JP2004315281A - Method for manufacturing single crystal using temperature gradient furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously manufacturing a single crystal, with which a desired temperature gradient can be formed without necessitating the movement of a heating source, and the temperature distribution in the lateral cross section is made uniform by using a temperature gradient furnace. <P>SOLUTION: In the method, the single crystal is manufactured from a solution by using the temperature gradient furnace for imparting a temperature gradient to a columnar work in the longitudinal direction. The temperature gradient furnace equipped with a heat-insulating wall surrounding the periphery of the columnar work, a heating section for heating the lower end of the columnar work via a heating susceptor, and a cooling section for cooling the upper end of the columnar work via a cooling susceptor is used. The columnar work is constituted by stacking a raw material rod 10, a solvent 12, a seed crystal 14, and a supporting rod 16. The temperature gradient is formed in the columnar work so that the temperature at the upper end surface of the solvent becomes lower than that at the lower end surface of the solvent by heating by the heating section while utilizing the lower end of the raw material rod as the lower end of the columnar work, and at the same time, cooling by the cooling section while utilizing the upper end of the supporting rod as the upper end of the columnar work. Further, the single crystal is continuously grown downward from the seed crystal as a starting point by gradually lowering the heating temperature at the lower end of the columnar work. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５４】
成長速度０．４ｍｍ／ｈの場合を比較すると、断熱円筒なし（図１）の場合には柱状ワーク径φ１２ｍｍで長さ３０ｍｍの高品質なＳｉＣ単結晶が得られた。また黒鉛製断熱円筒２０２（図２）を用いることにより柱状ワーク径φ２０ｍｍでも長さ３０ｍｍのＳｉＣ単結晶を成長させることが可能であった。更に、断熱円筒２０２（図２）の材質をＢＮとすることで柱状ワーク径φ３５ｍｍでも成長長さ３０ｍｍのＳｉＣ単結晶が得られた。
【００５５】
また、冷却器１１２の冷媒シリコンオイルの温度を一定にした場合には、ＢＮ製の断熱円筒２０２を用いた場合でも、φ３５ｍｍの柱状ワーク径では３０ｍｍの成長長さを得られる成長速度は１．５ｍｍ／ｈまでであった。これに対して、冷媒シリコンオイルの温度を下端温度Ｔｂに同期して変化させた場合には、成長速度を２．５ｍｍ／ｈまで高速にしても長さ３０ｍｍの高品質なＳｉＣ単結晶が得られた。
【００５６】
〔実施例２〕
図１、図２、図３に示した温度勾配炉１００、２００、３００を用いてＳｉＣ単結晶成長を行なった。図３の温度勾配炉３００は、柱状ワークＷを収容する耐熱材料製密閉容器２０４を炉内に備え、かつ溶媒供給源として溶媒容器２０６を炉底に配置した点以外は、図１の温度勾配炉１００と同じ構成である。図１に示した部位と対応する部位には図１中と同じ参照符号を付した。密閉容器２０４は等方性黒鉛焼結体を用いた。なお、図３の温度勾配炉３００については、溶媒容器２０６を配置しない場合についても実験を行なった。
【００５７】
柱状ワーク径φ１２ｍｍ、溶媒ペレット径φ７ｍｍ×厚さｔ０．６ｍｍ、柱状ワーク下端ＷＢの初期設定温度２１００℃、降温速度０．４℃／ｈ（成長速度０．１ｍｍ／ｈ）とし、長時間の操業で溶媒が揮発して成長が停止するまでのＳｉＣ単結晶成長長さを測定した。他の諸条件は実施例１に準ずる。結果を表２に示す。密閉容器２０４を用いかつ溶媒容器２０６を配置した場合に最も長時間の操業が可能になることが分かる。
【００５８】
【表２】

【００５９】
〔実施例３〕
実施例１と同様な装置構成において、ＳｉＣ単結晶成長過程における柱状ワークＷの下端ＷＢと上端ＷＴとの間の電気抵抗率を測定した。結果を図５に示す。なお実施条件は表１に示した諸条件のうち、降温速度１０．０℃／ｈ、成長速度２．５ｍｍ／ｈ、柱状ワーク径（成長単結晶径）φ３５ｍｍ、ＢＮ製断熱円筒使用の場合である。
【００６０】
柱状ワークＷの下端ＷＢ、上端ＷＴをそれぞれ測定端とした場合（図５（ａ））は、結晶の成長と共に電気抵抗値が直線的に低下し、成長途中の変曲点（矢印）は、時間の対応から見て多結晶化の開始時点と一致しており、単結晶成長過程での異常発生が明瞭に検出されている。また上下のサセプタ１１４，１１０を測定端とした場合（図５（ａ））でも、同様に異常点が明瞭に検出されている。
【００６１】
また、径φ３５ｍｍ×長さＬ１００ｍｍの黒鉛中実棒をダミーワークとして、各測定点でのワーク下端面きんぶの半径方向の温度分布を測定した。測定は、ダミーワークの下面から１ｍｍの位置に穿孔した測定孔に、φ５ｍｍのＷ−Ｒｅ熱電対を挿入して行なった。結果を図６に示す。上下のサセプタを測定端とすることで面内温度分布の均一性が確保されることが分かる。
【００６２】
〔実施例４〕
図４に示す温度勾配炉４００を用いてＳｉＣ単結晶の析出による種結晶の作製を行なった。温度勾配炉４００は、図３の温度勾配炉３００において種結晶１４を用いず、その代わりに支持棒１６の下端に円錐形の座繰り凹部２０８を設け、この凹部先端から単結晶を核生成させ、これを種結晶として長尺の単結晶を成長させるための構成である。表３に示す諸条件で処理を行なった結果、支持棒下端から約１ｍｍ（円錐座繰り先端部から７ｍｍ）の長さの高品質のＳｉＣ単結晶を得ることができ、すなわち装置内部でＳｉＣ種結晶を創製することができた。
【００６３】
【表３】

【００６４】
【発明の効果】
本発明によれば、温度勾配炉を用いて、加熱源の移動を必要とせずに単結晶の成長に適した所望の温度勾配を形成し、かつ、成長方向に対して垂直な面内の温度分布も均一化し、連続的に単結晶を製造する方法が提供される。
【図面の簡単な説明】
【図１】図１は、本発明の方法に用いる温度勾配炉の一実施形態を示す断面図およびプロセスを説明するグラフである。
【図２】図２は、本発明の方法に用いる温度勾配炉の他の実施形態を示す断面図である。
【図３】図３は、本発明の方法に用いる温度勾配炉のもう１つ実施形態を示す断面図である。
【図４】図４は、本発明の方法に用いる温度勾配炉の更にもう１つの実施形態を示す断面図である。
【図５】図５は、本発明の方法により測定した柱状ワークの電気抵抗の経時変化を示すグラフである。
【図６】図６は、本発明の方法により柱状ワーク端およびサセプタ端での半径方向温度分布を示すグラフである。
【符号の説明】
１００、２００、３００、４００…温度勾配炉
１０４…胴体部
１０６…中空部
１０８…誘導加熱コイル
１１０…加熱用サセプタ
１１２…冷却器
１１４…冷却用サセプタ
１０…原料棒
１２…溶媒
１４…種結晶
１６…支持棒
Ｗ…ワーク
ＷＴ…ワーク上端面（冷却端面）
