JP2005207802A - Resist pattern inspection method, and inspection device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a resist hole pattern inspection method and device capable of determining an opening condition of a complicated shape of contact hole by a simple method. <P>SOLUTION: When a resist of an inspected object is irradiated with an electron beam and when a shape of a resist hole pattern is inspected using a secondary electron generated from a resist surface, using a scanning electron microscope or the like, a signal of the output secondary electron is divided into a plurality of two-dimensional network picture elements, an intensity distribution of the each picture element is classified by an optional threshold value, and the quality of the resist pattern is determined based on a shape or an area of a class of the picture elements in the same classification. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a semiconductor pattern inspection method using secondary electrons and an apparatus therefor, and more particularly, to an inspection method capable of discriminating an opening state of a fine hole pattern or the like, and an inspection apparatus therefor. Is.

  In a semiconductor element manufacturing process, a semiconductor element in the semiconductor element manufacturing process is observed and evaluated using a scanning electron microscope (SEM). In particular, in the case of a resist pattern, dimensions and shapes do not satisfy predetermined standards. In some cases, the resist pattern is removed and re-exposure is performed to improve the manufacturing yield.

  In recent semiconductor device manufacturing, miniaturization has progressed and the manufacturing process has become complicated, so the loss caused by passing defective products through the manufacturing process without being confirmed until the final stage of the manufacturing process is large. is there. Therefore, inspection of defects in the semiconductor element manufacturing process has become increasingly important.

  Conventionally, in the dimension measuring apparatus using the scanning electron microscope (SEM) using secondary electrons, the dimension of the observation pattern is calculated by using the contrast information of the secondary electrons. This will be described with reference to FIG. FIG. 5A shows the cross-sectional shape of the hole pattern 53 formed in the resist 52 formed on the substrate 51, and FIG. 5B shows the contrast of secondary electrons obtained from the hole pattern 53. Waveform H is shown. Generally, a value about 50% of the maximum value (Max) and the minimum value (Min) of the contrast of secondary electrons is used as a threshold value (dotted line I), and the length of the line segment J at this threshold value is monitored as a hole size. ing. Since the threshold value is generally variable, the smaller the threshold value, the closer to the bottom of the contact hole can be monitored. However, when the threshold value is set small, the hole size to be monitored varies greatly due to slight contrast fluctuations. Therefore, the measurement of the hole size becomes unstable. Therefore, in order to perform stable measurement, conventionally, a value of about 50% is often used as a threshold value for measuring a hole pattern.

  Further, the contact hole 53 is not limited to a square (design value), but is often a rectangle (design value). In such a case, the shape of the contact hole is approximated to an ellipse and the major axis and minor axis are monitored. In this case, a threshold value of about 50% is used.

  However, as described above, when the threshold is set to 50%, measurement stability can be obtained, but when the footing phenomenon in which the bottom of the contact hole 53 is narrow is generated, It does not accurately grasp the opening diameter of the contact hole.

As a means for detecting such contact hole opening abnormality, it is known to set the threshold value to a value other than 50% (see Patent Document 1). In the technique of this Patent Document 1, a plurality of threshold values are used to detect cross-sectional shape anomalies, the dimensions at each threshold value are calculated based on the edge information obtained at each threshold value, and the values are determined in advance. The shape abnormality detection is performed by determining whether or not the standard is satisfied. However, this method has a drawback that complicated processing is required.

JP-A-8-14836

  As described above, in the measurement of a particularly fine hole pattern, it is necessary to monitor the bottom of the hole pattern. For example, in the resist pattern, if it is an unopened hole or a skirted shape at the bottom, the influence on the subsequent etching process is great, and eventually a conduction failure is caused. In particular, in the case where the bottom portion of the resist pattern is a so-called traced shape with a fine contact hole, an image as shown in FIG. 2 is obtained when the contact hole is observed with a dimension measuring apparatus using secondary electrons. In FIG. 2, a black region A in the center portion of the contact hole is an opening of the resist, and a gray region B in FIG. 2 is a bottom skirting region or a side wall region. In the measurement with the threshold value of 50%, the diameter of the opening A that is a black region is not measured, but according to the conventional method, the opening A that is the bottom of the contact hole that needs to be truly monitored is monitored. Difficult to do.

