METHOD AND CRUCIBLE FOR PRODUCING PARTICLE-FREE AND NITROGEN-FREE SILICON INGOTS BY MEANS OF TARGETED SOLIDIFICATION, SILICON INGOT, AND THE USE OF THE CRUCIBLE

Abstract

The present invention relates to a method and to a crucible for producing particle-free and nitrogen-free silicon ingots by means of targeted solidification, in which method a crucible is provided, the inner surface of the crucible having a coating containing Si.sub.xN.sub.y over its full surface or at least in regions, which coating is coated with a protective layer containing SiO.sub.x in order to reduce or prevent the introduction of nitrogen and Si.sub.xN.sub.y particles into the silicon. The invention also relates to a silicon ingot, which is virtually free from nitrogen or Si.sub.xN.sub.y particles.

Claims

1-29. (canceled)

30. A method for producing particle-free and nitrogen-free silicon ingots by directional solidification, in which a) a crucible is provided, the inner surface of the crucible having a coating containing Si.sub.xN.sub.y over the entire surface or at least in regions, which coating is coated with a protective layer containing SiO.sub.x for reducing or avoiding the entry of nitrogen and entry of Si.sub.xN.sub.y particles into the silicon, b) the crucible is filled with silicon raw material, c) the silicon raw material is melted in the crucible to form a silicon melt, and d) the silicon melt is subjected to a directional solidification, whereby particle-free and nitrogen-free silicon is formed.

31. The method according to claim 30, wherein the protective layer is applied to the Si.sub.xN.sub.y-containing coating by means of a spraying method, a brushing method, a spreading method and/or a dipping method of a suspension containing SiO.sub.x and the SiO.sub.x-containing moist protective layer produced in this way is dried.

32. The method according to claim 31, wherein the suspension contains 5 to 90% by weight SiO.sub.x, and 95 to 10% by weight of a suspending agent.

33. The method according to claim 30, wherein the protective layer is applied to the Si.sub.xN.sub.y-containing coating by a spraying method, a brushing method, a spreading method, and/or a dipping method of a suspension containing Si and the Si-containing moist protective layer produced in this way is dried and/or oxidized.

34. The method according to claim 33, wherein the suspension contains 5 to 90% by weight of Si and 95 to 10% by weight of a suspending agent.

35. The method according to claim 33, wherein the Si layer is oxidized under an air atmosphere or an inert gas atmosphere enriched with oxygen at a temperature of 800 and 1400° C. to form an SiO.sub.x layer.

36. The method according to claim 35, wherein the duration of the oxidation is in the range from 0.5 h to 12 h.

37. The method according to claim 31, wherein when the SiO.sub.x or Si-containing suspension is applied, the crucible or the coating containing Si.sub.xN.sub.y has a temperature of 10° C. to 200° C.

38. The method according to claim 30, wherein the SiO.sub.x has at least one of the following properties: an iron content of 0 ppm to 5 ppm, an aluminum content of 0 ppm to 20 ppm, a content of metals other than iron and aluminum of 0 ppm to 5 ppm, a particle size d50 of 0.05 to 100 μm, a particle size d90 of 0.01 to 200 μm.

39. The method according to claim 30, wherein the crucible contains or consists of a material which is selected from the group consisting of SiC, C, BN, pBN, Si.sub.xN.sub.y, SiO.sub.x, and mixtures and combinations thereof.

40. The method according to claim 30, wherein the coating containing Si.sub.xN.sub.y has at least one of the following properties: a content of up to 100% by weight, Si.sub.xN.sub.y a thickness of 10 μm to 2500 μm, a square mean roughness value R.sub.q of 1 μm to 100 μm, an adhesive strength on the crucible bottom of 0.5 MPa to 5 MPa, and a porosity of 0.5% to 60%.

41. The method according to claim 30, wherein the coating containing Si.sub.xN.sub.y is produced in that an Si.sub.xN.sub.y-containing suspension is applied to the inner surface of the crucible and the moist Si.sub.xN.sub.y-containing coating produced in this way is dried.

42. The method according to claim 30, wherein the Si.sub.xN.sub.y-containing suspension has a composition having the following components: 10% by weight to 60% by weight Si.sub.xN.sub.y, 30% by weight to 80% by weight organic solvent or water, 0% by weight to 30% by weight silicon, 0.5% by weight to 10% by weight dispersant, 0.01% by weight to 0.2% by weight defoamer, and 0.05% by weight to 2% by weight organic binder, wherein the proportions of the components add up to 100% by weight.

