The present invention relates to a scanning micro-lithographic apparatus and method for projecting a large field-of-view image on a substrate and, more particularly, to such apparatus that preferably employs a wide-field catadioptric projection system (e. g., a projection system incorporating a Wynne Dyson optical relay).

Description of the Prior Art : Some micro-lithographic applications, like flat display panel manufacturing, require a fast, seamless, high-resolution (e. g., 2-3 micrometers), large area exposure. This kind of exposure can be achieved effectively by scanning the substrate under a large exposure projection system with a field-of-view for exposure.

It is well known that micro-lithography can be done over a large area by combining two-1X projection systems having parallel object and image planes with a raster scanning system that moves the mask and substrate together so as to produce one strip of imagery at a time. The precision requirements on the scanning system are relaxed if adjacent strips of imagery are not butted together, but overlapped in a small area containing a linear variation in exposure intensity, such as can be obtained using a tapered illumination slit. A micro- lithography approach employing this principle is described in US patent 5, 298, 939 and its division US patent 5, 835, 195, both of which are entitled'Method and Apparatus for Transfer of a Reticle Pattern onto a Substrate by Scanning". The drawback with this approach is that to obtain a +1X relay system it is either necessary to employ two-1X relays in series or to add an odd number of folds to the optical system which is often inconvenient or impossible. Also the requirements on the raster scanning system lead to substantial expense and complexity in the stage components.

An alternate approach, described in U. S. patent 5, 585, 972, entitled"Arbitrarily Wide Lens Array with an Image Field to Span the Width of a Substrate,"employs an array of+1X projection systems, which span the width of the substrate, to reduce the scanning requirement to a single linear scan. The drawback with this approach is that it requires a great many

projection optical systems all of which have to be aligned very accurately and the illumination apertures are a staggered array of rectangles which is difficult to illuminate uniformly.

Therefore, there is a need for a scanning micro-lithographic apparatus and method that derives a high-resolution, large area exposure over a large area with a greatly simplified projection and illumination optical system, while not introducing too much complexity in the scanning system. In this regard, the teachings of U. S. patent 5, 852, 693, entitled"Low-loss Light Redirection Apparatus"which discloses a uniform illumination system employing light guiding technology using multiple light-pipes, is incorporated herein by reference.

SUMMARY OF THE INVENTION The present invention is directed to a scanning micro-lithographic apparatus that employs a fixed-IX projection system (preferably, a wide-field catadioptric projection system) having a limited field of view in which image patterns located in its object plane can be imaged onto a substrate located in its image plane. These patterns, which are contained on a reticle or mask, are wider than the limited field size of the projection system. The mask is illuminated over the area corresponding to the field of the projection system and is moved in the object plane reticle in a direction parallel to that in which a vector in the object plane would be imaged parallel to its image in the object plane. Synchronous motion of the substrate in the same direction, scanning, copies the pattern from the reticle onto the substrate. In this fashion, a strip of imagery spanning the length of the pattern on the reticle may be copied onto the substrate. Other strips of imagery may be added in subsequent scans but, because the magnification is-lX, it is necessary to re-register the reticle and substrate by stepping them equally in opposite directions normal to the scanning direction. A second synchronous scan of the reticle and substrate then results in a pattern exposed on the substrate that is congruent with the reticle pattern. Subsequent stepping and scanning operations can be used to copy an arbitrarily large pattern on a reticle to a similarly sized substrate using a-1X relay having a smaller field size than the reticle pattern.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE la is a diagrammatic showing in the vertical section through the scanning g microlithographic apparatus of the present invention comprising an embodiment of an imaging means in which a movable mask structure and a movable substrate structure of the apparatus are each shown in a first of two relative positions thereofwith respect to a fixed-1X

projection system of the imaging means ; FIGURE lb is a diagrammatic showing in the vertical section through the scanning microlithographic apparatus of the present invention in which the movable mask structure and the movable substrate structure of this embodiment of the imaging means are each shown in a second of the two relative positions thereof with respect to the fixed-IX projection system of the imaging means ; FIGURE lc indicates the respective directions of the 2 horizontal spatial coordinates X and Y and the vertical spatial coordinate Z with respect to the plane of the paper in which each of FIGURES la and lb is shown ; FIGURES 2a is a diagrammatic showing in the horizontal plane ofthe movable mask structure shown in FIGURE la ; FIGURES 2b is a diagrammatic showing in the horizontal plane of the movable mask structure shown in FIGURE 1b ; FIGURE 3 diagrammatically illustrates the successive steps of one complete exposure scanning cycle of the movable mask structure and movable substrate structure of the imaging means of the scanning micro-lithographic apparatus incorporating present invention ; FIGURE 3 a illustrates the inverted image exposed on the substrate of spatial patterns disposed on the mask of the movable mask structure at the end of one complete exposure scanning cycle ; and FIGURES 4a, 4b, 4c and 4d relate to a preferred embodiment of the imaging means shown in FIGURES la and lb that employs a fixed-1X projection system comprising a design of a catadioptric optical system design employing a plurality of lenses defining a modified Wynne-Dyson relay.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Scanning microlithographic apparatus 100 shown in each of FIGURES la and 1b comprises fixed base 102, scanning carriage 104, movable mask structure 106, fixed -1X projection system 108 and movable substrate structure 110.

