JPH0851117A - Semiconductor device - Google Patents

Abstract

PURPOSE:To provide a semiconductor device having high breakdown voltage and excellent characteristics by improving the junction breakdown voltage between the well and an element isolation region of an IC, and eliminating the influence of the substrate resistance of a semiconductor substrate to a ground electrode. CONSTITUTION:A one conductivity type epitaxially grown layer having different conductivity type of a semiconductor substrate 1 is formed on a semiconductor substrate 1, and an element isolation region 3 reaching the substrate 1 is formed on the grown layer thereby to form a plurality of wells 2 partitioned by the region 3 and the substrate 2, semiconductor elements are respectively formed at the wells 2, and an electrode 12 is formed on the rear surface of the substrate 1 in a semiconductor device. The impurity concentration of a predetermined thickness of the grown layer side of the substrate 1 is smaller than that of the grown layer, and the impurity concentration of the residual part of the substrate is formed higher than that of the grown layer.

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 plurality of elements such as IC and LSI. More specifically, the present invention relates to a semiconductor device that improves the breakdown voltage between the well and the semiconductor substrate and does not deteriorate the operating characteristics, such as an IC that grounds the back surface of the semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, various measures for improving the breakdown voltage of a pn junction have been taken in individual semiconductors such as power transistors. For example, p in the base region and collector region of the transistor
In the n-junction, the pn junction at the curved portion and the semiconductor layer surface is particularly weak against breakdown voltage, and at the curved portion, the depletion layer is expanded by reducing the impurity concentration in the collector region, or adjacent to the periphery of the base region on the semiconductor layer surface. A field limiting ring (FLR) that has the same conductivity type as the base region and is electrically independent of the base region is provided so that the end of the depletion layer on the semiconductor layer surface bypasses the field limiting ring and moves away from the base region. By doing so, the breakdown voltage is improved.

On the other hand, ICs are also required to have a high withstand voltage of about 200V or 300V from the conventional withstand voltage of 35 to 50V as they are used in complicated machines and precision equipment. An ordinary IC has a well 2 formed by separating an epitaxial growth layer provided on a p-type semiconductor substrate 21 by an element isolation region (isolation) 3 as shown in a sectional view of FIG. Then, each semiconductor element such as a transistor including the base region 4, the emitter region 5 and the contact region 6 provided in each well 2 is formed. Reference numeral 7 is a buried layer for reducing the resistance of the collector region, which may not be provided. Also, 8, 9,
10 is a collector electrode, a base electrode, and an emitter electrode, 11 and 12 are earth electrodes, and 13 is a depletion layer spread.

When an IC having such a structure is required to have a high breakdown voltage as described above, the breakdown voltage of each element formed in the well 2, for example, the collector-base breakdown voltage BV _CBO and the collector-emitter breakdown voltage BV. _It is necessary to increase the breakdown voltage between the well 2 and the element isolation region 3 as well as the _CEO . Generally, the following relationship exists between each breakdown voltage of the transistor and the junction breakdown voltage BV _ISO of the element isolation region 3.

BV _CEO <BV _CBO <BV _ISO (1) In order to increase the breakdown voltage of the pn junction, it is effective to lower the impurity concentration in the portion of the pn junction where the depletion layer is formed, because the depletion layer expands, and is generally Has been done. Therefore (1)
From the equation, in order to increase the breakdown voltage in the element isolation region junction including the semiconductor substrate, it is necessary to lower the impurity concentration of the epitaxial growth layer than the base region 4 and the impurity concentration of the semiconductor substrate than the epitaxial growth layer.

[0006]

However, in the IC, the electrode 12 is provided on the back surface of the semiconductor substrate 21 and is directly bonded to a lead frame or the like, and the back surface side of the substrate 21 is used as a ground electrode. When becomes lower, it means that the substrate resistance R _SUB is inserted in series.
This may become a parasitic resistance and deteriorate the characteristics of the IC as a whole. Moreover, the thickness of the semiconductor substrate 21 is 5 which is the thickness d of the effective layer which is the epitaxial growth layer (well 2).
.About.7 times or more, and since the semiconductor substrate 21 having a uniform impurity concentration is used, the substrate resistance R _SUB of the semiconductor substrate 21 due to the reduction of the impurity concentration becomes a serious problem, and the breakdown voltage is improved. It has the conflicting problem of maintaining the characteristics of ICs.

