1. Field of the Invention
The present invention relates to an apparatus and method for washing a substrate, in which a substrate such as a semiconductor wafer or an LCD substrate is washed by scrubbing.
2. Discussion of the Background
In a process of manufacturing a semiconductor device such as an LSI, a surface of a wafer on which a circuit pattern is formed is required to maintain a strictly high cleanliness, making it necessary to wash the wafer surface frequently both before and after various process steps. Particularly, in a photolithography process, it is absolutely necessary to apply a washing treatment to a wafer surface.
A scrubber disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 57-102024 or Japanese Patent Disclosure No. 62-259447 is used in the photolithography process for scrubbing the wafer surface for the washing purpose. In the scrubber disclosed in these prior art, a washing liquid is supplied onto a surface of a wafer revolved on its own axis. Also, a washing member such as a brush or sponge, which is kept rotated, is brought into contact with the revolving wafer surface so as to remove the foreign matter attached to the wafer surface.
FIGS. 1 and 2 collectively show a conventional front face washing section 101. As shown in the drawings, the front face washing section 101 comprises a holder 103 having a washing liquid supply hole 102 formed in a central portion, and 6 washing members 104 held by the holder 103. The washing section 101 is supported by a support mechanism (not shown) so as to be rotatable on its own axis and movable in a vertical direction. The washing member 104 consists of a columnar sponge having a tip portion cut to form a flat surface. A washing liquid such as pure water is supplied through the washing liquid supply hole 102 into each of the washing members 104 while the washing section 101 is kept revolved on its own axis. Under this condition, the tip portions of the washing members 104 are pressed against a front face, i.e., circuit pattern-forming face, of a wafer which is kept revolved on its own axis, so as to cleanse the wafer front face.
FIGS. 3 and 4 collectively show a conventional rear face washing section 111. As shown in the drawings, the washing section 111 comprises a holder 112 having a washing liquid supply hole 115 formed in a central portion and a plurality of washing members 113, 114. The washing section 111 is supported by a supporting mechanism (not shown) so as to be rotatable on its own axis and movable in a vertical direction. The washing members consist of 8 brushes 113 and 4 sponges 114. These brushes 113 and sponges 114 are used in combination in the conventional rear face washing section 111 partly because the rear face of the wafer tends to be stained more severely than the front face and partly because the rear face can be scrubbed more strongly than the front face. Each of these brushes 113 and sponges 114 has its tip portion cut to form a flat surface which is brought into contact with the wafer surface. A washing liquid such as pure water is supplied through the washing liquid supply hole 115 onto each of the washing members 113, 114, while revolving the washing section 111 on its own axis. Under this condition, the washing members 113, 114 are pressed against a rear face (back face opposite to the circuit pattern-forming face), of the wafer W which is kept revolved on its own axis so as to cleanse the rear face of the wafer W.
In the conventional scrubbers 101, 111 shown in FIGS. 1 to 4, only a slight inclination of the supporting arm (not shown) causes the tip portions (wafer-contact portions) of the sponges 104, 114 to fail to be brought into contact uniformly with the wafer faces. In other words, peripheral portions alone of the sponges 104, 114 are strongly pressed against the wafer faces. Since the contact pressure between the sponges 104, 114 and the wafer face is locally concentrated, the entire wafer face cannot be washed uniformly. In addition, stains are attached to and remain on the peripheral portions alone of the sponges 104, 114. It follows that, if these sponges 104, 114 are used repeatedly, a serious problem is brought about that the wafer faces are stained.