Model-based emissivity correction in pyrometer temperature controlof rapid thermal processing systems

Single-wavelength pyrometers are most often used to infer wafer temperature in rapid-thermal-processing (RTP) systems. A constant wafer emissivity is assumed with a pyrometer, but a variation in the wafer's surface emissivity can result in an error in the inferred temperature which affects the temperature control of the RTP system. A time-dependent variation is evident in rapid thermal chemical vapor deposition where the emissivity is a function of the film type and thickness. An approach which uses a physically based model of the emissivity variation as part of the feedback control loop is described. The technique employs a first-order model of the emissivity as a function of film thickness from which a projected actual wafer temperature is inferred. The film thickness is approximated using a valid growth-rate expression and temperature as a function of time. These models are then incorporated into the feedback loop of the RTP control system     

A global model for rapid thermal processors

A simple model for the components that make up a rapid thermal processing system is given. These components are the furnace, the pyrometer used to measure temperature, and the control system that utilizes the pyrometer measurement to control the power to the lamps. The models for each of the components are integrated in a numerical code to give a computer simulation of the complete furnace operation. The simulation can be used to investigate the interaction of the furnace, temperature-sensing technique, and the control system. Therefore, the interplay of heat transfer (furnace) properties, optical (pyrometer) parameters, and control gains can be studied. The objective is to define variability in wafer temperature as process parameters change. The following three applications of the model are included: (1) a simulation of open-loop operation; (2) a simulation of the ramp up and subsequent operation with a step change in wafer optical properties; and (3) a simulation of the rapid thermal chemical vapor deposition of polysilicon on silicon oxide which demonstrates the applicability model for actual processes. A technique for correction of pyrometer output to improve temperature control is also presented     

Model identification in rapid thermal processing systems

Of the various techniques for controlling the temperature in rapid thermal processing (RTP), model-based control has the greatest potential for attaining the best performance, when the model is accurate. Some system identification methods are introduced to help obtain more accurate models from measured input-output data. For the first identification method, techniques for estimating the parameters (time constant and gain) of a particular physics-based model are presented. For the other, it is shown how to use the input-output measurements to obtain a black-box (autoregressive exogenous) model of the RTP system, which turns out to have better predictive capability. For each problem, the theoretical derivation of the identification technique and assumptions on which it is based are summarized, and experimental results based on data collected from an RTP system are described. Studying the DC response using the identified model led to a reconfiguration of the chamber geometry of the existing RTP system to more effectively distribute the light energy from the lamps     

Semi-Empirical Model-Based Multivariable Iterative Learning Control of an RTP System

Comprehensive study on control system design for a rapid thermal processing (RTP) equipment has been conducted with the purpose to obtain maximum temperature uniformity across the wafer surface, while precisely tracking a given reference trajectory. The study covers from model development, identification, optimum multivariable iterative learning control (ILC), to reduced-order controller design. The highlight of the study is the ILC technique on the basis of a semi-empirical dynamic radiation model named as$T^4$-model. It was shown that the$T^4$-model-based ILC technique can remarkably improve the performance of RTP control compared with the ordinary linear model-based ILC. In addition, reduced-order control methods and the associated optimum sensor location have been addressed. The proposed techniques have been evaluated in an RTP equipment fabricating 8-in wafers.     

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     

Modelling and off-line optimization of a 300 mm rapid thermal processing system

The modelling of a new 300 mm rapid thermal processing (RTP) system is described. Conventional raytracing techniques are used to determine lamp intensity distributions on both 200 and 300 mm wafers. Simulation results are verified using the ‘difference method' (difference between two process parameter distributions such as oxide thickness, where the absolute power of one single lamp is varied). Wafer rotation is incorporated in the model and its influence on the temperature distribution will be discussed. Off-line optimization of the temperature distribution is utilized using model-based control. Experimental results of implant annealing on both 200 and 300 mm are shown and critical parameters influencing the temperature uniformity are discussed.     

High performance scaled flash-type EEPROMs fabricated by in situ multiple rapid thermal processing

Flash-type EEPROMs were fabricated for the first time by in situ multiple rapid thermal processing (RTP) modules. In the paper, rapid thermal oxynitridation tunnel oxide (RTONO) formation followed by in situ arsenic (As)-doped floating gate polysilicon growth by rapid thermal chemical vapour deposition (RTCVD) were introduced. The flash cell indicates only 20% narrowing of the V/sub t/ window after 5*10/sup 4/ program/erase cycle stress. Moreover, there is a higher breakdown field of the ONO film on the floating-gate polysilicon film owing to extremely flat poly-Si surface. Thus, the in situ multiple RTP technology is the key for future flash memory fabrication processes.<>     

半导体激光器多环控制策略研究

提出了一种以半导体激光器的功率稳定作为外环、电流稳定和温度稳定作为内环的全数字多闭环控制策略,将PID控制与模糊控制、神经网络相结合,根据不同时刻的偏差和偏差变化率对PID参数进行自动调整.温度环采用PID控制和模糊控制相结合的控制策略,解决半导体激光器温度控制系统的动态品质和稳定精度相矛盾的问题.电流环和功率环采用多模态PID控制策略,满足在不同偏差下系统对PID参数的实时自整定要求,提高控制精度.仿真实验表明,系统具有良好的动态和稳态性能.     

