<title>Influence of pyrometer signal absorption due to process gas on temperature control in rapid thermal processing</title>

Abstract

Influence of Pyrometer Signal Absorption due toProcess Gas on Temperature Control in Rapid Thermal ProcessingJulius C. Chang, Tue Nguyen, James S. Nakos, and JosefW. KorejwaIBM General Technology DivisionEssex Junction, Vermont, USAABSTRACTFuture DRAM devices require higher performance dielectrics for which novel process chemistries must bestudied. Nitrous oxide (N20) has shown promising results as a process gas for rapid thermal oxidation.However, current practice in rapid thermal processing (RTP) has neglected the effect of process gas ontemperature control. For N20, this results in a large temperature offset and oscillation, and poor thicknessuniformity. Evidence is presented indicating that gas-phase absorption of the pyrometer signal produces thedifficulties observed when using N20. These difficulties do not occur if the pyrometer is operated at awavelength not absorbed by the N20. This behavior also does not occur when using 02 as the process gassince it is transparent at the pyrometer wavelengths used. The data shows that one must examine theabsorption spectra of the process gas for compatibility with the pyrometer wavelength used for temperaturemeasurements.2. INTRODUCTIONAccurate temperature control during rapid thermal processing (RTP) is critical for many steps in state-of-the-art semiconductor manufacturing, from oxidation to annealing to forming silicide junctions. Typically,pyrometry is used for remote high-temperature (above 600 °C) measurement and control of a feedback loop.The pyrometer measures the intensity of a specific wavelength of radiation emitted from the backside of awafer. Temperature is computed through a second-order polynomial function of intensity.The accuracy of pyrometry control can be strongly influenced by absorption of the desired wavelength ofradiation by the process gas used for RTP. This absorption can have a negative effect on process control,impacting product development.Consider the example ofa pyrometer that uses a wavelength of4.5 im for temperature measurement.Several commerically available RTP systems use pyrometers that measure temperature using a wavelengthnear this value. Absorption of a 4.5 tm signal by the process gas is not a problem in the present technology.Oxygen, ammonia, and dilute HCI are some ofthe process gases commonly used for formation ofthin gatedielectrics in RTP and their absorption spectra show that these gases are transparent at 4.5 jim.For certain other ambients, however, 4.5 jim may be a poor choice. Current industry practice has notaccounted for the influence of different process gases and the associated problem of signal absorption inpyrometer temperature measurements. For future DRAM technology, it is clear that new process gaschemistries must be explored to develop higher performance dielectrics; therefore, absorption effects must be