One of the difficult challenges faced by the semiconductor manufacturingindustry is the pressure to create ever more powerful, complex chips with smaller geometries. Currently, the demands for smaller feature sizes are being met by utilizing exposure wavelengths in the deep-UV range (248 nm and 193 nm). To further reduce feature size and squeeze the very last potential out of optical lithography, the technology has moved towards the incorporation of phase-shift materials. For such materials, rapid and accurate measurement is imperative to produce and maintain the correct phase-shift. The complete and accurate characterization of phase-shift materials requires that the measuring instrument provide phase-shift information plus thickness of the phase-shift material and values oin (the index of refraction and k (the extinction coefficient) at the specified wavelength. Furthermore, transmittance through both the phase-shift material and substrate must be measured at that specified wavelength. Specifically, the characterization data must indicate whether the ideal phase-shift of 180°, in addition to pre-specified transmittance in the 5-10% range, has been achieved. In this article we present a method of data collection and analysis that allows the phase-shift, film thickness and values of n and k to be determined simultaneously from the concurrent measurements of transmittance and reflectance, allowing the detection of non-uniformities in phase-shift in either patterned or un-pattemed films, with close correlation to direct-measured values. This technique offers the advantage of high throughput (entire masks can be characterized in minutes) and can be applied equally well to patterned or unpattemed masks.
In this paper we describe a non-destructive technique that characterizes Silicon-On-Insulator (SOI) wafers. With this technique, the thickness of the crystalline silicon and BOX layers, as well as the thickness of the native oxide that naturally forms on SOI are determined. Additionally the degree of smoothness of SOI interfaces are measured. The spectra of optical constant, n and k, of the BOX are also determined. The thicknesses, n and k spectra, and interface roughness are determined simultaneously by analyzing broad-band reflectance with the Forouhi-Bloomer equations for n and k. The reflectance measurement is based on all-reflective optics to generale a highest possible signal-to-noise ratio over the entire measured wavelength range. The total measurement time is about 1 second. We show that the result obtained with the present technique are in excellent agreement with cross-section TEM.
Reduction of the thickness of the diamond-like-carbon (DLC) overcoat deposited on media and head, plays an important role in enhancing areal density. This is because the DLC layer contributes directly to the spacing between media and head and increases in areal density are achieved by reducing this spacing. In fact, nowadays DLC thicknesses of the order of 50 Angstrom are required. With such ultra-thin DLC overcoats, quick and accurate thickness measurements are becoming a must. In this article, an optical technique for measuring the DLC thickness, rapidly and nondestructively is presented. The technique, termed the 'n&k Method,' is based on broad band reflectance spectrophotometry and Forouhi-Bloomer dispersion equations in the data analysis. Results for samples with DLC thicknesses ranging from approximately 25 Angstrom to 300 Angstrom are given. In addition, a typical uniformity map of DLC on a magnetic disk is presented, whereby the thickness ranges from 46 Angstrom to 50 Angstrom, with a mean value of 50 Angstrom, and standard deviation of 2 Angstrom. The determined thicknesses obtained using the 'n&k Method' is compared with those from step height measurements using stylus and atomic force microscopy (AFM). The results are consistent within the measurement error and the optical measurement has by far much better precision and repeatability.
The optical properties of materials comprising photolithographic masks are investigated at wavelengths covering the vacuum-ultra-violet (VUV) to the near-infra-red (NIR). Broadband reflectance (R) and transmittance (T) spectra from 130 to 1000-nm are obtained from a variety of single layer absorber and bi-layer absorber/anti-reflection coating (ARC) samples deposited on MgF2 and CaF2 substrates. These experimental data are analyzed using the Forouhi-Bloomer (F-B) dispersion equations, in conjunction with a least squares fitting algorithm, to infer the thickness and n and k spectra of the materials under investigation. Once determined, the optical properties of the component materials are used to calculate the optical density of the single layer absorbers at 157-nm. These preliminary calculations are performed to investigate the feasibility of extending the use of traditional mask materials to wavelengths below 193-nm. In addition, theoretical swing-curve and standing wave functions are predicted for a mask structure based on the CrOxNy/Cr material system.
