JPH11322487A - Single crystal diameter measurement instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an instrument capable of continuously and automatically measuring the diameter of a single crystal being grown by a pulling-up method (Czochralski method) with good accuracy over the range from a seed crystal to a straight body. SOLUTION: This instrument 20 for measuring the diameter of a single crystal being grown by a pulling-up method over the range from a seed crystal to a straight body, is provided with: a camera 11 for photographing a growing part of the single crystal and outputting a video signal; a frame memory 12 and a CPU 13, each for executing the operations of a binarization diameter calculation means and an appropriate threshold determination means, wherein the binarization diameter calculation means is used for binarizing the video signal and calculating the diameter by the threshold, and also, the appropriate threshold determination means is used for performing statistical comparison of the diameter value calculated by the binarization diameter calculation means with the values obtained in the past, thereby determining the threshold as an appropriate threshold when the diameter value is a continuous value for a short time, or as an inappropriate threshold when the diameter value is a value other than the above value or an immeasurable value, then automatically detecting a threshold such that the diameter value is continuous to the preceding value before becoming inappropriate and determining the detected threshold as an appropriate threshold; and an analog output means 14 for outputting the diameter value calculated by the appropriate threshold.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for measuring the diameter of a single crystal grown by the pulling method (Czochralski method) from a seed crystal to a straight body continuously with high accuracy by a proper threshold value determining method. It relates to a possible single crystal diameter measuring device.

[0002]

2. Description of the Related Art Conventionally, methods for measuring the diameter of a single crystal grown by a pulling method using a threshold include a method based on binarization determination and a method based on peak determination for searching for a peak position. These methods are usually used for controlling the diameter of the straight body of a single crystal and have relatively good results. However, in recent years, in order to stably and accurately produce a single crystal, it has been required to continuously measure a diameter from a single crystal seed crystal to a straight body.

[0003]

In the case of continuously measuring the diameter from a single crystal seed crystal to a straight body, even if the above-mentioned conventional measuring method is used, manual operation is often required. In the method based on the binarization determination, there must be a clear luminance difference between the crystal and the solution, and the threshold value must be constantly constant. on the other hand,
In the actual lifting, the meniscus shape at the solidification point differs between the neck, the cone and the straight body, so that the brightness of the fusion ring greatly differs.
In particular, no meniscus is formed in the cone portion, and the characteristic fusion ring peak may disappear. Under such conditions, there is a problem that the measurement may be erroneously performed with a constant threshold value as in the related art.

[0004] Further, in the above-described method based on peak determination for searching for a peak position, this is always based on the assumption that a fusion ring exists. Therefore, although this method is suitable for measuring the diameter of the straight body where the fusion ring clearly appears, once the threshold is determined, it is necessary to raise the straight body once and grasp the appropriate threshold. There is a need. In this case, it takes several hours to understand the parameters, and in the seed crystal part and the cone part, in addition to the fusion ring at the solid-liquid interface, the holder holding the crystal and the step of the crystal reflect the radiated light from the crucible and There is a problem that a high-brightness part that occurs may be erroneously detected.

This will be described with reference to the drawings. 8 to 11
Is a schematic diagram of a typical line profile in a single crystal seed crystal part, a cone part, and a straight body part, where the threshold value is set to a constant value of 150. FIG. 8 shows a line profile when the seed crystal is pulled up. A clear fusion ring appears, and the diameter D ₁ is obtained from the threshold value. FIG. 9 shows a line profile of the cone portion where the fusion ring has disappeared and the brightness has been reduced. Figure 10 is a line profile of the cone portion of the reflected light appears in a part of the crystal, the diameter D ₂ erroneous in threshold 150
Is required, it is not required correct diameter D _3. FIG. 11 shows a line profile of the straight body portion where a clear fusion ring appears. The diameter D ₄ is obtained from the threshold value. As described above, it is impossible to perform continuous measurement from the seed crystal to the straight body at a certain threshold value, or it is necessary to measure with great care in determining the threshold value. In addition, there is a problem that whenever the furnace structure changes or the pulling conditions change, it is necessary to spend some time searching for the optimum threshold value.

