1. A method for manufacturing an insulated circuit board including a ceramic substrate and a circuit layer having a circuit pattern disposed on one surface of the ceramic substrate,wherein the circuit layer includes an aluminum layer disposed on the one surface of the ceramic substrate, and a titanium layer formed on a surface of the aluminum layer on a side opposite to the ceramic substrate, and
the method comprises:
a ceramic/aluminum-joining step of joining an aluminum material to the ceramic substrate and thereby, forming the aluminum layer;
a titanium material-disposing step of disposing a titanium material, which is to become the titanium layer, on a surface of the aluminum layer or the aluminum material in the circuit pattern shape;
a titanium layer-forming step of performing a heat treatment in a state where the titanium material is laminated on the surface of the aluminum layer or the aluminum material and thereby, forming the titanium layer;
an etching treatment step of etching the aluminum layer on which the titanium layer is formed, into the circuit pattern shape; and
the method further comprises a Si-enriched layer-forming step of forming a Si-enriched layer containing Si in an amount of 0.03 mass % or more and 1.0 mass % or less on the surface of the aluminum layer or the aluminum material on which the titanium layer is to be formed, before the titanium material-disposing step.