JPH0414263A - Insulated gate type bipolar transistor - Google Patents

Abstract

PURPOSE:To prevent the carrier re-injection at the time of turn-OFF, and realize high speed operation, by forming a recessed part reaching a base layer, in a part of a collector layer, and bringing a subcollector electrode into ohmic contact with the base layer, at the bottom surface of said recessed part. CONSTITUTION:The collector side surface of a base layer 3 is made uneven, and an N<+> layer 2 and a P<+> layer 1 are formed on a protrusion and a recess, respectively, with which a collector electrode 8 and a subcollector electrode 81 are brought into contact, respectively. At the time of turn-OFF, a gate is turned OFF at a gate part; also on the collector side, a subcollector terminal is brought into contact with a collector side circuit. Said terminal 31 is connected with the subcollector electrode 81, and connected only with the N<+> layer 2, so that an MOSFET structure is constituted and high speed switching is available for turn-OFF. Said terminal 31 is connected with a collector terminal 21 in the collector part at the time of turn-ON. As a result, a collector is connected with the P<+> layer 1 from the collector electrode 8, and the action as an IGBT is performed. Thereby high speed turn-OFF characteristics are obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an insulated gate bipolar transistor (hereinafter referred to as I
The present invention relates to an element 1lIa (denoted as GBT).

[Prior art; IGBT-, conventional power vertical MOS FET
Although it is similar to IIIa, it includes a bipolar transistor inside and has the advantage of reducing the voltage drop in a conductive state by utilizing so-called conductivity modulation. The cross-sectional structure of the N-channel IGBT is as shown in FIG.
The collector electrode 8 connected to the N
An N-base layer 3 is laminated with a buff layer 2 in between, and a P-type channel layer 4 is formed on the surface of the N-' base layer 3, and an N-source layer 5 is formed on the surface thereof.

Surface layer 6 between source layer 5 and base layer 3 of channel layer 4
In order to form an N channel, a polycrystalline silicon gate electrode is connected through the insulating film 7. 1tlO is provided and connected to the gate terminal 23. An emitter electrode 9 connected to an emitter terminal 22 contacts a part of the source layer 5 and the base layer 4 therebetween. is provided. This IG
The structure of the BT is such that a different conductivity type 1, ie, a collector layer 1, is added below the drain layer of a power vertical MO3FET. The operation of this IGBT is as follows:
is grounded and a positive voltage is applied to the collector voltage ff18 and the gate electrode 10, the P-type chaffle layer 4 directly under the gate
An N channel is formed in the surface layer 6 of the N source layer 5, and electrons flow from the N source layer 5 into the N base layer 3 through the N channel. Due to the holes injected into the N- base layer 3, N
- conductivity modulation is induced in layer 3; This conductivity modulation causes the N layer 3 to have a low resistance. In addition, P channel type ■GB
In the case of T, the conductivity types and carriers are all reversed. Recently, for such IGBTs, a part of the collector electrode 8 is not brought into contact with the collector layer 1, and the N layer 2 is
or a collector short type IG that contacts the N-layer 3.
The purpose of BT is to increase the speed (lower loss) during turn-off of switching! li has been proposed.

Figure 3 shows the structure of a short collector type IGBT.
The difference from FIG. 2 is that the P3 layer 1 and the N' layer 2 are electrically short-circuited by the collector electrode 8. The rest of the structure is the same as that in FIG. Due to this collector short structure, electrons can escape from the N layer 2 to the collector electrode without using the second layer 1 during turn-off, so that re-injection of holes does not occur. Therefore, faster turn-off (lower loss) can be achieved.

[Problem to be solved by the invention]

The operation of the short-collector type IGET shown in FIG. 3 at turn-off is as follows. In the N-base layer 3 in a low resistance state filled with carriers and causing conductivity modulation, the gate is turned off and a depletion layer spreads into the base layer,
As a result, holes fall into this depletion layer and are accelerated by the electric field and discharged.

On the other hand, electrons are pushed toward the P collector layer l side by the expansion of this depletion layer. Some of these electrons are collected by collector i
The voltage drop due to the resistance at the top of il lowers the potential near this area, causing hole injection. Further, some electrons easily escape from the N layer 2 to the collector electrode. In order to prevent reinjection of holes, it is desirable that the collector electrode contact only the N layer. At turn-on, the decisive factor for turn-on loss is how quickly conductivity modulation occurs.In short collector type IGBTs, it is certainly possible to achieve a certain degree of speed at turn-off.However, the conductivity modulation In order to cause modulation to occur quickly, it is desirable that the collector electrode be in contact with only the collector layer, and since conductivity modulation is suppressed by the collector short structure, it becomes slow transiently.

