JPH11153548A - Method and apparatus for surface inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect lumpish foreign matters and small foreign matters in isolation by utilizing continuous data without increasing memory storages by high-frequency sampling, and to judge the continuity in the direction of feeding as well by judging a lap from positional information in the direction of feeding, using continuous data in the direction of scanning. SOLUTION: This apparatus inspects a foreign matter on the surface of an object substance of inspection by irradiating the surface of the object substance of inspection with a detecting light, receiving scattered lights reflected from the surface of the object substance of inspection along with it, and causing the detecting light to perform scanning spirally during that period. If the scatter signal of each foreign matter Da, Db, Dc exceeds a threshold signal, when scanning by the detecting light in a specified direction is performed, it is stored as a start point Start. If the scatter signal by the foreign matter becomes lower than the threshold signal after that, it is stored as an end point End. The largest place of the scatter signal by the foreign matter between the start point Start and the end point End is stored as a peak Peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection method for inspecting foreign matter (in this specification, a broad term including dust, scratches and the like) on the surface of a wafer or other inspection object, and an apparatus for executing the method. About.

[0002]

2. Description of the Related Art Detection light is applied to the surface of an inspection object via an optical system, and scattered light reflected from the surface of the inspection object is received. 2. Description of the Related Art A surface inspection method and apparatus for inspecting foreign matter on the surface of an inspection target by scanning the detection light in a spiral shape by displacing the detection light in a spiral manner are known. In such a conventional spiral scanning type surface inspection method and apparatus, detection of a foreign substance signal is divided into predetermined sections (for example, divided by an encoder signal), and the detection light is sampled in the scanning direction.
The largest signal was detected and only that data was recorded. Such a method of storing only the largest data in the same section is called a pixel method.

FIG. 2 shows a conventional pixel-based processing method. In the section A, the data of Da has the maximum value.
In the section B, the data of Db has the maximum value. According to the known pixel-based software processing method, the number of foreign substances in this case is determined to be one or two. For example, one piece of software is determined to be continuous. If it is not determined to be continuous, the number is two.

FIG. 7 shows another conventional pixel type surface inspection method from the viewpoint of continuity determination.

In FIG. 7, the determination of the scanning direction is as follows.
Proceed as follows. That is, in section A, the data of Da has the maximum value, and in section B, the data of Db has the maximum value. The number of foreign substances is 1
Or two. 1 for software that is judged to be continuous
The number is two, and if it is not determined to be continuous, it is two.

In the inspection state shown in FIG. 7, the continuity in the feed direction indicated by an arrow is determined as shown in FIG. The portions shown in black are determined to be continuous because the pixels are adjacent.

[0007] In the pixel method, since one foreign matter is processed in one section, foreign matter determination over a section is determined as follows.
Processing is performed based on only the adjacent information of pixels without having data indicating that they are continuous.

In data processing in the feed direction, point information is developed into a pixel image, and determination is made based on neighboring information as in the scan direction.

In the surface inspection method of performing a constant scan using a galvanomira or the like, the sampling frequency is related to the scanning speed and the size of the detection light, and all signals exceeding the threshold signal are stored. Was treated as data. Such a method is called a scan method.

In the scanning method, when the sampling frequency is high, the number of data increases, and the memory capacity increases. Therefore, the sampling frequency is set low, and data is detected at intervals of several tens of μm with respect to the movement of the detection light. Therefore, the determination of the continuity largely depends on the moving speed of the detection light and the sampling frequency. That is, data collected at intervals of a low sampling frequency is regarded as a set of points, and the continuity is determined by software.

[0011]

In any of the conventional techniques (pixel method and scan method), the continuity is determined by processing based on uncertain data.

In both the pixel method and the scan method, the continuity is determined in a state where the continuity data itself is missing. Therefore, when there is a lump of foreign matter or when a small foreign matter exists in an isolated state. In the case where there was, foreign matter could not be accurately and reliably detected.

Further, the continuity of the feed direction is determined without having any information.

