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     

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.     

Pheromone Propagation Controller: The Linkage of Swarm Intelligence and Advanced Process Control

Statistical process control (SPC) is traditionally used in advanced process control (APC). However, SPC, which treats measurements as a series of isolated statistical data, employs different methods to deal with different problems. In this paper, we present a new perspective on process control, which treats the intercepts of the process in different runs as a social insect colony. Our novel algorithm, called the pheromone propagation controller (PPC), is a meta-heuristic method based on the assumption that the intercepts of the linear regression model have their own behavior and affect others nearby on different runs. The pheromone basket is an environment initially filled with intercepts, and then the “intercepts pheromones” in the basket propagate according to the modified digital pheromone infrastructure. After propagation, the intercept in the next run can be forecast by extrapolating the last two entities of the pheromone basket. Consequently, a revised process recipe can be obtained from the forecast intercepts and the linear regression model. We also propose a workable scheme for adaptively tuning the PPC propagation parameter. We discuss the PPC stability region and the strategy for tuning the propagation parameter as well as the effects of size of pheromone basket, model mismatch on the performance. Our simulation results show that the standard deviation and the mean square error for PPC, whether fixed or self-tuning, are more consistent than that of the EWMA, the predictor corrector control (PCC), and the double EWMA for five types of anthropogenic disturbance. We also examined a hybrid disturbance obtained from semiconductor fabrication. When system drifts, the PPC was superior to the other candidate controllers for all values of the PPC propagation parameters and weightings of the other controllers, whether fixed or self-tuning.      

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.      

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。     

Large-Scale Network Parameter Configuration Using an On-Line Simulation Framework

As the Internet infrastructure grows to support a variety of services, its legacy protocols are being overloaded with new functions such as traffic engineering. Today, operators engineer such capabilities through clever, but manual parameter tuning. In this paper, we propose a back-end support tool for large-scale parameter configuration that is based on efficient parameter state space search techniques and on-line simulation. The framework is useful when the network protocol performance is sensitive to its parameter settings, and its performance can be reasonably modeled in simulation. In particular, our system imports the network topology, relevant protocol models and latest monitored traffic patterns into a simulation that runs on-line in a network operations center (NOC). Each simulation evaluates the network performance for a particular setting of protocol parameters. We propose an efficient large-dimensional parameter state space search technique called “recursive random search (RRS).” Each sample point chosen by RRS results in a single simulation. An important feature of this framework is its flexibility: it allows arbitrary choices in terms of the simulation engines used (e.g., ns-2, SSFnet), network protocols to be simulated (e.g., OSPF, BGP), and in the specification of the optimization objectives. We demonstrate the flexibility and relevance of this framework in three scenarios: joint tuning of the RED buffer management parameters at multiple bottlenecks, traffic engineering using OSPF link weight tuning, and outbound load-balancing of traffic at peering/transit points using BGP LOCAL_PREF parameter.      

Parameter design using the Taguchi methodology

This article aims to give an overview of the Taguchi methodology and more specific of its key step: parameter design. The purpose of parameter design is to bring quality into the product/process by determining the relevant parameters and their optimal settings such that the quality characteristics of the product are optimised and have minimal sensitivity to “noise” (i.e., those disturbing factors which are difficult or too expensive to control). The (mainly statistical) tools used in the methodology will be handled and some actual Bell cases will be mentioned as practical examples.     

Age-based double EWMA controller and its application to CMPprocesses

In the originally proposed run-by-run control scheme, the EWMA statistic is used as an estimate of the process deviation from its target. However, the controller based on the EWMA statistic is not sufficient for controlling a wearing out process. The PCC controller has been thus proposed to enhance the run-by-run controller capability. In this paper, we first reexamine the fundamentals of the PCC formulations and propose an adjustment that is advantageous in controlling processes subject to both random shifts and drifts. The adjusted PCC controller is then further refined to take into account the process age. This age-based double EWMA scheme is then applied to the CMP process, which is known in the semiconductor industry to be rather unstable     

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.     

