RU2370568C1 - Method of fabrication of quartz containers - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: organic silanes with atomic ratio of silicon and carbon 1.0:(1.0÷4.0) are used as source carbon containing compound. Coatings are made by successive multiple alternative moistening of surface of the container with organic silanes, by drying them under normal conditions, by forming polymer film and by annealing. The first annealing of settled polymer film is performed in oxidising atmosphere at 450-650°C within 20-30 min, while the second and successive annealing of settled polymer films onto formed oxide coating is carried out in inert atmosphere at 700-800°C during 30-60 minutes.

EFFECT: invention improves quality of protective coating on quartz surface of containers due to their upgraded density and strength preventing interaction of melted material with working walls of container of any shape, it also reduces impurity of produced material with diffusing additives of chemical elements from quartz.

2 tbl, 6 ex

Description

The invention relates to methods for manufacturing quartz containers with a protective coating for the synthesis and crystallization of melts of semiconductor materials, as well as for the production of highly pure metals and polymetallic alloys.

One of the main structural elements in the preparation of semiconductor crystals from melts is growth containers such as ampoules, crucibles, glasses, cups, boats, etc., made of various materials: graphite, quartz, glassy carbon, alundum, pyrolytic boron nitride (p-NB), platinum, etc.

Fused quartz in its composition initially contains impurities of chemical elements introduced by the feedstock. Additional pollution occurs in the manufacturing process of containerized products associated with quartz work using an open flame of a gas (propane-butane mixture) burner with metal tips, asbestos equipment and other devices and consumables in contact with a heated surface. The concentration of chemical elements lithium (Li), sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), aluminum (Al), iron (Fe) and titanium (Ti) the results of analysis by spark mass spectrometry in quartz products reaches (total) 0.02 ÷ 44.0 ppm. These impurities are a potential source of contamination of metal melts in contact with the walls as a result of diffusion.

To eliminate these drawbacks, quartz containers are made with protective coatings on the working surface. As protective coatings, tridimite, pyrocarbon, carbon graphite of the Aqadag type and others are used, which are obtained on the surface by known methods, mainly high-temperature pyrolysis decomposition of carbon-containing precursors: a mixture of propane-butane, acetone, cyclohexane, toluene, etc.

An increase in the requirements for the purity of the grown crystals and a decrease in the defectiveness of their structure is accompanied by a simultaneous requirement to reduce the cost of manufacturing containers.

A known method of manufacturing a container in the form of a quartz boat with the application on the inner working surface of the container of the coating with a molten metal, for example gallium, at a temperature of 830 ÷ 1200 ° C, for 1-2 hours. The molten metal forms a structural layer of polycrystalline tridimite on the rough surface of amorphous quartz, which leads to a significant decrease in the contact area (Japan, Application No. 0151863, M. Cl. C30B 11/00, publ. Aszuge aus den EP, No. 34 (85.08.21 ). A growth method of an inorganic compound single crystal and a boat used therefore.

The disadvantage of this method is the occurrence of significant mechanical stresses at the quartz-tridymite interface, which lead to the destruction of the container during a long process of crystal growth. In addition, the melt is contaminated with impurities of chemical elements diffusing from tridymite and the walls of amorphous quartz. It should also be noted the complexity and high cost of manufacturing other types of containers in this way, for example, ampoules with a narrow loading nozzle, ampoules with a drive, crucibles, tubes, glasses, etc.

A known method of manufacturing a growth container in the form of a quartz boat from billets of a quartz tube, followed by deposition on the working surface of carbon graphite of the type "Aquadag" from the decomposition products of a gas-vapor mixture of toluene in a stream of nitrogen at a temperature of 1050 ° C (Beels R, De Sutter W. Pyrolytic coating of quartz and ceramic snapchatis used for zone melting. Jornal of Scientific Instrument. Val. 37, No. 10, October 1960, p. 397).

The disadvantage of this method is the complex and expensive technology for the manufacture of coated containers, which in a thin layer does not eliminate the interaction of the molten material with the walls. Thick layers (> 20 μm), which are deposits of soot ("lamp soot"), are destroyed by contact with the molten solution and pollute the grown crystals with carbon.

