1. Field of the Invention
The invention relates generally to Schottky diode devices. More particularly, this invention relates to a device configuration and method of manufacturing Schottky diodes on a P-substrate or forming Schottky diodes with a bottom-anode for multiple applications.
2. Description of the Prior Art
Conventional Schottky diodes with a vertical structure formed on an N-type substrate that have the cathode disposed at the bottom of a substrate are limited by several difficulties of application. As a high voltage bias is applied to the substrate, the Schottky diodes formed on an N-substrate with cathode at the bottom of the substrate are not compatible with some assembly configurations. Furthermore, for high voltage devices, such device configuration requires an electrical isolation of the heat sink where the die is mounted which causes limitations on heat dissipation and adds to complications to system designs when the vertical Schottky diodes supported on an N-type substrate are provided with the cathode disposed at the bottom of a substrate.
Different types of vertical Schottky diodes have been disclosed.
Therefore, a need still exists in the art of device design and manufacture of Schottky diodes to provide new device configurations and manufacturing method to provide new and improved Schottky diodes with anode on the bottom of the substrate such that the above discussed problems and limitations can be resolved.
It is therefore an aspect of the present invention to provide a new and improved Schottky diode implemented with a Schottky barrier controlling layer disposed immediate below the Schottky barrier metal to control the Schottky barrier height and width for improving the performance of Schottky diode.
It is another aspect of the present invention to provide a new and improved bottom-anode Schottky (BAS) diode by forming a low energy shallow N-implant whereby the barrier height and width of the Schottky may be adjusted by using a low energy shallow implant to allow for control over the leakage current versus the forward voltage tradeoffs.
It is another aspect of the present invention to provide improved bottom-anode Schottky diode device implemented with an increased aspect ratio represent by D/W, i.e., the depth of the doped N+ regions functioning as JBS regions, versus the width of the Schottky contact regions such that a reverse leakage current is reduced.
It is another aspect of the present invention to provide improved bottom-anode Schottky diode device implemented with placing Schottky contact metal in trenches with doped regions implanted surrounding sidewalls and below bottom surface of trenches to further increasing the aspect ratio between the depth of the N+ doped region functioning as JBS regions, versus the width of Schottky contact regions such that a reverse leakage current is further reduced.
It is another aspect of the present invention to provide improved bottom-anode Schottky diode device by application of a thin layer of lightly doped narrow bandgap material disposed immediate below the Schottky barrier metal for controlling the barrier height and width through the control of layer thickness, and composition.
Briefly in a preferred embodiment this invention discloses a bottom-anode Schottky (BAS) device supported on a semiconductor substrate having a bottom surface functioning as an anode electrode with an epitaxial layer having a same conductivity type overlying the substrate. The BAS device further includes a plurality of doped regions disposed near a top surface of the epitaxial layer doped with an opposite conductivity type from the substrate constituting a junction barrier Schottky (JBS) with the epitaxial layer disposed between the plurality of doped JBS regions. The BAS device further includes an Schottky barrier metal disposed on top of the semiconductor constituting an ohmic contact to the plurality of doped JBS regions and Schottky contact to the epitaxial layer between the plurality of doped JBS regions. The BAS device further includes an Schottky barrier-controlling layer disposed immediate below the Schottky contact metal in the epitaxial layer between the plurality of doped JBS regions. In an exemplary embodiment, the semiconductor substrate is a P-type substrate and the plurality of doped JBS regions includes N-type doped JBS regions and the Schottky barrier controlling layer includes an ultra-shallow N-Shannon implant layer. In another exemplary embodiment, a barrier height of the Schottky contact is adjusted by a low energy shallow implant of the N-Shannon layer to allow a control of the leakage current versus the forward voltage tradeoffs. In another exemplary embodiment, a minority carrier injection from the doped JBS regions is suppressed when a forward voltage VF is below approximately 0.7 volts. In another exemplary embodiment, a majority carrier from the anode electrode having a reduced barrier to reach the Schottky contact metal constituting a cathode electrode. In another exemplary embodiment, the ultra-shallow N-Shannon implanted layer includes an arsenic implanted layer. In another exemplary embodiment, the Schottky barrier controlling layer comprising a lightly doped narrow bandgap material. In another exemplary embodiment, the height and width of an Schottky barrier are controlled by adjusting composition and layer thickness of narrow bandgap material. In another exemplary embodiment, narrow bandgap material comprising silicon rich SiGe with a layer thickness in the range from 100 Å to 1000 Å.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment, which is illustrated in the various drawing figures.
Referring to
A Schottky barrier metal layer 120 is deposited on top of the epitaxial layer 110 that forms ohmic contact to the N+ regions 115 and forms Schottky contact with ultra-shallow N− Shannon implant region 125.
The dopant concentration of ultra-shallow layer 125 and the layer depth are controlled such that under zero bias condition, the charge carriers are depleted and dopant concentration is controlled to adjust the Schottky diode forward voltage. The Schottky barrier height is thus adjusted without affecting the reversed characteristic of the Schottky diode, which is determined by the dopant concentration and depth of P-epitaxial layer 110.
With the ultra-shallow light N− Shannon layer 125, a junction is formed near the top surface that is depleted by the built-in potential of the Schottky. Compared with conventional PN junctions, the holes from the anode now have a reduced barrier to reach the cathode. The minority carrier injection from the N+ regions 115 is suppressed as long as the forward voltage VF is below the intrinsic PN junction forward voltage of 0.7 volts. Improvement of reverse performance is further achieved because in the meantime, the N+ regions 115 shield the Schottky area in the condition of reverse bias, thus attaining lower leakage current. The bottom anode Schottky diode has several advantages. The ultra-shallow light N− Shannon layer 125 has the effect of pulling back the body regions right before the metal deposition. More compact and reduced area requirement is achieved for the Schottky diode. Furthermore, the barrier height of the Schottky may be adjusted by a low energy shallow implant of the N− Shannon layer 125 to allow a control of the leakage current versus the forward voltage tradeoffs. For the purpose of further reducing the leakage current, it is beneficial to have a large aspect ratio of D/W as shown in
The purpose of controlling the barrier height and width of the Schottky may also be realized by the application of a thin layer of narrow bandgap material. Referring to
According to above drawings and descriptions, this invention also discloses a semiconductor power device supported on a semiconductor substrate of a first conductivity type having a bottom layer functioning as a bottom anode electrode and an epitaxial layer having a same conductivity type overlying the bottom layer. In an exemplary embodiment, the shallow layer of doped region further includes a shallow doped region with ions of the first conductivity type with an ion concentration higher than the epitaxial layer. In another exemplary embodiment, the shallow layer of doped region further includes a shallow Shannon doped region with ions of the second conductivity type for adjusting a barrier height of the Schottky diodes. In another exemplary embodiment, the power device further includes a layer of narrow bandgap metal disposed immediately below an Schottky barrier metal layer over the epitaxial layer to form a low forward voltage junction to function as an Schottky.
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.
This patent application is a Divisional Application and claims the Priority Date of a co-pending application Ser. No. 11/890,851 filed on Aug. 8, 2007 by common Inventors of this Application. The Disclosures made in the patent application Ser. No. 11/890,851 are hereby incorporated by reference.
Number | Date | Country | |
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Parent | 11890851 | Aug 2007 | US |
Child | 13199264 | US |