Single crystal coating for reactor components suitable for

Abstract

The invention relates to a deposition unit for a reactor for epitaxially depositing a semiconductor film on a substrate, in which selected internal components of the unit are provided with one or more layers of a single crystal chemically inert material, it is suitable for operation at temperatures up to 1700 DEG C and for inhibiting dendritic growth of semiconducting agglomerates on the inner part. The invention also relates to an epitaxial reactor comprising one or more deposition units as described above.

Description

Technical Field

[0001] The present invention relates to the field of epitaxial deposition of semiconductor films on substrates; in particular, to a deposition unit suitable for reducing preventive maintenance time.

[0002] Additionally, but not exclusively, the present invention relates to the field of deposition of silicon carbide films on semiconductor substrates in hot-wall, cross-flow homoepitaxial or heteroepitaxial reactors. Background Art

[0003] Semiconductor films produced by epitaxial growth (also known as epilayers) are formed by deposition in a reactor chamber. The deposited material can be the same as the substrate, or it can involve a different semiconductor with specific desired qualities. Epitaxial techniques allow for control of the crystal structure formed on the substrate and refinement of the epilayer surface characteristics, making them suitable for the manufacture of highly complex microprocessors and memory devices.

[0004] Typically, the reaction chamber is heated to the desired temperature prior to film deposition and then maintained at a substantially constant temperature throughout the deposition process.

[0005] In the case of an epitaxial reactor for depositing silicon carbide, the temperature reached within the chamber cavity may be in the range of 1500-1700°C. These temperatures can be reached in many ways, and the chamber can be of "hot wall" or "cold wall" type. In the former non-limiting example, the walls of the reaction chamber and the enclosed cavity reach the high deposition temperature. In this case, the reaction chamber may include one or more graphite partition elements, which can be effectively heated to the desired temperature via induction means. The reaction chamber may additionally include other graphite functional components, such as graphite substrate holders, rings, and upstream and downstream elements.

[0006] During the epitaxial deposition process, semiconductor films grow in a controlled manner on a substrate. However, semiconductors can also grow on other areas of the reaction chamber. For example, in reactors used to deposit single-crystalline silicon carbide (such as its 4H and 6H polytypes), uncontrolled accumulation of polycrystalline silicon carbide has been observed on separators and functional components of the chamber. It should be noted that this undesirable accumulation of silicon carbide is very difficult to remove, and its hardness is comparable to that of diamond.

[0007] The aforementioned parasitic phenomenon is particularly relevant in hot-wall reactors, where it particularly affects the upstream end of the chamber (i.e., where the precursor gases enter the reaction chamber), as well as elements close to or in contact with the substrate. These can be made entirely or partially of graphite and coated in TaC or poly-SiC.

[0008] It has been observed that these parasitic deposits often lead to the rapid growth of cauliflower-like, porous, dendritic structures, which ultimately affects the quality of the deposited films.

[0009] To prevent these side effects, the reactor chamber undergoes frequent preventive maintenance (PM) operations, for example after every 300 to 3000 μm, preferably 500 to 700 μm, of film growth. During PM, the machine is cooled and purged, and some or all affected components are manually removed from the chamber for cleaning / disposal and replacement. PM operations affect the productivity of the reactor and negatively impact the economics of the epitaxial deposition process, as they can result in up to 8-12 hours of reactor downtime.

[0010] It should be noted that undesirable SiC accumulation occurs not only on the bare graphite surfaces of the reaction chamber, but also on those components that are preventively coated with TaC or SiC.

[0011] In practice, some or all components of the reaction chamber are often coated with a TaC layer to protect the graphite surface during cleaning operations. Alternatively, a thin layer of SiC is used to seal the exposed porous graphite surface to avoid contamination. In this case, SiC is always used in its polycrystalline form because it can be deposited easily and is cost-effective.

[0012] The problem of parasitic deposition is not specific to epitaxial reactors, but can also occur in physical vapor transport systems (also called sublimators) used for substrate fabrication.

