TWI551734B - Polycrystalline silicon ingot and production method thereof - Google Patents

Description

Method for producing polycrystalline germanium ingot and polycrystalline germanium ingot

The present invention relates to a polycrystalline germanium ingot composed of a solidified structure in a single direction, and a method of producing the polycrystalline germanium ingot.

The polycrystalline germanium ingot described above is, for example, described in Patent Document 1, and is cut into a specific shape and sliced to a specific thickness to form a tantalum wafer. This wafer is mainly used as a material for a substrate for a solar cell.

In addition, the polycrystalline bismuth ingot is used as a material of a component used in a semiconductor manufacturing apparatus such as a liquid crystal sputtering apparatus, a plasma etching apparatus, or a CVD apparatus, as described in Patent Document 2.

Here, since 矽 is a metal which expands during solidification, it is necessary to solidify in one direction so that the mash does not remain in the inside of the ingot when casting. In addition, by performing the unidirectional solidification structure, the impurities in the mash liquid are accompanied by the phase change of the solidification, and are distributed on the liquid phase side according to the equilibrium segregation coefficient, and the impurities in the ruthenium are from the solid phase (ingot) to the liquid phase ( The mash is discharged, so that a polycrystalline bismuth ingot with few impurities can be obtained.

As described above, since the polycrystalline iridium ingot is produced by solidification in one direction, at the time when the solidification is completed, a temperature difference occurs between the bottom and the upper portion, the center and the outer periphery of the bismuth ingot, and when the temperature difference is maintained and cooled, the polycrystalline silicon is cooled. There is a residual strain in the interior due to the aforementioned temperature difference.

Here, when the polycrystalline bismuth ingot is subjected to the cutting process, cracking occurs due to residual strain, and it is not damaged, and it is impossible to visually treat the micro crack or the like, and it cannot be used as a product.

On the other hand, for example, Patent Document 3 proposes a method in which a polycrystalline ruthenium ingot is taken out from a crucible, and the residual strain is reduced by heat treatment to suppress cracking or chipping, microcracking, or the like.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 10-245216

[Patent Document 2] Japanese Patent No. 4531435

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2004-161575

However, recently, in order to efficiently manufacture a substrate for a solar cell from a germanium wafer, and to pursue a large area of a germanium wafer, the polycrystalline germanium ingot itself has also been enlarged. As described above, in the enlarged polycrystalline ingot, the temperature difference is also increased, and the maximum main strain amount is increased, and defects such as cracking, fragmentation, and micro cracking are likely to occur.

Further, since the polycrystalline bismuth ingot is used as a raw material of various bismuth members, the shape of the product is also greatly different, and the processing conditions thereof are also various.

In this way, since the size of the polycrystalline germanium ingot and the subsequent processing conditions are different, as in Patent Document 3, only the heat treatment conditions are specified, and the maximum main strain of the polycrystalline tantalum ingot cannot be sufficiently reduced, and cracking or fragmentation cannot be suppressed. The occurrence of tiny cracks, etc.

That is, the maximum main strain of the polycrystalline germanium ingot itself cannot be fully evaluated.

The present invention has been made in view of the above-described circumstances, and an object of the invention is to provide a polycrystalline iridium ingot capable of suppressing occurrence of cracks, fragments, microscopic cracks, and the like, and a method for producing a polycrystalline iridium ingot, even when cutting processing or the like is performed. .

In order to solve such a problem, in order to achieve the above object, the polycrystalline iridium ingot according to the present invention is composed of a unidirectional solidified structure, and is characterized in that it has no crack and has a maximum main strain of 100 με or less.

In the polycrystalline iridium ingot having such a configuration, the maximum main strain is 100 με or less. Therefore, even when cutting processing or the like is performed, occurrence of cracking or fragmentation can be suppressed. That is, the maximum principal strain of the polycrystalline germanium ingot is evaluated, so that the occurrence of defects caused by subsequent processing can be suppressed.

Here, the maximum main strain is preferably 50 με or less. Further, the maximum main strain is preferably 10 με or less.

Cracks or fragments, invisible tiny cracks, etc., are also greatly affected by the size and shape of the polycrystalline ingot, the processing conditions, and the shape after processing. ring. Therefore, by considering the processing conditions and the like, the maximum principal strain of the polycrystalline germanium ingot is defined as described above, and occurrence of cracking or fragmentation during processing, micro cracking which is invisible, and the like can be suppressed.

