JPS5990947A - Semiconductor device - Google Patents

Abstract

PURPOSE:To effectively prevent the generation of soft error and improve fantastically the reliability by covering the active region of semiconductor substrate with an insulating cloth impregnated previously with the resin to be applied. CONSTITUTION:An insulating cloth 5 is formed as follow: namely, an insulating woven cloth of the nylong thread 6 in diameter of 100mum used as the raw material is impregnated with an impregnating agent 7 mixing an epoxy regin of the biphenol type and a hardening agent and it is then cut in accordance with the size of active region of the semiconductor substrate 1 of which surface should be protected. The surface of semiconductor substrate 1 is covered under the condition that a semiconductor device assembling body which has completed the processes up to electrode connection with fine gold lead 3 is heated up to about 150 deg.C. The insulated woven cloth is impregnated with resin and the substrate is heated and is covered using the insulating cloth under the condition that the impregnated resin is semi-hardened. Thereby, the impregnated resin once melts. The hardening reaction advances by continuing the heating under the equal temperature and it is hardened after about 30min. During such melting, the impregnated resin flows toward the edge of semiconductor substrate. As a result, the gradually inclined resin surface is formed at the area near the edge part.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to large scale integrated circuit memory devices whose storage signal meters are perturbed by alpha radiation emitted from uranium, thorium, etc. contained in the packaging material. The present invention relates to a semiconductor device having a structure that can effectively eliminate so-called soft errors.

Conventional Structure and Problems The package material, which is indispensable for manufacturing semiconductor devices, usually contains alpha-ray emitting atoms. The energy of the alpha rays emitted from this atom is 5 MeV on average.
It is said that the degree of The alpha rays with an energy of 5 MeV penetrate into Noricon to a depth of about 30 microns and disappear there. Until this extinction, the α rays generate electron-hole pairs in silicon, and the n-channel M
In an OS device, some of these electrons collect in the active region, causing malfunction. This malfunction is called a soft error. As a countermeasure to reduce soft errors caused by alpha rays, there are conventional methods by changing the air circuit or elemental structure constituting the semiconductor device, or by applying a retention film to the surface of the semiconductor element. 4) The former method includes, for example, a circuit method that increases the signal amount of the bit line, a circuit method that reduces the word line voltage by 4, a method that increases the sensitivity of the sense amplifier, or a method that increases the sensitivity of the sense amplifier.
The influence of alpha rays is reduced by increasing the size of the cell 7 and increasing the capacity. However, the latter method prevents alpha rays from reaching the active region of the semiconductor element by applying a protective film to the surface of the semiconductor element, and the thickness of the protective film is selected to be greater than the penetration depth of the alpha rays. This is a method in which α rays are extinguished within a protective film. The coating agents generally used for forming this protective film are polyimide resins and silicone resins, and in order to prevent soft errors, both
A coating thickness of microns or more is required.

By the way, in order to prevent soft errors, countermeasures such as changing the electric circuit or element structure constituting a semiconductor device include making a major change in the mask for manufacturing the semiconductor device due to the change in the electric circuit, or changing the memory cell size. There were disadvantages such as a decrease in the degree of integration due to an increase in .

On the other hand, the countermeasure method of applying a protective film is much simpler than the above-mentioned countermeasure methods, and does not have the above-mentioned disadvantages.

FIG. 1 is a diagram illustrating a conventional method of coating a surface of a semiconductor element with a protective film for preventing soft errors.

As shown in the figure, after bonding the semiconductor substrate 1 to the substrate bonding part 2 of the package and connecting the bonding panode on the semiconductor substrate 1 and the external leads with thin metal wires 3 such as gold wires, the surface is protected. It has a structure in which the film 4 is applied and cured. The surface protective film 4 is formed by a coating method in which a polyimide resin or a silicone resin is used as a coating agent, and a suitable amount of the resin is dropped onto the surface of the semiconductor substrate 1.

By the way, the cross-sectional shape of the coating film applied by this method has a circular arc shape. For example, if the size of the semiconductor substrate 1 is about 6 mm square and the distance a from the edge of the substrate to the active region is about 200 microns, the coating film thickness t1 will be maintained at 30 microns. The coating film thickness t2 at the center of the substrate is 350
~380 microns. Considering this coating film thickness t2r1, the depth of the cage cavity when sealing with ceramic or resin, or the height of the cage when sealing with resin, the desired coating film thickness exceeds 300 microns. Therefore, consideration must be given to keeping the coating film thickness t2 to 300 microns or less.

Another problem is that the resin dropped in the center of the board is
Due to the effect of surface tension, the end face is difficult to spread to the periphery of the substrate. It may be necessary to allow the solution to stand for one hour or more after dropping. On the other hand, if the substrate shape is rectangular, it may take even longer. Yet another problem is that it is difficult to control the amount of dripping. The dropping amount for the above substrate size is 9.7
The appropriate amount was 10.3 mg to 10.3 mg, but if this value was exceeded, the coating resin would flow out from the edge of the substrate and a protective film of the required thickness could be formed on the surface of the substrate. On the other hand, if the amount of dripping is small,
Inconveniences occur such as the resin not spreading at the edge of the substrate at -1. In order to regularly control the amount of drops of 1 milligram or less, it is necessary to maintain the dispenser reliably, which is one of the troublesome tasks in the manufacturing process.

