Patent Publication Number: US-2021172054-A1

Title: Multicathode deposition system and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure claims priority to U.S. provisional application Ser. No. 62/944,103, filed on Dec. 5, 2019, the entire content of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to substrate processing systems, and more specifically, to deposition systems with multiple cathode assemblies (multi-cathodes) having one or more features to reduce particles and control temperature during processing. 
     BACKGROUND 
     Physical vapor deposition (PVD) is used for the deposition of metals and related materials in the fabrication of semiconductor integrated circuits. Use of PVD has been extended to depositing metal layers onto the sidewalls of high aspect-ratio holes such as vias or other vertical interconnect structures, as well as in the manufacture of extreme ultraviolet (EUV) mask blanks. In the manufacture of EUV mask blanks minimization of particle generation is desired, because particles negatively affect the properties of the final product. 
     During the manufacture of mask blanks, the EUV mask blank reticle is transported inside a processing chamber such as a PVD processing chamber. The EUV mask blank reticle is placed on top of a carrier base, which is placed on a rotatable pedestal of the PVD processing chamber. Because of stresses placed on the carrier base during manufacturing and cleaning of the carrier base, it is difficult to obtain flatness of less than 0.01 inches across the bottom surface of the carrier base. As will be described further below, the PVD processing chamber includes a deposition ring which bridges a gap between a cover ring and the rotatable pedestal to prevent deposition material from entering therebetween, which causes generation of particles. When the carrier base is placed on the rotatable pedestal, the outer edge of the carrier base overlaps the deposition ring. There is a gap of less than 0.01 inches between the bottom surface of the carrier base and the top surface of the deposition ring. Any deviation in flatness of the carrier base will lead to friction between the adjacent parts. Friction not only causes generation of particles, but the friction also creates vibrations. The vibrations can cause the reticle from its position on the carrier. 
     While advancements in PVD chamber design have been made, there remains a need to reduce defect sources such as particles in PVD processing chambers. 
     SUMMARY 
     A first embodiment pertains to physical vapor deposition (PVD) chamber comprising a plurality of cathode assemblies; a rotatable pedestal configured to support a substrate, the pedestal comprising an edge; an inner deposition ring adjacent to the edge of the edge of the pedestal; and an outer deposition ring adjacent to the inner deposition ring. 
     According to a second embodiment, a physical vapor deposition (PVD) chamber comprises a plurality of cathode assemblies; a rotatable pedestal configured to support a substrate, the pedestal comprising an edge; an inner deposition ring adjacent to the edge of the edge of the pedestal; an outer deposition ring adjacent to the inner deposition ring; and a motor coupled to a shaft to rotate the rotatable pedestal in a range of 10-20 revolutions per minute (RPM), a rotational acceleration in a range of 0.10-15 RPM/second and a deceleration in a range of 0.10-0.15 RPM/second. 
     According to a third embodiment, a method of depositing a material layer comprises placing a substrate in a PVD chamber comprising a plurality of cathode assemblies; a rotatable pedestal configured to support a substrate, the pedestal comprising an edge; an inner deposition ring adjacent to the edge of the edge of the pedestal; an outer deposition ring adjacent to the inner deposition ring; and depositing a material layer on the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  is a side view of a PVD deposition chamber; 
         FIG. 2  is a side view of a PVD deposition chamber according to one or more embodiments; 
         FIG. 3  is an enlarged side view of a portion of the PVD chamber depicted in  FIG. 2  showing a prior art deposition ring; 
         FIG. 4  is an enlarged isometric view of a portion of the PVD chamber shown in  FIG. 2  showing a deposition ring assembly according to an embodiment of the disclosure; 
         FIG. 5  is an enlarged side view showing a deposition ring assembly according to one or more embodiments of the disclosure; 
         FIG. 6A  is side view a deposition ring assembly and a rotatable pedestal according to an embodiment of the disclosure; and 
         FIG. 6B  is a side view of a prior art deposition ring and a rotatable pedestal. 
     
    
    
     DETAILED DESCRIPTION 
     Before describing several exemplary embodiments of the disclosure, it is to be understood that the disclosure is not limited to the details of construction or process steps set forth in the following description. The disclosure is capable of other embodiments and of being practiced or being carried out in various ways. 
