JP2018168052A - Method of manufacturing silicon carbide single crystal ingot - Google Patents

Abstract

To provide a method capable of manufacturing an SiC single crystal ingot of high quality having small variance in electric resistivity over the ingot in a growth direction.SOLUTION: A method of manufacturing a silicon carbide single crystal ingot comprises: covering with a heat insulator a graphite-made crucible which has a seed crystal fitted to an inner side face of a crucible upper lid and a silicon carbide raw material charged in a crucible body, and then installing the crucible in quartz double pipes; heating the graphite-made crucible at a high frequency in an atmosphere in which an inert gas having nitrogen mixed is circulated as a doping gas; sublimating the silicon carbide raw material and thus recrystallizing the silicon carbide single crystal doped with the nitrogen on the seed crystal. The method of manufacturing the silicon carbide single crystal ingot further comprises: arranging a cylindrical member in a temperature measurement hole provided in the heat insulator covering the crucible upper lid; measuring an outer surface temperature of the crucible upper lid from the start to the end of crystal growth through the cylindrical member; and adjusting the amount of the doping gas mixed with the inert gas according to the outer surface temperature.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for manufacturing a silicon carbide single crystal ingot capable of manufacturing a high-quality silicon carbide single crystal ingot excellent in crystallinity with few defects and suitable as a substrate for manufacturing a semiconductor element.

  Silicon carbide (SiC) is attracting attention as an environmentally resistant semiconductor material because of its excellent heat resistance and mechanical strength, and physical and chemical properties such as resistance to radiation. SiC is a typical substance having a crystal polymorphic (polytype) structure having many different crystal structures even though the chemical composition is the same. Polytype means that when a unit of Si and C bonded molecules in the crystal structure is considered as a unit, the unit structure molecule is different in the periodic structure when stacked in the c-axis direction ([0001] direction) of the crystal. Arise. Typical polytypes include 6H, 4H, 15R or 3C. Here, the first number indicates the repetition period of the lamination, and the alphabet represents the crystal system (H is hexagonal, R is rhombohedral, and C is cubic). Each polytype has different physical and electrical characteristics, and application to various uses is considered using the difference. For example, 6H is recently used as a substrate wafer for short-wavelength optical devices from blue to ultraviolet, and 4H is considered to be used as a substrate wafer for high-frequency, high-voltage electronic devices.

  However, a crystal growth technique that can stably supply a high-quality SiC single crystal wafer having a large area on an industrial scale has not yet been established. Therefore, practical use of SiC has been hindered despite the semiconductor material having many advantages and possibilities as described above.

Conventionally, on a laboratory scale, for example, a SiC single crystal was grown by a sublimation recrystallization method (Rayleigh method) to obtain a SiC single crystal ingot (hereinafter referred to as an ingot) having a size capable of producing a semiconductor element. . However, with this method, the diameter of the obtained ingot is small, and it is difficult to control its size and shape with high accuracy. Also, it is not easy to control the crystal polymorphism and the additive element carrier concentration of SiC. Also, a cubic silicon carbide single crystal is grown by heteroepitaxial growth on a heterogeneous substrate such as silicon (Si) using a chemical vapor deposition method (CVD method). In this method, an ingot with a large diameter can be obtained, but only a SiC single crystal containing many defects (˜10 ⁷ cm ⁻² ) can be grown due to a lattice mismatch with the substrate of about 20%. It is not possible to manufacture high quality ingots.

  In order to solve these problems, an improved Rayleigh method has been proposed in which sublimation recrystallization is performed using a SiC single crystal {0001} substrate as a seed crystal (Non-patent Document 1). In this method, the seed nucleation process can be used to control the nucleation process of the crystal, and the atmosphere pressure is controlled to about 100 Pa to 15 kPa with an inert gas, so that the growth rate of the SiC single crystal can be reproduced with good reproducibility. I can control it. The principle of the improved Rayleigh method will be described with reference to FIG. The SiC single crystal and SiC raw material powder to be seed crystals are stored in a crucible (usually graphite) and heated to 2000 to 2400 ° C. in an inert gas atmosphere (133 Pa to 13.3 kPa) such as argon. At this time, the temperature gradient is set so that the seed crystal is slightly cooler than the SiC raw material powder. After sublimation, the SiC raw material is diffused and transported in the seed crystal direction by a concentration gradient (formed by a temperature gradient). By recrystallizing the SiC sublimation gas on the seed crystal, an SiC single crystal grows and an ingot can be manufactured. At present, SiC single crystal substrates having a diameter of 4 inches (100 mm) to 6 inches (150 mm) are cut out from ingots produced by the above-described improved Rayleigh method, and are used for growth of epitaxial thin films and device fabrication.