A symmetrical 6-GHz fully integrated cascode coupling CMOS LC quadrature VCO

A fully symmetrical integrated quadrature LC oscillator with a wide tuning range of 1.2GHz is presented. The quadrature voltage-controlled oscillator (QVCO) is implemented using a symmetrical coupling method which has been used to produce the large tuning range with a low control voltage and to achieve good phase noise performance in 0.18/spl mu/m complementary metal oxide semiconductor technology. The measured phase noise at 1MHz offset from the center frequency (5.5GHz) is -115 dBc/Hz. The QVCO draws 3.2mA from a 1.8V supply. The equivalent phase error between I and Q signal was at most 0.5/spl deg/.     

A 12-GHz Fully Integrated Cascode CMOS LC VCO With Q-Enhancement Circuit

A fully integrated complementary metal oxide semiconductor (CMOS) cascode LC voltage controlled oscillator (VCO) with Q-enhancement technique has been designed for high frequency and low phase noise. The symmetrical cascode architecture is implemented with negative conductance circuit for improving phase noise performance in 0.18 mum CMOS technology. The measured phase noise is -110.8 dBc/Hz at the offset frequency of 1 MHz. The tuning range of 630 MHz is achieved with the control voltage from 0.6 to 1.4 V. The VCO draws 4.5 mA in a differential core circuit from 1.8 V supply.     

Decoupled Current Control of Sensorless Induction-Motor Drives by Integral Sliding Mode

This paper discusses the problems of current decoupling control and controller tuning associated with sensorless vector-controlled induction-motor (IM) drives. In field-oriented control, the $d$–$q$ synchronous-frame currents should be regulated to have independent dynamics such that the torque production of the IM resembles that of a separately excited dc motor. However, these currents are not naturally decoupled, and decoupling compensators should be used. Current loop tuning is an additional problem, since controller gains obtained by theoretical methods or simulation, quite often, do not work well on the real system. This paper proposes a new approach for current control that uses integral-sliding-mode (ISM) controllers to achieve decoupling. The synchronous-frame control voltages are synthesized as the sum of two controller outputs: a traditional one (PI) that acts on an ideal plant model and an ISM controller. The ISM controller decouples the $d$–$q$ currents and compensates the parameter variations in the current loops of the machine. Simulations and experimental tests on a 0.25-hp three-phase induction machine show satisfactory results.      

Improved Model-Based Parameter Estimation Approach for Accelerated Periodic Method of Moments Solutions With Application to the Analysis of Convoluted Frequency Selected Surfaces and Metamaterials

An improved “smart” interpolation approach known as model-based parameter estimation (MBPE) is applied to the wide-band interpolation of periodic method of moments (PMM) impedance matrices for normal and oblique incidence cases. Prior to interpolation, easy to calculate but hard to interpolate, phase terms are removed from the impedance matrices. An efficient spectral-domain PMM formulation is introduced for the accelerated analysis of frequency selective surface (FSS) problems with a large number of unknowns, employing a one dimensional $O(Nlog N)$ FFT-based method to speed up the computation of matrix-vector products within the bi-conjugate gradient (BCG) iterative solver, which is made possible by the asymmetric multilevel block-Toeplitz structure of the impedance-matrix. The MBPE interpolation algorithm provides a faster matrix fill time than the brute force method and is comparable or even faster than the 2-D FFT-based method for a large number of unknowns. It also has the advantage that it can be applied to non-uniform gridding cases. The accuracy and efficiency of the proposed techniques for large FSS problems are demonstrated by several design examples for both the normal and oblique incidence cases. We also apply this efficient analysis tool to the design of multiband single-layer FSS filters and artificial magnetic conductors (AMC) comprised of a 2-D periodic arrangement of convoluted metallic strips in the shape of a Hilbert curve. The multiband properties of the Hilbert curve FSS filters are studied for different iteration orders (i.e., different degrees of space-filling).      

An Intelligent Run-to-Run Control Strategy for Chemical–Mechanical Polishing Processes

This paper presents a novel intelligent run-to-run control strategy for chemical–mechanical polishing (CMP) processes. With the help of the recursive least squares identification method for model building, a real-coded genetic algorithm is applied to adaptively adjust the discount coefficients for double exponentially weighted moving average (EWMA) controller. The online intelligent scheme can effectively prevent the CMP processes from reaching unstable condition and can thus achieve high control performance. To demonstrate the effectiveness and applicability of the proposed intelligent run-to-run control strategy, two typical case studies are worked out in this paper. Extensive simulation comparisons with traditional double EWMA run-to-run control were performed. The simulation results show that the proposed intelligent run-to-run control is able to achieve better control performance than conventional schemes, especially for a process that has nonlinearities, process noise, and extra large metrology delays.      

