JP5261893B2 - Trench type insulated gate bipolar transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cellular trench-type insulated gate bipolar transistor in which low on-resistance and enhancement of durability of turnoff can be achieved. <P>SOLUTION: A cell divided trench-type insulated gate bipolar transistor arranged such that a second conductivity type base region and the substrate surface appear alternately in the longitudinal direction between parallel trenches, in which a contact hole formed in an interlayer insulating film for insulating and isolating the gate electrode and the emitter electrode has a length corresponding to the longitudinal direction of the trench longer than the first conductivity type source region. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a trench type insulated gate bipolar transistor used for a power conversion device or the like. More specifically, a trench-type insulated gate bipolar transistor (hereinafter referred to as a trench-type insulated gate bipolar transistor) comprising a trench formed in a striped surface pattern, a gate insulating film formed on the side wall thereof, and a control electrode embedded in the trench through the gate insulating film. , Sometimes abbreviated as trench IGBT).

  In response to the recent demand for miniaturization and high performance of power supply equipment in the field of power electronics, power semiconductor devices have high breakdown voltage and large current, as well as low loss, high destruction resistance, and high speed performance. Focus is on improvement. As a result, a vertical power MOS semiconductor device having an insulated gate such as a power IGBT has been developed as a power semiconductor device capable of increasing the current and reducing the loss. Two types of power MOS semiconductor devices are widely known: a planar insulated gate structure in which a MOS gate is provided in a flat plate shape on a substrate surface, and a trench insulated gate structure in which a MOS gate is embedded in a trench. In recent power MOS semiconductor devices, since a low on-resistance characteristic is easily obtained structurally, a trench type MOS semiconductor device having the latter trench type insulated gate structure has attracted attention.

  A vertical trench type MOS semiconductor device having such a trench type insulated gate structure has a trench type insulated gate structure in which a gate electrode is embedded in the trench through an insulating film, and the stripe-like surface of the trench A trench gate type IGBT having a cell-divided pattern structure in which a p-type channel region and an n-type semiconductor substrate region appear alternately on the substrate surface in the longitudinal direction between patterns can realize low on-resistance and high breakdown voltage simultaneously It is already known (Patent Document 1).

In the trench gate IGBT, the p-type base region is formed in an island shape in a direction perpendicular to the longitudinal direction of the trench gate, and the channel length of the unit cell between the trenches is the same as that of the conventional trench IGBT. Alternatively, an invention that improves the load short-circuit withstand capability by forming a substantially constant length so as to be short is disclosed (Patent Document 2).
Among such trench IGBTs, in particular, an example of the structure of a cell-divided trench gate bipolar transistor expressed as a cell-type trench IGBT is a plan view of FIG. 5 and a trench IGBT cut along the line BB in FIG. FIG. 6 shows a sectional view. Hereinafter, the structure and operation of the cell type trench IGBT will be described with reference to the drawings.

The semiconductor substrate 111 has a p-type base region 112 selectively formed on one main surface (hereinafter also referred to as a surface), and the other main surface (hereinafter referred to as a back surface) has a p-type. A collector layer 151 and a collector electrode 150, and a large number of trenches 113 have a surface stripe pattern orthogonal to the p-type base region 112 and penetrate the p-type base region 112 from the surface of the semiconductor substrate 111. The n ⁻ type drain layer (n type semiconductor substrate region) 111 is formed to a depth reaching the n ⁻ type drain layer (n type semiconductor substrate region) 111. A gate oxide film 114 is coated on the inner surface of the trench 113, and a gate electrode 115 made of conductive polycrystalline silicon or the like is buried on the inner surface side. A p ⁺ -type contact region 117 is disposed substantially in the middle of the surface of the p base region 112 between another trench 113 that is spaced apart. An n ⁺ type source region 116 is provided adjacent to each of the p ⁺ type contact region 117 and the trench 113. An insulating layer 118 is disposed on the gate electrode 115, and an emitter electrode 119 such as aluminum is provided on the entire surface of the cell region. The insulating layer 118 insulates and separates the gate electrode 115 and the emitter electrode 119 from each other. The emitter electrode 119 is configured to make ohmic contact with both surfaces of the n ⁺ type source region 116 and the p ⁺ type contact region 117 through the contact hole 120 opened in the insulating film 118.

