Improving the etching performance of high-aspect-ratio contacts by wafer temperature control: Uniform temperature design and etching rate enhancement

A novel wafer temperature control system using direct expansion cycles is developed to improve etching performance. This system enables rapid temperature control of a wafer with low power consumption. In a previous report, we confirmed that the etching rate and mask selectivity of high-aspect-ratio contact etching could be increased by around 6% and 14%, respectively, by controlling the temperature of the wafer during the etching process. In this study, an advanced wafer temperature control system that realizes not only rapid response but also uniform wafer cooling is developed, and a new etching process that controls O₂ gas flow rate as well as wafer temperature during etching is evaluated to decrease the etching rate depression of high-aspect-ratio contact etching. As a result, a rate of wafer temperature change of 1 °C/s and uniformity of ±0.7% with a coefficient of performance exceeding 3 is achieved over a wafer with a diameter of 300 mm during the etching process. Furthermore, etching rate depression in C₄F₆/Ar/O₂ plasma is decreased from 14.4% to 7.8% for a sample with a diameter of 100 nm and aspect ratio of 30.     

Three-point-support method based on position determination of supports and wafers to eliminate gravity-induced deflection of wafers

The flatness measurement of large and thin wafers is affected greatly by gravity. Inverting method is often used to cancel the effect. However, it is required that the positions of the supports and wafers are perfectly symmetric about the inversion axis. In this study a three-point-support method based on position determination of supports and wafers was proposed. The supporting balls and the wafer were placed in arbitrary positions and their positions were obtained by measurement and fed into the FEM model which was developed to calculate the gravity-induced deflection (GID). The methods to acquire the positions of the supports and the wafer were proposed. The position measurement accuracy of the supports was improved greatly by circle fitting to the profile of the supporting ball. Wafer edge point was obtained accurately as the intersection point between the wafer surface line and the edge profile. The method to measure the wafer thickness using only one displacement sensor on the same equipment was presented. The simulation results were verified by experimental results. The centering device for the wafer and the positioning accuracy requirements of the supports are not needed any more. The effect of the positions of the supports and the wafer was reduced to be less than 1 μm for a 300 mm diameter and 397 μm thickness wafer with GID over 140 μm. This method could also be used for accurate flatness measurement of other large and thin panels.     

A practical control method for precision motion—Improvement of NCTF control method for continuous motion control

The present paper describes a practical control method for a precision motion system and the performance thereof. For practical use, high motion control performance and ease of design and controller adjustment are desired. A nominal characteristic trajectory following control (NCTF control) has been investigated to realize high performance and ease of application of point-to-point (PTP) positioning. The controller comprising a nominal characteristic trajectory (NCT) and a PI compensator is free from exact modeling and parameter identification. In the present paper, the NCTF control is modified in order to improve the control performance of continuous motions such as tracking and contouring motions. The NCTF controller for continuous motion (referred to as Continuous Motion NCTF controller) has a structure that is almost identical to the conventional NCTF controller and is designed using the same design procedure. The Continuous Motion NCTF controller is applied to ball screw mechanisms, and its motion control performance is evaluated from the experimental tracking, contouring, and positioning control results. The experimental results prove that the Continuous Motion NCTF controller achieves the same positioning performance as the conventional NCTF controller, and generally achieves better continuous motion control performances than PI-D or conventional NCTF controllers. In 0.25 Hz and 100-nm radius circular motion, the experimental tracking errors for Continuous Motion NCTF were smaller than 10 nm.     

High-precision and high-speed positioning of 100 G linear synchronous motor

The present paper describes a moving permanent magnet linear synchronous motor (MPM LSM) that can move with an acceleration above 100 G (=980 m/s²), and is also capable of high-precision and high-speed positioning. The MPM LSM consists of a mover including permanent magnets and a double-sided electromagnet stator. It can produce a thrust of 4.56 × 10³ N and has a working range wider than 1 m. The MPM LSM mover is improved for light weight and is driven using a suitable phase lead for flux weakening. The combination of the improved mover and the suitable phase lead provides motion at an acceleration above 100 G and a velocity above 12 m/s. The positioning characteristics of the improved MPM LSM are examined using a controller with two suitable phase lead functions. The control system shows a positioning accuracy and a positioning resolution of 500 nm, which is similar to the vibration amplitude of the sensor output in open loop. In 300-mm step positioning, the improved MPM LSM shows an acceleration above 660 m/s² and a velocity above 8.3 m/s. It takes less than 101 ms to reduce the positioning error to less than 5 μm. The temperature rise during positioning is also examined experimentally. Continuous positioning for longer than 30 minutes increases the temperature of the MPM LSM, but by less than 6 °C.     

