High efficient negative ion production by electron temperature control

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The formation of negative hydrogen ions is investigated in a pure hydrogen RF plasma using a grid method for the electron temperature control. Using the grid method we produce both high and low electron temperature plasmas in the separated regions in the vacuum chamber, i.e., a high electron temperature plasma in the plasma production region and a low electron temperature plasma in the downstream region which is separated by the grid. The electron temperature is decreased by applying negative potential to the grid.The production rate of negative hydrogen ions depends on both the electron temperature in the plasma production region and that in the downstream region. In case of 8 mTorr we did not detect marked negative ions even in the low electron temperature plasma. In this case, the electron temperature in the production region is relatively low. However, in case 2 mTorr, the electron temperature in the production region is increased, then we observe an efficient negative ion formation in the downstream region when the electron temperature is decreased by the grid. The density ratio of negative to positive ions attains to about 95% in this case.The results show the presence of threshold electron temprature for vibrational excitations, and also the production of low electron temperature is important for dissociative attachments.We made a procedure to get a patent for this new RF plasma reactor using a grid method. In this plasma reactor it is possible to control the chemical reaction for establishing efficient plasma processing such as the negative hydrogen ion production.