JPH06334188A - Semiconductor device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a termination structure suitable for further increasing the withstand voltage. [Structure] A termination structure in which a low-concentration p-layer is deeply formed so as to cover a corner portion of the main-junction p-layer has a distance from a tip in the lateral direction of the main-junction p-layer to a tip of the electrode from the main-junction p-layer. The distance from the tip of the main junction p-layer in the lateral direction to the end of the low-concentration p-layer is not substantially the same. [Effect] The withstand voltage characteristic of the semiconductor element is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a termination structure suitable for high breakdown voltage.

[0002]

2. Description of the Related Art Conventionally, as a termination structure for increasing the breakdown voltage (ISPSD 88, p107-p11
0) The structure described in the paper is known. An example of the structure is shown in FIG. 1 is an n-type substrate, 2 is an n-buried layer, 3,
9 is an insulating film, 4 is a support substrate, 5 is an electrode, and 6 is a main junction p
The electric field relaxation layers 71, 72 and 73 are formed by a junction having a shallower concentration and a shallower concentration than the layer and the p layer 6 of the main junction. Reference numeral 31 indicates a certain equipotential line. The electrode 5 extends in the lateral direction, but stops inside the end of the low-concentration p-layer 71. When the main junction layer 6 and the substrate 1 are reverse biased, the depletion layer extends from the pn junction. As described above, there is known a method of relaxing the electric field concentration at the end of the junction by sequentially forming a low concentration and shallow p layer in contact with the end of the high breakdown voltage junction. Prototype (IEEE 1979 years, P238-P241) of the method is described in detail in, briefly described below what is called RESURF (Re duced Sur face F ield ) effect.

For example, p is formed in an n-type substrate by boron diffusion or the like.
When an n-junction is formed, the impurity concentration on the surface of the p-layer is inevitably higher than that on the surface of the semiconductor, and the semiconductor surface has many instability factors and weak electric field strength. Since the depletion layer does not extend in the vertical direction (depth direction),
The breakdown voltage is determined in the lateral direction (surface direction).

In the RESURF structure, a low-concentration p-layer is provided at an appropriate concentration and a junction depth in the termination portion of the device, and the depletion layer easily extends in the low-concentration p-layer, thereby relaxing the electric field. is there. Before the electric field in the lateral direction reaches the critical electric field (breakdown occurs), the depletion layer edge extending from the lower junction portion (that is, from the vertical direction) in the low-concentration p-layer reaches the semiconductor element surface. Then, the entire low-concentration p-layer becomes a depletion layer, and the lateral depletion layer expands.
Therefore, the electric field in the lateral direction is relaxed and the breakdown voltage of the device is improved.

FIG. 11 shows that the low-concentration p-layers 71, 72, 73 are gradually reduced in concentration and the junction is shallowed to artificially increase the corner curvature of the main-junction p-layer to increase the breakdown voltage. I am doing it.

As a typical conventional termination structure, a method is known in which the electric field concentration in the vicinity of the surface junction is relaxed laterally by the potential from the p-layer main junction to the electrode to increase the breakdown voltage. It is called a plate (hereinafter abbreviated as FP) effect. In FIG. 11, although not described in detail in the paper, the structure mainly expects the RESURF effect because the electrode from the main junction extends only within the range not exceeding the low-concentration p-layer. I can say.

[0007]

The methods such as RESURF and FP are intended to increase the breakdown voltage by relaxing the electric field near the surface of the p-layer main junction in the lateral direction of the semiconductor surface.
When the main junction is deep, the electric field in the corner portion (A in the figure) of the p layer in the depth direction, which is the maximum electric field, cannot be relaxed so much. Therefore, even if the low-concentration p-layer is further extended in the lateral direction, the withstand voltage can be improved only slightly, and a large increase in withstand voltage cannot be expected despite the increase in the element area.

On the surface of the low concentration p-layer, the fluctuation of the surface concentration induced by an external factor is remarkable, which affects the spread of the depletion layer. However, since the low-concentration p-layer 7 is covered with the electrode 5 from the main junction, the reliability of the device can be improved. In this respect the electrode 5 from the main junction
Is most desirable to extend beyond the low-concentration p-layer, but when the device is in the blocking state, the electrode 5 is reverse biased and has a negative potential with respect to the surface junction. Since holes are accumulated and a high-concentration p-layer is formed, the effect of RESURF disappears. FIG. 11 shows a structure in which the RESURF effect is expected, and it is better not to extend the electrode from the main junction on the p-layer having a low concentration, but it is necessary to ensure the reliability of the device to some extent as described above. .

An object of the present invention is to provide a termination structure suitable for achieving a high breakdown voltage with a small termination area.

