Abstract:
An enclosure for generating a secondary environment within a processing chamber for coating a substrate. An enclosure wall forms a secondary environment encompassing the coating source, plasma, and the substrate, and separating them from interior of the processing chamber. The enclosure wall includes a plurality of pumping channels for diverting gaseous flow away from the substrate. The channels have an intake of larger diameter from the exhaust opening and are oriented at an angle with the intake opening pointing away from the deposition source. A movable seal enables transport of the substrate in open position and processing the substrate in closed position. The seal may be formed as a labyrinth seal to avoid particle generation from a standard contact seal.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority benefit of U.S. Provisional Application Ser. No. 61/353,164, filed on Jun. 9, 2010, the content of which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Application 
         [0003]    This application is in the field of thin film deposition, such as physical vapor deposition (PVD), Plasma Enhanced Chemical Vapor Deposition, (PECVD), etc. 
         [0004]    2. Related Art 
         [0005]    In state-of-the-art microelectronics (semiconductor ICs, flat panel displays, computer hard-disk drive, etc.) manufacturing, a majority of the critical process steps, such as thin film deposition (coating) and etching, are carried out in specially constructed vacuum apparatus that provide a clean and controlled environment free of ambient contaminants so as to ensure process controllability, stability, and repeatability. 
         [0006]      FIG. 1  is a schematic of a prior art processing apparatus, which, in this specific example is a PVD chamber. A fairly high vacuum level, typically between 10 −3  Torr and 10 −9  Torr, is maintained within such apparatus by one or more vacuum pumps (mechanical pumps, diffusion pumps, ion pumps, cryopumps, turbomolecular pumps, etc.). Plasma is maintained between a target and the processed substrate. The plasma species impinge and eject atoms from the target, which are then deposited on the substrate to form the desired thin film. 
         [0007]    In practice, even under the best vacuum environment, a small amount of various gaseous species, such as hydrogen (H 2 ), water (H 2 O), nitrogen (N 2 ), carbon monoxide (CO), and carbon dioxide (CO 2 ), are always present within these apparatus. These gaseous species, sometimes called residual gas, come from the following sources, i) leaks to the ambient environment, ii) outgassing from the system components such as stainless steel, aluminum or polymer insulator parts, and/or iii) permeation through elastomer seals. Various practices attempt to reduce the amount of residual gases. For example, careful leak-checking could rectify most leaks and the use of electro-polished stainless steel and OFHC (oxygen-free high thermal conductivity) copper gasket seals, in conjunction with long bake-out at elevated temperature. While these practices could help reduce outgassing and permeation, a small but yet detectable amount of aforementioned residual gas would always be present albeit at a much lower level. 
         [0008]    For a high productivity manufacturing system common in the microelectronics industries, cost, throughput and ease-of-maintenance requirements make some of the high vacuum solutions, such as long bake-out or single-use OFHC copper gaskets, inapplicable. In addition, a high productivity manufacturing system inevitably has to process a large number of substrates (silicon wafers, glass panels, or glass or aluminum disks) every hour for days on end, exposing itself to ambient contaminants which may either migrate through the loading/unloading chambers or enter the system by clinging onto incoming substrates. In short, there is always a small amount of gaseous contaminants present within any given vacuum apparatus, including high productivity manufacturing systems in the microelectronics industries. 
         [0009]    With the unrelenting advances of microelectronics manufacturing technologies, the design rules of semiconductor ICs approach the 18 nm nodes, following the ever-extending Moore&#39;s Law, while hard-disk drives are packing hundreds of billions bits (Gigabits) of data on a mere square inch of disk surface. The trace contaminants in the vacuum processing, now more than ever, are of great concern. In the hard-disk drive industry, for example, a disk is methodically coated in sequence a number of ultra-thin metal film layers (tens of nanometers in thickness each), which are extremely susceptible to the trace contaminants, in particular H 2 O. The H 2 O molecules react readily with fresh deposited metallic films, such as Cr, Ti, Al, and Ni, to form oxides or sub-oxides, and alter the compositional as well as physical integrity of the metal thin films. The film properties, such as grain size or crystalline orientation, when compromised by contamination, adversely affect the performance of the end product. 
