Fig. 3. Typical semiconductor processing flow. CONCEPT OF SPACE SEMICONDUCTOR PROCESSING FACTORY Figure 3 shows a typical VLSI processing flow diagram. In this figure, a silicon wafer directly crystallized from molten is surface treated, then oxidation or deposition is performed. A photoresist such as PMMA is coated and pattern transfer or direct writing using E-beam, ion beam or X-ray lithography equipment is made. Then, the etching process, using RF plasma, engraves silicon dioxide. The photoresist is next removed by a plasma apparatus; sometimes selective impurity doping follows. The process from deposition to lithography is repeated more than 10 times in usual VLSI fabrication. A wafer is scribed next and each tip is put on a plate and bonded. A packaging robot encapsulates the chip. It is not known whether all process including packaging is best done in space. We propose basic considerations and research directions of a space semiconductor processing factory (SSPF) to realize our idea mentioned above (4). BASIC CONSIDERATIONS FOR PROCESSING FACTORY Sun-synchronous orbit is selected for a LEO (low Earth orbit) space factory. There are two candidates for continuous manufacturing. The one is low sun- synchronous orbit, the other is geosynchronous one. For the latter, inaccessibility by the space shuttle to the factory is a problem. In addition, half of the shuttle payload capability will be lost. Therefore, we select a low Earth-sun synchronous orbit. The processing factory will be sun illuminated about 98% of the time. If we want 100% sun illumination, orbital altitude between 1389 and 3334 km will be appropriate. However, this orbital range is not protected from radiation damage. An early factory is shown in Fig. 4. A cylindrical processing container which is delivered to orbit by a shuttle is docked with a berthing adapter on a space platform (5). The necessary processing equipment is installed on top of the cylinder and gas container and raw material are showed inside the cylinder. A dexterous manipulator loads and unloads wafers to or from each equipment. A waste retainer is also contained in the cylinder.
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