DEVICE AND METHOD OF MANUFACTURING AIII-BV-CRYSTALS AND SUBSTRATE WAFERS MANUFACTURED THEREOF FREE OF RESIDUAL STRESS AND DISLOCATIONS

Abstract

A device (1′, 1″, 1′″) for manufacturing III-V-crystals and wafers (14) manufactured therefrom, which are free of residual stress and dislocations, from melt (16) of a raw material optionally supplemented by lattice hardening dopants comprises a crucible (2′, 2″, 2′″) for receiving the melt (16) having a first section (4′, 4″) including a first cross-sectional area and a second section (6′) for receiving a seed crystal (12) and having a second cross-sectional area, wherein the second cross-sectional area is smaller than the first cross-sectional area and the first and second sections are connected with each other directly or via third section (8, 8′) which tapers from the first section towards the second section, in order to allow a crystallization starting from the seed crystal (12) within the directed temperature field (T) into the solidifying melt. The first section (4′, 4″) of the crucible (2′, 2″, 2′″) has a central axis (M), and the second section (6′) is arranged being offset (v) with regard to the central axis (M) of the first section (4′, 4″).

Claims

1. A device for manufacturing a crystal from a melt of a raw material, comprising: a crucible for receiving the melt having a first section including a first cross-sectional area and having a second section for receiving a seed crystal and including a second cross-sectional area, wherein the second cross-sectional area is smaller than the first cross-sectional area and the first and the second section of connected with each other directly or via a third section which tapers from the first to the second section, in order to allow a crystallization starting from the seed crystal within a directed temperature field into the solidifying melt, wherein the first section of the crucible has a central axis, and the second section is arranged to be laterally offset from the central axis of the first section.

2. The device according to claim 1, wherein the second section includes a longitudinal axis, which, when it is extended into a region of the first section, extends in a distance of 15 mm or less from an inner wall of the crucible within the first section.

3. The device according to claim 2, wherein the second section is at least partially formed in cylindrical shape and has an inner diameter of 15 mm or less.

4. The device according to claim 1, wherein the first section is at least partially formed in cylindrical shape.

5-6. (canceled)

7. The device according to claim 1, wherein the second section has a length along a direction of the central axis, wherein the length amounts to between 40 mm and 120 mm.

8. The device according to claim 1, further comprising a heating device which includes one or more heating elements, the heating device configured to generate the directed temperature field having a temperature gradient, wherein the crucible is arranged in the temperature field.

9. The device according to claim 1, wherein the crucible is formed from boron nitride (BN) or pyrolytically deposited boron nitride (pBN), which is suitable to receive a melt formed from gallium arsenide (GaAs) or indium phosphide (InP).

10. The device according to claim 1, wherein in addition to the crucible, further identical crucibles are provided being arranged symmetrically and in parallel and at the same height, and wherein the one direction, in which the second section is offset from the central axis, is oriented towards the symmetry axis of the arrangement of crucibles.

11-19. (canceled)

20. An AIII-BV-single-crystal or wafer obtained by separation therefrom, comprising an average density of dislocations in the lattice of the crystal determined as an average edge pit density (EPD.sub.av) within the cross-sectional area of the single-crystal perpendicular to its central axis (M) in amount of 10 cm.sup.−2 or less.

21. The AIII-BV-single-crystal or wafer obtained by separation therefrom according to claim 20, wherein boron, silicon, zinc, sulphur, or indium, are incorporated in the lattice of the single-crystal alone or in combination.

22. The AIII-BV-single-crystal or wafer obtained by separation therefrom according to claim 20, comprising a distribution of the residual stress at maximum of +/−30 kPa or less on a cross-sectional area of the single-crystal or of the wafer, obtained by a spatially resolved measurement according to the SIRD method.

23. The AIII-BV-single-crystal or wafer obtained by separation therefrom according to claim 20, wherein within a cross-sectional area of the single-crystal or of the wafer, a fraction of measurement fields sized as 0.25 mm.sup.2 within the measurement grid, all measurement fields completely covering the cross-sectional area, the fraction of measurement fields being completely free of dislocations, amounts to 99% of total area of the cross-sectional area, or more.

