JP6778376B2 - Floating zone melting method and equipment using it - Google Patents

Description

The present invention relates to, for example, a method of arranging raw material rods when producing a single crystal by an infrared concentrated heating floating zone melting method.

Many of the large market-sized single crystal materials such as silicon, sapphire, gallium arsenide (gallium arsenide), lithium niobate, lithium tantalate, and lithium tetraborate melt all of the raw materials once and crystallize from some of them. It is produced by methods such as the Czochralski (Cz) method and the Bridgeman method. The feature of these methods is that high quality and large diameter crystals can be mass-produced. On the other hand, the drawbacks are that a crucible is indispensable for crystal growth and that segregation control is difficult.

The problems with crucibles are that quartz crucibles used for growing silicon crystals are disposable, and precious metal crucibles such as iridium and platinum, which are sometimes used for growing crystals of sapphire and lithium niobate, are very expensive. .. In the case of a precious metal crucible, shape deformation progresses with use, so regular recasting is required. These factors are major factors that hinder further cost reduction.

The problem with segregation is that it is difficult to control segregation, so mass production is centered on crystalline materials that do not require segregation control. In the case of silicon, since boron whose segregation coefficient is close to 0.8 and 1 can be used as a dopant in p-type silicon, the segregation of the dopant is unlikely to be a problem even when grown by the Cz method, whereas in n-type silicon, the segregation coefficient is high. Segregation of the dopant becomes a problem because only phosphorus, which is smaller than 0.35 and 1, can be used as the dopant at most. Therefore, the solidification rate in the crystal growth process must be limited, and it is difficult to increase the length of n-type silicon, and it is difficult to mass-produce n-type silicon at a lower cost than p-type silicon. In single crystal silicon solar cells, which have been attracting attention in recent years, the conversion efficiency of the type that uses n-type silicon for the substrate is higher than that that uses p-type silicon, so it is effective to reduce the cost of n-type silicon. .. On the other hand, in single crystals such as lithium niobate and lithium tantalate, it is known that crystals having a composition ratio of lithium to niobium or lithium to tantalum closer to a constant ratio composition of 1: 1 have higher performance as a surface elastic wave element. However, what is actually mass-produced is a crystal having a matching melt composition in which niobium and tantalum that can be grown by the Cz method are excessive.

Based on these points, it can be said that the crystal materials currently being industrialized are limited to crystals of substances having a matching melt composition in which an appropriate crucible can be used. Due to the high reactivity of the melt, it is currently difficult to industrially use crystals of substances that do not have an appropriate crucible or substances that cause extreme segregation, even if they have excellent properties.

The infrared intensive heating floating zone melting (IR-FZ) method was developed as one of the methods that can compensate for the shortcomings of the Cz method and Bridgeman method, such as crucible material consumption and dopant segregation. Similar to the (rf-FZ) method, this is a zone melting method that does not require a crucible (for example, Patent Document 1). Since no crucible is required, crystals can be grown even if the melt has high reactivity. Furthermore, since it is a band melting method, it is possible to grow long crystals with a uniform composition in principle by using a melting band with an appropriate composition regardless of whether the segregation coefficient of the dopant is extremely large or small compared to 1. It has features. However, since it was difficult to grow a large-diameter single crystal, it was rarely used industrially, and it was only used for growing a small amount of various compound single crystals for research.

Attempts have also been made to improve the growth crystal diameter in this IR-FZ method. For example, in Patent Document 2, the size of the silicon crystal could be increased by moving the spheroid mirror to an appropriate position according to the diameter of the raw material by growing silicon using a device capable of moving the spheroid mirror in the major axis direction.

JP-A-2007-99602 JP 2013-224237

The floating zone melting device of Patent Document 1 is a four-elliptical mirror type, and has four rotary ellipsoidal reflectors (inner surface is a reflective surface) arranged on a horizontal orthogonal axis intersecting at the heating position of the sample rod. It is a thing. An infrared lamp is arranged at the first focal point of each spheroidal reflector, and the four spheroidal reflectors are arranged so as to share the second focal point at the heating position (the intersection of the orthogonal axes is the second). focus). The light emitted from the infrared lamp is reflected by each retroreflector and focused on the heating position to heat the sample.

However, in order to grow a large-diameter single crystal, it is necessary to control the shape of the solid-liquid interface of the molten zone, not just condensing and heating.

