DE2126662A1 - Process for the production of dislocation-free A deep III B deep V single crystals - Google Patents

Description

Process for the production of dislocation-free

It is known to produce AjjjBy single crystals, in particular gallium arsenide, from the melt of semiconducting compounds which contain a highly volatile component and whose vapor pressure at the melting point of the compound is approx. 1 atm in a closed vessel according to Czochralski. A suitable drawing device is the condensation of the released arsenic to prevent the object of German patent 1044769 · in the manufacture of gallium arsenide monocrystals, is to keep the whole system at an average temperature of 65O ⁰ C. The up and down movement as well as the rotation of the seed crystal is achieved by magnetic coupling of the drive elements, whereby the magnet segments arranged in the pulling system must also be kept at a temperature of 65O ° C.

According to another known process, what is known as the protective melting process is used. For this purpose, the Semiconductor melt covered with an approximately 1 cm thick boron oxide layer and an inert gas overpressure of in a pulling chamber approx. 1 to 1.5 atm generated. This causes the volatile component to evaporate at the melting point of the compound largely prevented. The drawing chamber remains at room temperature, so that the implementation of the pull rod in the chamber can be sealed with commercially available sealing rings. This method enables the pulling of AjjjBy single crystals with a vapor pressure of the volatile component of 25 to 35 atm, such as gallium phosphide and indium phosphide the melt. Here, the melt is about 1-2 cm

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strong boron oxide layer covered in a special pressure chamber and about dei? Boron oxide layer has an inert gas pressure of approx. 50 atm built up. Such a method is the subject of many publications and is, for example, in the Journal of Applied Physics, June 1962, vol. 33, pages 2016-2017 and in J.Phys.Chem. Solids.Vol.26, pages 782-784 (1965).

You can do this procedure and the known devices A-j-T-jB ^ -semiconductor single crystals, especially gallium arsenide-, Gallium phosphide and indium phosphide single crystals up to one maximum diameter of approx. 20 mm and a length of approx. 50 mm, i.e. a weight of approx. 80 to 100 g will.

The range of applications of compound semiconductors of the type Äj-rjB ^, especially gallium arsenide, gallium phosphide and Indium phosphide is becoming wider and wider in modern semiconductor technology and extends from the use of these materials as luminous materials. diodes in both the visible and the infrared wavelength range via optoelectronic coupling elements and microwave oscillators to modulation of gas lasers. There are So, not least for economic reasons, single crystals with larger dimensions are in demand in modern semiconductor technology.

It has been found that dislocation-free, in particular those with low and considerable vapor pressures, are obtained at the melting point after the boron oxide protection melt process in can produce a metal pulling chamber with a rigid tube in a technically advantageous manner if only part of the crystal pulling necessary amount of the semiconductor in a crucible given in pieces and melted under boron oxide, - while the other part of the semiconductor material in compact rod form from above into the already present under a boron oxide melt Melt of the semiconductor is immersed and melted into the melt surface after reaching temperature equilibrium a crystal nucleus is immersed in the melt and a single crystal is pulled from it.

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According to the method according to the invention can be economical Aj-j-jBy single crystals of large dimensions, especially large ones Cross-section. They have a diameter of about 40 mm, a length of about 250 mm and a weight of approx. 1000 g. They are well defined in shape and have a cubic crystal structure and are much purer than that used starting material.

By partially introducing the semiconductor material in With a compact rod shape from above as opposed to charging the crucible with the same total amount of granular semiconductor material, crucibles with a minimal height can be used where the semiconductor melt in the crucible is still optimal, should stand. Even if the crucible is loaded with smaller ones Semiconductor quantities must meet this requirement. By that It is possible to use the geometry of the crucible to observe the Crystal growth necessary per se rigid sight tubes at the metal drawing chamber offset from one another by 180 ° a favorable viewing angle of 40 to 70 °, preferably 60 °, to be attached to the pressure vessel. This only makes one Optimal observation of the crystal growth from germination to the final crystal thickness possible. At an enlargement of the crucible diameter, the visibility would be more favorable due to the smaller angle of incidence of the tubes (<60 °), however, an increase in the crucible diameter causes an increase in the radial temperature gradient, which in turn unfavorable effects on the location of the Wachatum front respectively the undisturbed crystal growth.

To achieve or keep constant the optimally high level of the semiconductor melt in the. Crucibles, in particular, too In the case of small weights, a height-adjustable intermediate floor can be installed in the crucible.

Suitable semiconductor materials are gallium arsenide, gallium antimonide, Gallium phosphide, gallium nitride, indium arsenide, indium antimonide, indium phosphide, aluminum arsenide and Aluminum antimonide.

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To carry out the method according to the invention, according to a preferred embodiment of the invention, is primarily the The crucible is completely filled with the maximum amount of lumpy semiconductor to be introduced and the boron oxide layer the space created during melting for optimal use of the crucible height with a correspondingly large additional space Amount of the semiconductor in the form of a rod filled from above. The ultimately resulting surface of the semiconductor melt, which in the progressive crystal growth continuously decreases, is through the crucible approach from below unchanged in the iage to HF system held.

