Method for classifying unknown particles on a surface of a semi-conductor wafer
Unknown particles on a surface of a semiconductor wafer are classified by applying a range of particles of known chemical composition and different sizes onto a test wafer, measuring the sizes of a plurality of the particles and spectrally analyzing a makeup of the particles by energy-dispersive x-ray spectroscopy, followed by ascertaining a substantive content therefrom; creating a best-fit curve to the size and substantive content of the particles; measuring the particle size of an unknown particle and recording its spectrum by energy-dispersive x-ray spectroscopy and classifying the unknown particle as the result of a comparison of the size and the substantive content of the unknown particle with the best-fit curve.
1 . A method for classifying unknown particles on a surface of a semiconductor wafer, comprising:
applying SiO 2 particles of different sizes in the form of a suspension of the SiO 2 particles in a liquid to a test wafer, ascertaining a size of a plurality of the SiO 2 particles, and recording a spectrum of an energy-dispersive x-ray spectroscopy of the plurality of the SiO 2 particles;
subsequently respectively ascertaining a substantive content of the plurality of the SiO 2 particles therefrom, and constructing a best-fit curve of size and substantive content of the plurality of the SiO 2 particles; and
ascertaining a particle size of an unknown particle by means of an electron microscope, recording a spectrum of an energy-dispersive x-ray spectroscopy of the unknown particle, and determining therefrom the substantive content of the unknown particle on the semiconductor wafer, and classifying the unknown particle as the result of the comparison of the size and the substantive content of the unknown particle with the best-fit curve;
wherein the semiconductor wafer comprises silicon; and
wherein the particles are in a size range of 20 nm-200 nm.
2 . The method of claim 1 , wherein the best-fit curve is a straight line.
3 . The method of claim 1 , wherein the test wafer comprises silicon.
4 . The method of claim 1 , wherein the size of the plurality of SiO 2 particles is determined by means of an electron microscope.