The present invention solves such a problem, improves the junction breakdown voltage between the IC well and the element isolation region, eliminates the influence of the substrate resistance of the semiconductor substrate reaching the ground electrode, and has a high breakdown voltage and high characteristics. An object is to provide a semiconductor device.

[0008]

According to the present invention, there is provided a semiconductor device comprising:
An epitaxial growth layer having a conductivity type different from that of the semiconductor substrate is formed on the semiconductor substrate, and an element isolation region reaching the semiconductor substrate is formed in the epitaxial growth layer, so that the element isolation region is separated from the semiconductor substrate. A semiconductor device comprising a plurality of wells, a semiconductor element formed in each well, and an electrode formed on the back surface of the semiconductor substrate, wherein an impurity concentration of a predetermined thickness on the epitaxial growth layer side of the semiconductor substrate. Is lower than the impurity concentration of the epitaxial growth layer, and the impurity concentration of the remaining portion of the semiconductor substrate is higher than the impurity concentration of the epitaxial growth layer.

The semiconductor layer having a low impurity concentration has an impurity concentration of 10 ¹⁴ to 10 ¹⁶ / cm ³ and a thickness of 5 to 30 μm.
It is preferable that m is to obtain a high breakdown voltage of 100 to 200 V or more.

[0010]

According to the present invention, since the impurity concentration of the surface of the semiconductor substrate on the epitaxial growth layer side is set lower than that of the epitaxial growth layer, the pn junction between the well formed by the epitaxial growth layer and the element isolation region is formed. The depletion layer spreads and the breakdown voltage is improved. On the other hand, the region where the impurity concentration is low in the semiconductor substrate is formed to have only the predetermined thickness of the junction and the remaining portion is formed to have a high impurity concentration. Substrate resistance can be almost ignored, and characteristics as an IC are not deteriorated.

[0011]

The semiconductor device of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an explanatory sectional view showing an embodiment of a semiconductor device of the present invention, FIG. 2 is an explanatory view showing one manufacturing method of the semiconductor substrate shown in FIG. 1, and FIG. 3 is another manufacturing method of the semiconductor substrate shown in FIG. It is an explanatory view shown.

The semiconductor device of the present invention has a high impurity concentration of, for example, 10 ¹⁷ to 10 ¹⁸ / cm ^{3 and a} high impurity concentration.
^{The ++} type high-concentration semiconductor layer 1a and the impurity concentration formed on the surface side of the semiconductor layer to have a predetermined thickness of about 10 ¹⁴ to 10 ¹⁶ / cm ³ and, for example, about 5 to 30 μm. An n-type epitaxial growth layer is provided on the low-concentration semiconductor layer 1b side of a semiconductor substrate 1 including a low-p-type low-concentration semiconductor layer 1b, and an element isolation region 3 and a semiconductor substrate formed by diffusion of p-type impurities. A well 2 defined by 1 and 1 is formed, and in the well 2, a transistor including a base region 4, an emitter region 5, an ohmic contact region 6 of a collector region, a buried layer 7 and the like is formed. Further, electrodes 8, 9, 10, 11, and 12 are connected to these regions as in the conventional example shown in FIG.

In the present invention, as the semiconductor substrate 1, for example, a p ⁺ type low concentration semiconductor layer 1b is provided on a p ^{+ +} type high concentration semiconductor layer 1a by a predetermined thickness. The n-type semiconductor layer to be the well 2 is epitaxially grown on 1b.