An object of the present invention is to enable continuous detection of massive foreign substances and small foreign substances by having continuity data without increasing the memory by sampling at a high frequency.

Another object of the present invention is to enable continuity in the feed direction by determining overlap based on position information in the feed direction using continuous data in the scan direction.

[0016]

One of the solutions of the present invention is to irradiate detection light to the surface of an inspection object through an optical system and receive scattered light reflected from the surface of the inspection object. In the meantime, the inspection light is scanned in a predetermined direction in the surface inspection method of inspecting foreign matter on the surface of the inspection object by relatively displacing the inspection object and the optical system and scanning the detection light. When the scattering signal of the foreign matter exceeds the threshold signal, it is stored as a start point.After that, when the foreign matter scattering signal falls below the threshold signal, it is stored as an end point, and the start point and the end point are stored. This is a surface inspection method in which a point where the foreign substance scattering signal is largest is stored as a peak.

Preferably, a foreign substance on the surface of the inspection object is inspected based on positional information including at least a start point, a peak, and an end point as position data of the foreign substance scattering signal. If the scanning direction of the detection light is a combination of the scan direction and the feed direction, and the position information of the start point and end point of one data overlaps in the feed direction, it is determined that there is continuity of the foreign matter scattering signal in the feed direction. I do. It is determined that the foreign matter is continuous from the start point to the end point, and a process for constantly detecting peak data is performed between the start point and the end point. When one data falls below the threshold signal for the first time, the end point is stored, and
The sampling clock is counted from the end point, and when the data exceeds the threshold signal again within the set data (variable), the previous end point is cleared and the processing of the peak data is continued.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface inspection method and apparatus according to the present invention provide the best effect when a semiconductor wafer is used as an inspection object. In particular, when the foreign matter on the surface of the inspection target is a large foreign matter that straddles the scanning line, the continuity is accurately determined. For example, continuity is accurately detected on a scan line. In addition, foreign substances that straddle the scanning line (in the vertical direction) are also detected as being continuous.

The surface inspection method and apparatus according to the present invention irradiates the surface of the inspection object with the detection light, receives the scattered light reflected from the surface of the inspection object, and scans the detection light in a spiral shape, for example. By, when inspecting foreign matter on the surface of the inspection object, and scanning the detection light in a predetermined direction, if the scattering signal of the foreign matter exceeds the threshold signal,
This is stored as a start point, and thereafter, when the foreign matter scattering signal falls below the threshold signal, it is stored as an end point, and the place where the foreign matter scattering signal is largest between the start point and the end point is stored as a peak. A surface inspection method and an apparatus for performing the method are described below. Among them, preferred embodiments of the main components of the present invention will be described below.

The data at the start point is the data at the address at the time when the level exceeds the threshold signal level.

The peak data is the data of the largest signal between the start point and the eledo point and the data of the address thereof.

The data at the end point is the data of the address at the time when the level falls below the threshold signal level after the peak signal. However, there are conditions for this, as described below.

A preferred data detection procedure is as follows.

(1) A sampling frequency (for example, 20 MHz) sufficiently fast in the scanning direction of the detection light is prepared.

(2) When the foreign matter scattering signal exceeds the threshold signal, the data at that point is stored as the start point data.

(3) Subsequently, peak data processing is performed.

(4) When the foreign matter scattering signal falls below the threshold signal, the data at that point is replaced with the data at the end point.
Stored as 1.

(5) Sampling is counter-started simultaneously with (4). Thereby, the time during which the signal is below the threshold signal is measured.

(6) Comparing with the preset data, when the value of the counter becomes larger, the processing of the end point is finished, and the data is transferred to the memory as one foreign matter data and stored. If the foreign matter scattering signal exceeds the threshold signal again below the comparison counter, the process continues.

(7) End point data E1 previously stored
Is cleared, and peak data processing is performed.

(8) Thereafter, the above-mentioned (4) to (7)
Is performed.

A data processing method for determining continuity is as follows.