  In order to solve this problem, if the threshold value is lowered, the size of the portion near the bottom of the contact hole can be measured. However, when the fine contact hole is formed near the resolution limit of the exposure apparatus, a stable shape is obtained. And the opening of the contact hole tends to be distorted, making measurement difficult.

The present invention has been made to solve the above-described problems in determining the shape of a contact hole, and an object thereof is to provide a method capable of determining the opening state of a contact hole having a complicated shape by a simple method. Yes.

The first aspect of the present invention is an inspection method for inspecting a resist hole pattern by irradiating an electron beam to a resist in which holes are formed and analyzing a signal intensity distribution of secondary electrons output from the resist surface.
The output signal of the resist hole pattern is divided into a plurality of two-dimensional mesh pixels, the signal intensity of each pixel is divided by an arbitrary number of thresholds, and the shape of a region that is an aggregate of pixels that have the same division or A resist hole pattern inspection method, wherein the quality of the formed resist hole pattern is determined from an area.

  In the first aspect of the present invention, it is preferable that the number of thresholds is 2, and the image of the resist hole pattern is divided into three regions.

  In the first aspect of the present invention, it is possible to determine that the area of the region having the lowest signal intensity among the divided regions is not less than a predetermined range as a non-defective product.

  In the first aspect of the present invention, it is possible to determine that the area of an area having an intermediate signal intensity in the divided areas is not more than a predetermined range as a non-defective product.

The second aspect of the present invention comprises means for irradiating the surface of the resist in which holes are formed while scanning with an electron beam,
Detection means for detecting a secondary electron beam output from the resist surface;
Means for dividing the detected intensity distribution of the secondary electron beam into a two-dimensional array of mesh pixels, and classifying the intensity signal output of each pixel by a predetermined threshold;
An inspection apparatus for a resist hole pattern, wherein the quality of a resist hole formed in the resist is determined from the shape or area of a collection of pixel regions having the same classification for the divided pixels.

A third aspect of the present invention is an inspection method for inspecting a resist pattern by irradiating a semiconductor surface on which a resist pattern is formed with an electron beam and analyzing a signal intensity distribution of secondary electrons output from the resist surface.
The resist pattern inspection method is characterized in that the formation state of the observation pattern is monitored by the amount of deviation from the design by superimposing the design pattern of the semiconductor and the image of the observation pattern of the scanning electron microscope apparatus.

  In the third aspect of the present invention, as the observation pattern of the scanning electron microscope apparatus, in the case of a hole pattern, it is preferable to target a region having the lowest secondary electron beam intensity in the pattern.

According to a fourth aspect of the present invention, there is provided: means for irradiating a semiconductor surface on which a resist pattern is formed while scanning an electron beam; detection means for detecting a secondary electron beam output from the resist surface; In this case, the resist pattern inspection apparatus includes means for comparing the observation pattern of the region having the lowest secondary electron beam intensity in the pattern with the design pattern.

According to the above-described present invention, it is possible to automatically determine the opening state of a contact hole having a complicated shape by a simple method.

[First embodiment]
The principle of this embodiment will be described below.
FIG. 2 shows an example of an image obtained from a contact hole formed of, for example, a resist in a dimension measuring apparatus using secondary electrons generated from the surface of an inspection object irradiated with an electron beam. In FIG. 2, when attention is paid to one contact hole, the upper portion (region C) of the contact hole is white, the resist (region B) remaining at the bottom of the contact hole is gray, and the portion (region) where the contact hole is opened It can be seen that A) is identified as black. This image is cut into a mesh as shown in FIG. 4 and analyzed by the intensity of the output signal. FIG. 4 shows a state in which the level of the secondary electron beam intensity in the region near the contact hole is classified into three levels. Thereafter, the bottom of the contact hole (the state of the opening) is monitored by judging from the shape of the portion classified into black (region A) or by calculating the area of the region A. By analyzing the portion classified as gray (region B), it is possible to monitor skirting or roughness of the side wall of the contact hole. By automating this, it is possible to automatically determine the quality of a resist hole such as a contact hole.

