Low-temperature Fabrication of a Crystallized Si Film Deposited on a Glass Substrate using an Yttria-stabilized Zirconia Seed Layer

Abstract

AbstractWe have been investigating fabrication of a crystallized Si (c-Si) film deposited on a glass substrate at low temperature, using a poly-yttria-stabilized zirconia (poly-YSZ) film as a seed layer. It can be expected that the crystallographic information of the YSZ layer transmits to the deposited Si film so that it stimulates its crystallization even at lower temperature. To reduce the crystallization temperature further, we focused on the surface treatment of the YSZ layer, in which it was dipped in the HF solution, followed by rinsing with deionized water (DIW) or with ethanol.After depositing the poly-YSZ layer by reactive magnetron sputtering on the quartz glass substrate, the Si film was deposited directly on it by e-beam vacuum evaporation in <10-6 Pa. The Raman spectra of the Si films deposited at 430 °C on the ethanol-rinsed glass without YSZ layer and on the DIW-rinsed YSZ layer showed amorphous phase. However, on the ethanol-rinsed YSZ layer, they showed a strong peak of c-Si of the deposited film, even at 350 °C, and indicated the beginning of the crystallization at 320 °C. This means that the YSZ layer enhanced the Si film crystallization, and that the ethanol-rinse was effective for low-temperature crystallization. The crystalline fraction of the Si film varied with the yttria content and the surface treatment of the YSZ layer prior to the Si film deposition. From the XPS results, we found out that fluorine F were adsorbed on the surface and were bonded with the Y. The Y 3d and F 1s peaks observed from the ethanol-rinsed YSZ were higher than those of the DIW rinse, which suggests that the Y and adsorbed F on the surface were removed by the DIW rinse, but remained even after the ethanol rinse. Based on the Raman and XPS results, we can speculate that the excessive amount of F on the YSZ layer surface prior to the Si film deposition play an important role on the Si film crystallization. We observed the surface of the Secco-etched Si/YSZ films deposited at 320, 350, and 430 °C by SEM. The number of crystallized Si grains was denser at higher temperature than that of lower temperature. That is, the Si film deposited at 430 °C was crystallized thoroughly on the whole substrate, but some regions of the Si films deposited at 350 and 320 °Cwere amorphous and removed by the Secco etching. The grain sizes were in the range from 20 to 40 nm, and the size at the lower deposition temperature was more uniform than the higher temperature. From SIMS observation, it was found that Zr atoms diffuse from the interface with the YSZ layer.