TW201447058A - Method for producing sapphire single crystal - Google Patents

Abstract

A method for manufacturing a sapphire single crystal by melt growth including the steps of: (i) observing an interface between a growing sapphire single crystal and a raw material melt by an optical means to obtain an image data; (ii) analyzing the image data to calculate the crystal diameter; and (iii) growing the sapphire single crystal while controlling the crystal diameter based on the calculated crystal diameter, wherein (A) the step (i) includes removing at least a part of light having wavelength of greater than 620 nm from light incident on the optical means; or (B) the step (ii) includes generating a secondary image data by removing at least a part of a component contributed by light having wavelength of greater than 620 nm from the brightness information of the image data and analyzing the secondary image data to calculate the crystal diameter.

Description

Method for manufacturing sapphire single crystal

The present invention relates to a method for producing a sapphire single crystal used as a substrate for epitaxial growth or an optical material.

A sapphire (alumina) single crystal is widely used as a nitride-based compound semiconductor, a substrate for epitaxial growth of germanium, and a high-strength window material. In recent years, from the viewpoint of energy saving, the demand for LEDs has been increasing in the case of LED televisions or LED lighting, and the demand for sapphire substrates for epitaxial growth of nitride-based compound semiconductors has increased. The LED wafer is formed by forming a nitride-based compound semiconductor light-emitting layer such as GaN, InGaN, or AlN on a c-plane sapphire substrate by using an MOCVD device, and then dividing it into a wafer to form a wafer (see, for example, Patent Document 1). Accordingly, it is an extremely important subject to provide a low-cost sapphire substrate having a large c-plane on the surface thereof in order to achieve high efficiency and low cost for producing LED chips.

In the method of producing a sapphire single crystal which is a material of a sapphire substrate, it is known that there is a white effort method, EFG (Edge-defined Film- The fed growth method, the Czochralski method, the Kyropoulos method, the HEM (Heat Exchange Method) method, and the like.

The Chaisky method is a kind of melt growth method. The seed crystal contacting the molten metal surface of the raw material is pulled at a speed of 0.5 to 10 mm/hour, and the pulling speed, the number of crystal rotations or the heater output are adjusted. A method of growing a crystal of a desired diameter on a melt surface. In the Chaichen method, crystallization is generally carried out by directly heating the crucible by induction heating to form a relatively large temperature gradient.

In this way, by performing crystallization in a relatively large temperature gradient, it is difficult to produce a difference in the growth length due to the growth orientation, so that the crystal can be cultured in the c-axis direction. The Chaucer method can easily obtain a single crystal of sapphire grown in the c-axis direction with the diameter and any length required for the substrate, so that it is not necessary to take out the cylinder by the core drill, and thus it is obtained from the single crystal grown. The substrate is extremely efficient.

In the Chaucer method, it is extremely important to properly control the diameter of a single crystal in terms of improving the quality of a single crystal or the yield of a product. As a method of calculating the diameter of a single crystal, a method of calculating a diameter based on weight data obtained from a weight detecting device such as a load cell, and detecting a single crystal and melting from an image of a camera or the like installed outside the furnace is known. The method of calculating the diameter from the detected solid-liquid interface at the interface of the liquid surface.

In the manufacture of a single crystal, the fusion ring of the single crystal and the melt surface is detected from the image of the camera, and the diameter calculated based on the detection point is taken into the control circuit, and fed back to the output of the heater, and the pulling of the crystal pulling shaft speed The degree of rotation, the number of rotations, and the speed of pushing up, and the control of the diameter of the single crystal with high precision (for example, refer to Patent Document 2).

In the production of a sapphire single crystal, a method of calculating a diameter based on weight data obtained from a weight detecting device such as a load cell is generally used (for example, see Patent Document 3).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-82676

[Patent Document 2] JP-A-2010-100453

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2011-6314

When calculating the diameter of the growing single crystal of sapphire according to the weight data, the pulling speed of the single crystal of sapphire is about 0.5 to 10 mm/hour, which is slower than the production of the single crystal, so the weight of the single crystal grown per unit time is small. Therefore, the weight data obtained has a large error. In particular, when the head and the shoulder of the initial stage of single crystal culture are cultivated, the error is large. Therefore, the diameter value calculated from the weight data contains a large error. When the control is carried out based on the diameter data containing a large error, the crystallization of the crystallization is likely to cause defects, and in particular, the quality of the head and the shoulder formed in the initial stage of single crystal growth is poor, and even the cultivating is performed under such a condition. The quality of the straight part is also decreasing.

When the diameter of the sapphire single crystal is calculated from the interface between the sapphire single crystal and the melt surface from the image of the camera or the like, it is necessary to use an image in which the temperature of the object exceeds the melting point of sapphire (2000 ° C or higher). However, at this time, the contrast of the obtained image is lowered due to the radiation light emitted from the object at a very high temperature.

In the past, it has been attempted to dispose the radiant light by arranging a dimming filter in an imaging device such as an observation object or a camera, and it is possible to obtain a visually visible image, but a relatively high contrast image cannot be obtained. When the interface between the single crystal and the melt surface is detected using a low-contrast (that is, unclear) image, it is difficult to use such image data because the error detection detected by using the non-interface point as an interface is frequently generated. The diameter control of the sapphire single crystal is performed.

