Abstract:
A chemical vapor deposition (CVD) reactor comprises a deposition zone, a substrate carrier and a liner assembly. The deposition zone is constructed so as to have a positive pressure reactant gases fixed showerhead introducing reactant gas supporting thin film CVD deposition. The substrate carrier movably supports a substrate and the liner assembly within the deposition zone and is heated so as to be subjected to a CVD process. The liner assembly partly encloses selected portions of the deposition zone, particularly portions of the substrate carrier and thereby enclose a hot zone surrounding a substrate to be processed so as to retain heat in that zone but allows gas flow radially outwardly toward walls of a surrounding cold-wall reactor with exhaust ports surrounding the deposition zone that exhaust spent reactant gases. The liner assembly is a sink for solid reaction byproducts while gaseous reaction byproducts are pumped out at the exhaust ports. The liner assembly is linearly movable away from the fixed showerhead.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to chemical vapor deposition thin-film deposition reactors, and relates particularly to protective liners that may be provided in such deposition reactors. 
       BACKGROUND ART 
       [0002]    Chemical vapor deposition (CVD) processes use induced chemical reactions of gaseous precursor molecules to deposit one or more thin-film layers onto the surface of a substrate. For example, a trimethylgallium and arsine reaction induced by a combination of elevated temperature and radio frequency energy can be used to produce a gallium arsenide film layer. A wide variety of CVD precursor substances are known. 
         [0003]    Frequently encountered challenges involving CVD reactors include uniformity of deposition, contamination issues, and downtime for reactor maintenance affecting throughput. Uniformity of deposition requires a corresponding uniformity of reactor environment conditions in the vicinity of substrate surface being processed, including uniform reaction gas mixture and concentration and uniform temperature. Ideally, deposition will occur only on the surface of the substrate being processed, with such deposition being substantially uniform over that substrate. In practice, unwanted deposition (as well as precursor condensation) may occur also on some surfaces of the reactor itself that are exposed to the precursor molecules or intermediate reaction products under conditions that allow deposition. When surface deposits build up in the reactor, material can break off to introduce contaminant particles to the reactor environment. The surface build-up can also adversely affect processing conditions that may lead to decreased deposition rates onto the substrate or deposition non-uniformity. To handle these issues, the reactor must be periodically cleaned to remove any unwanted depositions from the reactor surfaces, which leads in turn to reactor downtime and reduced throughput. 
       SUMMARY 
       [0004]    A chemical vapor deposition (CVD) reactor in accord with the present invention comprises a gas and heat isolated deposition zone protected by a movable liner assembly that partially shrouds the deposition zone within conventional reactor housing, over a workpiece, thereby forming a virtual reactor within a conventional reactor. The liner is movable because it is associated with a moving carrier but a stationary showerhead, so that the liner can be cleaned and replaced away from the deposition zone. The deposition zone is constructed so as to provide a positive pressure reactive gas first environment supporting thin film deposition thermally isolated from a surrounding lower pressure and energy providing second environment. A movable substrate carrier is constructed to support a substrate within the deposition zone so as to be subjected to a CVD process in the deposition zone. The liner assembly is made of a liner material with liner walls that are positioned so as to form inner and outer partial enclosures or shrouds that help to ensure uniformity of deposition such that the inner partial enclosure is protected within the outer partial enclosure. The liner assembly forms a hot zone surrounding a substrate to be processed so as to retain heat in that zone and also maintains a concentration of process gas in proximity to the substrate. A result is that the substrate receives good film deposition. The liners also protect selected portions of the deposition zone from any unwanted film deposition. Such a deposition zone may be housed in a larger cold-wall reactor that provides a lower pressure second environment, plus access ports for substrates when the substrates are mounted on a linearly movable carrier that transports substrates out of the deposition zone. 
