JPH02265238A - Formation of aluminum selective diffusion layer on silicon substrate - Google Patents

Abstract

PURPOSE:To form the title diffusion layer efficiently and with high accuracy by a method wherein an aluminum thin film which has been applied to a prescribed part on the surface of a silicon substrate is covered with a silicon nitride film which restrains aluminum from being diffused, a heat treatment is executed and aluminum is diffused. CONSTITUTION:An aluminum thin film 2 is applied to the whole surface of a main face of a silicon substrate 1; the aluminum thin film 2 is removed selectively by leaving a prescribed part; then, a surface protective film 3 which restrains aluminum from being diffused is formed on the whole surface including the silicon substrate 1 and the aluminum thin film 2 which has been left; after that, a heat treatment is executed at a prescribed temperature; and aluminum is diffused in a prescribed region 4. Since the part to which aluminum has not been applied on the surface of the silicon substrate is covered with the surface protective film 3, the aluminum is not diffused the region. Thereby, it is possible to form an aluminum selective diffusion layer on the prescribed region 4 of the silicon substrate 1 efficiently and with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for selectively diffusing aluminum into predetermined regions of a silicon substrate.

[Conventional technology]

In the manufacturing process of various types of conductors, the surface of the semiconductor substrate is covered with an oxide film (Si02 film), windows are opened at predetermined locations, and impurities with the required conductivity type and resistivity are introduced through these holes. It is common practice to form a selective diffusion layer.

For example, when impurities are introduced into a predetermined region of an n-type silicon substrate to form a p-type scattering layer, the impurity is usually oxide (B) and aluminum is not used. The reason for this is that the diffusion coefficient of aluminum in 5fOzll1E is extremely larger than that of boron. That is, the diffusion coefficients of aluminum and aluminum at each temperature l in the 5IO2 film are as follows.

Therefore, in the normal planar diffusion method in which the SiOz film is processed, SiOzg does not have the effect of blocking the diffusion of aluminum, so impurities can be deposited precisely in a predetermined region of the silicon substrate. A selective diffusion layer cannot be formed.

However, a method using aluminum, which has a large diffusion coefficient, as an impurity source is also promising;
This aluminum impurity selective diffusion layer is formed as follows. First, an aluminum diffusion layer is formed on the entire surface of a silicon substrate, and then a predetermined area is covered with pitch, wax, etc., and in this state, the substrate is immersed in a mixed solution mainly consisting of hydrofluoric acid and nitric acid. The method used is to remove unnecessary areas. However, this method has the following disadvantages.

[Problem to be solved by the invention]

In order to form an aluminum selective diffusion layer on a silicon substrate, the method of covering a predetermined area with pitch or wax and removing unnecessary portions by etching causes the following problems. First, dimensional accuracy on the order of pm cannot be obtained with respect to the mutual positional relationship l of the selective diffusion layers obtained. In the second step, a step is formed in the thickness direction at the boundary between the selective diffusion region formed in a predetermined region of the silicon substrate and the region removed by etching. For these reasons, the conventional method is not suitable for forming a pn junction in a Brehner type element using aluminum as an impurity source.

However, the diffusion coefficient of aluminum in a silicon substrate is 6 compared to that of boron, as shown in the table below.
~8 times thicker.

Therefore, it is desirable to eliminate the above-mentioned drawbacks and use aluminum as an impurity source to form a selective diffusion region of aluminum in a silicon substrate as an effective method from the viewpoint of saving energy and reducing manufacturing man-hours. .

The present invention has been made in view of the above points, and its purpose is to provide a method for efficiently and highly accurately forming a selective diffusion layer of aluminum in a predetermined region of a silicon substrate.
There it is.

[Means to solve the problem]

In order to solve the above problems, the present invention forms an aluminum selective diffusion layer on a silicon substrate using the following steps.

(1) First, an aluminum thin film is deposited on the entire main surface of the silicon substrate, and this aluminum thin film is selectively removed leaving only predetermined areas. Next, the entire surface including the silicon substrate and the remaining aluminum thin film is removed. After forming a surface protective film to prevent aluminum from diffusing, a heat treatment is performed at a predetermined temperature to diffuse aluminum in a predetermined region of the silicon substrate.

(2) First, an oxide film is formed on the entire main surface of the silicon substrate,
A predetermined portion of this oxide film was selectively removed to open a window, and then an aluminum thin film was deposited on the entire surface including the main surface of the silicon substrate and the remaining oxide film, and the oxide film was opened. After selectively removing only the thin aluminum film deposited on the silicon substrate and forming a surface protective film on the entire surface of the oxide film and aluminum thin film remaining on the silicon substrate to prevent diffusion of aluminum, Aluminum is diffused into a predetermined region of the silicon substrate by performing temperature heat treatment.

[Effect]

In any of the above methods, when heat treatment is performed at a predetermined temperature in the final step, aluminum diffuses into the silicon substrate from the interface between the aluminum thin film and the silicon substrate. However, since areas on the surface of the silicon substrate to which aluminum is not coated are covered with a surface protective film that prevents aluminum from diffusing, aluminum does not diffuse into these areas.

Therefore, selective aluminum diffusion layers can be formed with high precision only in predetermined regions of the silicon substrate.

〔Example〕

The present invention will be explained below based on examples.

