SE524279C2 - Preparing crystals of e.g. silicon carbide for semiconductors involves depositing vapor species containing elements of the crystals, to a seed crystal contained in a heated growth enclosure, followed by passing a gas containing a halogen - Google Patents

Abstract

Preparing crystals of silicon carbide, group III-nitride and/or its alloys involves continuously feeding vapor species containing elements of the crystal through an upstream opening (22) of the growth surface of a seed crystal contained in a heated growth enclosure; removing the undeposited vapor species through a opening downstream (25a) of the growth surface and passing an additional gas flow containing a halogen. An independent claim is included for a device for preparing the crystals.

Description

20 25 30 35 40 524 279 2 stoichiometry of the substances during growth. The instability in the supply of the source material and the operation of the temperature distribution in the feed layer for the source material and in the crystallization zone will, for example, cause operation of the growth rate and of the incorporation of dopants.

If these driving parameters are not properly controlled, they tend to greatly affect the efficiency of the crystal growth process. For example, until today, aluminum-doped p-type SiC disks, grown by sublimation, show high densities of defects in the form of micropores. From a larger perspective, in a closed PVT system, the depletion of the source material stock limits the duration of a continuous cultivation process and thus the crystal length.

These challenges may be solved by further improvements of the sublimation process and the possibility with the technology or variants thereof, to produce SiC disks on a relatively large scale is a measure of its industrial potential.

An alternative technology of industrial interest which offers a continuous control of the source material supply and has the potential for culturing long crystals from gas phase was introduced in 1995 by U.S. Patent No. 5,704,985. This technology is commonly described as High Temperature Chemical Vapor Deposition (HTCVD) and differs from sealed PVT configuration by the use of an open hot wall con som- gution that offers a high degree of freedom and control over source material and doping material supply. In particular, at least one of the components of the cultured material is continuously supplied in the form of a controlled gas fl and is fed into the high temperature zone through an inlet opening. In addition, an outlet device is provided downstream of the crystallization area to control the gas flow along the growing crystal surfaces and release by-products created in the crystallization process. This technique can be called Chemical Vapor Deposition (CVD) based on its conceptual similarity to the CVD techniques used for epitaxial culture layers as thin as a few μm or less.

However, as described in U.S. Patent Nos. 5,704,985 and 6,048,398, to achieve growth rates that are economically interesting for large crystal production, the HTCVD technology uses an order of magnitude higher source gas feed rates and several hundred degrees higher temperatures than normal CVD processes. For example, in an apparatus similar to that of the first figures of U.S. Patent No. 5,704,985 (Fig. 1), in the specific SiC case, by heating the seed crystal 13 to a temperature of 2250 ° C and feeding it in into a gas mixture containing 0.3 I / min silane and 0.1 I / min ethylene diluted in a helium carrier gas, achieve a crystallization rate of 0.5 mm / h.

However, when using the method for several hours, it is experimentally experienced that SiC is also crystallized around the seed crystal substrate 13, on the holder 12 made of, for example, graphite, and on the exposed surfaces at the outlet holes 14 in Fig. 1. On the surfaces in 10 The immediate vicinity of the seed crystal 13 crystallizes SiC in a dense polycrystalline body containing 6H and 15R polytypes. Further downstream in the outlet holes 14, SiC crystallizes in slightly less dense 3C-polytype needles. The dense polycrystalline deposit can be created at about twice the rate compared to the monocrystalline rate of crystallization. Further downstream, as the temperature decreases and the supersaturation increases, the 3C crystal needles form nuclei and grow even faster in size and possibly block the gas outlet path within 2 to 4 hours. When the outlet path downstream of the seed crystal is sufficiently blocked, a pressure difference builds up quickly between the source gas inlet 15 and the outlet port 16. If the pressure difference is allowed to reach a few mBar, it is reproducibly found that a rapid deterioration of the monocrystalline polytype and structural quality builds up. The source gases can also begin to flow along a path with a higher conductance than that through the blocked outlet 14, for example through some porous insulating material as in Fig. 1. The insulating properties of the material then deteriorate rapidly due to reaction with silicon, which forces cultivation to be discontinued. Alternatively, when the outlet path 14 is clogged under conditions where the source gases are not allowed to find any path with higher conductance, a very rapid blockage of the gas inlet occurs by polycrystalline silicon deposition. In this case, the cultivation must also be stopped because no source gases can be supplied to the single crystal. The parasitic deposition of solid polycrystalline phases thus leads to a catastrophic rampage of the system which forces the cultivation process to be stopped before a crystal of the desired length has been produced.