Parallel-kinematics XYZ MEMS part 2: Fabrication and experimental characterization

This paper, the second of a set of two papers addressing parallel-kinematics MEMS stages for spatial translation, deals with fabrication, characterization and control of such devices. Double device layer SOI (silicon-on-insulator) substrates are used, providing three layers (two device layers and the handle) into which the elements of the stage can be mapped. Using the mechanism concept, realization scheme, and kinematic and dynamic models developed in the first paper of this set, this paper provides a detailed approach to fabricating these devices. The stages fabricated have a workspace cube of roughly 20 μm on the side, an in-plane stiffness of 96 N/m, and an out-of-plane stiffness of 166 N/m. Further, it characterizes the performance of the individual actuating and sensing elements, configures feedback controllers for each actuated joint, and assesses and verifies the stage’s designed performance. Finally, it demonstrates full 3-axis, closed-loop positioning of a MEMS stage.     

Demonstrative fractional order – PID controller based DC motor drive on digital platform

In industrial drives applications, fractional order controllers can exhibit phenomenal impact due to realization through digital implementation. Digital fractional order controllers have created wide scope as it possess the inherent advantages like robustness against the plant parameter variation. This paper provides brief design procedure of fractional order proportional-integral-derivative (FO-PID) controller through the indirect approach of approximation using constant phase technique. The new modified dynamic particle swarm optimization (IdPSO) technique is proposed to find controller parameters. The FO-PID controller is implemented using floating point digital signal processor. The building blocks are designed and assembled with all peripheral components for the 1.5 kW industrial DC motor drive. The robust operation for parametric variation is ascertained by testing the controller with two separately excited DC motors with the same rating but different parameters.     

A 3-axis precision positioning device using PZT actuators with low interference motions

For expected applications of fast tool servo (FTS) and vibration machining, a 3-axis positioning device with low interference motions is proposed in this paper. The positioning device was composed of a XY stage and a Z-axis stage, which were actuated by piezoelectric (PZT) actuators combined with specially-designed symmetric flexure hinges. Through fundamental experiments, when the applied voltage was 50 V, the displacements along the X-, Y-, and Z-axes were measured as 6.35 μm, 6.61 μm, and 10.12 μm, respectively, with the corresponding small percentages of interference displacement of 3.80%, 4.02%, and 3.30%. In addition, the resonant frequencies were obtained as 1.06 kHz, 0.65 kHz, and 0.54 kHz. To examine control performances, a real-time control system considering hysteresis effect of PZT actuators was implemented by the field-programmable gate array (FPGA) modules to conduct tracing controls for sinusoidal waveform, 3D Lissajous motion, and 3D spiral motion. The tracing errors along 3-axis actuations were under 30 nm. The performances of a 3-axis positioning device were well demonstrated. Future work is to perform machining examinations on a machine tool.     

A piezoelectric motor for precision positioning applications

This study presents a novel precise piezoelectric motor capable of operating in either an AC drive mode or DC drive mode. In the AC drive mode, the motor acts as an ultrasonic motor which is driven by two orthogonal mechanical vibration modes to generate elliptical motion at the stator to push the slider into motion. In the DC drive mode, stick-slip friction between the stator and slider is used to drive the motor step-by-step. The experimental results show that the AC drive mode can drive the motor at a high moving speed, while the DC drive mode can simply drive the motor with a nanoscale resolution. In our experiments, a prototype motor is fabricated and its actions are measured. The results demonstrate that in the AC drive mode, the piezoelectric motor can achieve a 106 mm/s speed without a mechanical load and a 34 mm/s speed with 340 g of mechanical load when applying two sine waves with a drive of 11.3 V at 38.5 kHz. Meanwhile, in a DC driving mode, the motor is capable of performing precision positioning with a displacement resolution of 6 nm when driving at 100 Hz.     

