This invention relates to a wafer transfer hand to be used for handling wafers in a semiconductor producing apparatus which is operated in, for instance, a clean room or a vacuum chamber.
A conventional construction of the wafer transfer hand is illustrated in FIGS. 6(a) and 6(b) of the attached drawings. In the shown construction, a hand 20 made of aluminum and operable for transferring a wafer 1 is formed into an arcuate configuration conforming to the circumference of the wafer 1. The hand 20 has a groove 30 adapted to receive a peripheral portion of the wafer 1 which is to be transferred by the nand 20 when it is operated. More specifically, the conventional hand 20 does not seize the wafer 1 firmly, but it simply picks up the wafer 1, while the wafer is loosely received in the groove 30, so that the direct contact of the hand 20 with the principal surface of the wafer 1 can be avoided as far as possible.
The above described construction of the conventional wafer transfer hand, however, is found to be disadvantageous in the following points:
(1) The aluminum made hand 20 tends to create vibration and noise when it supports a hard wafer, and attenuation of the vibration is not sufficient.
(2) Since a marginal gap is required between the wafer 1 and the internal surface of the groove 30, such a gap tends to cause an additional inclination of the wafer 1 according to the disposition of the groove 30. FIGS. 7(a) through 7(c) illustrate such arrangements. In the drawing, it is assumed that d represents the thickness of the wafer 1, l represents the width of the hand 20, and l' represents the width of the groove 30. As a consequence, the gap is expressed by l'-d, and in a case where the disposition of the groove 30 is vertical, the wafe 1 is inclined to an arbitrary side of the groove 30. FIGS. 7(a) and 7(b) illustrate leftward and rightward dispositions. In a case where the groove 30 is beforehand tilted rightwardly as shown in FIG. 7(c), owing to a gravitational force W, the wafer 1 is further tilted rightwardly. That is, the degree of inclination L of the wafer 1 becomes larger than l. Accordingly, an end of the wafer 1 projects over the width l of the hand 20 supporting the wafer 1, thereby exhibiting a difficulty in a case where the wafer 1 is transferred through a narrow passage. Furthermore, any deviation in the inclination of the wafer tends to invite mishandling of the wafer during the transferring operation, thus making it difficult to obtain a constant locus during the wafer transferring operation.
(3) In a case where a marginal error exists in the arc 1a defining the periphery of the wafer 1, or where the center line 1c of the wafer 1 does not coincide with the center line 20c of the hand 20 as shown in FIG. 8(a), a forward edge 20a of the hand 20 is brought into abutment in the direction of an arrow mark U of FIG. 8(b) against the wafer 1 which is provided at a separated position from the center line 20c, thereby rotating the wafer 1 around the center as indicated by an arrow mark R in FIG. 8(b). The rotation of the wafer 1, varies the orientation of the wafer 1 and causes disadvantages in the subsequent processes.