JP2006018054A - Mask inspection apparatus and mask inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform mask defect inspection with high accuracy by quantitatively judging a stripe defect caused in a mask. <P>SOLUTION: A mask inspection apparatus 1 inspects a defect in a mask M by acquiring the light transmitted or reflected by a mask M having a predetermined pattern formed thereon, wherein the apparatus is equipped with: a light source 11 which irradiates the mask M with light at a wavelength longer than the minimum line width of the pattern in the mask M; a line sensor 12 which acquire transmitted light or reflected light by the mask M of the light emitting from the light source 11; and an operating unit 13 which obtains the intensity of the transmitted light or reflected light acquired by the line sensor 12 for each cell prepared by dividing the inspection region of the mask M into a matrix state, and performs calculation using the intensity of each cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mask inspection apparatus and a mask inspection method for inspecting a streak-like defect of a mask on which a predetermined pattern is formed.

  In a video system device (CCD, LCD, CMOS sensor, etc.), it is formed with a periodic pattern in which fine openings are repeatedly arranged. In such a product, when unevenness occurs on the device in the device manufacturing stage, it appears as an imaging result or a video output result. One cause of the occurrence of this unevenness is a problem in lithography technology using a photomask (hereinafter simply referred to as “mask”). In other words, when manufacturing a device pattern by transferring it onto a wafer or glass substrate using a lithography technique, if the pattern is misaligned or misaligned on the original photomask, this misalignment is transferred as it is. As a result, in an image system device such as a CCD, this leads to non-uniformity of the opening serving as a light receiving portion.

  Visual unevenness (stripes, bands, spots, discoloration) on the photomask is guaranteed. Projector light (100,000,000 Lux) is projected onto the front and back of the photomask to open the pattern. A human being visually detects (sensory inspection) a difference in light density (brightness / darkness) caused by a change in luminance from the portion or a refracted light reflected on the pattern. Also disclosed is a method of detecting image density unevenness by processing an image obtained by photographing an inspection object (see, for example, Patent Document 1).

JP 2003-91728 A

  However, in visual (sensory test) determination, individual differences are greatly affected by differences in skill level, subjectivity of inspectors, and the like, and the determination also varies. In addition, in the method of detecting the unevenness from the image shading by performing the signal processing of the luminance change from the pattern opening using image processing or a line sensor, the image processing (calculation time) for detecting the unevenness from the image shading is large. There is a problem that more time is required to obtain the inspection result as the area to be inspected becomes larger.

  The present invention has been made to solve such problems. That is, according to the present invention, in a mask inspection apparatus that inspects a mask defect by acquiring light that is transmitted or reflected through a mask on which a predetermined pattern is formed, light having a wavelength longer than the minimum line width in the mask pattern is used. A light source for irradiating the mask, a light receiving means for acquiring transmitted or reflected light of the light emitted from the light source, an intensity value of the transmitted light or reflected light acquired by the light receiving means, and an inspection area of the mask in a matrix form And a calculation means for performing calculation using the intensity value in each cell.

  According to another aspect of the present invention, there is provided a mask inspection method for inspecting a defect of a mask by acquiring light that is transmitted or reflected through a mask on which a predetermined pattern is formed, and light having a wavelength longer than a minimum line width in the mask pattern. The step of irradiating the mask, the step of acquiring the transmitted light or reflected light of the irradiated light by the mask, and the intensity value of the acquired transmitted light or reflected light for each cell obtained by dividing the inspection area of the mask into a matrix And calculating using the intensity value in each cell.

  In the present invention, the mask having a predetermined pattern is irradiated with light having a wavelength longer than the minimum line width of the pattern, and the transmitted light or reflected light is obtained. Accordingly, an intensity value of transmitted light or reflected light with a moderately reduced resolution can be obtained, and even a streak-like defect resulting from a slight shift in pattern dimensions can be detected accurately.