The method for producing a polycrystalline germanium ingot according to the present invention is characterized in that the method for producing a polycrystalline germanium ingot is characterized in that: a casting step of solidifying an ingot in a crucible in a crucible, and a crucible in which the solidified ingot is heat-treated in the crucible a heat treatment step and a reheat treatment step of removing the ingot from the crucible and then performing heat treatment; measuring a maximum main strain of the pre-manufactured polycrystalline ingot, and setting the in-furnace heat treatment step and the maximum main strain to be a specific value or less The heat treatment conditions of the aforementioned reheat treatment step.

According to the method for producing a polycrystalline iridium ingot having the above configuration, the maximum main strain of the pre-manufactured polycrystalline bismuth ingot is evaluated by measurement, and the heat treatment step of the ruthenium in which the maximum main strain is equal to or less than a specific value and the heat treatment of the aforementioned reheat treatment step can be set. condition. Therefore, as described above, it is possible to manufacture a polycrystalline germanium ingot in which the maximum principal strain is specified to be a specific value or less.

According to the present invention, it is possible to provide a polycrystalline ingot which can suppress the occurrence of cracks, defects, microscopic cracks which cannot be visually observed, and the like, and a method of producing a polycrystalline ingot, even when cutting processing or the like is performed.

1‧‧‧ polycrystalline germanium ingot

3‧‧‧矽融液

10‧‧‧ casting device

11‧‧‧vacuum room

12‧‧‧Insulation wall

13‧‧‧Insulated roof

14‧‧‧Insulated floor

15‧‧‧ venting holes

20‧‧‧坩埚

21‧‧‧ bottom

22‧‧‧ Sidewall

31‧‧‧ sloping plate

32‧‧‧Support

33‧‧‧lower heater

34‧‧‧electrode rod

42‧‧‧ gas supply pipe

43‧‧‧Upper heater

44‧‧‧electrode rod

50‧‧‧ 盖部

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic explanatory view showing a polycrystalline germanium ingot of an embodiment of the present invention.

Fig. 2 is a flow chart showing a method of measuring the maximum principal strain of the polycrystalline germanium ingot shown in Fig. 1.

Fig. 3 is an explanatory view showing an example of a sticking position and a cutting position of the strain gauge when the maximum main strain amount of the polycrystalline germanium ingot shown in Fig. 1 is measured.

Fig. 4 is a flow chart showing the method of producing the polycrystalline germanium ingot shown in Fig. 1.

Fig. 5 is a schematic explanatory view showing a casting apparatus used in the production of the polycrystalline germanium ingot of the embodiment of the present invention.

Hereinafter, a method for producing a polycrystalline germanium ingot or a polycrystalline germanium ingot according to an embodiment of the present invention will be described with reference to the drawings.

The polycrystalline silicon ingot 1 of the present embodiment is, for example, a tantalum wafer used as a substrate for a solar cell or a material for other tantalum parts. In the present embodiment, it is formed in a quadrangular column shape as shown in FIG.

This polycrystalline ingot 1 is produced, for example, by the casting apparatus 10 shown in FIG. In the crucible 20 having an angular shape (rectangular shape) in the casting apparatus 10, the crucible is solidified in one direction from the bottom side, and has a columnar crystal structure.

Next, the polycrystalline ingot 1 has a maximum principal strain of 100 με or less, preferably a maximum major strain of 50 με or less, and more preferably a maximum principal strain of 10 με or less.

Here, in the present embodiment, the maximum main strain of the polycrystalline germanium ingot 1 is It was measured by the following steps.

A method of measuring the maximum main strain of the polycrystalline ingot 1 will be described with reference to Figs. 2 and 3 .

First, in order to attach a strain gauge to the surface of the polycrystalline ingot 1, a pretreatment (pretreatment step S01) is carried out. The place to which the strain gauge is attached is ground using a grinder or sandpaper.

Next, at the position shown in Fig. 3, a strain gauge is attached using an adhesive (strain gauge attachment step S02). The attachment position of the strain gauge is preferably arranged along the one end surface of the ingot, at the vicinity of the end surface, in the vicinity of the center of the ingot, and at intervals corresponding to the intermediate position.

