Integrated critical dimension control for semiconductor device manufacturing

Abstract

A method and apparatus for reducing lot to lot CD variation in semiconductor wafer processing feeds back information gathered during inspection of a wafer, such as after photoresist application, exposure and development, to upcoming lots that will be going through the photolithography process, and feeds forward information to adjust the next process the inspected wafer will undergo (e.g., the etch process). Embodiments include forming a feature such as an etch mask on a semiconductor wafer at a “photo cell” by a photolithography process, then conventionally imaging the feature with a CD-SEM to measure its CD and other sensitive parameters. The measured parameters are linked, via the feature's SEM waveform, to photolithography adjustable parameters such as stepper focus and exposure settings. If the measured parameters deviate from design dimensions, the linked information on focus and exposure is fed back to the photo cell so the stepper can be adjusted, either automatically or at the user's discretion, to correct the deviation in following lots. The measured parameters are also linked to etch process adjustable parameters such as etch recipes for different over-etch and/or etch chemistry. If the measured parameters deviate from desired values, a linked etch recipe to correct the error is fed forward to the etcher and implemented automatically or at the user's discretion. This feedback and feed-forward mechanism improves lot to lot CD control at inspection following photoresist development and at final inspection as well.

What is claimed is:  
     
         1 . A method of controlling the processing of a semiconductor wafer, which method comprises: 
 performing a first process on the wafer;    imaging to obtain a critical dimension (CD) and target waveform of a target feature on the wafer formed using the first process;    determining a set of process parameter values for a second process based on the target waveform; and    performing the second process on the wafer based on the second process parameter values.    
     
     
         2 . The method of  claim 1 , comprising: 
 determining a set of process parameter values for the first process responsive to the target waveform; and    performing the first process on another semiconductor wafer responsive to the first process parameter values.    
     
     
         3 . The method of  claim 2 , wherein determining the second process parameter values comprises: 
 forming a plurality of reference features on a reference semiconductor wafer, the reference features having a CD and a waveform comparable to the target feature CD and target waveform, each of the reference features respectively associated with a different known set of second process parameter values; and    identifying the reference waveform that most closely matches the target waveform to obtain the second process parameter values for performing the second process.    
     
     
         4 . The method of  claim 3 , comprising: 
 selecting one of the reference waveforms as a golden waveform;    comparing the target waveform with the golden waveform; and    comparing the target waveform to other reference waveforms in the library to identify the reference waveform that most closely matches the target waveform when the target waveform deviates from the golden waveform by more than a predetermined threshold amount.    
     
     
         5 . The method of  claim 3 , wherein each reference feature is further associated with a different known set of first process parameter values, the method comprising performing the first process on another semiconductor wafer responsive to the first process parameter values associated with the reference waveform that most closely matches the target waveform.  
     
     
         6 . The method of  claim 5 , wherein the first process is performed on the wafer using a set of initial first process parameter values, the method comprising performing the first process on the other wafer using the initial first process parameter values when the target waveform deviates from the golden waveform less than the predetermined threshold amount.  
     
     
         7 . The method of  claim 3 , comprising obtaining the reference waveforms and target waveforms as SEM waveforms.  
     
     
         8 . The method of  claim 5 , wherein the first process is a photolithographic process and the first process parameter values comprise stepper focus and exposure settings, the method comprising forming the reference features as a focus-exposure matrix (FEM).  
     
     
         9 . The method of  claim 8 , wherein the second process is an etch process, and the second process parameter values comprise etch recipes.  
     
     
         10 . The method of  claim 9 , wherein the etch recipes are for adjusting the target feature CD during the second process.  
     
     
         11 . The method of  claim 3 , wherein each reference waveform is associated with a known cross-sectional profile.  
     
     
         12 . A computer-readable medium bearing instructions for controlling the processing of a semiconductor wafer, said instructions, when executed, being arranged to cause one or more processors to perform the steps of: 
 receiving a critical dimension (CD) and target waveform of a target feature on the wafer formed by a first process; and    determining a set of process parameter values for a second process based on the target waveform, the second process to be performed on the wafer based on the second process parameter values.    
     