Between the amount of semiconductor in the crucible and the. The proportion fed in from above should have a mass ratio of 1: 5 to 1 * 0.2, preferably from 1: 1, consist »where the supply of the compact semiconductor can be done from above from several subsets. The area ratio between semiconductor melt and the compact semiconductor material fed in from above should be 10s5 to 10: 1 when immersed.

The semiconductor material supplied from above is preferred attached to a seed crystal, the cross section of which is 6 x 6 mm, which after the temperature equilibrium of the melt has been established is immersed in this for crystal pulling. The seed can after the melting of the semiconductor material at the beginning Crystal growth can be extended by the proportion that has been melted off during immersion. This is a multiple Usability of the crystal nucleus is possible. The semiconductor material fed in from above can also be used on the seed crystal lining be attached and in some cases it is advantageous if it is through a second tube or another tube is introduced. A tube arranged centrally around the pull rod can serve as such.

Immersing the semiconductor material brought in from above can preferably be rotated into the already existing semiconductor melt at a speed of 0.5 to 30 cm / h,

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preferably 15 cm / h. It can be continuous and discontinuous be proceeded. Most of the time, the semiconductor component to be melted, including the connection point, is the seed supply material melted.

The single crystals obtained according to the invention with a large cross section are excellently suited for the construction of luminescent diodes, optoelectronic coupling elements, modulators and as a substrate for Gunn oscillators and in infrared technology.

In the drawing, the scheme of a pulling device is shown, on which the invention is easy to demonstrate.

The pulling device consists essentially of a metal pulling chamber 1 with an inner diameter of 260 mm. In the lower part of the metal pulling chamber is to receive the semiconductor melt introduced a quartz crucible with an inner diameter of 90 mm, which is located in the graphite susceptor 3 is located. This is in turn surrounded by graphite felt 4 for thermal insulation. The quartz crucible can have an intermediate floor 22 included. Between the water-cooled HP coil 5 », which is used for inductive heating of the graphite susceptor, is a quartz cylinder 6 attached, which prevents flashovers from the HP coil to the susceptor. The electrical supply for the HF coil is carried out via high pressure-resistant seals 7 through the splash 8. The graphite susceptor 3 and the quartz cylinder 6 stand on a pedestal 9 · With the help of the axle 10, which is inserted into the boiler via a high-pressure-resistant seal the crucible can be moved up and down and set in rotation will. At 11 is the surface of the granular semiconductor material and 12 denotes that of boron oxide. The one obtained after melting the lumpy semiconductor material Melt surface is denoted by 13. 14 is the rod made of the semiconductor material, which is over the dovetail connection 16 is attached to the crystal nucleus 15. This compact Material is passed through the protective boron oxide by moving the pull rod 17 downwards at a speed of 15 cm / h

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12 immersed in the semiconductor melt 13. It will Semiconductor material including the connection point 16 melted. The one resulting after melting The surface of the entire semiconductor material is denoted by 18. It lies under the thick boron oxide melt layer. The viewing tubes are marked with 19.

The crystal nucleus 15 is after the melting of the compact Semiconductor 14 with the aid of the pull rod 17, which is guided through the flange 21 via a high-pressure-resistant seal 20, moved upwards and only after reaching temperature equilibrium the melt is immersed in the melt surface 18 with rotation.

In some cases it is advantageous when in power transmission Both for pulling and for rotation between the drive motors and the pull rod 17, a slip clutch is built in. This causes the melt to become plagued an interruption due to the higher dcäjaoment occurring in the process the turning and pulling motion causes.

As already indicated above, the arrangement shown in the drawing is an exemplary embodiment of the inventive idea. This can also be found in run different variants, which is particularly true for the design of the individual elements of the device.

The invention is described in some of the drawings below Examples explained.

Example 1s . .

900 g of granular polycrystalline gallium arsenide are used in the crucible 2 located in the pressure vessel 1, that of the susceptor 3 and the heat-insulating graphite felt 4 as well the quartz cylinder 6 is surrounded by the flP coil 5, brought in.

With a crucible diameter of 90 mm and a height of 80 mm, the granular gallium arsenide fills the

