JPH0196088A - Method for controlling diameter of single crystal - Google Patents

Abstract

PURPOSE:To reduce the deformation rate of single crystal by measuring the diameter of single crystal plural times and controlling the pulling velocity of single crystal and/or the temp. of melting liquid of raw material so that the ratio of difference between the max. and the min. dimensional values of diameter to the min. dimensional value approaches to zero. CONSTITUTION:The output signal of CCD camera 6 is inputted to a diameter calculating unit 8 through a processing unit 7 and the brightness distribution is binarized by the threshold value in the calculating unit 8. The measurement of the diameter is carried out plural times during one revolution of single crystal, and the max. and the min. dimensional values are taken out from the measured values to obtain the deformation rate. Namely, the measured values of diameter are arranged from smaller one to larger one in order and the deformation rate is calculated. Thus, the pulling velocity and/or the temp. of melting raw material are/is controlled so that the deformation rate approaches to zero, and these controls are carried out all over the full length of single crystal. Thus the deviation from the target value of diameter is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for accurately controlling the diameter of a single crystal in the production of a single crystal by the CZ method (Chickralski method).

[Conventional technology]

The C2 method is well known as a method for manufacturing single crystals such as silicon used for manufacturing IC5LSIs and the like. In this method, as shown in the schematic diagram of Fig. 2, a rotating crucible 1
A raw material melt 2 of silicon or the like contained in a crucible is pulled up and solidified while being rotated with respect to a crucible 1 by a wire 3, thereby producing a columnar single crystal 4. The produced single crystal is finished into a cylindrical ingot, and in order to increase the yield at that time, it is required that each part of the single crystal 4 be controlled to have the same diameter.

Previously, JP-A-48-50983, JP-A-48-53
As proposed in 973, etc., as a method of controlling this diameter, the diameter of the single crystal 4 is estimated from the photometry of the fusine ring 11 of the single crystal growth part 5 by optical means 6. The pulling speed of the single crystal 4 is adjusted so that the estimated diameter matches the target value.

[Problem that the invention seeks to solve]

When pulling a single crystal to −m, the faster the pulling speed, the higher the production amount. However, as the pulling speed increases, the cross section of the single crystal tends to deviate from a perfect circle and has an irregular outer shape inherent to the crystal lattice. Figure 5 shows this tendency.
For crystal Miller index 100〉, it is a quadrilateral ((a) in the same figure),
<111> has a strong tendency to be hexagonal (see figure (b)), and <511> has a strong tendency to be pentagonal (see figure (c)). When this tendency becomes stronger, as shown in FIG. 4, the single crystal outer shape 12, where φmax: maximum diameter φmin: minimum diameter, increases, and the surface becomes smaller than the part of the inscribed circle 13 that is to become a product. The cutting allowance 14 due to the unevenness increases, reducing the yield.

The present invention provides a single crystal diameter control method that solves this problem and improves the yield.

[Means for solving problems]

As shown in FIG.
The diameter of the single crystal 4 is measured multiple times during one rotation of the single crystal 4, and the ratio of the difference between the maximum dimension and the minimum dimension to the minimum dimension, that is, the deformation rate, is preferably O~0.0 so as to approach 0.
The pulling speed of the single crystal 4 and/or the temperature of the raw material melt 2 are controlled to an arbitrary value between 2 and 2, and this is continued over the entire length of the single crystal 4.

In the method of the present invention, it is preferable to measure the diameter more often per rotation of the single crystal because the precision improves, but it is particularly preferable to measure the diameter more than 10 times per rotation for the following reasons.

For example, when a single crystal is pulled in the direction of the Miller index HOO), the thinnest portions appear around 10 degrees on both sides of the habit line. That is, it is necessary to measure every 20 degrees at most. Therefore, to reduce the measurement error to 0.1 mm or less, the circumference should be at least 2
It is necessary to perform 0 divisions, and this can be achieved by reducing the number of diameter measurements per revolution to 0.

[For production]

Is it possible to control the deformation rate to be close to 0 when pulling a single crystal? Therefore, the deformation rate can be maintained at an optimum level.

