Abstract:
The invention discloses a method and system for continuous deposition of thin films by chemical vapor reaction for the purposes of semiconductor device fabrication; in some embodiments a device is a photovoltaic device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related in part to U.S. application Ser. Nos. 12/074,651, 12/720,153, 12/749,160, 12/789,357, 12/860,048, 12/950,725, 12/860,088, 13/010,700, 13/019,965, 13/073,884, 13/077,870, 13/214,158, 13/234,316, 13/268,041, 13/272,073, and U.S. Pat. No. 7,789,331 all owned by the same assignee and all incorporated by reference in their entirety herein. Additional technical explanation and background is cited in the referenced material. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention discloses a method and system for continuous deposition of thin films by chemical vapor reaction for the purposes of semiconductor device fabrication; in some embodiments a device is a photovoltaic device. 
         [0004]    2. Description of Related Art 
         [0005]    The instant invention teaches an atmospheric pressure, chemical vapor deposition system for deposition of silicon based compounds. Prior art in this area is found in U.S. Pat. No. 4,834,020, U.S. Pat. No. 5,076,207, U.S. Pat. No. 5,122,391, U.S. Pat. No. 5,113,789, U.S. Pat. No. 5,122,391, U.S. Pat. No. 5,136,975, U.S. Pat. No. 5,393,563, U.S. Pat. No. 5,683,516, U.S. Pat. No. 5,849,088, U.S. Pat. No. 5,863,337, U.S. Pat. No. 5,863,338, U.S. Pat. No. 5,944,900, U.S. Pat. No. 6,143,080, U.S. Pat. No. 6,220,286, U.S. Pat. No. 6,231,673, U.S. Pat. No. 6,890,386, U.S.20060141290, U.S.20110195207; all incorporated herein in their entirety by reference. 
         [0006]    U.S.20110195207 discloses a roll-to-roll atmospheric pressure chemical vapor deposition system for the deposition of graphene on a metal substrate comprising a grapheme forming unit comprising one or more gas nozzles and a temperature controllable heating jacket operable to a temperature between about 300° C. and about 2000° C. Rollers may be provided at the inlets and outlets to assist with a “roll-to-roll” operating mode; deposition is typically done on a metallic substrate. No provision is made for preventive maintenance or chamber replacement. 
         [0007]    U.S. Pat. No. 4,834,020 discloses a APCVD system having a heated muffle and conveyor belt and a deposition zone with a gas injector assembly for each deposition zone. S. Reber of the Fraunhofer Institute has disclosed a high throughput deposition APCVD tool at the 24 th  Eurpean PV Solar Energy Conference, 21-25 Sep., 2009, Hamburg, Germany. The Fraunhofer apparatus comprises three independent modules, each module having a double track of six 156 mm by 156 mm substrates; each module is in a muffle of low-permeability graphite; each muffle heated by a graphite rod resistance heater. Each module has two consecutive reaction chambers. Chlorosilane consumption is projected at 500g/min. with a deposition rate of 3 microns/min providing a 20 micron thick layer on 30 m 2 /h. This calculates to a silicon “utilization” of about 17%; utilization is defined as amount of silicon deposited on a substrate divided by amount of silicon entering the reactor. The reactor is also described in SCHILLINGER, K., et al.; “Crystalline SiC deposited by APCVD as a multifunctional intermediate layer for the recrystallised wafer equivalent”; 25th European PV Solar Energy Conference, Sep. 6, 2010; Valencia, Spain. 
         [0008]    A key feature of any processing apparatus is time spent in production versus time spent in maintenance, including cleaning. A critical feature of the disclosed invention is the simplicity of design and resulting ease of performing maintenance and cleaning. A critical problem with the prior art is low utilization of deposition source material and the resulting maintenance problems caused by frequent apparatus cleaning. The instant invention enables rapid chamber replacement and/or chamber addition by the flexibility of a removeable central chamber  24 B. 
