Wafer measurement system and apparatus

Abstract

A method and apparatus for the measurement of wafer thickness, flatness and the trench depth of any trenches etched thereon using the back surface of the wafer to accurately measure the back side of a trench, rendering the trench an effective bump, capable of being measured on the top surface and the bottom surface through a non-contact optical instrument that simultaneously measures the wavelength of the top surface and bottom surface of the wafer, converting the distance between wavelengths to a thickness measurement, using a light source that renders the material of which the wafer is composed transparent in that wavelength range, i.e., using the near infrared region for measuring the thickness and trench depth measurement of wafers made of silicon, which is opaque in the visible region and transparent in the near infrared region. Thickness and flatness, as well as localized shape, can also be measured using a calibration method that utilizes a pair of optical styli.

1 . A method for measuring trench depth on a wafer comprising
 microscopically locating said trench on said wafer, said wafer having a front surface and a back surface such that said trench is on said front surface;   positioning a non-contact optical instrument facing said back surface so that said trench is effectively a bump on said second surface from said non-contact optical instrument, said non-contact optical instrument utilizing a light source such that said wafer is transparent and said non-contact optical instrument receives reflected light from said back surface and said front surface of said wafer such that said front surface indicates the interior of said trench;   taking the measurement of the height of said bump using a light source set in a wavelength range wherein said wafer is transparent;   calibration of said bump height through a conversion of said measured height differences between said top surface and said bottom surface thereby determining the shape and contour of said wafer at the site of said trench.   
   
   
       2 . A method according to  claim 1  wherein said wafer is composed of one of the following group: silicon, GaAs, GaAIAs, InP, SiC, SiO 2 . 
   
   
       3 . A method according to  claim 1  wherein said light source is in the near infrared region, having a wavelength range of 900 nm to 1700 nm. 
   
   
       4 . A method according to  claim 1  wherein said non-contact optical instrument is a chromatic confocal sensor. 
   
   
       5 . A method according to  claim 4  wherein said chromatic confocal sensor utilizes a calibration means that converts said collected data corresponding to said wavelengths of said reflected light from said top surface and said bottom surface of said wafer and the corresponding height differences into a measured thickness that determines the depth of said trench or said thickness of said localized area on said wafer. 
   
   
       6 . A method according to  claim 1  wherein said non-contact optical instrument uses white light interferometry. 
   
   
       7 . A method according to  claim 1  wherein said non-contact optical instrument uses phase shift interferometry. 
   
   
       8 . A method according to  claim 1  wherein said non-contact optical instrument uses scanning confocal microscopy. 
   
   
       9 . A method according to  claim 1  wherein said non-contact optical instrument uses laser triangulation. 
   
   
       10 . A method according to  claim 1  wherein said optical instrument mechanically scans said wafer in transverse directions at a pre-specified sample rate and density. 
   
   
       11 . A method for measuring localized thin wafer thickness comprising
 microscopically locating said localized thickness area on said wafer, said wafer having a front surface and a back surface;   positioning a non-contact optical instrument on one side of said wafer to receive reflected light from said top surface and said bottom surface simultaneously;   taking the measurement of the thickness of said wafer using a light source set in a wavelength range wherein said wafer is transparent;   calibration of said localized wafer thickness through a conversion of said measured height differences between said top surface and said bottom surface thereby determining the localized thickness of said wafer.   
   
   
       12 . A method according to  claim 11  wherein said wafer is composed of one of the following group: silicon, GaAs, GaAIAs, InP, SiC, SiO 2 . 
   
   
       13 . A method according to  claim 11  wherein said light source is in the near infrared region, having a wavelength range of 900 nm to 1700 nm. 
   
   
       14 . A method according to  claim 11  wherein said non-contact optical instrument is chromatic confocal sensor. 
   
   
       15 . A method according to  claim 14  wherein said chromatic confocal sensor utilizes a calibration means that converts said collected data corresponding to said wavelengths of said reflected light from said top surface and said bottom surface of said wafer and the corresponding height differences into a measured thickness that determines the depth of said trench or said thickness of said localized area on said wafer. 
   
   
       16 . A method according to  claim 11  wherein said non-contact optical instrument uses white light interferometry. 
   
   
       17 . A method according to  claim 11  wherein said non-contact optical instrument uses phase shift interferometry. 
   
   
       18 . A method according to  claim 11  wherein said non-contact optical instrument uses scanning confocal microscopy. 
   
   
       19 . A method according to  claim 11  wherein said non-contact optical instrument uses laser triangulation. 
   
   
       20 . A method according to  claim 11  wherein said optical instrument mechanically scans said wafer in transverse directions at a pre-specified sample rate and density. 
   
   
       21 . An apparatus for measuring trench depth on a wafer or localized thickness of said wafer, said wafer having a top side and a bottom side, said apparatus comprising
 a non-contact optical height measurement instrument;   a securing means located substantially beneath said non-contact optical height instrument for positioning of said wafer;   a light source set in a wavelength range wherein said wafer is transparent;   said non-contact optical instrument being positioned on one side of said wafer to receive reflected light from said top surface and said bottom surface simultaneously;   data collection means that receives data from said non-optical height measurement instrument.   
   
