Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Diffusing a dopant
Reexamination Certificate
1997-12-30
2001-05-08
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Diffusing a dopant
C438S561000
Reexamination Certificate
active
06228750
ABSTRACT:
BACKGROUND OF THE INVENTION
1.Field of the Invention
The present invention relates to the field of semiconductor device manufacturing, and more particularly, to a method of forming a uniformly doped layer angled with the respect to a substrate.
2.Related Art
Proper operation of a solid-state device depends, among other things, on the device geometry and the doping profile of the constituent semiconductor layers. Such solid-state devices are typically formed upon a generally planar substrate such as silicon. Impurities or dopants are introduced into semiconductor layers of the substrate to attain a desired doping profile, whereby, for instance, the conductivity of a layer may be enhanced or a pn-junction may be formed.
Certain semiconductor device geometries may require that dopants or impurities be introduced along a portion of a semiconductor region which is angled relative to the base substrate. Applying dopants uniformly along a vertical or angled semiconductor layer, however, is exceedingly difficult under current line-of-sight fabrication techniques.
For instance, during ion-implantation the depth of ion penetration and the uniformity of the resultant doping degenerate when the semiconductor layer is angled away from normal with respect to the bombarding ions. Thus, to dope vertical or angled junction sidewalls, complex tilting operations are required to maintain a perpendicular or near perpendicular angle of incidence.
Further limitations are encountered when doping regions of semiconductor devices which are difficult to access with a straight-line path from the ion source. For instance, narrow junction devices disposed in isolation tubs, e.g. trench or V-groove configurations, contain interior recesses and corners where ion-implantation techniques fail to achieve a sufficiently uniform doping profile.
Accordingly, a fabrication method for introducing dopants uniformly over angled semiconductor regions is desired.
SUMMARY OF THE INVENTION
The present invention is a method of doping a semiconductor surface on a substrate by first applying a doped coating material over the surface, and then driving dopants from the doped coating material into the semiconductor surface to form semiconductor regions which are uniformly doped. According to the present invention, a material containing the dopant source is first spread uniformly to coat the semiconductor regions requiring doping. After this deposition, the material is heated to drive dopants into the semiconductor region. In this manner, non-planar and planar regions of the semiconductor substrate are uniformly doped.
According to a first embodiment of the present invention, in-situ doped polysilicon may be used as the coating material for deposition over an etched silicon substrate surface. The coating material can be deposited directly on the substrate itself (n-type or p-type), or upon oxide layers or doped oxide layers which were previously grown, implanted, or etched on the substrate.
In a second embodiment of the present invention a doped glass layer, e.g. silicon dioxide, is used as the coating material which can be spun and baked, deposited by chemical vapor deposition, or by a plasma process on the silicon wafer to obtain an even distribution across planar and non-planar regions.
According to another aspect of the invention, after dopants are driven from the doped coating material into nearby semiconductor regions further processing can be performed to remove all or part of the coating material, for example, by an anisotropic plasma etching. Furthermore, the coating material itself, e.g. doped polysilicon, can be oxidized to form a dielectric isolation layer which imparts even less stress upon corner regions than direct oxidation of the etched corner layer.
The present invention then applies generally to the manufacture of semiconductor devices, and in particular, is well-suited for forming uniformly doped non-planar sides of dielectrically-isolated (DI) or silicon-on-isolator (SOI) structures including the non-planar regions found in wrap-around or vertical junctions with a trench or v-groove geometry.
Finally, the present invention can be further advantageously used in the fabrication of a semiconductor photodiode with a uniformly doped wrap around junction and in a double-diffused MOS (DMOS) manufacturing process where a high voltage switch such as an insulated gate bipolar transistor (IGBT) is fabricated along with the uniformly doped semiconductor photodiode.
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Lucent Technologies
Mulpuri Savitri
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