(1) Continuous processing in the scanning direction is performed. When the difference between the start point and the end point of the data is equal to or larger than a predetermined value, it is determined that a flaw exists there.
Otherwise, it is determined that garbage exists.

(2) In the processing of the feed direction, it is determined whether or not the position information of the start point and the end point of the data overlaps. If there is an overlap, it is determined that the continuity of the feed direction exists. I do. When the number of continuous data in the feed direction becomes equal to or more than a certain value, it is determined that there is a flaw. Others are judged as garbage.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment of FIGS. 1, 3 to 5 FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, the photoelectric conversion elements are
It is connected to a peak detection circuit section and a continuation determination circuit section via an MP circuit and an A / D conversion circuit. The peak detection circuit and the continuity determination circuit are connected to the data processing circuit. The data processing circuit is connected to the memory. The encoder signal is sent to the peak detection circuit section and the data processing circuit section.

FIG. 3 shows a method according to the present invention.

In the method of the present invention, when the detection light is scanned in a predetermined direction, if the scattering signal of the foreign substance exceeds a threshold signal (shown by a solid line in the horizontal direction in FIG. 3), the starting point is set there. (Start)
Thereafter, when the foreign matter scattering signal falls below the threshold signal, the signal is stored as an end point (End), and the place where the foreign matter scattering signal is largest between the start point and the end point is stored as a peak (Peak). A foreign substance on the surface of the inspection target is specified based on positional information including a start point (Start), a peak (Peak), and an end point (End) as position data of the foreign substance scattering signal.

In FIG. 3, the foreign substances are Da, Db, D
Since c is specified, the number of foreign substances becomes three. In this case, the data in the sections A and B become independent of the number of foreign substances,
The number of foreign substances is counted as three.

FIG. 4 is a conceptual diagram for judging as a single foreign substance. In particular, the foreign matter Db will be described.
Is once below the threshold signal (shown in FIG. 3 by a solid line in the horizontal direction) as shown in FIG.
Since the adjacent section is near, it is specified as one foreign object.

FIG. 5 shows an example of a flowchart of the method of the present invention.

In FIG. 5, first, when the measurement is started,
In step 1, the measurement data is input, and the process proceeds to step 2.

In step 2, the measured data obtained
It is determined whether Sn is greater than the slice level SL. If it is smaller, the process proceeds to step 3, and if larger, the process proceeds to step 7.

In step 3, it is determined whether or not the count of the width count SWcnt indicating the width of the foreign matter is 0, that is, the measured data
It is determined whether Sn has exceeded the slice level SL. In other words, it is determined whether the data of the foreign substance was measured immediately before. Here, “immediately before” means within the count of the predetermined value SEset determined in step 13.

If the count of SWcnt is 0, that is, if there is no foreign substance data immediately before, the process returns to step 1 and shifts to processing of the next measurement data. If the count of SWcnt is not 0, that is, if there is foreign matter data immediately before, the process proceeds to step 4, and the SEcnt count (no-signal period count) for counting the period in which the obtained measurement data Sn is smaller than the slice level SL is performed. A counting process is performed.

In step 4, when SEcnt = 0,
It is determined whether the end signal count is 0 and SEcnt
If = 0, go to step 5, otherwise go to step 1
Proceed to 2.

In step 5, that is, when the obtained measurement data Sn falls below the slice level SL from the state where it has exceeded the slice level SL, the coordinate values X and Y at that time are changed.
Store as Xend and Yend and proceed to step 6. In step 6, 1 is added to the SEcnt count, and step 1
Return to the next measurement data processing. If it is determined in step 2 whether the obtained measurement data Sn is higher than the slice level SL, the process proceeds to step 7. In step 7, whether the count of SWcnt is 0,
That is, it is determined whether or not the measurement data Sn has exceeded the slice level SL.
If it is not the first time, go to step 10.

In step 8, the coordinate values at this time are used as the start coordinates of the foreign matter (coordinate values of the start point) Xstart, Ystart
And proceeds to step 9.

