Method for producing quantum cascade laser element

A method for manufacturing a quantum cascade laser element including a semiconductor substrate, a semiconductor laminate formed on the semiconductor substrate to include an active layer having a quantum cascade structure, a first electrode formed on a surface on an opposite side of the semiconductor laminate from the semiconductor substrate, and a second electrode formed on a surface on an opposite side of the semiconductor substrate from the semiconductor laminate, the method comprising:

• a first step of preparing a semiconductor wafer including a plurality of portions each of which becomes the semiconductor substrate, and having a first major surface and a second major surface, and of forming a semiconductor layer including a plurality of portions each of which becomes the semiconductor laminate on the first major surface;
• a second step of removing a part of the semiconductor layer by etching such that each of the plurality of portions each of which becomes the semiconductor laminate includes a ridge portion, after the first step;
• a third step of forming an insulating layer on the semiconductor wafer and on a surface on an opposite side of the semiconductor layer from the second major surface such that at least a part of a surface on an opposite side of the ridge portion from the semiconductor wafer is exposed, after the second step;
• a fourth step of forming a plurality of metal plating layers each of which becomes the first electrode on the plurality of portions each of which becomes the semiconductor laminate, and of embedding the ridge portion in each of the plurality of metal plating layers, after the third step;
• a fifth step of flattening a surface on an opposite side of each of the plurality of metal plating layers from the semiconductor wafer by polishing in a state where a protective member is disposed in a region between each pair of the plurality of metal plating layers, after the fourth step;
• a sixth step of forming an electrode layer including a plurality of portions each of which becomes the second electrode on the second major surface;
• and
• a seventh step of cleaving the semiconductor wafer and the semiconductor layer along a line partitioning a plurality of portions each of which becomes the quantum cascade laser element off from each other, in a state where the protective member is removed, after the fifth step and the sixth step.