An attempt to solve this problem has been described in PCT application WO 98/14644. In the example of SiC crystal cultivation, this application describes an apparatus in which Si- and C-containing process gases are separated from the main heating element 7 in Fig. 2 by a thin inner cylinder 25. A protective inert gas is set to flow between the main heating element and the inner cylinder which terminates approximately as high as the growth front of the single crystal. The protective gas conducted along the walls of the main heating element downstream of the growth front of the monocrystalline is intended to counteract or greatly delay the deposition of polycrystalline SiC on the inner / eggs downstream and delay the growth of polycrystalline SiC on the seed holder 13 so that the outlet path 31 disappears. A similar solution is described in European Patent Application No. 97100682.0 where a shielding gas flowing parallel to the process gas stream is presented for an apparatus operating between 800 ° C and 2500 ° C.

It has been found that such a solution, as described in or derived from these documents, does not solve the above-described problem sufficiently to grow SiC or other crystals beyond a few mm. Experiments using an inert protective gas, such as helium or argon, have shown that the growth of 3C needles still takes place downstream of the growth front of the single crystal. When helium is used as a shielding gas, an even higher velocity is easily achieved, while the use of argon only displaces the deposition region a short distance downstream. This unexpected result can be explained by an increased flow of carbon carried by the shielding gas as it passes along an uncoated heating element and by the difference in thermal conductivity of the two mentioned gases. In a silicon-rich exhaust gas mixture, any increase in carbon supply leads to an increase in the polycrystalline SiC growth downstream. A similar phenomenon is observed when using a heating element 7 which is coated with SiC. To circumvent this, it is obvious, for a person experienced in the context, to use as an improvement a heating element and a control cylinder, either made of a metal carbide or of graphite coated with, for example, TaC or NbC. Preferably, the exposed surfaces should also have a low surface roughness to offer fewer nucleation sites for polycrystalline SiC. Under normal process conditions leading to a growth rate of the order of 0.5 mm / h to 1 mm / h of the single crystal, however, it is observed that such a design only leads to a further displacement downstream of the position of the uncontrollable SiC deposit. This small improvement in the time of blocking is not sufficient to continuously grow fl your cm 'long crystals. In addition, the use of metal carbide coated parts represents a significant additional cost to the manufacturing process.

In other prior art devices created to grow SiC crystals where at least one component of the material being cultured is fed as gas and the by-products of the process are discharged through an outlet, no solution is mentioned for parasitic deposition of the polycrystalline form of the material. which is grown. For example, European patent 0554 047 B1 describes the growth of SiC crystals by an apparatus which uses silane and propane as source gases, which react in a primary reaction zone to form SiC particles which are then gasified in a lower pressure sublimation zone. The by-products from this crystallization process and the carrier gas are claimed to be emitted only through an outlet. U.S. Patent 5,985,024, filed in 1997, discloses an apparatus in which silica gas is supplied from a heated silicon melt and a hydrocarbon gas, such as propane, is supplied to the growth zone through a passage or outlet channel. In this apparatus it is also claimed that the remaining gas downstream of the growing SiC ingot is removed from the culture zone through a passage or outlet channel. Depending on the temperature distribution required in the seed holder to allow the growth of the SiC crystal to be considered, it is considered likely that such passages will inevitably be subject to a catastrophic blockage of either polycrystalline SiC, pyrolytic graphite or polycrystalline Si deposit. A similar concept is described in U.S. Patent 6,048,398, filed in 1995, in which a molten silicon feed source in combination with a hydrocarbon gas can be used as source gases. The remaining gases are sucked out downstream of the seed crystal holder which is rotated and drawn as the monocrystalline growth continues. Despite an advantageous cleaning function for polycrystalline deposition induced by the rotation of the seed holder, stress is created in either the rotation mechanism or the seed holder and the elements which come into contact with it. This can lead to mechanical breakdown of either of the above mentioned parts.

