Backside Pressure Research Articles

Automatic Detection of Compensatory Movement Patterns by a Pressure Distribution Mattress Using Machine Learning Methods: A Pilot Study

For stroke patients with hemiplegia, reaching with the paretic arm is often associated with compensatory movements due to limited active arm movement and a loss of interjoint coordination. Detecting common compensatory movement patterns, such as excessive trunk displacement and scapular elevation, is critical for improving the motor function of the paretic arm. Existing compensatory movement pattern detection methods, including sensor-based systems and camera-based systems, suffer from object obstruction and require complex setups. In this paper, a compensatory movement pattern detection system using a pressure distribution mattress is presented. This method is a novel approach to detect compensations and has observed advantages; it is simple, unobtrusive and low cost. Fifteen healthy participants with no motor impairments performed three reaching tasks (back-and-forth, side-to-side, and up-and-down reaching) in a normal pattern and in compensatory movement patterns (trunk rotation and lean-forward, and scapular elevation). Pressure distribution data of all motions were recorded and processed to generate a group of features (average sensor values, the lateral center of pressure, longitudinal center of pressure, the ratio of left-side to right-side pressure, and the ratio of front-side to back-side pressure) reflecting the information of each predefined pattern. Four machine learning methods were implemented to detect compensatory movement patterns and showed good reliability and precision. Both k-nearest neighbor (kNN) and support vector machine (SVM) classifiers have achieved an excellent classification performance (F1-score = 0.934) in detecting compensation during all reaching tasks. For the multiclass classification of compensatory movement patterns, the SVM classifier exhibited a good classification performance for trunk lean-forward (F1-score = 0.933), scapular elevation (F1-score = 0.881), and trunk rotation (F1-score = 0.854) and outperformed previous reports. The study results provide initial evidence of a pressure distribution mattress for detecting compensatory movement patterns. Future work needs to test the approach on stroke survivors to verified the feasibility and validity.

Electret microphone modeling and optimization by combined finite element analysis and lumped-element techniques

Electret microphone performance modeling must represent detailed coupled mechanical, electrostatic, and fluid dynamics of the moving diaphragm, stationary back electrode and intervening air layer (the “motor”) while also evaluating the net performance characteristics which result. We model electret microphone response and noise by combined FEA and lumped-element methods. In detail, the diaphragm is treated as a tensioned membrane. Electrostatics are evaluated in locally parallel-plate fashion. Air layer dynamics are treated by reducing the exact thermoacoustic parallel-plate 3D squeeze solution to a 2D “transmission sheet” differential equation. Analyses (COMSOL FEA 2D PDE-mode) include initial diaphragm deflection upon back electrode polarization, then the harmonic responses to changes in frontside pressure, backside pressure, and polarization. Motor responses (frontside/backside volume flows and output current) are reduced to impedance and transfer characteristics of a three-port (front and back acoustic, electrical) element, which is then embedded in a traditional host lumped-element equivalent circuit (including amplifier). FEA-based motor characteristics over an array of frequencies lead to microphone frequency response and noise spectrum. Performance optimization is done by scripting motor geometry generation and FEA analysis as a subroutine, defining a space of adjusted parameters (motor dimensions, etc.) and running recurring FEA analyses generated by a downhill simplex algorithm.

Microscopic approach to an equation for the heat flow between wafer and E-chuck

Wafer cooling and heating by means of a gas at the wafer backside is a key technology in semiconductor manufacturing. A detailed understanding of the physical mechanisms is needed to yield the best process results. Besides the commonly used Smoluchowski interface condition, a microscopical approach is deduced describing the whole pressure range. Different thermal gas species and surface properties, as well as the velocity and angular distribution of the atoms, are basic features of the model. The angular distribution of the desorbed atoms is shown to have a significant influence on the wafer temperature. The heat transfer properties between the gas and two different surfaces are described by one value, the effective accommodation coefficient. The final wafer temperature is simulated as a function of the input power, the backside pressure, and the gas species. Helium has the best cooling properties of the inert gases, followed by neon. The influence of a pollution of the wafer surface on the uniformity of the wafer temperature has been determined. The surface roughness has no significant influence on the cooling abilities of an electrostatic chuck.

Monolithic silicon smart tactile image sensor with integrated strain sensor array on pneumatically swollen single-diaphragm structure

