JPH0634337A - Fluorescent pattern sensing device - Google Patents

Abstract

PURPOSE:To decrease influence of unnecessary fluorescence generated from the area surrounding a laser beam irradiation point by selecting only the fluores cent component generated from the laser irradiation point, and thereby making practicable to sense the fluorescence over the whole scanning region. CONSTITUTION:A laser beam emitted by a light source 11 is deflected by a rotary polygonal mirror 13 and cast by a scanning lens 9 onto an object to be inspected. As the returned reflected light includes a irradiative laser beam component and a fluorescent component, only the fluorescent component is separated through a wavelength filter 16, and image formation is made by a re-image forming lens 17. The deflection voltage of a scan type photoelectron multiplier tube 24 is comtrolled so that its light sensing position pursues after movement of the fluorescent image on the image plane. Therefore, a lattice sensing signal of a photo-sensor-2 22 is processed for sensing the preseb nt scanning position, and the deflection voltage of the multiplier tube 24 for the scanning position is determined. The obtained voltage is impressed on a deflection coil driver. Thereby only the fluorescence generated from the laser beam irradiation point is sensed at all times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent pattern detecting device used for defect inspection of via holes formed in a polyimide thin film.

A polyimide film is used as an interlayer insulating film between multi-layered wirings formed on a ceramic substrate, and it is necessary to inspect whether a via hole formed in the polyimide film is opened in a predetermined area at a predetermined position. .

[0003]

2. Description of the Related Art FIGS. 4 (A) and 4 (B) are explanatory views of detecting a via hole by fluorescence. In the figure, 1 is a ceramic substrate, 2 is a metal wiring, 3 is a polyimide film, 4 is a via hole, 5 is a laser beam, and 6 is fluorescent light.

Fluorescence is generated when laser light is applied to the polyimide film, but fluorescence is not generated even when laser light is applied to the metal wiring. Therefore, this phenomenon is used to distinguish between the via hole and the polyimide film.

The fluorescent light shown by the dotted line in the figure, which is generated by the reflected light striking the inner wall of the via hole, is unnecessary fluorescent light that becomes noise. This removal of unnecessary fluorescence is one of the objects of the present invention.

A wavelength filter having the characteristics shown in FIG. 4B is used to separate the fluorescent light from the laser light and to extract it. 5 (A) and 5 (B) are explanatory views of an example of a detection signal of a via hole.

The fluorescent component generated by irradiating the object to be inspected with laser light is separated using the above wavelength filter and detected by an optical sensor. By doing so, the signal intensity is increased on the polyimide film due to the generation of fluorescence, but the signal intensity is decreased on the metal wiring because no fluorescence is generated. This signal is binarized with two slice levels 1 and 2, the presence or size of a via hole is inspected at a high slice level 1, and the polyimide film residue is inspected at a low slice level 2. .

FIG. 6 is a diagram showing a circuit for binarizing a fluorescence signal. FIG. 7 is an explanatory diagram of the inspection logic of the via hole. In the figure, first, by using the pattern 1 binarized by the slice level 1, the via hole position data, and the stage position data on which the inspection object is placed, excess via holes and non-penetrations are made in the via hole presence / absence determination circuit. Inspect for the presence of via holes.

Next, the pattern 2 binarized by the slice level 2 is input to the area measuring circuit and the area (number of pixels) is measured. Then, the area (S) of the via hole measured by the area determination circuit is compared with the preset maximum / minimum area (S _max , S _min ) to detect the defect.

FIGS. 8A and 8B are sectional views showing an example of defects in via holes formed in a polyimide film. In the figure, (a) is a normal via hole, and (b) to (g) are defective via holes.

(B) shows a polyimide film remaining on a part of the via hole, (c) shows a polyimide film remaining on the entire surface of the via hole, and (d) shows a via hole diameter. Less than the allowable value, (e) the diameter of the via hole is larger than the allowable value, (f) there is no via hole at the position where it should be, (g) there is a via hole at the position where it should not exist. There is something.

FIG. 3 shows an outline of the detection optical system used in the inspection apparatus for detecting the defect generated in the via hole of the polyimide film. FIG. 3 is a configuration diagram of a fluorescence pattern detection optical system according to a conventional example.

The laser light having a wavelength of ultraviolet to blue emitted from the fluorescence excitation laser light source 11 is expanded by using the beam expander 12. The magnified laser beam is scanned using the rotating polygon mirror 13, and is focused on the inspection target by the scan lens 14.

