Influence of boron and fluorine incorporation on the network structure of ultrathin SiO2

Incorporation of boron and fluorine atoms into an ultrathin SiO2 layer during a p(+)-poly Si gate fabrication process with BF2+ or B+ implantation and its influence on the SiO2 bonding network have been studied by Fourier transform infrared absorption (FT-IR) and x-ray photoelectron spectroscopy (XPS) in conjunction with SiO2 thinning by dilute HF etching. The analysis of F1s core spectrum measured at each SiO2 thinning step shows that fluorine atoms pile up in the SiO2 network near the SiO2/Si(100) interface in bonding forms of mainly F-SiO3 or F-BO2 units and partly F-O units. Also, boron pile-up near the interface has been confirmed from the depth profiling of the IR absorption bands due to B-F and B-O bonds. The thickness dependence of the LO phonon frequency for the oxides with B or B/F incorporation indicates that not only fluorine atoms but also three-coordinate boron atoms in the interfacial region relax built-in compressive stress in the oxide network near the interface.