METHOD FOR PRODUCING SILICON-INGOTS

Abstract

Method for producing silicon-ingots (1) including the following steps: providing a silicon melt (3), growing a block (2) of silicon from the silicon melt (3), the block (2) having a predetermined crystal orientation, cutting the block (2) along at least one cutting plane (16, 17, 18) into a number of silicon-ingots (1).

Claims

1. A silicon block comprising: a length of at least 400 mm measured in a growth direction; and a cross sectional area of at least 320 mm320 mm, wherein silicon of the block has an interstitial oxygen content of less than 510.sup.16 atoms per cm.sup.3, wherein the silicon of the block has a nitrogen content of less than 110.sup.15 atoms per cm.sup.3.

2. A silicon block according to claim 1, wherein the growth direction is parallel to one of the following directions: <100>, <110> and <111>.

3. A silicon block according to claim 1, wherein side faces of the block have normals which are oriented parallel to one of the following directions: <100>, <110> and <111>.

4. A silicon block according to claim 1, wherein said length measured in said growth direction is an integer multiple of 156 mm.

5. A silicon block according to claim 1, wherein said block displays a monocrystalline structure in at least 50% of its volume.

6. A silicon block according to claim 1, wherein said block has a constant density of dislocations along its entire growth direction.

7. A silicon block according to claim 6, wherein said dislocation density is less than 10.sup.4 cm.sup.2.

8. A silicon block according to claim 1, wherein the block has a rectangular cross section.

9. A silicon block according to claim 8, wherein a side length of said cross section is an integer multiple of 156 mm.

10. A silicon block according to claim 9, wherein another side length of said cross section is around 500 mm.

11. A silicon block comprising: a block structure comprising silicon, a length of at least 400 mm measured in a grow direction and a cross sectional area of at least 320 mm320 mm, said silicon having an interstitial oxygen content of less than 510.sup.16 atoms per cm.sup.3 and a nitrogen content of less than 110.sup.15 atoms per cm.sup.3.

12. A silicon block according to claim 11, wherein the growth direction is parallel to one of the following directions: <100>, <110> and <111>.

13. A silicon block according to claim 11, wherein side faces of the block have normals which are oriented parallel to one of the following directions: <100>, <110> and <111>.

14. A silicon block according to claim 11, wherein said length measured in said growth direction is an integer multiple of 156 mm.

15. A silicon block according to claim 11, wherein said block displays a monocrystalline structure in at least 50% of its volume.

16. A silicon block according to claim 11, wherein said block has a constant density of dislocations along its entire growth direction.

17. A silicon block according to claim 16, wherein said dislocation density is less than 10.sup.4 cm.sup.2.

18. A silicon block according to claim 11, wherein the block has a rectangular cross section.

19. A silicon block according to claim 18, wherein a side length of said cross section is an integer multiple of 156 mm.

20. A silicon block according to claim 19, wherein another side length of said cross section is around 500 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In the drawings:

[0028] FIG. 1 is a schematic view of an apparatus for the production of silicon blocks;

[0029] FIG. 2 is a schematic view of a silicon block produced with the apparatus according to FIG. 1;

[0030] FIG. 3 is a schematic view of a seed crystal to be cut from a Czochralski ingot;

[0031] FIG. 4 is a schematic view of a cutting scheme for the cutting of the silicon block according to FIG. 2 into silicon ingots;

[0032] FIG. 5 is a view of a different embodiment of a silicon block;

[0033] FIG. 6 is a schematic view of the cutting scheme to cut seeds from a Czochralski ingot in order to grow the silicon block shown in FIG. 5;

[0034] FIG. 7 is a view of the seed assembly comprising a single seed cut according to the cutting scheme shown in FIG. 6;

[0035] FIG. 8 is view of a similar cutting scheme to FIG. 6 for cutting seeds from a different Czochralski ingot;