Here, in the present embodiment, three strained grease three-axis strain gauges are disposed at intervals of 45 degrees as attached strain gauges. (Strain, the strain of the two orthogonal strain gauges is ε ₁ and ε ₂ , and the strain of the strain gauge in the direction of 45 degrees by the two strains is ε ₃ ).

Moreover, the strain gauge to be attached is subjected to a water repellent treatment so as not to be affected by the cutting oil or the like when the polycrystalline ingot 1 is cut.

Next, the initial strain amount of the attached strain gauge (initial strain measurement step S03) is measured.

Next, the polycrystalline ingot 1 is cut by a cutter or the like along the cutting line (cutting step S04).

After the cutting, the strain amount of the strain gauge is measured (strain measurement step S05 after cutting).

These cutting step S04 and the post-cutting strain measuring step S05 are repeatedly carried out. Moreover, at the time of cutting, the distance between the strain gauge and the cut surface is In the range of 5 mm to 25 mm, it is preferable to set the cutting position at the start of cutting to the vicinity of each strain gauge. In the present embodiment, as shown in FIG. 3, the cutting is performed in the vertical direction from the end faces in the three positions of the cutting positions I, II, and III. That is, the cutting is performed in the order of the cutting position I → the cutting position II → the cutting position III.

Here, it is preferable to cut off to the center of the ingot. In the case of this embodiment, the cutting position III is the center of the ingot.

Then, after all the cuts are completed, the maximum main dependent variable is calculated from the difference between the cut strain and the initial strain. In the present embodiment, the maximum main strain calculated by using the triaxial strain is 100 με or less, preferably 50 με or less, and more preferably 10 με or less.

Here, the strain is defined as the strain gauge displacement length / strain gauge length. The actually measured displacement length is very small, so the dependent variable is expressed in units of μ ε, 1 μ ε = 1 × 10 ^-6 ε. This time, the strain gauge used for the measurement of the strain amount has a gauge length of 5 mm and a strain of 1000 με when the displacement length is 5 μm. Further, the displacement length at the time of strain gauge elongation (stretching) is expressed as positive, and the displacement length at the time of shortening (compression) of the strain gauge is expressed as negative. The strain coefficient used in the strain gauge for measuring the strain amount was 5 × 10 ^-6 / ° C, and a strain gauge close to the coefficient of linear expansion of 3.3 3.33 × 10 ^-6 / ° C was used.

In addition, the maximum principal strain of the case where a three-axis strain gauge is used is calculated by the following formula. Here, ε _max is the maximum principal strain, and the strains of the two orthogonal strain gauges are ε ₁ and ε ₂ , and the strain of the strain gauges in the direction of 45 degrees by the two strains is ε ₃ .

Thus, in the present embodiment, the maximum principal strain of the polycrystalline germanium ingot 1 is evaluated by the cutting method.

Next, a method of manufacturing the polycrystalline germanium ingot of this embodiment will be described with reference to Figs. 4 and 5 .

The polycrystalline germanium ingot 1, as shown in FIG. 4, is produced by a casting step S21, a crucible heat treatment step S22, and a reheat treatment step S23. Here, the maximum main strain amount of the polycrystalline silicon ingot 1 is determined mainly by the heat treatment conditions of the inner heat treatment step S22 and the reheat treatment step S23.

Here, in the present embodiment, the test piece is first tried by a certain heat treatment condition (try step S11). In the test step S11, the test piece is cast using the casting apparatus 10 shown in Fig. 5, and the inner heat treatment and the reheat treatment are performed.

Next, for the test ingot, the maximum main strain variable (maximum main strain variable evaluation step S12) is evaluated by the above-described cutting method. The maximum main strain of the test ingot is not more than a specific value, that is, when the main strain is not 100 με or less, preferably 50 με or less, and more preferably 10 με or less, the heat treatment conditions of the internal heat treatment and the reheat treatment are changed. Try again for the test. By repeating this step, the maximum main strain of the test ingot is below the specific duty, that is, the main strain is 100 με or less, preferably 50 με or less, and more preferably 10 με or less, and heat treatment conditions are set (heat treatment condition setting) Step S13).

In this manner, after the heat treatment conditions for the heat treatment and the reheat treatment in the crucible are set, the production of the polycrystalline ingot 1 is performed.

First, an ingot is manufactured using the casting apparatus 10 shown in FIG.