[0010]

The termination of the present invention basically has a structure in which a low-concentration p-layer is deeply formed so as to cover a corner portion of the main-junction p-layer. The distance from the tip to the tip of the electrode from the main junction p-layer (hereinafter abbreviated as LFP) is not approximately the same as the distance from the tip in the lateral direction of the surface of the main junction p-layer to the low-concentration p-layer edge (hereinafter abbreviated as LP). It is a structure.

The termination of the present invention, which is the first means for solving this problem, is a structure in which a low-concentration p-layer is deeply formed so as to cover the corner portion of the main junction p-layer, and the LFP is an LP.
It is a shorter structure.

The termination of the present invention, which is the second means for solving this problem, is a structure in which a low-concentration p-layer is deeply formed so as to cover the corner portion of the main junction p-layer.
It has a longer structure.

[0013]

According to the experiments by the present inventors, for example, a low concentration of p
When the concentration of the layer is about 10 ¹⁸ cm ^-3 or more, the corner portion of the low concentration p layer has the maximum electric field, and the breakdown voltage is determined here. At this time FP
Or RESURF has no effect.

When the concentration of the low-concentration p-layer is about 10 ¹⁷ cm ⁻³ or less, the concentration of the p-layer induced under the LFP by the reverse bias of the electrode is lower than that of the low-concentration p-layer. Is much higher, and the maximum electric field is at the edge of the high-concentration storage layer.

When LFP <LP, the RESURF effect appears due to the low concentration p layer corresponding to the length of (LP-LFP), and the breakdown voltage can be improved. The larger (LP-LFP) is, the more RESU
Although the RF effect is large, it is naturally limited due to the reliability problem mentioned above.

When LFP and LP are substantially equal, the RESURF effect becomes small.

When LFP> LP, the FP effect appears by the length of (LFP-LP). That is, since the portion of the electrode from the reverse-biased main junction beyond the low-concentration p-layer edge and depleted on the n-substrate is depleted, the maximum electric field at the edge of the storage layer is lowered, and the breakdown voltage is increased. However, in this case, since the edge of the storage layer is located at the corner of the low concentration p layer, the edge of the storage layer has a low concentration p.
The extension of the depletion layer in this portion is smaller than that in the case of LFP <LP inside the layer. Therefore, in the case of LFP> LP, the breakdown voltage characteristic becomes worse than in the case of LFP <LP. Further, stretching the electrode may lead to expansion of the termination region, in which case the element area will be increased.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The semiconductor device of the present invention will be specifically described below with reference to the drawings.

FIG. 1 is an embodiment in which the termination structure of the present invention is applied to a high voltage dielectric insulation isolation type power IC, and FIG. 2 is an explanatory view showing its operation. 1
Is an n-type substrate, 2 is an n-buried layer, 3 and 9 are insulating films, 4 is a support substrate, 5 is an electrode, 6 is a main junction p-layer, and 7 is a low-concentration p-layer for lateral electric field relaxation. . The electrode 5 extends in the lateral direction, but stops inside the end of the low-concentration p-layer 7. When the main junction layer 6 and the substrate 1 are reverse biased, the depletion layer extends from the pn junction. The storage layer 101 shown by the dotted line occurs when the electrode 5 is reverse biased. Naturally, the higher the reverse bias voltage, the higher the concentration. In the conventional structure of FIG. 11, the low concentration p layer 7 is formed.
Although there is a RESURF effect of 1, 72, 73, the breakdown voltage is determined by the maximum electric field in the A section.

In the structure of the present invention, the electric field relaxation effect (RESURF effect) due to the depletion of the low concentration p layer 7 due to the guard ring effect of the low concentration p layer 7 having a curvature larger than that of the main junction
Overlap with each other, and the maximum electric field in the area A becomes low. The breakdown voltage at this time is determined by the maximum electric field of the corner portion (B portion) of the storage layer 101 generated under the LFP by the reverse-biased electrode 5.
In order to alleviate the electric field at the point B, the low concentration p layer from the edge of the storage layer 101 to the edge of the low concentration p layer 7 becomes the RESURF effect for the point B.
Must be shortened. Of course, in order not to increase the element area, it is desirable that the LP is not extended and the LFP is shortened within the range in which the reliability of the element is guaranteed. Storage layer 101
Since the higher the reverse bias voltage is, the higher the concentration becomes, the higher the breakdown voltage of the element, the more remarkable the effect of the structure of the present invention. In an experiment conducted by the present inventors, when compared with a diode under the same conditions as in FIG. 11 except for the shapes of the low-concentration p layers 71, 72, 73, the n-type substrate 1 has a resistance of 150Ω and the p-layer 6 of the main junction has When the diffusion depth is 6 μm and the concentration is 1 × 10 ¹⁹ cm ⁻³ , and the diffusion depth of the low-concentration p-layer 7 for electric field relaxation is 7 μm and the concentration is 1 × 10 ¹⁶ cm ⁻³ , the breakdown voltage of the structure of FIG. The structure of FIG. 1 has a withstand voltage of about 2100V, which is 1200V. Incidentally, the breakdown voltage was about 600 V in the structure without the low-concentration p layers 72 and 73 in FIG.

