Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – Combined with field effect transistor
Reexamination Certificate
1998-06-15
2001-05-22
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
Combined with field effect transistor
C257S139000
Reexamination Certificate
active
06236068
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transistor component and a method of manufacturing the same, specifically a transistor component with a high current carrying capacity and good transmission properties.
BACKGROUND INFORMATION
A transistor component designed as a lateral bipolar transistor with an insulated gate having lateral and vertical current flow is described in D. N. Pattanayak et al., IEEE Trans. ED-33, pp. 1956-1963, 1986. The described transistor component is designed as an N-channel LIGBT (lateral isolated-gate bipolar transistor) on epitaxial silicon which is grown on a P substrate with high or low doping. The rear of the component can be connected by a rear contact. To achieve a high blocking ability in LIGBT, the resurf (reduced surface field) principle (see High Voltage Thin Layer Devices (Resurf Devices), J. A. Appels et al., IEDM Technical Digest, pp. 238-241, 1979) is usually adopted, again using an epitaxial layer.
SUMMARY OF THE INVENTION
The present invention provides a transistor component with a high-current carrying capability and low forward voltage drop in the “on” state plus the advantage of easy manufacture. The voltage drop amounts to only a few volts in the static “on” state at a current density on the order of 100 A/cm
2
. A good rear connection is achieved due to the fact that the rear contact is connected across a P−/P+ junction formed by diffusion in a P
−
substrate. For a given blocking ability of the device, many carriers are made available for good transmission properties in the “on” state, with the carriers present in a P
−
substrate region with rear diffusion having a longer lifetime in comparison with charge carriers moving in an epitaxial P
−
region on a P
+
substrate. This yields a further increase in current carrying capability. The increased current carrying capability achieved by increasing the vertical current in the device would also be possible by means of a reduced thickness of the P
−
epitaxial layer with an epitaxial P
−
/P
+
junction. However, this would lead to reduced blocking ability of the device in static turn-off and, especially in dynamic turn-off. In the case of rear diffusion, the diffusion profile runs down into the depth of the wafer far less abruptly than is the case with an epitaxial layer. Therefore, a high-current carrying capability is possible together with a guaranteed blocking ability at the same time in both static and dynamic turn-off.
According to the present invention, a multichannel principle contributes to a small effective total channel resistance with both LIGBT and MOS transistors due to parallel connected channel regions and thus contributes to an increase in current carrying capability and good transmission properties. Also, an increased robustness against latch-up is guaranteed simultaneously with the increased current carrying capability as a result of the rear diffusion. Due to the region which is designed as a diffusion region over which the device is connected to the rear contact, the required horizontal current device of the component is reduced, so that triggering of the lateral parasitic thyristor is suppressed. At the same time, the component as a whole has improved current carrying capability.
According to the present invention, reduction in the required horizontal current component and thus increased robustness against latch-up results in an optional reduction of the total area of the device.
In a LIGBT, the multichannel principle has also a positive effect on latch-up strength. Due to a plurality of parallel connected channel regions, a smaller current flows per parasitic thyristor, which also reduces the risk of triggering the parasitic thyristor. Rear contacting over a region designed as a diffusion region also ensures a high pulse strength, i.e., the device can handle the simultaneous occurrence of high voltage and high-current density. In contrast to the manipulative of the P
−
/P
+
junction by means of epitaxy, the design as a diffusion region results in smaller doping gradients. This ensures a high pulse strength, especially in a dynamic turn-off. As a result of the smaller doping gradient, the vertical current flow in the device and also the blocking ability react less sensitively to variations in thickness of the substrate. This permits a more simple design of the component.
According to the present invention, designing an n region arranged on the front of the device as a resurf region leads to a higher breakdown voltage, i.e., a large blocking capabilities of the device, as a result of a favorable field-strength distribution in the space-charge region due to the thinness of the resurf layer in combination with its dopant concentration. If the breakdown voltage is not to be increased, a smaller lateral extent may optionally be selected, to ensure a higher current carrying capability per crimp area and larger latch-up suppression in, for example, a multichannel arrangement, or simply in a parallel connection of several components on the same given chip area. If the possibility of ensuring a higher breakdowns voltage is selected instead of a smaller lateral extent, then a breakdown voltage of several hundred volts can be achieved in the static turn-off state by using the resurf region, i.e.; when no voltage is applied to the gate electrode. If the resurf region is produced by a diffusion process instead of epitaxial deposition, this yields by analogy with rear diffusion a longer lifetime of the charge carriers, which in turn has a positive effect on the forward voltage drop in the “on state”.
The transistor component according to the present invention is provided with a buffer layer around the anode region to avoid the punch-through effect. If the anode region has a high dopant concentration and thickness and consequently the buffer layer has a larger junction depth than the n region, this permits a good rear connection, i.e., on properties, while still reliably preventing any punch-through effect.
Providing highly doped dopant zones by means of which the cathode and source terminals are connected to the semiconductor substrate leads to a low contact resistance at the terminals.
REFERENCES:
patent: 4963951 (1990-10-01), Adler et al.
patent: 5920087 (1999-07-01), Nakagawa et al.
Appels, J.A. et al, “High Voltage Thin Layer Devices (Resurf Devices)”, IEDM Techn. Dig., pp. 238-241, 1979.
Pattanayak, D.N. et al., IEEE Trans. ED-33, pp. 1956-1963, 1986.
Kenyon & Kenyon
Meier Stephen D.
Robert & Bosch GmbH
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