CMOS ring VCO for UHF RFID readers

A complementary metal oxide semiconductor (CMOS) voltage controlled ring oscillator for ultra high frequency (UHF) radio frequency identification (RFID) readers has been realized and characterized. Fabricated in charter 0.35 μm CMOS process, the total chip size is 0.47×0.67 mm2. While excluding the pads, the core area is only 0.15×0.2 mm2. At a supply voltage of 3.3 V, the measured power consumption is 66 mW including the output buffer for 50 Ω testing load. This proposed voltage-controlled ring oscillator exhibits a low phase noise of - 116 dBc/Hz at 10 MHz offset from the center frequency of 922.5 MHz and a lower tuning gain through the use of coarse/fine frequency control.     

A Novel Statistical Method for Automatically Partitioning Tools According to Engineers' Tolerance Control in Process Improvement

In the semiconductor industry, tool comparison is a key task in yield or product quality enhancements. We develop a new method to automatically partition tools. The new method is called tolerance control partitioning (TCP). The advantages of TCP include 1) taking into account of unbalanced tool usage in manufacturing processes; 2) further partitioning these tools into several homogenous groups by related metrology results instead of detecting only the significant difference; and 3) partitioning these tools according to engineers' tolerance controls to avoid too many groups with small differences. TCP also could be applied in all similar cases such as experimental recipe or material comparisons. Therefore, using TCP, engineers could speed up yield or product quality ramping.      

Optimal automatic control of multistage production processes

Today's high-tech industries produce complicated products involving many processing steps. The usual approach of modeling and controlling each of these steps in isolation is re-evaluated. This work develops a data model of synchronized observations collected from several stages of a multistage manufacturing process, and proposes an across-stage automatic control scheme for adjusting nonstationary process drifts. The proposed controller applies dynamic programming tools to optimize multiple goals specified for individual process stages and possible mismatch between stages. Several examples and simulation studies demonstrate that the proposed method is a valuable tool for improving semiconductor manufacturing quality.     

Theoretical analysis of low phase noise design of CMOS VCO

A theoretical analysis on low phase noise of voltage-controlled oscillators (VCOs) based on complementary cross-coupled LC VCO by 0.35-/spl mu/m complementary metal oxide semiconductor technology is demonstrated. From the procedure of optimization steps, the excess noise factor of the amplifier coming from the active device has been determined. The proposed VCO operates at 2 GHz with phase noise of -116 dBc/Hz at offset frequency 600 kHz. The power consumption is 22.62 mW under 3 V bias with 9.1% frequency tuning. The achievement of low phase noise is also matched with prediction by formula in the frequency domain.     

Wafer level reliability: Process control for reliability

Wafer Level Reliability test techniques can be used to provide fast feedback process control information regarding the reliability of the product of a semiconductor process. The purpose of wafer level reliability (WLR) tests is the measurement of variation in the materials comprising the semiconductor device. They are not intended as modeling tools for the quantification of the effect of stress on these materials. As such, WLR tests must provide a repeatable stress, independent of normal process variation. The results of these tests will be a measurement of the “rate of degradation” of the basic circuit elements caused by a standard stress.     

A 38% Tuning Bandwidth Low Phase Noise Differential Voltage Controlled Oscillator Using a 0.5 $mu$m E/D-PHEMT Process

This paper presents a 38% tuning bandwidth low phase noise differential voltage controlled oscillator (VCO) using a 0.5 $mu$m enhancement/depletion-pseudomorphic high-electron mobility transistor (E/D-PHEMT) process. The proposed VCO is based on a differential topology with two common-gate transistors. To achieve a wide tuning range with low phase noise, varactor in the VCO core employs the E-mode PHEMT device. The frequency of the VCO is from 18.8 to 27.5 GHz with a tuning bandwidth of 38% and an output power of higher than 5 dBm. The VCO demonstrates a phase noise of ${-}109$ dBc/Hz at 1 MHz offset frequency. This circuit can be compared with the VCOs fabricated using the advanced InP HBT technologies.