Thermal Conductivity Measurement Method

Abstract

To provide a thermal conductivity measurement method for a molten body, capable of obtaining a high-accurate measurement result in a short time while preventing deterioration or the like of a sensor.SOLUTION: A heating device includes a chamber, a crucible arranged in the chamber and storing a molten body as a target material, a thermocouple whose one end is inserted into the molten body, a hot disc sensor that measures thermal conductivity of the molten body, and a heating mechanism that heats the crucible and the hot disc sensor. A method for measuring the thermal conductivity of the molten body in the heating device by using a hot disc approach, includes the steps of: filling the chamber with an inert gas; holding a hot disc sensor to heat it to a temperature close to a temperature of the molten body; and immersing the hot disc sensor into the molten body to measure thermal conductivity of the molten body.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for measuring the thermal conductivity of a melt, and more particularly to a method for measuring the thermal conductivity of a high-temperature melt using a hot disk method. [Background technology]

[0002] In casting CAE such as melt flow, heat transfer, and solidification analysis in the casting process of Al alloys, highly accurate physical properties of the molten state, such as thermal conductivity, are required. In addition, it is important to control heat transfer in refining metal materials and producing semiconductor single crystals, and for this reason, the thermal conductivity of the melt is required. For the above reasons, it is necessary to accurately measure the thermal conductivity. Methods for measuring the thermal conductivity of such melts include the steady-state plate method, the unsteady laser flash method, the unsteady thin-wire heating method, and the hot disk method. In particular, with regard to the measurement of the thermal conductivity of melts, there are problems such as corrosion due to the high reactivity of the melt and deviations in measured values ​​due to the influence of thermal convection, and ideas to deal with these problems are being considered. In the hot disk method, a hot disk sensor (see Patent Document 1) that can be used to measure melts has been reported, and it is possible to measure the thermal conductivity of the melt in a range that is not affected by thermal convection by measuring in a short time.

[0003] In the conventional hot disk method, for example, a hot disk sensor is inserted into a crucible placed in a chamber together with a solid target material, and the target material is heated and melted, and the thermal conductivity of the target material that has become a high-temperature melt is measured (see Patent Document 1).In addition, in the unsteady thin wire heating method, the target material is heated and melted, and then the sensor is immersed in the melt to measure the thermal conductivity (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-242734 A [Patent Document 2] JP 2000-310605 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the hot disk sensor described in Patent Document 1, the gap between the metal foil and the insulating thin plate is filled with inorganic fine powder to suppress the intrusion of the melt, but it is not possible to completely prevent the intrusion of gases such as oxygen that oxidize the metal foil. Therefore, if oxygen remains in the atmospheric gas, the metal foil of the hot disk sensor will oxidize and the sensor will deteriorate. In general, the higher the temperature, the more intense the oxidation of metals, and the higher the oxygen partial pressure, the more likely it is to occur. Therefore, in order to suppress the deterioration of the hot disk sensor, it is effective to shorten the time to hold at high temperatures or to actively remove oxygen in the system. In addition, when the target material is solid, the sensor is exposed to high temperatures for a long time until it is completely melted, which is not preferable, and when the shape of the target material is irregular, air bubbles often remain between the sensor and the sensor when it is melted, and the presence of air bubbles causes a large error in the measurement of thermal conductivity. Furthermore, in the case of a metal that is easily oxidized, an oxidized layer of the melt may be interposed between the sensor and the melt, which causes problems such as a decrease in measurement accuracy.

[0006] On the other hand, in the method of immersing a sensor in a melt after heating and melting a target material as in Patent Document 2, if the sensor is immersed in the melt when the temperature of the sensor is low, the surface of the melt may solidify and damage the sensor or adversely affect the temperature-sensing part of the sensor, such as by damaging it. In addition, after the sensor is immersed in the melt, it takes time for the temperature of the sensor to reach the same temperature as the melt to be measured, and during this time the sensor may deteriorate.

[0007] SUMMARY OF THE PRESENT DISCLOSURE ... An object of the present invention is to provide a method for measuring the thermal conductivity of a molten material, which is capable of obtaining highly accurate measurement results in a short period of time while preventing deterioration of the sensor. [Means for solving the problem]

[0008] One aspect of the present invention is a method for measuring the thermal conductivity of a melt in a heating device using a hot disk method, comprising the steps of: The heating device is A chamber; A crucible is disposed in the chamber and contains a melt of the target material; a thermocouple having one end inserted into the melt; a hot disk sensor for measuring the thermal conductivity of the melt; a heating mechanism for heating the crucible and the hot disk sensor; This measurement method is filling a chamber with an inert gas; holding the hot disk sensor and heating it to a temperature close to the temperature of the melt; and measuring the thermal conductivity of the melt by immersing the hot disk sensor in the melt.

