Abstract-Solid-phase crystallization for polysilicon thin-film transistors (TFT's) is generally limited by a tradeoff between throughput and device performance. Larger grains require lower crystallization temperatures, and hence, longer crystallization times. In this letter, a novel crystallization technique is presented which increases both throughput and device performance, using a two-step process, controlled using an in situ acoustic temperature/crystallinity sensor. A high-temperature rapid thermal annealing (RTA) nucleation step is followed by a low-temperature grain growth step to grow large-grain polysilicon. TFT's have been fabricated with a substantial improvement in throughput and device performance. This promises a high-throughput, highperformance, spatially uniform TFT process.
A novel technique is presented to simultaneously measure temperature and crystallinity insitu during the rapid thermal annealing of thin Si / SiGe films on transparent substrates for active matrix liquid crystal display applications. The technique uses acoustic waves to monitor temperature, by measuring changes in velocity with temperature. The technique enables accurate tracking of crystalline phase transitions along with temperature, since it is independent of emissivity. This provides a methodology for closed-loop control and end-point detection. The experiments on thin amorphous Si on Quartz demonstrate temperature repeatability of 2%. Also, the technique proved sensitive enough to detect the onset of nucleation, as evidenced by TEM.
Absfruct-This paper presents an overview of research at Stanford University on the development of concepts of a programmable factory, based on a new generation of flexible multifunctional equipment implemented in a smaller flexible factory. This approach is demonstrated through the development of a novel single wafer Rapid Thermal Multiprocessing (RTM) reactor with extensive integration of sensors, computers and related technology for specification, communication, execution, monitoring, control, and diagnosis to demonstrate the programmable nature of the RTM. The RTM combines rapid thermal processing and several other process environments in a single chamber, with applications for multilayer in-situ growth and deposition of dielectrics, semiconductors and metals. Because it is highly instrumented, the RTM is very flexible for in-situ multiprocessing, allowing rapid cycling of ambient gases, temperature, pressure, etc. It allows several processing steps to be executed sequentially in-situ, while providing sufficient flexibility to allow optimization of each processing step. This flexibility is partially the result of a new lamp system with three concentric rings each of which is independently and dynamically controlled to provide for better control over the spatial and temporal optical flux profile resulting in excellent temperature uniformity over a wide range of process conditions namely temperatures, pressures and gas flow rates. The lamp system has been optimally designed through the use of a newly developed thermal simulator. For equipment and process control, a variety of sensors for real-time measurements and a model based control system have been developed. The acoustic sensors noninvasively allow a complete wafer temperature tomography under all process conditioncritically important measurement never obtained before. In an exemplary demonstration of multiprocessing, we have integrated three different processes with disparate process conditions-cleaning, thermal oxidation and CVD of silicon-sequentially in-situ. This technology integrates an entire MOS capacitor stack into one process chamber as opposed to three stand alone pieces of equipment needed in conventional technology. This will result in reduced cost of the factory, reduction in cycle time and may provide better device characteristics, since the interfaces between the semiconductor, gate dielectric and gate electrode are free of contamination from the room ambient. In general, adaptable
A novel technique is presented for simultaneously measuring temperature and crystallinity in situ during the rapid thermal annealing of thin Si films on transparent substrates for active matrix liquid crystal display applications. This technique makes use of acoustic waves to monitor temperature by measuring changes in Lamb wave velocity with temperature. Since this technique is independent of emissivity, it enables accurate tracking of crystalline phase transitions along with temperature, based on changes in the optical absorption properties of the film. This provides a methodology for closed-loop control and end-point detection. The experiments on thin amorphous Si on fused silica demonstrate temperature repeatability of 2%. Also, the technique proved sensitive enough to detect the onset of nucleation, as evidenced by transmission electron microscopy. IntroductionThin film transistors (TFTs) find extensive applications in active matrix liquid crystal displays (AMLCDs). There is substantial interest in the development of a glass-compatible polycrystalline TFT technology. The ability to fabricate low temperature polysilicon TFTs will enable the incorporation of driver circuitry onto glass display substrates,' improving performance at a reduced cost. Lowcost glasses have strain points of approximately 600°C.
Precise wafer temperature control is crucial to the viability of the emerging technology of mpid thermal processing (RTP) for semiconductor manufacturing. In this paper we examine the problem of accurate noninvasive measurement of wafer temperature, which is required for precise tempemture control. Our work extends the work of Khuri-Yakub et al. (1993) on acoustic techniques for noninvasive wafer tempemture measurement. W e propose a method for estimation of wafer temperatures via regularized tomographic inversion using a priori knowledge of properties of the temperature distribution and data obtained by their technique. Results of simulation studies of the methods proposed are described.
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