Fabrication sub-10nm metallic grating template by carbon nanotube – A molecular dynamics simulation study

Since the advent of the carbon nanotube in 1991 [1], CNT has drawn lots of attentions due to its superior mechanical, electrical, and chemical properties. In terms of mechanical properties, CNTs have high tensile strength, high thermal conductivity and low thermal expansion coefficient. In addition, CNTs are also very elastically flexible. The properties mentioned above indicate that CNT could possibly be a good cutting tool in microscale precision machining. In the present work, a novel concept of microscale manufacturing process is proposed in fabricating sub-10nm wire gratings and a full scale three-dimension molecular dynamics (MD) simulation is utilized to demonstrate its feasibility. The procedures start with growing CNTs with equal and tunable distance in between; followed by coating a desired metal in between the gaps of CNTs While the ends on the same side of CNTs are pulled in the z direction, CNTs will precede the cutting process to form the patterns of wire gratings. Figure 1 shows the physical model includes the metallic film with the dimension of 24.7nm x 12.2 nm x 10.2nm and two open-ended, zigzag type CNTs with the diameter of 1.5nm and 20.4 nm in height. The distance between two CNTs is 10.5nm and both of CNTs are inlayed in the metallic film with the depth of 5.68nm. The initial positions of the gold atoms are arranged in face centered cubic (fcc) lattice crystal structure and the CNTs are inlaid in the metallic film. The bottom layer of gold film and the left ends of the CNTs, colored as blue, are assumed to be rigid, while the left ends of the CNTs, colored as orange, are the atoms to be steered in the z direction for the cutting process. Figure 2 is the snap shot of material removal process, showing the post process of the gratings and the distribution of removal chips in the space. The comparison between the beginning and final stage of the metallic film is also shown in Figure 3. The surface effect causes the shrinkage of the gratings corners and the fillet shape is also observed. Pile-ups phenomena appear and this make the grating height are taller than the prediction. The spaces between gratings are dependent of tunable diameters of CNTs and can be varied prior to the designed structures or applications. Figure 4 shows the cross section of the formation structure. The desired average width of center grating is shown to be 6.85nm and is proven to be achievable. Furthermore, the crystal structure circled by red line is still defect free which indicates few stresses penetrating and causing less damage in the region beneath the CNTs after the material removing process. When the CNTs are pulled in the z direction, the exerted forces on the orange atoms are monitored. In this case, the steering velocity is controlled to be 5 Å /fs. Figure 5 shows the relationship between exerted force and time required. During the grating process, the force applied on the CNTs is calculated to be 8.75x10 pN and is quite small compared to other current manufacturing process. In this study, a novel manufacturing process of gratings is proposed and investigated using a full scale MD simulation. The objective is to produce the sub-10nm grating templates. The dimension of the grating templates has been demonstrated to be smaller than 10nm. This indicates that the innovative concept is highly feasible. In addition, the machining force is small during the manufacturing process and few stresses and damages are generated beneath the structures were proved. This can be beneficial for prolonging the life cycle of machines and bringing the cost down in the long term. References: [1] S. Iijima, Nature, 354 (1991) 56-58 Figure 1. Physical model of simulation. Figure 2. Final configuration. Figure 3. Comparison between original and final (hide CNTs and chips) structural profile. Figure 4. Cross section dimensions grating. Figure 5. Force to time diagram