E-beam-Deposited Tungsten Contacts for Carbon Nanofiber Interconnect Test Devices

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Cambridge University Press / Microscopy Society of America


As the downward scaling of integrated circuits continues, the problem of electromigration in copper interconnects becomes increasingly severe. Carbon nanofiber (CNF) can potentially be a replacement for Cu in on-chip interconnects because of its excellent thermal and electrical properties and vertically aligned growth at low temperature. To consider CNF as an on-chip interconnect, the contact resistance between the CNF and the metal electrode must be optimized. Using lithography technique to form contact between CNF and metal requires a complicated and costly device fabrication process [1]. Thus we proposed an alternative method using focused ion beam (FIB) [2]. The resulting total resistance decreased by a factor of about 1000 from that for the pre-W-deposited device [2]. However, FIB has the risk of damaging the on-chip devices because of its high beam energy, and gallium from the ion beam could result in device contamination. To address this problem, we have developed a technique for W deposition using a well-controlled electron beam in a variablepressure scanning electron microscope (VP-SEM). In this technique, the source gas is delivered via a specially designed gas injection system (GIS) [3] and guided by the focused electron beam to yield deposition on a selected target at a lower energy than FIB.