Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2001-10-25
2003-05-06
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S765010
Reexamination Certificate
active
06559663
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for producing a substrate having a micro circuit pattern for a semiconductor device, a liquid crystal, or the like, and particularly relates to a technique for inspecting a pattern for a semiconductor device or a photomask, that is, the present invention relates to a technique for inspecting a pattern on a wafer in a way of semiconductor device producing process and a technique for performing comparison and inspection by using an electron beam.
Inspection of a semiconductor wafer will be described as an example.
A semiconductor device is produced by repeating a process of transferring, by lithographing and etching, a pattern formed in a photomask onto a semiconductor wafer. In a semiconductor device producing process, the state of lithographing, etching, or the like, generation of particles, and so on, exert a large influence on the yield of the semiconductor device. Accordingly, in order to detect occurrence of abnormality or failure in an early stage or preparatorily, conventionally, a method of inspecting a pattern on a semiconductor wafer is carried out in a way of producing process.
As for a method of inspecting a defect existing in a pattern on a semiconductor wafer, a defect inspecting apparatus in which white light is irradiated onto a semiconductor wafer so that circuit patterns of the same kind in a plurality of LSIs are compared with each other by using an optical image, has been put into practice. The outline of the inspecting method has been described in “Monthly Semiconductor World”, August issue, pp. 96-99, 1995. Further, as a inspecting method using an optical image, a method in which an optically illuminated region on a substrate is formed as an image by means of a time-delay integrating sensor so that the characteristic of the image is compared with designed characteristic inputted in advance to thereby detect a defect, has been disclosed in JP-A-3-167456 or a method in which the deterioration of an image at the time of acquisition of the image is monitored so that the deterioration of the image is corrected at the time of detection of the image to thereby perform comparison and inspection in a stabler optical image, has been disclosed in JP-B-6-58220. If a semiconductor wafer in a way of producing process was inspected by such an optical inspection method, the pattern residue or defect having a light-transmissible silicon oxide film or a photoresist material on its surface could not be detected. Further, an etching remainder or a incomplete-open failure in a micro conduct hole smaller than the resolution of an optical system could not be detected. Further, a defect generated in a wiring-pattern stepped bottom portion could not be detected.
As described above, with the advance of reduction in size of the circuit pattern and complication in shape of the circuit pattern and with the advance of diversification of the material, it has become difficult to detect a defect by using an optical image. Therefore, a method for comparing and inspecting a circuit pattern by using an electron beam image having higher resolution than that of the optical image has been proposed. When a circuit pattern is compared and inspected by means of an electron beam image, in order to obtain a practical inspection time, the image needs to be acquired at a very high speed in comparison with observation by using a scanning electron microscopy (hereinafter abbreviated to SEM). Further, it is necessary to secure resolution and an SN ratio in the image acquired at a high speed.
As a pattern comparison and inspection apparatus using an electron beam, a method in which an electron beam with an electron-beam current not smaller than 100 times (10 nA) as large as the current in the general SEM is irradiated onto an electrically conductive substrate (such as an X-ray mask, or the like) to detect any electrons among secondary electrons, reflected electrons and transmitted electrons generated therefrom and compare/inspect an image formed from a signal of the electrons to thereby automatically detect a defect is disclosed in J. Vac. Sci. Tech. B, Vol. 9, No. 6, pp. 3005-3009 (1991), J. Vac. Sci. Tech. B, Vol. 10, No. 6, pp. 2804-2808 (1992), JP-A-5-258703 and U.S. Pat. No. 5,502,306.
Further, as a method for inspecting or observing a circuit substrate having an insulating material by means of an electron beam, a method in which a stabler image is acquired by irradiation of a low-accelerated electron beam not higher than 2 keV in order to reduce the influence of charge has been disclosed in JP-A-59-155941 and “Electron and Ion Beams Handbook” (THE NIKKAN KOGYO SHINBUN, Ltd.), pp. 622-623. Further, a method in which ions are irradiated from the back of a semiconductor substrate has been disclosed in JP-A-2-15546 and a method in which light is irradiated onto a surface of a semiconductor substrate to thereby cancel charge of an insulating material is disclosed in JP-A-6-338280.
Further, in a large-current and low-accelerated electron beam, it is difficult to acquire a high-resolution image because of a space-charge effect. As a measure to solve this problem, a method in which a high-accelerated electron beam is retarded just before a sample so that a substantially low-accelerated electron beam is irradiated onto the sample is disclosed in JP-A-5-258703.
As a method for acquiring an electron-beam image at a high speed, a method in which an image is acquired by continuously irradiating an electron beam onto a semiconductor wafer on a sample stage while continuously moving the sample stage is disclosed in JP-A-59-160948 and JP-A-
5-258703.
Further, a structure constituted by a scintillator (Al-vapor deposited fluorescent material), a light guide and a photo-multiplier is used as a secondary electron detecting apparatus used conventionally in the SEM. A detecting apparatus of this type is, however, poor in frequency responsibility because light emission from the fluorescent material is detected, so that the detecting apparatus of this type is unsuitable for formation of an electron beam image at a high speed. As a detecting apparatus for detecting a high-frequency secondary electron signal to solve this problem, a detection means using a semiconductor detector is disclosed in JP-A-5-258703.
When a circuit pattern in a process for producing a micro-structure semiconductor device was detected by using the aforementioned prior art optical inspection method, it was possible to detect the residue of a silicon oxide film, a resist material, or the like, which was formed from an optically transmissible material and which was sufficiently short in the optical distance depending on the optical wavelength and refractive index used for inspection, and it was difficult to detect an etching remainder or a incomplete-open failure in a micro conduct hole which was linear so that the width of a short side thereof was not larger than the resolution of an optical system.
On the other hand, in the observation and inspection using the SEM, there are two problems as follows. One problem is that a very long time is required for inspecting a circuit pattern on the whole surface of a semiconductor wafer because the conventional method, by means of the SEM, for forming an electron-beam image needs a very long time. Accordingly, in order to obtain practical throughput in a semiconductor device producing process, or the like, it was necessary to acquire an electron-beam image at a very high speed. It was further necessary to secure the SN ratio of the electron-beam image acquired at a high speed and to keep accuracy in a predetermined value.
The other problem was that it was difficult to obtain a stable contrast image in inspection by means of an electron beam and to obtain a predetermined value of inspection accuracy in the case where the material constituting a circuit pattern as a subject to be inspected was formed from an electrically insulating material such as a resist, a silicon oxide film, or the like, or in the case where the material was
Ando Kimiaki
Hiroi Takashi
Ino Tadao
Kaneko Yutaka
Kubota Hitoshi
Hitachi , Ltd.
Karlsen Ernest
Mattingly Stanger & Malur, P.C.
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