We depict the microfabrication process in Fig. 2. First, a chromium layer of 30 nm is sputtered onto a single-crystal quartz substrate (X-cut), previously cleaned with a Piranha solution. Second, we spin-coat a thin layer of AZ 701 MIR photoresist (Merck Performance Materials GmbH) at 4000 rpm for 30 s, followed by soft baking at 95°C for 1 min. The photoresist is diluted (2∶1) to achieve a final thickness of 600 nm. The quartz sample is then exposed on the LIL setup, prepared for a fixed interference period (typically ). Exposure is made in two steps of 130 s each, rotating the sample by 90 deg in the interference plane. After exposure, the sample is postbaked at 110°C for 1 min and developed with AZ 726 developer for 17 s under smooth agitation. Figures 3(a) and 3(b) show two SEM images of lines and dots arrays obtained after development. The next step consists in transferring the photoresist pattern onto the quartz substrate. To achieve the high anisotropy required by the cylindrical geometry, we use inductive coupled plasma reactive ion etching (ICP-RIE). To improve the selectivity of the technique (which is low especially when using photoresists), the key is to use a hard mask, as a chromium layer, and a two-step ICP-RIE process, as described below. Hard masks are often used in plasma etching, in particular to prevent photoresist shrinking,19 and the materials employed include Ni, Al, or ZnO. Abe and Esashi20 reported the etching of deep quartz trenches by using a Ni metal mask with , , and RIE gas plasma. Also, a SU8 thick photoresist has been used as a hard mask for quartz etching.21 In our case, we find that the submicron dimensions of the quartz cylinders require a thin (30 nm) hard mask layer. Following LIL patterning, the chromium layer is etched with an Ar plasma in the absence of oxygen, using a Corial 250D ICP RIE (200 W RF and 400 W LF). The absence of oxygen prevents the photoresist from shrinking during etching, allowing the unprotected hard mask to be completely removed in 6 min with sufficient selectivity. Etching of quartz is achieved by a second ICP-RIE process, using a mixture of (200 sccm) and (100 sccm), an internal pressure of 1.2 mTorr, and incoming power of 200 W RF and 800 W LF. In these conditions, the etching rate of quartz is about .