The casting apparatus 10 includes a vacuum chamber 11 that maintains an airtight state inside, a crucible 20 that stores the crucible 3, an inclined plate 31 on which the crucible 20 is placed, and a lower heater 33 located below the inclined plate 31. The upper heater 43 above the 20, the lid portion 50 placed on the upper end of the crucible 20, and the gas supply tube 42 for introducing an inert gas (Ar gas) into the space between the crucible 20 and the lid portion 50.

Further, a heat insulating wall 12 is disposed on the outer peripheral side of the crucible 20, a heat insulating top plate 13 is disposed above the upper heater 43, and a heat insulating floor 14 is disposed below the lower heater 33. That is, the heat insulating material (the heat insulating wall 12, the heat insulating top plate 13, and the heat insulating floor 14) is disposed so as to surround the crucible 20, the upper heater 43, the lower heater 33, and the like. Further, a vent hole 15 is provided in the heat insulating floor 14.

The upper heater 43 and the lower heater 33 are connected to the electrode rods 44 and 34, respectively.

The electrode rod 44 connected to the upper heater 43 penetrates and is inserted into the heat insulating top plate 13. The electrode rod 34 connected to the lower heater 33 penetrates and is inserted into the heat insulating floor 14.

The inclined plate 31 on which the crucible 20 is placed is provided at the upper end of the support portion 32 that is inserted into the lower heater 33. The inclined plate 31 has a hollow structure and is configured to supply argon gas to the inside through a supply path (not shown) provided inside the support portion 32.

坩埚20, the horizontal cross-sectional shape is an angular shape (rectangular shape), and in the present embodiment, the horizontal cross-sectional shape is a square shape. The crucible 20 is made of quartz, and has a bottom surface 21 that is in contact with the bottom surface 21 of the inclined plate 31, and a side wall portion 22 that is raised upward from the bottom surface 21 thereof. The side wall portion 22 has a rectangular cross section in a horizontal cross section.

In the casting step S21, using the casting apparatus 10 described above, a crucible ingot is produced in the following steps.

First, the crucible material is placed in the crucible 20. Here, as the niobium raw material, a bulk material called "chunk" obtained by disintegrating 11N (purity of 99.999999999%) of high purity niobium was used. The particle size of the bulky raw material is, for example, 30 mm to 100 mm. Or it is a 6N raw material loaded with solar cell grade. Further, it is also possible to mix high-purity bismuth and solar cell grade cesium in a certain ratio.

Next, the crucible raw material charged in the crucible 20 is heated by being supplied to the upper heater 43 and the lower heater 33 to generate the crucible liquid 3. At this time, the liquid level of the mash liquid 3 in the crucible 20 is set to be lower than the upper end of the side wall portion 22 of the crucible 20.

Next, the mash 3 in the crucible 20 is solidified. First, the lower heater 33 is stopped from being energized, and argon gas is supplied to the inside of the inclined plate 31 through the supply path. Thereby, the bottom of the crucible 20 is cooled. At this time, by continuing the energization of the upper heater 43, a temperature gradient from the bottom surface 21 upward is generated in the crucible 20, and by this temperature gradient, the crucible 3 is solidified in one direction upward. Further, by gradually reducing the energization to the upper heater 43, the molten metal 3 in the crucible 20 is solidified upward, by means of a single The bismuth ingot is produced by the direction solidification method.

Next, a crucible heat treatment step S22 is carried out. In the inner heat treatment step S22, the upper heater 43 and the lower heater 33 are energized in a state in which the tantalum ingot obtained as described above is stored in the crucible 20, and the crucible is heated again. As described above, since the solidification is performed in a single direction from the bottom surface 21 upward, the temperature of the lower portion of the crucible ingot is low and the temperature of the upper portion is high at the time of completion of solidification. Here, by setting the output of the lower heater 33 to be high, the homogenization of the crucible ingot is performed, and furnace cooling is performed. In the inner heat treatment step S22, the heating temperature, the holding time, and the cooling rate at the time of furnace cooling are set by the heat treatment condition setting step S13.

Thereafter, the crucible ingot is taken out from the crucible 20, placed in a heat treatment furnace, and a reheating step S23 is performed.

In the heat treatment step S23, the heating rate, the heating temperature, the holding time, and the cooling rate during reheating are set by the heat treatment condition setting step S13.

