Threaded EWMA Controller Tuning and Performance Evaluation in a High-Mixed System

The exponentially weighted moving average (EWMA) controller is a very popular run-to-run (RtR) control scheme in the semiconductor industry. However, in any typical step of semiconductor process, many different products are produced on parallel tools. RtR control is usually implemented with a “threaded” control framework, i.e., different controllers are used for different combinations of tools and products. In this paper, the problem of EWMA controller tuning and performance evaluation in a mixed product system are investigated by simulation and time-series analysis. It was found that as the product frequency changed, the tuning guidelines of a threaded EWMA controller were different for different types of tool disturbances. For a stationary ARMA(1,1) noise, the tuning parameter $lambda$ should be decreased as product frequency decreases. If the tool exhibits nonstationary tool dynamics, e.g., ARIMA(1,1,1) noise, the tuning parameter should increase as the product frequency decreases.      

A study of variable EWMA controller

The exponentially weighted moving average (EWMA) feedback controller (with a fixed discount factor) is a popular run by run control scheme which primarily uses data from past process runs to adjust settings for the next run. Although the EWMA controller with a small discount factor can guarantee a long-term stability (under fairly regular conditions), it usually requires a moderately large number of runs to bring the output of a process to its target. This is impractical for process with small batches. The reason is that the output deviations are usually very large at the beginning of the first few runs and, as a result, the output may be out of process specifications. In order to reduce a possibly high rework rate, the authors propose a variable discount factor to tackle the problem. They state the main results in which the stability conditions and the optimal variable discount factor of the proposed EWMA controller are derived. An example is given to demonstrate the performance. Moreover, a heuristic is proposed to simplify the computation of the variable discount factor. It is seen that the proposed method is easy to implement and provides a good approximation to the optimal variable discount factor.     

Run by run process control: combining SPC and feedback control

The run by run controller provides a framework for controlling a process which is subject to disturbances such as shifts and drifts as a normal part of its operation. The run by run controller combines the advantages of both statistical process control (SPC) and feedback control. It has three components: rapid mode, gradual mode, and generalized SPC. Rapid mode adapts to sudden shifts in the process such as those caused by maintenance operations. Gradual mode adapts to gradual drifts in the process such as those caused by build-up of deposition inside a reactor. The choice between the two modes is determined by the outcome from generalized SPC which allows SPC to be applied to a process while it is being tuned. The run by run controller has been applied to the control of a silicon epitaxy process in a barrel reactor. Rapid mode recovered the process within 3 runs after a disturbance. Gradual mode reduced the variation of the process by a factor of 2.7 as compared to historical data     

DSP-Driven Self-Tuning of RF Circuits for Process-Induced Performance Variability

In the deep-submicrometer design regime, RF circuits are expected to be increasingly susceptible to process variations, and thereby suffer from significant loss of parametric yield. To address this problem, a postmanufacture self-tuning technique that aims to compensate for multiparameter variations is presented. The proposed method incorporates a “response feature” detector and “hardware tuning knobs,” designed into the RF circuit. The RF device test response to a specially crafted diagnostic test stimulus is logged via the built-in detector and embedded analog-to-digital converter. Analysis and prediction of the optimal tuning knob control values for performance compensation is performed using software running on the baseband DSP processor. As a result, the RF circuit performance can be diagnosed and tuned with minimal assistance from external test equipment. Multiple RF performance parameters can be adjusted simultaneously under tuning knob control. The proposed concepts are illustrated for an RF low-noise amplifier (LNA) design and can be applied to other RF circuits as well. A simulation case study and hardware measurements on a fabricated 1.9-GHz LNAs show significant parametric yield enhancement (up to 58%) across the critical RF performance specifications of interest.      

Neural-network-based self-tuning PI controller for precise motioncontrol of PMAC motors

In general, proportional plus integral (PI) controllers used in computer numerically controlled machines possess fixed gain. They may perform well under some operating conditions, but not all. To increase the robustness of fixed-gain PI controllers, we propose a new neural-network-based self-tuning PI control system. In this new approach, a well-trained neural network supplies the PI controller with suitable gain according to each operating condition pair (torque, angular velocity, and position error) detected. To demonstrate the advantages of our proposed neural-network-based self-tuning PI control technique, both computer simulations and experiments were executed in this research. During the computer simulation, the direct experiment method was adopted to better model the problem of hysteresis in the AC servo motor. In real experiments, a PC-based controller was used to carry out the control tasks. Results of both computer simulations and experiments show that the newly developed dynamic PI approach outperforms the fixed PI scheme in rise time, precise positioning, and robustness     

光刻过程RtR控制方法研究进展分析

首先对光刻过程和RtR(Run-to-Run)控制技术的产生背景进行了介绍,对统计过程控制的不足进行了分析并给出了RtR控制器的一般结构。然后从过程建模和控制算法两个角度对三种主要的光刻过程RtR控制器EWMA,MPC和ANN进行了综述和评价,对这三种控制器在非线性控制、单变量控制、多变量控制的适用性和优化控制效果进行了比较分析。最后指出基于MPC的非线性多变量控制器将成为光刻过程RtR控制器的主要研究方向。     

