| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Friday Sessions |
| Session PS2-FrM |
| Session: | Plasma Surface Interactions II |
| Presenter: | Faraz Choudhury, University of Wisconsin-Madison |
| Authors: | F.A. Choudhury, University of Wisconsin-Madison G. Sabat, University of Wisconsin-Madison Y. Nishi, Stanford University J.L. Shohet, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
During plasma processing, low-k dielectrics are exposed to free radicals from the plasma that may adversely affect the chemical, mechanical and electrical properties of the films. Modern low-k dielectrics have highly porous structures (up to 50%) and interconnected pores provide pathways for reactive species to enter into the material making them more susceptible to damage. Previous work utilized simulations1 to determine the free-radical density and doses from the processing plasma. Several techniques have been developed and tested over the years for radical measurements2, but the methods do not provide a direct measurement of the free radical concentrations at the location of the sample during processing. A new technique, using fluorophore dyes, can detect free radicals in a processing plasma and determine the their fluence at the surface of a sample during processing is investigated. The fluorophore used in this work is Alexa Fluor® 488. After reaction with reactive oxygen species (ROS), the bright green fluorescence (excitation/emission maxima ~490/515 nm) of the dye is significantly degraded. This degradation is measured using a fluorometer. The change in intensity of the fluorescence can be used to measure the free radical fluence from the plasma. This technique can also be used to determine the number of free radicals that can penetrate through a layer of low-k dielectric film as follows. Alexa 488 is placed under free-standing dielectric films such as SiO2 and SiCOH of various thicknesses to determine the penetration depth of free radicals that are present in a typical processing plasma. Fluorescent dyes that selectively react with specific types of free radicals can also be used. In particular, we will use hydroxyphenyl fluorescein (HPF) that is a hydroxyl (OH) radical sensor. The change in fluorescence of this dye after plasma exposure can be used to determine the OH radical fluence from the plasma. I-V, C-V and TDDB measurements can also be made as a function of plasma exposure time to determine the extent of damage to the electrical properties of the films.
This work has been supported by the Semiconductor Research Corporation under Contract No. 2012-KJ-2359 and the National Science Foundation under Grant No. CBET-1066231.
1 Shi, H. and Huang, H., Bao, J., Liu, J., Ho, P. S., Zhou, Y., Pender, J.T., Armacost, M. D. and Kyser, D., Journal of Vacuum Science & TechnologyB, 30, 011206 (2012)
2 Moon, C.S., Takeda, K., Takashima, S., Sekine, M., Setsuhara, Y., Shiratani, M., and Hori, M., Journal of Applied Physics, 107, 103310 (2010)