EP0580452A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Field effect trench transistor having lightly doped epitaxial region on the surface portion thereof
Assignee: Vishay Siliconix Inc
•
Filing: 1993-07-23
•
Granted: —
•
Expires: 2013-07-23
Abstract
Abstract A DMOS field effect transistor having its gate electrode located in a trench includes a lightly doped epitaxial layer overlying the usual epitaxial layer. The trench penetrates only part way through the upper epitaxial layer which is more lightly doped than is the underlying lower epitaxial layer. The lightly doped upper epitaxial layer reduces the electric field at the bottom of the trench, thus protecting the gate oxide from breakdown during high voltage operation. Advantageously, the upper portion of the lightly doped upper epitaxial layer has little adverse effect on the transistor's on resistance.
Inventors
- 👤 Mike F. Chang
- 👤 Fwu-Iuan Hshieh
- 👤 Sze-Hon Kwan
- 👤 King Owyang
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-25 19:27
CPC Classifications
H; H10; H10D; H10D62/00; H10D62/10; H10D62/13; H10D62/149; H10D62/151; H10D62/156; H10D62/157; H10D30/00; H10D30/01; H10D30/021; H10D30/028; H10D30/0291; H10D30/0297; H10D30/60; H10D30/64; H10D30/66; H10D30/668; H10D62/17; H10D62/393; H10D64/00; H10D64/20; H10D64/27; H10D64/311; H10D64/411; H10D64/511; H10D64/512; H10D64/513
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
192 words
A field effect transistor comprising: a substrate of a first conductivity type defining a trench extending from a principal surface of the substrate; a conductive gate electrode formed in the trench; a source region of the first conductivity type formed in the substrate adjacent to the sidewalls of the trench and extending to the principal surface; and a body region of a second conductivity type formed in the substrate adjacent to the sidewalls of the trench except at the lowest portion of the trench; wherein the substrate includes a first layer of the first conductivity type and a particular doping level less than that of underlying layers of the substrate and extending from the principal surface to a depth greater than a depth of the trench, and a second layer of the first conductivity type and having a doping level greater than that of the first layer and less than that of an underlying layer of the substrate, the second layer being in a portion of the substrate deeper than the lowest portion of the trench, the layer of the substrate underlying the second layer being the drain region of the transistor.
Claim 2
Dependent Claim
13 words
A transistor according to claim 1, wherein the trench is U-shaped in cross-section.
Claim 3
Dependent Claim
23 words
A transistor according to claim 1 or 2, wherein the first layer extends about 0.5 microns below the lowest portion of the trench.
Claim 4
Dependent Claim
22 words
A transistor according to any preceding claim, wherein the first layer has a doping level about 50% that of the second layer.
Claim 5
Dependent Claim
27 words
A transistor according to any preceding claim, wherein the body region extends to the principal surface only at locations spaced apart from the sidewalls of the trench.
Claim 6
Dependent Claim
16 words
A transistor according to any preceding claim, wherein the first and second layers are epitaxial layers.
Claim 7
Dependent Claim
173 words
A field effect transistor comprising: a substrate of a first conductivity type being a drain region; a first epitaxial layer of the first conductivity type formed on the substrate and having a doping level less than that of the substrate; a second epitaxial layer of the first conductivity type formed on the first epitaxial layer and having a doping level about 50% of that of the first epitaxial layer; a trench defined in only the second epitaxial layer and extending to within about 0.5µm of the first epitaxial layer, the trench being at least partially filled with a conductive gate electrode; a source region of the first conductivity type formed in the second epitaxial layer and extending to a principal surface thereof adjacent to the sidewalls of the trench; and a body region of a second conductivity type extending from a principal surface of the second epitaxial layer down to and into at least an upper portion of the first epitaxial layer and being spaced apart from the lower portion of the trench.
Claim 8
Independent Claim
179 words
A method of making a field effect transistor comprising the steps of: providing a substrate of a first conductivity type and having a principal surface; growing a first epitaxial layer of the first conductivity type on the principal surface, the first epitaxial layer having a doping level less than that of the substrate; growing a second epitaxial layer of the first conductivity type on the first epitaxial layer, the second epitaxial layer having a doping level less than that of the first epitaxial layer; forming a body region of a second conductivity type in the second epitaxial layer and extending to a principal surface thereof, the body region extending at least partly into the first epitaxial layer; forming a source region of the second conductivity type in the body region and extending to the principal surface thereof; forming a trench extending from the principal surface of the second epitaxial layer through the source region and the body region, but not extending into the first epitaxial layer; and filling the trench at least partially with a conductive gate electrode material.
Claim 9
Dependent Claim
37 words
The method of claim 8, wherein the trench extends to within 0.5 microns of the first epitaxial layer, and the level of doping of the second epitaxial layer is about 50% that of the first epitaxial layer.
Claim 10
Dependent Claim
21 words
A transistor according to claims 1 to 6, wherein the first and second layers are each less then about 8µm thick.
Claim 11
Dependent Claim
165 words
A field effect transistor comprising: a substrate of a first conductivity type being a drain region; a lower layer of the first conductivity type formed on the substrate and having a doping level less than that of the substrate; an upper layer of the first conductivity type formed on the lower layer and having a doping level less than that of the lower layer; a trench defined in only the upper layer and extending to within a predetermined distance of the lower layer, the trench being at least partially filled with a conductive gate electrode; a source region of the first conductivity type formed in the upper layer and extending to a principal surface thereof adjacent to the side walls of the trench; and a body region of a second conductivity type extending from a principal surface of the upper layer down to and into at least an upper portion of the lower layer and being spaced apart from the lower portion of the trench.
Claim 12
Dependent Claim
15 words
A transistor according to claim 11, wherein the upper and lower layers are epitaxial layers.
References Cited (Backward Citations)
US4941026A
Cited
US5072266A
Cited
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.