JP2008199033A - Foreign matter inspecting method and foreign matter inspecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of suppressing generation of misinformation without decreasing the detection sensitivity of foreign matters in a whole semiconductor wafer or in chip units. <P>SOLUTION: A laser device 10 irradiates light beams obliquely to the surface of a semiconductor wafer 1, a photoelectric conversion element 20 receives scattered light generated on the surface of the semiconductor wafer 1 and outputs an image signal. An image processing device 120 of a processing unit 100 compares mutual image signals of adjacent chips and outputs the difference. Coefficient tables 132, 133 input coordinate information from a coordinate managing device 140 and output coefficients stored corresponding to the coordinate information. A determination circuit 131 uses a threshold obtained by multiplying a predetermined value by the coefficients inputted from the coefficient tables 132, 133 to determine foreign matters. The coefficients are altered based on results of a preliminary inspection and the threshold is made larger in an inspection for a region where much misinformation has been generated than in the preliminary inspection. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a foreign matter inspection method and foreign matter inspection apparatus for detecting foreign matter, scratches, defects, dirt, etc. (hereinafter collectively referred to as foreign matter) present on the surface of an object to be inspected such as a semiconductor wafer. The present invention relates to a foreign matter inspection method and a foreign matter inspection apparatus that determine whether foreign matter is present using a threshold value.

  A foreign matter inspection apparatus for detecting foreign matter on a semiconductor wafer irradiates the surface of the semiconductor wafer with a light beam such as a laser beam and detects reflected light or scattered light generated on the surface of the semiconductor wafer, thereby detecting the surface of the semiconductor wafer. Is to detect foreign matter present in the. When a pattern constituting each chip is formed on the surface of the semiconductor wafer, an image signal is usually created from the detected intensity of reflected or scattered light, and an image signal of an adjacent chip or a good chip prepared in advance is generated. Compared with the image signal, if the difference between the two is equal to or greater than a threshold value, it is determined as a foreign object. Conventionally, the threshold value at the time of determination is constant for the entire semiconductor wafer, but in recent years, a method for determining a threshold value for each chip has been proposed.

If the threshold for judging foreign objects is reduced, it will be possible to detect even smaller foreign objects,
There are many so-called false reports that erroneously detect non-foreign matter as foreign matter. In particular, since the thickness of semiconductor wafers changes concentrically due to the manufacturing process, the intensity variation of reflected or scattered light differs between the vicinity of the center and the periphery of the semiconductor wafer, and the vicinity of the periphery of the semiconductor wafer. There were many cases of false information. Even within one chip, variations in the intensity of reflected light or scattered light differ depending on the type and density of the formed pattern, and a large amount of false information may be generated partially.

  For this reason, conventionally, the occurrence of false information has been suppressed by increasing the threshold value determined for the entire semiconductor wafer or for each chip. However, when the threshold value is increased, there is a problem that the detection sensitivity of foreign matters in the whole semiconductor wafer or in units of chips is lowered.

  An object of the present invention is to suppress the generation of false information without deteriorating the detection sensitivity of foreign matters in the whole semiconductor wafer or in units of chips.

  The foreign matter inspection method of the present invention irradiates an inspection object with an inspection light, detects the intensity of reflected or scattered light generated on the surface of the inspection object and the position in the inspection area, and uses a threshold value. A foreign matter inspection method for determining whether foreign matter is present on the surface of an object to be inspected based on the intensity of detected reflected light or scattered light, and performing preliminary inspection to confirm the position of the generated false information Then, the inspection area is divided into a plurality according to the density of the false information generated in the preliminary inspection, and a different threshold is used for each of the divided areas, and the inspection target is inspected from the intensity of the detected reflected light or scattered light. It is determined whether or not there is a foreign object on the surface of the object.

  Further, the foreign matter inspection apparatus of the present invention includes an irradiation means for irradiating the inspection object with the inspection light, an intensity detection means for detecting the intensity of the reflected light or scattered light generated on the surface of the inspection object, and the reflected light or scattering. Based on the detection result of the position detection means for detecting the position of the light in the inspection area and the detection result of the position detection means, the intensity detection means is detected using different threshold values for each of the plurality of areas obtained by dividing the inspection area. And processing means for determining whether or not there is a foreign substance on the surface of the inspection object from the intensity of the reflected light or scattered light.

