Projecting exposure apparatus and method of exposing a circuit substrate

Abstract

A scanning projection exposure apparatus having a projection optical system (11), for serially transferring a pattern on a reticle (7) onto a wafer (12). The exposure apparatus control the position and/or the tilt angle of the wafer (12) such that the surface of the wafer (12) may be continuously adjusted during the scanning exposure operation so as to be coincident with an image plane of the projection optical system (11), with a high tracking accuracy, even when the image plane of the projection optical system (11) tends to vary during the scanning exposure operation. An image of that portion of the pattern on the reticle (7) which is confined in an illumination area (8) is formed in a plane through the projection optical system. This plane is used as a first reference plane (62). Parameters of the first reference plane (62) such as the tilt angle θ p are determined by measurement. An image plane is defined by conjugate images (formed on the wafer side) of the points passing the center of the illumination area (8) when the reticle (7) is moved for scanning in the X-direction. This image plane is used as a second reference plane (65). The tilt angle Θ x of the second reference plane (65) is determined by measurement. When the scanning exposure operation is performed, the tilt angle of the illumination field (13) of the wafer (12) is made coincident with that of the first reference plane (62), and the focusing position of the wafer (12) is made coincident with that of the second reference plane (65).

What is claimed is: 
     
       1. A projection exposure apparatus having a projection optical system with an optical axis, in which a mask and a photosensitized substrate are moved for scanning in synchronism with each other and relative to said projection optical system while an image of a portion of a pattern on said mask is projected through said projection optical system onto a predetermined exposure area on said substrate, said projection exposure apparatus comprising: a position detection sensor for detecting i) a tilt angle of the surface of said predetermined exposure area relative to a plane perpendicular to said optical axis of said projection optical system and ii) a focusing position of the surface of said predetermined exposure area measured in the direction of said optical axis of said projection optical system;   a tilt angle control unit for controlling the surface of said substrate based on the tilt angle detected by said position detection sensor so as to cause the surface of said substrate to be parallel to a first reference plane, said first reference plane being defined by a projected image of said mask formed through said projection optical system; and   a focusing position control unit for controlling said substrate based on i) the focusing position of the surface of said predetermined exposure area and ii) a second reference plane, said second reference plane being defined by a distribution of focusing positions obtained when said mask is moved for scanning.   
     
     
       2. A projection exposure apparatus according to claim 1, wherein: said focusing position control unit is so arranged as to control said substrate based on i) the position of said first reference plane measured in the direction of said optical axis of said projection optical system and ii) said second reference plane.   
     
     
       3. A projection exposure apparatus according to claim 1, wherein: said tilt angle control unit and said focusing position control unit are provided with a storage unit for storing tilt angles of said first reference plane and of said second reference plane relative to said plane perpendicular to said optical axis of said projection optical system.   
     
     
       4. A projection exposure apparatus according to claim 3, wherein: said storage unit stores the position of said first reference plane measured in the direction of said optical axis of said projection optical system.   
     
     
       5. A projection exposure apparatus according to claim 4, wherein: i) the tilt angle of said first reference plane relative to said plane perpendicular to said optical axis of said projection optical system and ii) the position of said first reference plane measured in the direction of said optical axis of said projection optical system are determined from projected images obtained by positioning said mask stationary in the midpoint in the scanning direction and then moving said substrate in the direction of said optical axis of said projection optical system as well as in directions in said plane perpendicular to said optical axis of said projection optical system.   
     
     
       6. A projection exposure apparatus having a projection optical system with an optical axis, in which a mask and a photosensitized substrate are moved for scanning in synchronism with each other and relative to said projection optical system while an image of a portion of a pattern on said mask is projected through said projection optical system onto a predetermined exposure area on said substrate, said projection exposure apparatus comprising: a detection circuit for detecting i) a tilt angle of said substrate relative to a plane perpendicular to said optical axis of said projection optical system and ii) a focusing position of said substrate measured in the direction of said optical axis of said projection optical system;   a tilt angle calculation circuit for calculating the difference between i) a tilt angle of a first reference plane relative to said plane perpendicular to said optical axis of said projection optical system, said first reference plane being defined by a projected image of said mask formed through said projection optical system, and ii) the tilt angle detected by said detection circuit; and   a focusing position calculation circuit for calculating the difference between i) the focusing position of the surface of said predetermined exposure area and ii) focusing positions obtained when said mask is moved for scanning.   
     
