JPS6248371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device provided with a glass coating for surface stabilization.

Surface stabilization of semiconductor elements is an important issue especially for improving the reliability of semiconductor devices that require high breakdown voltage, and many techniques have been developed in this regard. On the other hand, a hermetically sealed type in which the element is hermetically sealed in a case is the best way to cut off the influence of the outside world on the element, but a resin sealed type is also widely adopted because it is extremely attractive from a cost standpoint. In order to obtain a resin-sealed semiconductor device with high breakdown voltage, the problem of surface stabilization becomes more important in order to prevent the influence of electric charge in the mold resin. There are silicon dioxide films, silicon nitride films, organic protective films, etc. as surface insulating protective films for surface stabilization, but glass protective films have a sufficient protective effect and are more effective than other surface protective films. It has the advantage of low processing cost.
However, if the thickness of the glass film is made thicker, the semiconductor chip becomes more warped, the glass film is more likely to crack, and subsequent microfabrication becomes difficult. On the other hand, when a glass film is made thinner, if its thickness is uneven and its cross section is corrugated, pinholes will occur more frequently in the thinner portion, resulting in a weak point as a protective film.

The object of the present invention is to obtain a highly reliable semiconductor device which is economically applicable and prevents pinholes from forming in a glass protective film, especially in a resin-sealed type.

The purpose of this is to attach a glass protective film to the surface of the guard ring part provided in the maximum depletion layer region in parts so as to remove an insulating thin film part that covers at least 40 μm of the width of the part, and to attach each protective film separately. This is achieved by setting the width of the membrane to 500 μm or less.

The present invention will be described in detail below with reference to figures and experimental data.

FIG. 1 shows a cross section of a semiconductor element of a high breakdown voltage planar structure thyristor. A p-type region is provided by diffusion from both sides of the n-type substrate, and an n ⁺ region is further provided by diffusion into one p-type region to form a pnpn structure, and an anode electrode 1, a cathode electrode 2, and a gate electrode 3 is fixed. Furthermore, during the above diffusion, a p-type guard ring layer 4 is simultaneously formed in the n-base region.
and n-type guard ring layer 5 are provided, respectively. In the figure, a glass film 7 covers the electrode parts 2 and 3 and the end part 6 of the semiconductor piece.
An oxide film is left on the end portion 6 to serve as a mask during selective diffusion. However, in such a case, since the glass film 7 is wide, the film thickness is not uniform and shows a waveform as shown in the figure, and pinholes occur more often in the thinner parts of the film, resulting in a decrease in the protective effect. . FIG. 2 shows the relationship between the glass film width W and the pinhole density in the glass film. The thickness t of the glass film in this case is 10~
The thickness is 20 μm, and if it is thicker than that, the above-mentioned disadvantages will occur, so it cannot be applied. As is clear from this figure, the pinhole density in the glass film increases rapidly when the width W of the glass film exceeds 600 μm.
As a result of research, it was found that this is related to the cross-sectional shape of the glass membrane. In other words, the width of the glass film is approximately
When it reaches 600 μm, it exhibits a waveform as shown in Figure 1.
Therefore, it is necessary to prevent the glass film from becoming corrugated. FIG. 3 shows a planar structure thyristor which is an embodiment of the present invention based on such knowledge.
In this thyristor element, a silicon dioxide film 8 used as a mask during selective diffusion is provided on the upper surface and end portion 6 of the p-type guard ring layer 4 provided in the n-base region and the n-type guard ring layer 5 for channel cutting. Only the other parts are covered with the glass film 9. As a result of such a glass film being divided, its width becomes 500 μm or less, but in order to satisfy this condition, placement of a guard ring may be considered if necessary.

It is desirable that the width of the oxide film sandwiched between the glass films is not too narrow. Otherwise, there is a risk that the glass film will climb over the oxide film and connect with the adjacent glass film, thereby loosing the effect of the present invention. According to experiments conducted by the present inventors, it has been confirmed that sufficiently satisfactory results can be obtained by setting the thickness to 40 μm or more. The remaining oxide film 8 is generally as thin as 2 μm or less, but since the surface potential gradient is low at the guard ring portion, it is sufficiently useful as a surface protective film. Other surface areas with high potential gradients are thicker than this and are covered with a glass film that has a reliable surface protection effect, making it possible to obtain a highly reliable semiconductor device even when resin-sealed. .

FIG. 4 shows a planar transistor according to another embodiment of the invention. In this case, the oxide film 8 covers the p-type guard ring layer 14 with a low surface potential gradient, the channel cut n-type layer, and the upper surface of the pn junction between the emitter bases, and the glass film 9 covers the surface between them. There is.

In the above embodiment, a silicon dioxide film is used as an insulating film other than a glass film, but this may be replaced with an oxide film containing phosphorus or boron, or a silicon nitride film or other insulating film. Since the insulating film other than the glass film is not limited to those having a surface protection effect inferior to that of the film, the portion covered with the insulating film other than the glass film does not need to be limited to a portion with a low surface potential gradient such as the guard ring portion in the above embodiment. Furthermore, any method such as electrophoresis, sedimentation, etc. can be used for installing the glass membrane on the surface.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional glass film-coated planar structure thyristor element, and FIG. 2 is a diagram showing the relationship between the width of the glass film and the pinhole density in the glass film.
FIG. 3 is a sectional view of a planar structure thyristor element showing one embodiment of the present invention, and FIG. 4 is a sectional view of a planar structure transistor element. 4, 14: p-type guard ring part, 5: n-type guard ring part, 8: silicon dioxide film, 9: glass film.

Claims (1)

[Claims] 1 At least one planar pn junction and the pn
It has a guard ring surrounding the junction, and a 500°
In the case where a glass protective film is applied with a width of 1 μm or more, the surface of the guard ring portion provided in the maximum depletion layer region is at least 40 μm in width.
The glass protective film is applied in parts to remove the insulating thin film covering the μm area, and the width of each protective film is
A semiconductor device characterized by having a thickness of 500 μm or less.