Electrostatic Chuck Research Articles

Factor Design for the Oxide Etching Process to Reduce Edge Particle Contamination in Capacitively Coupled Plasma Etching Equipment

During the oxide layer etching process, particles in capacitively coupled plasma etching equipment adhere to the wafer edge and cause defects that reduce the yield from semiconductor wafers. To reduce edge particle contamination in plasma etching equipment, we propose changes in the voltage and temperature of the electrostatic chuck, plasma discharge sequence, gas flow, and pressure parameters during the etching process. The proposed edge particle reduction method was developed by analyzing particle maps after wafer etching. Edge particle adherence in plasma etching equipment can be reduced by decreasing the voltage and temperature changes of the electrostatic chuck and generating a plasma sheath with a continuous discharge sequence of radio-frequency plasma. The gas pressure and flow rate also affect the number of wafer edge particles. Experimental results were used to optimize the equipment parameters to reduce edge particle contamination and improve edge wafer defects after dry etching.

딥러닝 알고리즘을 활용한 디스플레이 정전척 FAB 공정의 불량 탐지 및 원인 분석

Deep learning algorithms have been used in various production processes to reduce product defect rates and improve process management efficiency. In this study, we propose a method for defect detection and cause analysis in the field of display electrostatic chuck fabrication (FAB) processes. The proposed method consists of three steps. First, we construct an autoencoder model for detecting defects and obtain reconstruction errors. Second, we construct the deep neural network model based on reconstruction errors obtained from the preceding autoencoder model to predict defects. Lastly, we applied locally interpretable model-agnostic explanations (LIME) and Shapley additive explanations (SHAP) to the deep neural network model for identifying the major causes of defects. The usefulness and applicability of the proposed method was demonstrated using the actual electrostatic chuck FAB data. Our proposed model outperformed all comparative models by achieving the highest average recall score. Furthermore, lag time and electrostatic chuck driving environment were identified as major causes of the defect.

Fabrication of Sensor-on-Wafer (SoW) Temperature Monitoring Sensor

Monitoring the wafer temperature during etching is the most important step in maintaining the optimized process condition. The change in the wafer temperature in the high-volume manufacturing (HVM) environment can produce unwanted results such as process failure. In this study, a wafer-type temperature sensor with a diameter, thickness, and weight of 300 mm, 1.3 mm, and 207 g, respectively, was fabricated. The fabricated wafer sensor could measure temperature in the wide range of −30 to 140 °C with 73 points and obtain the wafer temperature with a temperature resolution of 0.065 °C. Particularly, it showed stable performance, collecting information steadily and transmitting information to the Front Opening Unified Pod (FOUP) even at temperatures below −30 °C. Additionally, for both the inductively-coupled-plasma (ICP) and capacitively-coupled-plasma etching processes, even under very large plasma power conditions, the wafer sensor exhibited a stable operation without deforming or damaging the process chamber. The outermost area had the greatest influence on the current yield and was the area where analysis and diagnosis were performed most carefully using the wafer temperature sensor. The temperature distribution of the wafer on the electrostatic chuck (ESC) obtained using the capacitively-coupled-plasma etching equipment ranged between 127.19 and 136.65 °C, and the standard deviation was about 2.34 °C over the entire 300 mm area.

On-Wafer Temperature Monitoring Sensor for Condition Monitoring of Repaired Electrostatic Chuck

The temperature of electrostatic chuck (ESC), a wafer susceptor used in semiconductor etch equipment, must accurately control the temperature of wafers during the etching process to obtain uniform and consistent process results. Failure to control the precise temperature can lead to rejection from the high-volume semiconductor manufacturing site (one of the most high-cost equipment components which can be repaired for its extended use). In this research, we propose a wireless-type on-wafer temperature monitoring system (OTMS) for easier and faster temperature monitoring to help temperature measurements of the repaired ESC in atmospheric and vacuum conditions. The proposed method, which can effectively measure the temperature distribution of the ESC, should manage the operational condition of ESC. A successful demonstration of the 300 mm size OTMS for the repaired parts enhanced the quality assurance with a temperature deviation of ±3.83 °C over 65 points of measurement.