   
       22 . An apparatus according to  claim 21  wherein said wafer is composed of one of the following group: silicon, GaAs, GaAIAs, InP, SiC, SiO 2 . 
   
   
       23 . An apparatus according to  claim 21  wherein said light source is in the near infrared region, having a wavelength range of 900 nm to 1700 nm. 
   
   
       24 . An apparatus according to  claim 21  wherein said non-contact optical instrument is a chromatic confocal sensor. 
   
   
       25 . An apparatus according to  claim 24  wherein said chromatic confocal sensor utilizes a calibration means that converts said collected data corresponding to said wavelengths of said reflected light from said top surface and said bottom surface of said wafer and the corresponding height differences into a measured thickness that determines the depth of said trench or said thickness of said localized area on said wafer. 
   
   
       26 . An apparatus according to  claim 21  wherein said non-contact optical instrument uses white light interferometry. 
   
   
       27 . An apparatus according to  claim 21  wherein said non-contact optical instrument uses phase shift interferometry. 
   
   
       28 . An apparatus according to  claim 21  wherein said non-contact optical instrument uses scanning confocal microscopy. 
   
   
       29 . An apparatus according to  claim 21  wherein said non-contact optical instrument uses laser triangulation. 
   
   
       30 . A method according to  claim 21  wherein said optical instrument mechanically scans said wafer in transverse directions at a pre-specified sample rate and density. 
   
   
       31 . A method of measuring the thickness, flatness and localized shape of a thin wafer, said wafer having a top side and a bottom side, said method comprising
 calibrating the distance of said wafer from a first sensor and a second sensor, said distance calibration further comprising
 placing a gage block of a known thickness and containing parallel surfaces between said first and second sensors in a suitable holder; 
 adjusting said first and second sensors in the Z plane such that the surface being sensed is placed at the middle of the sensor measurement range; 
   measuring the localized thickness of said wafer, said measurement further comprising
 placement of said wafer in a suitable holder allowing said first and second sensors to receive responses from both sides of said wafer; 
 moving said wafer in said suitable holder through a predetermined number of locations either individually at each of said locations or continuously; 
 recording the height values at each of said locations or continuously; 
 converting said height values to thickness values at each of said locations or continuously; 
 computing the shape and shape variations of said wafer through a mathematical calculation; 
 displaying said mathematical calculations of shape and shape variations through a displaying means. 
   
   
   
       32 . A method according to  claim 31  wherein a further calibration step is added, said calibration step further comprising
 calibrating said sensor height, said sensor height calibration further comprising
 first placement of an angle gage block of known angle between said first and second sensors in a suitable holder with the flat surface of said angle gage block being perpendicular to said first sensor, giving a surface of known angle to said first sensor; 
 rotating said angle gage block 180 degrees, placing the slope of said angle gage block in the opposite direction from said first placement with said angle gage block being perpendicular to said first sensor, giving a surface of known angle to said first sensor; 
 converting said collected height sensor calibration mathematically and thereby calculating the tilt of said angle block; 
 turning said angle gage block to present said angle gage block to said second sensor, repeating steps as applied to said first sensor. 
   
   
   
       33 . A method according to  claim 31  wherein said sensors are chromatic confocal. 
   
   
       34 . An apparatus for measuring the thickness, flatness and localized shape of a thin wafer, said wafer having a top side and a bottom side, said apparatus comprising
 a first stage for calibrating the distance of said wafer from a first sensor and a second sensor, said distance calibration further comprising
 placing a gage block of a known thickness and containing parallel surfaces between said first and second sensors in a suitable holder; 
 adjusting said first and second sensors in the Z plane such that the surface being sensed is placed at the middle of the sensor measurement range; 
   a second stage for measuring the localized thickness of said wafer, said measurement further comprising
 placement of said wafer in a suitable holder allowing said first and second sensors to receive responses from both sides of said wafer; 
 moving said wafer in said suitable holder through a predetermined number of locations either individually at each of said locations or continuously; 
 recording the height values at each of said locations or continuously; 
 converting said height values to thickness values at each of said locations or continuously; 
 computing the shape and shape variations of said wafer through a mathematical calculation; 
 displaying said mathematical calculations of shape and shape variations through a displaying means. 
   
   
   
       35 . An apparatus according to  claim 34  wherein there is a third stage for calibrating said sensor height, said sensor height calibration further comprising
 a second stage for calibrating said sensor height, said sensor height calibration further comprising   first placement of an angle gage block of known angle between said first and second sensors in a suitable holder with the flat surface of said angle gage block being perpendicular to said first sensor, giving a surface of known angle to said first sensor;   rotating said angle gage block 180 degrees, placing the slope of said angle gage block in the opposite direction from said first placement with said angle gage block being perpendicular to said first sensor, giving a surface of known angle to said first sensor;   converting said collected height sensor calibration mathematically and thereby calculating the tilt of said angle block;   turning said angle gage block to present said angle gage block to said second sensor, repeating steps as applied to said first sensor;   
   
   
       36 . An apparatus according to  claim 34  wherein said sensor is chromatic confocal.