  First, the preliminary inspection is performed, the result of the preliminary inspection is reviewed, and the position of the generated false alarm is confirmed. And, the inspection area was divided into multiple according to the density of the false alarms generated in the preliminary inspection, and in this inspection, the threshold used in the area where a lot of false alarms occurred in the preliminary inspection was less likely to occur in the preliminary inspection. It is larger than the threshold value used in the region. Thereby, the generation | occurrence | production of the false information in the area | region where many false information generate | occur | produced by the preliminary inspection is suppressed, without the detection sensitivity of the foreign material in the whole semiconductor wafer or a chip unit falling.

  Furthermore, the foreign matter inspection method of the present invention divides the inspection region of the entire semiconductor wafer, which is the inspection object, into a plurality of regions concentrically. In the foreign matter inspection apparatus of the present invention, the processing means uses a different threshold value for each of a plurality of regions obtained by concentrically dividing the inspection region of the entire semiconductor wafer that is the object to be inspected. Since the film thickness of a semiconductor wafer changes concentrically due to the manufacturing method, many false alarms may occur near the outer periphery. By dividing the inspection area of the entire semiconductor wafer into a plurality of areas concentrically, the threshold value used for the inspection near the outer peripheral portion is made larger than the threshold value used for the inspection near the central portion, thereby forming a film on the semiconductor wafer. The generation of false information due to the change in thickness is suppressed.

  Furthermore, the foreign matter inspection method of the present invention divides an inspection region in a chip formed on a semiconductor wafer as an inspection object into a plurality of regions. In the foreign matter inspection apparatus of the present invention, the processing means uses a different threshold value for each of a plurality of regions obtained by dividing the inspection region in the chip formed on the semiconductor wafer as the inspection object. Even in the same chip, a lot of false information may be generated due to the difference in the type and density of the formed pattern. By dividing the inspection area in the chip into multiple areas and making the threshold used in the inspection of the area where a lot of false alarms occur larger than the threshold used in the inspection of other areas, the pattern type and density Occurrence of false information due to the difference is suppressed.

  According to the present invention, it is possible to suppress the occurrence of false information without reducing the detection sensitivity of foreign matter in the whole semiconductor wafer or in units of chips.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of a foreign matter inspection apparatus according to an embodiment of the present invention. The foreign substance inspection apparatus according to the present embodiment includes a laser apparatus 10, a photoelectric conversion element 20, an X scale 30, a Y scale 40, and a processing apparatus 100.

  The laser device 10 generates laser light having a predetermined wavelength as inspection light, and irradiates the surface of the semiconductor wafer 1 that is an object to be inspected obliquely. The semiconductor wafer 1 having the chip 2 formed on the surface is mounted on a wafer table (not shown), and the wafer table moves in the Y direction and the X direction, so that the light beam emitted from the laser device 10 is converted into the semiconductor wafer. 1 surface is scanned.

  FIG. 2 is a diagram for explaining scanning of the light beam of the foreign substance inspection apparatus. When the wafer table on which the semiconductor wafer 1 is mounted moves in the Y direction, the light beam emitted from the laser device 10 is directed in the direction indicated by the arrow S1 on the surfaces of the chips 2a, 2b, 2c, and 2d formed on the semiconductor wafer 1. 1 line is scanned. Next, when the wafer table moves in the X direction, the scanning line moves in the X direction. When the wafer table moves in the Y direction opposite to the previous direction, the light beam moves on the surfaces of the chips 2d, 2c, 2b, and 2a in the direction indicated by the arrow S2, and the next line is scanned. By repeating these operations, the entire surface of the semiconductor wafer 1 is scanned.

  In FIG. 1, the light beam applied obliquely to the surface of the semiconductor wafer 1 is scattered by a pattern or foreign matter on the surface of the semiconductor wafer 1 to generate scattered light. The photoelectric conversion element 20 is composed of, for example, a photomultiplier tube (photomultiplier) or the like. The photoelectric conversion element 20 receives scattered light generated on the surface of the semiconductor wafer 1, converts the intensity thereof into an electrical signal, and processes the image as an image signal. Output to. The X scale 30 and the Y scale 40 are made of, for example, a laser scale, and detect the position in the X direction and the position in the Y direction of the semiconductor wafer 1, respectively, and output the position information to the processing apparatus 100.

