A method of growing single-crystal sapphire hemispherical blanks

 

(57) Abstract:

The invention relates to techniques for growing shaped crystals from the melt with variable cross-sectional shape. The essence of the proposed method lies in the fact that the persecution is produced on the seed plate around the perimeter of the tubular shaper with the formation of a hollow closed volume. While the end surface of the shaper perform with a Central recess having the shape of a spherical segment with a height that satisfies the relation: where R is the radius of the spherical segment, d is the wall thickness of the workpiece. Stretching is produced from the melt column, while after the transition of the hollow profile in a monolithic billet pull on a length equal to the height of the spherical segment h, and then make a sharp separation of the crystal from the shaper. You can get additional technical result is increased productivity growing hemispherical blanks, i.e., receiving multiple hemispherical parts in a single growth process. To do this, after the formation of the hemispherical harvesting its produce repeated persecution on the entire perimeter of the shaper and continue pulling each the ski result can be obtained more effectively. To do this, after extruding the billet to the required length reported the cavity shaper through the side hole with the atmosphere, and after the beginning of the growth of the next billet this message stop. 2 C.p. f-crystals, 7 Il.

The invention relates to techniques for growing single-crystal sapphire blanks hemispherical shape of the melt to obtain from them sapphire hemispheres, which are used in high-temperature optics.

There is a method of growing a shaped crystals of form element (method local formation) [1] provides a continuous change in a given program forms the side surface of the crystals, representing hollow and solid body rotation.

The disadvantage of this method is that in crystals grown by way of the local formation, there is a regular banding layer type growth layer growth in this case, the layer of crystal growing in one of its turnover). The banding is due to the periodic accumulation of pores and point defects of other types, which causes a significant reduction in optical performance, greatly limiting or making it impossible thus the application of these is m the persecution produced on the surface of solid bare plate simultaneously around the perimeter of the tubular shaper for the formation of a closed volume inside it, pre-grown hollow crystal, creating a differential between the pressure in the growth chamber and the pressure in the closed volume inside the hollow crystal to collapse it and grow a monolithic crystal.

The main disadvantage of this method is the impossibility of regular and controlled changes of the cross section of the grown crystal, and it is growing hemispherical pieces.

The technical result achieved by the present invention, consists in the possibility of growing monocrystalline workpieces made of sapphire while maintaining the quality of the crystals inherent in the prototype.

The essence of the proposed method lies in the fact that the persecution is produced on the seed plate around the perimeter of the tubular shaper with the formation of a hollow closed volume. While the end surface of the shaper perform with a Central recess having the shape of a spherical segment with a height that satisfies the relation:

,

where R is the radius of the spherical segment,

d wall thickness of the workpiece. The extrusion is made from post melt, while after the transition of the hollow profile in a monolithic billet pull on a length equal to the height of the spheres is to teach additional technical result increased productivity growing hemispherical blanks, i.e. getting several hemispherical parts in a single growth process. To do this, after the formation of the hemispherical procurement, it produces repeated persecution on the entire perimeter of the shaper and continue pulling the other workpiece. The number of stravlivanie depends on the required number of blanks. This additional effect can be obtained more effectively. To do this, after extruding the billet to the required length reported the cavity shaper through the side hole with the atmosphere, and after the beginning of the growth of the next billet this message stop.

Execution end surface of the shaper with a Central recess having the shape of a spherical segment height allows accurate control of the external shape of the hemispherical blanks, as the crystallization front monolithic part of the crystal coincides with the end surface of the shaper. Pulling a monolithic part of the crystal length equal to the height of the spherical segment h before separation of the workpiece from the shaper allows to achieve a desired wall thickness of the workpiece. The inner part of the hemispherical workpiece to a greater extent controlinveste acapillary channel, in which the melt rises due to the pressure difference in the growth chamber and the closed volume under the seed plate while pulling the hollow part of the crystal. The size of the Central cavity must ensure the adequacy of the revenues of the melt to the end surface of the shaper by pulling a monolithic part of the crystal, in particular when growing hemispherical workpieces of large dimensions, but at the same time should not be large in order to reduce distortion of the outer hemispherical shape of the workpiece.

