A study on the generation and control of electron beams and ultra-low electrons temperature plasma using two DC-biased grids.

To generate ultra-low electron temperature (ULET) plasma (T_e < 1 eV), two DC-biased grids are used. We can control the electron beam energy by adjusting the grid voltage. Since the gap between two grids is made shorter than the electron mean free path electrons can be fully accelerated from the grids. The electron beam energy in Ar & He ULET plasma in a two-grid system is investigated by measuring the electron energy distribution. It is observed that the electron beam energy is proportional to the grid voltage (-30 V ~ 0 V) at 3 mTorr. At high pressures (10 ~ 75 mTorr), ULET plasma (T_e < 0.7 eV) is produced. The ULET plasma is formed faster in He than in Ar because the sheath length of He is longer and thus forms potential surface in the grid holes faster. And the electron density of the He ULET plasma is higher than that of Ar. This is because the number of high-energy electrons in the source region, which is the biggest factor determining the density of the beam, is greater in He ULET plasma than in Ar. So, the electron beam distribution and ULET plasma is clearly observed by measuring electron energy distribution with the Langmuir probe. It is expected that the electron beam generated by the grid voltage can selectively dissociate the neutral species into radicals, which is crucial for ALE and ALD.