  The processing device 100 includes an A / D converter 110, an image processing device 120, a foreign matter determination device 130, a coordinate management device 140, and an inspection result storage device 150. The A / D converter 110 converts the analog image signal input from the photoelectric conversion element 20 into a digital image signal and outputs it.

  The image processing apparatus 120 includes, for example, a delay circuit and a difference detection circuit. The delay circuit inputs the image signal from the A / D converter 110 and delays it, so that the irradiation of the light beam immediately before the chip currently irradiated with the light beam in the scanning shown in FIG. The image signal of the chip is output. The difference detection circuit receives the image signal from the A / D converter 110 and the image signal from the delay circuit, and detects and outputs the difference between the two. As a result, the image processing apparatus 120 compares image signals between adjacent chips. When a foreign substance exists on the surface of a chip, scattered light generated by the foreign substance appears as a difference between image signals of adjacent chips.

  Note that the image processing device 120 may include a memory that stores image signal data of a good chip prepared in advance, instead of the delay circuit, and may perform comparison with the image signal of a good chip.

  The foreign matter determination device 130 includes a determination circuit 131 and coefficient tables 132 and 133. In the coefficient tables 132 and 133, coefficients for changing threshold values are stored in association with coordinate information. Coefficient tables 132 and 133 receive coordinate information from a coordinate management device 140 described later, and output coefficients stored in association with the coordinate information to the determination circuit 131.

  A difference between image signals between adjacent chips is input from the image processing apparatus 120 to the determination circuit 131, and a coefficient for changing the threshold value is input from the coefficient tables 132 and 133. The determination circuit 131 multiplies a predetermined value by the coefficient input from the coefficient tables 132 and 133 to create a threshold value. Then, the difference between the image signals is compared with a threshold value, and when the difference is equal to or larger than the threshold value, it is determined as a foreign object, and the inspection result is output to the inspection result storage device 150. The determination circuit 131 also outputs threshold information used for determination to the inspection result storage device 150.

  The coordinate management device 140 detects the X coordinate and the Y coordinate of the position irradiated with the current light beam on the semiconductor wafer 1 based on the position information of the semiconductor wafer 1 input from the X scale 30 and the Y scale 40, The coordinate information is output.

  The inspection result storage device 150 stores the inspection result input from the foreign matter determination device 130 and the coordinate information input from the coordinate management device 140 in association with each other. The inspection result storage device 150 also stores the threshold information input from the foreign matter determination device 130 in association with the inspection result or coordinate information.

  In the above configuration, first, a case where the threshold value is partially changed in the inspection region of the entire semiconductor wafer will be described.

  First, a preliminary inspection is performed on the entire surface of the semiconductor wafer 1. At this time, all the coefficient values stored in the coefficient tables 132 and 133 of the foreign substance determination device 130 are set to 1, and the determination circuit 131 performs determination using a certain threshold value. This preliminary inspection may be performed on one or several samples, and may be performed every inspection or at regular intervals.

  Subsequently, the result of the preliminary inspection is reviewed to classify foreign matters and false reports in which non-foreign matters are erroneously detected among those detected in the preliminary inspection. Then, a map showing the distribution of false information in the semiconductor wafer 1 is created. FIG. 3A is a diagram showing an example of the distribution of the false information during the preliminary inspection in the semiconductor wafer. In this example, many false reports 3 occur near the outer periphery of the semiconductor wafer 1 and do not occur near the center of the semiconductor wafer 1 across the boundary 4a. Therefore, in this example, the inspection area of the entire semiconductor wafer is divided into two areas by the boundary 4a. FIG. 3B is a diagram illustrating an example of a divided region in the semiconductor wafer. In FIG. 3B, the hatched portion indicates a region where a large amount of false information is generated outside the boundary 4a, and the non-shaded portion indicates a region where a small amount of false information is generated inside the boundary 4a.

