PATENT DOCUMENT

Publication Number: US-10403480-B2
Application Number: US-201715616839-A
Country: US
Kind Code: B2

Title: Durable 3D geometry conformal anti-reflection coating

Abstract:
Methods and systems for depositing a thin film are disclosed. The methods and systems can be used to deposit a film having a uniform thickness on a substrate surface that has a non-planar three-dimensional geometry, such as a curved surface. The methods involve the use of a deposition source that has a shape in accordance with the non-planar three-dimensional geometry of the substrate surface. In some embodiments, multiple layers of films are deposited onto each other forming multi-layered coatings. In some embodiments, the multi-layered coatings are antireflective (AR) coatings for windows or lenses.

Claims:
What is claimed is: 
     
       1. A method of depositing an anti-reflective coating on a curved surface of a lens using a plasma enhanced vapor deposition system, the method comprising:
 with a series of source elements of the plasma enhanced vapor deposition system, generating a plasma, wherein each of the source elements has a surface that faces the lens and wherein the surface has a curved shape that corresponds to the curved surface of the lens; 
 with the series of source elements, depositing ions from the plasma on the curved surface of the lens to form the anti-reflective coating; and 
 with a translation mechanism, while depositing the ions, translating the lens with respect to the series of source elements at a rate selected to control the thickness of the anti-reflective coating across the curved surface of the lens. 
 
     
     
       2. The method defined in  claim 1  further comprising:
 supplying a reaction gas to the series of source elements; and 
 with the series of source elements, discharging the plasma. 
 
     
     
       3. The method defined in  claim 1  wherein a distance between the surface of each of the source elements and the curved surface of the lens is the same for all of the source elements. 
     
     
       4. The method defined in  claim 1  wherein the anti-reflective coating includes one or more of Si3N4, SiO2, NB2O5, TiO2, and TaO2. 
     
     
       5. The method defined in  claim 1  further comprising:
 after forming the anti-reflective coating on the curved surface, forming an additional coating on the curved surface. 
 
     
     
       6. The method defined in  claim 1  method further comprising:
 with an additional series of source elements, generating additional plasma; and 
 with the additional series of source elements, depositing ions from the additional plasma on the curved surface of the lens to form an additional anti-reflective coating. 
 
     
     
       7. The method defined in  claim 6  wherein the anti-reflective coating and the additional anti-reflective coating are formed simultaneously. 
     
     
       8. The method defined in  claim 1  wherein the anti-reflective coating is an inorganic coating. 
     
     
       9. A method of depositing a coating on a curved surface of a substrate using a plasma enhanced vapor deposition system, the method comprising:
 aligning the substrate with a hollow cathode source element of the plasma enhanced vapor deposition system, wherein the hollow cathode source element has a curved surface that matches the curved surface of the substrate; 
 with the hollow cathode source element, generating a plasma; 
 with the hollow cathode source element, depositing ions from the plasma on the curved surface of the substrate to form the coating; and 
 while depositing the ions from the plasma, translating the substrate with respect to the hollow cathode source element. 
 
     
     
       10. The method defined in  claim 9  wherein translating the substrate with respect to the hollow cathode source element comprises translating the substrate perpendicular to a longitudinal axis of the hollow cathode source element. 
     
     
       11. The method defined in  claim 9  wherein the coating is an inorganic coating. 
     
     
       12. The method defined in  claim 11  wherein the inorganic coating includes one or more of Si3N4, SiO2, NB2O5, TiO2, and TaO2. 
     
     
       13. The method defined in  claim 11  wherein the inorganic coating is an antireflective coating. 
     
     
       14. The method defined in  claim 9  wherein the substrate is a lens. 
     
     
       15. A method of depositing an anti-reflective coating on a curved surface of a lens using a plasma enhanced vapor deposition system, wherein the plasma enhanced vapor deposition system comprises first and second hollow cathode plasma sources, the method comprising:
 placing the lens on a support such that the curved surface of the lens faces the first and second hollow cathode plasma sources, wherein each of the first and second hollow cathode plasma sources has a surface with a shape that matches the curved surface of the lens; 
 with the first and second hollow cathode plasma sources, depositing ions on the curved surface of the lens to form the anti-reflective coating; and 
 while depositing the ions, translating the support with respect to the first and second hollow cathode plasma sources at a rate selected to control a thickness of the anti-reflective coating across the lens. 
 
     
     
       16. The method defined in  claim 15  wherein the plasma enhanced vapor deposition system comprises a third hollow cathode plasma source, the method further comprising:
 placing an additional lens on an additional support such that a curved surface of the additional lens faces the third hollow cathode plasma source, wherein the third hollow cathode plasma source has a surface with a shape that matches the curved surface of the additional lens; 
 with the third hollow cathode plasma source, depositing ions on the curved surface of the additional lens to form an additional anti-reflective coating; and 
 while depositing the ions on the curved surface of the additional lens, translating the additional support with respect to the third hollow cathode plasma source, wherein the support and the additional support are translated in parallel. 
 
     
     
       17. The method defined in  claim 16  wherein depositing ions on the curved surface of the additional lens with the third hollow cathode plasma source comprises depositing ions on the curved surface of the additional lens with the third hollow cathode plasma source while depositing ions on the curved surface of the lens with the first and second hollow cathode plasma sources. 
     
     
       18. The method defined in  claim 15  wherein the anti-reflective coating is an inorganic coating.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 14/497,077, filed Sep. 25, 2014, which is a continuation of international application No. PCT/US14/57424, filed Sep. 25, 2014, both of which are hereby incorporated by reference herein in their entireties. 
    
