JPH0673350B2 - Method for manufacturing semiconductor device - Google Patents

Description

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 ion implantation of aluminum.

[Prior Art] When a p-type impurity region is formed on a silicon semiconductor substrate,
Group IIIb elements of the periodic table as dopants, especially boron,
Gallium, aluminum, etc. are used. Among them, aluminum has the largest diffusion coefficient in silicon, and has a shorter diffusion time than boron and gallium and can form a deep diffusion layer at a low concentration, so that it is most suitable for manufacturing a silicon semiconductor element that requires high breakdown voltage. It can be said that it is a suitable element.

Conventional aluminum diffusion has been performed in a sealed quartz tube using metallic aluminum as the diffusion source. However, in this case, since the degree of vacuum inside the quartz tube is 1.0 × 10 ⁻⁶ mmHg or less, there is a problem that the quartz tube is crushed during the heat treatment when the diameter of the quartz tube is large. In particular, with the recent increase in the capacity of silicon devices, the diameter of silicon wafers tends to become larger and larger, and quartz tubes for aluminum diffusion are also required to have larger diameters, and the above problems become more serious. Came.

In order to solve such a problem, it is possible to apply an ion implantation method to the aluminum diffusion step. According to this method, there is no problem associated with the use of the quartz tube as described above.

[Problems to be solved by the invention]

However, in the aluminum diffusion process by the ion implantation method, the implantation of aluminum ions concentrates on the surface of the silicon semiconductor substrate and causes a lattice defect of silicon. Therefore, an annealing process is required to electrically activate aluminum. However, there is a problem that aluminum in the semiconductor substrate is released to the outside of the substrate in this annealing step, so-called out diffusion occurs, and the desired impurity concentration cannot be obtained. Thus, there are still problems with aluminum ion implantation.

The object of the present invention is to prevent out-diffusion in the annealing process performed after ion implantation. Therefore, it is an object of the present invention to provide a method of manufacturing a semiconductor device capable of diffusing aluminum by ion implantation, in which the impurity concentration can be accurately controlled.

[Means for solving problems]

According to the present invention, in the method of manufacturing a semiconductor device made of silicon, a step of forming an aluminum impurity added region in a silicon semiconductor substrate by ion implantation of aluminum, and a step of forming a first oxide film on the surface of the semiconductor substrate after ion implantation of aluminum. , A step of sequentially coating with a nitride film and a second oxide film, and then a step of performing annealing.

[Action]

In a method of manufacturing a semiconductor device in which an aluminum impurity diffusion region is formed in a silicon semiconductor substrate by aluminum ion implantation according to the present invention, a surface of the semiconductor substrate after aluminum ion implantation is treated with a first oxide film, a nitride film and a second oxide film. Since the films are sequentially coated, the coating layer acts to prevent aluminum out-diffusion in the subsequent annealing step, and the aluminum impurity concentration in the silicon substrate can be accurately controlled.

〔Example〕

FIG. 1 shows steps of a method for manufacturing a semiconductor device according to the present invention. First, aluminum 2 is ion-implanted into the silicon substrate 1 (FIG. 1 (a)). The ion implantation conditions at this time are as follows: acceleration voltage 40 to 60 keV, dose amount 5 × 10 ¹⁴ to 1 × 10 ¹⁵ atoms
/ cm ² , ionic species ²⁷ Al ⁺ . When a defect on the surface of the silicon substrate caused by the implantation of ions poses a problem, a thermal oxide film is provided on the silicon substrate, and aluminum is ion-implanted from above on the thermal oxide film. In this case, the thermal oxide film is preferably as thin as possible and has a thickness of 0.1 μm or less. If the thermal oxide film is thick, the ion-implanted aluminum reacts with the thermal oxide film SiO ₂ ,
This is because uniform aluminum diffusion cannot be obtained.

Next, the 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 formed in the next step and the silicon substrate. That is,
When a nitride film is formed directly on a silicon substrate, Si and Si ₃ N
The difference in the thermal expansion coefficient of _4, thermal stress is generated between the Si and Si ₃ N _4, cracks in the nitride film. This is because aluminum is out-diffused through the cracks during annealing, and variations in the aluminum concentration in the surface of the silicon substrate occur. The oxide film 3 is formed at a temperature of 500 ° C. or lower. This is because out-diffusion of aluminum occurs above 500 ° C. Further, the thickness of the oxide film is set to 0.5 μm or less so that the time for attaching the oxide film is as short as possible and the amount of aluminum out-diffused in the oxide film is reduced. Since it serves as a buffer film between the silicon substrate and the nitride film, about 0.1 μm is optimal.

