Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
1998-02-03
2001-01-09
Kim, Robert (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237500
Reexamination Certificate
active
06172749
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and an apparatus for optically inspecting a semiconductor wafer for particular contamination.
2. Description of the Related Art
Processes for fabricating high-density integrated circuits (ICs) on Si wafers and GaAs wafers are-becoming more and more sophisticated year after year, and those integrated circuits are also becoming smaller and smaller in size. For these reasons, the contamination of semiconductor wafers with fine particles poses a serious problem. Because interconnections on semiconductor wafers have a width less than 5 &mgr;m, the performance of IC chips is lowered and the yield of IC chips is reduced by contamination caused by fine particles whose size ranges from 0.5 &mgr;m to several &mgr;m, and particularly contamination by fine metal particles. It is therefore necessary to inspect wafers for particular contamination at various stages of semiconductor wafer fabrication. It is of importance to quickly remove wafers from the fabrication process and inspect the removed wafers, and also to inspect wafers according to nondestructive testing.
For example, for detecting a single fine particle having a size of 0.5 &mgr;m on an 8-inch wafer, it is necessary to observe 10
6
spots on the wafer in its entirety because of the size of a detectable observation field that is available. Due to the many observation spots, it is highly time-consuming to inspect the wafer, and inspection processes that can meet the requirements for quick observation are limited.
Prerequisites for analyzing wafers for fine particles thereon include freedom from contamination of the wafers and also freedom from damage to the wafers. It is also important for such a wafer analysis to determine the number, sizes, and types of fine particles that are present on the wafers.
One inspection process that is under consideration at present is to detect Mie scattering by fine particles for thereby detecting the fine particles. It will take more than 10 minutes to scan a wafer in its entirety according to the Mie scattering inspection process.
When a fine particle is detected, it is customary to identify the type of the detected fine particle. General elemental analytic processes for identify the type of a fine particle include an EPMA (Electron Probe Micro Analysis) process and an AES (Auger Electron Spectroscopy) process. Either of these elemental analytic processes requires that the wafer under inspection be placed in vacuum container and each particle be analyzed for its type for a period of about 5 minutes.
According to those elemental analytic processes, it is necessary to irradiate the wafer with an electron beam having an energy level of 10 keV or higher for identifying the type of a fine particle on the wafer, resulting in damage to the wafer. When irradiated with an electron beam, an organic fine particle on the wafer is decomposed into a carbon impurity which will remain on the wafer. Inasmuch as the fabrication of IC chips is carried out in an ultra-high clean room, the particle inspection apparatus itself is liable to cause contamination.
Due to the various above technical limitations, no practical particle inspection apparatus that can be used in the process of fabricating IC chips has been available in the art.
As described above, it takes more than 10 minutes to scan an 8-inch wafer in its entirety according to the Mie scattering inspection process, and it takes more than 5 minutes additionally to identify the type of a detected fine particle. The Mie scattering inspection process and the process for identifying the type of a detected fine particle cannot meet desired requirements for quick observation.
The EPMA and AES processes for identifying the type of fine particles are disadvantageous in that wafers under inspection are damaged by an electron beam for inspection, and the particle inspection apparatus itself tends to contaminate the clean room.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of and an apparatus for detecting a surface condition of a wafer, which can practically be incorporated in a wafer fabrication system.
There has been desired a practical apparatus for detecting a fine particle on a wafer, which apparatus is capable of analyzing a wafer surface at a high speed and with high sensitivity, small in size and inexpensive to manufacture, will not serve as a source of contamination, and will not damage the wafer while analyzing same.
To avoid becoming a source of contamination, the apparatus is required to remove a wafer from a fabrication process, inspect the removed wafer to analyze contaminating fine particles quickly, and return the wafer back to the fabrication or line.
To accomplish the above object, there is provided in accordance with the present invention a method of detecting a surface condition of a wafer, comprising the steps of applying measuring light to a wafer from a reverse side thereof such that the measuring light undergoes total reflection from a surface of the wafer for thereby producing near-field leakage light on the surface of the wafer, and observing scattered light generated by said near-field leakage light to detect a surface condition of the wafer.
A phenomenon developed on the surface of the wafer may be determined based on a pattern of said scattered light.
Phenomena to be determined on the surface of the wafer may include a fine particle on the surface of the wafer, a surface irregularity of the surface of the wafer, and an IC pattern trench. The method may further comprise the step of comparing patterns of scattered light produced by the phenomena to be determined on the surface of the wafer with the pattern of said scattered light generated by the phenomenon thereby to determine the phenomenon developed on the surface of the wafer.
p-polarized light may be applied as said measuring light to produce said near-field leakage light as p-polarized light.
Alternatively, p-polarized light may be applied as said measuring light to produce said near-field leakage light as p-polarized light, s-polarized light may be applied as said measuring light to produce said near-field leakage light as s-polarized light, and the phenomenon developed on the surface of the wafer may be determined from a ratio between an intensity of first scattered light generated from said near-field leakage light as the p-polarized light at one spot on the surface of the wafer and an intensity of second scattered light generated from said near-field leakage light as the s-polarized light at said one spot.
The method may further comprise the step of comparing the intensity of the scattered light generated from said near-field leakage light as the p-polarized light at a spot on the surface of the wafer where a fine particle of metal has been judged as being present, with predetermined data to determine the type of metal of the fine particle at said spot.
According to the present invention, there is also provided an apparatus for detecting a surface condition of a wafer, comprising an X-Y stage for carrying a wafer thereon, a laser beam source for emitting a laser beam having a wavelength for transmission through said wafer, said laser beam source being positioned to apply said laser beam to said wafer from a reverse side thereof such that the laser beam undergoes total reflection from a surface of the wafer for thereby producing near-field leakage light on the surface of the wafer, a screen positioned such that scattered light generated by said near-field leakage light is projected onto said screen, an imaging device for imaging the scattered light projected onto said screen, a memory for storing patterns of scattered light produced by the phenomena and different combinations thereof on the surface of said wafer, and a controller for actuating said X-Y stage to scan said wafer with said laser beam and determining a surface condition of the wafer from a pattern of the scattered light imaged by said imaging device and said patterns of scatt
Advantest Corporation
Kim Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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