JPS5912634B2 - Crystal diameter measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal diameter measurement method, and more particularly to a method for measuring the diameter of a crystal directly above a crystal melt during single crystal growth using the Cochralski method.

The Czochralski method is a typical method for growing single crystals.

As shown in Fig. 1, polycrystalline raw material 1 is made into a melt in a crucible 2, and a single crystal seed 3 is immersed therein.
By blending them well and pulling them up while rotating from 5, a cylindrical single crystal 4 having the same crystal orientation as the seed crystal 3 can be obtained. In this method, a high frequency induction coil or a resistance heating element 5 is used as the heating method, and the atmosphere is an inert gas such as argon or a vacuum.
When growing a single crystal using the Czochralski method as described above, it is extremely necessary to know the diameter of the crystal immediately above the crystal melt 1 during growth in order to control the shape of the grown crystal. To know the diameter of the crystal grown directly above the conventional crystal melt 1
5) Three methods have been used: (b) A method using a television camera, and a method in which the radius is calculated by measuring the time change of the crystal melt in the crucible over a period of 5 to 15 minutes. It had the following drawbacks:

In other words, method (a) relies on human cancer, and the reliability is low due to large individual differences in measurement values.Method (b) is based on a furnace structure that allows the entire crystal directly above the crystal melt to be seen from the outside. Blur caused by clouds on the quartz window, etc.
There is a large reading error due to optical noise such as diffused reflection (25), and (the method described above is the most reliable method for measuring the diameter, but the measurement depends on changes in the crystal melt in the crucible over a period of 5 to 15 minutes). Since it is necessary to calculate the crystal diameter by reading the changing voltage at the same time, it is impossible to quickly control the crystal diameter.3
0 The purpose of the present invention is to suppress the time change in the weight of the crystal melt in a short period of time (
It is an object of the present invention to provide a crystal diameter measuring method that measures the crystal diameter within 0.5 to 1 minute) and converts the measurement to the crystal diameter.

According to the present invention, a single crystal seed crystal is immersed in a crystal melt,
In the method of growing a single crystal by rotating and pulling the seed crystal, a voltage that changes according to changes in the weight of the crystal melt and a reference voltage source that changes in proportion to the pulse repetition frequency are used. The crystal diameter is characterized in that the diameter of the single crystal grown directly above the crystal melt is measured by comparing and measuring the pulse repetition frequency when the difference between the voltage and the reference voltage becomes zero. A measurement method is proposed. The crystal measuring method according to the present invention will be explained in detail below. In the present invention, the crystal diameter is measured based on the change in crystal weight based on the following principle.

The following relationship exists between the crystal weight W and the crystal diameter D(t), assuming that the crystal length is 11 and the crystal density is ρs.

``When formula (1) is differentiated with respect to l, the set speed of crystal pulling is Dll/Dtl, and the effective speed of crystal pulling is Dl2/Dt, then D2: crucible diameter (substituting (3) into 2Y) - ~
, U2(4), the crystal diameter D can be expressed as.

When the crystal weight W is converted into a voltage V from the weight sensor, the crystal diameter can be determined from the voltage change d/Dt of the weight sensor. Conventionally, the value of DVdt has been calculated from voltage changes over 5 to 15 minutes, but in the present invention, the value of DVdt can be directly read using a reference weight signal generator. The reference weight signal generator includes a pulse oscillator 11, a pulse counter 12, and a DA converter 13, as shown in FIG. 2A.

The oscillation frequency of the pulse oscillator 11 can be changed freely, and its output is applied to the counter 12, and the output is applied to the DA converter 13 as a BCD code output. DA converter 13 is pulse oscillator 11
Obtain an analog output with a slope proportional to the number of pulses per unit time. Figure 2B shows the oscillation frequencies A, a' of the pulse oscillator 11 and the staircase wave outputs B, b' due to the oscillation frequencies.
, and the rectified analog outputs C and c', showing that the higher the oscillation frequency of the pulse oscillator 11, the steeper the change in the output voltage. That is, when the number of pulses increases from n1 to N2 during time Δt from time t1 to time T2, the increase Δv in the output voltage of the DA converter 13 becomes.

Here, if T, -T2 = l seconds, then N, -N2 are the oscillation frequency f of the pulse oscillator, so equation (6) becomes Δv
/person t is proportional to the oscillation frequency of the pulse oscillator. (3)
The relationship between the output voltage change of the weight sensor and the crystal diameter is −
Since one ＼ νZll, k
= 1V, and match the output voltage of the D-A converter and the output voltage of the crystal weight sensor using a differential amplifier, so that the output changes of both are equal, that is, the output voltage of the weight sensor. By changing the number of pulses so as to make the difference between the output voltage and the output voltage from the D-A converter zero, the crystal diameter D (
The following relationship holds true between t) and the pulse oscillation frequency f.

In this way, by adjusting the pulse oscillation frequency so that the difference between the output voltage of the reference weight signal generator and the output voltage of the crystal weight sensor becomes zero, it is almost proportional to the oscillation frequency and the square of the crystal diameter, so it is easy to adjust the pulse oscillation frequency during growth. You can find out the diameter of the crystal.

Example: Using a crucible with a diameter of 80φ, LiNbO with a diameter of 50φ
, and measured the crystal diameter while growing them.

It was found that the relationship between the time change in the weight of the grown crystal and the crystal diameter is as shown in FIG. 3, and that the pulse frequency and the weight change are proportional as shown in FIG. 4.

The crystal diameter measured by the pulse frequency during crystal growth is shown in FIG. 5, and the error from the actual value was within ±3 (f). In Figure 3, the horizontal axis is the weight change per hour 9/
The vertical axis shows the crystal diameter, and the vertical axis shows the crystal diameter.

In Figure 4, the horizontal axis is the weight change per hour 9/Nr
The vertical axis indicates the frequency in KHz. In FIG. 5, the horizontal axis shows growth time Hr, and the vertical axis shows diameter capacity. Here, FIGS. 3 and 4 are used to determine the diameter from the pulse repetition frequency. That is, first read the weight change from the pulse repetition frequency using Fig. 4, then use Fig. 3,
Read the crystal diameter from the weight change. As explained in detail above, in short, the present invention measures the diameter of the grown single crystal directly above the crystal melt during single crystal growth using the Czochralski method, which changes in accordance with the change in the weight of the grown single crystal. The diameter is measured by comparing the voltage with the voltage from a reference signal source and counting the repetition frequency of pulses per unit time. Although the reference signal generator shown is used, it is clear that there are various other variations of this signal generator.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the single crystal growth method using the Czochralski method, Fig. 2A is a process diagram of the crystal diameter measurement method according to the present invention, and Fig. 2B is the output waveform from the pulse oscillator and D- A diagram showing the relationship between the waveforms from the A converter, Figure 3 is a diagram showing the relationship between weight change per hour and diameter change, Figure 4 is a diagram showing the relationship between weight change per hour and frequency,
FIG. 5 is a diagram showing changes in diameter with respect to growth time.

Claims (1)

[Claims] 1. In the method of growing a single crystal by dipping a single crystal seed crystal into a polycrystalline raw material melt and pulling the seed crystal while rotating, the voltage and pulses are changed according to the change in the weight of the crystal melt. A single crystal grown directly above the crystal melt by comparing the pulse repetition frequency with a reference voltage that changes in proportion to the repetition frequency and measuring the pulse repetition frequency when the difference between the voltage and the reference voltage becomes zero. A crystal diameter measuring method characterized by measuring the diameter of a crystal.