Bridging CD metrology gaps of advanced patterning with assistance of nanomolding

Abstract

CD Metrology plays a critical role in the successful disposition of a semiconductor patterning process and eventually a product. With the advancements in the semiconductor technology such as sub-22 nm nodes, advanced patterning processes such as double patterning, dual-damascene processes, EUV patterning and the complex 3D device architectures such as FinFET devices, via-in-trench, elongated contacts have challenged the current state of CD metrology in terms of capability, measurement quality and time-to-solution. For these nodes, either the CD-metrology solution does not exists or it's not meeting the requirements resulting in gaps. CD-AFM providing reference metrology for resist and dielectric patterns is limited by the probe geometry. Due to probe geometry limitations CD-AFM is challenged in measuring the true bottom CD (< 15 nm from bottom), sub-5 nm foot and undercut, sub-40 nm trenches, charged samples, small CD high aspect ratio structures like via in trench, deep trench (DT) and through silicon via (TSV), and various CDs of interest in the FinFET type 3D devices. TEM cross section is used as another reference metrology for dielectric patterns but it is subject to error in sample preparation (especially for contacts in sub-22 nm nodes) and limited statistics. CD-SEM and scatterometry which are workhorse metrology, needing reference metrology for measurement accuracy, also face challenge in measurement of advanced patterning. Therefore, there is a critical need to enhance current and develop new 3D CD metrology techniques for advanced patterning technology. This paper reports an innovative non-destructive 3D CD metrology solution based on nanomolding of the master structure (via in trench, charged sample, trench < 40 nm, FinFET and EUV patterns) followed by the CD-AFM measurements with potential to address various metrology gaps. Nanoscale molding of the master produces an inverted replica where the top CD and profile correspond to the bottom CD and profile of the master enabling the measurements using currently existing CD-AFM capabilities which otherwise is not possible. The paper reports the nanomolding optimization study exploring different molding materials and methods on a variety of master samples and structures where the current CD-AFM capability is limited. CD-AFM measurements of the master and the mold are compared where the master can be measured via conventional CD-AFM to understand the accuracy of the nanomolding approach. Measurement of the common region in the master and molded replica allowed the self-referencing to ensure accuracy of the CD measurements. TEM cross section has been used as a secondary reference for additional validity of this approach. Successful molding of a small region of interest on a 300 mm wafer demonstrates the non destructive inline 3D CD metrology potential of nanomolding assisted CD-AFM 3D metrology. Molding-assisted metrology is faster and statistically robust compared to the TEM metrology and does not require to break the wafer. Molding of charged (buried) master sample with suitable polymer allows the accurate metrology of such samples. Nanomolding assisted measurement of CD in FinFET devices can help break the cross correlation of different parameters in scatterometry which is otherwise challenged in such cases. In summary, the innovative nanomolding assisted 3D CD-Metrology approach has shown the potential to enhance the CD-AFM capabilities as a non destructive physical 3D CD metrology solution and turn some of the red sections in the ITRS metrology roadmap to yellow or green. This is a major step in bridging the metrology gap posed by the advanced patterning technology. © 2012 SPIE.