    
     FIELD 
     This disclosure relates generally to anti-reflective (AR) coatings and methods for forming the same. In particular embodiments, systems and methods for forming AR coatings on surfaces having three-dimensional geometries, such as curved surfaces, are described. 
     BACKGROUND 
     Anti-reflective (AR) coatings are generally applied to surfaces of lenses or windows to reduce the reflection of light incident on the surfaces that can cause glare. Typically, the AR coatings are thin films structures that are applied to surfaces using deposition techniques such as sputter deposition, chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD) processes. In some cases, the AR coatings include multiple alternating layers of thin films, which provide materials of different refractive indexes and that improve the anti-reflective qualities of the AR coatings. 
     In some applications, the surface of a lens or a window has a three-dimensional geometry that makes applying a uniformly thick AR coating difficult. In some applications, CVD processes can offer the ability to conformally coat three-dimensional geometry parts. This is because CVD deposition of thin films occurs due to a chemical reaction at the surface of a part, while some other deposition technologies involve physical or chemical reaction in the gas phase and transport of chemical species to the substrate. However, many films formed using traditional CVD techniques are not adequately dense or durable for certain applications, such as AR coatings for exterior surfaces of consumer products. 
     SUMMARY 
     This paper describes various embodiments that relate to anti-reflective (AR) coatings and methods for forming the same. The systems and methods described are used to form AR coatings on curved surfaces or surfaces otherwise having three-dimensional geometries. 
     According to one embodiment, a method of depositing a film on a curved surface of a substrate is described. The method includes positioning the curved surface with respect to a source of a deposition system. The source includes an effective surface having a curved shape in accordance with the curved surface of the substrate. The method also includes causing the source to emit particles such that the particles become deposited on the curved surface as the film. The curved shape of the effective surface is associated with a thickness uniformity of the film. 
     According to another embodiment, a deposition system for depositing a film on a surface of a substrate is described. The surface is characterized as having a non-planar shape. The deposition system includes a source that has an effective surface configured to emit particles. The effective surface has a non-planar shape in accordance with the non-planar shape of the surface of the substrate. The deposition system also includes a support configured to position the substrate with respect to the source such that the particles emitted from the source deposit as the film on the surface of the substrate. The non-planar shape of the effective surface is associated with a thickness uniformity of the film. 
     According to a further embodiment, a plasma enhanced chemical vapor deposition (PECVD) apparatus for depositing a film on a curved surface of a substrate is described. The PECVD apparatus includes a hollow cathode source that has an effective surface configured to emit ions. The effective surface has a curved shape in accordance with a curved shape of the curved surface of the substrate. The PECVD apparatus also includes a support configured to position the substrate with respect to the hollow cathode source such that the ions emitted from the source deposit as the film on the curved surface of the substrate. The curved shape of the effective surface is associated with a thickness uniformity of the film. 
     These and other embodiments will be described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1A  shows a schematic view of a conventional deposition system used to deposit a film on a planar surface. 
         FIG. 1B  shows the conventional deposition system of  FIG. 1A  used to deposit a film on a non-planar surface. 
         FIG. 2A  shows a schematic view of a deposition system used to deposit a film on a non-planar surface in accordance with described embodiments. 
         FIG. 2B  shows the deposition system of  FIG. 2A  used to deposit a second film in accordance with described embodiments. 
         FIG. 2C  shows a substrate that has multiple layers of film deposited on a non-planar surface in accordance with described embodiments. 
         FIG. 3  shows a schematic view of an alternate deposition system used to deposit a film on a non-planar surface in accordance with described embodiments. 
         FIG. 4  shows a perspective view of one embodiment of a hollow cathode source in accordance with described embodiments. 
         FIG. 5  shows a perspective view of one embodiment of a curved-shaped hollow cathode source in accordance with described embodiments. 
         FIGS. 6A and 6B  show a schematic view of a hollow cathode system arranged to uniformly deposit one or more films on substrates having non-planar surfaces in accordance with described embodiments. 
         FIG. 7  shows a schematic view of a hollow cathode system arranged in series to uniformly deposit one or more films on substrates having non-planar surfaces in accordance with described embodiments. 
         FIG. 8  shows a schematic view of a hollow cathode system arranged in parallel to uniformly deposit one or more films on substrates having non-planar surfaces in accordance with described embodiments. 
         FIG. 9  shows a schematic view of a hollow cathode system having hollow cathode sources arranged in series and in parallel in accordance with described embodiments. 
         FIG. 10  shows a flowchart that indicates a process for depositing a film on a surface of a substrate in accordance with described embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, they are intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     Described herein are methods and systems for depositing a thin film on a substrate surface that has a three-dimensional geometry such that the resulting film is conformally deposited on the three-dimensional geometry and has a substantially uniform thickness. The methods involve designing a deposition source that mimics the three-dimensional surface geometry of the substrate. The deposition source can be positioned at a suitable distance to result in conformal coating on the three-dimensional surface geometry of the substrate. In some cases, multiple layers of films are deposited onto each other forming multi-layered coatings. In some embodiments, the multi-layered coatings are antireflective (AR) coatings for windows or lenses. 
     According to some embodiments, a sputtering system is used and the deposition source corresponds to a sputter target. According to other embodiments, a plasma enhanced chemical vapor deposition (PECVD) system is used and the deposition source corresponds to an ion source. In one specific example, a hollow cathode source as part of a PECVD system capable of depositing Si 3 N 4  and SiO 2  is used. Traditionally, this is done with a planar-shaped source, resulting in a film having a non-uniform thickness. Embodiments herein describe a source with an effective surface that has a curvature similar to the curvature of surface of substrate. In another specific example, a system of multiple sputtering sources angled appropriately to coat an entire three-dimensional geometry of a substrate surface is described. Additionally, translation and/or rotation of the substrate during coating can be implemented to smooth out any non-uniformities. 
