Combination thin-film stress and thickness measurement device

Abstract

A composite metrology tool, measures basic optical parameters of thin films (e.g., thickness, index of refraction, and birefringence) and stress (e.g., wafer displacements, such as bow and warp). These measurements are combined (e.g. in a processor) using optimization techniques to yield accurate overall information of the wafer parameters.

What is claimed is:  
     
         1 . A method of analyzing a wafer having a thin film thereon, comprising: 
 obtaining at least one optical property measurement of the thin film that is nominally indicative of the thickness of the thin film;    measuring a deformation of the thin film that is nominally indicative of an amount of stress on the thin film; and    combining the at least one optical property measurement with the deformation measurement to determine the thickness of the thin film and the stress on the thin film.    
     
     
         2 . The method of  claim 2 , wherein the combining step utilizes an optimization algorithm.  
     
     
         3 . The method of  claim 1 , wherein the step of measuring the deformation of the thin film includes: 
 directing a probe beam to the thin film;    determining an angle between the probe beam and a reflection of the probe beam from the thin film; and    determining the deformation based on the angle.    
     
     
         4 . The method of  claim 3 , wherein the deformation determining step includes accounting for a tilt detection system calibration factor.  
     
     
         5 . The method of  claim 4 , wherein the wafer rests on a movable stage, and wherein the tilt detection system calibration factor has been determined by: 
 resting a spherical mirror on the stage in place of the wafer;    directing the probe beam to the spherical mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is the tilt detection system calibration factor.    
     
     
         6 . The method of  claim 3 , wherein the wafer is resting on a stage, and wherein the deformation determining step includes accounting for a stage tilt calibration factor.  
     
     
         7 . The method of  claim 6 , wherein the stage tilt calibration factor has been determined by: 
 resting a flat mirror on the stage in place of the wafer;    directing the probe beam to the flat mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is the stage tilt calibration factor.    
     
     
         8 . The method of  claim 3 , wherein the step of determining the angle between the probe beam and the reflection of the probe beam includes: 
 directing the probe beam to be nominally normal to the thin film;    detecting a deviation of the probe beam after reflection from the thin film; and    determining the angle based on the deviation.    
     
     
         9 . The method of  claim 8 , wherein the step of detecting the position of the probe beam after reflection from the thin film includes determining relative intensities of the portions of the reflected probe beam on a plurality of cells of a photodetector.  
     
     
         10 . The method of  claim 1 , wherein the at least one optical property measurement is obtained using at least one of a spectrophotometer, an ellipsometer and a multiple angle of incidence device.  
     
     
         11 . The method of  claim 1 , wherein the combining step includes applying optimization routines used to solve Fresnel equations in an iterative process.  
     
     
         12 . The method of  claim 11 , wherein the iterative process includes a least squares fitting routine.  
     
     
         13 . The method of  claim 1 , wherein the combining step includes applying a genetic algorithm to concurrently optimize the determination of the stress as well as the thickness.  
     
     
         14 . The method of  claim 1 , wherein the at least one optical property measurement is affected by the stress on the thin film.  
     
     
         15 . The method of  claim 1 , wherein the result of the combining step also includes index of refraction and extinction coefficient.  
     
     
         16 . The method of  claim 1 , wherein the method further comprises: 
 supporting the wafer only at points substantially two-thirds of the distance from the center of the wafer.    
     
     
         17 . A method of analyzing the characteristics of a thin film on a semiconductor wafer comprising the steps of: 
 directing a first probe beam of radiation to reflect off the wafer surface;    measuring the change in magnitude or polarization of the reflected probe beam induced by the interaction with the wafer and generating first signals responsive thereto;    directing a second probe beam of radiation to reflect of the wafer;    measuring the angular deviation of the reflected probe induced by the interaction with the wafer and generating second signals responsive thereto;    analyzing the first and second signals in order to determine characteristics of the wafer including the thickness of the film and the stress in the film.    
     
     
         18 . The method of  claim 17 , wherein the first probe beam and the second probe beam are generated by the same source.  
     
     
         19 . The method of  claim 17 , wherein the analyzing step utilizes an optimization algorithm to combine the first and second signals.  
     
     
         20 . The method of  claim 17 , wherein the angular deviation measuring step includes accounting for a tilt detection system calibration factor.  
     
     
         21 . The method of  claim 20 , wherein the wafer rests on a movable stage, and wherein the tilt detection system calibration factor has been determined by: 
 resting a spherical mirror on the stage in place of the wafer;    directing a probe beam to the spherical mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is the tilt detection system calibration factor.    
     
