JP2854655B2 - Light firing thyristor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a light-firing thyristor that is optically fired, and is mainly used as an electronic switch for AC control.

2. Description of the Related Art Conventionally, thyristors that are optically fired are well known.
FIG. 3 shows the structure of a conventional light-ignition thyristor (Japanese Unexamined Patent Publication No.
No. 1463). On a surface of an N-type semiconductor substrate 1, a P-type anode region 2 and a P-type base region 3 are formed.
Are formed on the surface of the P-type base region 3.
The cathode region 4 is formed to form a lateral thyristor (lateral conduction type thyristor). further,
A field plate 28 made of polycrystalline silicon connected to the anode electrode 30, a field plate 29 made of polycrystalline silicon connected to the cathode electrode 31, and a space between the field plates 28 and 29 on the surface of the semiconductor substrate 1. And a P-type guard ring 6 formed in such a manner as to achieve a high breakdown voltage.

[Problems to be Solved by the Invention] The withstand voltage of the lateral thyristor shown in FIG.
In order to further increase the withstand voltage, the impurity concentration of the N-type semiconductor substrate 1 is reduced, and the insulating film 27 is formed.
And the overhang of the field plates 28 and 29 needs to be increased. Where field plate 2
The distance between the end of the guard ring 6 and the end of the guard ring 6 also needs to be increased according to the depletion layer extending from the field plates 28 and 29. If this distance is too small, the withstand voltage will decrease. Therefore, in the lateral thyristor shown in FIG. 3, if the breakdown voltage is further increased, the distance between the anode region 2 and the base region 3 is increased, resulting in an increase in the on-voltage drop and an increase in the chip area. was there.

Therefore, as shown in FIG. 1, another conductive type anode region 2 and another conductive type base region 3 and the base region 3 are formed on the surface of one conductive type semiconductor substrate 1 so as to be separated from each other. An optically ignited lateral thyristor comprising said one conductivity type cathode region 4 formed to be contained within said other region surrounding said base region 3 laterally spaced from said base region 3; And an electrode connected to the anode region 2 and formed on a plurality of insulating films 7, 8 formed on the semiconductor substrate 1 beyond the anode region 2. Of the first field plate 11 and the electrode connected to the cathode region 4, the plurality of insulating films formed on the semiconductor substrate 1 over the base region 3 and the junction protection region 5. Formed on 9,10 2 of the field plate 12
And a structure including the other conductive type guard ring 6 formed between the first and second field plates 11 and 12 and formed on the surface of the semiconductor substrate 1.

Hereinafter, the operation of the structure shown in FIG. 1 will be described with reference to FIG. In the structure of the conventional example shown in FIG. 4A, a field plate 34 extending from a P-type region 33 formed on the surface of an N-type semiconductor substrate 32 is formed. In the above structure, in order to increase the withstand voltage, it is necessary to increase the extension distance of the field plate 34 and increase the thickness of the insulating film 35 between the semiconductor substrate 32 and the field plate 34.
However, extending the overhang of the field plate 34 increases the on-voltage drop and the chip area. When the thickness of the insulating film 35 is increased, the radius of curvature of the portion A of the depletion layer 36 extending from the P-type region to the semiconductor substrate 32 is increased, the electric field is insufficiently reduced, and the breakdown voltage is limited.

Therefore, in the structure of FIG. 1, as shown in FIG. 4 (b), the insulating film 39 is made thicker than the insulating film 38 and the field plate 37 is provided with a step so that the field plate 37 has a step.
Depletion layer 36 generated by the potential of the portion above insulating film 38 of 37
Since the radius of curvature of the depletion layer in the portion B is increased and the electric field is relaxed by the portion C, the insulating film 39 is made thicker, the electric field concentration in the portion D is relaxed, and the breakdown voltage can be increased.

Further, as shown in FIG. 4C, the semiconductor substrate 32 is separated from the end of the field plate 37 by an appropriate distance.
By providing the guard ring 40 in the P-type region on the surface of the semiconductor device, the depletion layer 36 reaches the guard ring 40, the electric field at the end of the depletion layer is reduced, and the breakdown voltage can be improved.