[0036] FIG. 9 is a view of a seed assembly comprising two seeds cut according to the cutting scheme shown in FIG. 8;

[0037] FIG. 10 is a view of a cutting scheme to cut ingots from the silicon block shown in FIG. 5;

[0038] FIG. 11 is a view of another embodiment of a silicon block;

[0039] FIG. 12 is a schematic view of a cutting scheme to cut seeds from a Czochralski ingot in order to grow the silicon block shown in FIG. 11;

[0040] FIG. 13 is a view of a seed assembly comprising a single seed cut according to the cutting scheme shown in FIG. 12;

[0041] FIG. 14 is view of a similar cutting scheme to FIG. 12 for cutting seeds from a different Czochralski ingot;

[0042] FIG. 15 is a view of a seed assembly comprising two seeds cut according to the cutting scheme shown in FIG. 14;

[0043] FIG. 16 is a view of a cutting scheme to cut ingots from the silicon block shown in FIG. 11;

[0044] FIG. 17 is a view of yet another embodiment of a silicon block;

[0045] FIG. 18 is a schematic view of the cutting scheme to cut seeds from a Czochralski ingot in order to grow the silicon block shown in FIG. 17;

[0046] FIG. 19 is a view of the seed assembly comprising a single seed cut according to the cutting scheme shown in FIG. 18;

[0047] FIG. 20 is view of a similar cutting scheme to FIG. 18 for cutting seeds from a different Czochralski ingot;

[0048] FIG. 21 is a view of a seed assembly comprising two seeds cut according to the cutting scheme shown in FIG. 20; and

[0049] FIG. 22 is a view of a cutting scheme to cut ingots from the silicon block shown in FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] In the following a method for producing silicon ingots 1 is described. First a silicon block 2 is produced. The silicon block 2 can be grown from a silicon melt 3 in a crucible 4. The silicon block 2 can in particular be grown according to a Bridgman process or a vertical gradient freeze process. For that an apparatus schematically shown in FIG. 1 is used. The apparatus comprises a device for melting and crystallizing silicon. Such device comprises the crucible 4 as well as a temperature control device with heating- and/or cooling elements 5. The crucible 4 can also be part of the device. The crucible 4 comprises an inside, which can be filled with silicon, either in form of solid silicon pieces or in form of already melted silicon. Thus, the silicon melt 3 can be provided in the inside of said crucible 4.

[0051] At the bottom of the crucible 4 a seed assembly 6 is provided. The seed assembly will be described in more detail later.

[0052] The silicon melt 3 can be crystallized inside the crucible 4. Thus, the silicon block 2 can be produced.

[0053] For further details of the apparatus and method for the production of the silicon block 2 reference is made to DE 10 2013 200 079.0, which herewith is incorporated in its entirety into the present application. Further details of the apparatus and the method for the production of the silicon block 2 can also be found in DE 10 2010 029 741 A1, which is also incorporated by reference in its entirety.

[0054] Alternatively, the silicon block 2 can be produced by a crucible less method. It can in particular be produced according to the method described in U.S. Ser. No. 13/561,350, which herewith is also incorporated in its entirety by reference into the present application.

[0055] The silicon block 2 has at least zones with a monocrystalline structure. It has in at least 50%, in particular at least 70%, in particular at least 90% of its volume a monocrystalline structure. Thus, it is also referred to as quasi monocrystalline silicon block 2.

[0056] According to the embodiment shown in FIGS. 2 and 4, the silicon block 2 has a square cross section 7. The cross section 7 measures 318 mm318 mm.

[0057] As further indicated in FIG. 2 the silicon block 2 has side faces 14 and 15, which are parallel to the growth direction 10 and perpendicular to each other. The normal of the side face 14 has a <010>-orientation. The normal of the side face 15 has a <001>-orientation.

[0058] The silicon block 2 is grown from a seed crystal 8 shown in FIG. 3. The seed crystal 8 is produced from a Czochralski ingot 9 with a diameter of 450 mm. For that, the Czochralski ingot 9 is cut perpendicular to its longitudinal axis.

