Method for detecting particles using illumination with several wavelengths

A process for detecting small particles on a wafer surface, chosen from among patterned and smooth areas of semiconductor surfaces, which comprises:

• irradiating the wafer surface with two light beams having a small difference in wavelength, the light not passing through the wafer to reach the surface;
• collecting the light that is scattered by the wafer surface in at least on direction;
• separating the collected light, by filtering it, into two component beams, each of which has the wavelengths of one of the irradiating beams;
• and
• comparing the intensities of the two component beams.

An apparatus for the detection of small particles on surfaces, particularly surfaces of patterned, semiconductor wafers, which comprises:

• a) a stage for supporting a wafer;
• b) laser source and optics for generating at least two laser beams having different wavelengths;
• c) optical components for superimposing said beams and directing them onto the wafer to scan the wafer surface without the light passing througgh the wafer to reach the surface;
• d) a sensor for sensing the scattered light reflected by the wafer and separating it into two components having the wavelengths of said laser beams;
• e) A/D converter for generating digital signals corresponding to said two components;
• and
• a comparator for analyzing whether said digital signals indicate the presence of small particles.

An apparatus for the detection of small particles on surfaces, particularly patterned or smooth surfaces of semiconductor wafers, which comprises:

• a) a stage for supporting a wafer;
• b) laser source and optics for generating at least two laser beams having different wavelengths;
• c) optical components for directing and focusing said beams onto a surface of the wafer so as to produce thereon spots chosen from among overlapping and adjacent spots, without the light passing through the object to reach the surface;
• d) optical fiber for collecting the scattered light reflected from the surface of the wafer in at least one direction;
• e) a photoelectric circuit for generating electric analog signals representing said components;
• f) an A/D converter for sampling said electric analog signals at a predetermined frequency and converting them into digital signals;
• and
• g) a comparator for analyzing whether the digital signals thus obtained indicate the presence of small particles.