In such a cell (divided) trench IGBT, a voltage equal to or higher than a predetermined threshold is applied to the gate electrode 115 to form the surface layer of the p-type base region along the sidewall of the trench 113 via the gate insulating film. An n-type inversion layer (not shown in FIG. 6) is formed, and a current path as shown by an arrow in FIG. 7 described later is formed. As a result, the emitter-collector of the cell type trench IGBT is turned on. Further, by setting the voltage of the gate electrode 115 to a threshold value or less, the n-type inversion layer formed on the surface layer of the p-type base region 112 along the sidewall of the trench 113 disappears, and the current path disappears. The emitter-collector of the cell type trench IGBT is turned off. Furthermore, since current paths in the vertical direction (direction perpendicular to the main surface of the substrate) and in the horizontal direction (direction parallel to the main surface of the substrate) are formed along the trench 113, a known planar type or trench type vertical type is formed. Compared with the IGBT, the area of the current path is greatly expanded in the cell type trench IGBT. Furthermore, minority carrier accumulation occurs in the exposed surface region of the n-type semiconductor substrate layer 111 between the trenches 113 on the substrate surface side, and the on-resistance can be reduced.
JP 2000-228519 A JP 2001-274400 A

In general, in the IGBT turn-off process, minority carriers (holes) injected from the p-type collector layer 151 to the n-type base layer 111 in the ON state are discharged to the emitter electrode 119. At that time, particularly in the above-described cell type trench IGBT, the cell portion plan view of the conventional cell division type trench IGBT of FIG. Minority carrier current (hole current here) concentrates on the corners of the p-type base layer 111 and flows toward the narrow contact hole 120 as indicated by an arrow in a chain line circle. As a result, the current passing through the lower part of the n ⁺ type source region 116 in the hole current also increases. The hole current flowing under the n ⁺ -type source (or emitter) region 116 is from the n ⁺ -type source (same as the emitter) region 116 / p-type base region 112 / n-type semiconductor substrate layer (n-type base layer) 111. The increase in the current due to the concentration of the hole current facilitates the operation of the npn transistor. As a result, the n ⁺ type source (or emitter) region 116 / p type base region Since the IGBT parasitic thyristor composed of the 112 / n-type semiconductor substrate layer 111 / p-type collector layer 151 is latched up and the IGBT cannot be turned off, the turn-off resistance is reduced. In other words, the current that can be cut off at the time of turn-off is reduced, which may lead to destruction.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a cell-type trench insulated gate bipolar transistor that can achieve low on-resistance and improved turn-off resistance. .

According to the first aspect of the present invention, the first conductivity type semiconductor substrate, the second conductivity type base region selectively formed on one main surface layer of the semiconductor substrate, and the first conductivity type semiconductor substrate. A first conductive type source region selectively formed on the surface layer of the two conductive type base region, and a depth exceeding the second conductive type base region from the surface of the semiconductor substrate, and formed in a parallel striped surface pattern A trench, a polysilicon gate electrode embedded in the trench through a gate insulating film formed on the sidewall of the trench, and an emitter electrode formed on the polysilicon gate electrode through an interlayer insulating film A contact hole provided in the interlayer insulating film so that the emitter electrode contacts the surfaces of both the first conductivity type source region and the second conductivity type base region; and the first conductivity type semiconductor A second conductivity type collector layer formed on the other main surface layer of the plate, and a collector electrode in contact with the second conductivity type collector layer surface, on one main surface of the first conductivity type semiconductor substrate, In the trench type insulated gate bipolar transistor having a configuration in which the respective surfaces of the second conductive type base region and the first conductive type semiconductor substrate alternately appear in the longitudinal direction between the parallel trenches, The surface of the first conductivity type semiconductor substrate in the longitudinal direction is covered only by the interlayer insulating film and the emitter electrode in the configuration, and the contact hole has a length corresponding to the longitudinal direction of the trench of the contact hole. With respect to the present invention, the trench-type insulated gate bipolar transistor is made longer than the first conductivity type source region. The purpose is achieved.

According to a second aspect of the present invention, the length of the contact hole in one direction corresponding to the longitudinal direction of the trench is 0.5 μm to 4.4 μm from the first conductivity type source region. Preferably, the trench-type insulated gate bipolar transistor according to claim 1 is elongated in a range of 0 μm.
According to the invention of claim 3, the second conductivity type contact region having a higher concentration than the base region is formed in the second conductivity type base region. The trench-type insulated gate bipolar transistor according to Item 1 or 2 is desirable.