     Methods described herein are well suited for providing AR coatings on surfaces of consumer products. For example, the methods described herein can be used to form durable and effective AR coatings for portions of computers, portable electronic devices and electronic device accessories, such as those manufactured by Apple Inc., based in Cupertino, Calif. In some embodiments, the methods described herein can be used to form AR coatings on curved surfaces, such as curved windows or lenses of consumer electronic devices. 
     These and other embodiments are discussed below with reference to  FIGS. 1-10 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
     As described above, conventional methods for forming AR coatings are designed for forming the AR coatings on flat or planar surfaces.  FIG. 1A  shows a schematic view of system  100  used to deposit an AR coating on a planar surface using a conventional thin film deposition technique. During a deposition process, substrate  102  is positioned within deposition system  100 . Deposition system  100  can correspond to, for example, a sputter deposition system or a chemical vapor deposition (CVD) system, such as a plasma enhanced chemical vapor deposition (PECVD) system. Substrate  102  has surface  104  that is substantially flat or planar in shape. Particles  106  from source  108  move toward and deposit onto surface  104  of substrate  102  as film  112 . Arrows  110  indicate a general direction in which particles  106  move toward substrate  102  during a deposition process. As shown, particles  106  move primarily in a substantially perpendicular direction with respect to surface  104 . 
     In cases where system  100  is a sputter deposition system, source  108  corresponds to a sputter target from which particles  106  are sputtered. In cases where system  100  is a CVD system, source  108  corresponds to a source of volatile material or precursor material that flows toward and deposits onto surface  104 . In a PECVD system, particles  106  correspond to ions and/or other reactive chemical species within a plasma. Using system  100 , film  112  can be deposited on surface  104  uniformly. That is, the thickness of film  112  can be about the same across surface  104 . 
       FIG. 1B  shows system  100  used to deposit a film on a non-planar surface. Substrate  114  includes surface  116  having a non-planar shape. A non-planar surface is a surface having a three-dimensional geometry or topography that is not substantially planar. Surface  116 , in particular, has a curved shape. During a deposition process, particles  106  move toward and deposit onto surface  116  as film  118 . As shown, particles  106  move substantially in the same direction with respect to each other, as indicated by arrows  110 . Since surface  116  is curved, some particles  106  do not deposit onto surface  116  at a perpendicular direction, particularly at edge portions  120 . As a result, film  118  is deposited more thinly at edge portions  120  compared to center portion  122 . Thus, film  118  has a non-uniform thickness. If film  118  is a AR coating, this means that center portion  122  will function differently than edge portions  120  with respect to anti-reflective effectiveness. For example, center portion  122  may work more effectively than edge portions  120  with respect to anti-reflective effectiveness. If the deposition process is tuned to deposit more material onto edge portions  120 , center portion  122  will be deposited on too thickly. This can result in edge portions  120  of film  118  being more effective than center portion  122  with respect to providing anti-reflective functionality. In addition to reduced anti-reflective functionality, portions of film  118  that are too thick or too thin can take on a color or hue rather than being fully transparent, which can be undesirable in many applications. If multiple layers of film (not shown) are deposited to form the final AR coating, this non-uniformity can be exacerbated resulting in even more disparity between thicknesses of edge portions  120  compared to center portion  122 . 
     Methods and systems described herein can be used to form AR coatings on non-planar surfaces in such a manner such that the resulting AR coatings have substantially uniform thicknesses.  FIG. 2A  shows a schematic view of system  200  used to form an AR coating on a non-planar surface using a thin film deposition technique in accordance with described embodiments. Substrate  202  can be made of any suitable material. In some embodiments, substrate  202  is a window or lens that is made of glass or plastic, such as for an electronic device or part of an electronic device. Substrate  202  is placed in system  200  and positioned with respect to source  208  such that particles  206  can be deposited onto surface  204  of substrate  202 . In some embodiments, substrate  202  is supported and positioned using support  203 . Surface  204  is non-planar in that surface  204  has a three-dimensional geometry or topography that is substantially non-planar. In some embodiments, surface  204  has a curved three-dimensional shape. That is, surface  204  can be curved in x, y and z directions. It should be noted that the methods described herein can be used to form an AR coating having any suitable shape, including surfaces having multiple curved portions, planar portions and/or spline shaped portions. 
     Source  208  has effective surface  218  that corresponds to the surface from which particles  206  are emitted. For example, in sputtering systems effective surface  218  can correspond to a surface of a sputter target. In PECVD systems, effective surface  218  can correspond to a surface of an ion source (e.g., hollow cathode source) that emits reactive chemical species such as ions. According to described embodiments, effective surface  218  has a shape that substantially matches the shape of surface  204  of substrate  202 . For example, if surface  204  has a curved shape, effective surface  218  can have the same degree of curvature as surface  204 . In this way, effective surface  218  mimics the shape of surface  204  of substrate  202 . This configuration allows effective surface  218  to be substantially equidistant to surface  204  at substantially all points along surface  204 . The size of effective surface  218  can vary depending on the type of source (e.g., sputter target or ion source) and distance d between source  208  and surface  204  of substrate  202 . In general, greater distance d will require effective surface  218  to be larger. 