The inventors have studied the image of the interface between the sapphire single crystal and the melt surface, and obtained the contrast image by removing the red component of the image, thereby completing the present invention.

The method for producing a sapphire single crystal of the present invention comprises a method for producing a sapphire single crystal by a melt growth method, wherein at least a part of the crystal growth comprises (i) observing a growing sapphire single crystal by optical means. a project for obtaining image data at the interface with the raw material melt; (ii) a project for calculating the calculated value of the crystal diameter of the sapphire single crystal by analyzing the image data obtained in the project (i); (iii) According to the calculated value of the crystal diameter of the single crystal obtained in the project (ii), while controlling the crystal diameter of the sapphire single crystal, the sapphire single crystal is grown, and (A) the project (i) contains the shot. The light entering the optical means removes at least a portion of the light exceeding the wavelength of 620 nm, so that 80% or more of the light energy for detecting the optical means exists in the wavelength range of 380 to 620 nm, or (B) engineering (ii) including a process of generating a secondary image data by removing at least a portion of a component that contributes to light exceeding a wavelength of 620 nm from luminance information of the image data, and obtaining a sapphire single crystal by analyzing the secondary image data In the calculation of the calculated value of the crystal diameter, the generation of the secondary image data is recorded in the secondary image data by 80% or more of the light energy for detecting the optical means, and exists at the wavelength 380~ The wavelength range of light at 620 nm.

In the present invention, "80% or more of the light energy for detecting optical means exists in the wavelength range of 380 to 620 nm", which means that the wavelength range of the power spectrum of the light for detection by the optical means is 380~ Among the wavelength integral values in 830 nm, the ratio of the wavelength integral value in the wavelength range of 380 to 620 nm of the power spectrum is 80% or more.

In the present invention, when the requirement of the above (A) is satisfied, the light incident on the optical means is detected by optical means after removing at least a part of the light component exceeding the wavelength of 620 nm.

Further, in the present invention, "80% or more of the light energy for detecting optical means is recorded in the secondary image data, and is present in the wave. The wavelength range of light of 380 to 620 nm is the wavelength integral range of the wavelength range of 380 to 830 nm of the power spectrum of the light for detection by optical means, and the wavelength range and wavelength range of the residual image recorded in the secondary image 380 The wavelength integral value of the power spectrum in the wavelength range of ~620 nm repetition is 80% or more.

In the method for producing a sapphire single crystal according to the present invention, it is possible to adopt a configuration in which an optical element has an imaging element and a filter that removes light exceeding a wavelength of 620 nm from light incident on the imaging element. This form can be preferably used when the requirements of the above (A) are satisfied.

The method for manufacturing a sapphire single crystal according to the present invention can be an optical RGB color camera by optical means, and (ii) includes data obtained by excluding at least R information from RGB image data obtained from the RGB color camera. The form of the engineering for calculating the crystal diameter of the sapphire single crystal. This form can be preferably used when the requirements of the above (B) are satisfied.

The method for producing a sapphire single crystal according to the present invention can be characterized in that (X) is controlled according to the optical observation of the interface between the growing sapphire single crystal and the raw material melt, while controlling the crystal diameter of the sapphire single crystal. Engineering of sapphire single crystal growth; and (Y) according to the weight data of the growing sapphire single crystal, while controlling the crystal diameter of the single crystal, while performing the growth of the single crystal, the engineering (X) includes the above engineering (i) to ( Iii), and meet the above requirements (A) or (B), the project (Y) contains: (Yi) a project for obtaining the weight data of a growing sapphire single crystal by means of a weight detecting means; (Y-ii) calculating the crystal diameter of the sapphire single crystal by analyzing the weight data obtained in the engineering (Yi) The value of the project; and (Y-iii) according to the calculated value of the crystal diameter of the sapphire single crystal obtained in the project (Y-ii), while controlling the crystal diameter of the sapphire single crystal, the sapphire single crystal is grown. According to this form, it is easy to control the crystal diameter of the sapphire single crystal more accurately in the entire region during growth.

In the method for producing a sapphire single crystal of the present invention having the above-described works (X) and (Y), the following preferred embodiment can be employed, for example, at least the crystal diameter of the growing sapphire single crystal is not full. During the period of 60 mm, the above-mentioned work (X) is carried out, and at least the period of the above-mentioned work (Y) can be preferably used while the crystal diameter of the growing sapphire single crystal is 100 mm or more. Further, in this aspect, the crystal diameter of the growing sapphire single crystal may be 60 mm or more, and may be performed in any of the above-described processes (X) and (Y). Further, after the above-mentioned process (Y), in the process of separating the single crystal from the raw material melt, there is a case where the crystal diameter is less than 60 mm, and the single crystal is grown (for example, in the case of tailings treatment), even at this time, It is not necessary to carry out the above works (X) to (Y).

According to the present invention, in the case of observing the image at the interface between the single crystal of the sapphire and the melted surface, the image having a relatively high contrast can be obtained, so that the crystal diameter of the growing single crystal can be accurately grasped. By mastering The value of one side controls the crystal diameter to grow the sapphire single crystal, and the diameter of the sapphire single crystal can be controlled with high precision.

