JP2011046587A - Method of manufacturing aln single crystal, and aln single crystal substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an AlN single crystal capable of suppressing quality deterioration due to sublimation of a SiC substrate, and a AlN single crystal substrate formed by the method of manufacturing. <P>SOLUTION: The method of manufacturing an AlN single crystal (a nitride single crystal film 1) comprises: a process of preparing a SiC substrate (a base substrate 9); a process of preparing a (SiC)<SB>1-x</SB>(AlN)<SB>x</SB>powder (a raw material mixed powder 5) by mixing a SiC powder and an AlN powder; and a process of forming the nitride single crystal film 1 on one main surface of the base substrate 9 using the raw material mixed powder 5. In addition, SiC may be contained in the AlN single crystal (the nitride single crystal film 1). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an AlN single crystal and an AlN single crystal substrate, and more particularly, a method for producing a high-quality AlN single crystal substrate and an AlN single crystal substrate formed by using the above method. It is about.

  With recent miniaturization and higher performance of semiconductor elements, there is a problem of an increase in the amount of heat generated when an electronic circuit including the semiconductor elements is used. In order to efficiently release heat generated in the circuit, it is preferable to use a substrate formed of a material having high thermal conductivity. If a substrate having a high thermal conductivity, such as a single crystal of AlN (aluminum nitride), is introduced into the electronic circuit, the heat inside the circuit can be efficiently radiated.

  As a technique for forming such an AlN single crystal substrate, the following method is known. For example, a technique for forming an AlN layer made of an AlN single crystal on one main surface of an SiC substrate using a sublimation method is disclosed in, for example, the following Evaluation of AlN single-crystal grown by sublimation method (Non-patent Document 1). Has been. Non-Patent Document 1 discloses a method of growing an AlN single crystal on one main surface of a SiC substrate by the following method. Specifically, an SiC substrate is disposed in the processing apparatus, and an AlN material is disposed at a position facing one main surface of the SiC substrate. In this state, the AlN raw material in the processing apparatus is heated to a high temperature of 1900 ° C. or higher and 2250 ° C. to sublimate the AlN raw material, and a layer made of an AlN single crystal on one main surface of the SiC substrate facing the AlN raw material. As deposited.

Michimasa Miyanaga et al., “Science Direct”, Journal of Crystal Growth 300, 2007, p. 45-49

  In Non-Patent Document 1, when heating the AlN raw material, the region where the SiC substrate is disposed may be set so as to maintain a temperature lower than the temperature of heating the AlN raw material by, for example, 100 ° C. or more and 500 ° C. Are listed. By heating the SiC substrate to a temperature lower than that of the AlN raw material in this way, it is considered that the SiC substrate is controlled so as not to be sublimated and damaged during the heating. However, in the sublimation method, the inside of the processing apparatus is filled with the sublimated AlN gas during the heating for forming the AlN layer. For this reason, the partial pressure of SiC falls among the pressure of the gas in the said processing apparatus. For this reason, even if the SiC substrate is controlled so as to maintain a temperature lower than that of the AlN raw material, a part of the SiC substrate easily sublimates during heating when forming the AlN layer. For this reason, a part of the SiC substrate may be missing, for example, through holes are formed by sublimation. As a result, it becomes difficult to grow the AlN layer on the main surface of the SiC substrate, and the quality of the AlN layer is deteriorated.

  The above is also described in Non-Patent Document 1. Specifically, since the lattice mismatch between the SiC substrate and the AlN layer formed on the main surface occurs when the SiC substrate is decomposed, the quality of the AlN layer formed on the SiC substrate is improved. Is disclosed to be difficult.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an AlN single crystal manufacturing method capable of suppressing deterioration in quality due to sublimation of an SiC substrate, and AlN formed using the manufacturing method. It is to provide a single crystal substrate.

An AlN single crystal manufacturing method according to an embodiment of the present invention includes a step of preparing a SiC substrate, and preparing a powder of (SiC) _1-x (AlN) _{x obtained} by mixing SiC powder and AlN powder. And a step of forming an AlN single crystal on one main surface of the SiC substrate using the (SiC) _1-x (AlN) _x powder.

(SiC) _1-x (AlN) _x powder (0 ≦ x ≦ 1) prepared by adding and mixing SiC raw material powder constituting the SiC substrate to AlN raw material powder for producing an AlN single crystal Then, an AlN single crystal (AlN layer) is formed on one main surface of the SiC substrate. Here, the main surface means a main surface having the largest area among the surfaces.

  In this way, even if a partial region of the SiC substrate is sublimated by heating to form a through-hole and is missing (deteriorated), the SiC substrate sublimated with SiC contained in the raw material powder A new SiC layer is formed so as to fill up the missing region after sublimation. This is based on the same principle as when the raw material AlN powder is sublimated by the sublimation method and formed as an AlN layer on one main surface of the SiC substrate.

  As described above, the AlN layer can be formed without degrading the SiC substrate. That is, a high quality AlN layer having a uniform thickness and composition can be formed.

As described above, the raw material powder is represented by the composition formula of (SiC) _1-x (AlN) _x . For this reason, the AlN single crystal (AlN layer) formed in the method for producing an AlN single crystal according to the present invention may contain SiC. That is, the AlN single crystal may be composed only of AlN, or may include SiC in AlN.

In the AlN single crystal manufacturing method described above, it is preferable that 0.70 ≦ x <0.90 in the (SiC) _1-x (AlN) _x powder. That is, it is preferable to prepare the powder so that the composition ratio of the raw material powder is (SiC) :( AlN) = 1−x: x, and 0.70 ≦ x <0.90.

  If the composition ratio of SiC and AlN in the raw material powder is within the above range, when the AlN layer is formed on one main surface of the SiC substrate using the sublimation method, the SiC substrate deteriorates and becomes a uniform AlN layer. It is possible to suppress the inhibition of growth.