Control of MMST RTP: repeatability, uniformity, and integration forflexible manufacturing [ICs]

A real-time multivariable strategy is used to control the uniformity and repeatability of wafer temperature in rapid thermal processing (RTP) semiconductor device manufacturing equipment. This strategy is based on a physical model of the process where the model parameters are estimated using an experimental design procedure. The internal model control (IMC) law design methodology is used to automatically compute the lamp powers to a multizone array of concentric heating zones to achieve wafer temperature uniformity. Control actions are made in response to real-time feedback information provided by temperature sensing, via pyrometry, at multiple points across the wafer. Several modules, including model-scheduling and antiovershoot, are coordinated with IMC to achieve temperature control specifications. The control strategy, originally developed for prototype equipment at Stanford University, is analyzed via the customization, integration, and performance on eight RTP reactors at Texas Instruments conducting thirteen different thermal fabrication operations of two sub-half-micron CMOS process technologies used in the the Microelectronics Manufacturing Science and Technology (MMST) program     

快速热处理设备的电流环数字放大器设计

硅晶圆快速热处理（Rapid Thermal Processing,RTP）过程中,对于加热温度及温度均匀性的精确控制是保证晶圆热处理质量的关键。针对自行研制的RTP设备,通过分析其加热特性,初步建立了数学模型,设计了基于FPGA的电流环数字放大器。利用Matlab对电流控制器进行了优化与仿真,证明在保证稳态精度的情况下,电流环数字放大器能够提供系统准确稳定的电流输入,同时兼有电压闭环控制,从而可以实时监控输入负载的能量,这样就可以很好地解决快速升温中过冲问题。     

Adaptive control approach of rapid thermal processing

This paper presents an adaptive control approach for achieving the control of the wafer temperature in a rapid thermal processing system (RTP). Numerous studies have addressed the temperature control problem in RTP and most researches on this problem require exact knowledge of the systems dynamics. However, it is difficult to acquire this exact knowledge. Thus, various approaches cannot guarantee the desired performance in practical application when there exist some modeling errors between the model and the actual system. In this paper, an adaptive control scheme is applied to RTP without exact information on the dynamics. The system dynamics are assumed to be an affine nonlinear form, and the unknown portion of the dynamics are estimated by a neural network referred to a piecewise linear approximation network (PLAN). The controller architecture is based on an adaptive feedback linearization scheme and augmented by sliding mode control. The performance of the proposed method is demonstrated by experimental results on an RTP system of Kornic Systems Corporation, Korea.     

Intelligent control of via formation by photosensitive BCB forMCM-L/D applications

Via formation is a critical process sequence in multichip module (MCM) manufacturing, as it greatly impacts yield, density, and reliability. To achieve low-cost manufacturing, modeling, optimization, and control of via formation are crucial. In this paper, a model-based supervisory control algorithm is developed and applied to reduce undesirable behavior resulting from various process disturbances. A series of designed experiments are used to characterize the via formation workcell (which consists of the spin coat, soft bake, expose, develop, cure, and plasma descum unit process steps). The output characteristics considered are film thickness, uniformity, film retention, and via yield. Sequential neural network process models are used for system identification, and hybrid genetic algorithms are applied to synthesize process recipes. Computer simulation results show excellent control of output response shift and drift, resulting in a reduction of process variation. The performance limits of the supervisory control system are investigated based on these simulation results. The control algorithm is verified experimentally, and the results show 82.6, 64.4, and 17.3% improvements in maintaining target via yield, film thickness, and film uniformity, respectively, as compared to open loop operation     

A Model-Based Direct Power Control for Three-Phase Power Converters

The direct power control (DPC) technique has been widely used as a control strategy for three-phase power rectifiers due to its simplicity and good performance. DPC uses the instantaneous active and reactive power to control the power converter. The controller design has been proposed as a direct control with a lookup table and, in recent works, as an indirect control with an inner control loop with proportional-plus-integral controllers for the instantaneous active and reactive power errors. In this paper, a model-based DPC for three-phase power converters is designed, obtaining expressions for the input control signal, which allow the design of an adaptive control law that minimizes the errors introduced by parameter uncertainties as the smoothing inductor value or the grid frequency. A controller design process, a stability study of the system, and experimental results for a synchronous three-phase power rectifier prototype are presented to validate the proposed controller.     