[0059] Starting from the seed crystal 8 the silicon block 2 is grown in a growth direction 10. The growth direction 10 is also referred to as longitudinal direction of the silicon block 2. The growth direction 10 is parallel to a <100>-orientation. This can be achieved by choosing the seed crystal 8, such that the normal of its surface is parallel to a <100>-orientation. Preferably, the cleavage direction is oriented at 45 to an edge 11 of the seed crystal 8.

[0060] Preferably, the seed crystal 8 is dislocation free.

[0061] Preferably, the seed crystal 8 is at a temperature, which is close to a melting temperature when the silicon melt 3 is brought into contact with its surface. Further, the seed crystal 8 is slightly melted on the seeding surface. Further, the growth process is controlled, such that the solid-liquid interface is basically flat.

[0062] In FIG. 2 a top area 12 and a bottom area 13 are schematically indicated. The bottom area 13 comprises the seed crystal 8. The top area 12 and/or the bottom area 13 can be cut away after the growth of the silicon block 2 has been completed, in particular after the silicon block 2 has cooled down to room temperature. By that, it can be ensured, that the silicon block 2 has homogeneous properties along its entire extension in the growth direction 10. In particular, it can be ensured, that the silicon block 2 has a constant dislocation density over its entire length L. The length L of the silicon block 2 can be around 200 mm. It can be at least 320 mm. It can also be as large as 64 cm, 80 cm, 96 cm or more.

[0063] As schematically shown in FIG. 4 the silicon block 2 is cut along cutting planes 16, 17. The cutting planes 16 are parallel to the side face 14. The cutting planes 16 are parallel to the side face 15 of the silicon block 2. The cutting planes 16 are perpendicular to the cutting planes 16. The cutting planes 16 are equidistant to each other. The cutting planes 17 are equidistant to each other.

[0064] Thus, the silicon block 2 is cut into a matrix of 22 silicon-ingots 1.

[0065] The silicon-ingots 1 have a length 1 corresponding to the length L of the silicon block 2. The silicon-ingots 1 have in particular a longitudinal direction parallel to a <100>-orientation. Thus, wafer with a cross section corresponding to the cross section of the silicon-ingots 1 and a normal of the wafer surface with a <100>-orientation can be cut from the silicon-ingots 1. For that, the silicon-ingot 1 is divided along planes perpendicular to its longitudinal direction.

[0066] According to the invention dislocation free silicon blocks 2 are grown according to the method described above. In order to facilitate a dislocation free growth of the silicon block 2, the seed assembly 6 comprises a single seed crystal 8. However, a seed assembly 6 made of a plurality of different dislocation free seed crystals 8 is also possible.

[0067] According to another embodiment schematically shown in FIGS. 5 to 10 the growth direction 10 of the silicon block 2 is parallel to a <110>-orientation. In this case the normal of the side face 14 is parallel to a <110>-orientation. The normal of the side face 15 is parallel to a <001>-orientation.

[0068] The silicon block 2 is grown from one of the seed assemblies 6 shown in FIG. 7 and FIG. 9, respectively. Whereas the seed assembly 6 shown in FIG. 7 comprises a single seed crystal 8, the seed assembly 6 shown in FIG. 9 comprises two seed crystals 8. All the seed crystals 8 according to this embodiment have a surface the normal of which is parallel to a <110>-orientation. The seed crystals 8 are cut from Czochralski ingots as shown in FIG. 6 and FIG. 8, respectively. In particular, the single seed crystal 8 according to FIG. 7 is cut from a Czochralski ingot with a diameter of 450 mm. In contrast, the seed crystals 8 according to FIG. 9 are cut from a Czochralski ingot with a diameter of 225 mm. The seed crystals 8 are cut by cutting a Czochralski ingot along planes parallel to a <001>-orientation, which is parallel to the growth direction and thus the longitudinal direction of the Czochralski ingots 9.