In the AlN single crystal manufacturing method described above, it is preferable that the value of x of the (SiC) _1-x (AlN) _x powder is gradually increased in the step of forming the AlN single crystal.

When forming the AlN single crystal (AlN layer), it is preferable to use the raw material powder of (SiC) _1-x (AlN) _x as described above. However, it is preferable to change the value of x of (SiC) _1-x (AlN) _x with time so as to gradually increase in the process of forming the AlN layer. That is, in the initial stage of forming the AlN layer, the value of x is relatively small, and the value of x is increased as the process of growing the AlN layer proceeds. In this way, in the initial stage of growth of the AlN layer, it is possible to more reliably suppress the inhibition of uniform AlN layer growth due to the loss (degradation) of the SiC substrate. Further, by increasing the AlN ratio in the raw material powder as the AlN layer is formed to some extent and proceeding to the latter half, it is possible to control the AlN composition ratio in the formed AlN layer to be increased. Further, when the SiC substrate is unnecessary for the AlN single crystal substrate to be finally formed, the SiC substrate can be sublimated and disappeared by reducing the proportion of SiC in the raw material powder at the end of the process. For this reason, the process of removing a SiC substrate anew can be skipped. In this way, a high quality AlN single crystal (AlN single crystal substrate) can be formed.

An AlN single crystal manufacturing method according to another embodiment of the present invention includes a step of preparing a SiC substrate, and Si _{1-xy Cy} (AlN) obtained by mixing Si powder, C powder, and AlN powder. ) A step of preparing a powder of _x , and a step of forming an AlN single crystal on one main surface of the SiC substrate using the powder of the Si _{1-xy Cy} (AlN) _x .

  When forming the AlN single crystal, the powder mixed with the AlN raw material powder in order to suppress the sublimation and deterioration of the SiC substrate may be SiC powder, but Si powder and C powder May be a mixed powder. And as said composition formula shows, the composition ratio of the powder of Si and the powder of C may differ. Even in this case, even if a partial region of the SiC substrate is sublimated by heating to form a through-hole and is missing (deteriorated), the Si or C contained in the raw material powder is sublimated. A new SiC layer is formed so as to compensate for the sublimated and missing region of the substrate. Therefore, an AlN single crystal (AlN layer) can be formed without degrading the SiC substrate. That is, a high quality AlN layer having a uniform thickness and composition can be formed.

As described above, the raw material powder is represented by the composition formula of Si _{1-xy Cy} (AlN) _x . For this reason, the AlN single crystal (AlN layer) formed in the method for producing an AlN single crystal according to the present invention may contain SiC. That is, the AlN single crystal may be composed only of AlN, or may include SiC in AlN.

In the production method of the above-mentioned AlN single _crystal in a powder of _{Si 1-x-y C y} (AlN) x, it is preferable that 0.70 ≦ x <0.90,0.05 <y. That is, the raw material powder is prepared so that the composition ratio of the raw material powder is Si: C: AlN = (1-xy): y: x, and 0.70 ≦ x <0.90 and 0.05 <y. It is preferable to do.

  If the composition ratio of Si, C, and AlN in the raw material powder is within the above range, when the AlN layer is formed on one main surface of the SiC substrate using the sublimation method, the SiC substrate deteriorates and becomes uniform. The inhibition of the growth of the AlN layer can be suppressed.

In the AlN single crystal manufacturing method described above, Si _{1-xy Cy} (AlN) _x powder is formed in the step of forming the AlN layer, as in the case of manufacturing an AlN single crystal using SiC powder. It is preferable to gradually increase the value of x.

The AlN single crystal substrate formed by using the above AlN single crystal manufacturing method is represented by the composition formula of (SiC) _1-x (AlN) _x as described above. For this reason, for example, if the value of x is 1, an AlN single crystal substrate made of only AlN is obtained, but if x <1, an AlN single crystal substrate containing SiC and AlN is obtained.

The above-described AlN single crystal substrate represents the composition of the AlN single crystal substrate from one main surface toward the other main surface opposite to the one main surface (SiC) _1-x (AlN) _x x Preferably the value is decreasing. That is, in the AlN single crystal substrate described above, it is preferable that the value of x is relatively smaller in the region on the other main surface side than on the region on one main surface side. In other words, it is preferable that the above-described AlN single crystal substrate has a large value of x on one main surface side, that is, the ratio of AlN is large. A region where the value of x is large, that is, the proportion of AlN is large, such as the one main surface side of the AlN single crystal substrate, can exhibit the function as an AlN substrate with higher performance. The value of x on one main surface of the AlN single crystal substrate is preferably 0.90 or more and 1 or less. In this way, the AlN single crystal substrate can exhibit the function as an AlN substrate with higher performance.

  According to the method for producing an AlN single crystal of the present invention, a high-quality and large-diameter AlN single crystal can be stably obtained with good reproducibility.

It is a flowchart for demonstrating the manufacturing method of the AlN single crystal which concerns on Embodiment 1 of this invention. It is the schematic which shows the crystal structure of a hexagonal system. It is a schematic sectional drawing which shows the cross section of the furnace which forms an AlN single crystal using the manufacturing method of the AlN single crystal which concerns on embodiment of this invention. It is an enlarged view which shows the state of the raw material powder in the base substrate of FIG. 3 in Embodiment 2 of this invention, and a crucible. It is the schematic which shows the structure of the AlN single crystal formed in embodiment of this invention. It is a flowchart for demonstrating the manufacturing method of the AlN single crystal which concerns on Embodiment 4 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
As shown in FIG. 1, the AlN single crystal manufacturing method according to the first embodiment of the present invention includes a step of preparing an SiC substrate (S10), and a mixture of SiC powder and AlN powder (SiC) _1. A step of preparing a powder of _-x (AlN) _x (S20), and a step of forming an AlN layer on one main surface of the SiC substrate using the powder of (SiC) _1-x (AlN) _x (S30) ). Hereinafter, each process will be described in detail.