Therefore, production efficiency is high and yield can be improved.

〔Example〕

Hereinafter, the method of the present invention will be specifically explained with reference to Examples.

The conventional method can be applied as is to the diameter measurement method. To briefly explain FIG. 2 and FIG.
It was installed so that the horizontal brightness distribution was measured toward the center of the interface between the two. The output signal of the CCD camera 6 is input to a diameter calculation device 8 via a processing device 7. Processing device 8
Now, as shown in FIGS. 3(a) and 3(b), the above luminance distribution is disulfidized using a threshold value 9. As shown in the same figure (c), if the pixel numbers at both ends of the two 1 signals corresponding to both ends of the fusion ring in the photometric direction are NA and NA, the diameter φ (crane) of the single crystal is φ-8× (NA-NI) [1] A) where S: Width of pixel element (n) Measured by computing device date.

In the diameter control method of the present invention, such diameter measurement is performed multiple times, preferably 10 times or more, during one rotation of the single crystal. Then, the minimum dimension and maximum dimension are taken out from among them, and the deformation rate is determined.

For example, assuming that the diameter is measured 13 times per revolution of a single crystal, 1.2. −・−, diameter φ of the part indicated by 13
1. φ2.・−−１−−−・・φ1. is φ+=129
n φ, -128,4tm φ3=129.1 Cao φ,=131. On φS-129, 5 Soso φ = 128.5-1 φ,, -129. On, these φ, ~φ1. are sorted in descending order, and the maximum value φmax (in this case φ4-131.
0ryu) and the minimum value φm1n (in this case φ2=128.4
■Meeting) to calculate mm i n .

Once the deformation rate is determined, the pulling speed and/or raw material melt temperature is controlled so that the deformation rate approaches 0, and this control is performed over the entire length of the single crystal. In this case, it goes without saying that general diameter control is also carried out to ensure the target diameter.

To explain such diameter control more practically, the average diameter φ(1) of the pulled single crystal is set as the target diameter φ. The relationship between the pulling speed vP and the measured diameter φ(1) can generally be expressed by a diameter control function as shown in the following equation.

VP = V (jri 1P ・(φ(t)
+110)t However, vp: Pulling speed (mm/min) v<it'
>: Pulling length at average pulling speed! (determined by diameter φ) (mm/m1n) φ(t): Measured diameter and function of time t (min) (mm) φ. : Target diameter (mm) P : Coefficient (1/m1n)! = Integration time (17min) D: Differential coefficient, as shown in +11 formula, the pulling speed Vp is calculated by the average pulling speed v (g, the measured diameter φ (1) which is always continuously measured) A proportional value with a proportional coefficient P for the difference from the target diameter φ, an integral proportional value with an integral coefficient ! proportional to the integral value during the elapse of τ time, and a differential proportional value with a differential coefficient ! about the differential value. It is expressed as the sum of .

However, diameter control using the +11 formula cannot cope with disturbances such as polygonization caused by crystal orientation.Therefore, in the diameter control method of the present invention, in order to cope with such disturbance deformation, the above-mentioned [ The following diameter control function formula is used, which is improved by adding a correction function F(σ) which is a function of the deformation rate σ to the formula 1].

v,=v <t> +p・(φ(1)−φ.)t +F(σ) −・−・・−・−・・ (2
) (2) means that the deformation rate of the single crystal outer shape 12 is controlled to be small by controlling the change in diameter φ ([) and the pulling speed so that the single crystal has a constant average diameter. As a result, even if the single crystal has a constant average diameter, there is little variation in the outer shape in the circumferential direction, and the yield can be improved.

The results of actually controlling the diameter of single-crystal silicon using the above method will be explained below in comparison with the conventional method.