     As used in this specification and the appended claims, the term “substrate” refers to a surface, or portion of a surface, upon which a process acts. It will also be understood by those skilled in the art that reference to a substrate can also refer to only a portion of the substrate, unless the context clearly indicates otherwise. Additionally, reference to depositing on a substrate can mean both a bare substrate and a substrate with one or more films or features deposited or formed thereon 
     A “substrate” as used herein, refers to any substrate or material surface formed on a substrate upon which film processing is performed during a fabrication process. For example, a substrate surface on which processing can be performed include materials such as silicon, silicon oxide, strained silicon, silicon on insulator (SOI), carbon doped silicon oxides, amorphous silicon, doped silicon, germanium, gallium arsenide, glass, sapphire, and any other materials such as metals, metal nitrides, metal alloys, and other conductive materials, depending on the application. Substrates include, without limitation, semiconductor wafers. Substrates may be exposed to a pretreatment process to polish, etch, reduce, oxidize, hydroxylate, anneal, UV cure, e-beam cure and/or bake the substrate surface. In addition to film processing directly on the surface of the substrate itself, in the present disclosure, any of the film processing steps disclosed may also be performed on an underlayer formed on the substrate as disclosed in more detail below, and the term “substrate surface” is intended to include such underlayer as the context indicates. Thus, for example, where a film/layer or partial film/layer has been deposited onto a substrate surface, the exposed surface of the newly deposited film/layer becomes the substrate surface. 
     The term “horizontal” as used herein is defined as a plane parallel to the plane or surface of a mask blank, regardless of its orientation. The term “vertical” refers to a direction perpendicular to the horizontal as just defined. Terms, such as “above”, “below”, “bottom”, “top”, “side” (as in “sidewall”), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane, as shown in the figures. 
     The term “on” indicates that there is direct contact between elements. The term “directly on” indicates that there is direct contact between elements with no intervening elements. 
     Those skilled in the art will understand that the use of ordinals such as “first” and “second” to describe process regions do not imply a specific location within the processing chamber, or order of exposure within the processing chamber. 
     Embodiments of the disclosure pertain to a magnet design for a deposition system, for example a physical vapor deposition (“PVD”) chamber comprising at least one cathode assembly, and in particular embodiments, a PVD chamber comprising multiple cathode assemblies (referred to herein as a “multi-cathode chamber). 
       FIG. 1  shows a side view of deposition system in the form of a PVD chamber  100 . The deposition system in the form of a PVD chamber is shown as a multi-cathode PVD chamber  100  including a plurality of cathode assemblies  102 . The multi-cathode PVD chamber  100  is shown as including a multi-target PVD source configured to manufacture an MRAM (magnetoresistive random access memory) or a multi-target PVD source configured to manufacture an extreme ultraviolet (EUV) mask blank. 
     The multi-cathode PVD chamber comprises a chamber body  101 , comprising an adapter (not shown) configured to hold a plurality of cathode assemblies  102  in place in a spaced apart relationship. The multi-cathode PVD chamber  100  in some embodiments includes a plurality of cathode assemblies  102  for PVD and sputtering. Each of the cathode assemblies  102  is connected to a power supply  112  including direct current (DC) or radio frequency (RF). 
     The cross-sectional view depicts an example of a PVD chamber  100  including the chamber body  101  defining an inner volume  121 , where a substrate or carrier is processed. 
     The cathode assemblies  102  in the embodiment shown in  FIG. 1  are used for sputtering different materials as a material layer  103 . The cathode assemblies  102  are exposed through shield holes  104  of an upper shield  106 , which is disposed over the substrate or carrier  108  on a rotatable pedestal  110 . There may generally be only one carrier  108  over or on the rotatable pedestal  110 . 
     The substrate or carrier  108  is shown as a structure having a semiconductor material used for fabrication of integrated circuits. For example, the substrate or carrier  108  comprises a semiconductor structure including a wafer. Alternatively, the substrate or carrier  108  in some embodiments is another material, such as an ultra low expansion glass substrate used to form an EUV mask blank. The substrate or carrier  108  can be any suitable shape such as round, square, rectangular or any other polygonal shape. 
     The upper shield  106  is formed with the shield holes  104  so that the cathode assemblies  102  in some embodiments are used to deposit the material layers  103  through the shield holes  104 . A power supply  112  is applied to the cathode assemblies  102 . The power supply  112  in some embodiments includes a direct current (DC) or radio frequency (RF) power supply. 