[0009] Another aspect of the present invention is a method for manufacturing a semiconductor device that satisfies the following conditions (1) to (3): where the temperature detected by the hot disk sensor (hereinafter referred to as the "sensor temperature") is T1 (°C) and the temperature detected by the thermocouple (hereinafter referred to as the "thermocouple temperature") is T2 (°C): (1) T1 and T2 are equal to or higher than the melting point of the melt. (2)ΔT=|(T1×W1+T2×W2) / (W1+W2)-T0|<20℃, Where, T0 is the target temperature, W1 is the weight of the hot disk sensor (g), W2 is the weight of the melt (g), (3) |T1-T2|<20℃, This is a measurement method in which a hot disk sensor is immersed in the molten material when the above condition is met.

[0010] Another aspect of the invention is a method of measurement in which a reducing gas is further added to the chamber. Effect of the Invention

[0011] By using the measurement method according to the present invention, it becomes possible to measure the thermal conductivity of a melt accurately and in a short time using the hot disk method. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic cross-sectional view of a heating device used in the thermal conductivity measuring method according to the present invention. [Diagram 2] FIG. 2 is an exploded perspective view of a hot disk sensor used in the thermal conductivity measuring method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] FIG. 1 is a schematic cross-sectional view of a heating device, generally designated 100, used in the thermal conductivity measurement method according to the present invention. The heating device 100 includes a chamber 3. The chamber 3 is provided with a gas inlet 8 and a gas outlet 9. The gas inlet 8 and the gas outlet 9 are each provided with a valve. The chamber 3 is provided with a lid (not shown), which is sealed when the lid is closed. Furthermore, by using a single chamber 3, operability when immersing the sensor 2 in the melt 1 is improved, and temperature variation within the chamber 3 can be reduced.

[0014] An alumina crucible 5, for example, is placed in the chamber 3, and a melt 1 of the target material is held in the crucible 5. A thermocouple 4 for measuring temperature is inserted into the melt 1. Also, a sensor holding device 6 with a hot disk sensor 2 fixed to its tip is provided from the top to the bottom of the chamber 3. The sensor holding device 6 is made of, for example, a rod, and can change the position of the sensor 2 by moving up and down and left and right, and by rotating.

[0015] A heating mechanism 7 such as an electric furnace is provided around the chamber 3 so as to surround the chamber 3. The heating mechanism 7 is arranged to heat the hot disk sensor 2 and the crucible 5 before immersion. By heating the crucible 5 with the heating mechanism 7, the target material is melted in the crucible 5 to form the melt 1. Depending on the target material, it may be heated directly by the heating mechanism 7.

[0016] 2 is an exploded perspective view of a hot disk sensor 2, and for example, a sensor described in Patent Document 1 is used. The sensor 2 has a metal foil 21. The metal foil 21 has a spiral portion 21a in which a thin wire is wound in a double spiral shape, and electrode portions 21b connected to both ends of the spiral portion 21a. The metal foil 21 is made of a high-melting point metal such as molybdenum, tantalum, tungsten, niobium, platinum, ruthenium, rhodium, palladium, iridium, etc., or an alloy of these metals (for example, platinum-rhodium, tungsten-rhenium, etc.).

[0017] The metal foil 21 is sandwiched between thick insulating plates 25 from above and below. The thick insulating plates 25 are provided with a circular opening 27. Furthermore, a thin insulating plate 23 is sandwiched between the thick insulating plates 25 and the metal foil 21.

[0018] 2, the sensor 2 has a structure in which the spiral portion 21a of the metal foil 21 is disposed in the opening 27, and is covered above and below with the thin insulating plate 23. The thin insulating plate 23 and the thick insulating plate 25 are made of a material such as aluminum nitride, aluminum oxide, silicon nitride, magnesium oxide, zirconium oxide, boron nitride, or quartz glass. The metal foil 21, the thin insulating plate 23, and the thick insulating plate 25 are bonded together using an inorganic adhesive or inorganic fine powder such as boron nitride, and are further fixed in place with fixing screws or the like (not shown).