         [0010]    Consequently, to ensure the deposited film quality it becomes a top priority to prevent the trace contaminants in the vacuum system, especially H 2 O, from interacting with the deposited films during a deposition process. Known methods include one or a combination of the following: I) increasing pumping capacity, II) installing additional water-pumping capability (such as cryo-panel or Meissner coils), III) introducing a greater flow rate of inert process gas (argon) to “sweep” the contaminants into the pumps, IV) utilizing UV irradiation to promote water desorption, or V) erecting a barrier around the deposition zone between the substrate and the plasma source (sputter target). These methods provide some limited benefits. Increasing pumping capacity and/or adding water-pumping capability (Methods I and II) accelerate the removal of some contaminants permeating into the chamber but has little effect on contaminants adsorbed on the chamber wall whose evacuation rate, particularly that of H 2 O, is very much dictated by the desorption rate. At ambient temperature, most H 2 O molecules adsorbed on the chamber wall do not have enough energy to escape into the vacuum. Only when a great quantity of inert process gas (such as argon) is introduced, the collisions of the impinging argon atoms would dislodge H 2 O molecules from the chamber wall (Method III). By absorbing UV photons emitted from a UV source (Method IV) or the plasma during processing, H 2 O molecules may gain energy and desorb from the chamber wall. By themselves, Methods III and IV could elevate partial pressures of contaminants. To avoid such negative effect, Method III or IV tends to be employed in association with Method I or II. Still, the benefits produced by Methods Ito IV are limited since, more often than not, the substrate and the plasma source are centrally located in the vacuum chamber whereas the pumping paths are arranged in the peripheral. A freed H 2 O molecule from the chamber wall is more likely to enter and land on the substrate than to reach the pump. 
         [0011]    Method V attempts to create a so-called mini-environment to keep out the residual-gas contaminants ever present within the vacuum environment by erecting a barrier around the substrate and the sputter target, forming virtually a “chamber within a chamber”. This approach, illustrated in  FIG. 2 , is challenging to implement in practice because it has to maintain a gap between the edge of the substrate and the lip of the enclosure, providing only partial protection at best. As shown in  FIG. 3 , the width of the gap, g, would have to be as narrow as possible to keep the contaminants out, but also be wide enough to maintain a decent pumping conductance to enable maintaining the required high vacuum state. As a result, contaminants tend to collect at the edge of the substrate, just as dust collects at the edge of fan blades. 
         [0012]    On the other hand, since the process gas is introduced outside of the enclosure and flows into the enclosure through the narrow gap, the contaminants are equally likely to squeeze through the gap and into the mini-environment. More importantly, with the location of the gap right next to the substrate, any contaminant entering the mini-environment is most likely to land on the substrate, increasing the chance of contamination of the deposited film. 
         [0013]      FIGS. 1-3  illustrate a processing chamber that processes only a single surface of the substrate. Such chambers are mostly used for processing integrated circuits, solar cells, LED&#39;s, flat panel displays, etc. However, as indicated above, the gas contaminants issue also affects fabrication of disks used in hard disk drives (HDD).  FIG. 4  is a schematic of a prior art processing apparatus which enables simultaneous processing of two sides of a substrate, such as a disk for HDD&#39;s. The chamber  400  is somewhat similar to the chambers of  FIGS. 1-3 , except that plasma processing  430  is performed on both sides of the disk  425  simultaneously. Also, in state of the art disk fabrication systems the disk  425  is mounted on a carrier  435  and is processed while held by the carrier, generally in a vertical orientation. As illustrated, provisions are made for gas to flow to maintain vacuum condition. However, leakage, outgassing, and permeation still presents a contamination problem in such systems. 
         [0014]    Accordingly, a solution is needed to prevent residual gas contamination of deposited thin film in plasma processing apparatus. 
       SUMMARY 
       [0015]    The following summary is included in order to provide a basic understanding of some aspects and features of the disclosure. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
         [0016]    Embodiments of the invention enables creating a pristine clean environment for ultrapure thin film deposition by constructing an enclosure around the essential process components, such as the plasma sources, substrates, and working gas inlets, while diverting the gas flow to evacuation channels. 
         [0017]    According to embodiments of the invention, an enclosure for generating a secondary environment within a vacuum processing chamber for coating a substrate is provided. The enclosure comprises an enclosure wall forming a secondary environment within the interior of the processing chamber and encompassing the coating source (e.g. sputtering target), the plasma, and the substrate, and separating them from the interior of the processing chamber. The enclosure wall has a plurality of pumping channels positioned remotely from the substrate, for diverting gaseous flow away from the substrate. The pumping channels may be made in a “V” or other shapes that restricts direct line-of-sight flow. Also, the diameter of the channels may be larger at the opening to the interior of the enclosure and smaller at the opening to the processing chamber. For chambers utilizing coating source, such as sputtering target, the pumping channels are oriented away from the target and facing the substrate to be processed. In this manner, coating material from the target will not enter the channels, while coating material scattered from the substrate will enter the channels. 
