Abstract:
A production method of a semiconductor device which includes the steps of exposing a resist coated on a substrate of a semiconductor device by projecting a light pattern on the substrate of the semiconductor device through an object lens, developing the resist exposed by the light pattern to form a wafer pattern with the resist, and etching the substrate on which the wafer pattern with the resist is formed. In the step of exposing, the light pattern projected on the substrate is formed by excimer laser light which is emitted from an annular shaped light source and which is passed through a mask having a phase shifter.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. application Ser. No. 10/282,081, filed Oct. 29, 2002, now U.S. Pat. No. 7,012,671, which is a continuation of U.S. application Ser. No. 09/542,072, filed Apr. 3, 2000, now U.S. Pat. No. 6,485,891, which is with U.S. application Ser. No. 09/542,071, filed Apr. 13, 2000, now U.S. Pat. No. 6,335,146, which are continuations of U.S. application Ser. No. 09/447,243, filed Nov. 23, 1999, which is a continuation of U.S. application Ser. No. 09/003,141, filed Jan. 6, 1998, now U.S. Pat. No. 6,016,187, issued Jan. 18, 2000, which is a continuation of U.S. application Ser. No. 08/727,762, filed Oct. 8, 1996, now U.S. Pat. No. 5,767,949, issued Jun. 16, 1998, which is a continuation of U.S. application Ser. No. 08/501,178, filed Jul. 11, 1995, now abandoned, which is a continuation of U.S. application Ser. No. 08/235,654, filed Apr. 29, 1994, now U.S. Pat. No. 5,526,094, issued Jun. 11, 1996, which is a continuation of U.S. application Ser. No. 07/846,158, filed Mar. 5, 1992, now U.S. Pat. No. 5,329,333, issued Jul. 12, 1994, the subject matter of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an exposure method and apparatus therefor, an exposure system and a mask circuit pattern inspection system, which eliminate an influence of interference light generated in an extremely fine circuit pattern formed on a mask, so that an image is formed with a high resolving power on a substrate through a projection lens and exposed and, further, wherein the light source is an excimer laser light source. 
     In the manufacture of an LSI, a circuit pattern on a mask is exposed and transferred onto a wafer to form a fine circuit pattern on the wafer. However, to cope with the need of high integration of LSI, the circuit pattern transferred onto the wafer tends to be an extremely fine pattern, which constitutes a resolution limit of an imaging optical system. 
     In view of the foregoing, various techniques have been developed in order to transfer an extremely fine circuit pattern. 
     For example, there is a method for exposure using X-rays such as SOR (Synchrotron Organized Resonance) light. There is a further method which uses an EB (Electron Beam) exposure machine. Furthermore, there is another method using an excimer laser disclosed in “Excimer Laser Stepper for Sub-half Micron Lithography, Akikazu Tanimoto, SPIE, Vol. 1088 Optical Laser Microlithography 2 (1989)” or Japanese Patent Laid-Open No. 57(1982)-198631. 
     A theoretical analysis of partial coherent imaging is introduced in “Stepper&#39;s Optics (1), (2), (3) and (4)” (Optical Technical Contact: Vol. 27, No. 12, pp. 762-771, Vol. 28, No.1, pp. 59-67, Col. 28, No. 2, pp. 108-119, Vol. 28, No. 3, pp.165-175). 
     Also Japanese Patent Unexamined Publication No. 3-27516 describes an example in which a spatial filter is used to improve a resolving power. 
     Further, a phase shifter method for modifying a mask to improve a resolving power is known from Japanese Patent Publication No. 62(1987)-50811. According to this phase shifter method, light from a neighboring pattern is made to interfere, thereby enhancing the resolving power, which is realized by providing a film (a phase shifter) with phases alternately deviated through π so that phases of adjacent patterns are inverted. However, the prior art known from the aforementioned Patent Publication No. 62(1987)-50811 has a problem in that an arrangement of the phase shifter is difficult, and the manufacture of a mask provided with the phase shifter is difficult. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an exposure method and an apparatus therefor so that an extremely fine white and black circuit pattern formed on a mask can be transferred onto a substrate with a resolving power equal to or higher than a phase shifter, while solving the aforementioned problem noted with respect to the prior art. 
     It is a further object of the present invention to provide an exposure method and system, and particularly an excimer exposure method and system, in which data of a transferred pattern on a substrate actually transferred by an exposure apparatus can be confirmed through simulation by arithmetic processing. 
     It is another object of the present invention to provide a mask circuit pattern inspection system in which even in the case where an extremely fine circuit pattern formed on a mask is different from a pattern transferred onto a substrate, the extremely fine circuit pattern formed on the mask can be inspected with high accuracy. 
     The aforesaid problem can be solved by the present invention which provides an exposure apparatus or exposure method comprising an illuminating arrangement, such as an excimer laser light source, having coherent property to a certain degree, an imager for imaging light in which a mask (including a reticle) illuminated by the illuminating arrangement is imaged onto a wafer, and a shield for shielding at least a part of the O-order diffraction light out of light which transmits through or reflects from the mask. 
     The present invention further provides an excimer exposure apparatus wherein a spatial filter shields an area corresponding to the NA of the illuminating arrangement. 
     Furthermore, the present invention provides an excimer exposure apparatus wherein the illuminating arrangement comprises an integrator and a spatial filter. 
     Moreover, the present invention provides an excimer exposure apparatus wherein the mask has a circuit pattern formed to have a line width which is substantially ½ of an imaging resolving power. 
     The present invention also provides a projection type exposure apparatus and method comprising an illuminating arrangement for substantially uniformly applying ring-like diffused illumination formed from a number of imaginary point sources to a mask in an exposure area, and a reduction projection lens having an optical eye which shields at least a part of the O-order diffraction light or low-order diffraction light out of light which transmits through the mask substantially uniformly diffused and illuminated by the illuminating arrangement and imaging a circuit pattern formed on the mask onto a substrate in the exposure area, wherein the circuit pattern formed on the mask is sequentially exposed on the substrate by step-and-repeat processing. 
     The present invention further provides an excimer exposure method which includes the steps of illuminating a mask formed with a circuit pattern, shielding at least a part of the O-order diffraction light out of light which transmits through or reflects from the circuit pattern of the illuminated mask, imaging the light by an imager, and transferring the imaged light onto a substrate. 
     Furthermore, the present invention provides an excimer exposure method wherein the minimum line width of the circuit pattern on the mask is formed by being suited to an imaging resolving power of the imager. 
     Moreover, the present invention provides an excimer exposure method wherein the mask has a circuit pattern formed to have a line width which is substantially ½ of the imaging resolving power. 
     The present invention further provides an excimer exposure method wherein the circuit pattern on the mask is formed to have a line width which is substantially ½ of the imaging resolving power, and in a wide circuit pattern when transferred onto a substrate, a transmission portion on the mask is formed of a line and space having a pitch of substantially ½ to ⅓ of the imaging resolving power or a lattice pattern. 
     The present invention further provides an excimer exposure method which includes the steps of dividing a circuit pattern formed on a mask into a fine pattern portion and a large pattern portion, imaging them by an imager and transferring the same onto a substrate. 
     The present invention also provides an excimer exposure system including a mask data converter for converting and producing data of a mask from data, and a calculator for applying arithmetic processing based on a transmission function substantially equivalent to an imager for transferring a circuit pattern formed on the mask using excimer laser light with respect to mask data obtained from the mask data converter to calculate data of the transferred pattern onto a substrate. 
     The present invention additionally provides a mask circuit pattern inspection system including a mask data converter for converting and producing data of a mask from wiring data, a calculator for applying arithmetic processing based on a transmission function substantially equivalent to an imager for transferring a circuit pattern formed on the mask using excimer laser light with respect to mask data obtained from the mask data converter to calculate data of a transferred pattern on a wafer, an inspection device including an illuminating arrangement for illuminating a mask with the excimer light, an imager for imaging light which transmits through or reflects from a mask illuminated by the illuminating arrangement to a detection position, the imager having a transmission function substantially equivalent to that of the first-mentioned imager, and a light receiver for receiving an imaging circuit pattern imaged on the detection position to obtain an image signal, and a comparator for comparing an image signal obtained from the light receiver of the inspection device with data of a transferred pattern on a wafer calculated by the calculator. 
     In an exposure apparatus using excimer laser light, for example, the contrast of a circuit pattern transferred onto a substrate is degraded because diffraction light cannot be sufficiently taken into an opening (pupil) of the imager. Light is diffracted according to the using waveform and the dimension of the circuit pattern from the circuit pattern on the mask. At that time, in the case where a circuit pattern is extremely fine, a diffraction angle becomes large, and intensity of diffracted light also increases. As the result, light does not enter an opening of the imager (projection lens) used for transfer, which constitutes the cause for degrading the resolving power. 
     In order to minimize the loss of the diffracted light, it is contemplated that the wavelength is shortened to reduce diffraction components as in an excimer laser stepper or the NA of the imager (projection lens) is increased so as to receive diffraction light as much as possible. 
     On the other hand, according to the present invention, with a view to a phenomenon in which less components of diffraction light from a circuit pattern on a mask is received into imager (projection lens) whereas all components (O-order diffraction light) not diffracted from the circuit pattern on the mask are received therein, the O-order diffraction light alone in a large amount of light necessary for imaging is received into the imager (projection lens), and less diffraction light components is relatively received into the imager (projection lens). From a viewpoint of this, at least a part of the O-order diffraction light is shielded thereby to relatively improve a balance in quantity of light between the diffraction light emitted out of the imager (projection lens) and the O-order diffraction light and to improve the contrast of an extremely fine circuit pattern formed on the mask to be imaged and transferred onto the substrate through the imager (projection lens), thus realizing the exposure with high resolving power. 
     Particularly, in the present invention, there are provided an illuminating arrangement for substantially uniformly applying a ring-like diffused illumination formed from a number of imaginary point sources to a mask in an exposure area, and a reduction projection lens having an optical aye which shields at least a part of the O-order diffraction light or low-order diffraction light out of light which transmits through the mask substantially uniformly diffused and illuminated by the illuminating arrangement and imaging a circuit pattern formed on said mask on a substrate in the exposure area. With this structure, an extremely fine circuit pattern formed on the mask is imaged and transferred onto the substrate through the reduced projection lens to improve the contrast, thus realizing an exposure of high resolving power. 
