JP2004184142A - Defect inspection method and apparatus therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently separate a signal from a pattern from a signal from a defect, in a technique for inspecting a micro circuit pattern using an image formed by irradiation with a white light, a laser beam or an electron beam. <P>SOLUTION: This inspection apparatus for a semiconductor device is provided with a function for shielding selectively diffracted light of the circuit pattern existing on an object to be inspected. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for optically inspecting a defect generated on a substrate on which a pattern is formed in a manufacturing line of a semiconductor device, a liquid crystal, a magnetic head, or the like.
[0002]
[Prior art]
The inspection of a semiconductor wafer will be described as an example.
[0003]
In the conventional semiconductor manufacturing process, the presence of foreign matter on a semiconductor substrate (wafer) causes defects such as wiring insulation failure and short circuit, and furthermore, when a semiconductor element is miniaturized and fine foreign matter is present in the semiconductor substrate. In addition, the foreign matter causes a failure in insulation of the capacitor and a destruction of the gate oxide film. These contaminants are generated by various causes such as those generated from the movable part of the transfer device, those generated from the human body, those generated by reaction in the processing device by process gas, and those mixed in chemicals and materials. It is mixed in the state of. In a similar liquid crystal display element manufacturing process, if a foreign substance enters the pattern or some kind of defect occurs, the pattern cannot be used as a display element.
[0004]
The situation is the same in the manufacturing process of a printed circuit board, and the intrusion of foreign matter causes a short circuit of a pattern and a defective connection. As one of the conventional techniques for detecting foreign matter on a semiconductor substrate of this type, as described in Patent Document 1, when a semiconductor substrate is irradiated with a laser and foreign matter adheres to the semiconductor substrate, By detecting the scattered light from the foreign matter generated in the above and comparing it with the inspection result of the same type of semiconductor substrate inspected immediately before, eliminating false alarms due to patterns, enabling highly sensitive and highly reliable inspection of foreign matter and defects. There is something.
[0005]
Further, as a technique for inspecting the foreign matter, there is known a method of irradiating a wafer with coherent light, removing light emitted from a repetitive pattern on the wafer with a spatial filter, and emphasizing and detecting a foreign matter or defect having no repeatability. Have been. Further, a circuit pattern formed on the wafer is irradiated from a direction inclined by 45 degrees with respect to a main straight line group of the circuit pattern, and zero-order diffracted light from the main straight line group is input into the aperture of the objective lens. A foreign matter inspection apparatus that does not allow the foreign matter to be inspected is known from Patent Document 2. This prior art 3 also describes that a line group other than the main line group is shielded from light by a spatial filter. Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7 are known as conventional techniques relating to a defect inspection apparatus for foreign matter and the like and a method therefor.
[0006]
[Patent Document 1]
JP 62-89336 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 1-117024 [Patent Document 3]
JP-A-1-250847 [Patent Document 4]
JP-A-6-258239 [Patent Document 5]
JP-A-6-324003 [Patent Document 6]
Japanese Patent Application Laid-Open No. 8-21089 [Patent Document 7]
JP-A-8-271437
[Problems to be solved by the invention]
As described in the above prior art, in an apparatus for inspecting various fine patterns including a semiconductor device, a signal from a defect and a signal from the pattern (pattern noise) are efficiently separated by spatial filtering. Since a wide light-shielding plate is used due to the problem of mechanical accuracy, the number of diffracted lights from a light-shieldable pattern is limited.
[0008]
An object of the present invention is to inspect fine circuit patterns using an image formed by irradiating white light, single-wavelength light, or laser light. Is to detect.
[0009]
[Means for Solving the Problems]
In order to achieve the first object, a light-shielding pattern is transferred to (1) a mirror array or a reflective liquid crystal, or (2) a transparent liquid crystal, or (3) an optically transparent substrate as a means for shielding diffracted light. Or (4) a substrate or film etched leaving a light-shielding pattern, or (5) optically capable of changing the transmittance by heating, quenching or light irradiation, or a change in an electric or magnetic field. A transparent substrate or (6) a rod-shaped or plate-shaped light shielding plate was provided.
