Abstract:
Substrate processing systems, such as ion implantation systems, deposition systems and etch systems, having textured silicon liners are disclosed. The silicon liners are textured using a chemical treatment that produces small features, referred to as micropyramids, which may be less than 20 micrometers in height. Despite the fact that these micropyramids are much smaller than the textured features commonly found in graphite liners, the textured silicon is able to hold deposited coatings and resist flaking. Methods for performing preventative maintenance on these substrate processing systems are also disclosed.

Description:
[0001]    This application is a divisional of U.S. patent application Ser. No. 13/928,815 filed Jun. 27, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
       [0002]    Embodiments of the present disclosure relate to methods and apparatus for lining and texturing parts of a substrate processing system. 
       BACKGROUND 
       [0003]    Semiconductor, solar, or other types of substrates may be processed within various substrate processing systems, such as ion implantation systems, deposition systems and etching systems. Some ion implantation systems may comprise an ion source, extraction electrodes, a mass analyzer, a collimating magnet, one or more acceleration or deceleration stages and a process chamber that holds the substrate. Deposition systems may comprise an ion source, and a target and substrate disposed in a process chamber. These systems may include, for example, the acceleration and deceleration stages, the mass analyzer, the collimating magnet and the process chamber. It is common for components disposed within these systems, such as the interior walls, electrodes, insulators and other equipment to show signs of deterioration or to become coated. This may be due to two different causes. For example, ions or other materials may be deposited on these components. In addition, the components themselves may create particulates when struck by energetic ions, causing contamination downstream. For example, the inner walls of the mass analyzer may be impinged by energetic ions, causing the material used to construct the mass analyzer to sputter. Additionally, materials released further upstream, such as within the ion source, may be deposited on and coat the walls of the mass analyzer. After a layer of sufficient thickness forms, this coating may flake off, causing contamination downstream. In other embodiments, in regions near the substrate, a thin film of photoresist may form on these components. 
         [0004]    Currently, liners typically made from graphite are used to address these issues. Graphite is carbon based. Therefore, even if the liner is subject to sputtering, the release of carbon may have a minimal impact to components and substrates disposed downstream. In addition, graphite can be mechanically textured to form a rough inner surface. The textured graphite may have features that are about 0.3 mm in depth. The deposited materials that coat the liner adhere well to this textured surface, thereby reducing the likelihood of flaking. 
         [0005]    However, one disadvantage of graphite is that it tends to particulate when struck by energetic ions. This may be due to the microstructure of graphite, which is an assembly of small carbon grains held together in an amorphous carbon matrix. Therefore, it would be advantageous if there were a liner and a texturing method while could be used in ion implantation systems that resisted particulating and did not allow flaking of deposited coatings. 
       SUMMARY 
       [0006]    Substrate processing systems, such as ion implantation systems, deposition systems and etch system having textured silicon liners are disclosed. The silicon liners are textured using a chemical treatment that produces small features, referred to as micropyramids, which may be less than 20 micrometers in height. Despite the fact that these micropyramids are much smaller than the textured features commonly found in graphite liners, the textured silicon is able to hold deposited coatings and resist flaking. 
         [0007]    According to one embodiment, a substrate processing system is disclosed, which comprises a process chamber, having a plurality of chamber walls, in which the substrate is disposed; a feed gas source in communication with the process chamber; a plasma generator to create a plasma from the feed gas; and a silicon liner disposed on a surface of at least one of the chamber walls of the process chamber, wherein a surface of the silicon liner is textured. The textured silicon liner may have micropyramids having a height of less than 20 micrometers. 
         [0008]    According to another embodiment, an ion implantation system is disclosed, comprising an ion source; a process chamber in which a substrate is disposed; and a silicon liner, disposed within the system, where at least one surface of the silicon liner is textured. The textured silicon liner may have micropyramids having a height of less than 20 micrometers. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]    For a better understanding of the present disclosure, reference is made to the accompanying drawings, which are incorporated herein by reference and in which: 
           [0010]      FIG. 1  shows a representative ion implantation system according to one embodiment; and 
           [0011]      FIG. 2  shows a magnified view of the surface of a silicon liner; 
           [0012]      FIG. 3  shows a representative ion implantation system according to another embodiment; and 
           [0013]      FIG. 4  shows a representative deposition and etching system. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  shows a representative ion implantation system that may be used in accordance with one embodiment. In this system, there is an ion source  110 , which is in communication with a feed gas source  105 . Feed gas is supplied to the ion source  110  from a feed gas source  105 . The feed gas may be any suitable gas. For example, in some embodiments, a boron-containing gas, such as BF 3  or diborane, may be used. In other embodiments, a phosphorus containing gas, such as PH 3 , may be used. 
