Chih-Chiang Wang

Boron uphill diffusion during ultrashallow junction formation

The recently observed phenomenon of boron uphill diffusion during low-temperature annealing of ultrashallow ion-implanted junctions in silicon has been investigated. It is shown that the effect is enhanced by preamorphization, and that an increase in the depth of the preamorphized layer reduces uphill diffusion in the high-concentration portion of boron profile, while increasing transient enhanced diffusion in the tail. The data demonstrate that the magnitude of the uphill diffusion effect is determined by the proximity of boron and implant damage to the silicon surface.

Modeling mechanical stress effect on dopant diffusion in scaled MOSFETs

The effect of shallow trench isolation mechanical stress on MOSFET dopant diffusion has become significant, and affects device behavior for sub-100-nm technologies. This paper presents a stress-dependent dopant diffusion model and demonstrates its capability to reflect experimental results for a state-of-the-art logic CMOS technology. The proposed stress-dependent dopant diffusion model is shown to successfully reproduce device characteristics covering a wide range of active area sizes, gate lengths, and device operating conditions.

Interface induced uphill diffusion of boron: an effective approach for ultrashallow junction

This paper investigates anomalous diffusion behavior for ultra low energy implants in the extension or tip of PMOS devices. Transient enhanced diffusion (TED) is minimal at these low energies, since excess interstitials are very close to the surface. Instead, interface induced uphill diffusion is found, for the first time, to dominate during low temperature thermal cycles. The interface pile-up dynamics can be taken advantage of to produce shallower junctions and improve short channel effect control in PMOS devices. Attempts to minimize TED before spacer deposition by inclusion of extra RTA anneals are shown to be detrimental to forming boron ultra shallow junctions.

Effects of germanium and carbon coimplants on phosphorus diffusion in silicon

The authors have studied the interactions between implant defects and phosphorus diffusion in crystalline silicon. Defect engineering enables ultrashallow n+∕p junction formation using phosphorus, carbon, and germanium coimplants, and spike anneal. Their experimental data suggest that the positioning of a preamorphized layer using germanium implants plays an important role in phosphorus diffusion. They find that extending the overlap of germanium preamorphization and carbon profiles results in greater reduction of phosphorus transient-enhanced diffusion by trapping more excess interstitials. This conclusion is consistent with the end-of-range defects calculated by Monte Carlo simulation and annealed carbon profiles.

Modeling well edge proximity effect on highly-scaled MOSFETs

Well edge proximity effect caused by ion scattering during implantation in highly-scaled CMOS technology was explored from a process and physics point of view. TCAD simulation was employed to visualize the internal change of the MOSFETs. A new compact model for SPICE was proposed using physics-based understanding and was calibrated with experimental silicon test sets. Circuit simulation using the proposed model was conducted to evaluate the improvement in accuracy

Millisecond Anneal and Short-Channel Effect Control in Si CMOS Transistor Performance

In this letter, the effects of the millisecond anneal in conjunction with conventional spike anneal on the p-n junction formation in CMOS devices are studied. The results reveal that the millisecond and spike annealing sequence plays an important role in the implanted boron p+/n junction formation. On blanket Si wafers, the millisecond anneal followed by the spike anneal increases implanted boron solid solubility in crystalline silicon by ~18% compared to that obtained using reversed annealing sequence under the same annealing conditions. This result substantially alters the short-channel effect behaviors in the fabricated CMOS devices, resulting in opposite threshold-voltage behaviors in PMOS and NMOS devices when using boron as NMOS halo implant. The results also provide useful insights into ultrashallow-junction formation and short-channel effect control when scaling CMOS technology

Arsenic/phosphorus LDD optimization by taking advantage of phosphorus transient enhanced diffusion for high voltage input/output CMOS devices

Optimization of a LDD doping profile to enhance hot carrier resistance in 3.3 V input/output CMOS devices has been performed by utilizing phosphorus transient enhanced diffusion (TED). Hot carrier effects in hybrid arsenic/phosphorus LDD nMOSFETs with and without TED are characterized comprehensively. Our result shows that the substrate current in a nMOSFET with phosphorus TED can be substantially reduced, as compared to the one without TED. The reason is that the TED effect can yield a more graded n/sup -/ LDD doping profile and thus a smaller lateral electric field. Further improvement of hot carrier reliability can be achieved by optimizing arsenic implant energy. Secondary ion mass spectrometry analysis for TED effect and two-dimensional (2-D) device simulation for electric field and current flow distributions have been conducted. The phosphorus TED effects on transistor driving current and off-state leakage current are also investigated.

Boron Diffusion in Strained and Strain-Relaxed SiGe

SiGe has been utilized for aggressive CMOS technologies development recently and there are many literatures talking about the advantages brought by it. However, few publications discuss the impacts from both mechanical strain and Ge doping on boron diffusion. Moreover these effects have mostly been studied at low boron concentrations and with long high temperature anneals. They are not the possible conditions used in aggressive CMOS technologies. An experiment has been therefore designed to investigate boron diffusion in both strained and strain-relaxed SiGe including ultra-low energy, high concentration boron implant and spike RTA. Summarily, this paper describes the experiments, calibration and resulting diffusion constants for an ultra-shallow boron junction in SiGe that is popular in advanced CMOS technology.

Modeling and Characterization of Advanced Phosphorus Ultra Shallow Junction Using Germanium and Carbon Coimplants

A continuum model of phosphorus diffusion with germanium and carbon coimplant has been proposed and calibrated based on secondary ion mass spectroscopy (SIMS) profiles aiming at ultra shallow junction (USJ) formation in advanced CMOS technologies. The phosphorus diffusion behaviors are well captured by our model under various implant and annealing conditions, representing a significant step towards advanced n-type USJ formation technique using phosphorus and carbon coimplant for aggressively scaled CMOS technologies.

Modeling Dopant Diffusion in Strained and Strain-Relaxed Epi-SiGe

Ultra-shallow arsenic and boron diffusion in both strained and strain-relaxed SiGe has been investigated in this paper. Significant arsenic diffusion enhancement and boron diffusion retardation have been observed. Strained SiGe was found to have a stronger arsenic diffusion enhancement. Empirical equations in Arrhenius form have been created and incorporated into numerical simulation to successfully model the diffusion dopant profiles.