       SUMMARY OF THE INVENTION 
       [0009]    In some embodiments, as noted schematically in  FIG. 1 , a deposition apparatus, system  100 , for deposition of layers of various elements and/or compounds comprises a first portion  10  for establishing a desired atmosphere about a substrate; a second portion  20  comprising an outer, elongated chamber  22 , optionally, cylindrical and optionally of quartz, and second, inner, elongated chamber comprising three sections,  24 A,  24 B,  24 C, optionally, of quartz, and optionally, a rectangular shape; a third portion  30  comprises means for heating  32 ,  34 ,  36 ,  38 , operable to impose a temperature profile of predetermined variation along a portion of the chambers; a fourth portion  40  for exiting from the heated portion; and a fifth portion  50  for exiting from the apparatus; the disclosed deposition apparatus is operable for chemical vapor deposition, optionally, at atmospheric pressure, with discrete or flexible, semi-continuous substrates. In some embodiments system  100  is configured to deposit silicon and/or silicon-compounds resulting in a layer of silicon, and/or silicon carbide, optionally, on carbon foil; in some embodiments subsequent processing in a connected, or separate, deposition apparatus results in additional layers of silicon, carbon, other Group IV or Group III-V or II-VI materials; optionally, a recrystallization step may follow a deposition step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Non-limiting and non-exhaustive embodiments will be described in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be intended to limit its scope, the disclosure will be described with specificity and detail through use of the accompanying drawings, in which: 
           [0011]      FIG. 1  is a schematic view of an embodiment of the deposition system. 
           [0012]      FIG. 2  is a schematic view of an embodiment of the deposition system showing separation of chambers  24  A, B and C. 
           [0013]      FIG. 3  is a schematic view of an embodiment of the deposition system showing detail of interface between sections  10  and  20 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    However, it is to be noted that the present disclosure is not limited to the embodiments and the examples but can be implemented in various other ways. In the drawings, parts irrelevant to the description are omitted for the simplicity of explanation, and like reference numerals denote like parts through the whole document. 
         [0015]    In accordance with one aspect of the present disclosure, there is provided a deposition or coating apparatus wherein a substrate material is chosen from a group comprising carbon, graphite, graphite foil, glassy graphite, impregnated graphite, pyrolytic carbon, pyrolytic carbon coated graphite, flexible foil coated with graphite, glass, ceramic and silicon. In some embodiments a substrate is a plate, optionally about 150 mm square or larger; optionally a substrate is a semi-continuous sheet or tape moved through the deposition apparatus. In some embodiments a substrate is pushed through the deposition apparatus; in some embodiments a substrate is conveyed through the deposition apparatus on a means for conveying such as a flexible tape, optionally, graphitic. 
         [0016]      FIG. 1  shows schematically an embodiment of the disclosed CVD apparatus. A substrate, discreet or one or more semi-continuous strips, enters reactor  100  through entry portion  10 . Entry portion  10  comprises a plurality of gas curtains wherein a process gas is introduced, for example, through sections  2 ,  6 ,  12  and exhausted through portions  4 ,  8 , and  14  such that a minimum purity of process gas is achieved. Optionally, process and deposition gases are introduced in section  14 . Exemplary process gases are hydrogen, nitrogen, argon, helium; exemplary deposition gases are silane(s), silicon-halogen bearing compounds, silicon-halogen-carbon bearing compounds, halogen compounds, dopant gases, including diborane, phosphine, and other gases known to one knowledgeable in the art. Entry portion  10  is attached to portion  20  by means for attachment  16 ,  18  and  19 ; means for attachment may comprise glass to metal seals; optionally, water cooled, and feedthroughs for gas(es), electrical and vacuum. Exit portion  50  is attached in a similar manner to portion  40  wherein means for attachment  52  and  54  provide similar functionality. 
         [0017]    Portion  20  of CVD system  100  comprises outer, elongated chamber  22  and inner, elongated chamber section  24 A; inner chamber  24  comprises three separable sections,  24 A,  24 B and  24 C wherein sections  24 A and  24 C are detachable from section  24 B. Coupling piece  25  enables section  24 A to make contact and mate with upstream entrance of inner chamber section  24 B; coupling piece  26  enables sections  24 C to make contact and mate with downstream exhaust of inner chamber section  24 B. Coupling pieces  25  and  26  provide a non-hermetic seal for the union of  24 A to  24 B and  24 B to  24 C; coupling pieces may also comprise a high temperature gasket of carbon fiber or high temperature Kapton® or Vespel®. Should process or deposition gases leak from the coupling sections the leak is contained in the interior of chamber  22  and exhausted through attachment means  16 ,  18 ,  19 ,  52  or  54 . In some embodiments chamber  22  is maintained at a pressure somewhat higher than chamber  24 B; in some embodiments chamber  22  is maintained at a pressure somewhat lower than chamber  24 B; in some embodiments chamber  22  maintains a purge gas flowing through. 
