Fluorescence calibration is usually done by preparing bio-samples with a series of concentrations and measuring their corresponding fluorescence intensities. A simplified approach is studied by using a microfluidic chip and microspheres. The fluorescence calibration can be carried out on the chip with only one concentration of the microspheres. Microspheres with the diameter of 1~5μm are very useful in bio-detection research. These microspheres are manufactured using high-quality, ultraclean polystyrene microspheres and loaded with a variety of proprietary dyes. They can be labeled with biotin-, NeutrAvdin-, streptavidin- and protein, which can be used as tracers for bio-detections. A microfluidic chip was successfully fabricated for the experiment, and preliminary experimental results have proved the feasibility of the approach for fluorescence calibration.
The advanced requirements of bio-MEMS and MOEMS, i.e., low sidewall surface roughness, submicron critical dimension, and high aspect ratio, necessitate the use of an intermediate mask and a soft x-ray lithography process to fabricate working x-ray masks that are suitable for deep x-ray lithography. Intermediate masks consist of 2 to 2.5-µm gold patterns on membranes/substrates that are highly transparent to x-ray radiation, whereas working masks possess greater than 5 µm of gold patterns. In this work, 1-µm silicon nitride membranes are produced by a low pressure chemical vapor deposition (LPCVD) process on both the front and backside of 100 prime grade wafers and anisotropic wet etch through silicon nitride etch masks. E-beam lithography is used to pattern 0.8- to 3-µm-thick resist layers with submicron resolution. In the case of the 3-µm resist layers, the features are electroplated with approximately 2 µm of gold to form an intermediate mask. The 0.8-µm-thick layers are electroplated with gold up to a thickness of 0.6 µm and form initial masks, which are in turn used in a soft x-ray lithographical process to make intermediate masks. The process of building a high-resolution intermediate x-ray mask, directly by e-beam patterning a 3 µm layer of e-beam resist, followed by gold electroplating, is found to be viable but requires the use of a high energy (>100 keV) e-beam writer. The stability of the resist pattern during soft x-ray lithography (SXRL) by use of an initial mask is found to be problematic. Double-side lithography and gold electroplating, can effectively reduce the aspect ratio of the mask pattern, eliminates the problems associated with the use of an initial mask to fabricate intermediate x-ray masks.
A method to fabricate a high precision X-ray mask for Ultra Deep X-ray Lithography (UDXRL) is presented in this paper by use of a single substrate. Firstly, an 8-μm layer of positive photoresist is patterned on a 500 μm thick beryllium substrate by use of UV lithography and 5 μm gold is electroplated out of a sulfite based commercial plating solution. Secondly, the photoresist is removed and 15 μm of SU-8 is spincoated and baked. The layer of SU-8 is patterned by use of an exposure from the backside of the substrate with a soft X-ray source, followed by post-exposure bake and
development. An additional 5 μm layer of gold is electroplated on top of the first gold pattern thereby increasing the total thickness of the absorber on the X-ray mask to 10 μm. After the removal of the SU-8 resist, the second step of the process is repeated by use of a thicker layer of SU-8 (up to 100 μm) to obtain the high-precision and high-aspect ratio absorber pattern. Using this method, the maximum dimensional error of the fabricated gold pattern remains under 1 μm, while the smallest absorber feature size is 10 μm.
Challenging requirements in optical and BioMEMS application with high aspect ratios of microstructures in access of 20 and smallest structure details of less than 1 μm have motivated this work to irmpove x-ray mask fabrication. Several approaches to pattern an intermediate x-ray mask with the gold absorber thickness of 1.6-2.2μm using a 1μm thick silicon nitride membrane have been explored. E-beam lithography is employed for primary patterning and experimental results show that high energy (100keV) e-beam lithography is a very promising approach. So-called working x-ray mask can be fabricated from intermediate x-ray mask through x-ray lithography. More than 10μm thick PMMA x-ray resist has been coated on the silicon nitride membrane by multi-coating process without crack. First exposure results indicate that adhesion and stability of sub-micrometer structures wiht these heights is critical. In order to overcome these problems a novel approach has been proposed by coating resist on both sides of the silicon nitride membrane and simultaneous patterning of both sides using x-rays. First successful experimental results have been achieved for proving the feasibility.
X-ray lithography is commonly used to build high aspect ratio microstructures (HARMS) in a 1:1 proximity printing process. HARMS fabrication requires high energy X-rays to pattern thick resist layers; therefore the absorber thickness of the working X-ray mask needs to be 10-50 μm in order to provide high contrast. To realize high resolution working X ray masks, it is necessary to use intermediate X-ray masks which have been fabricated using e beam or laser lithographic techniques. The intermediate masks are characterized by submicron resolution critical dimensions (CD) but comparatively lower structural heights (~2 μm). This paper mainly focuses on the fabrication of high resolution X-ray intermediate masks. A three-step approach is used to build the high resolution X-ray masks. First, a so called initial mask with sub-micron absorber thickness is fabricated on a 1 μm thick silicon nitride membrane using a 50KeV e beam writer and gold electroplating. The initial X-ray mask has a gold thickness of 0.56 μm and a maximum aspect ratio of 4:1. Soft X-ray lithography and gold electroplating processes are used to copy the initial mask to form an intermediate mask with 1 μm of gold. The intermediate mask can be used to fabricate a working X-ray mask by following a similar set of procedures outlined above.
An improved signal processing method for laser interferometer is investigated to measure the radius of large precision centrifuge. Based on phase and integer periodic phase measurement, it not only makes the resolution up to 1 in 2000 of a wavelength, but also enlarges the range of the interferometer. The absolute radius measurement of the 5m centrifuge with the accuracy of +/- 3.4micrometers is achieved.