Showing papers on "Process variable published in 1995"

Method for setting and adjusting process parameters to maintain acceptable critical dimensions across each die of mass-produced semiconductor wafers

Abstract: A method and system are disclosed for: (a) matching a machine-implemented process simulator with an actual fabrication line, (b) using the matched model to simulate the statistical results of mass production by the modeled production line, (c) using the model to predict cross-reticle variance from collected data for in-scribe features, (d) using the model to decompose the variance contributions of each process parameter and identify the more prominent contributors, and (e) using the model to identify the process parameter adjustments which would provide best leverage when taken one at a time.

Model predictive control apparatus and method

Abstract: A model predictive control apparatus and method for controlling the operation of a process (34) having a process input signal (Xk) and a process output signal (Yk), which includes determining a predicted process output signal (Yk+n+m+2) at a future steady state condition according to a process model, determing a steady state error signal according to the difference between the predicted process output signal and a desired set point signal (Ysp), and determining a set of future process input change signals (x) requires to correct for the estimated steady state error (e) by providing at least one step response in the process output at a future time. The next net process input change is then applied according to the sum of the currently determined first element of the set of future process input change singals (x) summed with any future process input change signals that were previously calculated for the next process input change signal that is calculated according to this method. The model is expressed in velocity form. Process tuning parameters are available to dampen the net process input change as well as the currently determined first element of the process input change with respect to a process input change signal that is calculated according to the steady state error divided by the steady state process gain.

Method of predictive maintenance of a process control system having fluid movement

Abstract: A pipeline system of a process facility has a plurality of equipments, the equipments including at least one pipeline for providing a channel for a fluid of a process to flow. The process of the process facility is controlled by a process control system. The equipments also include at least one device for measuring a process variable of the fluid. The device comprises a sensor element for sensing a predetermined process variable of the fluid flowing in the pipeline to output a signal containing information about the process variable being measured and containing information about the fluid flowing in the pipeline. The device further includes a first filter to pass a first component of the signal containing the information of the process variable and a second filter to pass a second component of the signal containing the information about the fluid flowing in the pipeline. A first processor processes the first component of the signal to output the process variable to the process control system to control the process. A second processor processes the second component of the signal in a flow model of the pipeline system to output advisory information indicating imminent failure of the equipment when detected by said processing by the second processor.

Method of adapting and applying control parameters in non-linear process controllers

Abstract: A non-linear process controller drives a process variable to be substantially equivalent to a set point based on the expected load disturbances within the process and on a measurement of the actual magnitude of set point changes. The controller uses control parameters developed in an optimal manner to control the process in response to expected load disturbances when no set point change has occurred. Whenever a set point change is detected, the controller derives a set of set point change control parameters and uses these set point change control parameters in responding to the set point change. Each of the set point change control parameters may be developed as a function of the magnitude of the actual change in the set point and according to a set of process characteristics which may include the time delay and the dominant time constant of the process.

An adaptive sample size CUSUM control chart

Abstract: The Cumulative Sum Chart for process control is designed to detect relatively small shifts in the mean of the process variable. In this paper, we show that by using samples of two different sizes, rather than a fixed sample, improvements in the chart's ability to detect small shifts are possible. These improvements are obtained without increasing the likelihood of a false alarm when the process mean is on target. The average run length values for the adaptive sample scheme are compared to those for a fixed sample scheme for different magnitudes of shifts in the process mean. A fast initial response scheme is presented. An example from a manufacturing process is used to illustrate the advantages of the adaptive sampling scheme.

Tutorial Process analysis, monitoring and diagnosis, using multivariate projection methods

Abstract: Multivariate statistical methods for the analysis, monitoring and diagnosis of process operating performance are becoming more important because of the availability of on-line process computers which routinely collect measurements on large numbers of process variables. Traditional univariate control charts have been extended to multivariate quality control situations using the Hotelling T2 statistic. Recent approaches to multivariate statistical process control which utilize not only product quality data (Y), but also all of the available process variable data (X) are based on multivariate statistical projection methods (principal component analysis, (PCA), partial least squares, (PLS), multi-block PLS and multi-way PCA). An overview of these methods and their use in the statistical process control of multivariate continuous and batch processes is presented. Applications are provided on the analysis of historical data from the catalytic cracking section of a large petroleum refinery, on the monitoring and diagnosis of a continuous polymerization process and on the monitoring of an industrial batch process.