ＷＢ…ワーク下端面（加熱端面）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for continuously producing a single crystal by precipitation from a solution using a temperature gradient furnace for imparting a longitudinal temperature gradient to a columnar work.
[0002]
[Prior art]
In manufacturing a high-quality single crystal as a semiconductor material or the like, it is necessary to minimize defects such as mosaicity and dislocation. Since defects are closely related to the stability of crystal growth, it is important to maintain an appropriate deposition rate according to the crystal material. Therefore, it is indispensable to control the temperature gradient along the crystal growth direction between the crystal deposition part, which serves as a driving force for the precipitation, and the deposition substance supply part (gas phase, liquid phase).
Conventional typical single crystal growth techniques include the CZ method (Czochralski method), the FZ method (zone melting method), the Bridgman method, and the TSSG method (melt pulling method).
[0003]
In either method, a temperature gradient is realized by heating a part of the work and releasing the other atmosphere, and the temperature gradient is controlled by the temperature of the heat source, the shape of the heat source, the shape of the work (crucible), and the heat source and the work. The adjustment is performed by adjusting the relative positional relationship between them.
[0004]
Such a conventional method has the following problems.
1) It is difficult to achieve a desired temperature gradient. As described above, since the control factors of the temperature gradient, that is, the fluctuation factors are various, it is extremely difficult to stably maintain each factor in an optimum state.
[0005]
2) The temperature gradient fluctuates due to factors other than the apparatus, such as the shape of the work (crucible) and the amount of raw materials charged. As described above, not only the device factors but also the factors outside the device are involved in the temperature gradient control.In order to achieve the desired temperature gradient, the calculation at the design stage and the trial and error of repeating the actual temperature measurement of the actual device are required. is necessary.
[0006]
3) It is difficult to equalize the temperature distribution in a plane perpendicular to the crystal growth direction. This is because the direction of the heat flow with respect to this vertical plane is not constant in the plane.
[0007]
In addition, compound semiconductors such as silicon carbide (SiC), which are attracting attention as a semiconductor material having a high band gap, do not harmonizely melt (have no molten state by themselves), and thus are precipitated from the above-described melt. The single crystal growth method cannot be applied.
[0008]
As a method not using a melt, there is a sublimation method or a solution method. The sublimation method is a method in which a single crystal raw material sublimated in a high temperature part is deposited from a gas phase on a seed crystal arranged in a low temperature part. However, the problem is that the single crystal growth rate is low due to precipitation from a dilute phase, and it is difficult to avoid the formation of micropipes in principle because of the frank mechanism that grows spirally from the step around the screw dislocation of the seed crystal. There is. On the other hand, the solution method is a method in which a single-crystal raw material is sufficiently dissolved in a solvent in a high-temperature part, and is disposed in a low-temperature part to cause a supersaturated state to appear on a seed crystal to precipitate. Although the above-mentioned problem of the sublimation method can be overcome by adjusting the solvent concentration, the temperature gradient fluctuates depending on the deposition site due to the above problems 1) to 3). It was extremely difficult to obtain crystals.
