X-ray metrology for ULSI structures

Bowen, D. K.; Matney, Kevin; Wormington, Matthew

doi:10.1063/1.56889

Cited by 3 publications

(3 citation statements)

References 3 publications

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“…X-ray reflectometry is widely used for characterizing the thickness, roughness, and density of nanometer scale thin films. Because it uses wavelengths of a similar or smaller scale relative to the thicknesses of the layers being studied, the resulting data has a relatively direct connection to the structure and therefore has a rather straightforward traceability to the International System of Units (SI) [1,2,3]. This is a significant advantage over other techniques like spectroscopic ellipsometry (SE), whose results are somewhat more difficult to interpret.…”

Section: Introductionmentioning

confidence: 99%

Limitations of x-ray reflectometry in the presence of surface contamination

Gil¹

2012

J. Phys. D: Appl. Phys.

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Intentionally deposited thin films exposed to atmosphere often develop unintentionally deposited few monolayer films of surface contamination. This contamination arises from the diverse population of volatile organics and inorganics in the atmosphere. Such surface contamination can affect the uncertainties in determination of thickness, roughness and density of thin film structures by X-Ray Reflectometry (XRR). Here we study the effect of a 0.5 nm carbon surface contamination layer on thickness determination for a 20 nm titanium nitride thin film on silicon. Uncertainties calculated using Markov-Chain Monte Carlo Bayesian statistical methods from simulated data of clean and contaminated TiN thin films are compared at varying degrees of data quality to study (1) whether synchrotron sources cope better with contamination than laboratory sources and (2) whether cleaning off the surface of thin films prior to XRR measurement is necessary. We show that, surprisingly, contributions to uncertainty from surface contamination can dominate uncertainty estimates, leading to minimal advantages in using synchrotronover laboratory-intensity data. Further, even prior knowledge of the exact nature of the surface contamination does not significantly reduce the contamination's contribution to the uncertainty in the TiN layer thickness. We conclude, then, that effective and standardized cleaning protocols are necessary to achieve high levels of accuracy in XRR measurement.

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Section: Introductionmentioning

confidence: 99%

Limitations of x-ray reflectometry in the presence of surface contamination

Gil¹

2012

J. Phys. D: Appl. Phys.

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“…ii One is rarely struggling to obtain sensitivity to an important feature -and on those occasions, a complementary X-ray method can usually be found, such as the combination of XRR and XRF discussed later. 4 The metrology is traceable to international standards For the "interferometric" methods of XRD and XRR, the only parameters needed are the wavelength and the angle of scattering. The former is calibrated by NIST iii to better than 1 in 10 6 .…”

Section: Overview Of Xrm Methodsmentioning

confidence: 99%

X-Ray Metrology for the Semiconductor Industry

Bowen¹,

Ryan²

2007

ECS Trans.

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The scaling of traditional CMOS processes, and their associated metrologies, to produce smaller and faster devices was very successful down to the 90 nm node. However, to progress further, it has been found necessary to use novel materials, for which established metrologies are inadequate. In this article we demonstrate with examples that X-Ray Metrology (XRM) methods are particularly well-suited to provide characterization and measurement of the new materials systems being considered for advanced silicon processing, and for meeting the requirements of sub-90 nm nodes. These methods can be used for materials research, process development and integration and for in-line process control of product wafers.It has been clear for some time that lithography scaling alone will not meet Moore's Law projections in manufacturing at the 90 nm node and below. New materials, processes and manufacturing technologies are required to achieve the required improvements in device performance. As a result, various scaling strategies at the front end, other than lithography, are now being explored. These are illustrated in Figure 1 and include improved quality as well as scale of lithography, carrier mobility engineering through strained silicon and increased gate stack capacitance through use of high-κ dielectrics and metal gates. Even at the 65 nm node, the integration of at least one of these technologies is essential to achieve the desired level of performance in high-end logic devices, and many more new materials are being introduced at the 45 nm node. New high-κ materials are also required to reduce cell size for DRAM manufacturers. Exotic materials such as multi-layer nanolaminates are being explored to meet the need for a capacitor dielectric with both high-κ and a suitable band gap. Furthermore, a technology shrink is also required for back-end processing. For example, for the 65 nm nodes, a traditional PVD (plasma vapor deposition) barrier metal process would represent 40% of an overall copper interconnect, thus impacting overall resistivity. New barrier materials are being explored in order to maintain RC delays within ITRS i guidelines.It is a significant challenge simply to measure such extremely thin layers of these new materials. For example, their optical constants in very thin layers are normally not known and assuming bulk values is likely to give rise to large errors. Furthermore, monitoring thickness alone may not be sufficient, especially in cases where the microstructure of the layers is significant. The leakage current of high-κ dielectrics and the work functions of metal gates are affected by their crystalline/amorphous ratios. Information on the microstructure of deposited materials is now key to determining their electronic properties. This has never been required previously in semiconductor manufacturing i ITRS = International Technology Roadmap for Semiconductors

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“…Because it is derived from firstprinciples, XRR provides metrological and Sl-traceable thickness measurements for the semiconductor industry, see [8,9,10]. At the National Institute of Standards and Technology (NIST), we are establishing XRR's limits [11], and determining the apphcabihty and accuracy of the XRR method for novel material research.…”

Section: Introductionmentioning

confidence: 99%