A case study on process optimization using the gradient loss function

Abstract: This paper focuses on studies where the goal is to optimize the key quality characteristics of a specific product or process. In order to do that, the process parameters must be adjusted in such a way that deviations from target are minimized while robustness to noise and to process parameter fluctuations are maximized. Since this is a multi-response, multi-objective problem, the optimum solution is a compromise. In this paper we present a gradient loss function which captures all the desired objectives, and propose a general methodology to perform the optimization analysis. This methodology is then carried out experimentally on a cosmetic product and the results are discussed.

Rare earth-doped integrated glass components: modeling and optimization

Abstract: For the integrated optic erbium-doped phosphate silica-amplifier, a comprehensive model is presented which includes high-concentration dissipative ion-ion interactions. Based on actual waveguide parameters, the model is seen to reproduce measured gains closely. A rigorous design optimization is performed, and the influence of variations in the launched pump power, the core cross section, the waveguide length, the erbium concentration, and the background losses are evaluated. Optimal design proposals are given, and the process reproducibility of the proposed optimal design is examined. Requirements for process parameter control in the wafer fabrication are set up. >

Epi-film thickness measurements using emission Fourier transform infrared spectroscopy. II. Real-time in situ process monitoring and control

Abstract: Real-time in situ applications of the emission Fourier transform infrared (E/FT-IR) technique are reported in this paper. For real-time process monitoring, we found that the real-time growth rate measured by the E/FT-IR is responsive to variations of process parameter(s) (i.e., temperature, pressure, and gas composition). For real-time epi-film thickness control, two control algorithms were used: 1) first past the post (FPP) method; and 2) linear forecasting. A closed-loop precise epi-film thickness end-point control is demonstrated. Additionally, by real-time monitoring of the incubation time and growth rate, we are able to obtain qualitative information about the effectiveness of the predeposition wafer cleaning process. Thus, plasma cleaning process optimization time is shortened and postdeposition materials characterization cost is reduced. Using the optimized conditions, we have demonstrated the growth of defect free epitaxial silicon films. >

Proportional with variable bias batch reactor temperature control system

Abstract: An improved method of controlling the temperature of a batch reactor employing a cascaded master and slave controller architecture wherein the temperature of the reactor serves as the measured variable, MV1, in the master loop and the jacket temperature serves as the measured variable, MV2, in the slave loop and the feedback for the master loop, FB1, is intentional set equal to this measured variable, MV1, or to the master controller set point, SP1, corresponding to the temperature of the reactor thus inherently creating a bias feedback and proportional variable reset (PVR). The novel PVR temperature control system is useful in alleviating product variability caused by temperature control variation during heat, cod and hold steps.

Process for controlling the driving stability with the king pin inclination difference as the controlled variable

Abstract: A process for controlling the driving stability of a vehicle is provided. To avoid complicated models for determining the desired value of a variable characteristic of the travel behavior, which variable usually must be calculated by an expensive calculation circuit, a controlled variable is selected, which directly describes the driving stability and is compared with an actual value, which can be calculated in a relatively simple manner. An advantageous embodiment describes comparing an actual value of the variable, which can be determined in a simple manner, with a desired value. The range of tolerance of the variable is set directly by the driving stability limits. Advantageous variants pertain to the suitable scheme of calculation and the selection of a suitable range of tolerance.

An on-line method for monitoring of relative humidity using thermal sensors

Abstract: Relative humidity is an important process variable in many agro-based and food processing industries and continuous monitoring and control of it becomes necessary. There are a numbers of direct reading type measuring techniques using variable parameter sensors. Many attempts have also been made to measure relative humidity on-line with the classical concept of wet and dry bulb psychrometer. With this concept, the design of a robust technique by piecewise linearization of the psychrometric chart over a working temperature range and using thermal sensors, can be formulated. This paper illustrates the methodology applicable to a working temperature range in the tea industry. >

Optimization of Process Parameter and Temperature Uniformity On Wafers For Rapid Thermal Processing