The electric resistivity of the ingot is determined by mixing an impurity gas in an atmosphere made of an inert gas, or mixing an impurity element or a compound thereof in an SiC raw material powder, thereby allowing silicon or carbon atoms in the SiC single crystal structure to be mixed. The position can be controlled by substituting with an additive element (doping). As a representative substitutional impurity element in a SiC single crystal, nitrogen (N) is used to obtain n-type as a carrier type, and boron (B) or aluminum (to obtain p-type conductivity). Al) is used. As a method for introducing these additive elements into the crystal, N is generally performed by adding nitrogen (N ₂ ) gas to an inert gas during growth.

Yu. M. Tairov and V.F.Tsvetkov, Journal of Crystal Growth, vol. 52 (1981) pp.146-150.

  In the crystal growth process of the sublimation recrystallization method using a seed crystal (hereinafter simply referred to as “sublimation recrystallization method”), temperature control (adjusted by varying the current value each time so that the temperature becomes the target value) ) Method to control crystal growth, because the graphite member such as a graphite crucible has a large heat capacity, the time constant until the change in the current value input by heating is reflected in the temperature change becomes large, and the temperature is kept constant. It will be difficult to keep. Therefore, in general, a method of changing the current value with respect to the temperature change is not used during crystal growth, and the crystal growth is performed by setting a current value pattern that makes the temperature constant.

  On the other hand, the electrical resistivity is controlled by adjusting the flow rate of the doping gas (dopant gas) mixed with the inert gas. Impurity gas mixed with the inert gas, for example, nitrogen is decomposed at the growth surface on the seed crystal and incorporated into the crystal as nitrogen atoms. At that time, when the growth surface temperature changes, the amount of nitrogen atoms incorporated changes, and the electrical resistivity in the ingot height direction varies accordingly. In order to reduce the variation in electrical resistivity in the ingot height direction, it is sufficient to keep the growth surface temperature constant during growth, but in the first place, the growth surface temperature in the graphite crucible cannot be directly measured. . Therefore, it is common to measure the outer surface temperature of the crucible upper lid with a radiation thermometer using a temperature measuring hole (heat removal hole) provided in a heat insulating material covering the outer surface of the upper lid of the graphite crucible. Although the outer surface temperature of the crucible lid is not the same as the crystal growth surface temperature of the seed crystal, the outer surface temperature of this crucible lid changes corresponding to the crystal growth surface temperature, so it can be used as a surface temperature monitor during crystal growth. can do.

  Since the surface temperature of the crucible top cover can be used as a monitor of the crystal growth surface temperature as described above, it is conceivable to adjust the current value so that the surface temperature of the crucible top cover is kept constant during crystal growth. In actual growth, the sublimation gas leaked from the graphite crucible adheres to the temperature measuring hole, so that the outer surface temperature of the crucible upper lid can be measured accurately only in the very first half of the crystal growth. Therefore, the temperature in the latter half of the crystal growth cannot be measured substantially. In particular, in the latter half of the growth, for example, the growth rate was measured by intermittently doping nitrogen during the crystal growth and marking the grown crystal. On the basis of this result, it is necessary to rely on an indirect method such as adjusting the current value so that the growth rate is comparable.

  However, especially in the latter half of the growth, both the heat insulating material made of graphite crucibles, carbon felt, etc. are also deteriorated due to thermal history, and it is estimated that temperature variations occur in actual growth even with the same current value setting, There has been a problem that variation in the electrical resistivity of each substrate in the growth direction in the obtained ingot, that is, the ingot height direction, becomes large. Therefore, these factors make it difficult to produce a high quality ingot with little variation in electrical resistivity throughout the ingot.

  Therefore, the present invention provides a method for solving the above-mentioned problems in the prior art and producing a high-quality SiC single crystal ingot with little variation in electrical resistivity over the entire growth direction of the ingot. Objective.