Further, as shown in FIG. 1, by providing a P-type junction protection region 5 surrounding the base region 3, the anode
When a transient state involving a sudden voltage change (dV / dt) occurs between the cathodes, a transient current flowing to the base region 3 is trapped by the junction capacitance, and the thyristor can be prevented from being turned on.

In FIG. 1, the insulating film formed on the semiconductor substrate ₁ has a relatively small thickness t ₁ of the insulating films 7 and 9 in the vicinity of the anode region 2 and in the vicinity of the junction protection region 5. Insulating films 8 and 10 at portions remote from junction protection region 5
The thickness t ₂ is formed to be relatively thick, extending a field plate 12 connected to the field plate 11 and the cathode region 4 connected to the anode region 2 to the top of the relatively thick portion of the insulating film Formed. For example,
The resistivity of the N-type semiconductor substrate 1 is 40 Ω · cm, the interval S between the field plates 11 and 12 is 60 μm, t ₁ is 1 μm, and t ₂ is 3
If the length of l ₁ and l ₂ is 15 μm, withstand pressure 700
When the length of V, l ₁ and l ₂ is 20 μm, a withstand voltage of 750 V is achieved.

However, in the structure of FIG. 1, since a step-like insulating film is used, it is necessary to etch a portion where the insulating film is thinned after forming the insulating film. By the way, in the case of a light-ignition thyristor, it is common to form a MOSFET in a control circuit on the same chip in order to increase the dV / dt resistance, but it is embedded in an insulating film when the gate of this MOSFET is formed. If a plurality of field plates are formed in terms of potential using the semiconductor layer, the stepped insulating film shown in FIG. 1 is not required, which is considered to be advantageous.

The present invention has been made in view of such a point,
The aim is to provide a light-firing thyristor with high withstand voltage and large dV / dt withstand voltage by improving the structure of the field plate without increasing the on-voltage drop or the chip area. is there.

[Means for Solving the Problems] In the light-ignition thyristor according to the present invention, in order to solve the above-mentioned problems, as shown in FIG. Having an anode region 2 of another conductivity type, a base region 3 of another conductivity type, and the cathode region 4 of one conductivity type formed so as to be included in the base region 3. In a laterally thyristor that is locally fired, the other conductive type junction protection region 5 surrounding the base region 3 laterally separated from the base region 3 and an electrode connected to the anode region 2. A first field plate 11 formed on an insulating film 17 formed on the semiconductor substrate 1 over the anode region 2; and an electrode connected to the cathode region 4; 3 and the contact The semiconductor substrate 1 is located between a second field plate 12 formed on an insulating film 17 formed on the semiconductor substrate 1 over the protection region 5 and first and second field plates 11, 12. And a portion of the first field plate 11 closer to the anode region 2 than an end portion facing the guard ring 6 and a surface of the semiconductor substrate 1. Insulating film between 17
A first semiconductor layer 15 connected to the first field plate 11 is buried therein, and a portion of the second field plate 12 closer to the junction protection region 5 than the end portion facing the guard ring 6 and the semiconductor substrate. Insulating film 17 between surface 1
A second semiconductor layer 16 connected to the second field plate 12 is embedded therein.

[Operation] According to the present invention, a step-like insulating film as shown in FIG.
Even without forming 7, 8, 9, 10 as shown in FIG. 2, a plurality of field plates can be formed in potential using the semiconductor layers 15, 16 buried in the insulating film 17. Thus, the effect of improving the breakdown voltage described with reference to FIG. 4 can be obtained.

