Phosphorus and boron diffusion paths in polycrystalline silicon gate of a trench-type three-dimensional metal-oxide-semiconductor field effect transistor investigated by atom probe tomography

• Published in: Applied physics letters 2015-07, Vol.107 (2)
• Main Authors: Han, Bin, Takamizawa, Hisashi, Shimizu, Yasuo, Inoue, Koji, Nagai, Yasuyoshi, Yano, Fumiko, Kunimune, Yorinobu, Inoue, Masao, Nishida, Akio
• Format: Article
• Language: English
• Subjects: ANNEALING; Applied physics; Atomic properties; ATOMS; BORON; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DIFFUSION; DISTRIBUTION; Dopants; Field effect transistors; GRAIN BOUNDARIES; METALS; MOSFET; MOSFETs; OXIDES; PHOSPHORUS; POLYCRYSTALS; SEGREGATION; Semiconductor devices; SEMICONDUCTOR MATERIALS; SILICON; THREE-DIMENSIONAL CALCULATIONS; TIME DEPENDENCE; TOMOGRAPHY
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.4926970

The dopant (P and B) diffusion path in n- and p-types polycrystalline-Si gates of trench-type three-dimensional (3D) metal-oxide-semiconductor field-effect transistors (MOSFETs) were investigated using atom probe tomography, based on the annealing time dependence of the dopant distribution at 900 °C. Remarkable differences were observed between P and B diffusion behavior. In the initial stage of diffusion, P atoms diffuse into deeper regions from the implanted region along grain boundaries in the n-type polycrystalline-Si gate. With longer annealing times, segregation of P on the grain boundaries was observed; however, few P atoms were observed within the large grains or on the gate/gate oxide interface distant from grain boundaries. These results indicate that P atoms diffuse along grain boundaries much faster than through the bulk or along the gate/gate oxide interface. On the other hand, in the p-type polycrystalline-Si gate, segregation of B was observed only at the initial stage of diffusion. After further annealing, the B atoms became uniformly distributed, and no clear segregation of B was observed. Therefore, B atoms diffuse not only along the grain boundary but also through the bulk. Furthermore, B atoms diffused deeper than P atoms along the grain boundaries under the same annealing conditions. This information on the diffusion behavior of P and B is essential for optimizing annealing conditions in order to control the P and B distributions in the polycrystalline-Si gates of trench-type 3D MOSFETs.