[0013] WO2007088420 addresses the problem of unwanted material deposition on the walls of the reaction chamber during epitaxial growth processes at high temperatures. The application discloses a novel approach based on varying the temperature of the reaction chamber walls by modifying the geometry of the reaction chamber. However, in this case, identifying the correct design to balance competing interests (deposition quality, speed, and low parasitic accumulation) is difficult, as the temperature and temperature gradient within the reaction chamber cavity play a key role in the deposition process.

[0014] In summary, it is desirable to provide a new reaction chamber for silicon carbide deposition that is suitable for reducing the frequency of PM operation while ensuring high-quality film deposition. Furthermore, it is desirable to prevent or reduce parasitic SiC growth on the walls and other components of the reaction chamber. Furthermore, it would be advantageous to provide a new epitaxial reactor incorporating the aforementioned reaction chamber. Furthermore, it would be desirable to have a SiC physical vapor transport system with reduced parasitic SiC growth. Summary of the Invention

[0015] The present invention aims to overcome the shortcomings of the prior art. In particular, it is an object of the present invention to provide a deposition unit for reducing the frequency of PM operation, particularly, but not exclusively, when used in a hot-wall reactor for epitaxial deposition of SiC films on semiconductor substrates of the same or different materials. Another object of the present invention is to provide a deposition unit suitable for inhibiting parasitic growth of poly-SiC.

[0016] In a second aspect, it is an object of the present invention to provide a new reactor suitable for incorporating the above-mentioned deposition unit.

[0017] In a third aspect, it is an object of the present invention to provide a physical vapor delivery system for producing silicon carbide substrates.

[0018] The above-mentioned main object is achieved by the invention described in the appended claims, which form an integral part of this specification. The use of reference signs in the claims does not limit the scope of the claims. The sole purpose of the reference signs is to make the claims easier to understand.

[0019] This summary is provided to introduce a selection of concepts in a simplified form. These concepts are further described in the detailed description of example embodiments of the present disclosure below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a picture of a portion of a reaction chamber showing parasitic deposits. DETAILED DESCRIPTION

[0021] Although certain embodiments and examples are disclosed below, those skilled in the art will appreciate that the invention extends beyond the specifically disclosed embodiments and / or uses of the invention and obvious modifications and equivalents thereof. Accordingly, it is intended that the scope of the disclosed invention should not be limited by the specific disclosed embodiments described below.

[0022] In general, the present invention is based on the observation that parasitic growth in a deposition unit for epitaxially depositing semiconductor films on a substrate is hindered if the internal components exposed to the precursor gas flow are covered with at least one layer of a single-crystalline material. This material should be carbon-based, chemically inert at temperatures up to 1700°C, and have a melting point above 1700°C.

[0023] Typically, the precursor gas includes Si and C precursors. For example, the silicon precursor gas can be a chlorinated compound, preferably dichlorosilane, trichlorosilane, or tetrachlorosilane. The carbon precursor gas can be a hydrocarbon, particularly propane, ethylene, acetylene, or methane. Other types of precursors can also be used.

[0024] Other precursors, such as those for n- and p-doping, can flow in the deposition unit of the reactor. For example, the n-source can be nitrogen, acetonitrile, pyrrole, ammonia, hydrazine, hydrogen cyanide, methylamine.

[0025] Other gases may flow into the deposition cell, such as purge gas, cooling gas, and carrier gas. Examples of suitable gases include hydrogen, argon, and neon.

[0026] Typically, the pressure inside the deposition unit during the deposition process is about 50-200 mbar. Otherwise, the deposition unit is at ambient pressure (~1 bar).

[0027] Advantageously, the single crystal material may be chosen to be inert to the precursor gas at temperatures up to 1700° C., and advantageously also at pressures of 50-200 mbar.

[0028] In particular, the single-crystal material may be single-crystal diamond or single-crystal SiC, which have been observed to work particularly well in the field of epitaxial SiC deposition and meet the requirements of (i) being carbon-based, (ii) being chemically inert at temperatures up to 1700° C., and (iii) having a melting point above 1700° C. The internal components may be made of graphite and may be appropriately coated with the above-mentioned single-crystal materials. Advantageously, the internal components may be spare parts of the SiC reactor, such as substrate holders, centering rings, and / or upstream and downstream covers (upstream and downstream with respect to the precursor gas flow).

[0029] The present invention therefore relates to a graphite element which is a spare part of a SiC reactor, coated with the above-mentioned single crystal material and suitable for use in a deposition unit as described below.