Receive multiple hemispherical parts in a single growth process can be done in two ways. The first is that after the formation of the hemispherical workpiece from the shaper is repeated persecution it on the entire perimeter of the shaper. As the seed is used in this case itself hemispherical procurement. After the formation of the hemispherical procurement melt remains only in the capillary channel shaper from the Central acapillary cavity, the melt flows down into the crucible. With repeated persecution on the hemispherical preparation meniscus is formed only in the peripheral part of the shaper, the AE persecution on the seed plate, and hemispherical piece. The second way of obtaining multiple hemispherical pieces per growing process is carried out without isolation of the hemispherical workpiece from the shaper. For this shaper is equipped with side rethermalization acapillary hole, which is at the growth stage monolithic crystal is below the level of the melt. Pulling a monolithic part of the crystal length equal to the height of the spherical segment h before separation of the workpiece from the shaper allows to achieve a desired wall thickness of the workpiece. After pulling a monolithic part of the crystal to the height h of the Central cavity shaper reported through the side opening with the growth chamber by lowering the level of the melt in the crucible below the side razgermetiziruetsya holes. The melt from the Central cavity flows through the side hole in the crucible, leaving the engagement of the melt in the peripheral region of the end face of the former, where the melt flows through the capillary. Further, in order to obtain the following hemispherical workpiece, stop the communication between the Central cavity of the shaper and the growth chamber by raising the melt to full pogrugenie blanks are cut from the bare plate and machined, resulting polerowanie with both inner and outer sides of the hemisphere. Bare the same plate can be reused an unlimited number of times.

In Fig. 1 depicts a shaper for growing hemispherical blanks. In Fig. 2 postedin the process of growing hemispherical blanks; Fig. 3 the appearance of the hemispherical workpiece; Fig. 4 and 5 processes of cultivation of several hemispherical blanks during one growth cycle.

The shaper 1 has around the perimeter of the capillary channel 2, the end surface of the shaper 3 is made with a Central recess having the shape of a spherical segment with a height that satisfies the relation:

< / BR>
where R is the radius of the spherical segment,

d wall thickness of the workpiece.

In the Central part of the shaper has the entire length of the cavity 4, which is acapillary channel. To implement the method uses the crucible 5 with the melt 6 and the seed plate 7. Between the seed plate and shaper form the meniscus 8 melt at the initial stage of the crystal grows in the form of a pipe 9, after the lifting of the melt in the Central cavity formiruete the shaper is supplied side rethermalization hole 11.

The method works as follows. After melting in the crucible 5 charge the crucible 5 with the melt 6 pull on the shaper 1 to submerging the bottom of the shaper 1 in the melt 6. Melt 6 in the crucible 4 in the cavity 3 is on the same level as in the capillary channel 2 rises to the upper end of the shaper 1. This is followed by the persecution on solid bare plate 7 around the perimeter of the tubular shaper 1. Between the seed plate 7 and the end face of thermoablative formed meniscus 8 melt 6, Fig. 2,and. At the initial stage of pulling the crystal grows in the form of a pipe 9, thereby forming the difference between the pressure in the growth chamber and the pressure in the closed volume under the seed plate 7, which leads to the raising of the melt 6 in the cavity 4 and later in the Central recess 3, Fig. 2,b. When the melt 6, extending from the cavity 4, meets with the meniscus 8 melt 6 emerging from the capillary channel 2, the crystallization of the inner hemispherical surface of the workpiece 10, Fig. 3,a century After the formation of the inner hemispherical surface of the workpiece 10, the meniscus 8 of the melt 6 is formed along the end surface 3 of the shaper 1, Fig. 3,Since IMO pulling in a length equal to the height of the spherical segment (h, then make a sharp separation of the hemispherical workpiece 10 from the end surface 3 of the shaper 1, Fig. 4. In Fig.5 presents the hemispherical section of the workpiece 10, the shaded areas, which will be deleted when it is further mechanical processing. For more hemispherical blanks 10 for one growth process after the formation of the hemispherical workpiece 10 from the shaper 1 is repeated persecution it on the entire perimeter of the shaper 1. As the seed is used in this case itself hemispherical workpiece 10. With repeated persecution on hemispherical workpiece 10 meniscus 8 is formed only in the peripheral part of the shaper 1, as in the case of persecution on the seed plate 7. In Fig.6,and shows the initial cultivation after repeated persecution of Fig. 6,b the end of the second growing hemispherical workpiece 10. To implement the second method of obtaining multiple hemispherical blanks 10 in one growing process shaper 1 was supplied side rethermalization acapillary hole 11, which is at the stage of growth of the hemispherical workpiece 10 was below the level rates 4 reported through the side opening 11 with the growth chamber by lowering the level of the melt 6 in the crucible 5 below lateral razgermetiziruetsya holes 11. Melt 6 of the Central cavity 4 flows through the side hole 11 in the crucible 5, however, remains the meniscus 8 of the melt 6 in the peripheral region of the end face of the shaper 1, where the melt 6 flows through the capillary channel 2. In Fig. 7,b shows the time of cultivation after lowering the level of the melt 6 below lateral razgermetiziruetsya holes 11. Further, in order to obtain the following hemispherical workpiece 10 stop communication between the Central cavity of the shaper 4 and the growth chamber by raising the melt 6 to full immersion side razgermetiziruetsya holes 11 in the melt 6.

