Production of Large-Diameter-Low Electron Temperature ECR Plasma

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A 300 mm diameter plasma source is required from industry as a next generation semiconductor processing plasma source which operates at few mTorr. An electron cyclotron resonance plasma has paid much attention because it provides a high density plasma at low pressure. However, usually it is hard to produce a large diameter plasma with ECR, that is, the uniformity of ECR plasma strongly depends on magnetic field gradient, pressure, microwave powers and so on. Now a 200 mm diameter ECR plasma is mainly used. Furthermore, charging effect also becomes an important problem to solve. Thus, a large diameter-low electron temperature plasma is needed for plasma processing. Here, in order to realize a 300 mm diameter ECR plasma, we carried out the experiments on a large diameter-low electron temperature ECR plasma production using TM_<01> mode of 900 MHz as well as TE_<10> mode of 2.45 GHz,. The main results are as follows :(1) The upper hybrid wave resonance played an important role in ECR plasma uniformity. A uniform plasma of 300 mm in diameter was realized by controlling the microwave power, where the electron density was higher than 10^<11>cm^<-3>.(2) We succeeded in producing a low electron temperature plasma using the magnetic mirror. N_2 plasma with Te<2 eV was realized at the sloat using the magnetic mirror. Furthermore, the physical mechanism for low electron temperature production was discussed using the power and particle balance equations.(3) A powerful method to measure the negative ion density was proposed using the probe.(4) We succeeded in measuring the ion temperature in the ECR plasma with the optical emission spectroscopy, providing Ti<0.2 eV.These results contribute to producing a next generation plasma for plasma processing such as semiconductor processing devices.