Single crystal coating for reactor component suitable for epitaxially depositing semiconductor film

Abstract

To provide a single crystal coating for reactor components suitable for epitaxially depositing a semiconductor film.SOLUTION: In selected internal components in the deposition units of a reactor for epitaxially depositing a semiconductor film on a substrate, provided are one or more layers formed of a chemically inactive single crystal material suitable for operating at the maximum temperature of 1700°C and adapted so as to prevent a semiconductor aggregate from dendritically and parasitically growing on the internal components. The epitaxial reactor includes one or more deposition units.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of epitaxial deposition of semiconductor films on substrates, and in particular to a deposition unit adapted to reduce preventative maintenance time.

[0002] Additionally, although 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 technology]

[0003] Semiconductor films produced by epitaxial growth, also known as epilayers, are formed by deposition within a reaction chamber in a reactor. The deposited material may be the same as the substrate or may contain a different semiconductor with specific desired qualities. Epitaxial growth techniques allow for control over the crystalline structure formed on the substrate and improved surface characteristics of the epilayer, making them suitable for the fabrication of highly complex microprocessors and memory devices.

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

[0005] In the case of epitaxial reactors for silicon carbide deposition, temperatures within the chamber cavity can reach a range of 1500-1700°C. These temperatures can be reached in a variety of ways, and the chamber can be of the "hot-wall" or "cool-wall" type. In a non-limiting example of the former, the reaction chamber walls as well as the enclosed cavity reach the high deposition temperatures. In this case, the reaction chamber can include one or more graphite partition elements that can be effectively heated to the desired temperature via induction means. The reaction chamber can also 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 the substrate. However, semiconductors can also grow in other parts of the reaction chamber. For example, in reactors for the deposition of monocrystalline silicon carbide, such as the 4H and 6H polytypes, uncontrolled buildup of polycrystalline silicon carbide has been observed on the chamber's partition elements and functional components. Note that this unwanted buildup of silicon carbide is extremely difficult to remove, as its hardness is comparable to that of diamond.

[0007] The above parasitic phenomena are particularly relevant to hot-wall reactors, particularly affecting the upstream end of the chamber (i.e., where the precursor gases enter the reaction chamber) as well as elements in close proximity to or in contact with the substrate, which may be made entirely or partially of graphite and coated with TaC or poly-SiC.

[0008] These parasitic deposits have often been observed to result in the rapid growth of cauliflower-like porous dendritic structures, which ultimately affect the quality of the deposited film.

[0009] To prevent these side effects, the reaction chamber is subjected to frequent preventive maintenance (PM) operations, typically every 300-3000 μm, preferably every 500-700 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 impact reactor productivity and can cause reactor downtime of up to 8-12 hours, negatively impacting the economics of the epitaxial deposition process.

[0010] It should be noted that unwanted SiC buildup occurs not only on bare graphite surfaces of the reaction chamber, but also on parts that have been preventatively coated with TaC or SiC.

[0011] In fact, some or all parts of the reaction chamber are typically coated with a TaC layer to protect the graphite surfaces during cleaning operations. Alternatively, a thin layer of SiC is used to seal exposed porous graphite surfaces to avoid contamination. In this case, SiC is always used in its polycrystalline form because it is easy to deposit and cost-effective.

[0012] The problem of parasitic deposition is not unique to epitaxial reactors, but can also occur in physical vapor transport systems for substrate fabrication, also known as sublimators.

[0013] WO 2007 / 088420 addresses the problem of unwanted material deposition on reaction chamber walls during high-temperature epitaxial growth processes. The application discloses a novel approach based on temperature differentiation of the reaction chamber walls by modifying the geometry of the reaction cavity. However, in this case, the temperature and temperature gradient within the reaction chamber cavity play a key role in the deposition process, making it difficult to identify the correct design to balance the competing interests (deposition quality, speed, and lower parasitic buildup).