In U.S. Patent Application No. 2002/0056411 A1, a high temperature gas deposition apparatus for manufacturing SiC ingots is discussed in which the pressure of the gas mixture in the growth region is set higher than that of the gas mixture at the outlet to increase. 5 the efficiency of the process. This pressure difference can be achieved by designing the apparatus so that the conductance of the inlet is higher than that of the outlet. After a low conductance occurring downstream of the growth area of the monocrystalline, a reduced pressure of the gas mixture at the outlet, at a constant temperature, creates a decrease in the deposition rate of the parasitic polycrystalline material. This delays any catastrophic blockage along the road downstream of the conductance lowered area of the mixture at the outlet. However, as pointed out in the cited application, as the temperature drops along the road downstream, deposit will accumulate in a given area, described as a gas trap. Preventing this deposition, even in a monitored area, would allow a continued process, for a longer period of time, thereby producing longer crystals. In addition, in the said application, the system must be operated at a reduced pressure, at least downstream of the conductance lowering area. It may be desirable to run the device at practically atmospheric pressure instead, both in the growth area and in the outlet area, as this may be to the advantage of both efficiency and total cost of the system.

The origin of the problem described above is in some sense fundamental, since the maximum mass transport of reactants is arranged to the growing crystal, so the high temperature (2000 ° C - 2500 ° C) requires feeding of a certain amount of seed temperature dependent Si gas , which will not crystallize, to compensate for the continuous evaporation of Si from the heated crystal.

Object and Summary of the Invention This invention provides a method and apparatus for culturing, at high temperature, in a heated space (called a susceptor or crucible), a monocrystalline of either SiC, a Group III nitride, or alloys. of these, with a growth rate and over a period of time sufficient to produce a crystal several millimeters, or preferably several centimeters, long.

In particular, it is an object of this invention to delay or eliminate the formation of polycrystalline or other solid deposition downstream of the crystallization area of the monocrystalline to avoid a partial or complete blockage in any of the outlet paths of a susceptor of a gas mixture fed to the crystallization area. A correlated object of the invention is to control the diameter of the growing single crystal and prevent the growth of polycrystalline material around it, thereby preventing the occurrence of structural defects during the high temperature growth phase and the subsequent cooling phase.

A further object of the invention is to reduce the concentration of undesirable metal impurities in the epitaxially cultured material, by removing from the gas phase active metal substances which are released from parts which are heated downstream of the crystallization area. In order to prevent the creation of unwanted polycrystalline deposition on surfaces near and in areas downstream of the growth area of the monocrystalline, the invention proposes to reduce the local supersaturation of at least one of the components of the cultured material, by introducing, in the vicinity of these surfaces, a separate gas stream having the chemical property of etching the cultured material. In the case of SiC or GaN crystal culture, a gas stream containing at least one halogen substance such as hydrogen chloride, chlorine or a mixture of hydrogen and either chlorine or hydrogen chloride as an etching gas is advantageously used.

As will be apparent from the detailed description of the invention, other gases or gas mixtures containing halogens such as Br, F or I may also be used for similar purposes. The etching gas can also be distributed in such a way that one can actively control the shape of the growing crystal. Further preferred features and advantages of the invention will be disclosed and explained in the following drawings, descriptions and claims. General description of the drawings Figure 1 illustrates an HTCVD cultivation apparatus according to the prior art.

Figure 2 illustrates another prior art HTCVD cultivator.

Figure 3 is a cross-section of an apparatus according to the invention.

Figure 4 is a cross-section of a modified apparatus according to the invention.

Figure 5 shows the relationship between the supersaturation of condensed components of SiC (upper diagram), carbon (middle) and silicon (lower) at a [Cl] / [H] ratio of 0.5.

Figure 6 shows the ratio of the supersaturation of condensed components of SiC, carbon and silicon at a [Cl] / [H] ratio of 1.2.