(Inspection equipment)
Hereinafter, an inspection apparatus that can be used in the present invention will be described with reference to FIG.
The inspection apparatus of FIG. 1 mainly detects a secondary electron generated from the surface of an object to be inspected by electron beam irradiation and forms an image thereof, and operates the scanning electron microscope apparatus or It comprises a control device that processes the information and an interface device that exchanges signals between them. The scanning electron microscope apparatus includes an electron gun 11 for outputting an electron beam and a deflection coil 12 for scanning the electron beam in a casing of the scanning electron microscope apparatus 10 and is disposed at the bottom of the casing. The inspection substrate 14 on the stage 13 placed is irradiated with an electron beam. Secondary electrons output from the substrate 14 to be inspected by the irradiated electron beam are detected by the detector 15, and an output signal corresponding to the intensity of the secondary electrons output from the detector 15 is input to the signal processing device 17. And processed. The deflection coil 12 is controlled by a deflection coil controller 16 so that a desired region of the substrate 14 can be irradiated with an electron beam. Further, the stage 13 is controlled by a stage controller 18 so that the substrate 14 to be processed can be positioned. The deflection coil control device 16 and the stage control device 18 are controlled by an information processing device 19 such as a personal computer, a workstation, or a mini computer. An output signal from the signal processing device 17 is also input to the information processing device 19 so that it can be inspected according to an inspection method described in detail below. A display device 20 for displaying an image photographed by the scanning electron microscope device 10, an image processed by the information processing device 19, and various types of information processed by the information processing device 19 is connected to the information processing device 19. ing.

  In this apparatus, driving of the scanning electron microscope apparatus 10, processing of output signals from the signal processing apparatus 17, and evaluation of inspection results are stored in a storage device (not shown) that is built in or connected to the information processing apparatus 19. Can be executed by a program.

(Inspection method)
Hereinafter, an inspection method for monitoring the shape of a contact hole, which is a hole pattern formed in a resist, using the above-described inspection apparatus, and determining whether the contact hole is good or bad will be described.

(Acquisition of secondary electron beam image)
A substrate 14 in which contact holes are formed in a resist on the surface is placed in the scanning electron microscope apparatus 10 shown in FIG. 1, and an electron beam is irradiated onto the substrate 14 from an electron gun 11. This electron beam is positioned and scanned by the deflection coil 12 and the stage 13 on which the substrate 14 is placed, and irradiates the substrate 14.

  Secondary electrons are emitted from the surface of the substrate 14 irradiated with the electron beam, the secondary electrons are detected by the detector 15, and the electron beam irradiation position of the substrate 14 and the secondary detected by the detector 15 are detected. From the electron output intensity, the signal processor 17 maps and reconstructs the image on the two-dimensional plane, and an image (FIG. 2) representing the surface state of the substrate 14 is obtained. As such an image constructing means, a known technique can be adopted.

(Area classification)
As shown in FIG. 4, the two-dimensional image of the secondary electron beam obtained by the above means is divided into meshes of arbitrary size, that is, mesh-like pixels. At this time, the smaller the size of each pixel is, the higher resolution analysis can be performed and inspection with high accuracy can be performed, but the time required for the processing increases.