A known method of manufacturing a quartz container in the form of a glass with a conical bottom (tube) and applying a carbon-containing coating to the inner surface of the container by precipitation of the decomposition products of the vapor-gas mixture of acetone in a stream of nitrogen at a temperature of 900 ÷ 1170 ° C (Qingrun B., Ju G., Jinyi W ., Ji'an C. Carbon Film Coating Used in CdZnTe Cristal Growth. Rare Metals. Vol.16, No. 2, april 1997, p. 114-116). The method adopted for the prototype.

However, this method is characterized by a complex and explosive technology. In a heated reactor, high-temperature decomposition of acetone vapor occurs and a thin carbon-containing layer is deposited on the quartz surface of the container. Upon receipt of crystals in such a container, a partial interaction of the molten material with the walls and the formation of crystals with an increased density of structural defects occur.

An increase in the thickness of the protective carbon-containing layer to 25–30 μm leads to mechanical stresses at the interface with the walls of quartz and the destruction of the coating upon contact with the melt.

The technical result of the invention is to improve the quality of protective coatings on the quartz surfaces of containers by increasing their density and strength, thereby preventing the interaction of molten material with the working walls of a container of any shape and reducing contamination of the resulting material with diffusing impurities of chemical elements from quartz.

The technical result is achieved by the fact that in the method of manufacturing quartz containers for carrying out high-temperature processes, including applying a coating to the working surface of the container by deposition from a carbon-containing compound, according to the invention, organosilanes with an atomic ratio of silicon and carbon equal to 1.0 are used as the initial carbon-containing compound :( 1,0 ÷ 4,0), and the formation of coatings is carried out by sequential, multiple alternation of processes of wetting the surface of the container organ ylans, drying them under normal conditions to obtain a polymer film and annealing, while the first annealing of the deposited polymer layers is carried out in an oxidizing atmosphere at 450 ÷ 650 ° C for 20 ÷ 30 minutes, and the second and subsequent annealing of the deposited polymer layers is carried out in an inert atmosphere at 700 ÷ 800 ° C for 30 ÷ 60 minutes.

The essence of the invention lies in the fact that as the starting carbon-containing compound, organosilanes (OS) are used, which are successively deposited in the form of films on working walls by wetting the surface with organo (chloro, alkoxy, acetoxy) silanes, followed by combined annealing of the layers in oxidative and in an inert atmosphere.

The deposition of a polymer film from the OS and its annealing in an oxidizing atmosphere (in air) at a temperature of 450 ÷ 650 ° C leads to the formation of an oxide (a-SiO ₂ ) shell on the wall surface, which creates an anti-diffusion barrier for chemical impurities and a sublayer (adhesive) for subsequent formation of a carbon-containing coating. Repeated deposition and annealing of the polymer film in an inert atmosphere at a temperature of 700 ÷ 800 ° C leads to the formation on the surface of a carbon-containing (a-SiO _1,5 : C _n where n = 1 ÷ 4) coating, which ensures the walls are not wettable by the melts and in combination with a-SiO ₂ coating significantly improves the conditions for growing semiconductor crystals. In this case, wall defects are not formed in the form of shells, cracks, twins, small-angle boundaries, and other structural inhomogeneities in crystals due to the interaction of melts with walls.

Justification of the parameters.

For the deposition of polymer films on the surface of the quartz by wetting, drying under ordinary conditions and subsequent annealing in an oxygen-containing and inert atmosphere, organosilanes with an atomic ratio of silicon and carbon of 1.0: (1.0 ÷ 4.0) are used. This is especially critical during pyrolysis annealing, as a result of the formation of a carbon-containing coating in combination with oxide. When the ratio of silicon and carbon is 1.0: (<1.0) due to carbon deficiency and an increase in the siloxane component, a coating is formed as a result of film deposition and its pyrolysis annealing, which interacts with melts and leads to the formation of defects in the crystal and marriage. When using organosilanes with an atomic ratio of silicon to carbon of 1.0: (> 4.0), upon deposition of the film and its pyrolysis annealing, a significant carburization of the film and a sharp decrease in physicomechanical properties, in particular, adhesion to the lower-formed oxide coating on quartz walls , increasing brittleness, peeling, etc., which leads to contamination of the melts with carbon impurities and a decrease in the electrophysical properties of crystals.

