Patent Number: 052992519
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS A structure of an embodiment according to the invention is show in FIG. 4 to FIG. 6. One of the different points as compared to the conventional apparatuses shown in FIG. 1 and FIG. 2 is that three moving bases are arranged in the same plane. These moving bases are the X position alignment system moving base 16a, the Y position alignment system moving base 16b and the .theta. position alignment system moving base 16c as shown in FIG. 4. Three optical alignment systems, which are X position optical alignment system 11a, Y position optical alignment system 11b and .theta. position optical alignment system 11c are installed on the three bases 16a, 16b and 16c respectively. Therefore, these three optical alignment systems 11a, 11b and 11c are also arranged in the same plane. Common parts such as optical parts can be used in these systems. Three half-mirrors 14a, 14b and 14c, and three reflective mirrors 15a, 15b and 15c, are included in the three optical alignment systems 11a, 11b, and 11c, respectively, as shown in FIG. 4. The distance h.sub.1 is defined as a length between the optical axis of the optical alignment system 11a and the X-ray mask 6. The distance h.sub.2 is defined as a length between the optical axis of the optical alignment system 11b and the X-ray mask 6. The distance h.sub.3 is defined as a length between the optical axis of the optical alignment system 11c and the X-ray mask 6. These three distances h.sub.1, h.sub.2 and h.sub.3 become equal to each other because of the arrangement of these three systems in the same plane. The distance h.sub.1 ', h.sub.2 ' and h.sub.3 ' are also defined as lengths between the object lenses 12a, 12b and 12c, and the prisms 13a, 13b and 13c respectively. When the distances h.sub.1 ', h.sub.2 ' and h.sub.3 ' are made the same, the focal length f.sub.1 (=h.sub.1 +h.sub.1 ') of the optical alignment system 11a, f.sub.2 (=h.sub.2 +h.sub.2 ') of the optical alignment system 11b, and f.sub.3 (=h.sub.3 +h.sub.3 ') of the optical alignment system 11c can be made the same value. Therefore, the widths of the alignment marks 6a, 6b and 6c become the same C1=C2=C3) and the alignment detecting accuracies in the optical alignment systems 11a, 11b and 11c are made even with each other. Three narrow portions 106a, 106b and 106c are shaped in front of the moving bases 16a, 16b and 16c respectively. In this embodiment, by cutting both sides of the base, the narrow front portion is rectangle-shaped (as shown in FIG. 4) and the maximum width "a" of the moving base is larger than the maximum width "b" of the narrow front portion as Shown in FIG. 5 and FIG. 6. The moving bases 16a, 16b and 16c can move individually on the same plane without interferences with each other because of the narrow front portions as described above. When the chip size of the X-ray mask 6 is d.times.d length and breadth, a method to search for the marks on the mask by use of the alignment system is described hereunder. In the case of d.gtoreq.b (d is already defined above and b is the width of the narrow front portion), the search for the marks starts from the center of the chip to the edge of the chip as shown in FIG. 5. In the case of d&lt;b, the search for the marks starts from the edge of the chip as shown in FIG. 6. When the bases move to search for the marks, an interlock mechanism is necessary to prevent the clashing of the moving bases against each other. A software control is generally used as the interlock mechanism. First a interlock map is made The map shows the lashing points of the three moving bases 16a, 16b and 16c each other. Next, the actual locations of the three bases are compared with the points on the map, and the moving bases are stopped before the bases clash against each other. Thus, the interference of the optical alignment system is prevented. However, the software control has some problems. When the software control or a hardware control system including the software is broken, the moving bases may clash against each other. Under the software control, the X-Y positions of the moving bases always must be observed by the computer. This is one of the causes for increases in cost. Another preferred embodiment which doesn't have the problems as described above is shown in FIG. 7 and FIG. 8. As shown in these Figures, X interference blocks 17a and 17b are attached at both sides of the notches in the moving base 16a. In a similar way, Y interference block 17c and .theta. interference block 17d are attached to moving bases 16b and 16c, respectively. The size of these blocks 17a, 17b, 17c and 17d is slightly larger the size of the narrow front portions of the moving bases 11a, 11b and 11c, respectively. The shape of these blocks is the same as the narrow front portions of the moving bases (shown as A--A', B--B and C--C'). When the moving bases 16a, 16b and 16c on which the alignment systems 11a, 11b and 11c are installed move, the interference blocks 17a, 17b and 17d clash against each other before the optical alignment systems clash against each other, that is to say, the interference blocks work as a mechanical interlock. Another mechanical interlock is shown in FIG. 9. In this case, interference block 17d' shaped as shown in FIG. 9 is attached on the moving base 16c. The block 17d' can rotated on a axis 18. When the interference block 17a clashes against the interference block 17d' at the P1 or P2 position of the block 17a and 17d', which depends on the movement of the moving base 16a and 16c, the rotatable block 17d' rotates and a sensor 19 detects the movement of the block 17d' and the bases 16a or 16c are stopped before the clashing between the moving base 16a and 16c occurs. Another preferred embodiment shown in FIG. 10 is described hereunder. A interference block 17d" is attached to the moving base 16b. The interference block 17d" can also rotate on a axis. An interference block 17b is attached on the other side of the moving base 16a. A sensor 20 for detecting the clashing of the blocks is installed on the block 17d". Moreover limit sensors (not shown) are installed on each moving base 16a, 16b and 16c. The moving base 16a has two limit sensor detecting in two directions individually. One direction is described as X1+-X1-, and the other is described as X2+-X2-. The moving base 16b has two limit sensors detecting in the directions as described in Y1+-Y1- and Y2+-Y2-. The moving base 16c also has two limit sensors detecting in the directions as described in .theta.1+-.theta.1- and .theta.2+-.theta.2-. The moving bases cannot continue to move when the limit sensor signal is received. However, the moving base can move in the direction required to switch off the limit sensor. The limit sensor restricts the area in which each moving base can move around by electric mechanisms. The movement of this system as described above is as follows. In FIG. 11, the input signals from the limit sensors or the sensors 19, 20 are described in the left line, on the other hand the output signals to stop the movements of the bases are described in the right line. For example, when a signal of the YL from the sensor 20 is put on, movement in the directions of Y1+, Y2+, X1+ and X2- is locked as shown in FIG. 11 and the clashing between the moving base 16a and 16b is prevented. The movement in the direction of X1+ is locked when at least an input signal X1+ or .theta.L (from the sensor 19) is put on. The present invention has been described with respect to specific embodiments. However, other embodiments based on the principles of the present invention should be obvious to those of ordinary skill in the art Such embodiments are intended to be covered by the claims.