In FIGURE la, movable mask structure 106, supported by scanning carriage 104 toward the top thereof is shown in its extreme left indexed position and movable substrate structure 110, supported by scanning carriage 104 toward the bottom thereof is shown in its extreme right indexed position. In FIGURE lb, movable mask structure 106, supported by

scanning carriage 104 toward the top thereof is shown in its extreme right indexed position and movable substrate structure 110, supported by scanning carriage 104 toward the bottom thereof is shown in its extreme left indexed position. Movable mask structure 106-and movable substrate structure 110 may be switched to either the indexed position thereof shown in FIGURE la or the indexed position thereof shown in FIGURE lb by the operation of unshown indexing means (e. g., magnetic indexing means). When movable mask structure 106 and movable substrate structure 110 occupy their positions shown in FIGURE la, they comprise elements of imaging means that results in light (indicated by arrows) illuminating the patterns defined by the right half of mask structure 106 to be imaged by fixed-1X projection system 108 on the left half of movable substrate structure 110. Similarly, when movable mask structure 106 and movable substrate structure 110 occupy their positions shown in FIGURE lb, they comprise elements of imaging means that results in light illuminating the patterns defined by the left half of mask structure 106 is imaged by fixed-IX projection system 108 on the right half of movable substrate structure 110.

In operation, both mask structure 106 and substrate structure 110 are carried on common scanning carriage 104 that moves on a fixed axis that is accurately aligned with the axis of projection system 108. The axis of projection system 108 is defined as the direction in which a vector in the object plane and its image in the image plane are parallel. The carriage is shown shaded in the figure and is guided by air bearings that operate against a fixed base 102 so that it is only free to move in the scanning direction.

As indicated in FIGURE 1c, FIGURES la and 1b lie in an X, Z vertical plane that is parallel to the plane of the paper. Scanning carriage 104, mounted in fixed base 102 (e. g., by air bearings) and operated by motor means (e. g., a linear motor) is moved either forward or backward in the Y direction normal to the plane of the paper to effect a scan. Since movable mask structure 106 is supported by scanning carriage 104, such a scan results in the exposure of roughly half of the substrate by the half of mask structure 106 then being illuminated, FIGURES 2a and 2b, which, respectively, correspond in position to FIGURES la and lb, show mask structure 106 in its X, Y horizontal plane. As indicated in detail in FIGURES 2a and 2b, mask structure 106 comprises mask holder 200 which holds mask 202. Mask 202 constitutes a reticle that defines the patterns which are to be imaged on a substrate included in substrate structure 110. As shown in the plane of the paper, projecting from the corners of

mask holder 200 are the single upper-left prominence 204L, the single upper-right prominence 204R, the double lower-left prominences 206L and 208L and the double lower-right prominences 206R and 208R When mask structure 106 occupies its first position shown in FIGURE 2a, the prominences 204L, 206L and 208L are situated so that solely a first set of three points of mask holder 200 of mask structure 106 are in contact against edges of the left and lower interior edges of scanning carriage 104, thereby precisely controlling the position and the angular orientation of reticle 202 in the horizontal plane defined by the contact positions of the three points of this first set. Similarly, when mask structure 106 occupies its second position shown in FIGURE 2b, the three prominences 204R, 206R and 208R are situated so that solely a second set of three points of mask structure 106 are in contact against edges of the right and lower interior edges of scanning carriage 104, thereby precisely controlling the position and the angular orientation of reticle 202 in the horizontal plane defined by the contact positions of the three points of this second set. The left and right interior edges of scanning carriage 104 are in precise parallel relationship with one another and d unshown means comprising air bearings is employed in the support of mask structure 106 while (1) in its first position, (2) while in its second position and (3) while being moved between its first and second positions.