  As a result of intensive studies to solve the above problems, the present inventors measure the outer surface temperature of the crucible top cover through a cylindrical member disposed in a temperature measurement hole (heat removal hole) provided in a heat insulating material covering the crucible top cover. This eliminates the problem of sublimation gas leaking from the graphite crucible blocking the temperature measuring hole, and enables accurate measurement of the outer surface temperature of the crucible upper lid, and the inert gas according to the outer surface temperature. By adjusting the amount of the doping gas mixed with the ingot, it was found that a high-quality SiC single crystal ingot with little variation in electrical resistivity over the entire ingot can be produced, and the present invention has been completed.

That is, the gist of the present invention is as follows.
(1) A seed crystal is attached to the inner surface of the crucible upper lid, and a graphite crucible in which the crucible body is filled with a silicon carbide raw material is covered with a heat insulating material, placed in a quartz double tube, and nitrogen is mixed as a doping gas. The graphite crucible is heated at a high frequency in an atmosphere in which an inert gas is circulated, the silicon carbide raw material is sublimated, and a silicon carbide single crystal nitrogen-doped on the seed crystal is recrystallized to obtain a silicon carbide single crystal. In a method of manufacturing an ingot,
A cylindrical member is arranged in a temperature measuring hole provided in a heat insulating material covering the crucible upper lid, and the outer surface temperature of the crucible upper lid is measured through the cylindrical member from the start to the end of crystal growth, A method for producing a silicon carbide single crystal ingot, characterized by adjusting the amount of doping gas mixed with the inert gas according to the surface temperature,
(2) When the outer surface temperature of the crucible upper lid is lower than a predetermined temperature, the doping gas amount is reduced, and when the outer surface temperature of the crucible upper lid is higher than the predetermined temperature, adjustment is performed to increase the doping gas amount. (1) The method for producing a silicon carbide single crystal ingot according to (1),
(3) A silicon carbide single crystal ingot is produced with a constant doping gas amount mixed with the inert gas, and the relationship between the outer surface temperature of the crucible upper lid and the electrical resistivity in the silicon carbide single crystal ingot is examined. A pre-manufacturing test is performed, and based on the result of the pre-manufacturing test, the temperature for achieving the set electrical resistivity in the silicon carbide single crystal ingot set in the actual manufacturing is set as the predetermined temperature ( 2) A method for producing a silicon carbide single crystal ingot according to 2),
It is.

  According to the present invention, the outer surface temperature of the crucible upper lid is measured from the start to the end of the growth, and the doping gas flow rate is adjusted according to the measurement temperature at the time of crystal growth. Thus, it becomes possible to produce a SiC single crystal ingot with a small variation in electrical resistivity.

FIG. 1 is a schematic diagram for explaining the principle of the improved Rayleigh method. FIG. 2 is a schematic diagram for explaining an example of a cylindrical member used when measuring the outer surface temperature of the crucible upper lid. FIG. 3 is an example of a graph showing the relationship between the outer surface temperature of the crucible upper lid and the electrical resistivity of the ingot. FIG. 4 is an example of a graph showing the relationship between the nitrogen gas flow rate and the electrical resistivity of the ingot. FIG. 5 is an explanatory diagram showing an outline of the crystal growth apparatus used in the present invention. FIG. 6 is a graph showing the electrical resistivity distribution in the height direction of the growth ingot between the conventional method (Comparative Example 1) and the method of the present invention (Example 1).

The present invention will be described in detail below.
In the present invention, a seed crystal is attached to the inner surface of the crucible upper lid, and a graphite crucible in which the crucible body is filled with a silicon carbide (SiC) raw material is covered with a heat insulating material and installed in a quartz double tube as a doping gas. A graphite crucible is heated at a high frequency in an atmosphere in which an inert gas mixed with nitrogen is circulated, the SiC raw material is sublimated, the nitrogen-doped SiC single crystal is recrystallized on the seed crystal, and the SiC single crystal ingot is obtained. In manufacturing, the outer surface temperature of the crucible upper cover is measured from the start to the end of the crystal growth through a cylindrical member arranged in a temperature measuring hole provided in the heat insulating material covering the crucible upper cover, and this outer surface temperature is obtained. Accordingly, the amount of doping gas mixed with the inert gas is adjusted. Thereby, in the manufacturing method of the present invention, the flow rate of the doping gas can be controlled in conjunction with the change in the crystal growth surface temperature of the seed crystal during the growth of the SiC single crystal, and the electrical resistivity can be controlled over the entire ingot. The variation can be made extremely small.