  FIG. 3 shows a sectional view of a hole pattern for capturing a surface image in the above process and a graph showing the intensity distribution of the secondary electron beam. FIG. 3A is a cross-sectional view of a substrate to be inspected, which is a resist 32 formed on a substrate 31 such as a silicon wafer on which a base pattern such as a gate or wiring is formed, and its The hole pattern 33 is formed in the resist. And the graph which shows distribution of the secondary electron beam intensity acquired using the said inspection apparatus about the board | substrate which is a sample shown to Fig.3 (a) is FIG.3 (b). FIG. 3B is created for an arbitrary cross section of the hole pattern. In FIG. 3B, when the maximum value of the observed secondary electron beam is Max and the minimum value is Min, the intensity distribution of the secondary electron beam observed in the hole pattern of FIG. It is represented by curve E of 3 (b). As is clear from FIG. 3B, the electron beam intensity in the region A which is the opening at the center of the hole pattern is the lowest, and the regions B on both sides increase in intensity as the distance from the center increases. The electron beam intensity of the region C, which is the resist opening edge of the pattern, shows a maximum value, and there is a region D where the intensity is slightly reduced outside.

  The secondary electron beam intensity signal of each pixel divided into meshes in the above process is compared with an arbitrarily set threshold value and divided into a plurality of regions. In FIG. 3B, the two threshold values are represented by F and G. With this threshold as a boundary, each pixel decomposed into a mesh of the secondary electron beam image is classified into a plurality of sections. Specifically, the secondary electron beam image is divided into three regions by classifying the number of secondary electrons returned in each pixel divided into meshes by two set threshold values. An example is shown in FIG. FIG. 4 shows an example in which two hole threshold values are set for the hole pattern shown in FIG. In FIG. 4, a region A at the center of the hole pattern is an opening of the hole pattern, and a region B is a tailing region or a side wall of the hole pattern. A region C outside this region is a region around the resist pattern opening. Further, the region D outside the region C corresponds to the resist portion. In this way, the secondary electron beam image of the resist pattern is divided by a plurality of threshold values, and pixels corresponding to each division are collected to detect the hole pattern opening, tailing or side wall, and the periphery of the opening. Can do.

(Evaluation)
With respect to the area for each section formed in the above process, it is possible to determine the quality of the hole pattern to be inspected from the shape or area.
As a judgment criterion at this time, for example, the area and shape of the opening at the bottom of the hole pattern can be used. The area of the bottom of the hole pattern can be obtained from the number of pixels divided into the region A. If the area of the bottom of the hole pattern is small, does the contact resistance of electrical connection through the through hole increase? Alternatively, there is a risk of causing defects in the etching process, film forming process, etc., leading to poor electrical connection, and it is necessary to discriminate them as defective products. In addition, regarding the region B, the large area of the region B means that the tailing shape is remarkable, the shape of the side wall portion is tapered, or the resist roughness of the side wall portion is increased. It represents that.

  As described above, by dividing the hole pattern image into a plurality of regions and observing the shape and area of each region, information regarding the state of the hole pattern can be easily obtained. In addition, it is possible to determine the quality of the hole pattern shape. This method can also be applied to line patterns.

  Further, the bottom of the hole pattern can be easily monitored by analyzing the image according to color tone, shading, brightness, and the like.

[Second Embodiment]
In the first embodiment, the method for inspecting the property of the hole pattern by the secondary electron signal using the scanning electron microscope apparatus has been described. However, the quality of the pattern using the scanning electron microscope apparatus is confirmed. At the same time as the determination, it is possible to inspect the positional deviation. The method will be described below.

  In the case where the hole pattern is rectangular, the amount of shrink differs on both sides in the major axis direction depending on the pattern density of the periphery, and a positional shift may occur. This is shown in FIG. FIG. 6A shows a case where the rectangular hole patterns are regularly arranged. In this case, no positional deviation occurs. In FIG. 6B, the rectangular hole patterns are regularly arranged, but the peripheral pattern density is different. In such a case, the one end 62 side of the pattern 61 has a relatively sparse pattern without an adjacent pattern, whereas the adjacent pattern exists on the other end 63 side of the pattern and is relatively dense. It is a pattern. In this case, the amount of shrinkage differs between the one end 62 side of the pattern and the other end 63 side of the pattern, resulting in a positional shift. With respect to such partial positional deviation of the pattern, the conventional positional measurement apparatus cannot monitor the positional deviation.

