A view panel for a raised floor system is described which is constructed by an outer rigid frame, an upper plate of a tempered glass panel and a lower plate of an apertured steel panel for providing structural support of the view panel. The invention further describes a raised floor system that utilizes such view panels installed in floor panels in a semiconductor fabrication environment.

FIELD OF THE INVENTION 
     The present invention generally relates to a raised floor system for use in a semiconductor fabrication facility and more particularly, relates to a raised floor system that utilizes transparent view panels constructed by a tempered glass panel supported by an apertured steel panel to allow observation of utility gauges mounted under the raised floor system. 
     BACKGROUND OF THE INVENTION 
     In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 μm range, a cleanliness class of 100˜1000 (i.e., the number of particles at sizes larger than 0.5 μm per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 μm, a cleanliness class of 0.1 is required. It has been recognized that an inert mini-environment may be the solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness mini-environment that is constantly flushed with ultra-pure nitrogen that contains no oxygen and moisture. 
     Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16 M and 64 M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new mini-environment concept which is shown in FIG.  1 . Within the enclosure of the mini-environment of a process tool  10 , an extremely high cleanliness class of 0.1 (i.e., the number of particles at sizes larger than 0.1 μm per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area  12 . In order to maintain the high cleanliness class inside the process tool  10 , the loading and unloading sections  14  of the process tool must be handled automatically by an input/output device such as a SMIF (standard mechanical interfaces) apparatus. 
     FIG. 1 also shows a raised floor system  30 . The raised floor system  30  is normally installed between 45 and 60 cm above the finished concrete waffle slab  32 . The raised floor system  30  in general, covers the entire clean room production area. The grid  34  of the raised floor is based on a 60×60 cm system and is normally aligned with the center lines of the filter ceiling grid. Some of the floor tiles  36  are perforated for circulating the clean room air  38 . The adjustment of the air pressure in the clean room and the balancing of air flow can be achieved by selecting floor tiles with proper perforations. 
     In the raised floor system  30  shown in FIG. 1, the floor tiles  36  should be static-dissipative and made of non-combustible material that is also chemical abrasion resistance. A frequently used material is vinyl which is impact resistant and meets the electrostatic discharge isolation resistance requirement for the clean room environment. 
     A detailed, cross-sectional view of a raised floor system  30  is shown in FIG.  2 . The raised floor system  30  should be laterally stable in all directions with or without the presence of the floor tiles  36 . This is achieved by anchoring the pedestals  40  into the concrete slab floor  32  and by the further use of stringers  42  and steel braces  44 . The floor tiles are supported by the stringers  42  which are in turn supported at each corner by adjustable height pedestals  40 . As shown in FIG. 2, the pedestals  40  are bolted to the finished concrete waffle slab  32 . An insulation plate  46  placed on top of each pedestal  40  attenuates foot step sound and ensures electrical isolation. The steel braces  44  are used to further increase the rigidity of the raised floor system  30  and the pedestal support. 
     In recent years, for safety considerations such as for minimizing the risk from earthquake vibration in a highly stacked fab plant, screws or bolts are required at each corner of the raised floor panels  36 . This makes it impossible to easily remove the floor panels by just using suction cups and lifting the panels. The structural reinforcement on the raised floor design therefore presents great difficulties in accessing utility panels that are frequently mounted under the raised floor. In order to access the utility panels, the screws or bolts at the corners of the floor panels must first be removed before a suction device can be used to lift up the floor panels. Furthermore, since the floor panels are normally fabricated of a vinyl plastic material that is opaque, the display on the utility panels, i.e., various gauges and dials, cannot be read or accessed without first removing the floor panels. 
     It is therefore an object of the present invention to provide a raised floor system for a semiconductor clean room facility that does not have the drawbacks or shortcomings of the conventional raised floor systems. 
     It is another object of the present invention to provide a raised floor system for a semiconductor clean room facility wherein the floor panels can be easily removed for accessing the utility panels. 
     It is a further object of the present invention to provide a raised floor system for a semiconductor clean room facility wherein the floor panels are not screwed into the stringers underneath. 
     It is another further object of the present invention to provide a raised floor system for a semiconductor clean room facility that is equipped with transparent panels supported by apertured steel panels. 
     It is still another object of the present invention to provide a raised floor system for a semiconductor clean room facility that is equipped with transparent panels such that the utility panels mounted thereunder can be observed. 
     It is yet another object of the present invention to provide a raised floor system for a semiconductor clean room facility that is equipped with removable floor panels each equipped with four view panels. 
     It is still another further object of the present invention to provide a raised floor system for a semiconductor clean room facility that is equipped with transparent tempered glass panels that are coated with a shatter-proof coating. 