Detailed Description of the Invention Fig. 3 schematically shows an improved apparatus including a growth chamber in an HTCVD system based on the concepts described in U.S. Patents 5,704,985, 6,039,812 and 6,048,398. This apparatus will also be described here, since the invented apparatus may have a principle similar in construction to that in the above-mentioned documents, but differs in the particular features and improvements described in the present invention. The apparatus of Fig. 3 is suitable for culturing monocrystals of SiC, a group III nitride such as GaN. Some parts are schematic for simplicity and it is obvious to a person skilled in the art that the device also includes elements such as mass flow regulators, valves, pumps, control electronics, gas purifier, a neutralizer (scrubber) and other units that are normal in CVD -system. The high temperature vapor deposition apparatus comprises a housing 1 consisting of, for example, a single wall quartz tube 2 tightly mounted between a lower flange 3 and an upper flange 4. Each flange comprises a fixed housing 3a and 4a and a movable lower 3b and upper 4b lids which can be lowered and raised, respectively, for accessing the inner parts of the housing 1 for loading and unloading the hot zone of the apparatus. The housing 1 may alternatively consist of a double-walled, water-cooled quartz tube or may be surrounded by a water-cooled stainless steel housing (not shown). The inner parts of the housing 1 consist of a heating element 7, also called a susceptor or crucible in the literature, and are surrounded by a low-conductivity thermally insulating material 10 such as graphite blanket or other types of materials compatible with the process temperature range and heating method. The heating element 7 is axisymmetric and is made of a material compatible with high temperatures such as uncoated or coated graphite, a metal carbide or nitride, or a combination thereof. The heating element can be cylindrical, however, the diameter of the heating element can vary axially to converge in certain areas or diverge in other areas to achieve a specific gas flow pattern or a special spatial temperature distribution in the heating element 7 and in the vicinity of the crystal holder 12. The susceptor 7 is heated either by RF induction via a coil 11, or by resistive heating, to a temperature above 1900 ° C (and preferably in the range 2000 ° C to 2600 ° C) for SiC crystal growth, or above 1200 ° C (at least 110 ° C and preferably in range 12oo ° c rm 22oo ° c) for cam crystal growth. A seed crystal 13 is mounted mechanically or chemically to a seed holder 12 which is physically attached to a shaft 16 having at least one hollow channel through which the temperature of the seed holder can be measured with an optical pyrometer or a thermocouple (not shown). In order to achieve a desired crystallization on the surface of the seed crystal rather than on the surface 26 of the susceptor 7, the seed holder is kept at a lower temperature than the surface 26 and the upper part of chamber 33, thus creating a temperature gradient.

The crystallization process is carried out by feeding a gas phase containing the substances contained in the intended material through the heated Susceptor 7 against the seed crystal.

The amount of substances for the material to be grown is selected so that the heated gas becomes supersaturated when it reaches the crystallization front, here called the growth front 25a. In the particular case of SiC culture, the susceptor 7 is heated to temperatures from 2100 ° C to 2600 ° C while the seed holder is maintained at temperatures from 2000 ° C to 2400 ° C, depending on the feed rate of the source material and its C / Si ratio. polytype and the crystallographic orientation of the seed crystal. A desirable source material for growing SiC ingots consists of a SiHxCl 2 gas or liquid (x = 0 to 4, y = 0 to 4) and a hydrocarbon such as methane, ethylene or propane. As described in U.S. Patent No. 6,039,812, the Si-containing gas or liquid is fed through an inner channel 22.

The hydrocarbon can either be fed into the same inner channel 22 or into a concentric annular channel 23 which encloses said inner channel 22 and is delimited by a water-cooled stainless steel flange 21 which is part of the lower cover 3b. A carrier gas such as hydrogen, helium, argon or a mixture thereof is also fed into channel 23 and discharged downstream of the growth front 25a via an outlet channel 14. To prevent deposition of polycrystalline silicon carbide along surfaces 26 and 27 in outlet channel 14, the apparatus comprises further feeding possibilities such as channels opening in the vicinity of the growth area of the single crystal or in heated parts downstream which are exposed to Si- and C-containing gases. A gas mixture with properties that chemically etch SiC is fed through these additional channels. It has been experienced that the etch gas mixture for SiC cultivation must contain at least one halogen substance in order to neutralize the Si-containing gas components. The etching gas mixture should preferably also have the property of reacting with carbon-containing gas components, such as hydrogen. Effective etch gas mixtures that give the desired result have been found to be gases such as chlorine (Cl2), hydrogen chloride (HCl) or a mixture of hydrogen (H2) and hydrogen chloride or chlorine. A gas mixture containing halogens such as fluorine (F) or iodine (I) and hydrogen also achieves the desired etching effect.

To ensure etching rates comparable to the growth rates of monocrystalline and polycrystalline SiC used in the invention (0.5 mm / h to 2 mm / h), at least one of the etching gases is fed in before the exhaust gases are cooled to a temperature of 600 ° C lower than the temperature of the growth front 25a of the single crystal. In order to keep the outlet path 14 open, the position of the feed gas mixture, the amounts and the ratio of the halogen and hydrogen gases fed in must be selected to match the amount of Si and C containing gas components and the temperature of the surfaces exposed to condensation and the conductance of the outlet port 14. .

