Generally, an inductively coupled plasma (hereinafter, referred to as “ICP”) is widely used in semiconductor processing, micro electro mechanical system (MEMS) fabrication, for functional and tribological coatings, and the like.
Since the ICP provides higher plasma density even at a relatively low processing pressure of ˜1 mTorr as compared to capacitively coupled plasma (CCP), it possesses higher process throughput and better surface treatment conformity. In addition, the ICP features lower mean electron energy (temperature) and plasma potential, thus making better process control and lower contamination. However, capacitive coupling (CC) between RF antenna and plasma in ICP is an issue to be overcome in applications like dry etching, for example. A Faraday shield (FS) is used to damp the CC in a conventional ICP apparatus. An ICP apparatus having a function of controlling the value of such capacitive coupling has been proposed by S. A. Nikiforov.
ICP sources can be divided into the following two groups depending on whether an RF antenna is immersed in the plasma (called, “internal antenna ICP”) or is placed outside of the plasma process chamber (called, “exterior antenna ICP”). The latter type is mostly used in semiconductor processing. One of the reasons is lack of the Faraday shield for the former.
State-of-the-art plasma processing devices of this ICP apparatus is concentrated on the semiconductor industry for processing a planar silicon (Si) wafer. Thus, researches are in active progress on shape and structure of the ICP antenna, change in plasma behavior according to the electrical mutual relationship between the antenna and the substrate for the sake of improvement of plasma uniformity on the planar silicon wafer, process control and lower contamination-based process execution, etc.
However, the exterior antenna ICP has limited scalability in association with its application to a large area owing to the following drawbacks:
First, an increase in the area of a vacuum window (generally, quartz is mainly used) requires an accompanying increase in window thickness to maintain structural integrity. Hence, the separation between the antenna and plasma also leads to lower RF power transfer efficiency.
Second, a thick vacuum dielectric window is expensive.
Third, a larger area or volume workpiece implies an increase in size of the window area and the RF antenna, thereby resulting in an increase in its inductance. The latter leads to an increase in required RF voltage, and hence, the capacitive coupling between antenna and plasma which in turn leads to contamination due to the window sputtering. Besides, an increase of antenna inductance requires a corresponding decrease of the RF matching capacitance. The latter should be larger than the system stray capacitance to provide a matching control.
Fourth, the overall length of a helical or spiral antenna widely used to obtain a high-efficiency and high-density plasma increases due to the large-scaling of the process chamber or the substrate. Consequently, non-uniformity of sources deteriorate spatial uniformity of the coupling between antenna and plasma. In case of application of 13.56 MHz RF power to the antenna, a problem of the standing wave effect and the like is caused by a half wavelength antenna source.
Fifth, it is difficult to provide uniform plasma across a large area for a planar workpiece and through a large volume for a three-dimensional (3-D) workpiece.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgment or any form of suggestion that this information forms the prior art that is already known to a person skilled in that art.