Fabrication of micro DOE using micro tools shaped with focud ion beam
Z. W. Xu,1,2 F. Z. Fang,1,2* S. J. Zhang,1 X. D. Zhang,1,2 X. T. Hu,1 Y. Q. Fu,3 L. Li 4
1 State Key Laboratory of Precision Measuring Technology & Instruments
Centre of MicroNano Manufacturing Technology, Tianjin University, 300072, China,
2 Tianjin MicroNano Manufacturing Tech. Co., Ltd, TEDA, 300457, China
3 School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu, China
4 School of Mechanical, Aerospace and Civil Engineering, University of Manchester, UK
*
Abstract: A novel method is propod to fabricate micro Diffractive
Optical Elements (DOE) using micro cutting tools shaped with focud ion
beam (FIB) milling. Micro tools with nanometric cutting edges and
complicated shapes are fabricated by controlling the tool facet’s orientation
relative to the FIB. The tool edge radius of less than 30 nm is achieved for
the nano removal of the work materials. Semi-circular micro tools and
DOE-shaped micro tools are developed to fabricate micro-DOE and
sinusoidal modulation templates. Experiments show that the propod
method can be a high efficient way in fabricating micro-DOE with
nanoscale surface finishes.
© 2010 Optical Society of America
OCIS codes:(050.1970) Diffractive optics; (220.1920) Diamond machining; (230.4000)
体罚故事
Microstructure fabrication
References and links
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苯酚
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Express 16(10), 7323–7329 (2008).我是狗
1. Introduction
Micro optical elements (MOE) are key components for building compact optoelectronic systems. Micro Diffractive Optical Elements (MDOE) have shown many unique advantages, such as small volume and weight, good optical quality and large apertures. With the trend of device miniaturization, there is increasing demand for MDOE for applications in solar condenr lens, infrared nsors, lar beam shaping, and high-performance optical imaging systems.
#124107 - $15.00 USD Received 11 Feb 2010; revid 26 Mar 2010; accepted 26 Mar 2010; published 31 Mar 2010 (C) 2010 OSA12 April 2010 / Vol. 18, No. 8 / OPTICS EXPRESS 8025
Fig. 1. Shadowing effect comparison in MDOE fabrication with spherical and hemi-spherical
tools. (a) Traditional shape tool, (b) Micro hemi-spherical tool.
There are veral methods for fabricating micro optical elements, such as, Binary Optics Fabrication method [1], Direct Writing method using a lar or a focud ion beam [2,3], Single-point Diamond Turning (SPDT) technology [4], etc. The lithography method needs multi-step process with high cost, while the beam direct writing method shows lower fabrication efficiency. SPDT is considered as one of the most appropriate processing methods for various types of Micro Optical Elements. It can precily control the fabrication process with a high machining accuracy, and it is much suitable for processing complex micro diffractive optical elements.
However, with the optical elements miniaturization, the development of the micro tools with non-traditional shape and sharp edges ud in SPDT is becoming a very important topic in the MOE fabrication. Due to the size and configuration limitations of traditional cutting tools in SPDT, some areas with a high aspect ratio in the MDOE cannot be machined, as shown in Fig. 1(a). This will cau the shadowing effect, which will directly degrade the optical properties of the device and reduce its diffraction efficiency [5]. While this problem can be overcome by using a micro hemi-spherical tool, as shown in Fig. 1(b), the sharp cutting in the MOE demands non-traditional shape micro machining tool fabrication, which is a key topic in the micro fabrication rearch.
Micro tool processing methods mainly include precision mechanical grinding [6], micro electro discha
蚕豆的生长过程
rge machining (µEDM) [7], etc. In recent years, focud ion beam (FIB) milling has also been applied in the micro tool’s fabrication [8,9]. It can achieve high-precision material removal and geometry accuracy using high energy focud ion beam bombardment.
In this paper, micro diffractive optical elements were fabricated by using micro tools with non-traditional geometry, fabricated with a focud ion beam. The key fabrication techniques for the development of the complex shape micro tools and MDOE were investigated in detail. 2 Experimental tups
The experiments for micro tools fabrication were performed under a FIB/SEM dual beam system equipped with a high resolution rotational equipment. The FIB system us a focud Gallium ion beam working under an accelerating voltage ranging from 5 to 30 kV, and a probe current ranging from 1 pA to 20 nA. The translation stage can be tilted within 15°~60°. Tool rotation is controlled by a rotational axis that can rotate unlimitedly with a minimum step size of 10−7 rad per pul. Different tool faces can be milled by accurately adjusting their relative positions to the FIB by the rotation and sample tilt control. Tool blanks with end diameters of around 30~100 µm were ud here by a precision lapping method.
3 Results and discussions
3.1 Micro tool fabrication
During the process of the micro tool fabrication by the FIB milling, the FIB milling quence and tool position relative to ion beam are critical factors in determining micro tool characteristics, such as cutting edges, rake face, and relief angle. The FIB would produce t R
θ
(a) R x h (b)
做梦梦见剪头发#124107 - $15.00 USD Received 11 Feb 2010; revid 26 Mar 2010; accepted 26 Mar 2010; published 31 Mar 2010
(C) 2010 OSA 12 April 2010 / Vol. 18, No. 8 / OPTICS EXPRESS 8026
sharp edges on the side of facets furthest from the ion source, while the facet edge clost to the ion source is rounded becau the part of the Gaussian beam intensity would extend outside the de fined pattern boundary, as shown in Fig. 2.
Fig. 2. Illustration of micro tool sharp edge formation.
Fig. 3. Micro tools machining using FIB.
Fig. 4. SEM images of the FIB fabricated arc-shaped micro tool. (a) Spherical micro tool, (b)
hemi-spherical micro tool.