1‧‧‧ chamber

2‧‧‧Single crystal pulling rod

3‧‧‧ seed holder

4‧‧‧ seed body

5‧‧‧坩埚

6‧‧‧ load weight

7a, 7b‧‧‧ insulated wall

8‧‧‧ top board

9‧‧‧High frequency coil

11‧‧‧ Window Department

12‧‧‧ bandpass filter

13‧‧‧High frequency power supply

20‧‧‧ camera

21‧‧‧Portrait input device

22‧‧‧Portrait processing device

23‧‧‧Diameter operation circuit

24‧‧‧Control device

30‧‧‧ seed body

31‧‧‧Single crystal

32‧‧‧ melt surface

33‧‧‧Interface of single crystal and melt surface

34‧‧‧ Rotating Center

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view schematically showing an example of a structure and a diameter control method of a Chalcowski single crystal pulling furnace.

Fig. 2 is a view schematically showing an example of a structure and a diameter control method of a conventional Chaucer method single crystal pulling furnace.

Figure 3 is a graph showing the wavelength distribution of radiant energy according to Planck radiation law.

Fig. 4 is a graph showing sensitivity characteristics in respective wavelengths of photosensitive elements of a general electronic RGB color camera.

Fig. 5 is a view schematically showing an image of an observation object after comparison adjustment.

Fig. 6 is a graph showing the crystal diameter data calculated in Example 1.

Fig. 7 is a graph showing measured data of the single crystal diameter in the first embodiment.

Fig. 8 is a graph showing crystal diameter data calculated in Example 2.

Fig. 9 is a graph showing measured data of the single crystal diameter in the second embodiment.

Figure 10 is a graph showing the crystal diameter data calculated in Comparative Example 1. Graph.

Fig. 11 is a graph showing measured data of a single crystal diameter in Comparative Example 2.

In the present invention, the method of producing a sapphire ingot by the Chaisky method can be directly applied to the public method in addition to the analysis of the data which is the source of the diameter control, and the outline is as follows.

The sapphire ingots in the Chaucer method are manufactured in batch mode. Fig. 2 is a view schematically showing an example of a structure and a diameter control method of a conventional Chaucer method single crystal pulling furnace. Using the crystal growth apparatus shown in Fig. 2, for example, an ingot having a diameter of 50 to 160 mm and a length of 50 to 500 mm is pulled from the raw material melt.

The single crystal pulling device shown in Fig. 2 includes a chamber 1 constituting a crystal growth furnace, and a single wall on the upper wall of the chamber is suspended and moved by a driving mechanism (not shown). Crystal pulling rod 2. At the front end of the single crystal pulling rod 2, the seed body 4 is mounted via the holder 3, and the seed body 4 is disposed on the central axis of the crucible 5. Further, a load cell 6 for measuring the crystal weight is disposed at the upper end of the single crystal pulling device.

The chamber 1 is provided with a window portion 11 for observing the seed crystal 4 or a single crystal (not shown) by observing the imaging device 20 such as a camera, and the observation of the inside of the furnace by the optical means by the window portion 11. The material of the window material constituting the window portion 11 may be a material that transmits light in the visible light region, and is suitable for use in an infrared region as it is difficult to be heated by radiation from a high temperature portion. Less quartz, calcium fluoride and other materials. As the image pickup device 20 for obtaining data by an optical means, an electronic camera using an electronic photosensitive element such as a CCD or a CMOS is preferable.

坩埚5 can use the 形状 of the known shape as the 柴 used by the Chaucer method. Generally, the opening portion viewed from the upper portion has a circular shape, and has a cylindrical crotch portion, and the shape of the bottom surface is a flat shape, a bowl shape, or a reverse conical shape. Further, in the case of the material of the crucible 5, it is suitable for the melting point of the alumina which can be used as the raw material melt, and further, the reactivity with alumina is low, and generally, niobium, molybdenum, tungsten, niobium or these alloys are used. . In particular, ruthenium which is excellent in heat resistance and oxidation resistance is preferred.

A heat insulating wall 7a is provided around the crucible 5 so as to surround the bottom and the outer circumference of the crucible 5. Further, a heat insulating wall 7b is provided so as to surround the side peripheral portion of the single crystal pulling region above the weir 5. The heat insulating walls 7a and 7b are not particularly limited, and a known heat insulating material or a heat insulating structure can be used, and it is particularly suitable for the material layer to be stabilized by adding cerium oxide, calcium oxide, magnesium oxide or the like. The zirconia-based and yttria-based materials, the alumina-based materials, the carbon-based materials, and the reflective materials of the metal plates such as tungsten and molybdenum.

Since these heat insulating walls are used in an environment in which the temperature difference between the inner surface and the outer surface is extremely large, it is easy to cause significant deformation or cracking of the material by repeated heating and cooling. When the temperature gradient of the crystal growth region is constantly changed by deformation or cracking of such a heat insulating wall, it is difficult to stably produce crystals. Therefore, the heat insulating walls are designed to reduce the cracking of the heat insulating wall caused by the above-described deformation or stress or the temperature environment change generated thereby. It is not preferable that the entire material is formed as a whole, and it is preferable to form a combination of a plurality of heat insulating members.