[0069] Whereas the seed crystal 8 according to FIG. 7 has a square shape with a side length of 320 mm, the seed crystals 8 according to FIG. 9 each have a rectangular shape with side length of 160 mm and 320 mm, respectively.

[0070] Again, the cross section 7 of the silicon block 2 is identical to the area of the seed assembly 6.

[0071] The silicon block 2 is grown to a length L, which preferably corresponds to an integer multiple of the desired side length of the cross section of the silicon-ingots 1 to be cut from the silicon block 2. In case of a desired side length of 156 mm, the length L of the silicon block 2 can be about 313 mm, 470 mm, 626 mm, 940 mm, or more.

[0072] As shown schematically in FIG. 10, the silicon block 2 is cut into a 23 matrix of silicon-ingots 1. For other alternative references made to the description of the embodiment according to FIGS. 2 to 4.

[0073] In this embodiment the silicon block 2 is cut into silicon-ingots 1 by a number of first cutting planes 16 which are parallel to the side face 14 and second cutting planes 18, which are parallel to the cross section 7, i.e. perpendicular to the growth direction 10 of the silicon block 2.

[0074] As can be seen from FIG. 10, the silicon-ingots 1 have a length 1 of 320 mm.

[0075] By using a seed assembly 6 with dimensions of 320 mm480 mm (cf. FIGS. 13 and 15) it is possible to produce silicon-ingots 1 with a length 1 of about 470 mm as shown in the embodiment according to FIGS. 11 to 16.

[0076] Such a seed assembly can be made from Czochralski ingots 9 with a length in longitudinal direction of 480 mm. Apart from that the embodiment according to FIG. 11 to FIG. 16 corresponds to the embodiment shown in FIGS. 5 to 10.

[0077] The cross section 7 of the silicon block 2 can be further increased by using yet larger seed assemblies 6 as for example shown in FIGS. 17 to 22.

[0078] According to the embodiment shown in FIG. 19 the seed assembly 6 comprises two seed crystals 8 each with dimensions of 240 mm480 mm.

[0079] According to the embodiment shown in FIG. 21 the seed assembly 6 comprises three seed crystals 8, each with dimensions of 160 mm480 mm.

[0080] Although in the figures the seed assembly 6 comprises arrangements of seed crystals 8, which, in at least one direction have a side length corresponding to the side length of the seed assembly 6, it is also possible, that the seed assembly 6 comprises a two dimensional arrangement of seed crystals 8. The seed assembly 6 can in particular comprise an arrangement of 22, 23, 24, 25, 26, 33, 34, 35, 36, 44, 45, 46, 55, 56, 66 or more seed crystals 8.

[0081] Further alternatives are also possible. In particular, whereas the seed assemblies 6 shown in the figures all comprise seed crystals 8 with identical shape, it is also possible to build a seed assembly 6 with seed crystals 8 of different sizes and/or shapes.

[0082] Furthermore, although the silicon-ingots 1 shown and described in the embodiments according to the Figs. all have a longitudinal direction which is parallel to a <100>-orientation, it is also possible to chose the cutting planes 16, 17, 18, such that the silicon-ingots 1 have a longitudinal direction parallel to a <111>-orientation or parallel to a different orientation.

[0083] With the method described above the throughput of the production of silicon-ingots 1 could be increased by more than 50%, in particular by more than 100%, in particular by more than 125% compared to previous methods.

[0084] The silicon of the block produced with the method according to the present invention can have an interstitial oxygen content of less than 510.sup.16 atoms per cm.sup.3. It can have a nitrogen content of less than 510.sup.15 atoms per cm.sup.3. This includes single nitrogen atoms, nitrogen dimers NN and triplets out of two nitrogen atoms and one oxygen atom NNO. Silicon ingots cut from these blocks and wafers cut therefrom have according features.

[0085] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.