Carrying out annealing of containers with polymer films in an oxidizing atmosphere (in air) below 450 ° C and a time of less than 20 minutes does not lead to complete thermal oxidative degradation of hydrocarbon substituents at silicon atoms. The result of low-temperature annealing is the formation of metastable or “loose” a-SiO ₂ protective coatings. In this case, subsequent deposited films of organosilanes are unevenly deposited and fixed on the surface of the a-SiO ₂ coating, and upon annealing in an inert atmosphere, the carbon-containing material is detached and the entire combined coating formed in the form of flakes is destroyed.

Annealing in an oxidizing atmosphere at temperatures above 650 ° C and a time of more than 30 minutes leads to additional energy costs and an increase in the cost of manufacturing containers, but the quality of the a-SiO ₂ coating does not improve.

The annealing time of the films in the above temperature range is 20–30 minutes, during which the method of forming high-quality oxide coatings on quartz walls is best implemented.

Pyrolysis annealing of carbon-containing polymer films on an oxide coating in an inert atmosphere is carried out in the temperature range 700 ÷ 800 ° C. At temperatures below 700 ° C and a time of less than 30 minutes, an a-SiO _1.5 : C _n (where 1≤n≤4) coating is loose, which breaks down upon contact with the melt, contaminating it with carbon impurities. Carrying out annealing in an inert atmosphere at a temperature above 800 ° C and a time of more than 60 minutes does not lead to a significant improvement in the quality of the carbon-containing coating and the entire combined protective coating with a-SiO ₂ shell, but leads to additional and unjustified costs. To obtain containers with a high-quality carbon-containing coating in combination with oxide annealing in an inert atmosphere, carry out for 30 ÷ 60 minutes.

The implementation of the proposed method is illustrated by the following examples.

Example 1

The quartz tube blank (⌀ _ext. 60 mm; ι _slave = 110 mm; d _st = 2.5 mm) was sealed on one side in the open flame of the propane-butane mixture burner, and a narrow loading nozzle was coaxially soldered to the second (⌀ _ext. 10 mm; ι _slave. = 200 mm). An equimolar mixture consisting of 45 ml of vinyl trichlorosilane (C ₂ H ₃ SiCl ₃ ) and 47.4 ml of silicon tetrachloride was poured into the manufactured ampoule under a hood, then the entire surface was moistened, then chlorosilanes (CS) were poured into a collection bottle, and the ampoule was left upright boot part to dry. As drying occurs on the walls of the ampoule, a polymer film forms as a result of surface hydrolytic polycondensation. Annealed in air at a temperature of 500 ° C for 30 minutes. As a result of thermal oxidative degradation of [C ₂ H ₃ SiO _1,5 SiO _4/2 ] _n , a total oxide (a-SiO ₂ ) coating in the form of a continuous shell formed on the ampule working wall. Then, the ampoule was re-filled with one vinyl trichlorosilane (BTXC), followed by wetting of the working surface and drying in air. This operation was repeated one more time. After that, an ampoule with a polymer film of vinylsiloxane (VCO) was placed in a reactor of a resistance furnace and evacuated to 1.5.10 ^-3 mm Hg. Then the reactor was filled with argon and in the argon flow (1 ÷ 100 ml / min), the container with the formed oxide coating and with the applied polymer film was annealed at a temperature of 800 ° C for 30 minutes. Then, the temperature in the furnace reactor was reduced to room temperature and the ampoule with the formed protective coating was removed from the combination of a-SiO ₂ and a-SiO _1,5 : C _2,0 layers.

To determine the thickness of the coatings, their organochlorosilanes (by wetting) of polymer films were deposited in parallel and annealed on samples of polished silicon wafers of the KDB-1 brand. The thickness was measured on a MII-4 microscope using the standard method. The measured thickness of the formed combined protective coating of a-SiO ₂ / a-SiO _1.5 : C _2.0 was 0.45 μm.