         [0018]    A movable seal opens to transport the substrate to the secondary environment and closes to seal the secondary environment about the substrate. A gas inlet introduces process gas into the secondary environment so as to ensure positive pressure gradient inside the secondary environment versus that outside of the secondary environment. 
         [0019]    Embodiment of the invention also provide for a plasma processing chamber, such as, e.g., a PVD chamber, having the enclosure described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Other aspects and features of the invention would be apparent from the detailed description, which is made with reference to the following drawings. It should be appreciated that the detailed description and the drawings provides various non-limiting examples of various embodiments of the invention, which is defined by the appended claims. 
           [0021]      FIG. 1  is a schematic of a prior art processing apparatus. 
           [0022]      FIG. 2  is a schematic of a prior art apparatus having a shield. 
           [0023]      FIG. 3  is a schematic of a prior art apparatus having a shield, and illustrating the causes of contamination in such systems in spite of the shield. 
           [0024]      FIG. 4  is a schematic of a prior art processing apparatus which enables simultaneous processing of two sides of a substrate, such as a disk for hard disk drive (HDD). 
           [0025]      FIG. 5  illustrates an embodiment of the invention having the sealed mini-environment and flow diversion features. 
           [0026]      FIG. 6  illustrates an embodiment of the invention implemented in a chamber for simultaneous processing of both sides of the substrate. 
           [0027]      FIG. 7  illustrates an embodiment of the secondary enclosure. 
           [0028]      FIG. 8  illustrates an example of the pumping channel according to an embodiment of the invention. 
           [0029]      FIG. 9  illustrates a cross-section of a secondary enclosure wall according to an embodiment of the invention. 
           [0030]      FIGS. 10A and 10B  illustrate an actuated seal according to an embodiment of the invention. 
           [0031]      FIG. 11  illustrates a secondary enclosure having a movable seal, according to an embodiment of the invention. 
           [0032]      FIG. 12  illustrates an embodiment of the secondary enclosure with the labyrinth seal. 
           [0033]      FIG. 13  illustrates the construction of the enclosure wall of two parts with mating holes, according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    According to embodiments of the invention, a system having two elements is provided in order to enable ultra-pure processing environment. The first is an enclosure that seals off a volume around the deposition source and the substrate, creating a fully enclosed mini-environment. This separates the essential participants of the deposition processes from the rest of the larger process chamber including, in particular, potential sources of contaminants (such as leaks, outgassing, permeation, etc.). The second is a series of holes or channels of pre-determined sizes and shapes through the wall of the enclosure that facilitate the diversion and evacuation of the gases or byproducts from the enclosure in a controlled/desired manner while minimizing the probability of outside contaminants entering the enclosure. In combination, the movable enclosure and the exhaust channels provide a method for controlled-flow of gases, promoting outward gas flow from the mini-environment and preventing contaminants from entering it. 
         [0035]      FIG. 5  illustrates an embodiment of the invention having the sealed mini-environment and flow diversion features. In  FIG. 5 , the exterior enclosure  510  of the chamber  500  is coupled to a vacuum pump  505  to evacuate the interior of the chamber. A secondary enclosure  515  is positioned inside the chamber  500  and forms a secondary, mini-environment within the interior of chamber  500 . Enclosure  515  completely encloses the sputtering target  520 , the substrate  525 , and the plasma  530 . Enclosure  515  is generally made of two parts,  517  and  519 , at least one of which is movable to enable transporting of the substrate  525  in a retracted position, and processing of the substrate in its engaged position when engaging seal  513 . At least one of parts  517  and  519  includes evacuation holes or channels  511 . In the embodiment shown in  FIG. 5 , the evacuation channels  511  are in a V-shape, so as to enable pumping while preventing transport of contaminants into the mini-environment. 
         [0036]      FIG. 6  illustrates an embodiment of the invention implemented in a chamber for simultaneous processing of both sides of the substrate, such as a HDD disk. In  FIG. 6  disk  625  is held vertically by carrier  635 . Plasma  630  is ignited between each surface of the disk  625  and a corresponding sputtering target  640 . The disk  625 , plasma  630  and carrier  635  are enclosed by secondary enclosure  617 , which forms seal to the carrier  635 . Enclosure  617  includes pumping channels  611 , which are situated away from the surface of the disk  625 . Consequently, pumping flow is diverted away from the surface of the disk, so as to avoid contamination of the disk. Also, unlike the prior art, in the embodiment of  FIG. 6  the gas used for the plasma processing is injected directly into the secondary enclosure  617  by injectors  655 . 
