Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1999-04-23
2001-01-23
Johns, Andrew W. (Department: 2721)
Image analysis
Applications
Manufacturing or product inspection
C382S270000, C382S318000
Reexamination Certificate
active
06178257
ABSTRACT:
FILED AND BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for optically inspecting the surface of an article for defects. The invention is particularly useful for optically inspecting patterned semiconductor wafers used in producing integrated-circuit dies or chips, and the invention is therefore described below particularly with respect to this application.
The inspection of unpatterned semiconductor wafers for surface-lying particles is relatively simple and can be easily automated. In one known type of such system, the wafer is scanned by a laser beam, and a photodetector detects the presence of a particle by collecting the light scattered by the particle. However, the inspection of patterned semiconductor wafers for defects in the pattern is considerably more difficult because the light scattered by the pattern overwhelms the light scattered from the particles or defects, thereby producing high rates of false alarms.
The existing inspection systems for inspecting patterned wafers are generally based on analysing high resolution two-dimensional images of the patterned wafer utilizing an opto-electric converter, such as a CCD (charge-coupled device), on a pixel-by-pixel basis. However, the extremely large number of pixels involved makes such systems extremely slow. For this reason, the inspection of patterned wafers is done at the present time almost only for statistical sampling purposes. As a result, microdefects in patterned semiconductor wafers remain largely undetected until a considerable number of such wafers have been fabricated and have begun to exhibit problems caused by the defects. The late discovery of such defects can therefore result in considerable losses, low yields, and large downtimes.
There is therefore an urgent need to inspect patterned semiconductor wafers at relatively high speeds and with a relatively low false alarm rate in order to permit inspection during or immediately after the fabrication of the wafer so as to quickly identify any process producing defects and thereby to enable immediate corrective action to be taken. This need is made even more critical by the increasing element density, die size, and number of layers in the integrated circuits not being produced from these wafers, and now being designed for future production, which requires that the number of microdefects per wafer be drastically reduced to attain a reasonable die yield.
OBJECTS AND BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel method and apparatus having advantages in the above respects for inspecting the surface of articles for defects.
In particular, an object of the invention is to provide a method and apparatus for automatically inspecting patterned semiconductor wafers characterized by a relatively high speed and relatively low rate of false alarms such that the patterned wafers may be tested while the wafers are in the production line to quickly enable the fabrication personnel to identify any process or equipment causing yield reduction, to receive fast feedback information after corrective actions, and to predict potential yield loss.
A still further object of the invention is to provide and inspection method and apparatus which are capable of inspecting all the critical layers, and which supply data on defects caused by the presence of particles and defects in the patterns.
According to one aspect of the present invention, there is provided a method of inspecting the surface of an article for defects by: optically examining, in a first phase examination, the complete surface of the article and electrically outputting information indicating locations on the article suspected of having defects; storing the suspected locations in a storage device; and, in a second phase examination, optically examining with high resolution only the suspected locations of the article's surface for determining the presence or absence of a defect in the suspected locations; characterized in that the first phase examination is effected by optically scanning the complete surface of the article at a high speed with an optical beam of small diameter. Thus, by selecting the diameter of the optical beam used in the first phase examination, the first phase examination may be made at any desired resolution, as compared to the second phase examination, according to the particular application.
According to further features of the invention, the first examining phase is effected by optically scanning the complete article surface to be inspected with a laser beam of small diameter and the second examining phase is automatically effected immediately after the first phase by imaging only the suspected locations on an image converter which converts the images to electrical signals and than analyzes the electrical signals.
According to still further features in preferred embodiments of the invention described below, the surface of the article to be inspected includes a pattern, e.g., a patterned wafer used for producing a plurality of integrated-circuit dies or chips. The first examination phase is effected by making a comparison between the inspected pattern and another pattern, serving as a reference pattern, to identify locations on the inspected pattern wherein there are sufficient differences with respect to the reference pattern to indicate a high probability of a defect in the inspected pattern. The second examination phase is also effected by making a comparison between the inspected pattern and the reference pattern, to identify locations on the inspected pattern wherein the comparison shows sufficient differences with respect to the reference pattern to indicate the presence of a defect in the suspected location of the inspected pattern.
The reference pattern may be a pattern on another like article (e.g., die-to-die comparison), another like pattern on the same article (repetitive pattern comparison), or data stored in a database (die-to-database comparison).
It will thus be seen that the novel method of the present invention primarily monitors changes in the defect density while maintaining a high throughput with a relatively low false alarm rate. Thus, the first examination is done at a relatively high speed and with a relatively low spatial resolution such as with a laser beam of small diameter to indicate only suspected locations having a high probability of a defect; and the second examination is done with a relatively high spatial resolution but only with respect to the suspected locations having a high probability of a defect. The sensitivity of the two phases may be adjusted according to the requirements for any particular application. Thus, where the application involves a relatively low number of defects, the sensitivity of the first examination phase may be increased by using a very small diameter laser beam to detect very small defects at a high speed but at the expense of an increased false alarm rate. However, since only relatively few suspected locations are examined in the second phase, the overall inspection can be effected relatively quickly to enable the fabrication personnel to identify defects caused by any process or equipment, and to immediately correct the cause for such defects.
According to a further feature of the invention, the first examining phase is effected by generating a first flow c′ N different streams of data representing the pixels of different views of the inspected pattern unit; generating a second flow of N different streams of data representing the pixels of different views of the reference pattern unit; and comparing the data of the first flow with the data of the second flow to provide an indication of the suspected locations of the inspected surface of the article having a high probability of a defect.
According to still further features of the invention, the pattern is based on a grid of angularly-spaced lines (e.g., 45° spacing); and the N streams of data in each flow are generated by a circular array of light collectors. The light collectors are located to c
Alumot David
Neumann Gad
Sherman Rivka
Tirosh Ehud
Applied Materials Inc.
Johns Andrew W.
Sughrue Mion Zinn McPeak & Seas
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