Die for EFG-based single crystal growth, EFG-based single crystal growth method, and EFG single crystal

Abstract

A die for EFG-based single crystal growth includes a lower surface to be immersed into a raw material melt with an impurity added, a rectangular upper surface facing a seed crystal and having a long side and a short side, and a plurality of slit sections extending from the lower surface to the upper surface and causing the raw material melt to ascend from the lower surface to the upper surface. Respective longitudinal directions of openings of the plurality of slit sections on the upper surface are parallel to one another and non-parallel to the long side of the upper surface.

Claims

1. A die for EFG-based single crystal growth comprising: a lower surface configured to be immersed into a raw material melt with an impurity added; a rectangular upper surface configured to face a seed crystal and having a long side and a short side shorter than the long side; a plurality of slit sections extending from the lower surface to the upper surface and configured to cause the raw material melt to ascend from the lower surface to the upper surface; a first plate member that (1) includes a side face of the die and (2) is parallel to the long side; and plate members forming the plurality of slit sections, wherein longitudinal directions of openings of the plurality of slit sections on the upper surface are parallel to one another and non-parallel to the long side of the upper surface, and the first plate member is supported at ends of the first plate member and by the plate members.

2. The die for EFG-based single crystal growth according to claim 1, wherein the longitudinal directions of the openings of the plurality of slit sections on the upper surface are parallel to the short side of the upper surface.

3. The die for EFG-based single crystal growth according to claim 1, wherein a distance of the opening of the slit section on the upper surface that is most proximate to an outer edge of the upper surface from the outer edge of is 2 mm or less.

4. The die for EFG-based single crystal growth according to claim 1, wherein an interval between center lines in the longitudinal direction of the openings of the neighboring slit sections on the upper surface is 2 mm or less.

5. The die for EFG-based single crystal growth according to claim 1, wherein respective lengths in a traverse direction of the openings of the plurality of slit sections on the upper surface is 2 mm or less.

6. An EFG-based single crystal growth method using the die for EFG-based single crystal growth according to claim 1.

7. An EFG-based single crystal grown using the EFG-based single crystal growth method according to claim 6, wherein an impurity concentration fluctuation coefficient is 30% or less in a region excluding a distance range of 1 mm from an outer edge of a cross section orthogonal to a growth direction of the single crystal.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a perspective view illustrating an EFG-based crucible, a die for EFG-based single crystal growth and an EFG-based single crystal according to an embodiment.

(2) FIG. 2 is a longitudinal cross-sectional view of the EFG-based crucible and the die for EFG-based single crystal growth in FIG. 1.

(3) FIG. 3 is a plan view of the die for EFG-based single crystal growth according to the embodiment.

(4) FIG. 4 is a plan view of a conventional die for EFG-based single crystal growth.

(5) FIG. 5 is a table illustrating specifications of the die for EFG-based single crystal growth according to an example.

(6) FIG. 6 is a table illustrating specifications of a die for EFG-based single crystal growth according to a comparative example.

(7) FIG. 7 is a graph illustrating an impurity concentration of the EFG-based single crystal according to the example.

(8) FIG. 8 is a graph illustrating an impurity concentration of an EFG-based single crystal according to the comparative example.

(9) FIG. 9 is another plan view of the die for EFG-based single crystal growth of FIGS. 1-3.

DESCRIPTION OF EMBODIMENTS

(10) Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. A die for EFG-based single crystal growth and an EFG-based single crystal growth method according to the present embodiment are intended to grow, for example, a β-Ga.sub.2O.sub.3 single crystal using an EFG method. As shown in FIG. 1 and FIG. 2, an EFG-based single crystal manufacturing apparatus 10 is provided with a crucible 11 accommodating a raw material melt 12 based on Ga.sub.2O.sub.3 or the like, a die 1 for EFG-based single crystal growth installed in the crucible 11, a lid 13 covering an upper surface of the crucible 11 except an upper surface 5 of the die 1, a seed crystal holder 16 holding a seed crystal 15 based on Ga.sub.2O.sub.3 or the like and a shaft 17 liftably supporting the seed crystal holder 16.