Here, for distinguishing between the polyimide film and the via hole, the fluorescence (fluorescence wavelength is yellow to red) generated from the polyimide film is used as described above. The fluorescence generated by the irradiation of the laser light is returned through the same path as that of the incident laser light, namely, the scan lens, the rotating polygon mirror, and the beam splitter-115, and is recursively returned to the optical path. The beam splitter-1 guides the retroreflected light to the detection system.

Since the retroreflected light contains a component of the irradiation laser light and a fluorescent component, only the fluorescent component is separated through the wavelength filter 16. The separated fluorescence is (re) formed by the reimaging lens 17.
It is imaged. That is, an image near the laser irradiation point is formed on the image plane.

Therefore, a pinhole is arranged as a spatial filter 18 on the image plane, and only the fluorescence at the central portion, that is, the irradiation point of the laser light is separated and extracted. The fluorescence passing through the pinhole is detected by an optical sensor-1 (for example, photomultiplier tube) 19 for detecting fluorescence and converted into an electric signal (fluorescence detection signal).

As described above, by recursively forming an image of the laser light irradiation point and performing spatial filtering on the image formation surface, only fluorescence generated at the irradiation point is separated and detected, The influence of unnecessary fluorescence around is reduced.

In order to monitor the scanning position of the laser beam, the laser light emitted from the scan lens 9 is received by the optical sensor-222 for detecting the grating through the beam splitter 220 and the grating plate 21.

[0019]

The fluorescence pattern detecting optical system of the above-mentioned via hole inspection apparatus has the following problems.

Generally, the scan lens is (f-θ lens)
Is optimized for the wavelength of the laser source used. That is, when light of the same wavelength as the laser light source is incident,
It is designed to maximize various performances such as aberration.
When the above-mentioned retro-imaging is obtained through such a scanning lens, the wavelength of the fluorescence is significantly different from that of the laser light, so the image at the laser light irradiation point on the re-imaging surface does not converge to one point and is scanned. It will move on the re-imaging plane. Therefore, the fluorescence generated at the center of the scan passes through the pinhole, but the fluorescence generated at both ends of the scan does not pass through, which makes detection difficult.

It is an object of the present invention to provide a fluorescence detection optical system capable of detecting fluorescence in the entire scanning area and reducing the influence of unnecessary fluorescence generated around the laser irradiation point.

[0022]

Means for Solving the Problems To solve the above problems, 1) a device for detecting a fluorescence signal generated when scanning a convergent laser beam applied to an inspection object, wherein a laser beam for fluorescence excitation is used. A means for scanning on the inspection object, a means for condensing the laser light scanned by a scanning lens optimized for the wavelength of the laser light on the inspection object, and a means for scanning the laser light Means for detecting an irradiation position, means for forming an image of retroreflected light from the irradiation point of the scanned laser light, means for extracting a fluorescent component from the retroreflected light,
Fluorescence emitted from a position corresponding to the irradiation point of the laser light by a light receiver that scans corresponding to the irradiation position obtained by the means for detecting the irradiation position of the laser light on the image plane of the retroreflected light. A fluorescence pattern detection device having means for selecting only a component and converting it into an electric signal, or 2) the photodetector is a scanning type photomultiplier tube or a photodiode having a switch type signal readout mechanism, 1). This is achieved by the described fluorescence pattern detection device.

[0023]

The present invention scans the light receiving position of the light receiver (optical sensor) corresponding to the laser scanning position on the inspection object, and always selects only the fluorescence component emitted from the position corresponding to the irradiation point of the laser light. By doing so, the fluorescence signal can be detected over the entire scanning region.

The following is used as an example of the means. (1) A scanning photomultiplier tube (image dissector) is placed instead of the spatial filter and photosensor. At this time, the diameter of the pinhole inside the image dissector is made substantially equal to the diameter of the laser light irradiation point on the re-imaging surface. Also,
The scan length is set to be substantially equal to or longer than the moving distance of the laser light irradiation point (fluorescent image) on the re-imaging surface. (2) A photodiode array is placed instead of the spatial filter and optical sensor. At this time, the pixel size of the photodiode array is set to be substantially equal to or smaller than the diameter of the laser light irradiation point on the re-imaging surface. The length of the array is the laser light irradiation point (fluorescent image) on the re-imaging surface.
Should be approximately equal to or greater than the travel distance of.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are block diagrams of a first embodiment of the present invention. In FIG. 1 (A), the operating principle is exactly the same as that of the conventional example except that the scanning type photomultiplier tube 14 replaces the spatial filter and the photosensor of the conventional example.

