Rajesh S. Ramanujam

Pyrometry for laser annealing

Laser annealing is one of the process solutions to enable ultra shallow junction (USJ) formation for the 45 nm technology node. However, variations in the front-side optical properties of device wafers cause large temperature variations on the wafer surface which, in turn, cause large variations in activation of the dopants that form the junction. As a result, pyrometry and closed loop temperature control are critical to establish process uniformity and repeatability for laser annealing. Pyrometry results are presented along with the correlation between the process results (dopant activation) and the pyrometer signal. Closed loop control and future technical challenges are discussed

Traceable emissivity measurements in RTP using room temperature reflectometry

The design of an integrating reflectometer specific to the optical and spectral requirements of rapid thermal processing (RTP) is discussed. We report reflectance measurements of various materials. These measurements are correlated to in-situ emittance measurements recorded during rapid thermal processing. We also present the design of an optimized emissometer for an RTP chamber. We propose a means for correlating room temperature reflectance measurements to emittance standards for RTP.

Si spontaneous emission during RTP and its impact on low-temperature pyrometry

Si fluorescence or spontaneous emission was discovered during the development of lower-temperature pyrometer. To reveal unambiguously the Si spontaneous emission, a high-power 980nm laser is used together with a high sensitivity IR spectrometer. Clear Si fluorescence spectra with peaks at ∼1140nm were obtained at different Si temperatures. The Si fluorescence peaks shift to longer wavelength, in agreement with Si bandgap narrowing with increasing temperatures. Wafers of different doping levels and types were studied for Si spontaneous emission. It is found that lightly doped (resisitivity ≪20 ohms-cm) Si has the highest level of Si spontaneous emission. On the other hand, heavily doped Si does not generate any Si spontaneous emission, mainly due to the higher recombination. Since the Si spontaneous emission has a broad spectrum, it spills into the RTP pyrometer spectral bandwidth and acts as s spurious pyrometer signal. Even though Si has very low efficiency for light emission due to its indirect bandgap, the fluorescence emitted light is still on the level of pyrometer signal equivalent to ∼200 to 250C.

Ultra Low Temperature NiSi Processing

Manuscript not released forpublication due to legal issues.