The resulting container with the formed combined protective coating was applied to the loading section of the initial charge. The mixture with a stoichiometrically specified ratio of the components Cd, Zn, Te was loaded into the ampoule and vacuum evacuated to 1.3 · 10 ^-6 mm Hg, then the ampoule was sealed and the CdZnTe crystal was synthesized and grown (at 1200 ° C) in one volume according to the known technology of vertically directed crystallization (WOC). After the implementation of the process, a control (visual) of the container, coatings was made and an analysis of the grown material was carried out.

Container and coating condition:

- no quartz areas on the inner and outer surface of the walls;

- there is no destruction of the coating on the walls and surface erosion.

Parameters of the grown ingot:

- the absence of visible traces of the interaction of the ingot with the walls of the container;

- the absence of cracks, shells, and other structural defects on the surface resulting from the interaction of the melt with the walls of quartz.

Crystal Parameters:

The ingot was subjected to oriented cutting into 1.5 mm thick plates and they were ground and chemically-mechanically polished by standard methods. We selected three prepared plates from the lower, middle, and upper parts of the ingot and measured the parameters whose values are given below:

- n-type conductivity;

- dislocation density 6 ÷ 9 · 10 ⁴ cm ^-2 ;

- resistivity 3.4 · 10 ⁷ Ohm · cm;

- the content of the main limiting impurities of chemical elements Li; Na; K, Ca; Mg; Cu; Fe; Al, TI was determined by spark mass spectrometry. Their concentration in the volume of the ingot varied in the range of 0.002-0.1 ppm. Technological parameters and analysis results are shown in Table 1 and 2.

Example 2

The blank of the quartz tube (⌀ _ext. 50 mm; ι _slave = 120 mm; d _st = 3.0 mm) was sealed in the form of a cone on one side (tube) in the open flame of a gas burner and an equimolar mixture was poured into the fabricated tube under the hood consisting of 20 ml of methyltrichlorosilane (CH ₃ SiCl ₃ ) and 22.7 ml of silicon tetrachloride (SiCl ₄ ). After wetting the entire surface of the walls, the mixture of chlorosilanes was poured into a collection bottle and a tube with a polymer film of methylsiloxane formed as a result of surface hydrolytic polycondensation with structural fragments SiO _4/2 ([CH ₃ SiO _1,5 · SiO _4/2 ] _n ), placed in a reactor resistance furnaces and annealed in air at 450 ° C for 30 minutes. As a result of thermal oxidative degradation of methylsiloxane (MCO) on the wall, a common oxide coating was formed in the form of a uniform a-SiO ₂ shell. Then, on the formed oxide film, in the same way, the MSO polymer film was applied three times from one methyltrichlorosilane (MTXS) and a tube with a-SiO ₂ coating and the newly deposited polymer film were placed in a resistance furnace reactor, which was vacuumized to 1.8.10 ^-3 mm Hg . After that, the reactor was purged with dried argon and the temperature was raised to 700 ° C. In the reactor, a tube with an oxide coating and an MCO polymer film deposited on it in an argon flow (1–100 ml / min) was kept for 50 minutes at this temperature. At the end of the process, the temperature was lowered to room temperature and the tube was removed with the a-SiO ₂ / a-SiO _1.5 : C _1.5 combined coating formed. The resulting container with the formed protective coating (2.5 μm) was applied to the loading section of the initial charge.

The mixture in the form of an ingot of pre-synthesized material from a stoichiometrically specified ratio of the components Cd and Te was loaded into a tube with a formed protective coating, which, in turn, was placed in a quartz ampoule of a larger diameter. This ampoule with a loaded tube was evacuated to 1.3 · 10 ^-6 mm RT.article. Then the ampoule was sealed off and the CdTe crystal was grown in a tube with a combined protective coating, as in Example 1.

After the implementation of the process, a control (visual) of the container, coatings was performed and an analysis of the grown material was performed. Technological parameters and results of the analysis of the grown material are shown in Table 1 and 2.

