Fabrication of 20 nm deep silicon dioxide channel using electron beam lithography for manipulation of DNA molecules

摘要

Recent advances in micro and nano-scale fabrication technologies have allowed the fabrication of fluidic channels with a characteristic dimension on the order of tens of nanometers [1, 2]. This nano-scale channel is used for DNA mapping [3–7] and separation [8–13] and single biomolecule manipulation. The depth and anisotropically of these nano-channel play an important role in device performance. So, many efforts are performed to fabricate the channels with various techniques. In this paper, silicon dioxide (SiO2) nano-channel for DNA molecule manipulation are proposed and fabricated. The fabrication processes of this dielectric SiO2 nano-channel are including the combination of wet anisotropic etching, Electron Beam Lithography (EBL) and plasma etching (RIE). At first, Si was cleaned in a wet chemical etch process (standard cleaning processes), using RCA cleaning method. This is followed with thermal oxidation to achieve SiO2 with desired thickness. The rectangle reservoirs was patterned by photolithography technique. The reservoirs on SiO2 were created with wet etching (HF; H2O, 2:50), as can be seen in figure 1. For making nano-channel electron beam lithography(EBL) was used. In order to get channel, an electron-beam writer has been used to drill channel on a 300-nm thick poly methyl methacrylate (PMMA) layer coated on SiO2/Si substrate. After the PMMA development, the remaining PMMA on the silicon substrate serves as mask for the RIE process. In this process, RIE facility (Oxford Instruments, PlasmaLab 80 Plus) has been utilized in order to fabricate the SiO2 nano-scale of etch depth 20 nm. The process parameters are: CHF3 flow rate of 25 sccm, Ar flow rate of 25 sccm, process pressure of 10 mTorr, and incident rf power of 150 W. Figure 1 shows the reservoirs which have been created by photolithography and wet etching on SiO2 Surface. The dimension-nof the reservoir is about 3mm×3mm. Figure 2 is the SEM image of nano-channel that has been fabricated between reservoirs. The channel length and width are 1.5 mm and 1.3 μm, respectively. AFM in figure 3 shows the depth of SiO2 etched channel is about 20 nm which is sufficient for Lambda DNA stretching. Figure 3 (b) shows the etched profile of nano-channel, which displays that it is almost anisotropic. The fabrication processes of nano-channel are shown in figure 4. In conclusion, we have shown a fabrication processes of nano-channel between two reservoirs. It was demonstrated that by combination of various etching and lithography techniques could achieve 1.5 mm length and 20 nm deep dielectric channel which is appropriate for biology applications. It is suggested that the fabricated nano-channel dimension is suitable for stretching of Lambda DNA, since it''s depth should not be larger than twice the radius of gyration (700 nm) DNA.