JP5074058B2 - Foreign matter inspection method and foreign matter inspection device - Google Patents

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 inspection object such as a semiconductor wafer (wafer). In particular, the present invention relates to a foreign matter inspection method and a foreign matter inspection apparatus that determine whether or not foreign matter is present using a threshold value.

  A foreign matter inspection device that detects foreign matter on a wafer exists on the surface of a wafer by irradiating the surface of the semiconductor wafer with a light beam such as a laser beam and detecting reflected or scattered light generated on the surface of the wafer. A foreign matter detection system for detecting foreign matter to be detected, and a surface detection system for keeping the distance of the wafer surface constant with respect to the foreign matter detection system.

  Conventionally, assembly and adjustment have been performed so that the distance between the objective lens of the foreign object detection system and the wafer surface is the focal length based on the design specifications of the objective lens.

  The adjusted state is always maintained in the same state and inspected even when the type of wafer to be inspected and the manufacturing process steps of the semiconductor device are changed.

  However, the focal position of the foreign object detection system differs depending on the type of wafer to be inspected and the manufacturing process steps of the semiconductor device.

  For this reason, the conventional foreign matter inspection apparatus cannot sufficiently utilize the detection performance of the foreign matter detection system, and there is a problem that the detection performance varies depending on the type and process of the wafer.

  That is, the surface height position of the wafer (inspection object) detected by the surface height position detection means (surface detection system) and the focal position of the foreign object detection system depend on the type of wafer to be inspected and the manufacturing process steps of the semiconductor device. It was different.

  The surface height position detected by the surface detection system shifts the focus position of the foreign matter detection system up or down depending on the type of wafer to be inspected or the manufacturing process of the semiconductor device.

  Since the amount of deviation differs depending on the type and process of the wafer, it is necessary to measure the amount of deviation when creating the recipe and set it in the recipe file.

  It is an object of the present invention to enable inspection of foreign matters appropriate for the type and process of a wafer and to provide information useful for yield management without deteriorating foreign matter detection performance.

  One feature of the present invention is that the inspection object including the wafer is irradiated with inspection light, the light reflected or scattered from the inspection object is received, and the foreign matter existing on the surface of the inspection object is detected based on the intensity of the received light. A foreign matter inspection method for inspecting the presence / absence of a wafer pattern formed on the object to be inspected, presence / absence of a film, presence / absence of a film, film material, film thickness, and focus offset so as to increase the intensity of received light. Can be adjusted. Thereby, an appropriate foreign matter inspection can be realized.

  Another feature of the present invention is that an appropriate foreign matter inspection is performed by adjusting the focus offset so that the received light intensity of the intensity detecting means is increased to the surface height position detected by the surface height position detecting means (surface detecting system). Can be realized.

  Still another feature of the present invention is that a function for calculating the offset amount can be incorporated into the recipe creation screen to create optimum conditions for the type and process of the wafer.

  According to the present invention, an appropriate foreign matter inspection can be performed even if the wafer type, the wafer type and the process are different, and the inspection can be performed without deteriorating the detection sensitivity of the foreign matter.

  The surface inspection apparatus of the present invention can be applied to a flat inspection object such as a semiconductor wafer, an insulator wafer (for example, a sapphire glass wafer, a quartz glass wafer, etc.) or a glass substrate for a liquid crystal panel display device. Below, the Example applied to the foreign material inspection of a semiconductor wafer is described according to an accompanying drawing.

  FIG. 1 is a diagram showing a schematic configuration of a foreign substance inspection apparatus according to an embodiment of the present invention.

  The foreign matter inspection apparatus according to the present embodiment includes a foreign matter detection system laser device 10, a foreign matter detection system photoelectric conversion element 20, an X scale 30, a Y scale 40, a surface height position detection system illumination device 50, and a surface height position detection. A system detector 60 (a set of two: 60a, 60b), a processing device 100, a control device 200 for the stage Z, and an image display device 300 are included.

  The laser device 10 generates laser light having a predetermined wavelength as inspection light, and irradiates the surface of the wafer 1 that is an object to be inspected obliquely.

  A wafer 1 having a chip 2 formed on the surface is mounted on a wafer table (stage Z) (not shown), and the stage Z moves in the Y direction and the X direction. Scans the surface of the wafer 1.

  FIG. 2 is a diagram for explaining scanning of the light beam of the foreign substance inspection apparatus.

  When the stage Z on which the wafer 1 is mounted moves in the Y direction, the light beam emitted from the laser device 10 moves on the surfaces of the chips 2a, 2b, 2c, 2d formed on the wafer 1 in the direction indicated by the arrow S1. Then, one line is scanned.