[0009]
Therefore, as a method for forming a melt by coexistence with another element, Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-264790) includes at least one kind of transition metal, Si, and C. A method has been proposed in which a raw material is melted by heating to form a melt, and the melt is cooled to precipitate and grow a single crystal of silicon carbide (SiC). However, in this method, in order to continuously grow a single crystal, it is necessary to move a heating source continuously, and nucleation occurs simultaneously and frequently due to mechanical vibrations, resulting in polycrystallization. There was a problem.
[0010]
[Patent Document 1]
JP-A-2000-264790 (Claims)
[0011]
[Problems to be solved by the invention]
The present invention uses a temperature gradient furnace to form a desired temperature gradient suitable for growing a single crystal without the need to move a heating source, and to also generate a temperature distribution in a plane perpendicular to the growth direction. It is an object of the present invention to provide a method for producing a single crystal uniformly and continuously.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a single crystal production method of the present invention is a method for producing a single crystal by precipitation from a solution using a temperature gradient furnace for imparting a longitudinal temperature gradient to a columnar work. As the temperature gradient furnace, a heat insulating wall surrounding the outer periphery of the columnar work, a heating unit for heating the lower end of the columnar work via a heating susceptor, and cooling the upper end of the columnar work via a cooling susceptor Using a temperature gradient furnace with a cooling unit to
The raw material rod, the solvent, and the seed crystal supported on the lower end of the support rod are stacked in the furnace in order from the bottom to form the columnar work, and the lower end of the raw material rod is set as the lower end of the columnar work. By heating by the heating unit and cooling by the cooling unit using the upper end of the support rod as the upper end of the columnar work, a temperature gradient is formed in the columnar work so that the upper end surface is lower in temperature with respect to the lower end surface of the solvent. To form
By gradually reducing the heating temperature of the lower end of the columnar work, a single crystal is continuously grown downward from the seed crystal as a starting point.
[0013]
In the method of the present invention, the single crystal raw material of the raw material rod dissolves in the high-temperature portion at the lower end of the solvent and precipitates at the low-temperature portion at the upper end of the solvent, whereby the single crystal grows downward. As the heating temperature of the lower end of the columnar work decreases, the position of the temperature gradient line in the columnar work lowers as a whole. At the same time, with the lowering of the position of the upper end of the raw material rod due to the dissolution of the upper end of the raw material rod in the solvent and the downward elongation of the single crystal growth end due to precipitation on the seed crystal (or the lower end of the growing single crystal = growing end), The position of the solvent sandwiched between the raw material rod and the seed crystal (growing edge) drops. The heating temperature of the lower end of the columnar work is gradually reduced so that the position of the temperature gradient line is lowered so as to synchronize with the lowering of the solvent position due to the crystal growth. Thereby, the single crystal can be continuously grown by lowering the solvent position (= the place where the raw material is converted to the single crystal) without mechanically moving the heating source.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The principle of the method of the present invention for producing a single crystal using a temperature gradient furnace will be described with reference to FIG.
[0015]
First, a configuration example of the temperature gradient furnace used in the method of the present invention will be described. The illustrated temperature gradient furnace 100 has a cylindrical body, and has a central axis of the cylindrical body along the vertical direction in the figure, and the figure is a longitudinal sectional view in a plane including the central axis. The cylindrical body 104 is made of a heat-insulating material, and its hollow portion 106 constitutes an effective furnace space.
[0016]
In the cylindrical hollow portion 106, a cylindrical work W composed of the raw material rod 10, the solvent 12, the seed crystal 14, and the support rod 16 is held in a state in which the upper end and the lower end are in close contact with the bottom surface and the ceiling surface of the hollow portion 106, respectively. Will be accommodated. Thereby, the heat flow through the outer periphery of the work W is substantially blocked, and the heat flow can flow only through the upper end and the lower end.
[0017]
Thus, the temperature gradient is such that the lower end of the columnar work W (= the lower end of the raw material rod 10 = heating end) is the highest hot spot, and the upper end of the columnar work W (= the upper end of the support rod 16 = cooling end) is the lowest hot spot. A temperature gradient that monotonously decreases in temperature from below to above the columnar work W is formed along the longitudinal direction of the columnar work W.
[0018]
The lower end surface WB of the cylindrical work W (the lower end surface of the raw material rod 10) is a circular flat surface, and is heated by the induction heating coil 108 below. The heating susceptor 110 interposed between the induction heating coil 108 and the lower end surface WB of the work W includes a disc-shaped flange portion 110A that is in close contact with the lower end surface WB of the columnar work W, and a cylindrical portion 110B that is heated by induction heating. Consisting of The induction heating coil 108 is arranged around the cylindrical portion 110B of the susceptor 110. With such a structure, compared to a structure in which the susceptor 110 has a simple disk shape, the ultimate temperature is increased and the uniformity of the in-plane temperature distribution is further improved.
