Techniques for Fabricating Nanochannels

Several techniques for fabrication of nanochannels on both glass and silicon substrates have been investigated. The techniques investigated here include glass to glass anodic bonding with an intermediate layer of amorphous silicon, silicon to silicon anodic bonding with an intermediate layer of glass, and AuAu thermo-compression bonding of silicon wafers. In each case, the conduit’s height is dictated by the thickness of the intermediate layer. slide/coverslip using a CO2 laser. The two slides/ coverslips were aligned by hand (matching the drilled holes with the channel pattern), brought into contact, and then bonded in a “homemade” anodic bonder. The anodic bonder consists of a hotplate and a high voltage power supply connected to a stainless steel plate (anode) and pin (cathode). Good bonding occurred at a hotplate setpoint of 450°C (375°C was measured on the top, exposed glass surface) and 500V (Figure 1). Next, techniques for fabricating nanochannels between silicon wafers were explored. Initially, silicon to silicon anodic bonding with an intermediate layer of spin on glass (SOG) was attempted [2]. The key to this technique is the development of a SOG that contains alkali compounds to facilitate anodic bonding. Attempts were made to dope commercially available SOG with salts (NaCl and KCl) dissolved in various solvents (methanol, ethanol, isopropanol) to produce a glass film similar in composition to Pyrex®. Unfortunately, this process did not produce good quality films. After spin-coating the doped SOG, the resulting film was often patchy, rough and uneven, with pinholes and large particles (possibly precipitated salt) scattered across the wafer. So another process, Au-Au thermocompression bonding, was pursued [3]. For the Au-Au thermocompression bonding, Si wafers were cleaned in Nanostrip 2X followed by buffered oxide etch (BOE) and then coated with 10 nm NiCr and 100 nm Au by ebeam evaporation. Five 1 mm x 1 Figure 1: Anodic bond in progress between 1′′ x 3′′ microscope slides. Temperature of the top glass surface is ~ 375°C. Bottom plate (anode) is at 500V, pin (cathode) is grounded. The bonded area (dark region) propagates outward from the pin. The photograph is taken 20 seconds after the bonding process started beneath the pin. Summary of Research: In the first approach to nanochannel fabrication, glass to glass anodic bonding of microscope slides and coverslips was performed [1]. Amorphous silicon was deposited by e-beam evaporation onto one slide/coverslip, patterned with photoresist, and then etched with CF4 and O2 in an inductively coupled plasma reactive ion etcher (ICPRIE) to pattern channels whose depth is defined by the thickness of amorphous silicon (~100 nm for these tests). Inlet and outlet holes were drilled in a second