         [0018]    A key design feature is the fact that chambers  24  A, B and C can be replaced quickly when preventive maintenance, such as cleaning, is required. Additionally additional process chambers can be added either between portion  30  and  40  and/or between portions  40  and  50 ; alternatively portion  30  can be extended while also extending chamber  22 . 
         [0019]    In some embodiments additional chambers, not shown,  24 A 2 ,  24 B 2 ,  24 C 2 , etc. may be added to enable additional processing steps such as oxidation, recrystallization and/or additional deposited layers. For instance in some embodiments a chamber  24 A 2  is added between  24 A and  24 B to heat a carbon substrate to a high temperature such that oxygen not purged through curtains  2 ,  4 ,  6 ,  8  and remaining in the process gases is reacted with a carbon based substrate. In some embodiments a chamber  24 B 2  is added between  24 B and  24 C to heat a deposited layer above its melting point such that large grained recrystallization occurs upon cooling as disclosed in U.S. Ser. No. 13/234,316. 
         [0020]    Portion  30  of CVD system  100  comprises outer, elongated chamber  22 , inner, elongated chamber section  24 B and means for heating comprising means  32 ,  34 ,  36  and  38 , all operable for continuous deposition of a thin film onto one or more substrates traversing chamber  24 B from entrance to exit. In some embodiments means for heating is circumferential about exterior of chamber  22 , as shown; in some embodiments means for heating is circumferential about exterior of chamber  24 B, shown in  FIG. 2  as  72 - 79 ; in some embodiments means for heating is a planar source exterior to chamber  22 , not shown; optionally, means for heating is two planar sources exterior to chamber  22  such that two substrates may be heated; in some embodiments means for heating is a planar source exterior to chamber  22  comprising a means for focusing optical energy onto a substrate. In some cases planar source(s) may be internal to chamber  22  and external to chamber  24 B. Means for heating  32 ,  34 ,  36  and  38  and  72 - 79  comprise one or more means for heating chosen from a group comprising lasers, LEDs, lamps, flash lamps, halogen lamps, radiant sources, resistant sources, RF, microwave, IR sources and others known to one knowledgeable in the art. In some embodiments means for heating  32 - 38  or  72 - 79  are a multiplicity of independent means operable such that a temperature profile may be imposed upon a substrate in chamber  24 B ranging from about 200° C. or greater at the upstream entrance region to a maximum of about 1430° C. and then declining to less than about 500° C. at the downstream exit end; in some embodiments a means for cooling may be added to facilitate a more rapid cool down. 
         [0021]    Portion  40  of apparatus  100  provides for at least radiant cooling of a substrate and a transition to exit portion  50  by means for attachment  52  and  54  comprising glass to metal seals; optionally, water cooled, and feedthroughs for gas(es), electrical and vacuum. Portion  50  comprises a process gas exhaust  13  and a plurality of gas curtains  3 ,  7 ,  11  and exhausts  9  and  5 . 
         [0022]    During periods of preventive maintenance or repair portions  10  and  20  of CVD system  100  are detachable from portion  30  by withdrawing chamber  24 A from coupling section  25 ; external brackets, not shown, may assist in maintaining chamber  24 A inserted in coupling piece  25  and in proximity to chamber  24 B. Similarly portion  24 C can be withdrawn from coupling piece  26  and chamber  24 B. 
         [0023]    In some embodiments a thin film of silicon is deposited onto a carbonaceous substrate and subsequently converted to SiC, optionally in chamber  24 B,  24 B 2  or chamber  24 C or chamber external to apparatus  100 . In some embodiments a thin film of silicon and carbon is deposited on a substrate as SiC. In some embodiments a thin film of carbon is deposited and reacts with a silicon based or coated substrate; optionally, converted to SiC in chamber  24 B or a subsequent chamber. In some embodiments a thin film of silicon is deposited onto a silicon based substrate. 