FIGS. 1(a) to (dl) are main IAM process diagrams for explaining the present invention in detail, and are represented by a schematic cross section of an element when forming a pn junction in a silicon substrate. Mirror-polished n-type silicon substrate 1 with resistance 5-10Ω
An aluminum thin film 2 having a thickness of ±5 A is deposited on the whole surface by electron beam evaporation or resistance heating channel method [FIG. 1(a)]. Next, only the predetermined portions of the aluminum thin film 2 where V is dispersed on the silicon substrate 1 are left, and the remaining portions are selectively removed by photoetching (FIG. 1(b)). Subsequently, a surface protective film for preventing the diffusion of aluminum, such as a silicon nitride film (5iaN) 3, is formed to a thickness of 0.1 μm over the entire surface of this state (FIG. 1(C)). For example, by heating at 1050"C for 20 minutes, the diffusion depth IQ pm and the impurity concentration 1.5 are applied to the silicon substrate 1.
A selective diffusion layer 4 of aluminum of XIO atoms/i is formed [FIG. 1(d)]. At this time, silicon substrate 1
In the region other than the selective diffusion layer 4, aluminum diffusion (
On the other hand, since the silicon nitride film 3 that blocks this is left alone, no aluminum diffusion layer is formed.

After this, a predetermined next step is continued.

FIG. 2 (J~(0) indicates a process different from that in FIG. 1 regarding the method of the present invention, and parts common to those in FIG. 1 are represented using the same reference numerals. An oxide film (Si20) 5 is formed on the entire surface of the silicon substrate 1 with a thickness of 0.1 μm (see FIG. 2(a)). This oxide film 5 is selectively removed by photo-etching to open a window (FIG. 2(b)).

In this state, a thin aluminum film 2 is deposited on the entire surface to a thickness of ±5 mm as in the case of FIG. 1 [FIG. 2(C)]. Subsequently, this aluminum thin film 2 is coated with an oxide film 5.
In the same way as for the area where the window was opened (photoetching is performed so that only this remains, and the other parts are selectively removed [Fig. 2 (d)]). A silicon nitride film 3 is formed to a thickness of 0.1 μm [FIG. 2(e)]. For example, by performing heat treatment at 1050°G for 20 minutes, the first
Figure (same as dl, diffusion depth 10pm, impurity concentration 1.
7) I/ of 5 X 10” a t oms/cffl
A selective diffusion layer 4 of aluminum is formed [FIG. 2(f)]
.

As described above, according to the method of the present invention, a p-type silicon region can be formed using aluminum as an impurity source and selectively diffused accurately in an n-type silicon substrate.

Moreover, as mentioned earlier, the diffusion coefficient of aluminum in a silicon substrate is 6 to 8 times greater than that of borosilicate, so when aluminum is used as a non-IE material source, borons are used. For example, at a heat treatment temperature of 1150° C., the heat treatment time is reduced to about 10%, and if the heat treatment time is kept the same, the heat treatment temperature can be lowered by about 100° C. This not only eases the introduction of defects into the silicon substrate crystal and reduces the risk of damaging the quality of the substrate crystal, but also prevents the introduction of defects into the silicon substrate, which were created in a diffusion process different from that of the present invention. When a layer is present, the advantage also arises that the heat treatment carried out according to the invention on the diffusion layer is less likely to have negative effects, such as, for example, changes in the diffusion depth.

〔Effect of the invention〕

The impurity elements used to selectively form a diffusion layer in a predetermined region of a silicon substrate are generally ζboron, phosphorus, arsenic, antimony, etc., and it is difficult and rare to use aluminum. .

This is because the diffusion coefficient of aluminum in the 8102 film is much higher than those of these impurity elements, making it unsuitable for a normal planar element formed by opening a window in the 5i02 film. In contrast, in the present invention, aluminum, which has an extremely large diffusion coefficient in a silicon substrate compared to boron, is used as an impurity source, and a thin aluminum film deposited on a predetermined location on the surface of a silicon substrate is used to prevent aluminum diffusion. A selective diffusion layer is formed in a predetermined region by covering the aluminum thin film with a blocking silicon nitride film, applying heat treatment, and diffusing this aluminum thin film into the silicon substrate, which is a method commonly used in the manufacture of semiconductor devices. Using this method, it was possible to obtain a desired selective impurity diffusion layer efficiently and with high precision.

[Brief explanation of drawings]

1(a) to 1(d) are manufacturing process diagrams showing the method of the present invention, and FIGS. 2(a) to 2(f) are manufacturing process diagrams showing the method of the present invention which is different from that shown in FIG.

Claims (1)

[Claims] 1) A method for forming a selective diffusion layer of aluminum in a predetermined region of a silicon substrate, the method comprises depositing an aluminum thin film over the entire main surface of the silicon substrate, and then depositing the aluminum thin film in a predetermined region. After selectively removing only a few spots, and then forming a surface protective film on the entire surface including the main surface of the silicon substrate and the remaining aluminum thin film to prevent aluminum diffusion,
A method for forming an aluminum selective diffusion layer in a silicon substrate, the method comprising diffusing aluminum into a predetermined region of the silicon substrate by performing heat treatment at a predetermined temperature. 2) A method of forming a selective diffusion layer of aluminum in a predetermined region of a silicon substrate, in which an oxide film is formed on the entire main surface of the silicon substrate, and predetermined portions of this oxide film are selectively removed to open a window. Next, an aluminum thin film is deposited on the entire surface including the main surface of the silicon substrate and the remaining oxide film, and this aluminum thin film is selectively removed leaving only the aluminum thin film deposited on the oxide film openings. Next, after forming a surface protection film to prevent aluminum diffusion on the entire surface of the oxide film and aluminum thin film left on the silicon substrate, heat treatment is performed at a predetermined temperature to diffuse aluminum into a predetermined area. A method for forming an aluminum selective diffusion layer on a silicon substrate, the method comprising: