JPS58128765A - High dielectric-resistance semiconductor element - Google Patents

Abstract

PURPOSE:To prevent the increase of field strength in the surface, and to improve dielectric resistance by making the gradient of impurity concentration smaller in a peripheral bevel section not related with the conduction of the high dielectric- resistance semiconductor element having negative bevel structure. CONSTITUTION:P-layers 2, 3 are formed by the diffusion of the impurity of both surfaces of an N type Si board 1, and an N<+> layer 4 is formed by the diffusion of a donor impurity. The exposing section of a reverse dielectric-resistance junction 8 is made a positive bevel and the exposing section of a forward dielectric- resistance junction 9 a negative bevel. In a high dielectric-resistance semiconductor having such constitution, high surface impurity-concentration is required only in an electrode coating region A, and a peripheral section B is releated only to the voltage stopping power of the element, not in conduction. Consequently, the profile of the impurity concentration of a layer such as the P- layer 3 is held in surface impurity-concentration required for ohmic contact with a cathode electrode in a central section A, and the profile is made gentle extending over the whole direction of depth in the peripheral section B. Accordingly, the field strength of the surface can be weakened by making a depletion layer extensible in a peripheral bevel section.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high voltage semiconductor element having a negative bevel structure at the periphery of one surface of the semiconductor and an electrode provided at the central plane portion.

In semiconductor devices that require high breakdown voltage, a bevel structure in which the surface of the semiconductor body is inclined with respect to the PM junction is well known. There are two types of bevel structures: positive bevel and negative bevel, and a typical example that utilizes both is the thyristor. FIG. 1 shows such a high voltage thyristor, in which pegs and 3 are formed by diffusion of acceptor impurities from both surfaces of a Y-shaped silicon plate 1, and then the entire surface of the silicon plate 1 is oxidized by a post-photoetching method. In the area where the membrane was removed,
Diffusion of donor impurities, such as phosphorus, provides a summer layer. pi@12 is provided with aluminum electrodes 6 and 7, which are made of aluminum and serve as a soode electrode and a gate electrode, respectively. Furthermore, by mechanical or chemical surface shaping, the exposed portion of the reverse pressure-resistant joint 8 is made to have a positive bevel, and the exposed portion of the forward-direction pressure-resistant joint 9 is made to be a negative bevel. After that, a surface protective film (not shown) is applied. For 2M13,
In order to make the gate electrode on the upper surface of the silicon plate 1 or the cathode electrode in the emitter short-circuit structure (not shown) light and reduce the electric field distribution on the surface, double diffusion of aluminum and gallium or aluminum and boron is used to form the structure shown in FIG. A bifurcated impurity distribution is created. In addition, in the thyristor, unless the impurity concentration of the P base layer 3 close to the junction with the end emitter layer 4 is high, there is a problem that the thyristor becomes too easy to ignite. In such an impurity distribution, as the forward blocking voltage applied to the thyristor increases, the depletion layer that spreads on both sides of the junction 9 expands toward the P base region side at the front of the Ga or 1 diffusion indicated by a in the aWJ. After that, the depletion layer will only expand towards the summer pace region.

In view of this, the present invention prevents the increase in electric field strength at the surface due to the prevention of the spread of the depletion layer near the surface of the negative bevel structure, and provides a semiconductor element with less risk of occurrence of breakdown at the surface. The purpose is to

The purpose of this is to create a layer on the high impurity concentration side of the junction formed by the bevel structure in a high-voltage semiconductor that has a negative bevel structure on the periphery of one surface of the semiconductor body and an electrode on the central plane part. This is achieved by making the slope of the impurity concentration in the peripheral portion in the thickness direction, at least in the region far from the junction, more gradual than that in the central portion.

Embodiments of the present invention will be described below with reference to the drawings. In the present invention, a high surface impurity concentration for ohmic contact or for adjusting the firing sensitivity of the thyristor is required only in the electrode deposition area shown as A in FIG. 1, and the peripheral area shown as B in FIG. Based on the recognition that the impurity concentration of the second layer 3 is the same as the conventional one, as shown by the solid line 31 in FIG. , dotted line 32 at the periphery B
Make it gentle throughout the depth direction as shown in .

In order to form these two types of impurity concentration profiles, as shown in FIG. The mixture is vacuum sealed in a quartz ampoule with the Mul sauce and the B sauce, and heated for a long time. Since the oxide film has a diffusion effect of 1, the diffusion front of Al reaches the point li[9 in Fig. 4, but the diffusion front of B reaches point l1.
It will have a shape like ll. That is, with only one diffusion step, a profile shown by the solid line 31 in FIG. 3 in the central part and a profile shown by the dotted line 3z in the peripheral part can be obtained. As a result, in the case of the conventional B diffusion front surface 12 in FIG. The electric field at the surface is suppressed to a low level, and breakdown at the surface is prevented, so the forward breakdown voltage of the thyristor is improved. In the beveled portion of the periphery, the slope of the impurity concentration is made smaller so that the depletion layer can expand, thereby weakening the strength of the electric field at the surface.

Such two types of impurity concentration profiles are, for example, 7.
In the layer, boron and aluminum can be simultaneously diffused in one diffusion process by utilizing the boron shielding effect of the oxide film, so it is possible to obtain an element with improved breakdown voltage extremely easily. The present invention can be effectively applied not only to diodes, triacs, etc., but also to diodes, triacs, etc., as long as they have a negative bevel structure.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a high voltage thyristor that is an example of the present invention, Figure 2 is an impurity concentration profile diagram of an example of a conventional high voltage thyristor, and Figure 3 is an embodiment of a high voltage thyristor according to the present invention. Figure 4 is a cross-sectional view showing the method of creating the impurity concentration profile, Figure 4 is a cross-sectional view showing the difference in the spread of the depletion layer between the conventional example and the embodiment of the present invention in a negative bevel structure It is. 1: silicon plate, 9FPN junction, 11: boron diffusion front. Fig. 2 Fig. 73 C-+ Tsukasa → Utsui Fig. 74 Fig. 5 2

Claims (1)

[Claims] 1) In a semiconductor element having a negative bevel structure at the periphery of one surface and an electrode provided at the central plane part,
A high-voltage semiconductor device characterized in that, in at least a region of a layer on the high impurity concentration side of a junction where a bevel structure is formed, the slope of the impurity concentration at the periphery in the thickness direction is gentler than that at the center. .