초록 ▼

A system for laser scanning a relatively movable reflective surface element and inspecting that surface by monitoring the reflected energy in both light and dark channel receivers. Flaws occurring on the surface of the element, depending on the types of flaws, cause various frequency components to b

A system for laser scanning a relatively movable reflective surface element and inspecting that surface by monitoring the reflected energy in both light and dark channel receivers. Flaws occurring on the surface of the element, depending on the types of flaws, cause various frequency components to be present in the reflected energy and affect the amount of energy reflected to the light and dark channel receivers. Circuitry is included to detect and classify the various types of flaws as they are scanned, to compute the condition of the inspected element and to grade that inspected element as being in an acceptable state or in one of a plurality of unacceptable states. The described reflective surface element is a silicon wafer of the type used as the base substrate in fabricating integrated circuits and other electronic components.

대표청구항 ▼

A flaw inspection system comprising: means defining an inspection surface; means for repeatedly scanning a narrow beam of electromagnetic radiation along a line across said defined inspection surface; means for transporting a reflective surface element to be inspected at a predetermined speed along

A flaw inspection system comprising: means defining an inspection surface; means for repeatedly scanning a narrow beam of electromagnetic radiation along a line across said defined inspection surface; means for transporting a reflective surface element to be inspected at a predetermined speed along said inspection surface in a direction transverse to said scanning line; means defining a normally light channel for receiving electromagnetic radiation specularly reflected from said transported element and producing a light channel output signal indicative of a change in said received specularly reflected radiation caused by flaws which may be present on said reflection surface; means defining a normally dark channel for receiving scattered electromagnetic radiation reflected from flaws which may be present on said reflection surface of said transported element and producing a dark channel output signal indicative of said scattered radiation received therein; first means connected to said light channel receiving means for comparing said light channel output signal with a first predetermined threshold level and outputting a predetermined signal level in a corresponding first threshold category channel whenever said light channel output signal and said first predetermined threshold level differ by a predetermined amount; second means connected to said light channel receiving means for passing portions of said light channel output signal having frequency components within a predetermined range of frequencies and for comparing said passed portions with a bandpass threshold level and outputting a predetermined signal level in a corresponding second threshold category channel whenever said passed portions of said light channel output signal and said bandpass threshold level differ by predetermined amounts; third means connected to said dark channel receiving means for comparing said dark channel output signal with a plurality of predetermined threshold levels and outputting a corresponding predetermined signal level in a corresponding threshold category channel whenever said dark channel output signal and a corresponding threshold level differ by predetermined amounts; means for time sampling said threshold category channels a plurality of times during each scan and over a plurality of successive scans to define a plurality of sampling areas; means for translating the occurrence of said output signal levels in said sampled threshold category channels into digital values according to the respective threshold category channels in which said output signal levels occurred; means for storing each digital value according to its time location in the scan; means for comparing said stored digital value with each successive digital value in a like time location within a corresponding sampling area and providing the greater of the compared digital values as the value designating the corresponding sampling area; means for accumulating the occurrences of like designated sampling areas; and means for evaluating the quality of said transported element according to preset accumulation values.