OBJECTS OF THE INVENTION The present invention has a structure in which the active region of a semiconductor substrate is covered with an insulating cloth pre-impregnated with the resin to be applied, thereby improving the conventional method of applying the resin before forming a surface protective film. The object of the present invention is to provide a semiconductor device 1σ which eliminates problems caused by the coating process such as variations in coating film thickness or problems in coating operations such as difficulty in controlling the amount of resin dripped. 'Structure of the Invention The semiconductor device of the present invention is characterized by a structure in which at least the active region of the semiconductor substrate is covered with an insulating cloth impregnated with resin, and the thickness of the surface protective film for preventing soft errors is The present invention not only facilitates control of the process, but also simplifies the process of forming the surface horizontal preservation film, and the present invention realizes a semiconductor device with sufficient measures against soft errors.

DESCRIPTION OF EMBODIMENTS In the semiconductor device of the present invention, polyimide resin or 1
,/Instead of a structure in which a polymer resin such as silicone resin is applied dropwise directly onto a semiconductor substrate, an insulating cloth impregnated with a polymer resin is cut to a predetermined size, and this insulating cloth is applied to an active area on a semiconductor substrate. It has a structure in which it is aligned and coated. The impregnating polymer resin, which is a component of this insulating cloth, is liquid at room temperature, and after being impregnated into the insulating cloth, it is heated to a semi-hardened state. Industrially, it is most desirable to use a resin such as a bisphenol type epoxy resin, which can be completely cured by heat treatment after being coated. Further, as the insulating cloth, a woven cloth made of synthetic resin fibers is excellent in terms of ease of use, but it does not necessarily have to be a woven cloth.

Furthermore, the polymeric resin for impregnation is
Fully cures within 11Jr! 1! It is desirable that the material has high properties, and it is satisfactory if it can be completely cured under four-temperature curing conditions of 150° C. for about 30 minutes. If an insulating cloth impregnated with such a polymer resin is used, the semiconductor device can be assembled by heat treatment during curing, although the thermal expansion coefficients of the materials used during assembly and the semiconductor substrate do not necessarily match. There is no risk of mechanical damage or deterioration of electrical characteristics.

FIGS. 2 and 3 are cross-sectional views illustrating the specific structure of the insulating cloth used in the present invention and the semiconductor device of the present invention having the above-described structure.

The present invention will be explained in detail below with reference to FIGS. 2 and 3. The insulating cloth 5 shown in FIG.
For example, it is formed by impregnating it with an impregnating agent 7 that is a mixture of a biphenol type epoxy resin and a curing agent, and cutting it in accordance with the XJ method of the active region of the semiconductor substrate 1 whose surface is to be excavated. FIG. 3 is a diagram showing the state in which the surface of the semiconductor substrate 1 is coated with this insulating iJ5, and the semiconductor device assembly structure, which has been completed with the electrode connection dimension using the gold wire + Mll wire 3, is heated to about 150°C. It is formed by covering the surface of the semiconductor substrate 1 in this state. By the way, when an insulating cloth is impregnated with a resin, heated and cooled, and the impregnated resin is semi-hardened, the insulating cloth is heated and coated under the temperature conditions specified in J2, the impregnated resin melts once. . and,
By further continuing isothermal heating, the curing reaction progresses and the film is cured in about 30 minutes. During this melting, the impregnated resin flows out toward the end surface of the semiconductor substrate. As a result, as shown in FIG. 3, a gently sloped resin surface is formed near the end. The thickness t2' of the surface protective film thus formed at the center of the semiconductor substrate is determined by the thickness of the insulation cloth 5, and is 200 to 250 microns thick. still,
The thickness t1' of the resin within the distance a from the edge of the semiconductor substrate to the substrate active region is also maintained at about 50 microns. In other words, the entire area on the semiconductor substrate was covered with a protective insulating film thick enough to prevent the knot error effect caused by alpha rays, and the maximum thickness was set to a value that would not cause any problems with packaging. A semiconductor device was formed.

Effects of the Invention According to the present invention, the thickness of the protective insulating film that prevents α rays emitted from the package material from reaching the surface of the semiconductor substrate is approximately equal to at least the entire area over the active region. A uniform semiconductor device is realized, the occurrence of soft errors is effectively prevented, and the reliability of the semiconductor device 1δ is dramatically improved.

However, as long as the thickness of the protective insulating film is uniform and less than a predetermined value, there will be no inconvenience during packaging.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the semiconductor substrate portion of a semiconductor device having a protective insulating film for preventing soft errors manufactured by a conventional method, and FIG. 2 is a diagram showing the configuration of an insulating cloth used in the semiconductor device of the present invention. , FIG. 3 is a cross-sectional view of the semiconductor substrate portion of the semiconductor device of the present invention. , 4... Surface protective film, 5... Insulating cloth, 6... Nylon thread,
7... Impregnating agent (resin).

Claims (3)

[Claims] (1) A semiconductor device characterized in that at least an active region of a semiconductor substrate is covered with a protective insulating film made of an insulating cloth impregnated with resin. (2) The semiconductor device according to claim 1, wherein the insulating cloth is formed by impregnating a synthetic fiber woven cloth with a resin. (3) The semiconductor device according to claim 1, wherein the semiconductor substrate is a large-scale integrated circuit memory element substrate.