     It is yet another further object of the present invention to provide a raised floor system for a semiconductor clean room facility that is equipped with transparent tempered glass panels mounted in a floor panel that are anti-electrostatic, highly rigid and scratch resistant. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a raised floor system for a semiconductor clean room facility can be provided which includes a first multiplicity of pedestals mounted to a floor at a lower end of the pedestals, a second multiplicity of stringers mounted to a top end of the first multiplicity of pedestals such that the stringers are parallel to the concrete floor, a third multiplicity of floor panels mounted to the second multiplicity of stringers, each of the floor panels includes at least one cavity therein adapted for receiving at least one view panel that is substantially transparent and is supported by at least one apertured steel panel in the third multiplicity of floor panels. 
     The raised floor system for a semiconductor clean room facility may further include a fourth multiplicity of braces for supporting the first multiplicity of pedestals. The at least one cavity in each of the third multiplicity of floor panels may further include a ridge portion along at least two sides in a rectangular shape cavity for supporting a view panel. The at least one cavity in each of the third multiplicity of floor panels may further include a ridge portion along four sides in a rectangular shaped cavity for supporting a view panel. The at least one cavity in each of the third multiplicity of floor panels may have a rectangular shape, or a square shape. 
     In the raised floor system for a semiconductor clean room facility, the at least one view panel may be formed of a transparent tempered glass panel supported by at least one apertured steel panel. The tempered glass panel may be coated on the backside with a shatter-proof coating. The at least one view panel may include four view panels of equal size. The at least one apertured steel panel may be fabricated of stainless steel. The at least one tempered glass panel may have a thickness of not less than 7 mm, or a thickness between about 7 mm and about 15 mm. The at least one apertured steel panel may have a thickness of at least 3 mm, or a thickness between about 3 mm and about 10 mm. The word “about” used in this writing indicates a range of value that is ±10% of the average value given. 
     The raised floor system for a clean room of a semiconductor fabrication facility may further include a plurality of utility panels mounted under the third multiplicity of floor panels which are visually inspectable through the at least one view panel. The at least one view panel has a top surface substantially flush with a top surface of the third multiplicity of floor panels when mounted in the third multiplicity of floor panels. The at least one view panel may further include two apertures therethrough adapted for opening the view panel by human fingers. The at least one panel insert may be fabricated of a material that is anti-electrostatic and abrasion resistant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description and the appended drawings in which: 
     FIG. 1 is an illustration showing a conventional clean room set up on a raised floor system. 
     FIG. 2 is an enlarged, cross-sectional view of a conventional raised floor system incorporating braces and stringers. 
     FIG. 3 is a plane view of the back side of a present invention floor panel showing four cavities for the view panel. 
     FIG. 4 is a plane view of the front side of a present invention floor panel showing ridges for holding the view panels in the cavities. 
     FIGS. 5A and 5B are a plane view and a perspective view, respectively, of an aluminum frame for the present invention view panel. 
     FIGS. 6A and 6B are a plane view and a perspective view of a tempered glass panel for the present invention view panel. 
     FIGS. 7A and 7B are a plane view and a perspective view, respectively, of a rubber gasket for the present invention view panel. 
     FIGS. 8A and 8B are a plane view and a perspective view, respectively, of an apertured steel panel for the present invention view panel. 
     FIGS. 9A and 9B are a plane view and a perspective view, respectively, of the components of the view panel positioned together. 
     FIGS. 10A and 10B are a plane view and a perspective view, respectively, of the view panels assembled into a floor panel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention discloses a view panel and a raised floor system for a semiconductor clean room facility that is equipped with removable floor panels each provided with at least one view panel. The transparent view panels enable the inspection of utility panels installed under the floor panels and the easy removal of the floor panels for accessing the various controls and gauges on the utility panels when necessary. The present invention raised floor system can be utilized in any factory environment that utilizes space under a raised floor for transporting gases or liquids used in the factory and for positioning of utility panels equipped with various control apparatus. However, the present invention raised floor system is particularly suited for use in a semiconductor clean room facility where most fluids are transported and their passages are controlled by control apparatus installed under the raised floor. The floor panels utilized in the present invention raised floor system may also be screwed or bolted to stringers that are supported by pedestals and braces. 
     Each of the floor panels may be provided with a plurality of cavities equipped with a ridge portion along an inner periphery of the cavities adapted for receiving view panels. The view panels may be fabricated by tempered glass panels supported by apertured steel panels. The tempered glass panels have high rigidity, high abrasion resistance, superior chemical resistance and good anti-electrostatic properties. When utility panels are positioned under the transparent view panels, the gauges and the dials on the utility panels can be easily inspected through the view panels. When adjustment to the dials becomes necessary, the view panels can be easily picked up by fingers through apertures provided in the view panels. The ridges provided in the cavities are positioned such that when the view panels are laid inside the cavities, the top surface of the tempered glass panels are flush with the top surfaces of the floor panels. There are no protrusions above the surface of the floor panels and thus no hindrance for walking or rolling of carts on the floor panels. 