(11) The crucible 11 is heated by heating means (not shown) and heated up to, for example, 1800° C. or higher exceeding a melting point of β-Ga.sub.2O.sub.3. A solid raw material based on Ga.sub.2O.sub.3 or the like having an additive concentration of 0.016 mol % of an additive such as Sn accommodated in the crucible 11 is melted in a heating process and converts to the raw material melt 12 based on Ga.sub.2O.sub.3 or the like. The crucible 11 and the die 1 for EFG-based single crystal growth are made of iridium-based metal materials having heat resistance capable of accommodating the raw material melt 12 based on Ga.sub.2O.sub.3 or the like. The lid 13 prevents the raw material melt 12 based on Ga.sub.2O.sub.3 or the like from evaporating from the crucible 11 and further prevents a vapor of the raw material melt 12 based on Ga.sub.2O.sub.3 or the like from adhering to the seed crystal 15 based on Ga.sub.2O.sub.3 or the like.

(12) The die 1 for EFG-based single crystal growth is provided with a lower surface 2 to be immersed into the raw material melt 12 based on Ga.sub.2O.sub.3 or the like with an impurity such as Sn added, the rectangular upper surface 5 facing the seed crystal 15 based on Ga.sub.2O.sub.3 or the like and having a long side 3 and a short side 4 shorter than the long side 3, and a plurality of slit sections 6 extending from the lower surface 2 to the upper surface 5 and causing the raw material melt 12 to ascend from the lower surface 2 to the upper surface 5. Note that examples of the rectangular upper surface 5 include a surface in which corners formed of the long side 3 and the short side 4 of the upper surface 5 form angles other than exact 90° and a surface in which corners are rounded.

(13) As shown in FIG. 1, FIG. 2 and FIG. 3, openings 7 of the plurality of slit sections 6 on the upper surface 5 each have a rectangular shape, and a longitudinal direction 71 and a traverse direction 7s. The respective longitudinal directions 71 of the openings 7 of the plurality of slit sections 6 on the upper surface 5 are parallel to one another and non-parallel to the long side 3 of the upper surface 5. More specifically, the respective longitudinal directions 71 of the openings 7 of the plurality of slit sections 6 on the upper surface 5 are parallel to the short side 4 of the upper surface 5. Note that examples of the rectangular openings 7 also include a case where corners formed of the longitudinal direction 71 and the traverse direction 7s of the opening 7 form an angle other than exact 90° and a case where the corners are rounded.

(14) As shown in FIG. 3, a distance α of the opening 7 of the slit section 6 on the upper surface 5 in which the opening 7 on the upper surface 5 is most proximate to an outer edge 5e of the upper surface 5 among the plurality of slit sections 6 from the outer edge 5e of the upper surface 5 is 2 mm or less. Intervals β between center lines 7c in the longitudinal direction 71 of the openings 7 of the neighboring slit sections 6 on the upper surface 5 are equal and are 2 mm or less. Respective lengths γ in the traverse direction 7s of the openings 7 of the plurality of slit sections 6 on the upper surface 5 is 2 mm or less. Respective intervals δ between the openings 7 of the neighboring slit sections 6 on the upper surface 5 are equal and are 2 mm or less. Note that the interval β and the interval δ between the openings 7 of the slit sections 6 need not always be equal.

(15) Hereinafter, an EFG-based single crystal growth method using the die 1 for EFG-based single crystal growth of the present embodiment will be described. As shown in FIG. 2, the die 1 for single crystal growth is installed in the crucible 11 so that the lower surface 2 of the die 1 is accommodated in the crucible 11 and is immersed into the raw material melt 12 based on Ga.sub.2O.sub.3 or the like with an impurity such as Sn added. Due to a capillary phenomenon, the raw material melt 12 based on Ga.sub.2O.sub.3 or the like ascends in the slit sections 6 and reaches the upper surface 5 of the die 1.

(16) An output of heating means (not shown) is adjusted so that the temperature of the upper surface 5 of the die 1 becomes a temperature suitable for growth. As shown in FIG. 1, the shaft 17 is caused to descend and the seed crystal 15 based on Ga.sub.2O.sub.3 or the like held by the seed crystal holder 16 comes into contact with the raw material melt 12 based on Ga.sub.2O.sub.3 or the like, which has reached the upper surface 5 of the die 1. The shaft 17 is caused to ascend and raise the seed crystal 15 based on Ga.sub.2O.sub.3 or the like in contact with the raw material melt 12 based on Ga.sub.2O.sub.3 or the like, thus causing a single crystal 14 based on Ga.sub.2O.sub.3 or the like to grow in a growth direction D from the upper surface 5 of the die 1.

