TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The kurtosis of the first surface of the first metal layer is smaller than that of a surface of the second metal layer, where the second metal layer has higher rigidity than the first metal layer. In the metal substrate, a difference between a thermal expansion coefficient of the second metal layer and a thermal expansion coefficient of the unit solar cell is smaller than a difference between a thermal expansion coefficient of the first metal layer and the thermal expansion coefficient of the unit solar cell. The difference between the thermal expansion coefficient of the second metal layer and the thermal expansion coefficient of the unit solar cell is not greater than 5x 10-6/ degrees C. The first metal layer has greater ductility than the second metal layer. The first metal layer is made of any one of aluminum, copper or their alloys, and the second metal layer is made of iron or ferritic stainless steel (preferred). The thickness of the second metal layer is at least 60% of a total thickness including at least a thickness of the first metal layer and a thickness of the second metal layer. The thickness of the first metal layer is at least 1.5 mu m. The first metal layer has an aluminum content of at least 99.7 mass%. In the metal substrate for a solar battery, a semiconductor layer of the unit solar cell is made of any one of silicon, copper-indium-diselenide, copper indium gallium selenide of formula (CuIn1-xGaxSe2), copper zinc tin sulfide of formula (Cu2ZnSnS4) or cadmium telluride is grown on the first surface of the first metal layer. At least one of an extraneous substance, a valley portion and a mountain portion exists on the first surface of the first metal layer, where the kurtosis of the first surface on which at least one of the extraneous substance, the valley portion and the mountain portion exists is not greater than 7. Preferred Method: The step of setting the kurtosis of the first surface of the first metal layer to not greater than 7 include a step of polishing the first surface of the first metal layer by chemical polishing. The step of forming the metal substrate comprises the cladding material including the first metal layer and the second metal layer by bonding the first metal plate made of any one of aluminum, copper or their alloys and the second metal plate made of iron or ferritic stainless steel to each other, and the step of polishing the first surface of the first metal layer by the chemical polishing comprises polishing the first surface of the first metal layer by dipping the metal substrate in a chemical polishing liquid containing phosphoric acid. The step of forming the metal substrate includes a step of cold-rolling the cladding material after forming the cladding material by bonding the first metal plate having greater ductility than the second metal plate and the second metal plate to each other. The step of forming the metal substrate includes a step of continuously forming the cladding material by bonding rolled first metal plate and rolled second metal plate to each other, and the step of setting the kurtosis of the first surface of the first metal layer to not greater than 7 includes a step of chemically polishing the first surface of the first metal layer of continuously formed cladding material.