Non-contact temperature measurement of silicon wafers based on the combined use of transmittance and radiance

We propose a non-contact temperature measurement method that combines the temperature dependence of transmittance below 600 °C and radiation thermometry above 600 °C. The combined method uses a polarization technique and the Brewster angle between air and a dielectric film such as SiO₂ or Si₃N₄ grown on silicon wafers. A prominent feature of this method is that both measurements of transmittance and radiance are performed with the same geometrical arrangement.For a semitransparent wafer, the measurement of p-polarized transmittance at the wavelengths of 1.1, 1.2 and 1.3 μm enables temperature measurement in the range from room temperature to 600 °C. For an opaque wafer above 600 °C, the p-polarized radiation thermometry at the wavelength of 4.5 μm allows the temperature measurement without the emissivity problem. The combined method with the use of transmittance and radiance is valid in the entire temperature range irrespective of variations of film thickness and resistivity.     

Measurement of highly reflective surface shape using wavelength tuning Fizeau interferometer and polynomial window function

In this study, a 5N − 4 phase shifting algorithm comprising a polynomial window function and a discrete Fourier transform is developed to measure interferometrically the surface shape of a silicon wafer, with suppression of the coupling errors between the higher harmonics and the phase shift error. A new polynomial window function is derived on the basis of the characteristic polynomial theory by locating five multiple roots on the characteristic diagram. The characteristics of the 5N − 4 algorithm are estimated with respect to the Fourier representation in the frequency domain. The phase error of the measurements performed using the 5N − 4 algorithm is discussed and compared with those of measurements obtained using other conventional phase shifting algorithms. Finally, the surface shape of a 4-in. silicon wafer is measured using the 5N − 4 algorithm and a wavelength tuning Fizeau interferometer. The accuracy of the measurement is discussed by comparing the amplitudes of the crosstalk noise calculated by other algorithms. The uncertainty of the entire measurement was 34 nm, better than that of any other conventional phase shifting algorithms.     

Design of multi-degree-of-freedom micromachined vibratory gyroscope with double sense-modes

This paper presents a novel multi-degree-of-freedom (multi-DOF) micromachined vibratory gyroscope design operated at atmospheric pressure. In this design, the complete 2-DOF vibratory structure is utilized in drive-mode and sense-mode and also, the 2-DOF sense-mode is implemented in both driving frame and proof frame, which form the double 2-DOF sense-modes. The 2-DOF vibratory structure could provide drive-mode and sense-mode with large bandwidth and the double 2-DOF sense-modes could provide high gain of gyroscope system, which improves the inherent robustness and sensitivity simultaneously. The simulation results demonstrate that the summed signal of drive-mode dynamic response is consistent with that of sense-mode and that the gain of proposed multi-DOF micromachined vibratory gyroscope can reach up to −10 dB, increased by above 8 dB compared to the design with single 2-DOF sense-mode. Meanwhile, the 3 dB bandwidth of gyroscope system is larger than 200 Hz.     

A low-cost centimeter-level acoustic localization system without time synchronization

In this paper, we present a range-based localization method without time synchronization. It uses only a speaker, a microphone, and some forms of device-to-device communication such as WIFI radio; thus, it is easily applied in most commercial off-the-shelf mobile devices such as cell phones. The localization scheme is composed of two stages. We obtain the initial distances between the moving object and the anchors in the first stage using a BeepBeep ranging system, in which they both send and receive sound signals. In the second stage, which is the main localization stage, the difference distances between the moving object and the anchors can be obtained using a OneBeep ranging system. Only the located object must emit sound signals periodically, and all of the anchors including the located object should receive the sound signals in the OneBeep system. The distances between the moving object and all the anchors can be obtained by adding the difference distances to the initial distances, and then, the moving object can be located. A localization experiment was conducted in a 6 × 9 m room with weak reflection, and the localization can reach centimeter-level accuracy in 5 min.     

