A 6-degree-of-freedom measurement system for the accuracy of X-Y stages

A precision 6-degree-of-freedom measurement system has been developed for simultaneous on-line measurements of six motion errors of an X-Y stage. The system employs four laser Doppler scales and two quadrant photo detectors to detect the positions and the rotations of an optical reflection device mounted on the top of the X-Y stage. Compared to the HP5528A system, the linear positioning accuracy of the developed measurement system is better than ±0.1 μm to the range of 200 mm and the vertical straightness error is within ±1.5 μm for the measuring range of ±0.1 mm. The yaw and pitch errors are about ±1 arcsec, and the roll error is about ±3 arcsec within the range of ±50 arcsec.     

Mechanisms and solutions to gate oxide degradation in flash memory by tunnel-oxide nitridation engineering

Increasing attention has been paid to the peripheral gate-oxide integrity degradation of Flash memory devices that is induced by the tunnel-oxide nitridation. In this letter, the mechanisms of tunnel-oxide nitridation-induced degradation are characterized. We report that both a local oxide thinning effect and nitrogen residue will impact the integrity of gate-oxide. Minimizing the local thinning effect with an in situ steam generation (ISSG) oxidation process and removing the nitrogen residues from the silicon wafer surface by either an additional sacrificial oxide process or over-dip are proven to be useful in recovering the gate-oxide integrity. An optimum approach with the tunnel-oxide nitridation is proposed in this work that results in comparable or even better gate-oxide property than other approaches that have no tunnel-oxide nitridation process.     

A Dynamic 3-D Surface Profilometer With Nanoscale Measurement Resolution and MHz Bandwidth for MEMS Characterization

Commercialization of microelectromechanical systems (MEMS) has made accurate dynamic characterization a major challenge in design and fabrication. In view of this need, a dynamic 3-D surface profilometer involving white light interferometric scanning principle with a stroboscopic LED light source was developed. The developed instrument was applied to a microcantilever beam used in atomic force microscopy (AFM) to analyze its full-field resonant vibratory behavior. The first five resonant vibration modes were fully characterized with vertical measurement accuracy of 3-5 nm and vertical measurement in the range of tens of micrometers. The experimental results were consistent with the outcomes of the theoretical simulation by ANSYS. Using stroboscopic illumination and white light vertical scanning techniques, the developed static and dynamic 3D nanoscale surface profilometry of MEMS devices can achieve measurement range of tens of micrometers and dynamic bandwidth of up to 1-MHz resonance frequency.     

Identification of strut and assembly errors of a 3-PRS serial–parallel machine tool

In a serial–parallel type machine tool, the parallel spindle platform plays the key role in manipulating three directions of movement. Spatial symmetry of the 3-PRS loops is essential to the machine’s systematic accuracy. Currently, however, there is no effective instrument capable of measuring the symmetrical errors of the corresponding joints and strut lengths during structure assembly. In this study, an experimental method is proposed to identify the mechanism symmetric errors of a 3-PRS serial–parallel machine tool during the test run. It is based on the differentiation of the inverse kinematics equations. The mechanism errors could be derived by an identification model. With the aid of a developed 3D laser ball bar to detect the spatial position and orientation of the spindle platform, and three laser Doppler scales to measure three sliders’ positions simultaneously, the length errors of three struts and the symmetrical errors of the R-joints and S-joints can be identified by the optimization technique. This technique can help shop floor engineers to tune the symmetrical errors of the 3-PRS mechanism during machine assembly.     

Development of a new meso-scale machine tool for fabricating micro V-grooves

This work presents the development of a meso-scale machine tool with a nanometer resolution. The newly developed meso-scale machine tool consists of a pagoda structure for Z-axis, four HR8 ultrasonic motors, three linear encoders with a resolution of 2 nm, a coaxial counter-balance system, a XY coplanar positioning stage, a rotary stage, a Galil 4-axis motion control card, an industrial PC and a CCD camera system. The optimal geometrical dimensions of the pagoda structure have been determined by ANSYS software. The designed meso-scale machine tool is equipped with an X–Y coplanar positioning stage with nanometer resolution. The coplanar stage developed by National Taiwan University was integrated with two linear encoders, so that a two-axis closed-loop control was possible. A circular positioning test with the radius of 1 mm using the developed stage was tested, and the overall circular positioning error was about 83 nm based on the test results. The micro V-grooves and the micro pyramid cutting tests of the polished oxygen free copper using a single crystal diamond tool on the developed meso-scale machine tool have been performed. The cutting tests under various combination of the depth of cut and cutting speed have been carried out. It revealed that the cutting speed had no great influence on the cutting force. The measured cutting forces for the depth of cut of 5, 10, 15 μm were 1.2, 1.6 and 2.4 N, respectively. The results showed the meso-scale machining tool can be used in micro pyramid structures manufacturing.     

