Chemical mechanical planarization (CMP) slurry quality control process and particle size distribution measuring systems

Abstract

A sensitive particle distribution probe uses special processing including a modified Twomey/Chahine iterative convergence technique and a specially constructed sample cell to obtain particle size distribution measurements from optically dense slurries, such as the slurries used in the semiconductor industry for chemical mechanical planarization. Spectral transmission data is taken over the spectral range of 0.20-2.5 microns, utilizing specially constructed, chemically resistant sample cells of 50-2000 microns thickness, and miniature, fixed grating, linear detector array spectrometers. At wavelengths greater than one micron, the preferred design utilizes InGaAs linear detector arrays. An ultrasonic disrupter can be employed to breakup harmless soft agglomerates. In addition to direct particle size distribution measurement, the invention described here could be used to detect other fundamental causes of slurry degradation, such as foaming and jelling. The probe accomplishes continuous, real time sampling of undiluted slurry. A three-position chopper allows automated operation in an industrial environment without the need for frequent reference spectra, which would require taking the probe off-line. In other embodiments, the invention provides a quality control and/or particle size measuring system for CMP slurries using transmission data through an as-used CMP slurry flow. The process of the invention detects transmission through the flow, at select wavelengths, and determines changes in the logarithmic slope of transmission versus wavelength to detect acceptable or unacceptable CMP slurries. The process can further determine CMP slurry particle size through empirical extinction data stored in memory.

1. A quality control process for detecting physical and/or chemical changes in a CMP slurry, comprising the steps of:
 transmitting radiation through a flow of an undiluted optically dense slurry as used in a chemical mechanical planarization (CMP) process, the radiation having one or more wavelengths;  
 determining transmission of the transmitted radiation at each of the  said one or more wavelengths; and  
 monitoring transmission, over time, to detect physical and/or chemical changes of the CMP slurry.  
 
     
     
       2. A process of  claim 1 , further comprising determining a slope of transmission as a function of the wavelengths. 
     
     
       3. A process of  claim 1 , further comprising the step of detecting changes in the particle size distribution of the CMP slurry. 
     
     
       4. A process of  claim 3 , further comprising the step of determining a change in the slope, over time, the change in slope indicating change in the particle size distribution. 
     
     
       5. A process of  claim 3 , further comprising determining a slope of a logarithmic of transmission. 
     
     
       6. A process of  claim 1 , further comprising the step of determining a slope of a logarithmic of transmission as a function of the wavelengths. 
     
     
       7. A process of  claim 6 , further comprising the step of determining a change in the logarithmic slope, over time, the change in the slope indicating change in a particle size distribution of the CMP slurry independent from a change in particle concentration. 
     
     
       8. A process of  claim 1 , further comprising the step of detecting changes in the particle size distribution of the CMP slurry wherein the particle size distribution corresponds to a value between about 0.03 and 1.0 micron. 
     
     
       9. A process of  claim 1 , further comprising the step of detecting changes in the particle size distribution of the CMP slurry wherein the particle size distribution corresponds to a value above about one micron. 
     
     
       10. A process of  claim 1 , wherein the step of transmitting the radiation comprises transmitting the radiation through the flow having a diameter of about 100 microns. 
     
     
       11. A process of  claim 1 , wherein the step of transmitting the radiation comprises transmitting the radiation through the flow having a diameter of between about 100-2000 microns. 
     
     
       12. A process of  claim 1 , wherein the step of transmitting the radiation comprises transmitting the radiation through a sample cell selected on the basis of desired accuracy. 
     
     
       13. A process of  claim 12 , further comprising selecting a sample cell defining a flow diameter of about 100 microns. 
     
     
       14. A process of  claim 12 , further comprising selecting a sample cell defining a flow diameter of between about 100-2000 microns. 
     
     
       15. A process of  claim 1 , wherein the step of determining transmission comprises determining transmission to an accuracy of at least about 1%. 
     
     
       16. A process of  claim 1 , wherein the step of transmitting comprises utilizing a grating to select the wavelengths of the radiation. 
     
     
       17. A process of  claim 1 , wherein the step of transmitting comprises using a laser. 
     
     
       18. A process of  claim 1 , wherein the step of transmitting comprises utilizing at least two filters to select the wavelengths. 
     
     
       19. A process of  claim 1 , further comprising generating a warning corresponding to the changes. 
     
     
       20. A process of  claim 1 , further comprising the steps of detecting changes in the particle size distribution of the CMP slurry and of comparing the transmission to a reference transmission indicative of a preferred particle size distribution within the flow. 
     
     
       21. A process of  claim 20 , further comprising the step of storing the reference transmission in memory. 
     
     
       22. A process of  claim 1 , further comprising the steps of:
 (a) detecting changes in the particle size distribution of the CMP slurry; 
 (b) storing a plurality of reference transmissions, each reference transmission corresponding to a particular CMP slurry flow and particle distribution;and  
 (c) selecting one reference transmission and comparing the transmission to the selected reference transmission.  
 
     
     
       23. A process of  claim 1 , further comprising utilizing Mie theory to calculate particle sizes within the CMP slurry. 
     
     
       24. A process of  claim 1 , further comprising comparing transmission information with an empirical curve of extinction efficiency versus particle size diameter to determine particle sizes within the CMP slurry. 
     
     
       25. A process of  claim 24 , wherein the particle size diameter comprises a function of (pi) D/ lambda, where D is the particle size diameter and lambda corresponds to wavelength associated with the transmission. 
     
     
       26. A system for evaluating chemical mechanical planarization (CMP) slurry quality in a process, comprising:
 a light source generating a beam of electromagnetic radiation for transmission through a flow of an undiluted optically dense slurry as used in a CMP process;  
 a spectral discriminator for isolating at least two wavelength bands of the radiation prior to transmission of the radiation through the flow;  
 a detector for detecting radiation transmitted through the flow; and  
 a processor for evaluating transmission of the wavelength bands through the flow to determine physical and/or chemical changes of the CMP slurry.  
 
     
     
       27. A system of  claim 26 , wherein the discriminator comprises two wavelength bandpass filters. 
     
     
       28. A system of  claim 26 , wherein the discriminator comprises a filter wheel. 
     
     
       29. A system of  claim 26 , wherein the discriminator is selected from the group consisting essentially of a laser and a grating. 
     
     
       30. A system of  claim 26 , wherein the processor comprises a computer. 
     
     
       31. A system of  claim 26 , further comprising memory, coupled to the processor, for storing one or more reference transmissions, each reference transmission corresponding to a particular CMP slurry flow and particle size distribution, the processor selecting one reference transmission and comparing the transmission to the selected reference transmission to detect changes in the particle size distribution. 
     
     
       32. A system of  claim 26 , further comprising memory, coupled to the processor, for storing data indicative of extinction efficiency as a function of particle size diameter, the processor comparing the transmission to the data to determine particle sizes within the CMP slurry. 
     
     
       33. A system of  claim 26 , wherein the processor comprises processing means to calculate a logarithm of transmission at each wavelength band and to determine a change in slope of logarithmic transmission versus wavelength band to detect changes in particle size distribution of the CMP slurry independently from changes in particle concentration.