[0014] In conclusion, it would be desirable to provide a new reaction chamber for silicon carbide deposition that is adapted to reduce the frequency of PM operations and ensure high-quality film deposition. It would also be desirable to prevent or reduce parasitic SiC growth on the walls and other elements of the reaction chamber. Additionally, it would be advantageous to provide a new epitaxial reactor that incorporates the aforementioned reaction chamber. It would also be desirable to have a SiC physical vapor transport system that reduces parasitic SiC growth. Summary of the Invention

[0015] It is an object of the present invention to overcome the drawbacks 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 operations, 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 material. A further object of the present invention is to provide a deposition unit adapted to prevent parasitic growth of poly-SiC.

[0016] In a second aspect, the object of the present invention is 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 transport system for the production of silicon carbide substrates.

[0018] The above-mentioned main object is achieved through the invention as set forth 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; their sole purpose is to make the claims easier to understand.

[0019] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description of Example Embodiments of the Disclosure. 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 explanation of the drawings]

[0020] [Figure 1] 1 is a photograph of a reaction chamber part showing parasitic deposits. DETAILED DESCRIPTION OF THE INVENTION

[0021] While certain specific embodiments and examples are disclosed below, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments and / or uses of the invention, and obvious modifications and equivalents thereof. It is therefore not intended that the scope of the disclosed invention should 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 epitaxial deposition of semiconductor films on a substrate is suppressed if the internal parts exposed to the flow of precursor gases are covered with at least one layer of monocrystalline material. The 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 gases include Si and C precursors. For example, the silicon precursor gas may be a chlorinated compound, preferably dichlorosilane, trichlorosilane, or tetrachlorosilane. The carbon precursor gas may be a hydrocarbon, particularly propane, ethylene, acetylene, or methane. Other types of precursors may also be used.

[0024] Other precursors, such as for n-doping and p-doping, can flow through 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 also be flowed into the deposition unit, such as purge gases, cooling gases, and carrier gases. 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 atmospheric pressure (about 1 bar).

[0027] Advantageously, the monocrystalline material may be chosen so as to be inert to the precursor gases at temperatures up to 1700° C. and also advantageously at pressures between 50 and 200 mbar.

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

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

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

[0031] The deposition unit comprises (i) at least one partition element provided with a receiving area adapted to receive a substrate holder, and (ii) at least one graphite element characterized by at least one coated surface exposed to the flow of precursor gas.

[0032] The coated surface is a surface covered or coated with at least one film, i.e., 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 under or over the layer of single crystal material without departing from the scope of the present invention.

[0034] The expression "deposition unit" means an enclosure in which epitaxial reactions and deposition processes take place, including the internal cavity defined by said enclosure. A deposition unit may coincide with a reaction chamber or may be a subassembly thereof.

[0035] The deposition unit 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 characterized by cross-flow, horizontal, and / or hot-wall configurations. In fact, the problem of parasitic deposition is particularly pronounced 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 buildup, and cleaning processes can ultimately damage the relevant components.

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

[0037] The deposition unit is configured to receive a flow of precursor gases. That is, it may include any suitable injection system, such as any adaptation to the deposition unit that allows for the injection of one or more precursors into its cavity, and is configured to direct those flows toward a substrate on a substrate holder when the substrate holder is positioned within the receiving region. 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 integrally cover the coated surface of at least one graphite element.

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

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

[0041] The deposition unit may further comprise other structural elements used to improve heating efficiency, such as additional graphite parts or enclosures.

[0042] The deposition unit according to the invention may also comprise an insulation system made of one or more casings of insulation material. For this purpose, a porous carbonaceous material can be used, for example a carbon composite made from short-cut carbon fibers, optionally interconnected in a matrix or pressed together.

[0043] The advantage of using the above-mentioned single crystal material is two-fold: first, the material can withstand the operating conditions of the deposition unit without interfering with the reaction and deposition process.

