479 / 2019-03-18 09:37:25

Investigation of ion energy and angular distribution in a dc-biased, collisional plasma sheath

ion beam,plasma diagnositics,Ion energydistribution,ion angular distribution,dc bias voltage

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ion energy and angular distribution functions were investigated at the grounded electrode of an inductively coupled discharge in hydrogen gas. The inductive RF driven in our study produces high densities (/ electron densities) for low gas pressure. In our chamber, an additional direct-current (dc) bias is applied to the accelerator electrode to extract and speed up ions. Under dc bias condition the shape of ion angular distribution function (IADF) shows a strong dependence on the bias voltage and weak dependence on gas pressure. High dc bias and low gas pressure can effectively narrow the IADF so that a tightly-focused ion beam can be formed. Average energy of ion energy distribution (IED) increases with increasing dc bias and ICP power, as a consequence of increasing sheath potential. While the average energy of IED decreases with increasing gas pressure for no dc bias and 50 V dc bias, moreover, there appears an inverse phenomenon for 450 V dc bias, which is attribute to the variation of electric potential with gas pressure oppositely inside and outside of sheath. The shape of the IED depends both on the ICP power and gas pressure, high ICP power or high gas pressure can increase the plasma density and decrease the sheath thickness, thereby shorting the transit time of ions across the sheath and producing wider IED