     It is noted that although the present invention is hereinafter described in relation to use of excimer laser light, the present invention is not limited to a projection type exposure method using excimer laser light. 
     These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show for purposes of illustration only, several embodiments in accordance with the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(   a ) and ( b ) show a diffraction phenomenon of light by a circuit pattern formed on a mask for explaining the principle of the present invention. 
         FIGS. 2(   a ) and ( b ) are views for explaining the principle of the present invention. 
         FIG. 3  is a view for further explaining the principle of the present invention. 
         FIG. 4  is a schematic perspective view showing one embodiment of an exposure system in a reduction projection exposure device according to the present invention. 
         FIG. 5  is a sectional view showing a relationship between a light source spatial filter and an imaging filter in an exposure system according to the present invention. 
         FIG. 6  is a sectional view showing a relationship of an imaging space in an exposure system according to the present invention. 
         FIGS. 7(   a ) and ( b ) are views showing an imaging relationship of a circuit pattern on a mask in a conventional reduction projection exposure device. 
         FIG. 8  is a graph showing response function of the system in accordance with the present invention. 
         FIG. 9  is a view for explaining the relative function between the shape of the light source and the shape of the pupil surface according to the present invention. 
         FIG. 10  is a view for explaining the relative function between the shape of the light source and the shape of the pupil surface according to the prior art. 
         FIGS. 11(   a )-( c ) are views for explaining the calculating method of the relative function between the shape of the light source and the shape of the pupil surface. 
         FIG. 12  is a view for explaining the calculating method of the relative function between the shape of the light source and the shape of the pupil surface. 
         FIG. 13  is a view showing the calculated result of OTF according to the present invention. 
         FIG. 14  is a view showing the focal depth according to the present invention. 
         FIG. 15(   a )-( b ) are views for explaining the effect of a ring-like light source and a ring-like filter. 
         FIG. 16(   a )-( b ) are views showing a ring-like filter. 
         FIGS. 17(   a )-( d ) are views-showing a ring-like light source and a ring-like filter. 
         FIG. 18(   a )-( b ) show intensity distributions of a ring-like light source and a ring-like filter in accordance with an embodiment of the present invention. 
         FIG. 19(   a )-( b ) intensity distributions of a ring-like light source and a ring-like filter in accordance with another embodiment. 
         FIG. 20(   a )-( c ) show the embodiments of a ring-like light source and a ring-like filter. 
         FIG. 21  shows OTF curves. 
         FIG. 22  shows other OTF curves. 
         FIG. 23  shows another embodiment of a ring-like light source and a ring-like filter. 
         FIG. 24  is a view showing a block diagram of an embodiment of a light source. 
         FIG. 25  show one embodiment of an integrator. 
         FIG. 26  show another embodiment of a ring-like light source and a ring-like filter. 
         FIG. 27  is a structural view showing one embodiment of the whole exposure system according to the present invention. 
         FIG. 28  is a perspective view showing an integrator having an light source spatial filter in an exposure system according to the present invention. 
         FIG. 29  is a perspective view showing another embodiment of an integrator having a light source spatial filter in an exposure system according to the present invention. 
         FIG. 30  is a perspective view showing an embodiment of an imaging lens having an imaging spatial filter in an exposure system according to the present invention. 
         FIG. 31  is a perspective view showing another embodiment of an imaging lens having an imaging spatial filter in an exposure system according to the present invention. 
         FIG. 32  is a plan view showing a relationship between a light source spatial filter of one embodiment and an imaging spatial filter of one embodiment according to the present invention. 
         FIG. 33  is a plan view showing a relationship between a light source spatial filter of another embodiment and an imaging spatial filter of another embodiment according to the present invention. 
         FIG. 34  is a plan view showing a light source spatial filter of a further embodiment and an imaging spatial filter of a further embodiment according to the present invention. 
         FIG. 35  is a plan view showing a light source spatial filter of another embodiment and an imaging spatial filter of another embodiment according to the present invention. 
         FIG. 36  is a plan view showing a relationship between a light source spatial filter of yet another embodiment and an imaging spatial filter of yet another embodiment according to the present invention. 
         FIGS. 37(   a ) and ( b ) show a plan view and a sectional view of one example of a wafer pattern transferred on a wafer. 
         FIGS. 38(   a ) and ( b ) show a plan view and a sectional view of a modified wafer pattern transferred onto a wafer according to the present invention. 
         FIGS. 39(   a ) and ( b ) is a plan view and a sectional view of one example of a mask pattern for obtaining the wafer pattern shown in  FIG. 37  according to the present invention. 
         FIGS. 40(   a ) and ( b ) show a plan view and a sectional view of one example of a mask pattern for obtaining the wafer pattern shown in  FIG. 38  according to the present invention. 
         FIGS. 41(   a )-( d ) show various modes of mask patterns according to the present invention. 
         FIGS. 42(   a ) and ( b ) show a view showing a relationship contrast on a wafer and {hacek over (S)}, Ÿ filter according to the present invention. 
         FIG. 43  shows a relationship between contrast on a wafer and Í in connection with a spatial filter according to the present invention. 
         FIG. 44  is a view showing a relationship between a line width of a circuit pattern on a mask and contrast on a wafer according to the present invention. 
         FIG. 45  shows a relationship between a pitch of a circuit pattern on a mask and contrast on a wafer according to the present invention. 
         FIG. 46  is a plan view showing one example of a circuit pattern on a mask according to the present invention. 
         FIG. 47  shows a transfer result of a circuit pattern of  FIG. 46  according to the present invention. 
         FIG. 48  shows a relationship between a pitch of an extremely fine circuit pattern formed on a mask and contrast on a wafer according to the present invention. 
         FIG. 49  shows a relationship between a focal depth and contrast according to the present invention. 
         FIG. 50  is a block diagram arrangement of another embodiment of the entire exposure system using an excimer laser light source according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First, the principle of the present invention will be described with reference to  FIGS. 1 to 7 . In the present invention, a circuit pattern on a mask is transferred with an improved contrast rather than the art in which the circuit pattern is faithfully transferred onto a substrate by the imager (projection lens). Namely, in projection exposure, the requirement that “a circuit pattern is transferred accurately” is not always necessary the present invention is based on a new technical feature that “a circuit pattern desirably formed on a substrate (wafer) is better transferred with high contrast”. 
       FIG. 1(   a ) is a sectional view of a mask  100  in which a mask circuit pattern  104  is formed on a glass substrate  101  by chrome  102 . In  FIG. 1(   b ), a waveform  301  shows, with respect to the mask circuit pattern  104 , a signal distribution of an imaging pattern imaged onto a substrate (wafer)  200  by a projection and exposure device  3000  as shown in  FIGS. 4 to 6 . The waveform  301  is divided into a waveform  302  by the O-order diffraction light and a waveform  303  by higher order diffraction light. In the case where the mask circuit pattern  104  is a fine circuit pattern  105  as shown in  FIG. 1(   a ), the waveform  301  detected is small in contrast AM/AV since the waveform  303  by the higher order diffraction light is small as compared with the O-order diffraction light. Since the component of the waveform  302  can be removed by shielding the O-order diffraction light, the detected waveform is high in contrast as in the waveform  302 . 
     A further principle of the present invention will be described hereinbelow. That is, the present invention is intended to invert phases of circuit patterns adjacent to each other on the mask (by D) without using a phase film. In the case where a shield portion between circuit patterns  321  and  323  adjacent to each other of a mask (reticle)  100  is narrow as shown in  FIGS. 2 and 3 , a completely complementary figure results, and in the case where the shield portion has a finite width, an approximately complementary figure results. The circuit patterns  321  and  323  adjacent to each other of the mask (reticle)  100  are equal in light intensity except at one central point (O-order diffraction light) with a phase deviated by D, in a Fraunhofer&#39;s diffraction image under the principle of Babinet, in a diffraction image surface  3203  by an imaging optical system (projection lens)  3201 . In the diffraction image surface  3203  and in diffraction patterns other than the O-order diffraction light, light from the circuit patterns  321  and  323  is inverted in phase (deviated by π), and at least a part of the O-order diffraction light is shielded by a shield plate  324  (an imaging spatial filter  3302 ) on the diffraction pattern (diffraction image surface), whereby light imaged onto a substrate  200  surface (an imaging surface) is equal to that light from the patterns adjacent to each other whose phases are inverted (deviated by π) and an extremely fine circuit pattern with high contrast (an extremely fine circuit pattern of 0.1 μm or less on a wafer) can be transferred onto a substrate  200 . 
     More specifically, as shown in  FIG. 2  or  3 , at least a O-order part of the diffraction light is shielded by the shield plate  324  (imaging spatial filter  3302 ) on the diffraction image surface whereby only the diffraction light with an inverted phase reaches the imaging surface and therefore, it appears as if a phase film is formed on the mask as viewed from the imaging surface. As a result, a circuit pattern which is the same as the phase shifter method is imaged onto the wafer, and in terms of intensity distribution of the imaging surface, an extremely fine circuit pattern with high contrast is obtained on the wafer  200  as compared with the case of a conventional reduction projection exposure shown in  FIG. 7 . 
       FIG. 7  is a view for explaining the case of the conventional reduction projection exposure, in which images of fine circuit patterns  321  and  323  adjacent to each other are high in contrast in the imaging surface. In short, in case of the reduction projection exposure according to the present invention, an extremely fine circuit pattern with high contrast (an extremely fine circuit pattern of 0.1 μm or less on a wafer) is transferred and exposed on the imaging surface as shown in  FIGS. 2 and 3  as compared with the conventional reduction projection exposure shown in  FIG. 7 . 
     The example shown in  FIG. 4  will be described hereinafter by way of expressions (formulae). In the example shown in  FIG. 4 , light from a mercury lamp  3101  is condensed at a light source spatial filter  3301  by a condenser lens  3103 , and the mask  100  is illuminated by the condenser lens  3106 . The light having transmitted through the mask is partly shielded by an imaging spatial filter  3302  and imaged on the wafer  200  by an imaging lens  3201 . Let 1 (u, v) be the shape of the light source spatial filter  3301 , f (x, y) be the shape of a pattern on the mask  100  and a (u, v) be the shape of the imaging spatial filter  3302 , then the intensity gp (x, y) of an image on the wafer  200  is calculated by an expression (1) below: 
     