  Subsequently, the threshold value at the time of the preliminary inspection stored in the inspection result storage device 150 is confirmed, and the coefficient stored in the coefficient table 132 is falsely reported in the area outside the boundary 4a shown in FIG. Is set to a value larger than 1 so as not to occur, and remains 1 in the region inside the boundary 4a. And this test | inspection is performed about the whole surface of a semiconductor wafer. The determination circuit 131 performs determination using a threshold value larger than that in the preliminary inspection in the region outside the boundary 4a shown in FIG. 3B, and the same threshold value as in the preliminary inspection in the region inside the boundary 4a. Make a determination using.

  FIG. 4A is a diagram illustrating an example of a difference between image signals and a threshold value during preliminary inspection, and FIG. 4B is a diagram illustrating an example of a difference between image signals and threshold value during main inspection. This shows how the difference between the image signals changes in one line scan in the region outside the boundary 4a shown in FIG. A is a portion where the difference is increased due to the foreign matter, and B and C are portions where the difference is increased due to a change in the film thickness of the semiconductor wafer 1 or the like. At the time of the preliminary inspection, as shown in FIG. 4A, the portion A is detected above the threshold, and the portions B and C are also detected as false information above the threshold. On the other hand, at the time of the main inspection, as shown in FIG. 4B, only the portion A is detected exceeding the threshold value, and the false information of the portions B and C is not generated.

  In this embodiment, the inspection area of the entire semiconductor wafer is divided into two areas. However, the present invention is not limited to this, and the inspection of the entire semiconductor wafer is performed according to the density of false information generated in the preliminary inspection. The area may be divided into three or more areas.

  According to the present embodiment, the inspection region of the entire semiconductor wafer is concentrically divided into a plurality of regions, and the threshold value used for the inspection near the outer peripheral portion is larger than the threshold value used for the inspection near the central portion. By doing so, it is possible to suppress the occurrence of false information due to the change in the film thickness of the semiconductor wafer.

  Next, a case where the threshold value is partially changed in the inspection area in the chip will be described.

  First, a preliminary inspection is performed on the entire surface of the semiconductor wafer 1. At this time, all the values of the coefficients stored in the coefficient table 133 of the foreign substance determination device 130 are set to 1, and the determination circuit 131 obtains a threshold value obtained by multiplying a predetermined value by the coefficient input from the coefficient table 132. Make a determination using. This preliminary inspection may be performed on one or several samples, and may be performed every inspection or at regular intervals.

  Subsequently, the preliminary inspection results are divided for each chip, and the preliminary inspection results of all the chips are overlapped. FIG. 5A is a diagram showing an example of the distribution in the chip as a result of the superimposed preliminary inspection. In this example, the results of the preliminary inspection are concentrated in the portion surrounded by the boundaries 4b and 4c. As described above, for the portion where the results of the preliminary inspection are concentrated, the result of the preliminary inspection is reviewed to classify foreign matters and false reports in which non-foreign matters are erroneously detected among those detected in the preliminary inspection. When the result of the preliminary inspection is mainly false information, the inspection area in the chip 2 is divided into three areas by the boundaries 4b and 4c in the example of FIG. FIG. 5B is a diagram illustrating an example of a divided area in the chip. In FIG. 5 (b), the hatched portion indicates a region where a large amount of false information is generated inside the boundaries 4b and 4c, and the portion without a hatched portion indicates a region where the generation of false information outside the boundaries 4b and 4c is small. .

  Subsequently, the threshold value when the false alarm is generated in the preliminary inspection stored in the inspection result storage device 150 is confirmed, and the coefficient stored in the coefficient table 133 is changed to the boundary 4b, It is set to a value larger than 1 so that false information does not occur in the area inside 4c, and remains 1 in the area outside the boundaries 4b and 4c. At this time, a different coefficient is set for the area inside the boundary 4b and the area inside the boundary 4c depending on the density of the false alarm. And this test | inspection is performed about the whole surface of a semiconductor wafer. The determination circuit 131 performs determination using a threshold value larger than that in the preliminary inspection in the regions inside the boundaries 4b and 4c shown in FIG. 5B, and in the region outside the boundaries 4b and 4c, Judgment is performed using the same threshold value.

  In this embodiment, the inspection area in the chip is divided into three areas. However, the present invention is not limited to this, and the inspection area in the chip is changed according to the density of false alarms generated in the preliminary inspection. You may divide | segment into 2 or 4 or more area | regions.