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Crucible up to about 1 cm below the top edge of the crucible. A tablet of solid, dehydrated boron oxide 1 cm thick and about 90 mm in diameter and weighing 110 g to 120 g is placed over the granular gallium arsenide. A further 900 g of polycrystalline gallium arsenide in rod form 14 are attached to the seed crystal 15 via the dovetail connection 16. After the pressure vessel 1 has been closed and evacuated and flooded several times with an inert gas such as purified nitrogen, a nitrogen overpressure of approximately 15 atmospheres is generated in the chamber at room temperature. After switching on the HF energy, the heat is transferred to the crucible via the glowing graphite susceptor through thermal conduction, whereby the boron oxide melts first and the melt fills the cavities of the granular gallium arsenide and covers the parts on the surface with a protective film. After reaching the melting temperature of gallium arsenide 1238 ⁰ C to the different densities of the gallium arsenide as well as boron oxide occurs due to a segregation so that above the semiconductor melt 15 is a 1 cm high boron-r oxidschmelzschicht formed. After the gallium arsenide melt in the crucible has been slightly overheated, the polycrystalline gallium arsenide rod is immersed into the gallium arsenide melt via the pull rod 17 while rotating at a speed of 15 cm / h through the boron oxide melt layer and, in the process, including the connection 16. After the complete melting of the rod material introduced from above, the melt surface 18 is finally formed. After the temperature equilibrium has been established, the pressure in the system increasing to about 25 atmospheres, the actual crystal pulling takes place at an average speed of 8 mm / h and a seed rotation of 20 TJ / min. As the crystal size increases, the gallium arsenide surface in the crucible 2 decreases. In order to prevent this, the crucible is tracked from below via the axis 10 to the extent that the surface of the gallium arsenide melt sinks.

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In order to obtain the necessary RF power controls that are required by the ongoing decrease in the mass of the semiconductor material at the crucible are required to be kept to a minimum, the Susceptor 3 including crucible 2 over the axis 10 in the dimension according to tracked above how the enamel surface sinks. at The production of a single crystal with a weight of 900 g requires a guide close to the crucible by 30 mm. Me tracking of the crucible from below is an enlargement of the Equate the height of the crucible, on which the viewing angle of the observation tubes depends. This fact underscores the requirement for a minimum crucible height with a constant diameter of 90 mm to accommodate a maximum Amount of semiconductor melt clearly.

Under these conditions, a gallium arsenide single crystal grows in about 30 hours with a diameter of 30 mm and a length of 250 mm and a weight of approx. 900 g.

Example 2:

Oa, 800 g of granular polycrystalline gallium phosphide are introduced into the crucible 2, which is located on the pressure vessel 1, and coated with a tablet of dehydrated boron oxide (thickness 2 cm, diameter 90 mm, weight 220-240 g). An inert gas pressure of eg purified nitrogen of 35 atmospheres is generated in the • drawing vessel at room temperature. After lirreichen the melting temperature of Galliumphosphids of 1470 ^o C-1480 ° G, a boron oxide-melt layer of 2 cm thickness is formed. A further 800 g of gallium phosphide are added from above to the gallium phosphide melt that has already been formed at a rate of 15 cm / h and melted in the process. After the temperature equilibrium has been established, with the pressure rising to approx. 50 atmospheres, the crystal is pulled out of the melt at a speed of 10 mm / h and a seed rotation of 8 rpm. The melting surface adjustment is carried out as in Example 1. Under the aforementioned conditions, a gallium oephid single crystal with a diameter of 30 mm and a length of approx. 230 mm grows in about 23 hours with a weight of about 800 g.

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Claims (7)

- 9 - VPA 71/7544 patent claims 1. Process for the preparation of dislocation-free Single crystals, especially those with low and considerable vapor pressures at the melting point near the boron oxide protection melt, proceed in a metal pulling chamber rigid! tube, characterized in that only one style of the amount of semiconductor necessary for crystal pulling is given in pieces in a crucible and melted under boron oxide, while the other part of the semiconductor material in compact rod form from above into the already Sohmelze present under a boron oxide melt de « Semiconductor is immersed and melted, into the melt surface after reaching the Xeaperaturglelong «- a crystal nucleus is dipped into the melt and a sink tube is pulled out. 2. The method according to claim 1, characterized in that the crucible with such amounts of lumpy and compact semiconductor material is charged so that the semiconductor melt in the crucible is optimally high and during dta Pulling is kept at this optimal height. 3. The method according to claims 1 and 2, characterized in that the mass ratio between that in the crucible The lumpy amount of the semiconductor and the compact semiconductor 1 * 1 to 115 to be fed in from above where the compact semiconductor is supplied from above in several partial quantities. 4. The method according to claims 1 to 3, characterized in that that the compact semiconductor material supplied from above is attached to a seed crystal. 5. The method according to claim 1 to 4 »daduroh characterized that the compact semiconductor material supplied from above is immersed under rotation in the semiconductor melt located in the crucible. - 1.0 - VPA 71/7544 6. The method na oh claim 1 to 5, characterized in that that the Sinkrietall is pulled out of the melt at a viewing angle of about 60 °. 7. Apparatus for carrying out the procedure according to an «vein several of the preceding claims, characterized in that a small crucible (2) is arranged in the metal drawing chamber (1) which is connected to the boron oxide Melted! rope (13) of the lumpy predetermined semiconductor material (11) is filled approximately up to the hand and into which the other part of the semiconductor material (14) attached to a suspension (16) is supplied in compact form from above and the downward movement of the pulling rod (17) is immersed in the semiconductor bulk melt (13), with on Rigid viewing tubes (19) offset from one another by 180 ° in the metal drawing chamber at a viewing angle of 40 to 70 ° are set and the Sohmelzoberflache (18) during the Crystal growths from below by an axis (10) leading to the Crucible tracking is used, is held in an unchanged position relative to the HP coil (5). 209850/0993