JPS6136709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and particularly to a semiconductor device formed by sealing a semiconductor element such as a dynamic memory.

In general, semiconductor elements are usually sealed with a sealing body made of ceramic, glass, plastic (resin), or the like. Among these sealed bodies (hereinafter referred to as packages), the ceramic materials of ceramic packages in particular contain about ppm of uranium (U), thorium (Th), and the like. These impurities are e.g.
proceedings of reliability physics (1978), p88
As described in
It is known that wires can cause memory devices to malfunction. For this reason, the reliability of the semiconductor device may be significantly reduced.

The energy distribution of spontaneous decay of U and Th is 4~
Although the α rays generated in the package material lose energy due to collisions with molecules before reaching the surface of the material, the energy distribution of the α rays emitted from the package is 0 to 9 MeV.

When this alpha ray enters the Si pellet, it excites electrons and travels while gradually losing energy. Therefore, the range of alpha rays in a substance is inversely proportional to the density of the substance and proportional to its initial energy. In Si
When exciting electrons at 3.6eV and 5MeV, the range is about 25μ
It is m. Further, when electrons are excited in Si, holes are also generated, and electron-hole pairs are generated along the trajectory of the α ray. The number of excited electrons Ne here is Ne5MeV/8.6eV=1.4×10 ⁶ when the α-ray energy is 5MeV. This is an amount of electricity of 0.22 pgrons. Thereafter, the charge disappears due to diffusion and recombination due to the concentration gradient, but this charge is captured by the bias, and when it reaches a value that cannot be ignored compared to the amount of charge under a certain boundary condition of the pellet, a malfunction occurs. This malfunction is called a soft error because it occurs without damaging the physical properties of the device.

To prevent such malfunctions, α is applied to the surface of the active region of the semiconductor chip before sealing the package.
It has already been proposed to apply a polyimide resin layer for radiation shielding. However, in this case, in order to obtain a sufficient α-ray shielding effect, it is necessary to
It is necessary to uniformly apply a resin coating to the above thickness, and the current coating technology has the drawback that it is not easy to apply such a coating.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device in which malfunctions caused by alpha rays in an active region are prevented without having such drawbacks.

In the semiconductor device according to the present invention, α-ray shielding resin is applied to the surface of the active region of the semiconductor chip, and an α-ray shielding member is provided on the inner surface of the recess of the cap of the package. The thickness of the shielding resin layer is reduced to simplify the formation process, and the embodiment shown in the accompanying drawings will be described in detail below.

FIG. 1 shows a semiconductor device according to an embodiment of the present invention, in which an insulating base 10 made of ceramic
A large number of lead wires 12 are bonded to the periphery of the upper surface by a low melting point glass layer 11, and the base 10
A semiconductor chip 14 is fixed to the bottom of the recess at the center of the upper surface via an adhesive layer 13 made of Au foil or an Au metallized layer. This semiconductor chip 14 is made of, for example, silicon, and has an active region, which is likely to malfunction when irradiated with alpha rays, and which includes a memory cell, etc. (to be described later), usually having a depth of about 4 to 5 .mu.m. A large number of electrodes on the semiconductor chip 14 are electrically connected to corresponding leads 12 by a large number of bonding wires 15, respectively.

Semiconductor chip 1 after wire bonding
An α-ray shielding resin layer 16 made of a polyimide-based resin such as polyimide-isoindolo-quinazolindeion is deposited on the substrate 4 so as to cover the active region on its surface. This resin layer 1
6 may have a thickness of 30 to 50 μm.

On the other hand, the insulating cap 17 made of ceramic has a recess 17a on one main surface.
is placed on the base 10 so as to face the semiconductor chip 14. cap 17
A low melting point glass layer 18 is preliminarily applied to the joint surface facing the base 10 of the cap 17, and a glass layer 18 made of high purity Al, preferably five nines or higher, is applied to the concave portion 17a of the cap 17 so as to cover the entire inner surface of the concave portion 17a.
The wire shielding body 20 is fixed in advance with an adhesive layer 19 such as a low-melting glass layer or a metal solder, and after the cap 17 is superimposed on the base 10, it is heated to the melting point of the sealing glass layer 18 and then cooled. The base 10 and cap 17 are bonded to each other.

Here, the material of the α-ray shielding body 20 is not limited to high-purity Al, high-purity Si, etc. can be used, and a resin having the same α-ray shielding ability as the resin layer 16 described above can also be used. can. When using a conductive material such as Al or Si as the α-ray shield 20,
It is preferable to make the surface insulating through appropriate oxidation treatment from the viewpoint of preventing short circuits of the bonding wire 15. Further, the thickness of the α-ray shielding member 20 is related to the α-ray shielding effect and is preferably thicker, but an appropriate thickness is determined in relation to the thickness of the resin layer 16 described above. As an example, when the resin layer 16 is set to 30 to 50 μm, an Al plate having an arbitrary thickness of at least 50 μm may be used. Note that the α-ray shield 2 is placed so as to cover the entire inner circumference of the recess 17a.
Although it is most preferable to provide 0, the extent to which the inner surface of the recess 17a is shielded from α rays can be determined as appropriate in relation to the thickness of the resin layer 16 described above.

