Thickness Analysis of Natural Oxide Films using a MSV-5000 Microscopic Spectrophotometer

Download PDF October 4, 2017

Introduction

MSV-5200
UV-Visible/NIR Microscopic
Spectrophotometer

The MSV-5000 series microscopic spectrophotometer is for transmission and reflection measurements in a wide wavelength range from the ultraviolet to near infrared. The built-in high resolution camera enables sample areas as small as 10 μm in diameter to be precisely measured and therefore is most suitable for samples having microstructure.

In this application note, a sample with silicon patterns 35 μm wide are lined up on a titanium substrate with 14 μm intervals. As silicon is oxidized in air, SiO2 films are formed and the thickness of these films is analysed after obtaining the reflectance spectrum.

Experimental

Measurement Conditions
UV-Vis Bandwidth5 nmNIR Bandwidth20 nm
ResponseSlowScan Speed100 nm/min
Data Interval0.5 nmCassegrain Objective16x
Incidence Angle23°IN/OUT Aperture10 μmΦ
Figure 1. Observation point of measurement position.

An aluminum vapor-deposited mirror is used as a reference for the baseline measurement. The high-resolution camera is used to determine the sample area (Figure 1). The red spot illustrates the size and position of the detected light. The sample reflectance spectrum is measured and the absolute reflectance spectrum is calculated by multiplying the obtained relative reflectance by the absolute reflectance of the aluminum mirror.

Keywords

UV-0023, MSV-5200 microscopic spectrophotometer, VWML-791 Multi-Layer analysis program, Materials

Results

Figure 2. Absolute reflectance spectrum of SiO2 film.

The measured absolute reflectance spectrum is shown in Figure 2. The MSV-5000 series adopts the confocal optical system that eliminates the influence of back side reflection when obtaining a sample measurement. Therefore, above 1100 nm where light passes through silicon, the spectrum is not influenced by back side reflection.

The results of fitting the absolute reflectance spectra using the Multi-Layer Analysis program is shown in Figure 3. The error between the measured and calculated spectrum was within 2% and the film thickness of SiO2 was calculated to be 7.6 nm. The reflectance (R) is expressed using the refractive index of the film (ni), extinction coefficient (ki), the angle of incidence (Φi), wavelength (λ), and the film thickness (di). The optical constants of Si and SiO2 were obtained from the literature values and the film thickness of SiO2 is estimated using the Multi-Layer Analysis program which fits the calculated reflectance spectrum to the measured spectrum.

Figure 3. Top: Calculated (red) and measured (blue) reflectance spectrum of SiO2 film.
Bottom: Error between the measured and calculated spectra.

About the Author

Leah Pandiscia received her PhD from Drexel University where she studied Biophysical Chemistry. She is a Spectroscopy Applications Scientist at JASCO.