         [0005]    The liner assembly may include a first set of liners forming an outer gas flow tunnel-like enclosure of the deposition zone with first outer side walls adapted to minimize heat loss from regions receiving the CVD process gas, as well as an inner deposition liner within that outer enclosure defined by the first set of liners. The inner deposition liner has second liner side walls that partially enclose a hot reaction zone immediately surrounding a perimeter of the substrate, except for an opening at the top provided to receive the CVD process gas. For example, the liner assembly may line any of (1) regions surrounding openings of a CVD process showerhead of the deposition zone, (2) a region immediately surrounding a location of the substrate (i.e., the hot zone defined by the inner liner) where spent reactant gas flows radially outwardly through the gas flow tunnel, and (3) gas isolation regions separating a concentration of CVD process gas in the deposition zone above the substrate from regions outside of the deposition zone in the nature of gas curtains surrounding deposition zones. 
         [0006]    Portions of the liner assembly of the first environment may be in thermal communication with a heat source of the second environment so as to be maintained at an elevated temperature higher than the substrate. The liner material may be made from any of quartz, a ceramic, and/or graphite, which retain heat. The liner material is also preferably resistant to selected cleaning processes, such as etchants, that remove deposited material. Additionally, the liner assembly or portions thereof may be selectively removable from the deposition zone for replacement. 
         [0007]    The carrier is supported on spaced apart rollers such that the carrier slides in a linear path. In this manner, one liner assembly can be moved away from a fixed showerhead while another liner assembly is placed below the showerhead. Such a structure allows assembly line deposition of substrates, one after another. 
         [0008]    In one embodiment, a substrate carrier may support a plurality of wafer substrates for simultaneous processing by a plurality of showerheads. The plurality of wafer substrates may be arranged in one or more groups, each having a showerhead and associated liners. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a cutaway side view of a CVD reactor in accord with the present invention. 
           [0010]      FIG. 2  is an enlarged view of a deposition zone of the reactor of  FIG. 1 , indicated by circle A, showing the presence of liners in accord with the present invention. 
           [0011]      FIGS. 3 and 4  are cutaway perspective views of a deposition zone of the reactor of  FIG. 1 , respectively from above and below a substrate to be treated, and showing the various liners of the liner assembly. 
           [0012]      FIG. 5  is a cutaway side view of an alternative CVD reactor with multiple deposition zones accommodating the processing of multiple semiconductor substrates or wafer substrates at one time. 
           [0013]      FIG. 6  is a top view of a substrate carrier with multiple substrates for processing in the reactor of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    With reference to  FIG. 1 , a CVD cold-wall reactor  11  is provided with a deposition zone  21  that is constructed so as to enclose an environment supporting thin film deposition onto a substrate. In particular, one or more process gas inlets  17  are provided for supplying gaseous CVD precursors via a showerhead assembly  19  toward a substrate  29  within the reactor  11 , while one or more exhaust outlets is provided for removing any excess process gas and reaction products from the chamber  21 . A movable carrier  25  receives and transports a substrate to be processed into the deposition zone  21 , where it can be subject to any known CVD process. In  FIG. 1 , the carrier  25  moves out of the plane of the drawing on opposed rollers  36 ,  38 . The deposition zone  21  may be considered as a central reactor within the larger cold-wall reactor  11  that provides the low pressure or vacuum environment for the deposition zone  21 , substrate access ports, heating and cooling sources, radio frequency energy and substrate rotation if needed. Such cold-wall reactors are commercially known. A typical film to be deposited is a gallium arsenide film. Precursor gases are typically trimethyl gallium and arsine. 
         [0015]    As seen in the enlarged view of the deposition zone  21  in  FIG. 2 , the carrier track  25  holds an oversized wafer susceptor  27  supporting a wafer substrate  29  thereon. The carrier  25  may be transparent material, such as fused silica or quartz, and the susceptor  27  may be preferably constructed from graphite material to form a thermal susceptor that is radiantly heatable by a set of lamps  28  located beneath the transparent carrier  25 . The wafer substrate  29  may be heated by thermal conduction from the heated susceptor  27  on which it sits. The wafer carrier  27  and wafer substrate  29  are received by the carrier  25  into the deposition zone  21 , e.g. through a port in the reactor  11 , and likewise exits the deposition zone  21  through the same or a different port. The reactor  11  may include multiple processing and/or inspection chambers connected to each other through such ports, with the carrier  25  facilitating transport of a substrate on a wafer carrier between such chambers. 