Although not shown in the drawing, the design of substrate structure 110 in FIGURES la and lb is substantially similar to that of above-described mask structure 106 shown in FIGURES 2a and 2b to permit substrate structure 110, in its X, Y horizontal plane, to be moved from its first position to its second position and to be precisely angularly oriented when in its first position and also when in its second position. It is important that neither mask structure 106 nor substrate structure 110 rotate between index positions and that the index distance be the same for both.

Referring now to FIGURE 3, there is diagrammatically illustrated each of the successive 8 steps 300a to 300h of one complete exposure scanning cycle of reticle 302 of movable mask structure 106 and substrate 304 of movable substrate structure 110 with respect to the fixed position of illumination slit 306. The width of illumination slit 306 is substantially one-half the width of each of reticle 302 and substrate 304. The spatial patterns defined by reticle 302 are represented by the letter"F"situated in the left half of reticle 302 and the letter"R"situated in the right half of reticle 302.

Step 300a shows that prior to the beginning of a scanning cycle, reticle 302 and substrate 304 are disposed in their first positions and illumination slit 306 is situated in the plane of the paper above reticle 302 and substrate 304. Step 300b shows that during the first half of a scanning cycle, reticle 302 and substrate 304 are moved upward in the plane of the paper (as indicated by the direction of the arrow in 300b), thereby exposing the spatial patterns, such as the letter'W', situated on the right half of reticle 302. Step 300c shows that at the end of the first half of a scanning cycle, reticle 302 and substrate 304 are still disposed in their first positions and illumination slit 306 is situated in the plane of the paper below reticle 302 and substrate 304. Step 300d shows that next indexing takes place, wherein reticle 302 is to be switched from its first (i. e., left) position to its second (i. e., right) position and substrate 304 is to be switched from its first (i. e., right) position to its second (ie., left) position (as indicated by the direction of the arrows in 300d). Step 300e shows that subsequent to such indexing and prior to the beginning of the second half of a scanning cycle, reticle 302 and substrate 304 are disposed in their second positions and illumination slit 306 is situated in the plane of the paper below reticle 302 and substrate 304. Step 300f shows that during the second half of a scanning cycle, reticle 302 and substrate 304 are moved downward in the plane of the paper (as indicated by the direction of the arrow in 300f), thereby exposing the spatial patterns, such as the letter"F", situated on the left half of reticle 302. Step 300g shows that at the end of the second half of a scanning cycle, reticle 302 and substrate 304 are still disposed in their second positions and illumination slit 306 is situated in the plane of the paper above reticle 302 and substrate 304. Step 300h shows that finally indexing takes place, wherein reticle 302 is to be switched from its second (i. e., right) position to its first (i. e., left) position and substrate 304 is to be switched from its second (ie., left) position to its first (i. e., right) position (as indicated by the direction of the arrows in 300h). The accomplishment of this final indexing completes the performance of an entire scanning cycle.

FIGURE 3a illustrates the inverted image exposed on substrate 304 of spatial patterns, represented by the letters F"and'", disposed on the reticle 302 at the end of one complete exposure scanning cycle.

Reference is now made to FIGURES 4a, 4b, 4c and 4d, which show various indicated views of a preferred embodiment of the FIGURES la and 1b imaging means that includes a design for the fixed-1X projection system 108 which comprises a catadioptric optical system

employing a plurality of lenses defining a modified Wynne-Dyson relay. More specifically, as indicated in FIGURES 4a and 4b, in the plane of the paper, shows a Y, Z-plane view through the optical axis of triangular fold-mirror element 400, reflector element 402 and the four lenses 404-1, 404-2, 404-3 and 404-4 (which constitute the structure of fixed-IX projection system 108) together with reticle 412, its protective window 414, substrate 416 and its protective window 418. Thus, as further indicated in FIGURE 4b, the X direction in FIGURE 4a is oriented normal to the plane of the paper. FIGURE 4c shows the X, Z-plane view of the shape of the periphery of any one of lenses 404-1, 404-2, 404-3 and 404-4 (which is designated lens 404-k in FIGURE 4c). FIGURE 4d shows (1) the respective sizes of the X and Y dimensions of the substantially rectangular illumination field incident on reticle 412 (as well as the corresponding field imaged on substrate 416) and (2) the relative offset between the rectangular illumination field and the center of the field on projection lens 422. In the example shown in FIGURE 4d the offset between the center of the field of the projection lens and the closest edge of the illuminated field is 15 mm This offset avoids vignetting that would otherwise occur on the folding prism 400. In FIGURE 4a the optical axis through the center of the lens would be folded by folding prism along the flat edge of lens element 404-1.