According to the invention of claim 4, the length of the second conductivity type contact region in one direction corresponding to the longitudinal direction of the trench is less than the first conductivity type source region. More preferably, the trench type insulated gate bipolar transistor according to claim 3 is elongated in the range of 5 μm to 4.0 μm.
In short, the present invention has a structure in which the contact hole protrudes from the end of the n ⁺ type source region in the longitudinal direction of the trench gate. By adopting such a pattern, the hole current concentration at the time of turn-off is alleviated, and the interruptable current increases.

  By applying the present invention, it is possible to provide a cell-divided trench IGBT that can achieve low on-resistance and improved turn-off resistance.

FIG. 1-1 is a plan view of a cell unit portion of a cell division type trench IGBT according to the present invention. FIG. 1-2 is a cross-sectional view of the cell division type trench IGBT cut along line AA in FIG. 1-1. FIG. 2 is a graph showing the relationship between the cutoff current and the on-voltage when the distance X of the cell division type trench IGBT according to the present invention is used as a parameter. FIG. 3 is a plan view of a cell unit portion of a different cell division type trench IGBT according to the present invention. FIG. 4 is a diagram showing the relationship between the breakable current and the on-voltage when the length of the n ⁺ -type source region in the trench longitudinal direction and the length of the contact hole and the p ⁺ -type contact region are used as parameters. It is.

Hereinafter, a cell division type trench insulated gate bipolar transistor according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the description of the examples described below unless it exceeds the gist.
1-1 is a plan view for one cell according to Example 1 of the present invention, and FIG. 1-2 is a cross-sectional view of the cell-divided trench IGBT cut along the line AA in FIG. 1-1. Compared to FIGS. 5, 6, and 7 showing the conventional cell-divided trench IGBT, in the first embodiment, the contact hole 10 has a longer pattern than the n ⁺ -type source region 6 with respect to the length in the trench longitudinal direction. However, since the other configurations are the same as those of the conventional cell-divided trench IGBT shown in FIGS. 7, 5, and 6, detailed description thereof is omitted. In FIG. 7 as well, the p ⁺ type contact region 117 is longer than the n ⁺ type source region 116 in the drawing, but it is due to the diffusion of impurity diffusion and is intentionally increased. It is not a little in length.

1-1 and 1-2, the contact hole 10 is made longer than the n ⁺ -type source region 6 by the length of “distance X”, so that the hole current indicated by the arrow in FIG. Since the effective cross-sectional area that can be generated is larger than that in FIG. 7 as in a round frame indicated by a chain line, excessive current concentration is less likely to occur. Due to this effect, the current that can be cut off at the time of turn-off can be greatly increased. However, if the “distance X” is too long as described above, minority carriers are discharged more in the on state, so that the conductivity modulation effect is reduced and the voltage drop in the on state (Vce (sat)) is reduced. Since the rise, that is, the ON voltage increases, the distance X naturally has an upper limit.

  FIG. 2 shows a relationship diagram between the on-voltage (Vce (sat)) and the turn-off resistance when the distance X is used as a parameter for the cell division type trench IGBT according to the first example. From FIG. 2, it can be seen that as the distance X increases from X = 0 to X = 4.0 μm, both the ON voltage (Vce (sat)) and the cutoff current increase. In addition, a standard is generally provided for the breakable current, and in FIG. 2, the breakable current standard is indicated by a dotted line. FIG. 2 shows that “distance X” is 0.5 μm or more and satisfies the interruptable current standard indicated by the dotted line. The standard of breakable current is often about 3 to 5 times the rated current value. As the distance X is further increased, the on-voltage (Vce (sat)) gradually increases. However, when the distance X is 4 μm or more, the on-voltage value increases rapidly and at the same time, the increase in the breakable current is saturated. Therefore, considering the on-state voltage as described above, the upper limit of the distance X is preferably about 4.0 μm, and therefore, the preferable range of the distance X according to the first embodiment can be 0.5 μm or more and 4 μm or less. However, even when the distance X is 4 μm or less, the length of the contact hole 10 should not exceed the length of the p-type base region 2 and reach the surface exposed region of the n-type base region 1. The reason is that the forward breakdown voltage between the collector and the emitter of the cell-divided trench IGBT is not obtained.

