JP4339282B2 - Single crystal diameter measuring device - Google Patents

Description

  The present invention relates to a single crystal diameter measuring apparatus that measures the diameter of a single crystal during the production of a single crystal such as an oxide by the Czochralski method (CZ method) or the like.

Conventionally, as a method for growing a single crystal by the CZ method, there is a method in which the diameter of the grown single crystal is visually confirmed through a viewing window of a chamber, and an operator controls the growth apparatus.
However, in this conventional method, it is necessary for the operator to constantly monitor the growth apparatus, and since the diameter of the single crystal is visually confirmed, it is difficult to make the diameter of the single crystal constant. Whether or not to grow according to the target dimensions largely depends on the skill of the operator.

Therefore, for example, a boundary portion between the grown single crystal and the raw material melt is photographed with a CCD camera, a plurality of boundary points are obtained from the photographed image, a circular shape of the single crystal is defined by a mathematical method, and the diameter is determined. There has been proposed a method of controlling the diameter during single crystal growth by a computer based on the calculated diameter value (see, for example, Patent Document 1).
JP-T-2001-518443

However, in the method in which a plurality of boundary points are obtained from an image taken with a CCD camera, the circular shape of the single crystal is defined by a mathematical method and the diameter is calculated, the diameter at the time of single crystal growth is directly calculated from the taken image. However, in order to define an accurate circular shape, it is necessary to obtain more boundary points, and there is a problem that the accuracy of the obtained diameter value is low.
An object of the present invention is to solve the above-mentioned problem in a single crystal diameter measuring apparatus, and to provide a single crystal diameter measuring apparatus capable of accurately obtaining a diameter value during single crystal growth.

The present invention is an apparatus for measuring the diameter of a single crystal during the production of the single crystal by the Czochralski method, wherein the boundary between the single crystal and the raw material melt is set for each set rotation angle of the single crystal. a photographing means for photographing at least twice, from each image photographed by the photographing means, said specifying means for specifying one measurement point on the boundary portion that rotates together with the single crystal, the single identified in the identifying means Calculation means for calculating the radius of the single crystal at the measurement point from the coordinates of the measurement point in each image, the mounting angle of the imaging means, and the horizontal distance from the focal point of the imaging means to the center of the single crystal. The above-mentioned problem is solved by obtaining the diameter of the single crystal by averaging a plurality of the radii calculated for each rotation angle of the set single crystal.

  In addition, a single crystal growth apparatus provided with a crucible containing molten raw material and a chamber that covers a single crystal pulled up by a pulling device, a viewing window for looking into the chamber, an opening and closing device for opening and closing the viewing window, When a CCD camera that captures the boundary between the single crystal and the raw material melt is provided in conjunction with the opening of the viewing window, the viewing window is automatically opened every predetermined time, and in conjunction with the opening of the viewing window, By photographing the boundary between the single crystal and the raw material melt with a CCD camera, it is possible to solve the problem that the evaporated raw material adheres to the glass of the viewing window and the single crystal cannot be photographed.

  According to the present invention, since the radius can be obtained directly based on the photographed image, for example, a plurality of boundary points are obtained from the photographed image, and a single crystal circular shape is defined by a mathematical method. Compared with the method of calculating the diameter, the diameter value at the time of single crystal growth can be obtained with higher accuracy.

Hereinafter, an embodiment in which the single crystal diameter measuring apparatus of the present invention is applied to a single crystal growth apparatus for manufacturing a single crystal by the Czochralski method (CZ method) or the like will be described with reference to the drawings.
That is, in this single crystal growth apparatus, a fixed camera (CCD camera) is formed every time the rotation angle of the single crystal is an integral multiple of 45 ° at the boundary between the grown single crystal and the raw material melt in the pulling process. Based on two images whose order of shooting is changed among the obtained images, the radius of the single crystal at the measurement point of the boundary (the point in front of the CCD camera in the image taken later), and the camera focus And calculate the vertical distance between the melt and the raw material melt.

<Configuration of single crystal growth apparatus>
FIG. 1 is a configuration diagram showing a configuration of a single crystal growth apparatus in an embodiment of the present invention. As shown in FIG. 1, the crucible 1 containing the raw material melt 4 is covered with a chamber 5.
A pipe 15 is provided in the upper center of the chamber 5. The pipe 15 is inserted with a pulling shaft 6 having a seed crystal 3 attached to the lower portion thereof, and the grown single crystal 2 is pulled up by moving the pulling shaft 6 upward while rotating the pulling shaft 6 clockwise.
A viewing window 7 is provided on the upper side of the chamber 5. The viewing window 7 is attached to an arm 17 that is pivotally supported so as to be rotatable up and down, and the tip of a wire 8 that is wound up and down by a motor 9 is connected to the center of the upper surface of the viewing window 7. Yes.

