Display device manufacturing apparatus and method

A display device manufacturing method comprising:

• annealing a display substrate by irradiating a laser to the display substrate in different energy values;
• measuring a transmittance of the annealed display substrate;
• and
• determining an optimal crystallization value of the display substrate based on the transmittance,
• wherein the annealing of the display substrate comprises:
• dividing the display substrate into a plurality of areas;
• and
• irradiating the laser having different energy values corresponding to the plurality of areas, respectively, of the display substrate,
• wherein the determining of the optimal crystallization value comprises:
• calculating an absorbance of the annealed display substrate for each energy value of the laser based on the transmittance;
• calculating a band gap energy of the annealed display substrate for each energy value of the laser based on the absorbance;
• and
• determining an energy value of the laser corresponding to a minimum value of the band gap energy as the optimal crystallization value.