     The upper shield  106  is configured to expose one of the cathode assemblies  102  at a time and protect other cathode assemblies  102  from cross-contamination. The cross-contamination is a physical movement or transfer of a deposition material from one of the cathode assemblies  102  to another of the cathode assemblies  102 . The cathode assemblies  102  are positioned over targets  114 . A design of a chamber in some embodiments is compact. The targets  114  in some embodiments are any suitable size. For example, each of the targets  114  in some embodiments has a diameter in a range of from about 4 inches to about 20 inches, or from about 4 inches to about 15 inches, or from about 4 inches to about 10 inches, or from about 4 inches to about 8 inches or from about 4 inches to about 6 inches. 
     In  FIG. 1 , the substrate or carrier  108  is shown as being on the rotatable pedestal  110 , which in some embodiments move vertically move up and down. Before the substrate or carrier  108  moves out of the chamber, the substrate or carrier  108  in some embodiments moves below a lower shield  118 . A telescopic cover ring  120  abuts the lower shield  118 . Then, the rotatable pedestal  110  in some embodiments move down, and then the carrier  108  is raised with a robotic arm before the carrier  108  moves out of the chamber. 
     When the material layers  103  are sputtered, the materials sputtered from the targets  114  in some embodiments are retained inside and not outside of the lower shield  118 . In this prior art embodiment, telescopic cover ring  120  includes a raised ring portion  122  that curves up and has a predefined thickness. The telescopic cover ring  120  in some embodiments are includes a predefined gap  124  and a predefined length with respect to the lower shield  118 . Thus, the materials that form material layers  103  will not be below the rotatable pedestal  110  thereby eliminating contaminants from spreading to the substrate or carrier  108 . 
       FIG. 1  depicts individual shrouds  126 . The shrouds  126  in some embodiments are designed such that a majority of the materials from the targets  114  that does not deposit on the carrier  108  is contained in the shrouds  126 , hence making it easy to reclaim and conserve the materials. This also enables one of the shrouds  126  for each of the targets  114  to be optimized for that target to enable better adhesion and reduced defects. 
     The shrouds  126  in some embodiments are designed to minimize cross-talk or cross-target contamination between the cathode assemblies  102  and to maximize the materials captured for each of the cathode assemblies  102 . Therefore, the materials from each of the cathode assemblies  102  would just be individually captured by one of the shrouds  126  over which the cathode assemblies  102  are positioned. The captured materials may not be deposited on the substrate or carrier  108 . For example, a first cathode assembly and a second cathode assembly in some embodiments apply alternating layers of different materials in the formation of an extreme ultraviolet mask blank, for example, alternating layers of silicon deposited from a first target and cathode assembly  102  and a molybdenum from a second target and cathode assembly  102 . 
     The substrate or carrier  108  in some embodiments are coated with uniform material layer  103  deposited on a surface of the substrate or carrier  108  using the deposition materials including a metal from the targets  114  over the shrouds  126 . Then, the shrouds  126  are taken through a recovery process. The recovery process not only cleans the shrouds  126  but also recovers a residual amount of the deposition materials remained on or in the shrouds  126 . For example, there may be molybdenum on one of the shrouds  126  and then silicon on another of the shrouds  126 . Since molybdenum is more expensive than silicon, the shrouds  126  with molybdenum are sent out for the recovery process. 
     As shown in  FIG. 1 , the lower shield  118  is provided with a first bend resulting from small angle  130  and a second bend resulting from large angle  132 , which results in a knee  119  in the lower shield  118 . This knee  119  provides an area in which particles can accumulate during deposition, and is thus a possible source for processing defects. 
       FIG. 2  depicts a PVD chamber  200  in accordance with a first embodiment of the disclosure. PVD chamber  200  includes a plurality of cathode assemblies  202 . An upper shield  206  is provided below the plurality of cathode assemblies  202 , the upper shield  206  having one or more shield holes  204  to expose the cathode assembly to the interior space  221  of the chamber (only one shield hole  204  depicted in  FIG. 2  for clarity). A lower shield  218  is provided below and adjacent upper shield  206 . 
     A modular chamber body is disclosed in  FIG. 2 , in which an intermediate chamber body  225  is located above and adjacent a lower chamber body  227 . The intermediate chamber body  225  is secured to the lower chamber body  227  to form the modular chamber body, which surrounds lower shield  218 . A lower shield liner  223  maintains the same general contour as lower shield  218 , lower shield liner  223  being disposed between intermediate chamber body  225  and lower chamber body  227  (i.e., the modular chamber body) and the lower shield  218  to also surround lower shield  218 . A top adapter  273  is disposed above intermediate chamber body  225  to surround upper shield  206 . 
