Semiconductor processing module with integrated feedback/feed forward metrology

Abstract

A method and apparatus for processing a semiconductor wafer to reduce CD variation feeds back information gathered during inspection of the wafer to a previously visited processing tool and feeds forward information to adjust the next process the wafer will undergo. The inspection and processing are performed at a single processing module without exposing the wafer to ambient atmospheric conditions. Embodiments include removing a wafer from a wafer cassette, and measuring a dimension of a feature on the surface of the wafer, such as the feature's CD using an optical measuring tool. A process, such as an etch process, is then performed on the wafer using a set of process parameter values, such as an etch recipe, selected based on the CD measurement, and the wafer is returned to a cassette. The CD measurements are also linked to photolithography adjustable parameters such as stepper focus and exposure settings. The linked information on focus and exposure is fed back to the previously visited photo cell so the stepper can be adjusted, either automatically or at the user's discretion, to correct the deviation in following lots. In some embodiments, post-etch processing, such as ash stripping, wet cleaning and/or further CD measurement, are performed by the module before the wafer is returned to a cassette. All of the transfer and processing steps performed by the module are performed in a clean environment, thereby increasing yield by avoiding exposing the wafer to the atmosphere and possible contamination between steps. This feedback and feed-forward mechanism improves CD control by adjusting processing parameters for every wafer based on the wafer's measured CD.

What is claimed is:  
     
         1 . An apparatus for processing a semiconductor wafer, comprising: 
 a measuring tool for measuring a dimension of a structure on the wafer;    a first processing tool for performing a first process on the wafer using a first set of process parameter values;    a transfer mechanism for transferring the wafer between the measuring tool and the first processing tool;    a chamber for enclosing the transfer mechanism and allowing communication between the transfer mechanism, the measuring tool and the first processing tool in a clean environment; and    a processor configured to select the first set of process parameter values based on the measurement of the dimension.    
     
     
         2 . The apparatus of  claim 1 , wherein the processor is further configured to: 
 select a second set of process parameter values based on the measurement of the wafer dimension, and    provide the second set of process parameter values to a previously visited processing tool.    
     
     
         3 . The apparatus of  claim 1 , wherein the measuring tool is for measuring a critical dimension (CD) of a target feature on the wafer.  
     
     
         4 . The apparatus of  claim 3 , wherein measuring tool optically measures the CD of the target feature.  
     
     
         5 . The apparatus of  claim 4 , wherein the target feature CD is measured using scatterometry or reflectometry.  
     
     
         6 . The apparatus of  claim 3 , wherein the chamber comprises: 
 a mainframe for mounting a plurality of processing tools, including the first processing tool;    a factory interface for housing the measurement tool and for mounting a wafer cassette; and    a transfer chamber between and in communication with the mainframe and the factory interface;    wherein the transfer mechanism comprises a first robot for transferring the wafer between the measurement tool, the transfer chamber and the wafer cassette, and a second robot for transferring the wafer between the transfer chamber and the first processing tool.    
     
     
         7 . The apparatus of  claim 3 , wherein the first processing tool comprises an etcher, and the first process parameter values comprise an etch recipe.  
     
     
         8 . The apparatus of  claim 3 , wherein the measuring tool is for aligning the wafer.  
     
     
         9 . The apparatus of  claim 1 , wherein the processor is configured to: 
 control the transfer mechanism to transfer the wafer from the first processing tool to the measuring tool after the first process is performed on the wafer; and    control the measuring tool to re-measure the dimension of the wafer.    
     
     
         10 . The apparatus of  claim 7 , wherein the chamber comprises a mainframe to which the etcher is mounted, a factory interface to which the measurement tool and a wafer cassette are mounted, and a transfer chamber between the mainframe and the factory interface; and 
 wherein the transfer mechanism comprises a robot for transferring the wafer between the measurement tool, the transfer chamber and the wafer cassette.    
     
     
         11 . The apparatus of  claim 10 , further comprising an ashing strip processing unit mounted to the mainframe for removing residue from the wafer after the first process is performed on the wafer.  
     
     
         12 . The apparatus of  claim 10 , further comprising a cleaning module mounted to the factory interface for cleaning the wafer; 
 wherein the processor is configured to control the transfer mechanism to transfer the wafer from the cassette to the measuring tool, to transfer the wafer from the measuring tool to the first processing tool after the CD of the target feature is measured, to transfer the wafer from the first processing tool to the cleaning module after the first process is performed on the wafer; and to transfer the wafer from the cleaning module to the cassette after the wafer has been cleaned.    
     
     
         13 . A method of processing a semiconductor wafer, comprising: 
 (a) removing the wafer from a wafer cassette;    (b) measuring a dimension of a structure on the wafer at a measuring tool;    (c) performing a process on the wafer at a processing tool using a set of process parameter values based on the measurement of the dimension;    (d) re-measuring the dimension; and    (e) returning the wafer to the cassette;    wherein steps (a)-(e) are performed in a contiguous clean environment.    
     
     
         14 . The method of  claim 13 , comprising selecting the set of process parameter values for a subsequently processed wafer using the re-measurement of the dimension.  
     