  Next, when the stage Z moves in the X direction, the scanning line moves in the X direction. When the stage Z 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 wafer 1 is scanned.

  That is, it is possible to scan the inspection light over the entire surface of the wafer 1 by moving the stage Z in the horizontal and vertical directions.

  In FIG. 1, the light beam irradiated obliquely onto the surface of the wafer 1 is scattered by a pattern or foreign matter on the surface of the wafer 1 to generate scattered light.

  The photoelectric conversion element 20 includes, for example, a TDI (Time Delay and Integration) sensor, a CCD (Charge Coupled Device) sensor, a photomultiplier tube (photomultiplier), and the like, and receives scattered light generated on the surface of the wafer 1. The intensity is converted into an electric signal and output to the processing apparatus 100 as an image signal.

  The X scale 30 and the Y scale 40 are made of, for example, a laser scale, and detect the position of the wafer 1 in the X direction and the Y direction, 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 an 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 of the inspection light is completed. The image signal 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 apparatus 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, a coefficient for changing the threshold value is stored in association with the 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 where the current light beam is irradiated on the wafer 1 based on the position information of the wafer 1 input from the X scale 30 and the Y scale 40, and the coordinates Output information.

  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.

  The foreign substance detection system laser device 10 is referred to as irradiation means for irradiating the inspection object with inspection light.

  The photoelectric conversion element 20 of the foreign substance detection system is referred to as light intensity detection means that receives light reflected or scattered from the surface of the inspection object and detects the light intensity.

  The illumination device 50 of the surface height position detection system is referred to as surface height position detection irradiating means for irradiating the inspection object with detection light for detecting the surface height position.

  The detector 60 (a set of two: 60a, 60b) of the surface height position detection system is called surface height position detecting means for detecting the surface height position of the object to be inspected. The surface height position detecting means has two detectors having different detection center positions in the vertical direction of the inspection object.

  The foreign matter determination device 130 is referred to as foreign matter determination means that inspects or determines the presence or absence of foreign matter present on the surface of the object to be inspected based on the light intensity data detected by the light intensity detection means.

  The control device 200 controls vertical position varying means that varies the vertical position of the object to be inspected by moving the stage up and down.

  A case where the threshold value is partially changed in the inspection area of the entire wafer 1 will be described.

  First, a preliminary inspection is performed on the entire surface of the 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.

  The focal position of the foreign object detection system will be described.

  The function of detecting reflected light or scattered light generated on the surface of the wafer 1 is a foreign matter detection system. The detection system includes a lighting device (laser device 10) and a lens (photoelectric conversion element 20) that collects reflected light or scattered light. The focus is on the optimal wafer surface position for detecting foreign matter. For example, the surface position of the wafer is aligned with the focal position of the detection lens. This position is the focal position of the foreign object detection system.

  The alignment focus position of the surface detection (surface height position detection) system will be described.

  Beam illumination of the illumination device 50 of the surface height position detection system is incident on the surface of the wafer 1 from an oblique direction, and the beam regularly reflected on the surface of the wafer 1 is detected by the two photoelectric conversion elements 60a and 60b, and an electric signal is detected. Get. It is possible to detect the position of the surface of the wafer 1 by appropriately arranging the angle and beam diameter of the beam illumination and the positions of the two photoelectric conversion elements 60a and 60b.

  This surface height position detection function is a surface detection system. When the position of the wafer 1 is changed in the height direction, there are two points at which the detection of the electric signals obtained from the two photoelectric conversion elements 60a and 60b is maximized. Between the two points where the two detection maxima are shown, there is an intermediate point where both electrical signals have the same value. The intermediate point is set as the alignment focus position of the surface detection system. This alignment focal position is calculated and calculated by the foreign substance inspection apparatus.

  The relationship between surface detection (surface height position detection) and foreign object detection will be described with reference to FIGS. 3, 4, and 5.

  The factory adjustment shown in FIG. 3 will be described.

  Adjustment is performed using a sample that has no film or pattern on the surface, such as a silicon wafer.

  Beam illumination of the illumination device 50 shown in FIG. 3A is performed, the wafer 1 is moved in the stage Z direction (up and down direction), and electric signals detected by the two photoelectric conversion elements 60a and 60b are taken.

  Two detection maximum electric signals as shown in the upper part of FIG. 3B are obtained. An intermediate point between the electric signal of 60a indicating the maximum value at the lower height position and the electric signal of 60b indicating the maximum value at the upper height position is calculated as the alignment focal position.

  The stage is moved up and down, and the surface (foreign particle observation point) of the wafer 1 is aligned with the alignment focal position. Thereby, since the focal point of the photoelectric conversion element 20 coincides with the surface of the wafer 1, the received light intensity of the intensity detecting means is adjusted to be maximum (strongest).

