JPS63138767A - Semiconductor substrate for vertical type semi-conductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To sufficiently reduce the forward voltage VF by a method wherein a first semiconductor layer having high impurity density is formed on the surface of a semiconductor substrate by deeply diffusing one-conductive type impurities, and a second semiconductor layer containing the impurities having a small coefficient of diffusion is formed thereon. CONSTITUTION:A silicon substrate 11 containing n-type impurities is prepared as a starting material, high density of silicon impurities are diffused from the upper and the lower surfaces of the substrate 11, and phosphorus is deeply diffused to the extent wherein both n<+> type diffusion layers 12 and 13 are contacted with each other. Then, n<++> diffusion layers 14 and 15 are formed by diffusing the n-type impurities, having the diffusion coefficient smaller than that of phosphorus impurities, from the surfaces of both n<+> type diffusion layers 12 and 13. Subsequently, an n<-> type epitaxial layer 16 of low impurity density is formed by deposition on the n<++> diffusion layer 14, and the manufacture of a semiconductor substrate is completed. As a result, the forward voltage VF of the substrate can be made small, and the area of a chip can also be reduced to the extent of the reduction in forward voltage.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a Schottky barrier type semiconductor device, a vertical MOS
The present invention relates to semiconductor substrates used in vertical semiconductor devices such as FETs and vertical bipolar transistors, and methods for manufacturing the same, and particularly to techniques that can improve the performance of vertical semiconductor devices and reduce costs.

(Prior Art) Among vertical semiconductor devices, for example, high-power Schottky barrier diodes are widely used, especially as rectifying elements for switching power supplies, and their high-speed performance is extremely excellent. However, the price cannot necessarily be called cheap. One of the reasons for the high price of Schottky barrier diodes is the high cost of their silicon substrates. Generally, among the rated performance, forward voltage (■) and reverse voltage (■□) are important characteristics.

Therefore, in a conventional Schottky barrier diode, an epitaxial wafer with an n-on-n9 structure is used as a silicon substrate, and the silicon substrate is doped with an impurity having a small diffusion coefficient of the n' structure, such as arsenic, at a high concentration.

FIG. 4 shows the structure of a conventional Schottky barrier diode, in which a specific resistance of 0.5 to 1 Ω-
An n-type epitaxial layer N2 of No. 1 is deposited to a thickness of 5 to 7 μm to form a semiconductor substrate having an n-on-n structure.

The surface of this epitaxial layer 2 has 5,000 to 8,000
A thick silicon oxide film 3 is formed by thermal oxidation.

This silicon oxide film 3 is selectively removed by photoetching to form an opening 3a with a tapered periphery.
is formed at the location of the active region.

A barrier metal film 4 made of molybdenum or the like is formed on the silicon oxide film 3 so as to cover this opening.
4, and on top of that is an aluminum plate.
i! 5 is formed to have a thickness of about 8 μm, and a wire 6 is further bonded onto this aluminum film. Further, a back electrode film 7 is formed on the back surface of the silicon substrate l.

(Problems to be Solved by the Invention) In the conventional semiconductor substrate 1.2 described above, when the impurity concentration of the n'-type semiconductor substrate 1 is equal to or higher than the concentration that provides a specific resistance of 0.01Ω-value, Even when the thickness was increased to about 400 μm, there was no adverse effect on the forward voltage (2) of the Schottky barrier diode. However, in order to form such an N3 type semiconductor substrate 1 by the crystal pulling method, it is difficult to increase the diameter of the wafer due to the high concentration, and conventionally, a wafer of 3 to 4 inches is obtained. was the limit. By lowering the impurity concentration of the n0 type semiconductor substrate 1, it is possible to manufacture a wafer with a larger diameter. However, as the impurity concentration decreases, V tends to become high. In order to reduce the number of chips that can be formed per Uninoa, the chip area of the Schottky barrier diode formed on the n0 type semiconductor substrate 1 must be increased. This has the disadvantage of inevitably increasing costs.

