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.     

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.      

Performance Analysis of EWMA Controllers Subject to Metrology Delay

Metrology delay is a natural problem in the implementation of advanced process control scheme in semiconductor manufacturing systems. It is very important to understand the effect of metrology delay on performance of advanced process control systems. In this paper, the influences of metrology delay on both the transient and asymptotic properties of the product quality are analyzed for the case when a linear system with an initial bias and a stochastic autoregressive moving average (ARMA) disturbance is under an exponentially weighted moving average (EWMA) run-to-run control. Tuning guidelines are developed based on the study of numerical optimization results of the analytical closed-loop output response. In addition, effective metrology delay of a variable time delay system is analyzed based on the resampling technique implemented to a randomized time delay system. A virtual metrology technique is a possible solution to tackle the problem of metrology delay. The tradeoff between additional error of virtual metrology and reduction in time delay is studied. The results are illustrated using an example of control of the tungsten deposition rate in a tungsten chemical–vapor deposition reactor. The basic conclusion is that metrology delay is only important for processes that experience nonstationary stochastic disturbance. In such a case, use of virtual metrology is justified if the error of the virtual metrology method is less than the error caused by stochastic process noise. The accuracy of the virtual metrology noise with respect to the traditional metrology is not critical, provided that the error due to metrology is much less than that due to process disturbances.      

Formation of MOS Gates by rapid thermal/microwave remote-plasma multiprocessing

A novel cold-wall single-wafer lamp-heated rapid thermal/ microwave remote-plasma multiprocessing (RTMRPM) reactor has been developed for multilayer in-situ growth and deposition of dielectrics, silicon, and metals. This equipment is the result of an attempt to enhance semiconductor processing equipment versatility, to improve process reproducibility and uniformity, to increase growth and deposition rates at reduced processing temperatures, and to achieve in-situ processing. For high-performance MOS VLSI applications, a variety of selective and nonselective tungsten deposition processes were investigated in this work. The tungsten-gate MOS devices fabricated using the remote-plasma multiprocessing techniques exhibited negligible plasma damage and near-ideal electrical characteristics. The flexibility of the reactor allows independent optimization of each process step yet permits multiprocessing.     

Simulation of Semiconductor Manufacturing Supply-Chain Systems With DEVS, MPC, and KIB

The dynamics of high-volume discrete-part semiconductor manufacturing supply-chain systems can be described using a combination of Discrete EVent System Specification (DEVS) and model predictive control (MPC) modeling approaches. To formulate the interactions between the discrete process model and its controller, another model called Knowledge Interchange Broker (KIB) is used. A robust and scalable testbed supporting DEVS-based manufacturing process modeling, MPC-based controller design, and the ${hbox{KIB}}_{{{rm DEVS}/{rm{MPC}}}}$ interaction model is developed. A suite of experiments have been devised and simulated using this testbed. The flexibility of this approach for modeling, simulating, and evaluating stochastic discrete process models under alternative control schemes is detailed. The testbed illustrates the benefits and challenges associated with developing and using realistic manufacturing process models and process control policies. The simulation environment demonstrates the importance of explicitly defining and exposing the interactions between the manufacturing and control subsystems of complex semiconductor supply-chain systems.      

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。     

Simultaneous control of multiple measures of nonuniformity usingsite models and monitor wafer control

Present day semiconductor manufacturing processes are subject to tight specifications. High yields with tight process specifications require drive to target process control. As the size of the wafer in the semiconductor industry increases, nonuniformity across the wafer becomes a crucial yield limiting issue. Modeling nonuniformity in terms of the equipment settings permits calculation of recipes required to achieve the desired nonuniformity. However, models for single measures of nonuniformity, such as standard deviation, or range, do not capture all aspects of the nonuniformity and often do not model well in terms of the equipment settings. This paper describes the use of spatial models to simultaneously quantify multiple measures of nonuniformity, and a controller to keep the nonuniformities within specifications, Use of spatial models in conjunction with a monitor wafer controller (MWC) enables the simultaneous control of multiple nonuniformity measures. The paper presents the results of applying the MWC with spatial models to a plasma enhanced TEOS (PETEOS) deposition process on an Applied Materials Precision 5000 (AMT5000). The controller has been keeping the PETEOS process within specifications for over two years     

Toward observable UHVCVD: Modeling of flow dynamics and AAS partial pressure measurement implementation

Ultra-high vacuum chemical vapor deposition is a thin film deposition process that features excellent film purity, but is sensitive to the processing variations (such as, the precursors and their dispensers, the reactor’s initial condition, etc.). In this paper, we present the design of a ultra-high vacuum chemical vapor deposition reactor with in situ partial pressure atomic absorption spectroscopy measurement that improves reproducibility and observability of such a process. Our main contributions are: (i) a conceptual control systems design of ultra-high vacuum chemical vapor deposition; (ii) atomic absorption spectroscopy based sensor design for the real-time in situ partial pressure measurements; (iii) a flux dynamical model; (iv) experimental reactor design; and (v) experimental validation of model components and the atomic absorption spectroscopy measurement technique. Our results show that the proposed sensor systems are able to provide real-time measurements of the partial pressure inside the reactor and our proposed flux dynamical model agrees with the measured partial pressure. The latter allows us to use it in the design of model-based output feedback control of the partial pressure.     

