Semiconductor wafers such as silicon wafers which require a high degree of cleanliness are subjected to a variety of washing processes. For example, to describe a general immersion washing method, fine particles and organic material are removed by washing using ammonium hydroxide and aqueous hydrogen peroxide, the washing solution is removed by rinsing with pure water, contamination by metallic impurities incorporated in the natural oxide film generated during washing are removed by an acid or an alkali washing process, and the washing solution is removed by rinsing with pure water, whereupon the wafers are dried by centrifugal drying.
In any washing method, such as chemical washing, water washing, or the like, a carrier 1, as shown in the sole FIGURE for holding the semiconductor wafers 2 during washing provided with a plurality of slits 3 allowing the washing solution to contact all parts of the wafers is used, such that a plurality of semiconductor wafers can be processed simultaneously, and this holding carrier can also be used in this state during centrifugal drying. Conventionally, such carriers used in a washing process have been made from PFA (tetrafluoroethylene perfluoroalkylvinyl ether copolymer). Specifically, since PFA has excellent thermal resistance and chemical resistance, there is no change in the properties of the PFA carrier due to rise in temperature in the washing solution or infiltration of chemical solution during the washing process, and there is no liquation of impurities, and therefore carriers made from PFA are generally used at present.
However, PFA carriers of this kind are relatively soft and have a tensile elongation rate of 300% (test method: ASTM D638). In the drying method in the final washing stage for the semiconductor wafers, generally, a spin dryer is used. This spin dryer drying method expels water by centrifugal separation at approximately 1,000 rpm.
When the wafers and carrier are dried by this drying method, during rotation the wafers rise up due to centrifugal force and strongly contact the resin in the holding groove sections of the carrier. Since the PFA resin is relatively soft, as described previously, resin adheres to the wafers at the portions in contact with the wafers.
This resin that adheres to the wafers may cause particle contamination during preliminary washing before device processing, or diffusion of impurities into the wafers during heat treatment. For example, this preliminary washing may involve washing by etching to remove natural oxide films, and the drying method may involve drying by evaporation. In this case, if PFA resin adhering to the wafer is peeled off by the chemical solutions and floats about during drying by evaporation, whereupon it adheres once again to the wafer surface, then irregular growth will occur in the areas where the resin adheres when heat treatment is performed.
Furthermore, semiconductor wafers which have completed the mirror polishing and washing processes may be transported a long distance before entering device processing, and carriers comprising a resin-made holding frame provided with a plurality of U-shaped grooves for holding a plurality of wafers independently in an upright position are accommodated in a transporting vessel, and a resin-made wafer 4 as shown in the sole FIGURE press is used to prevent the wafers moving inside the grooves due to vibrations. However, during this transportation stage, the wafers rub against the resin due to vibrations, and the like, and resin from the carrier and the wafer press may adhere to the wafers.
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USPTO Backgrounds