  Therefore, according to the present invention, it is possible to objectively inspect streaky defects generated on the mask without relying on empirical ones by human eyes. In addition, by incorporating an element that can be expressed by a numerical value of the light quantity as an inspection determination material, it becomes possible to quantitatively determine the occurrence of streak-like defects. Furthermore, in the present invention, since inspection can be performed at several tens of microns to several tens of microns at a time, the inspection time can be significantly reduced as compared with the conventional inspection method. This makes it possible to improve mask quality control and reliability.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, before explaining the mask inspection apparatus and the mask inspection method according to the present embodiment, a stripe-like defect generated in the mask will be described. FIG. 1 is a schematic diagram for explaining streaky defects. For example, the pattern in which streak-like defects (unevenness) occur in the imaging system device is the same pattern regularly arranged, and when the line width of the light shielding part or the transmission part varies, the regularity of the pattern changes, When the mask is viewed macroscopically in this state, it can be seen as streak-like defects.

  As shown in FIG. 1A, in this case, in the pattern P made up of lines and spaces, if there is a part where the line pattern is thick only partly, the part becomes a streak when observed as the entire mask M. appear. On the other hand, as shown in FIG. 1B, when the lines and spaces are regularly produced as designed, they do not appear as streak-like defects (unevenness) even when viewed macroscopically.

  In this embodiment, when inspecting such a streak-like defect, an apparatus is used that irradiates a mask with light having a predetermined wavelength, takes in the transmitted light or reflected light, and inspects with an image. At this time, inspection is performed with a reduced resolution. When the resolution is lowered, the amount of fluctuation of the light amount increases, which is suitable for detecting streaky unevenness in a macro manner.

  FIG. 2 is a schematic diagram for explaining the mask inspection apparatus according to the present embodiment. That is, the mask inspection apparatus 1 includes a light source 11 that irradiates light to the mask M to be inspected, a zoom lens L1 that adjusts a range in which the light from the light source 11 is applied to the mask M, and light transmitted through the mask M (transmission). Zoom lens L2 that adjusts (light) to a predetermined range, a line sensor 12 that takes in light that has been adjusted by the zoom lens L2, and a calculation unit 13 that performs a predetermined calculation using an electrical signal acquired by the line sensor 12. And.

  Among these, the light source 11 can emit light having a wavelength longer than the minimum line width in the pattern of the mask M. By setting the wavelength of the light emitted from the light source 11 to a wavelength longer than the minimum line width in the pattern of the mask M, the line sensor 12 can acquire transmitted light with reduced resolution. In order to switch the wavelength of light emitted from the light source 11, a plurality of laser light sources having different wavelengths may be used, or light having a specific wavelength may be extracted by a spectroscope or an optical filter.

  In order to perform mask inspection using the mask inspection apparatus 1, first, light is applied to the mask M from the light source 11. At this time, the range of light applied onto the mask M is adjusted by the zoom lens L1 disposed between the light source 11 and the mask M. The zoom lens L2 and the line sensor 12 are installed on the opposite side with the mask M in between, and the range is adjusted by the zoom lens L2 so that the transmitted light is captured by the entire surface of the line sensor 12.

  In the mask inspection apparatus 1 of the present embodiment, since the light source 11 and the line sensor 12 are fixed, the mask M is moved in a direction perpendicular to the capturing direction of the line sensor 12 when changing the inspection range. The electrical signal obtained by the line sensor 12 is sent to the calculation unit 13, where a predetermined calculation is performed to detect streak-like defects.

  As light emitted from the light source 11, light having a wavelength longer than the minimum line width in the pattern of the mask M to be inspected as described above is used. In this embodiment, an infrared wavelength and Ar laser light are applied. The light that has been applied to the mask M passes through the mask M at a portion that is not shielded, and reaches the opposite side of the light source 11.

