JPS6150349A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent any erroneous operation due to alpha ray irradiation from happening by a method wherein a semiconductor chip is bonded on a substrate and then multiple electrodes on the chip are connected to corresponding external conductive means simultaneously bonding alpha ray shielding sheet on the surface of active region of semiconductor chip. CONSTITUTION:A semiconductor chip 14 is bonded on the surface of ceramics- made insulating base 10 through the intermediary of an adhesive layer 13 made of Au foil or Au metallized layer while multiple electrodes are electrically connected to corresponding leads 12 by bonding wires. An alpha ray shielding sheet 17 made of high purity (preferably exceeding 5-9) silicon several 100mum thick including the thickness of another adhesive layer 16 made of phosphorus silicide glass or lead glass etc. is bonded on the surface of active region of semiconductor chip 14 before or after wire bonding process while a ceramics-made insulating cap 18 is bonded on the base 10 through the intermediary of a low melting point glass layer 19.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device in which a semiconductor element such as a dynamic memory is sealed.

Generally, 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 material in the ceramic bag contains approximately several ppm of uranium (U) and thorium (Th).
) etc. are included. These impurities are, for example, 16t
hproc-ecdings of relayii
ity physics (1978) 'tp88 K
As mentioned above, it is known that alpha rays are emitted and memory devices malfunction due to these alpha rays.

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 to 9 MeV
However, the α rays generated in the cage material lose energy due to collisions with molecules before reaching the surface of the material, so the energy distribution of the α rays emitted from the cage is O to g.
MeV.

When this alpha ray enters the Si hole, it excites electrons,
It runs while losing energy little by little. Therefore, the range of α rays in a substance is inversely proportional to the density of the substance and is relative to the initial energy. In Si, electrons are excited at 3.6 eV, and at 5 MeV, the range is about 25 μm. Furthermore, when electrons are excited in Si, holes are also generated, and an electron-hole bear is generated along the locus of the α ray. The number of excited electrons Ne here is, assuming that the α-ray energy is 5 M e V, Ne = 5 MeV/ 8.6 eV = 1.4 X
There will be 10' pieces. This amounts to an amount of electricity of 0.22 pgrons.

Thereafter, the charge disappears due to diffusion and recombination due to the concentration gradient, but when this charge is captured by the bias and falls to a value that cannot be ignored compared to the amount of charge under a certain boundary condition of the pellet,
It will malfunction. This malfunction occurs without damaging the physical properties of the device, so it is a soft error (5of
Error).

It has already been proposed to apply a resin coating. However, in this case, it is difficult to uniformly apply a resin coating to the desired thickness of 70 μm or more, and applying a resin coating to a semiconductor chip after wire boring may reduce assembly yield and reliability. It has drawbacks such as being easy to use.

A method for manufacturing a semiconductor device that protects against alpha rays by directly coating the surface of a semiconductor chip, including the active region, with a high-purity material is described in Japanese Patent Laid-Open No. 55-088356.

An object of the present invention is to provide a method for manufacturing a semiconductor device that prevents malfunctions due to alpha ray irradiation in the active region without having such drawbacks.

In the method for manufacturing a semiconductor device according to the present invention, a semiconductor chip is fixed to a base, electrodes formed on the chip are connected to corresponding external conduction means, and silicon or silicon is applied to the surface of the active region of the semiconductor chip. It is characterized by attaching an α-ray shielding plate made of high-purity material such as quartz.
The embodiments shown in the accompanying drawings will be described in detail.

FIG. 1 shows a semiconductor device according to an embodiment of the present invention, in which an adhesive layer 13 made of an Au foil or an Au metallized layer is provided on the bottom of a recess at the center of the upper surface of an insulating base 10 made of ceramic. A semiconductor chip 14 is fixed thereto. This semiconductor chip 14 is made of silicon, for example, and includes α
The active area that is prone to malfunction due to radiation irradiation is usually 4 to 5 μm.
It is formed over a depth of . 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 covered with an adhesive layer 16 of, for example, phosphosilicate glass or lead glass, made of high-purity (preferably five nines or more) silicon with a thickness of several hundred μm, before or after wire bonding. An α-ray shielding plate 17 is attached.

FIG. 2 shows the semiconductor chip 14 after the shielding plate 17 has been attached.
11 indicates the surface condition of the bonding pad (
electrode). It is preferable that the surface of the α-ray shielding plate 17 manufactured by 7 Rico Co., Ltd. be subjected to surface oxidation treatment in advance to impart insulation properties.

In addition, the α-ray shielding plate 17 may also be made of surface-oxidized aluminum plate, quartz plate, fluorine such as Teflon (trade name), base resin, or polyimide such as polyimide-indo-quinazolindion (referred to as PI polymer). A plate material made of resin can be used. Here, the Teflon plate is preferably attached with glass or PI polymer applied by a spin-on method. In addition, when an adhesive material that requires drying is used as the adhesive layer 16, the VC
A large number of small holes may be provided in advance and processed into a mesh shape, etc., and this has the effect of facilitating drying.

On the other hand, the insulating cap 18 made of ceramic or resin has a recess 18a in the center of one main surface, and is placed over the base 10 with the recess 18a facing the semiconductor chip 14. A low melting point glass layer 19 is previously applied to the joint surface of the cap 18 facing the base 10, and after the cap 18 is superimposed on the base 10, it is heated to the melting point of the sealing glass layer 19 and then cooled. As a result, the base 10 and the cap 18 are bonded to each other.