The high-concentration semiconductor layer 1a has an impurity concentration of, for example, about 10 ¹⁷ to 10 ¹⁸ / cm ³ , that is, a specific resistance of about 0.06 to 0.3 Ω · cm, and a thickness thereof is usually 200 to 400 μm. It is a degree. As the high-concentration semiconductor layer 1a, an ingot may be manufactured by adding impurities so that the impurity concentration becomes the above-mentioned level during manufacturing of an ingot, and a semiconductor wafer cut out may be used. It is also possible to introduce impurities by diffusion or the like to increase the concentration.

The low-concentration semiconductor layer 1b has an impurity concentration of about 10 ¹⁴ to 10 ¹⁶ / cm ³ , that is, a specific resistance of about 1.5 to 200 Ω · cm, and has a predetermined thickness, that is, The width W of the depletion layer 13 required for the required breakdown voltage is formed to a thickness of about 5 to 30 μm for a breakdown voltage of 100 to 300 V, for example. Generally, between the breakdown voltage and the width of the depletion layer,

[0017]

[Equation 1]

Where q is electronic charge, ε is permittivity, N _A
Is the acceptor concentration, W ₁ is the width of the depletion layer on the acceptor side, N _D
Is the donor concentration, and W ₂ is the width of the depletion layer on the donor side.
In order to increase the breakdown voltage, it is necessary to widen the width of the depletion layer, that is, reduce the impurity concentration of the semiconductor substrate. For example, when the breakdown voltage is 35 to 50 V, the width of the depletion layer needs to be about several μm, and when the breakdown voltage is 100 V or more, the width W of the depletion layer 13 is 5 μm.
It is necessary to be m or more.

In order to obtain the semiconductor substrate 1 composed of the high-concentration semiconductor layer 1a and the low-concentration semiconductor layer 1b, a semiconductor substrate having an impurity concentration of the low-concentration semiconductor layer 1b is prepared, and the substrate is further provided from one side. An impurity of the same conductivity type is introduced and diffused to form a high-concentration semiconductor layer 1a leaving a predetermined thickness, or a semiconductor substrate having an impurity concentration of the high-concentration semiconductor layer 1a is prepared. It can be obtained by epitaxially growing the low-concentration semiconductor layer 1b on one surface.

According to the present invention, the semiconductor substrate 1 on which the epitaxial growth layer is formed has a well of a predetermined thickness (thickness of the depletion layer required for a desired breakdown voltage) on the surface side where the epitaxial growth layer (well 2) is formed. An impurity concentration of 2, for example, an impurity concentration lower than 10 ¹⁵ to 10 ¹⁷ / cm ³ 1
The low-concentration semiconductor layer 1b formed to have a concentration of 0 ¹⁴ to 10 ¹⁶ / cm ³ and the remaining portion has a high-concentration semiconductor layer having an impurity concentration of 10 ¹⁷ to 10 ¹⁸ / cm ³ which is higher than the impurity concentration of the well 2. Since the semiconductor substrate 1 made of 1a is used, the depletion layer formed at the pn junction with the well 2 is sufficiently expanded due to the low impurity concentration, and the breakdown voltage is improved. Further, the low-concentration semiconductor layer 1b has only a depletion layer of about 5 to 30 μm, and the rest of the semiconductor substrate 1 has an impurity concentration of 10 ¹⁷ to 1 μm.
Since the semiconductor layer 1a has a high concentration of about 0 ¹⁸ / cm ³ ,
The specific resistance of 0.06 to 0.3 Ω · cm hardly appears as a resistance component, and the characteristics of the semiconductor device using the back surface of the semiconductor substrate 1 as the ground electrode are not deteriorated.

Next, a specific method for manufacturing a semiconductor substrate which is used in the semiconductor device of the present invention and is composed of the high-concentration semiconductor layer 1a and the low-concentration semiconductor layer 1b will be described with reference to FIGS.