[0019]
The cylindrical portion 110B has a substantially cylindrical shape in which a portion other than a portion immediately adjacent to the flange portion 110A is hollow. When the cylindrical portion 110B is entirely solid, the outer peripheral portion of the cylindrical portion 110B directly heated by the induction coil 108 has a high temperature, and the core portion of the cylindrical portion 110B heated only by heat conduction from the outer peripheral portion. Tends to be low temperature, which is not desirable for ensuring uniformity of the temperature distribution in the cross section. By making the portion other than the portion immediately adjacent to the flange portion 110A hollow as in this embodiment, the uniformity of the in-plane temperature distribution can be further improved.
[0020]
As described above, the heat flow from the resistance heating coil 108 to the work lower end surface WB is equalized by the intervening heating susceptor 110 between the induction heating coil 108 and the work lower end surface WB, and the entire work lower end surface WB is equalized. Heated. The heating susceptor 110 is made of a disc made of a good heat conductive metal such as copper to secure high heating efficiency.
[0021]
The upper end surface WT of the columnar work W is also a circular flat surface, and is cooled by a water-cooled cooler 112 having a circular cooling flat surface opposed thereto. The cooler 112 is in the form of a cooling jacket made of a good heat conductive metal such as copper. In the illustrated example, the cooling water inlet CLI and the outlet CLO are open at the upper end, and the other parts are watertight. Structure. By the cooling susceptor 114 interposed between the cooler 112 and the work upper end surface WT, the heat flow from the work upper end surface WT to the cooler 112 is equalized, and the entire work upper end surface WB is uniformly cooled. The cooling susceptor 114 is made of graphite or the like having heat resistance and moderate heat insulating properties, since it is necessary to secure an appropriate heat removal effect so as to prevent excessive rapid cooling and allow necessary slow cooling. .
[0022]
The cooler 112 can be moved up and down as indicated by a double-headed arrow X in the figure, so that the distance Δt between the cooler 112 and the susceptor 114 can be appropriately adjusted as necessary to set a required heat removal amount. (In the illustrated example, Δt = 0, both are in close contact with each other).
[0023]
The temperature Tb of the workpiece lower end surface WB to be heated is externally observed by a pyrometer through a pipe T1 penetrating the center of the heating coil 108 and the heating susceptor 110 (observation optical path: arrow PB). The heating temperature is controlled by adjusting the output of the induction heating coil 108 based on the observed temperature value.
[0024]
The temperature Tt of the work upper end surface WT to be cooled is externally observed by a pyrometer through a pipe T2 penetrating the center of the cooler 112 and the cooling susceptor 114 (observation optical path: arrow PT). By adjusting the temperature and flow rate of the cooling water supplied to the water-cooled cooler 112 based on this observation value, the heat removal (cooling strength) can be adjusted.
[0025]
As described above, the heating at the lower end WB and the cooling at the upper end WT of the columnar work W are performed using the heating susceptor 110 and the cooling susceptor 114, respectively. And a uniform heat flow distribution in the cross section, so that a very high linearity is given to a temperature gradient that monotonously decreases in temperature from below to above the columnar work W. At the same time, the temperature distribution in the cross section can be made uniform.
[0026]
Next, the principle of a method for continuously growing a single crystal according to the present invention using the temperature gradient furnace 100 will be described.
[0027]
In the method of the present invention, a single crystal raw material is grown from a raw material rod 10 via a solvent 12 by being deposited on a seed crystal (or a crystal growth tip). This is because the upper end of the raw material rod 10 that is in contact with the lower end of the solvent 12 is lower under a temperature gradient that monotonously and linearly decreases in temperature from below to above the columnar work W as described above. This is because the temperature of the seed crystal (the crystal growth tip) in contact with the upper end of the solvent 12 is always maintained at a higher temperature by a certain temperature width. This will be described in detail in the following description.
[0028]
First, as an operation preparation, the upper end of the support rod 16 having the seed crystal 14 attached to the lower end is fixed to the furnace ceiling, the lower end of the new raw material rod 10 is fixed to the furnace bottom, and the gap between the raw material rod 10 and the seed crystal 14 is A solid of a substance to be used as the solvent 12 is inserted in close contact.
[0029]
By operating the induction heating coil 108 and the cooler 112, a temperature gradient that monotonously and linearly decreases in temperature from below to above the columnar work W is formed along the longitudinal direction of the columnar work W. At this time, a liquid solvent 12 is formed and is held between the upper end of the raw material rod 10 and the lower end of the seed crystal 14 by surface tension. This is the same as the state of the molten zone in the conventional zone melting method.
[0030]
At the start of crystal growth (elapsed time j = 0), the interface between the upper end of the raw material rod 10 and the solvent 12 has a height Z1. ₀ In a fresh solvent 12 that does not yet contain a medium ₁ The raw material is dissolved from the raw material rod 10 to a concentration corresponding to the high solubility of the raw material. The dissolved raw material is diffused in the solvent 12 to form an interface between the solvent 12 and the lower end of the seed crystal 14 (height Z2). ₀ ) And the high temperature T ₁ Low temperature T lower by a temperature width ΔT determined by the temperature gradient ₂ The crystal raw material of a supersaturated amount exceeding the concentration corresponding to the low solubility in the above is precipitated from the solvent 12 on the lower end face of the seed crystal 14 and crystal growth starts.
