JPH0266977A - Semiconductor diode - Google Patents

Abstract

PURPOSE:To perform high frequency switching without strikingly increasing the thickness of the entire body of a semiconductor layer by providing a buffer layer having intermediate concentration between both-conductivity type high impurity concentration regions and low impurity concentration layers which are provided for ohmic contact and sucking of minority carriers. CONSTITUTION:As an impurity element for forming a p-type semiconductor layer 1, B, Ga, Al or the like is diffused from one surface of an n-type silicon substrate. As impurity elements, P and the like are diffused from the other surface of the silicon substrate. An n-type buffer layer 7 with higher concentration than an n<-> layer 2 which is the substrate itself is formed. At first, a diode having a p-n<->-n structure is formed. After the formation of the n-type buffer layer 7, an n<+> layer 3 and a p<+> layer 4 having high impurity concentration are formed in a mosaic pattern from the surface of the layer 7 so that the regions are shallower than the depth of the n-type buffer layer 7. The impurity concentration of the n-type buffer 7 is made higher than that of the n<-> layer but made lower than that of the n<+> layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor diode having one pn junction and capable of high-speed switching.

[Conventional technology]

In order to ohmically connect one semiconductor layer forming a pn junction with a metal electrode, when minority carriers are injected into the semiconductor layer, majority carriers are immediately injected from the metal electrode side toward the semiconductor layer side. Therefore, a barrier to majority carriers is not formed so that the minority carriers injected into the semiconductor layer are neutralized, and the minority carriers injected into the semiconductor layer are absorbed and annihilated by the metal electrode side. It is desired that no barrier to minority carriers be formed so that minority carriers are not accumulated unnecessarily between the semiconductor layer and the metal electrode. To meet this demand, Japanese Patent Publication No. 59-49711 discloses a semiconductor diode having a cross-sectional structure shown in FIG. 2. In this structure, a low impurity concentration n-
A p-n junction is formed by layer 2, and high impurity concentration n, Sl regions 3 and p'' are formed on the surface of n-layer 2 opposite to pm.
The neck regions 4 are provided in contact with each other. And n +
A metal electrode 5 is provided on the exposed surfaces of the 61 region 3 and the p0 region 4.
is in ohmic contact and serves as a cathode electrode.

On the other hand, a metal electrode 6 is in ohmic contact with the exposed surface of the 9-layer 1, which has a higher impurity concentration than the n-layer 2, and serves as an anode electrode. The p' region 4 in contact with the n-layer 2 has pJ
It has the effect of sucking out holes, which are minority carriers, injected into the n-layer 2 from the il, reducing the amount of holes accumulated in the n-layer 2, and as a result, reducing the reverse recovery current of the diode. It also has the effect of shortening the reverse recovery time.On the other hand,
As shown in FIG. 3, the p9 region 4, which serves as a suction port for minority carriers, is provided dispersedly within the n'' region 3, where there is substantially no barrier to majority carriers between the p9 region 4 and the metal electrode 5. .

[Problem to be solved by the invention]

When the reverse breakdown voltage of the semiconductor diode is 1000 V or more, the layer on one side of the pn junction, in the case of Figure 2, the n-layer 2
It is necessary to select a high specific resistance. As a result, n-IW2
When a reverse voltage is applied, the depletion layer expands, and n
- The thickness of layer 2 increases. That is, the thickness of n-Ji2 needs to be increased so that the other end of the depletion layer does not reach p' region 4. However, as the thickness of the n-layer 2 increases, the total amount of minority carriers accumulated in the n-layer 2 inevitably increases, and even if a p''d region is provided that acts as a suction port for minority carriers, The drawback is that the reduction in reverse recovery current is insufficient and high frequency switching of the diode cannot be performed.

An object of the present invention is to solve the above-mentioned problems, and to provide a layer with high impurity concentration as a suction port for minority carriers between the first conductivity type layer with low impurity concentration in the semiconductor layer forming the pn junction and the metal electrode. An object of the present invention is to provide a semiconductor diode that can perform high-frequency switching without significantly increasing the thickness of the entire semiconductor layer even if layers of other conductivity types are provided.

[Means to solve the problem]

In order to solve the above problems, a p-n junction is formed by a low impurity concentration semiconductor layer of the -R conductivity type and a high impurity concentration semiconductor layer of the second conductivity type; A semiconductor layer of the first conductivity type is provided between the anti-pn junction side surface of the semiconductor layer and a plurality of semiconductor layer regions of the first and second conductivity types with high impurity concentrations that are adjacent to each other on the side surfaces and in ohmic contact with the metal electrodes at their respective end surfaces. It is assumed that a semiconductor layer having an impurity concentration between these is interposed.