[0019] The sensor 2 in Fig. 2 is connected to a measuring device (not shown). The measuring device includes a source meter for supplying current to the sensor 2 and measuring the resistance of the sensor 2, and a computer (neither shown) for controlling the source meter and acquiring and analyzing data. For example, a "Hot Disk Method Thermal Property Measuring Device TPS3500" manufactured by Kyoto Electronics Manufacturing Co., Ltd. is used as the measuring device.

[0020] The resistance value is measured by passing a constant current between the electrode parts 21b of the metal foil 21 of the sensor 2 from the measuring device. There is a one-to-one relationship between the resistance value and temperature of the metal foil used in the sensor 2, and by measuring the relationship between the temperature and resistance value of the sensor 2 in advance, the temperature T1 of the sensor 2 can be calculated from the measurement result of the resistance value.

[0021] Next, a method for measuring the thermal conductivity of a molten material using the hot disk method according to the present invention will be described with reference to FIGS.

[0022] 1, a lid (not shown) of the chamber 3 is opened and a target material is inserted into the crucible 5. The target material is a high-melting-point material, such as a metal material such as iron or aluminum, or a semiconductor material such as silicon, and is usually solid at room temperature.

[0023] The tip of the thermocouple 4 is inserted into the solid target material, while the sensor 2 is held above the crucible 5. In this state, the lid of the chamber 3 is closed, and the inside of the chamber 3 is sealed.

[0024] Next, an inert gas is introduced from the gas inlet 8 while being exhausted from the gas outlet 9, thereby filling the atmosphere 10 in the chamber 3 with the inert gas. For example, argon gas, nitrogen gas, etc. are used as the inert gas. This reduces the oxygen in the chamber 3, making it possible to prevent oxidation of the melt 1 and the metal foil 21 of the sensor 2.

[0025] It is more preferable that the atmosphere 10 is an inert gas plus a reducing gas. For example, hydrogen, carbon monoxide, or a hydrocarbon is used as the reducing gas. There is no particular restriction on the ratio of the reducing gas as long as it is within a range that does not interfere with the measurement of thermal conductivity. By adding a reducing gas preferably in the range of 1 to 10%, the oxygen remaining in the system is consumed and the oxygen partial pressure is further reduced, thereby improving the antioxidant effect.

[0026] In this state, the crucible 5 is heated using the heating mechanism 7, and the target material in the crucible 5 is melted to form the melt 1. The thermocouple 4 is immersed in the melt 1 and indicates the thermocouple temperature T2. Meanwhile, the position of the sensor 2 is adjusted by the sensor holding device 6, and it is placed above the liquid surface without contacting the melt 1, and indicates the sensor temperature T1. The melt 1 and the sensor 2 are placed in close temperature ranges and heated to a temperature close to that of the melt.

[0027] In the present invention, the timing for immersing the sensor 2 in the melt 1 is determined to be the timing when the sensor temperature T1 and the thermocouple temperature T2 satisfy the following conditions (1) to (3).

[0028] (1) T1 and T2 are equal to or higher than the melting point of melt 1 (2) If the target temperature of sensor 2 is T0 (℃), the weight of sensor 2 is W1 (g), and the weight of melt 1 is W2 (g), ΔT=|(T1×W1+T2×W2) / (W1+W2)-T0|<20℃ (3)|T1-T2|<20℃

[0029] At a timing when conditions (1) to (3) are satisfied, the sensor 2 is immersed in the melt 1 by the sensor holding device 6, and the thermal conductivity of the melt 1 is measured. The thermal conductivity can be obtained from the change in the sensor temperature. After the thermal conductivity of the melt 1 is measured, the sensor 2 is pulled out of the melt 1 by the sensor holding device 6, and the measurement of the thermal conductivity of the melt 1 is completed.

[0030] In this way, in the method of the present invention, by holding the sensor 2 in a non-contact state with the melt 1 before measurement, the temperatures of the melt 1 and the sensor 2 become close to each other, and when the sensor 2 is immersed in the melt 1, the sensor 2, which has a lower temperature than the melt 1, comes into contact with the melt 1, thereby preventing solidification of the contact surface.