         [0016]    Within a portion of the chamber  21 , a CVD hot zone is created as a first environment where CVD precursor gases  24  supplied to the chamber  21  by the showerhead assembly  19  through a plurality of apertures, not shown, react to form CVD reaction products that are formed on a substrate  29  present in the hot zone. In accord with the present invention, a box-like liner assembly comprising a plurality of stacked liners  33 ,  35 , and  37  are provided so as to enclose the hot zone and thereby maintain a uniform temperature above the substrate  29 . Liner  35  has legs  36  that support the liner from carrier  25 . That is, the liner assembly forms at least one box around the substrate  29 , creating the hot zone with small openings for radially outward gas flow. A first set of liners  33  and  35  may be arranged to form an outer box enclosure of that portion of the chamber  21  receiving the CVD precursor gases, with chamber lid liner  35  forming first outer side walls of that outer box enclosure, while the deposition liner  37  may form an inner enclosure, with second inner side walls of the deposition liner  37  immediately surrounding portions of the periphery of the substrate  29 . The liner material may be any of quartz, a ceramic, and graphite, which retain heat. The liners  33 ,  35  and  37  receive their heat generally by convection from the flowing CVD gases and reaction products, but mostly from energy supplied by radiation from the hot carrier  27  and substrate  29 . 
         [0017]    The substrate  29  may itself be heated by conduction from the susceptor  27 , which in turn may be heated by lamps, electrical induction, fluid passages, or any other convenient means in the cold-wall reactor, i.e., the second environment. The CVD precursor gases are preferably delivered to the hot zone already preheated to an elevated temperature (e.g., about 350° C.) just below a reaction temperature, and is then heated to its final reaction temperature (e.g., about 400 to 450° C.) for deposition by heat transfer onto the substrate  29  where CVD reactions occur. The surrounding inner liner material  37  maintains the heat in hot zone immediately above the substrate  29 , like the walls of an oven, for creating conditions conducive to uniform deposition by reactions on the substrate  29 . By maintaining the deposition zone at 400° C. or hotter, excess arsenic remains in a gaseous phase so that it can be pumped out through an exhaust port. Excess gallium tends to plate out onto the liners. At lateral edges of the showerhead, gas exhaust ports  34  and  38  may be provided to form part of a gas flow curtain around the showerhead. Such a gas flow curtain partly isolates the reaction chamber helping to form a reactor within a reactor, as explained further below. 
         [0018]    Additionally, the liners  33 ,  35  and  37  of the liner assembly are positioned to line selected portions of the deposition zone  21  so as to control byproducts of the CVD reaction during deposition and protect those selected portions of the chamber  21  from unwanted film deposition. Management of deposition byproducts and temperature control are the principal functions of the liner assembly. Thus, a showerhead liner  33  protects a first zone of the deposition zone  21  surrounding the CVD process gas outlets  31  of the showerhead assembly  19 . The showerhead liner  33  minimizes loss of heat from the showerhead assembly  19  to prevent condensation of preheated CVD precursor gases in the showerhead channels and especially at its gas outlets  31 . A chamber lid liner  35  protects a third zone of the deposition zone  21  outside of the deposition zone. It physically separates a concentration of the CVD process gas and reaction products in a hot deposition zone above the wafer substrate  29  from cooler isolation regions outside of the deposition zone. Additionally, pressure differences between the deposition zone and isolation regions may produce radially outward gas flows that direct any unreacted process gas and undeposited reaction products to an exhaust port of the chamber  21 , such as an exhaust port  34  or  38 . Finally, a deposition liner  37 , in addition to forming an inner hot zone of the deposition zone  21 , protects portions of the oversized wafer carrier  27  around the wafer substrate  29 . 
