Apparatus and method for focusing light beam and exposure apparatus

Abstract

Focusing method and exposure apparatus for focusing both a parallel light beam and a non-parallel light beam through a movable objective lens onto an object. A negative feedback loop is provided which has a detector for receiving a reflection light beam of the non-parallel light beam passed through the movable objective lens, reflected at the object and passed through the movable objective lens, for generating a detection signal corresponding to a focus deviation of the non-parallel light beam, and a driver for receiving the detection signal to control a position of the movable objective lens in accordance with the detection signal, so that the detection signal is decreased. The negative feedback loop further includes a correction signal generator for generating a correction signal and supplying it to the negative feedback loop as a disturbance of the loop so that the parallel light beam is focused onto the object.

1 . A focusing system for focusing both a parallel light beam and a non-parallel light beam through a movable objective lens onto an object, comprising: 
 a negative feedback loop including a detector for receiving a reflection light beam of said non-parallel light beam passed through said movable objective lens, reflected at said object and passed through again said movable objective lens, for thereby generating a detection signal corresponding to a focus deviation of said non-parallel light beam and driver means for receiving said detection signal for thereby controlling a position of said movable objective lens in accordance with said detection signal so that said detection signal is decreased; and    a correction signal generator for generating a correction signal and supplying it to said negative feedback loop as a disturbance of said loop so that said parallel light beam is focused onto said object.    
     
     
         2 . A focusing system according to  claim 1 , 
 wherein said correction signal generator is supplied with said detection signal and designed for separating a DC component and a high frequency component from said detection signal.    
     
     
         3 . A focusing system according to  claim 2 , 
 wherein said correction signal has a low frequency component of 0 to 200 Hz.    
     
     
         4 . A focusing method for focusing both a parallel light beam and a non-parallel light beam through a movable objective lens onto an object, comprising steps of: 
 detecting a focus deviation of said non-parallel light beam from a reflection light beam resulting from reflection of said non-parallel light beam at said object and passed through said movable objective lens, for thereby generating a signal indicative of said focus deviation;    displacing said movable objective lens on the basis of said detection signal indicative of said focus deviation so that said detection signal indicative of said focus deviation is decreased; and    extracting a correction signal from said signal indicative of said focus deviation and adding said correction signal to said signal indicative of said focus deviation as a disturbance to thereby cause said non-parallel light beam to be focused onto said object.    
     
     
         5 . A focusing method according to  claim 4 , 
 wherein said correction signal is derived by eliminating a DC component and a high-frequency component from said signal indicative of said focus deviation.    
     
     
         6 . A focusing method according to  claim 5 , 
 wherein said correction signal has a low frequency component of 0 to 200 Hz.    
     
     
         7 . An exposure apparatus focusing both a parallel light beam and a non-parallel light beam through a movable objective lens onto an object, comprising: 
 a negative feedback loop including a detector for receiving a reflection light beam of said non-parallel light beam passed through said movable objective lens, reflected at said object and passed through again said movable objective lens, for thereby generating a detection signal corresponding to a focus deviation of said non-parallel light beam and driver means for receiving said detection signal for thereby controlling a position of said movable objective lens in accordance with said detection signal so that said detection signal is decreased; and    a correction signal generator for generating a correction signal and supplying it to said negative feedback loop as a disturbance of said loop so that said parallel light beam is focused onto said object.    
     
     
         8 . An optical recording system according to  claim 7 , 
 wherein said correction signal generator is supplied with said detection signal and designed for separating a DC component and a high frequency component from said detection signal.    
     
     
         9 . An optical recording system according to  claim 8 , 
 wherein said correction signal has a low frequency component of 0 to 200 Hz.