METHOD FOR MANUFACTURING A SINGLE CRYSTAL BY SOLUTION GROWTH ENABLING TRAPPING OF PARASITIC CRYSTALS

Abstract

A method for manufacturing a single crystal may be by solution growth from a seed crystal, in a unit including a tank and a growth platform having a lower plate. The method may include: fastening the seed to the lower plate; introducing a crystallization solution of density d.sub.S into the tank; treating the solution in order to render it supersaturated; bringing the seed into contact with the supersaturated solution; rotating the platform until the single crystal is obtained. Before bringing the seed into contact with the supersaturated solution, the method may include forming, in the tank, of a zone for trapping parasitic crystals of density d.sub.C by introducing, into the tank, a liquid, immiscible with the growth solution, of density d>d.sub.S and d<d.sub.c, which forms with the growth solution an interface located below the lower plate.

Claims

1. A process for manufacturing a single crystal by solution growth from a seed crystal, the process comprising, in an apparatus comprising a vessel configured to contain a crystal growth solution; a growth platform capable of being rotated in the vessel, and comprising a lower tray, on which the single crystal is intended to grow: bonding the seed crystal to the lower tray of the growth platform; introducing the crystallization solution into the vessel; treating the solution to make it supersaturated, to obtain a supersaturated solution, prior to bringing the seed crystal into contact with a supersaturated solution, forming, in the vessel, a trapping zone for parasitic crystals likely to grow in a crystal growth solution, by introducing into the vessel, of an immiscible liquid, which is immiscible with the crystal growth solution, the immiscible liquid having a density greater than a growth solution density and lower than a parasitic crystal density, and the immiscible forming with the crystal growth solution an interface located below a lower tray of a growth platform; bringing the seed crystal into contact with the supersaturated solution; and rotating the platform until the single crystal is obtained.

2. The process of claim 1, wherein the liquid has a chemical composition that does not allow growth of parasitic crystals.

3. The process of claim 1, wherein the apparatus further comprises a seed crystal protection member, and wherein the process further comprises: after bonding the seed crystal to the lower tray of the growth platform, and before bringing the seed crystal into contact with the supersaturated solution, placing the seed crystal protective member around the seed crystal and holding the seed crystal on the lower tray of the growth platform; and after introducing the crystallization solution and the immiscible liquid into the vessel, and before treating the solution to make it supersaturated, comprising, successively: treating the solution to make it undersaturated; bringing the protective member into contact with the undersaturated crystallization solution by immersion of the lower tray of the growth platform in the undersaturated crystallization solution; and bringing the seed into contact with the undersaturated crystallization solution by moving the protective member away from the lower tray.

4. The process of claim 1, wherein the crystal growth solution is an aqueous medium and the immiscible liquid comprises a perfluoropolyether, a perfluorocarbon, or a mixture of two or more of any of these.

5. The process of claim 1, wherein the single crystal is a KDP single crystal.

6. The process of claim 1, wherein the single crystal is a DKDP single crystal.

7. The process of claim 1, wherein the immiscible liquid comprises a perfluoropolyether.

8. The process of claim 1, wherein the immiscible liquid comprises a perfluorocarbon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The invention will be better understood and other advantages and features will appear upon reading the description that follows, given by way of non-limiting example, accompanied by the appended drawings, among which:

[0046] FIG. 1, already described, is a schematic view of an example of a growth installation used in the prior art;

[0047] FIG. 2 is a schematic view of another example of a growth installation of the prior art, configured to limit the effects of nucleation during solution growth;

[0048] FIG. 3 is a schematic view of the growth installation illustrated in FIG. 1, implementing the manufacturing process according to the invention, in order to limit the effects of nucleation during solution growth.

[0049] On all these figures, identical or similar reference marks designate identical or similar elements or sets of elements.

DETAILED DISCLOSURE OF SPECIFIC EMBODIMENTS

[0050] An example of a growth installation with which the process according to the invention can be implemented is shown in FIG. 3. The installation is the same as the one described in FIG. 1. There is thus, in the vessel 1, a growth platform 12, a growth solution 2 and a growing crystal 10. The growth solution 2 and the growing crystal 10 form respectively a first phase (liquid) and a second phase (solid). In accordance with the process according to the invention, a liquid 21, which is immiscible with the growth solution 2, is also introduced into the vessel; thus the vessel 1 also contains a third phase (liquid), which forms a trapping zone 22 for the parasitic crystals.

[0051] The density of this immiscible liquid 21 is chosen higher than that of the growth solution 2, so that it covers the bottom of the vessel 1. Furthermore, the amount of immiscible liquid introduced into the vessel is such that the interface 24 between the immiscible liquid 21 and the growth solution 2 is located under the lower tray 5 of the growth platform.

[0052] Furthermore, the liquid 21 which is immiscible with the growth solution 2 is chosen so that its density is lower than that of the crystals resulting from nucleation, so that these crystals are trapped in this liquid by gravity.

[0053] Since the parasitic seed has a higher density than that of the growth solution, gravity carries it to the bottom of the vessel to the interface between the growth solution and the immiscible liquid. As the density of the seed is higher than that of the immiscible liquid, located at the bottom of the vessel, it crosses the interface to be trapped in the immiscible liquid, in which it no longer evolves during the further growth of the crystal on the lower tray of the platform.

[0054] The amount of immiscible liquid introduced into the vessel is a compromise between having a trapping zone with a minimum height able to trap all possible parasitic crystals and having a maximum volume of crystal solution in the vessel dedicated to the growth of the single crystal.

[0055] In rapid grow in supersaturated solution, in a growth installation for the production of very large KDP crystals for example, the seed is a cube with about 1 cm sides immersed in a growth solution of several liters, even tens or hundreds of liters. The growth installation illustrated in FIG. 3 has a seed protection member 25. To produce a single crystal in accordance with the process according to the invention, such an installation can be used.

[0056] According to an embodiment of the process in accordance with the invention, the seed crystal 4 is bonded to the lower tray 5 of the growth platform; then the protective member is placed around the seed while maintaining the stem 8 in contact with the lower tray 5 so that the seed is contained in the recess 9; then the crystallization solution 2 is introduced into the vessel; an immiscible liquid 21 is then poured into the vessel so as to form the parasitic crystal trapping zone 22; the protective member is brought into contact with the crystallization solution by immersing the lower tray (5) of the growth platform in the crystallization solution; the platform 12 is rotated; the crystallization solution is treated to make it undersaturated; the seed is brought into contact with the undersaturated crystallization solution by moving the protective member 25 away from the lower tray; before the complete disappearance of the seed, the solution is treated to make it supersaturated; the rotation of the platform in the supersaturated solution is maintained until the desired single crystal is obtained.

[0057] According to an example embodiment, to make a potassium di hydrogen phosphate (KDP) single crystal, 800 liters of KDP solution (growth solution, the solvent being water) having a density of 1.3 and 50 liters of perfluorinated polyether (PFPE) (immiscible liquid), which is immiscible with the growth solution, and has a density of the order of or greater than 1.8, are poured into a vessel. The parasite density, in the case of KDP, is of the order of 2.35. The density of the immiscible liquid is actually chosen higher than the density of the growth solution and lower than that of the parasitic crystals.

[0058] The process according to the invention has many advantages. It makes it possible to limit the effects of crystal nucleation in a supersaturated growth solution during the growth of a single crystal, without requiring any material modifications to the growth installation, and in particular to the vessel. Indeed, it allows the single crystal to continue growing despite the presence in the growth solution of a nucleation source other than the initial seed of the single crystal. Ultimately, the process according to the invention makes the manufacture of large single crystals more reliable.