1 In the above configuration, alpha rays are emitted from the ceramics of the base 10 and the cap 18, and the glass of the sealing glass layer 11.
The α rays emitted from the base 10 are absorbed by the semiconductor chip 14.
Since it has a thickness of 50 to 500 μm, by the time it reaches the active region on the chip surface, it is weakened to such an extent that it will not cause malfunction, so it will hardly be a problem. Therefore,
The problem is that the cap 18 and the sealing glass layer 11,
However, the α rays from the cap 18 are sufficiently weakened by the shielding plate 17, and the α rays from the sealing glass layer 11.
The shielding plate 17 sufficiently weakens alpha rays from the shielding plate 17 that have a relatively large incident angle with respect to the active region on the chip surface. The α rays that enter the active region from the sides of the chip 14 without passing through the α rays have a shallow angle of incidence, so the acting force on the active region is originally not very strong, so in many cases it does not pose a problem.

Therefore, by the method for manufacturing a semiconductor device of the present invention described above, i.
For example, malfunctions in the active region due to α rays can be effectively prevented. Furthermore, since the shielding plate 17 is pre-formed, there is an advantage that variations in thickness are much smaller than in the conventional case of mere resin coating. Moreover, the shielding plate 17
Since it also has the effect of protecting the chip surface, for example, when handling the semiconductor chip 14, the shielding plate 17 can be directly adsorbed with a vacuum chuck or the like, which has the advantage of making the chip 14 easier to handle. Note that the shielding plate 17 can be attached to the chip 14 even in a wafer state where the chip 14 forms one area of the wafer, and the shielding plate 17 can be attached only to the chip area determined to be good in the wafer inspection. The wafer may be selectively attached and then the wafer may be separated to obtain individual chips. Even in this case, the shielding plate 17 can chemically or physically protect the chip area or the chip from the outside world.

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. 3 shows the memory cell structure of a MO8O8 type diami RAM (random access memory), and its circuits are shown in FIG.

20 is a P type/recon substrate, on the surface of which a thick field SiO film 21 is formed, and this 5 inch
A thin 5 in 2 film 21A is formed within the opening of the 2 film 21. 22 is an N+ type diffusion region, 23 is a first low resistance polysilicon layer, 241d is an insulating film between the eyebrows made of phosphorus silicate glass, 25 is a second low resistance polysilicon layer,
Reference numeral 26 is made of a glass film made of phosphorous glass. A part of the second polysilicon layer 25 deposited 1A on the SiO□ film 21 acts as a gate of an MO8 type transistor Q whose source region is the N+ type diffusion region 22, and the N+ type north region 22 is a digit part. Line D
GK connection, while second polysilicon layer 25 is connected to word line W. The substrate surface portion 20A corresponding to the drain region of the transistor Q forms an information storage capacitor C together with a portion of the first polysilicon layer 23 located thereon via the 5in2 film 21A. Connected to potential source ■. 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.
The larger the storage capacity of an AM, the higher the integration density and the smaller the cell size. For this reason, in the MO'S die-type Dyno AM with a storage capacity of 16 bits or more, the capacitance of the capacitor C is very small, and α
Due to the generation of electron-hole pairs when the wire enters the substrate surface area 20AK, a situation arises in which stored information is easily reversed.
This is what is called a soft error.

Therefore, the present invention, which can reduce the amount of α-rays incident on the capacitor part which is the active region, is
If applied to such an MO8 type dynamic RAM, such soft errors can be prevented.

FIG. 5 shows the memory cell structure of an ECL (emitter coupled logic) type bipolar dynamic RAM, which is another application of the present invention, using both circuits. The illustrated memory cell has a clip 70 block made up of multi-emitter transistors Q, , Q and resistors R, , R2, where ycC is a potential source, AD is an address line, and D and D are data lines, respectively. Even in bipolar RAMs with such a memory cell structure, especially those with large capacity and high integration, electron-hole bears generated by alpha ray irradiation can easily reverse the 7-lip and 70-tub state, resulting in soft errors. cause

Such soft errors can also be effectively prevented by applying the present invention, as in the case of the MO8 type RAM described above.

[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 top view of a semiconductor chip to which an α-ray shielding plate is fixed, and FIG. 3 is an object to which the present invention is applied. 4 is an equivalent circuit diagram of the memory cell of FIG. 3, and FIG. 5 is a memory cell structure of a bipolar RAM as another application target of the present invention. FIG. 10... Insulating base, 11, 19... Sealing glass layer, 14... Semiconductor chip, 16... α-ray shielding plate,
18...Insulating cap. Figure 1 Figure 2

Claims (1)

[Claims] 1. (a) a step of preparing a semiconductor pellet having an electrode and an active region; (b) a step of preparing a base on which the semiconductor pellet is placed; and (c) an insulating material on at least the surface thereof. (d) fixing the semiconductor pellet to the substrate; and (e) providing an α-ray shielding plate having an insulating property on at least the surface of the active region of the semiconductor pellet. (f) connecting the electrodes of the semiconductor pellet to a corresponding external conduction means; and (g) the semiconductor pellet, the substrate, and an α-ray shielding plate having an insulating property on at least its surface. A method for manufacturing a semiconductor device, comprising the step of sealing at least a portion of the means for communicating with the outside with a sealing body. 2. The sealing body is composed of a ceramic insulating cap and a ceramic insulating base, and the means for communicating with the outside is a connection between the ceramic insulating cap and the ceramic insulating base. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the leads are bonded with a sealing glass layer interposed therebetween. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the α-ray shielding plate having insulating properties at least on its surface is made of polyimide resin.