Measurement Of Ion Parameters In An ECR Plasma

Electron cyclotron resonance (ECR) plasma is widely used in microelectronics etching, materials processing and low temperature surface technology due to producing high-density plasma at lower pressure. The plasma parameters, especially ion parameters, play a crucial impact on film quality, etching rate and etc. So the measurement of plasma parameters is the key to the application of ECR plasma. In ECR plasma, the measurement of electron parameters had been extensively carried out, but there are few measurements about ion parameters.In this paper, an automatic measurement system for ion parameters is established to measure the ion parameters in a self-designed microwave ECR plasma device. Major works are as follows:1. An automatic system including ion sensitive probes (ISP) and double probes has been constructed for measuring ion parameters. The ion and electron parameters can be measured simultaneously.2. In the higher and lower pressure mode, firstly, the impact factors of the ISP have been researched and the plasma potential has been measured. Secondly, it is analyzed that the variation mechanism of I-V characteristic curves in negative voltage zone. In addition, ion density (ni) measured by the ISP is certificated by electron density (ne) measured by the double probe. Finally, the effect of plasma parameters on the optimum height (hc) has been analyzed. Results show that:(1) At a suitable shielding distance h, the distance between the top surface of ion collector electrode and the upper end of the guard electrode, ion saturation current can be accurately measured because electrons can be shielded effectively and ions can be collected as many as possible. Too large value of h will shield the lower-energy ions and results in a larger ion temperature of measurements than that of its reality. A very small negative bias V_B, between the collector and the shield, can effectively inhibit the E×B drift motion of the electron in vicinity of probe to guarantee the accurate of measurement. But too large value of V_B will elevate ion temperature and saturation current.(2) ISP can measure plasma potential stably. The plasma potential is independent on the V_B. But it could be affected by value of the h, because the sheath potential surface would decline with the increasing of h, especially in the plasma region with more steep radial distribution of potential.(3) The I-V characteristic curve in negative voltage zone depends on the effective area of ion collection, the surface area of the sheath of ISP mouth. With h increasing, the ion current in negative voltage zone changes from monotonously increase to the first decrease and then increase. It is more evident in the zone of lower plasma potential.(4)Ion density measured by the ISP is in good agreement with electron density which measured by the double probe. It is consistent with the electro-neutrality of plasma.(5)The hc which range is 10 r_ge≤h_c≤10r_ge +8λD depends on the electron cyclotron radiusrge and Debye radius (λD).3. In ECR plasma, the effect of working pressure, microwave power and magnetic field configuration on the ion parameters has been studied. Results show that:(1)With the increase of the working pressure, the ion temperature decreases monotonically, the ion density firstly increases and then decreases; with the increase of the microwave power from 400W to 800W, the ion temperature increases slowly, while the ion density increases firstly and then trend to saturation.(2) The influence of pressure on spatial distribution of ion density is obvious. The ion density at lower pressure has better uniformity than that of higher pressure.(3) The nearer the resonance surface the position is, the higher the ion temperature. In a divergence magnetic field, the ion density reduces along the axial and radial and has good radial uniformity where is away from the resonance region. The position with minimum magnetic field in a mirror magnetic field has the highest density. The ion temperature and ion density in mirror magnetic field is higher than that in divergence magnetic field.