JPH02301130A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To completely eliminate a crack to be generate at a nitride film and to prevent aluminum from being externally diffused by forming to add a silicon film further on a second oxide film, and so disposing component materials disposed on and under the nitride film in a symmetrical way to the film. CONSTITUTION:Aluminum ions 2 are first implanted to a silicon board 1. Then, the first oxide film 3 is formed on the surface of the board 1. This is because a buffer film is provided between a nitride film 4 formed in next step and the board 1. Then, the film 4 is formed, for example, by a plasma CVD method. Thereafter, the second oxide film 5 is formed on the film 4. Further, a silicon film 6 is formed on the film 5 by sputtering. The film 6 is provided to completely eliminate the crack of the film 4 due to the incomplete prevention of the crack generated at the film 4 when a high temperature heat treatment is executed, because that films disposed above and below the film 4 in a symmetrical way to the center in a wiring structure is optimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device in which an aluminum impurity diffusion region is formed in a silicon semiconductor substrate by aluminum ion implantation.

[Conventional technology]

When forming a p-type impurity region in a silicon semiconductor substrate,
Group B elements of the periodic table as dopants.

In particular, boron, gallium, aluminum, etc. are used.

Among these, aluminum has the largest diffusion coefficient in silicon, and compared to boron and gallium, the diffusion time is shorter and a deep diffusion layer can be formed at a lower concentration. Therefore, aluminum is suitable for manufacturing silicon conductive elements that require high breakdown voltage. It can be said to be the most suitable element.

Traditional aluminum diffusion has been performed in sealed quartz tubes using metallic aluminum as the diffusion source. However, in this case, the degree of vacuum inside the quartz tube is 1. OXlo-6111H
g or less, there was a problem that the quartz tube would be crushed during the heat treatment. In particular, with the recent increase in the capacity of silicon devices, the diameter of silicon wafers is also becoming larger, and the quartz tubes in which aluminum is diffused are also required to have larger diameters, making the above problem even more serious. It's here.

In order to solve such problems, it is conceivable to apply an ion implantation method to the aluminum diffusion process. According to this method, there are no problems associated with the use of quartz tubes as described above. The ion implantation method creates an aluminum diffusion layer in the silicon substrate by ionizing aluminum, applying high acceleration energy, and implanting aluminum ions from the back surface of the silicon substrate. It is something that forms. The ion implantation method has the advantage that it is easy to control the impurity distribution, and that the penetration distance of aluminum ions from the silicon substrate surface can be precisely controlled by adjusting the magnitude of the accelerating electric field.

However, in the ion implantation method, after aluminum ions are implanted into a silicon substrate, a heat treatment is performed to prepare the silicon crystals, electrically activate the aluminum, and diffuse it. There is a problem in that an aluminum diffusion layer having a desired impurity concentration cannot be obtained due to emission to the outside.

Therefore, in order to prevent the ion-implanted AlS from diffusing outward during subsequent heat treatment, the inventors of the present invention formed a first oxide film (SiO2) on the surface of the silicon substrate after ion implantation. A manufacturing method in which a nitride film (SimN4) and a WJ2 oxide film (Si0) are sequentially formed and then heat-treated is currently being applied for by the same applicant, % 62-310504.

[Problem to be solved by the invention]

However, as described above, providing a three-layer coating film on the surface of the silicon substrate after ion implantation can suppress the outward diffusion of aluminum implanted into the silicon substrate. Although a diffusion layer was obtained, subsequent research by the present inventors revealed that the following problems still existed.

Of the three coating films formed on the silicon substrate surface, consisting of a first intensified film, a nitride film, and a second oxide film, the dense nitride film has the effect of preventing outward diffusion of aluminum during the heat treatment process; The two oxide films serve as buffer films to prevent cracks from occurring in the nitride film due to thermal stress during heat treatment caused by the difference in coefficient of thermal expansion between the silicon substrate and the nitride film.

However, although the nitride film has a sandwich structure between two oxide films, cracks that occur in the nitride film have not yet been completely prevented from being heat-treated, for example, at 1250°C to obtain a deep diffusion layer. I can't say that it is.

The present invention has been made in view of this point 1, and its purpose is to provide a surface coating film that suppresses outward diffusion of aluminum when forming an aluminum diffusion layer in a silicon substrate using ion implantation. Another object of the present invention is to provide a method for manufacturing a semiconductor device that does not produce any defects during high-temperature heat treatment.

