JP2017154919A - Floating zone melting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a floating zone melting apparatus that uses a semiconductor laser module as an infrared-ray irradiation source and can efficiently raise a single crystal while optionally and continuously varying a size of a light condensation region.SOLUTION: The present invention relates to an infrared-ray condensation heating type floating zone melting apparatus 10 that comprises a semiconductor laser module 30 for irradiation with laser light of infrared rays, and a condensation system which makes laser light of infrared rays 20 emitted by the semiconductor laser module 30 into parallel light of desired size to irradiate a sample rod 14. The condensation system has a cylindrical lens group 50 consisting of a plurality of cylindrical lenses 52, 54, 56, and 58 and a condenser lens 62 positioned between the cylindrical lens group 50 and the sample rod 14, and the condenser lens 62 is configured to vary and adjust a relative position to the sample rod 14 through a variable adjustment part 70, thereby raising a single crystal by heating and fusing the sample rod 14 through irradiation with the infrared rays 20 into a melt and then solidifying the melt on a seed crystal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an infrared concentrated heating type floating zone used for obtaining a melt by irradiating a sample with infrared rays and heating and melting it, and solidifying the melt on a seed crystal to grow a single crystal. It relates to a melting apparatus.

Infrared central heating type floating zone melting equipment
・ The sample can be melted without using a crucible.
・ Any atmosphere gas can be selected.
・ Grow single crystals of various compositions using the floating zone method,
・ The ability to conduct phase equilibrium studies by floating zone annealing.
・ High temperature can be easily obtained with relatively little power,
It is widely used for single crystal growth and phase equilibrium studies.

  In order to use such a floating zone melting apparatus for growing a single crystal, a high temperature is obtained in the melting part of the sample, and the temperature in the circumferential direction around the rod axis of the sample (sample rod) is uniform. There are also required conditions such as that the temperature distribution in the vertical direction (bar axis direction) is steep, local heating is easy, and the melt can be easily held on the sample bar.

  Conventionally, in order to achieve these conditions, various types of infrared concentrated heating type floating zone melting devices have been developed and used to grow single crystals of various materials such as insulators such as semiconductors and oxides. Yes.

When a single crystal is grown using such a floating zone melting apparatus, a wide range of materials, from an extremely high melting point material having a melting point of 3000 ° C. to a low melting point material of several hundred degrees, depending on the target substance.
As for the atmosphere for single crystal growth, air or oxygen is often used in ordinary oxide materials, but in many metal materials, the material is melted in an argon gas atmosphere in order to avoid reaction with oxygen. , Solidified to produce a single crystal.

  Furthermore, the size of a single crystal material for basic research is often about 10 mm or less in diameter, but for example, a large single crystal having a diameter of about 30 mm is desired for material research by neutron diffraction. In addition, when developing an application research application for a useful substance, a single crystal having a diameter as large as possible is required.

  Conventionally, when a single crystal is manufactured by irradiating infrared rays onto a rod-like sample (sample rod) and solidifying it as described above, a transparent quartz tube (not shown) is used as shown in FIG. ), A round bar-shaped sample bar 110 and a seed crystal 112 are arranged one above the other, and an infrared lamp 106 is installed at one of the two focal positions using the elliptical mirror 104 on the sample bar 110, The infrared ray 102 emitted from the infrared lamp 106 is reflected by the elliptical mirror 104 and condensed at the other focal position, and the infrared ray 102 heats the sample rod 110 at the condensed focal position to form a melt. In this way, as shown in FIG. 4B, the sample lamp 110 is continuously melted and solidified by gradually moving the infrared lamp 106 in the horizontal direction with respect to the sample bar 110. Growth crystal 114 There is growing, floating zone melting apparatus 100 of a so-called infrared concentration heating type is used (for example, Patent Document 1).

  Here, a halogen lamp is often used as the infrared lamp 106. In this case, the maximum temperature reached is about 2200 ° C., and a xenon lamp is used when a higher temperature is required.

