Semiconductor device manufacturing: process – Making regenerative-type switching device
Utility Patent
1999-02-03
2001-01-02
Nguyen, Tuan H. (Department: 2813)
Semiconductor device manufacturing: process
Making regenerative-type switching device
C438S455000, C438S460000
Utility Patent
active
06168978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for the production of a power component on a two-sided substrate which blocks (i.e., is switchable to a non-conducting state) on both sides of the substrate, such as a thyristor or a bipolar transistor with an insulated gate (IGBT=Insulated Gate Bipolar Transistor), of the type wherein semiconductor structures are created on a first side of the surface of a disc of a first conductivity type and the semiconductor structures have at least one trough of a second conductivity type at the surface of the disc.
2. Description of the Prior Art
In large-surface power semiconductors, such as thyristors and gate turn-off thyristors (GTOs), the reverse blocking ability is generally realized by means of mechanical processing such as oblique looping (lapping) or sand blasting (sanding) of positive or negative angles. By beveling at the edge, the surface field can be lowered considerably, and it thus can be guaranteed that a breakdown occurs inside the semiconductor rather than at its surface.
Edge beveling is not possible, however, in small components, such as an IGBT, for example, since it would be very costly and would require a change to a round chip, besides. In addition, considerably lower penetration depths of the pn-junctions are used in an IGBT, for example. To a large extent, this rules out the utilization of mechanically produced edge terminations. Planar edge terminations such as field ring structures are conventionally used for this purpose. A disadvantage of field ring structures, however, is that, in a component which blocks on both sides, an edge termination is required on each of the front side and back side of the semiconductor disc for both polarity directions. This is possible only with an expensive, double-sided photo-technique.
Isolation diffusion is one alternative, i.e., the diffusion of a separating layer into the substrate. A conductive connection between the front and back sides of the semiconductor disc can be created in the edge region with the separating layer.
Today, isolation diffusion is realized only in the form of an A1 diffusion, since A1 diffuses rapidly, significantly more so than boron, for example. It is disadvantageous, however, that even given the utilization of an A1 diffusion, and given a relatively low disc thickness of 300 &mgr;m and a relatively high diffusion temperature of ca. 1240° C., a push-in time of at least 50 hours is required, which is associated with a very high material load. Above all, however, the application of A1 diffusion in IC lines in which the production of IGBTs occurs is generally not permitted, since A1 can not be masked by SiO
2
, and cross-contaminations may arise, which can result in a degradation of the gate-oxide, among other things.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for producing a power component that blocks on both sides of a substrate which is easy to realize and which overcomes the aforementioned disadvantages.
The inventive solution is based on the placement of all the edge terminations of the power component on the front of the component. All processing steps in the production of the component thus can be related to the front side. This enables a simplification of the production method, and thus a more cost-effective production than in known methods. Particularly, an isolation diffusion, by boron diffusion, for example, can be realized with relatively little time outlay and low temperature load by means of a trench etching in the edge region of the discs. To support the disc mechanically, the disc to be etched is secured on a carrier substrate.
The inventive method for the production of a number of vertical power components that block on both sides on a wafer includes the steps of producing semiconductor structures on a first side of the surface of a disc, the disc being of a first conductivity type and the semiconductor structures having at least one trough of a second conductivity type at the surface of the disc.
The disc is joined to a substrate of a second conductivity type, on a second side of the disc, to form a wafer. A trench is produced in the disc at the edge of a power component on the wafer. A terminal region of the second conductivity type is produced on the first side of the disc and a first layer of the second conductivity type is applied on the exposed surface of the trench, so that an electrical contact is produced between the substrate and the terminal region.
A second layer of the second conductivity type is preferably created on the second side of the surface of the disc prior to the connection to the substrate, and the disc is subsequently connected to the substrate via the second layer. The space charge region is consequently formed in the disc and not directly over the boundary layer between the disc and the substrate. If the space charge region were formed around the boundary layer, a higher surface quality or finish would be required, not only in the disc but also in the substrate, which would raise the costs.
In a preferred embodiment of the method, the disc is joined with the substrate into a wafer using the wafer bonding method.
In a preferred embodiment of the method, the first and/or second layer and/or a terminal region is produced by the diffusion of boron, particularly by the diffusion of boroethane.
In another preferred embodiment of the method, the first and/or second layer and/or a terminal region is produced by the implantation of boron. The implantation dose is preferably between 10
14
/cm
2
and 10
16
/cm
2
. A subsequent high-temperature step is necessary for diffusing-in the boron atoms. This preferably occurs at a temperature of between about 1100 to about 1300° C. over a time period of about 10 hours.
The first layer preferably obtains a thickness of at least 3 &mgr;m.
The edge terminations, which adjoin the terminal region, which is electrically connected to the second side of the semiconductor disc, as well as at the base region of the second conductivity type on the first side of the semiconductor disc, are preferably created as field ring structures, or generally as a structure with laterally decreasing doping.
If the individual components are operated independently, the semiconductor is preferably separated into individual chips along the trench, it being possible for the separation to occur by sawing through the middle of the trench.
An advantage of the invention is that, unlike in the realization of an additional edge termination at the anode side (at the collector side), in this arrangement with edge termination at one side, a double-sided photo-technique (which necessarily includes optimally precise passivation and connection steps) is not necessary on the anode side (on the collector side), but instead, all the processing steps in the production of the power component can occur on one side thereof. Furthermore, the isolation diffusion with boron doping is possible given relatively short diffusion times and is thus compatible with IC production.
The power component produced with the inventive method has a reverse blocking ability in addition to a forward blocking ability. Not only is an edge termination for the pn-junction which blocks in the forward direction produced, but also an edge termination for the pn-junction which blocks in the reverse direction is realized on the cathode side (emitter side) of the component.
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Patent Abstracts of Japan, Japanese Application No. 60021884.
Patent Abstracts of Japan, Japanese
Nguyen Tuan H.
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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