Next, a nitride film 4 is formed on the oxide film 3 (FIG. 1 (c)). The nitride film is formed by, for example, the plasma CVD method. The nitride film is extremely dense and is effective in preventing aluminum out-diffusion during annealing. However, the solid solubility of aluminum in the nitride film is large,
The thicker the nitride film, the greater the amount of aluminum that forms a solid solution in the nitride film due to out diffusion during annealing. Therefore, it is preferable that the nitride film 4 be as thin as possible. However, if it is too thin, pinholes are likely to be formed, and there is a risk of out-diffusion occurring in the pinhole portion. The optimum thickness of the nitride film 4 is 0.07 to 0.1 μm. Further, if the nitride film thickness on the surface of the silicon substrate varies, a local difference occurs in the diffusion amount of aluminum into the silicon substrate. Therefore, variations in the aluminum concentration distribution in the silicon substrate occur within the surface of the silicon substrate. That is, the nitride film 4 needs to be formed to have the above-mentioned thickness and a uniform thickness within the surface of the silicon substrate.

Next, an oxide film 5 is formed on the nitride film 4 (FIG. 1 (d)). This is because the oxide film 3 is formed as a buffer film between the silicon substrate 1 and the nitride film 4 to suppress the generation of thermal stress due to the difference in the thermal expansion coefficient of Si and Si ₃ N ₄ , but it is deep. When the annealing temperature is increased to form the diffusion layer, the effect is not sufficient, and due to the difference in thermal expansion coefficient between SiO ₂ and Si ₃ N ₄ , thermal stress is generated between the two and the nitride film is formed. Cracks occur. The nitride film 4 is replaced with the oxide film 3 and the oxide film 5
By sandwiching between the two, the generation of thermal stress can be significantly suppressed.
According to the experiment, in the structure in which the protective film is composed of the oxide film 3 and the nitride film 4 (FIG. 1 (c)), cracks are generated in the nitride film 4 during annealing, and the cracks cause variations in the aluminum concentration distribution in the silicon substrate. However, the protective film has a structure of the oxide film 3, the nitride film 4, and the oxide film 5 (FIG. 1 (d)).
Then, no crack was generated after annealing. The formation of the oxide film 5 is also performed at a temperature of 500 ° C. or lower in order to prevent out-diffusion of aluminum similarly to the formation of the oxide film 3 described above. Further, it is effective to make the thickness of the oxide film 5 equal to the thickness of the oxide film 3 in order to prevent the nitride film 4 from cracking.

Annealing is 1200- with the protective film attached (Fig. 1 (d))
It is carried out at 1250 ° C in a nitrogen atmosphere for 10 to 30 hours.

The aluminum concentration distribution in the semiconductor substrate obtained through the above steps is shown in FIG. Aluminum concentration on the silicon substrate surface is 1 × 10 ¹⁶ atoms / cm ³ and diffusion depth is 50 μm.
The concentration distribution of is obtained. The variation in sheet resistance of the diffusion layer of the silicon substrate is σ _n-1 / 1% or less.

〔The invention's effect〕

According to the present invention, the formation of the protective film (SiO ₂ / Si ₃ N ₄ / SiO ₂ ) can effectively prevent the out-diffusion of aluminum during annealing. The formation of the aluminum diffusion region by the method, that is, the formation of the p base layer can be effectively applied to a large-diameter silicon substrate and a small-diameter silicon substrate. Further, as described above, it is possible to obtain a silicon substrate having a uniform and good impurity concentration.

[Brief description of drawings]

FIG. 1 is a diagram showing a process of one embodiment of the present invention, and FIG. 2 is a diagram showing an aluminum concentration distribution in a silicon substrate of one embodiment of the present invention. 1: Silicon substrate, 2: Aluminum ion, 3: Oxide film, 4:
Nitride film, 5: Oxide film.

Claims (1)

[Claims] 1. A step of forming an aluminum impurity added region in a silicon semiconductor substrate by ion implantation of aluminum, and a step of forming a first oxide film, a nitride film and a second oxide film on the surface of the semiconductor substrate after the ion implantation of aluminum. A method of manufacturing a semiconductor device, comprising: a step of covering, and a step of subsequently annealing.