Patent Number: 053902270
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a major portion of the exposure apparatus according to an embodiment of the present invention, and it best shows the feature of this embodiment. A mask MSK includes a pattern SLN corresponding to the scribe line of the mask MSK, and a pattern PTN of a semiconductor device circuit to be printed on an unshown semiconductor wafer and, an alignment mark AMK on the scribe line pattern SLN. The apparatus includes an alignment unit AAU1 for projecting an alignment beam AMB onto the alignment mark AMK to detect the deviation between the alignment mark on an unshown wafer and the alignment mark AMK on the mask MSK, a supporting member SPT on which the alignment unit AAU1 is fixedly supported, a semiconductor laser accommodating portion LD which is a light source for the alignment beam AMB, and a photosensor accommodating portion SEN for accommodating a photosensor for converting an optical deviation signal from the alignment mark AMK to an electric signal. The alignment unit AAU1 includes a collimator lens, a beam splitter means, a light receiving lens or other optical element. A blade BLD1 functions to limit the irradiation area of the mask MSK by the exposure beam EXB supplied in the direction indicated by an arrow (Z axis direction). The blade BLD1 is in the form of a rectangular plate and is securedly fixed on the supporting member SPT through an arm ARM. The blade BLD1 is provided with pipes CLI and CLO for cooling function, and cooling passages are formed in the blade. The apparatus includes a stage unit STG constituted by guiding and driving means movable in two orthogonal axes (X and Y axes) and position detecting means. The supporting member SPT is coupled with the stage unit STG so that the alignment beam ABM is positioned on the alignment mark AMK of the mask MSK. In the apparatus, four of the above-described alignment units are provided, corresponding to the alignment marks AMK in the four scribed lines around the pattern PTN. Therefore, one exposure apparatus is provided with four blades (BLD1, BLD2, BLD3 and BLD4) and four alignment units (AAU1, AAU2, AAU3 and AAU4). In the following description, therefore, the reference character for the blade is "BLD", and that for the alignment unit is "AAU", unless a particular one of them is referred to. FIGS. 2(A) and 2(B) a relationship between the blade and the exposure beam of the apparatus of FIG. 1, as seen in the direction y. As shown, the exposure beam EXB is a divergent beam having a point of origin O and having a divergent angle .theta.. In this embodiment, the exposure beam is X-rays contained in synchrotron orbital radiation. The exposure beam EXB is confined or limited first by a fixed aperture stop FAP. The limited beam is indicated by a reference EXBF. In FIG. 2(A), l.sub.max indicates the maximum exposure angle range of view on the mask MSK. The size of the aperture of the fixed aperture stop FAP is determined so that the exposure beam EXBF irradiates slightly beyond the maximum exposure view angle, as shown by chain lines. The exposure beam EXBF having passed through the fixed aperture FAP is further confined or limited by the blade BLD fixed on the alignment unit AAU. FIG. 3 shows the arrangement of the blades BLD1-BLD4 on the alignment unit AAU, as seen from the light (radiation) source, that is, in the direction of the z axis. The adjacent blades, for example, the blade BL1 and the blade BL2 are at different levels (positions in the z axis direction), and therefore, they do not interfere with each other irrespective of the size of the view angle. The description will be made as to the relation between the size of the view angle and the blade mounting position in this structure. In FIG. 2(A) shows the state wherein a spot SPT formed by the alignment beam AMB accesses the scribe line in the case of the maximum view angle l.sub.max, and FIG. 2(B) shows a state wherein the spot SPT by the alignment beam AMB accesses the scribe line in the case of the minimum view angle l.sub.min. The respective blades are fixed to the associated alignment unit AAU so that the exposure beam is incident slightly beyond the outer edges of the scribe lines. In order to accomplish this, the blade is projected beyond the outer edge of the scribe line into the view angle range in a direction parallel to the X-Y plane, more particularly, in the X axis direction in this figure, by the amount d.sub.max in FIG. 2(A) and d.sub.min in FIG. 2(B). The amount d of the projection of the blade BLD, is EQU d=L.sub.A .times.(l/2L.sub.M) (1) where l is a size of the view angle in the X (Y) axis direction, L.sub.M is a distance from the point of origin O of the exposure beam having a divergence angle .theta. to the mask MSK measured in the Z axis direction; and L.sub.A is a distance from the edge ADG of the blade BLD to the mask MSK measured in the Z axis direction. Therefore, d.sub.max and d.sub.min are: EQU d.sub.max =L.sub.A .times.(l.sub.max /2L.sub.M) (2) EQU d.sub.min =L.sub.A .times.