Robust Signal Processing Algorithm For End-Pointing Chemical-Mechanical Polishing Processes

Abstract

A signal processing system has the detected mechanical, chemical, optical, electrical, or thermal signals generated during chemical-mechanical polishing (CMP) process collected, analyzed and differentiated with respect to time in-situ, in order to reveal the different stages during CMP for process control and end-pointing purposes. This control and/or end-pointing scheme may be used to detect the interface between two material layers sharing similar properties such as those of low-k dielectric stacks for semiconductor applications.

1 . A system for identifying a change in a parameter of a workpiece comprising: 
 A sensor for sensing a discriminant of said parameter;    A signal processing unit connected to said sensor and capable of performing real-time signal processing including calculating at least a first derivative with time of said discriminant; and    A comparison module within said signal processing unit for comparing said at least first order derivative with a criterion.    
   
   
       2 . A system according to  claim 1 , in which said signal processing unit calculates a second derivative with time of said discriminant.  
   
   
       3 . A system according to  claim 1 , in which said parameter is the thickness of a film deposited on a surface of said workpiece.  
   
   
       4 . A system according to  claim 1 , in which said sensor is connected to a chemical-mechanical polishing system.  
   
   
       5 . A system according to  claim 4 , in which said chemical-mechanical polishing system is adapted to remove a first layer on said workpiece and to stop material removal when said first layer is removed, whereby said sensor senses an interface between said first layer and a second layer below said first layer.  
   
   
       6 . A system according to  claim 4 , in which said criterion is a fixed value of the first derivative of said discriminant.  
   
   
       7 . A system according to  claim 4 , in which the first dielectric layer is comprised of a material selected from the group consisting of SiLK™, GX-3™, porous SiLK™, GX-3p™, JSR LKD 5109™, JSR LKD 5130™, Black Diamond™, NCS™, porous spin-on or PECVD Si w C x O y H z  or other low k or porous low k dielectric materials.  
   
   
       8 . A system according to  claim 7 , in which said PECVD or spin-on CMP protective layer(s) is comprised of a material selected from the group consisting of TEOS-oxide, silane-oxide, SiN x , BLok™, N-BLok™, PECVD-based Si w C x O y H z  dielectric materials, AP 6000™, HOSP™, HOSP BESt™, Ensemble™ Etch Stop, Ensemble™ Hard Mask, hydrido silsesquioxanes, hydrido-organo silsesquioxanes copolymers, siloxanes, silsesquioxanes, or other spin-on or CVD material, or combination of the above.  
   
   
       9 . A system according to  claim 4 , in which said criterion is a magnitude of said first derivative less than a first reference value for a detection period of time and a magnitude of a second order derivative with time below a second reference value during said detection time.  
   
   
       10 . A method for identifying a change in a parameter of a workpiece comprising: 
 providing a sensor for sensing a discriminant of said parameter;    providing a signal processing unit connected to said sensor and capable of performing real-time signal processing including calculating at least a first derivative with time of said discriminant; and    A comparison module within said signal processing unit for comparing said at least first order derivative with a criterion, comprising the steps of:    Calculating said first order derivative with time of said discriminant;    Comparing a current value of said first order derivative with said criterion; and    Generating an output signal when said criterion is met.    
   
   
       11 . A method according to  claim 10 , in which said signal processing unit calculates a second derivative with time of said discriminant.  
   
   
       12 . A method according to  claim 10 , in which said parameter is the thickness of a film deposited on a surface of said workpiece.  
   
   
       13 . A method according to  claim 10 , in which said sensor is connected to a chemical-mechanical polishing system.  
   
   
       14 . A method according to  claim 13 , in which said chemical-mechanical polishing system is adapted to remove a first layer on said workpiece and to stop material removal when said first layer is removed, whereby said sensor senses an interface between said first layer and a second layer below said first layer.  
   
   
       15 . A method according to  claim 13 , in which said criterion is a fixed value of the first derivative of said discriminant.  
   
   
       16 . A method according to  claim 14 , in which said criterion is a fixed value of the first derivative of said discriminant.  
   
   
       17 . A method according to  claim 13 , in which said criterion is a magnitude of said first derivative less than a first reference value for a detection period of time and a magnitude of a order derivative with time below a second reference value during said detection time.  
   
   
       18 . A method according to  claim 14 , in which said criterion is a magnitude of said first derivative less than a first reference value for a detection period of time and a magnitude of a order derivative with time below a second reference value during said detection time.  
   
   
       19 . A method according to  claim 13 , in which the first dielectric layer is comprised of a material selected from the group consisting of SiLK™, GX-3™, porous SiLK™, GX-3p™, JSR LKD 5109™, JSR LKD 5130™, Black Diamond™, NCS™, porous spin-on or PECVD Si w C x O y H z  or other low k or porous low k dielectric materials.  
   
   
       20 . A method according to  claim 19 , in which said PECVD or spin-on CMP protective layer(s) is comprised of a material selected from the group consisting of TEOS-oxide, silane-oxide, SiN x , BLok™, N-BLok™, PECVD-based Si w C x O y H z  dielectric materials, AP 6000™, HOSP™, HOSP BESt™, Ensemble™ Etch Stop, Ensemble™ Hard Mask, hydrido silsesquioxanes, hydrido-organo silsesquioxanes copolymers, siloxanes, silsesquioxanes, or other spin-on or CVD material, or combination of the above.