Manufacturability issues in rapid thermal chemical vapor deposition

Rapid thermal processing (RTP) has been considered from a manufacturing point of view as a potential technology for depositing thin films by low-pressure chemical vapor deposition (LPCVD) in a single-wafer manufacturing environment. The results of this study suggest that new chemical processes must be developed to satisfy the throughput requirements of single-wafer manufacturing and the demands of cold-wall reactor design. Issues such as temperature measurement and uniformity are reviewed and reconsidered in the context of LPCVD. New tool requirements for reduced pressure operation are discussed. New advances in tool design are needed (especially in temperature measurement) before rapid thermal chemical vapor deposition (RTCVD) can be considered as a routine manufacturable process     

Feedforward control for reduced run-to-run variation inmicroelectronics manufacturing

Increased manufacturing yields can be obtained by reducing process variation. One potential method to achieve lower process variance is through interprocess feedforward control. During feedforward control, a process recipe is adjusted to compensate for measured input deviations. The potential benefits of feedforward control include reduced run-to-run variance, rework, and scrap. Feedforward control has been used often in manufacturing. However, there are two problematic issues associated with feedforward recipe adjustment: 1) there is noise in the measurement tool and adjusting for inaccurate measurements could increase the variance and 2) it is difficult to alter one parameter in a manufacturing process without worsening other key parameters. In this paper, we will address both issues using a systems approach. Measurement noise poses a significant threat to the success of feedforward control. If the measurement noise is sufficiently large, the variance under feedforward control could exceed the variance with no control. To address this concern, we have integrated statistics theory into the feedforward controller design. This detunes the recipe adjustment based on the confidence in the accuracy of the sensor. These algorithms have the effect of filtering the noise from the measurement tool. In order to address the problem of altering one parameter without adversely affecting others, one can use a feedforward controller that selects a recipe from within a predefined set of allowable qualified recipes. We call this feedforward recipe selection control (FRSC). We have developed a design methodology for this type of controller. Preliminary versions of our design algorithms have been implemented into a graphical user interface (GUI)-based computer-aided design (CAD) environment. This interactive software package guides the engineer through the design of feedforward controllers using process data as inputs     

Inverse model-based real-time control for temperature uniformity ofRTCVD

A reduced-order model describing a rapid thermal chemical vapor deposition (RTCVD) process is utilized for real-time model based control for temperature uniformity across the wafer. Feedback is based on temperature measurements at selected points on the wafer surface. The feedback controller is designed using the internal model control (IMC) structure, especially modified to handle systems described by ordinary differential and algebraic equations. The IMC controller is obtained using optimal control theory on singular arcs extended for multi-input systems. Its performance is also compared with one based on the Hirschorn inverse of the model. The proposed scheme is tested with extensive simulations where the full-order model is used to emulate the process. Several cases of significant uncertainty, including model parameter errors, process disturbances, actuator errors, and measurement noise are used to test the robustness of the controller to real life situations. Both controllers succeed in achieving temperature uniformity well within the desirable bounds, even in cases where several sources of uncertainty are simultaneously present with measurement noise     

W-Mo合金CMP工艺参数的影响与优化研究

简述了金属化学机械抛光的机理。将半导体制造工艺中的化学机械抛光技术拓展并应用到W-Mo合金表面加工中,在实现W-Mo合金材料表面高平坦度、低粗糙度的前提下,提高W-Mo合金去除速率。针对W-Mo合金的性质,选用碱性抛光液,并采用田口方法对抛光液pH值、抛光压力和抛光盘转速三个重要因素进行了优化设计,得到以去除速率为评价条件的综合最优抛光参数。实验分析表明,当抛光液pH值为11,抛光压力为80 kPa,抛光盘转速60 r/min时,可以获得较高的去除速率。     

A mechatronics approach to laser powder deposition process

This paper introduces a mechatronics approach for the development of a closed-loop control system utilized in laser powder deposition. The laser powder deposition process, as a manufacturing technique, is combined with a feedback control system to increase the quality of the final formed parts. The interconnections between the technologies involved in this complex mechatronics system along with the development of a CCD-based optical detector are explained. The optical CCD-based detector monitors the process zone to provide a series of single pass band images of the near-locus region. A pattern recognition algorithm is incorporated into the feedback device to obtain the clad’s height and angle of solid/liquid interface in real-time. This feedback device is blended in a PID-based controller, which is designed using a knowledge-based model, to adjust the laser pulse energy for enhancing the output of the process. The experimental assessments of the developed system are also presented at different process conditions and disturbances when Fe–20%Al was deposited on mild steel. It is shown that the PID-based controller can effectively improve the geometrical characteristics of the clad around the operating point by overcoming the effects of various disturbances.     

