Particle-optical projection system

Abstract

In a particle-optical projection system ( 32 ) a pattern (B) is imaged onto a target (tp) by means of energetic electrically charged particles. The pattern is represented in a patterned beam (pb) of said charged particles emerging from the object plane through at least one cross-over (c); it is imaged into an image (S) with a given size and distortion. To compensate for the Z-deviation of the image (S) position from the actual positioning of the target (tp) (Z denotes an axial coordinate substantially parallel to the optical axis cx), without changing the size of the image (S), the system comprises a position detection means (ZD) for measuring the Z-position of several locations of the target (tp), a control means ( 33 ) for calculating modifications (cr) of selected lens parameters of the final particle-optical lens (L 2 ) and controlling said lens parameters according to said modifications.

1 . A particle-optical projection system ( 32 ) for imaging a pattern onto a target (tp) by means of energetic electrically charged particles in a particle-beam exposure apparatus, adapted to produce, from the pattern positioned at an object plane (bp) and represented in a patterned beam (pb) of said charged particles emerging from the object plane through at least one cross-over (c), an image (S) at the position of the target, with said image (S) having a given size and distortion, said projection system comprising 
 a position detection means (ZD) for measuring the Z-position of several locations of the target (tp), with Z denoting a coordinate taken along a direction substantially parallel to the optical axis (cx) of the projection system,    a control means ( 33 ) adapted to calculate modifications (cr) of selected lens parameters of the final particle-optical lens (L 2 ) of said projection system and control said lens parameters according to said modifications, with said modifications being suitable to compensate for the Z-deviation of the image (S) position from the actual positioning of the target (tp) as determined from said Z-position measurements, without changing the size of the image.    
     
     
         2 . The projection system of  claim 1 , wherein the control means ( 33 ) is further adapted to calculate a beam current value (Ib) corresponding to the entire patterned beam, and calculate modifications (cr) of selected lens parameters of the final particle-optical lens (L 2 ), with said modifications being suitable to additionally compensate for the influence of said beam current value (Ib) upon the geometric imaging properties of the projection system.  
     
     
         3 . The projection system of  claim 1 , comprising an electromagnetic lens having, in a common pole-casing of magnetic material, at least two electroconductive coils ( 21 ,  22 ;  312 ,  322 ,  323 ) which are situated at different positions within the lens and to which different electric currents are applicable, wherein the control means is adapted to calculate modifications of the electric currents (I 1 , I 2 ; Ibase, Ic) fed to said electroconductive coils suitable to compensate for the Z-deviation of the actual positioning of the image (S) from the positioning of the target (tp), and control the electric currents (I 1 , I 2 ; Ibase, Ic) fed to said electromagnetic coils according to said modifications.  
     
     
         4 . The projection system of  claim 3 , wherein the electromagnetic lens comprises two electroconductive coils ( 21 ,  22 ) of corresponding size whose positions are different with respect to the direction parallel to the particle beam. ( FIG. 3   a )  
     
     
         5 . The projection system of  claim 3 , wherein the electromagnetic lens has a first electroconductive coil ( 321 ) which is fed a first electric current (Ibase) and at least one second electroconductive coil ( 322 ,  323 ) fed a second electric current (Ic), with the absolute value of the second electric current (Ic) being smaller than the first electric current (Ibase) by at least an order of magnitude. ( FIG. 3   b )  
     
     
         6 . The projection system of  claim 1 , comprising an electrostatic Einzel lens having an initial electrode ( 421 ), at least two central electrodes ( 431 ,  432 ) and a final electrode ( 422 ), wherein the central electrodes are adapted to be fed different electrostatic potentials (U1, U2), wherein the control means is adapted to calculate modifications of the electric potentials (U1, U2) of said central electrodes suitable to compensate for the Z-deviation of the actual positioning of the image (S) from the positioning of the target (tp), with the difference (U1−U2) between the potentials of the central electrodes being smaller than the difference between the potential of one of the central electrodes ( 431 ,  432 ) to the potential of the initial and the final electrode ( 421 ,  422 ) by at least an order of magnitude, and control the electric potentials (U1, U2) of the central electrodes according to said modifications.  
     
     
         7 . The projection system of  claim 1 , comprising a particle-optical lens provided with adjustable positioning means for adjustment of the axial position (Δz) of the lens as measured along the optical axis of the projection system, wherein the control means is adapted to calculate modifications of the axial position (Δz) of said lens suitable to compensate for the Z-deviation of the actual positioning of the image (S) from the positioning of the target (tp), and control said axial positions (z1, z2) according to said modifications by means of said positioning means.  
     
