Yao Zhi Hu

Low-temperature processing of semiconductor surfaces by use of a high-density microwave plasma

The required temperature in semiconductor process technology is going into two extreme directions. Either very high temperatures up to 1300 °C with very short durations in the order of a millisecond or even shorter for highest dopant activation is required, or extremely low temperatures near room temperature or slightly above are needed for forming high-quality dielectrics with minimum dopant deactivation and redistribution. This letter describes a new microwave plasma oxidation apparatus with unique features addressing the aforementioned low-temperature process. With this new technique the oxide growth rate was studied as a function of time, gaseous ambient, pressure, applied microwave power and silicon substrate parameters to determine crystallographic oxidation rate anisotropy and dopant concentration-dependent oxidation at temperatures much below 400 °C. Some tests have also been performed on doped and undoped SiGe material and on patterned structures. The plasma oxides grown on silicon have been electrically characterized regarding fixed charges, interface state densities and breakdown strength. In addition the selective oxidation regimes in the presence of various metals such as W, TiN and TaN were evaluated and determined.

Optimization of diffusion, activation and damage annealing in millisecond annealing

Advances in CMOS technology require continuous reductions in the thermal budget employed for activating ion implanted dopants. However, low thermal budget annealing approaches, such as millisecond annealing, must also remove implant damage to minimize junction leakage. This paper explores the trade-offs between dopant diffusion, electrical activation and damage annealing for ultra-shallow junctions (USJ) formed by low energy B implants into both crystalline and pre-amorphized silicon. The study also addressed how low-thermal budget annealing affects the use of strong halo-style doping from As implants. Several annealing methods were studied, with the main focus on flash-assisted RTP™ (fRTP™) at temperatures between 1250°C and 1350°C. Activation was assessed with RsL™ non-contact measurements and Hg-probe four point-probe sheet resistance measurements, as well as a continuous anodic oxidation technique for depth profiling of carrier concentrations and mobility. Residual damage was assessed by photoluminescence, thermal wave studies, optical reflectance and RsL junction leakage current measurements. fRTP effectively activates high-dose, low-energy B implants, while limiting the diffusion to a few nm of profile movement. The limited thermal budget of millisecond annealing reduces, but does not fully eliminate, implant damage from heavy ions implanted at high energy, although very high process temperatures, e.g. ∼1300°C, are more effective in this regard. Strong halo doping greatly increases the junction leakage and for future device nodes it will be important to reduce implantation damage from both USJ and halo implants. Non-invasive damage metrology can help rapid optimization of implantation and annealing conditions. Such measurements will be even more useful when quantitative models can accurately link them to doping and damage profiles.

New Approaches for Characterization of Advanced Annealing Techniques for Ultra‐Shallow Junction Formation

Low thermal budget annealing approaches, such as millisecond annealing or solid‐phase epitaxy (SPE), can electrically activate ultra‐shallow junctions (USJ) without excessive diffusion, but they must also remove implant damage to minimize junction leakage. This paper presents results from annealing low‐energy B implants into both crystalline and pre‐amorphized silicon. Some wafers also received As implants for halo‐style doping, and some halo‐implanted wafers were pre‐annealed at 1050 °C before B‐doping. The final anneal was either SPE at 650 °C, spike annealing at 1050 °C, or millisecond annealing with flash‐assisted RTP™ (fRTP™) at temperatures between 1250 °C and 1350 °C. Electrical activation was assessed by sheet resistance (Rs) measurements with conventional four‐point probing (4PP) as well as Hg‐probe 4PP and a non‐contact method. Residual damage was characterized by photoluminescence, thermal wave studies, optical reflectance and non‐contact junction leakage current measurements. Damage from the h...