JPH03275588A - Method for monitoring diameter of single crystal in pulling-up single crystal and automatically controlling method for diameter - Google Patents

Abstract

PURPOSE:To catch the fine change in weight and to precisely and automatically control the diameter of pulled-up crystal by substracting the reference signal changed at every unit time from the output signal of a weight sensor and performing the temp. regulation of melt with the signal of the changing part obtained by this substraction. CONSTITUTION:The reference signals b1, b2,... sent from a standard voltage generator 7 are changed at every unit time and substracted from a signal (a) output from a load cell 1 to catch only the change part of weight by a substraction circuit 1a. These reference signals b1, b2,... are made by sending a signal (d) to the generator 7 from the interface 8 of a computer 13. Thereby the signal (c) of the changing part of a voltage signal is obtained as data. In the computer 13, the diameter of single crystal is calculated from the selected signal and furthermore controlling treatment is performed and temp. regulation of the melt 3 performed by utilizing a regulating meter 12 for a high-frequency heating oscillator and a high-frequency heater 5 via an interface 11. Thus, diameter of pulled-up crystal is controlled according to a signal (e) inputted from a data input-output device 14 by controlling the temp. of the melt 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is based on the Czochralski method, which detects the weight of a pulled single crystal and controls the crystal diameter by changing the rate of increase according to a predetermined program. The present invention relates to a method for monitoring the diameter of a single crystal and an automatic diameter control method in single crystal pulling by the method.

[Prior art]

In the above-mentioned Czochralski method, a gravimetric measurement control technique for calculating the diameter change from the pulled crystal using a weight sensor and controlling the diameter is already known, for example, in Japanese Patent Application Laid-Open No. 50-8680.

[Problem to be solved by the invention]

However, since the measurement range of the load cell is wide and the pulled crystal is light, the weight signal of the crystal becomes very small. In reality, rotation noise, noise from slip rings, etc. are superimposed on this minute signal, and it is quite difficult to capture weight changes and calculate and control the diameter value. There is a method using a rotating transformer, but there is no method that can use DC signals without contact. There is also a method of differentiating the signal from the weight sensor and calculating and controlling the diameter value based on the change, but using a differentiator circuit amplifies noise and it is also quite difficult to use this method.

Further, in such a conventional method, since the weight signal containing noise is used as it is for calculating the diameter value, it is very difficult to perform accurate diameter control.

An object of the present invention is to perform accurate automatic control of a pulled crystal by detecting minute changes in weight even when noise is present in the signal from the weight sensor.

[Means to solve the problem]

In order to achieve the above object, the method of the present invention detects the weight of the pulled single crystal and controls the crystal diameter by changing the rate of increase according to a predetermined program. In the method of controlling the crystal diameter by calculating the diameter from the weight of the pulled crystal during pulling, a reference signal S which changes every unit time T in order to collect only the weight change from the output signal a of the weight sensor 1, By subtracting bl..., a signal C corresponding to the change is obtained, and the temperature of the melt is adjusted using the signal C corresponding to the change, making it possible to precisely control the diameter value of the single crystal. This is an automatic diameter control method.

In addition, there is a method for monitoring the diameter of a single crystal during single crystal pulling, in which a plurality of output signals a from the weight sensor 1 are sampled over time, a regression line is obtained using the least squares method, and the diameter is accurately estimated from the regression line. be.

Furthermore, there is provided a single crystal automatic diameter control method in single crystal pulling, which uses the single crystal diameter monitoring method described above in the single crystal automatic diameter control method.

[For production]

The reference signal b+ -bl . . . is subtracted from the output signal a of the weight sensor 1 so as to obtain only the change in the signal.

Thereby, even if the increase in weight of the pulled crystal is very small, minute changes in the output signal a of the weight sensor 1 can be detected. The signal C corresponding to the change is amplified, the minute change in weight is detected, the diameter is determined, and the diameter is automatically controlled. Furthermore, by sampling multiple output signals a from the noisy weight sensor 1 along with their time and finding a regression line using the least squares method, it is possible to estimate the crystal diameter and perform highly accurate automatic diameter control. can.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.
Figure (A) is an explanatory diagram showing an outline of a single crystal pulling system, and Figure (0) is a block diagram of a control circuit according to the present invention. FIG. 2 is a graph showing changes in the output signal from the load cell, and the shaded area represents the output voltage per unit time from the standard voltage generator.

In Figure 1 (a), l is a weight sensor (load cell)
, 2 is a rotating lot, 3 is a melt, 4 is a crucible, 5 is a high-frequency heating device, and 6 is a seed crystal.

As shown in the figure, the seed crystal 6 fixed on the lot 2 is placed in the melt 3 in the crucible 4, and the lot 2 is pulled up at a constant speed while rotating at a constant speed. Measure the weight of.

