Method of forming a low loss FET

• US 4,877,749 A
• Filed: 09/30/1988
• Issued: 10/31/1989
• Est. Priority Date: 02/28/1986
• Status: Expired due to Fees

• Current Assignee: Polyfet RF Devices Incorporated
• Original Assignee: Polyfet RF Devices Incorporated
• Inventors: Quigg, Fred L.
• Primary Examiner(s): Hearn, Brian E.
• Assistant Examiner(s): NGUYEN, TUAN H
• Application Number:
  US07/252,232
• Time in Patent Office: 396 Days
• Field of Search: 437/41, 437/150, 437/193, 437/974, 357/23.4, 357/59, 357/65, 148/DIG. 135
• US Class Current: 438/274
• 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 29/456 on silicon
• CPC Class Codes: H01L 29/665 using self aligned silicidation, i.e. salicide formation of conductive layers comprising silicides H01L21/28518
• CPC Class Codes: H01L 29/7802 Vertical DMOS transistors, i.e. VDMOS transistors

Abstract

An improved FET is described in which a conductive layer connects the source structure to a truncated source extension which underlies an insulative gate layer and connects to a channel region. The conductive layer is of substantially lower resistivity than the source extension, thereby significantly reducing the lateral resistance of the device to diminish losses and reduce the likelihood of a parasitic bipolar transistor turning on. The invention can be implemented in both vertical and lateral devices. For a lateral device the drain is connected by a low resistance conductive layer to the gate region in a manner similar to the source.

Claims

1. A method of forming a self-aligned, low loss field effect transistor (FET), comprising:

establishing a doped semiconductive substrate of a first polarity with a doped semiconductive body region of opposite polarity set in the substrate and characterized by a raised area and a lateral recessed area, a layer of gate insulative material over the raised area and extending above the recessed area, a gate member on the opposite side of the gate insulative layer from the body region, and a layer of doped semiconductive material of the same relative polarity as the substrate, the doped layer being spaced from the gate member by a lateral portion of the gate insulative layer and extending over the recessed area and under the gate insulative layer to the raised area,

substantially removing the doped layer lateral to the gate insulative layer,

coating the substrate with a refractory metal,

treating the refractory metal coating so that an adherent conductive layer is formed with the underlying gate member, doped layer and recessed area, but not with the underlying gate insulative layer,

removing the refractory metal coating from the gate insulative layer, the conductive layer overlying the recessed area providing a direct metal contact with the body region and doped layer, the conductive layer overlying the gate member providing a direct metal contact with the gate member, the lateral portion of the gate insulative layer electrically insulating the doped layer from the gate member, and

connecting a gate connection to the conductive layer overlying the gate member, a source connection to the conductive layer overlying the recessed area, and a drain connection at a drain location.

2. The method of claim 1, wherein the gate member is formed from polysilicon, the body region is formed from silicon, the refractory metal coating is treated by heating it to form a metallic silicide with the underlying gate member and body region, and the unconverted metal is stripped off, the refractory metal coating adhering to the underlying gate member and body region as a silicide.

3. The method of claim 1, wherein the doped layer lateral to the gate insulative layer is removed by etching.

4. The method of claim 1, wherein the doped layer lateral to the insulative layer is removed by milling.

5. The method of claim 1, wherein the drain connection is connected to the opposite side of the substrate from the gate and source connections.

6. The method of claim 1, wherein the lateral recessed area has first and second lateral recessed portions which are laterally spaced from each other by the raised area, the gate insulative layer extends above each of the first and second recessed portions, the doped layer has first and second doped portions extending over the respective first and second recessed portions and under spaced portions of the gate insulative layer to the opposed sides of the raised area, upper portions of the first and second doped portions lateral to the gate insulative layer are removed, the refractory metal coating is treated so that an adherent conductive layer is formed with the first and second recessed portions and first and second doped portions as well as the gate member, and the source and drain connections are connected to portions of the conductive layer overlying the respective first and second recessed portions.

7. The method of claim 1, wherein the raised area has first and second raised portions which are laterally spaced from each other by the recessed area, the gate insulative layer has first and second portions on the respective first and second raised portions extending above respective opposite end portions of the recessed area, the gate member has first and second gates formed on the respective first and second portions of the gate insulative layer, the doped layer extends over the recessed area under spaced portions of the gate insulative layer to the first and second raised portions, a central portion of the doped layer lateral to the gate insulative layer is removed, the refractory metal coating is treated so that an adherent conductive layer is formed with the body region underlying the recessed area and remaining end portions of the doped layer to provide a continuous direct metal contact therewith.