Field of the Invention
The present invention relates to a plating apparatus for plating a surface of a substrate, such as a semiconductor wafer, and more particularly to a plating apparatus for forming a metal film in fine interconnect trenches, plugs, or resist openings provided on a surface of a substrate, such as a semiconductor wafer, or for forming bumps (extruding electrodes), which electrically interconnect a semiconductor chip and a substrate, on a surface of a semiconductor wafer.
Description of the Related Art
It is a common practice in TAB (tape automated bonding) or flip chip to form protruding connection electrodes (i.e., bumps) of gold, copper, solder or nickel, or of multiple layers of such metals at predetermined portions (electrodes) of a surface of a semiconductor chip having interconnects formed therein so that the semiconductor chip can be electrically coupled via the bumps to substrate electrodes or TAB electrodes. There are various methods usable for forming the bumps, such as electroplating, vapor deposition, printing, and ball bumping. In recent years, electroplating, which can form fine bumps and can be performed in a relatively stable manner, has been widely used, as the number of I/O in a semiconductor chip increases and the electrode pitch becomes smaller.
The electroplating method can be classified roughly into a jet method (or a cup method) and a dip method. According to the jet method, a substrate, such as a semiconductor wafer, is held in a horizontal position with a surface, to be plated, facing downward, and a plating solution is jetted upward onto the surface to be plated. According to the dip method, a substrate is held in a vertical position in a plating bath and a plating solution is injected upward into the plating bath, while the plating solution overflows the plating bath during plating. Electroplating using the dip method has advantages of a small footprint and good release of bubbles which could adversely affect a quality of plating. Moreover, the electroplating using the dip method can be easily applied to a variety of wafer sizes. Therefore, the dip method is considered suitable for bump plating in which plating is performed on relatively large-sized holes and which requires a considerably long plating time.
The applicant has proposed a plating apparatus which uses the dip method with relatively good release of bubbles and which, in order to enable automatic formation of a metal film suited for protruding electrodes such as bumps, includes a substrate holder for holding a substrate in a vertical position, a plurality of processing baths for immersing the substrate, held by the substrate holder, in a processing liquid to process the substrate, and a vertically movable transporter (substrate holder transport device) for gripping the substrate holder holding the substrate, transporting the substrate holder in a horizontal direction, and immersing the substrate holder, holding the substrate, in a processing liquid in any one of the processing baths (see Japanese Patent No. 3,979,847 and Japanese Patent Laid-Open Publication No. 2012-107311).
The applicant has further proposed a plating apparatus which includes a substrate holder for holding a substrate in a vertical position, a plating unit having a plating bath for immersing the substrate, held by the substrate holder, in a plating solution to process the substrate, a substrate transport device for transporting the substrate and transferring the substrate to the substrate holder, and a vertically moving mechanism for lowering the substrate holder, holding the substrate, and immersing it in the plating solution (see Japanese Patent Laid-Open Publication No. 2004-76072).
Further, a cleaning apparatus has been proposed which includes a workpiece carrier for holding a plurality of workpieces in a vertical position, a plurality of processing baths for holding a processing liquid in which the workpieces, held by the workpiece carrier, are to be immersed for processing of the workpieces, and a workpiece transport means. The workpiece transport means includes a lateral workpiece transport mechanism for transporting the workpiece carrier, holding the workpieces, in a lateral direction, and a workpiece lifting mechanism for receiving the workpieces from the lateral workpiece transport mechanism, and lowering the workpieces and immersing them in a processing liquid in any one of the processing baths (see Japanese Patent Laid-Open Publication No. 7-299427).
In the apparatus disclosed in Japanese Patent No. 3,979,847 and Japanese Patent Laid-Open Publication No. 2012-107311, the transporter grips the substrate holder holding a substrate, moves the substrate holder horizontally to a position just above a processing bath, and lowers the substrate holder and immerses it in a processing liquid in the processing bath. After the completion of processing of the substrate, the substrate holder is raised and drawn out of the processing liquid. Thus, the transporter must stay in the position above the processing bath when raising and lowering the substrate holder, thus resulting in an increased takt time and a decreased throughput.
The takt time also increases, for example, (1) when the types of processing baths increase with an increase in the types of plating solutions as in the case of multi-layer plating, and therefore a substrate holder holding a substrate is raised/lowered by a transporter an increased number of times, or (2) when the speed of raising/lowering of a substrate holder by means of a transporter is decreased, in particular, when a substrate holder holding a substrate is lowered and immersed in a processing liquid at a slower speed in order to prevent splashing of the processing liquid or when a substrate holder holding a processed substrate is raised and drawn out of a processing liquid at a slower speed in order to better drain the processing liquid from the substrate holder.
It may be necessary in such cases to install a plurality of transporters. However, if a plurality of transporters are installed, it is necessary to avoid contact between the transporters. In addition, it takes a lot of time to transfer a substrate holder between transporters.
In particular, two transporters, depending on their sizes, may interfere with each other when they move to two adjacent processing baths and may not be capable of simultaneously raising/lowering substrate holders in the two adjacent processing baths. In order to transfer a substrate holder directly between the transporters, these transporters necessary have a complicated structure. When transferring a substrate holder between conventional transporters, one transporter should place a substrate holder on a processing bath or on a receiver once, and another transporter should grip the substrate holder on the processing bath or the receiver.
As described above, a conventional transporter moves a substrate holder horizontally above processing baths, and lowers and raises the substrate holder in each of the processing baths. The horizontal movement and lowering/raising of the substrate holder require a considerable amount of time. Therefore, an increase in the frequency of transport of the substrate holder by the transporter(s), due to an increase in the number of processing baths or the number of process steps, may cause an increase in the takt time and a decrease in the throughput.