Thickness Monitoring

4 Key excerpts on "Thickness Monitoring"

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  eBook - ePub

  Optical Thin Films and Coatings

  From Materials to Applications

  • Angela Piegari, François Flory(Authors)
  • 2013(Publication Date)
  • Woodhead Publishing

    (Publisher)

  Quartz crystal monitoring of thin film coating production is also widely employed in the case of stable deposition processes (Macleod, 2001). Nevertheless the interest in optical monitoring strategies has been only increased with the new developments in deposition technologies. This is obviously connected to the fact that such strategies monitor optical thicknesses of coating layers and not their physical thicknesses. Macleod (1981) wrote that this had always been considered as a strong argument in support of optical monitoring strategies. Indeed, an attentive study of the basics of thin film theory shows that only thin film optical thicknesses are physically sensible and are entirely responsible for the optical properties of a coating (Furman and Tikhonravov, 1992). Optical monitoring of thin film coating production has almost been as long a history as thin film optics itself. Macleod (2001, p. 500) mentions the early paper devoted to this subject (Banning, 1947) where a table allowing the monitoring of film optical thickness in quarter wave units by a color of reflected light was presented. Practically all early works on optical monitoring were connected to the production of multilayers with quarter wave optical thicknesses of their layers. For such multilayers reflectance/transmittance is monitored at a central wavelength which is four times quarter wave optical thickness. A monitoring signal reaches its maxima or minima exactly at an instant when a new quarter wave portion of layer optical thickness is deposited. Monitoring of reflectance/transmittance extrema in early days of thin film optics was done by a vacuum plant operator and a 5% accuracy of layer Thickness Monitoring was typical for a trained operator (Macleod, 2002, p

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  Handbook of Thin Film Deposition

  • Krishna Seshan(Author)
  • 2001(Publication Date)
  • William Andrew

    (Publisher)

  The final element of successful yield enhancement through defect reduction is close communication between defect metrology and process engineering groups. A highly effective defect reduction program seamlessly integrated with a strong process engineering program is well positioned for success in the semiconductor market. 4.0 THEORY OF OPERATION, EQUIPMENT DESIGN PRINCIPLES, MAIN APPLICATIONS, AND STRENGTHS AND LIMITATIONS OF METROLOGY AND INSPECTION SYSTEMS This section briefly discusses the theory of operation, main applica-tions, and the strengths and limitations of several thin film metrology systems. For a more detailed theoretical discussion, the reader is encouraged to consult Ref. 6. 256 Thin-Film Deposition Processes and Technologies 4.1 Film Thickness Measurement Systems Theory of Operation. The common optical measurement techniques include reflectometry (using unpolarized or polarized light) and ellipsometry. System implementations use multiple wavelength or multiple angles of incidence. Regardless of the type of system, the data analysis methods that transform the directly measured quantities to the parameters of interest such as thickness and refractive index are similar. The measurement recipe contains information about the film stack to be measured, such as the type of material, approximate thickness of the material, and (implicitly) the refractive index of the material. The Fresnel reflectance equations are used to calculate theoretical spectra for the film stack. The calculated spectra are compared with the measured spectra, and regression analysis is performed by varying the parameters of interest until the best fit is obtained. The best-fit values are reported, along with a figure of merit referred to as the goodness-of-fit (GOF). The capability of a system to report parameters of interest such as thickness and refractive index values derives from the amount and type of raw data measured by the system.

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  Electroplating

  Basic Principles, Processes and Practice

  • Nasser Kanani(Author)
  • 2004(Publication Date)
  • Elsevier Science

    (Publisher)

  CHAPTER 8 Coating Thickness and its Measurement 8.1 Introduction 8.2 Destructive Processes 8.2.1 Microscopic Methods 8.2.2 Coulometric Methods 8.3 Non-Destructive Methods 8.3.1 Eddy Current Method 8.3.2 X-ray Fluorescence Techniques 8.4 In situ Measurement Methods 8.4.1 Island Method 8.4.20ptipulse Method References 248 Electroplating- Basic Principles, Processes and Practice 8.1 Introduction A measurement of the thickness of a deposited coating is possibly the most important single test to be carried out after the deposition. Sometimes, if the resulting thickness value is out of specification, further tests will become necessary. It is fair to state that if only a single test is carried out, then this would be a thickness determination. Of thickness testing it can be said that sometimes, it is a mean value that is required. In other cases, however, it is the value at a particular location that becomes important. Such spot tests yield discrete values, not necessarily typical of the coat- ing as a whole. However if a large enough number of such discrete local values are recorded, it becomes meaningful to use them to derive a mean thickness value. It is thus good practice, whatever the measurement method used, to make as many me~ surements as possible, not only over the surface of the component, but also more than once at each location. In many cases, there will be locations more prone to wear, and at these, above all, an adequate coating thickness is essential. Though the number of measurements recommended cannot in every case be prescribed, five measurements across the surface of the work, with five values at each location, is sometimes suggested as a guideline. Because this parameter is so critical, an array of measurement methods has evolved over time, and only the most important are described here [l, 2]. Most such methods can be classified as destructive or non-destructive.

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  Introduction to Microfabrication

  • Sami Franssila(Author)
  • 2010(Publication Date)
  • Wiley

    (Publisher)

  Commonly used optical thickness measuring methods are ellipsometry and reflectometry. In ellipsometry the change in polarization is measured and the amplitude ratio of two different polarizations is computed. Film thickness can be obtained when the optical constants of the film are known. Ellipsometry can be used to measure those constants too, but then additional measurements are needed: for example, multiple angles or multiple wavelengths must be used. Ellipsometry works best for film thicknesses below the measurement wavelength (633 nm, most commonly) because periodicity makes interpretation of thick-film thicknesses difficult. The low end is just a few nanometers, but for very thin films uncertainty is introduced because optical constants are not really constants, but depend on film thickness.

  In reflectometry a wavelength scan is made (e.g., 300–800 nm) and this is fitted to a reflection model. Reflectometry can measure films from a few nanometers up to 50 µm thick.

  X-ray reflection (XRR) can be used to measure very thin films. Unlike optical methods, XRR is insensitive to changes in film refractive index. Measurement time, however, is minutes, or even hours, compared to seconds for optical tools. XRR is amenable only to surfaces with a roughness no more than a nanometer and thickness less than a hundred nanometers. There are many such applications in microtechnology: for example, CMOS gate oxides on single crystal silicon are thin and extremely smooth.

  2.3 Optical Techniques

  In addition to microscopy, optics has many attractive qualities for monitoring microfabrication: optical measurements are mostly quick, non-contact and accurate. Lasers can be focused down to micrometer spots, and rapidly scanned over the full wafer, proving both local and global information. Surface roughness, particles and defects can be measured by scatterometry (Figure 2.6

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