Method for growing of sapphire single crystals from melt

FIELD: physics.

SUBSTANCE: invention is related to the field of single crystals growing from melts and may be used in enterprises of chemical and electronic industry for growing of sapphire single crystals of 1-6 quality category by Kyropulos method from melts on seed crystal. Method includes preparation of charge, its loading and melting by means of heating element in vacuum, seeding and pulling of single crystal, at that growing of single crystal is carried out to seed of technical quality of 6 category, which contains gas inclusions with size of up to 500 mcm and their accumulation, by means of seed crystal lowering by 10 mm every 10-12 minutes until it touches melt with temperature of 2330 K, which has no nucleation centers on the surface, seed crystal submersion for 20-30 sec in melt at 10-15 mm, lowering of heating element power until melt supercooling, which is required for nucleation of crystallisation grains on seed crystal surface in process of constrictions growth, and formation of cone-shaped convex crystallisation front in direction of melt.

EFFECT: growth of sapphire single crystals of optical quality on seed crystal of technical quality with content of gas inclusions and their clusters with diameter of up to 500 mcm, which makes it possible to reduce prime cost of single-crystal sapphire.

 

The invention relates to the field of growing single crystals from the melt and can be used in the chemical and electronics industries for sapphire crystal growing from the melt.

There is a method of growing single crystals of sapphire, invented by Kyropoulos in 1930 ("the single Crystals of corundum", Dobrovinsky ER, Litvinov L.A., reed CENTURIES, Kiev, publishing house "Naukova Dumka", 1994). A modification of this method was the state optical Institute (GOI). The essence of this method of cultivation that the crystallization starts from the seed by reducing the power of the heating element and through heat sink cooling fluid. The growth processes are carried out in equipment of the type "omega". Growing single crystals of possible translations and rotations. In this method, apply the seed single crystal sapphire high structural perfection, without foreign and gas inclusions, not containing block sections.

A known method of growing sapphire seed (Musatov M.I. Influence of temperature gradients on the shape of the front and the crystallization rate. Proceedings of optical in-TA, 1983, 54, N 188, p.41-45)that allows to obtain single crystals with a diameter of 150 mm and weighing up to 10 kg

Closest to the claimed invention is SPO is about growing refractory single crystals (patent RF №2056463, SW 15/00, 29/20, publ. 1996)adopted for the prototype. The method allows to obtain single crystals of sapphire diameter up to 160 mm and weight up to 15 kg In the prototype of the growing single crystal type sapphire involves the values of the temperature gradients in the range of 0.05 to 1.0°C/mm and the vertical temperature gradients to the radial larger units, vacuum melting of the original charge, making priming and pulling the single crystal from the cooled melt. The temperature of depositing the seed set for the emergence of a single crystal of size 1 to 3 mm on the surface of the melt. The speed of pulling of the monocrystal change speed of 0.1 mm/h at the beginning of crystallization to 1.0 mm/h in the final stage of the process. When growing sapphire comes from the calculation of the cross-sectional area of the seed in 10 mm21 kg of the single crystal.

The disadvantage of the prototype is the high cost of the seed material used for the optical quality, without gas inclusions.

The technical result, which is manifested when using the present invention is to reduce the cost of monocrystalline sapphire.

The technical result is achieved by a method for sapphire crystal growing from the melt, including the preparation of the charge, the loading mixture, melting the mixture in a vacuum, seeding, you shall aguana of the single crystal in the presence of values of the temperature gradient in the range of 0.05 to 1.0° C/mm and the vertical temperature gradients to the radial greater than one. Growing produce single crystal on a seed crystal technical quality 6 categories containing gas include size up to 500 microns and their aggregations by making seed 10 mm every 10-12 min before contact with the melt temperature 2330 To not having the surface of the grains of crystallization, immersing the seed for 20-30 seconds in the melt 10-15 mm from the end surface, reducing the power of the heating element to obtain a supercooling of the melt required for the nucleation of grains of crystallization on the surface of the seed for growing banners, and forming a cone-shaped convex to the melt solidification front.

It is known that in growing single crystals of sapphire optical quality of the melt in the growth installations "omega" currently carried out on the seed 1-2 category. The first category is characterized by the following parameters: no inclusions, block boundaries, twins, microfuze, the scattering centers. The second category is characterized by the following parameters: no inclusions, block boundaries, twins. Resolved scattering centers (microfuze size up to 10 μm) (encyclopedia of Sapphire. Dabrowica, Llivina, Wpisy, Kharkov, STC "Institute for single crystals", 2004, Tr).

This is due to the fact that the growing single crystal repeats the structure of the seed, inheriting, therefore, the existing defects.

