Research Of SIMOX Technology For SGOI Fabrication

SGOI(SiGe-on insulator, SGOI) , the virtual substrate for strained silicon growth, combines the both advantages of the SOI and SiGe. For the improvement of the carrier mobility, the strained silicon based CMOS could get performance enhancement under the art technology. The mobility improvement factor is actually dependent on the strain factor of the strained silicon, which could be controlled by choosing the Ge fraction of the SGOI substrates. As the Ge fraction of the SGOI get to 30 at. %, the hole and electron mobility both get to the maximum, by which the best performance improvement is expectable. However, the fabrication of the SGOI substrate is difficult. The application of Separation-by-implantation-of-oxygen (SIMOX) for SGOI fabrication is always limited by the Ge loss, caused by the high temperature annealing. When the Ge fraction exceeds 10%, the high temperature annealing would bring on heavy Ge loss and crystalline problem.In the present work, the novel SIMOX techniques for high quality SGOI fabrication including the dose&energy curves for SIMOX were investigated systematically.Firstly, the research findings on thermal oxidation behavior dependence of the oxidation ambient were introduced. By processing optimization, the thermal oxidation of SiGe without Ge-Pileup was realized . The results showed that the oxidation mechanism is influenced by the reaction speed, which could also be controlled by ambient.For resolving the problem of Ge loss, the novel oxide layer capping SIMOX (CAP-SIMOX) approach is invented for SGOI fabrication. During the process, a thin oxide layer, designed as capping layer, is formed by thermal oxidation and then the oxygen implantation at 3×10¹⁷cm^-2 and 60KeV is carried out. The last step is the high temperature annealing. As the results shown, the SGOI materials prepared with this new SIMOX process exhibit high quality, which is indicated by the low defect transition of SGOI and bulk SiGe region, a high degree of surface planarity and a high-integrity BOX layerwithout detectable silicon islands. Furthermore, the derived channeling yield of the SiGe layer in the SGOI structure is evaluated about 14%, which is better than the original SiGe sample. The Ge fraction of SGOI is improved to 17% and the SGOI is fully relaxed. The SGOI substrate is applicable for high performance strained silicon based n-MOSFET application, for the saturation of electron mobility enhancement is attainable when Ge fraction exceeds 15%.Based on the unique CAP-SIMOX approach, another novel SIMOX method "oxidation enhanced SIMOX" is invented, by integrating the oxidation step and the annealing step. The oxidation enhanced SIMOX is simplified as the process steps reduced. Utilizing the oxidation enhanced SIMOX method, high quality of SGOI is fabricated, which is indicated by the RBS result that the derived channeling yield of the SiGe layer is reduced to 7%, which is the best as reported. The mechanism of the two novel modified SIMOX methods for SGOI fabrication is also investigated. And the mechanism of the both methods is described as " for the existence of the oxide barrier to reject the Ge out-diffusion, the Ge atoms rejected from preferential oxidation diffused throughout the SGOI layer, and the high integrity of buried oxide layer formed after the high temperature annealing." It is convinced that the oxidation enhanced SIMOX is preponderant for the simple steps and high quality of SGOI.For widen the application range of CAP-SIMOX method, the present work also carried out systematical research on the implantation dose and energy window. The impact on the microstructure of the SGOI dependence of the dose&energy is studied. The implant dose and energy range are 2.0 X 10i7 cm"2 to 5.6 X1017 cm"2 and 25KeV to 120 KeV, respectively. By altering the implant dose or energy, the high quality of SGOI could just be gained at a narrow range, which is also called the dose&energy window. By collecting the dose&energy window, the full implantation dose&energy curve is gained for the first time. The dose and energy window is proved to be linear, which is similar with the SOI-SIMOX. Furthermore, the formation mechanism of the SGOI structure is reviewed. The silicon interstitial and the viscous flow of the SiO2 are brought forward as the entitative mechanism.In the end, the Ge condensation effect happened during the over-dose implantation isinvestigated. The oxidation condensation process of the SGOI to get higher Ge fraction, is also showed. In order to get higher Ge fraction condensation, the idea of combination of the oxidation process into the annealing step is introduced.