Abstract:
An electrostatic chuck structure for holding an article is presented. The chuck structure comprises an electrically insulating chuck body layer having a first flat surface for holding the article thereon, and a second opposite surface having a honeycombed pattern in the form of an array of spaced-apart grooves. This second patterned surface of th4e chuck body surface for depositing thereon an electrically conductive layer (electrodes). A dielectric spacer between the electrodes and the article on the chuck body layer is defined by a portion of the chuck body layer between the grooves&#39; bottom and the flat surface.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of U.S. Provisional Patent Application 60/656,324, filed 24 Feb. 2005, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to an electrostatic chuck, particularly useful for holding semiconductor wafers. 
       BACKGROUND OF THE INVENTION 
       [0003]    Chucks are used for holding substrates in process chambers, and are generally of three types: mechanical, vacuum, and electrostatic chucks. Electrostatic chuck is a mechanism for holding a substrate (wafer) using electrostatic attraction forces used in vacuum chambers. Through the generation of an electric field between wafer and supporting chuck, an attractive force is exerted on the wafer. The force is distributed homogenously over the surface, can be switched on/off and adjusted electrically. It ensures flat wafer adherence to the support as well as good thermal contact. 
         [0004]      FIG. 1A  illustrates the basic design of a conventional electrostatic chuck  10 . It includes a three-layer structure formed by a chuck body. (or substrate)  12  made of a dielectric material (typically Ceramics), carrying an electrically conductive layer  14  containing an electrode arrangement defining one or two pairs of electrodes (not shown), and a top dielectric layer  16  (any dielectric material can be used, such as ceramics, plastics, etc, and even vacuum). Structure  10  closely resembles that of a parallel plate capacitor generating an electrostatic force that enables to flat silicon wafer structure W. Also, high acceleration motion systems can be used for wafer navigation. By applying a voltage between the two electrode plates, the wafer is attracted to the chuck. The generated electrostatic force is also affected by the thickness of dielectric film  16 , the relative dielectric constant of the film material, as well as the chuck area. This is expressed by the following relation: 
         [0000]    
       
         
           
             
               
                 
                   F 
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                         A 
                         · 
                         
                           ɛ 
                           0 
                         
                         · 
                         
                           ɛ 
                           R 
                           2 
                         
                       
                       2 
                     
                     · 
                     
                       
                         [ 
                         
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                           d 
                         
                         ] 
                       
