Abstract:
Embodiments of the present invention provide methods and apparatus for removing debris particles using a stream of charged species. One embodiment of the present invention provides an apparatus for removing debris particles from a beam of radiation comprising a charged species source configured to dispense electrically charged species, and a collecting plate biased electrically opposite to the charged species from the charged species source, wherein the collecting plate and the charged species source are disposed on opposite sides of the beam of radiation, a stream of charged species from the charged species source to the collecting plate intersects the beam of radiation, the stream of charged species is configured to attach and remove debris particles from the beam of radiation by electrostatic force, and the collecting plate is configured to receive the charged species and the debris particles removed from the beam of radiation.

Description:
BACKGROUND 
     1. Field 
     Embodiments of the present invention generally relate to methods and apparatus for preventing particle contamination. Particularly, embodiments of the present invention provide methods and apparatus for protecting masks and/or substrates during lithography. 
     2. Description of the Related Art 
     As the trend continues to reduce the size of semiconductor devices, optical lithography using conventional transmission masks, such as chrome on glass (COG) or phase shift (PSM) masks, will no longer suffice as a viable technique for printing advanced devices on semiconductor wafers. Transmission lithography has been extended to ever shorter wavelengths, down to 157 nm in the far ultraviolet (UV), in order to reduce the size of device features. However, the still shorter wavelengths necessary for printing even smaller device structures are readily absorbed in transmission materials. Alternative technological candidates to replace optical lithography include: electron projection lithography (EPL) and an all-reflective technology called extreme ultra-violet lithography (EUVL). 
     Generally, masks used in production today employ a pellicle to protect the mask surface from particulate contamination. The pellicle is a relatively inexpensive, thin, transparent, flexible sheet, which is stretched above and not touching the surface of the mask. Pellicles provide a functional and economic solution to particulate contamination by mechanically separating particles from the mask surface. The mask is transported and used for lithographic exposure with the pellicle in place. When a mask is used for exposure, with the pellicle in position above the mask, only the details of the mask&#39;s focal plane itself are printed. Particulate material located on the pellicle surface is maintained outside of the focal plane of projection. As a result, particulate material is not printed. When the pellicle eventually becomes damaged or too dirty to use, the mask is removed to a workshop, and the pellicle is replaced. 
     However, in EUV lithography, conventional pellicles can not be used to protect masks during process because all materials are opaque to EUV light. Even though, masks may be protected by pellicles when not in use. Masks must be exposed during lithography. Additionally, the minimum particle size to be removed has decreased with the decrease of the wavelength of the radiation source. For example, in EUV lithography for 65 nm features, particles as small as 52 nm must be removed. 
     Therefore, there is a need for apparatus and methods for protecting masks during lithography. 
     SUMMARY 
     Embodiments of the present invention generally provide apparatus and methods for removing particle contamination during lithography. Particularly, embodiments of the present invention provide methods and apparatus for removing debris particles using a stream of charged species. 
     One embodiment of the present invention provides an apparatus for removing debris particles from a beam of radiation. The apparatus comprises a charged species source configured to dispense electrically charged species, and a collecting plate biased electrically opposite to the charged species from the charged species source. The collecting plate and the charged species source are disposed on opposite sides of the beam of radiation. A stream of charged species from the charged species source to the collecting plate intersects the beam of radiation. The stream of charged species is configured to attach and remove debris particles from the beam of radiation by electrostatic force. The collecting plate is configured to receive the charged species and the debris particles removed from the beam of radiation. 
     Another embodiment of the present invention provides an apparatus for lithography. The apparatus comprises a radiation source configured to provide a beam of radiation, a mask holder configured to support a mask during process, a substrate stage configured to support and index a substrate being processed, a projection system configured to project the beam of radiation from the mask to the substrate, and a particle removal station disposed in the path of the beam of radiation. The mask receives and reflects the beam of radiation. The particle removal station comprises a charged species source configured to dispense electrically charged species. The particle removal station further comprises a collecting plate biased electrically opposite to the charged species from the charged species source, wherein the collecting plate and the charged species source are disposed on opposite sides of the beam of radiation. A stream of charged species from the charged species source to the collecting plate intersects the beam of radiation. The stream of charged species is configured to attach and remove debris particles from the beam of radiation by electrostatic force. The collecting plate is configured to receive the charged species and the debris particles removed from the beam of radiation. 