  That is, in the above-described sublimation recrystallization method, impurity doping into the ingot is performed by adding nitrogen gas to an inert gas that is circulated during growth for n-type nitrogen. The problem here is that the doping amount of nitrogen atoms in the grown crystal is affected by the crystal growth surface temperature. It is known that the nitrogen doping concentration when the flow rate of the nitrogen gas mixed with the inert gas is constant increases as the crystal growth surface temperature decreases. Therefore, in order to keep the nitrogen concentration constant throughout the growth, it is necessary to keep the crystal growth surface temperature constant from the start to the end of the growth. Thereafter, the outer surface temperature of the crucible upper lid cannot be grasped, and the temperature cannot be adjusted substantially thereafter.

  Therefore, in the present invention, a crystal member has been conventionally grown by arranging a cylindrical member in a temperature measuring hole provided in a heat insulating material covering the crucible upper lid, and measuring the outer surface temperature of the crucible upper lid through the cylindrical member. To improve the place where the temperature measurement hole was blocked by adhesion of sublimation gas at the initial stage and the temperature measurement after that became impossible, and to stably measure the outer surface temperature of the crucible top cover throughout the growth. Make it possible. Accordingly, the amount of nitrogen mixed with the inert gas can be adjusted in accordance with the outer surface temperature of the crucible upper lid, and the variation in the nitrogen concentration in the ingot in the growth direction can be kept small. As described above, the outer surface temperature of the crucible upper cover is not the same as the crystal growth surface temperature of the seed crystal, but the outer surface temperature of the crucible upper cover changes in accordance with the crystal growth surface temperature. The temperature can be estimated.

  Here, for the cylindrical member, for example, as shown in FIG. 2, a male screw part is formed on the outer peripheral side surface of one end, and a female screw part is formed on the outer surface of the crucible upper lid 4a, and these are screwed together. The other end is preferably protruded from the heat insulating material 7 covering the crucible upper lid 4a. Further, the cylindrical member 13 and the crucible upper lid 4a may be connected using a heat resistant adhesive or the like. In this way, if the hollow portion of the cylindrical member is used as the passage hole for the radiated light, the outer surface temperature of the crucible upper lid 4a can be measured through the cylindrical member, and the connecting portion between the cylindrical member 13 and the crucible upper lid 4a is Since intrusion of sublimation gas is suppressed, stable temperature measurement can be performed over the entire crystal growth time. The material of the cylindrical member is not particularly limited, but is preferably made of graphite.

  In such a cylindrical member, the outer surface temperature of the crucible upper lid is measured, and in adjusting the doping gas amount mixed with the inert gas according to the outer surface temperature, the SiC single crystal ingot in the SiC single crystal ingot with respect to the outer surface temperature of the upper lid The relationship with the electrical resistivity should be examined by conducting a pre-manufacturing test as described below.

  First, the nitrogen gas (dopant gas) flow rate mixed with the inert gas is kept constant at a flow rate that is expected to be close to the target electrical resistivity in the ingot, and the crucible top lid provides good growth. Crystal growth is performed once aiming at the temperature of the upper lid, and the outer surface temperature of the upper lid is measured with a radiation thermometer from the start to the end of crystal growth through the hollow portion of the cylindrical member. After the completion of crystal growth, the ingot obtained was measured by measuring the electrical resistivity of a plurality of SiC single crystal substrates cut while confirming the position (height) relative to the growth direction from the seed crystal position. A graph showing the relationship between the directional position and the electrical resistivity is created (Graph 1). In addition, the relationship between the growth time and the growth direction position (height) is previously examined by, for example, marking growth in which nitrogen is intermittently doped during crystal growth to mark the grown crystal (Graph 2). ). At that time, except for the flow rate of nitrogen gas, the growth condition when obtaining the graph 1 is the same as the growth condition so that the graph 2 is obtained. Then, by combining these graph 1 and graph 2, a calibration curve showing the relationship between the outer surface temperature of the crucible upper lid and the electrical resistivity of the ingot as shown in FIG. 3 is obtained (graph 3).