     During a deposition process, particles  206  from source  208  move toward and deposit onto substrate  202  in a substantially perpendicular direction with respect to surface  204 , as indicated by arrows  210 . That is, instead of particles  206  all moving in the same direction, as described above with respect to  FIGS. 1A and 1B , particles  206  converge toward surface  204 . This arrangement results in film  212  being deposited substantially uniformly and such that the final film  212  has a substantially uniform thickness. That is, the thickness of film  212  is about the same across surface  204 , including at center portion  216  and edge portions  214 . In some embodiments, substrate and/or source  208  is rotated or otherwise moved during a deposition process to smooth out any non-uniformities. For example, a rotating mechanism (not shown) can be coupled to support  203  such that support  203  and substrate  202  are rotated along the y-axis during a deposition process. 
     System  200  can be any suitable deposition system. In some embodiments, system  200  is a sputter deposition system where source  208  corresponds to a sputter target from which particles  206  are sputtered. The sputtering can be accomplished by introducing a sputter gas (not shown) such as argon gas, which impinges on sputter target source  208  creating particles  206 . The material of a sputter target source  208  will depend upon a desired material of film  212 . In some embodiments, the sputter target source  208  includes silicon such that film  212  containing silicon, such as Si 3 N 4  (silicon nitride) and/or SiO 2  (silicon dioxide). 
     In some embodiments, system  200  is a CVD system, such as a PECVD system. In embodiments where system  200  is a PECVD system, source  208  can correspond to an ion source that forms ions and/or other reactive species within a plasma. The type of reactive species can be controlled by choosing the appropriate reaction gas(es) supplied to source  208 . Source  208  breaks up the reactive gas and discharges particles  206  in the form of ions and/or other reactive species. The ions and/or other reactive species can react with other species within the plasma before deposition. For example, silane (SiH x ) can be supplied into source  208 , where it is broken up into silicon species (Si x H y ). These silicon species can react with a nitrogen-containing gas (e.g., N 2 , NH x ) to form a silicon nitride film. Alternatively, the silicon species can react with an oxygen-containing gas (e.g., NO x ) to form a silicon dioxide film. In particular embodiments, source  208  corresponds to a hollow cathode source of a PECVD system. Embodiments including a hollow cathode source will be described in detail below with respect to  FIGS. 4 and 5 . 
     Film  212  can be made of any suitable material. In some embodiments, film  212  is made of a material suitable for an AR coating. For example, film  212  can be substantially transparent or translucent such that substrate  202  is visible therethrough. In some applications where the AR coating is applied to a consumer product, the AR coating should be dense and durable enough to substantially avoid damage and delamination during normal use of the consumer product. In particular embodiments, film  212  includes Si 3 N 4  (silicon nitride), SiO 2  (silicon dioxide), NB 2 O 5 , TiO 2  (titanium oxide), TaO 2  (tantalum oxide) and/or other suitable AR film materials. In some embodiments, one or more subsequently deposited films are deposited on film  212  using one or more subsequent deposition processes, which will be described below with respect to  FIGS. 2B and 2C . 
     Distance d between source  208  and surface  204  of substrate  202  can vary depending on a number of factors including the type of system  200 . In general, the larger the distanced, the larger effective surface  218  should be in order to achieve full coverage of surface  204 . In embodiments where system  200  is a sputter deposition system and source  208  corresponds to a sputter target, distance d should be large enough to allow room for a sputter gas to sputter off particles  206  from source (sputter target)  208 , yet small enough for sufficient sputtering onto surface  204 . In embodiments where system  200  is a PECVD system and source  208  corresponds to an ion source (e.g., hollow cathode source), distance d should be large enough to allow adequate formation and discharge of ions and/or other reactive species. Generally, this means distance d for PECVD systems is generally smaller than for sputter deposition systems. In some embodiments, distance d is very small such that particles  206  can be very evenly distributed and deposited onto surface  204 . The angle and/or position of surface  204  of substrate  202  should be aligned relative to effective surface  218  to assure that particles  206  arrive at surface  204  substantially uniformly. Generally, the larger distance d is, the more accurately the angle and/or position of surface  204  should be aligned relative to effective surface  218  in order to achieve a uniformly thick film  212 . 
     In some applications, single film  212  is sufficient. In other embodiments, one or more subsequent layers are deposited onto film  212 . For example, some AR coatings include multiple layers of thin films having different refractive indexes, such as alternating layers of silicon nitride and silicon dioxide films. As described above, depositing more than one layer on a non-planar surface using conventional deposition techniques can exacerbate any non-uniformity of the final AR coating if the individual films are not deposited uniformly. The methods described herein can be used to deposit more than one layer of film onto a non-planar substrate such that a final multi-layered film has a uniform thickness. 
       FIG. 2B  shows a schematic view of system  200  used to form a multi-layered film coating in accordance with described embodiments. In particular, system  200  is used to deposit a second film  222  onto film  212 . Second film  222  can include the same or different material as film  212 . For example, film  212  can include silicon dioxide and second film  222  can include silicon nitride. As described above with respect to film  212 , the composition of second film  222  can be controlled by choosing the type of material at source  208  and/or gases within system  200 . In embodiments where system  200  is a sputter deposition system where source  208  corresponds to a sputter target, process conditions can be changed such that second film  222  has a different chemical composition than film  212 . In embodiments where system  200  is a PECVD system with source  208  corresponding to an ion source, the reaction gas that is supplied to source  208  can be changed to correspond to a desired film type. In some cases where films  212  and  222  are made of different materials, source  208  can be purged between deposition processes. 
     Because source  208  has effective surface  218  having a shape that corresponds to surface  204 , particles  220  move toward substrate  202  in a substantially perpendicular direction, as indicated by arrows  210 . In this way, second film  222  is uniformly deposited onto film  212 . That is, the thickness of second film  222  at edge portions  224  is substantially the same as the thickness of second film  222  at center portion  226 . After second film  222  is deposited, any suitable number of films can subsequently deposited onto substrate  202  until a desired number films are deposited. 