     Referring initially to FIG. 3, wherein a present invention floor panel  50  provided with a plurality of cavities  56  is shown. In the specific configuration shown in FIG. 3, four equally sized square cavities are utilized. It should be noted that any other suitable numbers of cavities in any suitable shapes, i.e., square or rectangular, may be utilized in the present invention novel floor panels. As shown in FIG. 3, the back side  52  is shown with a multiplicity of rib structures  54  reinforcing the floor panel. The floor panel  50  is normally constructed of a light weight, high strength metal such as aluminum. Any other high strength material including those of reinforced plastics may also be used. 
     FIG. 4 illustrates a top view of the present invention floor panel  50 . A ridge portion  58  is formed inside the cavities  56  along the inner peripheral edge of the cavities. The ridge portion  58  is used for supporting the view panels (not shown) installed therein. The ridge portion  58  should be designed such that it protrudes sufficiently outwardly from the inner periphery of the cavity to support the view panels when installed therein. The ridge portion  58  should further be designed with a depth measured from the top surface  62  of the floor panel  50  such that when the view panels(not shown) are positioned therein, the top surface of the view panels are flush with the top surface  62  of the floor panel  50 . Mounting holes  64  for screws or bolts may also be provided at the four corners of the floor panel  50  for mounting to the stringers. 
     FIGS. 5A and 5B illustrate a plane view and a perspective view, respectively, of a rigid frame  66  utilized in the present invention view panel  100  shown in FIG.  9 A. The rigid frame  66  may be suitably fabricated of aluminum, or of any material that has a rigidity of at least that of aluminum. The rigid frame  66  may have a “L” shaped cross-section such that the other components of the view panels, i.e., the glass panel  68 , the rubber gasket  70  and the apertured steel panel  72  can be fitted therein by frictional engagement. 
     The glass panel  68  utilized in the present invention view panels  100  is shown in a plane view in FIG. 6A, and in a perspective view in FIG.  6 B. The glass panel  68  should be fabricated of tempered glass that has significantly improved impact strength. The glass panel  68  may further be coated on a backside, i.e., the side that faces downwardly, a shatter-proof coating such that even when the glass panel  68  is broken, the broken pieces are held together for safety. 
     To absorb the impact of an operator walking on the tempered glass panel  68 , or the rolling of a cart, it may be desirable to install a gasket  70  in between the glass panel  68  and the apertured steel panel  72  during the assembly of the components of the view panel  100 . The gasket  70  can be fabricated of any suitable rubber material that can absorb impact and thus reduce the likelihood of breakage or cracking of the tempered glass panel  68 . 
     FIGS. 8A and 8B are a plane view and a perspective view, respectively, of an apertured steel panel  72  for used in the present invention view panel  100  for the support of the latter. While the tempered glass panel  68  may be provided in a thickness of at least 7 mm, and preferably in a thickness between about 7 mm and about 15 mm the apertured steel panel, preferably fabricated of stainless steel, should have a thickness smaller than the tempered glass panel  68 , i.e., of about 3 mm, or in a range between about 3 mm and about 10 mm. In a preferred embodiment, the glass panel has a thickness of about 10 mm, while the apertured steel panel has a thickness of about 5 mm. The apertured steel panel  72  is further provided with at least one aperture  74 , and preferably, four apertures as shown in FIGS. 8A and 8B, for easy observation of the utility panels mounted under the raised floor system. The diameter of the aperture  74  should be at least 2 cm and preferably at least 4 cm. 
     A plane view and a perspective view of the various components of the view panel  100  are shown in FIGS. 9A and 9B. It should be noted that the optional rubber gasket  70  is not shown in these figures. The components  66 ,  68  and  72  may be assembled together by frictional engagement, or by any other suitable mechanical means, i.e., clips (not shown) installed on the rigid frame  66 . 
     Each of the view panels  100  is then installed into the present invention floor panel  110 , shown in FIGS. 10A and 10B. The frame  112  on the floor panel  110  is constructed similarly to that shown in FIG. 4, i.e., with a ridge portion similar to the ridge portion  58  of FIG. 4 for use as a stop for the view panels  100  in an installed position. The view panels  100  are each installed in the frame  112  by at least one hinge means  114 . 
     In the preferred embodiment shown in FIG. 10A, two hinges  114  are used for installing each view panel  100  such that the view panel  100  can be pivotally opened, as shown in FIG.  10 B. Also shown in FIG. 10A, apertures  116  are provided in the view panels  100  for accessing the latter by either a finger or a screw driver to open the view panel  100 . 
     The present invention view panel  100  that is constructed by a tempered glass panel  68  and an apertured steel panel  72  in a rigid frame  66  has therefore been amply described in the above descriptions and in the appended drawings of FIGS.  3 ˜ 10 B. 
     While the present invention has been described in an illustrative manner, it should be understood that the terminology used is intended to be in a nature of words of description rather than of limitation. 
     Furthermore, while the present invention has been described in terms of a preferred embodiment, it is to be appreciated that those skilled in the art will readily apply these teachings to other possible variations of the inventions. 
     The embodiment of the invention in which an exclusive property or privilege is claimed are defined as follows.