  As can be seen from FIG. 3, even if the upper lid temperature during the growth time is aimed to be constant by setting the current value, the temperature actually varies as expected in the latter half of the growth. The corresponding change in electrical resistivity is confirmed. For the marking growth as described above, for example, when a flow of nitrogen gas is introduced in a pulse shape at a predetermined time interval during crystal growth to form a high nitrogen concentration region with a relatively high nitrogen concentration, Growth fringe markers can be provided at predetermined intervals in the growth direction. The region in which silicon carbide is grown with a high nitrogen concentration can be observed as colored stripes compared to other regions, so the relationship between the growth time and the growth direction position (height) is grasped. It is also possible to calculate the growth rate in the region between the growth fringe markers.

  On the other hand, the relationship between the nitrogen gas flow rate and the electrical resistivity of the ingot is also examined. At that time, the relationship is examined in the first half of the growth when the crystal growth is relatively stable and the temperature of the crucible upper cover is easily controlled by setting the current value (that is, the deterioration due to the thermal history of the graphite crucible and the heat insulating material is small). It is preferable to obtain a change in the electrical resistivity of the ingot when the predetermined amount is increased or decreased with respect to the standard nitrogen gas flow rate. Thereby, for example, as shown in FIG. 4, a graph can be obtained in which a calibration curve indicating the relationship between the nitrogen gas flow rate at the outer surface temperature of the crucible upper lid and the electrical resistivity can be drawn (Graph 4). Based on the “temperature-electric resistivity” relationship (graph 3) and the “gas flow rate-electric resistivity” relationship (graph 4) (graph 4) thus obtained, during actual growth (actual production) The nitrogen gas flow rate may be increased or decreased in accordance with the change in the outer surface temperature of the crucible upper lid.

  Here, in the crystal growth by the sublimation recrystallization method, the reaction in which nitrogen as a dopant is incorporated from the doping gas into the growing ingot is such that nitrogen atoms fly to the surface of the crystal growth and adsorb on the growth top surface, and then again It is thought that it is taken in contact with the atomic layer step that has moved along with the growth while leaving. Therefore, as the time for staying on the crystal growth surface from once adsorbing to separation becomes longer, more nitrogen is taken into the crystal. Here, since the higher the temperature, the more the separation from the crystal growth surface is promoted, the lower the temperature, the more doping gas atoms are taken into the crystal. For this reason, in order to reduce the change in the amount of doping atoms incorporated during crystal growth, when the outer surface temperature of the crucible upper lid falls below a predetermined temperature that is optimal as the growth rate, the doping gas amount is reduced, When the outer surface temperature rises above a predetermined temperature, it can be adjusted by increasing the doping gas amount. The predetermined temperature can be set based on the previous graph 1, and specifically, a temperature at which the electrical resistivity in the ingot becomes a target electrical resistivity (set electrical resistivity). Yes, a preliminary manufacturing test as described above is performed, and the relationship between the outer surface temperature of the crucible upper lid and the electrical resistivity in the SiC single crystal ingot can be determined and set.

  In the present invention, for the adjustment of the nitrogen gas flow rate with respect to the temperature change when the outer surface temperature of the crucible upper cover is measured from the start to the end of crystal growth, preferably, the temperature data of the radiation thermometer is the current value. In response to this output change (corresponding to temperature change increase / decrease), the power of the mass flow controller that controls the nitrogen gas flow rate (flow rate is also controlled by power increase / decrease) is interlocked and increased It is better to control. At that time, the change of the nitrogen gas flow rate with respect to the temperature change of 1 ° C should correspond to the fine fluctuation of temperature in temperature measurement (generally there is always a fluctuation of ± 1 ° C to measure the emitted light from the graphite member). It is desirable to apply to a change of ± 3 ° C. or more, which is a significant temperature difference. On the other hand, if the flow rate is adjusted after the temperature change becomes too large, the variation in the electrical resistivity of the growth ingot becomes large. Therefore, it is preferable to cope with a change of at least ± 8 ° C. or less, preferably ± 5 ° C. or less.