         [0015]    In one embodiment, the ion source  110  may include an indirectly heated cathode (IHC), housed within a tungsten chamber. This ion source  110  may be contained within a larger housing  100 . As the ion source  110  is typically biased at a substantial voltage, it may be necessary to electrically isolate the ion source  110  from the housing  100 . This may be achieved through the use of source bushings  115 . 
         [0016]    Outside the ion source  110  are one or more electrodes  120 , which are appropriately biased to attract ions generated in the ion source  110 . The electrodes  120  draw these ions to, and then through the electrode  120 . In some embodiments, there may be multiple electrodes  120 , such as an extraction electrode  121  and a suppression electrode  122 . These electrodes  120  may be at different voltages, and therefore must be electrically isolated from one another. These may be achieved through the use of an insulated manipulator assembly  125 , which holds the electrodes  120  in place. 
         [0017]    The extracted ion beam  130  may then enter a mass analyzer  140 . The ion beam flows through a guide tube (not shown) in the mass analyzer. In some embodiments, a focusing element, such as a quadrupole lens  144  or Einsel lens, may be used to focus the ion beam. A resolving aperture  145  is disposed at the output of the mass analyzer  140 , which extracts only ions having the desired charge/mass ratio. The analyzed ion beam  150 , which now contains only the ions of interest, is then implanted into the substrate  190 , which may be mounted on a substrate support  180 . In some embodiments, one or more acceleration or deceleration stages  170  may be employed to adjust the speed of the analyzed ion beam  150 . These acceleration or deceleration stages  170  may be disposed proximate a process chamber  185 . The substrate  190  and substrate support  180  may be disposed in the process chamber  185 . 
         [0018]    Those of ordinary skill in the art recognize that other components, not shown in  FIG. 1 , may also be part of the ion implantation system. Those of ordinary skill in the art also recognize that various components in  FIG. 1 , such as the mass analyzer  140  or acceleration or deceleration stages  170 , may be not used in certain ion implantation systems. 
         [0019]    Regions which are particularly susceptible to sputtering and coating, such as the walls of the mass analyzer  140  may be lined. Other susceptible regions may include the liners of focusing components, such as quadrupole and Einsel lens  144 , and acceleration or deceleration electrode assemblies where the ion beam travels in close proximity to liner materials. In accordance with one embodiment, the liner  195  may be silicon, rather than graphite. Silicon has several advantages. First, silicon is very inexpensive, readily available, and available at very high levels of purity. In addition, it may the same material as the substrate being processed. Therefore, any particulate generated by the liner  195  causes minimal contamination. In addition, silicon tends to generate less particulate than graphite. 
         [0020]    Despite all these benefits, unfortunately, polished silicon does not retain or hold deposited material well. Additionally, silicon, unlike graphite, is very difficult to mechanically texture. Therefore, the flaking off of coated materials may be problematic. 
         [0021]    Unlike conventional graphite liners, the silicon liners  195  of the present disclosure are textured using a chemical process. Texturing, as used in this disclosure, is defined as the introduction of imperfections to the surface of the liner to increase its surface area. Thus, texturing is used to roughen the surface of the liner. This increase in surface area improves the liner&#39;s ability to retain coated materials. Texturing may be performed using mechanical means or chemical means. This textured, or roughened surface, is disposed in the system so as to face the interior of the system. 
         [0022]    In one embodiment, silicon sheets are provided that may be sized to the area or region of the ion implantation system being lined. In another embodiment, the silicon sheets have known or specific sizes, and a plurality of sheets are used to create a liner of the desired size, which is used to line the desired region. 