As shown in Fig. 3, a feed system is suitably created by feeding a controlled flow of the etch gas through the hollow core of the shafts 16a and 16b and into an inner cavity mechanically created in the seed holder 12. The etch gas mixture is allowed to flow out through channels or pores 28, placed above the seed crystal 13, and mix with Si- and C-containing gases which have passed the growth front 25a.

The etching gas mixture is thereby heated to a temperature corresponding to the temperature of the seed holder, typically 2000 ° C to 2400 ° C, and thus reacts very efficiently with the gas and C-containing gas components. It can be noted that a plurality of feed configurations can be used in the seed holder 12 to achieve an even etch gas distribution.

For example, a plurality of peripheral holes with diameters from 0.1 to several mm may be distributed along the outer surface 26 of the seed holder 12. A high porosity ring may also be used, provided that it is made of a material which is high temperature resistant and chemically inert. against the etching gas mixture (for example graphite when a pure halogen gas such as F2 or Cl2 is used). An important advantage of this first feeding method is that as shaft 16 translates upward, at a rate similar to the growth rate of a SiC ingot 15, by means of a pulling mechanism (not shown), the etch gas flow is fed from a fixed position along the surface 27 of the seed holder assembly relative to to the growth front 25a of the crystal. This gives the possibility to keep the surface 27 free from parasitic solid deposits even when the crystal grows to lengths of several centimeters and is drawn correspondingly in height upwards. A recommended use of the invention includes pulling the seed holder 12 along a predetermined axial temperature profile to maintain a constant temperature of the crystallization surface 25a as the crystal length increases. As the seed holder 12 is drawn along this temperature profile, the etching gas flow can be ramped over time to maintain a constant etching rate. Another advantage of this first feeding method is that the temperature difference between the seed holder 12 and the lower heating element 7a can be increased, without inducing a higher deposition rate of polycrystalline material downstream of the single crystal 15. This can be achieved, for example, by lowering the RF power in the induction coil. current loops 11a, while an increase in the feed rate of the etch gas mixture in the shaft portion 16 compensates for the higher supersaturation of Si- and C-containing gases.

A second supply system for the etching gas mixture, which fulfills the purpose of the invention, consists in feeding the etching gas into a channel in the upper part 7b of the heating element surrounding the seed crystal holder 12. The flow rate of the etching gas is controlled by an external fate controller 30 and fed into the housing 4a connection to a quartz tube or tube inserted in the upper heating element 7b at connection 31 for feeding an internal conduit 32. The internal conduit 32 is suitably annular and communicates with the outlet duct 14 through a plurality of holes or a porous media. The internal line 32 suitably communicates with channel 14 in an area where the deposition of polycrystalline material occurs naturally in prior art devices. In cases where parasitic polycrystalline deposition occurs over a wide area of the surface 26, a second, or several new separate channels 32 are created in the heating element 7b to provide suitable etch gas den over all the surfaces which are desired to be kept free from such deposition. This second etching gas supply system serves two purposes. The first is to counteract the nucleation and growth of polycrystalline grains along the surfaces 26. However, the flow rate of the etching gas can also be adjusted to a higher value than is necessary to achieve this single first purpose, to also etch the sides 25b of the growing monocrystalline 15.

The ratio of halogen to hydrogen in this second gas mixture is adjusted to a value which creates a smooth, mirror-like etching of the sides of the growing crystal.

By varying the flow rate of the etching gas, the diameter of the growing crystal is controlled.

In particular, a low etch gas flow allows the crystal to expand at a radial velocity determined by the selected balance between the etch gas flow and the feed and carrier gas feed rate into the heating element 7a and the radial temperature gradient in heating element 7b. The rate of expansion of the crystal can be slowed down, or even stopped to create a cylindrical crystal by increasing the rate of etch gas flow. During this process, the shaft unit 16 should preferably be rotated to create a uniform radial etching profile.