The opening of the upper end of the heat insulating wall 7b surrounding the single crystal pulling region is closed by the top plate 8, and the top plate 8 is provided with at least a through hole for inserting the single crystal pulling rod 2, and is used by the image pickup device 20. The through hole of the sapphire single crystal and the molten liquid is imaged. Accordingly, since the single crystal pulling region is in the single crystal pulling chamber formed by the heat insulating walls 7a, 7b and the top plate 8, the heat retention property is greatly improved. If the top plate 8 is the same as the heat insulating walls 7a and 7b, it may be formed by a known heat insulating material or a structure for heat insulation. Further, the top plate 8 does not have to have a flat shape, and the opening of the upper end of the surrounding body of the heat insulating body 7b may be any shape other than the through hole portion. In the shape other than the flat shape, for example, the top plate 8 may have a shape such as a truncated cone shape, an inverted truncated cone shape, an umbrella shape, an inverted umbrella shape, a dome shape, or an inverted dome shape.

On the outer circumference of the heat insulating wall 7a, a high frequency coil 9 is provided so as to approximate the height of the ring. A high frequency power supply 13 is connected to the high frequency coil 9. The high-frequency power source 13 is connected to a control device 24 composed of a general computer, and the output is appropriately adjusted.

The control device 24 has a function of calculating the diameter by the change in the weight detected by the load cell 6, and comparing the target diameter set by the setter 25 with the calculated diameter, and adjusting the output of the high-frequency power source 13. In the diameter calculation method of the image analysis by the image analysis described later, the error of the diameter control is large, and the diameter of the single crystal can be 100 mm or more, and the diameter control after 60 mm or more is optimal. system.

Further, in addition to the output of the high-frequency power source 13, the number of rotations of the crystal pulling shaft 2 or the crucible 5, the pulling speed, the valve operation for inflow and out of the gas, and the like are generally controlled.

For the raw material for producing a sapphire single crystal core for a sapphire substrate for semiconductor, alumina (alumina) having a purity of 4 N (99.99%) or more is usually used. Since impurities are mixed into the lattice or lattice of the sapphire single crystal to form a starting point of crystal defects, when a raw material having a low purity is used, a subgrain boundary is likely to occur, and there is a tendency for crystal to be colored. The reason for the coloration of the crystal is the indirectness of the crystal defect due to the color center of the crystal defect formed by the impurity. In particular, since chromium as an impurity has a significant influence on coloring, it is preferred to use a raw material having a chromium content of less than 100 ppm.

Further, the raw material is preferably from 1.0 g/mL or more, and more preferably from 2.0 g/mL or more, from the viewpoint of filling a large amount of raw materials by ruthenium and suppressing scattering of the raw materials in the furnace. For the raw material having such a property, those which produce alumina powder by a roll press or the like, or broken sapphire (crack, collapsed sapphire, etc.) can be used.

The raw material is placed in a crucible 5 provided in a crystal growth furnace, and heated to become a raw material melt. The temperature increase rate at which the raw material reaches the molten state is not particularly limited, and is preferably 50 to 200 ° C / hour.

The seed crystal 4 of the seed crystal holder 3 held at the tip end of the crystal pulling rod 2 is brought into contact with the molten metal surface of the raw material, and then slowly pulled to grow a single crystal. Stable in order not to cause abnormal growth of crystals The temperature of the raw material melt in the portion where the seed crystal is in contact with the single crystal pulling is inevitably a temperature slightly lower than the melting point (supercooling temperature). The pulling of the sapphire single crystal is preferably carried out so that the temperature becomes a temperature of 2,000 to 2050 °C.

The seed crystal 4 for pulling is a sapphire single crystal, which is formed and held in an arbitrary desired crystal orientation to be perpendicular to the front end of the raw material melt surface. The shape of the end before the contact with the raw material melt is not particularly limited, and may be a flat surface, even if it is formed by an unspecified surface. Further, the shape of the side surface of the seed crystal 4 can be selected from any shape without particular limitation, and is preferably a columnar shape or a quadrangular prism shape. In order to avoid the influence of the radiation from the holder 3 when the seed crystal 4 is brought into contact with the surface of the molten metal, the seed crystal 4 is melted to use a seed crystal having a length of 90 mm or more from the lower end of the holder 3 to the lower end of the seed crystal 4. 4 is better.

Further, at the upper end portion of the seed crystal 4, an enlarged portion, a constricted portion, and/or a through hole for holding the holder 3 are usually provided.

After the seed crystal 4 is brought into contact with the raw material melt, the shoulder portion (expanded diameter portion) is formed while controlling the number of rotations of the seed crystal 4 and/or the crucible 5, the pulling speed, the output of the high frequency coil 9, and the like. After the crystal diameter is expanded to the desired crystal diameter, the pulling is performed so as to maintain the desired crystal diameter.