Therefore, an object of the present invention is to measure the diameter of a single crystal grown by the pulling method (Czochralski method) continuously and automatically from the seed crystal to the straight body portion with high accuracy. It is an object of the present invention to provide an apparatus for measuring the diameter of a single crystal which is capable of measuring the diameter.

[0007]

Under such circumstances, the present inventors have conducted intensive studies and as a result, when measuring the diameter of a single crystal grown by the pulling method, before outputting the measured value, the measured value was measured. Evaluate the validity and, based on the premise that the diameter of the single crystal always changes continuously in the short term, exclude inappropriate values from the measurement results in comparison with past values, and It has been found that the above problem can be solved by providing a suitable threshold value determining means for automatically changing the threshold value while evaluating the above, and the present invention has been completed.

That is, the single crystal diameter measuring apparatus according to the first aspect of the present invention is a single crystal diameter measuring apparatus for continuously measuring the diameter of a single crystal grown by a pulling method from a seed crystal to a straight body. A camera for photographing a growing portion of a single crystal and outputting a video signal, a binarized diameter calculating means for binarizing the video signal to obtain a diameter by a threshold value, and a diameter obtained by the binarized diameter calculating means In comparison with the past value, if it is a continuous value in the short term, it is determined as an appropriate threshold, and if it is other value or measurement is impossible, it will be an inappropriate threshold, and the diameter will be an inappropriate value A suitable threshold value determining means for searching for a threshold value that is a continuous value from the previous value and determining this as a changed valid threshold value, and an analog output means for outputting a diameter obtained by the valid threshold value It is characterized by. As a result, the diameter of the single crystal grown by the pulling method, especially the fusion ring seen as it is in the cone portion disappears, and even in the case of a line profile in which the luminance is reduced, reflected light is partially reflected in the crystal. Even if the line profile appears, it is possible to measure continuously and automatically from the seed crystal to the straight body with high accuracy.

According to a second aspect of the present invention, in the single crystal diameter measuring apparatus, the appropriate threshold value determining means calculates at least an averaging process of the measured value obtained by the appropriate threshold value to obtain past value data. Features. Thus, in addition to the same effect as the first aspect of the present invention, the averaging process is performed for a certain period of time only for the value determined as an appropriate value, and the reliability of the average value serving as the past value of the validity evaluation is improved. Enhanced. For example, the representative diameter of a crystal that is not a perfect circle is determined with high accuracy in comparison with past values without being dragged by measurement errors.

According to a third aspect of the present invention, in the single crystal diameter measuring apparatus, the camera is a two-dimensional CCD camera having a wavelength sensitivity of 800 nm or more. Thereby, in addition to the same effect as the above invention, the external unnecessary light such as a fluorescent lamp is not detected, and the influence of the external light can be removed. In addition, the measurement accuracy can be further improved because it can follow the fluctuation of the melt and the fluctuation of the crystal.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an overall configuration diagram of a single crystal diameter measuring apparatus 20 according to an embodiment of the present invention. FIG.
In the drawing, reference numeral 1 denotes a single crystal pulling device, which heats and melts a silicon polycrystal put in a quartz crucible 2 by a heater 4 and is pulled into the silicon melt 9 and supported by the tip of a wire 6. A silicon single crystal rod 10 is manufactured by immersing a silicon seed crystal and gradually pulling it while rotating the pulling wire 6 to grow a single crystal. In the present invention, the silicon single crystal rod 10
In order to measure the diameters of the seed crystal portion 10a, the cone portion 10b, and the straight body portion 10c, a camera 11 is used to photograph the growing portion of the silicon single crystal rod 10 from obliquely above the single crystal pulling apparatus 1, and a video signal Is output.