[0031]
In order to set the initial temperature of the heating end (lower end) WB and the cooling end (upper end) WT of the columnar work W, a cooler in which a refrigerant of a predetermined temperature is circulated while the output of the induction heating coil 108 is adjusted. The state in which the height of the cooling 112 is adjusted to leave an interval Δt with the cooling susceptor 114 (Δt = Δt ₀ ≠ 0) and wait until the temperature at both ends is stabilized.
[0032]
When the crystal growth starts, the output of the induction heating coil 108 is continuously lowered to lower the temperature of the lower end WB continuously, and in synchronism with this, the cooler 112 is continuously lowered so that the cooling susceptor 114 Is the initial value Δt ₀ , The temperature of the upper end WT is continuously reduced. Accordingly, the temperature gradient line is continuously moved as a whole toward a lower temperature while the temperature gradient is maintained at the initial setting value, that is, the temperature gradient line is continuously moved as a whole from the lower end WB of the columnar work W. The speed of the continuous movement of the temperature gradient line is set so as to coincide with the speed of crystal growth by dissolution and precipitation of the raw material. The relationship between the two is determined in advance by an experiment.
[0033]
As described above, with the continuous drop of the temperature gradient line, the solvent 12 for dissolving and depositing the raw material also continuously drops at the same speed, and the single crystal continuously grows downward starting from the seed crystal. This will be described with reference to FIG. ₁ At the point of time, the temperature gradient line is the initial position D ₀ To D ₁ And at the same time, the solvent position is expressed as [lower end height / upper end height], and the initial [Z1 ₀ / Z2 ₀ ] To time j ₁ [Z1 ₁ / Z2 ₁ ]. However, the temperature difference between the lower end and the upper end of the solvent 12 is maintained at the initial value ΔT.
[0034]
As shown, the initial temperature gradient line D ₀ Is the initial lower end temperature / upper end temperature [Tb ₀ / Tt ₀ At time j ₁ Temperature gradient line D1 at time j ₁ Temperature / top temperature [Tb ₁ / Tt ₁ ]. Temperature gradient line D ₀ , D ₁ Are straight lines, and the temperature difference between the upper and lower ends is always constant.
[0035]
In this way, by lowering the position of the solvent in synchronization with the parallel movement of the temperature gradient, a single crystal can be grown continuously without requiring mechanical movement.
[0036]
As the solvent 12, a solvent having a melting point lower than the melting point of the single crystal raw material or the decomposition / sublimation temperature is used. If the temperature zone of the solvent 12 (the melting end T1 to the precipitation end T2) is high, the moving range of the solvent is limited by the allowable operating temperature range of the furnace 100. By making the solvent temperature as low as possible, the length of a single crystal that can be continuously grown becomes large.
[0037]
As the raw material rod 10, a material made of a dense sintered body of a single crystal raw material and containing a dopant as a sintering aid can be used. In this way, the crystal can be doped at the manufacturing stage. If the raw material rod is porous, the solvent may be absorbed or the solvent may climb on the side surface of the support rod due to the presence of unevenness on the surface, leading to a decrease or disappearance of the solvent, which may cause a shutdown of the operation. Therefore, the raw material rod is made dense.
[0038]
It is desirable to arrange the columnar work W in a cylinder made of a heat-resistant material. There is a gap between the furnace wall defined by the inner peripheral surface of the heat insulating material 104 and the outer peripheral surface of the columnar work W. Therefore, heat loss due to radiation from the outer peripheral surface of the columnar work W occurs, which causes a change in a temperature gradient and a decrease in uniformity of a temperature distribution in a cross section. This tendency becomes more apparent as the diameter of the columnar workpiece increases. As a result, the precipitation state becomes non-uniform, and defects such as dislocations are introduced, and in a severe case, polycrystallization occurs. By arranging the columnar work in a cylinder made of a heat-resistant material, a constant and small gap is formed around the outer periphery of the columnar work, stable temperature gradients and uniform temperature distribution in the cross section are ensured. Crystallization can be prevented and a high-quality single crystal can be grown.
[0039]
It is desirable to arrange the columnar work in a closed container made of a heat-resistant material. This further ensures temperature gradient stabilization and temperature uniformity in the cross section.
[0040]
As the heat-resistant material constituting the cylinder or the closed container, one selected from the group consisting of graphite sintered bodies, alumina sintered bodies, zirconia sintered bodies, and boron nitride sintered bodies can be used. Among them, the alumina sintered body, the zirconia sintered body and the boron nitride sintered body have low emissivity, and are effective in reducing radiation loss.
[0041]
When using a closed container, it is desirable to arrange a solvent supply source inside. Depending on the type of the solvent and the temperature conditions of the operation, the decrease in the solvent due to volatilization becomes prominent in the operation for a long time, and the length of a single crystal that can be produced may be limited. In such a case, by arranging the solvent supply source in a closed container containing the columnar work, the solvent vapor pressure can be easily maintained in a saturated state in the container. A long single crystal can be manufactured by time operation.
