Nondestructive Characterization of Ge Content and Ge Depth Profile Variations in Si_1-xGe_x/Si by Multiwavelength Raman Spectroscopy

Abstract

A multi-wavelength, micro Raman spectroscopy system was designed and used for non-contact and non-destructive thickness and Ge content characterization of Si1-xGex/Si. The thickness and Ge content estimated by Raman measurements were compared to those values obtained from X-ray diffraction (XRD) and X-ray reflectance (XRR) measurements for cross-reference and showed very good agreement. The multi-wavelength excitation capability of the Raman system allows non-contact and non-destructive probing of Ge concentration as well as Si stress in Si1-xGex/Si along the depth direction. The Ge concentration gradient of small size test pads (as small as 10μm x 10μm) in depth direction were successfully measured using the multi-wavelength Raman system. The multi-wavelength Raman system with high spectral and spatial resolution is found to be very attractive and powerful for characterizing advanced semiconductor materials, such as Si1-xGex/Si and strained Si. It is also very useful for monitoring and controlling process equipment and process conditions.

Noncontact In-Line Monitoring of Ge Content and Thickness Variations of Epitaxial Si1-xGexLayers on Si(100) Using Polychromator-Based Multiwavelength Micro-Raman Spectroscopy

“…Furthermore, Ge content values estimated by Raman measurement data, in test pads, were very consistent with sizes down to 10 m 2 . 15) From this work, we can conclude that multiwavelength micro-Raman spectroscopy shows excellent agreement with other conventional measurement techniques for Ge content and thickness. However, the important advantage of nondestructive and noncontact measurement, together with simultaneous analytical capabilities of Ge depth profiling and stress/strain measurement, makes this new technology extremely useful as an in-line process and material property monitoring technique.…”

“…The Raman intensity ratio of I Si{Si =I Si has direct correlation with Si 1Àx Ge x layer thickness measured by XRR. This agreement indicates the Si 1Àx Ge x layer thickness can be quantified by simple calibration with XRR 12,15) and SIMS measurement data.…”

“…% at all three excitation wavelengths. 12,14,15) UV (363.8 nm excitation) Raman spectra, with shallower probing depth, shows a stronger Si-Si peak from the thin Si 1Àx Ge x layer compared to the Raman spectra from the longer (visible) excitation wavelengths with deeper probing depths. All probing depths estimated from the absorption coefficients at the excitation wavelengths, appear to be shallower than the actual probing depths.…”

“…Nondestructive depth profiling is also possible by selecting an appropriate combination of excitation wavelengths. [11][12][13][14][15] Repeatability and stability of measurement in conventional monochromator-based Raman systems are inadequate for some applications due to certain aspects of their design and use of moving parts. For the proper characterization and monitoring of high-quality crystalline semiconductor materials, very high spectral resolution (typically <0:1 cm À1 before curve fitting), measurement repeatability, and longterm stability are required.…”

“…The separation of the second peak of Si 1Àx Ge x from the bulk Si peak is used to determine the Ge content in Si 1Àx Ge x . 2,[4][5][6]12,14,15) As the Ge content increases, a monotonic increase of the separation of the second peak of Si 1Àx Ge x from the bulk Si peak occurs at a rate of À0:35 cm À1 /Ge at. % at all three excitation wavelengths.…”