Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-04-10
2001-10-30
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C257S263000
Reexamination Certificate
active
06309920
ABSTRACT:
The invention relates to a field effect-controllable vertical bipolar transistor, and in particular the structure of the same, and also to a method for fabricating a field effect-controllable vertical bipolar transistor.
Field effect-controllable vertical bipolar transistors or Insulated Gate Bipolar (IGBT) transistors are known from the literature or products and have a number of advantages over MOS-FETs, since their conductivity is determined by two charge-carrier types instead of just one. In order to inject a second charge-carrier type, their chip structure is modified by comparison with that of the MOS-FET to the effect that they have a layer on the rear side of the chip whose conduction type is opposite to that of the epitaxial layer or of the substrate: minority carriers are injected via a diode structure, and the layer sequence of the IGBT is similar to that of the thyristor. Another option for injecting minority carriers is to use a Schottky contact on the rear side.
Nowadays IGBTs are fabricated essentially in two forms, namely as a punch through- (PT-) and as a non-punch through- (NPT-) IGBT. Their structures differ in that, in the case of the PT-IGBT, a heavily doped (buffer) layer of the same conduction type as the inner zone lies between the rear side of the semiconductor chip with the collector terminal and the inner zone. This layer serves to weaken the heavily doped rear-side emitter (usually referred to as “collector”), and, like the inner zone, is generally allowed to grow epitaxially, as a result of which the fabrication is made considerably more expensive. Moreover, in the case of reverse-biasing, such a buffer layer reduces the field strength before the rear-side emitter layer is reached, thus serves as “field stop zone”. This layer is not necessary in the case of the NPT-IGBT according to the prior art, since this NPT-IGBT has a sufficiently weakly injecting rear-side emitter. A sufficiently weakly injecting rear-side emitter is established in the case of the NPT according to the prior art. In order to achieve the same reverse voltage with the NPT-IGBT as with a PT-IGBT, the NPT-IGBTs must, in return, regularly be provided with a thicker n
−
-type layer than the PT-IGBT. However, the thicker n
−
-type layer has the disadvantage that it leads to larger forward voltages, i.e. to a larger voltage drop across the transistor in the on-state. Overall, however, the NPT-IGBT is constructed more simply and is less expensive to fabricate. These IGBTs and a method for fabricating them are disclosed in EP 0 330 122.
The object of the present invention is a method for fabricating a field effect-controllable bipolar transistor that a small forward voltage at a high reverse voltage and is simple to fabricate.
The inventive method for fabricating a field effect-controllable vertical bipolar transistor comprising an inner zone, which is of a first conduction type, a first zone having at least one first supply terminal (emitter) and at least one control electrode (gate), the said first zone adjoining the inner zone, and a second zone having a second supply terminal (collector), the said second zone adjoining the inner zone, having the following step: construction of the at least one supply terminal and the at least one control electrode on a first side of the substrate, is characterized by the following steps: production of a field stop zone, having a predetermined thickness, of the first conduction type on the second side of the substrate, adjoining the inner zone, and production of a collector layer as a Schottky or rectifying contact on the rear side.
In a preferred embodiment, the field stop zone is produced by the implantation of first ions in the inner zone, resulting in the formation of a layer of the first conduction type in the inner zone. It is preferable for the doping concentration in the field stop zone to be higher than that in the inner zone.
In a further preferred embodiment, the field stop zone is produced by the deposition of polysilicon doped to be of the first conduction type on the inner zone, resulting in the formation of a layer of the first conduction type on the inner zone.
As an alternative to producing the field stop zone by the deposition of doped polysilicon, in a further preferred embodiment of the methods the field stop zone is deposited as undoped polysilicon on the inner zone and subsequently doped by means of ion implantation.
The collector layer may be produced by the implantation of second ions in the field stop zone, and metal is deposited thereon, which metal may comprise a plurality of layer of different metals. The crystal defects produced during implantation are only partly annealed. The nature of the ion impairs the quality of the rectifying contact and thus influences the injection of the minority carriers. The second implantation may be made e.g. of gallium, argon, phosphorus, nitrogen, boron, arsenic. The implantation energy and the dose as well as the annealing temperature should be chosen such that ultimately the desired component properties, such as small stored charges, are achieved and the imperfections are annealed. A temperature <600° C. is suitable for this purpose.
After an implantation step, the bipolar transistor is preferably annealed at a predetermined temperature and for a predetermined time.
In a preferred embodiment, the method is implemented in such a way that the implantation of the field stop zone is carried out with a dose of essentially 10
12
/cm
2
and the implantation of the collector layer is carried out with a dose of more than 10
12
/cm
2
.
The inventive field effect-controllable vertical bipolar transistor comprising an inner zone, which is of a first conduction type, a first zone having at least one first supply terminal (emitter) and at least one control electrode (gate), the said first zone adjoining the inner zone, and a second zone having a second supply terminal (collector), is characterized in that the second zone comprises a field stop zone, which adjoins the inner zone, and a collector layer, which adjoins the field stop zone, the thickness of the field stop zone and the thickness of the collector layer being less than 2 &mgr;m and the doping of the field stop zone corresponding to the first conduction type and the doping of the collector layer corresponding to a second conduction type. The inner zone is preferably homogeneously doped.
In the text below, “transistor” is to be understood to mean n- and p-channel transistors and also depletion-mode and enhancement-mode transistors.
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patent: 5216275 (1993-06-01), Chen
patent: 5360983 (1994-11-01), Iwamuro
patent: 5444271 (1995-08-01), Kuwahara
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Article entitled “A simple Inexpensive Power Device”, by F. Y. Robb, published on May 20, 1996, proceedings of the 8th International Symposium on Power Semiconductor Devices and IC'S (ISPSD), Maui, Hawaii, May 20-23, 1966.
Article entitled “Analysis of Direct Wafer Bond IGBTs With Heavy doped N+ Buffer Layer”, by S. Larry Tu et al., published on May 20, 1996, Proceedings of the 8th International Symposium On Power Semiconductor Devices and IC'S (ISPSD), Maui, Hawaii, May 20-23, 1996.
Auerbach Franz
Brunner Heinrich
Laska Thomas
Miller Gerhard
Porst Alfred
Hoang Quoc
Nelms David
Ostroff Irwin
Siemens Aktiengesellschaft
Torsiglieri Arthur J.
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