[0042]
The electric resistance between the upper end and the lower end of the columnar work is measured, and the single crystal growth length can be detected based on the measured value. Compared with a single crystal to be grown, the sintered body used for the support rod and the raw material rod has a higher electric resistance as a whole due to the electric resistance of the existing grain boundaries. Therefore, the electrical resistance in the axial direction of the columnar work decreases as the single crystal grows. Using this, the growth length of the single crystal can always be detected. From the rate of change of the electric resistance, a growth rate (= descent rate of the solvent position) in the solvent band range is obtained, and by using this, the solvent position movement speed and the temperature gradient line movement speed can be matched.
[0043]
The measurement of the electric resistance can be performed between the upper end of the cooling susceptor and the lower end of the heating susceptor. If the single crystal to be grown has a large diameter or the operating temperature is high, the uniformity of the temperature distribution in the cross section may be reduced due to the influence of the disturbance of the temperature field due to the installation of the measuring terminal. In such a case, it is possible to avoid the disturbance due to the disturbance of the temperature field by measuring not through the upper end and the lower end of the columnar work but through the susceptor having high in-plane temperature uniformity.
[0044]
It is desirable to set the temperature of the solvent to just below the boiling point of the solvent. The crystal growth rate is determined by the degree of supersaturation. The degree of supersaturation can be controlled by the temperature gradient and the difference in solubility of the solute (single crystal raw material) with temperature. Solubility is temperature-dependent and increases with increasing temperature, and the rate of increase also increases with increasing temperature. Therefore, by setting the temperature of the solvent to just below the boiling point of the solvent, that is, the maximum temperature usable in the solvent used, the maximum degree of supersaturation achievable with the solvent is obtained, and the crystal growth rate can be maximized.
[0045]
Here, in the above description with reference to FIG. 1, at the start of the growth of the single crystal, a gap Δt is provided between the cooler 112 and the cooling susceptor 114, and the heating temperature Tb of the lower end WB of the columnar work W decreases. The constant temperature gradient was always maintained by lowering the cooler 112 in synchronism with the above to reduce the gap Δt. However, the present invention is not limited to this, and a constant temperature gradient can be always maintained by lowering the temperature of the refrigerant supplied to the cooler 112 in synchronization with the lowering of the heating temperature of the lower end WB of the columnar work W. .
[0046]
If the temperature gradient cannot be constantly maintained, normal single crystal growth cannot be performed for the following reasons.
[0047]
For example, if the temperature of the lower end WB is changed while keeping the temperature of the upper end WT constant while keeping the cooling capacity of the cooler 112 constant, the temperature gradient naturally changes. In particular, when a long single crystal is manufactured, the change in the temperature gradient becomes large. In the present invention, a temperature gradient has a substantial meaning in a solvent existing zone where a raw material is dissolved and precipitated. Under the condition that the temperature Tt at the upper end WT = constant, the temperature Tb of the lower end WB is changed to the growth start temperature Tb. ₀ From the end of growth Tb ₁ Then, the temperature gradient formed based on the temperature difference of Tb-Tt monotonously decreases from the maximum value at the start of growth to the minimum value at the end of growth.
[0048]
In general, a single crystal has a different degree of supersaturation optimum for growth when its constituent materials are different. Therefore, under the condition where the temperature gradient gradually decreases as described above, in the case of a substance having a small degree of supersaturation due to a small temperature gradient at the end of growth as an optimal growth condition, a large supersaturation due to a large temperature gradient at the start of growth is not sufficient. It is too much, and heterogeneous nucleation is promoted to cause another crystallization. Conversely, in the case of a substance having a high degree of supersaturation at the start of growth as an optimal growth condition, the dissolution / precipitation cannot catch up with the lowering rate of the lower end temperature Tb which drops at a constant rate, so that the solvent lowering rate decreases. The solvent solidifies before reaching the lower end of the raw material rod (the lower end of the columnar work WB).
[0049]
Also, the seed crystal can be generated at the tip of a conical recess formed at the lower end of the support rod. In order to grow a large single crystal, a seed crystal serving as a nucleus for growth is required. However, depending on the substance, it may be difficult to obtain the seed crystal itself. In such a case, a conical counterbore is provided at the lower end of the support rod as described above, and nucleation is first generated at the tip, and then continuously deposited on this small nucleus to cover the entire cross section. Can be formed. At that time, in order to prevent polycrystallization due to heterogeneous nucleation, it is important that the conical counterbore provided at the lower end of the support rod be processed into a mirror surface, and that the tip be a shape that gradually changes as an R surface. .
[0050]
【Example】
[Example 1]
Using the temperature gradient furnaces 100 and 200 shown in FIGS. 1 and 2, production experiments of SiC single crystals were performed under various conditions. The temperature gradient furnace 200 in FIG. 2 has the same configuration as the temperature gradient furnace 100 in FIG. 1 except that a temperature-resistant material cylinder 202 for accommodating the columnar work W is provided in the furnace. Parts corresponding to those shown in FIG. 1 are denoted by the same reference numerals as those in FIG. The heat-insulating cylinder 104 constituting the body of the furnace has an inner diameter of 110 mm, and the heat-resistant material cylinder 202 has an inner diameter of 50 mm. As the material of the heat-resistant cylinder 202, two types of isotropic graphite sintered bodies and BN sintered bodies were used.