The motor 9 is connected to the computer 13 via the motor driver 10. An upper limit switch 11 and a lower limit switch 12 that detect the open and closed states of the viewing window 7 are also connected to the computer 13.
On the other hand, a CCD camera 14 is installed at a position where the inside of the crucible 1 can be photographed with the viewing window 7 opened. A CCD camera 14 is also connected to the computer 13. Specifically, as shown in FIG. 2 (a side view and a plan view showing the positional relationship between the CCD camera 14 and the single crystal 2), the CCD camera 14 has an optical axis directed at the center of rotation of the single crystal 2. The angle α is inclined from the horizontal plane, and the horizontal distance between the rotation center and the camera focus F is set at a position where the specified value Ly is obtained. Further, the CCD camera 14 has the camera focal point F of the CCD camera 14 as the origin, the Xw axis extending rightward with respect to the rotation center of the single crystal 2, the Yw axis extending in the direction of the rotation center, and the vertical direction. A world coordinate system having a Zw axis extending upward is defined.

Then, as shown in FIG. 3, the CCD camera 14 projects an image of the single crystal 2 onto a CCD (an image pickup device of the CCD camera 14) 19 (the center of rotation of the single crystal 2 passes through the center of the CCD 19 and is viewed in plan view). The image is projected onto a pixel row extending in the vertical direction), and the obtained image is output to the computer 13. The CCD 19 has a predetermined CCD coordinate system having an Xc axis extending in the right direction in plan view and a Zc axis extending in the upward direction with the center of the CCD 19 as the origin. In the CCD coordinate system, coordinate values normalized with the focal length f as a unit length are represented. That is, the coordinate value is “number of pixels from the origin of the CCD coordinate system × size of one pixel of the CCD 19 / focal length f”.
Around the crucible 1, a heating device 18 that heats the crucible 1 by power supply from the heating power supply 16 is provided.

<Operation of single crystal growth equipment>
In the pulling process of the single crystal 2, first, power is supplied from the heating power source 16 to the heating device 18, the raw material is heated and melted in the crucible 1, and seeding is performed using the seed crystal 3. After completion of seeding, switch to automatic diameter control mode. In the automatic diameter control mode, the pulling shaft 6 is moved at a pulling speed and a rotating speed programmed in advance.
Although the viewing window 7 is normally closed, the motor 9 winds and unwinds the wire 8 by giving a command from the computer 13 to the motor driver 10 so that the motor 9 rotates forward or backward at every preprogrammed time. Go and open and close the viewing window 7.

  In synchronism with the opening of the viewing window 7, the computer 13 shoots the boundary between the single crystal 2 and the raw material melt 4 at different angular positions eight times while the pulling shaft 6 rotates once in the CCD camera 14. To do so. That is, as shown in FIGS. 4A to 4C, each time the rotation angle of the single crystal 2 becomes an integral multiple of 45 ° (the boundary between the single crystal 2 and the raw material melt 4 is changed to the single crystal 2). The angle between the line 0-i (line connecting the center of rotation of the single crystal 2 and the point i) and the Yw axis by the point i (i = 1 to 8) divided into eight at 45 ° intervals around the rotation axis of 2 The command is output (every time becomes 0 °).

  The CCD camera 14 images the boundary between the single crystal 2 and the raw material melt 4 and detects the boundary between the single crystal 2 and the raw material melt 4 from the captured image. Specifically, first, of the two images whose shooting order is before and after, an image taken later is extended in the vertical direction in plan view through the center of the image, as shown in FIG. A pixel row (scan line) is scanned from the upper side in the plan view to the lower side in the plan view to obtain the luminance of each pixel on the scan line. Then, by detecting a pixel whose luminance is greatly different from that of the adjacent pixel, the coordinate B when the measurement point i is at the B point (when the angle between the line 0-i and the Yw axis in FIG. 4 is 0 °) is obtained. '(A2, b2) is specified.