[0030] In one aspect, the present invention relates to a deposition cell for an epitaxial reactor adapted for depositing a semiconductor film on a substrate and configured to receive a flow of a precursor gas.

[0031] The deposition unit comprises: (i) at least one spacer element provided with a receiving area adapted to receive a substrate holder; and (ii) at least one graphite element having at least one coated surface exposed to a flow of precursor gas.

[0032] A coated surface is a surface covered or coated with at least one coating (ie layer) of a single crystal material having a melting point above 1700° C. Furthermore, the single crystal material is carbon-based and chemically inert at temperatures up to 1700° C.

[0033] It should be understood that additional coatings may be applied beneath or over the layer of single crystal material without departing from the scope of the present invention.

[0034] The expression "deposition unit" refers to an enclosure in which the epitaxial reaction and deposition processes occur, and includes an interior cavity defined by the enclosure. The deposition unit may coincide with the reaction chamber or be a subassembly thereof.

[0035] The deposition cell according to the present invention can be advantageously used for epitaxial or homoepitaxial deposition of silicon carbide films on semiconductor substrates. In particular, it can be satisfactorily used in epitaxial reactors with cross-flow, horizontal, and / or hot-wall configurations. In practice, the problem of parasitic deposition is particularly felt in these types of reactors. Furthermore, in the case of SiC reactors, the hardness of the material makes it particularly difficult to remove any unwanted accumulations, and the cleaning process can ultimately damage the components involved.

[0036] The deposition unit according to the invention may comprise one or more separation elements, such as walls, to form an enclosure. In case of an induction heated deposition unit, the one or more separation elements may advantageously be made of graphite.

[0037] The deposition unit is configured to receive a flow of precursor gases, i.e., it may include any suitable injection system, such as any adaptation to the deposition unit, which allows for the injection of one or more precursors into its chamber and directing their flow toward a substrate on a substrate holder when the substrate holder is placed in the receiving area. For example, the injection system may include one or more inlets, nozzles, or showerheads.

[0038] It should be noted that the layer of single crystal material may entirely cover the coated surface of the at least one graphite element.

[0039] Alternatively, the layer of single crystal material may consist of a plurality of tiles disposed on and coating the exposed surface of the graphite element.The term "tile" refers to a macroscopic piece of material.

[0040] The deposition unit will also likely be configured to exhaust exhaust gases, for example via one or more outlets.

[0041] The deposition unit may additionally comprise further structural elements for increasing its heating efficiency, such as further graphite components or an outer housing.

[0042] The deposition unit according to the invention may also comprise an insulation system made of one or more shells of insulating material.For this purpose, porous carbonaceous materials may be used, such as carbon composites made of chopped carbon fibers, optionally interconnected in a matrix, or pressed together.

[0043] The advantages of using the single crystal materials described above are twofold: First, the materials are able to withstand the operating conditions of the deposition unit without interfering with the reaction and deposition process.

[0044] Secondly, coating the graphite surface of the deposition unit with one or more layers of single-crystal material can produce advantageous effects. In the case of bare graphite surfaces or surfaces coated with poly-TaC or poly-SiC, parasitic semiconductor growth occurs in an uncontrolled dendritic manner, e.g. Figure 1Figure 1 shows a graphite reactor component 100 exposed to rough parasitic deposits 110. In contrast, if one or more layers of single-crystalline material are used to cover the graphite surface exposed to the precursor gas, they will promote ordered heteroepitaxial or homoepitaxial growth, depending on the material used. This heteroepitaxial growth rate will be the relevant growth rate to monitor and will require less frequent PM operations than uncontrolled dendritic growth. It should be noted that in the art, graphite elements of deposition units are typically coated to protect the elements during cleaning, or to "seal" the exposed porous graphite surface and avoid contamination.

[0045] In a first embodiment, the single-crystal material used to coat the surface in the deposition unit according to the present invention is single-crystal diamond or single-crystal SiC. Both materials are characterized by a controlled crystal structure and are advantageously able to withstand the operating temperatures of the deposition unit without melting or sublimating. Therefore, they can effectively coat the surface of the graphite element during reactor operation. In addition, due to their specific inert, carbon-based composition, the materials selected above do not interfere with the deposition process or contaminate the deposition unit.