  The step of preparing the SiC substrate (S10) is a step of preparing a substrate used as a base for growing a nitride single crystal such as AlN. As shown in FIG. 2, a nitride single crystal such as AlN has a hexagonal crystal structure (hexagonal crystal structure 10). Therefore, the substrate used as a base for growing the nitride single crystal is also preferably a substrate made of a material having a hexagonal crystal structure.

  The substrate prepared here may be a free-standing crystal substrate or a crystal layer formed on another substrate. A free-standing crystal substrate has better crystallinity and less warpage than a crystal layer formed on another substrate. For this reason, if a self-standing crystal substrate is used, an AlN single crystal with good crystallinity can be grown. In general, however, a free-standing crystal substrate is expensive. However, for example, a SiC substrate is relatively inexpensive and it is relatively easy to obtain a large-diameter substrate. From this point of view, as described above, it is preferable to use a base substrate made of a SiC free-standing crystal as the base substrate.

Next, a step (S20) of preparing a powder of (SiC) _1-x (AlN) _x is performed. Here, as described above, when an AlN single crystal is grown on a SiC substrate, a powder in which SiC powder and AlN powder are mixed is prepared. The mixed powder is represented by chemical formula (SiC) _1-x (AlN) _x , and 1-x and x represent respective composition ratios (ratio of the number of moles). Therefore, it can be generally expressed as 0 ≦ x ≦ 1.

  Here, in order to form an AlN single crystal substrate, it is preferable to use AlN powder as a raw material. However, when AlN is grown on a SiC substrate by a sublimation method using a powder made of only AlN as a raw material, AlN as a raw material powder is sublimated, and SiC of the SiC substrate also sublimes and generates a through hole. Problems may occur. Therefore, when growing an AlN single crystal on a SiC substrate, SiC powder constituting the SiC substrate is mixed with AlN powder as a raw material. In this way, even if a part of the SiC substrate undergoes sublimation and deteriorates when the AlN powder is heated and sublimated, the raw material SiC causes sublimation. This sublimated SiC compensates for the region of the SiC substrate that is missing due to sublimation according to the same principle as that of sublimating AlN powder to form an AlN single crystal.

  In order to replenish the missing region of the SiC substrate as described above, it is preferable to mix not only AlN but also SiC in the raw material powder. In order to sufficiently replenish the region of the SiC substrate that has been lost due to sublimation, the SiC powder preferably has a mole number exceeding 10% with respect to the entire mixed powder of SiC and AlN. Therefore, since 1-x> 0.10 is preferable, x <0.90 is preferable.

An AlN single crystal (AlN layer) is formed using (SiC) _1-x (AlN) _x powder in which SiC powder and AlN powder are thus mixed. For this reason, the formed AlN single crystal may contain SiC as well as AlN. However, even if it is contained in an AlN single crystal in which a small amount of SiC powder is formed, there is no particular problem in terms of the function of the AlN single crystal substrate. Therefore, SiC may be contained in the AlN single crystal. However, if the proportion of the SiC powder in the mixed powder becomes too high, the proportion of SiC contained in the formed AlN single crystal increases. Then, there is a possibility that a single crystal substrate having a property different from that of the AlN single crystal to be formed is formed. Therefore, in order to increase the composition ratio of AlN contained in the formed single crystal substrate, it is preferable that 1−x ≦ 0.30, and therefore 0.70 ≦ x is preferable. As mentioned above, it is preferable that the powder of (SiC) _1-x (AlN) _x prepared in a process (S20) is 0.70 <= x <0.90.

A step (S30) of forming an AlN layer on one main surface of the SiC substrate using the mixed powder thus prepared is performed. Here, the AlN layer is preferably formed using a sublimation method. Here, the sublimation method refers to FIG. 3 and sublimates an AlN raw material (mixed raw material powder 5) such as an AlN powder which is a nitride single crystal (AlN single crystal) to be formed, and then solidifies again. A method of obtaining an AlN single crystal (nitride single crystal film 1). In crystal growth by the sublimation method, for example, a high-frequency heating type vertical sublimation furnace 20 as shown in FIG. 3 is used. A silicon nitride (BN) crucible 23 having an exhaust port 23 c is provided at the center of the reaction vessel 21 in the vertical sublimation furnace 20, and air is passed around the crucible 23 from the inside of the crucible 23 to the outside. A heating element 25 is provided to ensure. In addition, a high-frequency heating coil 27 for heating the heating body 25 is provided in the outer central portion of the reaction vessel 21. Further, at the end of the reaction vessel 21, there are N ₂ gas introduction port 21 a and N ₂ gas introduction port 21 c for flowing N ₂ gas outside the crucible 23 of the reaction vessel 21, and the temperatures of the lower and upper surfaces of the crucible 23. A radiation thermometer 29 is provided for measuring.

Referring to FIG. 3, nitride single crystal film 1 used in the present embodiment can be formed as follows, for example, using vertical sublimation furnace 20 described above. When the nitride single crystal film 1 to be formed is an AlN single crystal and the base substrate 9 is a SiC substrate, the above-described SiC powder and AlN powder are mixed in the lower part of the crucible 23 (SiC) _{1- x} (AlN) The mixed raw material powder 5 such as _x is accommodated, and the heating body 25 is heated using the high-frequency heating coil 27 while flowing N ₂ gas into the reaction vessel 21. In this way, the temperature in the crucible 23 is raised, and the temperature on the crucible 23 side is kept higher than the temperature of the other portions, thereby sublimating AlN. In this way, AlN is solidified again by cooling at the upper part of the crucible 23, so that an AlN single crystal can be formed as the nitride single crystal film 1. Here, an AlN single crystal can be formed on the base substrate 9 by disposing the base substrate 9 (for example, SiC substrate) for forming the AlN single crystal on the crucible 23. In FIG. 3, the crucible 23 is disposed on the lower side and the base substrate 9 is disposed on the crucible 23. However, conversely, a face-up structure in which the crucible 23 is arranged on the upper side and the base substrate 9 is arranged in the lower part may be adopted.

