JPS5856255B2 - semiconductor element - Google Patents

Abstract

PURPOSE:To reduce a forward voltage drop by providing on the N<+> plane of a silicon substrate given numbers or more of crevices having a high contant of phosphorus so as to break off a re-grown layer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor element having a structure in which a metal support plate is adhered to the N0 surface of a silicon substrate.

A metal support plate made of tungsten or molybdenum is bonded to one or both sides of the silicon substrate in order to improve its mechanical properties.

On the one hand, this metal support plate also plays the role of an electrode.

Aluminum is used as an adhesive because of its good electrical conductivity,
Widely used due to its strong adhesive properties.

However, since the N0 surface of a silicon substrate generally has very coarse hemispherical protrusions with high P concentration, when aluminum is bonded to the N0 surface, the reaction between aluminum and N+ silicon causes P-type formation. A regrowth layer is generated over the entire surface of the N10 plane, resulting in an undesirable result that the forward voltage drop becomes large.

In order to solve these drawbacks, conventional methods have been to reduce the thickness of aluminum, rapidly cool the joint during joining, or add large amounts of pentavalent elements such as phosphorus and arsenic to the N-type surface layer. Methods have been taken to include it, but sufficient effects have not yet been achieved.

An object of the present invention is to provide a semiconductor element having a structure suitable for reducing forward voltage drop.

The present invention is based on the viewpoint that if the regrowth layer generated on the N0 surface of the silicon substrate is stopped, the forward voltage drop will be reduced, and a structure that can stop the regrowth layer has been investigated. The basic idea was that it was found that regrowth layers are difficult to grow in flea baths that contain phosphorus.

A flea bath with a high phosphorus concentration can be easily formed by diffusing red phosphorus into the N0 surface of a silicon substrate.

The number of flavours is controlled by adjusting the amount of red phosphorus and the temperature and diffusion time.

As an example, when the amount of red phosphorus is 3.6 to 4.6 g, phosphorus diffusion is performed at 1220°C for 1 hour and then at 1250°C for 4 hours, and the phosphorus glass produced during the diffusion is removed and then re-diffused. If 3.6 to 4.6 g of red phosphorus is diffused under the same conditions, 300 g of red phosphorus per 1 crfL is diffused on the N10 surface of the silicon substrate.
More than one frebas can be provided.

In addition, when making 13.8g of red phosphorus, 1 at 1160℃
ICrr if further diffused for 4 hours at 1250℃
300 or more flebaths can be provided per L.

An example of conditions when forming 350, 500, and 650 frevases is shown in the following table.

When the silicon substrate according to the present invention is provided with a high-phosphorus-concentration frebus on the N-plane, there is no need to add alloying elements to the aluminum adhesive, so there is an advantage that the adhesiveness does not deteriorate.

Examples of the present invention will be described in detail below.

FIG. 1 shows the relationship between the discontinuity rate of the regrown layer (ratio of areas where the regrown layer does not grow) and ΔFVD (increase in voltage drop due to the regrown layer).

It can be seen that as the breakage rate increases, ΔFVD decreases.

Figures 2a and 2b show the surface shape of the silicon substrate according to the present invention.

This figure a is enlarged 500 times on the N+ coating surface and has a vertical length of 52 μm1.
A 66 μm horizontal portion is shown.

The average number of freckles per ICr/L on this surface is 515, which is found to be larger than that of the conventional element, as will be described later.

FIG. 3 shows the relationship between the number of fleas per 1 cr/'L and the breakage rate of the regrowth layer.

It is clearly seen that as the number of flavours increases, the breakage rate of the regrowth layer increases.

Since a conventional semiconductor device has a ΔFVD of 0.3 to 0.4, it can be seen from FIG. 1 that this value can be obtained at a rate of discontinuity of the regrown layer of about 2.

Furthermore, it can be seen from FIG. 3 that in order to increase the breakage rate of the regrown layer to 2% or more, the number of flavours should be increased to 300 or more per 1 crI'L.

FIG. 4 is a photograph showing an embodiment of the present invention, and a is a scanning electron micrograph of a silicon substrate with aluminum deposited to a thickness of 5 μm on the N+ surface.

b is a scanning electron micrograph of the state shown in a after heat bonding at 720'C in a pure nitrogen atmosphere and after etching off the aluminum-silicon eutectic alloy.

Many frebuses are observed on the N plane of the silicon substrate.

C is a photograph showing the regrowth layer from both the cross section and the plane. Considering that the depression is the area where regrowth layer 1 has not grown, it is clear that the regrowth layer does not grow on the frebas. .

Reference numeral 2 represents the N+ surface of the silicon substrate.

Glass diodes were assembled using semiconductor devices according to the present invention and conventional semiconductor devices, and forward voltage drop values were measured.

The semiconductor device of the present invention has approximately 500 frebus per 1 cr/L.

In the conventional device, the forward voltage drop value varied in the range of 1.6 to 2.4 ■, with an average of 1.8 ■, but in the case of the embodiment of the present invention, the forward voltage drop value varied in the range of 1.6 to 2.4 ■. It only varied within a narrow range, and the average value was about 1.45V, which was significantly smaller than the conventional one.

In this manner, the semiconductor device of the present invention is produced with the regrowth layer interrupted.

Therefore, forward voltage drop can be reduced.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the relationship between the discontinuity rate of the regrown layer and ΔFVD, Fig. 2 a, l) are photographs showing the N-plane shape of the silicon substrate in an example of the present invention, and Fig. 3 is a characteristic diagram showing the relationship between the breakage rate of the regrown layer and ΔFVD. Characteristic diagram showing the relationship between the number and the breakage rate of the regrowth layer and Fig. 4a
, b, and c are photographs showing examples of the present invention. Explanation of symbols: 1...Regrowth layer; 2...N plane of silicon substrate.

Claims (1)

[Scope of Claims] 1. A metal support plate is bonded to the N0 surface of a silicon substrate, characterized in that 300 or more frebus having a high P concentration are provided per 1 crrL on the N1 surface of the silicon substrate. semiconductor elements. 2 Claim 1 in which the adhesive is made of aluminum
Semiconductor device described in section.