Methods for forming backside alignment markers useable in semiconductor lithography

Abstract

Disclosed herein are methods for forming photolithography alignment markers on the back side of a substrate, such as a crystalline silicon substrate used in the manufacture of semiconductor integrated circuits. According to the disclosed techniques, laser radiation is used to remove the material (e.g., silicon) from the back side of a substrate to form the back side alignment markers at specified areas. Such removal can comprise the use of laser ablation or laser-assisted etching. The substrate is placed on a motor-controlled substrate holding mechanism in a laser removal chamber, and the areas are automatically moved underneath the laser radiation to removal the material. The substrate holding mechanism can comprise a standard chuck (in which case use of a protective layer on the front side of the substrate is preferred), or a substrate clamping assembly which suspends the substrate at its edges (in which case the protective layer is not necessary). Alternatively, a stencil having holes corresponding to the shape of the back side alignment markers can be placed over the back side of the substrate to mitigate the need to move the substrate to the areas with precision.

1 . A laser removal tool, comprising: 
 a laser for producing radiation impingent on a substrate, wherein the impingent radiation removes material from a substrate; and    a moveable assembly for suspending the substrate in the tool such that the substrate does not substantially come into contact with a work surface.    
   
   
       2 . The tool of  claim 1 , wherein the impingent radiation removes the material by ablation.  
   
   
       3 . The tool of  claim 1 , wherein tool further comprises an input port for an etchant gas, and wherein the impingent radiation interacts with the etchant gas to remove the material.  
   
   
       4 . The tool of  claim 1 , further comprising motors to rotate the suspended substrate around a horizontal axis.  
   
   
       5 . The tool of  claim 1 , wherein the moveable assembly comprises clamps, and wherein the substrate is suspended in the tool using the clamps.  
   
   
       6 . A laser removal tool, comprising: 
 a moveable chuck for holding a substrate, wherein a back side of the substrate contacts the chuck; and    at least one laser for producing radiation impingent on the back side of the substrate, wherein the impingent radiation removes material from the back side of the substrate.    
   
   
       7 . The tool of  claim 1 , wherein the impingent radiation removes the material by ablation.  
   
   
       8 . The tool of  claim 1 , wherein tool further comprises an input port for an etchant gas, and wherein the impingent radiation interacts with the etchant gas to remove the material.  
   
   
       9 . The tool of  claim 1 , wherein the chuck comprises at least one optical channels through which the radiation impinges on the back side of the substrate.  
   
   
       10 . The tool of  claim 1 , wherein the laser is proximate to the front side of the substrate.  
   
   
       11 . The tool of  claim 1 , wherein the laser is proximate to a back side of the substrate.