In this manner, the polycrystalline germanium ingot 1 of the present embodiment was produced.

According to the polycrystalline silicon ingot 1 of the present embodiment configured as described above, the maximum main strain is 100 με or less, preferably 50 με or less, and more preferably 10 με or less. Therefore, even when the cutting process is performed, cracking or cracking can be suppressed. The occurrence of fragmentation. That is, the maximum main strain of the polycrystalline germanium ingot 1 is evaluated, so that the occurrence of defects caused by subsequent processing can be suppressed.

Further, in the present embodiment, the maximum principal strain is measured by the cutting method using a three-axis strain gauge, so that the polycrystal can be evaluated with high precision. The maximum main dependent variable of bismuth ingot 1.

Further, according to the method for producing a polycrystalline silicon ingot according to the present embodiment, the maximum main strain of the test spindle previously produced by the test step S11 is evaluated by measurement, and the maximum main strain should be set to a specific value or less. The heat treatment conditions of the heat treatment step S22 and the reheat treatment step S23. Therefore, as described above, it is possible to manufacture a polycrystalline germanium ingot in which the maximum principal strain is specified to be a specific value or less.

Although the method for producing the polycrystalline germanium ingot or the polycrystalline germanium ingot of the present embodiment has been described above, the design may be appropriately changed without being limited thereto.

For example, the polycrystalline germanium ingot is described as a square column, but it is not limited thereto, and may be cylindrical.

[Examples]

The results of the confirmation experiment performed to confirm the effects of the present invention are shown. An ingot was produced by using the casting apparatus described in the present embodiment, and the inside of the crucible heat treatment and the reheat treatment were changed to produce a polycrystalline ingot. Further, a polycrystalline germanium ingot was produced only by heat treatment in the crucible. Further, the polycrystalline iridium ingot was in the shape of a square of 670 mm wide and 250 mm in height, and casting was carried out in the following manner.

A crucible containing 260 kg of a high-purity niobium raw material was placed in a casting furnace, and the atmosphere was replaced with argon gas, and then melted, solidified, and cooled in an argon atmosphere. The melting system set the upper heater to 1500 ° C and the lower heater to 1450 ° C to melt the raw material. Thereafter, in order to perform solidification in one direction, cut off The lower heater supplies argon gas to the inclined plate of the hollow structure, and the temperature of the upper heater is lowered at a rate of 0.1 to 0.001 ° C / min. After the solidification is completed, the crucible ingots are cooled under the specific conditions described below.

The heat treatment in the crucible is carried out under the conditions of (1) to (3). (1) After the cooling starts, the heater is energized again, so that the upper and lower heaters are kept at a specific temperature in the range of 1350 ° C to 850 ° C for 1 hour to 5 hours, after which the furnace is cooled and taken out from the furnace at a specific temperature. . (2) After solidification, the heater is again energized, and the upper and lower heaters are gradually cooled from 1400 ° C to 500 ° C at a rate of 5 to 50 ° C / hr, and then taken out from the furnace when the furnace is cooled to a specific temperature. (3) After the solidification is completed, the furnace is directly cooled and taken out from the furnace at a specific temperature.

The heat treatment is carried out under the conditions of (4) and (5). (4) The temperature is maintained at a specific temperature in the range of 1300 ° C to 900 ° C for 1 hour to 10 hours, after which the furnace is cooled and taken out from the furnace at a specific temperature. (5) The temperature is raised to a specific temperature of 1300 ° C to 900 ° C, and the temperature is increased by a temperature of 100 ° C to 300 ° C lower than the temperature to reduce the temperature rise by 1 to 3 hours, which is repeated 2 to 10 times. The furnace is then cooled and taken out of the furnace at a specific temperature.

The heat treatment is taken out from the furnace to reduce the diffusion of impurities into the solid phase of the ingot. Further, by removing the outer periphery of the ingot having a high impurity concentration after being taken out from the furnace and performing reheat treatment, the diffusion of the impurities concentrated on the outer peripheral portion of the ingot can be further reduced, and high-purity columnar crystal ruthenium can be produced. Furthermore, once the heat treatment is performed in the same furnace after cooling, the occupation time of the furnace will become very long, and the working rate of the furnace will decrease. low.

