  A spectrally tunable VCSEL (vertical cavity surface-emitting laser) was used
as part of sensing hardware for measurements of the radial-integrated gas
temperature inside an inductively coupled plasma reactor. The data were
obtained by profiling the Doppler-broadened absorption of metastable Ar atoms
at 763.51 nm in argon and argon/nitrogen plasmas (3, 45, and 90% N2 in Ar) at
pressure 0.5-70 Pa and inductive power of 100 and 300 W. The results were
compared to rotational temperature derived from the N2 emission at the (0,0)
transition of the C - B system. The differences in integrated rotational and
Doppler temperatures were attributed to non-uniform spatial distributions of
both temperature and thermometric species (Ar* and N2*) that varied depending
on conditions. A two-dimensional, two-temperature fluid plasma simulation was
employed to explain these differences. This work should facilitate further
development of a miniature sensor for non-intrusive acquisition of data
(temperature and densities of multiple plasma species) during micro- and
nano-fabrication plasma processing, thus enabling the diagnostic-assisted
continuous optimization and advanced control over the processes. Such sensors
would also enable tracking the origins and pathways of damaging contaminants,
thereby providing real-time feedback for adjustment of processes. Our work
serves as an example of how two line-of-sight integrated temperatures derived
from different thermometric species make it possible to characterize the radial
non-uniformity of the plasma.