         [0023]    The silicon liners  195  are disposed on components of the implantation system. As described above, these liners may be disposed on the mass analyzer  140 , the resolving aperture  145 , the walls of the process chamber, focusing components, electrodes or other areas. In some embodiments, the silicon liners  195  are placed on components that are not electrically biased, such as non-powered electrodes. 
         [0024]    However, in other embodiments, the component to be lined by be biased at an electrical voltage, such as the mass analyzer  140 . Since silicon is naturally non-conductive, the silicon liner may be doped to cause the liner to be electrically conductive. For example, boron or phosphorus doping of the silicon liners may reduce the bulk resistivity to below 10 ohm-cm. 
         [0025]    In any of these embodiments, the liner  195  is applied such that the (100) crystalline surface is exposed to the ion beam. 
         [0026]    This surface, referred to as the exposed surface, is treated with a hydroxide, such as sodium hydroxide or barium hydroxide. This treatment causes the creation of micropyramids on the exposed surface of the silicon liner  195 . A magnified representation of this treated surface is shown in  FIG. 2 . The micropyramids seen in this FIG. may be about 5 micrometers in height. In other embodiments, these micropyramids may be about 10 micrometers in height. In other embodiments, these micropyramids may be as tall as 20 micrometers. Furthermore, as seen in  FIG. 2 , the height and spacing of these micropyramids is irregular, such that the micropyramids have a range of heights. Similarly, the distances between these micropyramids may vary as well. In other words, the chemical texturing of silicon creates features that may be more than 50 times smaller than the features traditionally found on textured graphite liners. Surprisingly, this textured surface may hold onto deposited materials more tenaciously than cut or polished silicon, and may hold onto the deposited materials as well as the more deeply textured graphite liners. 
         [0027]    Thus, in one embodiment, an ion implantation system comprises at least one surface, which is lined with a silicon liner that has been chemically treated to create a roughened exposed surface. This chemical treatment may be done via exposure to a hydroxide, such as a hot hydroxide solution. 
         [0028]    While  FIG. 1  and the above disclosure describe a beamline ion implantation system, the textured silicon liners may be employed in other types of ion implantation systems. For example,  FIG. 3  shows a substrate processing system  200 . In one embodiment, this substrate processing system  200  may be a PLAD implant system. In this embodiment, the PLAD implant system  200  includes a chamber  205  defined by several walls  207 , which may be constructed from graphite, silicon, silicon carbide or another suitable material. This chamber  205  may be supplied with a feed gas, which is contained in a feed gas source  211 , via a gas inlet  210 . This feed gas may be energized by a plasma generator. In some embodiments, an RF antenna  220  or another mechanism is used to create plasma  250 . The RF antenna  220  is in electrical communication with a RF power supply (not shown) which supplies power to the RF antenna  220 . A dielectric window  225 , such as a quartz or alumina window, may be disposed between the RF antenna  220  and the interior of the implant chamber  205 . The system  200  also includes a controller  275 . The controller  275  may receive input signals from a variety of systems and components and provide output signals to each to control the same. 
         [0029]    Positively charged ions  255  in the plasma  250  are attracted to the substrate  260  by the difference in potential between the chamber  205  (which defines the potential of the plasma  250 ) and the substrate  260 . In some embodiments, the walls  207  may be more positively biased than the substrate  260 . For example, the walls  207  may be in electrical communication with a chamber power supply  280 , which is positively biased. In this embodiment, the substrate  260  is in communication with a platen  230 , which is in communication with bias power supply  281 , which is biased at a voltage lower than that applied by chamber power supply  280 . In certain embodiments, the bias power supply  281  may be maintained at ground potential. In a second embodiment, the chamber power supply  280  may be grounded, while the bias power supply  281  may be biased at a negative voltage. While these two embodiments describe either the substrate  260  or the walls  207  being at ground potential, this is not required. The ions  255  from the plasma  250  are attracted to the substrate  260  as long as the walls  207  are biased at any voltage greater than that applied to the platen  230 . 
         [0030]    Liners  290  may be disposed within the chamber  205 , such as along the inner surfaces of walls  207 . The liner  290  may be glued or otherwise adhered to the chamber walls  207 , such that the (100) crystalline surface of the liner is facing towards the interior of chamber  205 . In other words, this (100) crystalline surface is exposed to the coating materials generated within the chamber  205 . 