Therefore, as a result of careful examination of the shape of the molten zone in the growth of this silicon, the raw material-melt interface and the crystal-melt interface were close to each other at the center of the molten zone. In addition, it was suggested that the temperature of the surface of the melt that was directly heated increased significantly as the diameter of the grown crystals increased. This means that the temperature difference between the outside and the inside of the melting zone is large, and it is considered that the melting zone becomes significantly unstable due to the contact between the raw material and the crystal in such a state. These were considered to be due to insufficient heat transfer to the vicinity of the center of the fusion zone. Considering qualitatively the heat transfer mechanism required for melting near the surface of the melting zone and near the center of the melting zone, in addition to the large radiant heat transfer effect due to the concentration of infrared rays from the rotating elliptical mirror near the surface of the melting zone. Since it is close to the outer periphery of the raw material and the grown crystal, the effect of heat transfer by forced convection due to these rotations is large. Therefore, the contribution of heat conduction is relatively small. On the other hand, in the central part of the molten zone, the radiant heat transfer effect can hardly be expected, and in the central part, the effect of heat transfer by forced convection due to the rotation of the raw material and the grown crystal is also small. Therefore, the contribution of heat conduction is relatively large. If measures can be taken to correct such a situation, it is expected that the grown crystals will be further enlarged, but such an attempt has not been made so far.

An object of the present invention is to provide an appropriate method for arranging raw material rods for stabilizing a melting zone when producing a single crystal by, for example, an infrared concentrated heating floating zone melting method.

The present invention is a floating zone melting method in which a plurality of raw material rods suspended in the vertical direction are arranged with a gap between the raw material rods in a floating zone melting method for growing a single crystal, and a melting zone is generated while maintaining the gap. This is a method in which the melting zone can be stabilized by changing the gap.

Further, according to the present invention, in the floating zone melting device for growing a single crystal, a holding mechanism capable of arranging a plurality of raw material rods suspended in the vertical direction with a gap between the raw material rods is provided to maintain the gap. It is a floating zone melting device that can stabilize the melting zone because the melting zone can be generated as it is.

An overview photograph of the melting zone when the size of the raw material rod is increased is shown. (Top) Two raw material rod arrangements of the embodiment of the present invention and (Bottom) a photograph of a vertical cross section of a rapidly cooled solidified body of a melting zone are shown. A schematic diagram of the melting zone is shown. It is a figure which shows the relationship between the distance between raw material rods, and the convexity of an interface shape. It is a figure which shows the relationship between the distance between raw material rods, and a lamp output. It is a figure which shows the relationship between the distance between raw material rods and the melting zone height, and the relationship between the distance between raw material rods and the minimum width of a melting zone. A schematic diagram of the arrangement between the raw material rods is shown. A schematic diagram of the arrangement between the raw material rods is shown. It is a figure which showed the raw material rod setting apparatus provided in the infrared centralized heating floating zone melting apparatus of this invention. It is a figure which shows the structural example of the raw material rod, and the application example in the raw material rod installation apparatus. An example of the state of the melting zone is shown. It is a figure which showed the raw material rod setting apparatus provided in the infrared centralized heating floating zone melting apparatus of this invention. It is a figure which shows the structural example of a plurality of raw material rods. It is a figure when a raw material (raw material rod) and a light source face each other. It is a figure when the gap of a raw material (raw material rod) and a light source face each other. It is a figure when a raw material (raw material rod) and a light source face each other. It is a figure when the gap of a raw material (raw material rod) and a light source face each other. It is a figure when a raw material (raw material rod) and a light source face each other. It is a figure when the gap of a raw material (raw material rod) and a light source face each other. It is a figure which shows an example of arrangement of a heating light source.

Silicon single crystals were grown by the infrared concentrated heating floating band melting method. Normally, a single raw material rod is used to form a melting zone and grow a single crystal, but the melting zone becomes unstable due to the temperature difference between the central part and the outer peripheral part of the melting zone, and as the size of the raw material rod increases. As shown in FIG. 1, there was a state in which the melting zone could not be maintained. A method for improving this was examined, and a plurality of raw material rods were arranged so as to avoid the vicinity on the rotation axis of the shaft, and crystals were grown using them at the same time.

Two 10 mm x 20 mm square raw material rods are used at the same time, and the long side is placed facing each other with the center of the rotation axis sandwiched between them, and the gap between the raw material rods is set to 2, 4, and 7 mm, and a growing test is performed. , A comparative study was carried out together with the results of a growing test using a single raw material rod of 20 mm × 20 mm square.