43. The method according to claim 30, wherein the Si.sub.xN.sub.y-containing suspension is applied by a spraying method, a brushing method, a spreading method, and/or a dipping method, and/or the crucible has a temperature of 10° C. to 200° C. when applying the Si.sub.xN.sub.y containing suspension, and/or the Si.sub.xN.sub.y-containing suspension is additionally applied to at least one further inner surface of the crucible.

44. The method according to claim 30, wherein after step a) and before step b), at least one seed plate, is arranged on the bottom of the crucible.

45. The method according to claim 44, wherein the at least one seed plate consists of or contains mono- or multi-crystalline silicon, wherein the at least one seed plate has an orientation perpendicular to the seed plate in the direction of crystal growth.

46. The method according to claim 40, wherein the at least one seed plate has a square shape, a rectangular shape, or a round shape, and/or the at least one seed plate has a thickness of 1 to 10 cm.

47. A crucible for producing particle-free and nitrogen-free silicon ingots by means of directional solidification, the inner surface of the crucible having a coating containing Si.sub.xN.sub.y over the entire surface or at least in regions, on which a protective layer containing SiO.sub.x for reducing or avoiding the entry of nitrogen and Si.sub.xN.sub.y particle entry is deposited in the silicon.

48. The crucible according to claim 47, wherein the protective layer containing SiO.sub.x has a thickness of 10 to 2000 μm.

49. The crucible according to claim 47, wherein the protective layer containing SiO.sub.x has a square mean roughness value R.sub.q of 1 to 250 μm.

50. The crucible according to claim 47, wherein the protective layer containing SiO.sub.x has a porosity of 20 to 80% after coating the Si.sub.xN.sub.y layer.

51. The crucible according to claim 45, wherein the crucible has at least one seed plate at the bottom of the crucible.

52. The crucible according to the claim 51, wherein the at least one seed plate consists of or contains mono- or multi-crystalline silicon, wherein the at least one seed plate has an orientation perpendicular to the seed plate in the direction of crystal growth.

53. The crucible according to claim 51, wherein the at least one seed plate has a square shape, a rectangular shape, or a round shape, having a diameter of 200 or 300 mm, and/or the at least one seed plate has a thickness of 1 to 10 cm.

54. A silicon ingot having a nitrogen concentration of <1E16 at/cm.sup.3.

55. The silicon ingot according to claim 54, wherein the silicon ingot has an Si.sub.xN.sub.y particle density of <10/cm.sup.3.

56. A silicon ingot produced according to the method of claim 30 which has a nitrogen concentration of <1E16 at/cm.sup.3.

57. The silicon ingot according to claim 54, wherein the silicon ingot consists of single crystal, quasi-monocrystalline or multicrystalline silicon.

58. A method of producing silicon ingots by means of directional solidification, comprising utilizing the crucible according to claim 47.

Description

[0061] The subject according to the invention is to be described in more detail with the aid of the following FIGURES and examples, without restricting them to the specific forms shown here.

[0062] FIG. 1 uses a diagram to show the nitrogen concentration in a silicon ingot according to the invention over the ingot height, each measured in the ingot center

EXEMPLARY EMBODIMENT

[0063] In a first exemplary embodiment, a series of laboratory crystallization experiments were carried out (Si initial weight 1.1 kg, ingot dimensions 100 mm in diameter, 60 mm in height).

[0064] First, a reference was grown without an SiO2 protective layer. The resulting nitrogen concentration in the ingot, measured by FTIR, is here [N]≥1E16 at/cm.sup.3 (see FIG. 1), which is in the range of the nitrogen solubility limit, thus leading to the formation of precipitates.

[0065] If a very thin SiO2 protective layer (2U) is now applied, the concentration over the major part of the block already falls below the detection limit of the FTIR measurement method of 1E15 at/cm.sup.3. A value of .sup.˜2E15 at/cm.sup.3 can only be measured at the end of the block, which is an indication of the dissolution of the SiO2 layer. With increased thickness (4U or 8U), practically no nitrogen can be measured using FTIR, that is, constantly below 1E15 at/cm.sup.3, and Si3N4 precipitation is reliably avoided. In addition, it can be assumed that no Si3N4 particles got into the melt, as otherwise they would have dissolved until nitrogen solubility was reached and nitrogen would therefore have to be detected. In the case of an SiO2 coating having a thickness of 20U, cracks occurred in the lower block bottom area due to the different thermal expansion of the SiO2 layer and the Si block.

[0066] In comparison to the experiments with the SiO2 layer, FIG. 1 shows a further experiment with forced melt convection. The nitrogen values show that the formation of precipitates cannot, however, completely avoid the entry of nitrogen.