JPS63126242A - Appearance inspection and device therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a visual inspection technique, and particularly to a technique that is effective when applied to visual inspection of a semiconductor wafer in a wafer processing step in the manufacture of semiconductor devices.

[Conventional technology]

For visual inspection of semiconductor wafers, etc., stock% formula% ~P221.

The outline of this method is to simultaneously detect image signals from a predetermined inspection area of a semiconductor wafer in which multiple element formation areas are regularly arranged, and image signals from other areas where a pattern congruent with this inspection area is formed. However, if the difference between the two is larger than a certain threshold value set in advance, it is determined that a defect exists in the inspection area.

[Problem that the invention seeks to solve]

By the way, the density of patterns formed on a semiconductor wafer varies even within the same element formation area. For example, in memory cells, etc., the pattern density is high;
The pattern density is low in the bonding pad, which is an electrode connected to the outside, and in the vicinity thereof, and the minimum size of a defect to be detected at each location is also different.

For this reason, the method of determining the presence or absence of defects based on a certain preset threshold as described above is difficult to detect due to small-sized defects that are not fatal in inspection areas with low pattern density.
The present inventor has discovered that there is a problem in that the reliability of the inspection results is lowered due to excessive detection of defects or failure to detect fatal defects in inspection areas with high pattern density.

In order to solve this problem, for example, it is possible to set different threshold values in advance for each inspection area with different pattern density and perform multiple inspections on the same semiconductor wafer, but this would reduce the productivity of the inspection process. This creates a new problem:

An object of the present invention is to provide a visual inspection technique that can improve the reliability of inspection results.

Another object of the present invention is to provide a visual inspection technique that can improve inspection productivity.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

In other words, in an appearance inspection apparatus for an object to be inspected on which a predetermined pattern is formed, there is a pattern density measurement section that calculates the density or dimension of the pattern existing in the inspection area of the object to be inspected, and a pattern calculated by the pattern density measurement section. a threshold calculation unit that sets a threshold value as a reference for defect detection in the inspection area according to the density or size of the pattern present in the inspection area; Defects in the inspection area are detected based on the values.

[Effect]

According to the above-mentioned means, it is possible to perform a visual inspection using the optimal threshold value according to the density of patterns existing in the inspection area of the object to be inspected, so that it is possible to perform a visual inspection using Excessive defects that are not
Failure to detect a fatal defect will not occur in an inspection area where the pattern density is relatively high, and the reliability of inspection results will be improved.

In addition, according to the above-mentioned means, there is no need to perform wasteful work such as performing multiple inspections on each part of the same object with different pattern densities, which improves productivity in visual inspection. be done.

〔Example〕

FIG. 1 is an explanatory diagram showing the main parts of a visual inspection device that is an embodiment of the present invention.

In this embodiment, the appearance inspection apparatus is configured as an appearance inspection apparatus for semiconductor wafers.

That is, a semiconductor wafer 1 (
Above the object to be inspected, a plurality of objective lenses 2 and 3 whose axes are perpendicular to the plane of the semiconductor evaluation board 1 are arranged in parallel at predetermined intervals.

The distance between the plurality of objective lenses 2 and 3 is, for example,
They are regularly arranged at predetermined intervals on the surface of the semiconductor wafer 1, and match the arrangement pitch of a plurality of element forming regions 1a in which mutually congruent patterns such as integrated circuits are formed. When the objective lens 2 observes the target inspection area in a predetermined element formation area 1a, the other objective lens 3 simultaneously observes a pattern congruent with the inspection area in the reference area R of another element formation area la. is configured to be

An image sensor 2a and an image sensor 3a are disposed above the plurality of objective lenses 2 and 3, respectively, and the inspection area of the semiconductor wafer 1 which is imaged through the plurality of objective lenses 2 and 3 and a reference image are provided. The image of the region R is converted into electrical signals and transmitted to the difference calculation unit 6 as an inspection image signal 4 and a reference image signal 5, respectively.