         [0024]      FIG. 2  Shows chambers  24 A and  24 C separated from chamber  24 B in preparation for chamber cleaning or replacement or additional chambers to be installed. Means for heating,  72 - 79  is shown about chamber  24 B. Means for heating may be attached to chamber  24 B in a circumferential manner or as planar elements covering the top and bottom. 
         [0025]      FIG. 3  shows the detail of interface portion between portion  10  and  20 . Chamber  22  is secured through interface plate  19  to plate  18 ; plate  18  is attached to interface plate  16  which also interfaces with chamber  24 A. 
         [0026]    In some embodiments deposition system  100  operates in a horizontal mode for processing rigid substrates or a single flexible, semi-continuous substrate. In some embodiments deposition system  100  is operable in a vertical mode for processing a single flexible, semi-continuous substrate or more than one flexible, semi-continuous substrates. When deposition system  100  is oriented vertically and processing two continuous substrates gas curtain supplies  2 ,  6 ,  12 ,  11 ,  7 ,  3 , gas curtain exhausts  4 ,  8 ,  9 ,  5  and process gas supply  14  and process gas exhaust  13  may be duplicated such that a set of supplies and exhausts is dedicated for each continuous substrate. 
         [0027]    In some embodiments deposition system  100  is operable as a hot-wall CVD reactor wherein first means for heating  32 ,  34 ,  36  and  38  are located external to chamber  22 ; optionally, a second or alternate means for heating  72 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  is located external to chamber  24 B of  FIG. 2 . In some embodiments a second means for heating comprise one or more from a group comprising lasers, LEDs, lamps, flash lamps, halogen lamps, radiant sources, resistant sources, RF, microwave, IR sources and others known to one knowledgeable in the art. 
         [0028]    In some embodiments deposition system  100  is operable as a cold-wall CVD reactor wherein first means for heating  32 ,  34 ,  36  and  38  are located external to chamber  22 ; optionally, second or alternate means for heating  72 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 ,  79  are located external to chamber  24 B of  FIG. 2 . In these embodiments first and/or second means for heating may be radiative heaters, such as lamps or lasers; optionally, a RF inductive type or microwave or IR source may be used; chambers  24 A, B and C may be of quartz or other transmissive material. In some embodiments the composition of chambers  24 A,  24 B and  24 C are not the same; exemplary chamber materials for chamber  22  and  24  are silicon, Pyrex, glass, quartz, carbon, graphite, SiC, Al 2 O 3 , a high temperature metal, or other material known to one knowledgeable in the art. 
         [0029]    In some embodiments chamber  24 B and optionally, chambers  24 B 2 ,  24 B 3 ,  24 B 4  are operable to deposit a first layer, optionally, SiC, and a second layer, optionally, Si, and a recrystallization step wherein the recrystallization step has at least two temperature zones, a first zone above 1410° C. and a second zone below 1410° C. and above 1200° C., the portion of the substrate and deposited layers being in the second zone more than 0.5 seconds. 
         [0030]    In some embodiments a method for forming a substantially continuous layer of silicon carbide between a carbon based substrate and a silicon layer comprises the steps selecting a carbon based substrate; depositing a first layer consisting of carbon and silicon of a first carbon/silicon ratio; optionally, the C/Si ratio may be zero; depositing the silicon layer consisting substantially of silicon; and recrystallizing at least a portion of the deposited silicon layer such that the mean lateral dimension of the recrystallized grains is greater than about 5 mm, optionally greater than about 10 mm; optionally, the recrystallization step is as described in U.S. Ser. No. 13/234,316; optionally, the deposited silicon layer is recrystallized such that the second layer is held at temperature above 1200° C. and below 1410° C. for longer than 5 seconds during the recrystallization. 
