JPS587057B2 - Hand tie souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a high-voltage planar element whose bonded end faces are protected with boron nitride.

In a conventional planar structure semiconductor device in which the PN junction end face is protected with a silicon oxide film, the causes of a decrease in breakdown voltage are (1) concentration of electric field on the curved part of the junction face and (2)
It is considered that the electric field is concentrated on the surface of the silicon oxide film and at the interface portion due to positive charges existing in the silicon oxide film.

To solve this problem, the depletion layer on the surface of the silicon substrate can be expanded to reduce electric field concentration.

For this purpose, a structure using a field plate extending to the substrate surface with an oxide film interposed between the center electrode or a structure including a guard ring has been considered.

In a structure using a field plate, a large voltage is applied to the oxide film between the tip of the depletion layer and the tip of the plate, so it is practically impossible to achieve a very high breakdown voltage.

Therefore, a structure in which a high-resistance layer is layered on top of the silicon oxide film has been tried, but this results in an increase in leakage current flowing through the high-resistance layer.

Note that the structure having a field plate has the disadvantage that it is unsuitable for high frequency devices because the capacitance between terminals increases.

In addition, the structure using a guard ring requires design and manufacturing considerations for various factors that determine withstand voltage, such as the distance between the main junction and the guard ring junction, the charge density at the interface between the insulating film and the substrate, and the depth of the junction. There are many problems, and in principle no great effect can be obtained, especially for shallow junctions.

The purpose of this invention is to induce positive charges on the surface of an N-type silicon substrate by using a boron nitride film, which is conventionally used as a crucible material, as an insulating film.
An object of the present invention is to provide a semiconductor device with a high breakdown voltage by widening the width of a depletion layer on the surface of a substrate.

Still another object of the present invention is that by depositing a boron nitride film,
It is an object of the present invention to provide a semiconductor device in which the depletion layer extends to the cut side surface of the element in an appropriate manner.

According to the present invention, it is possible to obtain a semiconductor device which has effectively improved breakdown voltage even for a planar type device with a shallow junction, without the disadvantages of the method using a field plate.

Furthermore, a semiconductor device that does not exhibit unstable characteristics due to excessive expansion of the depletion layer can be obtained.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a technology related to the present invention, in which 1
is an N-type silicon substrate, and 2 is a P-type silicon substrate formed by diffusing P-type impurities using an oxide film mask on the N-type silicon substrate.
It is a type layer.

3 shows a PN junction, and 4 shows a protective film of boron nitride that was coated on the silicon surface by sputtering after removing the oxide film after forming the P layer, and then masking it with a silicon oxide film and immersing it in a heated phosphoric acid solution. and partially remove the boron nitride film on the surface of the P layer 2 to expose the surface of the P layer 2,
An electrode 6 is formed there, and an electrode 7 is formed on the back surface.

5 represents a silicon oxide film used as a partial etching mask for the boron nitride film.In a semiconductor device having such a structure, 1012
Since there is a large amount of negative charge on the order of cm-2, the surface of the depletion layer 11 shown by the dotted lines 8 and 9 in the figure expands, resulting in a high breakdown voltage.

FIG. 5 is a diagram showing the effect of improving the withstand voltage characteristics of the diode having the structure shown in FIG. 1, where X on the horizontal axis is the junction depth and the vertical axis is the withstand voltage vB. Due to the characteristics of the diode according to the present invention, the specific resistance of the N-type substrate 1 is 30 to 40Ω-α
The thickness of the boron nitride film 3 is 5000.

Curve 13 shows the characteristics of a diode using a conventional SiO protective film, and as is clear from the figure, the withstand voltage has been significantly improved from the conventional approximately 600 volts to 1000 to 1050 volts, and the junction is shallow. In this case, no decrease in pressure resistance was observed.

FIG. 2 shows another example related to the present invention in which the surface layer with many recombination centers is removed by etching and then covered with a boron nitride film 4 and a silicon oxide film 5 to further reduce leakage current.

Figure 3 shows a guard ring 10 made of a highly concentrated n+ layer to prevent properties from deteriorating due to mechanical strain on the side surfaces during cutting, etc. when the depletion layer extends to the side surfaces of the device due to the deposition of the boron nitride film. was formed.

Due to the presence of the guard ring layer 10, the outer edge line 8 of the depletion layer
ends at the guard ring 10, and therefore the depletion layer does not extend to the cut side surface, where the characteristics are unstable, so that instability factors due to the cut side surface can be avoided.

FIG. 4 shows an embodiment of the present invention in which an undesired extension of the outer edge of the depletion layer is prevented by depositing a silicon oxide film on the surface near the periphery of the element. The film 3 is deposited only on the substrate surface where the depletion layer 11 extends from the exposed end of the PN junction 3 to the vicinity of the device periphery, and on and outside of this boron nitride film 3, silicon is deposited so as to surround this film. An oxide film 5 is deposited.

In the structure of the embodiment shown in FIG. 4, the outer edge line 8 of the depletion layer 11 ends at the silicon oxide film 5 at the periphery of the device and does not appear on the cut side surface. As in the case of the technology, the depletion layer is prevented from being exposed on the unstable cut side surface, and the device withstand voltage characteristics do not become unstable.

As mentioned above, the semiconductor device of the present invention has dramatically improved withstand voltage by using a boron nitride film instead of the conventional silicon oxide film as the insulating film for protecting the junction end face.
In particular, the withstand voltage has been effectively improved without any discrimination even for elements with shallow junctions where the effect of the guard ring was not so apparent. This combination has the superior effect of suppressing the undesired excessive expansion of the depletion layer and avoiding the adverse effects of the cut side surfaces.

Furthermore, since the boron nitride film has good thermal conductivity, it also has the effect of particularly improving heat dissipation characteristics.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an example of a semiconductor device related to the present invention, Figure 2 is a cross-sectional view of an example in which the surface is etched to further improve performance, and Figure 3 is a cross-sectional view of an example in which a guard ring is provided. 4 is a sectional view of a semiconductor device according to an embodiment of the present invention in which a silicon oxide film covers the periphery of the element and a boron chloride film is provided inside the silicon oxide film, and FIG. 5 is a diagram of FIG. 1 related to the present invention. FIG. 3 is a curve diagram for explaining the effect of the semiconductor device of FIG. In the figure, 1 is an N-type silicon substrate, 2 is a P-type impurity diffusion layer, 3 is a PN junction, 4 is a boron nitride film, 5 is a silicon oxide film, 8 is an outer edge line of the depletion layer, 9 is an inner edge line of the depletion layer, 11 indicates a depletion layer.

Claims (1)

[Claims] 1. In a planar semiconductor device that has a PN junction formed by diffusing P-type impurities into an N-type substrate, and the end face of this junction is protected by an insulating film, protection of the peripheral part of the element in the edge film protective film is used. 1. A semiconductor device characterized in that the film is made of a silicon oxide film, and the protective film on the inner side mainly in a portion where a depletion layer spreads is made of a boron nitride film.