Roughness Characterization of Nanoscale Structures with Small Angle X‑ray Scattering


Chengqing Wang, Ronald L. Jones, Eric K. Lin, Wen-li Wu, Kwang-Woo Choi, Bryan J. Rice, George Thompson


Polymers Division, MSEL

Bldg 224, Rm B304, MS 8541


301-975-3928 (fax)


Mentors:  Eric K. Lin, Wen-li Wu

Sigma Xi member:  No

Category:  Materials


The continued decrease in the dimensions of individual circuitry components will soon reach 40 nm where the acceptable tolerance in the variation of the line-width or feature roughness will be less than 1 nm.  This creates significant challenges for measurements based on electron microscopy and light scatterometry.  Device viability also requires the measurement be non-destructive.  In addition, the continuing development of new materials for extreme ultraviolet photoresists, nanoporous low-k dielectrics, and metallic interconnects all require high precision dimensional measurements for process development and optimization.   

The use of Small angle X-ray scattering (SAXS) as a dimensional metrology technique has been successfully demonstrated as a non-destructive tool for quantifying the critical dimension of line width, pitch periods and sidewall angle of lithographic patterns.  In this work, we have developed models for quantifying the line-edge roughness (LER) and line width roughness (LWR) of periodic line:space patterns.  

The problem is simplified to several model LER and LWR patterns (shown in Figures 1a-c) that can be modeled analytically.  To test these theoretical results, model line grating patterns with controlled LER/LWR were prepared and measured with SAXS.  The experimental results indicate that LER/LWR defects manifest themselves with specific scattering features that can be modeled and analyzed quantitatively.  An example SAXS result from one of the line gratings created by a mask shown in Figure 1c is given in Figure 2a.  Distinct satellites peaks appear and the intensity of these peaks have been fit successfully.  The roughness values from the SAXS measurement determined using a Debye-Waller factor approach from traditional crytallography are qualitatively similar to those extracted using CD-SEM data from the identical sample set.  An apparent Debye-Waller factor may serve as a useful parameter to quantify LER/LWR.