JPS6215442A - Pattern inspecting method and its device - Google Patents

Abstract

PURPOSE:To simultaneously inspect the upper width and the lower width of a trapezoidal section of a conductor by using a lighting spot having a dark field in a bright field. CONSTITUTION:A printed circuit board 3 has a conductor pattern 31 on an optical diffusion substrate 32. A lighting part 2 consists of a light source 21, a lens 22 and a mask 24, and an area to be inspected is illuminated by a lighting spot 27 having a dark field 26 in a bright field 25. A photodetecting part is provided with the first photodetector 51 for detecting a width of the conductor 31 in the bright field, and the second photodetector 52 for detecting a width of the conductor 31 in the dark field. The first photodetector 51 executes a measurement of a conductor pattern upper width 33, and the second photodetector 52 executes a measurement of a conductor pattern lower width 34.

Description

[Detailed Description of the Invention] [Summary] The conductor pattern formed on the substrate has a trapezoidal cross section, and if the -L width or lower width of the trapezoid deviates significantly from the predetermined dimension, , there is a high possibility that it will lead to disconnection or short circuit of the conductor pattern. In conventional pattern inspection, pass/fail was determined by detecting either one width or the top width of the trapezoid, but now the bottom and top widths of the trapezoid are simultaneously detected to determine pass/fail, improving defect detection accuracy. It has been improved.

[Industrial application field]

The present invention relates to a method for inspecting a printed wiring board, and more particularly to a method for inspecting a conductive pattern formed on an electrically insulating substrate.

In printed wiring boards, conductor patterns made of copper (Cu) or the like are selectively formed on electrically insulating substrates such as polyimide, epoxy resin, ceramic, etc., but these conductor patterns are becoming finer and more sophisticated. There is an area where design margins are reduced as density increases. Therefore, if a part of the conductor pattern has defects, bulges, or unnecessary conductor residue, it will not be possible to secure the desired circuit characteristics, resulting in a decrease in reliability. Therefore, the entire conductor pattern must be carefully inspected. It is necessary to detect defects in advance.

Although various pattern inspection methods have been developed so far, they are insufficient to be applied to the inspection of the finer, higher-density patterns mentioned above. It is hoped that this will be realized.

[Conventional technology]

3 and 4 are perspective views showing a conventional pattern inspection method.

Conventional pattern inspection methods include detecting defects with the naked eye through a magnifying glass, and automatically detecting defects by shining a lighting spot on the area to be inspected and detecting the reflected light. There are methods etc. However, the method of detecting defects with the naked eye is not suitable for inspecting finer, higher-density patterns because there is a degree of visibility in the size of defects that can be detected. A method is used to automatically detect defects by illuminating the area with a lighting spot. Among the methods for automatically detecting defects by irradiating a lighting spot onto the inspection area, the most commonly used method is the method using the difference in reflectance between the conductor pattern and the substrate, as shown in Figure 3. This is a method that utilizes the light diffusivity of the substrate (not shown in Figure t).

In FIG. 3, an illumination spot 13 emitted from an illumination unit 1 comprising a light source 11 and a lens 12 illuminates an area to be inspected on a printed wiring board 3, and the reflected light is transmitted to a photodetector 41.
The light is detected by the light detection section 4 equipped with a lens 42 and a lens 42.

That is, since the conductor 31 has a trapezoidal cross section and has a higher reflectance than the moon substrate 32, out of the light that is reflected in the area to be inspected and enters the photodetector 4, the light that is reflected on the upper surface of the conductor is not included. It is stronger than the light reflected from the trapezoidal slope of the conductor or the substrate. Therefore, for example, by using an element like a line sensor as the photodetector 41 that can detect the intensity of light and its section, the upper width of the conductor pattern 3
3. At the same time, it is possible to detect defects such as defects and bulges that appear on the upper part.

In addition, in FIG. 4, the illumination section 2 includes a light source 21, a lens 22,
and a mask 24 having a linear light shielding part 23, and a linear night vision! An illumination spot 27 having F26 illuminates the area of the printed wiring board 3 to be inspected. In the dark field 26, the part of the conductor 3 becomes completely dark, whereas the part of the substrate 32 becomes bright due to the light diffused into the board from the bright field 25, and the part of the board with this light diffusion is detected by a photodetector 41 The light is detected by the light detection section 4 equipped with a lens 42.