The above-mentioned problems appear not only in high-power Schottky barrier diodes, but also when trying to keep the on-resistance low in vertical semiconductor devices such as high-power MO5FETs and high-power bipolar transistors.

The object of the present invention is to eliminate the above-mentioned conventional drawbacks and to reduce the impurity concentration of the semiconductor substrate as a starting material, thereby making it possible to use wafers with larger diameters, thus increasing the yield and reducing costs. Moreover, by increasing the impurity concentration of the entire semiconductor substrate, the forward voltage vF can be increased, and as a result, the chip area can be reduced, making it possible to obtain multiple chips from one wafer. The purpose of this invention is to provide a semiconductor substrate that can be used as a semiconductor substrate and a method for manufacturing the same.

(Means and effects for solving the problem) The semiconductor substrate of the present invention is a semiconductor substrate used in a vertical semiconductor device, and includes a semiconductor substrate containing impurities of one conductivity type, and a semiconductor substrate containing an impurity of one conductivity type from one surface of the semiconductor substrate. a first semiconductor layer formed by deeply diffusing an impurity of one conductivity type; and a first semiconductor layer formed on the first semiconductor layer, the one conductivity type having a smaller diffusion coefficient than the impurity of the one conductivity type contained in the first semiconductor layer. The third semiconductor layer is formed on the second semiconductor layer and contains impurities of one conductivity type at a low concentration.

Further, in the method for manufacturing a semiconductor substrate according to the present invention, when manufacturing a semiconductor substrate for use in a vertical semiconductor device, impurities of one conductivity type are introduced at high concentration from both surfaces of a semiconductor substrate containing impurities of one conductivity type. a step of forming a first epitaxial layer containing an impurity of one conductivity type whose diffusion coefficient is smaller than that of the impurity contained therein on the surface of the first semiconductor layer; , a second layer containing impurities of one conductivity type at a low concentration is formed on this epitaxial layer.
The method is characterized by comprising a step of forming an epitaxial layer.

According to such a semiconductor substrate of the present invention, since the impurity concentration of the semiconductor substrate as a starting material does not need to be so high, a wafer with a large diameter can be manufactured by, for example, a crystal pulling method. Large wafers such as inch can be used. On the other hand, a first semiconductor layer with a high impurity concentration is formed by deeply diffusing impurities of one conductivity type into the surface of this semiconductor substrate,
Furthermore, since a second semiconductor layer containing impurities with a small diffusion coefficient is formed on top of the second semiconductor layer, the forward voltage V can be made sufficiently small in a Schottky barrier diode, and the on-state voltage can be made sufficiently small in a high power MOS FET. Resistance can be kept low.

Since the forward voltage vF can be reduced in this way, the chip area can be reduced, and together with the use of a large wafer, more chips can be formed from a single wafer, reducing costs. can be achieved.

(Example) FIGS. 1A to 1D are cross-sectional views showing the structure of a Schottky barrier diode in successive manufacturing steps using an example of a semiconductor substrate according to the present invention.

First, as a starting material, a material containing n-type impurities and having a thickness of 30 mm is used.
A silicon substrate 11 with a diameter of 0 to 400 μm is prepared, and silicon impurities are diffused in high concentration from the upper and lower surfaces of the substrate to form n-type scattering layers 12 and 13, as shown in FIG. Diffusion is performed to a depth of 150 to 200 μm, and at this time, the upper and lower n-type scattering layers 12 and 13 are as shown in FIG.
Although they may be separated from each other as shown in a), it is more desirable that they are connected to each other. Therefore, in the following description, it is assumed that phosphorus is diffused deeply to the extent that both n-type diffusion layers 12 and 13 come into contact with each other.

Next, an n-type impurity, such as arsenic (^S) or antimony (Sb), whose diffusion coefficient is smaller than that of Linnean obtuse, is diffused from the surfaces of both n-type diffusion layers 12 and 13, and the thickness of the n-type impurity is 1 to 1. N+4 diffusion layers 14 and 15 of about 4 μm are formed. The n″0 semiconductor layers 14 and 15 can also be formed by epitaxially growing a semiconductor layer containing an impurity with a small diffusion coefficient such as arsenic or antimony. Although it is preferable that the concentration be higher than that of the n-type scattering layers 12 and 13, it does not necessarily have to be higher, and may be about the same level or somewhat lower.