Silicon Oxynitride, denoted as SiOxNy or simply as SiON, can be effective as an anti-reflective coating (ARC) in advanced integrated circuit processing typically within a 'photoresist/SiON/Si' thin film structure. However, measured values of reflectance (R) from 'SiON/Si substrate' alone cannot provide the necessary information regarding the effectiveness of SiON as an ARC layer. This is because in order to obtain an effective ARC for a given wavelength (for example at 365, 248 or 193 nm), it is necessary to reduce the standing-wave effects by minimizing the reflectance of that wavelength at the interface between the photoresist and SiON. Obviously, reflectance at this interface cannot be measured directly. R at the 'photoresist/SiON' interface must be calculated. In order to calculate R, the refractive index (n) and extinction coefficient (k) of the coating at the wavelength of interest, as well as the thickness (d) of the coating, must be known. Furthermore, n of the photoresist is also needed. However, in general, determination n and k values (especially in the DUV), as well as d, is a non-trivial problem. In this paper, we describe a new methodology, the 'n&k Method,' that simultaneously determines n and k over the 190 nm to 900 spectral range, as well as d, of all types of thin film/substrate combinations. These parameters are measured simultaneously and unambiguously, allowing rapid determination (in seconds) of the characteristics of the SiON ARC. This information can then be used to determine R at the wavelength of interest at the interface between the photoresist and SiON film.
We present a method for the rapid characterization of indium tin oxide (ITO) films. The method determines, from a simple optical measurement, the values of the refractive index (n) and extinction coefficient (k) from 190 to 1100 nm, film thickness, and energy band gap. Also we show that the spectra of the extinction coefficient can be correlated to the film's resistivity. This capability allows the determination of values for the resistivity of ITO films from a very fast and simple optical measurement.
This paper describes a methodology that has been incorporated into a fully integrated measurement system, the n&k Analyzer, that determines simultaneously the thickness, energy band gap, and n and k spectra (from 190 to 900 nm) of various forms of silicon, i.e., a-Si, poly-Si films, and mixtures of a-Si and poly-Si films. Additionally, the system also measures the average surface roughness. In turn, the n and k spectra of such films can be correlated to processing conditions, temperature being the most important one in LPCVD method. The n&k Analyzer can be used to identify the amorphous-polycrystalline transition regime and characterization of films produced in this regime.
A new technique is presented that simultaneously and unambiguously determines thickness, index of refraction, (n), and extinction coefficient, (k), as well as energy bandgap of indium tin oxide (ITO) films deposited on either transparent substrates such as quartz or opaque substrates such as silicon. The quantities n and k are determined as a function of wavelength, (lambda) , covering deep UV through near IR wavelengths (from 190 to 900 nm). These quantities can then be correlated to transparency, conductivity, etchability, patternability and manufacturability of ITO.
During processing of microelectronic devices, the silicon substrate is typically subjected to a cleaning process in order to prepare its surface for deposition of various layers of thin films. Usually the cleaning process creates a damaged surface layer, which in turn can affect the characteriscs of a deposited film. In particular, plasma cleaning characterization technique that can simultaneously and unambiguously determine the thickness and n and k spectra of the damaged surface layer is described. The technique can be used for sustaining engineering, quality control, and research and development as a means to optimize the surface characteristics of silicon wafers subjected to plasma cleaning.
A new technique that furnishes simultaneous and unambiguous determination of thickness and n(A) and k(A) spectra as well as energy bandgap, Eg , of a wide variety of semiconductor and dielectric thin films deposited on either opaque or transparent substrates will be described. The n(A) and k(A) spectra are determined over a wide range of wavelengths from deep-ultraviolet to near-infrared (190 nm ) 900 nm). Films as thin as 20 A can be measured. The technique is based on reflection/absorption spectroscopy and optical dispersion equations derived by A.R. Forouhi and I. Bloomer. Applications include, but are not limited to: a-C:H on magnetic disks and on A1TiC (with or without a thin SiNX adhesion layer), SiN:H and SiO:H deposited on Si, a-Si:H deposited on oxidized Si, ITO deposited on glass or quartz, SiO on glass, and TiO on quartz. Furthermore, the technique can be used to characterize the damaged silicon surface layer produced by plasma cleaning of bare crystalline silicon wafers.