The offset between the folded axis and the field is apparent in the Y separation distance between the plano surface of lens element 404-1 and the illuminated field shwon on the reticle plane 412.

More particularly, in the rectangular object field 420 shown in FIGURE 4d, the size of the X dimension is 300 millimeters (mm) and the size of the Y dimension is 45 mm. Further, rectangular object field 420 is positioned so that its upper side would form a chord of a circle having a radius of 165 mm (i. e., 330 mm diameter) which is centered on optical axis position 422. This results, in the FIGURE 4d view, in the lower side of rectangular object field 420 being situated substantially 15 mm above optical axis 422, which, in the FIGURE 4a view, causes the left surface of lens 404-1 being situated 15 mm to the right of the right side of reticle 412.

While originally each of lenses 404-1, 404-2, 404-3 and 404-4 had a circular periphery somewhat larger than 300 mm in diameter, in accordance with the principles of this invention, a portion of both the top and bottom of these lenses has been sawed away. This results in the sawed periphery of each of these lenses having the shape of lens 404-k shown in FIGURE 4c,

which has a width in its X dimension which remains somewhat larger than 300 mm, but has a thickness in its Y dimension which (as shown in FIGURE 4c) may have been reduced to substantially one-half that of its X dimension. Sawing away the top and bottom portions of these lenses results in the dual advantages of both facilitating scanning of the reticle 412 and substrate 416 by aligning them parallel to each other, and reducing lens weight.

Returning to FIGURE 4a, reticle 412, which defines the patterns to be imaged, lies in the object plane of the projection system. While reticle 412 is being scanned in the horizontal Y direction, illumination from above, which is directed in the vertical Z direction (as indicated by arrow 424), is incident on the reticle 412. The shape and relative position of this incident light with respect to the folded position of the projection system optical axis is that shown in FIGURE 4d. The result is that light (indicated by dashed lines in FIGURE 4a) passes downward in the vertical Z direction through reticle 412 and its protective window 114 and is incident on the top mirror surface 400T (indicated by a thick line) of triangular fold-mirror element 400. Top mirror surface 400T, which is oriented at a 45 degree angle with respect to each of the horizontal Y and vertical Z directions, reflects the vertical Z direction light incident thereon into the horizontal Y direction. This horizontal Y direction light, subsequent to being acted upon by each of lenses 404-1, 404-2, 404-3 and 404-4 as it passes left-to right therethrough, is incident on concave-mirror surface 402C (indicated by a thick line) of reflector element 402. The horizontal Y direction light reflected from concave-mirror surface 402C, subsequent to passing right-to-left back through each of lenses 404-4, 404-3, 404-2 and 404-1, is incident on the bottom mirror surface 400B (indicated by a thick line) of triangular fold-mirror element 400. Bottom mirror surface 400B, which is oriented at a 45 degree angle with respect to each of the horizontal Y and vertical Z directions, reflects the horizontal Y direction light incident thereon into the downward vertical Z direction through substrate protective window 418 to a focus on substrate 416, while substrate 416 is being scanned together with reticle 412 in the horizontal Y direction. Operating in this manner, the imaging means shown in FIGURE 4a, is effective in imaging a-1X (i. e., inverted, same size) image of the patterns defined by reticle 412 on substrate 416 (as represented in above discussed FIGURE 3a).

The following Table 1 lists illustrative optical design criteria for the imaging means shown in FIGURE 4a (wherein each of the respective optical surfaces in FIGURE 4a, except

for the fold-mirror surfaces, is identified by a reference number within parentheses in FIGURE 4a). This optical design criteria (which ignores the presence ofthe fold mirrors), operates with light centered at a wavelength of 365 nanometers (nm) to provide a 0. 1 numerical aperture fixed-1X projection system : In Table 1, the axial separation 113. 685329 mm represents the sum of the vertical axial distance between the lower surface (3) of reticle protective window 414 and fold-mirror surface 400T and the horizontal axial distance between fold-mirror surface 400T and the left surface (4) of lens 404-1, as well as the sum of the vertical axial distance between the upper surface (14) of substrate protective window 418 and fold-mirror surface 400B and the horizontal axial distance between fold-mirror surface 400B and the left surface (15) of lens 404-1.

The imaging means shown in FIGURE 4a, employing the illustrative optical design criteria listed in Table 1 is capable of providing a resolution of better than 3 micrometers (mm), and, therefore, is capable of imaging fine patterns (such as needed for the manufacture of the majority of high resolution flat display panels) in a single complete scanning cycle without requiring any field stitching.