Example 1 FIG. 2 shows that a high-concentration semiconductor layer 1a is formed by further diffusing impurities of the same conductivity type from one surface of a substrate formed of a low-concentration semiconductor layer 1b having a low impurity concentration. Figure 2
For example, the impurity concentration shown in (a) is 10 ¹⁵ / cm 3.
³ and a thickness of about 200 to 400 μm, for example p
A p-type impurity such as boron is introduced by ion implantation or coating on one surface side of the substrate formed of the low-concentration type semiconductor layer 1b (see FIG. 2B). After that, 1100-
By heat treatment at 1250 ° C., the high concentration semiconductor layer 1a having an impurity concentration of about 10 ¹⁷ to 10 ¹⁸ / cm ³ is diffused so as to leave a portion not diffused to about 5 to 30 μm.
And the low-concentration semiconductor layer 1b is formed on the high-concentration semiconductor layer 1a.
A semiconductor substrate 1 having a thin thickness can be obtained. The semiconductor device of the present invention can be obtained by providing an n-type epitaxial growth layer on the low-concentration semiconductor layer 1b side of the semiconductor substrate 1, forming an element isolation region, and forming each element in the well.

Example 2 FIG. 3 shows a case where a low-concentration semiconductor layer 1b is provided by epitaxial growth on the surface of a substrate composed of a high-concentration semiconductor layer 1a. First, as shown in FIG. A substrate composed of a p-type high-concentration semiconductor layer 1a having a thickness of about 10 ¹⁷ to 10 ¹⁸ / cm ³ and a thickness of 200 to 400 μm is prepared (see FIG. 3A). For example, boron-doped p-type low-concentration semiconductor layer 1b having a concentration of 10 ¹⁴ to 10 ¹⁶ / cm ³ is formed on the surface of the substrate in an amount of 5 to 3
The semiconductor substrate 1 is grown to have a thickness of about 0 μm to form the semiconductor substrate 1 (see FIG. 3B).

After that, as in Example 1, an n-type epitaxial growth layer is provided on the side of the low-concentration semiconductor layer 1b, and each element is formed in the well to obtain the semiconductor device of the present invention.

[0025]

According to the semiconductor device of the present invention, a layer having a low impurity concentration is provided on the surface of a semiconductor substrate having a high impurity concentration, and an epitaxial growth layer having a conductivity type different from that of the substrate is provided thereon to form a well. The depletion layer of the pn junction, which becomes the boundary of the well, expands due to the layer with a low impurity concentration,
Withstand voltage is improved. On the other hand, since the other portions of the semiconductor substrate have a high impurity concentration and a low resistance, the substrate resistance does not pose a problem even when the back surface of the semiconductor substrate is used as a ground electrode. As a result, a semiconductor device having high breakdown voltage and high characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an embodiment of a semiconductor device of the present invention.

FIG. 2 is an explanatory view showing one manufacturing method of the semiconductor substrate in FIG.

FIG. 3 is an explanatory view showing another method for manufacturing the semiconductor substrate in FIG.

FIG. 4 is a sectional view showing a conventional semiconductor device.

[Explanation of symbols]

 1 semiconductor substrate 1a high-concentration semiconductor layer 1b low-concentration semiconductor layer 2 well 3 element isolation region

Claims (2)

[Claims] 1. An epitaxial growth layer having a conductivity type different from that of the semiconductor substrate is formed on a semiconductor substrate, and an element isolation region reaching the semiconductor substrate is formed in the epitaxial growth layer, thereby forming the element isolation region and the semiconductor. A semiconductor device comprising a plurality of wells partitioned by a substrate, a semiconductor element formed in each of the wells, and an electrode formed on the back surface of the semiconductor substrate, wherein the semiconductor device has a predetermined epitaxial growth layer side. A semiconductor device in which the impurity concentration of the thickness is lower than that of the epitaxial growth layer, and the impurity concentration of the remaining portion of the semiconductor substrate is higher than that of the epitaxial growth layer. 2. The semiconductor layer having a low impurity concentration has an impurity concentration of 10 ¹⁴ to 10 ¹⁶ / cm ³ and a thickness of 5 to 30.
The semiconductor device according to claim 1, which has a thickness of μm.