The temperature of the heater is carried out by a Mo-sheathed thermocouple (Pt-PtRh) placed near the heater, and the temperature of the ingot is respectively 3 sheathed thermocouples (Pt-PtRh) placed near the crucible (upper part The measurement was performed in the middle, the lower part, and the average of the three measured values was the temperature of the ingot.

In Example 1, 260 kg of a crucible raw material was placed in a crucible, and the atmosphere was replaced with argon gas, and then melted, solidified, and cooled in an argon atmosphere. The melting conditions are 1500 ° C for the upper heater and 1450 ° C for the lower heater. After melting, argon gas is supplied to the inside of the inclined plate of the hollow structure for solidification in one direction, and the lower heater is cut off so that the temperature of the upper heater is 0.01 ° C. The speed of /min drops. The solidification was completed when the upper heater temperature was 1410 °C. After the solidification was completed, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 1,100 ° C for 2 hours, after which the furnace was cooled and taken out from the furnace at 200 ° C. The heat treatment was carried out at a rate of 100 ° C / hour to 1200 ° C, and after 2 hours, the furnace was cooled and taken out from the furnace at 300 ° C. At this time, the ingot did not break.

In the second embodiment, the same conditions as in the first embodiment were obtained from the melting to the solidification. After the solidification was completed, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 1000 ° C for 2 hours, after which the furnace was cooled and taken out from the furnace at 100 ° C. The heat treatment was carried out at a rate of 100 ° C / hour to 1,100 ° C, and after 2 hours, the furnace was cooled and taken out from the furnace at 200 ° C. At this time, the ingot did not break.

In the third embodiment, the same conditions as in the first embodiment were obtained from the melting to the solidification. Next, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 900 ° C for 2 hours, after which the furnace was cooled and taken out from the furnace at 80 ° C. The heat treatment was carried out at a rate of 100 ° C / hour to 1000 ° C. After 2 hours, the furnace was cooled and taken out from the furnace at 150 ° C. At this time, the ingot did not break.

In the fourth embodiment, the same conditions as in the first embodiment were obtained from the melting to the solidification. Next, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 900 ° C for 2 hours, after which the furnace was cooled and taken out from the furnace at 80 ° C. The heat treatment was carried out at a rate of 100 ° C / hour to 950 ° C, and after 1 hour, the furnace was cooled and taken out from the furnace at 80 ° C. At this time, the ingot did not break.

In the fifth embodiment, the same conditions as in the fourth embodiment were carried out from the melting to the reheat treatment. After the heat treatment, it was taken out from the furnace at 100 °C. At this time, the ingot did not break.

In Example 6, 260 kg of a crucible raw material was placed in a crucible, and the atmosphere was replaced with argon gas, and then melted, solidified, and cooled in an argon atmosphere. The melting conditions are 1500 ° C for the upper heater and 1450 ° C for the lower heater. After melting, argon gas is supplied to the inside of the inclined plate of the hollow structure for solidification in one direction, and the lower heater is cut off so that the temperature of the upper heater is 0.01 ° C. The speed of /min drops. The solidification was completed when the upper heater temperature was 1410 °C. After the solidification was completed, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 1000 ° C for 2 hours, after which the furnace was cooled and taken out from the furnace at 100 ° C. The heat treatment was carried out at a rate of 100 ° C / hour to 1,100 ° C, and after 2 hours, the furnace was cooled and taken out from the furnace at 100 ° C. The ingot did not break.

In Comparative Example 1, the same conditions as in Example 1 were carried out until the solidification was completed. After the solidification is finished, cut off the upper heater and directly cool the furnace. It was taken out from the furnace at 80 °C. The heat treatment was carried out at a rate of 100 ° C / hour to 900 ° C, and after 2 hours, the furnace was cooled and taken out from the furnace at 80 ° C. At this time, the ingot did not break.

In Comparative Example 2, the same conditions as in Comparative Example 1 were carried out from the melting to the reheat treatment. After the heat treatment, it was taken out from the furnace at 100 °C. At this point, the ingot broke.

In Comparative Example 3, the same conditions as in Example 2 were carried out from the melting to the reheat treatment. After the heat treatment, it was taken out from the furnace at 250 °C. At this point, the ingot broke.

