Study On Radial Nonuniformity Of N₂ Capacitively Coupled Plasma

In the modern semiconductor industry, cold plasma is commonly used in thin film etching, deposition and surface modification. The capacitive coupled plasma has a simple structure in comparison with the inductively coupled plasma, and it's easy to generate large area plasma, so it is widely used in the semiconductor industry. The capacitively coupled plasma(CCP) source is an important tool for etching profile of thin gate oxide with high fidelity due to an independent control of ion flux and energy. Additionally, capacitively coupled plasma can also be used in film deposition with high rate due to its high density driven by higher frequency than conventional 13.56MHz.In this paper, the nonuniformity of N₂ capacitively coupled plasma driven by radio frequency (RF) of 40.68MHz is investigated by using scanning optical emission and Langmuir double probe measurements. The nonuniformity of electron temperature and electron density of CCP is studied by using Langmuir double probe measurements along the radial direction. By fitting the emission spectrum of N2 second positive system (C³∏_u^-B³∏_g) theoretically from 380.4nm to 367.1nm and comparing the calculated and the measured spectrum in N₂ capacitively coupled plasma driven by RF of 40.68MHz, uniformity of gas ro-vibrational temperature information along the radial direction in the plasma is also investigated. It is found that standing wave effect causes a central peak over the powered electrode surface for the emission profile, while a peak near the radial edge is caused by inductive field. These lead to optical emission nonuniformity more than 20% at high pressure and input power. However, ro-vibrational temperature of N₂ capacitive discharge shows nonuniformity less than 10%, which is thought to be caused by dominant collision of metastable particles in between with large radiation relaxation time and high density.