     
         13 . The computer-readable medium according to  claim 13 , wherein the instructions, when executed, are arranged to cause the one or more processors to perform the step of determining a set of process parameter values for the first process based on the target waveform, the first process to be performed on another semiconductor wafer responsive to the first process parameter values.  
     
     
         14 . The computer-readable medium according to  claim 13 , wherein the instructions, when executed, are arranged to cause the one or more processors to perform the step of determining the second process parameter values by: 
 receiving a plurality of reference features on a reference semiconductor wafer, the reference features having a CD and a waveform comparable to the target feature CD and target waveform, each of the reference features respectively associated with a different known set of second process parameter values; and    identifying the reference waveform that most closely matches the target waveform to determine the second process parameter values for performing the second process.    
     
     
         15 . The computer-readable medium according to  claim 14 , wherein the instructions, when executed, are arranged to cause the one or more processors to perform the steps of: 
 receiving one of the reference waveforms as a golden waveform;    comparing the target waveform with the golden waveform; and    comparing the target waveform to other reference waveforms to identify the reference waveform that most closely matches the target waveform when the target waveform deviates from the golden waveform by more than a predetermined threshold amount.    
     
     
         16 . The computer-readable medium according to  claim 14 , wherein each reference feature is further associated with a different known set of first process parameter values, and the instructions, when executed, are arranged to cause the one or more processors to perform the step of determining the first process parameter values associated with the reference waveform that most closely matches the target waveform, for performing the first process on another semiconductor wafer responsive to the first process parameter values.  
     
     
         17 . The computer-readable medium according to  claim 16 , wherein the first process is performed on the wafer using a set of initial first process parameter values, and wherein the instructions, when executed, are arranged to cause the one or more processors to perform the step of determining that the initial first process parameter values are to be used to perform the first process on the other wafer when the target waveform deviates from the golden waveform less than the predetermined threshold amount.  
     
     
         18 . The computer-readable medium according to  claim 14 , wherein the instructions, when executed, are arranged to cause the one or more processors to receive the reference waveforms and target waveforms as SEM waveforms.  
     
     
         19 . The computer-readable medium according to  claim 17 , wherein the first process is a photolithographic process and the first process parameter values comprise stepper focus and exposure settings, and wherein the instructions, when executed, are arranged to cause the one or more processors to perform the steps of receiving the reference waveforms as a focus-exposure matrix (FEM).  
     
     
         20 . The computer-readable medium according to  claim 19 , wherein the second process is an etch process, and the second process parameter values comprise etch recipes.  
     
     
         21 . The computer-readable medium according to  claim 20 , wherein the etch recipes are for adjusting the target feature CD during the second process.  
     
     
         22 . The computer-readable medium according to  claim 14 , wherein each reference waveform is associated with a known cross-sectional profile.  
     
     
         23 . An apparatus for controlling the processing of a semiconductor wafer, comprising: 
 an imager for obtaining a CD of a target feature on the wafer, the target feature formed using a first process, and for producing a target waveform corresponding to the target feature;    a storage medium that stores: 
 the target feature CD and the target waveform; and  
 a plurality of reference waveforms corresponding to a plurality of reference features on a reference semiconductor wafer, the reference features having a CD and a waveform comparable to the target feature CD and target waveforms, each of the reference features respectively associated with a different known set of second process parameter values; and  
   a processor configured to identify the reference waveform that most closely matches the target waveform to obtain the second process parameter values for performing a second process on the wafer.    
     
     
         24 . The apparatus of  claim 23 , wherein the processor is further configured to cause the second process to be performed on the wafer based on the obtained second process parameter values.  
     
     
         25 . The apparatus of  claim 24 , wherein the second process is an etch process and the second process parameter values comprise etch recipes for adjusting the target feature CD during the second process; 
 wherein the processor is further configured to cause the second process to adjust the target feature CD.    
     
