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Application of Spectroscopic Ellipsometry-based Scatterometry for Ultrathin Spacer Structure Ryan Chia-Jen Chen, Fang-Cheng Chen, Baw-Ching Perng, Yuan-Hung Chiu, and Hun-Jan Tao, Taiwan Semiconductor Manufacture Co. Ltd. Ying-Ying Luo, KLA-Tencor Corporation

Many applications for spectroscopic ellipsometry-based (SE) scatterometry have been developed for critical dimension (CD) control of the resist patterning and poly gate processes. Scatterometry’s many advantages include good precision, short cycle times, and multiple information outputs. The spacer structure has now emerged as a promising new application for SE-based scatterometry. In this work, we use SE-based scatterometry to demonstrate a two-dimensional profile of the ultrathin spacer with post-etched structure, as well as CD measurement of the spacer. Theory and measurement results taken of dense and isolated structures will be briefly discussed. Transmission electron microscope (TEM) cross-sections and the spectra fitting by scatterometry are also collected at the same location and compared. The data shows high correlation between the two. Finally, an example of minispacer fault detection methodology and repeatability test using scatterometry is also presented to show the technology’s capability for volume production.

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The minispacer structure has been actively studied as a means to maximize transistor performance and suppress the degradation of short channel effect (SCE)1 for sub-micron technology. Normally, the minispacer has a width ranging from 100Å to 250Å. However, its width could also be as thin as 50Å (or even lower) when the channel length dimensions continue to shrink in order to meet the requirements for device speed and to reduce SCE. The ability to measure the width of the minispacer with good precision control is paramount to device performance, because it will influence optimization of the implant condition. However, there is currently no inline metrology tool that is capable of measuring the minispacer width because it is too thin to be measured. Traditionally, a TEM is used to monitor the minispacer profile. However, TEMs have several drawbacks, such as their tendency to

be destructive, offer low throughput, and involve long sample preparation times. This technology is also not practical for volume production, when statistical sampling is required. Recently, there have been many studies for SE-based1 metrology used in lithography2, polysilicon gate3, and shallow trench isolation (STI)4, as well as on its precision control and correlation to scanning electron microscopy (SEM). In this paper, the measurement capability of SE-based metrology on minispacers down to 50Å is evaluated. Experiments and results

Experimental In this study, all scatterometry measurements were performed with KLA-Tencor’s SpectraCD, an SE-based scatterometry system. The spectroscopic ellipsometry technique is widely used for thin film metrology. SpectraCD utilizes a grating structure comprised of line/space features of uniform period to represent the device feature. The box size of the grating structure is designed as 50x50 µm in order to cover the spot size. Two different pitches, including 500 nm and 250 nm, Summer 2004

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