  In the mask inspection apparatus 1 of the present embodiment, one pixel cell is inspected by one inspection. The zoom lens L1 is inserted between the light source 11 and the mask M, and the range to be applied is varied according to the design rule of the pixel cell. In that case, the pixel cell portion to which the light is applied is captured by being enlarged or reduced to the same size as the light receiving portion of the line sensor 12. When the inspection of one pixel cell portion is completed, the photomask is moved in the direction perpendicular to the line direction of the line sensor 12 by the area (hereinafter referred to as inspection pitch) that has been inspected at a time, and the inspection is performed again. This operation is executed in the set inspection area.

  Next, as a specific example, an experimental result in a 1 μm line & space (1: 1) as shown in FIG. 3 is shown. The line width of the pattern A at the center of the five lines & spaces is increased or decreased by 0.05 μm and irradiated with light having a wavelength of 1 μm to 3 μm (in increments of 0.2 μm). Incorporation of transmitted light by the line sensor matches the direction of the line pattern with the direction of the line sensor, scans the mask in a direction perpendicular to the line pattern, and transmits the transmitted light using the five patterns shown in FIG. 3 as the inspection area. Capture. The waveforms shown in FIGS. 4 to 12 indicate the amount of received light along the direction orthogonal to the five line patterns in the inspection area.

  4 (a) to 4 (d), 5 (a) to 5 (d), and 6 (a) to 6 (c), the pattern A shown in FIG. Is taken in when 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm and 3.0 μm, respectively. It is a waveform.

  7 (a) to (d), FIGS. 8 (a) to (d), and FIGS. 9 (a) to 9 (c) show the light to be irradiated when the line width of the pattern A shown in FIG. 3 is 1.0 μm. When the wavelengths of the laser beam are 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, and 3.0 μm, respectively This is the waveform of the captured light.

  10 (a) to 10 (d), 11 (a) to 11 (d), and 12 (a) to 12 (c) show the light to be irradiated when the line width of the pattern A shown in FIG. When the wavelengths of the laser beam are 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, and 3.0 μm, respectively This is the waveform of the captured light.

  In the waveform of each captured light, the shorter the wavelength, the greater the amount of light and the waveform becomes sharper. Conversely, the longer the wavelength, the lower the amount of light and the waveform becomes dull. In other words, the longer the wavelength, the lower the resolution. In this way, while the waveform changes depending on the wavelength, the difference in the line width of the pattern A (difference from the line width of other patterns) is the waveform at a wavelength of about 1.8 to 2 times the line width of the target pattern. It appears as a disturbance.

  As a result, the waveform is not significantly disturbed at wavelengths of 1.0 μm to 1.6 μm and 2.2 μm to 3.0 μm, but the waveform is significantly disturbed at wavelengths of 1.8 μm and 2.0 μm. If the wavelength is too long, the pattern itself is not resolved, and cannot be detected.

  As another specific example, an experimental result with a mask in which 1 μm square hole patterns (1: 1) as shown in FIG. 13 are arranged in 5 × 5 is shown. In this experiment, the line width of the C row is increased or decreased by 0.05 μm, and light having a wavelength of 1 μm to 3 μm (in increments of 0.2 μm) is applied. The transmission of the transmitted light by the line sensor is performed by making the direction of each column of A to E of the hole pattern HP shown in FIG. 13 coincide with the direction of the line sensor and scanning the mask in the direction perpendicular to each column in FIG. The transmitted light is captured using the 5 × 5 hole pattern shown as an inspection area. The waveforms shown in FIGS. 14 to 22 show the amount of light received along the direction orthogonal to each column of the hole pattern at the center of each column among the hole patterns HP in the inspection area.

  14 (a) to (d), FIGS. 15 (a) to (d), and FIGS. 16 (a) to (c) are the wavelength of the light to be irradiated when the line width of the pattern A shown in FIG. 13 is 0.95 μm. Is taken in when 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm and 3.0 μm, respectively. It is a waveform.