Here, during the growth of the AlN single crystal, the temperature on the mixed raw material powder 5 side (AlN raw material side) of the crucible 23 is about 1800 ° C. to 2200 ° C., and the temperature of the base substrate 9 on the upper side of the crucible 23 is set on the AlN raw material side. The temperature is lowered by about 1 to 100 ° C. In this way, an AlN single crystal with good crystallinity that cannot be obtained by other growth methods can be obtained even when growing on the SiC substrate, which is a different type of base substrate 9 from the nitride single crystal film 1 to be formed. can get. Further, during the crystal growth, N ₂ gas continues to flow outside the crucible 23 in the reaction vessel 21 so that the gas partial pressure is about 101.3 hPa to 1013 hPa, thereby reducing the contamination of impurities into the AlN single crystal. can do.

  Even if the temperature of the base substrate 9 on the upper part of the crucible 23 is set to be about 1 ° C. to 100 ° C. lower than the temperature on the AlN source side as described above, the base substrate 9 made of SiC in the process of sublimating the AlN source is also used. Sublimate. As a result, a lack of a through hole or the like occurs in a partial region of the base substrate 9. However, the mixed raw material powder 5 contains not only the AlN raw material but also the SiC raw material (SiC powder). For this reason, the SiC powder of the mixed raw material powder 5 is sublimated, and is solidified again by cooling SiC at the upper part of the crucible 23 (in the vicinity of the region where the base substrate 9 is missing). For this reason, the missing part of the base substrate 9 is compensated and repaired by the cooling and solidification of the sublimated SiC raw material of the mixed raw material powder 5. In this way, the base substrate 9 can always be maintained in a state free from the lack of through-holes or the like by the SiC raw material contained in the mixed raw material powder 5. As a result, a high-quality AlN single crystal (nitride single crystal film 1) having a uniform thickness and composition can be formed by the above method. If a missing portion such as a through hole is present in a part of the main surface of the base substrate 9 on which the AlN single crystal grows, it is difficult to grow the AlN single crystal on the missing region. That is, in this case, it is difficult to form a high quality AlN single crystal uniformly over almost the entire main surface of the base substrate 9. Therefore, in order to form a high-quality AlN single crystal (nitride single crystal film 1) having a uniform thickness and composition, it is preferable to always keep the base substrate 9 in a state where there are no through holes or the like.

Here, the value of x of the powder of (SiC) _1-x (AlN) _x prepared in the step (S20) is adjusted to be a relatively large value within a range of 0.70 ≦ x <0.90, for example. Think about the case. At this time, an AlN single crystal (nitride single crystal film 1) is formed on the base substrate 9 while suppressing deterioration of the base substrate 9 by the SiC raw material of the mixed raw material powder 5 in the step (S30). However, in this case, the formed AlN single crystal (nitride single crystal film 1) contains SiC crystals formed by sublimation and solidification of SiC again. Therefore, the nitride single crystal film 1 formed by the above method has a crystal composition of (SiC) _1-x (AlN) _x .

  However, from the above chemical formula, it can be said that the number of moles of Si and C and the number of moles of Al and N are equal in the crystal in the nitride single crystal film 1. In this case, particularly when the value of x is large and the composition of the nitride single crystal film 1 is close to that of AlN, Al is present at a position where Si in the crystal of the nitride single crystal film 1 is to be disposed. A phenomenon occurs in which N is substituted and arranged at a position where C is to be arranged. Therefore, the composition of crystals in the nitride single crystal film 1 can be made very close to that of pure AlN. That is, a high quality AlN single crystal substrate having a composition very close to that of pure AlN can be formed.

If it is desired to form a desired substrate having excellent thermal conductivity as an AlN single crystal, for example, in (SiC) _1-x (AlN) _x which is the composition formula of the formed AlN single crystal substrate, x is It is preferably 0.90 or more and 1 or less.

  During the temperature increase inside the crucible 23, it is preferable that the temperature of the other part is higher than the temperature of the crucible 23 on the AlN raw material side. In this way, impurities inside the crucible 23 can be removed through the exhaust port 23c, and contamination of impurities into the AlN single crystal can be reduced.

By the sublimation method, an AlN single crystal with good crystallinity having a dislocation density of 1 × 10 ⁶ cm ⁻² or less is obtained. Note that by optimizing the conditions of the sublimation method, the dislocation density of the AlN single crystal can be reduced to about 1 × 10 ³ cm ⁻² to 1 × 10 ⁵ cm ⁻² .

  As described above, according to the sublimation method, an AlN single crystal with good crystallinity can be obtained regardless of the presence or absence of the base substrate 9. From the viewpoint of obtaining a large-diameter AlN single crystal, it is preferable to grow the AlN single crystal on the base substrate.

(Embodiment 2)
The AlN single crystal manufacturing method according to the second embodiment of the present invention has the same configuration and conditions as the manufacturing method according to the first embodiment described above. However, in the second embodiment, in the step of forming the AlN layer (S30), the composition (SiC) _1-x (AlN) _x of the mixed raw material powder 5 is changed over time. Specifically, the value of x is changed as the process (S30) proceeds.

  In the step (S30), in the initial stage of the treatment (when the AlN single crystal starts to be formed), it is particularly preferable to suppress the deterioration of the base substrate 9 due to sublimation. If the base substrate 9 is deteriorated by a through-hole or the like, it is difficult to grow an AlN single crystal on a region where a hole on one main surface of the base substrate 9 is formed, for example. For this reason, if there is a missing region in the base substrate 9 at the initial stage of processing, it becomes difficult to form a uniform and high-quality AlN single crystal. As a result, the formed AlN single crystal may be non-uniform throughout, or may be accompanied by a missing region, and the quality may be degraded.