FIG. 3 shows a second embodiment of the termination structure of the present invention, and FIG. 4 is an explanatory view showing the operation thereof. 1 is an n-type substrate, 2 is an n-buried layer, 3 and 9 are insulating films, 4
Is a support substrate, 5 is an electrode, 6 is a main junction p-layer, and 7 is a low-concentration p-layer for lateral electric field relaxation. Electrode 5 is low concentration p layer 7
It extends laterally beyond the edges. When the main junction layer 6 and the substrate 1 are reverse biased, the depletion layer extends from the pn junction.

The electrode 5 extending from the main junction makes the storage layer 102 on the low-concentration p-layer 7 (that is, the range of LP), and the maximum electric field at the point B becomes large, but on the n-substrate 1 (that is, (LF
Since the range 103) of (P-LP) is depleted, the maximum electric field at the point B is lowered and the breakdown voltage is increased. However, since the maximum electric field at point B is larger than the maximum electric field at point A, the breakdown voltage is determined at point B.

Since the concentration of the storage layer 102 increases as the reverse bias voltage increases, the effect of the structure of the present invention becomes more remarkable as the element has a higher breakdown voltage. In the experiments conducted by the present inventors, a comparison was made with a diode under the same conditions as in FIG. 11 except that the shape of the low-concentration p-layer 7 and the electrode 5 extend beyond the end of the low-concentration p-layer 7. n-type substrate 1 is 150Ω, main junction p-layer 6
Has a diffusion depth of 6 μm and a concentration of 1 × 10 ¹⁹ cm ⁻³ , 7
When the diffusion depth of the low-concentration p-layer 7 for electric field relaxation is 7 μm and the concentration is 1 × 10 ¹⁶ cm ⁻³ , the structure of FIG.
The breakdown voltage of the structure of FIG. 3 was about 1900V.

FIG. 5 shows the breakdown voltage in the termination structure shown in FIGS. 1, 3 and 11 with the LFP of the electrode 5 as a parameter. The solid line 11 shows the breakdown voltage of the structure of the present invention, and the dotted line 10 shows the breakdown voltage of the conventional structure. In the conventional structure, when the main junction p-layer is deep, the RESURF effect and the FP effect do not significantly appear.

In the structure of the present invention, the LFP is up to the point A in the figure.
Due to the effect of RESURF, the breakdown voltage is high, and the shorter the LFP, the higher the breakdown voltage. After point A, the breakdown voltage is high due to the effect of FP, and the longer the LFP, the higher the breakdown voltage. This point A is a point where LP and LFP are substantially equal.

For point A, increasing the LFP is less effective than decreasing the LFP. This is because the edge of the storage layer when aiming at the FP effect is located at the corner portion of the low-concentration p layer, so that the depletion layer of this portion is less than the case of LFP <LP where the edge of the storage layer is inside the low-concentration p layer. Since the growth is small, LFP <L
This is because the breakdown voltage characteristics are worse than in the case of P.

FIG. 6 shows an example of a plane pattern when the termination of the present invention is applied to a diode. The main junction 6 has a structure in which the periphery is surrounded by the low-concentration layer 7, and the electrode 5 covers the space between the main junction 6 and the low-concentration layer 7. There is also an n-layer 14 for making ohmic contact with the cathode. According to this structure, since the electric field of the termination portion can be relaxed, the breakdown voltage of the diode can be increased. Although a diode is used as an example here, a transistor, a thyristor, a MOSFET, an I
Similarly, with a GBT, a MOS thyristor, etc., the breakdown voltage can be increased. By applying the conditions described in the description of FIG. 1, the withstand voltage can be increased from the conventional about 600V to about 2100V.

FIG. 7 shows an example of a cross section when this termination structure is applied to a transistor. An n layer 16 of an emitter layer is formed in the p layer 6 based on the p layer of the main junction. 15 is a collector contact layer,
Reference numeral 17 is an emitter electrode, 18 is a base electrode, and 51 is a collector electrode. According to this structure, it is possible to increase the breakdown voltage with the conventional substrate resistance. Further, since a substrate having the same breakdown voltage as that of the conventional one and a lower resistance can be used, the collector resistance component of the transistor can be reduced.