Abstract: A new strategy based algorithm to optimize process parameter uniformity (e.g.sheet resistance, oxide thickness) and temperature uniformity on wafers in a commercially available Rapid Thermal Processing (RTP) system with independent lamp control is described. The computational algorithm uses an effective strategy to minimize the standard deviation of the considered parameter distribution. It is based on simulation software which is able to calculate the temperature and resulting parameter distribution on the wafer for a given lamp correction table. A cyclical variation of the correction values of all lamps is done while minimizing the standard deviation of the considered process parameter. After the input of experimentally obtained wafer maps the optimization can be done within a few minutes. This technique is an effective tool for the process engineer to use to quickly optimize the homogeneity of the RTP tool for particular process requirements. The methodology will be shown on the basis of three typical RTP applications (Rapid Thermal Oxidation, Titanium Silicidation and Implant Annealing). The impact of variations of correction values for single lamps on the resulting process uniformity for different applications will be discussed.

Verfahren zur Zustandsüberwachung dynamischer Rauschprozesse

Abstract: Disclosed is a method of monitoring the reliable operation and improving diagnosis of state of controlled stochastic processes, in particular of the energy-producing process in nuclear reactors, using process signals measured with the aid of suitable sensors (detectors) for measured values, e.g. neutron flux, temperature and pressure, including the constant components of said values (process values) and the fluctuating components (process noise). Specifically, measurements and analysis of the process signals from the stochastic process are used to calculate characteristic values based on statistical procedures, using statistical parameter estimation procedures of sequential analysis; variations in the calculated model parameters (characteristic vectors) are evaluated for monitoring and diagnosis of the wideband fluctuating components in the frequency range with the aid of characteristic values such as the pulse response function. The calculated residual function in the time range and the power density spectrum of the signal residue are used to improve diagnosis of the narrow-band fluctuating components in the frequency range such as deterministic oscillations and, with the aid of multivariate parameter models, the effect of fluctuations of process values of a particular process variable vector on the measured individual signal is separated for monitoring purposes and, using multivariate parameter models, signal and system transfer functions and signal and noise contributory factors for the signals of a measured process variable vector are calculated and used to diagnose process characteristics, in particular in feedback systems such as those in a nuclear reactor.

Method and apparatus for controlling spark erosion process

Abstract: A method and an apparatus for controlling a spark erosion process between a workpiece and an electrode for instance a microdrilling electrode, so that the erosion process becomes less susceptible to a malfunction, in that at least one process parameter is measured along a first test interval of the section to be eroded, at least one control value is deduced form the measured values, and this control value is used in a subsequent erosion interval of the section to be eroded. The control value is preferably used for controlling a suitable feed rate of the electrode. The susceptibility to malfunctions is further lessened, in that a differentiation is made between mechanical and other short circuits and in that the electrode movement is controlled differently for mechanical short circuits than for other short circuits.

Method and device for obtaining process characteristic in self-tuning controller

Abstract: PURPOSE: To obtain the characteristics of an on-site process system controlled by means of a self-tuning controller. CONSTITUTION: The open loop response to a process variable to a step impressed upon the control output of a controller is analyzed. A primary system having a pure time delay is used for approximating the actual response of a high-order on-site process system. The entire dead time 200 and time constant of the approximation by the primary system are decided. The maximum inclination 208 of the response of the process variable to the step is stored together with its occurring time and assigned process variable. The stored information is used for approximating the entire dead time 200. The time constant is decided by using a secondary time constant or a convergent point 68 existing within a prescribed range between the actual response data and primary approximation.

Centrifugal casting of glass plates : a finite-element analysis of process parameter influence

Abstract: For the first time, glass centrifugal casting is analyzed by finite-element viscoplastic models. First of all, the sensitivity of the process parameters is analyzed on the radius lengthening of a glass gob during casting using central processing unit time-saving models. The suitability of glass for centrifuging is evaluated, taking its temperature, viscosity, mould rotation speed and time dependency, casting time and initial gob shape into account. A refined finite-element analysis of an NBS-710 plate production is then achieved. The results are used in decision-aid process design curves which allow the manufacturer to efficiently adjust process parameters with regard to the desired final shape

Towards Decision Making in Knowledge-Based Systems for Composite Cure

Abstract: Current emphases on effective process control are targeted to achieve the desired product-property in a consistent and verifiable manner. The paradigm focuses on implementing knowledge derived from pre-and-after processing material properties, thermomechanical history, in-situ sensor data, and predictive process models. A series of pre-determined set points would be established to control the on-line process schedules. Since material properties are not directly measurable, the effectiveness of those schedules depends on knowing the evolution of property goal states as a function of the process variable set points.