Another advantage of this second feed system is that in the temperature range of the invention the use of an etching gas containing at least one halogen element, such as Cl, forms stable chlorides with several metallic impurities which can be inadvertently secreted into the source gas mixture. In particular, the concentration of residual metal impurities in the single crystal can be lowered by up to a factor of 100, to values below what is measurable with modern SIMS measurements, when a small amount of Cl-containing gas is allowed to diffuse to SiC growth fronts 25a and 25b. A third supply system for the etching gas mixture, which fulfills the object of the invention, comprises feeding the etching gas along a peripheral gap formed between the inner wall of the heating element 7a and a concentric, shaft-symmetrical inner crucible 7c. As shown in Fig. 4, the flow of Si- and C-containing source gases is trapped in the growth region 33 until its flow sweeps over the outer surface 25b of the single crystal 15 and is discharged through channel 14, while the etch gas flow is limited to the circular gap 34 until said etch gas flow meets the remaining Si- and C-containing gases in channel 14. As in the second feed mode, this third configuration of etch gas flow allows both surfaces 26 and 27 to be kept free of harmful polycrystalline deposition, while also allowing the shape of the growing single crystal. A cylindrical outer wall of the inner crucible 7c is suitable for creating a substantially cylindrical ingot 15, while an outer wall which diverges in some direction along the direction of the etching gas flow may favor a concave growth front 25a.

It is within the scope of the invention to use either the first, second or third feeding system described above, either individually or in any combination. However, the invention is best practiced by using the first feeding system throughout the process time, which may extend over several tens of hours, while the second and third feeding methods should preferably be used in addition, separately or together, during different process steps. A typical example may be an expansion step for the crystal diameter based on feed systems 1 and 2 as a first step, followed by a substantially cylindrical growth which also uses system 2 with a lower etch gas fate or in combination with feed system 3.

It should be noted that these features can be used to achieve the desired solution for a variety of configurations of the outlet channel 14, such as an outlet direction in the opposite direction to the growth direction of the crystal as in Fig. 2, or an outlet perpendicular to the growth direction or any angle between said opposite and right angles.

An important application of the method, which we learn from the present invention, involves the choice of halogen and hydrogen flow rates and their respective conditions. Although the authors do not wish to commit to any theory, lessons can still be learned from thermodynamic considerations. These are in what follows given a Si-C-H-Cl system, but similar findings can be observed for the case of crystal growth of III nitrides by using a Ga-N-H-Cl or Al-N-H-Cl system. In the following, the specific case is given when chlorine is added to a given Si-C-H system which is determined by the supply of source and carrier gas mixtures (for example SiH4, C3H8 and H2).

The effect of adding Cl to Si-C-H systems is known from previous plants in SiC CVD at temperatures in the range 1500 ° C-1600 ° C and means only a slight increase in the SiC etching rate. Typical etching conditions in previously hot-walled CVD systems involve Cl / H ratios of less than 0.03%, and the etching rate shows a weaker due to increased HCl input than increasing Hz input [Zhang et al., Mat. Sci. Forums Vol. 389-393 (2002) pp. 239]. In the prior art, the etching rates are too low (less than 10 μm / h at 1600 ° C) to be of any practical use to the present invention. It will be shown here that the invention will be used with much higher Cl / H to achieve etching rates ranging from 0.1 mm / h to more than 1 mm / h.

A quantification of the reduction in supersaturation of Si-C-H by the addition of Cl can be translated into a temperature reduction: when Cl is introduced, how much can the temperature drop before the supersaturation remains at the same level? The original Si-C-H composition is defined by the introduced source-Si-C-H mixture and the calculations are performed by driving the system to equilibrium. The equilibrium state is selected as the gas phase equilibrium, which represents a more difficult case than an equilibrium that includes solid Si, C and SiC phases. The experimental reality lies between these two cases, whereby the following calculations to some extent underestimate the etching efficiency. A given amount of Cl is introduced into the system, which lowers the supersaturation in the system by the creation of, for example, chlorosilanes. The temperature is then allowed to drop an amount of AT, which increases the supersaturation. The system is then operated to a new gas phase equilibrium and compared with the original system. The temperature difference ATT, which corresponds to a given amount of [Cl], can then be obtained from the isolation line of the supersaturation (SS) equal to 1 in contour plots as those in Figs. 5 and 6. Along this isolation line is SS (T, Si, C, H) = SS (T-AT, Si, C, H, Cl).