The technical essence of the method is illustrated with specific examples of its implementation.

Example 1. Grown sapphire polyfoniska workpiece outside diameter of R= 16 and 41 mm with a wall thickness of d=3 and 5 mm, respectively. The cultivation was carried out in argon atmosphere, the pressure in the chamber during growth was 0.3 ATM). speed drawing 15-60 mm/h For cultivation was used molybdenum formers, the end surface of which was carried out with a Central recess having the shape of a spherical segment with a height equal to 9.3 and 19,6 mm, respectively. The thickness of the ring karpooravalli. The diameter of the Central neipirskogo channel was 5 mm and 8 mm, respectively. The length of the formers was 50 mm For persecution were used sapphire plate whose axis lying in the plane of the ribbon and perpendicular to it. The persecution was carried out by plate-seed the entire working surface of the shaper. Due to the pressure difference in the chamber and in the volume under the seed plate in the Central acapillary cavity begins to rise melt with subsequent crystallization in the upper edge area of the shaper is growing monolithic piece of crystal. After pulling a monolithic part of the crystal length h produced a sharp separation of the accelerated movement of the upper stem. The claimed method were obtained hemispherical single crystal sapphire blanks of which, after final machining were made sapphire polished hemisphere with a radius of 15 and 40 mm, wall thickness 2 and 3 mm, respectively. The misorientation between the boundaries of the blocks does not exceed 1o, there was no gas inclusions and inclusions of other phases.

Example 2. Spent a few hemispherical sapphire blanks external dialogical example 1. After pulling a monolithic part of the crystal length h=9.3 mm and a sharp separation of the crystal from the shaper accelerated movement of the upper rod have repeated the persecution on the hemispherical piece. With repeated persecution on hemispherical workpiece engagement of the crystal with the melt were formed only in the peripheral part of the former, as in the case of persecution on the bare wafer. The further growing of the crystal was carried out as in the previous cycle. The claimed method were obtained hemispherical single crystal sapphire blanks (2-4 per process), of which, after final machining, were made sapphire polished hemisphere with a radius of 15 mm with a wall thickness of 2 mm Misorientation boundaries between blocks does not exceed 1o, there was no gas inclusions and inclusions of other phases.

Example 3. Spent a few hemispherical sapphire blanks external diameter R=16 mm with wall thickness d=3 mm in the course of one growing. The length of the shaper was 50 mm, the middle length side was razgermetiziruetsya a hole diameter of 6 mm Before the process stravlivanie analogously to example 1. After pulling a monolithic part of the crystal length h=9.3 mm, molybdenum crucible with the melt down to the point where the melt level in the crucible was lower side razgermetiziruetsya holes. The melt from the Central neipirskogo channel was poured over the side of the sealing hole, it has remained the engagement of the melt in the peripheral region of the end face of the former, where the melt flows through the capillary. In order to obtain the following hemispherical workpiece, the crucible with the melt again, advancing on the shaper to full immersion side razgermetiziruetsya holes in the melt, thereby stopping the communication between the Central cavity of the shaper and the growth chamber. Subsequent cultivation was similar to the initial cycle. The claimed method were obtained hemispherical single crystal sapphire blanks (2-4 per process), of which, after final machining, were made sapphire polished hemisphere with a radius of 15 mm with a wall thickness of 2 mm Misorientation boundaries between blocks does not exceed 1o, there was no gas inclusions and inclusions of other phases.

1. The method of growing the mo shaper with the formation of a hollow closed volume under the seed in the form of a plate and pulling out of the post of the melt at the end of the shaper of the hollow profile with the transition into a monolithic, immersed in the crucible in the growth chamber, characterized in that the end surface of the shaper perform with a Central recess having the shape of a spherical segment with a height that satisfies the relation

< / BR>
where R is the radius of the spherical segment;

h the wall thickness of the workpiece,

and pulling is made from post melt, while after the transition of the hollow profile in a monolithic workpiece is pulled to a length equal to the height of the spherical segment, and then make a sharp separation of the crystal from the shaper.

2. The method according to p. 1, characterized in that it further hold one or more cycles, realizing after the formation of the next persecution it on the entire perimeter of the shaper.

3. The method according to p. 2, characterized in that after extruding the billet to the required length reported the cavity shaper through the side hole with the atmosphere, and after the beginning of the growth of the next billet this message stop.

 

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