It is necessary to control the deflection voltage of the scanning photomultiplier so that the light detection position of the scanning photomultiplier follows the movement of the fluorescent image on the re-imaging plane. For this purpose, the grating detection signal is first processed to detect the current scanning position, and the deflection voltage of the scanning photomultiplier for that scanning position is obtained. The waveform of this deflection voltage is generally a sawtooth wave as shown. The position is converted into a sawtooth wave voltage, and this voltage is applied to the deflection coil driver of the scanning photomultiplier tube. This makes it possible to always detect only the fluorescence generated from the laser light irradiation point.

FIG. 1B is an explanatory view of the scanning photomultiplier tube. A scanning photomultiplier tube is a type of photomultiplier tube that has extremely high photosensitivity and is optimal for detecting minute fluorescence. In the figure, 14A is the photocathode, 14B is the deflection coil, and 1
4C is a pinhole.

FIGS. 2A and 2B are block diagrams of the second embodiment of the present invention. The operating principle of this example is exactly the same as that of the first embodiment, except that the scanning photomultiplier tube of the first embodiment is replaced with a photodiode array having a switch type data reading mechanism. In the second embodiment, it is necessary to select the cell of the diode array to be read so that the light detection position of the photodiode array follows the movement of the fluorescent image on the re-imaging plane. For this purpose, the grid detection signal is first processed to detect the current scanning position, and the timing of the read clock is controlled accordingly. This makes it possible to always detect only the fluorescence generated from the laser light irradiation point.

FIG. 2B is an explanatory diagram of the switch type photodiode array. In the switch type photodiode array, individual photodiode cells are arranged, and the light receiving signal of the array is output via a switch that is opened / closed by a read clock connected to each individual cell.

The following replacements can be made in the first and second embodiments. (1) The wavelength filter may be placed between the beam splitter-1 and the reimaging lens, or between the reimaging lens and the photosensor (scanning photomultiplier tube / switch photodiode array). You may. (2) A vibrating mirror (galvanic mirror) may be used instead of the rotating mirror. (3) The scanning position detection means is a combination of a grating plate and an optical sensor, a rotating mirror and a rotation detector (encoder, etc.).
May be used.

[0031]

According to the present invention, it is possible to obtain a fluorescence detection optical system capable of detecting fluorescence in the entire scanning area and reducing the influence of unnecessary fluorescence generated around the laser irradiation point. It was possible to contribute to the performance improvement of the device.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of Embodiment 1 of the present invention.

FIG. 3 is a block diagram of a conventional example

FIG. 4 is an explanatory diagram of via hole detection by fluorescence.

FIG. 5 is an explanatory diagram of an example of a detection signal of a via hole.

FIG. 6 is a diagram showing a circuit for binarizing a fluorescence signal.

FIG. 7 is an explanatory view of a via hole inspection logic according to a conventional example.

FIG. 8 is a cross-sectional view showing a defect example of a via hole formed in a polyimide film.

[Explanation of symbols]

 1 Ceramic Substrate 2 Metal Wiring 3 Polyimide Film 4 Via Hole 5 Laser Light 6 Fluorescence 9 Scan Lens 11 Fluorescence Excitation Laser Light Source 12 Beam Expander 13 Rotating Polygonal Mirror 14 Mirror 15 Beam Splitter-1 16 Wavelength Filter 17 Reimaging Lens 18 Spatial filter (pinhole) 19 Optical sensor-1 20 Beam splitter-2 21 Lattice plate 22 Optical sensor-2 24 Scanning photomultiplier tube (image dissector) 25 Switch type photodiode array

Claims (2)

[Claims] 1. A device for detecting a fluorescence signal generated when scanning a convergent laser beam applied to an inspection object, comprising means for scanning the inspection object with a laser beam for fluorescence excitation, and the laser. A means for condensing the laser light scanned by the scanning lens optimized for the wavelength of light on the inspection object, a means for detecting the irradiation position of the scanned laser light, and a means for scanning the laser light. Means for forming an image of the retroreflected light from the irradiation point of the laser light, means for extracting a fluorescent component from the retroreflected light, and detecting the irradiation position of the laser light on the image formation surface of the retroreflected light Fluorescent light having means for selecting only a fluorescent component emitted from a position corresponding to the irradiation point of the laser light by a light receiver for scanning corresponding to the irradiation position obtained by the means, and converting the fluorescent component into an electric signal. Pattern detector. 2. The fluorescence pattern detection device, wherein the photodetector is a scanning photomultiplier tube or a photodiode having a switch type signal reading mechanism.