As an example, the upper part of FIG. 2 shows a raw material rod arrangement in which the distance between two raw material rods of 10 mm × 20 mm × 180 mm suspended in the vertical direction is changed. The lower part of FIG. 2 shows a photograph of a vertical cross section of a rapidly cooled solidified body of a molten zone formed under almost the same conditions with a lamp output of 6.8 kW. Up to a distance of about 2 mm between the raw material rods, a phenomenon was observed in which the melt was sucked up to the raw material side by capillarity at approximately regular intervals. Such a phenomenon was suppressed when the distance between the raw material rods was close to 4 mm.

As a more detailed study, the relationship between the distance between the raw material rods, the convexity of the interface shape, the lamp output, and the height of the molten zone will be shown. FIG. 3 shows a schematic diagram of the melting zone. FIG. 4 shows the relationship between the distance between the raw material rods and the convexity of the interface shape. FIG. 5 shows the relationship between the distance between the raw material rods and the lamp output. FIG. 6 shows the relationship between the distance between the raw material rods and the height of the melting zone.

As shown in the schematic diagram of FIG. 7, it was found that as the distance between the raw material rods increased, the convexity of the interface shape on the raw material side decreased and became closer to flat. This is because a part of the heating light permeates through the gap between the raw material rods, and the raw material rods and the surface of the molten zone near the center of rotation of the shaft can be directly heated. In other words, under the conventional conditions of using one raw material rod, heat transfer near the center of rotation was mainly performed by heat conduction, but it can be said that the contribution of radiant heat transfer was added by the gaps between multiple raw material rods. .. In addition, the molten zone was stabilized as the interface shape of the molten zone changed. In addition, the fusion zone is stable because the gap between the two raw material rods is located directly above the center of rotation of the crystal where the interface between the fusion zone and the crystal is most convex, making it difficult for the raw material and the grown crystal to come into contact with each other. It is thought that it contributes to the conversion. Similar results were obtained even when the number of raw material rods was further increased and the gaps between the four raw material rods of 10 mm × 10 mm × 180 mm were arranged in a cross shape and the intervals were changed.

In addition, the infrared concentrated heating floating zone melting device used in this test is equipped with a clamp-like holding mechanism that can hold multiple raw material rods while maintaining the gap, and the gap was adjusted by adjusting the clamp position. ..

Due to the change in solid-liquid interface shape caused by the use of a plurality of raw material rods, contact between the raw material rods and the grown crystals is less likely to occur. Therefore, it can be expected that the grown crystals will be enlarged by the IR-FZ method. If the IR-FZ method can be used to increase the size, the zone melting method, which enables segregation control without using a crucible, can be used for mass production of crystalline materials. Therefore, segregation control for n-type silicon, etc., which was difficult with the Cz method. It is expected that the length of the crystal material that requires the above will be increased. In addition to reducing the cost of the crucible, it is expected that the cost will be reduced by increasing the length. Further, in the case of silicon, for example, since p-type crystals can be mass-produced by the Cz method at present, there are no restrictions in device design assuming a p-type substrate. For example, a solar cell using an n-type substrate with high conversion efficiency. Can be used for.

Further, this method is a method of melting not all of the raw materials but a part of the raw materials as a melting zone, and has an advantage that the required electric power can be reduced as compared with a method such as the Cz method in which all the raw materials are once melted.

As described above, in the usual infrared concentrated heating floating zone melting method, a melting zone is formed by using one raw material rod, and a single crystal is grown. Therefore, when the diameter of the grown crystal is increased by the infrared heating floating zone melting method, it is necessary to increase the cross-sectional area of the raw material rod. FIG. 1 shows a molten zone during silicon single crystal growth under the condition that the cross-sectional area of the raw material rod is changed ((a) 20 × 20 mm ² , (b) 25 × 25 mm ² , (c) 30 × 30 mm ² from the left). It is a photograph of the vicinity. The conditions for growing a silicon single crystal are that the raw material supply rate is 10 mm / h (cases (a) and (b)) and 5 mm / h (case (c)), and the condensing mirror position is 4 mm (cases (a) and (b)). (C)). Here, the position of the condensing mirror is the position of the focal point of the condensing mirror that concentrates infrared rays in the fusion zone, the rotation axis of the single crystal, and the distance. The lamp output is 6.8 kW (case (a)), 8.6 kW (case (b)), 7 for each case of the raw material rods of 20 × 20 mm ² , 25 × 25 mm ² , and 30 × 30 mm ^2. It was set to 9.9 kW (case (c)). FIG. 1 also shows a state about 1 minute after the start of growth of the silicon single crystal under the same conditions in the case of 30 × 30 mm ² (d). As is clear from the results shown here, the larger the raw material, the larger the lamp output required for forming the melting zone, and also the melting zone becomes large and constricted, making it difficult to maintain stability, and the minimum width of the melting zone. It can be seen that the ratio of the grown crystal diameter is small. Generally, the higher the temperature and the lower the viscosity of the melt, the easier it is for the melt zone to constrict. Therefore, this phenomenon is caused by the local heating of the surface of the melt zone as the output of the lamp increases, resulting in the viscosity of the melt surface. On the other hand, it is considered that the cause is that the raw material rods and the grown crystals are difficult to melt due to insufficient heating in the central part of the melting zone, and are easily approached and contacted with each other.