24. An AIII-BV-single-crystal or wafer obtained by separation therefrom, comprising a distribution of the residual stress at maximum of +/−30 kPa or less, preferably of +/−25 kPa or less, on a cross-sectional area of the single-crystal (14) or of the wafer, obtained by a spatially resolved measurement according to the SIRD method.

25. The AIII-BV-single-crystal or wafer obtained by separation therefrom according to claim 24, wherein the lateral resolution of the spatially resolved measurement amounts to 100 μm.

26. The AIII-BV-single-crystal or wafer obtained by separation therefrom according to claim 24, wherein the diameter of the single-crystal or of the wafer amounts to 150 mm or more.

27. An AIII-BV-single-crystal or wafer obtained by separation therefrom comprising an average density of dislocations in the lattice of the crystal determined as an average edge pit density (EPD.sub.av) within the cross-sectional area of the single-crystal (14) perpendicular to its central axis (M) in amount of 1000 cm.sup.−2 or less, wherein a charge carrier concentration including lattice hardening dopants, in particular boron, silicon, zinc, sulphur, indium, each alone or in combination, amounts to 7×10.sup.16 Atoms/cm.sup.3 or less, preferably 1×10.sup.16 atoms/cm.sup.3 or less.

28. (canceled)

29. The AIII-BV-single-crystal according to claim 20, wherein the single crystal comprises Gallium arsenide (GaAs) or Indium phosphide (InP).

30. The AIII-BV-single-crystal according to claim 24, wherein the single crystal comprises Gallium arsenide (GaAs) or Indium phosphide (InP).

31. The AIII-BV-single-crystal according to claim 27, wherein the single crystal comprises Gallium arsenide (GaAs) or Indium phosphide (InP).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further features, advantages, and purposive embodiments will be described in more detail below by virtue of a description of non-limiting embodiments pertaining to preferred embodiments taken in conjunction with drawings. Therein:

[0041] FIG. 1 shows a schematic illustration of a first embodiment of a device for manufacturing a single-crystal from a raw melt, according to the present invention, wherein the seed channel of the crucible is extended or elongated (top: lateral cross-sectional view, bottom: top view);

[0042] FIG. 2 shows a schematic illustration of a second embodiment of a device for manufacturing a single-crystal from a raw melt, according to the present invention, wherein the seed channel is offset towards the outer edge of the diameter (top: lateral cross-sectional view, bottom: top view);

[0043] FIG. 3 shows a schematic illustration of a third embodiment of a device for manufacturing a single-crystal from a raw melt, according to the present invention, wherein—starting from the second embodiment (having a short seed channel)—an asymmetrical reduction of the oversize towards the nominal diameter is intended (top: lateral cross-sectional view, bottom: top view);

[0044] FIG. 4 shows a schematic illustration of a fourth embodiment of a device for manufacturing a single-crystal from a raw melt, according to the present invention, wherein—starting from the third embodiment—the seed channel is extended or elongated similar to the first embodiment (top: lateral cross-sectional view, bottom: top view);

[0045] FIG. 5 shows a schematic illustration of an embodiment of a multiple crucible arrangement having seed channels offset towards the direction of the common central axis Z, composed of three of the devices shown in FIG. 3;

[0046] FIG. 6 shows a schematic illustration of an embodiment of a multiple crucible arrangement similar to that in FIG. 5, but composed of five of the devices shown in FIG. 3;

[0047] FIG. 7 shows a schematic illustration of a cross-sectional area of a single-crystal revealing edge dislocations;

[0048] FIG. 8 shows a schematic illustration of a cross-sectional area of a single-crystal revealing dislocations extending or propagating from the seed channel arranged on the central axis of the crucible;

[0049] FIG. 9 shows in a greyscale image a distribution of values of the density of locations in the atomic lattice of the crystal determined from spatially resolved measurements within a cross-sectional area of the wafer perpendicular to its central axis M, for a comparative example pursuant to a conventionally grown single-crystal, or wafer, respectively, having a diameter of 150 mm;