         [0031]    The system shown in  FIG. 4  may be used as a deposition or etching chamber. This system  300  is similar to that shown in  FIG. 3 . Elements having the same function are given the same reference designators and are not described again. Low temperature deposition system may belong to one of two categories: Physical Vapor Deposition (PVD) or Plasma Enhanced Chemical Vapor Deposition (PECVD). 
         [0032]    PVD, also called “atomic sputtering”, uses a target  251  of the material to be deposited and employs a power supply  282  to apply a negative potential to the target  251 . The vacuum process chamber, which may be chamber  205  in  FIG. 4 , contains both the target  251  and the substrate  260  that is to receive the coating. The chamber  205  is backfilled with a gas (typically Ar) to a pressure of a few millitorr. The potential applied to the target  251  by power supply  282  creates a plasma  250  of the gas, and positive ions within the plasma  250  are attracted to the target  251 , striking it with enough energy to dislodge target atoms. These atoms are ejected from the target  251 , travelling in all directions, the trajectories described as a cosine distribution, and strike chamber walls  207 , protective liners  290  and the substrate  260 . Thus, in this embodiment, the biased target  251  may serve as the plasma generator. In some embodiments, an ion source, typically of the Kauffman type, can be introduced to bombard the substrate  260  with ions during the deposition process (“ion assisted deposition”). PVD is typically used to apply metal coatings such as Al, Cu, Ni and Ti to form contacts and interconnects in integrated circuits. 
         [0033]    PECVD uses a process gas containing the material to be deposited and therefore does not include the target  251  and power supply  282  shown in  FIG. 4 . A plasma  250  is created in the vacuum process chamber  205  by a plasma generator, such as an inductively or capacitive coupling of RF power into the process gas, which may be performed using RF antenna  220  (see  FIG. 3 ). This plasma  250  causes the process gas to dissociate, causing all exposed surfaces including the substrate  260  to become coated. An example is the deposition of amorphous silicon by the dissociation of SiH 4 . A mixture of process gasses can also be employed to deposit compounds such as Si 3 N 4  or SiO 2 . PECVD is typically used to apply dielectric coatings serving as barriers or interlevel dielectrics in integrated circuits. 
         [0034]    In another embodiment, the chamber of  FIG. 4  can be used to create an etching station. In plasma or “dry” etching, the plasma generator may be capacitively coupled to the chamber  205 . For example, RF power is delivered to the substrate  260  through capacitive coupling. The vacuum process chamber  205  is backfilled with either an inert (typically Ar) gas for a process called “sputter etching,” or with a reactive gas (NF 3 , CF 4 , or a mixture of reactive gasses) for a process called “reactive ion etching.” The material removed from the substrate  260  may deposit on the chamber walls  207  and liners  290 , and may form a volatile compound with the reactive gas and be pumped away. 
         [0035]    As with all liners, eventually, in all of these embodiments, a coating builds on the liner which must be removed. These textured silicon liners may allow the substrate processing systems to remain operational longer than previously possible before preventative maintenance is required. In addition, cleaning of these textured silicon liners may be less burdensome and difficult than traditional graphite liners. According to one embodiment, a cleaner, such as a mixture of deionized water and isopropyl alcohol (IPA), which is used to remove a specific film may be used. In another embodiment, grit blasting may be employed to remove the coating. This grit blasting process may be a dry or wet process. In some embodiments, this cleaning process may remove the texture from the silicon liner. In these embodiments, the roughness of the liner may be restored by exposing the exposed surface to another chemical treatment, such as exposure to a hot hydroxide solution as described herein. Thus, a first cleaning step is performed, which may be mechanical (i.e. grit) or chemical (i.e. cleaning solution). After this, the cleaned liner is then exposed to a chemical treatment which retextures the liner. Thus, even after a cleaning cycle, the texture of the silicon liners can be quickly and economically restored. 
         [0036]    Texturing of the silicon liner removes about 5-10 micrometers of material. Since the silicon liner may be between 0.5 and 3 millimeters (several hundred times thicker than the depth of material removed by texturing), the liner may be reconditioned (i.e. retextured) many times before needing to be replaced. Thus, the silicon liner may be subjected to multiple preventative maintenance cycles before reaching the end of its useful life. 
         [0037]    The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.