The above-mentioned embodiment using two raw material rods will be reviewed again with reference to FIGS. 2 to 8. FIG. 8 is a schematic view of the arrangement between the raw material rods in which the components of FIG. 7 are numbered with reference to the following studies. Here, FIG. 8A shows a case where one raw material rod is used as before, FIG. 8B shows a case where two raw material rods are spaced by Sb, and FIG. 8C shows two raw materials. The cases where the bars are spaced Sc apart are shown. In addition, in FIGS. 8 (b) and 8 (c) and FIG. 7 corresponding thereto, it corresponds to a schematic view when the experiment is performed with Sb = 2 mm and Sc = 4 mm.

In FIGS. 8A to 8C, 1a, 1b, 1c are the center of rotation axis, 2a, 2b1, 2b2, 2c1, 2c2 are raw material rods, 3a, 3b1, 3b2, 3c1, and 3c2 are convex portions of the raw material rod. 4b and 4c are the liquid levels between the raw material rods of the molten zone solution, 5a, 5b and 5c are the convex portions of the produced single crystal, 6a, 6b and 6c are the produced single crystals, and 7a, 7b and 7c are melted. Shows a band. Further, the radii of the generated single crystals 6a, 6b, 6c are rca, rcb, rcc, and the distance from the rotation axis to the side surface of the raw material rod (2a, 2b1, 2b2, 2c1, 2c2) is rFa, rFb, rFc, the raw material. The height of the convex part of the rod is hFa, hFb, hFc, the height of the convex part of the single crystal is hca, hcb, hcc, the height of the melting zone is Ha, Hb, Hc, the minimum interval of the melting zone is hma, hmb, hmc, The minimum width of the melting zone is shown as Wa, Wb, Wc. RFa, rFb, and rFc in FIG. 8 correspond to rF in FIG. 3, hFa, hFb, and hFc correspond to hF, hca, hcb, and hcc correspond to hc, and rca, rccb, and rcc correspond to rc. Although the center of the rotation axis (1a to 1c) is the same, the raw material rod and the single crystal are manufactured by rotating in opposite directions.

In FIG. 4, the interface shape convexity (h / r) on the crystal side and the raw material side is indicated by black circles and white circles, respectively. The crystal-side interface shape convexity (hc / rc) indicates the ratio of the convex portion height hc of the single crystal to the radius rc of the single crystal as shown in FIGS. 3 and 8. The interface shape convexity (hF / rF) on the raw material side indicates the ratio of the convex portion height hF of the raw material rod to the distance rF from the center of the rotation axis to the side surface of the raw material rod. The larger the values of the crystal-side interface shape convexity (hc / rc) and the raw material-side interface shape convexity (hF / rF), the higher the convexity height. From this result, FIG. 4 shows that in the range of the distance between the raw material rods (distance S between the raw material rods) of 2 mm to 5 mm, the interface shape convexity (hF / rF) on the raw material side decreases as the distance between the raw material rods increases. However, it can be seen that the interface shape on the raw material side is flattened.

In FIG. 6, the relationship between the raw material rod distance S and the melting zone height H is shown by black circles. Further, the relationship between the raw material rod distance S and the minimum melting zone width W is indicated by white circles. In the range of the distance between the raw material rods (distance S between the raw material rods) of 0 to 7 mm, the melt zone height H decreases and the melt zone minimum width W increases as the distance between the raw material rods increases. You can see that. In this experiment, the relationship between the raw material rod distance (S) and the lamp output is almost constant as shown in FIG.

From the above, in the floating zone melting method for growing a single crystal, a plurality of raw material rods suspended in the vertical direction are arranged with a gap between the raw material rods, and when a melting zone is generated while maintaining the gap, melting occurs. It can be seen that the band is stable. This allows the production of larger (larger radii) single crystals by the floating zone melting method. According to the invention of the present application, it is possible to increase the size of a grown crystal by the IR-FZ method. The technique for large-scale mass production of an n-type silicon single crystal by the IR-FZ method of the present invention means that it is freed from the "restriction of using a p-type substrate" caused by using the conventional Cz method. Then, the effect is remarkably exhibited in a solar cell or the like using an n-type substrate having high conversion efficiency.