(l.sub.min /2L.sub.M) (3) If, for example, L.sub.A =150 mm, L.sub.M =50000 mm, l.sub.max =30 mm, l.sub.min =15 mm, then d.sub.max =0.45 mm, and d.sub.min =0.225 mm. In consideration of the blade function, it is preferable that the blade edge EDG provides a boundary between the exposure area and the non-exposure area, which is as close to the outer edge of the scribe line as possible. However, if the blade BLD is set in consideration only of the maximum view angle shown in FIG. 2(A), then the light blocking area extends into the view angle l.sub.min as shown in FIG. 4, in the case of the minimum view angle. Therefore, the required view angle cannot be obtained. Therefore, when the blade BLD is fixed to the alignment unit AAU, the blade is set to meet the minimum view angle l.sub.min, and the amount d of the projection is not more than EQU L.sub.A .times.l.sub.min /2.times.L.sub.M. By disposing the blade at such a position and by fixing the blade BLD on the alignment unit AAU, the blade BLD can be moved to a proper position in accordance with the view angle size without the necessity of employing the positioning means exclusively for the blade. Generally, the alignment between the alignment mark AMK and the alignment beam spot SPT is as accurate as not more than 10 microns, and therefore, the positioning of the blade BLD is automatically very high. It is possible for the blade BLD to block almost all of the exposure beam that is not desired to reach the mask MSK. Referring to FIGS. 5 and 6, the description will be made as to the cooling of the blade BLD. In FIG. 5, there are provided cooling water containers TNK1 and TNK2, which contain water maintained at 23.5.degree. C. and 10.degree. C., respectively. The cooling water delivered from the cooling water tank TNK1 is subjected to a heat exchanging operation by a heat exchanger TEX with the cooling water delivered from the cooling water container 2, so that the temperature of the cooling water from the container TNK1 is decreased to a temperature T.sub.B .degree.C. which is lower than 23.5.degree. C. It is then passed through the passage CLP in the blade BLD, and is returned to the container TNK1. The cooling water containers TNK1 and TNK2 are disposed at such a position as is sufficiently away from the unit wherein the alignment is performed, by which the alignment operation is not influenced by heat. Temperature sensors TSNI and TSNO are disposed adjacent to an inlet and outlet of the cooling passage in the blade BLD. The sensor may include a thin film resistance element of platinum or a thermistor. The outputs of the temperature sensor TSNI and TSNO are supplied to a controller CNT, and are used as data for controlling a degree of opening of a proportional controlling valve LNV. From the cooling water container TNK2, a constant rate of the cooling water is supplied, and the proportional control valve LNV controls a ratio of the rate of the cooling water flowing to a by-pass pipe BP and the rate flowing into the heat exchanger TEX, by which the temperature T.sub.B of the cooling water supplied into the passage of the blade BLD is controlled to be the set temperature by the controller CNT. The exposure operation will be described. Generally, the exposure beam is projected onto the mask MSK for a predetermined period of time controlled by a shutter or the like, and therefore, thermal energy is produced in the blade BLD as shown by a curve L1 in FIG. 6(A). For example, when the exposure period is 1 sec, and the energy absorbed by the blade BLD is 50 mJ, approximately 1.22 cc/sec of the water flows to suppress the temperature rise to be approximately 1/100.degree. C. by constant rate of the cooling water having the constant temperature of 23.degree. C. In view of the fact that the cooling is necessary only during the exposure operation, it is effective to decrease the temperature of the cooling water down to less than 23.degree. C. in timed relation with the exposure operation, as shown by a line L3 in FIG. 6(B). This is accomplished by the control of the controller CNT in timed relation with the exposure operation using the signal SIN from the main controller, as shown in FIG. 5. The energy absorbed by the blade BLD changes in accordance with the size of the view angle and the change in the intensity of the beam source. When, for example, a constant rate of the cooling water having the constant temperature of 23.degree. C. is supplied during the exposure operation, the temperature sensor TSNO produces a temperature change output as shown by a reference L2 in FIG. 6, and a control table for the proportional control valve ALV is made on the basis of the data. As described in the foregoing, according to this embodiment, even when the exposure beam is not reflected, as in the case of X-rays, and the exposure beam energy is converted into thermal energy in the blade BLD, the produced heat is transmitted outside the apparatus, using cooling water, and therefore, the heat transfer around the blade is suppressed, to enable the highly precise alignment of the blade to be accomplished. In this embodiment, the temperatures of the two cooling water systems are 23.5.degree. C. and 10.degree. C., but the present invention is not limited to those values. From the standpoint of suppressing the heat transfer from the blade BLD to the other member, the blade mounting portion may be made of low thermal conductivity material such as ceramic material, by which the temperature is more easily controlled. Referring to FIG. 7, another embodiment of the present invention