In this paper, a novel concept of silicon-microelectromechanical system tactile image sensor aimed at fingertip tactile applications and evaluation results of a prototype device are presented. Array of strain-sensitive sensor pixels is integrated on a pneumatically swollen silicon diaphragm with signal processing circuits in monolithic configuration. Elastic surface of the tactile image sensor is realized using repulsive force of the air pressure applied to diaphragm backside. Contact force distribution of an object is detected from the stress distribution change on the diaphragm using piezoresistor array. Force range and force sensitivity can be controlled by the pressure even after device packaging step. In this principle, fine pitch of pixels and a large-scale sensing array can be easily realized using the abilities of silicon CMOS technology. In addition, the movable stroke of sensor surface can be made much longer than the individually formed micromechanical pixels. A prototype device, of the new concept, with 3040 /spl times/ 3040 /spl mu/m/sup 2/ sensing diaphragm was fabricated with integrated 6 /spl times/ 6 array of 420-/spl mu/m pitch pixels. Increased movable stroke of the swollen diaphragm from the original surface is around 30 /spl mu/m at 23-kPa pressure at the top. Realized spatial resolution of the prototype device is approximately 400 /spl mu/m, which is determined by the relationship between the pixel pitch and mechanical crosstalk among the pixels. Positions of touch and their contact force amplitudes were detected as a two-dimensional distribution of the output voltage from the pixel array in a multipoint contact test. The maximum input-force range can be controlled from 21 to 176 mN by changing the backside pressure from 5 to 64 kPa. Through the evaluation of the fabricated device, major advantages of this tactile image sensor have been demonstrated successfully.

The relationship between wafer surface pressure and wafer backside loading in Chemical Mechanical Polishing

To have a good carrier head design, it is important to understand the relationship between wafer surface pressure distribution and wafer backside loading by the carrier head. A theoretical study based on a simplified Chemical Mechanical Polishing (CMP) system is presented in this paper. It shows that, to have a uniform pressure distribution, wafer backside pressure will not be uniform and, theoretically, it is impossible to achieve such loading. It also points out that, contradicting to common understanding, uniform backside pressure will lead to nonuniform wafer surface pressure and edge effect. The presented theory may be used as a tool for further optimization of carrier head design and a base for more realistic modeling on specific tool designs.

An Engineering Approach to Predict the Polishing Rate in CMP with Rotational Equipment

In this paper we present an approach for predicting polishing rate with the main parameters in the recipe. Compared with Preston’s equation, a dimensional analysis-based equation, was given. We used a method called “dimensional analysis” to deduce an empirical equation. We successfully correlated the polishing rate with the operational parameters, such as the turntable rotational speed, the top-ring rotational speed, downforce, and back-side pressure. For the convenience of chemical mechanical polishing (CMP) process engineers, we proposed a simple method to help predict the polishing rate. With the experimental data, the presented equation seems workable. © 2004 The Electrochemical Society. All rights reserved.

Study of a mechanically clamped cryo-chuck device in a high density plasma for deep anisotropic etching of silicon

This article presents a study concerning a cryo-chuck device used in an inductively coupled plasma reactor for deep anisotropic etching of narrow trenches (2 μm wide) in silicon wafers of 5 in. in diameter. Thermal mechanisms in a mechanically clamped cryo-chuck system have been studied. First, wafer deformations have been measured in the chuck device. Deformations occur because of the helium backside pressure allowing thermal transfer to cool the wafer. In a second step, these deformations have been used in calculations considering the heat transfers in the substrate. In a last step, in situ temperature measurements have been made on wafers during a process using a LUXTRON® probe. This study shows the influence of the backside helium gap variation and the clamping ring temperature on the uniformity of substrate cooling.

Modeling of Heat Transport and Wafer Heating Effects during Plasma Etching

Uniformity of plasma etching and deposition processes critically depends on the wafer temperature and its spatial variation across the wafer. The goal of this work is to use mathematical modeling to investigate the key factors that determine the wafer temperature and its radial uniformity during plasma etching. Toward this end, a mathematical model of energy transport in and out of a Si wafer in a plasma etching reactor that employs a substrate platen with a He back side cooling arrangement was developed. The possibility of wafer bowing due to high He back side pressure was considered and the effects of ion bombardment flux uniformity, He back side pressure, and different wafer clamping arrangements were studied. While an increase in He back side pressure increases the rate of heat transfer from the wafer to the electrode, excessive He pressure causes the wafer to bow. Bowing increases the electrode‐wafer gap, decreases the heat transfer rate, and adversely affects the temperature uniformity. These effects are most pronounced for large diameter wafers (>200 mm) and are predicted to be very important in the processing of 300 and 400 mm substrates. The manner in which the wafer is clamped to the cooled electrode is another key factor that determines the heat transport at the wafer edge and the radial temperature profile across the wafer. The uniformity of the wafer temperature depends on the heat transport at the wafer edges. Poor thermal contact at the wafer edge leads to a high but uniform wafer temperature; on the other hand, if a good thermal contact is made at the wafer edge, the average temperature is lower but less uniform. Model predictions compared well with the available experimental data.

Experiments with back side gas cooling using an electrostatic wafer holder in an electron cyclotron resonance etching tool

Wafer temperature, etch rate, and etch uniformity measurements of SiO2 wafers were made to characterize the use of back side helium cooling with an electrostatic wafer holder in an electron cyclotron resonance etching tool. The etch rate was found to be independent of the wafer temperature in the range between 20 and 110 °C. A 7% increase in etch nonuniformity (3σ) at higher backside pressures was attributed to helium, which leaked around the edge of the wafer, displacing the etchant gas. A back side pressure of 2–3 Torr provides a balance between wafer temperature control and helium leak rates.