Surface-Topography Simulations of Ionized Sputter Metal Deposition
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Abstract Numerical simulations are used to predict microscopic topography of deposited metal films in ionized magnetron sputter deposition experiments. The simulation takes into account ionized and neutral fluxes as deposition material sources and re-sputtering and re-deposition of the deposited material due to the ion bombardment. The shocktracking algorithm is used to advance the moving surface boundary. Applications of this deposition technique include lining and filling of trenches, vias and dual damascene. 1
Introduction
Recent advancements in semiconductor technologies require more densely packed interconnect lines with lower resistance on computer chips. To meet this requirement, highly-conductive metal needs to be deposited into high-aspect-ratio features such as narrow but relatively deep trenches and vias. Under the state-of-the-art technologies, the aspect ratio (i.e., the ratio of depth to lateral dimension) for interconnection lines can be as high as 3. Lining and filling such features with high reliability requires non-traditional deposition technologies. Recently it has been demonstrated that the ionized magnetron sputter deposition system can achieve some of these tasks [1]. As shown in Fig. 1, the system is simple enough to fit manufacturing environments. It is a combination of the conventional magnetron sputter system and an inductively coupled plasma generator. After being sputtered from the cathode target in the magnetron region, metal atoms are ionized around the center of the chamber by the high density plasma. A high-density, metalrich plasma can be obtained in this manner since ionization energies of most metals are low. The directionality and bombardment energy of the metal ion flux on the wafer surface is then controlled by the bias voltage at the electrode. The system used in the experiments has a 2-turn radio-frequency induction (RFI) coil connected to a 13.56 MHz RF generator with maximum power 3 kW. The DC magnetron power is set 10 kW for the 200 mm target cathode and 30 kW for the 300 mm cathode. A wafer of diameter 200 mm is mounted 90 mm below the target. The bias voltage can be varied up to -200 V. Numerical simulations of film topography offer useful guidance to the experiments [2]. Key parameters for the experiments are the shape of the feature to be filled, the Ar pressure and RF power (which determine the ionization rates and angular distributions of ion and neutral fluxes), and the bias voltage (which determines the sputtering yield). Even with only these variables, there are numerous possibilities for 113 Mat. Res. Soc. Symp. Proc. Vol. 389 01995 Materials Research Society
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Fig. 1 Schematic diagram of the ionized magnetron sputter deposition system
Fig. 2 ion and neutral fluxes near the sur face
different experimental conditions. Reliable simulations thus facilita
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