Further, the design of the imaging means shown in FIGURE 4a has the following desirable characteristics : 1. The use of single triangular fold-mirror element 400 to provide both top and bottom fold-mirror surfaces 400T and 400B, instead of employing two separate prisms for these purposes, makes not only the lens assembly but also the final imaging means adjustments much easier. In order to make the scanning mechanism simple, a mirror bar folds horizontal light paths to vertical directions. Further, the folding of the direction of the light from the reticle from vertical to horizontal and the folding of the light to the substrate from horizontal to vertical permits a simplified scanning mechanism to be employed ; however this orientation makes the total footprint of the tool rather large and it necessitates that the substrate be handled in the horizontal position. In some situations it is likely that the preferred embodiment will rotate the reticle and wafer planes so that they are vertical while retaining a horizontal axis for the scanning stage.

2. The imaging means design has a large enough working distance to allow reticle and substrate protective windows 414 and 416 to be installed, which not only provide a means to seal and protect the imaging system but also can be used for magnification correction. Bending these windows about the Y- axis changes the magnification in the X-direction. The magnification can be independently changed in the Y-direction by differentially moving the reticle with respect to the substrate in the Y-direction as the reticle and substrate are being scanned. Some control of the magnification (+/-30 ppm) is desirable to compensate for small changes in the scale of the substrate as compressive and tensile layers are added during successive process steps.

3. The design adds the two lenses 404-3 and 404-4 to the conventional Wynne-Dyson design to reduce aberrations and telecentricity errors across the large light field of 45x300 mm2. Lens 404-3, closer to the doublet lenses 404-1 and 404-2, has a positive power and lens 404-4, further from the doublet lenses 404-1 and 404-2, has a negative power.

It is important that the large object field of 45 mm x 300 mm be provided with substantially uniform illumination. While providing uniform illumination over such a wide field is challenging, it can be achieved by employing the light guiding technology using multiple lightpipes that is taught in the aforementioned U. S patent 5, 852, 693, which teaching has been incorporated herein by reference. The light pipes provide a means of obtaining uniform illumination over a field equivalent to 100 mm by 135 mm, which can then be divided into 6 fields, each 45 mm by 50 mm, that can be rearranged to provide a 45 mm by 300 mm field size. In order to conserve material this would likely be done at higher numerical aperture and at a smaller scale, possibly at 1/3 the required scale, and then magnified with a relay to obtain the correct scale at the reticle plane.

The 300 mm wide strip ofthe image pattern projected on substrate 418 by the imaging means shown in FIGURE 4a permits a 550 mm wide substrate to be exposed with the two scans comprising a complete cycle shown in FIGURE 3. A little extra field provided by the projection system permits the use of a slit with tapered ends and some overlap between the exposures of the two scans. A 550 mm wide substrate was chosen as an example because this size is believed to be representative of current state-of-the-art flat panel substrates. However

the present invention could be scaled up to handle substantially larger substrates. For example, a scaled-up projection system could be employed to achieve a span of 38Q mm wide field for use in accommodating a 720 mm wide substrate, which is expected to be the next standard substrate size.

Further, it is not intended that the present invention be limited to the above-described case in which the movable mask structure and movable substrate structure is situated in a selected one of a plurality of only two indexed positions. Rather, the present invention contemplates a scanning microlithographic apparatus in which the plurality of selectable indexed positions may be two or greater. In such a case, step 300h in FIGURE 3, in which the mask structure is moved right-to-left and the substrate structure is moved left-to-right, is repeated three and possibly more times. In each case the mask structure is moved left-to-right and the substrate structure is moved right-to-left by an identical amount, thereby permitting a new scan to continue until the entire reticle pattern has been copied onto the substrate and a new cycle with a new substrate can commence. In general if more than two scans are required, the re-registration of the reticle and substrate between scans becomes more complex, and the time required for more scans becomes longer.

Sn Surface Sn-Sn-1-mm Lens (Surface No.) Radius-mm (Axial Separation) Glass Type (1) & 12) (2) & (13) Infinity 20.000000 (3) & 14 Infinity 10.000000 BK7 SCHOTT (4) & (15) Infinity 113.685329 (5) -258.71918 152.627197 FSL5Y_O'HARA (6)-665. 58119 132. 232497 PBL6Y OHARA (7) 1513. 72957 53.185137 (8)-2294. 93750 219.718892 PBL6Y_O'HARA (9) 1185, 57361 100. 903748 (10) 833. 06562 73. 410281 PBL6Y 0' (11)-1400 00000 569. 305564 TABLE 1