  The halogen lamp is a resistance heating type lamp, whereas the xenon lamp is a discharge heating (arc heating) type, so the lighting system and the output control system are completely different. Accordingly, the compatibility between the halogen lamp and the xenon lamp is extremely low, and the xenon lamp type is used separately for ultra-high temperatures and the halogen lamp type is used separately for high temperatures.

  In addition, as a method capable of increasing the diameter of a single crystal, a so-called inclined irradiation type floating zone melting device (not shown) that irradiates a sample rod with an infrared ray obliquely from above has been developed. A single crystal having a larger diameter than that of the zone melting apparatus 100 can be grown.

  On the other hand, recently, a semiconductor laser type floating zone melting apparatus (not shown) using a semiconductor laser as an infrared irradiation source instead of an infrared lamp has been developed and put into practical use (for example, Patent Document 2).

  The semiconductor laser type floating zone melting apparatus does not require an elliptical mirror unlike the infrared lamp type, and the entire apparatus can be extremely miniaturized. In addition, the utilization efficiency of the supplied energy is about 50% in the case of the semiconductor laser type, whereas in the case of the infrared lamp type, the emission efficiency of the infrared lamp is about 30% and the light needs to be condensed with an elliptical mirror. Yes, the overall utilization efficiency of the supplied energy is about 15%.

For this reason, it is said that the infrared lamp type has only about 30% utilization efficiency of the semiconductor laser type.
Furthermore, since the halogen lamp uses a tungsten filament, the size of the infrared lamp is large, and it is difficult to obtain a small condensing region using an elliptical mirror, and the maximum temperature reached is a little over 2000 ° C. .

For this reason, when a temperature higher than this is required, a xenon lamp is used in which the size of the infrared lamp is small and high brightness can be obtained.
However, since the xenon lamp is a discharge heating (arc heating) type, it is inferior in irradiation stability and expensive in comparison with a halogen lamp. Therefore, the halogen lamp is generally used in a relatively low temperature range to which the halogen lamp can be applied, and the xenon lamp is generally used in a temperature range where a higher temperature is required.

  Since the semiconductor laser type can obtain a high temperature by reducing the condensing region, the size of the condensing region can be controlled according to the melting point of the material with a single floating zone melting device. Thus, it is not necessary to use a halogen lamp and a xenon lamp separately according to the melting point range.

  In the actual process of growing a single crystal by irradiating a sample bar with infrared rays to melt and solidify, the size of a light collection area (irradiation area) required for infrared irradiation varies greatly depending on the situation.

  For example, in the case of growing a silicon single crystal, a thin seed crystal is used, and when crystal growth is started by melting and solidifying a sample rod, the diameter is immediately maintained to be about 4 mm or less and is generated in the grown crystal. Dislocations, which are a type of crystal defect, are removed, and a large single crystal having a predetermined thickness is grown by gradually increasing the diameter.

  When a single crystal is grown by irradiating the sample bar with infrared rays to melt and solidify, a condensing area of the same size as the diameter is required to stably grow a single crystal with a diameter of several millimeters. Yes. This means that in order to grow a large single crystal having a diameter of about 300 mm, a large condensing area equivalent to that is necessary.

Japanese Patent No. 5279727 Japanese Patent Application No. 2015-046091

  In order to grow a high-quality single crystal using seed crystals, a condensing area with a diameter of about several millimeters is required at the beginning of the growth, and the condensing area is continuously increased as the diameter of the growing crystal is increased. It is important that it can be arbitrarily adjusted to an optimal size.

  In view of such circumstances, the present invention uses a semiconductor laser module as an infrared irradiation source, can arbitrarily continuously adjust the size of the infrared condensing region, and efficiently grows a single crystal. An object of the present invention is to provide an infrared concentrated heating type floating zone melting apparatus.