  As described above, at the time of shipment from the factory, the focus offset is adjusted to the focus position so that the light receiving intensity of the intensity detecting means is increased, so that an appropriate foreign object inspection can be performed. The user also performs foreign matter inspection on wafers with films and patterns.

  First, adjustment of the film-coated wafer on the user side shown in FIG. 4 will be described.

  In many cases, the foreign matter inspection of the film-coated wafer 1 shown in FIG. 4 includes the surface of the film and the surface of the wafer 1 positioned below the film.

  In the foreign matter inspection of the film-coated wafer 1, the alignment focal point position detected by the surface detection system comes to (A) (film surface) in FIG. In the foreign matter inspection of the film-coated wafer 1, it is necessary to focus on the position (b). Therefore, the wafer 1 is moved somewhat upward. By adjusting the focus offset, the surface of the wafer 1 under the film (foreign particle observation point) is moved to the alignment focus position, and the intensity detection means is focused, so that the light receiving intensity can be increased.

  This focus offset value is calculated by a focus offset calculation processing means described later.

  Next, in the foreign substance inspection of the patterned wafer 1 shown in FIG. 5, the focus offset is adjusted to move the foreign substance observation point from the calculated alignment focal position to a predetermined position.

  As shown in FIG. 5A, in the wafer 1 with a pattern, two light beams that are specularly reflected on the pattern surface of the wafer 1 and where there is no pattern are generated.

  The electrical signals of the two photoelectric conversion elements 60a and 60b that have detected the two light beams have slopes on the right side as shown by peaks (electrical signals) of 60a and 60b as shown in the upper side of FIG. It is detected in a state of moving from the dotted line position to the solid line position.

  That is, since the peaks of the peaks 60a and 60b (electrical signals) move in the stage Z direction, the calculated alignment focal position is detected at a position above the original position.

  Therefore, the position of the wafer 1 is moved somewhat downward from the calculated alignment focus position. By adjusting the focus offset, the wafer surface (foreign particle observation point) is adjusted to the original alignment focus position, and the intensity detection means is focused, so that the received light intensity can be increased.

  This focus offset value is calculated by a focus offset calculation processing means described later.

  The optimization of the focus offset will be described.

  This optimization is particularly effective for a wafer with a film or a pattern as described with reference to FIGS.

  First, a wafer sample to be measured is prepared, and general measurement conditions for measuring it are created.

  As this wafer sample, it is preferable to use a wafer 1 with a film or a pattern coated with PSL (polystyrene latex) for detection as a foreign substance, depending on the application to be adjusted. A foreign matter inspection is performed using these measurement conditions, and the result is obtained.

  Note that the focus offset at this time is a value at the time of factory shipment (usually zero). Then, the foreign substance inspection result is displayed on the image display device as a foreign substance map.

  One or a plurality of foreign substance inspection points to be noticed are selected by the user's operation (inspection area setting means), and then the focus optimization is instructed. In response to this, the inspection apparatus performs the next process (focus proper process instruction means).

  Image capture is performed (image collection unit) while changing the focus offset (position changing unit) at the designated foreign matter inspection location.

  That is, the stage is moved in the vertical direction, and the received light intensity data for each focus offset value is collected by the intensity detection means (the stage XY operation is performed to collect the output value of the foreign matter detection sensor in a planar shape).

  With this processing, foreign object images corresponding to the position of the foreign object inspection × the number of times of capturing can be collected. A part for inspection of foreign matter is extracted from the image and a luminance value (light reception intensity) of the part for inspection of foreign matter is obtained.

  Then, an appropriate focus offset value for inspection is obtained from a graph showing the luminance values with respect to those focus offset values.

  The appropriate focus offset value may be, for example, the peak position of the luminance value, or may be a value obtained by multiplying, dividing, or subtracting or adding a predetermined coefficient to the peak position value. .

  These calculation processes are executed by the processing apparatus 100 and are obtained from a predetermined algorithm (focus offset calculation processing means).

  The graph is displayed on an image display device 300 such as a CRT or a flat panel display (luminance value curve display means).

  In this way, it is possible to select a place where the light intensity of the light intensity detecting means is maximum even for the wafer with a film or pattern described with reference to FIGS.

  According to the above embodiment, it is possible to perform an appropriate inspection for the type and process of the wafer and to provide information useful for yield management without degrading the detection performance, which is useful for finding a problem in the process.

  In the above embodiment, the foreign substance inspection method and the foreign substance inspection apparatus using the dark field image due to the scattered light from the surface of the wafer have been described, but the present invention is not limited to the dark field type inspection apparatus, The present invention can also be applied to a bright field foreign matter inspection method and a foreign matter inspection apparatus using a bright field image by reflected light from the surface of a wafer.