FIG. 3 is a plan view of one cell of the cell division type trench IGBT according to the second embodiment. This embodiment differs from FIG. 1-1 according to the first embodiment in that not only the contact hole 13 but also the p ⁺ -type contact region 14 extends greatly in the longitudinal direction of the trench. As shown in FIG. 4, the broken line in the relationship diagram between the on-state voltage and the cut-off current when the relationship between the length of the n ⁺ -type source region in the trench longitudinal direction and the length of the contact hole and p ⁺ -type contact region is used as a parameter As shown in the figure, when both the p ⁺ -type contact region 14 and the contact hole 13 are extended, an effect obtained by combining the respective effects can be obtained. it can. The protrusion distance “Y” of the p ⁺ -type contact region 14 does not necessarily need to coincide with the protrusion distance “X” of the contact hole 13, and an optimum value can be selected in consideration of the cutoff current standard. As shown in FIG. 7 which is a plan view of the conventional cell portion described above, an increase in the cut-off current can be obtained even in the case where only the p ⁺ -type contact region 117 protrudes into the p-type base region. It is. FIG. 4 shows that the p ⁺ -type contact region has a protruding effect smaller than the case where only the contact hole is protruded, and the effect of increasing the breakable current is greater when the contact hole is made longer. It can also be seen that a great effect can be obtained.

It is a top view of the cell unit part of the cell division type trench IGBT concerning this invention. It is sectional drawing of the cell division | segmentation type | mold trench IGBT cut | disconnected by the AA line of FIGS. 1-1. FIG. 6 is a relationship diagram between a cutoff possible current and an on-voltage when the distance X of the cell division type trench IGBT according to the present invention is used as a parameter. It is a top view of the cell unit part of different cell division type trench IGBT concerning this invention. FIG. 6 is a relationship diagram between a breakable current and an on-voltage when the relationship between the length of the n ⁺ -type source region in the trench longitudinal direction and the length of the contact hole and the p ⁺ -type contact region is used as a parameter according to the present invention. It is a top view of the conventional cell division type trench gate bipolar transistor. It is sectional drawing of the cell division type trench IGBT cut | disconnected by the BB line of FIG. It is a top view of the cell unit part of the conventional cell division type trench IGBT.

Explanation of symbols

1,... First conductivity type semiconductor substrate, silicon substrate, n-type base layer,
2, ... second conductivity type base region, p-type base region,
3, ... trench,
4, ... Gate insulating film, gate oxide film,
5, ... polysilicon gate electrode,
6,... First conductivity type source region, n ⁺ type source region,
7, second conductivity type contact region, p ⁺ type contact region,
8, ... interlayer insulation film,
9, Emitter electrode,
10. Contact hole,
DESCRIPTION OF SYMBOLS 11, ... 2nd conductivity type collector layer 12, ... Collector electrode 13, ... Contact hole 14, ... 2nd conductivity type contact region, p ⁺ type contact region.

Claims (4)

A first conductivity type semiconductor substrate, a second conductivity type base region selectively formed on one main surface layer of the semiconductor substrate, and a surface layer of the second conductivity type base region selectively formed A first conductivity type source region; a trench having a depth exceeding a base region of the second conductivity type from the surface of the semiconductor substrate; and a gate insulation formed on a sidewall of the trench; A polysilicon gate electrode embedded in the trench through the film; an emitter electrode formed on the polysilicon gate electrode through an interlayer insulating film; and the emitter electrode comprising the first conductivity type source region and the first electrode A contact hole provided in the interlayer insulating film so as to be in contact with both surfaces of the two-conductivity type base region, and a second conductivity-type co And a collector electrode in contact with the surface of the second conductivity type collector layer, and on one main surface of the first conductivity type semiconductor substrate, a second conductivity type base region is provided in the longitudinal direction between the parallel trenches. In the trench type insulated gate bipolar transistor having a configuration in which the surfaces of the first conductivity type semiconductor substrate are alternately arranged, the surface of the first conductivity type semiconductor substrate in the longitudinal direction between the parallel trenches is the configuration described above. the interlayer insulating film and the only emitter electrode covers of the contact hole, the length corresponding to the longitudinal direction of the trench in the contact hole, and is longer than the first conductivity type source region A trench type insulated gate bipolar transistor characterized by the above. The contact hole has a length in one direction corresponding to a longitudinal direction of the trench, which is longer than the first conductivity type source region in a range of 0.5 μm to 4.0 μm. Item 2. The trench type insulated gate bipolar transistor according to Item 1. The second conductivity type contact region having a concentration higher than that of the base region is formed in a surface layer sandwiched between the first conductivity type source regions in the second conductivity type base region. 3. A trench type insulated gate bipolar transistor according to 1 or 2. The second conductivity type contact region has a length in one direction corresponding to the longitudinal direction of the trench that is longer than the first conductivity type source region by 0.5 μm to 4.0 μm. 4. The trench type insulated gate bipolar transistor according to claim 3, wherein:

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