Design and testing of a long-range,precision fast tool servo system for diamond turning

A long-range, precision fast tool servo (FTS) system was developed that is capable of accurately translating the cutting tool on a diamond turning machine (DTM) with maximum accelerations of 260 m s^?2 and bandwidths of up to 140 Hz. The maximum displacement range of the cutting tool is 2 mm. The FTS utilizes a flexure mechanism driven by a voice coil actuator, a custom linear current amplifier and a laser interferometer feedback system. This paper describes the design of the electromechanical system, controller configuration and cutting tests to evaluate the system. Initially, low disturbance rejection and poor command following degraded the surface finish of machined test parts. Several techniques to add damping to the dynamic system were investigated to improve the generated surface finishes. Electromotive damping was applied inside the voice coil actuator, and two different viscoelastic damping materials were applied to the flexure mechanism. A control strategy consisting of linear and non-linear feedforward controllers and a proportional, integral and derivative (PID) feedback controller was implemented to accommodate the changed system dynamics. The workpieces were analyzed using form and surface inspection instruments to evaluate the overall system performance. A cylindrical part with five lobes cut across the face had a surface finish value between 20 and 30 nm R_a.     

Cross-coupling effect of large range XY nanopositioning stage fabricated by stereolithography process

This paper presents cross-coupling effect of a polymer-based large range XY nanopositioner fabricated by an additive manufacturing (AM) process, stereolithography. The flexural properties were preliminary characterized to design the XY stage capable of ±1.0 mm range motion. The voice coil motors were aligned along the moving axes of the stage, and optical knife edge displacement sensors were placed at the center of the stage without Z-axis offset distance perpendicular to the moving axes to mitigate Abbe error and minimize cosine error. The cross-coupling of AM stage was 3.4% and 8.1% for XY and YX axes that is relatively larger than the value 1.0% estimated by the finite element method. It was considered to be responsible for AM fabrication tolerance or local irregularity in material properties because those properties are highly dependent on curing temperature and time even though the stage is fabricated layer-by-layer under the identical condition. The AM stage thus should be positioning feedback-controlled to avoid cross-coupling effect. As a result, the root-mean-square radial trajectory error was 3.62 μm under radius 1.0 mm and 1 Hz circular motion condition. These results indicated that the AM stages can be used for large range nanoprecision applications such as scanning, lithography, or fiber-optics alignments.     

Application of blue laser direct-writing equipment for manufacturing of periodic and aperiodic nanostructure patterns

This study presents the novel development of low cost, highly efficient blue laser direct-writing equipment for using mask-less laser lithography to manufacture periodic and aperiodic nanostructure patterns. The system includes a long-stroke linear motor precision stage (X, Y), a piezoelectric nano-precision stage (Y, θz), a 3-DOF (degrees of freedom) laser interferometer measurement system, and a blue laser direct-writing optical system. The 3-DOF laser interferometer measurement system gives the control system feedback for displacement (X, Y, θz) of the equipment. The laser processing equipment consists of a blue laser direct-writing optical head, a field-programmable gate array (FPGA) alignment interface, and an optical head servo controller. The optical head operates at a wavelength of 405 nm. Processing the nanostructures on thermo-reaction inorganic resists with precise control of the laser intensity, taking advantage of the threshold effect to exceed the limitations of optical diffraction, and reduces the nanostructure hole size. The equipment can be used to fabricate various periodic nanostructure patterns, aperiodic nanostructure patterns, and two-dimensional patterns. The equipment positioning accuracy is within 50 nm at a speed of 50 mm/s, and the minimum critical dimension can be achieved about 100 nm or so.     

Improved independent component analysis based modal identification of higher damping structures

Structural modal parameter identification under ambient excitation has strong engineering value and theoretical significance. As the most popular tool for solving Blind Source Separation (BSS) problems, Independent Component Analysis (ICA) is able to directly extract the time-domain modal parameters, including frequencies, damping ratios and modal shapes. ICA, however, has a fatal flaw of failing to identify structures with higher damping. To overcome the flaw above, the paper proposes a new method named “ICA + IDT”. Firstly, free vibration response of a structure is obtained from structural outputs under ambient excitation. Inverse damping transfer (IDT) is employed to turn a highly damped signal into a low damping response signal without changing of frequencies and mode shapes. Then, structural modal parameters are extracted from the low damping response signal by ICA. Finally, the identified damping ratios are adjusted to eliminate the impact of IDT. To verify the effectiveness and applicability of IDT + ICA proposed herein, two numerical simulations—mass-spring model and simply supported concrete beam—and an experiment model of three-story steel frame are built, and the analysis results reveal that presented method can identify structures with higher damping effectively.     

