Optics: measuring and testing – Shape or surface configuration – By focus detection
Reexamination Certificate
2002-05-16
2003-06-17
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
By focus detection
C359S368000, C359S385000, C359S388000
Reexamination Certificate
active
06580518
ABSTRACT:
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-275085, filed Sep. 11, 2000, No. 2000-275089, filed Sep. 11, 2000; and No. 2000-275090, filed Sep. 11, 2000, the entire contents of all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a confocal microscope using a confocal disk to obtain a sectioning image and a height measurement method using the confocal microscope.
2. Description of the Related Art
In recent years, with high integration of LSI, the number of electrodes of an LSI chip has increased, a packaging density has also increased, and a bump electrode has been used as the electrode of the LSI chip from such background.
A so-called flip chip connection is performed in which the LSI chip with such bump formed therein is laid upside down in contact with a substrate, and a bump is connected to an electrode on the substrate.
In this case, it is naturally important to accurately connect the electrode on the substrate to the bump, and it is therefore necessary to accurately form the shape and height of the bump.
As a solution, an optical height measurement apparatus in which the bump is used as a measurement object to optically measure the height of the bump has been proposed (see Jpn. Pat. Appln. KOKAI Publication Nos. 9-113253, and 9-126739). A laser scanning system or a disk system (Nipkow disk) is known as a confocal optical system of the optical height measurement apparatus, and either system has a function of converting the distribution of a height direction (light axis direction, that is, Z-axis direction) to a detected light intensity.
By this confocal optical system, a plurality of slice images are obtained for each movement position of the Z-axis direction of a sample, an IZ peak position is estimated from the maximum luminance of respective pixels of these slice images, and height information of the sample is obtained.
Additionally, when the focal point position of the Z-axis direction of the sample is moved in order to obtain the plurality of slice images, it is general to move a sample stage or an objective lens with the sample laid thereon in the Z-axis direction.
According to a sample stage movement system for moving the sample stage in the Z-axis direction, for example, when the bump height of the LSI chip formed as the sample on a large-sized 8-inches wafer is measured, the sample stage for vertically moving the 8-inch wafer with a high precision is required, and a very large-scale mechanism results. Therefore, a conventional apparatus becomes very expensive. Additionally, since the conventional apparatus also has a large mass, it is difficult to control vertical movement in a high speed, movement precision of a focal point is deteriorated, and movement also takes time. In an objective lens movement system in which the objective lens is moved in the Z-axis direction, to realize high-speed inspection in measuring the bump height of the LSI chip, the objective lens having a low magnification is used to obtain a optical system having a broad field of view, for example, having an optical system total magnification of about one time. Since this low-magnification objective lens has a large size and mass, it is difficult to control the vertical movement in the high speed. Even in this case, the movement precision of the focal point is deteriorated, and additionally the movement takes much time.
To realize the high speed of inspection, it is effective to use the low-magnification objective lens with which a large area can be observed at once and to raise a scanning speed of a two-dimensional direction. In general, a sectioning effect is valid with a larger NA of the objective lens, but the objective lens having a large NA usually has a high magnification and narrow field of view. That is, the high speed of the inspection is contradictory to the sectioning effect of a light axis direction. Therefore, in general, a high-speed inspection is performed by a low-magnification objective lens. Thereafter, when some defective portions are to be enlarged and observed, the objective lens is changed and adapted to indicate a high magnification. With the change, it is necessary to replace a rotary disk with another rotary disk in which a pinhole with a diameter corresponding to the magnification of the objective lens is formed.
However, the mechanism in which the objective lens and rotary disk are replaced in order to change the magnification has a remarkably large scale, and has a large-sized and complicated constitution. When the objective lens and rotary disk are replaced, the speed cannot be raised because of the size of the mechanism, and much changeover time is required.
On the other hand, to realize the high-speed inspection, it is proposed to use a special objective lens having large NA and low magnification, in which a broad view of field is secured at a certain degree of low magnification, and a high contrast can be realized by the sectioning effect. However, the objective lens is effective in measuring the height at a high speed, but a pixel resolution in a plane direction crossing at right angles to a light axis is not high. Therefore, in order to perform the enlargement/inspection of the defective portion, it is still necessary to replace the objective lens with the objective lens having a high magnification. Therefore, a plurality of special and expensive objective lenses having different magnifications are required, and this is economically disadvantageous.
There is also proposed a method of disposing variable magnification optical systems before and after the rotary disk, and replacing the objective lens simultaneously with varying of the magnification, so that it is unnecessary to replace the rotary disk and it is possible to prevent the sectioning effect from being deteriorated (see Jpn. Pat. Appln. KOKAI Publication No. 9-230245). Although this method is very effective, when the usual objective lens is used to perform observation with various magnifications, but it is necessary to replace the objective lens in accordance with the magnification depending on an object to be observed. Therefore, the replacement mechanism of the objective lens is large-sized, requires much time for replacement, and becomes expensive.
There is disclosed a technique of using I-Z characteristics (characteristics that a light intensity I is largest with a sample in a focal point position and the light intensity I decreases farther from the focal point position), disposing a rotary plate having a plurality of parallel plane glass plates mounted in the rear of the objective lens, and rotating this rotary plate at a high speed to move the focal point position and a relative position of the sample in Z-direction at a high speed (see Jpn. Pat. Appln. KOKAI Publication No. 9-126739). In this technique, the focal point position is discretely moved in accordance with the thickness of the parallel plane glass plate so that a slice image is obtained. In this case, the number of slice images is the same as that of parallel plane plates. A measurement range along Z direction is determined by the thickness of the thickest and thinnest parallel plane plates, and a sampling interval of the Z direction can be set to be fine with a larger number of parallel plane plates. In this manner, from the I-Z characteristics determined by a plurality of discrete slice images and the NA of the objective lens of the confocal optical system, an interpolation processing is performed in the Z direction, the focal point position of each pixel is estimated, and the speed of the height measurement of the sample can be raised.
The use of the confocal optical system is effective, when the bump becomes large to a certain degree. However, with a smaller bump, a problem occurs that much measurement time is required. That is, with an advance in miniaturization of the bump, for the CCD for use as a photodetector, it is naturally necessary to reduce a pixel size for image p
Eda Yukio
Hisata Nahoko
Kamihara Yasuhiro
Morita Terumasa
Font Frank G.
Frishauf Holtz Goodman & Chick P.C.
Nguyen Sang H.
Olympus Optical Co,. Ltd.
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