[Means to solve the problem]

According to the present invention, a method 1 for manufacturing a semiconductor device made of silicon includes a step of forming an aluminum impurity doped region in a silicon semiconductor substrate by implanting aluminum ions, and a step of forming an aluminum impurity doped region on a silicon semiconductor substrate after the aluminum ion implantation. oxide film.

The method includes a step of sequentially covering with a nitride film, a second oxide film, and a silicon film, and then a step of performing heat treatment.

[Effect′]

The surface coating film of a silicon substrate formed according to the present invention is
From the silicon substrate side, first oxide film, nitride film, second oxide film, silicon film (in this order).In the subsequent heat treatment process, the nitride film has the role of preventing aluminum from outward diffusion, The two oxide films act as a buffer film to prevent cracks from occurring in the nitride film due to thermal stress caused by the difference in thermal expansion coefficient between the silicon substrate and the nitride film during heat treatment.
Moreover, since the surface coating film has a vertically symmetrical material composition with the nitride film as the center, thermal stress is further alleviated, deformation in the vertical direction is suppressed, and cracks in the nitride film are completely prevented.

〔Example〕

Figure 1 (ml-(e>) shows the steps of the method for manufacturing a semiconductor device according to the present invention. First, aluminum 2 is ion-implanted into a silicon substrate 1 (Figure 1 (a)).Ion implantation conditions at this time is an accelerating voltage of 40 to 60 KeV, a % dose of 5 x 10 to 3 There is also a method of forming a thermal oxide film and implanting aluminum ions on top of it under the conditions described above, but in this case, it is best to make the thermal oxide film as thin as possible and less than 0.1 pm.If the thermal oxide film is thick, This is because the ion-implanted aluminum reacts with the thermal oxide film 5i (h), making it impossible to obtain a desired aluminum diffusion layer.

Next, a first oxide film 3 is formed on the surface of the silicon substrate 1 (FIG. 1(b)). This is to serve as a buffer film between the nitride film 4 and the silicon substrate 1, which will be formed in the next step.

That is, when the nitride film 4 is directly formed on a silicon substrate, cracks occur in the nitride film 4 due to the difference in thermal expansion coefficient between Sl and 51mNa, which generates thermal stress between the two. In order to prevent aluminum from diffusing outward through these cracks during annealing (heat treatment) and causing variations in the aluminum concentration within the silicon substrate surface,
A first oxide film 3 is required. 2. The first oxide film 3 is formed at a temperature of 500° C. or lower. This is because at temperatures above 500° C., outward diffusion of aluminum occurs during film formation. The thickness of the first oxide film 3 is set to 0.5 pm or less in order to shorten the oxide film deposition time and to reduce the amount of aluminum diffused outward into the oxide film. In order to form a buffer film between the silicon substrate 1 and the nitride film 4, the optimum thickness is about 0.1 uya.

Next, a nitride film 4 is formed on the first oxide film 3 (see FIG.
C)). The nitride film 4 is formed by, for example, a plasma CVD method. The nitride film 4 is very dense and effective in preventing outward diffusion of aluminum during annealing.

However, the solid bathing of aluminum in the nitride film 4 is large;
Since the amount of aluminum dissolved in solid solution increases, the oxidized film 4
(The thinner the better. However, if it is too thin, pinholes are likely to form, and outward diffusion may occur in the pinhole area. The thickness of the nitride film 4 is 0.07 to 0.1 p.
fF! is optimal.

Next, a second oxide film 5 is formed on the nitride film 4.
Figure (d)). The first oxide film 3 is formed as a buffer film between the silicon substrate 1 and the nitride film 4, and the St
However, when the annealing temperature is increased to form a deep diffusion layer, the effect is not sufficient (SiO
Due to the difference in coefficient of thermal expansion between the nitride and 5isNa, thermal stress is generated between the two, and cracks occur in the nitride film 4. Nitride film 4
By sandwiching the oxide film between the first oxide film 3 and the second oxide film 5, the generation of thermal stress can be significantly suppressed. Similarly to the formation of the first oxide film 3 described above, this oxide film 5 is also formed at a temperature of 500° C. or lower in order to prevent outward diffusion of aluminum. Further, it is effective to make the thickness of the second oxide film 5 equal to the thickness of the first oxide film 3 in order to prevent cracks from occurring in the nitride film 4.