On the other hand, if it is determined in step 7 that the count of the count value SWcnt from the start of the foreign object is not 0, that is, if it is initially determined that the measured data Sn does not exceed the slice level SL, the process proceeds to step 10 and the non-signal Period count
Determine whether the count value of SEcnt is not 0. If the count value of the no-signal period count SEcnt is not 0, the count value of SEcnt is set to 0 in step 11, and the process proceeds to step 9. If the count value of the no-signal period count SEcnt is 0, the process proceeds directly to step 9.

In step 9, it is determined whether or not the current measurement data is larger than the previous measurement data, and peak processing is performed to store the larger one as peak data.

In step 12, the count value SW from the point of the starting coordinates of the foreign matter (start point, corresponding to the front end of the foreign matter)
Add 1 to cnt and return to step 1.

If it is determined in step 4 that SEcnt is not 0, that is, if the count value of the non-signal period count SEcnt is not 0, the process proceeds to step 13. Here, it is determined whether or not the no-signal period count SEcnt is larger than a predetermined count value SEset. If the no-signal period count SEcnt is smaller than the predetermined count value SEset, the process proceeds to step 6 and the next measurement data processing is performed.

If the no-signal period count SEcnt is larger than the predetermined count value SEset, the process proceeds to step 14, where the next measurement data processing is performed.

In step 14, coordinate values Xstart and Ystart of the start point of the foreign matter stored in step 8 are calculated as follows:
The coordinate values Xend and Yend stored in step 5 are used as the peak values stored in the memory, respectively, as the coordinate value of the start point, the coordinate value of the end point of the foreign substance, and the peak value of the foreign substance to be measured this time. The data is transferred, stored in the memory, and the process proceeds to step S15.

In step 15, it is determined whether or not the measurement is completed. If the measurement is completed, the measurement is terminated.
Otherwise, go to step 16.

In step 16, initialization is performed. The start coordinate values Xstart and Ystart, the end coordinate values Xend and Yend and the peak value P of the foreign matter, and the non-signal period count SEcn
t and the count value SWcnt from the start of the foreign matter are set to 0, and the process returns to step 1.

Embodiment of FIGS. 6, 8 to 11 FIG. 6 shows a block diagram of a second embodiment of the present invention.

In FIG. 6, the photoelectric conversion elements are A in order.
It is connected to a peak detection circuit section and a continuation determination circuit section via an MP circuit and an A / D conversion circuit. The peak detection circuit and the continuity determination circuit are connected to the data processing circuit. The data processing circuit is connected to the memory. The encoder signal is sent to the peak detection circuit section and the data processing circuit section. The signal from the CPU is sent to the memory.

FIG. 9 shows a surface inspection method according to a second embodiment of the present invention.

In the inspection situation shown in FIG. 9, since the section data becomes irrelevant to the number of foreign substances, the foreign substances Da, Db, Dc
Are determined to be three.

To further explain this point, when the detection light is scanned in a predetermined direction, if the scattered signal of the foreign substance exceeds a threshold signal (shown by a solid line in the horizontal direction in FIG. 9), the scanning is started. It is stored as a point (Start), and thereafter, when the foreign matter scattering signal falls below the threshold signal, it is stored as an end point (End), and the point where the foreign matter scattering signal is the largest between the start point and the end point is peaked. (Peak). Start point (Start) as position data of the foreign matter scattering signal,
The foreign matter on the surface of the inspection target is specified based on the position information including the peak (Peak) and the end point (End). In FIG. 3, Da, Db, and Dc are specified as foreign substances, and the number of foreign substances is three. In this case, the data in the sections A and B become irrelevant to the number of foreign substances, and the number of foreign substances is counted as three.

FIG. 10 is a conceptual diagram for judging the continuity of foreign matter.