Evaluation of surface temperature uniformity of multi-zone ceramic heaters with embedded cooling channels for electrostatic chuck

Evaluation of surface temperature uniformity of multi-zone ceramic heaters with embedded cooling channels for electrostatic chuck

Development of a bipolar electrostatic chuck with a compliant beam-array assembly having four 3D-printed layers for large film handling

This study proposes and verifies bipolar electrostatic grippers stacking 3D-printed-layered modules consisting of arrays of elastically deformable bipolar beams. The influence of the mechanical compliance of grippers on the attractive force that it generates is clarified by comparing two types of modules having either high or low mechanical compliances. Experiments measured the attractive force of the gripper and demonstrated the pick-and-place performance of a thin film. The results show that mechanical compliance plays an important role in mitigating the attractive force decrease in stacking modules. The grippers’ ability for thin film handling is demonstrated by observing pick-and-place behaviours of the proposed bipolar electrostatic grippers.

Numerical evaluation on surface temperature uniformity of multi-zone and single-zone ceramic heaters with the electrostatic chuck

Numerical evaluation on surface temperature uniformity of multi-zone and single-zone ceramic heaters with the electrostatic chuck

Enhanced High-Temperature Electrical Resistivity of Aluminum Nitride Obtained by Engineering a Schottky Barrier at Grain Boundaries

An enhanced high-temperature electrical resistivity of AlN at high voltage was obtained by using MgO doping to modulate the Schottky barrier. Doped MgO was precipitated in an ∼100-nm-thick layer near grain boundaries, which reduced not only anionic carriers, but also the carrier mobility, due to the formation of defects (Mg′Al, O·N). According to an impedance analysis, the activation energy and the resistivity due to grain boundaries were increased by MgO doping, suggesting an elevated Schottky barrier. As a result, a remarkable high-voltage electrical resistivity, which is greater than 1010 Ω·cm at 550 °C/100 V, can be achieved, which is valuable for electrostatic chucking devices.

Fabrication and stacking of through-silicon-via array chip formed by notchless Si etching and wet cleaning of first metal layer

We combined a “via-last through-silicon via (TSV) process consisting of notchless Si etching and wet cleaning of the first metal layer” with the solder bonding process using Ar fast atom beam (FAB), and realized the fabrication and three-dimensional (3D) stacking of a high-density TSV array chip. The size of the TSV array was 76 × 500. The diameter and length of the TSV were 6 and 21–22 μm, respectively. As the TSV array chip was very thin (approximately 26 μm) and had a strip-like shape, it was fragile and warped by approximately 90 μm. Hence, an electrostatic chuck was introduced and the TSV array chip was stacked by using a soft material (Cu–Ni–Sn based solder) as a bump and performing low-pressing-load low-temperature bonding with Ar FAB. As a result, the warpage of TSV array chip was suppressed and the TSV array chip was stacked without causing damage to the TSV and Si region. In addition, it was confirmed that the (i) leakage current between TSV-bump pairs is small, (ii) multilayer wiring + TSV + bump connection exhibit low resistance, and (iii) daisy chain is perfectly connected to up to 38 000 TSVs. These results are due to the effects of notchless Si etching, wet cleaning of the first metal layer, introduction of an electrostatic chuck, low-pressing-load low-temperature bonding with a soft material, and Ar FAB. This process will facilitate the development of face-up type 3D stacked sensor systems.

Development of a bipolar electrostatic chuck module with a beam-array assembly using the multiple etching process

In this paper, we propose a successful fabrication method for a bipolar electrostatic chuck (ESC) device with a beam-array assembly, in order to achieve a fairly flat surface on the beam’s tip. A fabricated bipolar ESC device is expected to clamp a curved dielectric object due to its elastically-deformable beams, which are compliant with an object’s surface. As a fabrication process, the lithography technique including multiple etching processes against a single etching mask was performed to etch a three-layer material (conductor–dielectric–conductor). Due to the fairly flat surface of the beam’s tip (figure ), sufficient adhesional contact area with the target object for a large adhesional force can be obtained. In order to understand the adhesion performance of the device, an experimental force curve was measured and partially compared with the theoretical adhesional force calculated using finite element analysis. The Pascal-expression for future work dealing with a large surface area was also calculated, corresponding to stacked prototype modules.

Removal of CrN Contamination from EUV Mask Backside Using Dry Cleaning

For EUV lithography, a reflective mask is essential because of use of the strong energy, wavelength of 13.5 nm. The EUV mask consists of multi-layered, multi-material structure and is susceptible to various contaminants. Since EUV lithography process should be used in a high vacuum environment, an electrostatic chuck (ESC) is used to fix or hold the EUV mask using electrostatic force. In general, in order to use ESC chuck, it needs a thin conductive layer (CrN layer) on the backside. However, the contact points of the electrostatic pin chuck can make exfoliation of conductive CrN layer producing CrN particles. If these particles are present on the backside of the mask, CD or DOF may be affected during EUV exposure. The 1 μm particle can leads to a gap radius of 42mm [4]. Moreover, these backside particles may travel to the front side. Therefore, backside cleaning should be performed to remove particles from the mask backside surface.