  In the present invention, except for the measurement of the outer surface temperature of the crucible upper lid as described above and the adjustment of the doping gas amount to be mixed with the inert gas according to this measurement, a conventionally known method for producing a SiC single crystal ingot Can be similar. In particular, in the production of SiC single crystal ingots having a large diameter such as 100 mm (4 inches) or more, or 150 mm (6 inches) or more, which has recently been developed, the graphite crucible is loaded (filled). Since the amount of SiC raw material increases and the amount of sublimation gas leaking from the graphite crucible increases accordingly, it can be said that the method of the present invention exhibits a particularly remarkable effect. In addition, since the SiC single crystal ingot obtained by the present invention suppresses variation in electrical resistivity over the entire ingot, for example, the yield in device fabrication can be improved.

  Examples of the present invention will be described below. In the present invention, it is only necessary to adjust the mixing amount of the dopant gas on the basis of the measured value of the outer surface temperature of the crucible upper lid to suppress the variation in the electrical resistivity of the ingot, and is limited to the following contents. It is not a thing.

Example 1
First, the single crystal growth apparatus (SiC single crystal manufacturing apparatus according to the present invention) used in this example will be briefly described with reference to FIG. The crystal growth is the same as in the conventional sublimation recrystallization method using a seed crystal. The SiC single crystal used as a seed crystal is sublimated from the SiC crystal powder 2 charged in the crucible body 4b constituting the graphite crucible 3. 1 by recrystallization. The seed SiC single crystal 1 is attached to the inner surface of the crucible upper lid 4a constituting the graphite crucible 3. The raw material SiC crystal powder 2 is filled in the lower part of the crucible body 4b constituting the graphite crucible 3. Such a graphite crucible 3 is placed in a double quartz tube 5 and installed by a graphite support rod 6. Further, around the graphite crucible 3, a graphite felt (heat insulating material) 7 for improving heat insulation is installed.

The above-described double quartz tube 5 can be evacuated to high vacuum (10 ⁻³ Pa or less) by a vacuum evacuation device 11, and the internal atmosphere passes from a gas pipe 9 through a gas flow rate controller (mass flow controller) 10. The pressure can be controlled by the introduced Ar gas. Various doping gases (nitrogen in this embodiment) can also be introduced through the gas flow controller 10. Further, a work coil 8 is installed on the outer periphery of the double quartz tube 5, and the graphite crucible 3 is heated by flowing a high frequency current to heat the SiC raw material 2 and the seed crystal 1 to a desired temperature. be able to. Furthermore, in order to adjust the temperature distribution of the crystal surface during growth to a convex shape downward, a heat extraction hole (temperature measuring hole) is formed in the center of the graphite felt (heat insulating material) 7 covering the outer surface of the crucible upper lid 4a. 12 (22 mm in diameter) is provided, and a graphite cylindrical member 13 is disposed in a through hole penetrating in the thickness direction of the felt forming the heat removal hole 12. Then, the outer surface temperature of the crucible upper lid 4a can be measured using the radiation thermometer 14 by the radiated light detected through the cylindrical member 13.

  Here, the cylindrical member 13 made of graphite is inserted into the heat removal hole 12 in the central part of the felt covering the surface of the crucible upper lid 4a, and as shown in FIG. A male screw portion was formed, a female screw portion was formed on the outer surface of the crucible upper lid 4a, and these were fixed by screwing. The graphite cylindrical member 13 has an inner diameter of 16 mm and an outer diameter of 22 mm. Further, the thickness of the graphite felt 7 covering the surface of the crucible upper lid 4a was 10 mm, and the graphite cylindrical member 13 penetrated the felt and protruded on the felt with a length of about 60 mm. Then, as described above, the radiation light detected through the cylindrical member 13 was measured with the synchrotron thermometer 14 to monitor the temperature during crystal growth.