Embodiment An embodiment of the present invention will be described with reference to FIG. An anode region 2 and a base region 3 of another conductivity type (for example, P-type) are formed on the surface of a semiconductor substrate 1 of one conductivity type (for example, N-type) so as to be included in the P-type base region 3. An N-type cathode region 4 is formed to constitute a thyristor having a PNPN four-layer structure. Then, a P-type junction protection region 5 is formed so as to be separated from the base region 3 and surround the base region 3,
A guard ring 6 of a P-type region is formed substantially in the middle between the anode region 2 and the junction protection region 5. The junction protection region 5 is connected to the cathode electrode by a partial contact 14. Semiconductor layers (for example, polycrystalline silicon layers) 15 and 16 are embedded in an insulating film 17 on the semiconductor substrate 1, and the field plate 11 connected to the anode region 2 is connected to the semiconductor layer 15.
The field plate 12 connected to the cathode region 4 is connected to the semiconductor layer 16 to form a plurality of field plates. In the structure of the present invention, since the field plate is composed of the two layers of the semiconductor layers 15 and 16 and the anode and the cathode electrode, it is not necessary to etch the portion where the insulating film is thinned after the formation of the insulating film. Further, since it is common to form a MOSFET in a control circuit on the same chip in order to increase the dV / dt resistance of the light firing thyristor, the semiconductor layers 15 and 16 are simultaneously formed when the gate of the MOSFET is formed.
May be formed. The specific resistance of the N-type semiconductor substrate 1, S,
Assuming that t ₁ and t ₂ have the same value as the structure in FIG. ₁ , the lengths of l ₁ and l ₂ are
At 15 μm, the same withstand voltage of 700 V as in the structure of FIG. ₁ , l ₁ , l
_When the length of ₂ is 20 μm, a withstand voltage of 750 V similar to the structure of FIG. 1 is achieved.

In the embodiment, one conductivity type is N-type, and the other conductivity type is P-type.
However, it is needless to say that one conductivity type may be P-type and the other conductivity type may be N-type.

[Effect of the Invention] In the light-ignition thyristor of the present invention, a field plate extending from the anode and a field plate extending from the cathode are formed in a plurality of stages, and the distance between the field plates is set to an appropriate distance. A guard ring is provided almost in the middle of the base region, and a junction protection region surrounding the base region is provided at a distance from the base region, thereby increasing the withstand voltage without increasing the on-voltage drop and the chip area, and increasing the dV / There is an effect that the dt resistance can be increased. In addition, since a plurality of field plates are formed in potential using a semiconductor layer embedded in the insulating film, the insulating film is formed and then the insulating film is formed as in the case of using a step-like insulating film. There is no need to etch the thinned portion, and there is an effect that a plurality of field plates can be easily formed with a structure suitable for a light-ignition thyristor having a large dV / dt resistance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration of a light-firing thyristor on which the present invention is based, FIG. 2 is a cross-sectional view showing a configuration of one embodiment of a light-firing thyristor according to the present invention, and FIG. 4 (a) to 4 (c) are cross-sectional views showing a state of a depletion layer. 1 is a semiconductor substrate, 2 is an anode region, 3 is a base region,
4 is a cathode region, 5 is a junction protection region, 6 is a guard ring, 11 and 12 are field plates, 13 is a gate electrode,
16 is a semiconductor layer and 17 is an insulating film.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masato Miyamoto 1048 Oaza Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Works, Ltd. (56) References JP-A-59-151463 (JP, A) JP-A-60-62156 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/332 H01L 29/74-29/749

Claims (1)

(57) [Claims] 1. An anode region of another conductivity type and a base region of another conductivity type formed apart from each other on a surface of a semiconductor substrate of one conductivity type, and formed to be included in the base region. An optically ignited lateral thyristor comprising a cathode region of one conductivity type, wherein the junction protection region of another conductivity type surrounding the base region spaced laterally from the base region; and the anode region A first field plate formed on an insulating film formed on the semiconductor substrate beyond the anode region, and an electrode connected to the cathode region, A second field plate formed on an insulating film formed on the semiconductor substrate over the base region and the junction protection region is provided between the first and second field plates. A guard ring of the other conductivity type formed on the surface of the semiconductor substrate, a portion of the first field plate closer to the anode region than an end facing the guard ring, and a surface of the semiconductor substrate. A first semiconductor layer connected to the first field plate is buried in an insulating film between the first field plate and a portion of the second field plate which is closer to the junction protection region than an end facing the guard ring; A light-ignition thyristor, wherein a second semiconductor layer connected to a second field plate is buried in an insulating film between itself and a surface of a semiconductor substrate.