ICMCTF2003 Session F5-2: Characterization of Thin Film Growth Mechanism and Evolving Film Properties

We have used a combination of rapid in situ monitoring techniques during annealing of thin films in order to follow changes in phases, texture, resistivity and surface roughness up to 1100°C as reactions occur. The characterization apparatus combines time-resolved x-ray diffraction, elastic light scattering and resistivity measurements. To attain acceptable diffracted x-ray intensities during annealing of very thin films at rapid rates (RTA), the experiments are performed at the National Synchrotron Light Source (NSLS) X20C beamline at Brookhaven National Laboratory (NY, USA) where an x-ray flux greater than 10¹³ photons/s can be achieved. This corresponds to a gain of four orders of magnitude over a state of the art rotating anode XRD system and allows to follow in situ the formation of different phases via the development of their characteristic diffraction patterns. Indeed, the combination of the high x-ray photon flux with a linear position-sensitive detector allows for a diffraction spectrum (14° in 2θ) from a 10 nm metal film to be acquired in less than 100 ms. The experimental apparatus is designed so that one can simultaneously monitor both the resistance of the film and the evolution of the surface conditions via the elastic scattering of monochromatic light. The resistance is measured using a square four point probe geometry while the measurements of roughness are made using HeNe laser light coupled in and out of the annealing chamber with fiber optics. The detection geometry (two detectors) provides information on two lateral length scales of about 0.5 µm and 5 µm. The detection of low intensity scattered light during high temperature anneals requires optical filtering and lock-in detection in order to eliminate intense black body radiation from the sample.

Using these combined techniques, we have studied various thin film reactions for materials relevant to state-of-the-art microelectronic devices. In this talk we will show various examples of materials optimization in microelectronics. We will present results on the advantages and limitations of nickel silicide over the current cobalt silicide used for contacting CMOS devices^1,2. We will also cover examples of diffusion barrier stability and test and selection of metal gate materials³. Finally, we recently showed that the characterization system can also be used efficiently with solder materials when reaction occurs with liquid metals. The dependence of the rate of intermetallic compound formation on solder composition and under layer metallurgy was measured for some lead free system. We find that this technique is not only sensitive to the formation of intermetallics but also to the undesirable spalling of intermetallics from the interface into the melted solder.

¹ C. Lavoie, et al., Effects of alloying elements on cobalt silicide formation, J. Electron. Mater. 31, 597-609 (2002).

² C. Lavoie, et al., Exploring Thin Film Reactions by means of Simultaneous X-Ray, Surface Roughness and Resistance Measurements, Defect and Diffusion Forum 194-199, 1477 (2001).

³3 C.Cabral, Jr., et al., The use of in situ x-ray diffraction, optical scattering and resistance analysis techniques for evaluation of copper diffusion barriers in blanket and damascene structures, Thin Solid Films 397, 194 (2001).

The deposition techniques of dc magnetron sputtering and ion-assisted evaporation were examined with the goal of depositing Iridium (Ir) thin films with surface roughness less than 1 nm RMS and density greater than 90% of bulk Ir density for use in an x-ray microscope. Process parameters were optimized for both deposition methods to minimize the surface roughness of the deposited Ir. In all cases, surface roughness was measured using atomic force microscopy. The optimized sputtering process produced the highest quality Ir film, achieving a surface roughness of 0.44 nm RMS and near-bulk film density. Bombardment by energetic particles during the deposition process causes film densification in the Ir film as it is being deposited, and mitigates the columnar growth structure typical of Ir films. Since sputtering is typically a more highly energetic process than ion-assisted evaporation, sputtering is more efficient at producing an Ir film that is more highly dense with lower surface roughness.

The optimized sputtering process was used to deposit Ir on a set of super-polished Zerodur® mirrors for use in a high resolution Kirkpatrick-Baez x-ray microscope. This microsope is currently used on the OMEGA UV laser system at the Laboratory for Laser Energetics for x-ray radiography of inertial confinement fusion (ICF) targets. The near-bulk density of the deposited Ir film and the smooth Ir surface have resulted in a high-throughput, low-scattering optic which produces images with high signal to noise ratio.

¹This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this article.

1-Methoxy-8-hydroxy-9,10-anthraquinone compound has been synthesized and it is thermally evaporated onto the well cleaned glass and KBr substrates kept at different temperatures in a vacuum of 1.3 x 10 ^-3 Pa. These films are characterized by nuclear magnetic resonance (NMR), optical absorption (IR, visible, near-UV) spectroscopy, X-ray diffraction and scanning electron microscopy. In addition, the electrical properties of the films are determined in the temperature range 290-340 K.

The IR and NMR studies confirmed the formation of 1-methoxy-8-hydroxy-9,10-anthraquinone films. Observations reveal the amorphous behaviour of films deposited below 318K, whereas films deposited at higher temperature show increase in crystallinity. The optical absorption studies indicate that direct interband transition energies lies in the range 1.8-1.99 eV. The current-voltage characteristics of these films show ohmic behaviour of conduction within the investigated field and temperature range (10-60V, 290-340 K). The conduction appears to take place by thermally activated hopping mechanism. The electrical conductivity, carrier concentration and drift mobility of the films increases with increase in substrate temperature, whereas the extinction coefficient and refractive index decreases.