Int J Adv Manuf Technol (2009) 41:727–733 DOI 10.1007/s00170-008-1515-4
ORIGINAL ARTICLE
Applying the one-column, many pencil local scanning maskless lithography technology to micro-RP system Jia-Chang Wang & Ming-Zhe Hsieh
Received: 2 August 2007 / Accepted: 2 April 2008 / Published online: 7 May 2008 # Springer-Verlag London Limited 2008
Abstract This paper introduces an innovative one column, many pencil local scanning maskless lithography technology used in dynamic mask and applies it to rapid prototyping (RP) system. By using this technology in micro RP system, the resolution of the 3-D microstructures can be upgraded remarkably. In addition, some relevant experiments are conducted on this micro rapid prototyping system. In the experiment, light beam is projected onto a digital mirror device (DMD) chip [Hornbeck LJ. Digital light processing: A new MEMS-based display, 4th Sensor Symp, p. 297–304 (1996)], and the image is reflected through a micro mirror. Meanwhile, by making use of zoom lens and pins array mask (PAM), the continuing pixels can be scattered. Moreover, in order to project scattered pixels onto the resin surface, the optical system is exploited. Additionally, by using a micro-stage, it is able to control the micro X-Y movement between the scattered pixels. Furthermore, this paper makes use of the spray coating technology to improve the build up capability of the overhand structures of the traditional deep dip liquid-type RP system. Finally, combining the fore-mentioned technologies, one can produce 3-D prototypes with overhand structures in higher resolution. Keywords Maskless lithography . Rapid prototyping . Spray coating
J.-C. Wang (*) : M.-Z. Hsieh Mechanical Engineering, National Taipei University of Technology, Chung Hsiao E. Rd., Taipei 106, Taiwan, Republic of China e-mail:
[email protected]
1 Introduction Nowadays, many of the liquid-type RP systems are starting to utilize maskless photolithography. This is mainly because the function of RP technology is to produce 3D prototypes but not to massively reproduce the same product. A complicated prototype is usually produced by layer manufacturing, which means hundreds of layers are piled up to form a prototype. It is certainly inefficient and expensive to make one prototype for one time with real mask technology; however, using a micro RP system with a laser scanning method is even less economical. Besides, when scanning a complicated shape, it is also more timeconsuming than dynamic mask photolithography. As to the dynamic mask photolithography in micro RP, it mostly adopts a liquid crystal display (LCD) or digital mirror device (DMD) [2, 3]. However, it is restricted by the limited resolution of LCD or DMD, because the pixel size produced by DMD or LCD will affect the resolution of the dynamic image. As a result, resolution causes a big problem for dynamic mask. Pease classified maskless lithography technology into four types, with the main function of each type being to speed up the process of scanning [4]. As shown in Fig. 1: (a) One column, one pencil: the single light beam focuses on one point, use this point as a unit to scan (b) One column, many pencils in one or more bundles: the single light beam is distributed into many points onto a surface, use the surface as a unit to scan (c) Many column, one or more pencils each—uses many surfaces as a unit to scan (d) Uniform focus field, many axes one or more pencil each—many surfaces form a field, using this field as a unit to scan
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Int J Adv Manuf Technol (2009) 41:727–733
damage the process of layer manufacturing. Therefore, the micro RP system usually adopts a deep dip which exploits the up and down movement of the Z-axis stage to fill the layer surface with liquid material. However, this process would damage the microstructures of the prototype owing to the force incurred through the input and output process of the liquid. The study can upgrade the resolution of the image produced by the dynamic mask machine. Moreover, the spray coating technology proposed in this paper makes use of pressure to transform liquid material into mist which is further coated onto the layer surface. As a result, the influences caused by the flow of resin can now be reduced to the minimum. Therefore, when manufacturing an overhand prototype, this method can achieve more success than the Deep Dip method.
2 Alpha micro-RP system build up 2.1 The optical design of the one column, many pencil local scanning maskless lithography Fig. 1 Classification of maskless lithography technology
The conventional dynamic mask photolithography is restricted by limited resolution. Thus, there are research studies on the promotion of resolution. such as “Massively parallel, large-area maskless lithography” and “Alphaprototype system for zone-plate-array lithography” [5]. However, the methods adopted to upgrade resolution are to combine surfaces one by one, and the distance between the surfaces should not exceed 0.5 pixel in order to have a proper stitch between surfaces. This would cause a relatively long-distance movement of the X-Y stage. Therefore, the methods could lead to error, which is surely undesirable. The traditional dynamic mask photolithography in micro RP system belongs to Type (b) one column, many pencils in one or more bundles category. The 2D resolution of the product produced by micro RP system depends on the resolution of the dynamic mask machine. This paper adopts a new method called one column, many pencil local scanning, a method modified from Type (b). It is capable of scattering pixels of an image, and further using the scattered pixels as pencils to scan, which could result in the great improvement of the resolution of the dynamic mask machine. In general, the liquid-type RP system utilizes deep dip [5] and recoator [6] to achieve layer manufacture. Using a scraper could lead to deformations or the destruction of the part being manufactured. Moreover, the scraper will accumulate a huge mass of residues over a long period of time. Thus, when using a scraper, the residues would lead to damage of the prototype. As to the micro RP system, using the recoator is nearly forbidden. It is because that the layer thickness is thinner than 15 um and the shear force would
This paper develops a new system which uses the dynamic mask machine to manufacture prototypes. The resolution of the dynamic mask machine will directly influence the quality of the prototypes. Therefore, it is important to upgrade the resolution of the machine. In this study, a DMD chip is used in the dynamic mask machine. The image projected by the DMD chip can be drawn out through the relay lens. Afterward, the telecentric lens will be used to magnify the image with low distortion and minimum lateral projection. Subsequently, the magnified image will be projected on and fully covers the pins array mask (PAM). By matching each magnified pixel with each micro exit pupil, the pixels can be scattered by PAM. As shown in Fig. 2, the design of PAM is 2×2. The length and width of
Fig. 2 The design and the printed 2×2 pins array mask (PAM)