     PVD chamber  200  is also provided with a rotatable pedestal  210  similar to rotatable pedestal  110  in  FIG. 1 . A person of ordinary skill will readily appreciate that other components of a PVD chamber, such as those referenced above in  FIG. 1  but omitted in  FIG. 2  for the sake of clarity, are provided in PVD chamber  200  according to one or more embodiments. 
     In PVD chamber  200 , cover ring  220  is provided with a peripheral lip defining sidewalls  247  that face away from the upper shield  206 , whereas cover ring  120  in  FIG. 1  is provided with a raised ring portion  122  and thus has upward facing sidewalls (i.e., sidewalls that face toward upper shield  106 ). Furthermore, PVD chamber  200  is provided with a bottom liner  231  and a deposition ring  229 , as shown in  FIG. 2 . The deposition ring  229  bridges the gap between the cover ring  220  and rotatable pedestal  210  to prevent deposition material from entering therebetween. 
     Lower shield  218  is provided with an upper end  239  in contact with the upper shield  206 , and a lower end  241  opposite the upper end  239 . Lower shield wall  243  of lower shield  218  extends from upper end  239  to lower end  241 , and has a height H, as shown in  FIG. 2 . Lower shield wall  243  includes a lower shield wall inner surface  245  that has a straight region  244  that does not have any bends or curves, which minimizes collection of particles. Thus, the lower shield wall inner surface  245  has a contour that is substantially straight to minimize accumulation of particles on the shield. This straight region  244  extends in the embodiment shown from upper end  239  as shown in  FIG. 2 . This straight region  244  of the lower shield wall inner surface  245  is, in certain embodiments, free of bends having an angle in a range of from about 0.1 degrees and about 120 degrees and in a range of from about 210 degrees and about 360 degrees. For example, in some embodiments, angle  233  is in the range of from about 150 degrees to about 175 degrees, such as in a range of from between about 160 degrees and about 170 degrees. 
     For purposes of illustration, and not limitation, the lower shield wall inner surface  245  according to one or more embodiments has transition that provides an angle  235  that is in the range of from about 91 degrees to about 120 degrees, such as in a range of from about 100 degrees to about 110 degrees. Angle  237 , which is formed by a reference line parallel to the plane or surface of a mask blank, and the outer surface of lower shield liner  223 , is in the range of from about 89 degrees to about 65 degrees, such as in the range of from about 85 degrees to about 73 degrees. While other dimensions could be provided to yield angles  233 ,  235 , and  237  outside of these exemplary ranges, there are no bends or sharp curves in the straight region  244  of the lower shield wall inner surface  245  to form a knee, such as knee  119  in  FIG. 1 . The design according to one or more embodiments that is free of bends or sharp curves in the straight regions avoids collection of particles, thereby minimizing a defect source in the manufacture of articles in the chamber. 
     Referring now to  FIG. 3 , an enlarged view of the area  290  indicated by the dashed line box in  FIG. 2  is shown. As shown in  FIG. 3 , a carrier base  294  is disposed on the rotatable pedestal  210  (which is not shown in  FIG. 2 ). The rotatable pedestal  210  includes a tapered edge region  210   e , which has a thickness that is less than a central region of the rotatable pedestal  210 . The thickness of the rotatable pedestal tapers at a tapered edge region  210   e , which tapers from the thicker portion of the rotatable pedestal  210  to the tapered edge region  210   e  along a concave tapered section  210   r . The deposition ring  229  includes an edge portion  229   e  which substantially overlaps with the edge region  210   e  of the rotatable pedestal  210 , and the cover ring edge region  220   e  overlaps with the deposition ring edge portion  229   e . As mentioned above, there can be a gap G 1  as small as 0.01″ (0.254 mm) between a bottom surface  220   b  of the cover ring and a top surface  229   t  of the deposition ring  229 . Likewise, there can be a gap G 2  as small as 0.01″ (0.254 mm) between a bottom surface  229   b  of the deposition ring  229  and a top surface  210   t  of the rotatable pedestal  210 . The rotatable pedestal  210  coupled with rotation of the deposition ring can cause friction between the two rotating parts, which has a tendency to generate particles in the deposition chamber 
       FIG. 4  shows an enlarged cross-sectional portion of the area  300  of a deposition chamber  200  of the type shown in  FIG. 2  with a modified deposition ring and pedestal according to one or more embodiments of the disclosure.  FIG. 5  shows and enlarged view of the deposition ring assembly shown in  FIG. 4 . In  FIGS. 4 and 5 , a carrier base  294  is shown as supported on the rotatable pedestal  210 . In  FIG. 4 , an extreme ultraviolet mask blank reticle  298  is shown supported on the carrier base  294 , and a top shield  296  is supported on the carrier base  294  and surrounding the extreme ultraviolet mask blank reticle  298 . 