     Yet another embodiment of the present invention provides a method for removing debris particles in a beam of radiation. The method comprises providing a charged species source, providing a collecting plate so that a path between the collecting plate and the charged species source intersects the beam of radiation, charging the collecting plate with electrical potential opposite to charged species from the charged species source, and removing the debris particles from the beam of radiation by flowing a stream of charged species from the charged species source to the collecting plate. In the present embodiment, the charged species in the stream of charged species attracts the debris particles using electrostatic force, and carries the debris particles to the collecting plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  schematically illustrates a lithography system in accordance with one embodiment of the present invention. 
         FIG. 2  schematically illustrates an enlarged view of a particle removal station of the lithography system of  FIG. 1 . 
         FIG. 3  schematically illustrates a particle removal station in accordance with one embodiment of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. 
     DETAILED DESCRIPTION 
     Embodiments of the present invention generally provide apparatus and method for preventing particle contamination during lithography. Particularly, embodiments of the present invention provide methods and apparatus for removing debris particles from a beam of radiation during photolithography. 
     In one embodiment, a charged species source and a collecting plate are disposed on opposite sides of a beam of radiation used in lithography. The charged species source is configured to project a stream of charged species and the collecting plate is configured to receive the stream of charged species from the charges species source. The stream of the charged species is configured to intersect the beam of radiation, and to use electrostatic force to remove debris particles from the beam of radiation, thus, preventing the debris particles from contaminating the mask, the substrate being processed, and any devices in the path of the beam of radiation. The charged species source and the collecting plate may be positioned in front of a mask holder, any mirrors, or a radiation source. 
       FIG. 1  schematically illustrates a lithography system  100  in accordance with one embodiment of the present invention. 
     The lithography system  100  generally comprises a radiation system  101  configured to generate a beam of radiation  108  to be used in lithography. The lithography system  100  further comprises a lithography apparatus  102  in connection with the radiation system  101  via a wave train  109 . 
     The radiation system  101  generally comprises a radiation source  106  and a projection system  107 . In one embodiment, the radiation source  106  may comprise a laser produced plasma  106   a  and a collection mirror  106   b . In one embodiment, the radiation system  101  may be configured to generate extreme ultraviolet (EUV) radiation with a wavelength in the range of 5 nm to 20 nm. 
     The radiation system  101  is configured to project a beam of radiation  108  towards the lithography apparatus  102  for a lithographic process. 
     The lithography apparatus  102  comprises a body  103  defining an inner volume  104 . During process, the inner volume  104  may be vacuumed using a pumping system  105  as processing in a vacuum state is a typical method to prevent particle contamination. The lithography apparatus  102  further comprises a mask station  110 , a projection system  119 , a substrate stage  116 , and a particle removal station  120 , which are disposed in the inner volume  104 . 
     The mask station  110  is configured to precisely position a mask  113  which is configured to receive and reflect the beam of radiation  108  to the projection system  119 . The mask  113  has a pattern formed thereon and the pattern is reflected in the beam of radiation  108  reflected from the mask  113 . The projection system  119  is configured to project the beam of radiation  108  and convey the pattern to a substrate  118  positioned on the substrate stage  116  which is configured to precisely position the substrate  118 . The particle removal station  120  is disposed on a path of the beam of radiation  108  and configured to remove any debris particles travelling with the beam of radiation  108 . In one embodiment, the particle removal station  120  is positioned near the mask station  110  intersecting the input and output path of the beam of radiation  108  to and from the mask  113 . 
     The mask station  110  generally comprises a chamber body  111  having a shutter opening  114  configured to transmit the beam of radiation  108  during processing. The mask  113  is positioned on a mask stage  112  which is configured to precisely position the mask  113  to align with the beam of radiation  108  and the projection system  119 . In case of EUV lithography, the mask  113  is directly exposed to the beam of radiation  108  and the ambient of the inner volume  104  without any protection because all materials are opaque to EUV wavelength. However, an optional shutter may be disposed in the shutter opening  114  and be closed while not processing. 
