THIN FILM MANUFACTURING METHOD AND SILICON MATERIAL WHICH CAN BE USED IN THE METHOD
Particles coming from an evaporation source 9 are deposited on a substrate 21 at a specified film forming position 33 in a vacuum so as to form a thin film on the substrate 21 . A rod-shaped material 32 containing a source material of the thin film is melted above the evaporation source 9 and the melted material is supplied to the evaporation source 9 in the form of droplets 14 . As the rod-shaped material 32 , a rod-shaped silicon material in which a plurality of first regions each surrounded by a grain boundary are present at positions of 90% length from a center toward an outer peripheral part on a cross section perpendicular to a longitudinal direction of the material, and an area-weighted average value of major diameters of the first regions is 200 μm or less, and a plurality of second regions each surrounded by a grain boundary are present at positions of 50% length from the center toward the outer peripheral part, and an area-weighted average value of major diameters of the second regions is 1000 μm or more is used.
1 . A method for manufacturing a thin film, comprising the steps of:
depositing particles coming from an evaporation source on a substrate at a specified film forming position in a vacuum so as to form the thin film on the substrate; and
melting a rod-shaped material containing a source material of the thin film above the evaporation source and supplying the melted material to the evaporation source in the form of droplets,
wherein as the rod-shaped material, a rod-shaped silicon material in which (a) a plurality of first regions each surrounded by a grain boundary are present at positions of 90% length from a center toward an outer peripheral part on a cross section perpendicular to a longitudinal direction of the material, and an area-weighted average value of major diameters of the first regions is 200 μm or less, and (b) a plurality of second regions each surrounded by a grain boundary are present at positions of 50% length from the center toward the outer peripheral part, and an area-weighted average value of major diameters of the second regions is 1000 μm or more is used.
2 . The method for manufacturing the thin film according to claim 1 , wherein a plurality of third regions each surrounded by a grain boundary are present at positions of 10% length from the center toward the outer peripheral part on the cross section of the silicon material, and an area-weighted average value of major diameters of the third regions is 200 μm or less.
3 . The method for manufacturing the thin film according to claim 1 , wherein the silicon material is produced by a casting method.
4 . The method for manufacturing the thin film according to claim 1 , wherein the silicon material is melted by irradiation with an electron beam or a laser beam.
5 . The method for manufacturing the thin film according to claim 1 , wherein
the substrate is an elongated substrate,
the depositing step includes transferring the elongated substrate fed from a feed roll to a take-up roll through the specified film forming position, and
the supplying step is performed while the depositing step is performed.
6 . A method for manufacturing a negative electrode for a lithium ion secondary battery, comprising the step of depositing silicon as a negative electrode active material capable of absorbing and releasing lithium therein and therefrom, on a substrate serving as a negative electrode collector, by the method for manufacturing the thin film according to claim 1 .
7 . A rod-shaped silicon material, comprising:
a plurality of first regions each surrounded by a grain boundary, the first regions being present at positions of 90% length from a center toward an outer peripheral part on a cross section perpendicular to a longitudinal direction; and
a plurality of second regions each surrounded by a grain boundary, the second regions being present at positions of 50% length from the center toward the outer peripheral part,
wherein an area-weighted average value of major diameters of the first regions is 200 μm or less, and an area-weighted average value of major diameters of the second regions is 1000 μm or more.
8 . The silicon material according to claim 7 , wherein a plurality of third regions each surrounded by a grain boundary are present at positions of 10% length from the center toward the outer peripheral part on the cross section of the silicon material, and an area-weighted average value of major diameters of the third regions is 200 μm or less.
9 . The silicon material according to claim 7 , wherein the silicon material is produced by a casting method.