  Next, as shown in FIG. 5 (b), the two images are viewed in plan within a predetermined pixel region (region where the measurement point i is photographed, scan region) of the image photographed first. Scan lines extending in the vertical direction are sequentially selected from the left side in the plan view to the right side in the plan view. Next, the selected scan line is scanned from the upper side of the plan view to the lower side of the plan view to obtain the luminance of each pixel on the scan line, and a pixel having a greatly different luminance from the adjacent pixel is detected. Then, the coordinates of the boundary point between the single crystal 2 and the raw material melt 4 (coordinates in the CCD coordinate system) A ″ (a1 ′, b1 ′) are determined, and the coordinates A ″ are substituted into the following equation (1): By calculating the coordinate A ′ where the left side and the right side are the same, the coordinate when the measurement point i is at the point A (when the angle between the line 0-i in FIG. 4 and the Yw axis is 45 °) A ′ (a1, b1) is specified.

  Further, based on the specified coordinates A ′ (a1, b1), B ′ (a2, b2), the radius Ri of the single crystal 2 at the measurement point i and the camera focus according to the following formulas (2) and (3): A vertical distance hi between F and the raw material melt surface is calculated.

Further, the above flow is repeatedly executed for points 1 to 8 to obtain the radius Ri at each point and the vertical coordinate hi to the raw material melt 4. Then, based on the obtained radius Ri and vertical coordinate hi, the average value Dav of the boundary diameter between the single crystal 2 and the raw material melt 4 and the average value Zav of the vertical coordinate between the camera focus F and the raw material melt 4 are as follows: (4) Calculate according to equation (5).
Dav = (ΣRi / 8) × 2 = ΣRi / 4 (4)
Zav = Σhi / 8 (5)

  Then, the computer 13 determines the output of the heating power supply 16 using a technique such as PID control from the difference between the calculated average diameter Dav and the set diameter, and performs control so as to eliminate the difference from the set diameter. . At this time, if the diameter of the single crystal 2 becomes larger than the set diameter, the output of the heating power supply 18 is increased so that the diameter becomes smaller. Conversely, if the diameter becomes smaller than the set diameter, the heating power supply The operation is carried out so that the diameter is increased by lowering the output of 18.

  As described above, in the single crystal growth apparatus of the present embodiment, the boundary between the single crystal 2 and the raw material melt 4 is photographed at least twice for each rotation angle of the set single crystal, and each photographed image is taken. The measurement point of the boundary part is specified from the image, the coordinates A ′ and B ′ of the specified measurement point, the mounting angle α of the CCD camera 14, the horizontal distance from the camera focus F to the rotation center of the single crystal 2, From this, the radius Ri of the single crystal 2 at the measurement point is calculated. Therefore, since the diameter can be obtained directly based on the photographed image, for example, a plurality of boundary points are obtained from the photographed image, and the diameter is calculated by defining a single crystal circular shape by a mathematical method. Compared with the method, the diameter value at the time of single crystal growth can be obtained with higher accuracy.

Further, the inspection window 7 is automatically opened every predetermined time, and the boundary portion between the single crystal 2 and the raw material melt 4 is photographed by the CCD camera 14 in conjunction with the opening of the inspection window 7. Therefore, it is possible to solve the problem that the evaporated raw material adheres to the glass of the viewing window and the single crystal cannot be photographed.
Further, it is not necessary for the operator to constantly monitor the apparatus, and the evaporated raw material does not adhere to the viewing window 7 provided for photographing the boundary portion between the single crystal 2 and the raw material melt with the CCD camera 14. By doing so, the complicated structure for flowing gas into the inside of the observation window 7 becomes unnecessary. That is, it is possible to provide a single crystal growth apparatus based on the CZ method that enables stable crystal growth and low apparatus costs.

  By the way, in the conventional method of taking images through the window glass installed in the chamber 5 provided so as to cover the crucible 1 and the single crystal 2 containing the molten material, the evaporated material adheres to the window glass and becomes cloudy. As a result, it becomes impossible to photograph, and generally, a gas is flowed to the inner surface of the glass to prevent fogging. Therefore, there is a problem that an additional apparatus for flowing a gas at a constant flow rate on the inner surface of the viewing window glass is required, and the cost of the single crystal growth apparatus is increased.

<Derivation method of radius calculation formulas>
Next, a method for deriving the equations (2) and (3) for calculating the diameter Ri of the single crystal and the vertical distance hi between the camera focus F and the raw material melt surface from the image taken by the CCD camera 14 will be described. To do.
First, as shown in FIGS. 2 and 3, a conversion matrix wRc for converting the coordinates of the CCD coordinate system to the coordinates of the world coordinate system is expressed by the following equation (6).