The present invention was invented to solve the problems in the prior art as described above,
The floating zone melting apparatus of the present invention is
Infrared concentration heating type floating zone melting apparatus for irradiating a sample rod with infrared rays to obtain a melt by heating and melting, and solidifying the melt on a seed crystal to grow a single crystal,
The floating zone melting device is:
A semiconductor laser module for irradiating the infrared laser beam;
A condensing system for converting the infrared laser light emitted from the semiconductor laser module into parallel light of a desired size, further condensing the parallel light and irradiating the sample rod;
Comprising at least
The condensing system is
A cylindrical lens group composed of a plurality of cylindrical lenses;
A condenser lens positioned between the cylindrical lens group and the sample rod;
Have
The condensing lens is configured to be able to variably adjust a relative position with respect to the sample via a variable adjustment unit.

  As described above, if the concentration zone of the infrared laser light irradiated from the semiconductor laser module is variably adjustable by the variable adjustment unit, the infrared concentrated heating type floating zone melting apparatus can reach 3000 ° C. A wide temperature range can be covered from a melting point material to a relatively low melting point material of 1000 ° C. or lower.

  Therefore, at the initial stage of single crystal growth, a small condensing area for growing a thin single crystal having a diameter of 5 mm or less is realized, and by moving the condensing lens via the variable adjustment unit according to the growth of the single crystal, It is possible to obtain a large condensing region and continuously cope with increasing the diameter of the single crystal.

  For this reason, it is possible to continuously grow a large single crystal of high quality with a single device, and it is possible to prevent the cost of the floating zone melting device from being increased due to the relatively simplified structure. Thus, it is possible to provide a floating zone melting apparatus with extremely high practicality.

  When growing single crystals, the so-called melt method, in which the raw material powder is dissolved and carefully solidified, is the most efficient and versatile method, and is adopted as the method for producing most single crystal materials. Has been.

  A typical melt method is a so-called pulling method in which a raw material is melted in a suitable crucible, and seed crystals are immersed in the crucible and pulled upward while being thickened. This pulling method is known as a method capable of growing a large single crystal.

  However, with the pulling method, contamination from the crucible used is unavoidable, and all the raw materials in the crucible are first melted and solidified, causing segregation, and the composition in the grown single crystal is not uniform. There is a flaw.

  In the floating zone melting method performed in the floating zone melting apparatus of the present invention, a sample rod obtained by processing a raw material into a rod shape is prepared, and the lower end of the sample rod is continuously melted and solidified on a seed crystal. It is a method for growing crystals and does not use a crucible. Therefore, there is no contamination from the crucible material, and there is an advantage that the composition of the grown single crystal can be made homogeneous because the melting and solidification of the raw material is continued.

  Known floating zone melting apparatuses use a high-frequency induction heating method for melting raw materials, and a so-called infrared irradiation method for melting by irradiating infrared rays. The high-frequency induction heating method cannot be applied to insulators as raw materials, but the infrared irradiation method can be applied not only to insulators but also to semiconductors and metal materials. Therefore, the infrared irradiation method is widely used as a method for growing high-quality single crystals. ing.

  Infrared lamps such as halogen lamps or xenon lamps are used as the infrared irradiation source, and the infrared rays emitted from the infrared lamps are generally condensed and irradiated by an elliptical mirror. In recent years, semiconductor lasers have been used. In the near future, the semiconductor laser type is expected to become the mainstream. The present invention is a floating zone melting apparatus employing this semiconductor laser type.

  Here, in the process of growing a single crystal by irradiating infrared rays to melt and solidify a raw material sample rod, the size of the infrared irradiation area irradiated to the sample rod is high or low. Alternatively, it is necessary to arbitrarily set depending on whether the diameter of the single crystal to be grown is thinned or thickened.

  For example, it is possible to melt an ultra-high melting point material having a melting point exceeding 2000 ° C. by condensing infrared rays with high density. What is important here is that although it is possible to melt the low melting point material by irradiating the infrared rays condensed at a high density, it becomes difficult to grow a single crystal in this case.

  That is, if the concentration of infrared rays is made too high with respect to the melting point of the target substance, the melt that can be melted will continue to be overheated, but it will be difficult to solidify stably. .