       FIG. 2C  shows substrate  202  after multiple layers of film are deposited to form multi-layered coating  228 . In particular, multi-layered coating  228  includes film  212 , second film  222 , third film  230  and fourth film  232 . Note that the number of film layers indicated in  FIG. 2C  are representative of only some embodiments and any suitable number of layers can be formed. Film  212 , second film  222 , third film  230  and fourth film  232  can each be made of the same or different materials. In a particular embodiment, multi-layered coating  228  is an AR coating that includes alternating layers of material having different refractive indexes. This arrangement can allow for the optimal destructive interference of light incident exposed surface  234 , thereby reducing glare. For example, film  212  and third film  230  can be composed of silicon dioxide while second film  222  and fourth film  232  are composed of silicon nitride. In some embodiments, silicon nitride/silicon dioxide AR coatings are preferred because silicon nitride is relatively dense, durable and has a relatively high stiffness compared to some other AR coating material alternatives and silicon dioxide bonds well with silicon nitride bond since they each include base silicon matrixes. Thus, the silicon dioxide and silicon nitride film layers will be less prone to pealing from each other when exposed to abrasion forces compared to films made of more dissimilar materials. For at least these reasons, silicon dioxide and silicon nitride AR coatings can be well suited for application on exposed surfaces of consumer products that exposed to a lot of wear and abrasion. 
     The timing between depositing each of films  212 ,  222 ,  230  and  232  can vary depending on the deposition technique use as well as other processing parameters. For example, in sputtering systems, each successive film can generally be deposited very soon after each previous film is deposited. In PECVD systems where films  212 ,  222 ,  230  and  232  include different materials, it may be beneficial to allow time for the source to adequately pump down and purge of a first reaction gas before introducing a second type of reaction gas. 
       FIG. 3  shows a schematic view of system  300  used to form an AR coating on a non-planar surface using an alternative thin film deposition technique in accordance with described embodiments. System  300  is configured to deposit film  312  on surface  304  of substrate  302 . System  300  can be any suitable deposition system configured to deposit film  312 , such as a sputter deposition system or PECVD system. Surface  304  is non-planar (e.g., curved) and therefore difficult to deposit onto in a uniform fashion using conventional techniques described above. System  300  includes a series of sources  308  having elements a-g that are arranged to have effective surface  318  with a shape that closely corresponds to the shape of surface  304  of substrate  302 . In some embodiments, each of elements a-g can have a substantially planar surface but collectively form effective surface  318  that roughly mimics the curved surface  304  of substrate  302 . This series of sources  308  may be easier to implement when it is difficult to obtain a single source having a shape that corresponds to surface  304 , such as source  208  described above with reference to  FIGS. 2A and 2B . In some embodiments, system  300  includes support  303 , which supports and positions substrate  302  with respect to series of sources  308 . 
     Series of sources  308  can include any suitable number of elements a-g and are not limited to the number of elements a-g shown. In general, series of sources  308  should have a suitable number of elements a-g for providing film  312  having a sufficiently uniform thickness. This can vary depending on the type of system  300  (e.g., sputter or PECVD), distance d between series of sources  308 , the three-dimensional geometry of surface  304 , and particular application film uniformity requirements. In embodiments where system  300  is a sputter deposition system, elements a-g can each correspond to a sputter target. In embodiments where system  300  is a PECVD system, elements a-g can each correspond to an ion source. Film  312  can be made of any suitable material, including Si 3 N 4  (silicon nitride), SiO 2  (silicon dioxide), NB 2 O 5 , TiO 2  (titanium oxide), TaO 2  (tantalum oxide) and/or other suitable AR film materials. System  300  can be used to form subsequent layers of film, similar to described above with reference to  FIGS. 2B and 2C . 
     As described above, in some embodiments a PECVD system using a hollow cathode source is used to deposit an AR film.  FIG. 4  shows a perspective view of one embodiment of a hollow cathode source  400 , which has a linear shape. Hollow cathode source  400  has a tubular shape that includes cavity  402 . A radio frequency (RF) and/or other current discharge can be applied to hollow cathode source  400  as a gas passes through cavity  402  forming a plasma. For example, a silicon-containing gas, such as a silane gas, can be passed through cavity  402  to form a plasma with silicon-containing ions and reactive species. The ions and reactive species flow toward and deposit conformally onto a substrate surface as a film. 
     Since hollow cathode source  400  has a substantially linear shape, it can be used to form a film having a substantially uniform surface on a linear or planar surface of a substrate, such as shown in  FIG. 1A . However, use of a single linearly shaped hollow cathode source  400  to deposit onto a curved surface can cause the resultant film to have a non-uniform thickness, such as shown in  FIG. 1B . To accommodate a non-planar substrate surface, two or more hollow cathode sources  400  can be used in conjunction with other, such as shown in  FIG. 3 . In particular, the two or more hollow cathode sources  400  can form an effective surface that mimics the non-planar surface of a substrate. This way, the ions and reactive species within the plasma can flow toward the non-planar surface of the substrate in a substantially perpendicular direction with respect to the surface of the substrate, thereby forming a film having a substantially uniform thickness. 
     In some embodiments, the shape of a hollow cathode source is customized to form an effective surface that mimics a non-planar surface of a substrate.  FIG. 5  shows hollow cathode source  500  having a curved shape effective surface  504  in accordance with some embodiments. Hollow cathode source  500  includes cavity  502  where a radio frequency (RF) and/or other current discharge is applied to a gas forming a plasma having ions and/or other reactive chemical species. The curved shape effective surface  504  mimics a shape of curved surface of a substrate, such as shown in  FIGS. 2A-2D . The ions and/or other reactive species can then flow toward the curved substrate in a substantially perpendicular direction with respect to the curved substrate surface, thereby forming a film having a substantially uniform thickness. 
     Note that effective surface  504  of hollow cathode source  500  can have any suitable shape in accordance with a shape of a substrate surface and is not limited to the curved shape shown in  FIG. 5 . In some embodiments, effective surface  504  mimics a two-dimensional surface of a substrate. In other embodiments, effective surface  504  mimics a three-dimensional surface of a substrate. In some embodiments, two or more hollow cathode sources  500  can have the same or different shaped effective surfaces  504  are combined to mimic the shape of a substrate surface. In some embodiments, one or more non-planar shaped hollow cathode sources  500  are combined with one or more linear shaped hollow cathode sources  400  to mimic a three-dimensional shape of a substrate surface. Some combinations of hollow cathode sources are described below with reference to  FIGS. 6-9 . 
