1. Field of the Invention
The present invention relates to semiconductor device fabrication equipment. More particularly, the present invention relates to a method of cleaning the inside of a processing chamber of semiconductor device fabrication equipment.
2. Description of the Related Art
Semiconductor devices are constantly being improved in accordance with rapid developments in the fields of information processing and communications and along with the growing popularity of personal computers and the like. In particular, today's semiconductor devices must operate at high speeds, must store large amounts of information and yet must be compact. To this end, memory cells of semiconductor devices must be kept as small as possible and the devices must be highly integrated. However, the utmost accuracy is required in carrying out the individual processes required for fabricating compact and highly integrated semiconductor devices. That is, process margins in the fabricating of semiconductor devices become smaller as the devices become more highly integrated.
In general, a semiconductor device is made up of various geometrical circuit structures. These structures are fabricated by selectively and repeatedly performing several individual processes on a semiconductor wafer. These processes include: an ion implantation process of implanting 3B (for example, B) or 5B (for example, P or As) group impurity ions into the semiconductor wafer, a thin film deposition process of forming an insulating or conductive layer on the semiconductor wafer, an etching process of etching the layer formed by the thin film deposition process to thereby pattern the layer, a process of forming an interlayer insulating layer over the patterned layer, and a chemical mechanical polishing (CMP) process of polishing the wafer to remove steps formed as the result of forming the interlayer insulating layer on the patterned layer. The deposition and etching processes, in particular, are performed in processing chambers. The inside of such processing chambers must be periodically cleaned to remove particles and the like which may potentially contaminate the wafers.
Of the abovementioned individual processes, the etching process is one of the most frequently performed processes in semiconductor device fabrication. The etching process is carried out while a mask (a patterned film of photosensitive material) is disposed over the layer of material to be etched (target layer). The etching process removes a portion of the target layer that is exposed by the mask. Etching is largely divided into wet and dry etching processes. Wet etching uses a chemical solution as an etchant to remove a portion of the target layer, whereas dry etching uses plasma or an ion beam to remove a portion of the target layer.
However, wet etching is problematic in that the etchant can penetrate between the film of photosensitive material (the mask) and the underlying target layer. In this case, the pattern produced using wet etching does not have the desired profile. Accordingly, wet etching is used restrictively in the fabrication of semiconductor devices. On the other hand, films of photosensitive material remain relatively well adhered to underlying target layers in dry etching processes. Therefore, the patterns formed by dry etching have better (more desired) profiles. Accordingly, dry etching is used more widely than wet etching throughout the industry.
Reactive ion etching is one of the dry etching processes that use plasma. In a direct plasma etch process, an inactive gas (usually argon (Ar)) is injected into a processing chamber, the gas is excited to form a plasma, and the inactive gas ions of the plasma collide with the wafer. The etching thus occurs due to the physical impact of the ions with the target layer. In reactive ion etching, both an inactive gas and a reactive gas (a gas of the halogen group having very strong activity) are injected into the processing chamber. The inactive gas is used to generate the plasma. The reactive gas is adsorbed by the target layer as atoms, ions, radicals and the like. As a result, etching occurs due to the collisions between the inactive gas ions of the plasma and the target layer, and due to a chemical reaction between the atoms, ions, radicals and the target layer.
Although reactive ion etching has several advantages with respect to the forming of fine patterns, polymers comprising Si, F, Cl, Br, SiO2, C, Si—Br, Si—Cl and Si—F are generated inside the processing chamber as by-products of the chemical reaction effected by reactive ion etching. These polymers accumulate on surfaces inside the process chamber and may eventually flake off of as fine particles which float in the air inside the process chamber. Preventing foreign particles from contaminating a wafer, though, is necessary to attain high yields of quality semiconductor devices. In particular, particle control is critical in forming a gate or a trench (key features of a semiconductor device). Accordingly, polymers and residual gases are discharged from the processing chamber using vacuum equipment (turbo pump) after a gate or a trench has been formed. However, there is a limit to the degree to which polymers can be removed from a processing chamber using vacuum equipment.
Thus, a dedicated cleaning process is performed to remove the polymers from the processing chamber after the chamber has been exhausted using vacuum equipment. A conventional cleaning process entails blowing O2 into the process chamber. However, this method is only partly effective in removing polymer from the process chamber. Another conventional cleaning process involves using chemicals, such as H2SO4, for removing polymer adhering to inner surfaces of the process chamber. However, the use of chemicals, such as H2SO4, requires opening the process chamber which action can cause lumps of polymer to fall onto a wafer in the process chamber. Although fine particles of the polymer (dust) present in the air inside the process chamber are enough to significantly reduce the reliability and yield of semiconductor devices, lumps of the polymer, which are several hundreds times larger than the dust particles, can create a total process failure if they are allowed to fall onto the wafer.