       
         
           
             
               
                 
                   
                     
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     In the expression (1), the intensity at the imaging surface is integrated after calculation since lights exited from (u, v) on the light source spatial filter  3103  are not interfered with each other. According to “Vibration Optics” (Iwanami Shoten) written by Kubota, generally, a resolving power of an optical system can be considered using a response function or OTF (Optical Transfer Function) of the optical system. A response function (u, v) in the example shown in  FIG. 4  is calculated by the following expression (2) using a pattern f (x; y) on an object surface and the strength gp (x, y) of an image thereof. 
     
       
         
           
             
               
                 
                   
                     
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       FIG. 8  shows the response function of the optical system calculated for a curve  351 . The abscissa indicates the spatial frequency s, and shows the number of openings (in case of NA=0.38) of the corresponding imaging lens for reference. The ordinate indicates the response function normalized by the O-order component. The position of point  355  indicates the size of an opening of the imaging lens. The curve  352  indicates the response function in the case where conventional optical systems, i.e. the light source spatial filter  3301  and the imaging spatial filter  3302  are not used; the, curve  353  indicates the apparent response function by way of the phase shift method; and the curve  354  indicates the response function in the case where coherent light such as laser is used for reference. In the response function  352  according to the conventional method, the response function extends to a position S 1  indicated by the following expression (3): 
     
       
         
           
             
               
                 
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                   3 
                   ) 
                 
               
             
           
         
       
     
     The method of the present invention is the same as the conventional method in that the response function extends to the position shown in the above-described expression (3) but the curve is in the shape stabilized to the position of 0.6 from a portion near N.A.=0.2. Furthermore, in the present invention, the response function, of a low frequency component is lowered by devising the shape of the mask pattern as described later so that the response function of the whole system according to the present invention has a shape of curve  356 . A curve  357  is shown normalized, and a stabilized response function extends over a wide zone from the low frequency component to the high frequency component. Thereby, a fine pattern can be imaged with high contrast according to the present invention. More specifically, for example, a line and space of 3 μm is at a position of point  358 , and this contrast is C 1  in the conventional method whereas it will be a high value, C 2 , in the present invention. In the present invention, shapes of the light source filter  3301  and the imaging spatial filter  3302  are determined so as to optimize the response function calculated by the aforesaid expression (1). According to the present invention, the value of the response function of the high frequency component can be relatively increased by decreasing the response function of the low frequency component. In addition, a ring-like light source spatial filter can be used to extend the response function to the area set by the expression (3). 
     The size and width of the light source spatial filter  3301  and imaging spatial filter  3302  can be optimized by calculating the response function using the aforesaid expression (2). 
     The method for calculating the imaging state at the wafer  200  by simulation to confirm the shape of a mask will be described later but the expression (1) cannot be analytically solved, and numerical calculation based on the expression (1) is used for calculation. When the response function capable of being calculated by the expression (2) is obtained and calculated by the expression (4) below, calculation time can be shortened.
 
 gp ( x, y )=| F[H ( u, v )* F[f ( x, y )]]|^  (4)
 
     A method for determining shapes of a light source spatial filter  3301  and an imaging spatial filter  3302  is shown in  FIGS. 9 to 14 . An optical system of the present invention is an optical system of so-called partial coherent imaging. An optical system of partial coherent imaging that cannot be fully explained using a so-called response function is explained in “Stepper&#39;s Optics” (Optical Technical Contact, Vol. 27, No. 12, pp. 762-771). The imaging characteristics of the optical system using a ring-like light source and a ring-like spatial filter according to the present invention on the basis of the aforementioned concept are calculated. 
     The imaging characteristic of the partial coherence imaging is calculated by expression (5) below using the concept of Transmission Cross-Coefficient, T(X 1 , X 2 ) showing the relationship between a shape of a light source and a shape of the pupil, surface of a detection optical system. According to the aforementioned “Stepper&#39;s Optics”, OTF (Optical Transfer Function) of the optical system is approximately determined by Transmission Cross-Coefficient, T(x, 0) of the minimum order. T(x, 0) is shown by the relative function between the shape of the light source and the shape of the pupil surface.
 
 gp ( v )=∫∫ T ( x   1   , x   2 ) f ( x   1 ) {circumflex over (f)} *( x   2 ) exp[− zπiv· ( x   1   −x   2 )] dx   1   dx   2  
 
where v=(x, y) . . . Coordinates on image surface
         x 1 =(u 1 , v 1 ) Coordinates on pupil (u 2 , v 2 ) surface   f(x 1 ) . . . Intensity distribution on image surface   ^ . . . Fourier conversion   * . . . Conjugate complex number
 
 T ( x   1   , x   2 )=∫l( x   3 ) a ( x   1   +x   3 ) a *( x   2   +x   3 ) dx   3   (5)
       