The control of the single crystal diameter in the present invention will be described based on the drawings. The sapphire single crystal is grown in a temperature region around 2050 ° C of the melting point of sapphire. Light energy is emitted from high temperature objects in accordance with Planck radiation law. Figure 3 is only A graph showing the radiant energy of each temperature determined from Planck's law of radiation in the visible light region. As shown in Fig. 3, as the temperature of the substance rises, the emitted light energy also increases. Further, as the temperature rises, the light energy radiated on the long wavelength side, particularly in the wavelength region of 600 nm or more, increases.

Fig. 4 is a graph showing sensitivity characteristics in respective wavelengths of respective photosensitive elements (Red, Green, Blue) of a general RGB electronic color camera. The reading has sensitivity in the entire visible light area.

In the single crystal growth of sapphire, light having a wavelength distribution of radiant energy represented by "2400K" in Fig. 3 is emitted from the surface of the single crystal or the molten liquid of the observation object, and the camera is converted by the photosensitive member receiving its light energy. Image data. Since the emitted light has high energy in a long wavelength region, particularly in a red region of 600 nm or more, the photosensitive element of the camera is light-sensitive by the light on the long wavelength side, and the contrast of the image thus obtained is lowered.

In the method for producing a sapphire single crystal according to the present invention, by removing light on the long wavelength side, image energy of light having a wavelength of 380 to 620 nm is obtained as image data of 80% or more, and the diameter of the single crystal is performed based on the image data. Analysis. Further, the "removal of light on the long wavelength side" is not necessarily removed by physical means such as an optical filter, and may be removed by data processing.

In the specific form of the method of removing the light on the long wavelength side, (a) an optical filter in which light exceeding a wavelength of 620 nm is removed between the observation target and the camera, and (b) a color camera is provided. The captured image data is RGB-decomposed and only the shape of the R component is removed. State or form of R component and B component.

In the case of (a) a filter that removes light having a wavelength of 620 nm or more between the observation target and the camera, and obtains a contrast-high image and controls the diameter, a description will be given with reference to FIG. 1 . As described above, the imaging device 20 such as a camera transmits an image of an observation object (here, a seed crystal, a single crystal, or a molten liquid surface) through the window portion 11. The filter 12, which removes light exceeding a wavelength of 620 nm, is disposed between the window portion 11 and the camera 20. The photosensitive element of the camera 20 receives light that is turned off or attenuated by light having a wavelength exceeding 620 nm. The image captured by the camera 20 is captured by an image input device 21 into an arithmetic device such as a computer. In this case, if the sensitivity is in the wavelength range of 380 to 620 nm, the camera can be a color camera, even a monochrome camera.

In the case of a filter for removing light exceeding a wavelength of 620 nm, a commercially available optical filter having such optical characteristics can be used without particular limitation. Further, since the light energy in the wavelength region of 380 to 620 nm in the light transmitted through the filter is 80% or more, the wavelength end of the removed light need not be strictly 620 nm. An example of such an optical filter is a "long wavelength cutoff filter VIS 610 nm" manufactured by Asahi Separation Co., Ltd., and a "TS OD2 short pass filter 600 NM" manufactured by Edmund Optics. Further, when the light energy on the short-wavelength side is sufficiently high, even a part of light having a shorter wavelength than 620 nm may be removed. For example, in addition to light having a wavelength exceeding 620 nm, light having a wavelength of less than 450 nm may be removed.

Further, for example, when the light emitted from the crystal and the molten liquid is excessively bright to the camera, the light energy can be reduced even at the entire wavelength. Specifically, light energy can be reduced throughout the entire wavelength by, for example, installing a dimming filter on the camera. The dimming filter is commercially available for a wide variety of dimming rates, and can be used without particular limitation.

As described above, when the seed body is brought into contact with the melt at a temperature suitable for crystal growth, a single crystal is grown at the front end of the seed crystal. As described above, the image of the seed crystal, the single crystal, and the molten liquid surface of the observation object obtained by the camera 20 is extracted into an arithmetic device such as a computer by electronic data. The light energy of the image of the wavelength of 380 to 620 nm which is captured is 80% or more of the total. That is, 80% or more of the light energy for detecting by the camera 20 exists in the wavelength range of 380 to 620 nm, and at least a part of the light that has entered the camera 20 is removed by more than 620 nm. The contrast of the captured image is adjusted by the image processing device 22.

Fig. 5 is a schematic view showing an image of the object to be observed (the seed crystal 30, the single crystal 31, and the molten liquid surface 32) after the adjustment. Further, in the lower part of Fig. 5, a diagram schematically illustrating the luminance distribution on the imaginary line L of the captured image is arranged.

The image data after the comparison adjustment is sent to the diameter calculation circuit 23 and analyzed. In the diameter operation circuit 23, the data is binarized with an appropriate threshold (TV line in Fig. 5). The interface 33 between the single crystal 31 and the molten liquid surface 32 is detected by the critical value, and the distance between the portion where the luminance is lower than the critical value is calculated as the diameter D of the single crystal.

The calculated diameter data is sent to the control device 24. The control unit 24 adjusts the output of the high-frequency power source 13 from the difference between the calculated diameter data and the target diameter set by the setter 25, and controls the diameter of the single crystal.

(b) A mode in which an image having a high contrast ratio is subjected to diameter control in addition to the R information in the RGB image information acquired from the camera will be described with reference to FIG. 1 . As described above, the imaging device 20 such as a camera transmits the observation object through the window portion 11. Further, in the present embodiment, the filter 12 in Fig. 1 is not disposed. The image captured by the camera 20 is captured by an image input device 21 into an arithmetic device such as a computer.

