1. Field of the Invention
The present invention relates to a transportation method and its system, and more particularly to a wafer cassette transportation method and its system.
2. Description of Related Art
With reference to FIG. 1 for a conventional wafer cassette (or wafer carrier) transportation method, a transportation system includes a central monitoring system, a plurality of transportation systems (OHT Systems: Overhead Transportation Systems), and an automatic warehouse system (Stocker), wherein different transportation systems are respectively installed in a factory at positions of different heights and electrically connected with the central monitoring system. The stocker generally comprises a goods receiving unit, a storage shelf, a forklift, a conveyor belt, and a goods exiting unit. The wafer cassette sequentially goes through the aforementioned goods receiving unit, storage shelf, forklift, conveyor belt, and goods exiting unit before it is transferred to another transportation system.
Since the wafer cassette has to go through the aforementioned complicated procedure in the stocker before it is transferred from one transportation system to another transportation system, the stocker creates many limitations and act as a bottleneck for operators act upon so as to improve the overall transportation speed of the transportation system to a desired level, and the volume of the stocker is very large, which occupies a considerable area of a factory, and its manufacturing cost is very high, and thus it creates burdens to manufacturers.
In view of the foregoing shortcomings of the prior art, the inventor of the present invention based on years of experience conducted extensive researches and experiments, and finally invented a wafer cassette transportation method and developed a wafer cassette transportation system to overcome the shortcoming of the prior art.