     That is, the characteristic of the partial coherent imaging shown by the complicated expression (5) poses a problem of geometry which is the relative function between the shape of the optical source and the shape of the pupil surface.  FIG. 9  shows a light transmission portion  3305  of a light source spatial filter  3301  and a light shield portion  3306  of an imaging spatial filter  3302 . The relative function between the light source and the pupil surface with coordinates x is shown by an area of an oblique line portion or hatched portion  364  in  FIG. 9 . Similarly, the relative function between the light source and the pupil surface in the prior art is shown by an oblique line portion or hatched portion in  FIG. 10 . 
     A curve  367  in  FIG. 13  shows a calculated value of the relative function in the case of  FIG. 9 , in other words, Transmission Cross-Coefficient, T(x, 0). The relative function in case of the prior art shown in  FIG. 10  is large in value in a high frequency area as compared with the curve  366 . That is, the contrast increases.  FIG. 13  shows the calculated result in case of N.A.=0.38, σ=0.9. In  FIG. 13 , an abscissa shows the minimum pattern dimension corresponding to each N.A. in the case where wavelength is 0.365 micron. (For example, 0.3, means line and space of 0.3 micron.) It is understood that OTF of 0.3 micron is about twice as large as that of the prior art. 
       FIGS. 12 and 13  are views for increasing the intuitive understanding of and helping the setting of shapes of the light source spatial filter  3301  and the imaging spatial filter  3302 . A hatched portion A in  FIG. 11(   a ) shows the relative function between the outer diameter of the light source and the shield portion  3306 , and a hatched portion B in  FIG. 11(   b ) shows the relative function between the inner diameter of the light source and the shield portion  3306 . A hatched portion C in  FIG. 11(   c ) shows the relative function between the transmission portion  3305  of the light source and the maximum pupil of the optical system. The relative function between the final light-source shape and the spatial filter is shown by the hatched portion  367  in  FIG. 12 . This can be obtained by C−A+B. By obtaining the relative functions as described above, the effect of the spatial filter or ring-like illumination can be intuitively understood, and conversely, that is helpful in determining the shape thereof. More specifically, the value of the high frequency area  382  is larger in value than the intermediate frequency area  381 . In the case where the value of the low frequency area  383  is excessively large, the value of the low frequency area is further reduced from the effects A and B of the spatial filter. In this way, the effect of the ring-like illumination and the spatial filter is intuitively explained. 
     Of course, the shape of the light source and the shape of the spatial filter should be evaluated on the basis of expression (5) and should be approximately evaluated by the relative function between the light source and the spatial filter. 
     Since the ring-like light source can make the coherence high, the depth of the optical system can be increased. The narrower the band width of the ring-like power source the higher the coherence of the light source. Thus, the focal depth increases. The larger the diameter of the ring of the ring-like light source the greater the coherence degree of space. Thus, the resolution increases. 
     The effects of the ring-like light source and ring-like spatial-filter used in the present invention will be described with reference to  FIG. 15 .  FIG. 15(   a ) shows an eye  3301  of an imaging lens, an image  3305   a  (the O-order diffraction light) of a light source imaged on the eye, and diffraction images  3305   b  and  3305   c  of a light source resulting from a pattern (a circuit pattern) formed in a direction of y on a mask  100 .  FIG. 15(   a ) shows the case where the light source is ring-like, and  FIG. 15(   b ) shows the case where the light source is circular. A filter for shielding the O-order diffraction light is shown by an hatched portion  371 . A cross-hatched portion  372  which is also a part of the diffraction light  3305   b  and  3305   c  of the light source is simultaneously shielded by the oblique line  37 . In case of  FIG. 15(   a ), only 10% to 20% are shielded, but in case of  FIG. 15(   b ), 40% or more are shielded. That is, the object for efficiently shielding only the O-order diffraction light is effectively achieved by the ring-like light source of  FIG. 15(   a ). Namely, the ring-like light source is improved in performance. The smaller the width of the ring-like light source, the smaller the ratio of the diffraction light to be shielded becomes. 
     In the present invention, a spatial filter  3306  having a ring width of narrowness about 30% of the ring width of the light source as shown in  FIG. 16(   a ) is used in order to shield a part of the O-order diffraction light. However, since a part of the O-order diffraction light will suffice to be shielded, a spatial filter as shown in  FIG. 40(   b ) can be used in which the ring width is substantially the same as the light source and the transmittance is approximately 70%. Of course, the ring width can be made smaller than that of the image of the light source and the transmittance can be lowered than 70%. Furthermore, while here, the case where the light transmittance is 30% or less, it is to be noted that the light transmittance is not limited to 30%. It is to be further noted that as a spatial filter portion  3306 , use can be made of a phase plate in which the transmittance is 100% and a phase at the using wavelength is deviated by π in order to shield a part of the O-order diffraction light. Such a filter may serve as a filter for substantially shielding a part of the O-order diffraction light. Furthermore, polarized light and a polarizing plate may be used for shielding. 
     Further, as shown in  FIG. 26 , the ring width of the filter in which transmittance is 70% may be made larger than that of the light source. With this structure, not only the O-order diffraction light, but also a part of the low-order diffraction light can be shielded, and an MTF curve can be improved. Also in an example shown in  FIG. 16(   a ), a structure is shown in which a part of the low-order diffraction light is shielded as in the example of  FIG. 26 . 
     As described above, in order to efficiently shield the O-order diffraction light, the ring-like light source exhibits the effect. When the width of the ring is made small, the effect increases. It can be here considered that a ring-like light source comprises light sources aligned in a ring-like fashion. That is, it can be considered as an assembly of coherent point sources. Thus, the object of the present invention is achieved even by the provision of an assembly of light sources  375  having a spatial coherence in the order of 0.1 to 0.3 close to point sources and shield plates  376  smaller than the light sources  375  positioned corresponding thereto. Needless to say, the shield plate  376  of low transmittance may be used.  FIG. 17(   a ) shows an example in which the light sources  375  and the shield plates  376  are aligned in a ring-like fashion. When this type of arrangement is employed, the shielding of the O-order diffraction light is achieved even if the ring-like shape is not formed, as shown in  FIG. 17(   b ). At the same time, several plies of light sources and shield plates can be aligned as a ring, as shown in  FIG. 17(   c ). A shield plate may be mounted with respect to only a part of the corresponding light source in order to shield a part of the O-order diffraction light as shown in  FIG. 17(   d ). 
       FIGS. 18(   a ) and  18 ( b ) show the distribution of light intensities of a light source and the transmittance of a spatial filter in connection with the radius direction. While in  FIG. 18 , both the light intensity distribution and transmittance distribution are shown in the rectangular distribution, it is to be noted that a gentle distribution as shown in  FIGS. 19(   a ) and  19 ( b ) may be employed without problem. This can be understood if one considers that OTF is shown by their relative functions. That is, since an integrated one while taking weighting is the relative function with respect to duplicated portions, even if the gentle distribution is exhibited, the value of the relative function does not change greatly. In any case, radially equal distributions and concentrical distributions are obtained, which are important. The fact that the light source described herein may have the distribution as shown in  FIG. 19(   a ) indicates that the intensities of the light sources shown in  FIGS. 17(   b ), ( c ) and ( d ) become small toward the center. In such an embodiment, there are effects in that a light source with less coherency can be prepared and at the same time a frequency component can be further made small. 
     As described above, in the present invention, the effective shielding of a part of the O-order diffraction light by the exposure apparatus or other imaging optical systems enabling the enhancing of the resolution and enhancing of the focal depth. However, in order to efficiently shield the O-order diffraction light, it is necessary not to superpose the O-order diffraction light and the diffraction light on a Fourier transform surface in which a spatial filter is arranged, but where they are separated. To this end, the coherency of the illuminated light should be high. That is, it is desirable to be close to a point source. On the other hand, in order to enhance the resolution of the imaging optical system, it is desirable to increase the spatial, coherence of the light source, namely, the a value. That is, a large light source is desired. As a contradiction to each other (a point source and a large light source) need be compatible. The ring-like light source and the spatial filter according to the present invention makes such contradiction as noted above compatible. One way of efficiently fulfilling this is to use an assembly of small light sources. Further, if this assembly is arranged in the form of a large ring, the condition of a large light source is fulfilled. That is, if the width of the ring is made small, the coherency increases and the focal depth enhances, whereas if the radius of the ring is made large, the spatial coherency increases and the resolution enhances. 
     There is present a condition that when the radius of the ring increases while shielding a part of the O-order diffraction light, the diameter of the spatial filter  3306  becomes about the same as that of the eye of the optical system. This condition is a condition that a part of the O-order diffraction light is shielded and the size of the ring-like light source is maximum. That is, this is a condition that the maximum resolution is obtained in connection with the reduction projection lens.  FIGS. 20(   a ), ( b ) and ( c ) show such arrangement. In these embodiments, the size of the light source is larger than the lens eye. Generally, it has been said that when the size of a light source is increased, the focal depth becomes shallow, and cannot be properly used for lithography. However, as already explained above, a ring-like light source can be used to thereby make the focal depth deep. Therefore, it is possible to use a light source larger than an eye as shown in  FIG. 20 . The individual embodiments have a structure in which a part  377  of the O-order diffraction light is shielded. The OTF of this structure is indicated by the relative function. Therefore, there is an effect that the shut-off frequency of the OTF is extended in comparison to the case where the size of a light source is smaller than an eye. Furthermore, a further effect obtained by this structure lies in that the resolution can be enhanced only by an improvement in an illuminating system which facilitates a large N.A. implementation without using a reduction projection lens which requires high precision. In this embodiment, it is possible to transfer a pattern of approximately 0.2 μm with an i line using a lens of N.A. 0.4. 
     It is important for an imaging system of the O-order diffraction light shield to gently and monotonously reduce an OTF curve.  FIG. 21  shows an OTF curve  378  according to the present invention. In the case where the OTF is not a gentle or smooth curve, but rather is wavy as shown by curve  379 , the contrast in the vicinity of an extremely small point of the wave lowers, and in an actual LSI pattern having various spatial frequency components, the pattern is not properly transferred. However, a special pattern formed from only specific spatial frequency components is not included herein, and the contrast will suffice to be increased with respect to the specific spatial frequency. That is, the OTF curve need be in the range of the specific width Wb as shown in  FIG. 22 . This Wb should be calculated from the transfer result calculated by a transfer simulator later described. 
     Accordingly, also in the case where a light source shown in  FIG. 20  is large, the OTF which gently and monotonously reduces is required. It is desired from this that when a pattern of actual LSI is transferred, a difference  10  between an inner diameter of a light source and a diameter of an eye of a reduction projection lens is substantially equal to a difference between an outer diameter of a light source and a diameter of an eye of a reduction projection lens. In order to obtain an actual focal depth, it is desired that the ratio between the eye diameter of the reduction projection lens and the inner diameter is 0.6 or more. 
     In the example of  FIG. 20(   a ), a filter having a transmittance of a suitable value may be arranged at a portion of a portion  380 , as shown in  FIG. 25 , exposed to the O-order diffraction light of the light-source within the eye of the reduction projection lens. In this case, it is possible to reduce the width of a portion  377  externally of the eye of the light source, and thus, there is also an effect that the size of the light source can be reduced. 
     Conversely, it is possible to increase the width of a portion  380  in the eye of the reduction projection lens as compared with portion  377 . This brings forth effects such that a stabilized contrast is easily maintained in a wide area where the light intensity is easily increased. 
     Furthermore, even if the outer diameter of the light source of the ring is made to be the same as that of the eye of the reduction projection lens, the object of the present invention can be achieved to some extent. In the structure shown in  FIG. 20(   a ), a spatial filter is not introduced into the eye of the reduction projection lens so that a part of the O-order diffraction light can be cut. Therefore, the structure is simple and the operation can be easily performed. 