[0044] Second, coating the graphite surface of the deposition unit with one or more layers of a single-crystalline material can be beneficial. On bare graphite surfaces, or surfaces coated with poly-TaC or poly-SiC, parasitic semiconductor growth occurs in an uncontrolled dendritic form, as shown in Figure 1, leaving the graphite reactor component 100 susceptible to rough parasitic deposits 110. Conversely, covering the graphite surface exposed to the precursor gas with one or more layers of a single-crystalline material promotes ordered heteroepitaxial or homoepitaxial growth, depending on the material used. This heteroepitaxial growth rate is the relevant growth rate to monitor and requires less frequent PM operations than uncontrolled dendritic growth. It should be noted that in the art, graphite elements of deposition units are commonly coated to protect the elements during cleaning or to "seal" the exposed porous graphite surface to avoid contamination.

[0045] In a first embodiment, the monocrystalline material used to coat the surfaces in the deposition unit according to the present invention is monocrystalline diamond or monocrystalline SiC. Both materials are characterized by a controlled crystalline structure and can advantageously 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. Additionally, thanks to their specific inert carbon-based composition, the selected materials do not interfere with the deposition process or contaminate the deposition unit.

[0046] It should be noted that polycrystalline SiC does not perform well in the practice of the present invention. In fact, the growth rate of porous poly-SiC is significantly higher than that of mono-SiC under identical growth conditions. In fact, the inventors observed that poly-SiC buildup increases in height exponentially over a 3-4 day reactor run, while mono-SiC follows linear behavior over the same time frame and under identical operating conditions. In addition, the effective growth rate of the porous parasitic layer increases with increasing thickness due to its tendency to grow preferentially at edges, tips, and the ends of other protruding features.

[0047] In the case of SiC deposition, it has been observed that the use of poly-SiC coatings to shield graphite components is not successful in inhibiting parasitic growth, given that the epitaxy substrate is necessarily formed of single-crystal SiC.

[0048] This leads to a significant mismatch between the growth rate on the graphite elements of the deposition unit (such as consumable parts or partitions) and the substrate. By modifying the exposed surfaces so that they are covered with mono-SiC (rather than poly-SiC, TaC, or left bare), the mismatch can be equalized and the maximum epitaxial growth during the PM step can be advantageously and significantly increased. Because parasitic deposition of SiC is more rapid at the upstream end of the deposition unit, it may be preferable to use mono-SiC parts specifically corresponding to the upstream portion of the unit.

[0049] Additionally, it should be noted that polycrystalline diamond does not work well in the practice of the present invention. Indeed, due to its non-uniform crystalline structure, uncontrolled parasitic growth can still occur on this type of material.

[0050] However, the use of one or more single-crystal diamond layers may offer some advantages. In this case, the relevant growth rate is the heteroepitaxial growth rate of SiC on diamond, which is expected to be much lower than the growth of SiC on poly-SiC and bare graphite. Therefore, even in the case of single-crystal diamond, PM operations can be spaced apart, resulting in an advantageous reduction in overall reactor downtime.

[0051] For SiC reactors, the use of a non-SiC monocrystalline cover layer offers the advantage of being chemically distinct from parasitic SiC deposits. Any chemical differences can be exploited to develop selective in-situ and / or ex-situ cleaning methods for the deposition unit 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 monocrystalline materials.

[0052] The one or more single crystal diamond layers described above may be obtained by applying one or more tiles of commercially available synthetic single crystal diamond onto the surface to be coated, the tiles being suitably cut, for example by laser machining, to provide continuous coverage of the surface of interest.

[0053] When mono-SiC is selected as the single-crystal material to be layered on the graphite element, it is possible to use a mono-SiC wafer, which has been appropriately shaped into one or more pieces, for example by laser cutting the mono-SiC substrate, and the mono-SiC pieces thus obtained can be placed on the surface most susceptible to parasitic growth.

[0054] While larger mono-SiC cover pieces can be beneficial from a cleanliness standpoint, utilizing smaller pieces can also reduce the need for costly larger diameter SiC wafers as starting material and / or reduce waste.

