Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2000-02-22
2003-01-28
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237200, C250S559370
Reexamination Certificate
active
06512578
ABSTRACT:
TECHNICAL FIELD
The present invention relates to technology for performing inspection of surfaces of substrates used in the manufacture of liquid crystal devices or semiconductor wafers used in the manufacture of ICs, and in particular relates to an apparatus and method for performing so-called macro inspections in which the entire surface of the object is examined.
BACKGROUND ART
The macro inspection of the surfaces of the substrates used in the manufacture of liquid crystal devices and the semiconductor wafers used in the manufacture of ICs (hereinafter these items may also be described as the ‘object’) refers to a visual inspection of the entire surface of the object. This inspection is performed to detect scratches or marks on the surface of the substrate or wafer, irregularities in the resist coating, or defects arising during the photolithography process. In conventional macro inspections, a spot light type white diffuse light source illuminates the object being rotated, and visual judgement by an examiner is performed to inspect the above-mentioned defects.
However, visual judgment by an examiner results in a variation in the level of inspection due to factors such as the difference in technical skill level between individual examiners and the physical condition of the examiner. This results in problems such as inefficiency and unstable inspection results. Furthermore, in the manufacture of substrates for liquid crystal devices and of wafers for ICs, because any surface contamination must be avoided, inspection processes performed by humans, which are one of the major causes of dust contamination, need to be avoided as much as possible.
As a result of the above-described situation, automated macro inspection processes have been proposed, such as the apparatus presented in Japanese Patent Application, Second Publication No. Hei 6-8789. In this apparatus, the surface of a wafer is illuminated with light and the reflected light therefrom is received via an ITV camera, and a surface defect inspection on the object is performed by comparing the reflected light image with a pre-recorded reflected light image of an object without defects. Because the field of view of the camera is smaller than the object, the object can be moved for inspection of the whole of the whole of the object. Furthermore, in this apparatus, in order to enable inspection under various illumination angles with respect to the object surface, the ITV camera is held in a stationary position and the angle of the object is varied.
However with the above type of surface inspection apparatus, a mechanism for setting the illumination angle is required, and when the mechanism is activated, dust may be generated by the moving parts of the mechanism, leading to the possibility of unwanted contamination of the surface of the object. The apparatus proposed in the aforementioned Japanese Patent Application performs macro inspections by using the light directly reflected off the surface of the object, and the camera is located so that the incident angle of the irradiated light on the surface of the object is equal to the reflection angle of the reflected light.
However, recently, the use of diffracted light or scattered light generated in accordance with the repeating pattern on the surface of the object has been investigated for use in surface inspection. In such a case, because the reception angle of the light from the object will vary due to factors such as the pattern pitch of the object, it is necessary to adjust the illumination angle of the illumination apparatus and the light reception angle of the image pick-up camera. Consequently, this case also requires a mechanism for adjusting the angles of illumination and reception, which generates dust and leads to the problem of unwanted contamination of the surface of the object.
In another case, Japanese Patent Application, First Publication No. Hei 8-75661 proposes an automatic inspection apparatus which is configured so that light from a light source is irradiated on to the object such as a wafer, and detection is performed by a single light reception optical system. With such an inspection apparatus, in the case where diffracted light from the object is to be detected, the diffraction angle will vary depending on the pattern pitch. Therefore, with wafers such as memory elements in which the elements are formed in a uniform pitch across the entire surface of the wafer, the inspection can be performed with a single measurement. However, in the case of CPU or ASIC (Application Specified IC) wafers where a variety of different types of elements are grouped together in different regions, the pattern pitch will differ for each of the regions, and therefore portions of the surface cannot be examined because no diffracted light is generated. Moreover, when an inspection is attempted on an object in which the pattern has been resist coated, the amount of diffracted light will vary considerably because the interference caused by the resist film will be heavily influenced by irregularities in the thickness of the film. Therefore, even thickness irregularities which have almost no effect on the process will be sufficient to cause the detection of a defect. Cases where the thickness of the resist is asymmetrical are particularly problematic, because the diffracted light image is very likely to develop irregularities and it is almost impossible to obtain a reliable inspection.
DISCLOSURE OF THE INVENTION
It is an object of the first embodiment of the present invention to provide a surface inspection apparatus which is able to efficiently carry out macro inspections on a variety of objects without requiring the variable adjustment of the illumination angle, the surface angle of the object, or the light reception angle for the light reception apparatus or image projection apparatus, that is, by maintaining the illumination apparatus and the image projection apparatus in fixed positions.
In order to achieve the above object, a first surface inspection apparatus according to the present invention (also referred to as a macro inspection apparatus) is characterized by comprising an illumination apparatus which is fixed in a position facing the object at a first predetermined angle with respect to the object and which irradiates an illuminating light beam which is a substantially parallel light beam, on to the inspection region of the object; an image projection apparatus which is fixed in a position facing the object at a second predetermined angle with respect to the object and which receives the diffracted light or scattered light generated from the illumination of the object by the aforementioned illuminating light beam and creates an image for the object; an image processing apparatus which is connected to the image projection apparatus and which takes the image signal obtained by the image projection apparatus and performs an inspection of the aforementioned inspection region by carrying out certain image processing; and a wavelength alteration member which is positioned within the optical path of the aforementioned illuminating light beam for altering the wavelength of the illuminating light. The operation of the apparatus may also be automated.
With a surface inspection apparatus of this construction, the wavelength of the illuminating light beam can be varied using the wavelength alteration member. Therefore, highly efficient macro inspection can be achieved by setting the wavelength so that the direction of the diffracted light or scattered light generated from the inspection region of the object coincides with the light reception direction of the image projection apparatus. Thus with this macro inspection apparatus, the illumination apparatus and the image projection apparatus can be fixed, making the provision of conventional moving mechanisms for altering the orientation of the illumination and image projection apparatus unnecessary, and hence reducing the generation of unnecessary dust and suppressing contamination of the object.
The illumination apparatus preferably h
Kitamura Toshiaki
Komatsu Koichiro
Omori Takeo
Nguyen Sang H.
Nikon Corporation
Oliff & Berridg,e PLC
Pham Hoa Q.
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