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   1 
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         [0000]    wherein F is the chucking force [N], A is the effective chucking area [m 2 ]; ε 0  is 8.85 e-12 F/m—absolute permittivity of vacuum; ε R  is the dielectric constant of the chosen material; V is the potential difference between the electrode and the substrate [Volts]; and d is the thickness of the upper dielectric layer. 
         [0005]      FIG. 1B  shows the typical process of manufacturing such a conventional chuck structure  10 . The main structure (chuck body)  12  is prepared. Thin conductive layer  14  is deposited on top of structure  12 . A planarization process (mechanical lapping) is applied to layer  14  to flat the top surface thereof. Then, thin dielectric layer  16  is deposited on top of conductive layer  14  and a further mechanical lapping is applied to layer  16  for lapping and polishing its top surface. 
         [0006]    Conventional chucks can also be appropriately designed to support wafers of different diameters. To this end, the electrically conductive layer is appropriately patterned to define different electrode pairs. 
       SUMMARY OF THE INVENTION 
       [0007]    There is a need in the art to facilitate the electrostatic chuck design and manufacture, so as to reduce the manufacturing costs and also to simplify the chuck construction, as well as its adjustment to different wafer sizes. 
         [0008]    The main idea of the present invention consists in providing a novel electrostatic chuck which is made of two layers only. Thus chuck can be manufactured by three manufacturing steps. 
         [0009]    This is implemented by providing a patterned chuck body layer, where the pattern is in the form of an array of spaced-apart grooves (which may for example be of a circular or oval cross section). Such a chuck body layer serves for carrying both the electrode arrangement on its patterned surface and an article (wafer) on its opposite flat surface. The patterned chuck body layer can be produced by conventional machining or CNC-based technique, as well as by molding/casting technique. An electrically conductive layer can be deposited onto the patterned surface of the chuck body layer (for example by thermal spraying to cover the inner surface of the grooves and spaces between the grooves within at least two spaced-apart continuous surface regions of the patterned surface to define at least one pair of electrodes. The other surface of the chuck body layer is made flat by applying lapping and polishing. Hence, according to the invention, the same chuck body layer is used for carrying the electrodes containing layer and the article under processing. The manufacture of such a chuck is simpler and cheaper than the convention technique. 
         [0010]    There is thus provided according to one broad aspect of the invention, a chuck body structure for use in an electrostatic chuck for holding an article under processing, the chuck body structure comprising an electrically insulating layer having a first flat surface for holding the article thereon and a second opposite surface having a pattern in the form of an array of spaced-apart grooves for carrying an electrically conductive layer thereon. 
         [0011]    According to another broad aspect of the invention, there is provided an electrostatic chuck structure for holding an article, the chuck structure comprising: an electrically insulating substrate layer having a first flat surface for holding the article thereon and a second opposite surface having a pattern in the form of an array of spaced-apart grooves; and an electrode arrangement containing layer within at least some of the spaced-apart grooves and the spaces between the grooves. 
         [0012]    The substrate layer (chuck body layer) can be made of any sufficiently rigid dielectric material, for example ceramic alumina or any other type of ceramics, or plastic material. 
         [0013]    It is typical in the semiconductor industry to configure the electrically conductive layer to match different article dimensions. To this end, as indicated above, in the chuck of the present invention, the electrically conductive layer may be formed by at least two spaced-apart continuous layer regions defining at least one pair, respectively, of the electrode arrangement. These two spaced-apart continuous layer regions are arranged to define an area corresponding to that of the article to be supported. Preferably, the electrically conductive layer is formed by four spaced-apart continuous layer regions defining two pairs, respectively, of the electrode arrangement. The electrodes of each pair are arranged to define an area corresponding to that of the article to be supported, different from that defined by the other pair of electrodes. Such a chuck structure can be designed for holding 200 mm and 300 mm wafers. 
         [0014]    According to another broad aspect of the invention, there is provided a method of manufacturing an electrostatic chuck structure for holding an article, the method comprising producing a chuck body in the form of an electrically insulating substrate layer having a first flat surface for holding the article thereon and a second opposite surface having a pattern in the form of an array of spaced-apart grooves; thereby enabling deposition of an electrically conductive layer onto the second surface to define at least two spaced-apart electrodes, a portion of the electrically insulating substrate layer between the bottom of the grooves and said flat surface defining a dielectric spacer between the electrodes and the article held by the flat surface of the electrically insulating substrate layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
           [0016]      FIG. 1  is a schematic illustration of a convention electrostatic chuck structure; 
           [0017]      FIG. 2A  illustrates a section view of an example of an electrostatic chuck structure according to the invention; 
           [0018]      FIGS. 2A and 2B  show the bottom and top views, respectively, of an example of a chuck body (substrate) according to the invention; 
           [0019]      FIGS. 3A and 3B  illustrate an examples of the chuck structure of the invention; and 
           [0020]      FIG. 4  is a flow diagram of the main steps in a method according to the invention for manufacturing the electrostatic chuck structure. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0021]      FIG. 1A  illustrates the basic design of the conventional electrostatic chuck. Such a chuck is composed of three layers: an electrically conductive layer enclosed between a chuck body layer and an upper dielectric layer. As shown in  FIG. 1B , the manufacture of this chuck requires two deposition processes and two planarization processes; making the manufacture process too complicated and expensive. 
         [0022]    Reference is made to  FIG. 2A  showing a section view of an electrostatic chuck structure  100  according to the invention. To facilitate understanding the same reference numbers are used for identifying common chuck components in all the illustrations. 