In FIG. 10, the scanning direction of the detection light is a combination of the scanning direction and the feed direction. When the position information of the start point and the end point of one data overlaps in the feed direction, the foreign matter scattering signal in the feed direction. Is determined to be continuous. It is determined that the foreign matter is continuous from the start point to the end point, and a process for constantly detecting peak data is performed between the start point and the end point. When one data falls below the threshold signal for the first time, the end point is stored, and the sampling clock is counted from the point of the end point. When the data exceeds the threshold signal within the set data, Clear the previous end point and continue processing the peak data. In particular, in the data processing, the continuity is determined as follows.

(1) In the continuous processing in the scanning direction, when the difference from the start point to the end point of the data becomes equal to or larger than a certain value, it is determined that the data is flawed.

(2) Regarding the feed direction, it is determined whether or not the position information of the start point and the end point of the data overlap, and if there is an overlap, it is determined that the feed direction is continuous. If the number of continuous data in the feed direction exceeds a certain value, it is determined to be flawed, and otherwise, it is determined to be dust.

In the example of FIG. 10, the upper two pieces of position information have no overlapping parts and are not continuous, so it is determined that there are two foreign substances, and the lower three pieces of position information have overlapping parts. Since there is continuity, it is determined to be one.

FIG. 11 shows an example of a flowchart of the method of the present invention.

In FIG. 11, when the measurement is started, the scanning line Sn to be measured is specified in step 1, and the process proceeds to step 2. In step 2, the scanning line Sn to be measured is
Is called, and the process proceeds to step 3. Step 3
Then, it is determined whether or not there is foreign matter data in the scanning line, that is, whether or not a signal exceeding the slice level SL is included. If there is foreign matter data, the procedure proceeds to step 4, and if there is no foreign matter data, the procedure returns to step 2 and repeats while foreign matter data is output. In step 4, when foreign matter data is found in the scan line Sn to be measured, the foreign matter data in the immediately preceding scan line Sn-1 is called, and the process proceeds to step 5.

In step 5, the scan line to be measured this time
It is determined whether or not there is an overlap between the foreign substance data of Sn and the foreign substance data in the previous target scanning line Sn-1, and if there is an overlap, the process proceeds to step 6; otherwise, the process returns to step 2.

An example of the overlap means that there is an overlap between the start coordinates and the end coordinates of the foreign matter in the scanning direction. In step 6, continuity processing is performed, and the process proceeds to step 7.

The continuity processing is a scanning line to be measured this time.
If there is an overlap between the foreign substance data of Sn and the foreign substance data in the previous target scanning line Sn-1, both are determined to be measuring the same foreign substance, and the foreign substance count is treated as one unit. Therefore, various processes for associating the two data are applicable. For example, data with continuity is treated as a group, or each time continuity is recognized, a correction value is incremented by 1, and the correction value is subtracted from the total count value of the foreign substance signal for each scanning line. Includes those that require the correct number of foreign objects.

In step 7, it is determined whether or not the measurement of all the scanning lines to be measured has been completed. If the measurement has not been completed, the process returns to step 1 and the measurement of the next scanning line is performed.

When the measurement of all the scanning lines to be measured has been completed, in step 8 the number of foreign substances counted as one unit of the foreign substance having continuity and the number of foreign substances having Display or the like is performed so as to be distinguished on the graphic display, and the measurement ends.

Embodiment of FIG . 12 FIG . 12 shows an example of a helical scanning type surface inspection apparatus according to the present invention for implementing the above two embodiments. A light source 110, an irradiation optical system 112 for irradiating the surface 111 of the object with light from the light source 110, and a scattered light irradiated by the irradiation optical system 112 and reflected from the surface of the object 111 to receive a light reception signal. Light receiving optical system 113 to be formed
A photoelectric conversion element 114 that outputs light received by the light receiving optical system 113 as a light reception signal; an edge detection element 120 that receives light from the light source 110 through a concave portion of the measurement object in an outer peripheral range of the measurement object; A linear displacement unit 115 for providing a relative linear displacement between the surface of the object 111 and the irradiation optical system 112 and the light receiving optical system 113;
And a rotation displacement unit 116 that provides a relative rotation displacement to the surface of the object 111 and the irradiation optical system 112 and the light receiving optical system 113, and is configured such that the irradiated light spirally scans the surface of the measurement object 111. I have. Linear displacement unit 115 and rotational displacement unit 11
6 are connected to motors 117 and 118, respectively.

