Mid-infrared optical characterization of thin SiN_x membranes

Area of Science:

• Materials Science
• Optics and Photonics
• Solid State Physics

Background:

• Accurate determination of optical constants is crucial for designing optical devices.
• Silicon nitride (SiNx) is a versatile material used in various optoelectronic applications.
• Mid-infrared spectroscopy offers unique insights into material properties.

Purpose of the Study:

• To investigate and determine the optical constants (refractive index n and extinction coefficient κ) of silicon nitride (SiNx) thin films.
• To validate the accuracy and reliability of the calculated optical parameters.
• To analyze the inherent limitations of the employed characterization method.

Main Methods:

• Utilized photometric measurements of transmission and reflection.
• Employed the transfer matrix method for iterative calculation of optical constants.
• Characterized SiNx films of three different thicknesses (600, 200, and 100 nm) for validation.

Main Results:

• The transfer matrix method accurately determined the refractive index (n) and extinction coefficient (κ) for SiNx films.
• Experimental and calculated values showed a low average relative error (<1.5%) across the spectrum.
• Reliability of optical constants was confirmed through validation using different film thicknesses.

Conclusions:

• The transfer matrix method, combined with photometric measurements, provides a reliable approach for determining SiNx optical constants in the mid-infrared.
• The validated optical constants are accurate for practical applications in optical device design.
• Understanding the method's limitations is essential for precise material characterization.