论文标题:微纳压印关键技术研究
Basic Research on Key Techniques for Microimprint and Nanoimprint
论文作者
论文导师 陈迪；刘景全,论文学位 博士,论文专业 微电子学与固体电子学
论文单位 上海交通大学,点击次数 133,论文页数 146页File Size20337K
2007-12-01论文网 http://www.lw23.com/lunwen_44398022/
hot embossing;; nanoimprint lithography;; soft lithography;; focused ion beam;; PETG;; PDMS;; grating;; cell growth
传统微电子工业中所使用的紫外曝光光刻技术面临昂贵的光刻设备和复杂的技术难题,如避免光学衍射和透镜材料选择等。而微纳米压印技术只需制作一块印章就可以运用物理原理复制出许多图案化的微纳结构,具有简单易行、成本低廉、批量高效等优点。但是,现行压印技术存在诸多缺点,如制备印章需要较长时间,压印所需温度过高等。本文尝试采用加工印章的新方法对低玻璃化温度的聚合物实施低温压印和室温压印,并进行工艺优化。 压印技术具体可分为热压印、紫外压印和微接触印刷为代表的软刻蚀技术。热压印所用的印章通常为硬质材料,而紫外压印和软刻蚀可以使用柔软的PDMS印章来转移图案。目前PDMS印章制备主要是在母板上浇铸而成,需要长时间占用母板进行固化,本文开拓新的批量加工PDMS印章的方法,主要有旋涂法和热压法(MMS技术)大规模制备PDMS印章。旋涂法是在母板上旋涂而非浇铸然后固化,该技术固化时间短、复制品均匀、且与微电子工艺兼容。MMS技术先通过热压印的方法制备聚合物模板,以此作为中间媒介,旋涂或浇铸PDMS预聚体和固化剂的混合物至聚合物模板上,最后固化脱模即可以达到批量生产PDMS印章的目的。由于热压印所需时间较短,热压印一次后,母板可以继续用于热压印而不像传统方法中母板一直被占用,这样在短时间内即可压印出大量的聚合物模板,继而复制出大量的PDMS印章。 制备热压印印章通常使用效率低下的电子束逐行扫描,然后用反应离子刻蚀(RIE)进行刻蚀,本文提出采用聚焦离子束(FIB)的方法直接在衬底上刻蚀出所需的印章,且并不需要RIE过程,用该方法的另一个显著特点是可在同一块衬底上同时加工微米、纳米量级的复杂图案,结合微纳压印技术,可以达到同时复制微纳图案的目的。无论是硅基底还是金衬底,线条,曲线或者奥运、世博会徽等复杂图案,都可以得到比较均匀致密的微纳米图案印章。另外一种高效制备微纳米压印印章的方法是全息曝光结合感应耦合等离子体刻蚀(ICP)的方法。利用这种方法,成功制作了几种不同周期,不同深度的熔融石英深刻蚀光栅。 通常压印的材料PMMA、PC具有玻璃化温度高的缺点,本文尝试采用新的压印材料PETG、SU-8 2000.1、Hybrane胶等,它们的共同点是玻璃转化温度很低,可以在较低的温度下进行压印且复制精度高。不同点是PETG适用于微米压印,SU-8 2000.1和Hybrane适用于纳米压印,Hybrane还可在室温下进行压印。 从理论角度改善压印工艺:(a)根据FIB刻蚀形成U型槽的特点推导了聚合物填充印章所需的时间;(b)经过对压印过程的仔细分析,发现压印过程中起实质作用的是有效压强,可以采用梯度压力法来缓解对印章的压力损伤;(c)分子动力学模拟(MD)具有沟通宏观特性和微观结构的作用,利用MD方法,分析了含氟物质和二氧化硅衬底之间的相互作用能,发现CF2与SiO2衬底间的相互作用能较小。根据理论分析,采用RIE中CHF3和SF6进行干法抗粘,另外还采用了(1,1,2,2 H过氟辛基)-三氯硅烷湿法形成自组装分子层的方法进行湿法抗粘。实验中采用正交法来进行工艺参数的优化,分别使用不同的印章对玻璃化温度只有55℃的SU-8 2000.1和可以在室温下压印的Hybrane胶和抗RIE刻蚀能力好的mr-I 9020胶进行纳米压印研究。用SEM、AFM等进行表征,各种图案复制的精度都很高,能较精确地复制印章中的图案。 微纳米压印技术可用于批量、廉价加工聚合物光栅、柔性光栅等;还可以广泛用于生物领域,如转移蛋白图案和为细胞定向生长提供衬底。使用线宽550 nm沟槽和线条均匀组成的石英印章压印培养皿材料PS和PETG,在图案化的培养皿材料PS上生长SD大鼠成骨细胞和C6神经细胞;在图案化的PETG衬底上培养血管平滑肌细胞。这三种细胞在周期性线条图案上都沿着沟槽指定的方向拉长生长,表明压印后的微纳结构对细胞生长具有良好的导向作用。
Traditional ultraviolet lithography in microelectronics industry meets expensive lithography tool and complex technical problems, such as optic diffraction and choice of lens material. In the Next Generation Lithography, imprint technique has the advantage of high throughput because one single stamp can replicate many patterned micro/nanostructures in a low cost. However, current imprint technique has drawbacks such as long time needed to fabricate stamp and high temperature demanded to imprint. In this dissertation, novel stamp fabrication method and low Tg (glass transition temperature) polymers were studied in the imprint process with the optimized parameters. Finally, imprinted samples were taken as polymer gratings and substrates for bio experiment. Imprint technique includes three different methods: hot embossing lithography (HEL), ultraviolet nanoimpirnt lithography (UV-NIL) and soft lithography (SL). HEL usually needs a hard stamp, while UV-NIL and SL can use soft imprint stamp, which is outstanding for 3D fabrication and applications. The common feature of SL is that all of techniques need soft PDMS stamps. Conventional method of fabricating PDMS is to cast mixture of PDMS prepolymer and its curing agent directly on a master, which is time-consuming because it occupies the master a long time for curing. Two novel methods have been innovated to manufacture PDMS quickly. One technique is using spin-coating instead of casting on the master. The other is using