In the above configuration, the α rays are transmitted to the ceramics of the base 10 and the cap 17, the sealing glass layer 11,
Among them, alpha rays emitted from the base 10 are emitted from the semiconductor chip 14.
Since it has a thickness of 150 to 500 μm, by the time it reaches the active region on the chip surface, it has been weakened to the extent that it will not cause any malfunction, so it poses little problem. Therefore, the problem is that cap 17
The alpha rays from the cap 17 are sufficiently weakened by the alpha ray shield 20 and the resin layer 16, and the alpha rays from the sealing glass layers 11 and 18 are also weakened. Those having a relatively large angle of incidence on the chip 14 are sufficiently weakened by the α-ray shield 20 and the resin layer 16. and,
The chip 1 is designed to prevent alpha rays emitted from the sealing glass layers 11 and 18 from passing through the alpha ray shielding body 20.
The α rays entering the active region from the sides of the active region have a shallow angle of incidence, have a long distance to pass through the resin layer 16, and are hardly a problem due to the α ray attenuating effect of the resin layer 16.

Therefore, according to the above-described semiconductor device of the present invention, the α-ray shielding body 20 and the α-ray shielding resin layer 16 work together to sufficiently reduce the amount of α-rays incident on the active region, thereby reducing the amount of α-rays generated in the active region. This makes it possible to prevent malfunctions that may occur. Besides, α
By providing the radiation shielding body 20, the thickness of the α-ray shielding resin layer 16 to be deposited on the chip 14 can be reduced to a level that is easy to process in manufacturing, which simplifies the manufacturing process and facilitates manufacturing. Ancillary effects that can improve yield can also be obtained. In addition, inexpensive Al used as the α-ray shield 20
Generally speaking, metal materials such as
Although it is difficult to increase the degree of purification, the shielding effect of the resin layer 16 does not pose a problem even if a small amount of α-ray source is included, as long as it is below a certain limit, so an advantage of the combination is that there is no need to be too concerned about purity.

By the way, as mentioned above, the semiconductor device to which the present invention is applied has a semiconductor chip in which an active region is formed that may malfunction due to alpha ray irradiation.Next, some specific examples will be explained. do.

FIG. 2 shows the memory cell structure of a MOS type dynamic RAM (random access memory), and its equivalent circuit is shown in FIG.
20 is a P-type silicon substrate, on the surface of which a thick field SiO ₂ film 21 is formed;
A thin SiO ₂ film 21A is formed within the opening of the SiO ₂ film 21. 22 is an N ⁺ type diffusion region, 23 is a first low-resistance polysilicon layer, 24 is an interlayer insulating film made of phosphosilicate glass, 25 is a second low-resistance polysilicon layer, and 26 is a passivation film made of phosphosilicate glass. It is 26.
A part of the second polysilicon layer 25 disposed on the SiO ₂ film 21A acts as a gate of a MOS transistor Q whose source region is the N ^{+ type} diffusion region 22. The second polysilicon layer 25 is connected to the word layer W while being connected to the digit line DG. Substrate surface portion 2 corresponding to the drain region of transistor Q
0A forms an information storage capacitor C together with a portion of the first polysilicon layer 23 located thereon via the SiO ₂ film 21A, and the polysilicon layer 23 is connected to a potential source V. Capacitor C
The writing of information charges to or the reading of information charges from capacitor C is controlled by the switching action of transistor Q.

A large number of memory cells having the above configuration are formed in the semiconductor chip described above to constitute a RAM, and as the storage capacity of the RAM increases, the integration density increases and the cell size decreases. For this reason, for example, a MOS with a storage capacity of 16K bits or more
In the type dynamic RAM, the capacitance of the capacitor C is very small, and the generation of electron-hole pairs when α rays enter the substrate surface area 20A easily causes stored information to be reversed, resulting in a so-called soft error. That's why.

Therefore, if the present invention, which can reduce the amount of α-rays incident on the capacitor part which is the active region, is applied to the above-mentioned MOS type dynamic RAM,
Such soft errors can be prevented.

FIG. 4 shows another application target of the present invention.
This is an equivalent circuit diagram of the memory cell structure of an ECL (emitter coupled logic) type bipolar dynamic RAM. The illustrated memory cells are multi-emitter transistors Q ₁ , Q ₂
and resistors R ₁ and R ₂ constitute a flip-flop, where Vcc is a potential source, AD is an address line, D,
Each D indicates a data line. Even in bipolar RAM with such a memory cell structure,
Particularly in large-capacity, highly integrated devices, electron-hole pairs generated by alpha ray irradiation easily reverse the state of the flip-flop, causing soft errors.

This kind of soft error is also the same as the MOS type mentioned above.
Similar to the case of RAM, this can be effectively prevented by applying the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a substrate showing a memory cell structure of a MOS RAM to which the present invention is applied, and FIG. FIG. 2 is an equivalent circuit diagram of the memory cell, and FIG. 4 is an equivalent circuit diagram showing the memory cell structure of a bipolar RAM to which the present invention is applied. 10... Insulating base layer, 11, 18... Sealing glass layer, 14... Semiconductor chip, 16... Alpha ray shielding resin layer, 17... Insulating cap, 19
... Adhesive layer, 20 ... α-ray shielding body.

Claims (1)

[Claims] 1. A semiconductor chip, a base to which the back side of the semiconductor chip is fixed, an α-ray shielding resin layer deposited over the surface of the semiconductor chip, and a package for accommodating the chip together with the base. A cap stacked on the base with the recess facing the base, means for electrically leading out the electrodes on the chip to the outside of the package, and an α-ray shielding member provided on the inner surface of the recess of the cap. A semiconductor device characterized by: