Impacto da rotação do substrato sobre as características elétricas de FINFETS de porta tripla
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Dissertação
Data
2016
Autores
Ribeiro, T. A.
Orientador
Pavanello, M. A.
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Texto completo (DOI)
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Circuitos integrados,Tecnologia FinFet
Resumo
Esse trabalho estuda o transporte de portadores de carga em SOI n-FinFETs totalmente depletados de porta tripla, fabricados tradicionalmente e com a rotação do substrato em um angulo de 45º, com e sem tensão biaxial. Nos FinFETs tradicionais, o canal possui dois tipos de orientação cristalográfica sendo, {110} nas paredes laterais e {100} no topo do canal. Já com a fabricação com o substrato rotacionado, todas as orientações cristalográficas do canal ficam {100}. Para o transporte de cargas, a orientação {100} é benéfica para o transporte de elétrons, em comparação com a orientação {110}. Para analisar a influência da orientação das paredes e do topo da aleta desses dispositivos, foram extraídos e analisados os parâmetros referente a mobilidade em função da largura da aleta de silício dos FinFETs, que para larguras pequenas os parâmetros das paredes laterais são mais importantes, e com o aumento da largura, o topo da aleta passa a exercer maior influência. A caracterização elétrica foi feita, principalmente, pelo método Y-Function, com um algoritmo para melhorar a precisão. Para FinFETs com aleta de silício de 20nm, foram obtidos valores de mobilidade dos elétrons de 183 cm2/Vs em dispositivos tradicionais, em comparação com 220 cm2/Vs dos dispositivos rotacionados, que mostra a vantagem da rotação do substrato. Já para aletas de silício bem largas (570nm), a mobilidade dos elétrons tende ao valor de 145 cm2/V.s, independentemente da rotação do substrato. Foi extraída a mobilidade para dispositivos tensionados e foi obtida uma melhora relativa na mobilidade dos dispositivos tradicionais, entre 40% a 60% dependendo da largura da aleta, contra uma melhora de 20% a 40% para os dispositivos rotacionados, em comparação aos não tensionados. Foram analisados também os mecanismos de degradação da mobilidade por espalhamento de rede, espalhamento Coulomb e espalhamento por rugosidade de superfície. Pelo coeficiente de degradação linear da mobilidade obtido ser negativo, mostra uma grande degradação pelo espalhamento Coulomb. Com o coeficiente de degradação quadrático da mobilidade, pode-se analisar que a rugosidade de superfície dos dispositivos rotacionados é menor que a dos tradicionais. Porém, com a aplicação de tensão mecânica esses parâmetros variam, sendo que para os rotacionados a rugosidade aumenta, mas para os tradicionais a rugosidade diminui, em comparação com os dispositivos sem tensão mecânica. Os valores obtidos foram então comprovados por simulações tridimensionais, a fim de compreender os efeitos da orientação cristalográfica sobre a mobilidade e sua degradação. Para a calibração do simulador foram adotados valores máximos para mobilidade diferentes para o topo e as laterais dos FinFETs. No primeiro caso foram admitidos valores iguais de mobilidade no topo e nas paredes laterais,
no segundo caso valores de mobilidade maiores no topo do que nas paredes laterais da aleta e no último caso, valores de mobilidade maiores nas paredes laterais do que no topo da aleta, onde nessa última combinação, os resultados obtidos pelas simulações reproduzem os mesmos resultados obtidos pelos FinFETs experimentais.
This work studies the carrier transport in fully depleted SOI triple gate n-FinFETs traditionally manufactured and with a rotation of the substrate at an angle of 45° with and without biaxial strain. In traditional FinFETs the channel have two types of crystallographic orientation, {110} at the sidewalls and {100} at the top of the channel. Manufacturing with a rotated substrate, all crystallographic orientations of the channel becomes {100}. For the carrier transport, the {100} orientation is beneficial for the transport of electrons, when compared to the {110} orientation. To analyze the influence of the orientation of the sidewalls and the top of the fin in FinFETs, parameters relating to the mobility were extracted and analyzed as a function of the fin width, that for small fin width the parameters of the sidewalls are more important, and with increasing fin width, the top fin has a greater influence. The electrical characterization was done mainly by the Y-Function method with an algorithm to improve the accuracy. For FinFETs with fin width of 20nm, the electron mobility values obtained were 183 cm2/Vs in traditional devices, as compared to 220 cm2/V.s of rotated devices showing the advantage of substrate rotation. As for wide fins (570nm), the electron mobility tends to the value of 145 cm2/Vs independent of the substrate rotation. The mobility was extracted for strained devices and it was obtained a relative improvement of the mobility of traditional devices from 40% to 60% depending on the fin width, against an improvement of 20% to 40% for the rotated devices compared to the non-strained devices. It was also analyzed the mobility degradation mechanisms by the phonon scattering, Coulomb scattering and surface roughness scattering. By the negative linear mobility degradation coefficient obtained, it shows a big degradation by Coulomb scattering. With the quadratic mobility coefficient degradation, it is possible analyze that the surface roughness of the rotated devices is lower than that of traditional ones. However, with the application of mechanical stress these parameters vary and for rotated devices the roughness increases, but for the traditional ones the surface roughness decreases compared to the unstressed devices. The values obtained were then supported by three dimensional simulations, in order to understand the effect of crystallographic orientation on the mobility and its degradation. For the calibration of the simulator, different maximum values of mobility were adopted for the fin's top and sidewalls of the FinFET. The first case, it was adopted mobility values equal for the top and the sidewalls, the second case mobility values higher at the top than at the sidewalls of the fin and the last case mobility values higher at the sidewalls than the top of the fin, where in this last combination, the results obtained by simulation reproduce the same results obtained by experimental FinF.
This work studies the carrier transport in fully depleted SOI triple gate n-FinFETs traditionally manufactured and with a rotation of the substrate at an angle of 45° with and without biaxial strain. In traditional FinFETs the channel have two types of crystallographic orientation, {110} at the sidewalls and {100} at the top of the channel. Manufacturing with a rotated substrate, all crystallographic orientations of the channel becomes {100}. For the carrier transport, the {100} orientation is beneficial for the transport of electrons, when compared to the {110} orientation. To analyze the influence of the orientation of the sidewalls and the top of the fin in FinFETs, parameters relating to the mobility were extracted and analyzed as a function of the fin width, that for small fin width the parameters of the sidewalls are more important, and with increasing fin width, the top fin has a greater influence. The electrical characterization was done mainly by the Y-Function method with an algorithm to improve the accuracy. For FinFETs with fin width of 20nm, the electron mobility values obtained were 183 cm2/Vs in traditional devices, as compared to 220 cm2/V.s of rotated devices showing the advantage of substrate rotation. As for wide fins (570nm), the electron mobility tends to the value of 145 cm2/Vs independent of the substrate rotation. The mobility was extracted for strained devices and it was obtained a relative improvement of the mobility of traditional devices from 40% to 60% depending on the fin width, against an improvement of 20% to 40% for the rotated devices compared to the non-strained devices. It was also analyzed the mobility degradation mechanisms by the phonon scattering, Coulomb scattering and surface roughness scattering. By the negative linear mobility degradation coefficient obtained, it shows a big degradation by Coulomb scattering. With the quadratic mobility coefficient degradation, it is possible analyze that the surface roughness of the rotated devices is lower than that of traditional ones. However, with the application of mechanical stress these parameters vary and for rotated devices the roughness increases, but for the traditional ones the surface roughness decreases compared to the unstressed devices. The values obtained were then supported by three dimensional simulations, in order to understand the effect of crystallographic orientation on the mobility and its degradation. For the calibration of the simulator, different maximum values of mobility were adopted for the fin's top and sidewalls of the FinFET. The first case, it was adopted mobility values equal for the top and the sidewalls, the second case mobility values higher at the top than at the sidewalls of the fin and the last case mobility values higher at the sidewalls than the top of the fin, where in this last combination, the results obtained by simulation reproduce the same results obtained by experimental FinF.