Inspection apparatus and inspection method

An inspection apparatus comprising:

• a light source that emits light having a predetermined wavelength;
• a first lens that transmits the light having the predetermined wavelength toward a sample;
• a second lens that forms an image of the light transmitted through or reflected by the sample via the first lens;
• a first image sensor that obtains optical image data of a pattern formed on the sample from the light of which the image is formed by the second lens;
• an optical path splitting unit that is disposed between the second lens and the first image sensor to split the light transmitted through the second lens;
• a second image sensor that obtains pieces of image information on focal points ahead and behind the pattern from the pieces of light split by the optical path splitting unit;
• a focal position detector that detects a reference focal position of an image plane of the sample in the first image sensor from a variation of an output value in the pieces of image information on the focal points ahead and behind the pattern, the output value being acquired by changing a distance between the first lens and the sample, and detects an optimum focal position of an inspection from the reference focal position;
• an image processor that obtains at least one of either an average gradation value in each predetermined unit region or a variation of a gradation value in the unit region with respect to the optical image data obtained at the optimum focal position;
• and
• a defect detector that detects a defect of the sample based on at least one of either the average gradation value or the variation of the gradation value,
• wherein a resolution limit determined by a wavelength of the light source and a numerical aperture of the second lens is a value in which the pattern is not resolved.

An inspection method comprising the steps of:

• irradiating a sample with light having a predetermined wavelength via a first lens, forming an image of the light transmitted through or reflected by the sample on an image sensor via a second lens, and obtaining optical image data of a pattern by performing an action to obtain the optical image data of the pattern formed in the sample with a distance between the first lens and the sample changed;
• detecting a reference focal position of an image plane of the sample from a variation of an output value in optical image data, and detecting an optimum focal position of an inspection from the reference focal position;
• adjusting a level of a table on which the sample is placed based on the optimum focal position;
• obtaining at least one of either an average gradation value in each predetermined unit region or a variation of a gradation value in the unit region with respect to the optical image data obtained at the optimum focal position;
• and
• detecting a defect of the sample based on at least one of either the average gradation value or the variation of the gradation value,
• wherein the pattern is a repetitive pattern having a period less than or equal to resolution determined by the wavelength and a numerical aperture of the second lens.