In the difference calculation section 4, a difference signal 7 between the inspection image signal 4 and the reference image signal 5 is calculated, and this difference signal 7 is transmitted to the determination section 9 via the difference signal delay section 8.

In this case, the reference image signal 5 obtained based on the image of the reference region R in which a pattern congruent with the inspection region R exists is configured to be manually input to the pattern density calculation section 10 at the same time as the difference calculation section 6. There is.

In this pattern density measurement section 10, for example, the differential value of the reference image signal 5 is binarized, and the number of edge portions of the pattern in the reference region R, that is, the number of edge portions of the pattern in the congruent inspection region is measured. As a result, the pattern density 11 existing in the inspection area is measured, and this pattern density 11 is transmitted to the threshold value calculation section 12.

The threshold calculation section 12 calculates an optimal threshold value 13 according to the pattern density 11 in the inspection area ascertained by the pattern density measurement section 10 and inputs it to the determination section 9.

Then, the delay time of the difference signal 7 in the difference signal delay unit 8 is determined by the pattern density measurement unit 10 and the threshold value calculation unit 1.
By matching the time required to determine the threshold value 13 based on 2, the judgment unit 9 inputs the human input from the difference calculation unit 6 via the difference signal delay unit 8, and the inspection image signal 4 of the inspection area and the reference area The difference signal 7 representing the difference between the reference image signal 5 of The presence or absence of the defects is determined, and a defect detection signal 14 is output to a display section, a recording section, etc. (not shown).

The pattern density measurement unit 10 receives a coordinate signal 1 of the inspection area.
5 is input, and areas that do not require inspection, such as boundaries between multiple element formation areas 1a on the semiconductor wafer 1, are designated as Kl.
jFJi.

Furthermore, the pattern density measuring section 10 also receives a synchronization control signal 16.
is input, and is configured to operate in synchronization with other parts.

The operation of this embodiment will be explained below.

First, a semiconductor wafer 1 placed on an The semiconductor wafer 1 is relatively moved so as to scan the entire surface.

At this time, the image of the predetermined test site R observed by the objective lens 2 and the image of the reference site R observed by the objective lens 3 are converted into a test image signal 4 and a reference image signal 5 by the image sensors 2a and 3a, respectively. A portion of the reference image signal 5 is also manually input to the pattern density measurement unit 10 at the same time.

A difference signal 7 representing the difference between the inspection image signal 4 and the reference image signal 5 calculated in the difference calculation section 6 is transmitted to the determination section 9 via the difference signal delay section 8 after being delayed by a predetermined time.

On the other hand, the pattern density measuring section 10 and the threshold calculating section 1
2, while the difference signal 7 is delayed by a predetermined time and transmitted to the determining section 9, the pattern density 11 in the reference region R, that is, the pattern density 11 in the inspection region When density 11 is large (small), threshold 13 is small (large)
The optimal threshold value 13 is calculated and manually inputted to the determination unit 9.

Then, in the determination unit 9, a difference signal 7 representing the difference between the inspection image signal 4 from the inspection site R and the reference image signal 5 from the reference site R, and the density of the pattern at the reference site R1, that is, the inspection site at that time. By comparing the optimal threshold value 13 according to The presence or absence is accurately determined, and when the difference signal 7 is greater than the threshold value 13, the defect detection signal 14 is outputted to the outside.

In this way, in this embodiment, the sensitivity in the determination section 9 is optimally adjusted by decreasing or increasing the threshold value 13 depending on the magnitude of the pattern density 11 at the inspection site. The reliability of the defect detection results at the inspection site is improved without being affected by the size of the density 11.

In this way, the following effects can be obtained in this embodiment.

(1) A pattern density measurement unit 10 that calculates the density of patterns existing in the inspection area of the semiconductor wafer 1, and a defect detection unit in the inspection area according to the density of the pattern calculated in the pattern density measurement unit 10. A threshold calculation unit 12 is provided which outputs a reference threshold value 13, and detects defects in the inspection area based on the optimum threshold value 13 output according to the density of patterns existing in the inspection area. As a result, non-fatal defects may be excessively detected in inspection areas where the pattern density is relatively low, or fatal defects may be overlooked in inspection areas where the pattern density is relatively high. This improves the reliability of defect detection results.