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     

等离子体刻蚀过程的APC技术研究进展

先进过程控制(APC)是一个多层次的控制系统,其包含了实时的设备及工艺控制和非实时的RtR控制.APC引入等离子体刻蚀过程控制可极大提高刻蚀机的使用效率.针对等离子体刻蚀过程,本文分别从实时控制和RtR控制两个不同层次展开了论述,概述了RtR控制器中所使用的线性回归模型和神经网络模型.最后,讨论了APC技术的发展趋势.     

A General Harmonic Rule Controller for Run-to-Run Process Control

The existence of initial bias in parameter estimation is an important issue in controlling short-run processes in semiconductor manufacturing. Harmonic rule has been widely used in machine setup adjustment problems. This paper generalizes the harmonic rule to a new controller called general harmonic rule (GHR) controller in run-to-run process control. The stability and optimality of the GHR controller is discussed for a wide range of stochastic disturbances. A numerical study is performed to compare the sensitivity of the GHR controller, the exponentially weighted moving average (EWMA) controller and the variable EWMA controller. It is shown that the GHR controller is more robust than the EWMA controller when the process parameters are estimated with uncertainty.      

An adaptive run-to-run optimizing controller for linear andnonlinear semiconductor processes

This paper presents a new run-to-run (R2R) multiple-input-multiple-output controller for semiconductor manufacturing processes. The controller, termed optimizing adaptive quality controller (OAQC), can act both as an optimizer-in case equipment models are not available-or as a controller for given models. The main components of the OAQC are shown and a study of its performance is presented. The controller allows one to specify input and output constraints and weights, and input resolutions. A multivariate control chart can be applied either as a deadband on the controller or simply to provide out of control alarms. Experimental designs can be utilized for on-line (recursive) model identification in the optimization phase. For testing purposes, two chemical mechanical planarization processes were simulated based on real equipment models. It is shown that the OAQC allows one to keep adequate control even if the input-output transfer function is severely nonlinear. Software implementation including the integration of the OAQC with the University of Michigan's Generic Cell Controller (GCC) is briefly discussed     

Polysilicon RTCVD process optimization forenvironmentally-conscious manufacturing

In the semiconductor manufacturing industry, optimization of advanced equipment and process designs must include both manufacturing metrics (such as cycle time, consumables cost, and product quality) and environmental consequences (such as reactant utilization and by-product emission). We have investigated the optimization of rapid thermal chemical vapor deposition (RTCVD) of polysilicon from SiH₄ as a function of process parameters using a physically-based dynamic simulation approach. The simulator captures essential time-dependent behaviors of gas flow, heat transfer, reaction chemistry, and sensor and control systems, and is validated by our experimental data. Significant improvements in SiH₄ utilization (up to 7×) and process cycle time (up to 3×) can be achieved by changes in 1) timing for initiating wafer heating relative to starting process gas flow; 2) process temperature (650-750°C); and 3) gas flow rate (100-1000 seem). Enhanced gas utilization efficiency and reduced process cycle time provide benefits for both environmental considerations and manufacturing productivity (throughput). Dynamic simulation proves to be a versatile and powerful technique for identifying optimal process parameters and for assessing tradeoffs between various manufacturing and environmental metrics     

Implementing a carrier-band node using VLSI

With the IEEE 802.4 token bus standard rapidly gaining acceptance because of its useful features and inclusion in the GM MAP (General Motors manufacturing automation protocol) specification, semiconductor companies are implementing this standard. A carrier-band implementation can provide a low-cost token bus node with up to 10 Mbs data rates. A carrier-band node that includes a token bus controller (TBC), carrier-band modem (CBM), host processor, and memory can be quickly and inexpensively designed using VLSI computer-aided design (CAD) techniques. One such implementation is presented. The token bus controller (TBC) implements the medium-access control (MAC) function in accordance with the IEEE 802.4 standard. The carrier-band modem (CBM) chip implements the 802.4 carrier-band physical layer. An IEEE recommended standard serial interface is used to pass information between the carrier-band modem and the token bus controller     

基于半导体激光器的Tornambe控制算法研究

为了给热电偶时间常数测试中提供更加准确的阶跃温升信号,优化控制效果,提高热电偶时间常数测量的准确性,采用Tornambe控制器来反馈控制半导体激光器的输出功率,在MATLAB下的Simulink模块中实现整个系统的搭建,并对系统进行同一输入信号下的仿真研究,通过实验来比较2阶Tornambe控制器与比例-积分-微分(PID)控制在系统运行过程中的控制效果。结果表明,采用PID控制器测得CO1-K型热电偶的时间常数为456.2ms,而采用Tornambe控制器测得的热电偶时间常数为284.6ms。2阶Tornambe控制器能够有效缩短热电偶达到平衡温度的时间,且在控制器结构参量整定上也更加简便,具有较强的实用价值。