In the proposed method after fusion of the charge a seed crystal is lowered by 10 mm every 10-12 minutes until it touches the melt in order to avoid thermal shock. Then down for 20-30 seconds a seed crystal in the melt 10-15 mm to the edge of the melt and thus was dropped from the surface defects and contamination. In that case, if the seed be lowered to a depth of less than 10 mm, the area from which removes impurities and defects in the melt, will be insufficient and the growing single crystal inherits these defects. If you omit the seed to a depth of more than 15 mm, it will lead to the melting of the part of the end surface of the seed, which is located at a depth of 15 mm in the melt. The temperature of the melt, in which shall be entered the seed must be 2330 K (the melting point of single crystal sapphire) and the seed single crystal - melt must be in equilibrium, i.e. the presence of crystals on the surface of the melt size of 1-3 mm (as in the prototype) is not permitted as this indicates a significant degree of supercooling of the melt and lead to the rapid growth of the single crystal with many defects. Thus, the material of the seed is exposed to viscotester the business annealing. No Pets seeding in the presence on the surface of the seed foreign inclusions, having a melting point higher than that of aluminum oxide, because this will lead to the formation of the block structure. Next, reduce the power of the heating element to obtain a supercooling of the melt required for the nucleation of grains of crystallization on the surface of the seed. thermal field during cultivation should be formed so that the isotherms had the shape of a cone, which is directed downwards, while the solidification front will have a corresponding shape. This geometry facilitates the movement of gas bubbles from the volume to the surface of the melt under the action of the Archimedean force. The presence of pores and clusters of bubbles in the priming does not increase the saturation of the melt and is not inherited by the growing single crystal, even if they are on the boundary crystal - melt (Nikolenko M.V., Eskov EV, Ignatov, A. "Gas inclusions in single crystals of sapphire grown by the kyropoulos method", 6th international scientific conference "solid state Chemistry and modern micro - and nanotechnologies", Kislovodsk, 2006).

The amount of gas inclusions in the seed should not exceed 500 microns due to the fact that the larger the size of the bubbles to the mechanical strength of sapphire is reduced, which can lead to the destruction of seed by the action of gravity of the growing single crystal. This is due to the fact that the strength properties of sapphire are structure-sensitive.

Unlike the prototype, which originate from the calculation of the cross-sectional area of the seed in 10 mm21 kg of the single crystal, it is proposed to apply the seed with a cross-sectional dimension of 5 mm21 kg

The proposed method for sapphire crystal growing from the melt can grow quite perfect in its structure single crystals without bubbles, using as seed technical material 6 quality category.

Specific examples for growing sapphire crystal from the melt

The grown single crystals of sapphire in the amount of 5 pieces up to a diameter of 200 mm and a weight of 24 kg and 1 single crystal with a diameter of 300 mm and weighing less than 60 kg with the use of nucleating technical quality 6 categories containing gas include size up to 500 microns and their aggregations. The cultivation was carried out in growth installations "omega" in the following way. The mixture of aluminum oxide, sintered method of induction garnissage melt, the content of impurities presented in the table prepared for the growth process (crushed mechanically and subjected to magnetic separation).

Table of composition and quantity of impurities in the initial charge

Chemical elements, wt.%ToSiMnFeNiCTiMgYMo
Al2About3obtained by the method of garnissage0,00010,0001is 0.00020,00010,0001is 0.00020,00010,00010,00010,00005

Vacuum and electrical parts of cultivating plants "omega" prepare to Rostova process. The charge is loaded into the crucible installation. Installation of vacuum to reach the target pressure of 10-5mm Hg Power of the heating element increases until the melting of the charge. The melt is maintained at the attained temperature for 1 hour, in order to place the allocation from the melt. Seeding is produced as follows. A seed crystal is lowered by 10 mm every 10-12 min before contact with the melt temperature 2330 To not having the surface of the grains of crystallization. Then immerse the seed for 20-30 seconds. in the melt 10-15 mm, and then reduce the power of the heating element prior to the advent of grain crystallization on the surface of the seed. The cultivation is carried out at a pulling speed of 3-8 mm/hour. The temperature gradient support in INTA the shaft 0,05-1,0° C/mm until crystallization of the entire melt. The percentage yield 2 quality category (optical quality) in the thus grown single crystals averaged 54%.

Extract from "the Encyclopedia of Sapphire, Dabrowica, Llivina, Wpisy, Kharkov, STC "Institute for single crystals", 2004, page 490. Quality category sapphire.

Optical quality

1. No inclusions, block boundaries, twins, microfuze, the scattering centers.

2. No inclusions, block boundaries, twins. Resolved scattering centers (microfuze size up to 10 microns).

3. No inclusions, block boundaries, twins. Permitted evenly distributed bubbles of size not exceeding 50 μm, at least 500 microns.

4. No inclusions, block boundaries, twins. Permitted evenly distributed bubbles of size not exceeding 50 μm, at least 500 microns and clusters of bubbles with diameter less than 200 microns and at least 20 mm

The technical quality

5. No inclusions, block boundaries, twins. Permitted evenly distributed bubbles of size not exceeding 50 μm, at least 500 microns and clusters of bubbles with a diameter less than 500 microns and at least 20 mm

6. No inclusions, twins, block boundaries with misorientation angle more than 15 min to Develop the scena bubbles and their clusters with a diameter of not more than 500 μm and a minimum distance of 15 mm

Mechanical quality

7. Enabled enable, block boundaries, twins, clusters of bubbles with diameter less than 200 microns.

8. Allowed any kind of defects, with the exception of the cracks.

Note

Quality categories 1-6 are controlled under a focused light source with a capacity of not less than 100 watts and in polarized light. Quality category 7 and 8 are controlled in diffused light.

The way of sapphire crystal growing from the melt, including the preparation of the charge, its loading and melting through the heating element in a vacuum, seeding and pulling the single crystal, wherein the growing of the single crystal is carried out on the seed technical quality 6-th category containing gas include size up to 500 microns and their accumulation by lowering the dose of 10 mm every 10-12 min before contact with the melt temperature 2330 To not having on the surface of nuclei of crystallization, immersing the seed for 20-30 s in the melt 10-15 mm, reducing the power of the heating element to the supercooling of the melt required for the nucleation of grains crystallization on the surface of the seed for growing banners, and forming a convex cone in the direction of melt solidification front.



 

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