[0051]
The raw material rods 10 and the support rods 16 were cylindrical SiC sintered bodies (B added as a sintering aid, density 99.5% TD). In each case, the diameter was three types of φ12 mm, φ20 mm, and φ35 mm, and the length was 78 mm for the raw material rod and 20 mm for the support rod. High-purity silicon was used as the solvent 12, and processed into pellets having a diameter of 10 mm, 18 mm, and 32 mm and a thickness of 1.5 mm. The seed crystal 14 had the same diameter as the support rod 16, was processed into a disk shape having a thickness of 0.4 mm, and was attached to the lower end of the support rod 16 with a carbon adhesive.
[0052]
As an initial state, the temperature Tb of the lower end WB of the columnar work W was set to 1800 ° C., and the temperature Tt of the upper end WT was set to 1400 ° C. by the initial setting of Δt. The temperature gradient was always maintained at 4 ° C / mm. Further, the control of the upper end temperature Tt was performed in two forms, that is, when the temperature of the silicon oil of the refrigerant was kept constant and when the temperature was changed in synchronization with the drop of the lower end temperature Tb. The temperature lowering rate of the lower end temperature Tb was set at four levels of 1.6, 3.2, 6.0, and 10.0 ° C./h, and the temperature was lowered to 1780 ° C. Table 1 shows the manufacturing conditions and the obtained single crystal length. Under the conditions of this experiment, the upper limit of the single crystal growth length is 30 mm, which is the movement length limit of the solvent 12.
[0053]
[Table 1]

[0054]
Comparing the case with a growth rate of 0.4 mm / h, a high-quality SiC single crystal having a columnar workpiece diameter of φ12 mm and a length of 30 mm was obtained without the heat insulating cylinder (FIG. 1). Further, by using the heat insulating cylinder 202 made of graphite (FIG. 2), it was possible to grow a SiC single crystal having a length of 30 mm even with a columnar work diameter of 20 mm. Further, by using BN as the material of the heat insulating cylinder 202 (FIG. 2), a SiC single crystal having a growth length of 30 mm was obtained even with a columnar work diameter of 35 mm.
[0055]
Further, when the temperature of the refrigerant silicon oil in the cooler 112 is kept constant, the growth rate at which a growth length of 30 mm can be obtained with a φ35 mm columnar work diameter even when the BN heat insulating cylinder 202 is used is 1. It was up to 5 mm / h. On the other hand, when the temperature of the refrigerant silicon oil is changed in synchronization with the lower end temperature Tb, a high-quality SiC single crystal having a length of 30 mm can be obtained even when the growth rate is increased to 2.5 mm / h. Was done.
[0056]
[Example 2]
The SiC single crystal was grown using the temperature gradient furnaces 100, 200, and 300 shown in FIGS. The temperature gradient furnace 300 shown in FIG. 3 has a temperature gradient shown in FIG. 1 except that a closed container 204 made of a heat-resistant material for accommodating the columnar work W is provided in the furnace, and a solvent container 206 is disposed at the bottom of the furnace as a solvent supply source. It has the same configuration as the furnace 100. Parts corresponding to those shown in FIG. 1 are denoted by the same reference numerals as those in FIG. The closed container 204 was made of an isotropic graphite sintered body. An experiment was also performed on the temperature gradient furnace 300 shown in FIG. 3 when the solvent container 206 was not provided.
[0057]
Column work diameter φ12mm, solvent pellet diameter φ7mm x thickness t0.6mm, initial setting temperature of column work lower end WB 2100 ° C, cooling rate 0.4 ° C / h (growth rate 0.1mm / h), long-term operation , The growth length of the SiC single crystal until the solvent was volatilized and the growth was stopped was measured. Other conditions are the same as in Example 1. Table 2 shows the results. It can be seen that the longest operation is possible when the closed container 204 is used and the solvent container 206 is arranged.
[0058]
[Table 2]

[0059]
[Example 3]
In the same device configuration as in Example 1, the electrical resistivity between the lower end WB and the upper end WT of the columnar workpiece W during the SiC single crystal growth process was measured. FIG. 5 shows the results. The operating conditions are the conditions shown in Table 1, where the temperature drop rate is 10.0 ° C./h, the growth rate is 2.5 mm / h, the columnar work diameter (growth single crystal diameter) is φ35 mm, and the BN heat insulating cylinder is used. is there.
[0060]
In the case where the lower end WB and the upper end WT of the columnar work W are each a measurement end (FIG. 5A), the electric resistance value decreases linearly with the growth of the crystal, and the inflection point (arrow) during the growth is From the time point of view, it coincides with the start point of polycrystallization, and abnormal occurrence in the single crystal growth process is clearly detected. Also, when the upper and lower susceptors 114 and 110 are used as the measurement ends (FIG. 5A), the abnormal point is similarly detected clearly.