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

[0056] The inventors have observed that selecting the 4H-SiC or 6H-SiC polytype as the monocrystalline material works particularly well in the practice of the present invention. Indeed, in the case of a deposition unit for epitaxial SiC deposition, the mono-SiC film deposited is of the 4H-SiC or 6H-SiC polytype. By matching the crystalline structure of the monocrystalline material layer of the graphite element with the crystalline structure of the film deposited on the substrate, it is observed that a particularly compact and regular growth accumulates on the monocrystalline material layer.

[0057] In another embodiment, in a deposition unit according to the present invention, the graphite element may be a removable part, e.g., a spare or consumable component of the deposition unit adapted to be removable from the deposition unit. By way of non-limiting example, removable parts may include a substrate centering ring, a substrate holder, an upstream and / or downstream cover, etc.

[0058] Additionally or alternatively to the above-described embodiments, the at least one graphite element may be a partition element, for example, a bottom wall of the deposition unit exposed to the flow of precursor gas, or a portion thereof.

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

[0060] It is understood that the reactor according to the invention may include other elements required for its operation according to standard practice. For example, it may comprise an enclosure, optionally made of quartz and preferably cooled with a cooling fluid such as water. The deposition unit may be inserted into said enclosure, and both may be surrounded by a guide system.

[0061] Preferably, the epitaxial reactor according to the present invention is adapted to receive a flow of precursor gases in a cross-flow configuration and is adapted for the deposition of silicon carbide. 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 transport system for producing silicon carbide according to the present invention may comprise an enclosure and at least one graphite element contained within the enclosure. The graphite element is characterized by at least one coated surface exposed to a stream of sublimated silicon carbide containing at least one layer of single-crystal material. The single-crystal material is carbon-based, chemically inert at temperatures up to 1700°C, and characterized by a melting point above 1700°C.

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

[0065] In the description and claims of this application, the word "comprise" and variations thereof, such as "comprising" and "comprises", do not exclude the presence of other additional elements, components or steps.

[0066] The discussion of documents, acts, materials, devices, articles and the like is included in this text solely for the purpose of providing a context for the invention, and neither this material nor any portion thereof should be understood to constitute common general knowledge in the art relative to the invention prior to the priority date of each of the claims appended to this application. [Explanation of symbols]

[0067] 100 Graphite reactor parts 110 Parasitic Deposits

Claims

1. 1. A deposition unit for an epitaxial reactor for deposition of a semiconductor film on a substrate and configured to receive a flow of precursor gas, the deposition unit comprising: at least one separation element provided with a receiving area, said receiving area being adapted to receive a substrate holder; at least one graphite element characterized by at least one coated surface exposed to the flow of said precursor gas; A deposition unit, wherein the coated surface comprises at least one layer of a monocrystalline material, the monocrystalline material being carbon-based, chemically inert at temperatures up to 1700°C, and characterized by a melting point above 1700°C.

2. The deposition unit of claim 1 , wherein the single crystal material is single crystal diamond and / or single crystal SiC.

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

4. The deposition unit of claim 1 , wherein the at least one graphite element is a removable part.

5. The deposition unit of claim 4 , wherein the at least one graphite element is the at least one partition element.

6. The deposition unit according to any one of claims 1 to 5, wherein at least one layer of said single crystal material integrally covers the coated surface of said at least one graphite element.

7. The deposition unit according to any one of claims 1 to 5, wherein at least one layer of monocrystalline material comprises a plurality of tiles.

8. 1. An epitaxial reactor for the deposition of a semiconductor film on a substrate, comprising: at least one deposition unit according to claim 1; an induction system for heating at least one of said deposition units; a gas management system for delivering precursor gases to at least one of said deposition units.

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

10. 1. A physical vapor transport system for the production of silicon carbide, comprising: an enclosure; and at least one graphite element contained within said enclosure, said graphite element characterized by at least one coated surface exposed to a stream of sublimated silicon carbide, said coated surface comprising at least one layer of a single crystal material, said single crystal material being carbon-based and chemically inert at temperatures up to 1700°C and characterized by a melting point above 1700°C.

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

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