As the camera 11, a one-dimensional camera (line sensor), a two-dimensional camera, or the like can be used, and among them, a lens having a diameter capable of keeping the diameter from the seed crystal to the straight body within the field of view is provided, and A two-dimensional CCD camera having a wavelength sensitivity of 800 nm or more is preferable. In this case, 8
In order to respond to a wavelength of 00 nm or more, a color filter that cuts a wavelength of 800 nm or less may be attached.
As a result, it is possible to eliminate the influence of external light without detecting external unnecessary light such as fluorescent lamps, and to follow the fluctuation of the melt and the fluctuation of the crystal. it can. The two-dimensional CCD camera preferably has a screen resolution of 640 × 480 or more.

The single crystal diameter measuring apparatus according to the present invention further comprises:
It has a frame memory 12 and an arithmetic CPU 13 for executing both calculation of the quantified diameter and determination of the appropriate threshold value. That is, an analog NTSC or PAL standard video signal obtained from the camera 11 is sent to the frame memory 12 (image processing device). The frame memory 12 preferably has a memory with a resolution of 8 bits and a spatial resolution of 512 × 480 or more, and can exchange data with the CPU by I / O access or direct memory map.

The arithmetic CPU 13 preferably uses a processor having a floating-point arithmetic mechanism in order to enable a high-speed statistical calculation in determining the appropriate threshold value. Further, it is preferable that the analog output unit 14 outputs 12 bits or more of analog data. In addition, as the type, in addition to the voltage output type, depending on the type of the diameter control controller 15,
For example, a current output type may be used.

Next, the diameter of the single crystal is calculated according to the flow shown in FIG. In the figure, the appropriate threshold value determining means is tracking mode O
It means from N to tracking mode OFF. Also, the symbol "y"
Indicates Yes, and the symbol “n” indicates No. For convenience of explanation, the numbers of items used in the following description correspond to the numbers in the flow of FIG. 1. Acquire a screen image. 2. Next, the binarized diameter is calculated by the binarized diameter calculating means. The camera is set so that the diameter from the single crystal seed crystal to the straight body can be contained within the field of view of the lens. Specifically, as shown in FIG. 3, to measure the diameter of all of the horizontal lines within the dotted line, and the measured value D ₅ is the highest value among all the measured values. As the threshold value used for the binary determination, a valid threshold value specified in advance or a valid threshold value redefined by a threshold change described later is used. If an appropriate measurement value cannot be obtained, the value is invalid.

3. Check whether the tracking mode is ON. The tracking mode is checked during the recalculation of the threshold. In the tracking mode, there is no guarantee that the measured value is a correct value. Therefore, the averaging process is not performed, and only the statistical calculation such as the standard deviation or the abnormal value ratio is performed. This allows
The average value that was correctly measured until the previous time is maintained, and the average value is used for comparison with an appropriate threshold value described later. In the present invention, statistical calculation means calculation of standard deviation, outlier ratio, variance, and the like.

4. Evaluate the validity of the measured values. That is, the average value of the previous value or the past value is compared with the obtained value, and if a significantly different value or a clearly different value is obtained, it is discarded as an invalid value. This invalid value is sent to statistical processing such as a standard deviation or an abnormal value ratio, and is not averaged. This does not destroy the average value of the previously correctly measured diameter values.

5. If it is determined that the measured value is appropriate, the measured value is given to the statistical processing buffer, and both statistical processing calculation such as standard deviation or abnormal value ratio and averaging processing calculation are performed. The statistical processing buffer performs calculation for obtaining data such as an average, a standard deviation, a variance, and an abnormal value ratio, which are used as a basis for determining whether or not the current threshold value is appropriate. For example, if the standard deviation is found and the variation is large, it is determined that the threshold is inappropriate, or the upper and lower limits from the average for the measured values are set and the frequency of deviation from this is traced to determine the validity of the threshold. Or to judge.

