New optical range inspection and improving optical response for spectroscopic based endpoint detection

Optical emission spectroscopy (OES) is widely used for in situ characterization and control of plasma processing, as for instance in dry etching end point detection. In current practice, only UV-VIS range is used, which corresponds to electronic transitions of molecular or atomic levels. However, when areas to be patterned become smaller, and etching selectivity are far to exist, this may give insufficient results. To overcome this problem, we have developed a new method to detect optical end point, involving the IR portion of the spectra (corresponding to molecular vibrational modes) and its emission enhancement. When introducing a suitable gas (the enhancer) to the current etching chemistry, the spectroscopic fingerprint intensities may be improved. Under these conditions, the infrared portion of emission spectrum proves to give valuable information for tracking the etching process. In the present work we present the results obtained with this innovative method in the definition of a small trenches of 60 nm of depth for 15 nm of width, into SiN layer. We have demonstrated that in spite of a non selective etching process of SiN over SiO₂, for small patterning area ( 5% with respect of total wafer area and defined by the patterning mask) reliable and repeatable end point detection can be achieved by monitoring selected wavelengths within the infrared range. Vibrational emission variations through etching process are enhanced by the addition of a suitable gas, which increases the emission intensity without impacting the etching process. Negligible impact of the enhancer has been proven by comparing the fundamental etching parameters (etching rate, etching uniformity, wafer-to-wafer repeatability, etc.) for the current etching process and with the addition of the enhancer. The entire etching process is carried out in a LAM TCP 9600 PTX metal etching tool