Methods and apparatuses for applying wafer-alignment marks

Abstract

Embodiments of the invention provide methods and apparatuses for efficient and cost-effective imaging of alignment marks. For one embodiment, alignment mark imaging is accomplished separately from, and independent of product imaging through use of a relatively low cost, low resolution, imaging tool. For one embodiment a wafer is exposed to low-resolution light source through a reticle having a number of alignment patterns corresponding to desired alignment marks. For one embodiment, global alignment marks are imaged on a backside of a wafer. Various embodiments of the invention obviate the need for a highly accurate stage and a high-resolution imaging device, and therefore reduce processing costs and processing time.

1 . A method comprising; 
 depositing a layer of photoresist upon a wafer, the wafer having an orientation indicator;    placing the wafer in a desired position, the desired position determined by the orientation indicator; and    imaging alignment marks on the wafer by exposing the photoresist with a light source directed through a plurality of alignment mark patterns formed within a reticle unit.    
   
   
       2 . The method of  claim 1  wherein the reticle unit is a single reticle.  
   
   
       3 . The method of  claim 2  wherein the light source is a broadband light source.  
   
   
       4 . The method of  claim 2  wherein the alignment mark patterns are positioned on the reticle unit within 5 nm of a desired position.  
   
   
       5 . The method of  claim 2  wherein the reticle is a quartz wafer.  
   
   
       6 . The method of  claim 2  wherein the light source has a uniformity based upon a resolution required to image the alignment marks.  
   
   
       7 . The method of  claim 6  wherein the resolution required to image the desired alignment mark is approximately 8 μm.  
   
   
       8 . A method comprising: 
 determining a position for each of two or more alignment marks; and    creating a reticle having two or more alignment mark patterns formed thereon, each alignment mark pattern formed on the reticle in a position corresponding to a determined position for an alignment mark.    
   
   
       9 . The method of  claim 8  further comprising: 
 measuring the position of the alignment mark patterns to determine a reticle offset.    
   
   
       10 . The method of  claim 9  wherein the reticle offset is less than 5 nm.  
   
   
       11 . The method of  claim 10  wherein the reticle is quartz wafer having a chrome layer deposited thereon, and wherein the alignment mark patterns are formed by etching the chrome layer.  
   
   
       12 . A method comprising: 
 polishing a front side of a wafer and a backside of the wafer;    applying a protective layer to both the front side of the wafer and the backside of the wafer;    depositing a photoresist layer on the back side of the wafer; and    imaging alignment marks on the backside of the wafer using a reduction lithography process.    
   
   
       13 . The method of  claim 12  further comprising: 
 stripping the photoresist from the backside of the wafer;    stripping the protective layer from both the front side of the wafer and the back side of the wafer; and    imaging products on the front side of the wafer.    
   
   
       14 . The method of  claim 12  wherein the protective layer comprises an oxide layer.  
   
   
       15 . The method of  claim 12  wherein imaging alignment marks on the back side of the wafer is accomplished using an apparatus including a reticle unit having formed thereon two or more alignment mark patterns corresponding to a desired alignment mark, a light source capable transmitting light through the alignment mark patterns of the reticle, and two or more objectives each objective positioned to receive light transmitted through one of the alignment mark patterns, each objective having an effective imaging area approximately equal to the area of the desired alignment mark.  
   
   
       16 . The method of  claim 15  wherein the reticle unit is a single reticle.  
   
   
       17 . The method of  claim 16  wherein the effective imaging area of each objective is less than 1 mm 2 .  
   
   
       18 . The method of  claim 17  wherein the light source is a broadband light source.  
   
   
       19 . The method of  claim 16  wherein the light source includes a plurality of distinct light sources each corresponding to one of the objectives.  
   
   
       20 . The method of  claim 15  wherein the alignment mark patterns are positioned on the reticle unit within 5 nm of a desired position.  
   
   
       21 . The method of  claim 19  wherein light from each of the distinct light sources is transmitted to a corresponding objective via an optic fiber.  
   
   
       22 . The method of  claim 16  wherein the reticle is a quartz wafer.  
   
   
       23 . The method of  claim 16  wherein the light source has a uniformity based upon a resolution required to image the desired alignment mark.  
   
   
       24 . The method of  claim 23  wherein the resolution required to image the desired alignment mark is approximately 8 μm.