[0050] FIG. 10 shows in a greyscale image a distribution of values of the respective shear stress determined from spatially resolved measurements for the comparative example of FIG. 9;

[0051] FIG. 11 shows a greyscale image as in FIG. 9 with the distribution of values of the density of dislocations in the atomic lattice of the crystal determined from spatially resolved measurements, but for a corresponding embodiment of the invention;

[0052] FIG. 12 shows a greyscale image as in FIG. 10 having the distribution of values of the respective shear stress determined from spatially resolved measurements, but for the corresponding embodiment of the invention of FIG. 11;

[0053] FIG. 13 shows an example in a diagram as an example distributions (frequency P.sub.W per interval of values of shear stress T that has occurred per wafer) of the shear stress measured respectively based on the SIRD method for 3 comparative examples (“wafer 22”, “wafer 27”, “wafer 37”) according to prior art as published in Geiler, Karge, H.; Wagner, M.; Eichler, St.; Jurisch, M.; Kretzer U. Scheffer-Czygan, M.: “Photoelastic characterization of residual stress in GaAs— wafers” in: Materials Science in Semi-conductor Processing 9 (2006), S. 345-350);

[0054] FIG. 14 shows a diagram as in FIG. 13, but for the embodiment of FIGS. 12 and 13 of a single-crystal grown according to the invention, or of the wafer separated therefrom.

DETAILED DESCRIPTION OF THE INVENTION

[0055] A first embodiment of a device for manufacturing single-crystal from a raw melt pursuant to the present invention is depicted in FIG. 1. The device 1 comprises a crucible 2 as well as the heating device 10 having annularly arranged heating elements encompassing the crucible. In the upper part of FIG. 1 a cross-sectional view is shown while the bottom part shows a top view of the crucible 2 omitting the heating device 10. The crucible may be received in a quartz glass container (not shown) and closed with respect to its outer environment. The arrangement may correspond to a device for growing crystals pursuant to the Vertical Gradient Freeze (VGF)—method.

[0056] The crucible 2 is formed from boron nitride or pyrolytically deposited boron nitride (pBN) and comprises a first cylindrically shaped section 4, which receives the raw melt 16—herein composed of gallium arsenide GaAs—and a second section 6 formed as a seed channel and the third section 8 which forms the transition between the first 4 and the second section 6 and connects these sections. In a region of its second section, the crucible 2 has an inner diameter of at least 152 mm, which is composed of a nominal diameter d of 150 mm that is to be minutely yielded or achieved for the finished single-crystal and of an oversize of up to 2 mm that is conventionally added in the growth process, and which accounts for a grinding step that is subsequently applied to an outer cylinder shell portion of the single-crystal to be manufactured (and that is sacrificed during that step). This grinding step serves for providing a positional accurate, high quality cylinder surface of the crystal required for subsequent alignment steps with regard to the subsequently separated wafer.

[0057] In this specific embodiment the seed channel, or the second section 6 respectively, is also shaped cylindrically and has a diameter of for example 10 mm and a length k′ of 100 mm. Seed channels according to the invention may also require spatial shapes different from cylindrical and the invention is not limited to the specific shape. The seed channel may also be of a cuboid shape, or may have a polygonal or oval shape in cross-section, etc.

[0058] A seed crystal 12 (herein formed from GaAs) is received in the second section 6 having a length of 20 mm and a diameter of slightly less than 10 mm (e.g., 8 or 9 mm) in order to ensure that the distance from the crucible wall is present within the seed channel. The gap in the seed channel maybe filled with liquid boron oxide (B.sub.2O.sub.3) such that the melt and crystal is floating in the liquid during crystallization. Due to the considerable difference between the length of the seed crystal 12 and the length k′ of the seed channel, the seed crystal 12 is arranged deeply at the bottom in the second section 6. The top face or seed face of the seed crystal is thus distant from the upper end of the second section 6, or the seed channel respectively, by 80 mm. A ratio of the length to the inner diameter of the free space portion not occupied by the seed crystal thus amounts to 8:1.