Figure 5 shows the result in the case where a system operates at a reduced pressure of 0.12 bar and has a [Cl] / [H] ratio of 0.5. In particular, Fig. 5 indicates that the problem of blocking channel 14 is at least partially solved in this case: the growth of solid SiC is significantly reduced and the growth of Si is completely stopped. Unfortunately, the effect of CI is smaller at higher temperatures where the Si and C content in the gas phase is greater. At 2200 ° C, Cl can enable the postponement of a substantial fixed deposition along a temperature drop AT of 200 ° C, while this drop at 1900 ° C can exceed 600 ° C.

By using a [Cl] / [H] ratio higher than 1, so that less Cl is consumed to form HCl, the blockage of channel 14 can be completely avoided. As shown in Fig. 6 where a [Cl] / [H] ratio of 1.2 is used at the same pressure and initial composition as in Fig. 5, no solid phases of SiC or Si are possible even over a temperature drop AT of 600 ° C. A solid phase of C can be deposited (for example pyrolytic graphite) because the supersaturation nevertheless exceeds 1. If this deposit is large enough to possibly block channel 14 within 20 to 40 hours, it can be removed by practicing the invention, i.e. by to supply an additional flow of H2 in the cooler region where no more solid SiC deposition occurs. This additional flow of hydrogen can be fed into a specially designed channel through the shaft part 16 or into a separate channel running through the heating element 7, as previously described.

The large monocrystals somiodlas of this invention can be sliced and polished into thin sheets for semiconductor applications or used for other applications. Depending on the intended use of the crystals, it is a given that they can be doped to achieve either low n- or p-type resistivity or made very pure to achieve a high resistivity. Substances such as nitrogen, aluminum or other elements are conveniently introduced into growth chamber 33 by a controlled flow of gas or organometallic source material as is customary in SiC-CVD and Group III-MOCVD of thin layers for semiconductor applications.

Although it has been indicated in the figures and in the above description that the source gas flow is directed upwards (substantially opposite the local gravity vector), it is within the scope of the invention to arrange the apparatus in the opposite direction, where the seed crystal is placed on the bottom of the apparatus , or to use a horizontal direction, where the seed holder is placed either downwards or upwards. In its present description, the growth chamber 33 can be maintained either at substantially atmospheric pressure or at a low pressure in the range of 50 mBar to 800 mBar, however, for other orientations of the apparatus a low pressure, for example less than 500 mBar, may be required to achieve the desired monocrystalline growth rates. .

It should be noted that a person skilled in the art easily understands that many components, shapes and process parameters can be varied or changed to a certain extent without departing from the scope and purpose of the invention.

Claims (1)