In Comparative Example 4, the same conditions as in Example 6 were carried out from the melting to the reheat treatment. After the heat treatment, it was taken out from the furnace at 300 °C. The heat treatment was carried out at a rate of 100 ° C / hour to 1,100 ° C, and after 2 hours, the furnace was cooled and taken out from the furnace at 300 ° C. At this point, the ingot broke.

In Comparative Example 5, the same conditions as in Example 6 were carried out until the solidification was completed. Next, the upper heater and the lower heater were controlled so that the temperature of the ingot was maintained at 1,150 ° C for 3 hours, after which the furnace was cooled and taken out from the furnace at 200 ° C. At this point, the ingot broke.

In Comparative Example 6, the same conditions as in Example 6 were carried out until melting to solidification. After the solidification was completed, the upper heater was cut off, the furnace was directly cooled, and it was taken out from the furnace at 200 °C. At this point, the ingot broke.

The maximum principal strain is evaluated by the cutting method shown in this embodiment. The measurement position is 5 to 9 column positions as shown in FIG. In Fig. 3, a = 150 mm, b1 = 150 mm, b2 = 110 mm, c = 100 mm, d = e = g = 25 mm, f = 55 mm, h = 35 mm, i = 150 mm, j = 150 mm. B1 display The distance between AB, b2 shows the distance between BC.

Further, as described above, in Comparative Examples 2 to 6, the ingot was broken at the time of taking out from the furnace, and therefore the maximum main strain amount was measured in the region on the side where the crack did not occur. When the rupture is large, prepare other ingots.

The evaluation results are shown in Tables 1 to 6.

Table 1 shows the maximum main strain of each of the measurement points of the bismuth ingots produced under the conditions of Example 1 and Example 2 after cutting 1, 2, and 3.

Table 2 shows the maximum main strain of each of the measurement points of the bismuth ingots produced under the conditions of Example 3 and Example 4 after cutting 1, 2, and 3.

Table 3 shows the maximum main strain of each of the measurement points of the bismuth ingots produced under the conditions of Example 5 and Example 6 after cutting 1, 2, and 3.

Table 4 shows the maximum main strain of each of the measurement points of the bismuth ingot prepared under the conditions of Comparative Example 1 and Comparative Example 2 after cutting 1, 2, and 3.

Table 5 shows the maximum main strain of each of the measurement points of the tantalum ingots produced under the conditions of Comparative Example 3 and Comparative Example 4 after cutting 1, 2, and 3.

Table 6 shows the maximum main strain of each of the measurement points of the bismuth ingots produced under the conditions of Comparative Example 5 and Comparative Example 6 after cutting 1, 2, and 3.

In Examples 1 to 6, no crack occurred when the furnace was taken out, and the measured maximum main strain was confirmed to be 100 με or less. In particular, in Examples 2 and 6 in which the maximum main strain was 50 με or less, no crack occurred even when it was taken out from the furnace at 200 ° C. Further, in Example 1 in which the maximum main strain was 10 με or less, no crack occurred even when it was taken out from the furnace at 300 ° C.

On the other hand, in Comparative Examples 2 to 6, cracking occurred when taken out from the furnace. In Comparative Example 1, which was taken out from the furnace at 80 ° C without cracking, the maximum main strain amount exceeded 100 με.

From the above results, it is possible to set conditions for obtaining a polycrystalline germanium ingot having no crack and having a maximum main strain of 100 με or less. However, since this condition is a condition peculiar to the furnace used in the present embodiment, when another furnace is used, it is necessary to separately perform measurement and set the conditions again.

Claims (4)

A polycrystalline bismuth ingot consisting of a unidirectional solidified structure characterized by no cracking and a maximum main strain of less than 100 με. For example, the polycrystalline germanium ingot of claim 1 wherein the maximum main strain is below 50 με. For example, the polycrystalline germanium ingot of claim 2, wherein the maximum main strain is below 10 με. A method for producing a polycrystalline bismuth ingot according to any one of claims 1 to 3, which is characterized in that the method for producing an ingot by solidification in a single direction in a crucible, after solidification a step of heat treatment in the crucible in which the ingot is heat-treated, and a reheating step in which the ingot is taken out from the crucible and then subjected to heat treatment; and the maximum main strain of the pre-manufactured polycrystalline ingot is measured, whereby the maximum main strain becomes a specific value In the following manner, the heat treatment conditions of the above-described crucible heat treatment step and the above-described reheat treatment step are set.