     
         8 . The projection system of  claim 7 , wherein the positioning means are realized as piezoelectric actuators.  
     
     
         9 . A particle-optical projection system ( 32 ) for imaging a pattern onto a target (tp) by means of energetic electrically charged particles in a particle-beam exposure apparatus, adapted to produce, from the pattern positioned at an object plane (bp) and represented in a patterned beam (pb) of said charged particles emerging from the object plane through at least one cross-over (c), an image (S) at the position of the target, with said image (S) having a given size and distortion, said projection system comprising 
 a multi-beam pattern definition means for defining the patterned beam with a time-variable pattern, having 
 an aperture array means ( 203 ) having a plurality of apertures ( 230 ) defining the shape of beamlets (bm) permeating said apertures and  
 at least one deflector array means ( 501 ,  502 ,  503 ) separate from the aperture array means ( 203 ), with said deflector array means ( 501 ,  502 ,  503 ) having a plurality of openings ( 250 ) surrounding the beamlets (bm), wherein for each opening or group of openings are provided at least two deflecting electrodes (ea 1 , ea 2 ; eb 1 , eb 2 ) to which different electrostatic potentials are applicable, thus correcting the path of the beamlet(s) passing through the respective opening according to a desired path through the device ( 102 ),  
 wherein at least one of said deflector array means ( 502 ) is adapted to adjust the angles of the beamlets passing the apertures (bm) to minimize the aberration of the crossover (c).  
   
     
     
         10 . The projection system of  claim 9 , wherein said deflector array means ( 502 ) is positioned immediately before the aperture array means ( 203 ).  
     
     
         11 . The projection system of  claim 9 , wherein the multi-beam pattern definition means comprises a deflector array means ( 503 ) which is adapted to produce a virtual object ( 203 ′) different from the object as defined by the apertures ( 230 ) of the aperture array means.  
     
     
         12 . The projection system of  claim 9 , wherein the multi-beam pattern definition means comprises 
 a first deflector array means ( 502 ) which is adapted to adjust the angles of the beamlets passing the apertures (bm) to minimize the aberration of the crossover (c),    a second deflector array means ( 503 ) which is adapted to produce a virtual object ( 203 ′) different from the object as defined by the aperture ( 230 ),    said first and second deflector array means ( 502 ,  503 ) being adapted to adjust the position of the virtual object ( 230 ′) and the angles of the beamlets independently from each other.    
     
     
         13 . The projection system of  claim 9 , wherein the modifications of said deflecting electrode potentials are calculated to compensate for the beam current influence upon the axial position of the image and the size of the image.  
     
     
         14 . The projection system of  claim 9 , wherein the modifications of said deflecting electrode potentials are calculated to additionally compensate for the beam current influence upon the distortion of the image.  
     
     
         15 . The projection system of  claim 9 , further comprising an electrostatic Einzel lens having an initial electrode ( 421 ), at least two central electrodes ( 431 ,  432 ) and a final electrode ( 422 ), wherein the central electrodes are adapted to be fed different electrostatic potentials (U1, U2), wherein the control means is adapted to 
 calculate a beam current value (Ib) corresponding to the entire patterned beam,    calculate modifications of the electric potentials (U1, U2) of said central electrodes suitable to compensate for the influence of said beam current value (Ib) upon the geometric imaging properties of the projection system, with the difference (U1−U2) between the potentials of the central electrodes being smaller than the difference between the potential of one of the central electrodes ( 431 ,  432 ) to the potential of the initial and the final electrode ( 421 ,  422 ) by at least an order of magnitude, and    control the electric potentials (U1, U2) of the central electrodes according to said modifications.    
     
     
         16 . The projection system of  claim 9 , further comprising an particle-optical lens provided with adjustable positioning means for adjustment of the axial position (Δz) of the lens as measured along the optical axis of the projection system, wherein the control means is adapted to 
 calculate a beam current value (Ib) corresponding to the entire patterned beam,    calculate modifications of the axial position (Δz) of said lens suitable to compensate for the influence of said beam current value (Ib) upon the geometric imaging properties of the projection system, and    control said axial positions (z1, z2) according to said modifications by means of said positioning means.    
     
     
         17 . The projection system of  claim 16 , wherein the positioning means are realized as piezoelectric actuators.