1. Field of the Invention
The present invention relates to equipment for processing substrates, such as semiconductor substrates. More particularly, the present invention relates to apparatus for catching byproducts of a deposition or etching process, or the like.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by repeatedly performing a variety of processes on a substrate. These processes include a deposition process for forming a film on the substrate, a selective etching process for etching the film, and a diffusion process for doping a region on the substrate with specific atoms. Each of these processes must be performed in a certain specific process environment, namely at a high temperature and at a pressure that is lower than atmospheric pressure. Therefore, the processes are each carried out in a process chamber. In addition, the deposition and etching processes are typically carried out by introducing process gas into the process chamber and applying an RF power to the process gas. As a result, the process gas undergoes a chemical reaction in which the gas is transformed into plasma. The plasma is used to form a film on the substrate or etch a film that has already been formed on the substrate.
In addition, the plasma process produces byproducts such as portions of the process gas that fail to react. Although the byproducts are usually maintained in a gaseous state while under the low pressure and high temperature prevailing in the process chamber, the byproducts can solidify and thereby form a powder under higher pressures or lower temperatures.
A vacuum pump, such as that used to create the low pressure in the process chamber, exhausts the gaseous byproducts from the process chamber through an exhaust line after the deposition or etching process has been completed. However, the vacuum pump and a valve disposed in the exhaust line are in communication with the environment outside the process chamber while the byproducts are being exhausted through the exhaust line. Hence, the byproducts will begin to solidify. The solidified byproducts have a strong adhesive characteristic. Accordingly, the byproducts adhere in large quantities on the blades of the vacuum pump and on the valve disposed in the exhaust line.
That is, the environment under which the byproducts are exhausted differs from that prevailing in the process chamber at the time the byproducts are generated, i.e., the pressure is higher and the temperature is lower at the valve and vacuum pump of the exhaust system than in the process chamber. Therefore, the byproducts tend to solidify to a much greater extent in the exhaust system than in the process chamber, and the solidified byproducts become more adhesive in the exhaust system than in the process chamber. Accordingly, a large amount of the byproducts accumulate in the exhaust system.
As the solidified byproducts accumulate within the exhaust line or the vacuum pump, the cross-sectional area of the exhaust line is reduced and the force that can be exerted by the vacuum pump on the gaseous byproducts is also reduced. Ultimately, the exhaust force is decreased significantly, causing many problems such as a decrease in the quality of the products processed in the process chamber, a reduction in the useful life of the vacuum pump, and a decrease in the productivity of the process due to a need to frequently clean the exhaust system.
One apparatus that has been proposed to obviate these problems is shown in FIG. 1. The apparatus includes a separate cooling trap 1 provided in the exhaust line 3 extending from the process chamber, and a cooling pipe 2 extending through the cooling trap 1.
The byproducts passing through the inside of the cooling trap 1 are cooled by a refrigerant passing through the cooling pipe 2 so as to be solidified. Consequently, the solidified byproducts adhere to the inner circumferential surface of the cooling trap 1 or to the outer surface of the cooling pipe 2 in the cooling trap 1. Thus, the quantity of byproducts passing to the vacuum pump 4 is minimized.
However, most of the byproducts caught by the cooling trap 1 are those that adhere to the cooling pipe 2 where the temperature is lowest. The cooling pipe 2 has a relatively small surface area in the cooling trap 1 and thus, only a small amount of the byproducts are actually caught by the cooling trap 1. That is, a large amount of the byproducts still flow to the vacuum pump 4. Accordingly, the above-described problems, e.g., a decrease in the effectiveness and useful life of the vacuum pump 4, still persist.