JPH07321060A - Boron diffusion method - Google Patents

Abstract

PURPOSE:To provide a method for diffusing boron, which makes even the boron impurity concentration all over the surface of a silicon substrate, keeps the diffusion depth of the boron constant and is high in reproducibility. CONSTITUTION:In a two-step diffusion method consisting of an impurity concentration reduction treatment process and an impurity concentration redistribution treatment process, the time to.start a substitution of boron for dry O2 is staggered after the heat treatment temperature of the boron reaches a prescribed heat treatment temperature (950 deg.C or higher) in the former impurity concentration reduction treatment process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diffusing boron in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In the case of deeply diffusing impurities into a silicon substrate, for example, boron nitride (BN) or boron tribromide is used, and then a predeposition is performed to form a boron-glass layer on the surface of the silicon substrate. A method is known in which heat treatment is performed in a wet O ₂ atmosphere at a temperature of 1100 ° C. or higher to deeply diffuse the impurities doped on the substrate surface into a silicon substrate. However, such a method does not cause any particular problem when a relatively high surface concentration is obtained, but it is relatively low, that is, 4.0.
In order to obtain a surface concentration of × 10 ¹⁹ cm ^-3 or less without significantly reducing the diffusion depth, a heat treatment (impurity redistribution treatment) step performed at a temperature of 1100 ° C. or higher in a wet O ₂ atmosphere. Before 950 ℃, above 1100
It has been used to perform a preliminary heat treatment performed in a dry O ₂ atmosphere at a constant temperature in a temperature range lower than ° C.

[0003]

However, when this preliminary heat treatment is used, the impurity concentration and the diffusion depth are controlled by adjusting the temperature and time of the dry O ₂ atmosphere. In that case, the diffusion depth is controlled. Has a drawback that it is difficult to control the constant. When the concentration is to be obtained in 0.1 to 0.5 × 10 ¹⁹ cm ^-3 unit while keeping the diffusion depth constant,
There is a problem that the variation of the impurity concentration in the silicon substrate and between the substrates becomes large, the accuracy of the desired concentration cannot be ensured, and the heat treatment time is significantly increased.

The present invention provides a diffusion method which is excellent in reproducibility and mass productivity when performing a preliminary heat treatment in a dry O ₂ atmosphere and keeps the diffusion depth constant while maintaining the uniformity of the impurity concentration over the entire silicon substrate. This is an issue.

[0005]

As a means for solving the above problems, when performing a preheat treatment at a predetermined temperature higher than 950 ° C., the atmosphere is replaced with dry O ₂ when the predetermined temperature is reached. Instead of doing it, after a certain amount of time,
By replacing with a dry O ₂ atmosphere, the boron ion concentration in the boron-glass layer is controlled, and the boron concentration can be finely controlled while keeping the concentration of the entire silicon substrate surface uniform.

[0006]

The boron diffusion process of the present invention is as follows. That is, the sample after completion of the predeposition step in which a boron-glass layer was formed on the surface of the silicon substrate was subjected to T ₁ (for example,
The temperature is raised to 1025 ° C. After reaching T ₁ , a certain time (for example, 1 minute or 3 minutes) has elapsed, and then the gas atmosphere is switched to dry O ₂ . A preliminary heat treatment at a dry O ₂ atmosphere at a constant temperature of T _1, then, T ₂ (e.g., 1100 ° C.) in an N ₂ atmosphere was heated to a temperature of, it switched to a wet O ₂ atmosphere, constant temperature T _This is a two-step boron diffusion method in which the impurity is redistributed while being held at ₂ . The preliminary heat treatment (impurity concentration reduction treatment) performed in this dry O ₂ atmosphere enables reduction of the impurity concentration to be controlled over a wide range at a constant temperature.

In order to obtain the same impurity concentration without using the present invention, the temperature and gas atmosphere shown in FIG. 2 are used, but T ₁ 'is lowered or dry O ₂ treatment time at T ₁ ' It is conceivable that the former will reduce the diffusion depth,
The latter is a significant time increase (dry O ₂ treatment time is 30 minutes or more)
Moreover, the diffusion depth varies.

[0008] preliminary heat treatment method delayed the substitution of dry O ₂ atmosphere according to the present invention, by delaying the substitution of a dry O ₂ atmosphere, presumably by controlling the protrusion of impurities into the atmosphere. In this respect, the concentration can be finely controlled over a wide range more finely than the conventional preliminary heat treatment method, and the diffusion depth can be kept constant by keeping the heat treatment temperature constant.

[0009]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 shows an example of the temporal structure of temperature and gas atmosphere in the boron diffusion treatment step of the present invention.

After the pre-devolution, the sample was treated with T in accordance with the temperature and gas atmosphere program shown in FIG.
_The temperature is raised to ₁ (1025 ° C). After reaching T ₁ , time t
= 1 minute later, the N ₂ gas atmosphere is switched to the dry O ₂ atmosphere. 5 l / min for 10 minutes at temperature T ₁
Impurity concentration reduction treatment is performed in a dry O ₂ atmosphere, and then the temperature is raised to a temperature of T ₂ (1100 ° C.) in an N ₂ atmosphere, and then at a temperature of T ₂ for 50 minutes, 5 l / min wet O ₂ When impurities are redistributed in an atmosphere,
Surface concentration is 3.0-3.5 × 10 impurities ¹⁹ cm ^-3 next, t = 3 min and the case 3.5 to 4.0 × 10 ¹⁹ cm ^-3
Becomes

[0011] Without using the present invention, in order to obtain the same impurity concentration, reduce the T _1, it is conceivable to lengthen the dry O ₂ processing time at T _1, the former diffusion depth However, in the latter case, the time is significantly increased (processing time in the dry O ₂ atmosphere is 30 minutes or more), and it is difficult to control the diffusion depth.

Therefore, according to the present invention, since it is not necessary to remove the boron-glass layer for reducing impurities, 4.0 × 10 while maintaining the advantage that there is no fear of contamination with metal ions or the like. It is possible to finely control the boron surface concentration and the diffusion depth of ¹⁹ cm ⁻³ or less.

It was also confirmed that the gas was not easily affected by the turbulent flow of the gas in the reaction tube and a slight change in concentration.

[0014]

As described above, in the preheat treatment (impurity reduction treatment) method of the present invention, when the predetermined heat treatment temperature is reached, the atmosphere is not switched to dry O ₂ but is delayed for a certain time. The boron diffusion method is capable of finely adjusting the concentration of low-concentration impurities over a wide range, the impurity concentration on the entire surface of the silicon substrate is constant everywhere, and the diffusion depth hardly changes.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a temporal structure of temperature and gas atmosphere in a boron diffusion heat treatment method according to the present invention.

FIG. 2 is an explanatory diagram showing a temporal structure of temperature and gas atmosphere in a conventional boron diffusion heat treatment method.

Claims (1)

[Claims] 1. A predeposition step of diffusing boron into a silicon substrate to form a boron-glass layer on the substrate, a preliminary heat treatment step of heat treatment in a dry O ₂ atmosphere, and a heat treatment in a wet O ₂ atmosphere. In the method for diffusing boron, which comprises an impurity redistribution treatment step, the temperature of the silicon substrate after the predeposition step is raised to 95
A method of diffusing boron, characterized in that the atmosphere is switched to dry O ₂ after a predetermined time has elapsed after reaching a preheat treatment temperature higher than 0 ° C.