JPH08259374A - Method for growing si single crystal with radially uniform impurity concentration distribution - Google Patents

Abstract

PURPOSE: To obtain, through Czochralski process, a Si single crystal uniformized in impurity concentration distribution in its radial direction. CONSTITUTION: When a Si single crystal is pulled up from a Si melt added with Ga or Sb through Czochralski process, element(s) capable of increasing the thermal expansion coefficient of the melt in the vicinity of its melting point (at least one kind of element selected from between B and P) is further added to the melt. As the result, agitation of the melt just under the growth interface can be promoted, and as the Si single crystal is pulled up from the melt uniformized in impurity concentration distribution, the Si single crystal uniform in impurity concentration distribution in its radial direction can be grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a Si single crystal having a uniform impurity concentration distribution in the radial direction from a melt.

[0002]

2. Description of the Related Art The Czochralski method is a typical method for growing a Si single crystal from a melt. In the Czochralski method, as shown in FIG. 1, a crucible 2 arranged inside an airtight container 1 is supported by a support 3 so as to be rotatable and vertically movable. A heater 4 and a heat insulating material 5 are concentrically provided on the outer periphery of the crucible 2, and the raw material contained in the crucible 2 is intensively heated by the heater 4 to prepare a melt 6. Melt 6 is S
i is maintained at a temperature suitable for single crystal growth. A seed crystal 7 is brought into contact with the melt 6 to grow a Si single crystal 8 following the crystal orientation of the seed crystal 7. The seed crystal 7 is hung from a rotary winding mechanism 10 or a rigid pulling rod via a wire 9, and is pulled while rotating according to the growth of the Si single crystal 8. The crucible 2 also descends while rotating appropriately via the support 3. The descending speed and rotating speed of the support 3 and the rotating speed and rising speed of the seed crystal 7 are controlled according to the growth speed of the Si single crystal 8 pulled up from the melt 6.

[0003]

Various impurities are added to the melt 6 in order to impart various required characteristics to the Si single crystal 8. However, the behavior of the melt at the growth interface may vary depending on the type of added impurities. Above all, Si doped with impurities such as Ga and Sb
In the melt, the melt stirring effect is easily reduced, and accordingly, the impurity distribution in the radial direction becomes nonuniform. The present inventors presume the cause of non-uniform impurity concentration as follows. That is, the melt containing Ga or Sb has a thermal expansion coefficient of about 6.0 × 10 ⁻⁶ / ° C. near the melting point, and the turbulent flow effect depending on the thermal expansion coefficient is reduced. Therefore, the added impurities are not sufficiently agitated, and as a result, the impurity concentration in the radial direction is non-uniform immediately below the growth interface. The non-uniform impurity concentration distribution is preserved as it is in the impurity boundary layer formed immediately below the interface and taken into the crystal. as a result,
The impurity concentration of the pulled Si single crystal becomes unstable in the radial direction, which deteriorates the quality stability of the obtained Si single crystal. The present invention has been devised to solve such a problem, and an element that increases the coefficient of thermal expansion is Si.
It is an object of the present invention to improve the action of diffusing the melt just below the growth interface by additionally adding it to the melt, and to obtain a high-quality Si single crystal having a uniform impurity concentration in the radial direction.

[0004]

Means for Solving the Problems The method for growing a Si single crystal of the present invention is such that when a Si single crystal is pulled from a Si melt added with Ga or Sb by the Czochralski method, the heat of the melt near the melting point is increased. It is characterized in that an element for increasing the expansion coefficient is additionally added to the melt. B or P is used as an element for increasing the coefficient of thermal expansion. These elements are added so that the added impurities (Ga or Sb) and the group (group III or IV) belonging to the periodic table are the same, and the resistance value after addition is 0.001 to 10 Ω · cm. The addition amount is set in the range of 1 × 10 ^{18 to} 5 × 10 ²⁰ atoms / cm ³ .

[0005]

The non-uniformity of the impurity concentration distribution in the radial direction of the single crystal pulled from the Si melt depends on the uniformity of the impurity concentration distribution of the melt just below the growth interface.
Therefore, in order to make the impurity concentration distribution in the radial direction uniform, it is necessary to activate the stirring of the melt immediately below the growth interface. According to the study by the present inventors, when elements such as B and P which increase the thermal expansion of the melt are added,
It was found that the stirring of the melt was promoted just below the growth interface. That is, in the melt containing elements such as B and P, the thermal expansion locally increases just below the growth interface near the freezing point. Therefore, the difference in thermal expansion between the melt and the surrounding melt becomes large, and the circulating flow of the melt is accelerated due to the difference in thermal expansion. As a result, the melt immediately below the growth interface is sufficiently stirred, and the impurity concentration distribution in the radial direction is made uniform. Therefore, the Si single crystal pulled up from this melt becomes a high-quality crystal with a uniform impurity concentration distribution in the radial direction.

