant the first portion of dopant forms a region of the first conductivity type located below the bottom of the trench and not extending to the first epitaxial layer;

implanting a second portion of the dopant between the sidewall spacers and through the intact bottom of the trench at a dose and energy such that following the implant the second portion of the dopant forms a deep layer substantially separated from the trench;

heating the first epitaxial layer so as to diffuse the first portion of dopant downward and to diffuse the second portion of dopant upward such that the first and second portions merge, thereby forming a drain-drift region extending between the bottom of the trench and the first epitaxial layer;

forming a bottom insulating layer on the intact bottom of the trench between the sidewall spacers;

removing the sidewall spacers;

forming a gate insulating layer on a sidewall of the trench, the gate insulating layer being thinner than the bottom insulating layer;

introducing a conductive material into the trench;

implanting dopant of the first conductivity type into the second epitaxial layer to form a source region adjacent the sidewall of the trench and a top surface of the second epitaxial layer;

implanting dopant of the second conductivity type into the second epitaxial layer to form a body contact region adjacent the top surface of the second epitaxial layer;

forming a third insulating layer over the conductive material in the trench; and

depositing a metal layer, the metal layer being in electrical contact with the source region and the body contact region, the metal layer being electrically insulated from the conductive material in the trench by the third insulating layer.

12. A process of fabricating a trench MIS device comprising:

providing a substrate of a first conductivity type;

forming a first epitaxial layer on the substrate, the first epitaxial layer being doped with a dopant of the first conductivity type to a doping concentration that is less than the doping concentration of the substrate;

forming a second epitaxial layer on the first epitaxial layer, the second epitaxial layer being generally of a second conductivity type;

forming a trench in the second epitaxial layer;

forming sidewall spacers in the trench;

implanting a dopant of the first conductivity type between the sidewall spacers and through a bottom of the trench at a dose and energy such that following the implant the dopant forms a deep layer substantially separated from the trench;

heating the first epitaxial layer so as to diffuse the dopant upward, thereby forming a drain-drift region extending between the bottom of the trench and the first epitaxial layer;

forming a bottom insulating layer on the bottom of the trench between the sidewall spacers;

removing the sidewall spacers;

forming a gate insulating layer on a sidewall of the trench, the gate insulating layer being thinner than the bottom insulating layer; and

introducing a conductive material into the trench.

13. A process of fabricating a trench MIS device comprising:

providing a substrate of a first conductivity type;

forming a first epitaxial layer on the substrate, the first epitaxial layer being doped with a dopant of the first conductivity type to a doping concentration that is less than the doping concentration of the substrate;

forming a second epitaxial layer on the first epitaxial layer, the second epitaxial layer being generally of a second conductivity type;

forming a trench in the second epitaxial layer;

forming sidewall spacers in the trench;

implanting a first portion of a dopant of the first conductivity type between the sidewall spacers and through a bottom of the trench at a dose and energy such that following the implant the first portion of dopant forms a region of the first conductivity type located below the bottom of the trench and not extending to the first epitaxial layer;

implanting a second portion of the dopant between the sidewall spacers and through a bottom of the trench at a dose and energy such that following the implant the second portion of the dopant forms a deep layer substantially separated from the trench;

heating the first epitaxial layer so as to diffuse the first portion of dopant downward and to diffuse the second portion of dopant upward such that the first and second portions merge, thereby forming a drain-drift region extending between the bottom of the trench and the first epitaxial layer;

forming a bottom insulating layer on the bottom of the trench between the sidewall spacers;

removing the sidewall spacers;

forming a gate insulating layer on a sidewall of the trench, the gate insulating layer being thinner than the bottom insulating layer; and

introducing a conductive material into the trench.