     According to one or more embodiments of the disclosure, the components of the deposition chamber correspond to the description of  FIG. 2 , except for the differences noted with respect to  FIG. 4  and  FIG. 5 . The deposition ring  229  shown in  FIG. 3  comprises a unitary ring which rotates and create a friction with the rotatable pedestal  210 . In embodiments described herein and shown in  FIG. 4  and  FIG. 5 , the deposition ring  229  shown in  FIG. 3  is replaced with a deposition ring assembly  329 . The deposition ring assembly  329  comprises an outer deposition ring  350  and an inner deposition ring  352 . Thus, the deposition ring assembly  329  comprises two distinct segments, which eliminate friction between the rotatable pedestal  210  and the rotating deposition ring  229  shown in  FIG. 3 . 
     According to one or more embodiments, during operation of the PVD chamber  200 , such as during a physical vapor deposition process, there is relative rotational motion between the inner deposition ring  352  and the outer deposition ring  350 . However, there is no relative rotational motion between the inner deposition ring  352  and the adjacent rotatable pedestal  210 . Instead, the rotatable pedestal  210  and the adjacent inner deposition ring  352  both rotate, and the outer deposition ring  350  remain stationary or fixed in position during a physical vapor deposition process. In the prior art design shown in  FIG. 3 , there is relative rotational motion between deposition ring  229 , which is fixed or static, and the rotatable pedestal  210  during operation of a PVD chamber such as during a physical vapor deposition process. 
     Referring again to  FIG. 4 , a carrier base  294 , which is configured to support an extreme ultraviolet mask blank reticle  298  is place on top of the rotatable pedestal  210 . In the embodiment shown a top shield cover  296  is place on top of the carrier base  294  and surrounds the extreme ultraviolet mask blank reticle  298 .  FIG. 4  also shows the lower shield wall  243  shown in  FIG. 2  overlapping with the bottom liner  231 . The top cover  220  is shown as overlapping with the bottom liner  231  and engaged with the outer deposition ring  350 . 
       FIG. 5  shows additional details of the split or bifurcated deposition ring assembly  329 . The inner deposition ring has a bottom surface  352   b  which engages and is in contact with a top surface  211  of the rotatable pedestal  210 . The inner deposition ring  352  comprises a protruding rim  352   r  extending downwardly from the inner deposition ring  352 . The outer deposition ring  350  comprises a protruding rim  350   r  extending upwardly from the outer deposition ring  350 . As shown in  FIG. 5 , the outer deposition ring protruding rim  350   r  and the inner deposition ring protruding rim  352   r  overlap for a distance  355 . 
     As shown in  FIG. 5 , the carrier base  294  rests upon the rotatable pedestal  210  and there is a gap defining a distance A between a bottom surface  294   b  of the carrier base  294  and a top surface  352   t  of the inner deposition ring  352 . In one or more embodiments, the distance “A” defining the gap between the bottom surface  294   b  of the carrier base  294  and the top surface  352   t  of the inner deposition ring  352  is 0.010 inches (0.254 mm) or greater, for example 0.012 inches (0.305 mm). Even if the carrier base is not manufactured with precise flatness, the gap reduces or eliminates the possibility of friction between the carrier base  294  and the inner deposition ring  352  when the rotatable pedestal  210  and inner deposition ring  352  are rotating during PVD deposition process. In some embodiments, there is a gap defining a distance “B” between the bottom surface  352   b  of the inner deposition ring and the top surface  351  of the outer deposition ring  350 . In one or more embodiments, the distance “B” defining the gap between the bottom surface  352   b  of the inner deposition ring and the top surface  351  of the outer deposition ring  350  is 0.020 inches (0.508 mm). 
