1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus. More specifically, the present invention relates to a substrate processing method and a substrate processing apparatus for processing objects, such as semiconductor wafers or LCD substrates, with a processing liquid and cleaning the objects with a cleaning liquid.
2. Description of the Related Art
Generally, a semiconductor wafer processing apparatus has prevalently been used in fabricating semiconductor devices to remove particles, organic substances, metallic contaminants and/or an oxide film from objects, such as semiconductor wafers, (hereinafter referred to as xe2x80x9cwafersxe2x80x9d) by sequentially conveying the wafers through processing tanks containing processing liquids (chemical liquids) and cleaning tanks containing cleaning liquids (rinsing liquids) to immerse the wafers in the processing liquids and the cleaning liquids and to dry the wafers.
A wafer processing apparatus of this kind comprises processing tanks respectively containing processing liquids (chemical liquids), such as HF+H2O (a hydrogen fluoride solution (hereinafter referred to as xe2x80x9cHFxe2x80x9d)), NH4OH+H2O2+H2O (an ammonia peroxide solution) and HCl+H2O2+H2O (a hydrochloric acid peroxide solution), cleaning tanks respectively containing cleaning liquids, such as rinsing liquids (pure water), wafer holders, such as wafer boats, for holding a plurality of wafers, for example, fifty wafers, in a vertical attitude, and lifting devices for immersing the wafer boat holding wafers in, and taking out the same from the processing tanks and the cleaning tanks.
The processing tanks, the cleaning tanks and the wafer boats are placed in a downflow atmosphere in which a clean gas, for example, clean air flows down to handle the wafers or the like in a clean atmosphere.
Generally, the wafers or the like made of silicon are provided on their surfaces with an oxide film serving as an insulating film, and a predetermined pattern or the like. When a silicon wafer provided on its surface with an oxide film is processed with a processing liquid, the processing liquid remains on the surface of the silicon wafer because the oxide film is hydrophilic while silicon is hydrophobic. Experiments were conducted to verify this fact. In the experiments, a wafer boat B holding coated silicon wafers Wa coated with an oxide film and bare silicon wafers Wb as shown in FIG. 18A was immersed in a processing liquid, such as HF, contained in a processing tank for processing, and then the wafer boat was taken out of the processing liquid. At this stage, the processing liquid (HF) remained on the surfaces of the coated silicon wafers Wa as shown in FIG. 18B. When the coated silicon wafers Wa and the bear silicon wafers Wb were immersed in a processing liquid or a cleaning liquid for the subsequent process, particles P contained in the processing liquid (HF) remaining on the coated silicon wafers Wa adhered to the surfaces of the coated silicon wafers Wa and therefrom to the surfaces of the adjacent bare silicon wafers Wb as shown in FIG. 18B. As is obvious from the results of the experiments, particles adhere to the surfaces of wafers when silicon wafers coated with an oxide film are processed with a processing liquid and cleaned with a cleaning liquid, and those particles reduces the yield of products.
When etching oxide films formed on the surfaces of wafers W with a processing liquid, such as HF, the wafers W are immersed in the processing liquid (HF) contained in a processing tank, the wafers W are taken out of the processing tank, and the wafers W are carried to a cleaning tank. While the wafers W are thus being carried to the cleaning tank, the processing liquid (HF) remaining on the wafers W flows downward along the surfaces of the wafers W held in a vertical attitude and, consequently, the oxide films coating the wafers W are exposed partly as shown in FIGS. 19A and 19B. Since the etching of the exposed parts of the oxide films is stopped, while the etching of the coated parts of the oxide films continues, the oxide films cannot uniformly be etched, which reduces the yield of products.
Accordingly, it is an object of the present invention to prevent the reattachment of particles to wafers or substrates by removing dust contained in a processing liquid remaining on the surfaces of the substrates after the substrates have been processed with the processing liquid by recleaning the substrates when processing the substrates by immersing the same in the processing liquid and cleaning the substrates by immersing the same in a cleaning liquid, in order that the yield of products can be improved.
Another object of the present invention is to prevent the downward flow of a processing liquid remaining on substrates along the surfaces of the substrates after the substrates have been processed with the processing liquid in order that etching uniformity and the yield of products can be improved.