(2) As a result of (1) above, the occurrence of product defects due to defects being overlooked or misidentified during visual inspection is prevented,
Yield can be improved.

(3) As a result of (1), there is no need to perform wasteful work such as performing multiple inspections on the same semiconductor wafer 11 for each inspection area with different pattern densities. Productivity in visual inspection is improved.

(4) As a result of (1) to (3) above, productivity in manufacturing semiconductor devices is improved.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. Nor.

For example, pattern design data or the like may be used as a method of knowing the pattern density 11 at the inspection site.

Furthermore, the defect detection is not limited to comparing the image of the inspection site R with the image of the reference site R, but the inspection may be performed by observing only the image of the inspection site R.

The above explanation has mainly been about the application of the invention made by the present inventor to the application field for semiconductor wafer appearance inspection technology, which is the background of the invention, but the invention is not limited to this. It can be widely applied to original plates in photolithography such as reticles and reticles, as well as visual inspection of printed circuit boards.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

That is, the apparatus for inspecting the appearance of an object to be inspected on which a predetermined pattern is formed includes a pattern density measuring section that calculates the density or dimension of the pattern present in an inspection region of the object to be inspected, and the pattern density measuring section. a threshold calculation unit that outputs a threshold value serving as a reference for defect detection in the inspection area according to the density or size of the pattern that is calculated in the inspection area; Since the presence or absence of a defect in the inspection area is determined based on the threshold output according to the size, the optimum threshold value can be determined according to the density or size of the pattern existing in the inspection area of the object to be inspected. This can be used to conduct visual inspections using the same technology, so non-fatal defects may be excessively detected in inspection areas with relatively low pattern density, or fatal defects may not be detected in inspection areas with relatively high pattern density. This improves the reliability of test results.

Further, there is no need to carry out wasteful work such as carrying out multiple inspections for each part of the same object to be inspected with different pattern densities, and productivity in visual inspection is improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the main parts of a visual inspection device that is an embodiment of the present invention. 1... Semiconductor wafer (object to be inspected), 1a... Element formation region, 2.3... Objective lens, 2a. 3a...Image sensor, 4...Inspection image signal, 5...
Reference image signal, 6... Difference calculation unit, 7... Difference signal, 8... Difference signal delay unit, 9... Judgment unit, 10...
- Pattern density measuring section, 11...Pattern density, 12
...Threshold calculation unit, 13...Threshold value, 14...
- Defect detection signal, 15... Coordinate signal, 16... Synchronization control signal, D... Inspection site, R... Reference site.

Claims (1)

[Scope of Claims] 1. A method for visually inspecting an object to be inspected on which a predetermined pattern is formed, which detects defects in the inspection area according to the density or size of the pattern present in the inspection area of the object to be inspected. A visual inspection method characterized by setting a threshold value as a detection standard. 2. The scope of the present invention is characterized in that defect detection in the inspection area is performed by comparing an image of the inspection area with an image of another area in which a pattern congruent with the inspection area is formed. Appearance inspection device according to item 1. 3. The external appearance inspection method according to claim 1, wherein the object to be inspected is a semiconductor wafer. 4. An appearance inspection device for an object to be inspected on which a predetermined pattern is formed, comprising a pattern density measuring section that calculates the density or dimension of the pattern present in an inspection region of the object to be inspected, and the pattern density measuring section. a threshold calculation unit that outputs a threshold value as a reference for defect detection in the inspection area according to the density or size of the pattern calculated in the inspection area; An appearance inspection apparatus characterized in that defect detection in the inspection part is performed based on the threshold value outputted according to the size. 5. Claims characterized in that defect detection in the inspection area is performed by comparing an image of the inspection area with an image of another area in which a pattern congruent with the inspection area is formed. Appearance inspection device according to item 4. 6. The appearance inspection apparatus according to claim 4, wherein the object to be inspected is a semiconductor wafer.