6. If it is determined that the threshold value is inappropriate in the tracking mode ON or the validity evaluation, the measurement value obtained from the threshold value is not included in the averaging processing data, and the standard deviation or abnormal value ratio calculation is used as data for statistical processing. Statistical calculations such as are performed. As a result, the measurement value obtained by the inappropriate threshold value is not taken into the average value, and the measurement accuracy is improved. 7. A certain number of samples is required to judge appropriateness based on the above average, standard deviation, variance, outlier ratio, and the like. Therefore, until a certain number is subjected to statistical processing,
Do not perform the appropriate or inappropriate evaluation.

8. From the statistics such as the average value and the standard deviation or the abnormal value ratio, it is evaluated whether the measured value obtained at present has continuity with past data and does not vary greatly.
The silicon single crystal always has continuity within a range of several tens of seconds, and undergoes only a smooth diameter change. Therefore, when a discontinuous value is taken, it is determined that the crystal is broken or that measurement cannot be performed correctly.

9. If the standard deviation or the abnormal value ratio is appropriate, it is determined that the measurement has been correctly performed, and the tracking mode is turned off in the tracking mode. 10. If it is determined in step 8 that the measurement value is inappropriate, the threshold value is changed from the current threshold value for each predetermined step to search for an appropriate threshold value. 11. The data is reset once to check the validity of the threshold. 12. The tracking mode is turned on so that the threshold provisionally determined in the above 10 does not destroy the average value. Then, after that, the diameter measurement is tried again with the new threshold value, and a threshold value that is a continuous measurement value before the measurement value becomes an inappropriate value is searched. 13. When all conditions are satisfied and the appropriate threshold value is determined, the average value at that time is output as an analog signal.

According to the present embodiment, a camera 11 for photographing a growing portion of a single crystal and outputting a video signal, a frame memory 12, an operation CPU 13, and an analog output for outputting a diameter determined by the appropriate threshold value Means 14, wherein the frame memory 12 and the operation CPU 13 binarize the video signal to obtain a diameter based on a threshold value, and calculate the diameter obtained by the binarized diameter calculation means into a past value. In the statistical comparison with the above, if it is a continuous value in the short term, it is determined as an appropriate threshold, if it is other value or measurement is impossible, it will be an inappropriate threshold, and the diameter will be an inappropriate value In order to automatically detect a threshold value that becomes a continuous value from the previous value and determine the threshold value as a changed appropriate threshold value, a process of determining the appropriate threshold value is performed. Even if the line profile in which the fusion ring seen in the cone part disappears and the brightness is reduced, or the line profile in which reflected light appears in a part of the crystal, the seed crystal From the body to the straight body. Further, in the appropriate threshold value determining means, the measured value obtained by the appropriate threshold value is calculated as at least an averaging process, in particular, a statistical process and an averaging process, and is used as a past value data. The averaging process is performed only for the given value for a certain period of time, and the reliability of the average value serving as the past value of the validity evaluation is enhanced. For example, the representative diameter of a crystal that is not a perfect circle can be determined with high accuracy in comparison with past values without being dragged by measurement errors. Further, since the camera 11 is a two-dimensional CCD camera having a wavelength sensitivity of 800 nm or more, it is possible to eliminate the influence of external light without detecting external unnecessary light such as a fluorescent lamp. In addition, the measurement accuracy can be further improved because it can follow the fluctuation of the melt and the fluctuation of the crystal.

[0023]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but this is merely an example and does not limit the present invention. Example A two-dimensional CCD camera having a lens capable of holding the diameter from the seed crystal to the straight body within the field of view, having a wavelength limited to 800 nm or more, having a depth of 8 Bit per pixel, and having 64 bits.
8 bit frame memory with screen resolution of 0 × 480, 32
BitCISC 40MHz Pentium processor and 0-10V
An analog output section was prepared for each output and connected so that the diameter could be calculated. That is, the inside of a 6-inch silicon single crystal pulling furnace was photographed using a single crystal diameter measuring device incorporating the logic shown in the flow of FIG. 2, and the output was obtained. This will be described with reference to the schematic diagrams of the line profiles of the obtained single crystals (FIGS. 4 to 6).