[0010]
In order to achieve the second object, a function is provided for changing a light-shielding pattern in accordance with a change in the pattern of diffracted light caused by a difference in the shape of a circuit pattern present on a test object at each location.
[0011]
In order to achieve the third object, a light-shielding pattern according to at least two or more diffracted light patterns in accordance with a change in the pattern of diffracted light resulting from a difference in the shape of a circuit pattern present on an object to be inspected at each location. With the ability to change
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of the configuration of the inspection apparatus. The scattered light from the wafer passes through the Fourier transform lens, and an image of the wafer is formed on the sensor surface. The scattered light from the repetitive pattern has a periodic light intensity distribution, and therefore forms a diffraction image on the Fourier transform surface of the lens according to the pattern repetition pitch. On the other hand, since the light intensity distribution of the scattered light from the defect is generally composed of random frequency components, no image is formed on the Fourier transform plane. Here, by shielding the diffracted light from the repetitive pattern by the spatial filter, most of the scattered light from the pattern can be shielded, while most of the scattered light from the defect can be passed. Thus, the scattered light from the pattern can be removed, and only the scattered light from the defect can be imaged on the sensor, so that a defect signal can be obtained with a high S / N.
[0013]
Since the purpose of the light-shielding plate is to shield the diffracted light, the light-shielding plate needs to be wider than the width of the diffracted light. Since the size of the aperture of the Fourier transform surface is a finite size determined by the design of the lens, the maximum number of spatial filters is determined by (Fourier transform surface opening diameter) 直径 (filter width). The conventional inspection apparatus uses a filter that is sufficiently wide compared to the width of the diffracted light due to the problem of mechanical accuracy, so that the number of light shielding plates is small. Therefore, only the diffracted light of the repetitive pattern of 5 mm pitch or less can be shielded on the wafer, and only a part of the diffracted light from the pattern of the SRAM area, the CCD circuit, and the liquid crystal circuit having the large pattern pitch can be shielded.
[0014]
In the present invention, high-precision positioning is enabled by changing the structure of the spatial filter. As a result, the filter width can be reduced, and it becomes possible to shield diffracted light from a repetitive pattern having a pitch of 25 mm or less using a large number of filters.
[0015]
FIG. 2 shows an example of the light blocking mechanism. A plate is soldered to a helical spring. This utilizes the fact that the spring expands and contracts accurately within the range of elastic deformation according to Hook's law. When a light-shielding material is attached to the corresponding portions of the two springs, the pitch of the filter can be accurately changed by simultaneously expanding and contracting the two springs.
[0016]
As a method of attaching the light shielding material to the spring, soldering, an adhesive, welding, or the like can be considered. When the filter and the spring are thick, welding is possible, but when the filter and the spring are thin, the filter or the spring is melted during welding, so that it becomes difficult to mount the filter and the spring. Therefore, when the filter and the spring become thin, soldering and an adhesive are preferred.
[0017]
FIG. 4 shows an example in which a light shielding plate is formed by using etching. It is easier to solder when the thickness of the spring attachment portion is almost the same as the diameter of the spring. Further, since the thickness of the light shielding plate is determined by the condensing diameter of the diffracted light and the mechanical accuracy of the filtering unit, the thickness of the light shielding plate may be different between the spring mounting portion and the light shielding position. In such a case, it is desirable to perform an arc-shaped processing as shown in an enlarged view of FIG. 4 in order to prevent concentration of mechanical stress at the time of spring expansion and contraction and thermal stress at the time of soldering.
[0018]
When springs having the same winding direction are used, stress generated between the filter and the spring when the spring is expanded and contracted becomes a problem. By combining the right-handed spring and the left-handed spring, it is possible to cancel the stress generated on both sides of the light-shielding material, and it is possible to further improve the accuracy.
[0019]
FIG. 3 is an example of a spatial filter combining a right-handed spring and a left-handed spring. The graph of FIG. 19 plots the inclination of the light shielding plate when the filter spring is expanded and contracted, and it can be seen that the accuracy is improved by using a spring having a different winding direction.