As described above, when the seed body 4 is brought into contact with the raw material melt at a temperature suitable for crystal growth, the single crystal 31 is grown at the front end of the seed body 4. As described above, the image of the observation object (the seed crystal 4, the single crystal 31, and the molten liquid surface 32) obtained by the camera 20 is captured by an electronic device to an arithmetic unit such as a computer. The image processing device 22 performs image processing on the captured image. The image processing device 22 performs RGB decomposition on the captured image and removes only the R (Red) component. In the image data after image processing, the light energy of light having a wavelength of from 380 nm to 620 nm is 80% or more of the total. In other words, the image processing device 22 generates secondary image data by removing at least a part of the component that contributes to light exceeding the wavelength of 620 nm from the luminance information of the captured image data, and generates the secondary image data. More than 80% of the light energy of the light that is detected by the camera 20 is recorded in the secondary image data, and exists at a wavelength of 380~ The wavelength range of light at 620 nm. Thereafter, the image processing device 22 adjusts the comparison of the secondary image data.

Further, in the above description, the form in which the R component is removed by RGB decomposition of the captured image is exemplified, but the form of the B (Blue) component may be removed in addition to the R component.

Further, in the present embodiment (b), as in the above-described mode (a), even if a dimming filter is used, light of all wavelengths incident on the camera can be reduced.

The method of calculating the diameter D of the single crystal 31 from the image data after the contrast adjustment is the same as that of the above (a).

After the seed body 30 is brought into contact with the raw material melt, the value of the final diameter reached by the diameter expansion is determined by the size of the single crystal to be produced. However, generally, in the cultivation of the Chaisky method, the larger the crystal diameter, the more likely the subgrain boundary or the microbubble is to be generated. Accordingly, from the viewpoint of mass production of, for example, a 6-inch substrate, it is preferable to expand the diameter to a diameter of 150 to 170 mm.

The calculation of the diameter D of the single crystal 31 uses an image from the camera. When the diameter of the single crystal 31 is increased to a certain extent by the diameter expansion, the molten liquid surface 32 is lowered, from the center of rotation 34 to the interface 33 between the single crystal and the molten liquid surface. The distance produces an error. Accordingly, after the crystal diameter of the sapphire single crystal is expanded to a certain extent, the calculated value of the diameter obtained by analyzing the weight data from the load cell 6 is substituted for the calculated value of the diameter obtained by image analysis. The sapphire single crystal is preferably grown while the diameter is controlled. Specifically, when the diameter of the single crystal 31 becomes When the thickness is 100 mm or more, the above error becomes large, and the error of the calculated diameter also becomes large. Therefore, when the diameter of the single crystal is 100 mm or more, and preferably 60 mm or more, the diameter control is preferably performed based on the weight data from the load cell 6.

The pulling of single crystal can usually be carried out at a speed of 0.1~20mm/hour. However, when the pulling speed is too small, the crystal growth amount per unit time is reduced, the productivity is decreased, and when the pulling speed is too large, the fluctuation of the breeding environment becomes Large, it is easy to produce subgrain boundaries or tiny bubbles. When considering both productivity and crystallization quality, the pulling speed is preferably 0.5 to 10 mm/hour, and more preferably 1 to 5 mm/hour.

In the single crystal growth, the seed crystal 4 is preferably rotated at a speed of 0.1 to 30 rotations/minutes around the pulling rod 2. Further, at the same time as the rotation of the seed crystal 4, even if the crucible 5 is rotated in a direction opposite to the rotation direction of the seed crystal 4 or in the same direction, the rotation speed thereof may be, for example, 0.1 to 30 rotations/min.

The pressure in the furnace in the single crystal pulling may be any one of pressurization, normal pressure, and reduced pressure, but it is simple to carry out under normal pressure. In the atmosphere of the furnace, it is preferred that the inert gas such as nitrogen or argon or the inert gas contains an oxygen amount of any amount of 0 to 10% by volume.

The length of the straight portion of the single crystal is arbitrary, and in the case of manufacturing a substrate, the multi-wire saw can be efficiently processed, preferably 200 mm or more, more preferably 250 mm or more. When the length of the straight portion is less than 200 mm, since the multi-wire saw is efficiently cut, it is necessary to precisely align the crystal orientation with the plurality of cores, and the total length is set to 200 mm. Since the additional work of cutting by the multi-wire saw is performed after the above, the manufacturing efficiency is lowered and the manufacturing cost is increased. Further, when the length of the straight portion exceeds 500 mm, the temperature environment change in the hot zone in the furnace during the cultivation tends to be excessively large, so that it is difficult to stably grow.

In this way, after the sapphire single crystal having the desired straight diameter and length is pulled, the single crystal is cut away from the raw material melt. The method of cutting off the single crystal from the raw material melt is not particularly limited, and the method of cutting off by the increase in the output of the heater (the rise in the temperature of the raw material melt) is carried out by increasing the crystallization pulling speed. Any method such as a method of cutting off, a method of cutting away by a drop of sputum, or the like may be used. Further, in order to reduce the temperature fluctuation (thermal shock) at the moment when the single crystal is cut off from the raw material melt, the crystal diameter is gradually increased by gradually increasing the heater output or slowly increasing the crystal pulling speed. The tail reduction is effective.