  In addition to foreign matter inspection devices, it should be widely applied to inspection devices using light, such as surface inspection devices, defect inspection devices, appearance inspection devices, mask inspection devices, liquid crystal substrate inspection devices, bevel inspection devices, disk inspection devices, etc. Can do.

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

1 is a diagram illustrating a schematic configuration of a foreign matter inspection apparatus according to an embodiment of the present invention. FIG. 5 is a diagram showing a foreign matter inspection by scanning the surface of a wafer with a light beam according to an embodiment of the present invention. It is a figure which concerns on the Example of this invention, and is a figure which shows the focusing at the time of factory shipments. FIG. 10 is a diagram illustrating a focus offset when a user handles a film-coated wafer according to an embodiment of the present invention. It is a figure which concerns on the Example of this invention, and is a figure which shows the focus offset when the user side handled the wafer with a pattern.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wafer, 2, 2a, 2b, 2c, 2d ... Chip | tip ... 10 ... Laser apparatus (irradiation means to irradiate inspection light), 20 ... Photoelectric conversion element (Light intensity detection means to detect light intensity), 30 ... X Scale, 40 ... Y scale, 50 ... Surface detection system illumination device (surface height position detection irradiation means), 60 ... Surface detection system detector (surface height position detection means), 100 ... Processing device, 110 ... A / D converter, 120 ... image processing device, 130 ... foreign matter determination device (foreign matter determination means), 131 ... determination circuit, 132, 133 ... coefficient table, 140 ... coordinate management device, 150 ... inspection result storage device, 200 ... stage Z control device, 300... Image display device.

Claims (3)

An irradiation means for irradiating the inspection object with inspection light;
A light intensity detecting means for detecting light intensity by receiving light reflected or scattered from the surface of the inspection object;
Foreign matter determination means for inspecting or determining the presence or absence of foreign matter present on the surface of the inspection object from the light intensity data detected by the light intensity detection means;
A stage for placing the inspection object;
Vertical position varying means for varying the vertical position of the object to be inspected by moving the stage up and down;
Surface height position detecting means for detecting the surface height position of the inspection object,
A foreign matter inspection method for adjusting the surface height position detection means so that the light reception intensity of the light intensity detection means is increased,
The surface height position detecting means has two detectors having different detection center positions in the vertical direction of the inspection object,
The stage to be moved up and down detects the two points where the electrical signals from the two detectors are respectively maximum, and the test object is in the middle between the height position for one of the two points and the height position for the other. The height position of the object is the focal position on the film of the inspection object ,
Further, the vertical position changing means, the relative difference between the focal position on the surface of the focal position and the object to be inspected on the membrane of the object to be inspected, detected by the light receiving intensity of the light intensity detecting means the Change the vertical position of the inspection object based on the electrical signal detected by the surface height position detection means so as to strengthen on the surface of the inspection object,
The light intensity data inspected by the light intensity detecting means is light intensity data when the focal position is a focal position on the surface of the object to be inspected. An irradiation means for irradiating the inspection object with inspection light;
A light intensity detecting means for detecting light intensity by receiving light reflected or scattered from the surface of the inspection object;
Foreign matter determination means for inspecting or determining the presence or absence of foreign matter present on the surface of the inspection object from the light intensity data detected by the light intensity detection means;
A stage for placing the inspection object;
Vertical position varying means for varying the vertical position of the object to be inspected by moving the stage up and down;
Surface height position detecting means for detecting the surface height position of the inspection object,
A foreign matter inspection apparatus that adjusts the surface height position detection means so that the light reception intensity of the light intensity detection means increases,
The surface height position detecting means has two detectors having different detection center positions in the vertical direction of the inspection object,
The stage to be moved up and down detects the two points where the electrical signals from the two detectors are respectively maximum, and the test object is in the middle between the height position for one of the two points and the height position for the other. The height position of the object is the focal position on the film of the inspection object ,
Further, the vertical position changing means, the relative difference between the focal position on the surface of the focal position and the object to be inspected on the membrane of the object to be inspected, detected by the light receiving intensity of the light intensity detecting means the Change the vertical position of the inspection object based on the electrical signal detected by the surface height position detection means so as to strengthen on the surface of the inspection object,
The light intensity data inspected by the light intensity detecting means is light intensity data when the focal position is a focal position on the surface of the object to be inspected. In the foreign matter inspection apparatus according to claim 2,
In the surface inspection of the inspection object, the foreign object inspection apparatus is characterized in that the focal position is moved from the film of the inspection object to the surface of the inspection object by moving the inspection object upward.

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