the master to imprint many polymer molds and then spin-coating or casting PDMS mixture on the polymer molds to produce many PDMS stamps. We call the later method MMS technique (from Master via Mold to Stamp). Because imprint has a short process cycle, the master can imprint may polymer molds in a short time, and then use them to manufacture PDMS stamps. The disadvantage of current HEL technique is that long time is needed to manufacture the imprint stamp because e-beam writing is a slow technique since its low energy. New method of using Focused Ion Beam (FIB) was taken to fabricate all kinds of patterns, such as lines, curves, and emblems of Beijing 2008 Olympic Games and Shanghai 2010 World Expo on different substrates. The advantage of FIB method is that it can form pattern directly on the final substrate without RIE process needed in the common method. The other notable merit is that it can fabricate micron and nano sized patterns on one single substrate at the same time. Another fast method of fabricating imprint stamp is using holographical lithography combined with ICP etching. Using this method, we fabricated quartz gratings with different pitch and depth. The disadvantage of conventional imprint technique is that imprint temperature is high as the conventional imprint materials such as PMMA and PC have a high Tg. Novel imprint polymers PETG (polyethylene terephthalate glycol), SU-8 2000.1 and Hybrane resist were imprinted. All of them have a low Tg and can be imprinted at a lower temperature. PETG is suitable for imprint at micron sized pattern, while SU-8 2000.1 and Hybrane suitable for nanoimprint and Hybrane can be imprinted at room temperature. From theory, we calculated the filling time of polymer into FIB fabricated stamp cavities, analyzed the imprint process and found the concept of effective intensity of pressure, simulated the anti-sticking material by Molecular Dynamics (MD) method. With the help of MD, we investigated the combination energy of CF2 and SiO2 substrate, and indicated that CF2 has the effect of anti-sticking property. In experiment, we used CHF3 and SF6 in RIE machine to produce anti-sticking film on stamps because they can produce CF2. (1,1,2,2 H perfluorooctyl)-trichlorosilane is also a good choice for helping to release stamp from substrate. Orthogonal method was employed to optimize experiment parameters. SU-8 2000.1 with the Tg of which is only 55℃was used for NIL. We also imprint Hybrane resist under room temperature. Mr-I 9020 was also taken for NIL because it is a good mask material for later pattern transfer. Diverse stamps were used to imprint different polymer. SEM and AFM were taken to characterize the stamps and their replicas and the result indicates that the imprint quality is high. Imprint technique can be widely used in manufacturing plastic gratings, soft PDMS gratings, etc. It can also be used in bio experiment and applications, such as protein transfer and cell growth. We cultivated C6 glioma and SD mouse ostoblast cells on the patterned polystyrene samples and vascular smooth muscle cells on patterned PETG substrates, both with uniform grooves replicated from silica master. The results indicated that ordered groove microstructures on substrate can guide cell alignment and oriented growth along definite directions, which has a vital implication for cell biology and biosensor research.
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