     In some applications, a substrate surface has a relatively large three-dimensional surface that is not easily covered using a single hollow cathode source.  FIGS. 6A and 6B  show hollow cathode systems that can be used as part of a PECVD apparatus in order to uniformly deposit films on substrates having relatively large surfaces.  FIG. 6A  shows a schematic view of hollow cathode system  600 , which includes hollow cathode source  602  for depositing film  603  onto substrate  604 . Substrate  604  has surface  606  with a non-planar shape. In some embodiments, substrate  604  is a window or lens for an electronic device. In some embodiments, system  600  includes support  601 , which supports and positions substrate  604  relative to hollow cathode source  602 . Surface  606  is relatively large in that surface  606  substantially spans in x, y and z directions. 
     Hollow cathode source  602  has effective surface  610  that has a shape in accordance with a portion of surface  606  of substrate  604 . In order to cover surface  606  in its three-dimensional entirety, substrate  604  is translated relative to hollow cathode source  602  during a deposition process, as indicated by arrow  608  (z direction). This way, hollow cathode source  602  can provide a plasma having ions and/or other reactive species sufficiently proximate different regions of surface  606  to deposit film  603  thereon at different times during the deposition process. In some embodiments, support  601  includes a translational mechanism, such as a conveyor belt system, that translates substrate  604  while hollow cathode source  602  remains stationary. In other embodiments, hollow cathode source  602  is translated while substrate  604  remains stationary. In other embodiments, both hollow cathode source  602  and substrate  604  are translated and neither remains stationary. 
     In some embodiments, the rate at which substrate  604  is translated relative to hollow cathode source  602  is controlled in order to control the rate of deposition onto surface  606 . For example, the rate of translation can be tuned such that film  603  has a predetermined thickness. In general, the faster the translation, the thinner film  603  will be. In some embodiments, the rate of translation is consistent throughout a deposition process. In other embodiments, the rate of translation is varied during a deposition process. That is, the rate of translation can be increased or decreased at different points of the deposition process. This technique can be used, for example, to compensate for different regions of surface  606  being different distances from effective surface  610 . For example, surface  606  at regions  612  and  614  are farther from effective surface  610  of hollow cathode source  602  compared to region  616  (i.e., in the y and x directions). This varied distance can lead to film  603  having a greater thickness at region  616  compared to regions  612  and  614 . To provide film  603  having a uniform thickness at region  616  and regions  612  and  614 , the rate of translation can slower when effective surface  610  of hollow cathode source  602  is positioned over regions  612  and  614  and faster when positioned over region  616 . This can allow more dwell time and depositing of more material at regions  612  and  614  to compensate for the greater distance from effective surface  610 . Resultant film  603  over surface  606  will have a uniform thickness. 
     According to some embodiments, a flow rate of reaction gas provided to hollow cathode source  602  is varied in order to control the rate of deposition onto surface  606 . Different flow rates can be implemented instead of or in addition to varying a translation rate of substrate  604  relative to hollow cathode source  602 . In general, higher gas flow rates will result in higher rates of deposition and lower gas flow rates will result in lower rates of deposition. For example, a higher gas flow rate can be applied when effective surface  610  of hollow cathode source  602  is positioned over regions  612  and  614  and lower flow rate when positioned over region  616 . This can compensate for the greater distance of regions  612  and  614  from effective surface  610 . 
     As described above, in some applications multiple layers of film are deposited to form an AR coating. After a first deposition process used to deposit film  603  is sufficiently complete, substrate  604  can be either moved to a second hollow cathode source (not shown) to deposit a second film, or substrate  604  can be transferred through hollow cathode source  602  a second time.  FIG. 6B  shows hollow cathode system  600  during a second deposition process where substrate  604  is transferred through hollow cathode source  602  a second time. The second deposition process deposits second film  616  onto the already deposited film  603 . In one embodiment, the second deposition process involves transferring substrate  604  through hollow cathode source  602  in an opposite direction (as indicated by arrow  618 ) compared to the first deposition process for depositing film  603 . In some embodiments, support  601  includes a translational mechanism, such as a conveyer belt system, that translates substrate  604  while hollow cathode source  602 . In other embodiments, hollow cathode source  602  is translated while substrate  604  remains stationary. 
     In some embodiments, second film  616  includes substantially the same material as film  603 . In other embodiments, second film  616  includes a different material than film  603 . In cases where second film  616  includes a different material, hollow cathode source  602  is configured to form a first type of ions and/or other reactive chemical species when depositing film  603  and a second type of ions and/or other reactive chemical species when depositing second film  616 . For example, hollow cathode source  602  can be supplied with a first reaction gas to form film  603  of a silicon dioxide material and a second reaction gas to form second film  616  of a silicon nitride material, or vice versa. 
     In some embodiments, a number of hollow cathode sources are used in order to uniformly cover a three-dimensional surface of a substrate.  FIG. 7  shows a schematic view of hollow cathode system  700 , which includes hollow cathode sources  702   a ,  702   b ,  702   c  and  702   d  arranged in series for depositing film  703  onto substrate  704 . In some embodiments, system  700  includes support  701  that supports and positions substrate  704  relative to hollow cathode sources  702   a ,  702   b ,  702   c  and  702   d . Substrate  704  has three-dimensional surface  606 , which includes regions  712 ,  714  and  716 . 