Development and calibration of an integrated 3D scanning system for high-accuracy large-scale metrology

Quality control in advanced manufacturing requires automated and high-accuracy large-scale 3D measurement. This paper proposes a high-accuracy, low-cost 3D scanning system by integrating industrial robot with precise linear rail and laser sensor. The measuring principle and system construction of the integrated system are introduced in detail. A mathematical model is established for mapping the change of the laser sensor frame while it scans along the linear rail and a sphere-based algorithm for rail orientation calibration is introduced. Subsequently, taking the robot positioning error into consideration, an enhanced hand–eye calibration method is proposed to determine the relationship between robot end-effector and rail scanning frame. Validation experiments were performed, a maximum distance error of 0.071 mm was detected within the rail range and a mean/maximum distance error of 0.309/0.604 mm was detected in the robot volume. A large-scale scanning instance also shows that integrated robotic scanning system features high-efficiency and high-accuracy.     

A real-time polishing force control system for ultraprecision finishing of micro-optics

Polishing force condition plays a key role in the ultraprecision finishing of micro-optics because it strongly affects the polishing performance. In this paper, a novel polishing force control system is developed to improve the polishing stability. It is proposed for the first time to precisely control polishing force in real-time and has a simple mechanism which mainly composes of a load cell, a piezo stage and a linear stage. The load cell is used to measure the polishing force, whereas the piezo-stage is applied to adjust the force with nano/micro positioning change. The linear stage driven by a stepper motor is employed to prevent force change beyond the travel range of piezo stage which leads to the system out of control. A PID controller is adopted to calculate the command voltage for driving the piezo-stage based on the measured force. The system enables polishing force to be controlled within a range of 0–200 mN with a resolution of 0.1 mN. Some fundamental experiments are conducted to evaluate the performance of newly developed system. The results indicate that the proposed polishing force control system enables a stable polishing, and the polishing force conditions which generate suitable material removal function are acquired.     

Development and precise positioning control of a thin and compact linear switched reluctance motor

This paper describes the development and precise positioning control of a thin and compact linear switched reluctance motor (LSRM). The LSRM that has been developed has a mover that is easy to fabricate and can be disposable. The mover can be easily separated from the stator, allowing it to be changed frequently or discarded in a hazardous application. The prototyped LSRM mover is only 0.128 mm thick with the stator measuring 2.0 mm at its thickest point. These features are highly desirable for space savings while being cost-effective. However, the LSRM has a strong nonlinear driving characteristic that presents a challenge with respect to precision control. In order to overcome this problem and achieve precision positioning, a linearizer unit was designed and integrated into the controller to compensate for the nonlinear relationships among the effective thrust force, mover position, and excitation current. The usefulness of the designed controller was examined experimentally. The experimental positioning results show that the steady-state errors were all less than 1 μm in the working range of the LSRM. In addition, the redesign for the improvement of thrust characteristic and easy fabrication of the LSRM is explained.     

Large stroke and high precision positioning using iron–gallium alloy (Galfenol) based multi-DOF impact drive mechanism

A miniature-positioning device with a large stroke motion has attracted more and more attentions in these years because of the intensive development in precision engineering. In this paper, we have achieved the large stroke actuating and the high precision positioning, as well as realized a multi-degree-of-freedom in-plane motion using the developed Galfenol impact drive mechanism (IDM) actuator. In order to enhance the system robustness, two pieces of U-shape Galfenol (iron–gallium alloy) have been employed as the driving elements with a bias magnetic field contributed by a permanent magnet to generate the swing motion that amplifies the propelling inertia force. The current amplitude modulation has been applied in the precision positioning of the actuator under the quasi-static condition because of the motion step-size fineness. The results show that the actuator is able to achieve a sub-micrometer positioning accuracy that has reached the measurement limit of our setup. Meanwhile, the frequency modulation method has been explored in the large stroke actuation with a high motion speed. We have found out that this design is capable of achieving an accurate positioning without the frequency modulation because of the intrinsic fine step-size of the actuator. In addition, a rectangular in-plane motion has been realized with the image-based control for the multi-degree-of-freedom positioning. The actuator has an inductive impedance with a resistance of 3.796 Ω and an inductance of 0.4697 mH. Under the present driving ratings, the power consumption is smaller than 1.97 W while the reactive power can be ignored. Moreover, the experimental load analysis indicates that the design can achieve a maximum carry-load-to-weight ratio of 6.5.