Abstract
In the semiconductor manufacturing process, the stability of plasma processing influence greatly to yield rate, while the plasma density is the key parameters for plasma processing. Therefore, monitoring and maintaining the plasma, by adjusting procedure parameter to achieve its needed state, it the important step to the process. The density of the plasma discharge governs the basic characteristics of these plasma processes. In this study, microwave based diagnostics are developed for plasma density measurement or even process monitoring. In our previous work, we have demonstrated a microstrip line microwave interferometer for monitoring of plasma density in plasma tools. The resonant type probe under development is a spiral probe (SP). We design two structure. One structure is a shorted microstrip transmission line. The first resonance of this structure occurs at the frequency where the transmission line becoming a half wavelength resonant structure. Another structure is an opened microstrip transmission line, which is quarter wavelength resonant structure. The spiral probe is designed for mounting on a chamber wall to minimize perturbation to the plasma discharges. The probe is designed by employing three dimensional electromagnetic numerical simulation analysis (HFSS, ANSYS Corp) where the plasma is treated as a dielectric with dielectric functions determined by plasma density, microwave frequency and collision frequency of electrons. We make the probe by silver. When the probe measure the resonant frequency usually use more expensive network analyzer like Agilent. In this study, measure the resonant frequency by Vector Reflectometer which is lower cost. Then we will compare different network analyzer. Make sure the consistency of experiment result and simulation result. Furthermore, the resonators were improved in four different structure in the simulation. The first is to increase the dielectric layer, and the peak may be cavity modes by verification. The second is U-shaped resonator. It can get larger reflection by reducing the length of antenna. It can’t observe the peak at plasma density 5x1010 cm-3. It is presumed that the operating frequency may be lower than the plasma frequency, and recommend that the length of the U-shaped resonator be shortened. The third is to increase the gap between the antenna and the spiral. It can get larger reflection by increasing the gap. The fourth is to narrow the antenna of spiral microstrip-line microwave resonant probe. It will measure the noise signal in the experiment. It may be the power radiate out, and reflect with metal chamber wall. The simulation results show that the radiation efficiency value is 97 %. In order to improve the radiation efficiency, we try to reduce the size of antenna. Use 1 mm radius of the antenna to replace the original antenna. It can be observe that the thickness of the antenna will affect the radiation efficiency at the same length.