Self-tuning PID controllers for dead time processes

A number of proportional-integral-derivative (PID) based self-tuning controllers exist for the control of difficult processes. A common weakness of these self-tuning PID controllers is their inability to cope with dead-time processes. Here, self-tuning controllers based on a pole-assignment approach, which can overcome fractional dead time, constant and known dead time, plus time-varying dead time, are presented. It is shown using the simulation and experimental results that the controllers work well in handling dead-time processes     

Performance Assessment of Run-to-Run EWMA Controllers

An iterative method is developed to optimize a performance criterion for best achievable performance for discrete integral controllers used in run-to-run control. An analytical expression is derived so that a realistic assessment of the given integral controller is obtained. Using the theoretical equivalence of discrete integral and exponentially weighted moving average (EWMA) controllers, the method is then extended to performance assessment of EWMA controllers. A semiconductor manufacturing example is used to illustrate the utility of the method.     

基于Dahlin算法变风量空调自校正PID控制

变风量空调具有时变、延时、非线性等特点,在此类系统中传统的PID控制算法难以取得最佳的控制效果.基于广义预测自校正的控制算法,控制精度高,具有较强的跟踪性能,但是以增大的计算量和频繁的调节系统参数为代价的.文中提出一种基于改进的Dahlin参数整定方法的自校正PID控制器,该算法在理论建模的基础上,采用在线的带遗忘因子最小二乘法,实现传递函数的参数估计,建立了系统PID参数之间的关系式,实现变风量空调系统的末端控制.算法仿真运算及实验表明,与传统PID及广义预测自校正控制方法相比,文中方法控制精度高于传统PID,同时计算复杂度低于通常广义预测自校正控制.     

Statistical process control in semiconductor manufacturing

The author presents a brief survey of standard SPC (statistical process control) schemes, and illustrates them through examples taken from the semiconductor industry. These methods range from contamination control to the monitoring of continuous process parameters. It is noted that, even as SPC is transforming IC production, the peculiarities of semiconductor manufacturing technology are transforming SPC. Therefore, the author describes novel SPC applications which are now emerging in semiconductor production. These methods are being developed to monitor the short production runs that are characteristic of flexible manufacturing. Additional SPC techniques suitable for in situ multivariate sensor readings are also discussed     

基于LS-SVM的光刻过程R2R预测控制方法

针对光刻过程非线性、时变和产品质量不易在线测量的特性,提出了一种基于最小二乘支持向量机预测模型和微粒群滚动优化方法的批次控制预测控制器。通过历史批次样本数据构建光刻过程的最小二乘支持向量机预测模型,解决了复杂光刻过程难以建立精确数学模型的难题,提高了预测模型的精度。通过预测误差的反馈校正和微粒群滚动优化算法求解最优控制律,提高了控制精度。性能分析结果表明,与指数加权移动平均方法及非线性模型预测控制方法相比较,批次控制预测控制器控制器减小了不同批次关键尺寸输出的差异,显著降低了关键尺寸输出的均方根误差,有效抑制了过程扰动影响。     

Extensions and performance/robustness tradeoffs of the EWMArun-to-run controller by using the internal model control structure

We consider the run-to-run (RtR) correction of input recipes for semiconductor manufacturing processes using measurement information from previous runs. A RtR control algorithm that has been experimentally tested by industry and academia is the EWMA (exponentially weighted moving average) RtR controller. In this paper we provide extensions to this algorithm to address some of its drawbacks and also provide a rigorous theoretical analysis of its properties based on discrete control theory. By formulating the RtR control problem in the internal model control (IMC) structure used in feedback process control, we are able to extend the algorithm to completely eliminate offsets due to unmodeled process drifts, which is a common problem in semiconductor manufacturing. We also develop conditions for robustness with respect to modeling error and measurement delays. Tradeoffs between robustness guarantees and fast RtR response as well as handling of measurement noise are developed and presented in the form of plots that can be used for tuning the parameters of the RtR-IMC controller to accomplish the objectives set by the process engineer. The results are illustrated through several simulations including control of film deposition uniformity in an epitaxial reactor and tungsten deposition rate in a tungsten CVD reactor     

一种实现自调谐频率综合器的算法和结构

在集成的频率综合器中 ,工艺、温度和电源电压的变化使得频率综合器产生的中心频率和频率调谐范围与期望值发生偏移。文中指出了一种自调谐频率综合器的算法和结构 ,利用特殊结构的可编程压控振荡器和自调谐算法实现宽调谐范围的频率综合器 ,进而充分涵盖期望的输出频段。用 0 2 5 μmCMOS工艺设计了一个中心频率 2 2GHz,调谐范围为 338MHz的频率综合器 ,用于IEEE80 2 11b/g无线局域网系统的超外差收发机中 ,可以充分满足标准要求的 80MHz的调谐范围 ;给出了锁定某一目标频率时自调谐算法的具体工作过程 ,结果表明该算法和结构是正确的。     

