Abstract:
A particle beam system having a beam source for generating a particle beam and a vacuum air bearing. The beam source is mounted to a first side of the vacuum air bearing, with an active side of the vacuum air bearing disposed on an opposing second side of the vacuum air bearing. The active side is adapted to receive and retain a substrate. A beam port is formed completely through the vacuum air bearing from the first side to the second side. Means are provided for moving the substrate across the second side of the vacuum air bearing and positioning the substrate under the beam port. Means are also provided for sealing an interior of the beam source from exposure to atmosphere through the beam port.

Description:
FIELD 
   This invention relates to the field of substrate handling. More particularly, this invention relates to presenting a substrate for inspection by a system, such as a charged particle beam inspection system, without the use of a vacuum chamber that encloses the substrate on a stage. 
   BACKGROUND 
   Particle beam systems, such as scanning electron microscopes, are typically used during integrated circuit fabrication for a variety of purposes. Some particle beam systems are used for etching layers of material on the substrates on which the integrated circuits are formed, others are used for depositing material onto the surface of the substrate, and others still—such as scanning electron microscopes—are used for inspection of the integrated circuits. 
   Particle beam systems typically operate by accelerating a charged species, such as an electron, positron, or proton, toward a target of some sort. In the example of an electron microscope, electrons are accelerated toward an inspection sample, and detection of the resultant scattering of secondary electrons is used to resolve images of the sample, or to determine the chemical composition of the sample. 
   Particle beam systems make use of a low pressure, or high vacuum, area that is formed around the sample. The high vacuum area is typically formed within a chamber that encompasses both the sample itself, and a movable stage upon which the sample resides. The high vacuum environment is important for the proper operation of the particle beam system. Further, the ability to move the sample, such as on the movable stage, also tends to be important to the convenient operation of the system. 
   However, providing a vacuum chamber of a sufficient size to contain the entire sample and movable stage adds cost, complexity, and size to the particle beam system. 
   What is needed, therefore, is a system that overcomes problems such as those described above, at least in part. 
   SUMMARY 
   The above and other needs are met by a particle beam system having a beam source for generating a particle beam and a vacuum air bearing. The beam source is mounted to a first side of the vacuum air bearing, with an active side of the vacuum air bearing disposed on an opposing second side of the vacuum air bearing. The active side is adapted to receive and retain a substrate. A beam port is formed completely through the vacuum air bearing from the first side to the second side. Means are provided for moving the substrate across the second side of the vacuum air bearing and positioning the substrate under the beam port. Means are also provided for sealing an interior of the beam source from exposure to atmosphere through the beam port. 
   In various embodiments, the particle beam system is a scanning electron microscope. The substrate may be a semiconductor wafer. In various embodiments, the means for moving the substrate includes at least one of a rotary chuck, a linear slide, a rotary chuck connected to a linear slide, and a controller for applying differential vacuum and gas flows to the vacuum air bearing in a manner to selectively cause at least one of rotation and translation of the substrate. The means for sealing variously includes at least one of a gate valve mounted inside of the beam port, a seal plate disposed on the second side of the vacuum air bearing, and the substrate. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein: 
       FIG. 1  is a bottom perspective view of a system according to an embodiment of the present invention. 
       FIG. 2  is a side cross sectional view of a vacuum air bearing and substrate according to an embodiment of the present invention. 
       FIG. 3  is a bottom plan view of a substrate handling system in a first position according to an embodiment of the present invention. 
       FIG. 4  is a side cross sectional view of a substrate handling system in a first position according to an embodiment of the present invention. 
       FIG. 5  is a bottom plan view of a substrate handling system in a second position according to an embodiment of the present invention. 
       FIG. 6  is a side cross sectional view of a substrate handling system in a second position according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   With reference now to  FIG. 1 , there is depicted a simplified bottom perspective view of a system  10  according to one embodiment of the present invention. The system  10  of this embodiment includes a beam source or column  12 , such as which emits a particle beam—for example, an electron beam, such as might be used in a scanning electron microscope. The system also includes a substrate handling system, including a vacuum air bearing  14 , which is used as described in more detail below. A beam port  16  is provided so that the particle beam from the beam source  12  can contact the sample. In some embodiments, a gate valve or other means (not depicted) is placed just inside the beam port  16 , so as to isolate the beam source  12  from the atmosphere. This may be useful when other methods of doing so are not provided. 
     FIG. 2  provides additional detail in regard to the vacuum air bearing  14 . The vacuum air bearing  14  operates by simultaneously drawing a vacuum in the direction indicated through relatively larger channels  18  and providing a gas flow  20  through relatively smaller channels (not depicted) in the opposite direction. The net effect is to create a thin gas buffer  22  having properties such that the substrate  24  is retained in proximity to the vacuum air bearing  14 , but is not held in direct physical contact with the vacuum air bearing  14 . 