  The melt formed by the floating zone melting method in which the sample bar is irradiated with infrared rays and melted and solidified to grow the single crystal is stably held on the single crystal grown below and is also stable. It needs to be cooled and solidified. However, if the melt is overheated and becomes too hot, there is an increased risk of the melt falling without being stably held at the top of the lower single crystal and cooling to the melting point, and the growth of the single crystal is not possible. It becomes stable.

  Therefore, in order to grow a single crystal stably, an infrared condensing density and a condensing range that match the melting point of the material are required, and accurate control is required. Since melting and solidification of the raw material is a continuous series of operations, a floating zone melting apparatus that can continuously and arbitrarily adjust the concentration density of infrared rays and the size of the collection area is required depending on the situation.

  In the present invention, a semiconductor laser module is used as an infrared radiation source. The infrared laser light emitted from the semiconductor laser module is converted into parallel light of a desired size by a cylindrical lens group, and the parallel light is further converted by a condenser lens. Focusing and irradiating the sample rod, especially by making the position of this condensing lens variable via the variable adjustment section, it is possible to adjust the infrared condensing range, thereby gradually increasing the single crystal A continuous single crystal having a large diameter can be grown.

The floating zone melting apparatus of the present invention is
The variable adjustment unit has an automatic adjustment function of adjusting a position and / or an angle according to the growth rate of the single crystal.

  With such an automatic adjustment function, the diameter of the single crystal can be continuously increased by adjusting the position and / or angle of the condensing lens according to the growth rate of the single crystal. .

The floating zone melting apparatus of the present invention is
The cylindrical lens group is
A vertical cylindrical lens and a horizontal cylindrical lens that convert the infrared laser beam into parallel light in the vertical and horizontal directions;
An expanded cylindrical lens that enlarges the diameter of light that is parallel to the vertical axis direction and the horizontal axis direction by the vertical axis cylindrical lens and the horizontal axis cylindrical lens;
A parallel-changing cylindrical lens that converts the light expanded by the extended cylindrical lens into parallel light again;
It is characterized by having.

  As described above, if these cylindrical lenses are provided as the cylindrical lens group, the infrared laser beam can be surely converted into parallel light of a desired size.

  According to the present invention, a semiconductor laser module is used as an infrared radiation source. The infrared laser light emitted from the semiconductor laser module is first converted into parallel light of a desired size, and the parallel light is collected by a condenser lens. It is possible to adjust the infrared condensing range by adjusting the position of the condensing lens, especially through the variable adjustment unit. Thus, it is possible to provide a floating zone melting apparatus that can be continuously varied and can grow a single crystal efficiently.

FIG. 1 is a schematic view of an infrared concentrated heating type floating zone melting apparatus of the present invention. FIG. 2 is an enlarged view of a main part of the floating zone melting apparatus shown in FIG. FIG. 3 is an enlarged view of a main part of the floating zone melting apparatus similar to FIG. 2 showing a state in which the condenser lens is moved by the variable adjustment unit. FIG. 4 is a schematic diagram of a floating zone melting apparatus using a conventional infrared lamp, FIG. 4 (a) is a diagram showing an initial stage of single crystal growth, and FIG. 4 (b) is a diagram in which the infrared lamp is moved. It is the figure which showed the growth late stage of the single crystal which changed the condensing area | region.

Hereinafter, embodiments (examples) of the present invention will be described in more detail with reference to the drawings.
The infrared concentrated heating type floating zone melting apparatus of the present invention grows a rod-like single crystal by irradiating a part of a sample rod with infrared rays to heat and dissolve it and solidifying it on a seed crystal or the like. is there.

  Further, in the present specification, the “seed crystal” refers to the first form of the crystal when growing a large-diameter single crystal using a floating zone melting apparatus. It refers to a single crystal that is being grown.

  As shown in FIG. 1, the floating zone melting apparatus 10 of the present invention has a round bar-shaped sample bar 14 formed by molding a raw material powder of a target substance above a sample chamber 12 made of a transparent quartz tube, A seed crystal 16 of the target substance is arranged below the sample rod 14, and in this state, an atmospheric gas 18 is caused to flow into the sample chamber 12, and infrared rays 20 are irradiated from the semiconductor laser module 30. The sample rod 14 is condensed and the sample rod 14 is heated and melted to obtain a melt, and the melt is solidified on the seed crystal 16 to grow a single crystal.