     Hollow cathode sources  702   a ,  702   b ,  702   c  and  702   d  each have effective surfaces  710   a ,  710   b ,  710   c  and  710   d , respectively, that compensate for the three-dimensional shape of surface  606 . In particular, hollow cathode source  702   a  has an offset position in the x and y directions compared to each of hollow cathode sources  702   b  and  702   c  in order to bring hollow cathode source  702   a  close enough region  714  of surface  706  to provide film  703  the same thickness over region  714  as over region  716 . Similarly, hollow cathode source  704   d  has an offset position in the x and y directions compared to each of hollow cathode sources  702   b  and  702   c  in order to bring hollow cathode source  702   a  close enough to region  712  of surface  706  to provide film  703  the same thickness over region  712  as over region  716 . The result is film  703  having a uniform thickness over regions  712 ,  714  and  716  of surface  706 . In some embodiments, effective surfaces  710   a ,  710   b ,  710   c  and  710   d  are each positioned at the same distance from surface  706 . In some embodiments, the flow of gas provided to each of hollow cathode sources  702   a ,  702   b ,  702   c  and  702   d  is varied in order to control the rate of deposition onto different regions  712 ,  714  and  716  of surface  706 . Note that any suitable number of hollow cathode sources can be used in order to provide a film  703  having a sufficiently uniform thickness. 
     In some cases, the relative positions of substrate  704  and cathode sources  702   a ,  702   b ,  702   c  and  702   d  can be changed. For example, support  701  can include a translational mechanism, such as a conveyor belt system, that translates substrate  704  that accurately positions substrate  704  under hollow cathode sources  702   a ,  702   b ,  702   c  and  702   d  for a deposition process and removes substrate  704  after a deposition process. In one embodiment, substrate  704  is translated in directions  708  and  718 . For example, substrate  704  can be translated in direction  708  before a deposition process and then translated in direction  718  after the deposition process is complete. In other embodiments, substrate is translated in direction  708  before and after a deposition process. In some embodiments, system  700  is used to deposit a second film (not shown) onto film  703 . 
     According to some embodiments, multiple substrates are processed simultaneously, which may be beneficial in some manufacturing situations where throughput is an important factor.  FIG. 8  shows a schematic view of hollow cathode system  800 , which includes hollow cathode sources  802   a ,  802   b  and  802   c  arranged in parallel for depositing films  803   a ,  803   b  and  803   c  onto substrates  804   a ,  804   b  and  804   c , respectively. In some embodiments, system  800  includes supports  801   a ,  801   b  and  801   c , which support and position substrates  804   a ,  804   b  and  804   c , respectively. Hollow cathode source  802   a  has effective surface  810   a  that is in accordance with curved surface  806   a  of substrate  804   a . Hollow cathode source  802   b  has effective surface  810   b  that is in accordance with curved surface  806   b  of substrate  804   b . Hollow cathode source  802   c  has effective surface  810   c  that is in accordance with curved surface  806   c  of substrate  804   c . In some embodiments, the shapes of surfaces  806   a ,  806   b  and  806   c  substrates  804   a ,  804   b  and  804   c  are the same. In other embodiments, one or more of surfaces  806   a ,  806   b  and  806   c  have different shapes. 
     As shown, hollow cathode sources  802   a ,  802   b  and  802   c  are positioned in parallel such that substrates  804   a ,  804   b  and  804   c  can be deposited onto simultaneously. For example, a translation mechanism can be used to translate either substrates  804   a ,  804   b  and  804   c  or cathode sources  802   a ,  802   b  and  802   c  in direction  808 . In some embodiments, hollow cathode sources  802   a ,  802   b  and  802   c  are all part of a single hollow cathode source that has curved portions to accommodate each of substrates  804   a ,  804   b  and  804   c . If hollow cathode sources  802   a ,  802   b  and  802   c  are all part of a single hollow cathode source, a single gas source can be used to supply gas to hollow cathode sources  802   a ,  802   b  and  802   c . In other embodiments, hollow cathode sources  802   a ,  802   b  and  802   c  are each separate hollow cathode sources that are supplied gas by different gas sources. In some embodiments, system  800  is used to deposit second films (not shown) onto films  803   a ,  803   b  and  803   c  by, for example, translating either  804   a ,  804   b  and  804   c  or hollow cathode sources  802   a ,  802   b  and  802   c  in direction  818  and changing the source gases supplied to hollow cathode sources  802   a ,  802   b  and  802   c.    
     As described above with respect to  FIGS. 6A and 6B , the rate of relative translation of substrates  804   a ,  804   b  and  804   c  with respect to hollow cathode sources  802   a ,  802   b  and  802   c  can be varied in order to compensate for the three-dimensional variation of surfaces  806   a ,  806   b  and  806   c  and in order to provide films  803   a ,  803   b  and  803   c  having uniform thicknesses. For example, the rate of translation can slower when effective surfaces  810   a ,  810   b  and  810   c  are positioned over regions that are farther away, (e.g., regions  612   a ,  612   b , and  612   c  and  614   a ,  614   b , and  614   c ) and faster when positioned over regions that are closer (e.g., regions  616   a ,  616   b , and  616   c ). Alternatively or in addition to varying a translation rate, a flow rate of reaction gas(es) provided to hollow cathode sources  802   a ,  802   b  and  802   c  is varied in order to control the rate of deposition onto different regions of surfaces  806   a ,  806   b  and  806   c , respectively. In some embodiments, system  800  is used to deposit second films (not shown) onto films  803   a ,  803   b  and  803   c.    
     According to some embodiments, a hollow cathode system includes a number of hollow cathodes sources arranged in series, such as described above with reference to  FIG. 7 , as well as a number of hollow cathode sources arranged in parallel, such as described above with reference to  FIG. 8 .  FIG. 9  shows a schematic view of system  900 , which includes multiple hollow cathodes for depositing films  903   a ,  903   b  and  903   c  on substrates  904   a ,  904   b  and  904   c , respectively. System  900  includes a first set of parallel hollow cathode sources  902   a ,  902   b  and  902   c  and a second set of parallel hollow cathode sources  905   a ,  905   b  and  905   c . Hollow cathode sources  902   a  and  905   a  can have an effective surface with a shape in accordance with a curved portion of surface  906   a  of substrate  904   a . Hollow cathode sources  902   b  and  905   b  can have an effective surface with a shape in accordance with a curved portion of surface  906   b  of substrate  904   b . Hollow cathode sources  902   c  and  905   c  can have an effective surface with a shape in accordance with a curved portion of surface  906   c  of substrate  904   c . In some embodiments, surfaces  906   a ,  906   b  and  906   c  have substantially the same shape. In other embodiments, surfaces  906   a ,  906   b  and  906   c  have different shapes. 