Next, on one of the n9'' diffusion layers 14, for example, 0.5~
Figure 1 (C
Shown in 1.

In this example, a Schottky barrier diode is formed using the semiconductor substrate formed as described above, and for this purpose, after forming an insulating film 17 having a tapered opening, molybdenum (Mo) is formed on the insulating film 17. ), etc., and the aluminum electrode film 19, each having a thickness of 3000
Figure 1 (d
Shown in l. Furthermore, as usual, the aluminum electrode film 19
Bond a wire on top to complete the Schottky barrier diode.

The Schottky barrier diode thus obtained has a breakdown voltage of about 40 to 60V, and a forward voltage v7 of 170 to 60V.
It is 20011v.

FIGS. 2(a) to 2(d) show the structure in the sequential steps of forming a Schottky barrier diode using another embodiment of the semiconductor substrate according to the present invention. In this example, the starting materials An n-type silicon substrate 21 having an impurity concentration of 10" to 1019 atoms/cm is prepared, and an n-type impurity with a large diffusion coefficient, such as Linnean blunt, is highly concentrated on both surfaces of the substrate to shorten the diffusion time. FIG. 2+8) shows how n''0-type diffusion layers 22 and 23 having a high impurity concentration of 101 atoms/ell' or more are formed to a depth of about 250 μI.

Next, on the surface of one of the n diffusion layers 220, an n
A +゛ type epitaxial layer 24 is formed.

The impurity concentration of this epitaxial layer 24 can be higher than or about the same as that of the n04 type phosphorus diffusion layer 22. Furthermore, although the n++ layer 24 is formed by epitaxial growth in this example, it may be formed by diffusion or ion implantation. Next, on the n = type epitaxial layer 24, an n type epitaxial layer 25 having a lower impurity concentration and a specific resistance of, for example, 0.5 to 1.0 Ω-R is formed to a thickness of about 5 to 8 μm. A completed semiconductor substrate is shown in Fig. 2 (Fig. 2).

Next, as in the previous example, an oxide film 26 provided with a tapered opening, a barrier metal film 27, and a metal electrode film 28 are sequentially formed, as shown in FIG. 2(C).

Furthermore, the forward voltage V of the Schottky barrier diode
In order to reduce F, the back surface of the semiconductor substrate is scraped off using, for example, a surface grinder or a lapping machine, a part of the substrate 21 and the lower n''0 type diffusion layer 23 are removed, and a back electrode film 29 is further formed. is shown in FIG. 2(d).

FIG. 3 shows still another embodiment of a Schottky barrier diode formed using the semiconductor substrate according to the present invention. In this example, a silicon substrate 31 containing a relatively large amount of Linnean obtuse is used as a starting material, and the upper and lower surfaces of the silicon substrate 31 contain n-type impurities having a smaller diffusion coefficient than the Linnean obtuse, such as arsenic or antimony. Epitaxial layers 32 and 33 are formed. In this case, it is desirable that the impurity concentration of arsenic or antimony be higher than the impurity concentration of the silicon substrate 31, but it may be about the same level or somewhat lower.

The n+1 type layers 32 and 33 can also be formed by a diffusion method or an ion implantation method, but in this case, the impurity concentration will be higher than that of the silicon substrate. Furthermore, a resistivity of 0 is applied on one of the n=type epitaxial layers 32.
．． An n-type epitaxial layer 34 with a low impurity concentration of 5 to 1.0 Ω is grown, and an oxide film 35 having a tapered opening, a barrier metal film 36, and a metal electrode film 37 are formed thereon.
are formed sequentially. Furthermore, in this example, the silicon substrate 31
Since the impurity concentration is high, the backside electric bridge [38] is formed without scraping off the backside. The forward voltage V of the Schottky barrier diode thus formed is sufficiently low. Depositing an n''3 type epitaxial layer in this manner is particularly suitable for a Schottky barrier diode that does not require high-temperature heat treatment.