The temperature at which the single crystal separated from the raw material melt is cooled to a degree of being taken out of the furnace. The faster the cooling rate, the more the productivity of the breeding process can be improved, but when it is too fast, the stress deformation remaining inside the single crystal becomes large, and as a result, there is a possibility of breakage or cracking during processing at the time of cooling or after. Or an abnormal warpage of the substrate obtained in the end. Conversely, when the cooling rate is too slow, the time for occupying the crystal growth furnace becomes long, and the productivity of the cultivation process decreases. When considering these points, the cooling rate is preferably 10 to 200 ° C / hour.

[Examples]

Hereinafter, the embodiment of the present invention will be described in more detail by way of experimental examples, but the present invention is not limited thereto.

(Example 1)

In the Chaucer method crystal pulling furnace, as shown in Fig. 1, the light from the furnace passes through the filter and enters the configuration of the camera, and an electronic RGB color camera (XC-505 made by SONY) is set. A filter that exceeds light of 620 nm ("TS OD2 short-pass filter 600NM" and dimming filter (HMC filter made by HOYA) manufactured by Edmund Optics Co., Ltd. (however, the dimming filter is not shown). Then, 50 kg of high-purity aluminum (AKX-5 Sumitomo Chemical Co., Ltd.) having a purity of 4 N (99.99%) was introduced as a starting material, and a cylindrical seed crystal having a diameter of 10 mm at the front end of the c-plane was used. In the method of introducing the raw material into the furnace, the vacuum is evacuated to 100 Pa or less, and then 1.0% by volume of nitrogen is introduced to the atmospheric pressure. After reaching the atmospheric pressure, the side is 2.0 L/min. The gas having the same composition as described above is introduced into the furnace, and is exhausted to maintain the pressure in the furnace at atmospheric pressure.

The image input device, the image processing device, and the diameter calculation circuit are also provided for input from the camera. The image input device, the image processing device, the diameter calculation circuit, and the control device are constituted by a single electronic computer. The enthalpy was heated and slowly heated to the melting temperature of the alumina raw material in the crucible for 9 hours. After appropriately adjusting the heater output with reference to the convection of the surface of the raw material melt (spoke pattern), the seed crystal of the sapphire single crystal is gradually lowered at a rate of 1 rotation/minute to make the seed crystal The front end is in contact with the raw material melt. Further, fine adjustment of the heater output is performed to insolubilize the seed crystal, and no crystal growth is formed on the surface of the raw material melt.

With the image input device, the computer captures the image of the seed crystal, the single crystal, and the molten liquid surface photographed by the camera, and performs contrast adjustment by the image processing device. The image subjected to the contrast adjustment is displayed on the screen, and the brightness which becomes the critical value (refer to the TV line in FIG. 5) is set so that the interface between the single crystal and the melt coincides with the diameter calculated by the diameter calculation circuit. Accordingly, the diameter calculation circuit calculates the diameter of the single crystal. The seeding is started at a pulling speed of 2 mm/hour.

After the start of the pulling, the control device is subjected to the breeding program shown in Table 1 input from the setter, and the crystal growth is performed while controlling the operation of the furnace, so that the crystal diameter and the rising speed of the crystal pulling bar become the breeding program. The target value shown.

Figure 6 shows the pull-up calculated by the diameter calculation circuit The value of the diameter after the start. The diameter of the single crystal can be obtained very stably. Based on this data, the head and shoulders of step numbers 1 to 5 of the single crystal are developed by adjusting the high frequency output by the control circuit. By the step number No. 6, the diameter calculation is changed to a method based on the weight data from the load cell, and the shoulder, the straight portion, and the tail portion are developed along with the above program. After the completion of the cultivating program, the single crystal was cut out from the raw material melt at a lifting speed of 10 mm/min. The excised single crystals were cooled to room temperature over a period of 20 hours. As a result, a sapphire single crystal having a diameter of 160 mm in the c-axis and a length of 150 mm in the straight direction was obtained in the vertical direction (longitudinal direction of the single crystal). Fig. 7 shows the measured values of the diameter of the obtained crystal. Even in the head having a small diameter, crystals having a small difference from the target diameter are obtained.

(Example 2)

In the Chaichensky crystal pulling furnace, the same camera as that used in Example 1 was set. However, unlike the first embodiment, only the light reduction filter is provided between the camera and the window portion, and the filter for removing light exceeding the wavelength of 620 nm is not provided. The image input device picks up the image of the seed crystal, the single crystal, and the molten liquid surface photographed by the camera to the computer, and the image processing device performs RGB decomposition to obtain an image in which only the R component is removed, and then performs contrast adjustment. . Crystallization was carried out in the same manner as in Example 1 except for these points.

Fig. 8 shows the value of the diameter after the start of the pulling by the diameter calculation circuit. The diameter of the single crystal can be obtained very stably. Fig. 9 shows the measured values of the diameter of the obtained crystal. Even in diameter The fine head also has a crystal with a small difference from the target diameter.