[0006]

Example To 5 kg of Si raw material added with 0.1 atom% of Ga or Sb, 10 ¹⁵ atom / cm ^{3 of} B or P was further added, and melted in a crucible. Then, the Si melt was held in a chamber filled with argon gas until the start of pulling the single crystal. From the temperature dependence of the density shown in FIG. 2, the melt added with Ga or Sb is estimated to have a thermal expansion coefficient of about 6.0 × 10 ⁻⁶ / ° C. in the temperature range of melting point to 1430 ° C. Particularly, in the temperature range from the melting point to 1430 ° C., the rapid fluctuation of the density is alleviated, the sufficient stirring action cannot be obtained, and the impurity distribution in the melt is homogenous. In the case where B or P is further added to this melt, the melting point to 1 is obtained from the temperature dependence of the density when 0.1 atom% B or P is added as shown in FIG.
Coefficient of thermal expansion in the temperature range of 430 ° C is about 1.5 x 10
It is estimated to be ^-3 / ° C. That is, it is expected that the coefficient of thermal expansion will increase as compared with the case of adding Ga or Sb, and the circulation flow becomes active in the melt.

Actually, a diameter of 3 inches and a length of 200 are obtained from the Ga-doped Si melt and the Ga, B-doped Si melt, respectively.
The Si single crystal of mm was pulled up, and the impurity concentration in the growth direction was measured. As shown in FIG. 3, which shows the measurement results, when B was not added to the Ga-doped Si melt, the radial resistivity variation was ± 20%. On the other hand, when B is further added, the fluctuation of the resistivity is suppressed within the range of ± 5%. As is clear from this contrast,
By adding an element that increases the coefficient of thermal expansion,
It was confirmed that sufficient stirring of the melt was ensured just below the growth interface, and a Si single crystal with a uniform impurity concentration distribution in the radial direction was obtained.

[0008]

As described above, in the present invention, Ga or S added with an element that increases the coefficient of thermal expansion.
S from the b-doped Si melt by the Czochralski method
i Single crystal is grown. The element that increases the coefficient of thermal expansion exhibits an action of sufficiently stirring the melt just below the growth interface,
It enables a single crystal to be grown from a melt with a uniform impurity concentration distribution. Therefore, the obtained Si single crystal is a high-quality single crystal with a uniform impurity concentration distribution in the radial direction.

[Brief description of drawings]

FIG. 1 Czochralski method for pulling Si single crystal from melt

FIG. 2 is a graph showing the relationship between the density and the temperature of a Si melt to which various impurities are added.

FIG. 3 is a graph showing a resistance value of an impurity concentration distribution in a growth direction of a pulled Si single crystal.

[Explanation of symbols]

1: Airtight container 2: Crucible 3: Support 4:
Heater 5: Heat insulating material 6: Melt 7: Seed crystal 8: Si single crystal 9: Wire 10: Rotating winding mechanism

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 595056491 Hitoshi Sasaki 1-545 Taiseicho, Omiya-shi, Saitama Prefecture (71) Applicant 595056505 Atsushi Ikari 2-12-15 Tokodai, Tsukuba-shi, Ibaraki (72) Inventor Kawanishi Zhuang (6) 1-16-2 Tokodai, Tsukuba, Ibaraki Prefecture (72) Koji Izumizuma 1770-1-502, Arakawa-oki, Ami-cho, Inashiki-gun, Ibaraki Prefecture (72) Shinji Togawa 4182-3, Imakashima, Tsukuba-shi, Ibaraki ( 72) Inventor Hitoshi Sasaki 1-545 Taisei-cho, Omiya-shi, Saitama Prefecture (72) Inventor Shigeyuki Kimura 3-712 Takezono, Tsukuba-shi, Ibaraki (72) Inventor Atsushi Ikari 2-12-15 Tokodai, Tsukuba-shi, Ibaraki

Claims (2)

[Claims] 1. When pulling a Si single crystal from a Si melt added with Ga or Sb by the Czochralski method, an element for increasing the thermal expansion coefficient of the melt near the melting point is additionally added to the melt. A method for growing a Si single crystal having a uniform impurity concentration distribution in the radial direction, characterized in that 2. A method for growing a Si single crystal, wherein the element for increasing the coefficient of thermal expansion according to claim 1 is B or P.