Crystallinity Evaluation of Low Temperature Polycrystalline Silicon Thin Film Using UV/Visible Raman Spectroscopy

Abstract

Low temperature poly-Si (LTPS) is one of the most important high mobility channel materials for thin film transistors (TFTs). However, the improvement of the LTPS TFT performance is limited by the grain size and crystallinity variation. Thus, advanced nondestructive and high-resolution evaluation techniques are needed for LTPS thin film to monitor its crystallinity and grain size distribution. We evaluated the crystallinity of LTPS thin film during the fabrication process with various conditions using UV/visible Raman spectroscopy. As a result, we confirmed from Raman imaging measurements that a-Si deposited at higher temperature and lower pressure is crystallized rapidly. It can be considered that slow crystallization is caused by strong tensile strain and high hydrogen concentration in LTPS thin films. Furthermore, good crystallinity can be obtained with increasing annealing duration and deposition temperature of a-Si. In conclusion, we believe Raman spectroscopy, especially when used as imaging technique, is useful for in-line process evaluation.

Thermal conductivity characteristics in polycrystalline silicon with different average sizes of grain and nanostructures in the grains by UV Raman spectroscopy

“…The excitation source was a UV (λ = 355 nm) laser with a penetration depth in the bulk Si of approximately 5 nm under the backscattering geometry. 25,26) In addition, we confirmed that the absorption coefficients do not change with the annealing conditions by ellipsometry. Therefore, it is possible to measure Raman spectra from poly-Si without disturbance from the Si substrate.…”

Evaluation of Thermal Conductivity Characteristics in Polycrystalline Silicon - The Effect of Nanostructure in the Grains

“…The numerical aperture (NA) of the lens was 0.5 for the refractive index of air at 1.0. The excitation source was a UV ( = 355 nm) laser with a penetration depth in the bulk Si of approximately 5 nm under the backscattering geometry (15,16). In addition, we confirmed that the absorption coefficients of poly-Si thin films did not change with the annealing conditions by spectroscopic ellipsometry.…”

Suppression of Sulfur Desorption of High-Temperature Sputtered MoS2Film by Applying DC Bias

“…At present stage, oxide semiconductors are widely used in TFT (Thin Film Transistors) as a channel material (16)(17)(18)(19)(20)(21)(22). Another candidate material is poly-Si (23)(24). In order to demonstrate comparable properties to these materials, the film has to operate in enhancement mode when used as channel.…”