     
       7. A projection exposure apparatus according to claim 6, wherein: said focusing position calculation circuit comprises a focusing position correction circuit for calculating the difference between i) the position of said first reference plane measured in the direction of said optical axis of said projection optical system and ii) focusing positions obtained when said mask is moved for scanning.   
     
     
       8. A projection exposure apparatus according to claim 6, further comprising: a control unit for controlling said substrate based on i) the tilt angle difference calculated by said tilt angle calculation circuit and ii) the focusing position difference calculated by said focusing position calculation circuit.   
     
     
       9. A method of exposing a circuit substrate by using a projection optical system with an optical axis, in which a mask and a photosensitized substrate are moved for scanning in synchronism with each other and relative to said projection optical system while an image of a portion of a pattern on said mask is projected through said projection optical system onto a predetermined exposure area on said substrate, said method comprising the steps of: a) detecting i) a tilt angle of the surface of said predetermined exposure area relative to a plane perpendicular to said optical axis of said projection optical system and ii) a focusing position of the surface of said predetermined exposure area measured in the direction of said optical axis of said projection optical system;   b) controlling the surface of said predetermined exposure area based on the detected tilt angle so as to cause the surface of said predetermined exposure area to be parallel to a first reference plane, said first reference plane being defined by a projected image of said mask formed through said projection optical system; and   c) controlling said substrate based on i) the focusing position of the surface of said predetermined exposure area and ii) a second reference plane, said second reference plane being defined by a distribution of focusing positions obtained when said mask is moved for scanning.   
     
     
       10. A method of exposing a circuit substrate according to claim 9, wherein: said distribution of focusing positions defining said second reference plane is defined depending on the focusing position of said first reference plane.   
     
     
       11. A method of exposing a circuit substrate by using a projection optical system with an optical axis, in which a mask and a photosensitized substrate are moved for scanning in synchronism with each other and relative to said projection optical system while an image of a portion of a pattern on said mask is projected through said projection optical system onto a predetermined exposure area on said substrate, said method comprising the steps of: a) detecting i) a tilt angle of the surface of said predetermined exposure area relative to a plane perpendicular to said optical axis of said projection optical system and ii) a focusing position of the surface of said predetermined exposure area measured in the direction of said optical axis of said projection optical system;   b) calculating the difference between i) a tilt angle of a first reference plane relative to said plane perpendicular to said optical axis of said projection optical system, said first reference plane being defined by a projected image of said mask formed through said projection optical system, and ii) the tilt angle of the surface of said predetermined exposure area detected in said step a; and   c) calculating a focusing error between i) the focusing position of the surface of said predetermined exposure area and ii) a second reference plane, said second reference plane being defined by a distribution of focusing positions obtained when said mask is moved for scanning.   
     
     
       12. A method of exposing a circuit substrate according to claim 11, further comprising the steps of: d) calculating the difference between i) the focusing error calculated in said step c and ii) the focusing position of the surface of said predetermined exposure area detected in said step a; and   e) adjusting said substrate based on i) the tilt angle difference calculated in said step b and ii) the focusing position difference calculated in said step d.   
     
     
       13. A method of exposing a circuit substrate according to claim 11, wherein: the focusing error calculated in said step c varies depending on the coordinate of said substrate in the scanning direction.   
     
     
       14. An exposure apparatus including a projection optical system with an optical axis for projecting a pattern on a mask onto a photosensitized substrate and a substrate stage for moving said substrate on the image side of said projection optical system, said exposure apparatus comprising: a substrate focusing position detection unit for detecting a first focusing position of said substrate measured in the direction of said optical axis of said projection optical system;   a stage focusing position detection unit for detecting a second focusing position of said substrate stage measured in the direction of said optical axis of said projection optical system;   a focusing position selection unit for selecting one of said first and second focusing positions depending on the condition of the surface of said substrate; and   a focusing position control unit for controlling the focusing position of said substrate depending on the focusing position selected by said focusing position selection unit.   
     
     
       15. An exposure apparatus according to claim 14, wherein: said stage focusing position detection unit comprises:   a sensor for detecting the height of said substrate stage; and   a substrate modelling unit for detecting said second focusing position based on i) the height detected by said sensor and ii) a predefined substrate model.   
     
     
       16. An exposure apparatus according to claim 14, wherein: said substrate focusing position detection unit is so arranged as to detect a tilt angle of said substrate; and   said stage focusing position detection unit is so arranged as to detect a tilt angle of said substrate stage.   
     
