JPS6211497B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for improving a semiconductor substrate.

Generally, silicon is used as a manufacturing substrate for semiconductor devices, and by diffusing impurities into the silicon substrate once or several times using photolithography or selective diffusion, transistors, diodes, or diffused resistance layers are formed partially. has been done. In this case, the problem is that if even a small amount of impurities other than the diffused impurity, such as heavy metals such as iron or copper, enter the silicon substrate or diffusion layer during the pre-diffusion process or during the diffusion, they will be absorbed into the silicon crystal. Accumulates in defective areas.

When a voltage is applied to the P-N junction formed by such diffusion, the accumulation of heavy metals causes leakage current. In order to prevent this leak from occurring,
Conventionally, as part of the diffusion process, heavy metals contained in the silicon substrate were gettered (sucked out) by diffusing phosphorous impurities into the silicon surface where active elements are formed or the opposite silicon surface.

However, the method of gettering heavy metals by diffusing phosphorus is effective against sucking out large amounts of metal and large leaks in the bonding layer, but it prevents micro leaks in the P-N junction due to ultra-trace metal impurities. There was no significant effect on.

The present invention eliminates the above-mentioned drawbacks, removes trace amounts of heavy metals from the semiconductor substrate, extremely reduces the PN junction leakage current, and provides a method for manufacturing a highly reliable semiconductor device.

The method for manufacturing a semiconductor device of the present invention includes a step of applying solid particles having a harder hardness than the semiconductor to the surface of the semiconductor substrate opposite to the active element forming surface to form a strained layer on the semiconductor substrate surface; The method is characterized in that it includes a step of diffusing phosphorus into part or all of the strained layer.

According to the present invention, a highly reliable semiconductor device with extremely small P-N junction leakage current can be obtained. This also solves the problem of shortening the storage time of memory information due to leaks.

The present invention will be explained by examples.

FIGS. 1 to 3 are cross-sectional views of the main steps when the present invention is applied to the manufacture of diodes. A mixture of solid quartz particles 2 and water is placed in a container 5, pressurized by a pump 4, and applied onto a P-type silicon substrate 1 through a nozzle 3 (FIG. 1). When particles hit the surface of the silicon substrate 1, mechanical strain is introduced, forming a strained layer 6 (second layer).
figure).

By appropriately selecting the pump pressure, the diameter and hardness of the particles, and the time during which the particles are exposed to the substrate using this method, processing strain on the silicon substrate can be created to any desired depth. In particular, control in the depth direction is important in order to increase the effect of the strained layer. If the depth of the strained layer 6 is too shallow, the effect will be small, and if it is too deep, it will have the opposite effect, so a depth of about 0.2 to 10 μm is desirable.

It is preferable that the hardness of the particles accelerated here is greater than that of the silicon substrate, and here the particles that collide with the silicon are made of quartz, but alumina or silicon carbide may also be used.

In general, silicon substrates used in semiconductor devices are made to have good crystallinity and have as few crystal defects as possible. For example, the number of surface crystal defects is from several to several thousand defects/cm ² . On the other hand, in the strained layer made by this method, the number of crystal defects ranges from tens of thousands to tens of millions/ ^cm2 , and the number of crystal defects ranges from one digit to five.
There are so many digits. Therefore, the strained layer referred to here can be said to be a silicon layer with a high crystal defect density of 10 ⁴ to ^{10 8} /cm ² .

To measure the strained layer depth mentioned here, silicon is used.
After heat treatment for about 2 hours in an oxidizing atmosphere at about 1100°C, the silicone was cleaved in the thickness direction and treated with a well-known dilute etching solution (a mixture of 50g of chromic anhydride dissolved in 100ml of water and 100ml of hydrofluoric acid). , Details in E. Sirtl, A. Adler: Z. Metallkde., Vol.52
(1961) p. 529) or dossier etching solution (a mixture of 10 ml of hydrofluoric acid, 30 ml of nitric acid, and 120 ml of acetic acid, details: WCDash: J.Appl.Phys., Vol. 27)
(1958) (see page 705) for 5 to 15 minutes, silicon dislocations are etched and crystal defects appear. The crystal defect density is 10 ⁴ to ^{10 8} /cm ² , and the depth of the strained layer can be measured by measuring the depth with a micrometer using a microscope.

Next, a silicon oxide film 7 is provided on the side opposite to the side where the strained layer 6 is present on the P-type silicon substrate 1 having this strained layer, and a phosphorus diffusion layer 8 is formed using a selective diffusion method.
form. At this time, the phosphorus diffusion layer 9 was also formed on the strained layer 6 on the back surface at the same time. The diffusion of phosphorus into the silicon strained layer portion becomes more effective as the time increases at a high temperature of 1000° C. or higher, so it may be diffused in a separate process from the formation of the phosphorus diffusion layer 8. Further, when forming a boron diffusion layer on an N-type substrate, phosphorus must be separately diffused into the strained layer 6. After that, the wiring electrode 10 of aluminum is formed by the usual method.
(Figure 3).

FIG. 4 is a characteristic diagram showing the relationship between strain layer depth and reverse leakage current of a diode manufactured according to the present invention.

The diode used here has a diffusion layer depth of 2μ.
It has a width of 10 μm and a length of 20 mm. Compared to the one without a strained layer (marked with a circle on the left end of Figure 4), the strained layer is reduced by 0.1.
It can be seen that the diode formed at a depth of ~10 μm has a small leakage current. In particular, the depth of the strained layer is 1~
It was found that the effect was large when the thickness was about 5 μm.

In addition, using this method, N-channel MOS
When we fabricated a memory integrated circuit, we found that by reducing leakage current, the hold time was more than doubled, making it possible to obtain a highly reliable semiconductor device. It was also found that when a semiconductor device having back surface strain is assembled as a product, the above-mentioned effect does not change even if the back surface strain layer is removed.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views of the main steps when the present invention is applied to diode manufacturing, and Figure 4 shows the relationship between the strain layer depth and reverse leakage current of the diode manufactured according to the present invention. It is a characteristic diagram. 1... P-type silicon substrate, 2... Quartz particles, 3
... Nozzle, 4 ... Pump, 5 ... Container, 6 ...
Strained layer, 7... Silicon oxide film, 8... N-type diffusion layer, 9... Phosphorus diffusion layer, 10... Wiring electrode.

Claims (1)

[Claims] 1. Solid particles having a harder hardness than the semiconductor substrate are bombarded onto a surface of the semiconductor substrate different from the active element forming surface to a depth of 0.2 to the different surface of the conductor substrate.
A method for manufacturing a semiconductor device, comprising the steps of forming a strained layer with a thickness of ~10 μm, and diffusing phosphorus into part or all of a surface having the strained layer.