     
         22 . The method of  claim 17 , wherein the wafer is resting on a stage, and wherein the angular deviation measuring step includes accounting for a stage tilt calibration factor.  
     
     
         23 . The method of  claim 22 , wherein the stage tilt calibration factor has been determined by: 
 resting a flat mirror on the stage in place of the wafer;    directing the probe beam to the flat mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is the stage tilt calibration factor.    
     
     
         24 . The method of  claim 17 , wherein the step of determining the angular deviation of the reflection of the second probe beam includes: 
 directing the second probe beam to be nominally normal to the thin film;    detecting a deviation of the reflection of the second probe beam; and    determining the angle based on the deviation.    
     
     
         25 . The method of  claim 24 , wherein the step of detecting the position of the reflection of the second probe beam includes determining relative intensities of the portions of the reflected second probe beam on a plurality of cells of a photodetector.  
     
     
         26 . The method of  claim 18 , wherein the analyzing step includes applying optimization routines used to solve Fresnel equations in an iterative process.  
     
     
         27 . The method of  claim 26 , wherein the iterative process includes a least squares fitting routine.  
     
     
         28 . The method of  claim 17 , wherein the analyzing step includes applying a genetic algorithm to concurrently optimize the determination of the stress as well as the thickness.  
     
     
         29 . The method of  claim 17 , wherein the method further comprises: 
 initially supporting the wafer only at points substantially two-thirds of the distance from the center of the wafer.    
     
     
         30 . A method of measuring parameters of a substantially planar wafer, comprising: 
 supporting the wafer only at points substantially two-thirds of the distance from the center of the wafer;    directing a probe beam of radiation onto the wafer; and    determining at least one parameter based on an observation of the interaction of the probe beam with the wafer.    
     
     
         31 . The method of  claim 29 , wherein the points at which the wafer is supported in the supporting step includes at least three points.  
     
     
         32 . The method of  claim 29 , wherein the parameter determining step includes: 
 determining an angle between the probe beam and a reflection of the probe beam from the wafer; and    determining the deformation based on the determined angle, wherein the determined parameter is the determined deformation.    
     
     
         33 . The method of  claim 29 , wherein the parameter determining step includes: 
 measuring the change in magnitude or polarization of the reflected probe beam induced by the interaction with the wafer; and    determining optical properties of the wafer based on the measured change in magnitude or polarization.    
     
     
         34 . A method of calibrating a wafer tilt detection system for use in correcting a measured tilt of a wafer resting on a movable stage, comprising: 
 resting a spherical mirror on the stage in place of the wafer;    directing the probe beam to the spherical mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is a tilt detection system calibration factor by which an actual tilt measurement of the wafer may be adjusted.    
     
     
         35 . The method of  claim 34 , wherein the relationship is a linear relationship.  
     
     
         36 . The method of  claim 34 , wherein the spherical mirror has a surface quality characterized by λ/4 and δR<1%R) and wherein the stage motion is characterized by δd<5 μm), whereby the tilt detection system calibration factor may be precisely determined.  
     
     
         37 . A method of determining a stage tilt calibration factor for use in correcting a measured tilt of a wafer resting on a movable stage, comprising: 
 resting a flat mirror on the stage in place of the wafer;    directing the probe beam to the flat mirror;    moving the stage and, at a plurality of positions of the stage, determining the angle between the probe beam and the reflection of the probe beam; and    determining a relationship between the positions and the determined angles, whereby the relationship is the stage tilt calibration factor.    
     
     
         38 . An apparatus for analyzing a wafer having a thin film thereon, comprising: 
 a first light generator that directs a first probe beam of radiation to reflect off the wafer surface;    an analyzer that measures the change in magnitude or polarization of the reflected probe beam induced by the interaction with the wafer and generates first signals responsive thereto;    a second light generator that directs a second probe beam of radiation to reflect of the wafer;    a detector that detects the angular deviation of the reflected probe induced by the interaction with the wafer and generates second signals responsive thereto,    wherein the first light generator, the analyzer, the second light generator and the detector are provided in a single tool.    
     
     
         39 . The wafer analyzing apparatus of  claim 38 , and further comprising: 
 a processor in the single tool programmed to analyze the first and second signals in order to determine characteristics of the wafer including the thickness of the film and the stress in the film.    
     
     
         40 . The wafer analyzing apparatus of  claim 38 , and further comprising: 
 an interface via which the first and second signals may be provided to a processor in order to determine characteristics of the wafer including the thickness of the film and the stress in the film.    
     
     
         41 . The wafer analyzing apparatus of  claim 38 , wherein the light generator and the second light generator are the same light generator.