First, when the seed crystal was grown, measurement of the diameter of the seed crystal was started. At this time, the measurement of the crystal diameter was started with a threshold change step 0 and a start threshold 150 so that the threshold did not change. As shown in FIG. 4, a clear fusion ring appeared in the seed crystal part, and the diameter of the seed crystal part could be measured normally at a threshold value of 150. At the stage of measuring the seed crystal, there was a rotation (crystal fluctuation) of about 1/3 of the crystal diameter, but the measured value was stable. Next, when the light was transferred to the cone portion, the luminance was reduced after about 5 minutes, and the measurement became impossible. When the line profile of the single crystal was observed, the fusion ring as shown in FIG. 5 disappeared, and the luminance peak was below the threshold value 150. The maximum brightness at this time is 1
It was about 40.

Next, when the step is changed to the threshold change step 3, an appropriate measurement can be performed without changing the threshold in the seed crystal portion.
Three minutes after the transition to the cone section, the threshold became inappropriate and the tracking mode was set. After changing the threshold several times, the threshold 1 is changed as shown in FIG.
At 38, the measurement of the cone became possible and stabilized. This threshold determination was completed in 4 minutes. FIG. 7 shows an example of this measurement. As shown in FIG. 7, according to the present example, the diameters of the seed crystal portion, the cone portion, and the straight body portion could be continuously and accurately measured.

[0026]

According to the present invention, the diameter of a single crystal grown by the pulling method can be measured accurately and continuously and automatically from the seed crystal to the straight body. Therefore, unlike the related art, productivity is improved without labor. Further, the yield of the product is improved.

[Brief description of the drawings]

FIG. 1 shows an overall configuration diagram of a single crystal diameter measuring apparatus according to an embodiment of the present invention.

FIG. 2 shows a flow of calculating the diameter of a single crystal.

FIG. 3 shows a schematic view of a plane of a single crystal diameter portion to be measured.

FIG. 4 shows an example of a line profile of a seed crystal part in the embodiment of the present invention.

FIG. 5 shows an example of a line profile of a cone portion according to the embodiment of the present invention.

FIG. 6 shows a state in which the threshold value of FIG. 5 is changed.

FIG. 7 shows an example of measuring the diameter of a single crystal in an example.

FIG. 8 shows an example of a line profile of a seed crystal part according to a conventional method.

FIG. 9 shows an example of a line profile of a cone portion according to a conventional method.

FIG. 10 shows another example of a line profile of a cone portion according to a conventional method.

FIG. 11 shows an example of a line profile of a straight body portion according to a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Quartz crucible 4 Heater 6 Wire 9 Silicon melt 10 Silicon single crystal rod 10a Seed crystal part 10b Cone part 10c Straight body part 11 Camera 12 Frame memory 13 Operation CPU 14 Analog output means 15 Diameter control controller 16 Fusion ring 20 Single crystal diameter measuring device

Claims (3)

[Claims] 1. A single crystal diameter measuring device for continuously measuring the diameter of a single crystal grown by a pulling method from a seed crystal to a straight body portion, wherein a camera for photographing the single crystal growth portion and outputting a video signal. And a binarized diameter calculating means for binarizing the video signal to obtain a diameter based on a threshold value, and comparing a diameter obtained by the binarized diameter calculating means with a past value to obtain a continuous value in a short term. In some cases, it is determined to be a reasonable threshold, and when it is not possible to measure other values or it is not appropriate, an inappropriate threshold is used. A single crystal diameter measuring apparatus, comprising: a proper threshold value determining means for determining the changed valid threshold value; and an analog output means for outputting a diameter determined by the valid threshold value. 2. The diameter measurement of a single crystal according to claim 1, wherein said appropriate threshold value determining means calculates at least an averaging process of the measured value obtained by said appropriate threshold value to obtain past value data. apparatus. 3. The single crystal diameter measuring apparatus according to claim 1, wherein the camera is a two-dimensional CCD camera having a wavelength sensitivity of 800 nm or more.