Next, examples of manufacturing a SiC single crystal using the crystal growth apparatus of the present invention will be described.
First, a 4H polytype SiC single crystal substrate 1 having a (0001) face with a diameter of 150 mm was prepared as a seed crystal. The seed crystal having an offset angle of 4 ° from the {0001} plane was used. Next, the seed crystal 1 was attached to the inner surface of the crucible upper lid 4a of the graphite crucible 3. The crucible body 4b of the graphite crucible 3 was filled with SiC crystal powder (SiC raw material) 2 produced by the Atchison method. Next, the graphite crucible 3 filled with the SiC raw material 2 was closed with the crucible upper lid 4 a and covered with the graphite felt 7, and then placed on the graphite support rod 6 and installed inside the double quartz tube 5. Then, after the inside of the double quartz tube 5 was evacuated, a current was passed through the work coil 8 to raise the outer surface temperature of the crucible upper lid 4a to 2000 ° C. Thereafter, high-purity Ar gas (purity 99.9995%) was introduced as the atmospheric gas, and the pressure in the double quartz tube 5 was maintained at 1.3 kPa throughout the growth. Under this pressure, the outer surface temperature of the crucible upper lid 4a is increased from 2000 ° C. to the target temperature of 2240 ° C., and then, as a pre-production test (I), about 100 as a current value pattern set to be the same temperature. The time crystal growth was continued to obtain a SiC single crystal ingot having a diameter of about 150 mm and a height of about 40 mm.

  During this crystal growth time, the growth was carried out while maintaining the nitrogen gas flow rate at the start of growth at 50 sccm. With respect to the obtained ingot, while confirming the position (height) with respect to the crystal growth direction from the seed crystal position, four SiC single crystal substrates were cut out so as to be approximately equidistant from the entire length of the ingot, and their electrical resistivity Was measured to examine the change in electrical resistivity with respect to the ingot height. Next, in order to confirm the ingot height with respect to the growth time in this pre-manufacturing test (I), as the pre-manufacturing test (II), marking growth obtained by introducing nitrogen gas at regular time intervals is performed, The relationship between growth time and ingot height was sought. Based on these two measurements, a graph of the relationship of the change in electrical resistivity of the surface of the grown crystal with respect to the outer surface temperature of the crucible upper lid 4a was created, and a calibration curve showing the correlation between the two was obtained. The results are as shown in FIG.

  Next, in order to investigate the relationship between the flow rate of nitrogen gas and the electrical resistivity of the ingot, the temperature control of the crucible upper lid 4a by setting the current value is relatively easy to perform in the first half of the growth period (up to 30 hours after the start of growth). The outer surface temperature of the crucible upper lid 4a was set to a target temperature of 2400 ° C., the nitrogen gas flow rate was changed within a range of ± 25 cc from the standard flow rate of 50 cc, and an ingot was manufactured to change the nitrogen gas flow rate. The electrical resistivity of the ingot was obtained, a graph showing the correlation of “nitrogen gas flow rate—electric resistivity” at the same temperature was created, and a calibration curve was obtained. The results are as shown in FIG.

  Using the calibration curves obtained from these two graphs (FIGS. 3 and 4), crystal growth in actual production was performed. Here, since the optimum electrical resistivity for the SiC single crystal wafer is 17.5 mΩcm, 2240 ° C. which is the temperature showing the electrical resistivity in the graph of FIG. 3 was determined as the growth temperature. During crystal growth, from the time when the outer surface temperature of the crucible upper lid 4a reaches 2240 ° C., the growth is completed while monitoring the temperature change of the outer surface of the crucible upper lid 4a and finely changing the nitrogen gas flow rate each time the temperature changes. The crystal growth was performed for about 100 hours under controlled time. Specifically, from the result of FIG. 3 measured in advance, the electrical resistivity change rate with respect to a temperature change of 1 ° C. is “0.08 mΩcm / ° C.”, and this is also a figure obtained by the prior measurement. From the result of No. 4, the rate of change in electrical resistivity with respect to a change in nitrogen gas flow rate of 0.05 sccm was “0.01 mΩcm / 0.05 sccm”. The amount of doping gas (nitrogen gas flow rate) set to “1.2 sccm / ° C.” and mixed with the inert gas in conjunction with the mass flow controller 10 according to the output of the temperature data (current value) of the synchrotron radiation thermometer 14 The doping gas amount was decreased when the outer surface temperature of the crucible upper lid 4a was lower than 2240 ° C., and the doping gas amount was increased when the outer surface temperature was higher than that.