[0059] In the state shown in FIG. 1 a raw melt 16 composed of gallium arsenide has been provided to the crucible 2, which has already been crystallized into a doped GaAs single-crystal 14 starting from the seed face or seed position at the seed crystal 12 within the seed channel, beyond the conical transition, or the third section 8 respectively, and into the cylindrical second section 6, respectively. Further, a lattice hardening dopant such as for example silicon, boron, indium, zinc, sulphur, etc. has been added to the melt.

[0060] In the corresponding method (VGF) an amount of silicon is for example added to the melt before or after heating the same (or to its compact or granular precursor). Above the raw melt 16 and between the crystal and the crucible wall there is a layer 18 of liquid (molten) diboron trioxide (B.sub.2O.sub.3) because of its lower density, that serves to protect the GaAs melt below as described above. By means of the heating device, a directed temperature field T is generated (the arrow in FIG. 1 points upwards away from the seed crystal 12 towards higher temperatures) using the control device not shown. When the seed crystal 12 starts to be molten, cooling of the raw melt 16 is initiated (by further control of the heating device 10) maintaining the temperature gradient, such that the single-crystal 14 starts to grow upwards starting from the seed face of the seed crystal 12—firstly still within the second section 6 or seed channel, respectively.

[0061] Due to the large ratio between the free length open to crystallization and the inner diameter in the narrow seed channel, the central dislocations 101 as shown in FIG. 8 which due to the seed process as such may hardly be avoided propagate in the crystallization process in an acute angle with regard to the central axis M of the crucible, which in this embodiment also coincides with a central axis of the seed channel, such that it impinges on the crucible wall prior to the crystallization front between the single-crystal 14 and the raw melt 16 reaching the upper end of the seed channel (second section 6). As a consequence, the dislocations thus generated do not exert any further influence onto the further growth. Commonly, dislocations propagate perpendicular to the phase boundary, which itself is slightly curved.

[0062] After the dislocations 101 have vanished in the cross-sectional areas of the single-crystal still within the second section 6 (seed channel) of the crucible 2, a single crystal 14 is grown upon further propagation of the crystallization front which is substantially free of dislocations considering an exclusion of the edge areas (80 cm.sup.2). A listing of relevant parameters of several samples shown in table 1. Therein sample 1a is a GaAs single-crystal manufactured using a crucible with conventional seed channel, sample 1a serving as a comparative example, while samples 2-5 are manufactured according to the method of the invention in a crucible as shown in FIG. 1 (also GaAs). The values of the parameters EPD.sub.av and EPC.sub.total listed in table 1 were obtained from wafers after separation from the grown single-crystal. The diameters of the samples amounts to 150 mm.

TABLE-US-00001 TABLE 1 Sample 1a (comparative example) Sample 2 Sample 3 Sample 4 Sample 5 EPD.sub.av 235 cm.sup.−2  12 cm.sup.−2  4 cm.sup.−2 0 cm.sup.−2  2 cm.sup.−2 EPC.sub.total  18.000 960 320 0 640

[0063] A second embodiment of a device 1′ according to the invention is shown in FIG. 2. In order to avoid repetitions, the same reference numerals as in FIG. 1 denote the same or similar features and in the following it is only referred to the relevant modifications of the device with respect to the first embodiment. The other properties described with regard to the first embodiment are also valid with regard to the second and subsequent embodiments.

[0064] The crucible 2′ of the second embodiment includes, similar to the first embodiment, a first section 4′ for receiving raw melt 16, a second section 6′ serving as a seed channel, and a third section 8′ serving as the transition region between the seed channel and the first section 4′. The second section 6′ has a diameter of 10 mm like in the first embodiment, its length k amounts, however, like in conventional crystal growth devices to 30 mm, for example, such that the seed face of the seed crystal 12 inserted into the seed channel and having a length of 20 mm has a distance from an upper end of the seed channel 12 of only 10 mm. Without general limitation the seed channel in this embodiment is also formed being cylindrical as a mere example. The third section is not provided with rotational symmetry any more in view of the offset v of the second section 6′ with regard to the first section 4′, and rather tapers laterally outwards in an asymmetrical manner when viewed from the cylindrical first section 4′ having the larger inner diameter towards the second section 6′ having the smaller diameter.

