Active solid-state devices (e.g. – transistors – solid-state diode – Integrated circuit structure with electrically isolated... – Including dielectric isolation means
Reexamination Certificate
1998-07-14
2001-08-14
Chaudhuri, Olik (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Integrated circuit structure with electrically isolated...
Including dielectric isolation means
C257S520000, C257S640000
Reexamination Certificate
active
06274919
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to semiconductor devices, and relates in particular to a semiconductor device having a field-shield device isolation structure for isolation of devices in a high density MOSLSI circuit and a method of fabrication thereof.
2. Description of the Related Art
Isolation of device elements fabricated on silicon substrate has often been carried out by forming thick oxide films on selected local areas by the so-called Local Oxidation of Silicon method (shortened to LOCOS method hereinbelow). However, one of the serious barriers to achieving a higher density of integration by the LOCOS method has been a lateral growth of oxide film from the peripheries of the oxide film towards active device regions, the so-called bird's beak growth phenomenon which occurs during the thermal oxidation process. For this reason, there have been interests in other methods of isolation of active devices in large scale integration circuits, and particular interests have been focused on an isolation approach called field-shield device isolation method.
Field-shield device isolation method relates to a MOS (metal oxide semiconductor) structure for separating devices by forming a field-shield insulator film and a field-shield electrode between two active regions of a device. By fixing the field-shield electrode potential at a reference potential (e.g, GND or OV), the formation of parasitic channels on the device surface is prevented, thereby providing insulative isolation of the active regions of the devices. In the presentation below, the field-shield device isolation is referred to as FSDI.
An improved version of the FSDI structure is known in which the field-shield insulator film and the field-shield electrode are buried in a trench. By utilizing such a buried-structure configuration, it is expected that higher integration of circuits may be realized.
However, the conventional FSDI structure is still inadequate for the purposes of attaining the degree of integration densities required in modern semiconductor devices. For example, even in those devices having the buried FSDI structure intending to increase the integration density, the top portion of T-shaped cross-section field-shield electrode is exposed on the surface of the substrate such that the width of the top end of the field-shield electrode is wider than the width of the trench width. In other words, much of the valuable surface space is occupied by the non-active regions serving the purpose of device isolation. This is obviously an undesirable aspect of the conventional FSDI structure, and there has been a need to improve the structural configuration of the existing FSDI stricture to meet the increasing demand for higher integration density in modern semiconductor devices.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device having a field-shield structure which would enable to attain a higher degree of integration of circuits in the semiconductor device, and a method of making such a field-shield structure.
The object has been achieved in a semiconductor device means having a field-shield device isolation structure fabricated in non-active regions of the semiconductor device arranged on a semiconductor substrate, the field-shield device isolation structure comprising: a field-shield insulator film for providing inter-device electrical isolation among a plurality of devices fabricated on the semiconductor substrate; a field-shield electrode for being provided with a reference potential; wherein the field-shield insulator film is formed on interior surfaces of a trench cavity whose cavity opening faces an upper surface of the semiconductor substrate and whose depth dimension is deeper than a diffusion distance of a dopant species associated with a device of the plurality of devices, and the field-shield electrode is buried in an interior space of the trench cavity lined with the field-shield insulator film so that a top surface of the field-shield electrode is level with the upper surface of the semiconductor substrate.
According to the semiconductor device presented above, because both the field-shield insulator film and the field-shield electrode are buried within their own trenches having a depth dimension larger than those for the source and drain diffusion layers, the effective isolation distance between the diffusion layers is equal to the distance of the width and twice the depth dimensions of a trench. Therefore, compared with a conventional non-buried type device, the effective isolation dimension is increased substantially. Additionally, in the case of the present device, because the top surface of the field-shield electrode is coplanar or level with the upper surface of the substrate, the area required for the device isolation structure is only that area required for the width of the trench cavity. Therefore, compared with the conventional buried-type field-shield device isolation structures, a higher degree of integration density can be achieved in a given area of a substrate.
An aspect of the semiconductor device is that the field-shield device isolation structure comprises: a field-shield insulator film for providing inter-device electrical isolation for a plurality of devices fabricated on the semiconductor substrate; a field-shield electrode for being provided with a reference potential; wherein the field-shield insulator film is formed on interior surfaces of a trench cavity whose cavity opening faces an upper surface of the semiconductor substrate, and whose depth dimension is deeper than a diffusion distance of a dopant species associated with a device of the plurality of devices, and the field-shield electrode is buried in an interior space of the trench cavity lined with the field-shield insulator film so that a top surface of the field-shield electrode is level with the upper surface of the semi-conductor substrate and that a bottom surface of the field-shield electrode is in electrical contact with the semiconductor substrate.
According to the aspect of the device presented above, because the bottom surface of the field-shield electrode is in electrical contact with the substrate, the overall interconnection design, including the electrode lines for applying voltages to the field-shield electrode and the substrate, can be greatly simplified. The advantage of this design approach is that, compared with the conventional buried-type isolation devices, a higher degree of integration can be achieved within a given area of a substrate.
Another aspect of the present invention relates to a method for making a semiconductor device presented above, and comprises the steps of: forming a trench cavity, which opens to an upper surface of the semiconductor substrate and has a depth dimension deeper than a diffusion distance of a dopant species associated with a device, on an upper surface of the semiconductor substrate; forming a field-shield insulator film on interior surfaces of the trench cavity; and forming a field-shield electrode by filling an interior space of the trench cavity and terminating a top surface of the field-shield electrode so as to be level with the upper surface of the semiconductor substrate.
Another approach to the method for making a semiconductor device means comprises the steps of: forming a trench cavity, which opens to an upper surface of the semiconductor substrate and has a depth dimension deeper than a diffusion distance of a dopant species associated with a device, on an upper surface of the semiconductor substrate; forming a field-shield insulator film on interior surfaces of the trench cavity; removing the field-shield insulator film only from a bottom surface of the trench cavity so as to expose an internal surface of the semiconductor substrate; fabricating a doped region, of an identical conductivity type to the given conductivity type, on the internal surface and forming a field-shield electrode by filling an interior space of the trench cavity and termina
Chaudhuri Olik
Nippon Steel Semiconductor Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pham Hoai
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