Process and Apparatus for Controlling and/or Regulating a Solids-Liquid Separation Process

Abstract: A process and apparatus for controlling and/or regulating a solids-liquid separation process, such as in a dewatering or drying device, includes at least two photodetectors, each associated with a light source, a detector to detect light of the associated light source reflected from the surface of the solids-liquid mass, a controller generating an output signal as a function of the detected light and converting and processing the output signals of the photodetectors into correcting variables for controlling and/or regulating at least one process parameter of the separation process. At least one of the photodetectors is associated with at least one second photodetector for detecting light reflected into the photodetector at an angle, preferably an angle of 30.degree. to the main direction of reflection. The output signals of the photodetectors are advantageously processed into correcting variables for the step-wise adjustment of the at least one process parameter to optimize the separation process.

Predicting process evolution with a neural network. A window on relevant data

Abstract: Nowadays process automation has become as common thread in industrial processes as the television is in every household. Every company that is involved in some production process is keeping track of what is happening in the plant, This should result in a better understanding and management of the process. However, this is seldom the case, the culprit being an overdose of information. As a result, a lot of useful information remains hidden in these data. In this article the authors present a system that is capable of distilling knowledge out of process data. Based on the current process situation and using information from previous operations, knowledge is generated on the fly by the use of a modelling technique. With a neural network as a model, relations between process and quality parameters are revealed, including the range of validity and the order of magnitude. This information can be used to manage the process in the most economic way. The proposed system is generally applicable throughout the process industry. Two industrial examples are referred to: a waste paper plant (continuous operation), and a pulp factory (batch operation).

Improving flow measurement by real-time flow calculation in transmitters having multiple process variables

Abstract: Over the years the functionality and performance of instrumentation used with head type has steadily improved. The technology employed in pressure instrumentation has resulted in a migration from mechanical/pneumatic transmitters to analog electronic transmitters to microprocessor based smart electronic transmitters. Similar improvements have occurred in temperature instrumentation. The logical next step in this progression is the consolidation of multiple process measurements in a single transmitter package. With all of the process measurements available, the benefits to the user can be further enhanced by performing flow calculation within the transmitter. The benefits of using the process variables to continuously calculate the terms in the equation for flow through a head type meters are presented. A comparison is made between this method and the commonly used method in which many terms are considered to be constant. Significant improvements can be realized by the real-time calculation of these terms, particularly the discharge coefficient and fluid density. Calculated performance results are presented for both liquid and gas flow application. The results show that a multiple process variable transmitter with on-board flow calculations can extend flow range beyond the typically accepted 3:1 range.

Symbolic approach in design of BaTiO/sub 3/-ceramics capacitive properties [bandpass filters]

Abstract: This paper presents a method that can establish a correlation between circuit function and manufacturing process parameters of a device The method is based on the symbolic network function generation and relationship between technological and electrical parameters of an electronic device The circuit function in the symbolic form enables direct substitution of any electrical parameter with any process parameter needed for the device manufacture We consider the method in respect of the capacitive property of BaTiO/sub 3/-ceramic The effects of pressing pressure and sintering temperature on the electrical characteristics of pure barium-titanate were researched An interpolation function is used for mapping results obtained by measurements on ceramic samples, to the algebraic expression The approach is illustrated on an example

Apparatus for controlling the bank size in the production of films and sheets

Abstract: A device for controlling bead height (9) at the nip of a polishing roll stack (1,2,3) during prodn. of thermoplastic film or plate comprises measuring sensors (8) which identify the edges of the strip material beyond the initial polishing roll gap. Deviation of the strip edges from a set width initiates changes to a process variable which returns the strip to a set width. Pref. variable process parameters may be roll (1,2,3) speed or melt output (6) from the extruder (4). Sensors (8) are located either at the second roll (2) or behind the third roll (3). The device controls the bead ht at the nip of polishing stack rolls following an extruder producing thermoplastic film or plate. Measurement of width changes guarantees greater sensitivity in relation to changes in bead height.