1. Field of the Invention
The present invention relates to a wafer bonding device for bonding two substrates together and, in particular, to a wafer bonding device suitable for use in bonding two silicon substrates together in a semiconductor manufacturing process.
2. Description of the Related Art
FIGS. 6A through 6F are process diagrams illustrating a process for preparing an SOI (silicon on insulator) substrate using a wafer bonding technique of this type.
In the preparation of this SOI substrate, first, as shown in FIG. 6A, patterning is performed on a first silicon substrate 30 by photolithography, etching or the like, and, on the uneven surface thereby formed, an insulating layer 31 consisting of SiO.sub.2 is formed. Further, a polysilicon layer 32 is formed on this insulating layer 31.
Next, as shown in FIG. 6B, the surface of the polysilicon layer 32 is flattened by grinding, and then, as shown in FIG. 6C, using the polysilicon layer 32 as the joint layer, a second silicon substrate 33 is bonded.
Subsequently, as shown in FIG. 6D, the peripheral edge portion of the substrate is chamfered, and then, as shown in FIG. 6E, the surface of the first silicon layer 30 is ground. In this process, a portion 34 of the first silicon substrate 30 is left on the protruding surfaces of the insulating layer 31.
Finally, as shown in FIG. 6F, selective grinding is performed until the insulating layer 31 is exposed, whereby there is obtained a so-called element-separated device structure, in which silicon portions 34 exist in the recesses of the insulating layer 31.
Conventionally, when bonding the first and second silicon substrates 30 and 33 to each other, a wafer bonding device as shown in FIG. 7 has been used.
In this conventional device shown in FIG. 7, a suction member 51 is engaged with and secured to a support member 50 serving as the base, and grooves 52 are formed concentrically in the upper surface of the suction member 51, thereby forming a chuck surface 53. When bonding the substrates together, the first silicon substrate 30 is placed on the chuck surface 53, and evacuation is effected as indicated by the arrow in the drawing, whereby the first silicon substrate 30 is attracted to the chuck surface 53 by vacuum suction, and, in this condition, the second silicon substrate 33 is bonded.
However, the above-described conventional wafer bonding device involves the following problem when, for example, an airborne particle 54 falls and, as shown in FIG. 8, adheres to a chuck surface (protruding surface) 53.
That is, when vacuum suction is effected with the silicon substrate 30 having been placed on the chuck surface 53, the silicon substrate 30 is partially pushed up due to the presence of the particle 54, whereby the silicon substrate 30 undergoes deformation, such as swell. As a result, the flatness of the substrate 30 markedly deteriorates, and, when bonded to the other silicon substrate 33, the substrate 30 entails the generation of voids 55 in the vicinity of the deformed portion or pattern expansion on the substrate, resulting in a deterioration in yield in the bonding process.