[Effect]

The first conductivity type layer with an intermediate impurity concentration, which is provided on the anti-pn junction side of the first conductivity type layer with a low impurity concentration forming the pn junction, has a depletion layer that expands when a reverse voltage is applied to the pn junction. It acts as a buffer layer to prevent minority carriers from reaching the high impurity concentration region of the second conductivity type, which serves as a suction port for the metal electrode. The minority carrier extraction ability of the shaped region is not significantly reduced.

〔Example〕

FIGS. 1(al) and (b) show an embodiment of the present invention, and FIG.
゜The same parts as in Fig. 3 are given the same reference numerals.

As is clear from FIG. 1 (al), in this embodiment, an n-buffer layer 7 is provided between the low impurity concentration n-layer 2 and the high impurity concentration n'' region 3 and p'' region 4. is produced in the following process. B, Ga,
Or spread M etc. P or the like is diffused as an impurity element from the other surface of the silicon substrate to form an n buffer layer 7 having a higher n-N2 than the original substrate. In this way p
First, a diode having an nn structure, a so-called pin junction structure, is formed. At this time, since there is an n buffer layer 6, n-
The thickness of layer 2 is as follows when applying the required rated reverse voltage:
The thickness of the depletion layer can be chosen to be smaller than the thickness of the depletion layer in the case of a diode without the 18771 layer. The expansion of the depletion layer stops within the n-buffer layer 7. After the formation of the n-buffer layer 1i, the n'' region 3 and the p0 region 4 having a high impurity concentration are selectively formed from the surface thereof in a mosaic shape as shown in Figure 1), and at a depth shallower than the depth of the n-buffer layer 7. do.

The n'' region 3 is used to efficiently inject electrons, and the p'' region 4 serves as a suction port for holes, which are minority carriers injected in n-N2. is higher than that of the n-layer 2, but lower than that of the n 6 ml region 3, so it does not have a negative effect on the effect of sucking out holes from the p0 region. By forming the p0 region 4 into a mosaic shape, the total area of the p0 region 4 becomes larger, so that the sucking effect becomes larger than in the case shown in FIG.

a metal electrode in ohmic contact with the surface of pIiIl, n″
The semiconductor diode shown in FIG. , it is also possible to form an inverted n-type semiconductor diode.

〔Effect of the invention〕

According to the present invention, a double conductivity type is provided for ohmic contact and for sucking out minority carriers on the anti-pn junction side of a low impurity concentration forming a pn junction of a semiconductor diode, which is known from Japanese Patent Publication No. 59-49711. By interposing an intermediate concentration buffer layer between the high impurity concentration region and the low impurity concentration layer, it is possible to stop a depletion layer from expanding to the low impurity concentration layer when a reverse voltage is applied. As a result, the thickness of the low impurity concentration layer can be made 20% or more thinner than the conventional one, which greatly improves the reverse recovery characteristics of high voltage diodes, making them usable for high frequency switching applications.

Furthermore, it has been confirmed that the reverse recovery current can be further reduced by implanting a heavy metal element such as gold or irradiating the semiconductor diode according to the present invention with a high-energy particle beam such as electrons or radiation.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) show an embodiment of the present invention, and (a)
1 is a cross-sectional view, (b) is a plan view of the (al) semiconductor substrate as seen from the cathode electrode side, FIG. 2 is a cross-sectional view of a known semiconductor cross-sectional view, and FIG. FIG. 1: 9 layer, 2: n-layer, 3: n0 ohmic contact area,
4: p゛minority carrier sucking region, 5: cathode electrode, 6: anode electrode, 7: n bar Fig. 2 Fig. 1 Fig. 3

Claims (1)

[Claims] 1) having a pn junction formed by a semiconductor layer of a first conductivity type with a low impurity concentration and a semiconductor layer of a second conductivity type with a high impurity concentration, and an anti-pn junction side surface of the semiconductor layer of the first conductivity type; A semiconductor having a first conductivity type and an intermediate impurity concentration between the first and second conductivity type semiconductor layer regions having high impurity concentrations that are adjacent to each other on the side surfaces and in ohmic contact with the metal electrodes at the respective end faces. A semiconductor diode characterized by intervening layers.