[0046] It should be noted that polycrystalline SiC does not work well in the implementation of the present invention. In fact, under the same growth conditions, the growth rate of porous poly-SiC is significantly higher than that of mono-SiC. In fact, the inventors have observed that the accumulation of poly-SiC increases in height following an exponential curve over a 3-4 day reactor operation period, while mono-SiC follows a linear behavior over the same time frame and under the same operating conditions. In addition, the effective growth rate of the porous parasitic layer increases with increasing thickness, due to the tendency of growth to occur preferentially at the edges, tips, and ends of other protruding shapes.

[0047] It has been observed that the use of poly-SiC coatings to shield graphite components has not been successful in suppressing parasitic growth, given that in the case of SiC deposition, the epitaxial substrate must be formed of single-crystal SiC.

[0048] This results in a considerable difference in growth rate between the graphite elements of the deposition cell (such as consumable parts or separators) and on the substrate. By modifying the exposed surfaces so that they are covered with single SiC (rather than poly-SiC, TaC, or left bare), the difference can be evened out and the maximum epitaxial growth between PM steps can be advantageously and significantly increased. Since parasitic deposition of SiC is faster at the upstream end of the deposition cell, it may be preferable to use a single SiC section, particularly corresponding to the upstream portion of the cell.

[0049] It should also be noted that polycrystalline diamond does not work well in implementing the present invention. In fact, due to its inhomogeneous crystal structure, uncontrolled parasitic growth may still occur on this type of material.

[0050] However, using one or more single-crystal diamond layers can offer several advantages. In this case, the relevant growth rate will be the heteroepitaxial growth rate of SiC on diamond, which is expected to be much lower than that of SiC growth on polySiC and bare graphite. Therefore, also in the case of single-crystal diamond, PM operations can be spaced out, thereby advantageously reducing overall reactor downtime.

[0051] In the case of SiC reactors, using a single-crystal capping layer other than SiC can have the benefit of being chemically distinct from the parasitic SiC deposit. Any chemical differences can be exploited to develop selective in-situ and / or ex-situ cleaning methods for the deposition cell and its components. For example, in the case of ex-situ wet cleaning, chemistries can be developed that preferentially remove poly-SiC without significantly attacking the underlying layers of different single-crystal materials.

[0052] The one or more single crystal diamond layers described above may be obtained by applying one or more commercial synthetic single crystal diamond tiles to the surface to be coated. The tiles may be appropriately cut to continuously cover the surface of interest, for example by laser machining.

[0053] In the case where single-crystalline SiC is chosen as the single-crystalline material to be layered on the graphite element, a single-crystalline SiC wafer suitably formed into one or more pieces can be used, for example by cutting a single-crystalline SiC substrate by laser machining. The single SiC pieces thus obtained can be placed on the surface where parasitic growth is of greatest concern.

[0054] While larger single SiC capping pieces may be beneficial from a cleanliness perspective, smaller pieces may also be utilized to reduce the need for costly larger diameter SiC wafers as starting material and / or to reduce waste.

[0055] It should be noted that one or more single crystal non-SiC materials may be used in conjunction with single SiC material to cover the walls of the processing chamber.

[0056] The inventors have observed that using 4H-SiC or 6H-SiC polytypes as the single-crystalline material of choice works particularly well in carrying out the present invention. In fact, in the case of a deposition unit for epitaxial SiC deposition, the deposited single-SiC film is a 4H-SiC or 6H-SiC polytype. By matching the crystal structure of the single-crystalline material layer of the graphite element with the crystal structure of the film deposited on the substrate, a particularly compact and regular growth is observed, accumulating on the single-crystalline material layer.

[0057] In another embodiment, in a deposition unit according to the present invention, the graphite element may be a removable component, such as a spare or consumable component of the deposition unit adapted to be removed therefrom. As non-limiting examples, the removable component may include a substrate centering ring, a substrate holder, an upstream and / or downstream cover, etc.

[0058] Additionally or alternatively to the above embodiments, the at least one graphite element may be a spacer element. For example, it may be a bottom wall of the deposition unit, or a portion thereof, that is exposed to the precursor gas flow.

