Gaseous atmosphere control apparatus for a semiconductor manufacturing system
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a gaseous atmosphere control apparatus for use in a semiconductor manufacturing system and more particularly for use in a semiconductor heat-treatment process. 
     (2) Description of the Prior Art 
     It is a well known matter that semiconductor wafers are heat-treated in the semiconductor manufacturing process. A conventional gaseous atmosphere control apparatus, therefore, is provided with a gas distribution pipe having a blow-off hole through which heat-treating gas is supplied. It is, however, a great disadvantage of the conventional apparatus that the gaseous atmosphere cannot be kept uniform during heat-treating process and the semiconductor wafers cannot be exposed to the uniform gaseous atmosphere. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of this invention to provide a gaseous atmosphere control apparatus, wherein gaseous atmosphere is kept uniform. 
     It is another object of this invention to provide a gaseous atmosphere control apparatus, wherein a gas distribution pipe having a plurality of blow-off holes of different diameters is provided. 
     It is a further object of this invention to provide a gaseous atmosphere control apparatus, wherein a gas distribution pipe is so provided as to guide the transfer of semiconductor wafers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic view illustrating a gaseous atmosphere control apparatus, in a preferred embodiment, according to the present invention; 
     FIG. 2 is an enlarged sectional view taken along line II -- II of FIG. 1; and 
     FIG. 3 is a perspective view illustrating the gas distribution pipe used in the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is described in detail hereinunder with reference to FIGS. 1 through 3. Referring first to FIG. 1 which illustrates a gaseous atmosphere control apparatus for heat-treating, particularly heat-diffusing, semiconductor wafers, reference nemeral 1 designates a reaction pipe, 2 a boat on which wafers 3 are loaded, 4 a gas distribution pipe having blow-off holes 4a, 4b and 4c and fixed to the inside wall of the reaction pipe 1 and 5 clean benches which includes, as known well in the art, devices for automatically transferring the boats 2 through the reaction pipe 1 in such a direction as shown with the arrow A. The clean benches 5 cut off the communication between the inner atmosphere of the reaction pipe 1 and the outer atmosphere. 
     The structure of the reaction pipe 1, the boat 2, the wafer 3 and the gas distribution pipe 4 is shown in FIG. 2. The reaction pipe 1 is formed into a cylindrical pipe and the distribution pipe 4 is so welded to the inside wall of the reaction pipe 1 as to extend longitudinally, in parallel with the central axis of the reaction pipe 1. The boat 2 is so formed as that the cross section thereof becomes the numerical character &#34;3&#34;. The boat 2 is further provided with holes 2a and slits 2b by which the semiconductor wafer 3 is supported. The boat 2 loaded with the wafers 3 is slidably positioned in the reaction pipe 1 so that the longitudinal movement thereof is guided by the gas distribution pipe 4 and the holes 2a thereof communicates with the blow-off holes 4a of the gas distribution pipe 4. 
     The gas distribution pipe 4 has an open end 4&#39; which is connectable to a gas supply source (not shown) and a closed end 4&#34; as shown in FIG. 3. The blow-off holes 4a through 4c are provided between the end portions 4&#39; and 4&#34; in such a manner that hole diameter becomes wider as the blow-off hole becomes farther from the open end portion 4&#39;. 
     Operation of the above-described gaseous atmosphere control apparatus is described hereinunder. Each boat 2 is sequentially pushed into the reaction pipe 1 from the left side clean bench 5 and the boat 2, contacting with the adjacent boats 2 and guided by the gas distribution pipe 4, is moved toward the right side clean bench 5 through the reaction pipe 1. As the boat 2 slides through the reaction pipe 1 longitudinally contacting with the gas distribution pipe 4 and the inside cylindrical wall of the reaction pipe 1, the lateral movement of the boat 2 rarely occurs to result in that semiconductor wafers 3 loaded on the boat 2 are transferred smoothly through the reaction pipe 1. 
     During the transfer of the wafer 3, the heat-treating gas (oxygen gas for example) is supplied to the gas distribution pipe 4 and blowed off through the blow-off holes 4a, 4b, and 4c. The gas amount blowed off through each hole can be made almost equal, because the holes 4a, 4b and 4c are widened as they become distant from the gas supply source. The gas, then, passes through the holes 2a of the boat 2 and occupies the inner space of the reaction pipe 1 to form the uniform gaseous atmosphere therein. The semiconductor wafers 3, therefore, are exposed to the uniform gas to be heat-diffused, while the boat is transferred through the reaction pipe 1. Thus assuring the uniform gaseous atmosphere in the reaction pipe 1, the oxide film of uniform thickness can be formed on the surface of the semiconductor wafer 3. 
     The oxide film of 7,600 A thickness could be formed on the wafer 3 according to the experiment, wherein the gas distribution pipe 4 is specified as follows: 
     material: glass 
     length: 2,000 mm 
     inner diameter: 8 mm 
     outer diameter: 10 mm 
     diameter of the blow-off hole 4a: 1 mm 
     diameter of the blow-off hole 4b: 3 mm 
     diameter of the blow-off hole 4c: 5 mm 
     longitudinal distance between blow-off holes: 150 mm heat-treating gas: oxygen 
     gas supply amount: 3,000 cc per minute. 
     Although the above embodiment is described with reference to the heat-diffusion treatment in the semiconductor manufacturing process, the gaseous atmosphere control apparatus is also applicable to the deposit-treatment, wherein nitrogen gas is blowed off from the gas distribution pipe 4. Whatever the heat-treatment method may be, the gas blow-off amount from the respective blow-off holes is nearly equal to each other to result in the formation of the uniform gaseous atmosphere which is advantageous in heat-treating the semiconductor wafers.