(17) According to the EFG-based single crystal growth method using the die 1 for EFG-based single crystal growth of the above present embodiment, the EFG-based single crystal 14 is grown, the single crystal 14 having, for example, an impurity concentration fluctuation coefficient of 30% or less in the region excluding a distance range of 1 mm from an outer edge of a cross section orthogonal to the growth direction D of the single crystal 14.

(18) According to the present embodiment, the die 1 for EFG-based single crystal growth comprises the lower surface 2 to be immersed into the raw material melt 12 with an impurity added, the rectangular upper surface 5 facing the seed crystal 15 and having the long side 3 and the short side 4 shorter than the long side 3, and the plurality of slit sections 6 extending from the lower surface 2 to the upper surface 5 and causing the raw material melt 12 to ascend from the lower surface 2 to the upper surface 5. The respective longitudinal directions 71 of openings 7 of the plurality of slit sections 6 on the upper surface 5 are parallel to one another and non-parallel to the long side 3 of the upper surface 5. Therefore, if total areas of the openings 7 of slit sections 6 are same, the interval δ between the openings 7 of the neighboring slit sections 6 is shorter than the interval when the respective longitudinal directions 71 of the openings 7 of the slit sections 6 on the upper surface 5 are parallel to the long side 3 of the upper surface 5, and impurity segregation is less likely to occur between the respective slit sections 6, and so it is possible to improve uniformity of an impurity concentration of the grown single crystal 14.

(19) According to the present embodiment, since the respective longitudinal directions 71 of the openings 7 of the plurality of slit sections 6 on the upper surface 5 are parallel to the short side 4 of the upper surface 5, the respective intervals δ between the openings 7 of the neighboring slit sections 6 are shorter than the interval when the respective longitudinal directions 71 of the openings 7 of the slit sections 6 on the upper surface 5 are parallel to the long side 3 of the upper surface 5, and it is thereby possible to improve uniformity of an impurity concentration of the grown single crystal 14. Furthermore, since the length of the longitudinal direction 71 of the opening 7 of the slit section 6 on the upper surface 5 is shorter than the length when the respective longitudinal directions 71 of the openings 7 of the slit sections 6 on the upper surface 5 are parallel to the long side 3 of the upper surface 5, the die 1 is less likely to deform and durability of the die 1 can be improved.

(20) According to the present embodiment, the distance α of the opening 7 of the slit section 6 on the upper surface 5 in which the opening 7 on the upper surface 5 is most proximate to the outer edge 5e of the upper surface 5 among the plurality of slit sections 6 from the outer edge 5e is 2 mm or less, and it is thereby possible to expand the region where the impurity concentration of the grown single crystal 14 is made uniform.

(21) As described, for example, in paragraph (0006) of Patent Literature 1, according to the prior art in which the respective longitudinal directions of the openings of the plurality of slits on the upper surface of the die are parallel to the long side of the rectangular upper surface of the die, a warp is produced when the thickness of the plate member constituting the die is 1 mm or less, and accurate manufacturing of the die requires a plate member having a thickness of 2.4 mm or more. That is, according to the prior art, the plate member constituting a widest side face of the die extending over a long distance in the direction parallel to the long side of the upper surface of the die is supported only at two locations, at both ends on the short side of the upper surface of the die, and therefore the mechanical strength of the die is low and the thickness of the plate member needs to be increased. Therefore, it is difficult for the prior art to set the distance α to 2 mm or less.

(22) On the other hand, according to the present embodiment, as shown by FIG. 9, the plate members 20 constituting the widest side face of the die 1 extending over a long distance in the direction parallel to the long side 3 of the upper surface 5 of the die 1 are also supported by the plate members 21 partitioning the respective slit sections 6 in addition to the two locations, at both ends on the short side 4 of the die 1. That is, in the present embodiment, the plate members 20 constituting the widest side face of the die 1 are supported at many supporting points and the supporting points are distributed over the entire die 1, and so the mechanical strength of the entire die 1 improves and the die 1 can be manufactured accurately even using thin plate members.

