Substrate dividing method

A method of manufacturing a light emitting device from an object comprising a sapphire substrate having a front face of a (0001) plane of the sapphire substrate and a flat rear face, a gallium nitride compound semiconductor layer formed on the front face of the sapphire substrate, and a plurality of light emitting diodes formed in the gallium nitride compound semiconductor layer in a matrix, the method comprising:

• irradiating the sapphire substrate with laser light, thereby forming a plurality of modified regions embedded within the sapphire substrate along each line of a plurality of cutting lines arranged in a grid running between the light emitting diodes which are adjacent to one another, the cutting lines comprising lines extending in a direction along a (1120) plane of the sapphire substrate and in a direction along a (1100) plane of the sapphire substrate which is orthogonal thereto;
• and
• dividing the object by fractures generated in the sapphire substrate into a plurality of chips.