Recursive least squares estimation for run-to-run control with metrology delay and its application to STI etch process

Run-to-run (RtR) control technology has received tremendous interest in semiconductor manufacturing. Exponentially weighted moving average (EWMA), double-EWMA, and internal model control (IMC) filters are recognized methods for online RtR estimation. In this paper, we consider recursive least squares (RLS) as an alternative for online estimation and RtR control. The relationship between EWMA-type and RLS-type estimates is analyzed and verified with simulations. Because measurement delay is almost inevitable in semiconductor manufacturing, we discuss and compare the performance of EWMA, RtR-IMC, and RLS controllers in handling measurement delay and measurement noise for processes with a deterministic drift. An ad hoc solution is proposed to handle measurement delay for processes with time-varying drifts. The results are illustrated through several simulations and a shallow trench isolation (STI) etch process as an industrial example.     

电机软启动自整定模糊控制器的研究与设计

异步电动机软启动的过程中,传统的PID控制方法难以达到理想的控制效果。本文利用自适应控制理论和模糊控制理论的特性,结合二者的优点,设计出一种快速调节能力强的基于参数自整定模糊控制的电动机软启动控制器。利用自整定模糊决策对电动机启动过程中的电流大小进行控制,优化了系统的控制效果。仿真结果表明,系统具有良好的动静态性能,达到了平稳启动的目的。     

Experimental design of a fuzzy controller for improving power factor of boost rectifier

This article presents the design and the implementation of dSPACE DS1104 controller board-based PI and fuzzy logic peak current-mode controllers in the voltage loop and two controllers in the current loop based first on a standard fixed hysteresis band control, followed by a variable hysteresis band control to achieve constant switching frequency for a single-phase active power factor corrector in the continuous conduction mode. All these controllers have been verified via simulation in Simulink and a real-time implementation is performed on an experimental test bench utilising a rapid prototyping tool. The controllers are experimentally compared for steady-state performance and transient response. It is shown that the PI and fuzzy logic controllers give a superior steady-state performance, whereas the fuzzy logic inference based controller can achieve better dynamic response than its PI counterpart under large load disturbance and plant uncertainties. Furthermore, the variable hysteresis band control in the current loop gives a low total harmonic distortion of the input current compared to a standard fixed hysteresis band control.     

SHEWMA: an end-of-line SPC scheme using wafer acceptance test data

In this paper, an end-of-line quality control scheme based on wafer acceptance test (WAT) data is presented. Due to the multiple-stream and sequence-disorder effects typically present in the WAT data, an abnormal process shift caused by one machine at an in-line step may become vague for detection using end-of-line WAT data. A methodology for generating robust design parameters for the simultaneous application of Shewhart and EWMA control charts to WAT data is proposed. This SHEWMA scheme is implemented in a foundry environment and its detection and diagnosis-enhancing capabilities are validated using both numerical derivations and fab data. Results show that the SHEWMA scheme is superior to the current practices in detection speed. Its use is complementary to the existing in-line SPC for process integration     

A Comparison of Controller Design and Simulation for an Industrial Manipulator

This paper investigates the controller design for an industrial manipulator using two different approaches. One method applies the conventional servo control technique with suitable feedforward compensation. The other method adopts the self-tuning adaptive control strategy. Computer simulation is conducted so as to evaluate the performance of the proposed controllers on tracking accuracy, robustness, and speed of response. Simulation results indicate that both controllers perform well under various simulated conditions and are robust in terms of parameter sensitivity.     

基于自整定PID的烘干炉温度控制软件设计与仿真

传统的烘干炉温度控制系统在烘干过程中,烘干炉温度保持恒温,并不利于产品整体的烘干,而为了达到更好的效果,其温度应由低到高逐渐升高,以利于溶剂的充分挥发.本文分析了PID控制和模糊控制的优缺点,将PID控制和模糊控制的优点结合起来,采用模糊规则在线整定PID的PK、IK、DK三个参数的模糊自整定PID控制方法.基于模糊自整定PID控制算法的控制系统有相当好的灵活性,能进行数据实时采集、利用模糊PID算法进行处理及控制结果显示等功能,可以获得较高的控制精度.     

棱镜色散腔的自动调谐及计算机控制系统

本文对棱镜色散腔自动调谐的原理及实现方法以及计算机控制系统作了较为详细的阐述,该自动调谐系统适用于固体可调谐激光器,实现中该调谐方法用于Ｎｄ：ＹＡＧ锁模激光（５３２ｎｍ）泵浦的钛宝石激光器＾「１」,能实现６８０～９８０ｎｍ范围的波长自动调谐输出。