Xiaobo Ma

A high-quality SOI structure fabricated by low-temperature technology with B+/H+ co-implantation and plasma bonding

In order to decrease the heating temperature of Smart-Cut technology, plasma activation and B+/H+ co-implantation were used. B+/H+ co-implantation gave rise to a decrease of splitting temperature, and finally a high-quality silicon-on-insulator (SOI) structure was fabricated at 300 °C. A diluted Secco etching test indicated that the top Si surface defect density was 104–105 cm−2. An atomic force microscope (AFM) image showed that the surface roughness of the top Si layer was much smaller than that of the SOI structure formed from the H-only implanted wafer. The diluted Secco etching test also indicated that the top Si surface defect density would decrease with the increase of annealing temperature, and 500 °C was a critical temperature for reducing the defect density.

Void-free low-temperature silicon direct-bonding technique using plasma activation

A low-temperature silicon direct-bonding technique has been researched using variant plasma (N2, O2, Ar, and H∕He) pretreatment prior to bonding for surface activation. In plasma bonding, after annealing at 300°C for an hour the authors get a bonding energy of about 2–2.5J∕m2, which is near the fracture strength of bulk silicon. In Si–Si wafer bonding, our experiments demonstrate that the origin of voids appearing in low-temperature annealing is related to the plasma variety and activation conditions. The authors believe that the annealing voids and bubbles, which appear and accumulate at the microdefects, are caused by plasma activation. They used an optimized O2 and H∕He plasma-activation process for wafer direct bonding and obtained a high surface energy, void-free hydrophilic Si–Si wafer bonding. The wafers’ root-mean-square surface roughness after plasma activation was measured by an atomic force microscope. The cross-sectional image of the bonding interface was observed by a scanning electron micros...

Study of the Ge Wafer Surface Hydrophilicity after Low-Temperature Plasma Activation

Plasma activation has been investigated for its ability to induce a strong bonding energy even at low-temperature annealing. In this paper, Ge, Si, and SiO 2 surface hydrophilicities with oxygen and nitrogen plasma activation are analyzed by contact angle measurement. Compared to wet chemical treatments, such as solutions containing ammonium hydroxide, the hydrophilicity of Ge wafer surface is strongly enhanced by O 2 or N 2 plasma activation. For germanium, a highly hydrophilic and smooth surface has been obtained by O 2 plasma activation only for 10 s. The contact angle measurements indicate that O 2 plasma is more remarkable than N 2 plasma in the same activation conditions. A higher surface roughness, which is only observed in the O 2 plasma activated sample, is decreased greatly after rinsing in deionized water.

Fabrication of single-crystalline LiTaO3 film on silicon substrate using thin film transfer technology

High-quality LiTaO3 thin films on silicon substrates are important for the application of silicon-based optoelectronic integration technology. In this article, single-crystalline LiTaO3 thin films were achieved by wafer-bonding and layer-transfer technology. Cross-sectional transmission electronic microscopy (TEM) and x-ray diffraction results indicate that the LiTaO3 thin films are single crystalline and have good structural quality. After hydrogen implantation and annealing, the surfaces of LiTaO3 samples were investigated in detail using optical microscopy and TEM. Results show that dose and implantation energy of hydrogen can both have effect on the cleavage of a thin surface section from a LiTaO3 wafer.

Investigations of Fuch-Kliewer phonons and hydrogen adsorption of 6H-SiC surfaces by high-resolution electron-energy-loss spectroscopy

Abstract In this contribution, the optical Fuchs–Kliewer (FK) surface phonon and hydrogen adsorption of 6H–SiC surfaces were investigated with high-resolution electron-energy-loss spectroscopy (HREELS). The different HREEL spectra of the FK surface phonons were obtained from clean (0001) Si- and (0001) C-terminated surfaces. It was noticed that the full width at half maximum of elastic peaks for the reconstructed surfaces was smaller than that of unreconstructed surfaces for both (0001) Si- and (0001) C-terminated 6H–SiC. Under decomposing ammonia by hot filament at 1700°C, only the adsorption of hydrogen atoms on the surfaces for both Si- and C-terminated 6H–SiC was detected in the experiment.