(23) According to the present embodiment, since the interval β between the center lines 7c in the longitudinal direction 71 of the openings 7 of the neighboring slit sections 6 on the upper surface 5 is 2 mm or less, it is possible to further improve impurity concentration uniformity of the grown single crystal 14.

(24) Regarding the plate members partitioning the respective slit sections, according to the prior art described in Patent Literature 1, the plate members partitioning the respective slit sections are supported only at two locations, at both ends on the short side of the upper surface of the die and extend in a direction parallel to the long side of the upper surface of the die over a long distance, and so an influence when a warp is produced in the plate members partitioning the respective slit sections is considerably large and the thickness of the plate members needs to be increased to prevent warpage. Therefore, it is difficult for the prior art to set the interval β to 2 mm or less.

(25) On the other hand, according to the present embodiment, the distance between the two locations at both ends of the plate members at which the plate members partitioning the respective slit sections 6 are supported is the distance in a direction parallel to the short side 4, which is shorter than the distance in the direction parallel to the long side 3 of the upper surface 5 of the conventional die 1, and so even when a warp of the same radius of curvature is produced, the influence of the warp is minimal and it is possible to reduce the thickness of the plate members partitioning the respective slit sections 6.

(26) According to the present embodiment, the respective lengths γ in the traverse direction 7s of the openings 7 of the plurality of slit sections 6 on the upper surface 5 are 2 mm or less, and so it is possible to increase the height by which the slit sections 6 cause the raw material melt 12 to ascend from the lower surface 2 to the upper surface 5.

(27) According to the present embodiment, it is possible to grow the single crystal 14 in which impurity concentration uniformity is improved using the EFG method. Furthermore, according to the present embodiment, it is possible to provide the single crystal 14 in which impurity concentration uniformity is improved and characteristics are made more uniform.

(28) Although the embodiment of the present invention has been described so far, the present invention is not limited to the above embodiment but can be implemented in various modes. For example, the shape and arrangement of the openings 7 of the plurality of slit sections 6 on the upper surface 5 can be changed as appropriate.

Example

(29) The Ga.sub.2O.sub.3-based single crystal 14 with Sn added as an impurity was grown using the aforementioned EFG-based single crystal manufacturing apparatus 10 and die 1 for EFG-based single crystal growth. Dimensions or quantities of the respective regions of the die 1 are as shown in FIG. 5. Portions of the Ga.sub.2O.sub.3-based raw material melt 12 caused to ascend through the plurality of slit sections 6 formed in the die 1 for single crystal growth were united and spread over the upper surface 5 of the die 1, and a thick plate-like Ga.sub.2O.sub.3-based single crystal 14 having a cross-sectional shape of a straight barrel portion of approximately 57 mm in width, approximately 18 mm in thickness and approximately 112 mm in length was grown.

(30) The straight barrel portion was cut out from the grown single crystal 14, divided in two at a cross section intersecting in a length direction (growth direction D), each of the two single crystal blocks having a thickness of approximately 18 mm obtained was cut into 18 flat plates so that the cutting surfaces cut by a multi-saw were parallel to the main surface of the crystal. After each of the two single crystal blocks was cut into the 18 flat plates, both surfaces of the respective flat plates were then polished and 36 single crystal substrates having a thickness of 0.4 mm were manufactured from one single crystal 14.

(31) Sn concentrations of 32 single crystal substrates obtained by excluding 4 single crystal substrates located on an outermost side of the single crystal 14 during single crystal growth and having low crystallinity from the 36 single crystal substrates obtained were measured using SIMS (Secondary Ion Mass Spectrometry). That is, concentrations of Sn, which was an impurity, in the region obtained by excluding a distance range of 1 mm from the outer edge of a cross section orthogonal to the growth direction D of the single crystal 14 were measured. The measurement results are shown in FIG. 7. The abscissa of a graph in FIG. 7 represents order of the single crystal substrates in the thickness direction obtained by cutting the Ga.sub.2O.sub.3-based single crystal 14 grown into a thick plate shape in parallel with the main surface of the crystal. The ordinate of the graph in FIG. 7 represents a value obtained by dividing the respective measured values of Sn concentrations of the 32 single crystal substrates by an average value of Sn concentrations of the 32 substrates. A fluctuation coefficient (Cv) of the 32 single crystal substrates, that is, a value obtained by dividing a standard deviation of Sn concentrations by the average value was 12.1%, which is equal to or less than 30%. That is, it is seen that the impurity concentration of the single crystal 14 grown by the die 1 in the example exhibits a high level of uniformity.