[0065] Instead, the second section 6′ is arranged laterally offset with regard to the central axis M of the first section. In other words, a central axis M′ of the second section is parallel to the central axis M of the first section 4′ based on a mutual offset v between both. In this embodiment, the offset v has a sufficient dimension, such that the central axis M′ of the second section 6′, or of the sea channel, respectively, extends through an edge exclusion area of cross-sectional areas of the first section 4′, when such central axis M′ is extended into the first section 4′.

[0066] In the second embodiment the first section has an inner diameter d′″ of 172 mm. However, the nominal diameter d of the single-crystal 14 to be manufactured also in the present embodiment amounts to only 152 mm. The crucible 2′ is thus provided with a considerably larger diameter d′″ as compared with the crucible 2 of the first embodiment but also with respect to conventional crucibles, with which a single-crystal is to be manufactured having the given nominal diameter. In this second embodiment, the (extended) central axis M′ of the second section 6′, or of the seed channel, respectively, thus extends through an edge area of the cross-sectional area as shown in FIG. 2, which is outside and beyond the nominal diameter d of the single-crystal 14 to be manufactured (the central axis M′ is at a distance from the crucible wall amounting to 5 mm, since the seed channel has an inner diameter of 10 mm, and, if projected along the central axis M (see bottom of FIG. 2), completely extends through the cross-sectional area of the crucible in order to ensure an unimpeded growth in actual direction). The lateral offset v in this embodiment amounts to 80 mm.

[0067] The method for manufacturing the single-crystal is similar to that in the previous embodiment (for example including the addition of one or more lattice hardening dopants to the melt). However, the subsequent grinding step of the post-processing for smoothing and finishing the cylinder surface of the optionally doped GaAs single-crystal 14 according to prior art is supplemented or even replaced by a further step, in which the oversize of herein 20 mm in diameter (or herein 10 mm in radius) is reduced or removed by drilling or another step capable of more strongly removing material from the cylindrical surface of the single-crystal. Thereby, in the second embodiment material is removed from the cylindrical surface of the single-crystal in symmetrical manner about the central axis of the single-crystal 14 (which coincides with the centre axis M of the first section of the crucible 2′). Advantageously, edge areas of the single-crystal 14 are removed, which had been close to the walls during growth and thus were—as shown in FIG. 7—subjected to a comparatively larger dislocation density conditional of manufacturing. In particular, in connection therewith, the edge dislocations 102 shown in FIG. 7 by means of the schematically depicted single-crystal 14b are removed.

[0068] Since moreover due to the specific arrangement, or the offset v respectively, the dislocations 101 (cf. FIG. 8) originating from the seed process propagated into the edge area are removed in the post processing step, a single-crystal 14 is obtained that is free of dislocations or at least substantially free of dislocations. A listing of relevant parameters of several samples are shown in table 2. Therein, sample 1b is a GaAs single-crystal manufactured using a crucible having a conventional seed channel, and serves as a comparative example, while the samples 6-9 (also GaAs) have been manufactured according to the method of the invention using a crucible as shown in FIG. 2. The values of the parameters EPD.sub.av and EPC.sub.total listed in table 2 were obtained from wafers after separation from the grown single-crystals. The diameter of the samples amounts to 150 m.

TABLE-US-00002 TABLE 2 Sample 1b (comparative example) Sample 6 Sample 7 Sample 8 Sample 9 EPD.sub.av 56 cm.sup.−2 8 cm.sup.−2  1 cm.sup.−2 0 cm.sup.−2  2 cm.sup.−2 EPC.sub.total  8.400 1.200 150 0 300