     Substrates  904   a ,  904   b  and  904   c  can be positioned on supports  901   a ,  901   b  and  901   c , respectively. In some embodiments, supports  901   a ,  901   b  and  901   c  include a translational mechanism, such as a conveyor belt system, for translating substrates  904   a ,  904   b  and  904   c , respectively, in directions  908  and/or  918 . It should be understood that the number and arrangement of hollow cathode sources shown in  FIGS. 7, 8 and 9  are representative of some embodiments and are not meant to represent all possible numbers and configurations. In addition, the substrate surface shapes and corresponding effective surface shapes of the hollow cathode sources shown in  FIGS. 7, 8 and 9  are not meant to represent all possible shapes of substrate surfaces and effective surface shapes. For example, a substrate can have a surface with one or more curved portions and one or more substantially planar portions. The hollow cathode sources can mimic an entire substrate surface shape or portions of the substrate surface. 
       FIG. 10  shows flowchart  1000  indicating a high level process for depositing a film having a uniform thickness on a surface of a substrate in accordance with described embodiments. At  1002 , a substrate having a non-planar surface is positioned with respect to an effective surface of a source of a deposition system. The effective surface has a non-planar shape in accordance with the non-planar surface of the substrate. A non-planar surface is defined as having a three-dimensional surface geometry or topography that is not substantially planar. The non-planar surface of the substrate can encompass substantially an entire surface of the substrate or can include one or more regions of the substrate. In some embodiments, the non-planar surface has at least one curved region. In some embodiments, the substrate is a curved surface of a window or lens for an electronic device. In some embodiments, the film is an AR coating or one layer of a multi-layered AR coating. 
     The source can be any suitable deposition source. For example, in a sputter deposition system, the source can correspond to a sputter target. In a PECVD system, the source can correspond to an ion source, such as a hollow cathode source. The non-planar surface of the substrate can be positioned or aligned with respect to the effective such that particles emitted from the source deposit as a film on the non-planar surface. In some embodiments, the substrate is supported and/or positioned using a support. In some embodiments the support includes a translational mechanism configured to translate the substrate with respect to the source. In some embodiments, the translational mechanism is configured to translate the substrate before and after a deposition process. In some embodiments, the translational mechanism is configured to additionally translate the substrate during one or more deposition processes. 
     At  1004 , the source is caused to emit particles such that the particles deposit as a film on the non-planar surface. The particles can be any suitable material capable of forming a film on the substrate. In a sputter deposition system, the particles can correspond to material sputtered from the sputter target. In a PECVD system, the particles can correspond to ions and/or other reactive chemical species of a plasma. Since the effective surface has a non-planar shape in accordance with the non-planar surface of the substrate, the film has a substantially uniform thickness. 
     At  1006 , after depositing the film, the source is optionally used to deposit one or more additional films, forming a coating having multiple layers of film on the non-planar surface of the substrate. In some embodiments, the multiple layers of film make up an AR coating. In one embodiment, the AR coating includes alternating films of Si 3 N 4  and SiO 2  films. In other embodiments, a different source is used to form the one or more additional films. In some embodiments, the same source is used to form the one or more additional films. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20170607
Publication Date: 20190903
Grant Date: 20190903
Priority Date: 20140925
Inventors: ROGERS, MATTHEW S.
Assignee: APPLE INC
CPC Classifications: [{"code": "C23C14/3464", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/542", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32541", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3417", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/006", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01J2237/327", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C14/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/081", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C16/52", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/455", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3435", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32596", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01J37/342", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/458", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3417", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32541", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32403", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/3321", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C28/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/3464", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32403", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3423", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/542", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/52", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/3407", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C28/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3423", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32614", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/458", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32596", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C16/455", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/458", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B1/113", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/3464", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C16/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/081", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C14/0021", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/3423", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/542", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/3321", "inventive": false, "first": false, "tree": "[]"}, {"code": "C23C16/52", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/0036", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32541", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32403", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/342", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C28/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32596", "inventive": true, "first": true, "tree": "[]"}, {"code": "C23C16/455", "inventive": true, "first": false, "tree": "[]"}, {"code": "C23C14/3407", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01J37/3435", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J37/32614", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01J2237/006", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01J37/3417", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 55581645