Apparatus for real-time dynamic chemical analysis

Abstract

An apparatus comprising a near infrared (NIR) spectrometer and a processor with an algorithm configured to acquire NIR spectral data and perform a chemometric data manipulation provides direct measurement of the etch rate for semiconductor wafer etchant solutions. The apparatus may also provide the concentrations of species in etchant and cleaning solutions, and automated process control. The apparatus may be used for analysis and control of other processing solutions.

1 . An apparatus for determining the rate of a chemical reaction involving one or more chemical reactants and a solid in a processing solution, comprising:
 an electromagnetic radiation source operative to provide a measurement beam of electromagnetic radiation;   a sampling element containing a test solution, which may be either a calibration solution or a sample of the processing solution;   an optical element operative to pass the measurement beam through the test solution;   a first fiber optic transmission element operative to transmit the measurement beam from said electromagnetic radiation source to said optical element;   a detector operative to measure the intensity of the measurement beam passed through the test solution as a function of the electromagnetic radiation wavelength over a predetermined spectral region so as to generate a spectrum of the test solution;   a second fiber optic transmission element operative to transmit the measurement beam passed through the test solution from said optical element to said detector; and   a processor including an algorithm operative to determine the rate of the chemical reaction for the processing solution by effecting the steps of an analysis method, comprising
 generating spectra over the predetermined spectral region for a plurality of calibration solutions each comprising at least some of the constituents of the processing solution, wherein the constituents include the chemical reactants and byproducts of the chemical reaction, 
 measuring the rates of the chemical reaction for the plurality of calibration solutions using a standard procedure, 
 correlating the spectra generated for the plurality of calibration solutions and the chemical reaction rates measured by the standard procedure for the plurality of calibration solutions via a chemometric data manipulation to develop a calibration model and a calibration database, 
 generating a spectrum over the predetermined spectral region for a sample of the processing solution, and 
 comparing the spectrum generated for the sample of the processing solution with the calibration database to determine the rate of the chemical reaction for the processing solution. 
   
   
   
       2 . The apparatus of  claim 1 , wherein the electromagnetic radiation source is further operative to provide a reference beam of the electromagnetic radiation and the intensity of the measurement beam is corrected for fluctuations in the intensity of the electromagnetic radiation provided by the electromagnetic radiation source based on the intensity of the reference beam. 
   
   
       3 . The apparatus of  claim 1 , wherein the process is an etching process, the chemical reaction is a chemical etching reaction, the one or more chemical reactants comprise one or more etchant species, and the processing solution is an etching solution, such that the process comprises chemical etching of the solid by one or more etchant species in an etching solution and the reaction rate is an etch rate of the solid. 
   
   
       4 . The apparatus of  claim 3 , wherein the solid comprises a material selected from the group consisting of silicon, silicon oxide and silicon nitride, and combinations thereof. 
   
   
       5 . The apparatus of  claim 3 , wherein the etching solution comprises an aqueous solution comprising at least one chemical species selected from the group consisting of H + , HF, F − , HF 2− , SiF 4 , H 2 SiF 6 , SiF 6   2− , OH − , H 2 O 2 , HO 2− , S 2 O 8   2− , SO 4   2− , SO 3   2− , C 2 H 3 OH 2 , C 2 H 3 OH − , C 2 H 3 O 2− , Cl − , Br − , I − , NH 4   − , NO 3   − , NO 2   − , N 3− , and combinations thereof. 
   
   
       6 . The apparatus of  claim 3 , wherein the etching solution is selected from the group consisting of an acid, a base, HF:H 2 O, HF1:5, HF1:50, H 2 S0 4 :HNO 3 :HF, acetic acid:NH 4 F, H 3 PO 4 :HNO 3 :acetic acid, HNO 3 :HF, H 2 SO 4 :H 2 O 2 , H 2 SO 4 :HNO 3 , H 2 SO 4 :persulfate, ethylene glycol+HF, buffered oxide etch (BOE), a commercial oxide etchant, a commercial silicon etchant, and a commercial metallic etchant. 
   
   
       7 . The apparatus of  claim 1 , wherein the predetermined spectral region comprises at least part of the near infrared (NIR) spectral range from 700 to 2500 nm. 
   
   
       8 . The apparatus of  claim 1 , wherein said sampling element comprises a tube of a material that is substantially transparent to electromagnetic radiation in the predetermined spectral region. 
   
   
       9 . The apparatus of  claim 8 , wherein the material comprises at least one material selected from the group consisting of Teflon, glass, polyethylene, polypropylene, PET, polyvinylchloride, nylon, Tygon, polystyrene, silicone rubber PVA, and quartz. 
   
   
       10 . The apparatus of  claim 8 , wherein the processing solution is flowed through said tube. 
   
   
       11 . The apparatus of  claim 1 , wherein the steps of correlating and comparing are performed using at least one data analysis method selected from the group consisting of principal component analysis, partial least squares analysis, multiple linear regression analysis, and neural network analysis. 
   
