US-12618170-B2 - Growth method for single crystals of magnesium aluminate spinel by edge-defined film-fed growth technique

US12618170B2US 12618170 B2US12618170 B2US 12618170B2US-12618170-B2

Abstract

The present application provides a growth method for single crystals of magnesia-alumina spinel by an edge-defined film-fed growth technique, comprising: putting seed crystals and crystal growth raw materials into a crystal growth furnace; vacuuming the crystal growth furnace, filling with inert gas, heating and melting the crystal growth raw materials; making the seed crystals contact a top end of a seam of a mold, pulling the seed crystals, shouldering, making crystals grow, and annealing to cool down after crystal growth. An upper heat shield and a lower heat shield are arranged above the mold, and a cross section of a slit between the heat shields is a curved surface. The cross section of the slit between the heat shields is controlled as a curved surface, so that the present application achieves the effect of uniform heating of the single crystals of magnesia-alumina spinel in an upward pulling process.

Inventors

Cunxin Huang
Muyun Lei
Haili Wang
Xiaoliang Wang

Assignees

Sinoma Synthetic Crystals Co., Ltd.
BEIJING SINOMA SYNTHETIC CRYSTALS CO., LTD.

Dates

Publication Date: 20260505
Application Date: 20240301
Priority Date: 20230302

Claims (11)

1 . A growth method for single crystals of magnesium aluminate spinel by an edge-defined film-fed growth technique, comprising: 1) loading: putting seed crystals and crystal growth raw materials into a crystal growth furnace; 2) vacuuming and gas-filling: vacuuming the crystal growth furnace and then filling with inert gas; 3) heating and melting: raising the temperature of the crystal growth furnace to 2130-2200° C., so that the crystal growth raw materials are melted; 4) seeding: making the seed crystals contact a top end of a seam of a mold, and then pulling the seed crystals so that the crystal growth raw materials condense and grow on the seed crystals; an upper heat shield and a lower heat shield are arranged above the mold, and a cross section of a slit between the upper heat shield and the lower heat shield is a curved surface; 5) necking: pulling the seed crystals to shrink the crystals crystallized on the surfaces of the seed crystals; 6) shouldering: thickening and widening the crystals in an upward pulling process; 7) equal-width growth: making the crystals grow with the width of the mold in the upward pulling process; 8) annealing: after the end of crystal growth, starting annealing to cool down.
2 . The method according to claim 1 , wherein an upper surface of the lower heat shield is a plane, and a lower surface of the upper heat shield is a curved surface; or the upper surface of the lower heat shield is a curved surface, and the lower surface of the upper heat shield is a plane.
3 . The method according to claim 2 , wherein the upper surface of the lower heat shield is a curved surface, the lower surface of the upper heat shield is a plane, and the upper surface of the lower heat shield satisfies at least one of the following features: (1) a chord length D of the upper surface of the lower heat shield is 200 mm-400 mm, and a chord height h is 10 mm-30 mm; (2) the chord length D of the upper surface of the lower heat shield is 400 mm-700 mm, and the chord height h is 15 mm-60 mm; (3) the chord length D of the upper surface of the lower heat shield is 700 mm-1000 mm, and the chord height h is 30 mm-80 mm; (4) the chord length D of the upper surface of the lower heat shield is 1000 mm-1500 mm, and the chord height h is 40 mm-100 mm.
4 . The method according to claim 2 , wherein the upper surface of the lower heat shield is a plane, the lower surface of the upper heat shield is a curved surface, and the lower surface of the upper heat shield satisfies at least one of the following features: (1) a chord length D of the lower surface of the upper heat shield is 200 mm-400 mm, and a chord height h is 10 mm-30 mm; (2) the chord length D of the lower surface of the upper heat shield is 400 mm-700 mm, and the chord height h is 15 mm-60 mm; (3) the chord length D of the lower surface of the upper heat shield is 700 mm-1000 mm, and the chord height h is 30 mm-80 mm; (4) the chord length D of the lower surface of the upper heat shield is 1000 mm-1500 mm, and the chord height h is 40 mm-100 mm.
5 . The method according to claim 1 , wherein the mold has two different temperature gradients in horizontal and vertical directions; the temperature of the mold is gradually reduced from edge to middle on the crystal width, with a temperature gradient of 0.1 to 0.3° C./cm; and the temperature is reduced from bottom to top in the vertical direction above the mold, with a temperature gradient of 1-30° C./cm.
6 . The method according to claim 1 , wherein the steps of heating and melting comprise: heating the crystal growth furnace to 2130-2200° C., and then holding the temperature for 30-180 min to melt the crystal growth raw materials, so that the crystal growth raw material melt rises to the top end of the seam of the mold.
7 . The method according to claim 1 , wherein the steps of seeding comprise: lowering the seed crystals to make the seed crystals contact the top end of the seam of the mold, then raising the temperature by 3-10° C. to melt the seed crystals, holding the temperature for 1-30 min, then lowering the temperature by 5-30° C. and pulling the seed crystals at a rate of 1-100 mm/h so that the crystal growth raw materials condense and grow on the seed crystals.
8 . The method according to claim 1 , wherein the steps of necking comprise: pulling the seed crystals and increasing the temperature by 3-20° C., so that the crystals on the surfaces of the seed crystals shrink to ¼-¾ of the area of the seed crystals.
9 . The method according to claim 1 , wherein the steps of shouldering comprise: reducing the temperature by 5-30° C. and adjusting a pulling speed to 1-100 mm/h so that the crystals become thicker and wider in the upward pulling process until the crystal width reaches the width of the mold.
10 . The method according to claim 1 , wherein the mold is composed of two metal plates; space between the two metal plates is 0.1-1 mm to form a seam; the top end of the seam of the mold is provided with an opening; and an angle of the opening is 80°-180°.
11 . The method according to claim 1 , wherein the inert gas is at least one of Ar or N 2 .

