High-speed Processing with Reactive Cluster Ion Beams
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High-speed Processing with Reactive Cluster Ion Beams Toshio Seki1,2 and Jiro Matsuo1 Quantum Science and Engineering Center, Kyoto Univ., Gokasyo, Uji, Kyoto 611-0011, Japan 2 Osaka Science and Technology Center, Utsubo Honmachi Nishi-ku, Osaka 550-0004, Japan 1
ABSTRACT Cluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Especially, it is expected that extreme high rate sputtering can be obtained using reactive cluster ion beams. Reactive cluster ion beams, such as SF6, CF4, CHF3, and CH2F2, were generated and their cluster size distributions were measured using Time-of-Flight (TOF) method. Si substrates were irradiated with the reactive cluster ions at the acceleration energy of 5-65 keV. Each sputtering yield was increased with acceleration energy and was about 1000 times higher than that of Ar monomer ions. The sputtering yield of SF6 cluster ions was about 4600 atoms/ion at 65 keV. With this beam, 12 inches wafers can be etched 0.5 µm per minute at 1 mA of beam current. The TOF measurement showed that the size of SF6 cluster was about 550 molecules and the number of fluorine atoms in a SF6 cluster was about 3300. If the sputtered product was SiF, the yield has to be less than 3300 atoms/ion. These results indicate that the reactive cluster ions etch targets not only chemically, but also physically. This high-speed processing with reactive cluster ion beam can be applied to fabricate nano-devices. INTRODUCTION Cluster ion beam process has high potential for material processing in nano-technology, such as photonic crystal and MEMS. In order to fabricate the devices, it is needed to etch targets with high-speed, low-damage, and ultra-smooth process. A cluster is an aggregate of a few to several thousands atoms. When many atoms constituting a cluster ion bombard a local area, high-density energy deposition and multiple-collision processes are realized. Because of the unique interaction between cluster ions and surface atoms, new surface modification processes, such as surface smoothing [1-3], shallow implantation [4,5] and high rate sputtering [6], have been demonstrated using gas cluster ions. The cluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Moreover, cluster ion beam etching can smooth both bottom surface and sidewall. Especially, it is expected that the extreme high rate sputtering can be realized with using reactive cluster ion beams. Figure 1 shows a schematic diagram of the cluster ion beam irradiation system. Adiabatic expansion of a high-pressure gas through a Laval nozzle is utilized for the formation of gas cluster beams [7]. The nozzle was made from glass. The diameter of the throat of nozzle is 0.1 mm. The neutral beam intensity can be measured with an ion gauge. The pressure measured by the ion gauge on the beam line in process chamber was regarded as the neutral beam intensity. The neutral clusters were ionized by the electron bombardment metho
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