For this reason, in the initial stage of the process (S30), it is preferable that the composition (SiC) _1-x (AlN) _x of the mixed raw material powder 5 has a relatively small value of x. That is, it is preferable that the ratio of SiC is relatively large. In this way, it is possible to more reliably suppress deterioration of the base substrate 9 at the initial stage of processing.

In particular, if the value of _x in (SiC) _1-x (AlN) _x of the mixed raw material powder 5 is increased, the SiC raw material in the mixed raw material powder 5 is consumed as the process (S30) proceeds, If the SiC raw material disappears, the sublimation of the base substrate 9 (SiC) proceeds and defects in the base substrate 9 occur. However, if the desired AlN single crystal (nitride single crystal film 1) is completely formed, there is no problem even if the base substrate 9 disappears by sublimation. Rather, at the stage where the AlN single crystal is completely formed on the base substrate 9, it is more preferable that the base substrate 9 has completely disappeared. This is because if the underlying substrate 9 remains partially or entirely, it may be necessary to separately perform a process of extracting only the portion of the nitride single crystal film 1 made of AlN single crystal.

From the above, it is preferable that the composition (SiC) _1-x (AlN) _x of the mixed raw material powder 5 has a relatively large value of x particularly in the later stage of the process (S30). That is, it is preferable that the ratio of AlN is relatively large. In this way, the base substrate 9 can be eliminated by sublimation at a later stage of the process.

Further, as described above, the ratio of AlN in nitride single crystal film 1 formed in the later stage of the process (S30) can be increased. Therefore, as described above, for example, it is possible to promote a phenomenon in which Al is arranged in a place where Si is to be arranged in nitride single crystal film 1 and N is arranged in a place where C is arranged. Therefore, the finally formed nitride single crystal film 1 (AlN single crystal substrate) can have a composition close to that of pure AlN more reliably. As described above, even if a small amount of SiC powder is included in the AlN single crystal, there is no particular problem in terms of the function of the AlN single crystal substrate. However, it is more preferable that the finally formed AlN single crystal substrate has a composition close to that of pure AlN. For this reason, in the step of forming the AlN layer, it is more preferable to gradually increase the value of _{x in} the powder of (SiC) _1-x (AlN) _x .

As described above, it is preferable that the composition (SiC) _1-x (AlN) _x of the mixed raw material powder 5 has a relatively small value of x at the initial stage of the process (S30). It is preferable that the value of x is relatively large. For this reason, in Embodiment 2, the value of x in the composition formula of the mixed raw material powder is changed in the process (S30).

  For this purpose, for example, as shown in FIG. 4, it is preferable to arrange the mixed raw material powder 5 arranged in the crucible 23 so as to have a different composition for each region. Specifically, the upper mixed powder 5 a far from the inner wall surface (bottom surface) of the crucible 23 and close to the base substrate 9 is arranged so that the value of x is larger than the lower mixed powder 5 b near the inner wall surface of the crucible 23. It is preferable to do. In addition, it is more preferable to arrange so that the value of x monotonously increases from 0 to 1 from the lower end portion to the upper end portion of the mixed raw material powder 5 shown in FIG.

  In the step (S30), the mixed raw material powder 5 sublimes faster because the lower part (lower mixed powder 5b side) near the wall surface of the crucible 23 is heated faster than the upper part (upper mixed powder 5a side). Therefore, the lower mixed powder 5b is used to form an AlN single crystal or repair the SiC substrate at the initial stage of the step (S30). That is, the upper mixed powder 5a is used for forming an AlN single crystal or repairing the SiC substrate in the later stage of the step (S30).

  For this reason, as mentioned above, it can be said that the lower mixed powder 5b preferably has a smaller value of x than the upper mixed powder 5a and the SiC ratio is relatively large. In this way, the quality deterioration of the AlN single crystal formed due to the deterioration of the base substrate 9 is more reliably suppressed, and a high-quality and large-diameter AlN single crystal (AlN single crystal substrate) can be stably reproduced with high reproducibility. Can be formed. For example, even when it is desired to remove the SiC base substrate 9, the base substrate 9 is removed by controlling the SiC base substrate 9 to completely disappear when the formation of the AlN single crystal substrate is completed. The subsequent process can be omitted.

  As described above, the composition ratio of the mixed raw material powder 5 may be controlled so that the base substrate 9 is completely extinguished just when the formation of the AlN single crystal substrate is completed.

Also, as described above, instead of changing the composition in the mixed raw material powder 5, a plurality of types of mixed raw material powders 5 are prepared so that, for example, the composition ratio of (SiC) _1-x (AlN) _x is different. A method may be used. Specifically, for example, in step (S20), a total of five types of mixed raw material powders 5 in which _x of (SiC) _1-x (AlN) _x is 0, 0.25, 0.5, 0.75, ₁ Prepare. In carrying out the step (S30), first, processing is performed using the mixed raw material powder 5 in which x is 0, and then processing is performed using the mixed raw material powder 5 in which x is 0.25. Thereafter, the processing is carried out by putting them into the crucible 23 of the sublimation furnace 20 in the order of increasing x.

  If it does in this way, the effect similar to the case where it processes by providing the area | region of said upper mixed powder 5a and lower mixed powder 5b can be acquired. However, if a method of preparing a plurality of kinds of mixed raw material powders 5 is used, it is difficult to continuously change the value of x. Further, every time the mixed raw material powder 5 having a different value of x is changed, the inside of the crucible 23 needs to be released from vacuum and the work of replacing the raw material needs to be performed.