         [0019]    At least some portions of the liner assembly may be in thermal communication with one or more heat sources (radiant, convective, or conductive) so as to be maintained at an elevated temperature different from than the substrate so as to discourage deposition anywhere other than onto the wafer substrate  29 . Even so, some deposition and/or condensation may occur onto the liners  33 ,  35  and  37 . Accordingly, the preferred liner materials (e.g., quartz, a ceramic, or graphite), in addition to retaining heat, are preferably selected so as to be resistant to various cleaning processes. The liners are preferably removable from the reaction chamber for maintenance or replacement. The deposition liner  37  nearest to the wafer substrate  29  is especially designed to be removable along with the substrate  29  and its susceptor  27  after each substrate processed. The reaction chamber with its gas curtain isolation provides a reduction in contaminants that is at least an order of magnitude less than in the surrounding reactor environment. 
         [0020]    With reference to  FIGS. 3 and 4 , cutaway perspective views with the showerhead assembly  19  removed reveal the showerhead liner  33  surrounded by one or more plates of a chamber lid liner  35  overlying a susceptor  27  and carrier  25  carrying a wafer substrate  29 . The showerhead liner  33 , which generally corresponds in its location, shape and size with that of the showerhead assembly&#39;s process gat inlet, overlays the processing location of a wafer substrate  29  inserted into the reactor. The chamber lid liner  35  surrounds the showerhead liner  33 . In the depicted embodiment, the chamber lid liner  35  is seen to have legs  36  extending downward along the sides of the susceptor  27  onto the carrier  25 . Alternatively, the legs  36  could be replaced by side panels. In either case, the legs  36  or side panels form a tunnel or cap with the chamber lid liner  35  around the deposition zone that both confines process reaction gas and minimizes heat loss in the lateral direction, yet allows excess or spent gas to flow out. A deposition liner  37  seated on the susceptor  27  and the movable carrier surrounds a perimeter of the wafer substrate  29  so as to form a kind of partial inner “box” or “dome”, with the fixed showerhead liner  33  forming the box or dome&#39;s cover and the deposition liner  37  defining its side walls on all sides of the wafer substrate  29 . The deposition liner therefore ensures temperature and process gas uniformity over the wafer substrate surface. 
         [0021]    With reference to  FIGS. 5 and 6 , another CVD reactor embodiment  61  illustrates the possibility of scaling to accommodate the processing of multiple wafer substrates  79 A 1 - 79 D 4  at one time, while still maintaining the use of liners for promoting deposition uniformity. The illustrated embodiment provides for 16 wafer substrates, shown here as grouped into four sets of four,  79 A 1 - 79 A 4 ,  79 B 1 - 79 B 4 ,  79 C 1 - 79 C 4  and  79 D 1 - 79 D 4 . Different numbers of wafers and different groupings are possible in a variety of reactor embodiments. Each set of wafers has an associated showerhead, of which showerheads  69 A and  69 B are seen in  FIG. 5 . The showerheads are connected to one or more supplies of process gases, represented by conduits  67 . Each of the showerheads has a showerhead liner, e.g.,  83 A and  83 B, and the showerhead liners are in turn surrounded by one or more plates forming a chamber lid liner  87  with side panels or legs  86  at lateral sides of each deposition zone associated with a group of wafers, such that the combination of showerhead liners and chamber lid liners forms a tunnel or cap around the respective deposition zones that both confine process gas and minimizes heat loss in the later direction. Additionally, each group of wafer substrates  79 A 1 - 79 A 4 ,  79 B 1 - 79 B 4 ,  79 C 1 - 79 C 4 , and  79 D 1 - 79 D 4 , has a corresponding deposition liner  85 A- 85 D positioned on the movable wafer carriers  77 A- 77 D surrounding the parameter of each group. In combination with the showerhead liners, the deposition liners form a kind of partial inner box or dome around the wafer substrates that ensure temperature and process gas uniformity over each wafer substrate surface and isolate one environment from another. The movable carriers allow liner assemblies to be moved away from fixed showerheads for cleaning. 
         [0022]    The reactor structure provided by the present invention allows better uniformity of deposition by creating an environment where the substrate has uniform temperature over its entire surface and where the CVD process gases over the substrate are likewise at a uniform temperature in a hot zone. The regions or zones enclosed by the various sets of liners facilitate heat retention for such temperature uniformity, while the liners themselves also serve to protect selected portions of the chamber from unwanted deposition and to facilitate short downtimes for cleaning and maintenance.