[0020]
As the spatial filter, it is conceivable to use a transparent liquid crystal, a mirror array device, or the like in addition to the combination of the spring and the light shielding material.
[0021]
FIG. 5 is an example of a transmissive liquid crystal. By setting ON and OFF for each pixel, light transmission and light shielding can be selected, so that the degree of freedom in generating a light shielding pattern is higher than that of the above-described spring-type spatial filter. In general, a liquid crystal device uses polarized light to reduce the amount of light. However, a countermeasure can be taken by increasing the intensity of illumination light.
[0022]
Also, as shown in FIG. 7, a liquid crystal device generally has a drive circuit for each pixel, and thus has a problem that the aperture ratio is low. Since a low aperture ratio causes a decrease in transmittance and a diffraction phenomenon due to a lattice of liquid crystal pixels, it is desirable to use a liquid crystal device having an aperture ratio as high as possible (at least 60% or more). On the other hand, from the viewpoint of light shielding performance, it is desirable that the transmittance at the time of light shielding be as low as possible.
[0023]
In general, the contrast of a liquid crystal device is defined by the ratio of the amount of transmitted light during transmission and the amount of transmitted light during light shielding. The contrast value is preferably 800: 1 or more. FIG. 6 shows a mirror array device. Since the mirror array device generally has a high aperture ratio of 80% or more, the attenuation of the light amount and the influence of diffraction by the pixel grid are lower than those of the transmissive liquid crystal device, which is desirable as a spatial filtering device.
[0024]
FIG. 8 shows the configuration of the inspection apparatus when a mirror array device is used. The optical system has a mechanism for splitting an optical path in the middle of the optical system, and a sensor for observing a spatial filter surface at the same time. A light-shielding pattern is generated based on the image of the spatial filter captured by the sensor, and the mirror is driven by a unit that controls the mirror array. At this time, the diffracted light to be shielded is reflected by a mirror in a direction without a sensor. The light that is not blocked is reflected by the mirror as it is, and the light is captured by the sensor.
[0025]
FIGS. 9 and 10 illustrate cross sections of two types of mirror arrays. Mirrors are microelectronic devices made using semiconductor processes. The mirror supported by the support is driven by electrostatic attraction and repulsion with the electrode. When the system shown in FIG. 10 that can maintain an optically flat state is combined with an image forming optical system, the image forming accuracy is increased, which is desirable.
[0026]
As shown in FIG. 14, a semiconductor has a different wiring pattern depending on its function among chips (dies). Therefore, as shown in FIG. 15, the pattern of the diffracted light and the optimal light-shielding pattern corresponding thereto differ depending on the region.
[0027]
FIG. 16 shows an example of an inspection method, which is a method of inspecting a wafer by adjusting a spatial filter to a pattern having the largest area. This method has a problem that the sensitivity of an area where the filter is combined can be inspected with high sensitivity, but the sensitivity of other areas is reduced.
[0028]
FIG. 17 shows a method in which diffracted light of each pattern is merged (by taking a logical sum) to generate and inspect a light-shielding pattern. With this method, inspection can be performed evenly regardless of the pattern shape, but there is a problem that high-sensitivity inspection cannot be performed.
[0029]
FIG. 18 shows a method of inspecting a plurality of times by matching a spatial filter to each pattern. By merging inspection results of a plurality of times, highly sensitive inspection can be performed in any region. However, the problem is that the throughput is reduced because the inspection is performed a plurality of times. Considering a strategy of efficient inspection, the inspection method shown in FIG. 17 is desirable when an inspection apparatus sufficiently sensitive to a semiconductor process is used. When it is desired to inspect a specific pattern with high sensitivity when introducing a new process or starting up a line, the inspection method shown in FIG. 16 or FIG. 18 is desirable.
[0030]
FIG. 11 shows an example of an inspection apparatus provided with a plurality of spatial filter units. If a sufficient amount of illumination light can be secured, this method can inspect all areas with high sensitivity and high throughput. FIG. 12 shows a Fourier optical system. FIG. 13 shows an optical system for observing a Fourier transform plane.