FIG. 5 shows an AlN single crystal substrate as the nitride single crystal film 1 of FIG. 4 formed by the manufacturing method described above. Here, it is assumed that upper main surface 1a in FIG. 5 is a main surface on the upper side (side closer to base substrate 9) of nitride single crystal film 1 in FIG. 4, and lower main surface 1b in FIG. Is assumed to be the main surface on the lower side (the side far from the base substrate 9) of the nitride single crystal film 1 in FIG. That is, the main surface 1a side is the nitride single crystal film 1 formed in the initial stage of the process (S30), and the main surface 1b side is the nitride single crystal film formed in the late stage of the process (S30). 1. The AlN single crystal substrate represents the composition of the AlN single crystal substrate from one main surface (main surface 1b) to the other main surface (main surface 1a). (SiC) _1-x (AlN) _x Preferably the value is decreasing. That is, it is preferable that the concentration of AlN in the AlN single crystal substrate is inclined with respect to the direction intersecting the main surfaces 1a and 1b. In particular, x is preferably 0.90 or more and 1 or less in the main surface 1b formed at a later stage of the process (S30) and having a high concentration of AlN.

  It is more preferable that the concentration of AlN in the AlN single crystal substrate monotonously decreases in the direction from main surface 1b toward main surface 1a. However, in some regions in the AlN single crystal substrate, there may be a region where the concentration of AlN increases in the direction from main surface 1b to main surface 1a, for example.

  The second embodiment of the present invention is different from the first embodiment of the present invention only in each point described above. That is, the configuration, conditions, procedures, effects, and the like that have not been described above for the second embodiment of the present invention are all in accordance with the first embodiment of the present invention.

(Embodiment 3)
The method for producing an AlN single crystal according to the third embodiment of the present invention has substantially the same configuration and conditions as the production method according to the first or second embodiment described above. However, for example, the material constituting the base substrate 9 is not necessarily SiC, and for example, ZnO may be used. The nitride single crystal film 1 to be formed is not necessarily AlN, and may be GaN, for example. Even when these materials are used, a high-quality nitride single crystal substrate (GaN single crystal substrate) can be formed using a method similar to the manufacturing method according to the first or second embodiment described above.

  GaN and ZnO are materials having the hexagonal crystal shown in FIG. 2, like AlN and SiC. ZnO has a property of sublimating at a temperature close to SiC, and GaN has a property of sublimating at a temperature close to AlN. For this reason, even if SiC of base substrate 9 in Embodiment 1 or 2 is replaced with ZnO and AlN of nitride single crystal film 1 is replaced with GaN, it is substantially the same as Embodiment 1 or 2 of the present invention described above. Become.

  The third embodiment of the present invention is different from the first or second embodiment of the present invention only in the points described above. That is, the configuration, conditions, procedures, effects, and the like that have not been described above for the third embodiment of the present invention are all in accordance with the first or second embodiment of the present invention.

(Embodiment 4)
The AlN single crystal manufacturing method according to the fourth embodiment of the present invention has the same configuration and conditions as the manufacturing method according to the first or second embodiment described above. However, in this embodiment, the procedure shown in the flowchart of FIG. 6 is followed. Specifically, in the step (S20) shown in FIG. 1, instead of preparing a powder of (SiC) _1-x (AlN) _x, a powder of Si _{1-xy Cy} (AlN) _x is prepared. . That is, as the mixed raw material powder 5 in FIG. 3, an AlN single crystal is grown using Si _{1-xy Cy} (AlN) _x powder obtained by mixing Si powder, C powder, and AlN powder. 1-xy, y, and x show each composition ratio (ratio of the number of moles). Therefore, it can be generally expressed as 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1.

  Similar to the first and second embodiments, it is preferable to mix not only AlN but also Si and C in the raw material powder in order to replenish the missing region of the SiC substrate. Even when Si powder and C powder are used as the raw material powder, the same effects as when the SiC powder is used as the raw material powder are obtained.

As the composition formula Si _1-xy C _y (AlN) _{x of the} mixed raw material powder 5 indicates, the composition ratio of the Si powder and the C powder may be different. However, the composition ratio of AlN with respect to the entire mixed raw material powder 5 is preferably 0.70 ≦ x <0.90 as in the mixed raw material powder 5 of the first and second embodiments.

  In addition, when the ratio of y indicating the ratio of the C powder is very small, it is difficult to supplement the missing region of the SiC substrate with SiC. For this reason, it is preferable that 0.05 <y. From this and 0.70 ≦ x <0.90, and 1-xy, which is the Si composition ratio, is preferably 0.05 <(1-xy). .05 <y <0.25 is preferred.

Using the mixed raw material powder 5 described above, a step (S30) of forming an AlN layer on one main surface of the SiC substrate is performed in the same manner as in the first and second embodiments. The AlN single crystal (nitride single crystal film 1) formed at this time contains SiC crystals formed by sublimation and solidification of SiC again. Therefore, the nitride single crystal film 1 formed by the above method has a crystal composition of (SiC) _1-x (AlN) _x .

In the present embodiment, as in the second embodiment, the composition (SiC) _1-x (AlN) _x of the mixed raw material powder 5 may be changed over time in the step of forming the AlN layer (S30). . Specifically, in the initial stage of the process (S30), the composition Si _{1-xy Cy} (AlN) _x of the mixed raw material powder 5 preferably has a relatively small value of x. That it is preferable that the ratio of the _{Si 1-x-y} and _{C y} is relatively large. In this way, it is possible to more reliably suppress deterioration of the base substrate 9 at the initial stage of processing. In the late stage of the processing of step (S30), in particular a composition _{Si 1-x-y C y} (AlN) x of the mixed raw material powder 5 is preferably the value of x is relatively large. That is, it is preferable that the ratio of AlN is relatively large. In this way, the base substrate 9 can be eliminated by sublimation at a later stage of the process.

  Also in the present embodiment, as in the third embodiment, for example, the material constituting the base substrate 9 is not necessarily SiC, and for example, ZnO may be used. The nitride single crystal film 1 to be formed is not necessarily AlN, and may be GaN, for example.

  The fourth embodiment of the present invention is different from the first embodiment of the present invention only in each point described above. That is, in the fourth embodiment of the present invention, all the configurations, conditions, procedures, effects, and the like not described above are in accordance with the first embodiment of the present invention.