  FIGS. 17A to 17D, FIGS. 18A to 18D, and FIGS. 19A to 19C show the light to be irradiated when the line width of the pattern A shown in FIG. 13 is 1.0 μm. When the wavelengths of the laser beam are 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, and 3.0 μm, respectively This is the waveform of the captured light.

  20 (a) to 20 (d), 21 (a) to 21 (d), and 22 (a) to 22 (c) show the light to be irradiated when the line width of the pattern A shown in FIG. When the wavelengths of the laser beam are 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, and 3.0 μm, respectively This is the waveform of the captured light.

  In the example of the hole pattern as well, in the waveform of each captured light, the amount of light increases as the wavelength becomes shorter and the waveform becomes sharper, whereas the amount of light decreases as the wavelength increases. Bluntness occurs. If the line width of the target pattern is narrower than the reference while the waveform changes depending on the wavelength in this way, the pattern width difference (other pattern widths) is about 1.4 to 2 times the pattern width. If the pattern is thicker than the reference, the pattern width difference (difference from other pattern widths) is the waveform distortion. It appears as

  As a result, in the pattern thinner than the reference, the waveform is not disturbed at wavelengths of 1.0 μm to 1.2 μm and 2.2 μm to 3.0 μm, but the waveform is disturbed at a wavelength of 1.4 μm to 2.0 μm. It has become prominent. Also, in the pattern thicker than the reference, the waveform is not significantly disturbed at wavelengths of 1.0 μm to 1.6 μm and 2.2 μm to 3.0 μm, but the waveform is significantly disturbed at wavelengths of 1.8 μm and 2.0 μm. It has become. If the wavelength is too long, the pattern itself is not resolved, and cannot be detected.

  As described above, the wavelength of the light emitted from the light source is longer than the minimum line width of the pattern to be inspected, preferably about 1.4 to 2 times the minimum line width. It is possible to capture the difference in line width as a change in waveform.

  Next, image processing in the calculation unit 13 for transmitted light detected by the line sensor 12 will be described. The arithmetic unit 13 performs an operation to clearly represent the degree of waveform disturbance by numerical values or display using a signal (waveform intensity) captured using light having a wavelength at which the difference in pattern width described above is significant. Do.

  First, at the time of image processing, the light amount of a predetermined wavelength detected by the line sensor 12 in one inspection is digitized for each cell by dividing the inspection area into a matrix. FIG. 23A shows a predetermined inspection area divided into 6 × 6 cells, and the amount of light (intensity value) in each cell is expressed numerically. In addition, the numerical value shown corresponding to each cell is an example for making the explanation easy to understand.

  Next, when the digitization of the light amount is completed, the calculation is performed based on the digitized light amount value of each cell. The difference in the amount of light from the cell at the end is calculated in order from the end cell, and the same processing is performed up to the cell at the opposite end. The result is shown in FIG. Thereafter, the maximum value and the minimum value are calculated from the numerical values of the processed differences, and color separation is performed between them. For example, the color classification is performed in two steps, three steps, and four steps. FIG. 23 (c) shows a two-stage display, FIG. 24 (a) shows a three-stage display, and FIG. 24 (b) shows a four-stage display. This color-coded display is displayed on a display means such as a monitor. In the figure, instead of color coding, the dot density is different.

  And the part which becomes the nonuniformity of a mask is recognized from the result of these three types of color classification. For example, if the line & space pattern is accurately manufactured, the two colors corresponding to the line & space are alternately arranged. However, if the line width of one of the lines is different, the color coding is disturbed, and the portion where the unevenness is generated can be accurately recognized.

  In the example described above, good results have been obtained by irradiating light having a wavelength approximately twice the minimum line width of the pattern, but actually, irradiating light of a plurality of wavelengths simultaneously, A method of confirming a change in the amount of light at each wavelength may be used. Further, although transmitted light is taken as an example at the time of inspection, reflected light can also be applied. In addition, the scanning direction at the time of inspection is not limited to the vertical direction, and vertical scanning can be inspected if horizontal scanning is performed. Regarding image processing, the above example is merely an example, and the present invention is not limited to this method.

