Characterization and Metrology of Low Pressure Chemical Vapor Deposited (LPCVD) Polysilicon
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ABSTRACT Polycrystalline silicon (polySi) is widely used in the semiconductor industry as a gate electrode, interconnect material and for various other applications. Small variations in deposition conditions can significantly affect this material's properties, cause errors in metrology control of the film thicknesses and, ultimately, in device performance. In this work polySi was LPCVD deposited in a vertical reactor with multiple gas inlets and a flat temperature distribution. Deposition conditions were controllably changed to create a matrix of wafers. Characterization is done using production dual wavelength, multiple-angle-of-incidence and research grade spectroscopic ellipsometers. PolySi thickness and composition uniformity are analyzed. INTRODUCTION Low Pressure Chemical Vapor Deposition (LPCVD) is a dominant process for growth of the high-quality polySi used in semiconductor manufacturing, due to the high purity and uniformity of the deposited material as well as good process control. Uniformity of the polysilicon thickness across the reactor was historically one of the important characteristics. In the single gas inlet reactors, which are widely used in industry, thickness uniformity is achieved by biasing the temperature across the wafer load -- typically 20-30 'C -- to compensate for silane depletion. Physical properties (e.g., composition and surface morphology ) are critically
dependent on deposition temperature and, to a lesser extent, are sensitive to some other deposition parameters. Ignoring physical properties variation, which is common with use of the reflectometry and related techniques, can cause errors in metrology control of the film thickness. Both the optical constants and thickness of the polySi must be measured simultaneously, even when uniformity of the polySi composition is not by itself critical for device performance. In most cases surface roughness and native oxide layers must be also taken into account to achieve meaningful and reliable metrology control of the process. Recent studies [1] done with the 100-150 mm wafers in a biased temperature furnace, have shown significant influence of the deposition parameters on the physical properties and thickness of the polySi. In this paper we use a state of the art vertical reactor with a 5-zone heater core to analyze the influence of the process parameters on uniformity of polySi deposition on 200 mm production wafers. To optimize and control the deposition process, it is essential to have metrology equipment that is capable of measuring simultaneously and independently physical properties and thickness of the film. We show that a production-oriented Dual Wavelength Multiple-Angle-of-Incidence (DW-MAI) ellipsometer meets all the requirements of a reliable metrology tool, and provides an excellent capability of tracking variation of both composition and thickness of the polySi. Measurements were found to be consistent with the results of a research grade spectroscopic ellipsometer (SE).
1013 Mat. Res. Soc. Symp. Proc. Vol. 452 01997 Mater
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