The precision displacement control in high-resolution instrument is influenced by non-linearity effects of PZT actuators. The capacitive sensor within PZT actuator is often used as a displacement sensor for feedback control, but the calibration and traceability of capacitive sensor are hardly to be accomplished. The optic fiber sensor is a useful high-resolution displacement sensor to perform the measurement in space-limited instrument, and it’s also capable of a non-contact function. In this paper, the structure of an optic fiber sensor was introduced, and the hysteresis characteristic of PZT actuator was evaluated. In addition, the performance of the capacitive sensor within PZT actuator for close-loop control was compared with those of the optic fiber sensor, and the differences ratio between both was less than 0.12 %. Following the scanned images by interference microscope, the images have some distortions before applying the compensated curve function for non-linearity. Thus, the optic fiber sensor could be provided a calibration service for displacement measurement of interference microscope.
For dimensional researches and applications, the end standard measurements are the popular subjects in high precision standard systems or instruments. In general, the gauge blocks are the representative of the end standards. The universal measurement machines (UMM) are usually utilized for the dimensional length of gauge blocks. However, for measuring the dimensional lengths of test gauge blocks (TGBs), they should be compared with the same lengths of the master gauge blocks (MGBs). Thus, there are different lengths of the MGBs needed to be prepared and the measuring procedures are usually very time consuming. In order to lower the cost of procurement and maintenance of MGBs, a continuous end standard measurement system (CESMS) was built for many different test ranges of TGBs. The features of the CESMS included at least one gauge block, the LVDT probes for positioning, the real lengths of the TGBs measured from the display value of the laser interferometer, and total procedures controlled by automation software. All of these parts were integrated onto a large platform and its moving carriage could travel up to 1.2-meter in distance. Within these ranges, the CESMS could measure different dimensional lengths of the TGBs and many pieces at the same time. The CESMS utilized the laser interferometer to acquire the accurate display values between two ends when the LVDT probe was touched and triggered the automation software to record. Owing to the recommended radiation of laser head, the CESMS could be traced to the meter, SI unit. Furthermore, the experiment results showed that the comparison results of certificated gauge block at 800 mm suited for calibration certificate by PTB.
A fiber optic interferometer for a novel application is proposed in this paper. This new configuration and decoding scheme is in particular suitable for an AFM-tip tailoring system. A theoretical analysis method for simulating the relation of displacement and interfering intensity from the fiber optic sensor is thoroughly discussed. Experimental data for evaluating interfering efficiency agree well with simulation results. Higher resolution becomes achievable with the help of the two-channel interferometer decoding scheme. Moreover, the properties of the piezoelectric actuator used in this system are characterized by the optical sensor. This compact sensor exhibits satisfactory performance for the nanometer-resolution requirement of the developing AFM tip tailoring system.
Linear variable differential transformer (LVDT) sensors are usually used in precision measurement system for dimensional displacement measurements, especially in long gauge block comparator or gauge block. In order to ensure the accuracy of the LVDT sensor, the research provides static calibration methods to measure the displacement linearity to within ± 12mm. Our experiment structures include a laser interferometer and mechanical devices to setup optical alignments on SIP universal measuring machine. The experiment results show the read values from LVDT sensor and laser interferometer, and the correction values are defined as the read values of LVDT subtracted from the ones of laser interferometer. These corrections were calculated statistically as regression and residual analysis. Statistical results show that correctional error is 0.04 mm in short-term operations, and the displacement linearity is -0.016 mm /1 mm. For precision measuring systems, LVDT sensors should be calibrated periodically and the research results could provide both a static calibration method and plotting linearity curves for users’ references.
For dimensional measurements and positioning, laser interferometers are often used to obtain highly accurate readings. To service their reliability, a system of laser interferometry standards is made available at the National Measurement Laboratory to offer instrument calibration as well as to ensure their traceability to the SI units. Owing much to their great sensitivity, the accuracy of laser interferometers undergoing calibration is strictly influenced by surrounding conditions, especially the correction parameter in the refractive index of air - a complex combination of ambient temperature, humidity, and atmosphere pressure. In order to minimize the deviation, an automated calibration system is constructed by employing a computer-controlled driver stage to perform linear displacement and data acquisition in the absence of operator intervention. A supplementary displacement measurement sub-system was set up to serve as an independent control on the stage. An average of 12 data points were taken at each predefined positions along the 20-m travel to support the comparison between the original system and the automated one. Several test runs from the calibration operation showed a standard deviation of 2.4×10-8 for the automated system and 6.5×10-8 for the previous. In addition to lower operational cost, experimental data also indicated improved calibration reliability benefited from the automation.
The lens heating focus correction on stepper is not good enough on the current procedure provided by ASML. It can only solve the wafer to wafer CD variation but not within wafer. It caused the CD at a wafer top and bottom is different. This is because there is no correction for lens heating if no special trigger while exposing within one wafer. In small UDOF process like 0.3 micrometers poly gate, CD is very sensitive to the focus drift. The within wafer lens heating effect cause the focus drift and worsen focus control. Even the lens heating correction factor has been optimized, it still suffers the poor within wafer CD uniformity issue. One tricky method, using of multi-image setting, to trigger the lens heating correction is proposed to improve the within wafer CD uniformity in this report. The poly gate CD uniformity on 0.3 micrometers production were improved from 25nm to 15nm.
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