Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-09-29
2002-04-02
Patel, Jayanti K. (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
C382S151000, C382S174000, C382S181000, C382S204000, C382S224000, C250S306000, C250S311000, C250S338400, C250S339110
Reexamination Certificate
active
06366688
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of inspection of semiconductor devices. More particularly, the invention involves detection of contact failures such as not-open contact holes using a scanning electron microscope.
BACKGROUND OF THE INVENTION
Integrated circuits are manufactured by first forming discrete semiconductor devices within silicon wafers. A multi-level metallic interconnection network is then formed in the devices contacting their active elements and connecting them together to create the desired circuits. The interconnection layers are formed by depositing an insulating layer over the discrete devices, patterning and etching contact openings into this layer, and then depositing conductive material into the openings. A conductive layer is then typically applied over the insulating layer. The conductive layer is then patterned and etched to form interconnections between the device contacts to create a first level of circuitry. Deposition of an insulating layer, formation of contact holes or via holes, formation of conductive material layers, and patterning, etc., are repeatedly carried out to create multi-level circuitry.
Depending upon the complexity of the overall integrated circuit, many levels, e.g., two to four levels, of metal are typically required to form the necessary interconnections and to connect the interconnections to contact pads which allow for the external connections to the completed circuit. A high density of integrated circuits designed to sub-micron dimensions requires extremely precise dimensional control and highly sensitive inspection methods to inspect the pattern of interconnections and/or the contact holes to assure the dimensional and structural integrity of the design patterns. These requirements are becoming more strict as circuits become more dense and miniaturized, such as with the mass-production of semiconductor memory devices such as 64M DRAM or 256M DRAM, which presently can typically require circuitry dimensions of 0.25 to 0.30 &mgr;m.
Inspection of contact holes for conditions such as not-open conditions is becoming increasingly important because the aspect ratio (A/R) of a contact hole, i.e., the ratio of its depth to its diameter, has increased with the increasing demand for high density in semiconductor devices. However, normal optical microscopy using 488 nm wavelength visible light has a technical limitation in inspecting the inner features of contact holes because it does not permit a high enough degree of resolution to inspect inside features of the contact holes, which can be on the order of 200 nm or less in size. Optical microscopy is also not capable of providing beam spot size of 1 &mgr;m or less.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a contact failure inspection method and apparatus for semiconductor devices which provides for precise contact failure inspection for contact images by means of digitized values, not via naked eyes or microscope, which substantially obviates one or more problems due to the limitations and the disadvantages of the related art.
Another object of the present invention is to provide a contact failure inspection method for semiconductor devices and a contact failure inspection system for detecting the presence of contact failures for contacts having high aspect ratio, i.e., the ratio of a contact hole depth to its diameter.
Still another object of the present invention is to provide a contact failure inspection method for semiconductor devices and a contact failure inspection system for detecting contact failures on a wafer surface in a short time so as to be applied in mass production settings.
A further object of the present invention is to provide a method of manufacturing semiconductor devices using a contact failure inspection method and contact failure inspection system.
Another object of the present invention is to provide a contact failure inspection method and system for quickly detecting the location of contact failures to improve the production yield of semiconductor devices.
Another object of the present invention is to provide an inspection method and an inspection system for detecting the presence of pattern failures in semiconductor devices as well as photoresist pattern failures after a development processing during a photolithography process.
To achieve these and other objects, the present invention is directed to a method and apparatus for inspecting at least a portion of a semiconductor wafer. In the invention, scanning electron microscope (SEM) image data for the portion of the semiconductor wafer are read. Within the SEM image data, image data for a feature on the wafer are identified. A parameter related to the feature is computed and compared to a range of acceptable values for the parameter. Based on the comparison between the parameter and the range of acceptable values, the feature can be classified.
In one embodiment, the computed parameter is the dimension or size of the feature. For example, where the feature is a contact hole in an integrated circuit, the parameter may be the diameter of the hole measured in image data pixels. For example, a particular contact hole may be determined to be twenty pixels wide. In another embodiment, the parameter can be an average pixel intensity for pixels that are within the feature. Again, for example, where the feature is a contact hole, the parameter can be the average of the pixel intensities for the pixels that arc associated with the contact hole. Where the measured parameter is within the range of acceptable values for the parameter, the feature can be classified as acceptable. Where the parameter is outside the range of acceptable values for the parameter, the feature can be classified as a failure. For example, where the feature is a contact hole, the hole can be concluded to be a failure because, for example, it is not open.
In one embodiment of the invention, two parameters are calculated for the feature. The two parameters can be, for example, a dimension of a feature such as a contact hole, measured in pixels associated with the feature. The second parameter can be the average of the pixel intensities for the pixels associated with the feature. Both parameters are compared with predetermined ranges of acceptable values for the parameters. In one embodiment, where both parameters are simultaneously within their respective acceptable ranges, the feature, e.g., contact hole, can be classified as being acceptable. For example, a contact hole under these circumstances can be classified as open and properly sized and shaped. The relationship between the parameters and their respective ranges can be used to classify the feature as belonging to one of several types or categories. For example, each of the parameters can be used to classify a feature based on whether the parameter is below, within or above its acceptable range of values.
In one embodiment, the SEM image data are generated from both secondary electrons and higher-energy backscattered electrons in the scanning electron microscope. The data values are digitized and can be in the form of digitized grey scale pixel levels or color coded pixel values.
In one embodiment of the invention, a grid or mesh structure is used to characterize the features being inspected, such as by determining location and/or size of features being inspected. The grid or mesh structure typically includes a pair of mutually orthogonal axes superimposed over the image of the portion of the wafer being analyzed. Alternatively, the mesh axes can form any other appropriate geometric relationship, e.g., triangular, trapezoidal, etc. In one embodiment, the mesh location procedure determines location, shape and/or periodic patterns of the features by analyzing pixel values along a line parallel to one of the orthogonal axes which is successively positioned at pixel locations along the other orthogonal axis. For example, the mesh approach may include positioning a vertical line at multiple horizontal pixel positions and adding the
Choi Sang-bong
Chon Sang-moon
Jun Chung-sam
Kim Jeong-kon
Chawan Sheela
Mills & Onello LLP
Patel Jayanti K.
Samsung Electronics Co,. Ltd.
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