Enhanced surface blistering of germanium with B+/H+ coimplantation

The surface blisters in B+∕H+ coimplanted germanium (Ge) and H-only-implanted Ge were compared. The surface-blister phenomenon in B+∕H+ coimplanted Ge emerged after annealing at 330–340°C; but in H-only-implanted Ge, the blistering emerged after annealing at over 400°C. The results indicate that the preimplanted boron can facilitate the coalescence of implanted H into bubbles, and so, it decreases the temperature for surface-blister formation. The exfoliation mechanism of B+∕H+ coimplanted Ge during the annealing step was investigated. The transmission electron microscopy results indicate that the B+∕H+ coimplantation creates both (100) and {111} platelet defects, and the nucleation of H bubbles occurs at regions where the (100) defects are concentrated. The bottoms of popped-off blisters show a very rough surface because the (100) and {111} platelets occur at different depths, and the wide distribution of (100) platelets also contributes to this roughness. The results show that boron appears to be one of...

Germanium surface hydrophilicity and low-temperature Ge layer transfer by Ge–SiO2 bonding

Wafer bonding and layer transfer are two fundamental technologies in the fabrication of advanced microsystems. In the authors’ experiments, prior to Ge wafer bonding, the hydrophilicity of the germanium surface after wet chemical treatment and O2/N2 plasma activation is evaluated by contact angle measurement. The effects and mechanism of wet or dry treatments on the Ge surface roughness are also characterized. The results are used to tailor the Ge–SiO2 direct bonding process. Finally, oxygen plasma activation for 10 s and B+/H+ coimplantation are employed to facilitate Ge–SiO2 direct bonding and Ge layer transfer at a low temperature. In comparison with hydrogen only ion implantation using the same fluence, coimplantation of B+ and H+ decreases the layer transfer temperature from over 400–320 °C.

Modified postannealing of the Ge condensation process for better-strained Si material and devices

A modified postannealing at 1000 °C in N2 ambient has been carried out to improve the Ge distribution in the SiGe layer fabricated by the Ge condensation process, which is a potential technique for strained Si fabrication. Three kinds of SiGe-on-insulator samples have been fabricated by so-called Ge condensation, which is the oxidation of the SiGe layer on an insulator to enhance the Ge fraction. After different postannealing processes and the necessary cleaning steps, 20-nm-thick strained Si films are epitaxially grown on them. Though the differences of surface topography among the three samples are not great, the one with the modified postannealing process has the most uniform Ge element distribution and the least misfit dislocations. Meanwhile, the strain values obtained by Raman spectra are coherent with the Ge fraction in SiGe near the Si/SiGe interface and the sample with the modified postannealing process has a larger strain value than the one with a conventional postannealing. The performance of m...

Strain Stability and Carrier Mobility Enhancement in Strained Si on Relaxed SiGe-on-Insulator

A low thermal budget process to fabricate strained Si metal-oxide-semiconductor field-effect transistors (MOSFETs) on a strain-relaxed silicon-germanium-on-insulator (SGOI) by strain engineering is described. The strain stability in the top strained Si is studied after low temperature oxidation, ion implantation, and rapid thermal annealing, and only 7-9% relaxation is observed. The Ge content distribution in a strained-silicon-on-insulator (SOI) is investigated to validate the process with a low thermal budget. Ge, reaching the strained Si/SiO 2 interface, inevitably degrades the gate oxide properties. The electron and hole mobility values in the biaxial strained-SOI are investigated and compared to those in MOSFETs fabricated in strain-relaxed SGOI and SOI substrates. Both carrier mobilities are enhanced, and the process is much simpler than using uniaxial strained Si. The relaxed-SGOI MOSFETs possess the lowest carrier mobility, and both the electron and hole mobility values in the strained-SOI MOSFETs are enhanced compared to the devices fabricated in the control samples and bulk Si. The SiGe layer in strained-SOI can lead to a larger leakage current.

Hybrid particle-in-cell (PIC) ions and Boltzmann electron distribution simulation of direct-current plasma immersion ion implantation into three-dimensional objects

A hybrid protocol including particle-in-cell (PIC) ions and Boltzmann electron distribution is developed to simulate plasma immersion ion implantation (PIII) into an S-shaped bar inside a grounded cylindrical cage consisting of a mesh. A multiple-grid system with three cell confinements is adopted to achieve sufficient accuracy and acceptable computational time. The simulation results reveal that the implantation fluence distribution along the major curvature is more uniform than that obtained by conventional PIII.