will be described. This Figure shows the portion of the blade BLD having connectors for the cooling type in FIG. 1, as seen from the radiation source side. As contrasted to FIG. 1, a parallel link PLK for supporting the blade BLD for movement in the Y (X) axis direction and an inch worm INC are connected through a rod ROD to the back side of the blade BLD in series. The unit is mounted on the alignment unit AAU by four screws SCR. In the embodiment of FIG. 1 wherein an exposure beam having a divergence angle is used, an inside edge of the beam blocking area formed by an edge EDG of the blade BLD fixed on the alignment unit AAU approaches the outside edge of the scribe line, and therefore, the blade BLD on the alignment unit AAU is set to meet the minimum view angle l.sub.min for safety. In order for the distance between the inside edge of the beam blocking area provided by the edge EDG and the outside edge of the scribe line to be constant, the amount of projection of the blade is corrected in consideration of the equation (1). Using the dimensions of the FIG. 1 embodiment, that is, d.sub.min =0.225 mm, and d.sub.max =0.45 mm, the difference is 0.225 mm. This is a stroke required to be corrected in the amount of blade projection in consideration of the size of the view angle. In this embodiment, the actuator is constituted by the inch worm INC, and the guiding mechanism is constituted by a parallel link PLK, and therefore, sufficient stroke and accuracy required for the correction can be provided. In addition, the parallel link PLK does not have a scribing portion, and therefore, no particles are produced. The inch worm INC used for the actuator hardly produces heat after the positioning, so that it does not influence the other constituent elements. FIG. 8 shows another example of a mechanism for correcting the amount of projection of the blade. In this Figure, blade BLD is seen in the y direction. In this Figure, a reference BO designates a common rotational center of the blade BLD and the worm wheel WH. The blade edge EDG is rotatable about this center by operation of a small size motor MTR with a reduction mechanism. When, for example, the distance from the blade edge EDG to the rotational center BOl is 20 mm, and the stroke required for the correction is 0.225 mm (same as the above), a necessary stroke can be obtained by rotating the blade BLD by approximately .theta.=8.6.degree.. In this example, the amount of projection of the blade edge EDG relative to the exposure beam can be controlled without use of an expensive linear movement guide. As described in the foregoing, according to this embodiment, the means for detecting the deviation between the substrate and the original and the means for limiting the exposure beam are made integral, so that they are integrally positioned. This eliminates the necessity of positioning means exclusively for the exposure beam limiting means. Therefore, the size of the apparatus is reduced, and the reliability of the apparatus is improved. Furthermore, when the exposure beam limiting means is made integral with the deviation detecting means, the unnecessary irradiation area of the exposure beam projected on the original is minimized, and in addition, the beam blocking area does not extend into the pattern, for any size of the view angle, and therefore, the unnecessary energy absorbed by the original can be minimized. The exposure beam limiting means is provided with cooling means to externally transmit the exposure beam energy absorbed by the exposure beam limiting means, and therefore, the thermal deformation is prevented, thus improving the alignment accuracy and reducing the line width of the exposure pattern which can be produced by the apparatus. FIG. 9 shows the relationship between the blade BLD and the exposure beam EXB, and it is a schematic view as seen in the direction y. The exposure beam EXB is first limited by the fixed aperture stop FAP, so that the view angle is limited from l.sub.EXB to l.sub.EX. The limited exposure beam is indicated by a reference EXBF. The maximum exposure view angle of this apparatus is indicated by l.sub.max. The size of the aperture of the fixed aperture stop FAP is so determined that the limited exposure beam EXBF irradiates slightly beyond the maximum exposure view angle. The exposure beam EXBF having passed through the fixed aperture FAP is further limited by the blade BLD fixed on the alignment unit AAU. The further limited exposure beam is depicted by a reference EXDB. The size of the view angle of the further limited exposure beam EXBB is l.sub.EXBB on the mask MSK. FIGS. 11(A) and 11(B) show the relationship between the alignment mark and the blade. FIG. 11(A) is a top plan view as seen from the radiation source side; and FIG. 11(B) is a side view thereof. When the alignment unit AAU is placed at such a position that the alignment beam ABM accesses the alignment mark AMK in the scribe line SLN, the exposure beam EXBB is blocked by the blade edge EDG at a position slightly outside the outer edge of the scribe line SLN. The blade BLD is fixedly mounted on the alignment unit AAU in the manner described in the foregoing so as to satisfy this. In FIG. 11(A), a center of the alignment mark AMK in the scribe line SLN is within an area l.sub.STG. The blade