     
         26 . The apparatus of  claim 23 , wherein the processor is further configured to: 
 select one of the reference waveforms as a golden waveform;    compare the target waveform with the golden waveform; and    compare the target waveform to other reference waveforms to identify the reference waveform that most closely matches the target waveform when the target waveform deviates from the golden waveform by more than a predetermined threshold amount.    
     
     
         27 . The apparatus of  claim 25 , wherein each reference feature is further associated with a different known set of first process parameter values; and 
 wherein the processor is further configured to obtain the first process parameter values associated with the reference waveform that most closely matches the target waveform for performing the first process on another semiconductor wafer.    
     
     
         28 . The apparatus of  claim 27 , wherein the processor is further configured to cause the first process to be performed on the other wafer responsive to the obtained first process parameter values.  
     
     
         29 . The apparatus of  claim 28 , wherein the first process is performed on the wafer using a set of initial first process parameter values; and 
 wherein the processor is further configured to cause the first process to be performed on the other wafer using the initial first process parameter values when the target waveform deviates from the golden waveform less than the predetermined threshold amount.    
     
     
         30 . The apparatus of  claim 28 , wherein the first process is a photolithographic process and the first process parameter values comprise stepper focus and exposure settings.  
     
     
         31 . The apparatus of  claim 23 , wherein the imager is a scanning electron microscope (SEM).  
     
     
         32 . The apparatus of  claim 23 , wherein the storage medium is a digital storage device.  
     
     
         33 . The method of  claim 5 , wherein the wafer has a plurality of features, one feature being at a selected location on the wafer, the method comprising: 
 imaging more than one of the plurality of features, including the feature at the selected location, to obtain CDs and target waveforms of a plurality of target features;    comparing the CDs of the target features to a predetermined nominal CD value; and    performing the first process on the other semiconductor wafer responsive to the first process parameter values associated with the reference waveform that most closely matches the target waveform of the feature at the selected location when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.    
     
     
         34 . The method of  claim 34 , comprising: 
 averaging the CDs of the target features to obtain an average CD; and    identifying the reference waveform associated with a CD that most closely matches the average CD to obtain the second process parameter values for performing the second process when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.    
     
     
         35 . The computer-readable medium according to  claim 16 , wherein the wafer has a plurality of features, one feature being at a selected location on the wafer, and wherein the instructions, when executed, are arranged to cause the one or more processors to perform the steps of: 
 receiving CDs and target waveforms of a plurality of target features;    comparing the CDs of the target features to a predetermined nominal CD value; and    performing the first process on the other semiconductor wafer responsive to the first process parameter values associated with the reference waveform that most closely matches the target waveform of the feature at the selected location when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.    
     
     
         36 . The computer-readable medium according to  claim 35 , wherein the instructions, when executed, are arranged to cause the one or more processors to perform the steps of: 
 averaging the CDs of the target features to obtain an average CD; and    identifying the reference waveform associated with a CD that most closely matches the average CD to obtain the second process parameter values for performing the second process when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.    
     
     
         37 . The apparatus of  claim 27 , wherein the wafer has a plurality of features, one feature being at a selected location on the wafer; 
 wherein the imager is for obtaining CDs and for producing target waveforms corresponding to more than one of the plurality of features, including the feature at the selected location; and    wherein the processor is further configured to compare the CDs of the target features to a predetermined nominal CD value, and cause the first process to be performed on the other semiconductor wafer responsive to the first process parameter values associated with the reference waveform that most closely matches the target waveform of the feature at the selected location when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.    
     
     
         38 . The apparatus of  claim 37 , wherein the processor is further configured to: 
 average the CDs of the target features to obtain an average CD; and    identify the reference waveform associated with a CD that most closely matches the average CD to obtain the second process parameter values for performing the second process when the CD of one of the target features deviates from the nominal CD value more than a predetermined amount.