JPS627700B2 - - 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 several ppm of uranium (U), thorium (Th), and the like. These impurities are e.g.
proceedings of reliability physics (1978), P38
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. Moreover, when electrons are excited in Si, holes are also generated, and electron-hole pairs are generated along the locus of the α ray. The number of excited electrons Ne here is Ne5MeV/3.6eV=1.4×10 ⁶ when the α-ray energy is 5MeV. This is the amount of electricity of 0.22P groins. 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.

In order to prevent such malfunctions, it has already been proposed to apply a resin coating to the surface of the active region of a semiconductor chip for shielding alpha rays. However, in this case, there is a problem that it is not easy to apply a uniform resin coating to a desired thickness of, for example, 70 μm or more.

The purpose of the present invention is to solve these problems,
An object of the present invention is to provide a semiconductor device that prevents malfunctions caused by alpha ray irradiation in an active region.

A semiconductor device according to the present invention is characterized in that an α-ray shielding layer made of particles of a high-purity silicon or quartz material mixed with a binder is deposited on the surface of an active region of a semiconductor chip. The illustrated embodiment will be described in detail.

FIG. 1 shows a semiconductor device according to an embodiment of the present invention, in which an insulating base 10 made of ceramic
There is Au foil or Au on the bottom of the recess in the center of the top surface.
A semiconductor chip 14 is fixed via an adhesive layer 13 made of a metallized layer or the like. The semiconductor chip 14 is made of silicon, for example, and has an active region on its surface that is usually 4 to 5 .mu.m deep and is prone to malfunction when irradiated with alpha rays, including memory cells, which will be described later. A large number of electrodes on the semiconductor chip 14 are electrically connected to corresponding leads 12 by a large number of bonding wires.

The surface of the active region of the semiconductor chip 14 is coated with alpha rays made of particles (beads) of high-purity (preferably five nines or higher) silicon bound with high-purity (no metals included) spin-on glass as a binder. A shielding layer 16 is applied. The application of such a shielding layer 16 is carried out after the completion of wire bonding, but it can also be carried out locally in the chip or wafer state before wire bonding. Here, as the binder, polyimide resins such as polyimide, isoindolo, quinazolinedeion, etc. can also be used. Furthermore, quartz beads or the like can be used as the high-purity particles constituting the α-ray shielding layer.

Silicon or quartz particles can be obtained by pulverizing these materials and then repeating the etching process several times.

The α-ray shielding layer 16 can be applied almost uniformly to a thickness of several tens to several hundred μm, and after being applied, the adhered layer is solidified or dried by an appropriate heat treatment.

On the other hand, the insulating cap 17 made of ceramic has a recess 17a in the center of one main surface, and is superimposed on the base 10 with the recess 17a facing the semiconductor chip 14. A low melting point glass layer 18 is previously applied to the joint surface of the cap 16 facing the base 10.
After the cap 17 is superimposed on the base 10 and the cap 17, the base 10 and the cap 17 are bonded to each other by heating the sealing glass layer 18 to its melting point and cooling it.

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
and α rays from the sealing glass layers 11 and 18, but since the shielding layer 16 is formed to cover the side and top surfaces of the semiconductor chip 14, these α rays are sufficiently attenuated by the shielding layer 16, and are not absorbed by the semiconductor chip. Chip 14
The amount of alpha radiation incident on the active region becomes virtually negligible.

Therefore, according to the semiconductor device of the present invention described above, malfunctions in the active region due to α rays can be effectively prevented. Furthermore, since the α-ray shielding layer 16 is made of high-purity material particles mixed with a binder, it has the advantage that it can be easily formed to a desired thickness uniformly.

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. 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. While connected to the digit line DG, the second polysilicon layer 2
5 is connected to word line W. The substrate surface portion 20A corresponding to the drain region of the transistor Q is
An information storage capacitor C is formed together with a portion of the first polysilicon layer 23 located thereon via the SiO ₂ film 21A.
is connected to a potential source V. The writing of information charges into the capacitor C and the reading of information charges from the capacitor C are controlled by the switching action of the 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 type dynamic RAM, the capacitance of capacitor C is very small, and the generation of electron-hole pairs when α rays enter the substrate surface area 20A can easily cause 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 V _CC is a potential source, AD is an address line, D,
indicate data lines, respectively. 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, 11, 18: Sealing glass layer, 14: Semiconductor chip, 16: α-ray shielding layer, 17: Insulating cap.

Claims (1)

[Claims] 1. A semiconductor device characterized in that an insulating layer made of particles of a high-purity silicon or quartz material bound with a binder is deposited on the surface of an active region of a semiconductor chip.