For example, as a photodetector 4, an element like a line sensor that can detect the intensity of light and its area is used.
By detecting the dark section sandwiched between the areas brightened by the diffused light, the bottom width 34 of the conductor pattern can be measured and defects such as defects, bulges, and unnecessary conductor residue appearing at the bottom can be detected. can do.

[Problem that the invention seeks to solve]

However, the method that utilizes the difference in reflectance between the conductor pattern and the substrate cannot measure the lower width 34 of the conductor pattern, and therefore cannot detect a short circuit between adjacent conductor patterns due to unnecessary conductor residue, for example. Furthermore, the method using the light diffusivity of the substrate cannot measure the upper width 33 of the conductor pattern, so there is a problem that, for example, even if the upper part of the conductor pattern is damaged and is about to break, it cannot be detected.

[Failure to solve the problem]

FIG. 1 is a perspective view showing an embodiment of a pattern inspection apparatus according to the present invention, and the same objects are represented by the same symbols throughout the figures.

The above problem is caused by the illumination unit 2 which illuminates the inspection area with an illumination spot 27 having a dark field 26 in the bright field 25 as shown in FIG.
A pattern inspection device including a photodetector 51 and a second photodetector 52 that detects a substrate portion with light diffusion in the darkfield 26 is used to detect a linear darkfield 2 in the brightfield 25.
6 is irradiated onto the inspection area, the width of the conductor 31 detected in the bright field 25 is taken as the lower width 33 of the trapezoidal cross section, and the width of the conductor 31 detected in the dark field 26 is
This problem is solved by the pattern inspection method of the present invention, in which the width of the trapezoidal 1tli surface is set as the lower width 34, and the 1width 33 and the F width 34 of the trapezoidal cross section are simultaneously detected.

[Effect]

By inspecting the upper width 33 and lower width 34 of the trapezoidal cross section of the conductor on the same day using the pattern inspection device shown in FIG. Defects such as chips 11, bulges, unnecessary conductor residues, etc. appearing at the bottom can be detected, and defect detection can be performed in a single direction, such as determining pass/fail.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to FIG. Note that FIG. 2 is a block diagram showing the positional deviation correction means.

In FIG. 1, a printed wiring board 3 in which a conductive pattern 3I is selectively formed on a light-diffusing substrate 32 is mounted on a stage 6 that moves at a constant speed in the direction of the arrow shown. Further, the illumination section 2 is composed of a light source 21, a lens 22, and a mask 24 having a linear light shielding section 23, and a linear dark field 26 is formed in a bright field 25 emitted from the illumination section 2. The illumination spot 27 with which the printed wiring board 3
The area to be inspected is irradiated. -The light detection unit 5 has clear vision!
! The first photodetector 51 detects the width of the conductor 31 at F25 and the dark? 11! A second photodetector 52 detects the width of the conductor 31 in the field 26, the light in the bright field 25 is sent to the first photodetector 51, and the light in the dark field 26 is sent to the second photodetector 51.
half mirror for separate input to the photodetector 52 of
53 and a lens 54.

Although FIG. 2 shows that the light reflected by the half mirror 53 is input to the first photodetector 51 and the light transmitted through the half mirror 53 is input to the second photodetector 52, the opposite is true. It is also possible to configure such that the light transmitted through the half mirror 53 is input to the first photodetector 51 and the light reflected by the half mirror 53 is input to the second photodetector 52.

The photodetectors 51 and 52 may be, for example, charge-coupling devices.
A line sensor such as s CCD) is used.

As described above, among the light reflected in the bright field 25 and incident on the photodetector 51, the light reflected on the upper surface of the conductor is stronger than the light reflected on the trapezoidal slope portion of the other conductor or the substrate portion. Therefore, by using the first photodetector 51 to detect the section where strong reflected light is obtained, the conductor pattern
1: Measure width 33.

On the other hand, in the linear dark field 26, the portion of the conductor 31 becomes completely dark, whereas the portion of the substrate 32 becomes bright due to the light diffused into the substrate from the bright field 27. The lower width 3 of the conductor pattern is detected by using the second photodetector 52 to detect the dark area sandwiched between the substrate parts with such light diffusion.
Measure the length of step 4. That is, the pattern inspection device according to the present invention inspects the upper width 33 and lower width 3 of a conductor pattern having a trapezoidal cross section.
It is possible to perform four length measurements at the same time.