[0031] In addition, in the case where the target material is a material that originally has an oxide film, such as aluminum, when heating in a state where the sensor 2 is inserted into the solid target material as in the prior art, an oxide layer of the target material is sandwiched between the sensor 2 and the melt 1 during the heating process and fixed, and accurate thermal conductivity measurement may not be possible. Further, when the shape of the solid target material is irregular, bubbles may remain between the sensor and the melt during melting, and the presence of the bubbles causes a large error in the measurement of the thermal conductivity. On the other hand, in the method of the present invention, since the sensor 2 is immersed in the melt 1 after the target material becomes the melt 1, the oxide layer sandwiching and bubbles can be actively removed by moving the sensor 2 vertically, horizontally, or rotating it with the sensor holding device 6, and the thermal conductivity of the melt 1 can be accurately measured.

[0032] In addition, since it is not necessary to previously place the sensor 2 in the crucible 5, a sufficient margin is secured for the crucible volume, so that even if the shape of the solid target material is irregular, an amount that can be accommodated in the crucible 5 can be secured.

[0033] Furthermore, by setting the timing of immersing the sensor 2 in the melt 1 to the timing that satisfies the conditions (1) to (3), the timing of immersing the sensor 2 in the melt 1, that is, the timing of starting the measurement, can be known from the temperatures of T1 and T2, and it is not necessary to wait unnecessarily long for the temperatures of T1 and T2 to approach each other. Deterioration of the sensor can be suppressed and efficient thermal conductivity measurement becomes possible.

[0034] As in the condition (1), since both the sensor temperature T1 and the thermocouple temperature T2 are equal to or higher than the temperature (melting point) at which the target material becomes the melt, solidification at the contact surface with the melt 1 during immersion of the sensor 2 can be prevented.

[0035] Also, according to the condition (2), it becomes easy to bring both the sensor temperature T1 and the thermocouple temperature T2 close to the measurement target temperature T0, and the time from when the sensor 2 is immersed until the temperature stabilizes and measurement can be shortened. Here, the heat capacities of the sensor 2 and the melt 1 are approximated by weights W1 and W2, and adjustment in a range that satisfies 10W1 < W2 is preferable.

[0036] Moreover, condition (3) can shorten the time it takes for the sensor temperature T1 to reach the equilibrium temperature. In order to suppress deterioration of the sensor 2, it is preferable that the sensor temperature T1 is lower than the thermocouple temperature T2, and it is preferable to adjust the sensor temperature T1 within a range that satisfies T2-T1<20°C.

[0037] Furthermore, by filling the atmosphere 10 inside the chamber 3 with an inert gas, it is possible to prevent oxidation of the metal parts (e.g., the metal foil 21) of the sensor 2 that is maintained at a high temperature. Furthermore, by adding a reducing gas to the inert gas, the oxygen remaining in the chamber 3 reacts with the reducing gas, thereby reducing the oxygen partial pressure, and the oxidation prevention effect of the metal parts (e.g., the metal foil 21) of the sensor 2 is improved. EXAMPLES

[0038] Table 1 shows the measurement conditions and results when the measurement was performed using the measurement method of the present invention (Examples 1 and 2) and when the measurement was performed using a method different from the present invention (Comparative Example 1). Note that the present invention is not limited to these Examples.

[0039] The target material is aluminum (melting point: 660°C), the assumed temperature (measurement target temperature) T0 of the melt 1 is 700°C, the weight W1 of the sensor 2 is 10g, and the weight W2 of the melt 1 is 200g, all of which are common to all of the above. In the sensor 2, the metal foil 21 is made of molybdenum, and the insulating thin plate 23 and the insulating thick plate 25 are made of aluminum nitride. In the comparative example 1 and the example 1, the atmosphere 10 is argon gas, and in the example 2, hydrogen gas (3 vol%) is added to the argon gas. In the examples 1 and 2 and the comparative example 1, the sensor 2 is immersed in the melt 1 after being held in a non-contact state with the melt 1, but in the examples 1 and 2, the sensor 2 is immersed in the melt 1 when the above-mentioned conditions (1) to (3) are satisfied, whereas in the comparative example 1, the sensor 2 is immersed in the melt 1 in a state where the conditions (1) and (2) are satisfied but the condition (3) has not been reached. The thermal conductivity of melt 1 was measured once the temperature of sensor 2 had reached equilibrium.

[0040] [Table 1]

[0041] As can be seen from the results in Table 1, in all of Examples 1 and 2 and Comparative Example 1, when the sensor 2 was immersed in the melt 1, solidification of the melt 1 did not occur on the surface of the sensor 2, and no oxide layer or air bubbles were trapped between the sensor 2 and the melt 1, allowing accurate thermal conductivity measurement.