[0069] A third embodiment of a device 1″ according to the invention is shown in FIG. 3. The structure of the device as well as the manufacturing of the single-crystal is similar to that of the second embodiment. A difference merely exists in the diameter d″ of the first section 4″ of the crucible 2″. As can be derived from the bottom illustration of the top view in FIG. 3, in the method underlying the third embodiment, an asymmetrical reduction of the oversize is performed in the post-processing step after the proper growth in crucible 2″, in order to obtain the nominal diameter d of 152 mm for the single-crystal 14. This line of action allows to exclude substantially only that edge area which shown in FIG. 3 at the bottom on the right side, i.e., to remove in the post-processing step specifically that edge area being affected by dislocations 101 resulting from the seed process, such that as a consequence overall less oversize can be selected for the inner diameter d″ of the crucible 2″. In the embodiment the inner diameter d″ amounts to 162 mm, i.e., 10 mm more than the nominal diameter d of the single-crystal, whose manufacturing device 1″ is configured for (d=152 mm). As becomes apparent from FIG. 3, the cross-section of the seed channel, or of the second section 6″ respectively, projected into the cross-sectional area of the first section 4″ of the crucible 2″ completely extends within the edge area of the cross-sectional area of the single-crystal 14 to be manufactured, which is to be removed in the post-processing step. The offset v of the central axis M′ of the seed channel with respect to the central axis M of the first section 4″ amounts in this embodiment to only 75 mm.

[0070] In this embodiment, it is accepted that edge dislocations 102 particularly positioned at the bottom on the left side in FIG. 3 may remain even after the post-processing step in the single-crystal 14, which may originate from a contact with the inner crucible wall during growth. However, the amount of material to be removed as required in the post-processing step is considerably reduced as compared with the second embodiment, which yields from an economical point of view and optimal cost-benefit-ratio. Moreover, there are still achieved excellent values for the average dislocation density of 10 cm.sup.−2 or less, or of 5 cm.sup.−2 or less, as well as with regard to the fraction P(EPD.sub.L=0 cm.sup.−2) of measurement fields completely free of dislocations pursuant to the standardized measurement method according to SEMI-M83 with values of 97% or more, or even 99% or more. The relevant parameters for two samples are listed in table 3. Therein sample 1c is a GaAs single-crystal manufactured using a crucible having a conventional seed channel and serves as a comparative example, while sample 10 is manufactured according to the method of the invention using a crucible as shown in FIG. 3 (also GaAs). The values of parameters EPD.sub.av and EPC.sub.total listed in table 3 were obtained from wafers separated from the grown crystals. The diameter of the samples amounts to 150 mm.

TABLE-US-00003 TABLE 3 Sample 1c (comparative example) Sample 10 EPD.sub.av 56 cm.sup.−2 7 cm.sup.−2 EPC.sub.total  8.400 1.000

[0071] A fourth embodiment of a device 1″ according to the invention is shown in FIG. 4. The embodiment includes features of both the first and third embodiments and combines them. The device 1″ consequently comprises a crucible 2″ formed from boron nitride or pyrolytic boron nitride has the cylindrically shaped first section 4″ having an oversize of 2 mm or more with respect to the nominal diameter (in this embodiment 10 mm), wherein the crucible 2″ receives the raw melt 16—herein formed from gallium arsenide. The device 1″ further comprises the second section 6 formed as a seed channel and extended to length k′ with k′=100 mm, and the asymmetric third section 8′, which forms the transition between the first section 4″ at the second section 6 and connects both with each other.

[0072] The advantages and effects are the same as those described above with reference to the first through third embodiments, wherein the advantages are accumulated. Relevant parameters of a sample of single-crystal 14 manufactured using the device are provided in table 4. Therein, a sample 1d is a GaAs single-crystal manufactured using a crucible having a conventional seat channel, and serves as a comparative example, while the sample 11 has been manufactured using the crucible as shown in FIG. 4 (also GaAs). The values of parameters EPD.sub.av and EPC.sub.total listed in table 4 were obtained from wafers after separation from the grown crystals. The diameter of the samples amounts to 150 m. It shall be remarked, that the samples 1b to 1d are identical.