Fabrication of dense yttrium oxyfluoride ceramics by hot pressing and their mechanical, thermal, and electrical properties

Excellent corrosion-resistant materials have been strongly required to reduce particle contamination during the plasma process in semiconductor production. Yttrium oxyfluoride can be a candidate as highly corrosion-resistant material. In this study, three types of dense yttrium oxyfluoride ceramics with different oxygen contents, namely, YOF, Y5O4F7 and Y5O4F7 + YF3, were fabricated by hot pressing, and their mechanical, thermal, and electrical properties were evaluated. Y5O4F7 ceramics showed an excellent thermal stability up to 800 °C, a low loss factor, and volume resistivity comparable to conventional plasma-resistant oxides, such as Y2O3. From these results, yttrium oxyfluoride ceramics are strongly suggested to be used as electrostatic chucks in semiconductor production.

Prediction of residual clamping force for Coulomb type and Johnsen–Rahbek type of bipolar electrostatic chucks

As a key component in semiconductor manufacturing equipment, electrostatic chuck is conventionally divided into Coulomb type and J–R type depending on the generating mechanism of clamping force. After supply voltage is cut off, residual clamping force usually remains and becomes a serious issue for production efficiency and process reliability. Hence, it is significant to propose a general prediction model and reveal changing laws of residual force with time for both types. This paper establishes an equivalent circuit model for a bipolar electrostatic chuck containing distributed embosses on dielectric layer surface, and deduces a unified form of mathematical expression describing decaying force, which can cover the two types. The obtained equations can also predict steady force in working state. Furthermore, an experimental method for measuring clamping force and de-clamping time is presented. The results indicate relative deviations tend to decrease as voltages rise. It is found that prediction precision for J–R type is lower than that for Coulomb type. Main reasons are explained and relevant mechanisms are discussed. Overall, the calculations coincide with the measurements within an acceptable error range. The comparisons suggest the theoretical model is effective for simulating the characteristics of residual clamping force for both types of electrostatic chucks.

Effect of smoothness of contact tips and length of micro-hairs on electrostatic force of the silicon bipolar electrostatic chuck having hairy microstructure

Effect of smoothness of contact tips and length of micro-hairs on electrostatic force of the silicon bipolar electrostatic chuck having hairy microstructure

A variable stiffness dielectric elastomer actuator based on electrostatic chucking.

Dielectric elastomer actuators (DEA) are one type of promising artificial muscle; however, applications of bending-type DEA for robotic end-effectors may be limited by their low stiffness and ability to resist external loads without buckling. Unimorph DEA can produce large out-of-plane deformation suitable for use as robotic end effectors; however, design of such actuators for large displacement comes at the cost of low stiffness and blocking force. This work proposes and demonstrates a variable stiffness dielectric elastomer actuator (VSDEA) consisting of a plurality of unimorph DEA units operating in parallel, which can exhibit variable electrostatic chucking to modulate the structure's bending stiffness. The unimorph DEA units are additively manufactured using a high-resolution pneumatic dispenser, and VSDEA comprising various numbers of units are assembled. The performance of the DEA units and VSDEA are compared to model predictions, exhibiting a maximum stiffness change of 39.2×. A claw actuator comprising two VSDEA and weighing 0.6 grams is demonstrated grasping and lifting a 10 gram object.

폴리실라잔계 실란트를 이용한 정전척 실링특성 향상 연구

We have analyzed chemical properties of polysiloxane and polysilazane films, respectively, as sealing materials for electrostatic chuck (ESC) and have investigated the possibility of polysilazane as an alternative sealant to polysiloxane. It has been revealed that Si-O with organic bonding (<TEX>$Si-CH_3$</TEX>) existed in polysiloxane films compared to only pure Si-O bonding in polysilazane films. The sealing property of polysilazane has been found outstanding even in a short time of application. In the polysiloxane films containing <TEX>$H_2O$</TEX>, pin holes have been found possibly due to <TEX>$CO_2$</TEX> gas evolution, and low adhesion with Si substrate has been observed after heat stress test in connection with the existence of organic bonding. After acid resistance test in 0.5 vol.% HF, 68 wt.% <TEX>$HNO_3$</TEX>, and 37 wt.% HCl solution, polyilazane films have shown a longer survival times. Compared to the conventional polysiloxane sealant, polysilazane is expected as a new sealing material because of good thermal and chemical stability.