It is a schematic diagram explaining a stripe-like defect. It is a schematic diagram explaining the mask inspection apparatus which concerns on this embodiment. It is a schematic diagram which shows the pattern of a line & space. It is FIG. (1) which shows the light reception amount along the direction orthogonal to a line pattern. It is a figure (the 2) which shows the light reception amount along the direction orthogonal to a line pattern. FIG. 10 is a diagram (No. 3) illustrating the amount of received light along a direction orthogonal to the line pattern. It is FIG. (4) which shows the light reception amount along the direction orthogonal to a line pattern. It is FIG. (5) which shows the light reception amount along the direction orthogonal to a line pattern. It is FIG. (6) which shows the light reception amount along the direction orthogonal to a line pattern. It is FIG. (7) which shows the light reception amount along the direction orthogonal to a line pattern. It is FIG. (8) which shows the received light quantity along the direction orthogonal to a line pattern. It is FIG. (9) which shows the light reception amount along the direction orthogonal to a line pattern. It is a schematic diagram which shows a hole pattern. It is FIG. (1) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. It is FIG. (2) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. FIG. 11 is a diagram (No. 3) illustrating the amount of received light along a direction orthogonal to the row of hole patterns. FIG. 14 is a diagram (No. 4) illustrating the amount of received light along the direction orthogonal to the hole pattern rows; It is FIG. (5) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. It is FIG. (6) which shows the received light quantity along the direction orthogonal to the row | line | column of a hole pattern. It is FIG. (7) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. It is FIG. (8) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. It is FIG. (9) which shows the light reception amount along the direction orthogonal to the row | line | column of a hole pattern. It is a schematic diagram (the 1) explaining the example of a calculation. It is a schematic diagram (the 2) explaining the example of a calculation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Mask inspection apparatus, 11 ... Light source, 12 ... Line sensor, 13 ... Operation part, L1 ... Zoom lens, L2 ... Zoom lens, M ... Mask

Claims (6)

In a mask inspection apparatus for inspecting a defect of a mask by acquiring light that transmits or reflects through a mask on which a predetermined pattern is formed,
A light source for irradiating the mask with light having a wavelength longer than the minimum line width in the mask pattern;
A light receiving means for acquiring transmitted light or reflected light by the mask of the light emitted from the light source;
Calculating means for obtaining an intensity value of the transmitted light or reflected light obtained by the light receiving means for each cell obtained by dividing the inspection area of the mask into a matrix, and performing an operation using the intensity value in each cell; A mask inspection apparatus comprising: The mask inspection apparatus according to claim 1, wherein the light source includes a switching unit that switches and emits light having a plurality of wavelengths. The mask inspection apparatus according to claim 1, wherein the calculation unit calculates a difference between intensity values of adjacent cells divided among the cells. In a mask inspection method for inspecting a defect of a mask by acquiring light that passes through or reflects a mask on which a predetermined pattern is formed,
Irradiating the mask with light having a wavelength longer than the minimum line width in the mask pattern;
Obtaining transmitted light or reflected light by the mask of the irradiated light;
Obtaining the intensity value of the acquired transmitted light or reflected light for each cell obtained by dividing the inspection area of the mask into a matrix, and performing a calculation using the intensity value in each cell. Mask inspection method. In the step of irradiating the mask with light, the light having a plurality of wavelengths is sequentially switched and irradiated,
The step of acquiring the transmitted light or the reflected light of the irradiated light sequentially acquires the transmitted light or the reflected light from the mask of the light having the plurality of wavelengths. Mask inspection method. The mask inspection method according to claim 4, wherein, in the step of performing the calculation using the intensity value in each cell, a difference in intensity value between adjacent cells among the cells divided in the matrix is calculated.

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