In this way, by simultaneously inspecting the -L width 33 and the bottom width 34 of the conductor pattern, not only defects such as chips and bulges that appear on the second part of the conductor, but also defects and bulges that appear on the top part of the conductor can be detected. It is possible to improve defect detection accuracy by detecting defects such as unnecessary conductor residue and determining pass/fail.

However, the upper width 33 of the conductor pattern detected by the first photodetector 51 is the upper width of the conductor pattern in the bright field 25, and the lower width 33 of the exclusive pattern detected by the second photodetector 52.
4 is the upper width of the conductor pattern in the dark field 26.

It is not possible to immediately determine the quality of the conductor pattern from the lower width and upper width detected at the W position. Therefore, the pattern inspection apparatus according to the present invention is equipped with a positional deviation correcting means shown in FIG.

After the signals detected by the first photodetector 51 and the second photodetector 52 are respectively binarized, the signal becomes WFr 55.5 times.
At step 6, it is converted into a width or bottom width dimension value and inputted to a comparison circuit 57. The comparison circuit 57 compares the input upper width and the preset upper width 1m limit/lower 19II], the input lower width and the preset lower width 111/lower limit, and the input The difference between the upper and lower widths is compared with the preset upper and lower limits of the difference between the upper and lower widths.

The printed wiring board 3 is mounted on a stage 6, and the area to be inspected moves at a constant speed. Therefore, a means for correcting the positional deviation, that is, a delay circuit 58, is inserted into the circuit on the side that outputs the detected signal first, and compared with the side that outputs the detected signal later! /357 is made to match in time. Note that whether the circuit 58 is inserted into the first photodetector 51 or the second photodetector 520 depends on the movement of the stage 6 and the h direction, and the delay circuit 5H
This can be handled by switching the J-selection switch 59 inserted before and after the .

[Effects of the Invention] As described above, the present invention can provide a pattern inspection method that is suitable for inspecting finer, higher-density patterns and further improves defect detection accuracy.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a pattern inspection device according to the present invention, FIG. 2 is a block diagram showing a positional deviation correction means, and FIGS. 3 and 4 are perspective views showing a conventional pattern inspection method. In the figures, Fig. 3 shows a method that uses the difference in reflectance between the conductor pattern and the substrate, and Fig. 4 shows a method that uses the light diffusivity of the substrate. In the figure, 2 is a bright part, 3 is a printed wiring board, 5 is a light detection part, 6 is a stage, 21 is a light source,
22 is a lens, 23 is a light shielding part, 24 is a mask, 25 is a bright field, 26 is a dark field, 27 is an illumination spot, 31 is a conductive pattern, 32 is a substrate,
33 is the conductor 1 width, 34 is the lower width of the conductor,
51.52 is a photodetector, 53 is a half mirror 154
is the lens, 55.56 is the length measurement circuit, 57 is the comparison lI former Raku, 58
59 represents a delay circuit, and 59 represents a selector 17 (switch).

Claims (1)

[Claims] 1) When inspecting defects in a conductive pattern, etc. formed on a substrate having light diffusing properties, an illumination spot (27) having a linear dark field (26) in a bright field (25) is used. ) to the area to be inspected, the width of the conductor (31) detected in the bright field (25) is taken as the upper width (33) of the trapezoidal cross section, and the conductor (31) detected in the dark field (26) is set as the lower width (34) of the trapezoidal cross-section, and the upper width (33) and lower width (34) of the trapezoidal cross-section are simultaneously detected. 2) Illumination that illuminates the inspection area with an illumination spot (27) having a dark field (26) in a bright field (25) when inspecting defects such as a conductor pattern formed on a substrate with light diffusing properties. (2), a first photodetector (51) that detects reflected light in the bright field (25), and a second photodetector (51) that detects a substrate portion with light diffusion in the dark field (26). A pattern inspection device comprising: a photodetector (52). 3) The position of the conductor width detected by the first photodetector (51) and the position of the conductor width detected by the second photodetector (52),
The pattern inspection apparatus according to claim 2, further comprising means for correcting positional deviation.