Chaochao Fu

Ultra-shallow junctions formed using microwave annealing

Microwave annealing is shown to be viable for achieving low thermal budget formation of ultra-shallow junctions. Regrowth of a 10 nm thick amorphous Si layer that is generated during a Ge amorphization process prior to BF2 or As dopant implantation proceeds at rates up to 0.53 nm/min for BF2 and up to 0.33 nm/min for As at 370 °C. The fraction of electrical activation for implanted dopants is as high as 13% for BF2 and 32% for As with negligible diffusion at 540 °C.

Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing

Microwave annealing (MWA) is investigated as an alternative technique to rapid thermal processing with halogen lamp heating (RTP) for low-temperature silicide formation on epitaxially grown Si0.81Ge0.19 layers. Phase formation, resistivity mapping, morphology analysis, and composition evaluation indicate that the formation of low-resistivity NiSi1−xGex by means of MWA occurs at temperatures about 100 °C lower than by RTP. Under similar annealing conditions, more severe strain relaxation and defect generation are therefore found in the remaining Si0.81Ge0.19 layers treated by MWA. Although silicidation by microwave heating is in essence also due to thermal effects, details in heating mechanisms differ from RTP.

Understanding the microwave annealing of silicon

Though microwave annealing appears to be very appealing due to its unique features, lacking an in-depth understanding and accurate model hinder its application in semiconductor processing. In this paper, the physics-based model and accurate calculation for the microwave annealing of silicon are presented. Both thermal effects, including ohmic conduction loss and dielectric polarization loss, and non-thermal effects are thoroughly analyzed. We designed unique experiments to verify the mechanism and extract relevant parameters. We also explicitly illustrate the dynamic interaction processes of the microwave annealing of silicon. This work provides an in-depth understanding that can expedite the application of microwave annealing in semiconductor processing and open the door to implementing microwave annealing for future research and applications.

Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing

The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4–0.7 eV to 0.2–0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature.

Microwave Annealing as a Low Thermal Budget Technique for ZnO Thin-Film Transistors Fabricated Using Atomic Layer Deposition

Microwave annealing (MWA) and furnace annealing are compared for their low thermal budget capability to improve the characteristics of ZnO-based thin-film transistors (TFTs). Both the ZnO channel and the Al2O3 gate dielectric are fabricated using atomic layer deposition. Using Si-wafer-susceptor assisted MWA with a substantial reduction of both annealing temperature and duration, significant improvements of the characteristics of the ZnO TFTs can be attained. A multi-step MWA process is found to further improve the characteristics of the TFTs. For the same microwave power and total duration, the field-effect mobility of the multi-step MWA TFT is 42% greater than that of the one-step MWA TFT with a similar sub-threshold swing. The multi-step MWA process can serve the purpose at temperatures as low as 220 °C.

Investigation of Ni/epi-SiGe layer stacks annealed by microwave heating

The Ni/epi-SiGe/Si layer stacks were annealed by microwave annealing and rapid thermal annealing via halogen lamp heating. Sheet resistance, X-ray diffraction and micro-Raman spectroscopy results indicate that the reaction and diffusion rates of the related Ni, Si and Ge atoms were accelerated for the samples annealed by microwave annealing, compared with the samples annealed by rapid thermal annealing under the same substrate temperature and duration. Since the diffusion and reaction are in principle thermally driven processes, the volumetric and selective heating properties of microwave annealing, which can result in higher local temperature, are thought to be responsible for the accelerated reaction and diffusion rates.

Tuning of Schottky Barrier Height at NiSi/Si Contact by Combining Dual Implantation of Boron and Aluminum and Microwave Annealing

Dopant-segregated source/drain contacts in a p-channel Schottky-barrier metal-oxide semiconductor field-effect transistor (SB-MOSFET) require further hole Schottky barrier height (SBH) regulation toward sub-0.1 eV levels to improve their competitiveness with conventional field-effect transistors. Because of the solubility limits of dopants in silicon, the requirements for effective hole SBH reduction with dopant segregation cannot be satisfied using mono-implantation. In this study, we demonstrate a potential solution for further SBH tuning by implementing the dual implantation of boron (B) and aluminum (Al) in combination with microwave annealing (MWA). By using such a method, not only has the lowest hole SBH ever with 0.07 eV in NiSi/n-Si contacts been realized, but also the annealing duration of MWA was sharply reduced to 60 s. Moreover, we investigated the SBH tuning mechanisms of the dual-implanted diodes with microwave annealing, including the dopant segregation, activation effect, and dual-barrier tuning effect of Al. With the selection of appropriate implantation conditions, the dual implantation of B and Al combined with the MWA technique shows promise for the fabrication of future p-channel SB-MOSFETs with a lower thermal budget.

Accurate temperature monitoring scheme for microwave annealing with silicon substrate

Accurate temperature monitoring of the silicon substrate remains to be a key issue for application of novel microwave annealing technology in advanced semiconductor processing. In this paper, a calibration system for temperature monitoring using infrared thermometer pyrometer is designed and temperature accuracy of silicon substrates with various doping concentrations is analyzed. Furthermore, an accurate temperature monitoring scheme for microwave annealing with silicon substrates is presented and successfully testified with the calibration system.

Crystallization of amorphous silicon on glass substrate by microwave annealing for thin-film-transistor applications

There is a rising demand for low temperature polysilicon TFT these years due to the rapidly increasing market of high resolution display panels. In this paper, both low temperature microwave annealing and laser annealing were used to crystallize amorphous silicon film on glass substrate. It is found that both methods had successfully transferred the amorphous silicon into polysilicon according to Raman spectra results. The microwave crystallized polysilicon had smaller grain size and lower tensile stress than the laser crystallized one. After implantation and activation of BF2 and P, sheet resistance values of the BF2-implanted microwave crystallized samples were similar to that of laser crystallized ones. However, for the P implanted samples, the microwave crystallized samples had two to three magnitude higher sheet resistance compared with the laser crystallized ones.

Schottky barrier height tuning via nickel silicide as diffusion source dopant segregation scheme with microwave annealing

In this work, microwave annealing is explored to tune the Schottky barrier height between NiSi and Si via boron and arsenic dopant segregation using silicide as diffusion source scheme. The microwave annealing is found to be able to obtain equivalent electron and hole Schottky barrier heights at significantly lower temperature (>100 °C) compared with conventional rapid thermal annealing. A plausible interpretation has been further proposed to explain the impact of low temperature microwave annealing on formation of dopant segregated Schottky junctions. The effectiveness of Schottky barrier height tuning below 400 °C by microwave annealing paves the way to form advanced source/drain and contact structures for future ultra-scaled MOSFETs and monolithic 3D sequential integration.