The semiconductor laser module 30 used in the floating zone melting apparatus 10 of the present invention outputs an infrared laser beam to the outside by passing a current through the semiconductor laser element 32.
The semiconductor laser module 30 includes a semiconductor laser element 32, an electrode body 36 joined to the lower surface of the semiconductor laser element 32 via a conductive plate 34, and a conductive plate 38 on the upper surface of the semiconductor laser element 32. The electrode body 40 is joined so as to be conductive, and an insulating plate 42 is inserted between the electrode body 36 and the electrode body 40.

  The semiconductor laser device 32 is generally made of a single crystal in which materials such as gallium, arsenic, phosphorus, and indium are mixed at a specified ratio and formed on a gallium arsenide substrate by a vapor phase synthesis method. . Although the semiconductor laser device 32 obtained by such a method has high mechanical strength, it has a strong cleaving property and is easily cracked. A surface obtained by cleaving in a specific direction by utilizing this cleavage property serves as a laser beam resonator as an optical surface.

  A cylindrical lens group that converts the laser light of the infrared rays 20 emitted from the semiconductor laser element 32 of the semiconductor laser module 30 into parallel light of a desired size is provided on the side of the semiconductor laser element 32 of the semiconductor laser module 30. 50 is provided.

  In the present embodiment, the cylindrical lens group 50 includes a vertical axis cylindrical lens 52 and a horizontal axis cylindrical lens 54 that convert infrared laser light into parallel light in the vertical axis direction and the horizontal axis direction, and a vertical axis cylindrical lens 52 and a horizontal axis cylindrical lens. An extended cylindrical lens 56 that enlarges the diameter of light that has been made parallel to the vertical and horizontal axes by the lens 54, and a parallel-changing cylindrical lens 58 that makes the light extended by the extended cylindrical lens 56 parallel light again. Have.

  Here, since the laser beam of the infrared ray 20 irradiated from the semiconductor laser element 32 has a characteristic of diffusing immediately after being emitted, the vertical axis cylindrical lens 52 and the horizontal axis cylindrical lens 54 are arranged, and the laser beam is transmitted in the vertical direction and It is converted to parallel in any of the horizontal directions.

  The converted light has a size of about 1 mm in the vertical direction and a size of about 10 mm in the horizontal direction that is about the same as the horizontal direction of the semiconductor laser element 32. For this reason, the beam size is further increased by the extended cylindrical lens 56 and converted into parallel light having a large aperture again by the parallel changing cylindrical lens 58.

A condensing lens 62 that condenses the expanded parallel light is provided on the side of the cylindrical lens group 50.
The parallel light having a large diameter by the parallel-changing cylindrical lens 58 is collected by the condenser lens 62 so that the collected infrared ray 20 is irradiated on the sample rod 14 in the sample chamber 12. It has become.

The semiconductor laser module 30, the cylindrical lens group 50, and the condenser lens 62 are disposed in the irradiation source chamber 60.
As shown in FIG. 2, the condensing lens 62 is configured so that the relative position with respect to the sample rod 14 can be variably adjusted via the variable adjustment unit 70, thereby reducing the size of the condensing area of the infrared ray 20 to that of a single crystal. It can be changed according to the growth condition.

  That is, in order to reduce the size of the condensing area, the position of the condensing lens 62 is moved away from the sample bar 14 and the focal position and the position of the sample bar 14 are adjusted to the same level. In the case of increasing the size, as shown in FIG. 3, the condenser lens 62 is brought close to the sample rod 14 and controlled to a desired size.

  Such a variable adjustment unit 70 may be configured, for example, by providing a slider member 72 at the bottom of the irradiation source chamber 60 so that the condenser lens 62 moves in the left-right direction on the slider member 72. However, any structure may be used as long as the distance between the sample rod 14 and the condenser lens 62 can be adjusted by stepless adjustment, for example, by providing a tire so as to be movable. Is.