Example 3

The quartz tube blank (⌀ _ext. 60 mm; ι _slave = 210 mm; d _st = 2.5 mm) was cut symmetrically along the axis in half and at one half the ends were sealed on both sides, making a container in the form of a boat. Then, 50 ml of a mixture (1: 1) of trichlorosilane and silicon tetrachloride (HSiCl ₃ and SiCl ₄ ) were poured into the boat and the entire surface of the walls was moistened. After 10 minutes, a mixture of trichlorosilane with silicon tetrachloride (TCS / CHC) was poured into a collection bottle and the boat was dried in air. A boat with a hydride siloxane polymer film deposited as a result of surface hydrolytic polycondensation with structural fragments of SiO _4/2 ([HSiO _1.5 · SiO _4/2 ] _n ) was annealed in air at a temperature of 500 ° C for 30 minutes. As a result of thermal oxidative degradation of hydridosiloxane (GSO), a total coating of a-SiO ₂ in the form of a continuous shell was formed on the working surface of the boat. Then re-applied by wetting on the surface of the boat a polymer film consisting of a mixture of BSO and MCO (1: 1). This operation was repeated two more times, after which the boat with the applied film was annealed in a stream of argon (1 ÷ 100 ml / min) at a temperature of 800 ° C for 30 minutes. The resulting container with the formed combined protective coating a-SiO ₂ / a-SiO _1.5 : C _1.5 (4.5 μm) was transferred to the loading section of the initial charge.

A mixture with a stoichiometrically specified ratio of the components Cd, Zn and Te was loaded into a boat with a combined protective coating and the CdZnTe crystal was synthesized and grown (at 1200 ° C) by horizontal crystallization using the known technology. Technological parameters and results of the analysis of the grown material are shown in Table 1 and 2.

Example 4

A crucible ⌀ _{top was} made from a quartz billet (⌀ _ext. 100 mm; ι _slave. = 235 mm; d _st. = 3.5 mm) _. = 110 mm; ⌀ _visas. = 90 mm; ι _slave = 225 mm and formed on the working surface of the walls a combined protective coating of a-SiO ₂ / a-SiO _1,5 : C _{4,0 in the} same manner as described in Example 2. The technological parameters and results of the analysis of the resulting final CdTe material are shown in Table 1 and 2.

Examples 5 ÷ 6: Examples of the process of obtaining a combined protective coating technological parameters that go beyond the declared parameters.

Thus, the claimed method allows to simplify the process of obtaining a coating of the inner walls of containers of any configuration, to increase the density and strength of the coating, thereby improving the reliability of containers with its repeated use.

The use of a quartz container with a protective coating obtained by the claimed method can significantly improve the perfection of the grown crystals and obtain materials with high electrophysical parameters due to:

- preventing the interaction of molten material with the working surface of quartz due to the high strength of the coating;

- reduction of pollution of the grown crystals by diffusing impurities from quartz due to the high density of the coating.

Another positive feature of coated quartz containers manufactured by the claimed method is that the coating plays an additional role as a “color indicator” of high-temperature processes for extremely undesirable oxygen-containing impurities (traces of moisture, metal oxides, air, etc.) that may accidentally appear in the container’s volume, for example, with the initial acidified charge or with insufficient drying and vacuum pumping. As a result of such technological pollution at a temperature of 600 ÷ 650 ° C, carbon is oxidized (burned out) in the coating layer and discolored. In this case, near-wall interaction of quartz-melt occurs, an increase in defectiveness and a decrease in the electrophysical properties of the obtained semiconductor materials. Thus, the color of the coating allows you to indirectly judge the nature of the process and the quality of the material obtained.

Claims (1)

A method of manufacturing quartz containers for high-temperature processes, comprising applying a carbon-containing compound to the working surface of the container, characterized in that organosilanes with an atomic ratio of silicon and carbon equal to 1.0 are used as the carbon-containing compound: (1.0 ÷ 4.0) and the formation of coatings is carried out by successive multiple alternation of processes of wetting the surface of the container with organosilanes, drying it under normal conditions to obtain a polymer film and annealing, while the first annealing of the deposited polymer layers is carried out in an oxidizing atmosphere at 450 ÷ 650 ° C for 20-30 minutes, and the second and subsequent annealing of the deposited polymer layers is carried out in an inert atmosphere at 700-800 ° C for 30-60 minutes .