[0076]

The present invention has the following remarkable effects.

(1) Since one data can have a width and a size, it is possible to measure an accurate number of foreign substances according to the sampling frequency.

(2) Software processing in the scanning direction is not required, and the processing speed is improved.

(3) By introducing the concept of continuity judgment based on the setting data, it is possible to deal with a problem caused by the directivity of scattering and the shape of a foreign substance. The decrease in scattered light in a short time can be ignored.

(4) By having the data structure of the overlap in the feed direction, it is possible to easily determine the continuous scratch and the nearby dust.

(5) Since the data structure indicating continuity is simple, data can be measured without consuming much memory. Even if there is a lot of scratches or large dust on the surface, the memory can be used. The problem that measurement is impossible due to insufficient capacity can be solved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 shows a conventional pixel-based processing method.

FIG. 3 shows how the method according to the first embodiment of the invention works.

FIG. 4 is a conceptual diagram for judging the continuity of foreign matter in the method of FIG. 3;

FIG. 5 shows a flowchart of a method according to a first embodiment of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the present invention.

FIG. 7 shows another conventional pixel-based processing method.

8 shows how to determine continuity in the feed direction in FIG.

FIG. 9 illustrates how the method according to the first embodiment of the present invention operates.

FIG. 10 shows how to determine continuity in the feed direction in FIG.

FIG. 11 shows an example of a flowchart of a method according to a first embodiment of the present invention.

FIG. 12 shows an example of a surface inspection apparatus according to the present invention for implementing the first and second embodiments.

[Explanation of symbols]

 Reference Signs List 110 light source 111 surface 112 irradiation optical system 113 light receiving optical system 114 photoelectric conversion element 115 linear displacement section 116 rotational displacement section 117 motor 118 motor 120 edge detection element

Claims (7)

[Claims] 1. A method for irradiating a detection light onto a surface of an inspection object via an optical system and receiving scattered light reflected from the surface of the inspection object, and thereby, the inspection object and the optical system are relatively moved. In the surface inspection method for inspecting foreign matter on the surface of the inspection object by scanning the detection light by displacing the detection light, when the detection light is scanned in a predetermined direction, the scattering signal of the foreign matter exceeds the threshold signal. Then, store that as the start point, and then, when the foreign matter scattering signal falls below the threshold signal, store it as the end point,
A surface inspection method in which a point where a foreign matter scattering signal is largest between a start point and an end point is stored as a peak. 2. The surface inspection method according to claim 1, wherein a foreign substance on the surface of the inspection target is inspected based on positional information including at least a start point, a peak, and an end point as position data of the foreign substance scattering signal. 3. If the scanning direction of the detection light is a combination of the scanning direction and the feed direction, and the position information of the start point and the end point of one data overlaps in the feed direction, the continuation of the foreign matter scattering signal in the feed direction. The surface inspection method according to any one of claims 1 to 2, wherein the surface inspection method is determined to have a property. 4. The method according to claim 1, wherein a foreign object is determined to be continuous from the start point to the end point, and peak data is always detected between the start point and the end point. Surface inspection method as described. 5. An end point is stored when one data falls below the threshold signal for the first time, and a sampling clock is counted from the end point, and the data is re-set within the set data. The surface inspection method according to any one of claims 1 to 4, wherein when the value exceeds the predetermined value, the previous end point is cleared and the processing of the peak data is further continued. 6. The surface inspection method according to claim 5, wherein the setting data is variable. 7. A light source, an illumination optical system for illuminating a surface to be inspected with a light beam from the light source, a light receiving optical system for receiving reflected light from the object to be inspected, and a light receiving optical system A wafer surface inspection apparatus comprising: a light receiving unit that receives reflected light; and a signal processing unit that processes a signal from the light receiving unit. A surface that performs the surface inspection method according to claim 1. Inspection equipment.