Characterizing SiOx Ny ARC materials with laser ellipsometry and DUV reflectometry

SiO X N Y ARCs are critical for maintaining CD control in current and future generations of designs. However, even minor fluctuations in t , n , and k across the wafer, or from wafer to wafer, can have a significant impact on ARC performance. For process control of ARC deposition, metrology tools must be able to reproducibly measure thickness and optical properties to 6 σ, translating into 1.5 a for a nominally 500 a SiO X N Y ARC and 0.0015 for index. A combination of laser ellipsometry and DUV reflectometry has demonstrated the ability to meet these requirements, with two tool-matching results of 0.8 a for thickness and 0.001 for index. The accuracy of the thickness measurements was further tested at SiO X N Y ARC films were etched to clear. TEM confirmation of thickness measurements demonstrated the metrology was accurate with films as thin as 75 a. The metrology method was subsequently used to monitor both the thickness and reflectivity at 49-points across a wafer at various etch times until the film was thinner than 25 a.