[0031]
FIG. 20 shows an example of a scanning method when a diffraction image for one chip is taken in when a spatial filter is automatically set. As shown in FIG. 21, since the pattern of the diffracted light is determined by the circuit pattern of the chip, the change in the pattern of the diffracted light indicates that the circuit pattern on the chip has changed from one pattern to another. That is, by paying attention to the change in the pattern of the diffracted light, the layout information of the chip can be understood. Paying attention to this point, by taking in a diffraction light pattern for one chip and examining each diffraction pattern, it is possible to determine which region should use which spatial filter. This makes it possible to automatically set the spatial filter by combining the capturing of the diffracted light pattern for one chip with the image processing.
[0032]
FIG. 22 shows a setting sequence of the spatial filter. A diffraction image is obtained by directly observing design data, a wafer pattern, or a diffracted light pattern. Thereafter, a light-shielding pattern is generated by image processing, and a desired filter pattern can be generated. FIG. 23 shows an example of the inspection condition setting sequence.
[0033]
FIG. 24 shows a method of obtaining the pitch of the diffracted light from the pattern pitch.
[0034]
FIG. 25 shows the signal intensity of the pattern when the spatial filter is used and when it is not used. When a spatial filter is not used, a signal of a defect cannot be detected by a signal of a pattern. However, by using a spatial filter, a signal of a pattern is greatly attenuated, and a signal of a defect is acquired with a high S / N. It becomes possible.
[0035]
FIG. 26 shows the relationship between the inspection apparatus and the semiconductor manufacturing process. The inspection device inspects the wafer after the specific process. After the inspection, it is possible to give feedback to the original process by determining the details of the defect using a review device or the like. By repeating this, the yield of the semiconductor device can be improved.
[0036]
【The invention's effect】
According to the present invention, in a technology for inspecting a fine circuit pattern using an image formed by irradiating white light, single-wavelength light, or laser light, a foreign object defect can be detected with high sensitivity by high-precision spatial filtering. Can be detected.
[Brief description of the drawings]
FIG. 1 is a front view showing a schematic configuration of an inspection apparatus using spatial filtering.
FIG. 2 is a front view of a spatial filter example 1 (using a light-shielding plate and a right spring).
FIG. 3 is a front view of a spatial filter example II (combination of a light shielding plate, a right spring, and a left spring).
FIG. 4 is a front view of an etching plate.
FIG. 5 is a front view of a spatial filter example 3 (transmissive liquid crystal).
FIG. 6 is a front view of a spatial filter example 4 (mirror array device).
FIG. 7 is a comparison diagram of a transmissive liquid crystal and a mirror array device.
FIG. 8 is a front view showing a schematic configuration of an inspection apparatus when a mirror array device is used as a spatial filtering unit.
FIG. 9 is a front view showing Example 1 of a mirror array device.
FIG. 10 is a front view showing Example 2 of the mirror array device.
FIG. 11 is a front view showing a schematic configuration of an inspection apparatus using a plurality of spatial filtering units.
FIG. 12 is a front view of the Fourier optical system showing an optical path diagram of the Fourier optical system.
FIG. 13 is a front view of the Fourier optical system showing an optical path diagram of the optical system for observing the Fourier transform plane.
FIG. 14 is a chip (die) layout diagram.
FIG. 15 is a diagram comparing a diffracted light pattern for each chip area with an optimal light-shielding pattern.
FIG. 16 is a diagram showing an inspection method example 1;
FIG. 17 is a diagram showing an inspection method example 2;
FIG. 18 is a diagram showing an inspection method example 3;
FIG. 19 is a diagram comparing a configuration of a spatial filter of a right spring type, a combination of a right spring and a left spring type, and a filter inclination.
FIG. 20 is a plan view of a chip showing an example of scanning one chip (die).
FIG. 21 is a diagram showing a diffracted light pattern for each region and a corresponding positional relationship in a chip.
FIG. 22 is a diagram illustrating an example of a setting method of a filter pattern.
FIG. 23 is a diagram illustrating an example of a method of setting inspection conditions.
FIG. 24 is a diagram illustrating an example of a setting method of a spatial filter.