Model reduction for optimization of rapid thermal chemical vapordeposition systems

A model of a three-zone rapid thermal chemical vapor deposition (RTCVD) system is developed to study the effects of spatial wafer temperature patterns on polysilicon deposition uniformity. A sequence of simulated runs is performed, varying the lamp power profiles so that different wafer temperature modes are excited. The dominant spatial wafer thermal modes are extracted via proper orthogonal decomposition and subsequently used as a set of trial functions to represent both the wafer temperature and deposition thickness. A collocation formulation of Galerkin's method is used to discretize the original modeling equations, giving a low-order model which loses little of the original, high order model's fidelity. We make use of the excellent predictive capabilities of the reduced model to optimize power inputs to the lamp banks to achieve a desired polysilicon deposition thickness at the end of a run with minimal deposition spatial nonuniformity. Since the results illustrate that the optimization procedure benefits from the use of the reduced-order model, our future goal is to integrate the model reduction methodology into real-time and run-to-run control algorithms. While developed in the context of optimizing a specific RTP process, the model reduction techniques presented in this paper are applicable to other materials processing systems     

Manufacturability issues related to transient thermal annealing oftitanium silicide films in a rapid thermal processor

Transient thermal annealing of sputtered titanium films in a rapid thermal processor (RTP) is critically evaluated from the viewpoint of manufacturability-related considerations. In particular, the thin-film properties of the resulting titanium silicide on polysilicon and silicon, process uniformity, and unit step wafer yield of high-density scaled device structures are investigated. The experimental results suggest that RTP silicides show good thin-film properties for manufacturability on planar wafer surfaces. Transient thermal gradients in an RTP system are shown to cause substantial variations in the electrical and structural properties of TiSi_x films formed on silicon substrates with varying substrate thicknesses. Closed-loop temperature control in an RTP reactor provided stoichiometrically identical TiSi_x films with negligible substrate thickness dependence. The experimental results also suggest that careful wafer surface temperature control is needed when forming titanium silicide films on nonplanar silicon surfaces, silicon trenches, and process monitor wafers without predetermined wafer thicknesses     

Temperature control in a rapid thermal processor

Temperature control problems in a rapid thermal processor (RTP) are addressed by using a conventional proportional-integral-derivative (PID) controller and an autoadaptive algorithm. So far, temperature control in most RTP systems has usually been accomplished by using PID controllers. In RTP systems using only classical control schemes, the setting of the control module is a long and complicated task, which often provides optimum results within a limited temperature range. It is shown that adaptive control is less affected by process dynamics     

Mechanism of hemispherical-grained Si formation for dynamic random access memory cells by rapid thermal chemical vapor deposition

An uneven coating made of hemispherical-grained Si (HSG) was formed on an amorphous Si layer by a rapid thermal chemical vapor deposition (CVD) (RTCVD) process. The uneven coating increases the effective surface area of a capacitor electrode in dynamic random access memory (DRAM) cells. The formation of the HSG consists of “seeding” and subsequent isothermal annealing stages. During the seeding stage, nanometer size Si single crystals are formed on the surface of the amorphous Si layer. During rapid thermal annealing at 665°C, under high vacuum, the Si grains grow linearly with increasing temperature and reach an average size of 95 nm after 20 sec. The nucleation and growth of the HSG occurs within a narrow range of temperature and time, which is sufficient for a short diffusion path of Si atoms on the surface of the amorphous Si layer, but insufficient for crystallization of the amorphous Si layer: The HSG coating increases the capacitance of a memory cell by a factor of 2.     

高压断路器三相永磁无刷直流电机机构控制算法研究

针对高压断路器三相永磁无刷直流电机机构,研究了不同控制策略下电机操动机构的运动特性.考虑高压断路器的分、合闸操作过程,建立了永磁无刷直流电机操动机构运动控制系统的仿真模型,采用数字式双闲环控制,内环为电流环,采用PI控制,外环为速度环,基于传统PID控制器、单神经元PID控制两种不同控制策略控制.通过对伺服控制系统的仿真分析得到了电机操动机构速度跟踪控制特性.结果表明,单神经元PID控制器能够较好的实现触头速度的跟踪控制,使其按理想运动特性曲线运动,是一种较理想、有效的控制方法.     

双闭环控制感应加热电源的设计与仿真分析

针对目前20kHz/10kW感应加热电源开关功耗大的缺点,提出了一种基于DSP的容性移相PWM和PFM控制的设计方案。确定以全桥IGBT逆变为主拓扑电路,采用PID和DPLL相结合的双闭环控制策略,对系统进行SIMULINK平台仿真建模。在开环和闭环条件下对仿真结果进行对比分析,实现了负载频率自动跟踪和功率闭环控制。仿真系统到达恒定功率输出的时间为0.2ms,功率因数近似为1,且无周期跳变的现象。改善系统动态特性和稳定控制的同时,验证了该方案的可行性和有效性。     

An Integrated Diagnostic Development Process for Automotive Engine Control Systems

Theory and applications of model-based fault diagnosis have progressed significantly in the last four decades. In addition, there has been increased use of model-based design and testing in the automotive industry to reduce design errors, perform rapid prototyping, and hardware-in-the-loop simulation (HILS). This paper presents a new model-based diagnostic development process for automotive engine control systems. This process seamlessly employs a graph-based dependency model and mathematical models for online/offline diagnosis. The hybrid method improves the diagnostic system's accuracy and consistency, utilizes existing validated knowledge on empirical models, enables remote diagnosis, and responds to the challenges of increased system complexity. The development platform consists of an engine electronic control unit (ECU) rapid prototyping system and HILS equipment - the air intake subsystem (AIS). The diagnostic strategy is tested and validated using the HILS platform.