[0059] In different aspects, the present invention relates to an epitaxial reactor for depositing semiconductor films on a substrate, comprising: (i) at least one deposition unit according to any of the preceding claims; (ii) an induction system for heating at least one deposition unit; and (iii) a gas management system for delivering precursor gases to at least one deposition unit.

[0060] It will be appreciated that, in accordance with standard practice, the reactor according to the present invention may include other elements necessary for its operation. For example, it may include a housing, optionally made of quartz and preferably cooled with a cooling fluid such as water. The deposition unit may be inserted into the housing, and both may be surrounded by the induction system.

[0061] Preferably, the epitaxial reactor according to the present invention is adapted to receive a precursor gas flow in a cross-flow configuration and is suitable for silicon carbide deposition.Even more preferably, the epitaxial reactor according to the present invention is a hot wall reactor.

[0062] In another aspect, the present invention relates to a physical vapor transport system comprising the deposition unit described above.

[0063] For example, a physical vapor delivery system for producing silicon carbide according to the present invention may include a housing and at least one graphite element contained within the housing. The graphite element has at least one coated surface exposed to a stream of sublimated silicon carbide, the surface comprising at least one layer of a single crystal material. The single crystal material is carbon-based, chemically inert at temperatures up to 1700°C, and has a melting point greater than 1700°C.

[0064] The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems and configurations, and other features, functions, acts, and / or properties disclosed herein, as well as any and all equivalents thereof.

[0065] In the description and claims of the present application, the word "comprise" and its variations do not exclude the presence of other additional elements, components or stages.

[0066] The discussion of documents, contracts, materials, devices, articles and the like is included in the text solely for the purpose of providing a context for the present invention; however, it should not be understood that this material or any portion of it constitutes general knowledge in the field relevant to the present invention before the priority date of each claim appended to this application.

Claims

1. A deposition unit for an epitaxial reactor, configured to deposit a semiconductor film on a substrate and configured to receive a flow of a precursor gas; the deposition unit comprising: - at least one separating element provided with a receiving area adapted to receive a substrate holder; - at least one graphite element having at least one coated surface exposed to a flow of precursor gas; Wherein, the coated surface comprises at least one layer of a single crystal material; the single crystal material is carbon-based, is chemically inert at temperatures up to 1700°C, and has a melting point above 1700°C.

2. The deposition unit according to claim 1, wherein: The single crystal material is single crystal diamond and / or single crystal SiC.

3. The deposition unit according to claim 2, wherein: The single crystal SiC material is a 4H-SiC or 6H-SiC polytype.

4. The deposition unit according to any one of claims 1 to 3, wherein: The at least one graphite element is a removable component.

5. The deposition unit according to claim 4, wherein: The at least one graphite element is the at least one separator element.

6. A deposition unit according to any one of the preceding claims, wherein: The at least one layer of single crystal material entirely covers the coated surface of the at least one graphite element.

7. The deposition unit according to any one of claims 1 to 5, wherein: The at least one layer of single crystal material includes a plurality of tiles.

8. An epitaxial reactor for depositing a semiconductor film on a substrate, comprising: - at least one deposition unit according to any one of the preceding claims; - an induction system for heating at least one deposition unit; - A gas management system for delivering precursor gases to at least one deposition unit.

9. The epitaxial reactor according to claim 8, wherein The deposition unit is adapted to receive a flow of SiC precursor gas in a cross-flow configuration.

10. A physical vapor delivery system for producing silicon carbide, comprising a housing and at least one graphite element contained within the housing; wherein: The graphite element has at least one coated surface exposed to a flow of sublimating silicon carbide; the coated surface comprises at least one layer of a single crystal material; the single crystal material is carbon-based, chemically inert at temperatures up to 1700°C, and has a melting point above 1700°C.

11. A graphite element suitable for a deposition unit of an epitaxial reactor, wherein: The graphite element is a substrate holder, a centering ring, an upstream cover or a downstream cover, which has at least one coated surface exposed to the precursor gas flow; wherein the coated surface includes at least one layer of single crystal material; the single crystal material is carbon-based, chemically inert at temperatures up to 1700°C, and has a melting point above 1700°C.

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