Apparatus and method for determining the elemental compositions and relative locations of particles on the surface of a semiconductor wafer

An apparatus for determining the elemental composition and relative location of a particle located upon a surface of a semiconductor wafer, comprising:

• an X-ray source configured to produce a beam of polychromatic primary X-ray photons;
• a multilayer monochromator aligned to receive said beam of polychromatic primary X-ray photons and configured to produce a beam of monochromatic primary X-ray photons, wherein said beam of monochromatic primary X-ray photons is incident upon the surface of the semiconductor wafer;
• an X-ray detector array comprising a plurality of laterally displaced X-ray detectors, wherein each of said plurality of X-ray detectors is (i) positioned to receive a secondary X-ray photon emitted by at least one atom present within said particle, and (ii) configured to produce a detector output signal in response to said secondary X-ray photon;
• a displacement sensor configured to produce a displacement signal reflecting the distance between the surface of the semiconductor wafer and the X-ray detector array;
• a position control unit coupled to receive said displacement signal and configured to produce a position control signal;
• a sample stage upon which the semiconductor wafer is placed, wherein the sample stage is coupled to receive said position control signal and configured to position the semiconductor wafer relative to the incident beam of monochromatic primary X-ray photons in response to the position control signal;
• and
• a computer system coupled to receive the detector output signal produced by each of said plurality of X-ray detectors.

A method for determining the elemental composition and relative location of a particle located upon a surface of a semiconductor wafer, comprising the steps of:

• positioning an array of X-ray detectors adjacent to the surface of the semiconductor wafer, wherein the array of X-ray detectors comprises a plurality of laterally displaced X-ray detectors, and each of the plurality of X-ray detectors is (i) oriented to receive a secondary X-ray photon emitted by at least one atom present within said particle, and (ii) configured to produce an output signal in response to said secondary X-ray photon;
• exposing the surface of the semiconductor wafer to a beam of primary X-ray photons;
• measuring and recording the output signal produced by each of the plurality of X-ray detectors comprising the array of X-ray detectors;
• converting the recorded output signals to corresponding energy levels of detected X-ray photons;
• forming a histogram representing the frequency distribution of the energy levels of detected X-ray photons;
• using the characteristic energy levels corresponding to peaks in the histogram to identify the elemental composition of the particle;
• searching the recorded output signals and the corresponding energy levels to determine the relative locations of X-ray detectors receiving secondary X-ray photons emitted by elements comprising the particle within the array of X-ray detectors;
• and
• determining the relative location of the particle by mapping the relative locations of X-ray detectors receiving secondary x-ray photons emitted by elements comprising the particle to corresponding locations on the surface of the semiconductor wafer.