  Furthermore, it is preferable that the variable adjustment unit 70 has an angle adjustment function so that the angle of the condenser lens 62 can be adjusted, and by performing the angle adjustment in this way, the irradiation angle of the infrared rays 20 is inclined from the horizontal direction. It is possible to optimally control the tilt position from above.

  Here, it is preferable that the variable adjustment unit 70 has an automatic adjustment function of adjusting the irradiation position and the irradiation angle in accordance with the growth rate of the single crystal. By moving the condensing lens 62 relative to the sample rod 14 according to the speed and further irradiating the infrared rays 20 from the optimum height to the optimum angle by the angle adjustment function, the single crystal is continuously formed. The diameter can be increased.

  As described above, the floating zone melting apparatus 10 according to the present invention uses the semiconductor laser module 30 as the irradiation source of the infrared rays 20, and the laser beam of the infrared rays 20 emitted from the semiconductor laser module 30 is collimated in a desired size by the cylindrical lens group 50. After the light is condensed, the light is condensed by the condensing lens 62 and irradiated to the sample rod 14, and the condensing area of the infrared ray 20 is made variable by moving the condensing lens 62 according to the growth rate of the single crystal. It can be variably adjusted.

  For this reason, a large-diameter single crystal can be efficiently and stably grown. Further, the floating zone melting apparatus 10 does not use the conventional infrared lamp 106 or the elliptical mirror 104, but allows the condenser lens 62 to move within a predetermined range. Also when growing, it is not necessary to enlarge the floating zone melting apparatus 10 more than necessary, and the manufacturing cost can be suppressed.

  The embodiment of the floating zone melting apparatus 10 of the present invention has been described above. However, the present invention is not limited to the above-described form. For example, in the cylindrical lens group 50, the number of lenses and the combination of lenses can be changed as appropriate. Various modifications can be made without departing from the object of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Floating zone melting apparatus 12 ... Sample chamber 14 ... Sample rod 16 ... Seed crystal 18 ... Atmospheric gas 20 ... Infrared 30 ... Semiconductor laser module 32 ... Semiconductor laser Element 34 ... Conductive plate 36 ... Electrode body 38 ... Conductive plate 40 ... Electrode body 42 ... Insulating plate 50 ... Cylindrical lens group 52 ... Vertical axis cylindrical lens 54 ... Horizontal axis cylindrical lens 56... Expanded cylindrical lens 58... Cylindrical lens for parallel change 60... Irradiation source chamber 62... Condensing lens 70.・ Floating zone melting apparatus 102... Infrared 104... Elliptic mirror 106. Infrared lamp 110. Sample rod 112. Seed crystal 114.

Claims (3)

Infrared concentration heating type floating zone melting apparatus for irradiating a sample rod with infrared rays to obtain a melt by heating and melting, and solidifying the melt on a seed crystal to grow a single crystal,
The floating zone melting device is:
A semiconductor laser module for irradiating the infrared laser beam;
A condensing system for converting the infrared laser light emitted from the semiconductor laser module into parallel light of a desired size, further condensing the parallel light and irradiating the sample rod;
Comprising at least
The condensing system is
A cylindrical lens group composed of a plurality of cylindrical lenses;
A condenser lens positioned between the cylindrical lens group and the sample rod;
Have
The condensing lens is configured to variably adjust a relative position with respect to the sample via a variable adjustment unit.   2. The floating zone melting apparatus according to claim 1, wherein the variable adjustment unit has an automatic adjustment function of adjusting a position and / or an angle according to a growth rate of the single crystal. The cylindrical lens group is
A vertical cylindrical lens and a horizontal cylindrical lens that convert the infrared laser beam into parallel light in the vertical and horizontal directions;
An expanded cylindrical lens that enlarges the diameter of light that is parallel to the vertical axis direction and the horizontal axis direction by the vertical axis cylindrical lens and the horizontal axis cylindrical lens;
A parallel-changing cylindrical lens that converts the light expanded by the extended cylindrical lens into parallel light again;
The floating zone melting apparatus according to claim 1 or 2, characterized by comprising:

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