     Moreover, as shown in  FIG. 23 , a ring-like light source  378  is installed externally of the light source shown in  FIG. 20  to further enhance the  10  resolution.  FIG. 24  shows an example in which the light source shown in  FIG. 23  is embodied. Since the light source with N.A. increased as described above is difficult in the lens system, a laser light source  3121 , a beam scanning means  3122 , ring-like mirrors  3123  and  3124  are used. In the case of this embodiment, a lens of N.A. 0.4 of an i line is used, and 0.15 μm can be resolved. Such embodiment does not differ from the fundamental idea of the present invention in that a part of the O-order diffraction light is shielded. 
     One embodiment of a pattern transfer system  3000  (a reduction projection exposure optical system) according to the present invention will be described hereinbelow with reference to  FIGS. 4 to 6 . In the pattern transfer system (reduction projection exposure optical system)  3000 , an i-ray having a wavelength of 365 nm out of light from a Hg lamp  3101  is selectively transmitted by a color filter  3102 , and the light is condensed on the surface of an-integrator  3104  by a condenser lens  3103 . Light incident upon elements  3107  ( FIG. 28 ) in the integrator  3104  are individually emitted with an angle of exit α, and a mask  100  is illuminated by a condenser lens  3106 . The integrator  3104  will be described later. A ring-like light source spatial filter  3301  is installed in the vicinity of an output end of the integrator  3104 . 
     The light having transmitted through a mask circuit pattern  104  (shown, for example, in  FIG. 39 ) on the mask  100  and diffracted is imaged and transferred as a wafer circuit pattern  204  (shown, for example, in  FIG. 37 ) having a high contrast on the wafer (substrate)  200  through an imaging lens (reduction projection lens)  3201  and an imaging spatial filter  3302  mounted in the vicinity of a pupil of the imaging lens. 
     It is noted that an image of a light source spatial filter  3301  in the form of a ring is imaged at a position of an imaging spatial filter  3302  in the form of a ring by the condenser lens  3106  and the imaging lens (reduction projection lens)  3201 . The imaging relationship between the light source spatial filter  3301  and the imaging spatial filter  3302  in the present embodiment is shown in  FIGS. 32 and 33 . The light source spatial filter  3301  forms a light source of a ring portion  3305  having an outside diameter DLO and an inside diameter DLI, and both inside and outside of the ring portion  3305  are shielded. The imaging spatial filter  3302  has a construction in which a ring portion  3306  having an outside diameter DIO and an inside diameter DII is shielded, and light transmits through both inside and outside of the ring portion  3306 . An incident portion of the imaging lens (reduction projection lens)  3201  is indicated at  3205  and an exit portion is indicated at  3206 . 
     The imaging spatial filter  3302  may be at a position  3202  in front  3205  of the imaging lens (reduction projection lens)  3201 , at a position  3204  at the rear  3206  of the imaging lens  3201  or at a position  3203  of a pupil in the imaging lens. The best effect in design is obtained at the position  3203 , and a position at which cost is minimum and sufficient effect is obtained is the position  3204 . 
       FIG. 11  is a perspective view of the imaging lens  3201  in which the imaging spatial filter  3302  is arranged at the position  3204 . In this case, the imaging spatial filter  3302  is formed from a metal plate and therefore supported by support rods  3311 . Needless to say, the smaller in number and smaller in diameter of the support rods  3311 , the better.  FIG. 31  shows an embodiment of the imaging spatial filter  3302  formed in front of or at the rear of the imaging lens  3201  by forming a shield film  3313  on a glass substrate  3312 . In this case, the support rod is not necessary but the imaging lens  3201  need be designed in consideration of aberration caused by the glass substrate  3312 . 
     Let M be the, imaging magnification between the light source spatial filter  3301  and the imaging spatial filter  3302 , the relationship between DLO which is an outside diameter of the light source spatial filter  3301 , DLI which is an inside diameter of the light source spatial filter  3301 , DIO which is an outside diameter of the imaging spatial filter  3302  and DII which is an inside diameter of the imaging spatial filter  3302  as shown in  FIG. 32  will be described later. In short, if a part or the whole of the O-order diffraction light is shielded, a fine circuit pattern on a mask can be imaged on a wafer with high contrast. 
     As described above, with respect to DIO and DII of the imaging spatial filter  3302  as well as DLO and DLI of the light source spatial filter  3301 , a variable spatial filter such as a liquid crystal display element is constituted or a plurality of spatial filters which are different in dimension from one another are exchangeably provided whereby the ring-like dimension of the spatial filters can be controlled. 
     One embodiment of the entirety of a projection exposure system according to the present invention will be described hereinafter with reference to  FIGS. 27 to 36 . 
     First, a pattern data producing system  1000  as shown in  FIG. 27  will be described. In the pattern data producing system  1000  and in a wiring data preparing portion  1102 , wafer pattern shape data  1103  desirably formed on a substrate (wafer)  200  is formed on the basis of a wiring drawing data  1101  such as design data. A pattern conversion portion  1104  converts a mask pattern shape data  1105  desirably formed on a mask (reticle)  100  on the basis of the wafer pattern shape data  1103 . At that time, a pattern transfer simulator  1108  checks whether or not a mask pattern on the mask converted by the pattern conversion portion  1104  approximately coincides with the wafer pattern shape data  1103  when actually exposed on the substrate  200  by a pattern transfer optical system on the basis of the wafer pattern shape data  1103  formed by the wiring data preparation portion, the setting conditions such as the outside diameter DLO, the inside diameter DII or the like of a ring portion  3305  of a light source spatial filter  3301  and the setting conditions of the outside diameter DIO, the inside diameter DLI or the like of a ring portion  3306  of an imaging spatial filter  3302 . The mask pattern is then fed back to the pattern conversion portion  1104  for correction to obtain an optimum shape (such as the outside diameter DLO, the inside diameter DLI or the like of the ring portion  3305 , and the outside diameter DIO, the inside diameter DII or the like of the ring portion  3306 ) of the spatial filter adjusted to the wafer pattern shape data  1103 , results of which are sent to a light source spatial filter control portion (an adjusting portion)  3303  and an imaging spatial filter control portion (adjusting portion)  3304  through a spatial filter control system  3305  to control (adjust) the shape of the light source spatial filter  3301  and imaging spatial filter  3302 . The pattern producing portion  1106  converts an EB data  1107  suited to an electron beam depicting device  2103  on the basis of the mask pattern shape data  1105  converted by the S pattern conversion portion  1104 . 
     Next, a mask fabrication system  2000  will be described. A film forming device  2101  forms a plurality of stacked films  202  formed of metal chrome or chrome oxide or metal chrome and chrome oxide on a mask substrate  101 . A coating device  2101  coats a resist film  203  on the mask substrate  101  formed by the film forming device  2101 . The electron beam depicting device  2103  depicts and forms the same circuit pattern as the mask pattern shape  1105  in accordance with the EB data  1107  produced from the pattern producing portion  106 . Thereafter, a circuit pattern on the mask substrate  201  is developed by a developing device  2104  to complete a mask  100 . The completed mask  100  is inspected in pattern by comparing image data detected by a pattern inspection device  2106  with mask pattern data  1103  or wafer pattern data  1105  or data from the transfer simulator  1108 . If a defect is present, it is corrected by a pattern correction device  2105  composed of an ion beam machine or the like, and finally, a foreign particle on the mask  100  is inspected by a foreign particle inspection device  2107 . If a foreign particle is present, it is washed by a washing device  2108 . The mask  100  according to the present invention is characterized in that it is easily washed as compared with a mask of a phase shifter since the mask can be formed of a single layer film  102  as shown in  FIG. 39 , for example. Furthermore, the mask  100  can be easily manufactured as compared with a mask of the phase shifter. In the pattern inspection device  2105 , the detected image data may be compared with any of the mask pattern data  1103  or the wafer pattern data  1105  or data from the transfer simulator  1108 . However, most effectively, the light source of the pattern inspection device  2105  and the forming optical system is made equivalent to a pattern transfer system (reduction projection exposure system)  3000  according to the present invention to compare it with the wafer pattern data  1105 . More specifically, the pattern inspection device  2105  is composed of an optical system equivalent to the pattern transfer system (reduction projection exposure system)  3000 , and a mask  100  to be inspected is placed on a mask stage  3401  and a light receiving element is arranged at a position in which a wafer (substrate)  200  is placed so as to detect an image to be imaged on the light receiving element. With the pattern inspection device  2105  designed as described above, the same circuit pattern as an extremely fine circuit pattern actually projected and exposed to the wafer (an extremely fine circuit pattern of 0.1 μm or less on a wafer) can be detected as an image signal with high contrast from the light receiving element without being effected by interference of light, and as the result, it is compared with the wafer pattern data  1105  whereby even a fine circuit pattern can be inspected accurately. 
     Next, a pattern transfer system (reduction projection exposure optical system)  3000  of the present invention will be described hereinafter. In the pattern transfer system  3000 , an i-ray having a wavelength of 365 nm out of light from a Hg lamp  3101  is selectively transmitted by a color filter  3102  and condensed on the surface of an integrator  3104  by a condenser lens  3103 . Light incident on elements  3107  ( FIG. 28 ) in the integrator  3104  individually exit at an angle of exit to illuminate the upper portion of the mask  100  by a condenser lens  3106 .  FIGS. 28 and 29  show different modes of the integrator  3104 .  FIG. 28  shows the case where a section of the integrator  3104  is in the form of a ring.  FIG. 29  shows an embodiment of the integrator  3104  in which a ring-like shape is formed by a shield plate  3105 . In short, it is obvious that other configurations may be employed as long as one performs a role of a spatial filter, that is, a ring has a shield function. Preferably, the DLI and DLO of the light source spatial filter  3301  configured as described above can be controlled by the provision of a plurality of spatial filters different in dimension from one another so that they are exchanged whereby they can be controlled or adjusted by a command from a light source spatial filter control portion (adjusting portion)  3303 . Otherwise, a freedom is greatly restricted. 
     In the present invention, when a shield plate is placed on a light source surface, a synthetic light quantity is reduced. Accordingly, it is necessary to increase the light intensity of the light source. In a conventional lamp, it has been difficult to increase the light intensity. The strobe light source for fiber illumination is disclosed in “Development and Research of Strobe Light Source for Fiber Illumination” written by Yamamoto, Lecture Meeting of Society of Applied Physics, 1991, 11p-ZH-8-. The strobe light source as disclosed therein has not been used for an exposure apparatus. However, it is effective for the present invention which requires to sufficiently obtain the light intensity to use a lamp as described. This light source is suited to the present invention because it has a larger diameter. 
     In the embodiment shown in  FIG. 23 , an integrator using an optical fiber as shown in  FIG. 25  is effective. The integrator using an optical fiber comprises a bundle of a number of optical fibers  380 . A light introducing surface  3131  is circular in shape so as to easily condense light from a light source  3101 , and a light emitting surface comprises a bundle of optical fibers so as to be a ring-like configuration. By using the optical fibers, a light source having a circular light source shape such as a mercury lamp can be used to efficiently prepare a ring-like light source. An integrator  3104  can be prepared to be flexible by using the optical fibers. This brings fourth an effect in that a light source as a hearing source can be installed at a position away from the apparatus body which requires temperature control. 
     It is suggested that a bundle of fibers shown in Fig. is scattered so that the outer and inner diameters can be varied. Such a variable mechanism is controlled by a light source spatial filter control mechanism  3303 . 
     Light having transmitted through a mask pattern  104  ( FIG. 34 ) on a mask  100  and diffracted is imaged as a wafer pattern  204  (shown, for example, in  FIG. 37 ) on a wafer  200  through an imaging lens  3201  and an imaging spatial filter  3302 . 
     The imaging spatial filter  3302  may be at a position  3202  in front of the imaging lens  3201  or at a position  3204  at the rear of the imaging lens or at a position  3203  of a pupil in the imaging lens. 
     An image of the light source spatial filter  3301  is imaged at a position of the imaging spatial filter  3302  by the condenser lens  3106  and the imaging lens  3201 .  FIGS. 32 and 33  show the imaging relationship between the light source spatial filter  3301  and the imaging spatial filter  3302  in the present embodiment. The light source spatial filter as well as the imaging spatial filter have a shape of a ring. The light source spatial filter  3301  has a ring portion  3305  having the outside diameter DLO and the inside diameter DLI, and both the inside and outside of the ring portion  3305  are shielded. In the imaging spatial filter  3302 , the ring portion  3306  having the outside diameter DIO and inside diameter DII is shielded, and it is designed so that light transmits through both the inside and outside of the ring portion  3306 . Let M be the imaging magnification between the light-source spatial filter  3301  and the imaging spatial filter  3302 , the relationship of the following expression (6) is established between DLO, DLI, DIO and DII:
 
