Rananavare Shankar B, Morakinyo Moshood K
Department of Chemistry, Portland State University;
Logic Technology Department, Intel Corporation.
J Vis Exp. 2017 Feb 12(120):54551. doi: 10.3791/54551.
Nano-patterns fabricated with extreme ultraviolet (EUV) or electron-beam (E-beam) lithography exhibit unexpected variations in size. This variation has been attributed to statistical fluctuations in the number of photons/electrons arriving at a given nano-region arising from shot-noise (SN). The SN varies inversely to the square root of a number of photons/electrons. For a fixed dosage, the SN is larger in EUV and E-beam lithographies than for traditional (193 nm) optical lithography. Bottom-up and top-down patterning approaches are combined to minimize the effects of shot noise in nano-hole patterning. Specifically, an amino-silane surfactant self-assembles on a silicon wafer that is subsequently spin-coated with a 100 nm film of a PMMA-based E-beam photoresist. Exposure to the E-beam and the subsequent development uncover the underlying surfactant film at the bottoms of the holes. Dipping the wafer in a suspension of negatively charged, citrate-capped, 20 nm gold nanoparticles (GNP) deposits one particle per hole. The exposed positively charged surfactant film in the hole electrostatically funnels the negatively charged nanoparticle to the center of an exposed hole, which permanently fixes the positional registry. Next, by heating near the glass transition temperature of the photoresist polymer, the photoresist film reflows and engulfs the nanoparticles. This process erases the holes affected by SN but leaves the deposited GNPs locked in place by strong electrostatic binding. Treatment with oxygen plasma exposes the GNPs by etching a thin layer of the photoresist. Wet-etching the exposed GNPs with a solution of I2/KI yields uniform holes located at the center of indentations patterned by E-beam lithography. The experiments presented show that the approach reduces the variation in the size of the holes caused by SN from 35% to below 10%. The method extends the patterning limits of transistor contact holes to below 20 nm.
用极紫外（EUV）光刻或电子束（E束）光刻制造的纳米图案在尺寸上呈现出意想不到的变化。这种变化归因于由散粒噪声（SN）引起的到达给定纳米区域的光子/电子数量的统计波动。散粒噪声与光子/电子数量的平方根成反比。对于固定剂量，EUV光刻和E束光刻中的散粒噪声比传统（193纳米）光学光刻中的要大。自下而上和自上而下的图案化方法相结合，以最小化纳米孔图案化中散粒噪声的影响。具体而言，氨基硅烷表面活性剂在硅晶片上自组装，随后在其上旋涂一层100纳米厚的基于聚甲基丙烯酸甲酯（PMMA）的E束光刻胶膜。用E束曝光并随后显影，会露出孔底部下面的表面活性剂膜。将晶片浸入带负电荷、柠檬酸盐包覆的20纳米金纳米颗粒（GNP）的悬浮液中，每个孔沉积一个颗粒。孔中暴露的带正电荷的表面活性剂膜通过静电作用将带负电荷的纳米颗粒引导到暴露孔的中心，从而永久固定位置配准。接下来，通过在光刻胶聚合物的玻璃化转变温度附近加热，光刻胶膜回流并吞没纳米颗粒。这个过程消除了受散粒噪声影响的孔，但留下了通过强静电结合锁定在原位的沉积GNP。用氧等离子体处理通过蚀刻一层薄光刻胶来暴露GNP。用I2/KI溶液对暴露的GNP进行湿蚀刻，会在由E束光刻图案化的压痕中心产生均匀的孔。所展示的实验表明，该方法将由散粒噪声引起的孔尺寸变化从35%降低到10%以下。该方法将晶体管接触孔的图案化极限扩展到20纳米以下。