Therefore, in order to produce sharp cutting edges, tool position with respect to the ion beam and the fabrication quences are crucial.
Bad on the sharp edge generation analysis above, only three steps were propod here to fabricate micro tool with sharp cutting edges by the FIB method. Figure 3 illustrates the fabrication procedure for an arc-shaped micro tool. The dark parts in the figure reprent the removal regions by the FIB milling. Firstly, a smooth rake face is created on one side of the tool by the FIB milling in Fig. 3(a). Secondly, the tool is rotated clockwi with its rake face away from the ion source. The two side faces of the micro tool are then created by FIB milling, respectively. Thirdly, a desired cross-ctional shape is milled by the FIB
bitmap
(b)
(a) (d)
论文下载(c) Round edge
Round edge Tool blank
Tool face Tool face Sharp edge
FIB
Sharp edge #124107 - $15.00 USD Received 11 Feb 2010; revid 26 Mar 2010; accepted 26 Mar 2010; published 31 Mar 2010
(C) 2010 OSA 12 April 2010 / Vol. 18, No. 8 / OPTICS EXPRESS 8027避孕套如何正确使用
patterning method [3], as shown in Fig. 3(c). In the bitmap patterning method, the FIB milling time at a location can be accurately controlled by the color value of the bitmap predefined. By controlling the sample stage tilt angle and the tool rotation, a proper relief angle can be achieved by adjusting the FIB incidence angle with respect to the surface normal. Finally, an arc micro tool with sharp cutting edges is obtained, as shown in Fig. 3(d). The SEM image of the arc micro tool fabricated is shown in Fig. 4.
In the FIB milling process, a large ion beam current can be lected first to mill the micro tool’s outline configuration to increa the process’s efficiency. Then a small ion beam current can be chon to create the final smooth tool face. The ion beam current ud in the area of A and B in Fig.
4(a) is 1 nA and 20 nA, respectively. In addition, precily controlling the beams’ overlapping is also very important to obtain a smooth micro tool face, which can be accurately controlled in the bitmap patterning method. The major advantages of the FIB bad micro tool fabrication method include the better geometry control of micro tools with sharp edge without the introduction of any machining stress comparing with ordinary precision grinding method.
The FIB-shaped micro tools’ edge radius has been measured by Atomic Force Microscope (AFM), as shown in Fig. 5. The scanning probe is sharpened by FIB milling before the tool’s edge radius measurement. By considering the AFM probe’s broadening effect from the AFM results, the developed micro tools’ edge radius is can be approximately 25nm.
Fig. 5. Results of the micro tool edge radius measured by AFM. (a) Sharpening AFM tip, (b)
Edge result of micro tool.
Comparing with the ordinary SEM cross-ction obrvation method [7,8], the AFM measurement method can show the three-dimensional morphology of the Micro tool edges without tool destruction.
3.2 Sinusoidal modulation template developed
A sinusoidal modulation template has been machined by an arc-shaped micro tool fabricated using single-point diamond turning. The arc-shaped micro tool is made from a single crystal diamond, as shown in Fig. 4(a). The micro tool’s no radius is 10 µm, with 0 ° rake angle and 12.4 ° relief angle.
For the micro optical elements’ fabrication using the micro tool, the micro-tool’s processing path, which is also called the Numerical Control (NC) path, should be defined
[10]. First, the three-dimensional data model of Sine surface array is built. Second, the two-dimensional track of tool path is designed according to the micro tool’s specific parameters. Then, project the tool path two-dimensional track to the three-dimensional Sine surface model, and the interctions between them would form the NC tool path. Finally, the required surface structure would be realized after the micro tool follows the tool path in ultra precision machining.
The machined sinusoidal modulation template is measured by a Veeco NT9300 interferometer, as shown in Fig. 6. From the figure we can e that the structure surface is X: 500nm/div Z: 640nm/div
500 1000
nm
(b)
#124107 - $15.00 USD Received 11 Feb 2010; revid 26 Mar 2010; accepted 26 Mar 2010; published 31 Mar 2010
(C) 2010 OSA 12 April 2010 / Vol. 18, No. 8 / OPTICS EXPRESS 8028
clo to the ideal of the sine graph, the cycle and amplitude of sine curve are clo to the defined values. The single-crystal diamond micro-cutting tools prepared by FIB were ud for the preci machining of sinusoidal surface array.
Fig. 6. The sinusoidal surface machined by micro tool. (a)A sinusoidal template by WLI, (b)
Cross-ction of the sinusoidal results.
3.3 Micro Fresnel optical components fabrication
The working principle of a Fresnel lens is to divide the conventional lens into veral regions with equal spacing and remove the central part of each region while maintaining the required surface curvature, as shown in Fig. 7.
The Micro Fresnel optical element designed here has a diameter of 15 mm, a curvature radius of 30 mm, and the interval between the adjacent rings of 30 µm. The largest depth is calculated to be 7.678 µm, which provides an important reference for tool design and machining.
财富造句
Fig. 7. Schematic of the Fresnel lens fabrication
Fig. 8. The hemi-spherical micro tool shaped by FIB.
According to the geometric relationship, the incomplete machine parameters can be calculated. We define the width of the incomplete turning area in a ring as x, the sharp angle for the MDOE is θ, as s
hown in Fig. 1. Thus the relationship between the width of incomplete turning part using the traditional shape tool x t and hemispherical shape tool x h with the corresponding tool no radius R
should be:
(b)
#124107 - $15.00 USD Received 11 Feb 2010; revid 26 Mar 2010; accepted 26 Mar 2010; published 31 Mar 2010
(C) 2010 OSA 12 April 2010 / Vol. 18, No. 8 / OPTICS EXPRESS 8029