  In accordance with Embodiment 1 of the present invention described above, an experiment for growing nitride single crystal film 1 (AlN single crystal) was conducted. First, in the step of preparing an SiC substrate shown in the flowchart of FIG. 1 (S10), a total of five 4H—SiC substrates having a hexagonal crystal structure 10 (see FIG. 2) were prepared. These 4H—SiC substrates are used as the base substrate 9 in FIG. 3 and have a main surface of 2 inches in diameter.

Next, in the step of preparing (SiC) _1-x (AlN) _x powder in FIG. 1 (S20), five types of mixed raw material powders 5 shown in FIG. 3 having different values of x were prepared. Specifically, “AlN” where x = 1 in the composition formula (SiC) _1-x (AlN) _x , “(SiC) _0.05 (AlN) _0.95 ” where x = _0.95 , x = “(SiC) _0.10 (AlN) _0.90 ” which is _0.90 , “(SiC) _0.15 (AlN) _0.85 ” which is x = _0.85, “x = 0.70” (SiC) _0.30 (AlN) _0.70 ", which are five kinds of mixed raw material powders 5 having different compositions. Each of the mixed raw material powders 5 was subjected to a sintering process after the powders were mixed.

Subsequently, in the step of forming the AlN layer (S30), using the sublimation furnace 20 shown in FIG. 3, the base substrate 9 (the main surface having a diameter of 2 inches in diameter) prepared in the step (S10) is placed on the upper side of the crucible 23. A circular 4H—SiC substrate) was set. Further, any one of the five mixed raw material powders 5 prepared in the step (S20) was set on the lower side of the crucible 23 facing one main surface of the base substrate 9. Then, using the N ₂ gas introduction port 21 a and the N ₂ gas introduction port 21 c, N ₂ gas was allowed to flow outside the crucible 23 of the reaction vessel 21 to adjust the gas partial pressure outside the crucible 23.

In this state, the temperature on the mixed raw material powder 5 side inside the crucible 23 was heated to 2300 ° C., and the temperature on the base substrate 9 side inside the crucible 23 was heated to 2200 ° C. In this way, the mixed raw material powder 5 is sublimated, and a nitride single having the composition formula (SiC) _1-x (AlN) _x is formed on one main surface (lower side in FIG. 3) of the base substrate 9 by sublimation. Crystal film 1 (AlN single crystal substrate) was formed. As described above, since a total of five base substrates 9 are prepared, one AlN single crystal substrate is formed for each type of mixed raw material powder 5. In forming any single crystal substrate, the mass of the mixed raw material powder 5 used was adjusted to be substantially equal. Further, the heating time (the time during which the temperature was kept) was controlled so that the thickness of the formed nitride single crystal film 1 in the vertical direction in FIG. 3 was about 5 mm. When the nitride single crystal film 1 having a thickness of about 5 mm was formed, the AlN single crystal substrate formed after heating was lifted.

  According to the above procedure, one AlN single crystal substrate of each composition was formed, and the ratio of the area where the base substrate 9 in each sublimated and deteriorated (disappeared) was measured. Specifically, the ratio of the area having a region missing by sublimation in the thickness direction in the thickness direction in the area of the main surface of the base substrate 9 was evaluated by observing with an optical microscope. Table 1 below shows the ratio (%) of the deterioration area of the base substrate 9 of the formed AlN single crystal substrate to the composition of the mixed raw material powder 5 on which each AlN single crystal substrate was formed.

  In Table 1, “mixed raw material powder 5” indicates the type (composition formula) of the mixed raw material powder 5 used to form each AlN single crystal substrate. Further, “SiC substrate degradation area (%)” indicates the ratio of the area in which the base substrate 9 has a region missing due to sublimation even in the thickness direction after the formation of the AlN single crystal substrate as described above.

From Table 1, when the mixed raw material powder 5 is AlN, that is, a powder not containing SiC is used as the raw material, the base substrate 9 made of SiC is 100%, that is, completely disappeared when the AlN single crystal is formed to 5 mm. . However, as the proportion of SiC contained in the mixed raw material powder 5 increases, the proportion of the area where the SiC substrate (underlying substrate 9) deteriorates decreases. And about the AlN single crystal substrate formed using the mixed raw material powder 5 in which x = 0.85 or x = 0.70 in (SiC) _1-x (AlN) _x , when the AlN single crystal is formed 5 mm Also, the base substrate 9 made of SiC was not deteriorated at all. This is because even if SiC in the base substrate 9 is missing in a part of the region due to sublimation, the sublimated SiC in the mixed raw material powder 5 is supplied to the lacked region of the base substrate 9 and is cooled and solidified. It is thought that it was compensated by. Accordingly, since the AlN single crystal can be grown while maintaining the state in which the underlying SiC is uniformly formed on almost the entire surface in the direction along the main surface, the growing AlN single crystal substrate can be made uniform and high quality. Can be.

  From the above results of this example, when growing an AlN single crystal on one main surface of an SiC substrate, not only AlN powder but also SiC powder forming an underlying substrate was mixed as a raw material powder. It can be said that it is preferable to use a sintered material.

  In accordance with the fourth embodiment of the present invention described above, an experiment for growing the nitride single crystal film 1 (AlN single crystal) was conducted. First, in the step of preparing the SiC substrate shown in the flowchart of FIG. 6 (S10), a total of seven 4H—SiC substrates having the hexagonal crystal structure 10 (see FIG. 2) were prepared. These 4H—SiC substrates are used as the base substrate 9 in FIG. 3 and have a main surface of 2 inches in diameter.

