JPH0362679B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for growing crystals by pulling (CZ) method, and particularly to a method for growing crystals so that the specific resistance value in the direction of the pulling axis is constant.

Crystals such as silicon (Si) used in semiconductor device manufacturing contain boron (B) as a p-type impurity, and phosphorus (P), arsenic (As), and antimony (Sb) as n-type impurities.
etc., and set a certain specific resistance value (usually 0.01~
100Ωcm (selected depending on the application).

Due to design requirements, it is desirable for semiconductor devices to have a uniform resistivity distribution, but due to segregation in crystals grown by the normal CZ method, the impurity concentration distribution in the pulling axis direction changes according to the following equation. ¹⁾ C=KC ₀ (1-l) ^K-1 , where C ₀ is the initial impurity concentration in the melt, l is the ratio of the amount crystallized to the initial melt amount (solidification rate), and C is the solidification rate. The impurity concentration at a rate l, k is the segregation coefficient.

The specific resistance distribution in the direction of the pulling axis is determined by the concentration distribution of the impurities taken in according to the above equation.

Figure 3 shows the resistivity distribution of typical impurities, 20Kg
This is the calculated value when a 4-inch crystal is pulled from the melt.

As can be seen from the figure, when the uniformity of the crystal resistivity required for a semiconductor substrate becomes strict, only a portion of the pulled single crystal can be used, and the yield decreases. This tendency is more severe for impurities with a smaller segregation coefficient k.

Therefore, various methods are used to improve the uniformity of the specific resistance of the crystal.

(Reference) 1 WGPfann, AIME 194 , 747 (1952). [Prior Art] Below, a conventional example of a method for improving the uniformity of specific resistance of a crystal will be shown.

i Multiple Ingot Growth Method ²⁾ In this method, pulling of a single crystal is once completed at the limit of the required resistivity width, a new polycrystal is added to the melt, the impurity concentration is adjusted, and the crystal is pulled again.

Continuous Charge Method ³⁾ As shown in Figure 4, this is a method in which melt is continuously added during single crystal pulling. By making the pressure in the melting furnace 12 higher than that in the single crystal growth furnace 13, the melt 2 is moved so that the impurity concentration of the melt in the growth furnace 13 is always kept constant.

In the figure, 14 is a communication pipe for moving the melt, 15 is a heater, 16 is an argon gas inlet, 17 is an internal pressure control valve, 18 is a melt level position sensor, and 19 is an automatic diameter control sensor.

Double crucible method ⁴⁾ As shown in Fig. 5, the quartz crucible is doubled and the inner and outer crucibles 1A and 1B are connected through a thin tube 20, and the impurity concentration C' in the inner crucible is set as C'=C ₀ /K. If so, the concentration of impurities taken into the crystal will always be C ₀ .

However, each conventional method has the following drawbacks.

The yield rate is poor because the straight body portion of the single crystal obtained is small compared to the total amount of melt, and it is easily contaminated during recharging.

The equipment becomes large-scale and uneconomical.

The equipment becomes complex and the internal crucible is difficult to hold, rotate and adjust.

(Reference) 2 RLLane and AHKachare, J.Crys.Growth 50 , 437 (1983). 3 G. Fiegl, Solid State Technology, August,
121 (1983). 4 KEBenson, W.Lin and EPMartin, Semiconductor Silicon 1981, 33
(1981). [Problems to be solved by the invention] The conventional method of improving the uniformity of the resistivity of crystals using the CZ method has poor yields and may cause contamination, or the equipment is complicated and large-scale, making it difficult to operate and maintain the equipment. , difficult to adjust.

[Means for solving problems]

The solution to the above problem is to grow a silicon crystal by a pulling method using a silicon melt containing boron as an impurity. This is achieved by a crystal growth method characterized by growing the crystal while gradually melting it.

[Effect]

During crystal growth, a crystal containing impurities of the opposite conductivity type to the impurities contained in the melt is dissolved and both types of impurities are incorporated into the single crystal, and these impurities cancel each other out to produce a carrier corresponding to the compensated value. By keeping the concentration (this value is related to specific resistance) constant, uniformity in the specific resistance of the crystal can be obtained using a relatively simple device.

〔Example〕

FIG. 1a is a schematic cross-sectional view of a device showing an embodiment of the present invention.

The figure shows the case of growing a p-type Si crystal of about 10 Ωcm.

First, a Si single crystal doped with B is placed in a quartz crucible 1 and melted to obtain a melt 2. Immediately before entering the straight body after the start of growth, the n-type Si crystal 3 containing P is melted 2.
The Si single crystal 4 is immersed in water and gradually melted as the Si single crystal 4 grows. In this case, the n-type Si crystal 3 containing P is preferably cylindrical as shown in the figure in order to improve the resistivity distribution in the cross section perpendicular to the pulling axis.

In addition, the pulling down speed of the n-type Si crystal 3 containing P is:
Pulling speed, diameter, and n including P of Si single crystal 4
It varies depending on the P concentration of the type Si crystal 3 and the contact area with the melt, and is adjusted so that a p-type Si single crystal 4 of 10 Ωcm can be obtained.

Note that 5 is a motor, 6 is a molybdenum (Mo) wire, 7 is a motor, and 8 is a heater.

FIG. 1b is a perspective view of an n-type Si crystal 3 containing P.

FIG. 2 shows the distribution of crystals obtained according to the present invention in the direction of the pulling axis.

If the allowable range of specific resistance is 10 ± 1 Ωcm, the normal CZ method shown by the dotted line can only use about 25% of the total melt as shown in 10, but according to the present invention, 11
As shown in the figure, approximately 70% can be used.

Further, the pull-down drive section of the n-type Si crystal 3 containing P can be easily made.

Furthermore, consider the crystallinity of a crystal in which a P impurity is mixed with a B impurity. If the covalent bond radius of Si is 1, then B is 0.75 and P is 0.94, indicating that P has smaller distortion due to the difference in bond radius. ⁵⁾ When the microdefect density of the crystal actually obtained according to the present invention was evaluated using Secco etching, it was found that
It was found that the crystallinity was approximately 10 ³ cm ^-2 , which is the same level as when no P is introduced, and that it does not affect crystallinity.

(Reference) 5 Hideki Tsuya, Yojiro Kondo, Masaru Kanamori, Proceedings of the 30th Applied Physics Association Lecture (1983) p.662 [Effects of the Invention] As explained in detail above, according to the present invention,
In the CZ method, there is no risk of contamination, the equipment is easy to operate, maintain, and adjust, and the uniformity of the resistivity of the crystal is improved, and the defect density does not increase.

[Brief explanation of drawings]

FIGS. 1a and 1b are a schematic cross-sectional view of a device showing an embodiment of the present invention, a perspective view of an n-type Si crystal containing P,
Figure 2 is a distribution diagram of the crystal obtained by the present invention in the pulling axis direction, Figure 3 is a resistivity distribution diagram of typical impurities in the pulling axis direction by the ordinary CZ method, and Figure 4 is a diagram of the resistivity distribution diagram of the conventional continuous charge crystal. FIG. 5 is a schematic sectional view of an apparatus using the conventional double crucible method. In the figure, 1 is a quartz crucible, 2 is a melt, and 3 is a quartz crucible.
4 indicates an n-type Si crystal containing P, and 4 indicates a p-type Si single crystal.

Claims (1)

[Claims] 1. In a method of growing silicon crystals by a pulling method using a silicon melt containing boron as an impurity, as the crystal grows, a crystal containing phosphorus is grown while being gradually dissolved in the melt surrounding the growing crystal. A crystal growth method characterized by: