Abstract:
A substrate labeling system comprises a first laser assembly having a first laser and a first lens, a second laser assembly having a second laser and a second lens, and a controller for directing the first laser and the second laser incident on a portion of a subsurface of a substrate to mark the substrate without generating particle defects on a surface of the substrate.

Description:
BACKGROUND  
       [0001]     Photolithography is a process used in semiconductor device fabrication to transfer a pattern from a mask to the surface of a wafer or substrate. One type of mask is an extreme ultraviolet mask (EUV) for use with EUV lithography. Mask substrates, mask blanks, and finished patterned masks are subject to stringent defect specifications. These defect specifications are outlined in the Semiconductor Equipment and Materials International (SEMI) standards document SEMI P37-1102 and SEMI P38-1103, which call for 0.003 defects/cm 2  for the 45 nm node by the year 2009. Therefore, all processing steps, from the substrate level to a finished mask, have to generate as few defects as possible.  
         [0002]     For tracking masks in an automated manufacturing environment, masks have to carry a permanent identification label that allows tracing a specific mask throughout its useful lifetime. Typically, these labels are applied to the surface of the mask substrate and destroy parts of that substrate surface. By destroying parts of the substrate surface, particle defects are generated.  
       SUMMARY  
       [0003]     One embodiment of the present invention provides a substrate labeling system. The substrate labeling system comprises a first laser assembly having a first laser and a first lens, a second laser assembly having a second laser and a second lens, and a controller for directing the first laser and the second laser incident on a portion of a subsurface of a substrate to mark the substrate without generating particle defects on a surface of the substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     Embodiments of the invention are better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.  
         [0005]      FIG. 1  is a schematic diagram illustrating one embodiment of a mask substrate labeling system.  
         [0006]      FIG. 2  is a schematic diagram illustrating one embodiment of a mask substrate labeling system for generating subsurface barcodes.  
         [0007]      FIG. 3  is a schematic diagram illustrating one embodiment of a mask substrate labeling system for generating subsurface dot codes.  
         [0008]      FIG. 4  is a schematic diagram illustrating one embodiment of a mask substrate labeling system for generating pit features or bump features.  
         [0009]      FIG. 5  is a diagram illustrating one embodiment of generating a pit feature or a bump feature.  
         [0010]      FIG. 6A  is a diagram illustrating one embodiment of a pit feature.  
         [0011]      FIG. 6B  is a diagram illustrating one embodiment of a bump feature.  
         [0012]      FIG. 7  is a side view of one embodiment of an optical mask having a subsurface label.  
         [0013]      FIG. 8  is a side view of one embodiment of an extreme ultraviolet (EUV) mask having a subsurface label.  
         [0014]      FIG. 9  is a cross-sectional side view of one embodiment of an EUV mask having a label formed from pit features.  
         [0015]      FIG. 10  is cross-sectional side view of one embodiment of an EUV mask having a label formed from bump features. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 1  is a schematic diagram illustrating one embodiment of a mask substrate labeling system  100 A. Mask substrate labeling system  100 A operates to generate marks on mask substrates or on the subsurface of mask substrates without generating particle defects on the surface of the mask substrates. In one embodiment, the marks are used as unique identifiers for labeling masks. The marks can be read by label readers to enable tracking the masks in an automated manufacturing environment.  
         [0017]     In one embodiment, mask substrate labeling system  100 A includes a controller  102 , laser A assembly  114 , laser B assembly  106 , and positioning stage  136 . Laser A assembly  114  includes laser A  116  and lens  118 . Laser B assembly  106  includes laser B  108  and lens  110 . Controller  102  is electrically coupled to laser B assembly  106  through communication link  104 , laser A assembly  114  through communication link  112 , and positioning stage  136  through communication link  134 . Substrate  124  is positioned on positioning stage  136 . Substrate  124  includes a portion  126  where substrate  124  is labeled by laser assembly A  114  and laser assembly B  106 .  
         [0018]     In one embodiment, substrate  124  is a substrate for a mask used in lithography. For example, in one embodiment, substrate  124  is a substrate for a mask for extreme ultraviolet (EUV) lithography. In one form of the invention, substrate  124  comprises a transparent material. In one embodiment, substrate  124  is a near zero thermal expansion material, such as titania doped silica glass or two phase glass ceramics. In other embodiments, substrate  124  is another suitable material.  
         [0019]     Portion  126  of substrate  124  is beneath the surface of substrate  124 . In one embodiment, parts of portion  126  are melted to produces pit features or bump features on the surface of substrate  124  without generating defects on the surface of substrate  124 . In another embodiment, parts of portion  126  are marked to form a barcode or dot code beneath the surface of substrate  124  without generating defects on the surface of substrate  124 .  
         [0020]     Laser A  116  and laser B  108  are CO 2  lasers, ruby lasers, excimer lasers, or other suitable lasers. Laser A  116  is focused on portion  126  through lens  118  and laser B  108  is focused on portion  126  through lens  110 . Lens  118  is a cylindrical lens, convex lens, or other suitable lens, and lens  110  is a cylindrical lens, convex lens, or other suitable lens. Separately, the power densities of laser A  116  and laser B  108  are less than the power density required to damage substrate  124 . Combined, however, when focused on a common location in substrate  124 , the combined power densities of laser A  116  and laser B  108  have a magnitude greater than or equal to the power density required to damage substrate  124 . Therefore, by selectively focusing laser A  116  and laser B  108  on common locations in substrate  124 , substrate  124  is damaged or marked to generate a label in portion  126 .  
         [0021]     Positioning stage  136  moves substrate  124  relative to laser A assembly  114  and laser B assembly  106  in the X  128 , Y  130 , and Z  132  directions. In other embodiments, substrate  124  remains stationary while laser A assembly  114  and laser B assembly  106  are moved relative to substrate  124 .  
         [0022]     Controller  102  controls laser assembly A  114  through communication link  112 , laser assembly B  106  through communication link  104 , and positioning stage  136  though communication link  134  to generate a label in portion  126  of substrate  124 . In one embodiment, controller  102  controls the pulse durations of laser A  116  and laser B  108 . Controller  102 , in one embodiment, adjusts the position of positioning stage  136  in the X  128 , Y  130 , and Z  132  directions to focus laser A  116  and laser B  108  on parts of portion  126  for generating a label.  
         [0023]     In operation, laser A  116  provides a laser beam to lens  118 , which focuses the laser beam, indicated at  122 , on a part of portion  126  of substrate  124 . Laser B  108  provides a laser beam to lens  110 , which focuses the laser beam, indicated at  120 , on the same part of portion  126 . With the combined power density of both laser A  116  and laser B  108  focused on the same part of portion  126 , the damage threshold of the material of substrate  124  is exceeded, and the material is damaged at the focus point.  
         [0024]     In one embodiment, the damage at the focus point is a visible defect with thin hair like damage extending a short distance along the laser beam from the point defect. This damage leaves a permanent mark in the substrate. In another embodiment, the material is melted, and depending upon the ambient atmosphere and gas pressure, a pit feature or bump feature is generated on the surface of substrate  124  directly above the focus point.  
         [0025]      FIG. 2  is a schematic diagram illustrating one embodiment of a mask substrate labeling system  100 B for generating barcodes in the subsurface of substrate  124  without generating particle defects on the surface of substrate  124 . For mask substrate labeling system  100 B, lens  110  is a cylindrical lens, and lens  118  is a cylindrical lens. Laser B  108  ( FIG. 1 ) provides a laser beam to lens  110 , which line focuses the laser beam, indicated at  120 , on part of portion  126 . Laser A  116  ( FIG. 1 ) provides a laser beam to lens  118 , which line focuses the laser beam, indicated at  122 , on the same part of portion  126 .  
         [0026]     With the line focus of beam  120  and the line focus of beam  122  combined at the same location in portion  126 , the damage threshold for the material of substrate  124  is exceeded and a bar like feature or mark is formed in substrate  124 . By moving substrate  124  in the X  128 , Y  130 , and/or Z  132  direction to another position relative to laser A assembly  114  ( FIG. 1 ) and laser B assembly  106  ( FIG. 1 ), additional bars are written to generate a barcode in portion  126 . Laser intensities and focusing lenses are selected to produce bars of specific sizes. The barcode is created without generating particle defects on the surface of substrate  124 .  
         [0027]      FIG. 3  is a schematic diagram illustrating one embodiment of a mask labeling system  100 C for generating a dot code in the subsurface of substrate  124  without generating particle defects on the surface of substrate  124 . For mask substrate labeling system  100 C, lens  110  is a cylindrical lens, and lens  118  is a convex lens. Laser B  108  ( FIG. 1 ) provides a laser beam to lens  110 , which line focuses the laser beam, indicated at  120 , on part of portion  126 . Laser A  116  ( FIG. 1 ) provides a laser beam to lens  118 , which point focuses the laser beam, indicated at  122 , on the same part of portion  126 .  
         [0028]     With the line focus of beam  120  and the point focus of beam  122  combined at the same location in portion  126 , a dot like feature or mark is formed in substrate  124  at the intersection of the line focus and the point focus. By moving substrate  124  in the X  128 , Y  130 , and/or Z  132  direction to a new position relative to laser A assembly  114  ( FIG. 1 ) and laser B assembly  106  ( FIG. 1 ), additional dot like features are written to generate a dot code in portion  126 . For example, if substrate  124  is moved in the X  128  direction, laser A  116  ( FIG. 1 ) can produce marks along the length of the line focus from laser B  108  ( FIG. 1 ). Laser intensities and focusing lenses are selected to produce dots of specific sizes. In one embodiment, the dot code is a data matrix. In other embodiments, the dot code can be configured to be alphanumeric characters, symbols, or one or more other images. The dot code is created without generating particle defects on the surface of substrate  124 . In other embodiments, the lasers can be configured to produce alphanumeric characters, symbols, or one or more other images.  
         [0029]      FIG. 4  is a diagram illustrating one embodiment of a mask substrate labeling system  100 D for generating pit features or bump features on the surface of substrate  124  without generating particle defects on the surface of substrate  124 . For mask substrate labeling system  100 D, lens  110  is a cylindrical lens, and lens  118  is a convex lens. Laser B  108  ( FIG. 1 ) provides a laser beam to lens  110 , which line focuses the laser beam, indicated at  120 , on part of portion  126 . Laser A  116  ( FIG. 1 ) provides a laser beam to lens  118 , which point focuses the laser beam, indicated at  122 , on the same part of portion  126 .  
         [0030]     With the line focus of beam  120  and the point focus of beam  122  combined at the same location in portion  126 , the location in portion  126  is melted. As illustrated in  FIG. 5 , lens  110  provides a line focus  139  and lens  118  provides a point focus  140 . At point  140 , the material of substrate  124  becomes molten. The laser intensity and impulse duration is selected such that the material is slowly molten from behind the surface of substrate  124 .  
         [0031]     The volume where the substrate is made molten has a different density than the surrounding undamaged substrate material and a pit feature as illustrated in  FIG. 6A  at  142  is generated. The relative power of the beams  120  and  122  and the focal length of cylindrical lens  110  are selected such that the temperature gradients around the volume to be molten are low enough so that surface ablation due to thermal stress does not occur. In another embodiment, in a suitable ambient atmosphere and gas pressure (e.g., inert gas atmosphere, high pressure), a bump like surface feature as illustrated in  FIG. 6B  at  144  is generated using this subsurface melting method. By moving substrate  124  in the X  128 , Y  130 , and/or Z  132  direction to a new position relative to laser A assembly  114  ( FIG. 1 ) and laser B assembly  106  ( FIG. 1 ), additional pit features or bump features are written to generate a pit code or bump code, respectively, on the surface of substrate  124 .  
         [0032]     In one embodiment, if the pit features or bump features are generated in a suitable size, they are visible after substrate  124  is coated with another material, such as an EUV multilayer, and can therefore be registered even after coating. By choosing a suitable area at the rim of substrate  124  (i.e., outside the mask quality area as specified in SEMI P37-1102), and etching away absorber material deposited on top of this area during the mask patterning procedure, the labels (pit features or bump features) will be traceable as mask identifiers throughout the entire EUV mask lifetime.  
         [0033]      FIG. 7  is a side view of one embodiment of an optical mask  150 A. Optical mask  150 A includes substrate  124 , subsurface label  154 , and film layer  152 . Portions of film layer  152  can be etched away to generate a patterned optical mask to transmit light through substrate  124  in optical lithography. Subsurface label  154  is a barcode or dot code that permanently identifies mask  150 A without generating particle defects on the surface of substrate  124 . Depending on the orientation of subsurface label  154  and the etching of film layer  152 , subsurface label  154  is visible from the side, top, and/or bottom of substrate  124 .  
         [0034]      FIG. 8  is a side view of one embodiment of an EUV mask  150 B. EUV mask  150 B includes substrate  124 , subsurface label  154 , multilayer reflection layer  156 , and conductive or absorption layer  158 . Portions of conductive or absorption layer  158  can be etched away to generate a patterned EUV mask to reflect light from the multilayer reflection layer  156  in EUV lithography. Subsurface label  154  is a barcode or dot code that permanently identifies mask  150 B without generating particle defects on the surface of substrate  124 . Depending on the orientation of subsurface label  154  and the etching of conductive or absorption layer  158 , subsurface label  154  is visible from the side, top, and/or bottom of substrate  124 .  
         [0035]      FIG. 9  is a cross-sectional side view of one embodiment of an EUV mask  150 C. EUV mask  150 C includes substrate  124 , multilayer reflection layer  156 , conductive or absorption layer  158 , and a label  160 A formed from pit features. Portions of conductive or absorption layer  158  are etched away to expose label  160 A, which is visible in multilayer reflection layer  156 . Other portions of conductive or absorption layer  158  can be etched away to generate a patterned EUV mask to reflect light from the multilayer reflection layer  156  in EUV lithography. Label  160 A permanently identifies mask  150 C without generating particle defects on the surface of substrate  124 .  
         [0036]      FIG. 10  is a cross-sectional side view of one embodiment of an EUV mask  150 D. EUV mask  150 D includes substrate  124 , multilayer reflection layer  156 , conductive or absorption layer  158 , and a label  160 B formed from bump features. Portions of conductive or absorption layer  158  are etched away to expose label  160 B, which is visible in multilayer reflection layer  156 . Other portions of conductive or absorption layer  158  can be etched away to generate a patterned EUV mask to reflect light from the multilayer reflection layer  156  in EUV lithography. Label  160 B permanently identifies mask  150 D without generating particle defects on the surface of substrate  124 .