Paper EL+AS+EM+MS+TF-ThA10
Real Time Spectroscopic Ellipsometry Studies of Amorphous and Nanocrystalline Si_1-xGe_x:H Thin Films for Microbolometer Applications

Thursday, October 21, 2010, 5:00 pm, Room Cochiti

Hydrogenated amorphous and nanocrystalline silicon (a/nc-Si:H), germanium (a/nc-Ge:H), and their alloys have been used and continue to be assessed for use in uncooled infrared microbolometer applications. These materials may be deposited as uniform layers using equipment common to the manufacturing of displays and photovoltaics and are thus more amenable to manufacturing considerations than the ion beam deposited vanadium oxide films used in most commercial microbolometers. Real optimization of material in the a/nc-Si_1-xGe_x:H system for use in these devices requires a better understanding of the relationship between the key electrical properties of interest including resistivity (r ), temperature coefficient of resistance (TCR), and the 1/f noise character as a function of the degree of order and composition of the films. Si_1-xGe_x:H thin films were deposited using plasma enhanced chemical vapor deposition using SiH₄, GeH₄, and H₂ at variable H₂- dilution. These films have been monitored using in situ real time spectroscopic ellipsometry (RTSE) over a spectral range from 0.75 to 5.15 eV during deposition to detect changes in the film thickness and optical properties in the form of the complex dielectric function spectra (e = e₁ + ie₂) as a function of deposition time. From the RTSE measurements and analysis it is possible determine the structure of the material as amorphous, nanocrystalline, or mixed-phase and track the evolution of nanocrystallinity as a depth profile into the film. Ex situ Fourier transform infrared spectroscopic ellipsometry measurements over a spectral range from 0.05 to 0.75 eV were also performed to augment the complex dielectric function spectra and study absorption features relating to bonding. For electrical measurements, contacts were deposited in an isolated transfer length pattern for measurement of resistivity and TCR, while resistors with different volumes were made for volume normalization of the 1/f noise measurements. The TCR was measured from 20^oC to 55^oC. This study explores to correlations between the electrical and optical properties of a-Si_1-xGe_x:H and nc-Si_1-xGe_x:H as functions of film processing conditions, resultant composition, and order. a-Si_1-xGe_x:H films were prepared as a function of germanium content and hydrogen dilution to identify the impact that germanium and improved order at higher hydrogen dilution conditions have on the electrical properties (r, TCR, 1/f noise). The impact on the electrical properties due to the incorporation of small fractions of nanocrystallites are explored using mixed-phase (a+nc)-Ge:H films with nanocrystallite profiles guided by depth profile studies.