(Comparative Example 1)

Except that a camera that removes light exceeding a wavelength of 620 nm is not disposed between the camera and the window portion, and the image processing device does not perform RGB decomposition and removal of the R component, and the image is adjusted based on the comparison of only the captured image. The diameter calculation device was used to perform crystal growth in the same manner as in Examples 1 and 2, except that the diameter of the single crystal was calculated.

Fig. 10 shows the value of the diameter after the start of the pulling by the diameter calculation circuit. In the contrast-adjusted image, the brightness of the spoke pattern portion is equal to the brightness of the single crystal. By detecting the threshold value of the brightness, it is impossible to accurately detect the occurrence of the interface between the single crystal and the molten liquid surface. Therefore, the deviation of the calculated diameter values is very large. Since the output of the high-frequency power source is adjusted by the control circuit based on the calculated diameter data, the adjustment of the output is defective, and in the head development of step No. 3, the interface of the single crystal is separated from the molten liquid surface. Breaking, can't continue to grow.

(Comparative Example 2)

Crystallization was carried out in the same manner as in Example 1 except that the diameter was calculated based on the weight of the load cell and the diameter was controlled. Figure 11 shows the measured values of the diameter of the obtained crystal. In the head with a small diameter, the difference from the diameter of the target is large, and there is a crystal of necking.

1‧‧‧ chamber

2‧‧‧Single crystal pulling rod

3‧‧‧ seed holder

4‧‧‧ seed body

5‧‧‧坩埚

6‧‧‧ load weight

7a, 7b‧‧‧ insulated wall

8‧‧‧ top board

9‧‧‧High frequency coil

11‧‧‧ Window Department

12‧‧‧ bandpass filter

13‧‧‧High frequency power supply

20‧‧‧ camera

21‧‧‧Portrait input device

22‧‧‧Portrait processing device

23‧‧‧Diameter operation circuit

24‧‧‧Control device

25‧‧‧Setter

Claims (6)

A method for producing a sapphire single crystal, which is a method for producing a sapphire single crystal by a melt growth method, characterized in that, in at least a part of crystal growth, the following works are included: (i) by optical property a method of observing the interface between the growing sapphire single crystal and the raw material melt to obtain image data; (ii) calculating the calculated crystal diameter of the sapphire single crystal by analyzing the image data obtained in the above project (i) And (iii) a project for growing the sapphire single crystal while controlling the crystal diameter of the sapphire single crystal according to the calculated value of the crystal diameter of the single crystal obtained in the above-mentioned item (ii), (A) The above-mentioned item (i) includes removing at least a part of the light exceeding the wavelength of 620 nm from the light incident on the optical means, so that 80% or more of the light energy for detecting the optical means exists in the wavelength range 380. The project of ~620nm, or (B) the above project (ii) includes generating secondary image data by removing at least a portion of the component that contributes to light exceeding 620 nm from the luminance information of the image data. And a process of calculating the calculated value of the crystal diameter of the sapphire single crystal by analyzing the secondary image data, wherein the generation of the secondary image data is performed to provide light for detecting the optical means More than 80% of the energy is recorded in the above-mentioned secondary image data, and exists in the wavelength range of light having a wavelength of 380 to 620 nm. A method for producing a sapphire single crystal according to the first aspect of the patent application, wherein The optical means includes an image pickup element and a filter that removes light exceeding a wavelength of 620 nm from light incident on the image pickup element. The method for manufacturing a sapphire single crystal according to the first aspect of the invention, wherein the optical means is an electronic RGB color camera, and the item (ii) comprises at least RGB image data obtained by the RGB color camera. The data obtained by excluding the R information is used to calculate the crystal diameter of the sapphire single crystal. The method for producing a sapphire single crystal according to any one of claims 1 to 3, wherein the method for producing a sapphire single crystal by a melt growth method has (X) according to growth Optical observation of the interface between the sapphire single crystal and the raw material melt, while controlling the crystal diameter of the sapphire single crystal, while growing the sapphire single crystal; and (Y) according to the weight of the growing sapphire single crystal The above-mentioned project (X) includes the above-mentioned items (i) to (iii), and the above-mentioned requirements (A) or (B), the above-mentioned project (Y), is carried out to control the crystal growth of the single crystal. Including: (Yi) a project for obtaining weight data of a growing sapphire single crystal by means of weight detection; (Y-ii) a project for calculating the calculated value of the crystal diameter of the sapphire single crystal by analyzing the weight data obtained in the above-mentioned project (Yi); and (Y-iii) according to the above-mentioned project (Y-ii) The calculated value of the crystal diameter of the obtained sapphire single crystal is a project for growing the sapphire single crystal while controlling the crystal diameter of the sapphire single crystal. The method for producing a sapphire single crystal according to any one of the preceding claims, wherein at least the growth process is performed at least during a period in which the crystal diameter of the growing sapphire single crystal is less than 60 mm, at least in the growth. The above process (Y) is carried out while the crystal diameter of the medium sapphire single crystal is 100 mm or more. The method for producing a sapphire single crystal according to any one of claims 1 to 5, wherein the melt growth method is a Czochralski method.