     The mask station  110  may further comprise a mask transfer mechanism  125  configure to transfer the mask  113  to and from a mask storage  126 , where different masks may stored in a sealed condition. 
     The projection system  119  generally comprises a plurality of mirrors  115  configured to reflect the beam of radiation  108  towards the substrate  118 . The projection system  119  may comprise up to 11 mirrors. The projection system  119  may comprise a projecting column (not shown) configured to project the beam of radiation  108  from the plurality of mirrors  115  to the substrate  118  at a desired ratio and a desired location. 
     The substrate stage  116  generally comprises a substrate support  117  which is configured to support, translate and rotate the substrate  118  to enable the beam of radiation  108  to be projected to a plurality of dies. 
     The particle removal station  120  is configured to remove any debris particles travelling within the beam of radiation  108  to protect the mask  113 , the mirrors  115  and the substrate  118 . The particle removal station  120  may be positioned anywhere in the path of the beam of radiation  108 . 
       FIG. 2  schematically illustrates an enlarged view of the particle removal station  120  of  FIG. 1 . The particle removal station  120  generally comprises a charged species source  127  and a collecting plate  122 . The charged species source  127  is connected to a power source  121  and is configured to generate a stream of charged species  124  comprising charged species  124   a . The collecting plate  122  is connected to a potential source  123  and is charged with charges opposite to the charged species  124   a . The stream of charged species  124  is attracted to and collected by the collecting plate  122  without affecting other devices, such as optics in the system, that are sensitive to electric field. 
     During processing, the particle removal station  120  may be positioned in a way such that the collecting plate  122  and the charged species source  127  are on opposite sides of the beam of radiation  108 . The stream of charged species  124  is configured to intersect the beam of radiation  108  and to “grab” debris particles  108   a  presented in the beam of radiation  108  using electrostatic force. The grabbed debris particles  108   a  then travel with the stream of charged species  124  and are collected by the collecting plate  122 . 
     The charged species  124   a  may be electrons, ions of positive or negative changes. In one embodiment, the charge species source  127  may be a corona charge generator, a thermal emitter, or an ion generator. The collecting plate may be charged at a potential between about 200 volts to about 400 volts. 
     Although only one particle removal station  120  is described in the lithography system  100 , more similar particle removal stations may be positioned in suitable positions, such as in front of any mirrors  115 , and within the radiation source  101 . 
       FIG. 3  schematically illustrates a particle removal station  200  in accordance with one embodiment of the present invention. The particles removal station  200  is configured to remove particle contaminations using electrostatic force and may be used in a lithography system, such as the particle removal station  120  in  FIG. 1 . 
     The particle removal station  200  generally comprises a charged species source assembly  201  and a collecting assembly  202 . 
     The charged species source assembly  201  comprises a plurality of electrodes  203  connected to a power source  204 . Each of the plurality of electrodes  203  is configured to discharge charged species  209   a . The charged species  209   a  may be electrons or ions of positive or negative charges. In one embodiment, the plurality of electrodes  203  may be point or line electrodes positioned in a parallel manner. In one embodiment, the plurality of electrodes  203  may form a column having a diameter  207  of about 5 mm to 20 mm. The plurality of electrodes  203  collectively generate a stream of charged species  209 . 
     The collecting assembly  202  comprises a collecting plate  205  connected to a power source  206 . The collecting plate  205  is generally a conductive plate and the power source  206  is configured to charge to collective plate  205  with charges opposite to the charges of the charged species  209   a . The collecting plate may be charged at a potential between about 200 volts to about 400 volts. In one embodiment, the collecting plate  205  may have a diameter  208  slightly larger than the diameter  207  of the electrode column of the charged species source assembly  201 . In one embodiment, the collecting plate  205  may have a diameter  208  of about 5 mm to about 20 mm. 
     The stream of charged species  209  is configured to intersect with a beam of radiation  210  and to “grab” any debris particles  210   a  travelling in the beam of radiation  210  using electrostatic force. The grabbed debris particles  210   a  then travel with the stream of charged species  209  and are collected by the collecting plate  205 . 
     Even though only lithography process is described in accordance with the present invention, embodiments of the present invention may be applied to any suitable process and in any suitable processing tools that requires removal of particle contamination in a path of energy or fluid transmission. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.