With respect to the nitrogen-doped SiC single crystal ingot having a diameter of about 150 mm and a height of about 42 mm obtained in this manner, 35 SiC single crystal substrates having a thickness of 1.0 mm were cut out from the entire length at almost equal intervals. Among these, electrical resistivity using eddy currents was obtained for eight SiC single crystal substrates cut from positions of 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm from the seed crystal side. The electrical resistivity was measured by a measuring machine (Napson, NC-80MAP) (this measuring machine was also used for the measurement of electrical resistivity in the above-mentioned pre-manufacturing test). At that time, the electrical resistivity of each SiC single crystal substrate was measured at intervals of 10 mm in the diameter direction of the substrate, and an average value was calculated. As a result, as shown in FIG. 6, the electrical resistivity (average value) of the SiC single crystal substrate at the height of 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm from the seed crystal side. Are 17.6 mΩcm, 18.0 mΩcm, 18.3 mΩcm, 17.8 mΩcm, 18.1 mΩcm, 18.5 mΩcm, 17.9 mΩcm, and 17.7 mΩcm, respectively, and variations in electrical resistivity in the height direction of the ingot It was 2.5%, and it was confirmed that it was within a very small range of 3% or less.

(Comparative Example 1)
In the same manner as in Example 1, except that the nitrogen gas flow rate was kept at 50 sccm from the start to the end of crystal growth without any adjustment of the nitrogen gas flow rate according to the change in the outer surface temperature of the crucible upper lid. Crystal growth was performed for 100 hours.

For the nitrogen-doped SiC single crystal ingot having a diameter of about 150 mm and a height of about 42 mm obtained in this way, as in Example 1, 35 SiC single crystal substrates having a thickness of 1.0 mm at regular intervals from the entire length. The average electrical resistivity of each of the eight SiC single crystal substrates cut out and cut from the positions where the height from the seed crystal side is 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm is calculated. did. The result is as shown in FIG. 6, and the electrical resistivity (average value) of the SiC single crystal substrate at positions where the height from the seed crystal side is 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm. ) Are 17.5 mΩcm, 19.7 mΩcm, 20.2 mΩcm, 18.3 mΩcm, 17.9 mΩcm, 17.3 mΩcm, 16.5 mΩcm, and 18.6 mΩcm, respectively, and variations in electrical resistivity in the height direction of the ingot Was 10.1%, which was larger than that of Example 1.

  As described above, according to the present invention, variation in electrical resistivity can be suppressed over the entire ingot (full length). In particular, even when producing a SiC single crystal ingot having a large diameter, it can be said that the variation in electrical resistivity can be effectively suppressed, and it can be said that the invention is extremely useful industrially.

1 Seed crystal (SiC single crystal substrate)
2 SiC crystal powder (SiC raw material)
3 Graphite crucible
4a Crucible top lid
4b Crucible body 5 Double quartz tube 6 Support rod 7 Graphite felt (insulation)
8 Work coil 9 Gas piping 10 Gas flow controller (mass flow controller)
11 Vacuum exhaust device 12 Heat removal hole [also temperature measurement hole (radiated light transmission hole)]
13 Graphite Cylindrical Member 14 Radiation Thermometer

Claims (3)

An inert gas in which a seed crystal is attached to the inner surface of the crucible upper lid, a graphite crucible filled with a silicon carbide raw material is covered with a heat insulating material, and is installed in a quartz double tube and nitrogen is mixed as a doping gas The graphite crucible is heated at a high frequency in an atmosphere in which a silicon carbide single-crystal ingot is produced by sublimating the silicon carbide raw material and recrystallizing the nitrogen-doped silicon carbide single crystal on the seed crystal. In the way to
A cylindrical member is arranged in a temperature measuring hole provided in a heat insulating material covering the crucible upper lid, and the outer surface temperature of the crucible upper lid is measured through the cylindrical member from the start to the end of crystal growth, A method for producing a silicon carbide single crystal ingot, comprising adjusting a doping gas amount to be mixed with the inert gas according to a surface temperature.   When the outer surface temperature of the crucible upper lid is lower than a predetermined temperature, the doping gas amount is reduced, and when the outer surface temperature of the crucible upper lid is higher than the predetermined temperature, the doping gas amount is adjusted to increase. A method for producing a silicon carbide single crystal ingot according to claim 1.   A pre-manufacturing test for producing a silicon carbide single crystal ingot with a constant doping gas amount mixed with the inert gas and examining the relationship between the outer surface temperature of the crucible upper lid and the electrical resistivity in the silicon carbide single crystal ingot The temperature for achieving the set electrical resistivity in the silicon carbide single crystal ingot set in the actual production based on the result of the preliminary production test is set as the predetermined temperature. A method for producing a silicon carbide single crystal ingot.

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