Yoel Cohen

Product-driven material characterization for improved scatterometry time-to-solution

This paper discusses a novel methodology of material characterization that directly utilizes the scatterometry targets on the product wafer to determine the optical properties (n&k) of various constituent materials. Characterization of optical constants, or dispersions, is one of the first steps of scatterometry metrology implementation. A significant benefit of this new technique is faster time-to-solution, since neither multiple single-film depositions nor multi-film depositions on blanket/product wafers are needed, making obsolete a previously required-but very time-consuming-step in the scatterometry setup. We present the basic elements of this revolutionary method, describe its functionality as currently implemented, and contrast/compare results obtained by traditional methods of materials characterization with the new method. The paper covers scatterometry results from key enabling metrology applications, like high-k metal gate (postetch and post-litho) and Metal 2 level post-etch, to explore the performance of this new material characterization approach. CDSEM was used to verify the accuracy of scatterometry solutions. Furthermore, Total Measurement Uncertainty (TMU) analysis assisted in the interpretation of correlation data, and shows that the new technique provides measurement accuracy results equivalent to, and sometimes better than, traditional extraction techniques.

A novel method for pushing the limits of line edge roughness detection by scatterometry

Fluctuations in the line edge of lithographic features, termed line edge roughness (LER) always exist. At 32 nm line width (and below), LER can be a significant fraction of the feature dimensions. LER can be simply detected by AFM or SEM techniques, however, fast and nondestructive optical techniques should be developed in order to enable effective process control. Optical scatterometry is preferable over other existing measurement techniques, due to the relatively simple implementation in production and lower photoresist damage. In this article we show simulations of LER by 3-dimensional Rigorous Coupled Wave Theory (RCWT) calculations. The prediction of tool capabilities was done using simulations. The outcome of these simulations results where analyzed and used for the basic design of photoresist structures. The conclusions from sensitivity and correlation analysis of the simulation data were verified against measured scatterometry data. Well-defined features with controlled LER, in the range of 2.5 to 15nm, were fabricated by e-beam direct write technique (IMEC, Belgium). The photoresist features we created were a large matrix of different scatterometry targets with varying parameters of CD, Period, LER level, and LER frequency. These features were characterized by electron microscopy and AFM in order to verify the LER values and a NovaScan 3090 system and NovaMARS modeling software were used for the Scatterometry characterization. To achieve better sensitivity to the lower roughness dimensions, we used an option of Effective Medium Approximation (EMA) modeling for spectra analysis. Based on this reference data and the scatterometry measurements we have developed a novel scatterometry method that is sensitive to very low level of LER. This method is based on design of a special test structure which can show better sensitivities than the basic noise levels of the tool. The basic idea in this design is the calibration of the scatterometry measurement on a series of sites with LER steps. It will be shown that LER changes of about 1 nm can be detected based on these designed test structures. This is well below the normal capabilities of current optical tools.

Changes of UV Optical Properties of Plasma Damaged Low-k Dielectrics for Sidewall Damage Scatterometry

Porous low-k dielectrics were studied to determine the changes of optical properties after various plasma treatments for development of scatterometry technique for evaluation of the trench/via sidewall plasma damage. The SiCOH porogen based low-k films were prepared by PE-CVD. The deposited and UV-cured low-k films have been damaged by striping O 2 Cl 2 , O 2 , NH 3 and H 2 N 2 based plasmas and CF 4 /CH 2 F 2 /Ar etching plasma. Blanket wafers were studied in this work for the simplicity of thin film optical model. The optical properties of the damaged low-k dielectrics are evaluated the using various angle spectroscopic ellipsometry in range from 2 to 9 eV. Multilayer optical model is applied to fit the measured quantities and the validity is supported by other techniques. The atomic concentration profiles of Si, C, O and H were stated by TOF-SIMS and changes in overall chemical composition were derived from FTIR. Toluene and water based ellipsometric porosimetry is involved to examine the porosity, pore interconnectivity and internal hydrophilicity.

Alternative approach for direct APC using scatterometry data

Scatterometry is a promising method, capable of providing accurate profile information for a large range of applications. However, applying scatterometry to the production environment and applying it to APC is still difficult. In this paper we propose an alternative approach in which we apply a Neural Network to directly correlate scatterometry raw data and the lithography process control parameters. The proposed method is much easier to use than normal scatterometry, and can therefore be applied to APC much faster.