[0042] On the other hand, the time required to start measurement after the sensor temperature T1 is raised by immersing the sensor 2 in the melt 1, i.e., the time until the sensor temperature T1 reaches an equilibrium state, was 10 minutes in Examples 1 and 2, whereas it was 60 minutes in Comparative Example 1. In other words, by immersing the sensor 2 in the melt 1 after satisfying the conditions (1) to (3), the time until the sensor temperature T1 reaches an equilibrium state, i.e., the measurement time, could be shortened. As can be seen from the measurement conditions, Comparative Example 1 and Examples 1 and 2 all satisfied the conditions (1) and (2) (however, ΔT was larger in Comparative Example 1 than in Examples 1 and 2), but Comparative Example 1 did not satisfy the condition (3), and only Examples 1 and 2 satisfied it.

[0043] The same sensor was used to measure the thermal conductivity three times with a 10-minute rest period. The time required from the start to the end of the measurement was about 45 minutes in Examples 1 and 2, but about 1 hour and 35 minutes in Comparative Example 1. The measured thermal conductivity values ​​were similar when repeated in Examples 1 and 2, but in Comparative Example 1, there was a deviation in the measured value when repeated. When the sensor was removed after the measurement, a metallic luster was observed on the surface of the metal foil of the sensor of Example 1, but a slight discoloration was observed and it was thought to be slightly oxidized. The surface of the metal foil of the sensor of Example 2 had a metallic luster and no signs of oxidation were observed. On the other hand, the surface of the metal foil of the sensor of Comparative Example 1 did not have a metallic luster, and it was thought that the surface oxidation was more advanced than in Example 1 based on the degree of discoloration. This is because the oxidation of sensor 2 progressed over time due to residual oxygen in the atmosphere 10, and it is thought that the oxidation of Comparative Example 1, which was held at high temperature for a longer time, progressed more than that of Example 1, and the deterioration of the sensor became more noticeable, resulting in a deviation in the measured value. This is because in Example 2 in which a reducing gas was added to the atmosphere 10, oxidation of the sensor 2 did not occur, and it is believed that further repeated use is possible.

[0044] As an overall evaluation, Examples 1 and 2 were good, with Example 1 being given a "◯" and Example 2 being given a "◎". On the other hand, Comparative Example 1 was given a "×" because the measurement time was long and repeated measurement was not possible.

[0045] In this way, in the examples according to the present invention, the time from immersion to measurement could be significantly shortened by determining the timing of immersing the sensor 2 in the melt 1 using conditions (1) to (3). In particular, by adding a reducing gas to the inert gas of the measurement atmosphere 10, the thermal conductivity measurement could be performed repeatedly. [Industrial Applicability]

[0046] The present invention provides a method for measuring the thermal conductivity of a molten material accurately and in a short time using a hot disk method, and can be applied to the refining of metal materials and the production of semiconductor single crystals. [Explanation of symbols]

[0047] 1 molten body 2 Sensors 3. Chamber 4 Thermocouples 5. Crucible 6 Sensor holding device 7 Heating mechanism 8 Gas inlet 9 Gas exhaust port 10. Atmosphere 21 Metal foil 23 Insulating Sheet 25 Insulating plate 27 Opening 100 Heating device

Claims

1. A method for measuring the thermal conductivity of a melt in a heating device using a hot disk method, comprising the steps of: The heating device is A chamber; A crucible is disposed in the chamber and contains a melt of the target material; a thermocouple having one end inserted into the melt; a hot disk sensor for measuring the thermal conductivity of the melt; a heating mechanism for heating the crucible and the hot disk sensor; This measurement method is filling a chamber with an inert gas; holding the hot disk sensor and heating it to a temperature close to the temperature of the melt; and measuring the thermal conductivity of the melt by immersing the hot disk sensor in the melt.

2. If the detection temperature of the hot disk sensor is T1 (°C) and the detection temperature of the thermocouple is T2 (°C), the following conditions (1) to (3) are satisfied: (1) T1 and T2 are equal to or higher than the melting point of the melt; (2) ΔT=|(T1×W1+T2×W2) / (W1+W2)−T0|<20℃, Where, T0 is the measurement target temperature (°C), W1 is the weight of the hot disk sensor (g), W2 is the weight of the melt (g), (3) |T1-T2|<20℃, 2. The method according to claim 1, further comprising the step of immersing the hot disk sensor in the molten liquid when the temperature is below 100° C. and the hot disk sensor is immersed in the molten liquid.

3. 3. The method according to claim 1, further comprising adding a reducing gas to the chamber.

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