     
         15 . The method of  claim 13 , comprising performing an etch process on the wafer.  
     
     
         16 . The method of  claim 15 , comprising cleaning the wafer after performing the etch process and prior to returning the wafer to the cassette.  
     
     
         17 . The apparatus of  claim 1 , wherein the chamber comprises a mainframe for mounting a plurality of processing tools; 
 wherein the first processing tool is mounted to the mainframe; and    wherein the transfer mechanism comprises a robot.    
     
     
         18 . The apparatus of  claim 17 , wherein the measuring tool is mounted to the mainframe.  
     
     
         19 . The apparatus of  claim 10 , further comprising a particle monitor mounted to the factory interface and in communication with the transfer mechanism.  
     
     
         20 . An apparatus for processing a semiconductor wafer, comprising: 
 a measuring tool for imaging the wafer to obtain a waveform representative of a CD of a target feature on the wafer;    a storage medium that stores a plurality of reference waveforms, each reference waveform representative of a reference feature CD and associated with a different known set of first process parameter values; and    a processor configured to identify the reference waveform that most closely matches the target feature waveform to obtain the first process parameter values for performing a first process on the wafer.    
     
     
         21 . The apparatus of  claim 20 , comprising: 
 a first processing tool for performing the first process on the wafer;    a transfer mechanism for transferring the wafer between the measuring tool and the first processing tool; and    a chamber for enclosing the transfer mechanism and allowing communication between the transfer mechanism, the measuring tool and the first processing tool in a clean environment;    wherein the processor is further configured to control the first processing tool to perform the first process on the wafer using the first set of process parameter values.    
     
     
         22 . The apparatus of  claim 21 , wherein the processor is further configured to: 
 select a second set of process parameter values based on the imaging of the target feature CD, and    provide the second set of process parameter values to a previously visited processing tool.    
     
     
         23 . The apparatus of  claim 21 , wherein the measuring tool optically images the target feature CD.  
     
     
         24 . The apparatus of  claim 21 , wherein the first processing tool comprises an etcher, and the first process parameter values comprise an etch recipe.  
     
     
         25 . The apparatus of  claim 21 , wherein the processor is configured to: 
 control the transfer mechanism to transfer the wafer from the first processing tool to the measuring tool after the first process is performed on the wafer; and    control the measuring tool to re-measure the dimension of the wafer.    
     
     
         26 . The apparatus of  claim 21 , wherein the chamber comprises: 
 a mainframe for mounting a plurality of processing tools, including the first processing tool;    a factory interface for housing the measurement tool and for mounting a wafer cassette; and    a transfer chamber between and in communication with the mainframe and the factory interface;    wherein the transfer mechanism comprises a first robot for transferring the wafer between the measurement tool, the transfer chamber and the wafer cassette, and a second robot for transferring the wafer between the transfer chamber and the first processing tool.    
     
     
         27 . The apparatus of  claim 21 , wherein the chamber comprises a mainframe to which the etcher is mounted, a factory interface to which the measurement tool and a wafer cassette are mounted, and a transfer chamber between the mainframe and the factory interface; and 
 wherein the transfer mechanism comprises a robot for transferring the wafer between the measurement tool, the transfer chamber and the wafer cassette.    
     
     
         28 . The apparatus of  claim 20 , comprising: 
 selecting one of the reference waveforms as a golden waveform;    comparing the target feature waveform with the golden waveform; and    comparing the target feature waveform to other reference waveforms in the library to identify the reference waveform that most closely matches the target feature waveform when the target feature waveform deviates from the golden waveform by more than a predetermined threshold amount.    
     
     
         29 . The apparatus of  claim 22 , wherein the previously visited processing tool is a photolithographic processing tool, and the second set of process parameter values comprise stepper focus and exposure settings.  
     
     
         30 . The apparatus of  claim 1 , wherein the structure on the wafer is a pattern in a photoresist layer, the first processing tool is a first etcher, and the first process parameter values comprise a first etch recipe for trimming the pattern in the photoresist layer; 
 wherein the processor is further configured to:    control the transfer mechanism to transfer the wafer from the first etcher to the measuring tool after the first process is performed on the wafer;    control the measuring tool to re-measure the dimension of the photoresist pattern;    control the transfer mechanism to transfer the wafer from the measuring tool to a second etcher after the dimension of the photoresist pattern is re-measured;    control the second etcher to perform a second process on a layer of the wafer underlying the photoresist pattern using a second etch recipe to form an etched feature; and    select the first set of process parameter values for a subsequently processed wafer using the re-measurement of the dimension of the photoresist pattern.    
     
     
         31 . The apparatus of  claim 30 , wherein the processor is further configured to: 
 control the transfer mechanism to transfer the wafer from the second etcher to the measuring tool after the second process is performed; and    control the measuring tool to measure the dimension of the etched feature.    
     
     
         32 . The apparatus of  claim 31 , wherein the processor is further configured to select the second set of process parameter values for a subsequently processed wafer using the measurement of the dimension of the etched feature.  
     
     
         33 . The apparatus of  claim 32 , wherein the processor is further configured to select the first set of process parameter values for a subsequently processed wafer using the measurement of the dimension of the etched feature.