Modified Principal Component Analysis for Real-Time Endpoint Detection of SiO_2 Etching Using Plasma Impedance Monitoring

摘要

Plasma etching is used in microelectronic processing for patterning of micro- and nano-scale devices.[1] In plasma etcher, generated reactive ions and radicals react with a wafer surface, resulting in the removal of selected target materials for patterning. But materials which are not selected can be etched too much after the target material is fully removed. Severe over-etching can damage the underlying layer, which can decrease yield. Therefore, it is essential to detect the endpoint of etching to avoid excessive over-etching. This is known as endpoint detection (EPD).[2] Commonly, optical emission spectroscopy is widely used for real-time endpoint detection for plasma etching. However, if the viewport for optical-emission monitoring becomes blurred by polymer film due to prolonged use of the etching system, optical-emission monitoring becomes impossible. Hence, polymer film on the viewport has to be removed regularly. In addition, when the exposed area ratio on the wafer is small, changes in the optical emission are so slight that it is almost impossible to detect the endpoint of etching. For this reason, as a simple method of detecting variations in plasma without contamination of the reaction chamber at low cost, a method of measuring plasma impedance is being examined.[3] The object in this research is to investigate the suitability of using plasma impedance monitoring (PIM) with statistical approach for real-time endpoint detection of SiO_2 etching.