TABLE-US-00004 TABLE 4 Sample 1d (comparative example) Sample 11 EPD.sub.av 56 cm.sup.−2 0 cm.sup.−2 EPC.sub.total  8.400 0

[0073] Embodiments of the device 1″″ or 1″″″ comprising multiple crucible arrangement including 3 or 5 crucibles 2″ as shown in FIG. 3, respectively, are depicted in FIGS. 5 and 6, respectively. The heating device 10 having one or more heating elements, for example a magnetic field heater, surrounds and heats the crucible arrangement. Filling bodies (not shown), which provide a particular contribution to the home organisation of the temperature field T, in addition to the magnetic field heaters, by conducting heat anisotropically, such as for example graphite, may be arranged between the crucibles 2″. One such particularly advantageous arrangement is described for example in U.S. Pat. No. 9,368,585 B2, and the features of the arrangements depicted in FIGS. 1-3 and 11-12 therein are incorporated herein by reference along with corresponding description. The multiple crucible arrangement described in the patent is outstanding due to improved distributions of the etch pit density, i.e., a particularly homogeneous dislocation density.

[0074] In these two embodiments the crucible arrangement has a symmetry axis Z, which extends in parallel to the corresponding central axes M of the crucibles 2″ through the centre of the arrangement. As viewed from the respective central axes the direction of the offset v is exactly oriented towards the symmetry axis Z. In other words, the corresponding second sections 6′ of the crucibles 2″ are offset towards the centre of the arrangement.

[0075] Such a multiple crucible arrangement allows to generate excellent, stable and homogeneous temperature fields, in particular in a direction towards its centre. By providing offsets of the seed channels in the same manner, the conditions of crystallization are the same in each crucible. Due to the combination of the features of the device 1″ according to the invention shown in FIG. 3 (as also of the other embodiments according to FIGS. 1, 2 and 4) with the multiple crucible arrangement, it is particularly taken advantage of synergistic effects.

[0076] The above-described embodiments relate to a device configured to perform the VGF-method. However, the invention is not limited to the specific device, and attentive devices may for example also be based on the Vertical Bridgeman method.

[0077] The above-described crucibles include in the first section the cylindrical shape. Attentively, there may, however, also be used other shapes such as cuboid-shaped crucibles having a square or rectangular cross-sectional area, or those shapes in which circular segments are separated from generally round cross-sectional areas (for example for the formation of flats).

[0078] Modifications of the above described embodiments are possible within the scope of embodiments of the disclosure. Also, as in the fourth embodiment, single elements of the embodiments may be combined with those of other embodiments. For example it is conceivable and possible to put into practice, to arrange in the first embodiment having the symmetrically arranged seed channel first crucible section which is expanded in diameter according to aspects of the invention, .i.e., being provided with an increased inner diameter (e.g., d′″=172 mm) in order to perform a post-processing step (drilling, polishing, lapping, or grinding etc.) also therein yielding a corresponding removal of material in a cylinder-wall-shaped or tubular wall-shaped edge area of the single-crystal 14.

[0079] For the post-processing step, drilling, polishing, lapping, or grinding are cited as examples in the above embodiments. However, it is a matter of course for the person skilled in the art, that attentively also other methods known in the technical field of materials science for removing material may be applied.

[0080] It was also surprisingly found that the reduction of the dislocation density in the described range with respect to the reference values is connected with a further significant reduction of the amount of shear stress of the crystals and the wafers manufactured therefrom. For this purpose, the measurement method of SIRD as described above has been employed.

[0081] In order to obtain a unified parameter for the concrete single-crystal/wafer, values of the shear stress obtained for each position on the surface of the wafer (frequency versus shear stress under consideration of the sign) are recorded (see for example FIG. 4 in Geiler et al.), and for the Lorentz curve fitted to these data, for example, a value of the full width at half maximal of this curve is determined, in units of kPa.

[0082] FIG. 13 shows the distribution functions as obtained in Geiler et al. (2006) based on shear stress measured according to the SIRD method for three comparative examples (“wafer 22”, “wafer 27”, “wafer 37”). In the diagram, there is displayed a fraction P.sub.w (relative frequency per interval of occurred values of shear stress T per wafer) of measurement values obtained in a respective shear stress interval. Geiler et al. (2006) hereby provide a full-width-at-half-maximum FWHM of about 100 kPa with respect to all three comparative examples pertaining to prior art. The same value is approximately derived also as a maximum value (herein, however, as an absolute value) of the measured shear stress, which may be read out at the base of the curve on the left and/or right side.

