Toshiaki Makabe

Influence of Ar Metastable on the Discharge Structure in Ar and N2 Mixture in RF Discharges at 13.56 MHz.

The influence of Ar metastable atoms on the discharge structure in rf glow discharges is investigated in Ar and N2 mixed gas experimentally and theoretically. The purpose of adding a small amount of N2 is to control the metastable density. Time- and space-resolved optical emission spectroscopy is applied to investigate the behavior of high-energy electrons. The density profile of Ar metastables in Ar and N2 mixture is estimated from the optical emission intensity of the second positive band of N2, which results from the energy transfer from Ar metastables to N2 molecules. The decreases of current and optical emission intensity, as well as the Ar metastable density with increase of N2 ratio, are observed. It is concluded that ionization through metastables is one of the important processes in increasing the plasma density, especially at higher pressures.

Modeling of deep Si etching in two-frequency capacitively coupled plasma in SF6/O2

We developed the simulation model of deep Si etching for MEMS fabrication. This model includes the physical effect of ions under the presence of plasma molding, chemical etching by radicals, and the formation of a passivation layer on the wafer. The simulation was carried out in SF6/O2 in two-frequency capacitively coupled plasma using an extended vertically integrated computer aided design for device processing (VicAddress). We estimated the local characteristics of plasma structures (such as potential distribution, ion velocity distribution) near an artificial microscale hole pattern on the wafer. In this case, the sheath thickness is comparable to or even smaller than the size of the hole. Thus, the sheath tends to wrap around the hole on the wafer. The distorted sheath field directly affects the incident flux and velocity distributions of ions. The angular distribution of ions at the edge of the hole is strongly distorted from the normal incidence. The ion flux becomes radially nonuniform in the vicinity of the hole pattern. That is, the etching profile is distorted particularly at the bottom corner because of the removal of the passivation layer by energetic ion under the presence of plasma molding.