Dale Laird Hetherington

Interests

Teaching

Electronic circuits, embedded microcontrollers, solid-state devices, semiconductor processing and statistical process control.

Courses

Scholarly Contributions

Journals/Publications

• Sorooshian, J., Philipossian, A., Stein, D. J., Timon, R. P., & Hetherington, D. L. (2005). Dependence of Oxide Pattern Density Variation on Motor Current Endpoint Detection during Shallow Trench Isolation Chemical Mechanical Planarization. Japanese Journal of Applied Physics, 44(3), 1219-1224. doi:10.1143/jjap.44.1219
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  In this study, we evaluate the limitations associated with variable shallow trench isolation (STI) oxide pattern densities for accurate motor current endpoint detection during chemical mechanical planarization (CMP). Results indicate that repeatable motor current endpoint detection can be achieved for STI wafers with oxide pattern density variations of up to 17.4%. Furthermore, results show that a dependence exists between the STI oxide pattern density variation and motor current endpoint success during polishing. According to the findings of this study, a suitable motor current endpoint detection system could yield successful termination points for STI polishing, as well as reduce the need for polishing reworks.
• Shadman, F., Philipossian, A., Hetherington, D. L., Sorooshian, J., Shadman, F., Philipossian, A., Li, Z., Denardis, D., Charns, L., & Boning, D. S. (2004). Arrhenius Characterization of ILD and Copper CMP Processes. Journal of The Electrochemical Society, 151(2), G85. doi:10.1149/1.1635388
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  To date, chemical mechanical planarization (CMP) models have relied heavily on parameters such as pressure, velocity, slurry, and pad properties to describe material removal rates. One key parameter, temperature, which can impact both the mechanical and chemical facets of the CMP process, is often neglected. Using a modified definition of the generalized Preston's equation with the inclusion of an Arrhenius relationship, thermally controlled polishing experiments are shown to quantify the contribution of temperature to the relative magnitude of the thermally dependent and thermally independent aspects of copper and interlayer dielectric (ILD) CMP. The newly defined Preston's equation includes a modified definition of the activation energy parameter contained in the Arrhenius portion, the combined activation energy, which describes all events (chemical or mechanical) that are impacted by temperature during CMP. Studies indicate that for every consumable set combination (i.e., slurry and polishing pad) a characteristic combined Arrhenius activation energy can be calculated for each substrate material being polished.
• Stein, D. J., Cecchi, J. L., & Hetherington, D. L. (1999). Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms. Journal of Materials Research, 14(9), 3695-3706. doi:10.1557/jmr.1999.0499
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  We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO3 concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO3 concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP.
• Fleming, J. G., Hetherington, D. L., Smith, B. K., Biswas, R., Sigalas, M. M., Zubrzycki, W., Kurtz, S. R., Bur, J., Lin, S. Y., & Ho, K. M. (1998). A three-dimensional photonic crystal operating at infrared wavelengths. Nature, 394(6690), 251-253. doi:10.1038/28343
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  The ability to confine and control light in three dimensions would have important implications for quantum optics and quantum-optical devices: the modification of black-body radiation, the localization of light to a fraction of a cubic wavelength, and thus the realization of single-mode light-emitting diodes, are but a few examples1,2,3. Photonic crystals — the optical analogues of electronic crystal — provide a means for achieving these goals. Combinations of metallic and dielectric materials can be used to obtain the required three-dimensional periodic variations in dielectric constant, but dissipation due to free carrier absorption will limit application of such structures at the technologically useful infrared wavelengths4. On the other hand, three-dimensional photonic crystals fabricated in low-loss gallium arsenide show only a weak ‘stop band’ (that is, range of frequencies at which propagation of light is forbidden) at the wavelengths of interest5. Here we report the construction of a three-dimensional infrared photonic crystal on a silicon wafer using relatively standard microelectronics fabrication technology. Our crystal shows a large stop band (10–14.5 μm), strong attenuation of light within this band (∼12 dB per unit cell) and a spectral response uniform to better than 1 per cent over the area of the 6-inch wafer.

Proceedings Publications

• Hetherington, D. L., Stein, D. J., Lauffer, J. P., Wyckoff, E. E., & Shingledecker, D. M. (1999). Analysis of in-situ vibration monitoring for end-point detection of CMP planarization processes. In SPIE Proceedings, 3743, 89-101.
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  This paper details the analysis of vibration monitoring for end-point control in oxide CMP processes. Two piezoelectric accelerometers were integrated onto the backside of a stainless steel polishing steel polishing head of an IPEC 472 polisher. One sensor was placed perpendicular to the carrier plate and the other parallel to the plate. Wafers patterned with metal and coated with oxide material were polished at different speeds and pressures. Our results show that it is possible to sense a change in the vibration signal over time during planarization of oxide material on patterned wafers. The horizontal accelerometer showed more sensitivity to change in vibration amplitude compared to the vertical accelerator for a given polish condition. At low carrier and platen rotation rates, the change in vibration signal over time at fixed frequencies decreased approximately 1/2 to 1 order of magnitude. At high rotation speeds, the vibration signal remained essentially constant indicating that other factors dominated the vibration signal. These results show that while it is possible to sense changes in acceleration during polishing, more robust hardware and signal processing algorithms are required to ensure its use over a wide range of process conditions.
• Fleming, J. G., Hetherington, D. L., Smith, B. K., Biswas, R., Ho, K. M., Sigalas, M. M., Zubrzycki, W. J., & Lin, S. Y. (1998). A three-dimensional silicon photonic crystal. In Conference Proceedings. LEOS'98. 11th Annual Meeting. IEEE Lasers and Electro-Optics Society 1998 Annual Meeting (Cat. No.98CH36243), 1, 295-296.
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  We report the realization of an infrared 3D photonic crystal built directly on a Si-wafer. Our 3D crystal shows a large photonic stop band from 10 to 14.5 /spl mu/m along the crystallographic direction, a strong attenuation constant of -12 dB per unit cell, and a spectral response uniformity to better than 1% over a 6 inch Si wafer. This demonstration opens the door for Si-based photonic crystal devices that are compatible with the well-developed Si microelectronics processes and is suitable for large scale photonic integration.
• Lin, S., Wendt, J. R., Vawter, G. A., Fleming, J. G., Hetherington, D. L., Smith, B. K., Zubrzycki, W. J., Chow, E. K., Kurtz, S. R., Hammons, B. E., Villeneuve, P. R., Joannopoulos, J. D., Biswas, R., Ho, K. M., & Sigalas, M. M. (1998). Applications of photonic crystals in optoelectronics. In SPIE Proceedings, 3419, 268-272.
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  In this paper, I describe realistic applications of photonic band gap (PBG) materials in optoelectronics at the mm-wave, IR and optical wavelength regimes. Examples are highly dispersive PBG-prisms and PBG-lasers. I will also describe our recent breakthrough at Sandia in the successful fabrication of 3D silicon photonic crystal operating at IR wavelengths.