Accurate SIMS measurement of a boron profile in a SiO2-Si interfacial region under optimum incident angle of low-energy primary oxygen ion beam was made in order to demonstrate the mechanism of boron penetration through gate oxide. Degrees of ionization of Si and boron became almost equal in SiO2 and Si at the 20-degree incident angle with a practical sputtering rate. The estimation of an apparent shift of a boron profile toward surface and the determination of the SiO2-Si interface under measurement conditions achieving matrix-independent degree of ionization of Si were also examined. The SIMS measurement using optimum conditions revealed that the variation of flat band voltages was proportional to the variation of penetrating boron doses in the range of 0.85−1.30 V. It was also found that when a penetrating boron dose was equivalent to a flat band voltage over 1 V, the electrical activation of boron was lower than that of boron ion-implanted in a Si substrate.
