NOVELTY - Forming semiconductor substrate (112) involves producing ion species by exciting source gas, and introducing into first single crystal semiconductor substrate (100A) to form embrittlement layer; forming bonding layer (106); bonding crystal substrate and base substrate (108) with bonding layer; separating separate single crystal semiconductor layer (110) by heating crystal substrate; and reprocessing second single crystal semiconductor substrate by irradiating with laser light, to melt second crystal substrate at melting time per area of 0.5 microsecond to 1 millisecond.    USE - For forming semiconductor substrate which is useful for manufacturing a semiconductor device (claimed) such as a solar cell, a photo IC, and a semiconductor memory device.    ADVANTAGE - By the method for manufacturing a semiconductor substrate, a single crystal semiconductor substrate after separation can be planarized and reused, and resources are utilized efficiently. By manufacturing a semiconductor substrate using the reprocessed substrate, manufacturing cost of the semiconductor substrate and a semiconductor device using the semiconductor substrate is reduced. As for the surface state of the silicon wafer from which a thin film of single crystal semiconductor layer is separated by using the embrittlement layer into which hydrogen ions have been introduced, as a cleavage plane, the planarity and crystallinity of the surface is recovered by irradiation with continuous wave laser light having a wavelength whose penetration length to silicon which is the same as or substantially the same as the thickness of the silicon wafer and by a long-time melting of the surface and the vicinity. The entire surface of the silicon wafer is irradiated with laser light to recover the planarity and crystallinity, and thus it is possible that a thin film of single crystal silicon layer is formed again over a glass substrate by utilizing an embrittlement layer formed by introduction of hydrogen ions as a cleavage plane.    DETAILED DESCRIPTION - Manufacturing a semiconductor substrate (112) involves producing ion species by exciting a source gas including gases selected from hydrogen gas, rare gas, halogen gas or halide compound gas, and introducing the ion species into a first single crystal semiconductor substrate (100A) to form an embrittlement layer; forming a bonding layer (106) over the crystal substrate; bonding the crystal substrate and a base substrate (108) with the bonding layer interposed in between so that the crystal substrate and the base substrate are attached to each other; separating the crystal substrate by using the embrittlement layer as a cleavage plane by heating the crystal substrate so that a single crystal semiconductor layer (110) separated from the crystal substrate that is fixed over the base substrate; and reprocessing a second single crystal semiconductor substrate from which the single crystal semiconductor layer has been separated. The step of reprocessing is conducted in such a manner that the second crystal substrate is irradiated with a laser light from a surface side of the second crystal substrate from which the single crystal semiconductor layer has been separated, to melt the second crystal substrate, and a melting time per area is 0.5 microseconds to 1 millisecond. The method further involves forming a protective film over the first single crystal semiconductor substrate; and irradiating the crystal substrate with the ion species through the protective film. The second crystal substrate which is reprocessed has crystals grown in a direction parallel to a plane direction. The protective film is a single layer or a multilayer with at least two layers including at least one of a silicon nitride film and a silicon nitride oxide film. The bonding layer is a silicon oxide film formed by a chemical vapor deposition method using an organosilane gas as a silicon source gas. An INDEPENDENT CLAIM is included for manufacturing a semiconductor device using the formed semiconductor substrate involving forming a semiconductor element including the single crystal semiconductor layer over the base substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of a method for manufacturing a semiconductor substrate.    Single crystal semiconductor substrate (100A)    Bonding layer (106)    Base substrate (108)    Single crystal semiconductor layer (110)    Semiconductor substrate (112)