  According to the present embodiment, the inspection area in the chip is divided into a plurality of areas, and the threshold value used in the inspection of the area in which many false alarms are generated is larger than the threshold value used in the inspection of other areas. Thus, it is possible to suppress the occurrence of false information due to the difference in pattern type and density.

  According to the present embodiment described above, the threshold value can be easily reviewed by storing the threshold value used for determination in addition to the inspection result.

  In the embodiment described above, the foreign substance determination apparatus is configured to store the coefficient for changing the threshold value in the table, but the threshold value itself used in the determination circuit may be stored in the table. Good.

  In the embodiment described above, the foreign substance inspection method and the foreign substance inspection apparatus using the dark field image by the scattered light from the surface of the semiconductor wafer have been described. However, the present invention is based on the reflected light from the surface of the semiconductor wafer. The present invention can also be applied to a foreign matter inspection method and a foreign matter inspection apparatus using a bright field image.

  The present invention is not limited to inspection of semiconductor wafers, and can be widely applied to inspection of scratches, defects, dirt, etc. on the surface of various objects.

It is a figure which shows schematic structure of the foreign material inspection apparatus by one embodiment of this invention. It is a figure explaining the scanning of the light beam of a foreign material inspection apparatus. FIG. 3A is a view showing an example of the distribution of the false information at the time of the preliminary inspection in the semiconductor wafer, and FIG. 3B is a view showing an example of the divided area in the semiconductor wafer. FIG. 4A is a diagram illustrating an example of a difference between image signals and a threshold value during preliminary inspection, and FIG. 4B is a diagram illustrating an example of a difference between image signals and threshold value during main inspection. FIG. 5A is a diagram showing an example of the distribution in the chip as a result of the superimposed preliminary inspection, and FIG. 5B is a diagram showing an example of a divided area in the chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer 2, 2a, 2b, 2c, 2d ... Chip 3 ... False information 4a, 4b, 4c ... Boundary 10 ... Laser apparatus 20 ... Photoelectric conversion element 30 ... X scale 40 ... Y scale 100 ... Processing apparatus 110 ... A / D converter 120 ... image processing apparatus 130 ... foreign matter determination apparatus 131 ... determination circuits 132 and 133 ... coefficient table 140 ... coordinate management apparatus 150 ... inspection result storage apparatus.

Claims (6)

Irradiate the inspection object with the inspection light,
Detect the intensity of reflected or scattered light generated on the surface of the inspection object and the position in the inspection area,
A foreign matter inspection method for determining whether foreign matter is present on the surface of an inspection object from the intensity of detected reflected light or scattered light using a threshold value,
Preliminary inspection is performed to confirm the location of the generated false alarm,
Divide the inspection area into multiple according to the density of false alarms generated in the preliminary inspection,
Foreign matter characterized by determining whether foreign matter is present on the surface of the inspection object from the intensity of the detected reflected light or scattered light using different threshold values for each of the plurality of divided areas. Inspection method.   The foreign matter inspection method according to claim 1, wherein the inspection region of the entire semiconductor wafer as the inspection object is concentrically divided into a plurality of regions.   2. The foreign substance inspection method according to claim 1, wherein an inspection area in a chip formed on a semiconductor wafer as an object to be inspected is divided into a plurality of areas. Irradiating means for irradiating the inspection object with inspection light;
Intensity detecting means for detecting the intensity of reflected or scattered light generated on the surface of the object to be inspected;
Position detecting means for detecting the position of the reflected light or scattered light within the inspection region;
Based on the detection result of the position detection means, using a different threshold value for each of a plurality of areas obtained by dividing the inspection area, the intensity of the reflected light or scattered light detected by the intensity detection means is applied to the surface of the inspection object. A foreign matter inspection apparatus comprising: processing means for determining whether foreign matter is present.   The foreign matter inspection apparatus according to claim 4, wherein the processing unit uses a different threshold value for each of a plurality of regions obtained by concentrically dividing the inspection region of the entire semiconductor wafer as an inspection object.   5. The foreign substance inspection apparatus according to claim 4, wherein the processing means uses a different threshold value for each of a plurality of areas obtained by dividing an inspection area in a chip formed on a semiconductor wafer as an object to be inspected. .

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