Substrate-floatation-type laser processing apparatus and method for measuring floating height

1. A substrate-floatation-type laser processing apparatus comprising:

a floating stage configured to float and convey a substrate;

a floating-height measurement apparatus configured to measure a floating height of the substrate in the floating stage, the floating height being a distance between a top surface of the floating stage and a bottom surface of the substrate in the floating stage; and

a controller to which the measured floating height is input from the floating-height measurement apparatus, the controller being configured to determine a difference between the measured floating height and a preset target value, wherein

a distance along a vertical axis between the floating-height measurement apparatus and the substrate in the floating stage is automatically adjusted based on the determined difference by moving the floating-height measurement apparatus along the vertical axis,

wherein the distance between the floating-height measurement apparatus and the substrate is adjusted so as to make the floating height larger than the preset target value when the difference is negative, and so as to make the floating height smaller than the preset target value when the difference is positive.

2. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein the floating height of the substrate is measured by applying laser light to the substrate and the floating stage.

3. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein the distance between the floating-height measurement apparatus and the substrate is adjusted by using a feedback mechanism in which the measured floating height of the substrate is used as an input.

4. The substrate-floatation-type laser processing apparatus according to claim 2 , wherein

the floating-height measurement apparatus comprises a laser displacement gauge configured to apply the laser light to the substrate and the floating stage and receive reflected light of the laser light reflected by the substrate and the floating stage, and

the laser displacement gauge measures the floating height of the substrate from reflected light of the laser light reflected by a bottom surface of the substrate and reflected light of the laser light reflected by a top surface of the floating stage.

5. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the floating-height measurement apparatus comprises a camera configured to take an image of a top surface of the substrate, and

the camera measures the floating height of the substrate based on its position at which its focal point coincides with the top surface of the substrate when the substrate is brought into contact with the floating stage and its position at which its focal point coincides with the top surface of the substrate when the substrate is floated over the floating stage.

6. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the floating-height measurement apparatus comprises a camera configured to take an image of a top surface of the substrate, and

the camera measures the floating height of the substrate based on its position at which its focal point coincides with the top surface or a bottom surface of the substrate and its position at which its focal point coincides with the top surface of the floating stage.

7. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the floating-height measurement apparatus comprises a length measurement device configured to measure a distance to a top surface of the substrate, and

the length measurement device measures the floating height of the substrate based on a distance to the top surface of the substrate when the substrate is brought into contact with the floating stage and a distance to the top surface of the substrate when the substrate is floated over the floating stage.

8. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the floating-height measurement apparatus comprises a translation movement stage extending in one direction on a horizontal plane above the floating stage, and

the floating-height measurement apparatus measures the floating height of the substrate along the one direction.

9. The substrate-floatation-type laser processing apparatus according to claim 8 , wherein the translation movement stage is movable in another direction perpendicular to the one direction on the horizontal plane above the floating stage.

10. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the floating stage comprises a plurality of floatation units configured to eject air for floating the substrate, and

a top surface of the floating stage includes top surfaces of the plurality of floatation units.

11. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein the controller excludes the input floating height from data for adjusting the distance when the difference between the target value and the input floating height exceeds a predetermined range.

12. The substrate-floatation-type laser processing apparatus according to claim 1 , wherein

the controller comprises a storage unit in which a distance between the floating-height measurement apparatus and the floating stage is stored, and

the controller corrects the measured floating height of the substrate by using the distance stored in the storage unit.