         [0037]      FIG. 7  illustrates an embodiment of the secondary enclosure, such as the one that can be used in the embodiments of  FIGS. 5 and 6 . In  FIG. 7  only one side of the substrate is shown processed, but by mirroring the structures shown in  FIG. 7 , both sides of the substrate can be processed simultaneously. In  FIG. 7 , substrate  725  is held by carrier  735 . Movable seal  745  seals the gap between the carrier  735  and the wall  717  of the secondary enclosure. In this manner, no flow is generated on the surface of the substrate  625 . Pumping channels  711  are provided on the sidewall  717  of the secondary enclosure. The pumping channels  717  are provided in a position away from the surface of the disk. In this embodiment, the pumping channels  711  are in a “V” shape, to prevent contaminants from entering the secondary chamber&#39;s enclosure. Also, in this embodiment the channels  711  are made in two parts, a first part,  711   b , which is an oblique hole leading from the exterior of the wall  717  and is of small diameter to prevent contaminants from flowing thereto, and a second part,  711   a , which is an oblique hole leading from the interior of wall  717  in a somewhat opposite angle to that of hole  711   b , but is of larger diameter. Hole  711   a  is of larger diameter so as to prevent various deposits from target  740  from occluding the hole after a short time of usage. Also shown in  FIG. 7  is an optional Meissner trap positioned on the exterior of the secondary enclosure, so as to remove water vapors. 
         [0038]    Another feature illustrated in  FIG. 7  is the orientation of the interior pumping channels  711   a . As illustrated, the interior pumping channels  711   a  are angled in an orientation facing the substrate and away from the thin-film source  723 . In this manner, it is unlikely that coating material  723  from the thin-film source enter the pumping channel  711   a . On the other hand, the channels  711   a  are oriented to accept coating material scattered from gas-phase collision, e.g., particle  723 ′, to pump such scattered material out of the secondary enclosure. This helps maintaining the secondary environment clean and reduces the possibility of scattered material from later landing on the substrate. 
         [0039]      FIG. 8  illustrates an example of the pumping channel according to an embodiment of the invention. As is implied by the callout, the arrangement illustrated in  FIG. 8  can be used in the embodiment illustrated in  FIG. 7 . As shown in  FIG. 8 , interior pumping channel or hole  811   a  is of larger diameter than exterior pumping channel or hole  811   b . The diameter of hole  811   a  is designed such that sputtered species  823  may adhere to the entrance of the hole, but the buildup will not occlude the hole, since the diameter is large enough to allow for buildup without hole occlusion. On the other hand, exterior hole  811   b  is made sufficiently narrow so as to prevent contaminant species  827  from entering the pumping channel. Also, the interior and exterior holes are each made at an oblique angle to the surface of the wall  817 , to further prevent introduction of contaminants. 
         [0040]    For ease of manufacture, enclosure  817  of the embodiment of  FIG. 8  is manufactured as two parts, interior wall  817   a  having holes  811   a  drilled therein and exterior wall  817   b  having exterior holes  811   b  drilled therein. The exterior wall  817   b  and interior wall  817   a  are assembled together and aligned such that the exterior holes  817   b  are aligned with the interior holes  817   a . Also, in the embodiment of  FIG. 8  the interior wall  817   a  is thicker than the exterior wall  811   b , such that interior holes  811   a  are longer than exterior holes  811   b . This ensures that interior holes  811   a  can withstand long processing time without occluding. 
         [0041]      FIG. 9  illustrates a cross-section of a secondary enclosure wall  917  which, in this example, is made of a single part. As can be understood, the cross section is taken at the center of the enclosure wall, as in this embodiment the enclosure wall is circular. Interior pumping holes  911   a  are shown having large diameter and in a rather conical shape. Exterior pumping holes  911   b  have a smaller diameter, which is constant throughout the length of the hole. When the two holes connect, they form a somewhat v shape. 
         [0042]      FIGS. 10A and 10B  illustrate an actuated seal according to an embodiment of the invention. Disk  1025  is held by carrier  1035  via clip  1055 . Secondary chamber wall  1017  encloses the disk  1025  and carrier  1035  so as to create a mini-environment within the processing chamber. To seal off the mini environment from the interior of the processing chamber, a movable labyrinth seal  1045  is implemented. In  FIG. 10A  the actuated seal  1045  in its engaged position, sealing off the interior of secondary enclosure from the interior of the processing chamber. In this condition the disk  1025  can be processed.  FIG. 10B  illustrates the actuated seal  1045  in its retracted position. In this position, the processed disk  1025  can be removed from the chamber and a new disk loaded for processing. 