DIO=M δ DLO
 
DII=M ε DLI
 
M DLI≦DII≦DIO≦M DLO  (6)
 
wherein d and d are the coefficients, which are fulfilled with the following expression (7):
 
0.7≦δ≦1.0
 
1.0≦ε≦1.3  (7)
 
     When these coefficients are fulfilled with the above described expression (7), the effect of the present invention is most conspicuous. However, these expressions need not always be satisfied but a part or the whole of the O-order diffraction light may be shielded. In setting δ and ε, values of δ and ε of the spatial filter with highest contrast are selected by the pattern transfer simulator  1108 . 
       FIG. 42  shows the contrast when the values of δ and ε are changed. In this figure, when δ is 0.8 and ε is 1.1, the best contrast is obtained. However, it is apparent from  FIG. 3  that the best contrast is not obtained only at the time of the aforesaid values. 
     Let NAO be the number of openings of the imaging lens (reduction projection optical system)  3200  on the exit side  3204 , and NAL be the number of openings of one in which a light source image is projected at the same position  3204 . The NAL/NAO is defined as a spatial coherence degree σ.  FIG. 43  shows the relationship between σ and the contrast. When σ is about 0.9, the best contrast is obtained. However, even if σ is somewhat deviated from 0.9, high contrast is obtained. 
     The object of the present invention is achieved most conspicuously in the case where a light source spatial filter  3301  and an imaging spatial filter  3302  shown in  FIG. 13  are used. However, since the object of the present invention is achieved by shielding a part of the entirety of the O-order diffraction light, even if an air filter shown in  FIGS. 14 to 17  is used, a circuit pattern with high contrast can be imaged on a wafer. In the air filter shown in  FIGS. 14 to 17 , an oblique line shown therein comprises a shield portion. A pattern transfer system  3000  comprises a light source portion  3100  comprising a Hg lamp  3101 , a color filter  3102 , a condenser lens  3103 , an integrator  3104  and a condenser lens  3106 ; an imaging optical system  3200  comprising an imaging lens  3201 ; a spatial filter control system (a regulating system)  3300  comprising an entirety control portion  3305  for delivering control signals to a light source spatial filter control portion (regulating portion)  3303 , an imaging spatial filter control portion (regulating portion)  3304  and a locating mark detection portion  3403  on the basis of command signals such as DLO, DLI, DIO, DII, etc. obtained from a light source spatial filter control portion (regulating portion)  3303  for controlling a light source spatial filter  3301 , an imaging spatial filter  3302  and a light source spatial filter  3301 , an imaging spatial filter control portion (regulating portion) for controlling an imaging spatial filter  3302  and a pattern transfer simulator  1108  to control, the entirety; and a locating portion  3400  comprising a mask stage  3401  placing thereon a mask  100 , a wafer stage  3402  placing thereon a wafer  200 , a locating mark detection portion  3403  for detecting a locating mark on the wafer, a mask stage control system  3404  for controlling a mask stage  3304  in accordance with a command from the locating mark detection portion  3403  and a wafer stage control system  3405  for controlling the wafer stage  3402  in accordance with a command from the locating mark detection portion  3403 . 
     With the above-described arrangement, the operation is as follows: A mask  100  fabricated by a mask fabrication system  2000  is placed on the mask stage  3401  and illuminated by the light source portion  3100 . A part of the O-order diffraction light having transmitted from the mask and from the light source spatial filter  3301  in the light source portion  3100  is shielded by the imaging spatial filter  3302 , and high order diffraction light and part of the O-order diffraction light pass through the imaging optical system (reduction projection lens)  3200  to form a circuit pattern on the wafer  200 . 
     A ring-like spatial filter as shown in  FIG. 32  is used as the spatial filter because a coherence is provided on the light source. The coherence has two types, one for time, and the other for space. The time coherence is a wavelength band of the light source, the shorter band of light, the higher the coherence. The spatial coherence is the magnitude of the light source, which corresponds to the magnitude of the light source spatial filter  3301 . However, when the magnitude of the light source is made small in order to increase the coherence, the light intensity of the light source becomes small and the exposure time becomes extended, as a consequence of which through-put of the exposure falls. When the ring-like light source spatial filter  3301  is used, an image of the light source spatial filter  3301  formed at the imaging position is the O-order diffraction light. That is, the use of the ring-like spatial filter  3301  can realize a light source which is high in intensity and has a coherence. This is the same art as that uses a ring-like spatial filter to obtain a coherent light from a white light in a phase difference microscope, which is disclosed in “Wave Optics” (Iwanami Shoten) written by Kubota. 
     There is a further reason why the light source spatial filter  3301  has a ring-like shape. As previously explained, there is a relationship, as shown, between a dimension of a pattern on a wafer desired to be transferred and a spatial coherence degree of a light source by which a pattern with that dimension is transferred with highest contrast. Thus, when the space coherence degree adjusted to a dimension (pitch) of a pattern desired to be transferred, the effect of the present invention conspicuously appears. If the light source spatial filter  3301  and the imaging spatial filter  3302  are formed on the ring, the spatial coherence degree, i.e., the size of the ring is easily controlled. 
     However, needless to say, the ring radius (spatial coherence degree) of the ring-like light source and space filter is made as large as possible to enhance the resolution. 
     In the present invention, the ring-like light source as well as the space filter are of a concentric circle. By the provision of a concentric circle, a directivity with respect to a circuit pattern to be transferred by MTF cannot be provided. In transferring an LSI circuit pattern having circuit patterns of various directions, it is important that MTF has no directivity. The concentric filter has an effect that complicated aberrations are hard to enter a lens as compared with a non-concentric filter as shown in  FIG. 36 . 
     Since the aforesaid effect can be achieved if the intensities of the O-order diffraction light and the high order diffraction light are balanced, the effect though somewhat low can be achieved even when the imaging spatial filter  3302  is omitted and only the light source filter  3301  is provided. Conversely, even the light source spatial filter  3301  is omitted and only the imaging spatial filter  3302  is provided, the aforesaid effect though somewhat low can be achieved. 
     Next, a method for forming a pattern will be described in more detail with reference to  FIGS. 37 to 41 . As described above, the object of the present invention can be achieved by using the light source spatial filter  3301  and the imaging spatial filter  3302  but the effect of the present invention can be further enhanced by devising a mask pattern  104  as will be described below. 
       FIG. 45  shows an imaging optical system  3200  with a line width (light transmission) of a line spatial pattern having the same pitch formed on a mask  100  changed and a contrast of a circuit pattern projected on a wafer  200 . As shown in  FIG. 44 , contrast becomes large as the line width becomes small. That is, the line width is suggested to make small. When the line width is made small, the light intensity is small, and therefore, it is necessary to extend the exposure time. The line width of the circuit pattern formed on the mask  100  is determined in consideration of the contrast and exposure time required to transfer a circuit pattern. 
     Accordingly, preferably, in the exposure method according to the present invention, the line width for forming the mask pattern  104  is made constant. For this reason, in the case where a wide wafer pattern  204  is desired to be formed, a device is required. In the case where the line width is not constant but wide, the light intensity at the imaging surface is high with respect to a pattern in which a peripheral line width is constant, and a shape of a transferred pattern after resist development is far apart from a circuit pattern to be obtained originally. In the case where there is partly a circuit pattern whose light intensity is high, this results from light which comes therefrom. 
     To properly form a wide circuit pattern, it is necessary to form the light intensity with the same light intensity as the circuit pattern whose peripheral line width is constant. The method for forming a wide circuit pattern will be described with reference to the figure. When a circuit pattern is transferred by use of the imaging optical system  3200 , a circuit pattern which is sufficiently small than a resolving power of the imaging optical system cannot be resolved but imaged evenly. In imaging the aforesaid wide circuit pattern, this phenomenon is utilized. That is, when a fine pattern less than a resolving power of the present optical system is formed on a mask  100  as indicated at  105 ,  106  and  108  in  FIGS. 39 and 40 , a wide circuit pattern can be transferred to a wafer  200  as shown in  FIGS. 37 and 38 . 
       FIG. 45  shows a contrast when the pitch of a line space pattern changed. As shown in  FIG. 45 , as the pitch becomes small, the contrast becomes small. That is, when the pitch is made small, there is a position  331  at which the contrast is approximately 0. In the case where the whole surface of the wide circuit pattern is desired to be white, a pattern having the pitch at that position  331  may be used. More specifically, most preferably, there is used a pattern having a pitch approximately ½ of a pitch of a pattern to be resolved. At this pitch, the light intensity of the wide circuit pattern is about the same as that of the minimum pattern. 
     More specifically, in the case where a wafer pattern  204  as shown in  FIG. 37  is to be obtained, a mask pattern as shown in  FIG. 39  is fabricated, and a negative resist is used, or a mask pattern as shown in  FIG. 40  is fabricated and a positive resist is used. In this case, patterns  105 ,  106 ,  107 , and  108  desired to transmit light there through are formed by patterns having a small pitch as shown in  FIG. 41 . A mask pattern  104  in the case where light is transmitted over a wide range as in these patterns  105 ,  106 ,  107  and  108  is automatically produced by a pattern conversion portion  1104  and is simulated by a pattern transfer simulator  1108  as needed. 