Next, in the step of preparing the powder of Si _{1-xy Cy} (AlN) _x in FIG. 6 (S20), seven kinds of mixed raw material powders 5 shown in FIG. 3 having different values of x and y were prepared. . The specific composition formula _{Si 1-x-y C y} (AlN) x of x = 0.95, a y = 0.025 _{"Si 0.025} C _{0.025 (AlN) 0.95",} x = 0.85, y = 0.025 “Si _0.125 C _0.025 (AlN) _0.85 ”, x = 0.90, y = 0.05 “Si _0.05 C _{0. 05} (AlN) _0.90 ”, x = 0.80, y = 0.05“ Si _0.15 C _0.05 (AlN) _0.80 ”, x = 0.85, y = 0.075 “Si _0.075 C _0.075 (AlN) _0.85 ”, x = 0.75, y = 0.175 “Si _0.075 C _0.175 (AlN) _0.75 ”, x = 0.70, a y = 0.075 in the _{"Si 0.175} C _{0.075 (AlN) 0.70",} the composition is different That 7 is a mixed raw material powder 5 type. Each of the mixed raw material powders 5 was subjected to a sintering process after the powders were mixed.

Subsequently, in the step of forming the AlN layer (S30), similarly to Example 1, the mixed raw material powder 5 is sublimated using the sublimation furnace 20 shown in FIG. 3, and one of the base substrates 9 (FIG. 3) is sublimated by the sublimation method. A nitride single crystal film 1 (AlN single crystal substrate) whose composition formula is (SiC) _1-x (AlN) _x was formed on the main surface on the lower side in FIG. As described above, since a total of seven base substrates 9 are prepared, one AlN single crystal substrate is formed for each type of mixed raw material powder 5.

  One AlN single crystal substrate of each composition was formed one by one, and the ratio of the area where the base substrate 9 sublimated and deteriorated (disappeared) was measured in the same manner as in Example 1. Table 2 below shows the ratio (%) of the deterioration area of the base substrate 9 of the formed AlN single crystal substrate to the composition of the mixed raw material powder 5 on which each AlN single crystal substrate was formed. Each item shown in Table 2 is the same as Table 1.

From Table 2, when the mixed raw material powder 5 is Si _0.025 C _0.025 (AlN) _0.95 or Si _0.125 C _0.025 (AlN) _0.85 , an AlN single crystal is formed to 5 mm. At this point, it can be seen that the base substrate 9 made of SiC has deteriorated by an area of 70%. On the other hand, when the mixed raw material powder 5 is Si _0.05 C _0.05 (AlN) _0.90 or Si _0.15 C _0.05 (AlN) _0.80 , the AlN single crystal is 5 mm. At the time of formation, the base substrate 9 made of SiC has deteriorated by an area of 30%. Further, the mixed raw material powder 5 is Si _0.075 C _0.075 (AlN) _0.85 , Si _0.075 C _0.175 (AlN) _0.75 , Si _0.175 C _0.075 (AlN) _{0. In} the case of ₇₀ , the base substrate 9 made of SiC was not deteriorated at all.

From the results of Table 2, in order to suppress the deterioration of the base substrate 9 during the formation of the AlN single crystal and to make the formed AlN single crystal of high quality, the composition formula Si _{1-x of the} mixed raw material powder 5 is obtained. for x and y in _-y C _{y (AlN) x,} it can be said that it is preferable that 0.70 ≦ x <0.90,0.05 <y.

  From the above results of the present example, when growing an AlN single crystal on one main surface of an SiC substrate, not only a raw material powder obtained by mixing SiC powder with AlN powder, but also Si powder It can be seen that mixed raw material powders having different composition ratios of C and C may be used.

  Each embodiment and each example disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is particularly excellent as a technique for producing a high-quality AlN single crystal substrate.

1 Nitride single crystal film, 1a, 1b main surface, 5 mixed raw material powder, 5a upper mixed powder, 5b lower mixed powder, 9 base substrate, 10 hexagonal crystal structure, 20 sublimation furnace, 21 reaction vessel, 21a, 21c N ₂ gas introduction port, 23 crucible, 23c exhaust port, 25 heating element, 27 high frequency heating coil, 29 radiation thermometer.

Claims (11)

Preparing a SiC substrate;
Preparing a powder of (SiC) _1-x (AlN) _x in which SiC powder and AlN powder are mixed;
Forming an AlN single crystal on one main surface of the SiC substrate using the (SiC) _1-x (AlN) _x powder.   The method for producing an AlN single crystal according to claim 1, wherein the AlN single crystal contains SiC. 3. The method for producing an AlN single crystal according to claim 1, wherein 0.70 ≦ x <0.90 in the (SiC) _1-x (AlN) _x powder. 4. The production of an AlN single crystal according to claim 1, wherein in the step of forming the AlN single crystal, the value of x of the powder of (SiC) _1-x (AlN) _x is gradually increased. Method. Preparing a SiC substrate;
Preparing a powder of Si _{1-xy Cy} (AlN) _{x obtained} by mixing Si powder, C powder, and AlN powder;
Forming an AlN single crystal on one main surface of the SiC substrate using the powder of Si _{1-xy Cy} (AlN) _x .   The method for producing an AlN single crystal according to claim 5, wherein the AlN single crystal contains SiC. In the powder of the _{Si 1-x-y C y} (AlN) x, is 0.70 ≦ x <0.90,0.05 <y, the manufacturing method of the AlN single crystal according to claim 5 or 6. 8. The AlN single crystal according to claim 5, wherein in the step of forming the AlN single crystal, the value of x of the powder of Si _{1-xy Cy} (AlN) _x is gradually increased. Manufacturing method.   An AlN single crystal substrate formed using the method for producing an AlN single crystal according to claim 1. The value of x of (SiC) _1-x (AlN) _x representing the composition of the AlN single crystal substrate from one main surface of the AlN single crystal substrate toward the other main surface facing the one main surface is 10. The AlN single crystal substrate according to claim 9, which is reduced.   The AlN single crystal substrate according to claim 10, wherein the x on the one main surface is 0.90 or more and 1 or less.

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