Single-wafer integrated semiconductor device processing

The authors present an overview of various single-wafer fabrication techniques for integrated processing of microelectronic devices. Numerous processing modules, sensors, and associated fabrication processes have been developed for advanced semiconductor device manufacturing. The combination of single-wafer processing, cluster tools, sensors, and advanced factory control/computer-integrated manufacturing techniques provides a capability for flexible fast-cycle-time device manufacturing. Specific developments and results are described in the areas of dry/vapor-phase surface cleaning, epitaxy, plasma processing, rapid thermal processing, and in situ sensors. An integrated sub-half micrometer CMOS technology based on these single-wafer fabrication methods including rapid thermal processing is also described     

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.     

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     

DSP-based multi-purpose control system for laser processing

In modern laser processing[1],the operations per-formed by a motion control system have to be done inreal ti me at high frequency. While PC hardware andsoftware are not opti mizedfor these kinds of operations ,the DSPandthe software onthe motioncontrol sy…     

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.     

Manufacturing issues related to RTP induced overlay errors in aglobal alignment stepper technology

The effect of rapid thermal processing on wafer distortion and overlay accuracy in global alignment photolithography in the fabrication of 0.85 μm CMOS Flash EPROM integrated circuits was studied. Both rapid thermal process parameters and system design (single and multi-lamp processors) were evaluated for their effect on overlay accuracy. It was found that a rapid thermal process (following contact etch and ion implantation) at set temperatures greater than or equal to 950°C resulted in interconnect metallization-to-contact overlay errors in excess of 1.0 μm across the wafer, which led to a 20% functional circuit yield loss. In the case of the single lamp processor, this misalignment was attributed to wafer distortion due to the temperature overshoot during the ramp step, which subsequently resulted in an across wafer temperature range of greater than 120°C. This temperature overshoot and nonuniformity was eliminated by reducing the ramp rate below 100°C/s. This ramp rate reduction, however, decreased the system wafer throughput, and required optimization to eliminate the overlay errors and minimize the effect on throughput. In this study, a 60°C/s ramp rate was found to be optimum. For the multi-lamp RTP system, the metal-to-contact overlay error was not observed. This was believed to be due to the design of the heating mechanism in the multi-lamp processor, which did not produce the large wafer temperature overshoot and nonuniformity that was observed in the single lamp processor     

Rapid thermal processing uniformity using multivariable control ofa circularly symmetric 3 zone lamp

Defect introduction and process variations commonly observed in conventional rapid thermal processing (RTP) systems have impeded its widespread acceptance in manufacturing. The main problem lies in the conventional approach of using scalar control, where optimal steady-state temperature uniformity at one set of processing conditions is used to fix the hardware geometry, leaving only one input variable-the lamp power-for control. It is demonstrated that this control is inadequate, since the radiative and convective heat exchange at the wafer are functions of the processing conditions, and that the resultant nonuniformity can be corrected by dynamic control of the spatial optical flux profile. Such control is demonstrated through two key innovations: a lamp system in which tungsten-halogen point sources are configured in three concentric rings to provide a circularly symmetric flux profile, and multivariable control whereby each of the three rings is independently and dynamically controlled to provide for control over the spatial flux profile. This approach offers good temperature uniformity over transients, thus improving reliability of individual processes     

Industrial electronics [technology analysis and forecast]

A rapprochement among different vendors of industrial control equipment may be at hand if several systems presented as “open architecture” ones are any indication. Meanwhile, the advent of single-chip microcontrollers for motor drives, more powerful insulated-gate bipolar transistors (IGBTs), and improved integration of sensors with power devices are salient advances on the factory floor. The new crop of industrial computers, including single-board types embedded in larger systems, emphasizes increased power often in a smaller package. As for signal processing, gains include a system for surveillance (in the plant and on the battlefield) that fuses data from two sources into one stream of enhanced precision, while digital signal processing pushes a PC-based vision system to some 10¹¹ operations per second     