         [0023]    Chuck structure  100  is composed of two layer materials: an electrically insulating substrate or chuck body  12  carrying an electrically conductive layer  14  in which an electrode arrangement is formed (not shown here). According to the invention, substrate  12  is configured as the so-called “honeycomb structure”, namely its surface  12 A (constituting a second surface) is patterned to form an array of grooves, generally at  18 A, arranged with spaces  18 B between them, and its opposite surface  12 B (constituting a first surface) is flat (polished) and serves for holding an article (e.g. wafer). Layer  14  is formed by an electrically conductive material located within the grooves and spaces between them. 
         [0024]    It should be understood, although not shown in the figure, that layer  14  covers at least one pair of spaced-apart regions of surface  12 A to form at least one pair of spaced-apart electrodes, and electrical contacts (pads) to electrodes are appropriately provided. More than one pair of electrodes can be formed to enable the same chuck to be used for supporting articles of different sizes (wafers of different diameters); each electrode pair defines a surface region corresponding to the respective article size. This aspect is known per se and therefore need not be specifically described, except to note that the invention provides for simplifying the electrodes creation as will be described further below. 
         [0025]      FIGS. 2B and 2C  show more specifically the bottom and top views of patterned substrate structure  12  of the present invention. The first, top surface  12 B of substrate  12  is made flat (polished) and thus serves for holding an article (not shown), while the second bottom surface is patterned. In the present example, the groove has a substantially circular cross section, but it should be understood that the invention is not limited to this specific example. 
         [0026]    Preferably, the substrate  12  thickness and the groove  18 A depth are selected to define a desired thickness of a dielectric spacer between the electrode (bottom of the groove) and the article (flat surface of the substrate). For example, the dielectric spacer thickness may be 100-300 microns; the groove depth may be 2-3 mm; the thickness of the electrode layer (e.g. aluminum powder thermal-sprayed at 700-800° C.) is about  100  microns. It should be understood that the rigidity of the entire structure might be even more increased by attaching the structure (its bottom, electrically conductive surface) to a solid body ceramics. 
         [0027]    Reference is made to  FIGS. 3A and 3B  exemplifying the bottom and top view, respectively, of a honeycomb-like chuck body layer of the present invention, configured for supporting 200 mm and 300 mm diameter wafers. 
         [0028]    Thus, according to the invention, the chuck body of the conventional electrostatic chuck structure and its upper dielectric layer are combined to form a single structural body. In other words, the chuck body and the dielectric support are constituted by the same electrically insulating layer (the same material). The conductive layer on the bottom surface of the chuck body layer is formed by electrically conductive regions inside the grooves and in between. Chuck structure  100  can thus be made lighter than the conventional one by about 30% or more. 
         [0029]    The honeycomb-like chuck structure of the present invention can be manufactured by only three steps. This is shown in  FIG. 4 . Patterned chuck body structure  12  is prepared, e.g. using a simple machining technique. Lapping and polishing is applied to its upper surface  12 B. Thin conductive layer  14  is applied on the patterned surface  12 A (e.g. by thermal spraying of aluminum powder). Preferably, the lapping and polishing is applied prior to depositing the conductive layer. 
         [0030]    This manufacturing process is simpler and cheaper than the conventional one. The chuck structure has a lower weight, while being sufficiently rigid. Applying lapping and polishing as the first manufacturing step results in the high flatness and roughness performances. Therefore, heat generated during the lapping process will not affect the conductive layer or main body. It should also be noted that in case lapping and polishing of the upper flat surface is applied after the deposition of the electrically conductive layer onto the opposite surface, the heat generation will still not affect the conductive layer, since it could expand into the free space of the groove. The manufacturing process does not provide any potential de-lamination of the dielectric layer from the conductive layer. The invention is not limited to any specific dielectric material. As indicated above, the conductive layer may be applied so as to define more than one pair of electrodes to enable the same chuck to be used for supporting articles of different sizes, e.g. 200 mm and 300 mm wafers. The method of the present invention makes this technique simpler, as well. It should also be noted that the technique of the invention provides for no glue or air between the dielectric layer and the conductive layer. 
         [0031]    The technique of the present invention provides for obtaining a required chucking force. This is associated with the following: 
         [0032]    The loss of the chucking force due to the reduction of the effective chucking area (depending on the grooves array character) can be compensated for by choosing high dielectric constant materials, reduce the thin dielectric layer “walls” or increasing the chucking voltage, as shown by the above equation (1) for the chucking force F. It should be noted, that considering the chuck structure of the invention, parameter d in eq. (1) is the thickness of the dielectric spacer between the bottom of the groove and the flat top surface of the chuck body layer. 
         [0033]    The following is the calculation of a chucking force for an exemplary honeycomb-like chuck structure with the electrodes arrangement configured for 300 mm wafer. In this example, Ceramic Alumina of 99.8% purity and dielectric constant of 10 is considered as the chuck body material; a dielectric layer thickness is 200 microns; a honeycomb array includes 1500 grooves, each of a 3 mm diameter, with the total chucking area of 0.029 m 2 ; and chucking voltage of 800V. 
         [0000]    
       
         
           
             
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                 208 
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         [0000]    or approximately 3000 Pascal chucking pressure on a 300 mm wafer. 
         [0034]    Thus, the present invention provides for a novel electrostatic chuck which has a simpler and cheaper configuration as the conventional chucks of the kind specified, while providing for generation of the required chucking force. 
         [0035]    Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore exemplified without departing form its force defined in and by the appended claims.