FIG. 8 shows a case where this termination structure is applied to a vertical nMOSFET. P of channel layer and main junction
The source layer 19 is formed in the layer 6. 211 is a drain contact layer, 20 is a gate, 21 is a source electrode,
52 is a drain electrode. According to this structure, it is possible to increase the breakdown voltage with the conventional substrate resistance. Moreover, since a substrate having the same breakdown voltage as that of the conventional one and a lower resistance can be used, the on-resistance of the MOSFET can be reduced. FIG. 9 shows a case where this termination structure is applied to a lateral thyristor. The anode layer 22 and the p base layer 23 are high breakdown voltage junction layers, and the cathode layer 24 is formed in the p base layer 23. Reference numeral 25 is a gate contact layer, 26 is an anode electrode, 27 is a p gate electrode, 28 is a cathode electrode, and 29 is an n gate electrode. As described above, it does not matter if a plurality of high breakdown voltage layers are present in one element.

FIG. 10 shows a case where the present termination structure is applied to a vertical IGBT. An emitter layer 204 is formed in the p layer 205 of the channel layer and the main junction. 9
1 is a collector layer, 203 is a gate, 202 is an emitter electrode, and 53 is a collector electrode. According to this structure, it is possible to increase the breakdown voltage with the conventional substrate resistance. In addition, since it is possible to use a substrate with the same breakdown voltage and lower resistance as the conventional one, the IGBT
ON resistance of can be reduced. In our experiments, n
The mold substrate 1 has a thickness of 100Ω and a thickness of 300 μm, the main junction p-layer 6 has a diffusion depth of 6 μm and a concentration of 1 × 10 ¹⁸ cm ⁻³ , and the electric field relaxation low-concentration p-layer 7 has a diffusion depth of 7 μm. Is 1 × 10
When the pressure was ¹⁶ cm ^-3 , the breakdown voltage was about 2000V.

[0031]

According to the present invention, it is possible to provide a termination structure suitable for a high breakdown voltage while suppressing an increase in the device area occupied by termination, and a semiconductor device excellent in breakdown voltage characteristics, and a circuit configuration using the same or a semiconductor device using the same. A built-in semiconductor integrated circuit can be obtained.

[Brief description of drawings]

FIG. 1 shows an example of a cross section of a termination structure of a semiconductor device of the present invention.

FIG. 2 is an operation explanatory diagram of the termination structure of FIG.

FIG. 3 shows an example of a cross section of a termination structure of the present invention.

FIG. 4 is an operation explanatory view of the termination structure of FIG.

FIG. 5 shows the results of comparison of the breakdown voltages of the present invention and the conventional termination structure depending on the distance (LFP) from the tip in the lateral direction of the main junction p-layer to the tip of the electrode from the main junction p-layer.

FIG. 6 shows an example of a plane pattern of a diode using the termination structure of the present invention.

FIG. 7 is an npn using the termination structure of the present invention.
The cross-sectional structure of a transistor is shown.

FIG. 8 is a vertical n using the termination structure of the present invention.
An example of the cross-sectional structure of a MOSFET is shown.

FIG. 9 shows a cross-sectional structure of a high breakdown voltage lateral thyristor using the termination structure of the present invention.

FIG. 10 shows an example of a cross-sectional structure of a vertical IGBT using the termination structure of the present invention.

FIG. 11 shows an example of a cross section of a conventional termination structure.

[Explanation of symbols]

1 ... Substrate, 2 ... Buried layer, 3, 9 ... Insulating film, 4 ... Support substrate, 5, 17, 18, 21, 26, 27, 28, 29,
51, 52, 53, 202, 203 ... Electrodes, 6,205
... Main junction, 7, 71, 72, 73 ... Electric field relaxation layer, 14,
15 ... 25 n layer, 16, 204 ... Transistor emitter layer, 19 ... nMOSFET source layer, 20 ... MOSFET gate, 22 ... Thyristor anode layer, 23 ... Thyristor p base layer, 24 ... Thyristor cathode layer , 31
... equipotential lines, 91 ... IGBT collector layer, 101, 1
02 ... Accumulation layer, 103 ... Depleted portion, 201 ... Buffer layer, 211 ... Drain contact layer.

Continuation of front page (72) Inventor Yoshiteru Shimizu 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (2)

[Claims] 1. A semiconductor device having a main junction formed of at least a first-conductivity-type first semiconductor layer and a second-conductivity-type second semiconductor layer having a higher impurity concentration than the first-conductivity-type second semiconductor layer. A third semiconductor layer of the second conductivity type having a concentration lower than that of the semiconductor layer is formed in contact with the second semiconductor layer of the main junction, and further formed of the third semiconductor layer of the low concentration and the first semiconductor layer. The junction formed is the same as or deeper than the second semiconductor layer of the main junction, and the tip position of the junction in the lateral direction of the surface is not substantially the same as the tip of the electrode from the second semiconductor layer of the main junction. A semiconductor device having a characteristic termination structure. 2. The tip in the lateral direction of the surface of the junction formed by the low-concentration third semiconductor layer and the first semiconductor layer is outside the tip of the electrode from the second semiconductor layer of the main junction. And a semiconductor device having a termination structure.