  Further, according to the conversion matrix wRc (the above equation (6)), the following (7) is established between the coordinates P (X, Y, Z) of the world coordinate system and the coordinates P ′ (a, b) of the CCD coordinate system. ) To (10).

That is,
X = a / k (8)
Y = (cosα−b · sinα) / k (9)
Z = (sin α + b · cos α) / k (10)
When the above equations (9) and (10) are used, the following (11) (12) between the coordinates A (X1, Y1, h) of the world coordinate system and the coordinates A ′ (a1, b1) of the CCD coordinate system. ) Is established (see FIG. 6).
Y1 = (cosα−b1 · sinα) / k1 (11)
h = (sin α + b 1 · cos α) / k 1 (12)
Here, from Y1 = Ly−R · cos 45 °, the following equation (13) holds.

Similarly, when the above equations (9) and (10) are used, the following (between the coordinates B (X2, Y2, h) in the world coordinate system and the coordinates B ′ (a2, b2) in the CCD coordinate system are expressed as follows: 14) The relationship of equation (15) is established.
Y2 = (cosα−b2 · sinα) / k2 (14)
h = (sin α + b 2 · cos α) / k 2 (15)
Here, the relationship of the following equation (16) is established from Y2 = Ly-R.

  Furthermore, when the above (13) and (16) are used, the relationship of the following equation (17) for calculating the radius Ri of the single crystal 2 is established (the above equation (2) is derived).

  The relationship of the following equation (18) for calculating the vertical distance h between the camera focal point F and the raw material melt surface is established by the radius Ri of the single crystal 2 calculated by the above equation (17) (above) (3) is derived).

<Calculation method of coordinate A ′ detection formula>
Next, a method for deriving equation (1) for specifying the coordinate A ′ of the CCD coordinate system will be described.
First, when the above equations (8), (9), and (10) are used, the following (19) to (22) are set between the coordinates A and B in the world coordinate system and the coordinates A ′ and B ′ in the CCD coordinate system. The relationship of the formula holds.

  Further, in terms of geometry, the relationship of the following formula (23) is established for the coordinates A and B.

  Therefore, when the above equations (19) to (23) are used, the relationship of the following equation (24) is established (the above equation (1) is derived).

As described above, in the above-described embodiment, the CCD camera 14 in FIG. 1 constitutes the photographing means in the claims, and similarly, the computer 13 in FIG. 1 constitutes the specifying means and the calculating means.
The single crystal diameter measuring apparatus of the present invention is not limited to the contents of the above embodiment, and can be appropriately changed without departing from the gist of the present invention.
In the above embodiment, an example is shown in which eight images are taken while the single crystal 2 rotates once (images are taken every time the rotation angle is an integral multiple of 45 °), but the present invention is not limited to this.

It is a block diagram of the single crystal growth apparatus which is one Embodiment of this invention. It is the side view and top view which show the positional relationship of a CCD camera and a single crystal. It is explanatory drawing for demonstrating the image of the single crystal projected on CCD. It is the side view and top view which show the measurement point on the boundary line of a single crystal and raw material melt. It is explanatory drawing for demonstrating the detection method of the boundary part of a single crystal and raw material melt. It is explanatory drawing for demonstrating derivation methods, such as a radius calculation formula.

Explanation of symbols

1 is a crucible, 2 is a single crystal, 3 is a seed crystal, 4 is a raw material melt, 5 is a chamber, 6 is a lifting shaft, 7 is a viewing window, 8 is a wire, 9 is a motor, 10 is a motor driver, and 11 is an upper limit. Limit switch, 12 is a lower limit switch, 13 is a computer, 14 is a CCD camera, 15 is a pipe, 16 is a heating power source, 17 is an arm, 18 is a heating device, and 19 is a CCD.

Claims (1)

An apparatus for measuring the diameter of a single crystal during the production of the single crystal by the Czochralski method,
Photographing means for photographing the boundary between the single crystal and the raw material melt at least twice for each rotation angle of the set single crystal;
From each image photographed by the photographing means, a specifying means for specifying one measurement point on the boundary that rotates together with the single crystal,
From each coordinate in the respective images of the one measuring point specified by the specifying means, the mounting angle of the photographing means, and the horizontal distance from the focal point of the photographing means to the center of the single crystal, at the measuring point. A calculating means for calculating the radius of the single crystal;
A single crystal diameter measuring device characterized in that a diameter of a single crystal is obtained by averaging a plurality of the radii calculated for each rotation angle of the set single crystal.

Images