FIG. 9 is a diagram showing a raw material rod setting device included in the infrared centralized heating floating zone melting device of the present invention. FIG. 9A shows a raw material rod installation portion used in the above-described embodiment, in which a plurality of raw material rods are grouped together while maintaining a certain gap and hung from a hook of a shaft. B) shows the improved form.

In FIG. 9A, the raw material rod setting device 100 includes a shaft 11, a hook 12, and a wire 13. The two raw material rods (102-1 and 102-2) are integrated with a predetermined gap by the spacer 14. By hooking the wire 13 on the hook 12, the raw material rod integrated with the shaft 11 is suspended. The infrared centralized heating floating zone melting device of the present invention includes a rotation mechanism (not shown) in which the shaft 11 rotates in the direction indicated by 10.

In FIG. 9B, the raw material rod installation device 200 includes a shaft with a suspension function. The outer shaft 21 and the inner shaft 22 are suspended inside the outer shaft 21 via a spring 23. The inner shaft 22 is fitted in a hollowed out region of the outer shaft 21 and hung from the outer shaft 21 via a spring 23. When the outer shaft 21 rotates in the direction of 10, the inner shaft 22 is also configured to rotate. Further, the internal shaft is provided with a spacer portion 24, and the raw material rods (202-1, 202-2) are integrated with a predetermined gap so as to sandwich the spacer portion 24. Similar to FIG. 9A, the infrared centralized heating floating zone melting device of the present invention includes a rotation mechanism (not shown) in which the shafts 21 and 22 rotate in the direction indicated by 10.

Although FIGS. 9A and 9B show an example of integrating two raw material rods, it is also possible to integrate three or more raw material rods as described later. FIG. 10 is a diagram showing a configuration example of a raw material rod and an application example in a raw material rod installation device. 10 (A) to 10 (E) are views of the raw material rods viewed from the shaft (11) side on which the raw material rods are installed in the single crystal (106) direction (vertically downward). FIG. 10 (F) shows, as an example, the case where FIG. 10 (A) is applied to the raw material rod setting device 100 of FIG. 9 (A). FIG. 10 (A) shows two raw material rods 102-1a and 102-2a having a rectangular bottom surface integrally sandwiched by a spacer 14a, and FIG. 10 (B) shows four raw material rods 102 having a square bottom surface. When -1b to 102-4b are integrally formed by sandwiching the spacer 14b, FIG. 10C shows that three raw material rods 102-1c to 102-3c having a square bottom surface are integrally formed by sandwiching the spacer 14c. In the case of FIG. 10 (D), when four raw material rods 102-1d to 102-4d having a circular bottom surface are integrally formed with a spacer 14d interposed therebetween, FIG. 10 (E) shows three raw materials having a circular bottom surface. The case where the rods 102-1e to 102-3e are integrally formed with the spacer 14e interposed therebetween is shown. In any of the figures (A) to (E) of FIG. 10, the circumferential arrow on the outer circumference indicates the rotation direction of these integrated raw material rods as in the rotation direction 10 of FIG. 10 (F). ing. In this way, the raw material rods can be integrated with a plurality of raw material rods by sandwiching the spacer 14. In the example shown in FIG. 10 (F), the tip of the raw material rod is heated by infrared rays while the integrated raw material rods (102-1, 102-2) rotate around the rotation axis of the shaft 11, and the melting zone 107 To produce a single crystal 106. Reference numeral 105 is a convex portion of a single crystal, and 103-1 and 103-2 are convex portions of a raw material rod. The rotation axis of the single crystal 106 is at the same position as the rotation axis of the shaft 11, but the rotation direction is opposite. As described above, the number of raw material rods is increased in this way, and three raw material rods of 10 mm × 10 mm × 180 mm are arranged in a Mitsubishi shape with a gap around them, or four are arranged so that the gap becomes a cross shape. As a result, the result was obtained that the interface shape of the fusion zone was flattened and the fusion zone was stabilized as a result even when the interval was changed.

FIG. 9A shows a configuration in which the rotation of the shaft 11 is transmitted to the integrated raw material rod by the wire 13 and the shaking of the raw material rod during crystal growth due to the rotation is absorbed by the wire 13. However, even with the configuration shown in FIG. 9A, when the raw material rod comes into contact with the grown crystal, it may shake significantly in the horizontal direction. FIG. 9A shows a state of swinging from side to side.