[0061]
Further, using a solid graphite rod having a diameter of φ35 mm and a length of L100 mm as a dummy work, the temperature distribution in the radial direction of the bottom end face of the work at each measurement point was measured. The measurement was performed by inserting a φ5 mm W-Re thermocouple into a measurement hole drilled 1 mm from the lower surface of the dummy work. FIG. 6 shows the results. It can be seen that the uniformity of the in-plane temperature distribution is secured by using the upper and lower susceptors as the measurement ends.
[0062]
[Example 4]
Using a temperature gradient furnace 400 shown in FIG. 4, a seed crystal was produced by depositing a SiC single crystal. The temperature gradient furnace 400 does not use the seed crystal 14 in the temperature gradient furnace 300 of FIG. 3, but instead has a conical counterbore recess 208 at the lower end of the support rod 16 and nucleates a single crystal from the tip of the recess. This is a configuration for growing a long single crystal using this as a seed crystal. As a result of performing the treatment under the conditions shown in Table 3, a high-quality SiC single crystal having a length of about 1 mm from the lower end of the support rod (7 mm from the tip of the conical counterbore) can be obtained. Crystals could be created.
[0063]
[Table 3]

[0064]
【The invention's effect】
According to the present invention, a temperature gradient furnace is used to form a desired temperature gradient suitable for growing a single crystal without requiring the movement of a heating source, and the temperature in a plane perpendicular to the growth direction. A method for producing a single crystal continuously with uniform distribution is provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one embodiment of a temperature gradient furnace used in the method of the present invention, and a graph illustrating a process.
FIG. 2 is a sectional view showing another embodiment of the temperature gradient furnace used in the method of the present invention.
FIG. 3 is a sectional view showing another embodiment of the temperature gradient furnace used in the method of the present invention.
FIG. 4 is a sectional view showing still another embodiment of the temperature gradient furnace used in the method of the present invention.
FIG. 5 is a graph showing the change over time in the electrical resistance of a columnar work measured by the method of the present invention.
FIG. 6 is a graph showing a radial temperature distribution at a columnar workpiece end and a susceptor end according to the method of the present invention.
[Explanation of symbols]
100, 200, 300, 400 ... temperature gradient furnace
104 ... body part
106 ... hollow part
108… Induction heating coil
110 ... Heating susceptor
112 ... cooler
114 ... Cooling susceptor
10. Raw material rod
12 ... Solvent
14 ... Seed crystal
16 ... Support rod
W… Work
WT: Work top end (cooling end)
WB: Work bottom surface (heating surface)

Claims (13)

A method for producing a single crystal by precipitation from a solution using a temperature gradient furnace that imparts a temperature gradient in the longitudinal direction to the columnar work, wherein, as the temperature gradient furnace, an insulating wall surrounding the outer periphery of the columnar work, A heating unit that heats the lower end of the columnar work through a heating susceptor, and a temperature gradient furnace including a cooling unit that cools the upper end of the columnar work through a cooling susceptor,
The raw material rod, the solvent, and the seed crystal supported on the lower end of the support rod are stacked in the furnace in order from the bottom to form the columnar work, and the lower end of the raw material rod is set as the lower end of the columnar work. By heating by the heating unit and cooling by the cooling unit using the upper end of the support rod as the upper end of the columnar work, a temperature gradient is formed in the columnar work so that the upper end surface is lower in temperature with respect to the lower end surface of the solvent. To form
A method for producing a single crystal using a temperature gradient furnace, wherein a single crystal is continuously grown downward from the seed crystal as a starting point by gradually decreasing a heating temperature of a lower end of the columnar work. The method of claim 1 wherein the solvent has a melting point lower than the melting point or decomposition / sublimation temperature of the single crystal source material. 3. The method according to claim 1, wherein the raw material rod is made of a dense sintered body of the single crystal raw material, and contains a dopant as a sintering aid. 4. The method according to claim 1, wherein the columnar workpiece is arranged in a cylinder made of a heat-resistant material. The method according to any one of claims 1 to 3, wherein the columnar work is arranged in a closed container made of a heat-resistant material. The method according to claim 4 or 5, wherein the heat-resistant material comprises one selected from the group consisting of graphite sintered body, alumina sintered body, zirconia sintered body and boron nitride sintered body. The method according to claim 5, wherein a solvent supply source is disposed in the closed container. The method according to any one of claims 1 to 7, wherein an electric resistance between an upper end and a lower end of the columnar work is measured, and a single crystal growth length is detected based on the measured value. . 9. The method according to claim 8, wherein an electrical resistance between an upper end of the cooling susceptor and a lower end of the heating susceptor is measured. 10. The method according to claim 1, wherein the temperature of the solvent is set just below the boiling point of the solvent. A gap is provided between the cooling unit and the cooling susceptor at the start of single crystal growth, and the gap is reduced by lowering the cooling unit in synchronization with a decrease in the heating temperature of the lower end of the columnar work. 11. The method according to claim 1, wherein the method comprises: The method according to any one of claims 1 to 11, wherein the temperature of the refrigerant supplied to the cooling unit is decreased in synchronization with a decrease in the heating temperature of the lower end of the columnar work. The method according to claim 1, wherein the seed crystal is formed at a point of a conical recess formed at a lower end of the support rod.

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