Programmable logic circuits for functional integrated smart plastic systems

In this paper, we present a functional integrated plastic system. We have fabricated arrays of organic thin-film transistors (OTFTs) and printed electronic components driving an electrophoretic ink display up to 70 mm by 70 mm on a single flexible transparent plastic foil. Transistor arrays were quickly and reliably configured for different logic functions by an additional process step of inkjet printing conductive silver wires and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) resistors between transistors or between logic blocks. Among the circuit functions and features demonstrated on the arrays are a 7-stage ring oscillator, a D-type flip-flop memory element, a 2:4 demultiplexer, a programmable array logic device (PAL), and printed wires and resistors. Touch input sensors were also printed, thus only external batteries were required for a complete electronic subsystem. The PAL featured 8 inputs, 8 outputs, 32 product terms, and had 1260 p-type polymer transistors in a 3-metal process using diode-load logic. To the best of our knowledge, this is the first time that a PAL concept with organic transistors has been demonstrated, and also the first time that organic transistors have been used as the control logic for a flexible display which have both been integrated on to a single plastic substrate. The versatility afforded by the additive inkjet printing process is well suited to organic programmable logic on plastic substrates, in effect, making flexible organic electronics more flexible.     

A system for MEA-based multisite stimulation

The capability for multisite stimulation is one of the biggest potential advantages of microelectrode arrays (MEAs). There remain, however, several technical problems which have hindered the development of a practical stimulation system. An important design goal is to allow programmable multisite stimulation, which produces minimal interference with simultaneous extracellular and patch or whole cell clamp recording. Here, we describe a multisite stimulation and recording system with novel interface circuit modules, in which preamplifiers and transistor transistor logic-driven solid-state switching devices are integrated. This integration permits PC-controlled remote switching of each substrate electrode. This allows not only flexible selection of stimulation sites, but also rapid switching of the selected sites between stimulation and recording, within 1.2 ms. This allowed almost continuous monitoring of extracellular signals at all the substrate-embedded electrodes, including those used for stimulation. In addition, the vibration-free solid-state switching made it possible to record whole-cell synaptic currents in one neuron, evoked from multiple sites in the network. We have used this system to visualize spatial propagation patterns of evoked responses in cultured networks of cortical neurons. This MEA-based stimulation system is a useful tool for studying neuronal signal processing in biological neuronal networks, as well as the process of synaptic integration within single neurons.     

A contribution to optimal lamp design in rapid thermal processing

Recent studies of wafer temperature control in rapid thermal processing systems have indicated that a multiring circularly symmetric lamp configuration with independent (multivariable) control of the power applied to each ring is likely to be more successful than the earlier lamp design approaches. An important issue in such multiring lamp systems is the optimal shaping of the output heat flux profile (HFP) of each ring to provide maximum controllability of the wafer temperature. In this paper we seek to optimize the ring HFP's via the lamp design parameters: ring positions and widths. We start by determining the heat loss profiles over the wafer surface for a variety of temperature setpoints and processing conditions. In order to maintain temperature uniformity across the wafer at a given setpoint, the lamp system should provide a compensating HFP. The total lamp HFP is the sum of the individual ring HFPs weighted by their respective applied powers. The HFP's are, in turn, functionally dependent on the lamp design parameters and this dependence can be measured through a calibration process. Therefore, the resulting optimization problem reduces to determining the lamp design parameters that result in lamp HFP's which best approximates the collection of the wafer heat loss profiles. Our method provides a practical technique for determining the optimal lamp design parameters     

