Wafer grinding method

Abstract

A wafer grinding method includes loading a wafer onto a first chuck, first lowering a spindle having a wheel from a first vertical position to a second vertical position, second lowering the spindle from the second vertical position to a third vertical position, grinding the wafer by the wheel, identifying the third vertical position of the spindle by determining whether amounts of change in an operation current of the spindle exceed a reference amount of change in current, calculating spindle feedback displacement, and applying the spindle feedback displacement to the second vertical position of the first chuck.

What is claimed is: 
     
         1 . A wafer grinding method comprising:
 loading a wafer onto a first chuck;   first lowering a spindle having a wheel from a first vertical position to a second vertical position;   second lowering the spindle from the second vertical position to a third vertical position;   grinding the wafer by the wheel;   identifying the third vertical position of the spindle by determining whether amounts of change in an operation current of the spindle exceed a reference amount of change in current;   calculating spindle feedback displacement; and   applying the spindle feedback displacement to the second vertical position of the first chuck,   wherein the third vertical position of the spindle is defined as a vertical position at which the wheel comes into contact with the wafer, and   the spindle feedback displacement is defined as a difference between a reference vertical position of a reference chuck and the third vertical position of the spindle, and the reference vertical position of the reference chuck is defined as the third vertical position of the reference chuck.   
     
     
         2 . The wafer grinding method of  claim 1 , wherein the identifying of the third vertical position of the spindle comprises
 identifying, as the third vertical position of the spindle, a position of the spindle at the moment when an amount of change in the operation current of the spindle, which first exceeds the reference amount of change in current among the amounts of change in the operation current of the spindle, occurs.   
     
     
         3 . The wafer grinding method of  claim 2 , wherein the reference amount of change in current is three times a current change standard deviation, which is a standard deviation of the amounts of change in the operation current of the spindle. 
     
     
         4 . The wafer grinding method of  claim 3 , wherein the reference amount of change in current is a positive number. 
     
     
         5 . The wafer grinding method of  claim 4 , wherein the current change standard deviation is calculated based on the amounts of change in the operation current of the spindle from a time the spindle reaches the second vertical position to a time the grinding of the wafer is completed. 
     
     
         6 . The wafer grinding method of  claim 4 , wherein the current change standard deviation is calculated based on the amounts of change in the operation current of the spindle within 60 seconds from a time when the spindle reaches the second vertical position. 
     
     
         7 . The wafer grinding method of  claim 4 , wherein a spindle feedback time is defined as a difference between a reference time when the spindle reaches the reference vertical position and a reference time when the spindle reaches the third vertical position, and the spindle feedback displacement is calculated by multiplying the spindle feedback time and an average descending speed during the second lowering of the spindle. 
     
     
         8 . The wafer grinding method of  claim 4 , wherein the spindle feedback displacement is calculated by adding an amount of wear of the wheel to the difference between the reference vertical position of the reference chuck and the third vertical position of the spindle. 
     
     
         9 . The wafer grinding method of  claim 4 , wherein the reference vertical position of the reference chuck is at a distance of 8 μm to 20 μm downward from the second vertical position of the reference chuck. 
     
     
         10 . The wafer grinding method of  claim 4 , wherein a number of rotations per unit time of the wheel is maintained constant after reaching the second vertical position of the spindle. 
     
     
         11 . The wafer grinding method of  claim 4 , wherein the applying of the spindle feedback displacement to the second vertical position of the first chuck comprises not applying the spindle feedback displacement to the second vertical position of the first chuck when the spindle feedback displacement is greater than a vertical distance from the second vertical position to the third vertical position of the spindle. 
     
     
         12 . A wafer grinding method comprising:
 loading a wafer onto a first chuck;   first lowering a spindle having a wheel from a first vertical position to a second vertical position;   second lowering the spindle from the second vertical position to a third vertical position;   grinding the wafer by the wheel;   identifying the third vertical position of the spindle by determining whether amounts of change in an operation current of the spindle exceed a reference amount of change in current;   calculating spindle feedback displacement; and   applying the spindle feedback displacement to the second vertical position of the first chuck,   wherein the third vertical position of the spindle is defined as a vertical position at which the wheel comes into contact with the wafer,   the spindle feedback displacement is defined as a difference between a reference vertical position of the first chuck and the third vertical position of the spindle, and   the reference vertical position of the first chuck is defined as the third vertical position of the first chuck during a previous grinding process.   
     
     
         13 . The wafer grinding method of  claim 12 , wherein the identifying of the third vertical position of the spindle comprises
 identifying, as the third vertical position of the spindle, a position of the spindle at the moment when an amount of change in the operation current of the spindle, which first exceeds the reference amount of change in current among the amounts of change in the operation current of the spindle, occurs.   
     
     
         14 . The wafer grinding method of  claim 13 , wherein the reference amount of change in current is three times a current change standard deviation, which is a standard deviation of the amounts of change in the operation current of the spindle, and the reference amount of change in current is a positive number. 
     
     
         15 . The wafer grinding method of  claim 14 , wherein the current change standard deviation is calculated based on the amounts of change in the operation current of the spindle from a time the spindle reaches the second vertical position to a time the grinding of the wafer is completed. 
     
     
         16 . The wafer grinding method of  claim 14 , wherein the current change standard deviation is calculated based on the amounts of change in the operation current of the spindle within 60 seconds from a time when the spindle reaches the second vertical position. 
     
     
         17 . The wafer grinding method of  claim 14 , wherein a spindle feedback time is defined as a difference between a reference time when the spindle reaches the reference vertical position and a reference time when the spindle reaches the third vertical position, and the spindle feedback displacement is calculated by multiplying the spindle feedback time and an average descending speed during the second lowering of the spindle. 
     
     
         18 . The wafer grinding method of  claim 13 , wherein the spindle feedback displacement is calculated by adding an amount of wear of the wheel to the difference between the reference vertical position of the first chuck and the third vertical position of the spindle. 
     
     
         19 . The wafer grinding method of  claim 14 , wherein a number of rotations per unit time of the wheel is maintained constant after reaching the second vertical position of the spindle. 
     
     
         20 . A wafer grinding method comprising:
 loading a wafer onto a first chuck;   first lowering a spindle having a wheel from a first vertical position to a second vertical position;   second lowering the spindle from the second vertical position to a third vertical position;   grinding the wafer by the wheel;   identifying the third vertical position of the spindle by determining whether amounts of change in an operation current of the spindle exceed a reference amount of change in current;   calculating spindle feedback displacement; and   applying the spindle feedback displacement to the second vertical position of the first chuck,   wherein the third vertical position of the spindle is defined as a vertical position at which the wheel comes into contact with the wafer,   the spindle feedback displacement is calculated by adding an amount of wear of the wheel to a difference between a reference vertical position of a reference chuck and the third vertical position of the spindle, and the reference vertical position of the reference chuck is defined as the third vertical position of the reference chuck,   identifying, as the third vertical position of the spindle, a position of the spindle at the moment when an amount of change in the operation current of the spindle, which first exceeds the reference amount of change in current among the amounts of change in the operation current of the spindle, occurs,   the reference amount of change in current is a positive number and three times a current change standard deviation, which is a standard deviation of the amounts of change in the operation current of the spindle,   the current change standard deviation is calculated based on the amounts of change in the operation current of the spindle from a time the spindle reaches the second vertical position to a time the grinding of the wafer is completed, and   a number of rotations per unit time of the wheel is maintained constant after reaching the second vertical position of the spindle.