Optimal shape error analysis of the matching image for a free-form surface

When using an optical non-contact scanning system to measure an object that has a large surface, large curvature, or a full 360° profile, one can acquire only one set of sectional measurement points each time. For reconstructing the entire object, every set of sectional measurement points acquired at different positions must match. Therefore, the optimal shape error analysis for the matching image of two or more sets of sectional measurement points is desired. This paper presents a measurement system that combines two CCD cameras, one line laser and a three-axis motion stage. It forms an optical non-contact scanning system in association with the mathematical method of direct shape error analysis for the use in reverse engineering. This analysis and measurement system can be used for the profile measurements of free-form objects. It analyzes the matching image of a free-form surface with high efficiency and accuracy. The validity and applicability of this system are demonstrated by two practical examples.     

Testing homogeneity of risk difference in stratified randomized trials with noncompliance

When assessing a treatment effect in the presence of confounders, we often employ stratified analysis and obtain a summary estimate of the risk difference (RD) under the assumption that the underlying RD is homogeneous across strata. In a randomized clinical trial (RCT), we may commonly come across the data in which there are patients who do not comply with their assigned treatments. Thus, to avoid reaching a misleading conclusion due to overlooking an interaction between treatments and strata, it is important that we can incorporate noncompliance into examining the homogeneity of the RD. In this paper, we develop four statistics for testing the homogeneity of the RD in a stratified RCT with noncompliance. These include the test statistic derived from the weighted-least-squares (WLS) method, the test statistic using the WLS method and tanh⁻¹(x) transformation, the test statistic using the weight similar to the Mantel–Haenszel (MH) estimator, and the test statistic using an optimal weight and the MH point estimator. We apply Monte Carlo simulation to evaluate the performance of these test statistics with respect to Type I error and power in a variety of situations. We use the data taken from a multiple risk factors intervention trial and a numerical example of simulated data to illustrate the practical use of these test statistics. Finally, we do a sensitivity analysis and discuss why applying test statistics for the ITT analysis to test the homogeneity of RD as focused in this paper can lead us to make an incorrect inference.     

Applications of single-wafer thermal processing to 0.15-/spl mu/m high-density MROM

Feasibility of single-wafer rapid-thermal process as an alternative to the conventional batch-type furnace process is evaluated on a 0.15-/spl mu/m 128-Mb mask read only memory (MROM) product. Excellent gate oxide integrity and device characteristics are achieved with a single-wafer rapid-thermal process. Superior yield and product reliability by using single-wafer process tool have also been achieved. Shortened process cycle time and better thermal process uniformity by using single-wafer rapid-thermal processing are demonstrated.     

Development of a drop-on-demand droplet generator for one-drop-fill technology

This paper presents the design, fabrication and tests of a piezoelectric-type droplet generator, which can be used for on-line liquid dispensing system. The principle is to actuate a disk-type PZT by a function generator to push the liquid out of the droplet generator and form a near-spherical droplet due to surface tension. A light-emitting diode (LED) is simultaneously triggered using the stroboscopic technique. In situ recording of the droplet formation is achieved by a CCD camera to measure the droplet dimension by image processing methods. The influence of the process parameters on the droplet quality is also studied. For different liquids the drive conditions shall be adjusted in order to obtain the optimum droplet formation. An application to the one-drop-fill (ODF) technology of liquid crystal displays (LCD) was carried out in order to control the droplet sizes and the repeatability of the quantity.     

Linear diffraction grating interferometer with high alignment tolerance and high accuracy

We present an innovative structure of a linear diffraction grating interferometer as a long stroke and nanometer resolution displacement sensor for any linear stage. The principle of this diffractive interferometer is based on the phase information encoded by the ±1st order beams diffracted by a holographic grating. Properly interfering these two beams leads to modulation similar to a Doppler frequency shift that can be translated to displacement measurements via phase decoding. A self-compensation structure is developed to improve the alignment tolerance. LightTool analysis shows that this new structure is completely immune to alignment errors of offset, standoff, yaw, and roll. The tolerance of the pitch is also acceptable for most installation conditions. In order to compact the structure and improve the signal quality, a new optical bonding technology by mechanical fixture is presented so that the miniature optics can be permanently bonded together without an air gap in between. For the output waveform signals, a software module is developed for fast real-time pulse counting and phase subdivision. A laser interferometer HP5529A is employed to test the repeatability of the whole system. Experimental data show that within 15?mm travel length, the repeatability is within 15?nm.