Temperature and density measurements of miniature microwave plasma discharges

Abstract

Summary form only given. The microwave plasma source used in this investigation has a microstripline coupling structure with the discharge created inside 1 mm and 2 mm inner diameter quartz tubes. The microwave energy couples to the discharge via the stripline. The stripline has a characteristic impedance of 50 ohms and is connected to a 2.45 GHz microwave power supply operating at 1 Watt to 100 Watts. The discharge tube is orientated perpendicular to the stripline conductor. Two discharge tube placement designs were investigated: one with the tube placed between the microstripline and the ground plane and the other with the tube placed across a gap in the microstripline. Measurements of the gas temperature and electron temperature were performed with pressures ranging from 1 Torr to 1 atmosphere. Gas temperature analysis was performed using optical emission spectroscopy (OES) on various mixtures of argon and nitrogen feed gases. The strongest band of the second positive system of nitrogen was chosen to measure the temperature of the discharge. The investigation indicates that as the percentage of nitrogen gas increases in the argon-nitrogen discharges, the gas temperature decreases. Also, the increase of pressure increases the gas temperature. The plasma densities were also investigated using OES. The Stark broadening of hydrogen /spl beta/ and /spl delta/ lines were measured to determine the discharge densities. Typical results for hydrogen plasma density are 10/sup 13/ cm/sup -3/-10/sup 14/ cm/sup -3/ at pressures of 1-100 Torr. Langmuir probes with 100 micron diameter and 1 mm length were used to obtain the electron temperature and electron density. For argon discharges in 2 mm tube with 1 Torr pressure, the electron temperature and the electron density were measured around 1.4 eV and 10/sup 13/ cm/sup -3/, respectively.