         [0031]    In some embodiments a method of recrystallizing a layer of material comprises the steps: selecting a composite substrate with the layer deposited onto the substrate; advancing the substrate through first zone, S, such that a temperature, T S , is established within at least a portion of the deposited layer wherein Ts is less than the melting point, T MP , of the layer; advancing the substrate through second zone, I, such that a temperature, T I , is established within at least a portion of the deposited layer wherein T I  is greater than T S ; advancing the substrate through third zone, M, such that a temperature, T M , is established within at least a portion of the deposited layer wherein T M  is greater than T MP ; and advancing the substrate through fourth zone, R, such that a temperature, T R , is established within at least a portion of the deposited layer wherein T R  is below T MP , of the deposited layer and above a predetermined temperature, X*T MP , for at least Y seconds wherein the substrate and layer are advanced through the first through fourth zones sequentially at a rate of about Q mm/sec. such that the temperature criteria of each zone is established within at least a portion of the deposited layer while that portion is physically within the respective zone; optionally, X is between about 0.99 and about 0.60; optionally, Y is between about 0.1 and about 30 seconds; optionally, the second zone comprises one or more means for heating chosen from a group consisting of a spot of radiation rapidly scanned over the substrate, a linear array of radiation projected onto the substrate, laser, flash lamp, resistance heaters, rf coils, microwave radiation, and infra-red heaters; optionally, the first and third zones comprise one or more means for temperature modulation chosen from a group consisting of a spot of radiation rapidly scanned over the substrate, a linear array of radiation projected onto the substrate, laser, flash lamp, resistance heaters, rf coils, microwave radiation, infra-red heaters and means for cooling comprising refrigeration coils, thermoelectric means, fans, and cooling coils; optionally, the deposited layer material is substantially one or more elements chosen from a group consisting of Group II, III, IV, V and VI elements; optionally, the second and third zone length combined are more than 5 mm long in the direction of substrate travel; optionally, the substrate advancing rate, Q, is at least 0.5 mm per second. 
         [0032]    In some embodiments a solid state device comprises a composite substrate; and a first layer comprising material recrystallized by the method of U.S. Ser. No. 13/234,316; optionally, the first layer comprises material recrystallized such that more than 90% of the recrystallized layer has crystal grains of a size greater than 3 mm in any lateral dimension parallel to the substrate surface; optionally, the first layer comprises material recrystallized such that more than 90% of the recrystallized semiconductor layer has crystal grains of a size greater than 50% of the smallest lateral dimension parallel to the substrate surface; optionally, the recombination velocity is between about 50 cm/s and about 500 cm/sec; optionally, a solid state device is a solar cell wherein the recrystallized layer comprises a crystal grain at least 90% of the size of the irradiated area of the solar cell or at least 90% of the size of an individual cell in a large area solar module; optionally, the composite substrate is chosen from a group consisting of silicon, silicon composite with graphite, glass, ceramic, carbon, and a material coated with SiO 2  or SiC; optionally, a solid state device further comprises a barrier layer within the composite substrate and the first layer. In some embodiments a solar cell with a composite substrate and recrystallized layer has a conversion efficiency greater than 10%; optionally, greater than 12%. As used herein, in some embodiments, a composite substrate is one disclosed in U.S. application Ser. No. 13/272,073, filed Oct. 12, 2011. 
         [0033]    It will be understood that when a layer is referred to as being “on top of” another layer, it can be directly on the other layer or intervening layers may also be present. In contrast, when a layer is referred to as “contacting” another layer, there are no intervening layers present. Similarly, it will be understood that when a layer is referred to as being “below” another layer, it can be directly under the other layer or intervening layers may also be present. 
         [0034]    In the previous description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these particular details. In other instances, methods, procedures, and components that are well known to those of ordinary skill in the art are not described in detail to avoid obscuring aspects of the present invention. In cases where reference is made to “an embodiment” or “one embodiment” or “some embodiments”, it is understood that embodiments may comprise one or more of the inventive features and/or limitations presented in the entire specification for all exemplary embodiments without regard to how a particular embodiment is described. 
         [0035]    It will also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first layer could be termed a second layer, and, similarly, a second layer could be termed a first layer, without departing from the scope of the present invention. 
         [0036]    The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0037]    Embodiments of the invention are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention. 
         [0038]    Unless otherwise defined, all terms used in disclosing embodiments of the invention, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and are not necessarily limited to the specific definitions known at the time of the present invention being described. Accordingly, these terms can include equivalent terms that are created after such time. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the present specification and in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. 
         [0039]    The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.