Patent ID: 8173212

Claim:
A method for manufacturing a carbon nano tube by a CVD method comprising: forming a catalyzer on a substrate, wherein the carbon nano tube is formed with using the catalyzer: arranging the substrate with the catalyzer in a reactor; heating the substrate to be a synthesis temperature; supplying a raw material gas into the reactor, the raw material gas providing a carbon supply source; measuring a reflectivity on a surface of the substrate; supplying a carrier gas into the reactor; and controlling at least one of a concentration and a flow rate of the raw material gas, wherein the controlling at least one of the concentration and the flow rate includes: setting the concentration to a first concentration or setting the flow rate to a first flow rate at a first step of synthesis of the carbon nano tube; and setting the concentration to a second concentration or setting the flow rate to a second flow rate at a second step of synthesis of the carbon nano tube, the second concentration is smaller than the first concentration, and the second flow rate is smaller than the first flow rate, and the second step is performed after the first step, wherein the catalyzer becomes super saturated in the first step of synthesis of the carbon nano tube, and a caulking layer is prevented from being formed on the catalyzer in the second step of synthesis of the carbon nano tube, wherein the first step is an initial step from a beginning of synthesis to a predetermined time, the controlling at least one of the concentration and the flow rate further includes switching the first step to the second step when a change rate of the reflectivity of the substrate becomes equal to or lower than one-tenth the change rate of the reflectivity of the substrate at the beginning of synthesis, and the synthesis temperature is 750° C., the raw material gas is ethylene gas, and the second concentration is smaller than one-tenth the first concentration, and the second flow rate is smaller than one-tenth the first flow rate.