         [0043]    A shown in this embodiment, the actuated seal  1045  is a labyrinth seal. That is, rather than implementing a contact seal, which may lead to generation of particles, a labyrinth seal is formed with the two parts of the seal, such that gas movement is restricted by a maze. That is, one part of the seal has an extrusion  1019 ′ that fits into a corresponding indentation  1019 ″ on the other side of the seal. As can be appreciated, in  FIG. 10A , any gas molecule that attempts to travel from the outside into the mini-environment through the labyrinth seal has to perform four 90° turns. Thus, even thought the two parts of the actuated seal  1045  do not contact even in its sealed position, gas leakage is greatly reduced. 
         [0044]      FIG. 11  is an exploded view illustrating a secondary enclosure (i.e., mini-environment) having a movable labyrinth seal  145 , according to an embodiment of the invention. In  FIG. 11  the secondary enclosure is formed using four parts. Enclosure wall  117  is formed of two parts, interior wall  117   a  and exterior wall  117   b , similar to the arrangement illustrated in  FIG. 8 . As shown, the interior pumping channels  111   a  are obliquely drilled on the interior wall  117   a , while the exterior pumping channels  111   b  are obliquely drilled on the interior wall  117   b . When exterior wall  117   b  is fitted over interior wall  117   a  (note exterior diameter of interior wall  117   a  matches the interior diameter of exterior wall  117   b ), exterior channels  111   b  align with interior channels  111   a . Interior channels  111   a  are of larger diameter than exterior channels  111   b . Interior wall part  117   a  also includes an extension  118 , which corresponds to the conical section of wall  617  illustrated in  FIG. 6 . The extension  118  forms the mini environment up to very close proximity to the disk. 
         [0045]    A third wall part,  117   c  is fitted to the interior wall part  117   a . In this embodiment, third part  117   c  is a stationary part of the labyrinth seal. An extrusion  119 ′ is formed on the face of part  117   a , so as to generate the extruded part of the labyrinth seal  119 . A corresponding indentation (not shown) is formed on the movable part of seal  145 . 
         [0046]    The substrate to be processed is positioned beyond the third wall part  117   c  and the movable seal  145 , as indicated by the arrow in  FIG. 11 . In this manner, the pumping channels are positioned away from the substrate, so that gas flow is diverted away from the substrate to avoid contamination. Once the substrate is positioned for processing, the actuated seal  145  encloses the substrate and seals the secondary environment created by the walls  117   a - c . Actuated seal  145  has extensions  146  that are coupled to actuators that move the seal  145  to enable transport of the substrate in retracted position and processing of the substrate in the extended position. 
         [0047]      FIG. 12  illustrates an embodiment of the secondary enclosure with the labyrinth seal. In the example of  FIG. 12 , the enclosure part of the mini environment covers the space between the source  120  and enclosing the disk  125 . In this example, only one side of the disk is processed, but it can be appreciated that by duplicating the elements of  FIG. 12  one can provide a system for processing both sides of the disk. 
         [0048]    In this example the wall section is also fabricated of several part. Exterior wall  117   b  is fitted over interior wall  117   a , only the extension  118  of which is visible. Holes  111   b  are aligned with holes  111   a , which are not visible. Section  117   c  is a fixed part of the labyrinth seal and has an extension  119 ′, which fits into indentation  119 ″ which is provided on the movable part  145  of the seal. 
         [0049]      FIG. 13  illustrates the construction of the enclosure wall of two parts with mating holes, according to an embodiment of the invention. Interior wall  17  is shown with large diameter holes  111   a  and extension  118 . Exterior wall is in the form of a ring  117   b , and is shown with smaller diameter holes  117 . 
         [0050]    According to embodiments of the invention, additional pumping devices, such as cryo-panels and/or Meissner coils which preferentially capture water vapors, can be installed near the exhaust channels of the secondary enclosure to further reduce the probability of the contaminants reaching the substrate. 
         [0051]    It should be understood that processes and techniques described herein are not inherently related to any particular apparatus and may be implemented by any suitable combination of components. Further, various types of general purpose devices may be used in accordance with the teachings described herein. It may also prove advantageous to construct specialized apparatus to perform the method steps described herein. 
         [0052]    The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.