FIG. 11 is an example of the state of the molten zone after the raw materials and the grown crystals come into contact with each other when the three raw materials are put together and are largely shaken left and right (horizontally). As shown in this figure, the raw material forming the molten zone with the grown crystal is limited to a part, and the remaining raw material may not be able to maintain the contact state with the grown crystal. In that case, the entire plurality of raw materials are tilted diagonally. If the raw material rod is sufficiently long and has a sufficient mass, the uncontacted raw material may come into contact with the melting zone again. However, if the raw material rod is short and the mass is small, the entire raw material remains tilted at an angle, and it becomes difficult to bring the raw material that does not form a melting zone into contact with the melting zone again even if the entire raw material is moved up and down. .. When the raw material rod is long and has a sufficient mass, the configuration shown in FIG. 9 (A) is sufficient. However, when this phenomenon becomes a problem, it is possible to suppress the phenomenon that a part of a plurality of raw materials does not come into contact with the melting zone by changing to the raw material rod setting device 200 as shown in FIG. 9 (B).

As another method, instead of rotating the entire plurality of raw materials in an integrated manner as shown in FIGS. 9 and 10, individual raw materials are fixed to a plurality of shafts and the shafts are individually rotated. , It is a method of moving it up and down. An example thereof is shown in FIG. FIG. 12 is a diagram showing a raw material rod installation device included in the infrared centralized heating floating zone melting device of the present invention, and is a diagram showing another form. The raw material rod installation device 300 of FIG. 12 includes a plurality of shafts with suspension functions (208-1, 208-2) shown in FIG. 9 (B), and one raw material rod (202-1, 208-2) for each shaft with suspension function. 202-2) is installed. Further, the raw material rod installation device 300 is configured so that each of the shafts with a suspension function rotates about the rotation axis of each shaft. The inner shaft (22-1,22-2), the outer shaft (21-1,1-2), and the spring (23-1,23-2) of the shaft with suspension function (208-1,208-2). Corresponds to the inner shaft (22), the outer shaft (21), and the spring (23) of FIG. 9B, respectively, and their structures are the same. Further, in FIG. 12, the melting zone is 207, the convex portions of the raw material rods (202-1, 202-2) are 203-1 and 203-2, the single crystal is 206, and the convex portion of the single crystal is 205. ..

Also in the method shown in FIG. 12, it is possible to use a plurality of raw material rods. FIG. 13 is a diagram showing a configuration example of a plurality of raw material rods, and shows variations thereof. As shown in FIG. 13 (A), four raw material rods 202-1a to 202-4a having a square bottom surface are attached to the shafts with suspension functions, respectively, and the raw material rods equipped with four shafts with suspension functions each rotate. The device may be configured. It may be applied to three raw material rods (202-1b to 202-3b) as shown in FIG. 13 (B), or may be applied to raw material rods (202-1c to 202-4c) as shown in FIGS. 13 (C) and 13 (D). , 202-1d to 202-3d) may be changed to a circular shape to form a raw material rod installation device provided with three or four shafts with a suspension function. That is, two or more N raw materials may be configured to be individually rotated in an arrangement such that they form a straight line or an N-sided polygon.

When a plurality of raw material rods are integrated and rotated, the surface that is directly radiated and the surface that is not directly radiated are always the same. Therefore, as shown in FIG. 2 or 7, the interface on the raw material side near the center of rotation has a shape protruding toward the melting zone side. On the other hand, when a plurality of raw material rods are individually rotated as shown in FIGS. 12 and 13, both sides of the individual raw materials are uniformly heated on an average time. As a result, the interface shape is flattened, which makes it possible to form a compact melting zone with a reduced height of the melting zone.

Under the condition that the individual raw materials are fixed to the plurality of shafts as shown in FIG. 12, the arrangement of the raw materials, the lamp as the heating light source, and the spheroid mirror is fixed. As a result, a new "arrangement" arises as a condition for consideration. An extreme example is the case where the raw material (raw material rod) and the light source face each other (FIG. 14) and the case where the gap between the raw material (raw material rod) and the light source face each other (FIG. 15). Here, both FIGS. 14 and 15 assume a case where three raw material rods (34-1 to 3-4-3) are rotated by using a shaft with a suspension function as shown in FIG. 12, for example. That is, three raw materials are provided by three light sources (33-13-3-3) consisting of a lamp (infrared lamp: 32-1 to 2-32-3) and a spheroid mirror (31 to 1-31-3) which are heating light sources. The case where the rod (34-1-4-3) is heated is shown. It should be noted that FIGS. 14 and 15 are views from the directions along the rotation axis of each raw material rod.