Recent developments in rapid thermal processing

Rapid thermal annealing (RTA) with a short dwell time at maximum temperature is used with ion implantation to form shallow junctions and polycrystalline-Si gate electrodes in complementary, metal-oxide semiconductor (CMOS) Si processing. Wafers are heated by electric lamps or steady heat sources with rapid wafer transfer. Advanced methods use “spike anneals,” wherein high-temperature ramp rates are used for both heating and cooling while also minimizing the dwell time at peak temperature to nominally zero. The fast thermal cycles are required to reduce the undesirable effects of transient-enhanced diffusion (TED) and thermal deactivation of the dopants. Because junction profiles are sensitive to annealing temperature, the challenge in spike annealing is to maintain temperature uniformity across the wafer and repeatability from wafer to wafer. Multiple lamp systems use arrayed temperature sensors for individual control zones. Other methods rely on process chambers that are designed for uniform wafer heating. Generally, sophisticated techniques for accurate temperature measurement and control by emissivity-compensated infrared pyrometry are required because processed Si wafers exhibit appreciable variation in emissivity.     

Statistical feedback control of a plasma etch process

This paper presents the methodology developed for the automatic feedback control of a silicon nitride plasma etch process. The methodology provides an augmented level of control for semiconductor manufacturing processes, to the level that the operator inputs the required process quality characteristics (e.g. etch rate and uniformity values) instead of the desired process conditions (e.g., specific RF power, pressure, gas flows). The optimal equipment settings are determined from previously generated process/equipment models. The control algorithm is driven by the in-situ measurements, using in-line sensors monitoring each wafer. The sensor data is subjected to Statistical Quality Control (SQC) to determine if deviations from the required process observable values can be attributed to noise in the system or are due to a sustained anomalous behavior of the equipment. Once a change in equipment behavior is detected, the process/equipment models are adjusted to match the new state of the equipment. The updated models are used to run subsequent wafers until a new SQC failure is observed. The algorithms developed have been implemented and tested, and are currently being used to control the etching of wafers under standard manufacturing conditions     

耐高压单面铝基板检测与设计案例分析

随着新兴LED市场的蓬勃发展,具有良好散热及机械加工性能的铝基板也得到了广泛应用,部分用于公共设施照明及路灯照明的LED产品,为保障在雷电、电压波动、开启关闭等瞬时过电压情况下能安全持续工作,要求对产品进行耐高压测试。本文主要针对耐高压单面铝基板的耐高压测试方法、板料选择、图形设计、工艺优化、生产控制等要点进行阐述,以确保产品能满足客户耐高压测试的严格要求。     

A model for rapid thermal processing: achieving uniformity throughlamp control

A first-principles approach to the modeling of a rapid thermal processing (RTP) system to obtain temperature uniformity is described. RTP systems are single wafer and typically have a bank of heating lamps which can be individually controlled. Temperature uniformity across a wafer is difficult to obtain in RTP systems. A temperature gradient exists outward from the center of the wafer due to cooling for a uniform heat flux density on the surface of the wafer from the lamps. Experiments have shown that the nonuniform temperature of a wafer in an RTP system can be counteracted by adjusting the relative power of the individual lamps, which alters the heat flux density at the wafer. The model is composed of two components. The first predicts a wafer's temperature profile given the individual lamp powers. The second determines the relative lamp power necessary to achieve uniform temperature everywhere but at the outermost edge of the wafer (cooling at the edge is always present). The model has been verified experimentally by rapid thermal chemical vapor deposition of polycrystalline silicon with a prototype LEISK RTP system. The wafer temperature profile is inferred from the poly-Si thickness. Results showed a temperature uniformity of ±1%, an average absolute temperature variation of 5.5°C, and a worst-case absolute temperature variation of 6.5°C for several wafers processed at different temperatures     

Decentralized control of wafer temperature for multizone rapidthermal processing systems