BLD has a length l.sub.w measured along the edge EDG, that is, in the Y axis direction in this Figure, wherein the length l.sub.w is l.sub.max +l.sub.STG +.alpha., when the maximum exposure view angle is l.sub.max .times.l.sub.max. Also, the blade BLD has a length l.sub.B measured in the direction perpendicular to the edge EDG, that is, in the X axis direction in this Figure, wherein the length l.sub.B =(l.sub.EX -l.sub.min)/2+.alpha., where the minimum exposure view angle is l.sub.min .times.l.sub.min. A length .alpha. is determined in consideration of an assembly error, a positioning error and diffraction or the like. As an example, .alpha. is equal to approximately 1 mm. When the view angle changes in the structure described above, the scribe line SLN moves in the direction perpendicular to the blade edge EDG in accordance with the change of the view angle, and simultaneously, the alignment mark AMK on the scribe line also moves in the direction perpendicular to the blade edge EDG. FIG. 10(A) shows the position of the blade BLD at the time of the maximum exposure view angle l.sub.max ; and FIG. 10(B) shows the position of the blade BLD at the time of the minimum exposure view angle l.sub.min. As shown in this Figure, since the length l.sub.B is (l.sub.EX -l.sub.min)/2+.alpha., the edge EDG can block the exposure beam while maintaining the relationship between the alignment mark AMK and the exposure beam EXBB shown in FIG. 3, when the alignment unit AAU is moved, and the blade BLD is positioned in accordance with the size of the view angle. At the time of the minimum exposure view angle, an edge EDGB opposite from the edge EDG of the blade BLD does not extend into the view angle l.sub.EX .times.l.sub.EX defined by the fixed aperture FAP, so that the portion outside the exposure view angle is completely blocked. The description will be made as to the case where the position of the alignment mark AMK in the scribe line SLN changes along the scribe line SLN. When the position where the alignment mark AMK is formed moves along the scribe line SLN, the alignment unit AAU also moves in parallel with the scribe line SLN, and the blade BLD fixed integrally on the alignment unit AAU also moves, similarly to the blade BLD. FIGS. 12(A)-12(C) movement of the blade BLD fixed on the alignment unit AAU, in accordance with the position of the alignment mark AMK. The adjacent blades are placed at different levels, as shown in FIG. 1, to avoid interference therebetween. For the simplicity of explanation, only one blade BLD1 of the four blades is moved. In this Figure, the "solid triangle" indicates the central position of the alignment mark AMK. FIG. 12(A) shows the state wherein the alignment mark is at the leftmost position; 12(B) shows the state wherein it is generally at the center; and 12(C) shows the state wherein it is at the rightmost position. In those Figures, the exposure view angle is maximum. As described in the foregoing, the longitudinal dimension of the blade BLD1, measured in the X axis direction in this Figure, l.sub.w is l.sub.max +l.sub.STG +.alpha., and therefore, the four blades BLD1, BLD2, BLD3 and BLD4 establish a regular square having a length l.sub.max of the sides by the overlapping of the adjacent edges, irrespective of the position of the alignment mark at the maximum exposure view angle. On the basis of the relationship between the exposure beam EXDB and the scribe line SLN shown in FIG. 11, the exposure beam is limited. Since the exposure beam is limited properly at the time of the maximum exposure view angle, the exposure beam can be also properly limited when the exposure view angle is a regular square or another rectangular shape having a length of side which is not more than l.sub.max. The size l.sub.EX .times.l.sub.EX of the fixed aperture FAP is only slightly larger than the maximum exposure view angle l.sub.max .times.l.sub.max, and therefore, almost all of the unnecessary exposure beam is blocked by the fixed aperture FAP, and the region corresponding to the change of the view angle is blocked by the blades BLD fixed on the alignment unit AAU, the area of the blade BLD being minimized. When the exposure beam source produces X-rays, the radiation incident on the exposure beam limiting means is not reflected but is absorbed, and therefore, it is converted to thermal energy. However, according to this embodiment, almost all of the unnecessary portion of the exposure beam is absorbed by the fixed aperture FAP, and only a minimum amount of an unnecessary portion of the exposure beam is absorbed by the blade BLD fixed on the alignment unit AAU. Therefore, the heat production attributable to absorption of the X-rays adjacent to the alignment unit AAU wherein the spatial positions of optical elements therein have to be maintained accurately, can be minimized. As described in the foregoing, according to this embodiment, the area of the blade moved and positioned integrally with the alignment unit for limiting the exposure beam is minimized in consideration of the moving region of the alignment unit and the view angle. Therefore, the space around the alignment unit is enlarged for accommodation of other parts, while maintaining the sufficient exposure beam limiting function. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.