Now, consider a case where the light sources 33-1 to 33-3 of FIGS. 14 and 15 irradiate the raw material rods 34-1 to 3-4-3 from the direction perpendicular to the rotation axis (right beside, horizontal direction). In this case, with respect to the dotted line P in FIG. 14, the raw material rod 34-1 facing the light source 33-1 is shown in FIG. 16, and with respect to the dotted line Q in FIG. 15, the raw material rod 34 facing the light source 33-2. The figure of -1 is schematically shown in FIG. FIG. 17 shows a case where the gap (gap) between the raw material rods 34-2 and 34-3 faces the light source. 16 and 17 are views perpendicular to the rotation axis of each raw material rod and parallel to the lines P and Q. Further, consider a case where the light sources 33-1 to 3-3 of FIGS. 14 and 15 irradiate the raw material rods 34-1 to 3-4-3 with an inclination with respect to the rotation axis. In this case, the figure corresponding to FIG. 16 is FIG. 18, and the figure corresponding to FIG. 17 is FIG. In FIGS. 16 to 19, 303 is a convex portion of the raw material rod 34-1, 305 is a convex portion of a single crystal, 306 is a single crystal, and 307 is a molten zone.

The light source 33-1 and the raw material rod 34-1 are facing each other and the light source is arranged with respect to the raw material rod from the side, and the light source 33-1 and the raw material rod 34-1 are facing each other and have an inclination. The arrangement in FIG. 18 is similar to the conventional single raw material situation. It is known that when a single raw material is used, the horizontal arrangement similar to FIG. 16 has higher light collection efficiency than the inclined arrangement similar to FIG. 18, and a melting zone can be formed with a smaller lamp output. .. This is similar to the effect of the angle of incidence of sunlight on how the ground warms. Similarly, when a plurality of raw materials are individually rotated, the one closer to the horizontal arrangement in FIG. 16 has higher light collection efficiency than the more inclined arrangement in FIG. 18, and a melting zone can be formed with a lower output lamp output. On the other hand, in the arrangement of FIGS. 17 and 19 in which the gap between the raw materials (raw material rods) and the light source face each other, the surface of the molten zone is inclined as shown in the drawing. Therefore, depending on the tilt angle, the tilted arrangement of FIG. 19 may have higher light collection efficiency than the case of being closer to the horizontal layout of FIG.

Based on this, it can be seen that it is effective to tilt the heating light source greatly or to arrange it near the horizontal depending on whether or not the plurality of raw materials themselves or the gaps between the raw materials are faced. Changing the inclination of the heating light source according to the positional relationship between the heating light source and the raw material in this way brings about another effect. FIG. 20 shows a diagram showing an example of the arrangement of the heating light source. As shown in FIG. 20, the heating light sources are arranged so that the inclinations of the heating light sources arranged so as to surround the grown crystal are exactly alternating. In FIG. 20, heating light sources 43-1 to 43-6 are arranged so as to surround the raw material rods 44-1 to 44-3. Here, heating light sources 43-2, 43-4, 43-6 arranged in the horizontal direction and heating light sources 43-1, 43-3, 43-5 arranged in an inclined direction are provided. Then, as shown in the projection drawings (45, 46) of FIG. 20, the spatial arrangement of the spheroid mirrors of each light source is arranged so as to easily avoid mutual interference. Therefore, it is less necessary to scrape off a part of the spheroidal mirror. As a result, it is possible to suppress a decrease in focusing efficiency caused by scraping off the spheroidal mirror. In FIG. 20, as the heating light source arranged so as to surround the growing crystal, two heating light sources having different inclinations with respect to the rotation axis of the growing crystal (single crystal) are arranged. You may increase it further. It is advisable to arrange at least two heating light sources having different inclinations from each other. That is, at least two heating light sources may be provided, and the irradiation angle of one of the heating light sources with respect to the rotation axis of the raw material rod and the irradiation angle of the other of the heating light sources may be different from each other.