   The gas flow  20  may be of air or of some other gas, such as nitrogen or argon, or of a mixture of such The channels through which the gas flow  20  are provided are, in some embodiments, machined channels or channels that are otherwise manufactured with a specified pattern. However, in other embodiments, the channels are formed by the porosity of the material from which the vacuum air bearing  14  is fabricated. By adjusting the relative flows of the vacuum in channels  18  and the gas flow  20 , the size of the gas buffer  22  and even the movement of the substrate  24  across the surface of the vacuum air bearing  14  can be adjusted. 
   With reference now to  FIGS. 3 and 4 , another embodiment of the system  10  is depicted, which includes additional substrate handling elements. In this embodiment, the substrate  24  is delivered to the system  10  such as by a robot or other substrate  24  handler (not depicted). The substrate  24  is delivered to the system with the working face of the substrate  24  disposed against the vacuum air bearing  14 . For example, if the system  10  is a scanning electron microscope, then the face of the substrate  24  that is to be inspected is placed toward the vacuum air bearing  14 . 
   A linear slide  26  is also provided, which provides for linear movement of various elements of the system  10  in this embodiment. For example, a rotary chuck  28  may be attached to the linear slide  26 . The rotary chuck  28  engages the open face of the substrate  24 , and provides one means for the rotary alignment of the substrate  24 . The linear slide  26  can then move the substrate  24  along the path of the linear slide  26 , as the substrate  24  is retained by the rotary chuck  28 , such as by vacuum, electrostatic, or other means. 
   A seal plate  30  may also be attached to the linear slide  26  in some embodiments, such that the seal plate  30  can be moved over the beam port  16 , and selectively moved away from the beam port  16 . In this manner, the seal plate  30  can provide a means for isolating the beam source  12  from atmosphere, which in some embodiments obviates the need for the gate or other valve mentioned above. In one embodiment, the seal plate  30  has an edge  32  that is shaped to receive the substrate  24  with a relatively high degree of precision, such that a very small gap can be maintained between the edge of the substrate  24  and the edge  32  of the seal plate  30 . In one embodiment, this gap is no more than about a thousandth of an inch in all places. In some embodiments, the seal plate  30  is also supported by the vacuum air bearing  14 , in the same manner as that described above in regard to the substrate  24 . 
     FIGS. 5 and 6  depict the system  10 , where the substrate  24  has been slid over, such as by the linear slide  26 , to where it either contacts the seal plate  30 , or comes in such close proximity to the seal plate  30  as to form the gap as described above. With the substrate  24  and the seal plate  30  in such contact or proximity, they are then both moved together, while the contact or proximity is maintained, so that the substrate  24  is disposed under the beam port  16 . By moving the substrate  24  under the beam port  16  in this manner, only a relatively slight additional and brief load is placed on the vacuum environment that is preferably maintained within the beam source  12 . 
   Further, the vacuum air bearing  14  forms a seal against the substrate  24 , such that the substrate  24  itself provides the functions of a gate valve or the seal plate  30  during the time that it is placed over the beam port  16 . Because of the vacuum drawn against the substrate  24  within the beam source  12 , the size of the beam port  16  is preferably determined based at least in part on limiting the air pressure force that is applied to the substrate  24 , so that the substrate  24  is not damaged or warped to too great a degree. 
   The substrate  24  can be rotated and translated, such as by the rotary chuck  28  and the linear slide  26 , such that any desired portion of the substrate  24  can be placed under at least a portion of the beam port  16 , and the particle beam can access a desired location on the substrate  24 . If it is desired to move an edge of the substrate  24  to a center portion of the beam port  16 , such that the substrate  24  does not cover all of the beam port  16 , then in one embodiment the seal plate  16  is moved with the substrate  24 , such that both of the substrate  24  and the seal plate  16  are used to maintain the vacuum within the beam source  12 . Most preferably, in such an embodiment, the gap between the substrate  24  and the edge  32  of the seal plate  30  is sufficiently small, and the capacity of the pump that is maintaining the vacuum in the beam source  12  is sufficiently large, that the desired level of vacuum within the beam source  12  can be maintained. 
   In some embodiments, some of the elements of the system  10 , such as the linear slide  26  and the rotary chuck  28 , are not provided. In these embodiments, the flows of the gas  20  and the vacuum in the channels  18  are differentially adjusted in different parts of the vacuum air bearing  14  such that the differential flows induce either rotation or translation of one or both of the substrate  24  and the seal plate  32 . A controller  34  preferably controls the functions of the system  10  as generally described herein. 
   The foregoing description of preferred embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide the best illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.