In the above embodiments, the semiconductor substrate of the present invention is used. 17 We have explained the case where it is applied to a barrier type diode, but
Power 805 PET or power transistor, SI
It can also be applied to other vertical semiconductor devices such as T.

(Effects of the Invention) According to the semiconductor substrate of the present invention described above, since the impurity concentration of the semiconductor substrate as a starting material is low, a wafer with a large diameter of 5 inches or 6 inches can be formed by the crystal pulling method. It is possible to reduce costs. Furthermore, when forming a Schottky barrier diode as a vertical semiconductor device, its forward voltage V
F can be made smaller, and the chip area can be made smaller accordingly. Therefore, in combination with the availability of large fetches as described above, a large number of chips can be formed from a single wafer, improving yields and further reducing costs. Furthermore, when a power MOS FET is formed as a vertical semiconductor device, there is an advantage that the on-resistance can be kept low.

[Brief explanation of the drawing]

1(a) to 1(d) are cross-sectional views showing the structure in sequential manufacturing steps when forming a Schottky barrier diode using an embodiment of the semiconductor substrate according to the present invention; 3 is a cross-sectional view showing the structure of a Schottky barrier diode formed in the sequential manufacturing process using another embodiment of the present invention, and FIG. A cross-sectional view showing the structure of a barrier type diode. FIG. 4 is a cross-sectional view showing the structure of an example of a conventional Schottky barrier diode. 11...n-type silicon substrate 12.13...n-type number Scattered layer 1415...n-type scattered layer 6...n-type epitaxial layer 17...oxide film 1st...barrier metal film 9...metal electrode film 20...back electrode Film 21...n゛゛Semiconductor substrate 22.23...n+-
Type diffusion layer 24...n~ Epitaxial layer 25...N type epitaxial layer 26...Oxide film 27...Barrier metal film 28...
Metal electrode film 29... Back electrode film 31...n
゛゛Semiconductor substrate 32, 33...n ~ Epitaxial layer 34...n
Type epitaxial layer 35...Oxide film 36...Barrier metal film 37...Metal electrode film 38...Metal electrode film Fig. 1 Fig. 2 (a)

Claims (1)

[Claims] 1. In a semiconductor substrate used for a vertical semiconductor device, a semiconductor substrate containing an impurity of one conductivity type, and an impurity of one conductivity type formed by deeply diffusing into the semiconductor substrate from one surface thereof. a second semiconductor layer formed on the first semiconductor layer and containing an impurity of one conductivity type having a smaller diffusion coefficient than an impurity of one conductivity type contained in the first conductor layer; A semiconductor substrate for a vertical semiconductor device, comprising a third semiconductor layer formed on the second semiconductor layer and containing impurities of one conductivity type at a low concentration. 2. In a semiconductor substrate used for a vertical semiconductor device, a semiconductor substrate containing an impurity of one conductivity type, and a semiconductor substrate containing impurities of one conductivity type having a diffusion coefficient smaller than the diffusion coefficient of the impurity on both surfaces of the semiconductor substrate. first and second semiconductor layers formed on the first semiconductor layer;
1. A semiconductor substrate for a vertical semiconductor device, comprising: a third semiconductor layer containing impurities of one conductivity type at a low concentration. 3. When manufacturing a semiconductor substrate for use in a vertical semiconductor device, first and second semiconductor layers are formed by introducing impurities of one conductivity type at a high concentration from both surfaces of the semiconductor substrate containing impurities of one conductivity type. a step of forming, on the surface of the first semiconductor layer, a first epitaxial layer containing an impurity of one conductivity type whose diffusion coefficient is smaller than that of the impurity contained therein; A method for manufacturing a semiconductor substrate for a vertical semiconductor device, comprising the step of forming a second epitaxial layer containing impurities at a low concentration.