In the method of the present invention, the diameter is measured 13 times each time the single crystal rotates, and the minimum and maximum dimensions are taken out of them.
The deformation rate was determined, and the single crystal diameter was controlled to the target diameter while adjusting the pulling speed so that the deformation rate was within 0.005 o, oos. In other words, when the deformation rate was 0.005 or more, the pulling speed was reduced (and when the deformation rate was smaller than o, o o s, the pulling speed was increased.On the other hand, in the conventional method, such deformation The pulling was performed while controlling the minimum diameter to the target diameter without making any corrections based on the rate.In addition, in the conventional method, the average pulling speed was set at 1°I, which is the same as in the method of the present invention.
n/min, smaller than 1. Table 1 summarizes the zero conditions under which two types of tests were carried out, with Owm/min.

Table 1 and Figure 6 show the maximum and minimum diameters of the obtained single crystal at seven points in the longitudinal direction of the single crystal (0.100.2 from the top of the effective part).
00 to 600).

As is clear from Fig. 6, in the method of the present invention, the deformation rate is controlled to less than 0.005±o,oos over the entire length of the single crystal, the deviation from the target diameter is small, and there is sufficient margin between the diameter and the product diameter. be. On the other hand, in conventional method I which gave the same average pulling speed as the method of the present invention, the deformation rate increased to 0.02 on average in the longitudinal direction. The cutting amount is approximately 1.5% compared to the method of the present invention.
It increased. In addition, although there is no particular problem with this conventional method I, if the deformation rate is large, there will be parts that are smaller than the product diameter locally, increasing the risk that the entire single crystal will become a defective product. In this case, the deformation rate was within 0.07, and the amount of cutting was not much different from that of the method of the present invention, but the pulling speed was reduced by 9% compared to the method of the present invention, which was significantly improved in terms of manufacturing efficiency. Inferior.

FIG. 7 shows the relationship between the number of measurements and the deformation rate (average value in the longitudinal direction) when the number of diameter measurements was varied under the conditions shown in Table 1 (method of the present invention).

From the same figure, it can be seen that the deformation rate decreases as the number of measurements increases, and a significant effect is obtained especially when the number of measurements is 10 or more.

〔Effect of the invention〕

As is clear from the above description, according to the method of the present invention, the deformation rate of the single crystal is reduced and deviation from the target diameter is suppressed. As a result, the amount of cutting during cutting is reduced, the risk of locally falling short of the product diameter is reduced, and the target diameter can be brought closer to the product diameter, so yield improvement can be measured from this perspective as well. It is possible,
Furthermore, since the pulling speed can be increased, a great effect is exhibited in reducing the manufacturing cost of single crystals or product wafers.

[Brief explanation of the drawings] Fig. 1 is a schematic diagram showing the diameter measurement position according to the method of the present invention, Fig. 2 is a schematic diagram showing general single crystal pulling and single crystal diameter measurement, and Fig. 3 is a schematic diagram showing the diameter measurement position of a single crystal according to the method of the present invention. A diagram showing the signal processing procedure in measuring the diameter of a crystal, Fig. 4 is a schematic diagram showing the cross-sectional shape of a single crystal, Fig. 5 is a schematic diagram showing cross-sectional deformation due to the crystal Miller index of a single crystal, Fig. 6 and FIG. 7 are graphs showing the effects of the present invention. l: crucible, 2: raw material melt, 3: wire, 4: single crystal,
5: Single crystal growth part, 6: Optical means (COD camera),
7: output signal processing device, 8: diameter needle n device, 9: threshold value, 11: fusion ring. Applicant Osaka Titanium Manufacturing Co., Ltd. 1st day 5th entry [1] 1> Fig. 6 Deformation rate crystal length [mm1 ff, Fig. 7

Claims (1)

[Scope of Claims] [1] The raw material melt (2) in the crucible (1) is transferred to the crucible (1).
In manufacturing the single crystal (4), which is pulled into a columnar shape and solidified while rotating, the diameter of the single crystal (4) is measured multiple times during one rotation of the single crystal (4), and its maximum and minimum dimensions are The pulling speed of the single crystal (4) and/or the raw material melt (
2) A method for controlling the diameter of a single crystal, comprising controlling the temperature. [2] Single crystal (4
2. The method for controlling the diameter of a single crystal according to claim 1, characterized in that the pulling speed of the raw material melt (2) and/or the temperature of the raw material melt (2) are controlled.