The purpose of the present invention is to solve the above-mentioned problems, to increase the speed by preventing carrier re-injection at turn-off, and to quickly generate conductivity modulation at turn-on, thereby achieving excellent switching characteristics at both turn-off and turn-on. I
The goal is to provide GBT.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a base 1 of a first conductivity type, a surface layer δ on one side of the base layer, and a base layer δ of a second conductivity type formed on the other side of the base layer. There is no &! A gate electrode is provided through the membrane,
In an IGBT in which the emitter is in common ohmic contact with the channel layer and the source layer, and the collector electrode is in ohmic contact with the collector layer, a recess that reaches the base layer is formed in a part of the collector layer, and the bottom surface of the recess is Deputy collector i! The poles shall be in ohmic contact with the base layer.

[Effect]

A collector electrode contacts the base layer via the collector layer, and a sub-collector electrode contacts the bottom surface of a recess formed in the collector layer. If the collector terminal is not connected to the collector electrode but connected to the sub-collector tpf1, this IGB
T operates in the same way as a MOS FET. On the other hand, if the collector terminal is connected to the collector electrode without being connected to the collector electrode, this IGBT operates in the same way as the IGBT shown in FIG. 2 without the collector short circuit. Therefore, when turned off, it operates as a MOS FET, and when turned on, it operates as an IGB with a non-collector short structure.
It can be operated as T. This allows the majority carriers in the base layer to escape to the sub bridge without reinjecting minority carriers during turn-off, and causes conductivity modulation to occur quickly by injecting minority carriers from the collector layer into the base layer during turn-on. It becomes possible to do so.

〔Example〕

FIG. 1 shows an embodiment of the present invention, and FIGS.
Parts common to those in the figure are given the same reference numerals.

ing. This I (1, BT) has a conventional IGBT and an open collar structure above the N-base 13.

A feature of the embodiments of the present invention lies in the collector electrode structure.

That is, as shown in the figure, the surface of the base layer 3 on the collector side is made uneven, and the nN- layer 2 and the P° layer 1 are formed on the surface of the concave and convex portions of the unevenness, respectively. At t8ia, the sub-collector electrode 81 is brought into contact. The collector terminal (C) 21 and the sub-collector terminal 181 are connected to the sub-collector terminal (SC) 31. Note that since the sub-collector electrode 8L is located in the recess, there is a step between it and the collector electrode a, and insulation between the electrodes or connecting conductors can be easily achieved, for example, by inserting an insulating material into the recess. On the other hand, the thickness of the N− base layer 3 on the N− layer 2 is P
Although it is thinner than the thickness on layer 1, the reverse voltage applied to the PN junction between N-layer 3 and P-type channel layer 4 causes N-layer 3 to
If the depletion layer expands, there is no problem in terms of breakdown voltage because the N2 layer serves as a buffer layer.

FIG. 4 conceptually shows how to use this IGBT. In the figure, numeral 40 indicates an element according to the present invention, and other parts are designated by corresponding terminal symbols in FIG.

At turn-off, the gate is turned off as shown by the broken line in the gate portion of the figure, and the sub-collector screw is connected to the collector side circuit through the collar shown by the broken line on the collector side.

This terminal 31 is connected to the sub-collector electrode 81,
MOSFET [fi
i, and the turn-off enables high-speed switching of the MOS FET. In addition, at turn-on, the gate part is turned on as shown by the solid line, and the collector part is connected to the collector terminal 21 as shown by the solid line. 1
connected and operates as an lGBT, resulting in high-speed turn-on characteristics.

〔Effect of the invention〕

According to the present invention, a part of the collector layer is made into four parts, and the bottom surface of the collector t8i is brought into direct ohmic contact with the base layer to form a MO3FET structure in which this part is completely separated from the IGBT structure. , T GBT and MOSFET can be fully exploited separately without compromising their respective characteristics. In other words, at turn-on, the GBTIII structure is used to achieve high-speed turn-on and a low resistance state, and at turn-off, the MO3FET structure is used to achieve high-speed turn-off (low loss), making it an ideal switching element. was gotten.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an IC 137 according to an embodiment of the present invention, and FIG.
3 is a sectional view of a conventional IGBT, FIG. 3 is a sectional view of a conventional short collector type IGBT, and FIG. 4 is a circuit diagram conceptually showing how to use the IGBT according to the present invention. 1: P° collector 1, 2: N° 1, 3: N-base 1,
4: P-type channels 1, 5; N source layer 6: channel,
7: Insulating film, 8: Collector electrode, 81: Sub-collector electrode, 9: Emitter electrode, 10: Gate electrode.

Claims (1)

[Claims] 1) A base 1 of a first conductivity type, a channel layer of a second conductivity type selectively formed on one surface of the base layer, and a first conductivity type selectively formed on the surface of the channel layer. A gate electrode is provided via an insulating film on a surface layer sandwiched between the base layer and the source layer of a semiconductor element having a collector layer of a second conductivity type formed on the other side of the base layer and the base layer. In the case where the emitter electrode is in common ohmic contact with the channel layer and the source layer, and the collector electrode is in ohmic contact with the collector layer, a recess that reaches the base layer is formed in a part of the collector layer, and the bottom surface of the recess is formed in a part of the collector layer. An insulated gate bipolar transistor characterized in that a sub-collector electrode is in ohmic contact with a base layer.