Decentralized control is shown through analysis and experimentation to be an appropriate strategy for wafer temperature control in certain multizone rapid thermal processing (RTP) systems. An input-output controllability analysis is conducted to illustrate that the direction associated with the reference command (set-point) corresponding to a spatially uniform temperature trajectory specification is nearly in alignment with the “most” controllable direction associated with the maximum singular value for a multiple concentric lamp configuration. Consequently, the control structure need not alter the directionality of the plant and, thus, can be achieved by a simple decentralized controller where the lamps are paired individually to sensors to achieve a multiloop structure where all interactions are not taken explicitly into account. This result is shown to produce acceptable performance even for an ill-conditioned plant since the directions corresponding to the smaller singular values are irrelevant to the uniform temperature control criteria. Moreover, straightforward nonmodel-based tuning of the controller is enabled due to the simplicity of the decentralized control structure     

A single mediaprocessor-based programmable ultrasound system

We have developed a programmable ultrasound imaging system using a single commercially available mediaprocessor. We have efficiently mapped all of the necessary B-mode processing algorithms on the underlying processor architecture, including envelope detection, dynamic range compression, lateral and axial filtering, persistence processing, and scan conversion. Our system can handle varying specifications ranging from 128 vectors and 512 samples per vector to more than 256 vectors and 1024 samples per vector. For an image size of 330 vectors and 512 samples per vector, it can process 30 frames per second using a 300-MHz MAP-CA mediaprocessor from Hitachi/Equator Technologies. This programmable ultrasound machine will not only offer significant advantages in terms of low cost, portability, scalability, and reduced development time, but also provide a flexible platform for developing and deploying new clinical applications to aid the clinicians and improve the quality of healthcare to patients.     

An 11 mm$^{2}$ , 70 mW Fully Programmable Baseband Processor for Mobile WiMAX and DVB-T/H in 0.12$ mu$ m CMOS

With the rapid evolution of wireless standards and increasing demand for multi-standard products, the need for flexible RF and baseband solutions is growing. Flexibility is required to be able to adapt to unstable standards and requirements without costly hardware re-spins, and also to enable hardware reuse between products and between multiple wireless standards in the same device, ultimately saving both development cost and silicon area. In this paper a fully programmable baseband processor suitable for standards such as DVB-T/H and mobile WiMAX is presented. The processor is based on the SIMT architecture which utilizes a unique type of vector instructions to provide processing parallelism while minimizing the control complexity of the processor. The architecture has been demonstrated in a prototype chip which was proven in a complete DVB-T/H system demonstrator. The chip occupies 11 mm² in a 0.12 mum CMOS process. It includes 1.5 Mbit of single port SRAM and 200 k logic gates. The measured power consumption for the highest DVB-T/H data rate (31.67 MBit/s) is 70 mW at 70 MHz. This outperforms both area and power figures of previously presented non-programmable DVB-T/H solutions.     

A programmable image processing system using FPGAs

Real-time image processing usually requires an enormous throughput rate and a huge number of operations. Parallel processing, in the form of specialized hardware, or multiprocessing are therefore indispensable. This piper describes a flexible programmable image processing system using the field programmable gate array (FPGA). The logic cell nature of currently available FPGA is most suitable for performing real-time bit-level image processing operations using the bit-level systolic concept. Here, we propose a novel architecture, the programmable image processing system (PIPS), for the integration of these programmable hardware and digital signal processors (DSPs) to handle the bit-level as well as the arithmetic operations found in many image processing applications. The versatility of the system is demonstrated by the implementation of a 1-D median filter.     

Applied RTP optical modeling: an argument for model-based control

A simulation of a complete rapid thermal processing (RTP) system is made to investigate the accuracy of various techniques for temperature control. The process simulated was the chemical vapor deposition (CVD) of polycrystalline silicon over an oxide. Control strategies considered were, open loop control, pyrometer control, pyrometer control with a correction for emissivity changes produced by CVD, and open loop control with the lamp heating programmed as a function of time, based an model predictions. The temperature variation and final film thickness of each was predicted by the simulation. The results indicate that model-based open loop control is viable strategy for practical RTCVD control. Based on this strategy, model-based open loop control was then implemented for the control of an existing RTP system. The experimental results confirm the simulations and provide improved temperature control for RTCVD