Experimental Investigation On Spatial Non-uniformity Of RF Capacitive Coupled Plasma

In the ultra-large scale integrated circuit production process, RF capacitive coupled plasma is used in film growth, wafer etching, and surface modification, etc. The structure of capacitive coupled plasma source is simple,it is easy to form a large-size plasma. Using the RF capacitive coupled plasma in the etcing process, an anisotropic etching can be achieved, therefore, RF capacitive coupled plasma has attracted much more interest. Capacitive coupled plasma is more suited for large area deposition and etching of the substrate, while in deposition and etching of a large area films,uniformity of the plasma have certain requirements.As the RF frequency increases, the discharge mode transition spatially from E mode to H mode occurs, and standing wave effect, telegraph effect, skin effect and other phenomena will cause a non-uniformity in the plasma. The standing-wave effect leads to non-uniform plasma excitation in high frequencies capacitive discharge when the reactor size is not considerably smaller than the excitation wavelength. When the transverse magnetic field is high, the skin effect will occur. An asymmetry of the upper and lower electrode will lead to telegraph effect. These effects will lead to non-uniformity of non-uniform capacitive coupled plasma, such as the standing wave effect could lead to enhanced plasma density in cavity center, telegraph effect and skin effect will result in the strong plasma density around electrodes. For the investigation of spatial non-uniformity of RF capacitive coupled plasma, a capacitive coupled plasma source is formed with the discharge chamber diameter of 300mm, the low electrode diameter of 200mm, the upper electrode is connected with the metallic cavity, that is, electrodes are not symmetrical. RF Plasma excitation power used mainly by the signal generator, RF signal directly transmit to the RF matching through the RF power amplifiers, power output of matching is connected with power electrode. Frequencies of13.56MHz, 19MHz, and 41MHz3 was used, respectively. High-resolution plasma emission spectroscopy system (OES) was used to determine radial distribution of 750.4nm spectral lines of radio-frequency capacitive coupled Ar plasma, it indirectly denote radial distribution of the Ar plasma electron density, and relationship between radial distribution and radio frequency, air pressure, chamber structure and the RF power. The results show that the spatial distribution of Plasma emission intensity has a strong dependence on the pressure, frequency and structure of discharge chamber. Edge effects (such as the telegraph effect, skin effect, etc.) make the plasma emission spectrum a strong spectral intensity near the edge of the electrode, that allow in-homogeneity within the range of 200mm plasma circumstances stronger than 100mm; Standing wave effect causes enhancement of spectral intensity at center of reactor; In addition, transmission of radio frequency waves in the dielectric plate makes plasma more non-uniform as the top plate covered with dielectric plate than that without coverage. When top electrode is covered with the dielectric plate, the skin depth increases, which makes the electrode edge of the peak width increased.Electrostatic probe (Langmuir probe) was used to measure electron density, ion density and ion flux. The results show that high frequency lead to high electron density and ion density in the discharge center. In the case of high pressure, there is obvious peak near electrode edge, and the width of the peaks is affected by dielectric plate. Test results are in agreement with the results from the emission spectrometry measurement.