As shown in FIG. 1 (b), the output signal a from the load cell l is a standard voltage that changes every unit time T as shown in FIG. Reference signal from generator 7 (shaded area in Figure 2),
, bl... is subtracted. These reference signals s, , b, . . . are generated by sending a signal d from the interface 8 of the computer 13 to the standard voltage generator 7. As a result, the signal C corresponding to the change in the voltage signal is obtained as data.

The signal C corresponding to this change is multiplied by 81 times by the DC amplifier 9.
The signals are amplified at amplification factors of 0 times, 20 times, 30 times, and 40 times to become signals c, , cl, etc., which are converted into digital signals by the A/D converter l valve and taken into the computer 13. It will be done. In the computer 13, the ^/D converter 1 is converted into the ^/D converter 1 from among the amplified change signals c, , cl...
The computer 13 selects a signal with a magnification that does not exceed the limit voltage of 10 V for input zero and has a value closest to the limit.

Inside the calculator 13, the diameter of the single crystal is calculated from the selected signal, further control processing is performed, and the interface 11
The temperature of the melt 3 is adjusted using a high-frequency heating device 5 with a high-frequency heating oscillator regulator 12°. By controlling the temperature of the melt 3 in this manner, the diameter of the pulled crystal is controlled in accordance with the signal e input from the data input/output device 14.

As described above, this method makes it possible to detect only minute changes in weight, and it is also possible to accurately respond to minute changes in diameter that are proportional to it.

In the above embodiment, the magnification of the DC amplifier 9 is 1.

Although the magnifications are 10x, 20x, 30x, and 40x, the number of nine types of magnification is arbitrary. Further, although the input limit voltage of the ^10 converter 10 is set to IOV, it is obvious that even more precise automatic diameter control is possible by reducing the voltage.

In addition, in the above embodiment, measurements are constantly repeated to obtain a plurality of measured values (X, ×2"...), and when measuring (tl
.

tl...) and estimate the diameter of the single crystal using the least squares method from these measured values, but since the diameter of the single crystal changes from moment to moment, it is assumed that it changes linearly. Then, use the least squares method to find the regression line (x=p+qt
, p, and q are constants) to estimate the pulling diameter.

As described above, by sampling the output signal from the load cell within a unit time and finding a regression line using the least squares method, it is possible to accurately estimate the diameter from the slope of the regression line, and the diameter of the crystal that is currently being pulled You can see the status of By using the above two methods, highly accurate automatic diameter control in single crystal pulling becomes possible.

〔Effect of the invention〕

According to the present invention, since the reference signal is subtracted from the weight signal of the load cell 1 so that only the variation can be obtained, the next time the signal is amplified by the DC amplifier 9, the signal from the load cell 1 is simply amplified as it is. It is now possible to select a larger amplification factor when amplifying after subtraction than when subtracting, and it has become possible to obtain minute changes in the weight signal. This made it possible to accurately capture minute changes in crystal diameter that are proportional to changes in weight.

Furthermore, when the weight signal a of the load cell 1 is sampled, a regression line is obtained using the least squares method, thereby making it possible and easy to estimate the pulling diameter. By using these methods, even more precise automatic diameter control can be achieved.

Furthermore, since it is fully automated, productivity is improved and costs are reduced compared to conventional methods.

In terms of quality, it is extremely useful in practice, as it improves reproducibility, provides crystals of constant quality, and is effective in increasing quality.

[Brief explanation of drawings]

Fig. 1 (A) is an explanatory diagram showing an overview of the single crystal pulling system, Fig. 1 (0) is a block diagram of the control circuit according to the present invention, and Fig. 2 is a graph showing changes in the output signal from the load cell. 1... Weight sensor (load cell), a...
・・Output signal, b,・b2・・・・Signal, C・・・・
... Signal of change, 2 ... Rotation lot, 3.
...melt, 4...crucible, 5...
・High frequency heating device, 6... Seed crystal.

Claims (3)

[Claims] (1) When pulling a single crystal using the Czochralski method, which detects the weight of the pulled single crystal and controls the crystal diameter by changing the rate of increase according to a predetermined program, the diameter is calculated from the weight of the pulled crystal. In the method of calculating the crystal diameter and controlling the crystal diameter, in order to collect only the weight change from the output signal of the weight sensor, a reference signal that changes every unit time is subtracted to obtain a signal for the change,
This is an automatic diameter control method for single crystal pulling that allows precise control of the diameter of a single crystal by adjusting the temperature of the melt using this change signal. (2) When pulling a single crystal using the Czochralski method, which detects the weight of the pulled single crystal and controls the crystal diameter by changing the rate of increase according to a predetermined program, the diameter is calculated from the weight of the pulled crystal. In the method of calculating the crystal diameter and measuring the crystal diameter, single crystal pulling involves sampling multiple output signals from the weight sensor over time, determining a regression line using the least squares method, and estimating the diameter precisely from the regression line. A method for monitoring the diameter of single crystals. (3) When pulling a single crystal by the Czochralski method, the single crystal automatic diameter control method according to claim 1 is combined with the single crystal diameter monitoring method according to claim 2. Crystal automatic diameter control method.