Furthermore, in the present invention, a silicon film 6 is formed by sputtering on the second oxide film 5 [FIG. 1(e)]. At this time as well, the oxidation is carried out at a temperature of 500° C. or lower for the same reason as in the case of the first oxide film 3 and the second oxidation@5. This silicon film 6
The reason for providing dl is as shown in Figure 1 (dl) because it is still incomplete in preventing cracks that occur in the nitride film 4 when high-temperature heat treatment is performed, and in order to completely eliminate cracks in the nitride film 4, This is based on the reason that it is optimal to arrange the film 4 at the center and the films above and below it to be symmetrical.Therefore, the thickness of the silicon film 6 is equal to the thickness of the silicon substrate 1. In other words, it is preferable to set the thickness to about several hundred pm, but it is not practical if the thickness is more than a few μm considering the film formation time, etc. Therefore, the thickness of the silicon film 6 is varied within a range of up to 1 μm, and the silicon substrate 1 is 500 pm thick, 1st
Oxide film 3. The surface coating of the structure shown in FIG. 1(e) in which the nitride film 4 and the second oxide film 5 each have a thickness of 0.1 μm is subjected to heat treatment at 1250° C. for 16 hours in a nitrogen atmosphere. The internal stress generated in the film was determined by X-ray diffraction, and the results are shown in FIG.

FIG. 2 is a diagram showing the silicon film thickness dependence of the internal stress caused by the Shishimen coating film, and the film stress on the vertical axis is for the structure of FIG. 1(d) without the silicon film 6, That is, the values are shown as relative values, with the film stress of the device corresponding to the device currently being applied for in the aforementioned Japanese Patent Application No. 62-310504 set to 1, and the horizontal axis represents the thickness of the silicon film 6.

According to FIG. 2, when the thickness of the silicon film 6 is set to 0.1 μm or more, this level of generated stress will not cause cranking in the nitride film 4 (and is also sufficient to prevent aluminum from outward diffusion). can be satisfied.

FIG. 3 shows the aluminum concentration distribution in the semiconductor substrate 1 when the same heat treatment as above is applied to the structure shown in FIG. FIG. From Figure 3, silicon substrate 1
The aluminum concentration on the surface of is I x 10 atoms
It can be seen that the aluminum diffusion depth is approximately 10 μm, and a deep aluminum diffusion layer with a high concentration can be obtained. Furthermore, the variation in the sheet resistance of this diffusion layer is less than 0.5% in terms of σ5-Jx, which is approximately % compared to the case where the silicon film 6 is not provided, and the uniformity of the resistance value of the diffusion layer is This shows that there has been an increase.

〔Effect of the invention〕

When forming an aluminum diffusion layer in a silicon substrate using ion implantation, a surface coating film is formed in the order of a first oxide film, a nitride film, and a second oxide film on the surface of the silicon substrate. This is effective in suppressing the outward diffusion of aluminum during the subsequent diffusion heat treatment, but it is also effective in suppressing the outward diffusion of aluminum during the high temperature heat treatment due to the difference in thermal expansion coefficient between the silicon substrate and the nitride film. Even though the nitride film is sandwiched between two oxide films that act as stress buffers, cracks cannot be completely prevented. In contrast, in the present invention, following the formation of the second oxide film, a silicon film is additionally formed on top of the second oxide film, and each constituent material located above and below the nitride film is symmetrical with respect to the nitride film. As a result, the vertical deformation of the nitride film caused by high-temperature heating ζ is suppressed, and cracks that occur in the nitride film are completely eliminated. A deep aluminum diffusion layer with the desired surface Uii concentration could be obtained.

[Brief explanation of the drawing]

Figures 1 (a) to (e) are manufacturing process diagrams of a semiconductor device according to the present invention, and Figure 2 shows the thickness of the silicon film of the semiconductor device obtained from the present invention and the stress of the surface coating film of the conventional element. A diagram showing the relationship between the surface coating film stress and the relative value of ! FIG. 3 is an aluminum concentration distribution diagram of a diffusion layer of a semiconductor device obtained according to the present invention. 1... Silicon substrate, 2... Aluminum ion,
3...First oxide film, 4...Nitride film, 5...Second
Oxidation of ↓1↓↓ 1 ↓, -27J Mi-Uhei Figure 1

Claims (1)

[Claims] 1) Forming an aluminum impurity doped region in a silicon semiconductor substrate by implanting aluminum ions, and sequentially covering the surface of the semiconductor substrate with a first oxide film, a nitride film, a second oxide film, and a silicon film after the aluminum ion implantation. A method for manufacturing a semiconductor device, comprising a step of coating and a step of subsequently performing heat treatment.