A method for culturing large, multicomponent multicomponent crystals of either a) silicon carbide, b) a group III nitride c) alloys thereof, characterized in that the method comprises the steps of: - providing, in a heated enclosure comprising a seed crystal, a mixture of gas components containing at least the elements of the multicomponent crystal, in such a way that, at least one of the elements is continuously supplied with the enclosure through an opening upstream of a growth surface of said crystal, - providing a separate opening downstream the growth surface of said crystal to remove a continuous flow of residual gas components which have not been deposited under conditions conducive to growth of said crystal, - providing an additional gas flow containing at least one halogen element, in such a way that said gas flow reduces a deposition rate of solids phases downstream of the growth surface of said crystal with a fa at least half of said growth rate of the crystal. The method according to claim 1, further comprises the steps of: - heating at least one area of the culture enclosure in the vicinity of, upstream of, said crystal to a temperature of at least 1900 ° C, and preferably in the area of 200 ° C to 2 ° C, - continuously feeding at least one silicon source gas such as silane, a chlorosilane or a methylsilane and a hydrocarbon source gas towards said opening downstream, - providing said additional gas fl desirably containing at least Cl or F. The method of claim 2 further comprises the step of: providing said additional gas stream consisting of chlorine (Cl2) or hydrogen chloride (HCl) or hydrogen (H2) or fluorine (F2) or a mixture thereof. The method according to claim 1, further comprises the steps of: - heating at least one area of the culture enclosure in the vicinity of, upstream of, said crystal to a temperature of at least 1100 ° C and preferably in the range 1zoo ° c and 2zoo ° c, - continuously feeding at least an organometallic source gas of gallium or aluminum and a nitrogen-containing gas towards said downstream orifice, - providing said additional gas flow preferably containing at least Cl or I. The method of claim 4 further comprises the step of: providing said additional gas flow consisting of chlorine (Cl2) or hydrogen chloride (HCl) ) or hydrogen (H2) or iodine hydrogen (HI) or iodine (12) or a mixture thereof. The method according to any one of claims 1 to 5, further comprising the steps of: attaching the seed to a seed holder mounted on a rotating and drawn shaft and feeding said additional gas flow acting as an etching gas through the shaft to be delivered downstream of the growth surface of said crystal. The method of any one of claims 1 to 5, further comprising the steps of: feeding said additional gas stream acting as an etch gas into at least one channel opening from a heated crucible into an area upstream of an initial position of the seed crystal before being drawn for a substantial period of time . The method according to any one of claims 1 to 5, wherein said extra gas flow acting as an etching gas is fed into a conduit formed between an outer heating element and an inner crucible, wherein said inner crucible extends along an axis of symmetry parallel to said growth direction of crystal and terminated in the absolute proximity to, upstream of, the initial seed crystal state. The method according to any one of claims 1 to 5, wherein a carrier gas is continuously fed with the gas component mixture containing at least the elements of the multicomponent crystal, said carrier gas consisting of either hydrogen, nitrogen, helium or argon or a mixture thereof. The method according to any one of claims 1 to 9, wherein a halogen-over-hydrogen ratio of the gases in any of the individual additional gas verk acts acting as an etching gas is adjusted to a value which prevents the formation of solid deposits along the surfaces which are desired to be maintained free of solid deposits. The method according to any one of claims 1 to 10, wherein said extra etch gas d velocity rate and its feed system are used to control the crystal diameter, either holding the crystal substantially cylindrical or allowing the crystal to expand during the process. A device for producing large, multicomponent crystals of monopoly type of either a) silicon carbide, b) a group III nitride c) alloys thereof, this apparatus comprising: - a susceptor with peripheral walls enclosing a space for receiving a seed crystal, - a system for continuously feeding in gas phase or in liquid form at least one of the elements of said crystal through an opening upstream of a growth surface of said crystal, - a system for continuously removing from space the flow of remaining gas components which have not been deposited under conditions which contribute to growth of said crystal, while maintaining a predefined pressure in the culture chamber, a system for heating the susceptor and thus the seed crystal to a predetermined process temperature characterized in that, the apparatus further comprises any or a combination of: - a system for continuous feeding and control of an etching gas mixture which comprises a halogen and hydrogen into a line of a rotating shaft supporting the seed crystal holder and said line communicating with an area downstream of the seed crystal, - a system for continuously feeding and directing an etch gas mixture comprising a halogen and hydrogen into lines created to open in a compartment downstream of the susceptor, said downstream compartment in contact with a compartment upstream of the susceptor and extending to the initial position of the seed holder, - a system for continuously feeding and controlling an etching gas mixture comprising a halogen and hydrogen into a peripheral conduit bounded by the inner wall of the space upstream of the susceptor and the outer wall of an inner crucible, said inner crucible extending along an axis of symmetry parallel to the direction of growth of said crystal and terminating in the immediate vicinity of, upstream of, the initial seed crystal position. The device according to claim 12, in which said element for culturing said multicomponent crystal is supplied through a gas source of silane, chlorosilane or methylsilane and through a gas source of hydrocarbon, or through an organometallic gas source containing gallium or aluminum and a gas source containing nitrogen. A device according to claim 12, comprising means for independently adjusting and varying the heat energy applied to the susceptor spaces downstream and upstream over time, said heat energy supplied by RF induction or by resistive heating or by a combination thereof. An apparatus according to claim 12, comprising means for varying the amount and ratio of halogen and hydrogen components in the etching gas mixture in a controlled manner over time. A device for producing large, multicomponent crystals of monopoly type of either a) silicon carbide, b) a group III nitride c) alloys thereof, this device comprising: - a crucible with peripheral walls enclosing a space for receiving a seed crystal in its upper part and a solid source, for example a powder, containing the elements of the multicomponent semiconductor to be grown, - means for heating the susceptor and establishing a temperature gradient between source material and seed crystal, 524 279 16 - effusion openings in the crucible which allow, for example, the control of the stoichiometry of the sublimated solid phase gas phase characterized in that the device further comprises means for feeding or diffusing a continuous flow of a gas mixture containing at least one halogen in the immediate vicinity of said effusion orifices to maintain said orifice free from tens of hours of said orifice. fixed deposits resulting from condensation of something t substance sublimated from the source material.