FIG. 25 is a diagram showing pattern signals when a spatial filter is used / not used.
FIG. 26 is a block diagram illustrating an example of a yield improvement system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wafer 21 ... Diffraction light pattern 1 22 ... Diffraction light pattern 2 23 ... Diffraction light pattern 3 24 ... Diffraction light pattern 425 ... Diffraction light pattern 5 31 ... Light shielding Pattern 1 32 ... Light-shielding pattern 2 33 ... Light-shielding pattern 3 34 ... Light-shielding pattern 4 35 ... Light-shielding pattern 5 41 ... Light-shielding pattern 6 50 ... Filter pattern setting sequence 60 ... Inspection Condition setting sequence 81: Process management system 82: Defect management system 91: Inspection device 92: Review device 100: Illumination optical system 101: Laser light source 200: Detection optical system 400 ··· Arithmetic processing system 500 ··· display device 600 ··· Fourier transform surface observation optical system 601 ··· optical path branching device 603 ··· optical path branching device 605: sensor 700: wafer observation optical system 2000: spatial filter unit 2100: right spring type spatial filter 2300: transparent liquid crystal spatial filter 2400: mirror array device spatial filter 2410 ..Mirror array device controllers

Claims (5)

The inspection target substrate having a pattern formed on its surface is irradiated with light, and of the reflected light from the inspection target substrate due to the irradiation, the diffraction light of the circuit pattern present on the inspection target substrate is selectively shielded to reflect the light. A defect inspection method for detecting a light and processing a signal of the detected reflected light to detect a defect on a surface of the inspection target substrate, wherein a diffraction light of a circuit pattern present on the inspection target substrate is selectively emitted. To shield light, a mirror array or reflective liquid crystal, or transparent liquid crystal, or a transfer of a light-shielding pattern to an optically transparent substrate, or a substrate or film etched leaving the light-shielding pattern, or heating Optically transparent substrate, or rod-shaped or plate-shaped, whose transmittance can be changed by quenching or light irradiation, or by changing the electric or magnetic field Defect inspection method and performing using any of the light plate. A plurality of chips on which a circuit pattern having the same shape is formed are formed on the inspection target substrate, and selectively cutting off the diffracted light of the circuit pattern is performed for one chip formed on the inspection target substrate. 2. A spatial filter for detecting a diffracted light pattern of the circuit pattern and setting a spatial filter for selectively blocking the diffracted light of the circuit pattern in accordance with a change in the diffracted pattern for each area in the one chip. Defect inspection method. An apparatus for inspecting a defect on the surface of a substrate to be inspected having a pattern formed on the surface, comprising: an illumination optical system illuminating a surface of the substrate to be inspected; and the inspection object illuminated by the illumination optical system. Detecting means for detecting scattered light from the substrate, and processing means for processing a detection signal of the scattered light detected by the detecting means to detect a defect on the surface of the inspection target substrate, the detecting means, A light-shielding portion that selectively shields the diffracted light of the circuit pattern present on the inspection target substrate out of the scattered light from the inspection target substrate illuminated by the illumination optical system means according to the pattern of the diffracted light; A defect inspection apparatus. The light-shielding portion that selectively shields light in accordance with the pattern of the diffracted light is a mirror array or a reflective liquid crystal, or a transmissive liquid crystal, or a light-shielded pattern transferred to an optically transparent substrate, or a light-shielded pattern. An etched substrate or film, or an optically transparent substrate whose transmittance can be changed by heating, quenching or light irradiation, or a change in electric or magnetic field, or a rod-shaped or plate-shaped light shielding plate The defect inspection apparatus according to claim 3, wherein the defect inspection apparatus is any one of the above. A plurality of chips on which a circuit pattern of the same shape is formed are formed on the inspection target substrate, and a light shielding unit that selectively shields light in accordance with the pattern of the diffracted light,
The diffracted light of the circuit pattern is selectively blocked based on information on a change in a diffracted light pattern for one chip formed on the substrate to be inspected obtained by the processing means for each region in the one chip. 4. The defect inspection apparatus according to claim 3, wherein the defect inspection is performed.

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