   
       12 . The apparatus of  claim 1 , wherein a chemical reactant is present at two different known concentrations in at least two of the calibration solutions, and said processor is further operative to determine the concentration of the chemical reactant in the processing solution. 
   
   
       13 . The apparatus of  claim 1 , wherein a chemical reactant is present at two different known concentrations in at least two of the calibration solutions, and said processor is further operative to determine the rate of change in the concentration of the chemical reactant in the processing solution over a period of time. 
   
   
       14 . The apparatus of  claim 1 , wherein a chemical reactant is present at two different known concentrations in at least two of the calibration solutions, and said processor is further operative to provide a derivative function of the rate of change in the concentration of the chemical reactant in the processing solution over a period of time. 
   
   
       15 . The apparatus of  claim 1 , wherein a plurality of chemical reactants is each present at two different known concentrations in at least two of the calibration solutions, and said processor is further operative to determine the concentration of each of the plurality of the chemical reactants in the processing solution. 
   
   
       16 . The apparatus of  claim 1 , wherein a plurality of chemical reactants is each present at two different known concentrations in at least two of the calibration solutions, and said processor is further operative to determine a rate of change in the concentration of each of the plurality of the chemical reactants in the processing solution. 
   
   
       17 . The apparatus of  claim 1 , further comprising:
 a chemical delivery system operative to replenish at least one of the chemical reactants in the processing solution so as to increase the reaction rate of the chemical reaction, or to add water to the processing solution so as to decrease the reaction rate of the chemical reaction.   
   
   
       18 . An apparatus for controlling an etching process by determining the etch rate of a solid in an etching solution containing one or more etchant species, comprising:
 an electromagnetic radiation source operative to provide a measurement beam of electromagnetic radiation;   a sampling element containing a test solution, which may be either a calibration solution or a sample of the etching solution;   an optical element operative to pass the measurement beam through the test solution;   a first fiber optic transmission element operative to transmit the measurement beam from said electromagnetic radiation source to said optical element;   a detector operative to measure the intensity of the measurement beam passed through the test solution as a function of the electromagnetic radiation wavelength over the spectral region from 700 to 2500 nm so as to generate an NIR spectrum of the test solution;   a second fiber optic transmission element operative to transmit the measurement beam passed through the test solution from said optical element to said detector; and   a processor including an algorithm operative to determine the etch rate of the solid in the etching solution by effecting the steps of an analysis method, comprising
 generating NIR spectra for a plurality of calibration solutions each comprising at least some of the constituents of the etching solution, wherein the constituents include the etchant species and byproducts of the etching process, 
 measuring the etch rates of the solid for the plurality of calibration solutions using a standard procedure, 
 correlating the NIR spectra generated for the plurality of calibration solutions and the etch rates measured by the standard procedure for the plurality of calibration solutions via a chemometric data manipulation to develop a calibration model and a calibration database, 
 generating an NIR spectrum for a sample of the etching solution, and 
 comparing the NIR spectrum generated for the sample of the etching solution with the calibration database to determine the etch rate for the etching solution. 
   
   
   
       19 . The apparatus of  claim 18 , wherein the electromagnetic radiation source is further operative to provide a reference beam of the electromagnetic radiation and the intensity of the measurement beam is corrected for fluctuations in the intensity of the electromagnetic radiation provided by the electromagnetic radiation source based on the intensity of the reference beam. 
   
   
       20 . The apparatus of  claim 18 , wherein the standard procedure for measuring the etch rate of the solid for a calibration solution comprises measuring the thickness of the solid before and after etching the solid in the calibration solution for a predetermined period of time. 
   
   
       21 . The apparatus of  claim 18 , wherein the solid comprises a material selected from the group consisting of silicon, silicon oxide and silicon nitride, and combinations thereof. 
   
   
       22 . The apparatus of  claim 18 , wherein the etching solution comprises an aqueous solution comprising at least one etchant species selected from the group consisting of H + , HF, F − , HF 2− , SiF 4 , H 2 SiF 6 , SiF 6   2− , OH − , H 2 O 2 , HO 2− , S 2 O 8   2− , SO 4   2− , SO 3   2− , C 2 H 3 OH 2 , C 2 H 3 OH − , C 2 H 3 O 2− , Cl − , Br − , I − , NH 4   − , NO 3   − , NO 2   − , N 3− , and combinations thereof. 
   
   
       23 . The apparatus of  claim 18 , wherein said processor is further operative to determine the concentration of a chemical constituent of a semiconductor cleaning solution. 
   
   
       24 . The apparatus of  claim 23 , wherein the semiconductor cleaning solution is an aqueous solution comprising at least one chemical constituent selected from the group consisting of H 2 O 2 , O 3 , NH 4 OH, HCl, HF, H 2 SO 4 , HNO 3 , acetic acid, and combinations thereof.