Description

TECHNICAL FIELD The present application relates to the technical field of crystal growth, in particular to a growth method for single crystals of magnesium aluminate spinel by an edge-defined film-fed growth technique. BACKGROUND Magnesium aluminate spinel crystal has the advantages of excellent sound transmission, thermal stability, chemical stability and good mechanical and physical properties, and can be widely used in acoustic and microwave devices, GaN epitaxial substrates and support materials for superhard tools. At present, the growth methods of the magnesium aluminate spinel crystal mainly include the flux method, Verneuil's method, the vertical temperature gradient method and the Czochralski method. However, the above growth method for crystals all have problems: because the melting point of the magnesium aluminate spinel crystal is as high as 2130° C., when MgO and Al2O3 are used as raw materials to grow the crystal, there is serious non-proportional volatilization of MgO and Al2O3 on the surface of raw material melt at high temperature, thereby causing defects of inclusions and cores in the crystal, resulting in poor crystal growth quality or small crystal size, which cannot achieve practical application. SUMMARY A purpose of the present application is to provide a growth method for single crystals of magnesium aluminate spinel by an edge-defined film-fed growth technique, so as to improve the growth quality of single crystals of magnesium aluminate spinel. A specific technical solution is as follows: The present application provides a growth method for single crystals of magnesium aluminate spinel by an edge-defined film-fed growth technique, comprising: 1) loading: putting seed crystals and crystal growth raw materials into a crystal growth furnace;2) vacuuming and gas-filling: vacuuming the crystal growth furnace and then filling with inert gas;3) heating and melting: raising the temperature of the crystal growth furnace to 2130-2200° C., so that the crystal growth raw materials are melted;4) seeding: making the seed crystals contact a top end of a seam of a mold, and then pulling the seed crystals so that the crystal growth raw materials condense and grow on the seed crystals;an upper heat shield and a lower heat shield are arranged above the mold, and a cross section of a slit between the upper heat shield and the lower heat shield is a curved surface;5) necking: pulling the seed crystals to shrink the crystals crystallized on the surfaces of the seed crystals;6) shouldering: thickening and widening the crystals in an upward pulling process;7) equal-width growth: making the crystals grow with the width of the mold in the upward pulling process;8) annealing: after the end of crystal growth, starting annealing to cool down. In an implementation solution of the present application, an upper surface of the lower heat shield is a plane, and a lower surface of the upper heat shield is a curved surface; or the upper surface of the lower heat shield is a curved surface, and the lower surface of the upper heat shield is a plane. In an implementation solution of the present application, the upper surface of the lower heat shield is a curved surface, the lower surface of the upper heat shield is a plane, and the upper surface of the lower heat shield satisfies at least one of the following features: (1) a chord length D of the upper surface of the lower heat shield is 200 mm-400 mm, and a chord height h is 10 mm-30 mm;(2) the chord length D of the upper surface of the lower heat shield is 400 mm-700 mm, and the chord height h is 15 mm-60 mm;(3) the chord length D of the upper surface of the lower heat shield is 700 mm-1000 mm, and the chord height h is 30 mm-80 mm;(4) the chord length D of the upper surface of the lower heat shield is 1000 mm-1500 mm, and the chord height h is 40 mm-100 mm. In an implementation solution of the present application, the upper surface of the lower heat shield is a plane, the lower surface of the upper heat shield is a curved surface, and the lower surface of the upper heat shield satisfies at least one of the following features: (1) a chord length D of the lower surface of the upper heat shield is 200 mm-400 mm, and a chord height h is 10 mm-30 mm;(2) the chord length D of the lower surface of the upper heat shield is 400 mm-700 mm, and the chord height h is 15 mm-60 mm;(3) the chord length D of the lower surface of the upper heat shield is 700 mm-1000 mm, and the chord height h is 30 mm-80 mm;(4) the chord length D of the lower surface of the upper heat shield is 1000 mm-1500 mm, and the chord height h is 40 mm-100 mm. In an implementation solution of the present application, the mold has two different temperature gradients in horizontal and vertical directions; the temperature of the mold is gradually reduced from edge to middle on the crystal width, with a temperature gradient of 0.1 to 0.3° C./cm; and the temperature is reduced from bottom to top in the vertical dire