With the foregoing object in view, according to an aspect of the present invention, a substrate processing method, which processes substrates by immersing the substrates held in a vertical attitude in a processing liquid and a cleaning liquid, is characterized in cleaning lower parts of the substrates at at least one of the time when the substrates are immersed in one of the processing liquid and the cleaning liquid contained in a tank and the time when the substrates have been exposed to one of the processing liquid and the cleaning liquid contained in the tank. The term xe2x80x9csubjected to one of the processing liquid and the cleaning liquidxe2x80x9d refers to either an act of pulling out the substrates from the processing liquid or the cleaning liquid contained in the tank or an act of draining the processing liquid or the cleaning liquid from the tank. Immersing the substrates in the processing liquid or the cleaning liquid signifies either an act of immersing the substrates in the processing liquid or the cleaning liquid contained in the tank or an act of wetting the substrates with the processing liquid or the cleaning liquid.
In the substrate processing method of the present invention, the lower parts of the substrates can be cleaned by ejecting a cleaning liquid on the lower parts of the substrates or by immersing the lower parts of the substrates in a cleaning liquid contained in a tank for a predetermined time. The lower parts of the substrates may be immersed in and kept stationary in the cleaning liquid. When thus immersing the lower parts of the substrates in the cleaning liquid, it is preferable that the cleaning liquid is supplied to the tank so that the cleaning liquid overflows the tank.
The substrates are supposed to be made of a hydrophobic material to have surfaces coated with hydrophilic films. Hydrophilic substrates are, for example, bare silicon substrates and metal substrates. Hydrophilic films are, for example, oxide films or insulating films.
According to another aspect of the present invention, a substrate processing method, which brings substrates held in a vertical attitude into a processing liquid and a cleaning liquid to process the substrates, processes the substrates in an atmosphere in which a clean gas flows down, and reduces or stops the flow of the clean gas when carrying the substrates processed by the processing liquid to the next processing unit for processing the substrates with another processing liquid or the cleaning liquid.
According to a further aspect of the present invention, a substrate processing method, which brings substrates held in a vertical attitude into a processing liquid and a cleaning liquid to process the substrates, blows a clean gas upward from below the substrates against the substrates when carrying the substrates processed with the processing liquid to the next processing unit for processing the substrates with another processing liquid or the cleaning liquid. The clean gas may be, for example, clean air or clean nitrogen gas.
According to a still further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank containing a processing liquid in which substrates are to be immersed, a cleaning tank containing a cleaning liquid in which the substrates are to be immersed, substrate holding means for holding the substrates in a vertical attitude, lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tanks or the cleaning tanks, in which liquid ejecting means for ejecting a processing liquid or a cleaning liquid toward lower parts of the substrates is disposed above the processing tanks or above the cleaning tanks.
According to another aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank containing a processing liquid in which substrates are to be immersed, a cleaning tank containing a cleaning liquid in which the substrates are to be immersed, substrate holding means for holding the substrates in a vertical attitude, lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tanks or the cleaning tank, in which a control means controls the lifting means so that the lifting means is stopped when lowering the substrate holding means holding the substrates to immerse the substrates in the cleaning liquid contained in the cleaning tank at a position where lower parts of the substrates are immersed in the cleaning liquid.
According to a further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank in which substrates are brought into contact with a processing liquid, a cleaning tank in which the substrates are brought into contact with a cleaning liquid, substrate holding means for holding the substrates in a vertical attitude, and lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tank or the cleaning tanks, in which the processing tanks are disposed in a downflow atmosphere in which a clean gas flows down, and a control means stops or reduces the downflow of the clean gas creating the atmosphere. Preferably, the control means stops or reduces the flow of the clean gas when the substrates are carried from the processing tank to another processing tank or the cleaning tank.
According to a still further aspect of the present invention, a substrate processing apparatus, which carries out a substrate processing method of the present invention, comprises a processing tank in which substrates are brought into contact with a processing liquid, a cleaning tank in which the substrates are brought into contact with a cleaning liquid, substrate holding means for holding the substrates in a vertical attitude, and lifting means for vertically moving the substrate holding means holding the substrates relative to the processing tank or the cleaning tank, in which a clean gas ejecting means ejects a clean gas upward from below the substrates when the substrates processed with the processing liquid are carried to another processing tank or the cleaning tank. The lifting means may include a carrying means for carrying the substrates between the processing tank and the cleaning tank. The substrate processing apparatus may further comprise, besides the lifting means, a carrying means for carrying the substrates between the processing tank and the cleaning tank. Although the cleaning tank may be of any type provided that the same are able to contain cleaning liquids, it is preferable that the cleaning tanks are overflow tanks that allow the overflow of the cleaning liquids.
In the present invention, the lower part of the substrate is a part having a region extending between the lower edge of the substrate and a region near a circuit region in which semiconductor devices are built.
The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in connection with the accompanying drawings.