     A pattern of ½ pitch may be ½ pitch in only one of X-direction and Y-direction. Needless to say, of course, a grating pattern which has ½ pitch in both X- and Y directions is employed. The pitch need not always be ½ but other pitches may be employed at which the light intensity on the wafer pattern  204  is sufficient as needed. 
     Even in the case of a mask in which an extremely fine circuit pattern and a large circuit pattern are mixed, the transfer can be made by one reduction projection exposure by the aforementioned method. However, in the case where an extremely fine circuit pattern and a large circuit pattern are transferred by more than twice reduction projection exposure, the aforementioned method need not be employed but a pattern  104  can be formed merely by a pattern whose line width is constant. In this case, there is an effect in that a system such as the pattern conversion portion  1104  is not necessary. 
     As described above, the method of the present invention has an effect in that since a phase shifter need not be arranged, processing by the pattern conversion portion  1104  is simple, and time can be saved and an error can be reduced. 
     While in the present embodiment, a mask pattern has been converted with a circuit pattern having a constant line width as a base, it is to be noted that in a circuit pattern which involves many repetitive portions such as memory, a mask pattern  104  so as to obtain an optimum wafer pattern  204  while being simulated by a transfer simulator  1108  can be obtained. Namely, the mask pattern  104  is obtained by the transfer simulator  1108  for every memory cell. 
     A transfer mechanism on a wafer of a mask pattern will be described referring again to  FIGS. 1 ,  2  and  3  wherein  FIG. 1(   a ) is a sectional view of a mask  100  in which a mask pattern  104  is formed of chrome  102  on a glass substrate  101 . A waveform  301  shown in  FIG. 1(   b ) is a strong signal degree distribution of an imaging pattern of a mask pattern  104 . The waveform  301  may be divided into a waveform  302  by the O-order diffraction light and a waveform  303  by high order diffraction light. In the case where the mask pattern  104  is a fine pattern  105  as shown, the waveform  303  by the high order diffraction light is small with respect to the waveform  302  by the O-order diffraction light, and therefore, the waveform  301  to be detected is small in contrast AM/AV. Since a component of the waveform  302  is removed by shielding the O-order diffraction light, the detected waveform is high in contrast as in the waveform  302 . 
     According to the Babinet principle, in diffraction patterns other than the O-order diffraction light, light from patterns adjacent to each other is viewed as if phases of patterns adjacent to each other are inverted (deviated by π). That is, if the O-order diffraction light is shielded on the diffraction pattern, light to be imaged on the wafer surface is equivalent to one in which light from patterns adjacent to each other in which as if phases are inverted (deviated by π) is imaged. At least a part of the O-order diffraction light is shielded by a shield plate  324  (an imaging spatial filter  3302 ) at a diffraction image surface as shown in  FIGS. 2 and 3  on the basis of the aforesaid technique, whereby only the diffraction light inverted in phase as shown in  FIGS. 2 and 3  reaches the imaging surface, and therefore, the strength distribution of the imaging surface is high in contrast. 
     A mechanism for enhancing a contrast will now be described. As an example,  FIG. 47  shows the transfer result of a circuit pattern formed on a mask shown in  FIG. 46 , and  FIG. 48  shows a change in contrast when a pitch PIT, as shown in  FIG. 46 , is changed. In the conventional reduction projection exposure method, a contrast rapidly goes down as a pattern size becomes finer as indicated by curve  342 , while in the reduction projection exposure method according to the present invention, it is understood that a contrast does not go down, as shown by curve  341 . 
       FIG. 49  shows an evaluation example of the focal depth in the reduction projection exposure method according to the present invention. According to the present invention, contrast indicates a value over about 80% in the range of ±1.5 μm as indicated by curve  343 . In the conventional reduction projection exposure method, contrast rapidly drops due to a deviation of focal point as indicated by curve  344 . This indicates that it can correspond to a resist whose film, is thick according to the present invention, and as a result, a wafer pattern with a resist at high aspect ratio can be formed. As the result, a pattern with a resist, well retained at etching and with a high aspect ratio can be formed. 
       FIG. 14  shows a focal depth  362  of the present invention and a focal depth  363  of the phase shifter method. Both the focal depths are substantially coincided. The focal depth  362  of the present invention shows the excellent result as compared with the focal depth  361  of prior art. 
       FIG. 50  shows an embodiment of an excimer stepper which uses, as a light source, an excimer laser shorter in wavelength than the i-ray. According to this embodiment, an excimer laser beam in the shape of a ring is scanned at a position of a light source spatial filter  3301  that the effect of the light source spatial filter  3301  can be achieved. Furthermore, according to this embodiment, the shape of the light source spatial filter  3301  can be easily controlled by controlling a scanning portion. That is, in this embodiment, as the light source portion  3100  in the embodiment shown in  FIG. 27 , there is used an excimer laser which uses gas such as KrF (krypton fluoride) having a shorter wavelength. A further fine circuit pattern can be transferred by using light having a shorter wavelength. Needless to say, in this embodiment, a laser having other wavelengths can be used. In this embodiment, the light source portion  3100  comprises an excimer laser  3111 , a shutter  3108 , a beam expander  3112 , an X galvanomirror  3113 , a Y galvanomirror  3114 , an integrator  3104 , an integrator cooling arrangement  3120  and a condenser lens  3106 . The spatial filter portion  3300  comprises a scan control system  3311 , a liquid crystal display element  3312  and a liquid crystal control system  3313 , and the light source filter regulating system  3303  in the embodiment shown in  FIG. 27  corresponds to the X galvanomirror  3113 , the Y galvanomirror  3114  and the scan control system  3311 . The integrator cooling arrangement is adapted to prevent an increase in temperature of the integrator  3104  due to excimer laser light concentrated to the integrator. It is noted that the cooling arrangement  3120  may be of a type to circulate cooling water or to spray nitrogen gas for cooling. Other constituent elements correspond to those shown in  FIG. 27 . That is, in this embodiment, the position of the light source spatial filter  3301  is the position of the integrator  3104 , and the X galvanomirror  3113  and the Y galvanomirror  3114  in the light source spatial filter regulating portion  3303  are scanned to thereby form a ring-like light source having the same shape as that of the light source spatial filter  3301 . In the imaging spatial filter  3302 , a shield portion is formed on the liquid crystal display element  3312  by the liquid crystal control system  3313  so as to have a shape which shields a part or the entirety of the O-order diffraction light as described in the embodiment shown in  FIG. 27 . Accordingly, it is necessary that the resolving power of the liquid crystal display element  3303  has sufficient accuracy to form the above-described ring-like shape. In addition, an imaging spatial filter will suffice to be formed, and instead of the liquid crystal display element, other elements, for example, a metal plate formed so as to shield in a ring-like fashion or one in which a ring-like shield film is formed on glass may also be employed. 
     Furthermore, an excimer laser beam is condensed at one point on the imaging spatial filter  3302 . A ring-like shape is obtained on the imaging spatial filter first by the scanning on the light source spatial filter in a ring-like fashion. If only respective points on the imaging spatial filter as well as the scanning on the light source spatial filter are shielded, the object of the present invention can be achieved. Thereby, light is not excessively shielded, and there provides effects that exposure time can be shortened, and the through-put can be increased. The mask  100  is placed on the mask stage  3401 , the mask stage  3401  is controlled by the mask stage control system  3404 , the mask  100  is located to a reference position, a position of an alignment mark on the wafer  200  is then detected by the locating mask detection portion  3403 , the wafer stage  3402  is controlled by the wafer stage control system  3405  in accordance with the detected signal, and the mask  100  and the wafer  200  are adjusted in position. After the adjustment of position, the shutter  3108  is opened, and a ring-like light source is formed by the light source spatial filter regulating portion  3303  so that the mask  100  is illuminated and a mask pattern is transferred onto the wafer  200  to form a wafer pattern. 
     In this embodiment, since the light from the excimer laser  3111  has a high coherence, this, coherence need be decreased to an adequate value. A ring-like light source can be formed on the light source spatial filter  3301  to thereby achieve the object simultaneously. 
     Particularly, in the present invention, it will suffice that uniform illumination can be made within an exposure field (within an exposure area). The ring-like illumination in which a number of imaginary point sources are arranged need not necessarily be illuminated simultaneously, but even if it is divided in time into plural numbers, scanning may be employed as in the previous embodiment. It is also apparent that the ring-like illumination in which a number of point sources are arranged may be divided into plural sections. 
     As described above, in the present invention, a large circuit pattern portion and a small circuit pattern portion can be exposed twice. Further, a mask with a phase shifter arranged can be used on at least a part (or whole) of the circuit pattern on the mask. In this case, a ring-like light source is used so that a center value of an incidence angle of illuminating light incident upon a reticle is large, and therefore, it is necessary to make a thickness of a phase shifter somewhat thin in order that a deviation of phase caused by the phase shifter is p. This value is calculated using an incidence angle according to expression (8).
 
