Jiping Li

Improved Subthreshold and Output Characteristics of Source-Pocket Si Tunnel FET by the Application of Laser Annealing

To reduce the power consumption and improve the device performance in scaled CMOS integrated circuits, transistors with steep subthreshold swing (SS) is highly desirable. The tunnel field-effect transistor (TFET) based on the band-to-band tunneling has been suggested as a replacement to conventional MOSFETs. In order to improve the device performance of TFET, enhanced carrier transport across the tunneling junction is crucial. In this paper, source-pocket Si TFET is presented and successfully fabricated by laser annealing. This TFET has enhanced lateral electric field across the source tunneling junction, resulting in a reduction of tunneling distance. The experimental data of the proposed paper, for the first time, shows steep SS (46 mV/dec at 1 pA/μm), excellent ION/IOFF ratio ( <; 107), and improved output characteristics at T = 300 K due to the dramatic reduction of the tunneling resistance. Compared with other TFET works, the proposed method is efficient to improve the device performance on TFET.

Evolution of dopants and defects in silicon under various annealing sequences

Several decades of research into understanding the mechanisms responsible for diffusion and activation of group-III acceptor and group-V donor impurities in silicon has been driven by the technological need for creating electrical junctions in the S/D and extensions of transistors in semiconductor integrated circuits. It is now conclusively known that anomalous diffusion of implanted impurities during annealing results from their interaction with the non-conservative evolution of excess point-defect damage created by the original implantation, and the effect annealing ambients, co-impurities, interfaces and surfaces have on that evolution [1–8]. Early experiments shown in Ref. [2] conclusively proved this by etching away the surface region containing implant damage before annealing, and demonstrating that the anomalous behavior disappeared. Starting from the as-implanted damage, the nucleation, growth and dissolution of a sequence of larger defects at the expense of smaller ones during the anneal, sets the point defect flux and super-saturation levels (the ratio of point defect concentration to its temperature equilibrium value), which then determine the magnitude and durations of the various phases of anomalous diffusion [9].

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.