JPS5823927B2 - hand tai souchi no seizou houhou - 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 diffusing impurities.

Semiconductor devices are manufactured by selectively introducing impurities onto a semiconductor substrate such as silicon.

One method for selectively introducing impurities into a semiconductor substrate is to form a silicon dioxide (S10□) film as a mask material on the semiconductor substrate, and then remove the silicon dioxide film in the region where the impurities are to be diffused to form a window. There is a method of creating a window and diffusing impurities through this window.

By the way, for impurity diffusion that does not increase the surface concentration of the diffusion layer, such as base diffusion of a transistor,
After depositing a diffusion source made of an insulating film containing impurities, such as a silicon oxide film, on the window, the impurities contained in the diffusion source are diffused into the semiconductor substrate (hereinafter referred to as drive-in) in two steps. Diffusion method is used.

Furthermore, as semiconductor devices have recently become smaller, the base diffusion layer has also become very shallow, with a depth of 1,500 people.

When forming such a shallow diffusion layer by the two-stage diffusion method, drive-in must be performed at a considerably low temperature.

When drive-in is performed at low temperatures in this way, the diffusion concentration profile becomes gentle, as shown by the curve in Figure 1, and this curve may also be an A thin line or an A'' curve. However, reproducibility is poor, and if a transistor is formed by performing emitter diffusion as shown in curve 8 on a semiconductor substrate that has undergone such diffusion, the impurity concentration at the comic-base junction will vary; The drawback is that the breakdown voltage between the bases is not constant.

Furthermore, since the base resistance does not have a constant value and its value is relatively high, there is also a drawback that the switching speed of the transistor does not maintain a constant value and becomes slow.

The present invention is a novel invention that improves the conventional drawbacks as described above, and its purpose is to improve the reproducibility of the impurity concentration distribution in the base region and to ensure that the impurity concentration does not change much in the depth direction. The object of the present invention is to provide a method for diffusing impurities.

In order to achieve the object, the method for manufacturing a semiconductor device of the present invention selectively deposits a diffusion source made of an oxide film containing impurities on a semiconductor substrate, and then transfers the impurities contained in the diffusion source to the semiconductor substrate. In the method for manufacturing a semiconductor device in which the diffusion source is diffused into the semiconductor device, after the step of depositing the diffusion source is completed, a drive-in is performed, the diffusion source is removed, and then the drive-in is further repeated one or more times. This is a characteristic feature, and examples will be described in detail below.

When forming a P-type base layer in the N-type collector region of a semiconductor substrate by conventional diffusion of boron B, if a two-step diffusion method is used, an oxide film containing boron B as an impurity is coated on the semiconductor substrate. The depth of diffusion of impurities deposited and diffused by drive-in is determined by the depth at which impurities penetrate into the interior through diffusion, and the growth of an oxide film that acts as a diffusion source due to heating during drive-in, which increases the diffusion depth from the semiconductor surface. The difference lies in the depth of the scraping.

When using a normal high temperature drive-in process,
The latter can be ignored because the speed at which impurities penetrate into the semiconductor substrate is fast, but if the temperature of the drive-in process is lowered to achieve shallow diffusion, it cannot be ignored and a certain level of drive-in Depending on the in conditions, the oxidation depth will exceed the increase in diffusion depth, ie, the longer the drive-in time, the shallower the diffusion depth.

Now drive i. If the conditions for the diffusion are appropriately selected, the depth of diffusion does not change much, only the impurity distribution profile changes, and the portion having the same impurity concentration can be expanded in the depth direction.

However, once the oxide film grows to a certain extent, the depth of diffusion inevitably increases, so in order to obtain a constant -1 depth, this oxide film must be removed before the next drive-in.

In other words, by repeating the process of depositing an oxide film as an impurity diffusion source and then (drive-in + removing the oxide film) at least once, it is possible to eliminate the problem.

It is possible to obtain an impurity distribution in which the depth of fine diffusion is shallow and the impurity concentration does not change much in the depth direction.

Example N-type evixial on a silicon semiconductor substrate.

The epitaxial layer is grown, a thermal oxide film is formed as a mask material on the epitaxial layer, and the thermal oxide film in the portion that will become the base region is opened in a diffusion furnace, and oxygen (02
) gas, nitrogen (N2) gas containing boron bromide (BBrs) as an impurity was flowed through a diffusion furnace, and the silicon semiconductor substrate was kept at about 800 [C] and heated for 25 minutes. An insulating film containing boron B (borosilicate glass in this case) is deposited thereon.

Due to the deposition of this impurity source, the surface concentration in the base region is approximately 3 x 1020 particles/cr, as shown by the curve ■ in Figure 2.
The surface concentration and the diffusion depth are not constant, but vary depending on the loft.

Next, the silicon semiconductor substrate that has undergone this process is taken out of the diffusion furnace, transferred to a heating furnace, and heated to 950 ('C) for about 30 minutes in a humid oxygen atmosphere to drive impurities into the epitaxial layer. .

Through this drive-in process, the impurity distribution is as shown in curve 2 in Figure 2, and the maximum impurity concentration on the surface is approximately 5X101.
9 (number/d), and the diffusion depth is also approximately 150.
0 (becomes an illusion.

Next, after taking out the silicon semiconductor substrate from the heating furnace, the oxide film as an impurity source and the drive-in process are removed.
The oxide film formed on the surface of the region to be diffused is removed by etching.

The silicon semiconductor substrate from which the impurity source oxide film and the oxide film generated during the drive-in process have been removed is further placed in a heating furnace and subjected to drive-in again under the same conditions as the drive-in process.
Do an in.

Through this step, the impurities diffused into the silicon semiconductor substrate are partially absorbed by the generated oxide film, but most of them are diffused into the silicon semiconductor substrate.

However, the depth of diffusion is almost not deep, and the impurity distribution becomes as shown by curve 2 in Figure 2.

In this way, when the process of drive-in + oxide film removal was repeated two more times, the maximum impurity concentration on the surface was approximately 1 x 1019 groups/cI, as shown by the curve ■ in Figure 2.
L], it has an almost flat impurity concentration distribution up to depth x, ooo(,4), and the diffusion depth is also about L 500 CA
'), we were able to obtain a shallow P-type diffusion layer.

As explained above, the present invention improves the conventional two-step diffusion method and adds the steps of drive-in and oxide film removal to this, so that the depth of the diffusion layer can be reduced even though the drive-in is performed at a low temperature. It is possible to obtain a shallow diffusion layer with good reproducibility and a uniform impurity concentration even inside the diffusion layer.

Therefore, when this diffusion layer is used as a base layer of a transistor, it is possible to obtain a transistor that has uniform emitter-base breakdown voltage characteristics, has a relatively large value, and is capable of high-speed operation.

In addition, in the drive-in process of the present invention, if high-pressure steam oxidation is performed, the depth of the diffusion layer can be made shallower than that of the above embodiment.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an impurity concentration distribution according to a conventional impurity diffusion method, and FIG. 2 is a diagram showing an impurity concentration distribution according to an embodiment of the method according to the present invention. In the figure, a curve IV indicates a change in impurity concentration distribution.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device in which a diffusion source made of an oxide film containing impurities is selectively deposited on a semiconductor substrate, and then the impurities contained in the diffusion source are diffused into the semiconductor substrate. 1. A method of manufacturing a semiconductor device, which comprises performing a drive-in after completing a process, removing the diffusion source, and then repeating the drive-in one or more times.