Silicon and Semiconductors
Raman Imaging and Microscopy in Semiconductor Applications
Strain and stress evaluation of silicon
In semiconductor applications silicon is chosen because it allows precise control over electrical properties, works well with insulators like silicon dioxide, and has excellent thermal conductivity. However, it is crucial to determine stress and strain in silicon to ensure the reliability and performance of the device. In this application example Raman spectroscopy was utilized to evaluate strain and stress in silicon materials.
Raman imaging reveals stress distribution in silicon crystals, offering insights into defects and strains. When pressure is exerted on silicon, its structure deforms, altering the frequency of Raman-scattered light. This method measures strain and stress by analyzing these frequency shifts. Compressive stress increases frequency shift, while tensile stress decreases it. Raman spectroscopy accurately measures these shifts, determining the material's strain and stress.
The Figure (A) illustrates a Raman peak shift, depicting the distribution of stress on a silicon substrate through a color scale. It reveals the variation in the silicon peak position surrounding a thin film on the substrate, analyzed within a specific plane. Figure B and C show the shift of Si peak along the dot line. RAMANtouch can determine peak position more precisely than 0.1cm-1.
Raman observation of grain boundaries in thin-film silicon
Crystalline silicon thin films are formed by annealing amorphous silicon often by a method called pulsed RTA which promotes crystallization throughout the film. This enhances electrical and optical properties, crucial for solar cells, displays, and sensors. Complete crystallization is vital for improving electrical and optical properties while reducing defect density.
The RAMANtouch was used to determine the distribution of crystalline and amorphous silicon before and after annealing, as well as to analyze the distribution of grain boundaries in the thin film post-annealing. Additionally, peak shift analysis with high precision was implemented to assess the degree of crystallization, aiming for a comprehensive understanding of the crystallization process and its impact on the electrical and optical properties of the thin film.
Figure (A) shows the distribution of crystalline silicon and amorphous silicon in optical microscopy and Raman imaging before annealing. Figure (B) depicts the distribution of grain boundaries in thin-film silicon after annealing. While the thin film appears to be uniformly crystallized under optical microscopy, utilizing peak shift analysis to visualize the shift in the silicon Raman peak positions shows that the crystallization process is not yet complete. The RAMANtouch provides high-precision peak shift analysis exceeding 0.1 cm-1 making this analysis possible.