(2 m+ 1)π≦( d /cos θ)·( n/λ )·2π  (8)
 
wherein m represents an integer, d represents a thickness of a phase shifter, λ represents a refractive index of the phase shifter, and X represents an exposure wavelength.
 
     As described above, the present invention brings forth a new effect such that it can correspond to various circuit patterns by a conventional exposure apparatus or a combination of a phase shifter and the like. 
     In carrying out the present invention, since the incidence angle of light illuminated on the reticle is large, a problem arises in a thickness of a circuit pattern such as chrome on the mask. Accordingly, it is desired that in carrying out the present invention, a thickness of a circuit pattern such as chrome on the mask is made thin in order to obtain an accurate dimension of a transferred pattern. Accordingly, the following expression (9) is required to be fulfilled.
 
 dm=pc/ 1  (9)
 
wherein dm represents a thickness of a circuit pattern such as chrome, pc represents an allowance value of a transferred pattern, and 1 represent a reduction rate of a reduction projection lens.
 
     In order to realize this, it is necessary to perform patterning of a mask with other materials which is lower in transmittance than that of chrome. However, if the dimension of a circuit pattern of a mask is determined taking a variation of dimension caused by the incidence angle of illumination into consideration, the aforesaid problem can be reduced. 
     Furthermore, when a coating in which the transmittance of luminous flux which is incident upon at a using incidence angle is maximum is applied to the transmission portion of the mask, the exposure quantity increases, enabling to reduce time required for exposure. 
     It is apparent that since the present invention makes use of the vibration property as mentioned above, it can be applied to an exposure device which uses an electron beam and X-rays. 
     According to the present invention, unbalance in light intensity between the O-order diffraction light and the diffraction light can be avoided when a mask pattern is transferred. The present invention has the effect that exposure can be made with a resolving power equal to or more than that which uses a phase shifter by a conventional white and black mask pattern. 
     While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.