(32) Although growth of the above single crystal 14 was repeated 12 times or more, no significant change in shape in the die 1 for single crystal growth was observed. That is, it is seen that the die 1 for single crystal growth hardly deforms and has excellent durability as well.

Comparative Example

(33) A plan view of a die 20 for single crystal growth used as a comparative example is shown in FIG. 4. In the die 20, the respective longitudinal directions 71 of the openings 7 of the plurality of slit sections 6 on the upper surface 5 are parallel to the long side 3 of the upper surface 5. The interval β and the interval δ are equal among the openings 7 of the slit sections 6. Dimensions or quantities of the respective regions of the die 20 are as shown in FIG. 6. The single crystal 14 was grown under completely the same conditions as the conditions in the example except for the die 20 for single crystal growth and 36 single crystal substrates were finally manufactured after being polished to have a thickness of 0.4 mm from one single crystal.

(34) Sn concentrations of 32 single crystal substrates obtained by excluding 4 single crystal substrates located on an outermost side of the single crystal 14 during single crystal growth and having low crystallinity from the 36 single crystal substrates obtained were measured using SIMS. That is, concentrations of Sn, which was an impurity, in the region obtained by excluding a distance range of 1 mm from the outer edge of a cross section orthogonal to the growth direction D of the single crystal 14 were measured. The measurement results are shown in FIG. 8. The abscissa of a graph in FIG. 8 represents order of the single crystal substrates in the thickness direction obtained by cutting the Ga.sub.2O.sub.3-based single crystal 14 grown into a thick plate shape in parallel with the main surface of the crystal. The ordinate of the graph in FIG. 8 represents a value obtained by dividing the respective measured values of Sn concentrations of the 32 single crystal substrates by an average value of Sn concentrations of the 32 substrates. A fluctuation coefficient (Cv) of the 32 single crystal substrates, that is, a value obtained by dividing a standard deviation of Sn concentrations by the average value was 35.5%, which exceeds 30%. That is, it is seen that the impurity concentration of the single crystal 14 grown by the die 20 in the comparative example exhibits a low level of uniformity.

(35) From a point in time at which growth of the above single crystal 14 was repeated 6 times, a distortion was observed in a middle part on the upper surface 5 of the die 20 for single crystal growth, and from the ninth growth onward, the amount of the Ga.sub.2O.sub.3-based raw material melt 12 supplied from the center of the slit sections 6 decreased in the openings 7 of the slit sections 6 located outside and the Ga.sub.2O.sub.3-based raw material melt 12 no longer became wet or spread over the entire upper surface 5 of the die 20. That is, it is seen that the conventional die 20 for single crystal growth is easily deformed and is inferior in durability to the die 1 in the example.

INDUSTRIAL APPLICABILITY

(36) According to the die for EFG-based single crystal growth, the EFG-based single crystal growth method and the EFG-based single crystal of the present invention, it is possible to improve impurity concentration uniformity of a grown single crystal.

REFERENCE SIGNS LIST

(37) 1 . . . die, 2 . . . lower surface, 3 . . . long side, 4 . . . short side, 5 . . . upper surface, 5e . . . outer edge, 6 . . . slit section, 7 . . . opening, 71 . . . longitudinal direction, 7s . . . traverse direction, 7c . . . center line, 10 . . . single crystal manufacturing apparatus, 11 . . . crucible, 12 . . . raw material melt, 13 . . . lid, 14 . . . single crystal, 15 . . . seed crystal, 16 . . . seed crystal holder, 17 . . . shaft, 20 . . . die, D . . . growth direction, α . . . distance, β . . . interval, γ . . . length, δ . . . interval