Kyeong-koo Chi

Surface Analysis for Selective SiO2 Etching by Reflectance Photoelastic Modulated Fourier Transform Infrared Spectroscopy

Photoelastic modulated fourier transform infrared (PEM FTIR) spectroscopy has been used to study the bonding structure and compositions of fluorocarbon films generated during etching with CHF3/CO surface wave plasma (SWP). The C=C (stretching vibration mode at 1600 cm-1), C–C (940 cm-1), C–F (1032, 1164, 1260, 1291 cm-1), =C–H (780 cm-1) and C=O (1790 cm-1) peaks on the polymer films were identified using reflectance PEM FTIR. In addition to the peak assignment, the C–F spectra were fitted to three peaks–1280, 1250, 1200 cm-1, with Gaussian splitting, respectively. Comparing the etching results with the variation of FTIR spectra, it was found that the selectivity of SiO2 to poly-Si and photoresist with CO mixing ratio to CHF3 is correlated to the area ratio of [C=C]/[C–F] and [C=C]/[C=O]. The XPS result was also compared to reflectance PEM FTIR data to reveal the availability of reflectance PEM FTIR application. It was confirmed that there existed a good agreement between PEM FTIR and XPS data. When we integrated all the results from PEM FTIR, XPS and optical emission spectroscopy (OES), we found that the element of the C=C bond on the polymer surface played an important role as an etch inhibitor. The reflectance PEM FTIR measurement on the etched surface is considered to lead to an understanding the properties of polymer films generated during oxide etching.

Effect of carbon enrichment induced by photoresist on highly selective SiO2 etching

We propose two models to discuss the behavior of the selective etching of SiO2 to the underlying Si3N4 with changing wafer surface temperatures. For this investigation, three specimens, SiO2, Si3N4, and poly-Si, which are nonpatterned, photoresist-patterned, and poly-silicon-patterned, respectively, have been etched in a surface wave plasma system equipped with an electrostatic chuck for wafer temperature control. The coolant temperature, which controls the wafer temperature, has been changed from −20 to 50 °C. For the nonpatterned wafer, the etch rates of SiO2, Si3N4, and poly-Si increase and the selectivities decreases with wafer temperature. However, for the samples patterned with either photoresist or poly-Si, the etch rates of SiO2 decrease with wafer temperature. The temperature rise also leads to an enhancement of selectivity of SiO2/Si3N4, and the steeper profile angles. The presence of a masking layer, even for the poly-Si-patterned samples, results in a different etching behavior. This is becaus...