In the examples shown in FIGS. 12 to 15 described above, the respective raw material rods (202-1, 202-2 in FIG. 12, 202-1a to 202-4a, 202-1b to 202- in FIG. 13). An example in which 3b, 202-1c to 202-4c, 202-1d to 202-3d, 34-1 to 3-4-3 in FIGS. 14 and 15) rotate individually, but are fixed as a whole. showed that. That is, in these examples, the rotation axis of the single crystal to be grown and the rotation axis of the raw material rod are not on the same line. In order to further average the light of the infrared lamp and hit the raw material rod, the raw material rod installation device may be configured so that the entire plurality of individually rotating shafts are collectively rotated in the direction opposite to that of the single crystal. For example, in the example of FIG. 14, each of the raw material rods 34-1 to 3-4-3 rotates about the center of each raw material rod, and the entire raw material rods 34-1 to 3-4-3 rotate about the axis X0. The raw material rod installation device may be configured so as to do so.

Further, instead of the raw material rod setting device in which the plurality of raw material rods are configured to rotate as a whole as described above, the light sources 33-1 to 33-3 shown in FIGS. 14 and 15 simply surround the raw material rods. It may be configured to rotate about the rotation axis of the crystal. In this case, the light sources 33-1 to 33-3 shown in FIGS. 14 and 15 may irradiate the rotation axis of the single crystal with the same inclination, but at least two or more as shown in FIG. Irradiation may be performed at different inclinations.

In the description of the above-mentioned example, for example, the shafts 11, 21, and 22 of FIG. 9 are installed for the rotation of the raw material rod, and are the upper shafts (upper shafts). In the description of the above-mentioned example, although not particularly shown, a single crystal (such as 106 in FIG. 10F) is fixed to a lower shaft (lower shaft) separately from the upper shaft for its rotation. The lower shaft rotates in the opposite direction to the upper shaft.

In the present invention, in the floating zone melting method for growing a single crystal (for example, 106 in FIG. 10), a plurality of raw material rods (102-1 and 102-2) suspended in the vertical direction are used as the raw material rods. A gap (a gap according to 104) is arranged between them, and a melting zone is generated while maintaining the gap.

Further, in the floating zone melting method of the present invention, a plurality of raw material rods (102-1 and 102-2) suspended in the vertical direction in the floating zone melting device for growing a single crystal (for example, 106 in FIG. 10) are used. A floating zone melting device is used which is provided with a holding mechanism (12, 13, 14) which can be arranged with a gap (gap by 104) between the raw material rods and generates a melting zone while maintaining this gap.

Further, instead of the holding mechanisms of 12 to 14 in FIG. 9A, a plurality of raw material rods are fixed to a shaft having a suspension function that can move up and down as shown in FIG. 9B, and these raw materials are used. It may be a holding mechanism that can be arranged with a predetermined gap between the rods.

Further, as shown in FIG. 12, a plurality of shafts having a suspension function that can be moved up and down are provided, a raw material rod is installed on each shaft, and a raw material that holds the shaft so that each of the raw material rods has a predetermined gap. It may be used as a rod installation device.

Furthermore, each of the shafts may be provided with a rotation function of rotating individually.
These disclosed floating zone melting devices are provided with at least two heating light sources, and even if one irradiation angle of the heating light source with respect to the rotation axis of the raw material rod and the other irradiation angle of the heating light source are configured to be different from each other. Good.

Claims (7)

In the infrared intensive heating floating zone melting method for growing a single crystal, a plurality of raw material rods suspended in the vertical direction are arranged with a gap larger than 2 mm between the raw material rods.
A floating zone melting method in which heating light by infrared rays is directly permeated through the gap while maintaining the gap to generate a melting zone. In the infrared concentrated heating floating zone melting device for growing a single crystal, a holding mechanism capable of arranging a plurality of raw material rods suspended in the vertical direction with a gap larger than 2 mm between the raw material rods is provided.
A floating zone melting device that creates a melting zone by directly infiltrating heating light by infrared rays through the gap while maintaining the gap . The floating zone melting according to claim 2, further comprising a raw material rod installation device having a holding mechanism capable of fixing a plurality of raw material rods to a shaft having a suspension function that can move up and down and arranging the raw material rods with the gap between the raw material rods. apparatus. Equipped with multiple shafts with a suspension function that can move up and down,
Raw material rods are installed on each of the shafts.
The floating zone melting device according to claim 2, further comprising a raw material rod installation device that holds the shaft so that each of the raw material rods has the gap. The floating zone melting device according to claim 4, wherein each of the shafts has a rotational function of rotating individually. The floating zone melting device according to claim 4 or 5, further comprising a heating light source. The floating zone melting device according to claim 6 , further comprising at least two heating light sources, wherein the irradiation angle of one of the heating light sources with respect to the rotation axis of the raw material rod and the irradiation angle of the other of the heating light sources are different from each other.