     
       17. An exposure apparatus according to claim 14, further comprising: a substrate step-like structure detection unit for detecting a step-like structure on said substrate, said substrate step-like structure detection unit being independent of said substrate focusing position detection unit;   wherein said focusing position selection unit is so arranged as to select one of said first and second focusing positions depending on the results of the detection of the step-like structure by said substrate step-like structure detection unit.   
     
     
       18. An exposure apparatus according to claim 14, wherein: said substrate focusing position detection unit is so arranged as to perform focusing position detection operation for both i) inside projection exposure areas on said substrate in which said pattern on said mask is projected and ii) outside said projection exposure areas; and   said focusing position selection unit is so arranged as to select one of said first and second focusing positions depending on the results of the focusing position detection operations performed outside said projection exposure areas.   
     
     
       19. A scanning exposure apparatus for serially transferring an image of a pattern on a mask onto a photosensitized substrate, comprising: a projection optical system with an optical axis for projecting an image of a portion of said pattern on said mask onto a predetermined exposure area on said substrate;   a substrate stage for moving said substrate on the image plane side of said projection optical system;   a drive system for moving said mask and said substrate in synchronism with each other and relative to said projection optical system;   a substrate focusing position detection sensor for detecting a first focusing position of said substrate measured in the direction of said optical axis of said projection optical system;   a stage focusing position detection sensor for detecting a second focusing position of said substrate stage measured in the direction of said optical axis of said projection optical system;   a storage unit for storing data relating to a step-like structure on the surface of said substrate;   a focusing position selection unit for selecting one of said first and second focusing positions depending on i) said data relating to the step-like structure on the surface of said substrate stored in said storage unit and ii) the position of said substrate driven by said drive unit; and   a focusing position control unit for controlling the focusing position of said substrate depending on the focusing position selected by said focusing position selection unit.   
     
     
       20. A scanning exposure apparatus according to claim 19, wherein: said stage focusing position detection unit comprises:   a sensor for detecting the height of said substrate stage; and   a substrate modelling unit for detecting said second focusing position based on i) a predefined substrate model and ii) the height detected by said sensor.   
     
     
       21. A method of exposing a circuit substrate by using a projection optical system with an optical axis, in which an image of a portion of a pattern on a mask is projected through said projection optical system onto a predetermined exposure area on a photosensitized substrate, said method comprising the steps of: a) detecting a first focusing position of said predetermined exposure area on said substrate measured in the direction of said optical axis of said projection optical system;   b) detecting a second focusing position of said substrate stage measured in the direction of said optical axis of said projection optical system;   c) selecting one of said first and second focusing positions depending on the condition of the surface of said substrate; and   d) controlling the focusing position of said substrate depending on the selected focusing position.   
     
     
       22. A method of exposing a circuit substrate according to claim 21, wherein: a1) said step of detecting said first focusing position includes detecting a tilt angle of said substrate; and   b1) said step of detecting said second focusing position includes detecting a tilt angle of said substrate stage.   
     
     
       23. A method of exposing a circuit substrate according to claim 21, wherein: said step of detecting said second focusing position comprises the steps of:   b2) detecting the height of said substrate stage; and   b3) detecting said second focusing position based on i) a predefined substrate model and ii) the detected height of said substrate stage.   
     
     
       24. A method of exposing a circuit substrate according to claim 21, further comprising the step of: c1) selecting one of said first and second focusing positions depending on the condition of the surface of said substrate, which condition is stored in a storage unit.   
     
     
       25. A method of exposing a circuit substrate by using a projection optical system with an optical axis, in which a mask having a pattern formed thereon is illuminated so that an image of a portion of said pattern on said mask is projected through said projection optical system onto a predetermined exposure area on a photosensitized substrate, said method comprising the steps of: a) detecting a first focusing position of said predetermined exposure area on said substrate measured in the direction of said optical axis of said projection optical system;   b) detecting a second focusing position of said substrate stage measured in the direction of said optical axis of said projection optical system;   c) selecting one of said first and second focusing positions depending on stored step-like structure data; and   d) controlling the focusing position of said substrate depending on the selected focusing position.   
     
     
       26. A method of exposing a circuit substrate according to claim 25, wherein: said step of detecting said second focusing position comprises the steps of:   detecting the height of said substrate stage; and   detecting said second focusing position based on i) a predefined substrate model and ii) the detected height of said substrate stage.