     Experiments were conducted used a rotating aluminum rotatable pedestal surrounded by a stationary deposition ring of the type shown in  FIG. 3  and made from a ceramic material. Even normal rotation of a carrier base and reticle in a PVD chamber caused large number of scratches on the backside of a wafer placed on the pedestal, which resulted in defects on the front side of the wafer. The large number of defects seen on the wafer were predominantly due to curvature of the aluminum rotatable pedestal. As shown in  FIG. 6B , the edge  210   e  of the rotatable pedestal  201  has a thickness that is less than the thickness of the deposition ring  229 . This design causes the wafer to contact the deposition ring  229  while the rotatable pedestal  210  is rotating during operation of the PVD chamber, which caused the wafer to slip on the rotatable pedestal  210  during rotation and caused concentric scratches on the backside of the wafer. 
     According to an embodiment of the disclosure, replacing the malleable metallic rotatable pedestal  210  and the deposition ring  229  with a flat, non-concave ceramic rotatable pedestal  210  and the deposition ring assembly  329  shown in  FIG. 5  helped mitigate the issues with the rotatable pedestal shown in  FIG. 6B . The thickness of the deposition ring assembly at the edge of the rotatable pedestal  210  was less than the edge of the rotatable pedestal  210 . 
     It was determined that reducing the rotational acceleration of the rotatable pedestal reduced particle defects on EUV mask blanks processed in the PVD chamber. Hence by simply reducing the rotational acceleration/deceleration of the rotatable pedestal, particle defects were reduced. In one or more embodiments rotating the rotatable pedestal in a range of 10-20 revolutions per minute (RPM), a rotational acceleration in a range of 0.10-15 RPM/second and a deceleration in a range of 0.10-0.15 RPM/second reduced particle defects. One or more embodiments comprise a PVD chamber as shown with respect to  FIGS. 2, 4, and 5  including a motor  250  coupled to a shaft to rotate the rotatable pedestal  249  in a range of 10-20 revolutions per minute (RPM), a rotational acceleration in a range of 0.10-15 RPM/second and a deceleration in a range of 0.10-0.15 RPM/second. 
     The PVD chambers  200  described herein may be particularly useful in the manufacture of extreme ultraviolet (EUV) mask blanks. An EUV mask blank is an optically flat structure used for forming a reflective mask having a mask pattern. In one or more embodiments, the reflective surface of the EUV mask blank forms a flat focal plane for reflecting the incident light, such as the extreme ultraviolet light. An EUV mask blank comprises a substrate providing structural support to an extreme ultraviolet reflective element such as an EUV reticle. In one or more embodiments, the substrate is made from a material having a low coefficient of thermal expansion (CTE) to provide stability during temperature changes. The substrate according to one or more embodiments is formed from a material such as silicon, glass, oxides, ceramics, glass ceramics, or a combination thereof. 
     An EUV mask blank includes a multilayer stack, which is a structure that is reflective to extreme ultraviolet light. The multilayer stack includes alternating reflective layers of a first reflective layer and a second reflective layer. The first reflective layer and the second reflective layer form a reflective pair. In a non-limiting embodiment, the multilayer stack includes a range of 20-60 of the reflective pairs for a total of up to 120 reflective layers. 
     The first reflective layer and the second reflective layer in some embodiments are formed from a variety of materials. In an embodiment, the first reflective layer and the second reflective layer are formed from silicon and molybdenum, respectively. The multilayer stack forms a reflective structure by having alternating thin layers of materials with different optical properties to create a Bragg reflector or mirror. The alternating layer of, for example, molybdenum and silicon are formed by physical vapor deposition, for example, in a multi-cathode source chamber. 
     The PVD chambers  200  described herein are utilized to form the multilayer stack, as well as capping layers and absorber layers. For example, the physical vapor deposition systems in some embodiments form layers of silicon, molybdenum, titanium oxide, titanium dioxide, ruthenium oxide, niobium oxide, ruthenium tungsten, ruthenium molybdenum, ruthenium niobium, chromium, tantalum, nitrides, compounds, or a combination thereof. Although some compounds are described as an oxide, it is understood that the compounds in some embodiments include oxides, dioxides, atomic mixtures having oxygen atoms, or a combination thereof. 
     Thus, in a specific embodiment, a method is provided in which any of the chambers  200  described herein are utilized to perform a method comprising placing a substrate in the PVD chamber comprising a plurality of cathode assemblies and a deposition ring assembly comprising an outer deposition ring and an inner deposition ring. 
     Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the disclosure. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. 
     Although the disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the method and apparatus of the present disclosure without departing from the spirit and scope of the disclosure. Thus, it is intended that the present disclosure include modifications and variations that are within the scope of the appended claims and their equivalents.