[0083] As shown in FIG. 14, a reduction of the corresponding values of residual stress or shear stress in the case of single crystals or wafers, respectively, manufactured according to the invention to +/−40 kPa or less, partially to +/−30 kPa or less, or even to +/−25 kPa was successful, beyond the values of residual stress or shear stress as shown in FIG. 9 with respect to the three comparative examples pursuant to Geiler et al. (2006). The Lorentz curve thus obtained is specifically narrow.

[0084] This means that measurements performed at wafers according to embodiments, which were obtained from reference crystals, revealed significantly reduced residual stress as compared with wafers examined in Geiler et al. (2006), according to the SIRD-method, see in this regard also a comparison shown in Table 5 between a comparative example and an embodiment.

TABLE-US-00005 TABLE 5 Comparative Parameter unit example Embodiment EPD.sub.av from full surface cm.sup.−2 130 3 measurement acc. to SEMI M83 EPD.sub.av from measurement of 69 cm.sup.−2 82 0 measurement fields according to SEMI M36 P(EPD.sub.L = 0 cm.sup.−2) from full % 94.0 99.7 surface measurement according to SEMI M83 Maximum value of shear stress kPa 200 <25

[0085] In the comparative example of Table 5, a conventionally manufactured GaAs wafer (as described in Geiler et al. (2006)) having a diameter of 150 mm and separated from a corresponding GaAs single-crystal is concerned. FIG. 9 shows in greyscale the distribution of the measured local etch density EPD.sub.L and FIG. 10 shows in greyscale the distribution of the measured residual or shear stress.

[0086] The corresponding values of maximum shear stress are displayed in Table 5, and in particular for the comparative example as well as for the embodiment. In FIGS. 11 and 12, scales of the greyscale in the upper right corners have to be considered, which reflect the range of corresponding values depicted herein.

[0087] It is noted, that in practice up to nowadays vanishing values of the shear stress, i.e., maximum values of the shear stress of about 0 kPa (throughout this analysis, only the absolute amount of shear stress is given, if no sign as stated), has not been reached. This value, or those equal to 0.1 kPa or less, or further even those equal to or less 1 kPa may thus optionally be excluded or disclaimed.

[0088] In the various aspects and embodiments explained in the forgoing, the second section includes a longitudinal axis, which, when it is extended into a region of the first section, may extend in a distance of 15 mm or less from an inner wall of the crucible within the first section, but preferably in a distance of 10 mm or less, and even more preferably in a distance of 5 mm or less.

[0089] Furthermore, with respect to such aspects and embodiments, the second section 6′ may at least partially formed in cylindrical shape and may have an inner diameter of 15 mm or less, in particular in a range from 10 mm to 15 mm, or from 5 mm to 10 mm.

[0090] In the various aspects and embodiments explained in the forgoing, the device 1 is configured for manufacturing a crystal having a nominal diameter, which is to be achieved in a post-processing step following a step of growing the crystal, wherein the first section has an inner diameter which is associated with its cross-sectional area perpendicular to the central axis. This inner diameter maybe larger than the nominal diameter by equal to or more than 2 mm, preferably by equal to or more than 3 mm, more preferably by equal to or more than 5 mm, and the inner diameter is larger than the nominal diameter by 10 mm at maximum.

[0091] In the various aspects and embodiments explained in the forgoing, the second section 6, 6′ has a length k′ along a direction of its central axis M, wherein the length may amount to between 40 mm and 120 mm, preferably between 50 mm and 90 mm, more preferably between 60 mm and 80 mm, each range including the boundary values.

[0092] Various aspects and embodiments explained in the forgoing concern an AIII-BV-single-crystal or wafer obtained by separation therefrom, i.e., in particular semiconductor compound materials. These may specifically comprise, for example, gallium arsenide (GaAs) or Indium phosphide (InP), etc.

[0093] In some of the various aspects and embodiments explained in the forgoing, lattice hardening dopants are included in the single crystal manufactured. In such a case, the lattice hardening dopants may be selected from at least one the group composed of: boron, silicon, zinc, sulphur, indium. However, alternative suitable elements may be encompassed as well and the aspects and embodiments are not limited to those specific dopants listed above.