Vacuum ultraviolet absorption spectroscopy employing a microdiacharge hollow-cathode lamp for absolute density measurements of hydrogen atoms in reactive plasmas

We have developed a measurement technique for absolute H-atom densities in process plasmas using vacuum ultraviolet absorption spectroscopy employing a high-pressure microdischarge hollow-cathode lamp (MHCL) as a Lyman alpha (L-alpha, 121.6 nm) emission light source. Characterization of the L-alpha emission-line profile could be simplified by using a high-pressure discharge at about 1 atm. The effect of self-absorption in the MHCL was reduced to an insignificant level by decreasing the H-2 partial pressure. The contribution of the collisional broadening to the L-alpha emission profile was estimated from the saturation characteristics of the absorption intensity when the optical thickness of the plasma was varied. The technique was applied to the measurement of the absolute H-atom density in an inductively coupled H-2 plasma. (C) 1999 American Institute of Physics. [S0003-6951(99)02851-X].