1. Field of the Invention
This invention relates generally to acid baths, and more particularly to high temperature acid baths as used for etching semiconductors and the like.
2. Description of the Prior Art
During the manufacture of integrated circuits and like semiconductor devices, it is generally necessary to place in a bath of a hot acid a usually rectangular rack known as a boat, holding one or more disks, called slices or wafers, of semiconductor material, usually pure silicon, on which a large number of integrated circuits have been formed by a known process using a material referred to as a "photoresist" in order to etch, or wash, away unwanted material on the disks. The disks subsequently are scored and broken into individual integrated circuit chips.
The container of the hot acid, which container is generally referred to as a beaker, is disposed over a sink or other drain, so to as much as possible prevent the acid, which is extremely toxic and highly volatile, from escaping the area of the bath. For this reason, it is imperative that a good seal be obtained between a peripheral portion of the open-top acid beaker and a structure supporting the beaker. Otherwise, acid and its fumes will collect beneath the beaker resulting in corrosive and possibly explosive conditions.
Although for safety reasons the acid bath usually is placed over some sort of drain, as opposed to what might be referred to as "free standing", this alone generally is not sufficient to remove the spilled acid and vapors rapidly enough. A principal difficulty arises in creating the aforementioned seal between an acid beaker or vessel and its support structure due to the fact that the vessel, which is generally constructed from either quartz or a borosilicate glass, is an open-topped device of rectangular configuration. While the rim area of round beakers constructed from quartz or glass can easily be molded into a configuration permitting a good seal with an associated support structure, it has been found to be very difficult to achieve a suitable seal with a rectangular beaker configuration. Round beaker, however, are not desirable for use in the semiconductor processing industries because such beakers waste much of the volume of the bath since the rectangular racks, or boats, will fit in only a small portion of the horizontal section of the beaker.
One prior art approach to achieving such a seal provided a horizontal flange on the upper rim of a vessel so as to be supported by a shelf forming part of the associated support structure. Inserted between the flange and the shelf was a room-temperature vulcanizing (RTV) elastomer for effecting the desired seal between the elements. A principal drawback encountered with this construction was that it permitted acid to collect immediately adjacent the seal, with the result that the acid eventually worked its way through the elastomer and permitted leakage by the seal, creating corrosive and possibly explosive conditions.