MIS high-voltage element with high-resistivity gate and field-plate

• US 4,590,509 A
• Filed: 10/06/1983
• Issued: 05/20/1986
• Est. Priority Date: 10/06/1982
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Ludikhuize, Adrianus W., Esser, Leonard J. M., Vaes, Henricus M. J.
• Primary Examiner(s): Edlow, Martin H.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/539,448
• Time in Patent Office: 957 Days
• Field of Search: 357/24 R, 357/24 M, 357/23.4, 357/23.8, 357/23.1, 357/23.7, 357/53, 357/59, 357/41, 357/23.14
• US Class Current: 257/339
• CPC Class Codes: H01L 29/402 Field plates
• CPC Class Codes: H01L 29/405 Resistive arrangements, e.g. resistive or semi-insulating field plates
• CPC Class Codes: H01L 29/42396 for charge coupled devices
• CPC Class Codes: H01L 29/435 Resistive materials for field effect devices, e.g. resistive gate for MOSFET or MESFET
• CPC Class Codes: H01L 29/4916 the conductor material next to the insulator being a silicon layer, e.g. polysilicon doped with boron, phosphorus or nitrogen H01L29/4908, H01L29/4983 take precedence
• CPC Class Codes: H01L 29/4983 with a lateral structure, e.g. a Polysilicon gate with a lateral doping variation or with a lateral composition variation or characterised by the sidewalls being composed of conductive, resistive or dielectric material
• CPC Class Codes: H01L 29/76841 Two-Phase CCD
• CPC Class Codes: H01L 29/7802 Vertical DMOS transistors, i.e. VDMOS transistors
• CPC Class Codes: H01L 29/7816 Lateral DMOS transistors, i.e. LDMOS transistors
• CPC Class Codes: H01L 29/7835 with asymmetrical source and drain regions, e.g. lateral high-voltage MISFETs with drain offset region, extended drain MISFETs

Abstract

By the use of high-ohmic polycrystalline silicon(poly) in MIS elements, a depletion layer can be formed in the poly material which brings about an electric decoupling between the poly (gate) and the underlying semiconductor body. This effect can be utilized advantageously in various circuit elements, such as in CCD'"'"'s, in order to obtain a favorable potential distribution in the substrate; in MOS transistors in order to reduce the parasitic capacities; and in high-voltage devices in order to increase the breakdown voltage at the edge of the field plate (resurf).

Claims

1. A semiconductor device comprising an element of the MIS type having a monocrystalline semiconductor body, one surface of which is provided with a comparatively thin dielectric layer which constitutes a gate dielectric of the MIS element and on which is formed a gate electrode of doped semiconductor material for influencing the surface potential in the semiconductor body, and means for electrically decoupling said gate electrode from said semiconductor body, said means comprising a high-resistivity part of said gate electrode adjoining said gate dielectric and having a sufficiently low doping concentration and a conductivity type such that, during operation of the device, while avoiding breakdown, a depletion layer can be formed which extends from the gate dielectric into the high-resistivity part of said gate electrode, wherein the device comprises a high-voltage element, at least the high-resistivity part of said gate electrode comprising a field plate, said field plate comprising adjacent regions of opposite conductivity types which form a rectifying junction for draining minority change carriers.

2. A semiconductor device as claimed in claim 1, wherein the semiconductor body comprises a substrate region of a first conductivity type and a semiconductor layer of a second, opposite, conductivity type which adjoins said substrate region and the surface of the semiconductor body, and which forms with the substrate region a pn junction, at least a zone of the high-voltage element being formed within the semiconductor layer, and the semiconductor layer can be depleted during operation at least locally over its whole thickness, and the substrate region over part of its thickness, at a reverse voltage across the pn junction which is lower than the breakdown voltage.

3. A semiconductor device as claimed in claim 2, wherein in that the doping concentration of the semiconductor layer is so high that at the breakdown voltage the first depletion layer associated with the pn junction extends over only part of the thickness of the semiconductor layer, and the gate electrode comprising the field plate is connected to a potential which, at least at a high voltage across the high-voltage element with respect to the semiconductor layer, has the same sign as that of the substrate region, as a result of which a second depletion zone extends below the field plate from the surface into the semiconductor layer.

4. A semiconductor device as claimed in claim 1, 2 or 3, wherein the high-voltage element is an insulated gate field effect transistor.

5. A semiconductor device as claimed in claim 4, wherein the field effect transistor is of the double diffused type, the gate electrode comprising a gate portion and a field plate portion, said gate portion being located above the channel region and said field plate portion being located above the drift region of the transistor, said gate portion and said field plate portion being electrically insulated from each other.

6. A semiconductor device as claimed in claim 5, wherein the field plate portion is electrically connected to the source zone of the field effect transistor.

7. A semiconductor device as claimed in claim 1, 2 or 3, wherein the thickness of the field plate is selected such that, in operation, a depletion layer can be formed at least locally throughout the thickness of the field plate.

8. A semiconductor device as claimed in claim 1, 2, or 3, wherein the high-resistivity part of the gate electrode comprises a layer of silicon, the doping concentration of which is at most about 10¹⁸ atoms/cm³.

9. A semiconductor device as claimed in claim 8, wherein the doping concentration of the high-resistivity part lies between 10¹⁵ and 5.10¹⁷ atoms/cm³.