Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – Plural non-isolated transistor structures in same structure
Reexamination Certificate
2002-05-13
2004-10-19
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
Plural non-isolated transistor structures in same structure
C257S585000, C257S591000, C257S592000, C257S593000, C257S565000, C257S574000
Reexamination Certificate
active
06806555
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of semiconductors. The invention relates to a semiconductor component having a substrate and an epitaxial layer situated thereon, at least a first and a second bipolar component being integrated in the layer, the first and second bipolar components having a buried layer and different collector widths.
In the case of bipolar transistors it is customary to connect the collector by a buried, highly doped layer, a so-called buried layer. The buried layer is produced by subjecting the substrate to an ion implantation before the application of the epitaxial layer at the desired location. The lightly doped epitaxial layer is subsequently applied. The base, emitter, and collector wells are subsequently produced on the side of the epitaxial layer that extends to the first main side of the semiconductor component. One possible process sequence in the fabrication of a bipolar transistor is described, for example, in the textbook “Technologie hochintegrierter Schaltungen” [Technology of Large Scale Integrated Circuits] by D. Widmann, H. Mader, H. Friedrich, Springer Verlag, 2
nd
edition, table 8.13 (page 326 to page 334).
The phrase collector width denotes that region of the epitaxial layer that is located between the well of the base located in the epitaxial layer and the buried layer. The collector width is consequently determined by the layer thickness of the epitaxial layer, minus the part of the buried layer that extends into the epitaxial layer, and minus the depth of the well of the base layer that is introduced from the first main side.
The dimensioning of the collector width determines the properties of the bipolar transistor. Bipolar transistors that are intended to be optimized for high limiting frequencies must have a small collector width and an increased doping in the collector. These bipolar transistors are referred to as so-called HF bipolar transistors. By contrast, high-voltage transistors (HV bipolar transistors), which are optimized toward high breakdown voltages, have a large collector width because the space charge zone must not reach the buried layer at maximum operating voltage. The typical collector width of such a bipolar transistor is approximately 450 mm, for an operating voltage of approximately 5 V. The epitaxial layer usually forms the collector in an HV bipolar transistor. The collector doping thus corresponds to the doping of the epitaxial layer, usually 10
16
.
Many integrated circuits require both bipolar transistors having a high limiting frequency and bipolar transistors having a high breakdown voltage. On account of the fabrication methods existing heretofore, it is necessary to find a compromise with regard to the properties in the case of the integration of bipolar transistors having different limiting frequencies and bipolar transistors having different breakdown voltages. This means that the performance of the semiconductor component cannot be utilized optimally.
However, if bipolar components having different collector widths are intended to be integrated together in a semiconductor component, then there are currently two possibilities in fabrication: firstly, the depth of the well in the epitaxial layer can be realized differently in the first and second bipolar components. As a result of the increased base width, the limiting frequency of that component whose well (base) extends more deeply into the epitaxial layer is reduced. Furthermore, it is necessary to use an additional mask for producing the base wells of different depths.
Another possibility is for the thickness of the lightly doped epitaxial layer to be implemented differently in the first and second components. However, the fabrication of a second epitaxial layer is associated with high costs, on one hand, and, on the other hand, the manufacturing outlay is thereby increased considerably.
On account of the complicated procedure and a generally identical epitaxial layer, i.e., the epitaxial layer has the same thickness at all points. A compromise is, therefore, sought with regard to the high limiting frequencies and the high breakdown voltages.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a semiconductor component and method for fabricating it that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that realizes bipolar components having different collector widths in a simple manner.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a semiconductor component including a substrate, only one epitaxial layer disposed on the substrate, at least a first bipolar component and a second bipolar component integrated in the epitaxial layer, the first bipolar component having a first buried layer having dopant in a first dopant concentration, and a first buried layer thickness, and a first collector with a first collector width, the second bipolar component having a second buried layer having dopant in a second dopant concentration substantially identical to the first dopant concentration, a second buried layer thickness larger than the first buried layer thickness, and a substance influencing diffusion of dopant in the second buried layer, and a second collector with a second collector width different from the first collector width.
With the objects of the invention in view, there is also provided a semiconductor component including a substrate, only one epitaxial layer disposed on the substrate, at least a first and a second bipolar component integrated in the epitaxial layer, the first and second bipolar components having a buried layer and different collector widths, the buried layer of the second bipolar component having a larger layer thickness than the buried layer of the first bipolar component, the buried layer of the first bipolar component and the buried layer of the second bipolar component having dopant with identical dopant concentrations, and at least the buried layer of the second bipolar component having an additional substance influencing diffusion of the dopant in the buried layer.
The invention provides for the buried layer of the second bipolar component to have a greater layer thickness than that of the first component, precisely one epitaxial layer being provided. The wells forming the base in the epitaxial layer may, but need not, have an identical depth.
The invention is based on the insight that the outdiffusion of the dopant of the buried layer can be influenced by other substances. This enables an extremely simple fabrication method because the buried layers of the first and second components are firstly implanted into the substrate with an identical dopant concentration. An additional substance is subsequently introduced into the buried layer of the second component, which additional substance influences the diffusion of the dopant in the buried layer of the second component. By way of example, the additional substance can be introduced by a mask technique and by ion implantation. The epitaxial layer is subsequently applied in a customary manner in a single step.
The invention has the advantage that only an additional mask technique and an additional implantation are necessary for an additional transistor variant, that is to say, for a bipolar transistor having a varying collector width. The costs in comparison with an additional epitaxial layer, as is provided for example, in the prior art, are, therefore, relatively low.
Because the collector always ends at the highly doped buried layer of the bipolar component, the transistor properties, thus, change to a lesser extent with an increased collector-emitter voltage than in contrast to a thicker (lightly doped) collector layer.
The semiconductor component according to the invention can be realized both with NPN transistors and with PNP transistors. In the case of NPN transistors, arsenic or antimony is advantageously used as the dopant of the buried layers. Phosphorus is used
Huber Jakob
Klein Wolfgang
Flynn Nathan J.
Greenberg Laurence A.
Infineon - Technologies AG
Locher Ralph E.
Mandala Jr. Victor A.
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