Determination of electrostatic force and its characteristics based on phase difference by amplitude modulation atomic force microscopy

Electrostatic force measurement at the micro/nano scale is of great significance in science and engineering. In this paper, a reasonable way of applying voltage is put forward by taking an electrostatic chuck in a real integrated circuit manufacturing process as a sample, applying voltage in the probe and the sample electrode, respectively, and comparing the measurement effect of the probe oscillation phase difference by amplitude modulation atomic force microscopy. Based on the phase difference obtained from the experiment, the quantitative dependence of the absolute magnitude of the electrostatic force on the tip-sample distance and applied voltage is established by means of theoretical analysis and numerical simulation. The results show that the varying characteristics of the electrostatic force with the distance and voltage at the micro/nano scale are similar to those at the macroscopic scale. Electrostatic force gradually decays with increasing distance. Electrostatic force is basically proportional to the square of applied voltage. Meanwhile, the applicable conditions of the above laws are discussed. In addition, a comparison of the results in this paper with the results of the energy dissipation method shows the two are consistent in general. The error decreases with increasing distance, and the effect of voltage on the error is small.

Feasibility study of detection of dielectric breakdown of gate oxide film by using acoustic emission method

An in situ detection method for the dielectric breakdown of oxide films for MOS gates has been required in the plasma etching process. In this feasibility study, a conventional MOSFET device is used and an acoustic emission (AE) method is employed for the detection of the dielectric breakdown of a gate oxide film. A thin type AE sensor is attached at the backside of an electrostatic chuck (ESC), and the dielectric breakdown in a MOSFET, which is set on the ESC, is detected. The results demonstrate that the thin type AE sensor can detect the dielectric breakdown with an energy on the order of µJ.

An analytical model for electrostatic adhesive dynamics on dielectric substrates

For electrostatic adhesion on a dielectric material, the electrostatic adhesion force gradually increases to a steady value after the voltage exerted onto the interdigital electrodes. However, little has been addressed to reveal governing mechanisms behind this dynamic phenomenon. In this paper, a theoretical model is presented for analysis of the dynamic properties of electrostatic adhesion on dielectric materials. Firstly, the electric field was derived by solving the Laplace equation of the electrical potential for each sub-area using general solution and boundary conditions. Then, the electrostatic adhesion force was obtained using the Maxwell stress tensor formulation. Finally, the dynamic properties of the electric field and electrostatic adhesion force were assessed by evaluating the transient response of the field and force under a step in applied voltages. Experimental studies for verification were conducted by evaluating the adhesion performance of an electrode panel on three different substrate plates: glass, wood and Polyvinylidene Fluoride (PVDF). Results from these experiments are highly consistent with the theoretical model. The overall results of this paper provide theoretical guidelines for systematic optimization of electrostatic adhesion technology in various application scenarios, such as electrostatic chucks, electrostatic suspension systems and electroadhesive wall-climbing robots.

A novel measuring method of clamping force for electrostatic chuck in semiconductor devices**Project supported by No. 02 National Science and Technology Major Project of China (No. 2011ZX02403-004).

Electrostatic chucks are one of the core components of semiconductor devices. As a key index of electrostatic chucks, the clamping force must be controlled within a reasonable range. Therefore, it is essential to accurately measure the clamping force. To reduce the negative factors influencing measurement precision and repeatability, this article presents a novel method to measure the clamping force and we elaborate both the principle and the key procedure. A micro-force probe component is introduced to monitor, adjust, and eliminate the gap between the wafer and the electrostatic chuck. The contact force between the ruby probe and the wafer is selected as an important parameter to characterize de-chucking, and we have found that the moment of de-chucking can be exactly judged. Moreover, this article derives the formula calibrating equivalent action area of backside gas pressure under real working conditions, which can effectively connect the backside gas pressure at the moment of de-chucking and the clamping force. The experiments were then performed on a self-designed measuring platform. The de-chucking mechanism is discussed in light of our analysis of the experimental data. Determination criteria for de-chucking point are summed up. It is found that the relationship between de-chucking pressure and applied voltage conforms well to quadratic equation. Meanwhile, the result reveals that actual de-chucking behavior is much more complicated than the description given in the classical empirical formula.