  The method according to the present embodiment superimposes the image created by the method of the first embodiment using the scanning electron microscope apparatus and the design drawing of this pattern layout, thereby forming the observation pattern formation state. This discriminates deviations from the design. In other words, by superimposing an image of an observation pattern created using a scanning electron microscope apparatus using secondary electrons and a design drawing, it is possible to monitor the asymmetry of the shrinkage amount and the overall positional deviation amount. .

  This embodiment will be described with reference to FIG. In FIG. 7, reference numeral 71 denotes a layout diagram of a design drawing, and 72 denotes an observation image of a hole pattern imaged using a scanning electron microscope apparatus. By monitoring the dimensions of the errors 73 and 74 between the design layout diagram of the resist pattern and the observation image of the hole pattern, the asymmetric shrinkage can be monitored. At this time, in the case of the hall pattern, among the images analyzed by the method described in the first embodiment, the positional deviation is monitored by superimposing the image of the region having the lowest electron beam intensity and the design drawing. can do. At this time, the registration of the resist pattern design layout and the observed image of the resist pattern can be overlaid by using the positioning marks provided for each.

Generally, pattern shrinkage is corrected by adding an auxiliary pattern to the design pattern. However, even if the pattern is formed asymmetrically as described above, more accurate patterns can be obtained by grasping the amount of shrinkage based on the design value. Correction can be made. This technique can be applied not only to the hole pattern but also to the line pattern.

It is the schematic which shows one Example of the resist pattern inspection apparatus of this invention. 3 is a photograph of a resist hole pattern for explaining an example of the present invention. It is sectional drawing of the board | substrate for demonstrating this invention, and the intensity distribution map of the secondary electron beam emitted from this board | substrate. It is a figure for demonstrating the analysis of the resist hole pattern of this invention. It is sectional drawing of the board | substrate for demonstrating a prior art, and the intensity distribution map of the secondary electron beam emitted from this board | substrate. It is a figure which shows the example of the layout which has a rectangular resist hole pattern. It is a figure for showing the 2nd example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Scanning electron microscope apparatus 11 ... Electron gun 12 ... Deflection coil 13 ... Sample stage 14 ... Non-measuring semiconductor substrate 15 ... Detector 16 ... Deflection coil controller 17 ... Signal processor 18 ... Sample stage controller 19 ... Information processing Device 20 ... Display device 31, 51 ... Substrate 32, 52 ... Resist 33, 53 ... Resist hole pattern 61 ... Rectangular hole pattern 62 ... One end of hole pattern 63 ... Other end of hole pattern 71 ... Design drawing of resist pattern 72 ... Image of resist pattern observation

Claims (8)

In an inspection method for inspecting a resist hole pattern by irradiating an electron beam to a resist in which holes are formed and analyzing a signal intensity distribution of secondary electrons output from the resist surface,
The output signal of the resist hole pattern is divided into a plurality of two-dimensional mesh pixels, the signal intensity of each pixel is divided by an arbitrary number of thresholds, and the shape of a region that is an aggregate of pixels that have the same division or A method for inspecting a resist hole pattern, wherein the quality of the formed resist hole pattern is determined from an area.   2. The resist hole pattern inspection method according to claim 1, wherein the number of the thresholds is 2, and the image of the resist hole pattern is divided into three regions.   3. The inspection of the resist hole pattern according to claim 1, wherein a region having the lowest signal intensity among the divided regions is determined as a non-defective product having a predetermined area or more. Method.   3. The resist hole pattern according to claim 1, wherein a region having an intermediate signal intensity among the divided regions is determined as a non-defective product if the area is equal to or less than a predetermined range. Inspection method. Means for irradiating the surface of the resist in which holes are formed while scanning with an electron beam;
Detection means for detecting a secondary electron beam output from the resist surface;
Means for dividing the detected intensity distribution of the secondary electron beam into a two-dimensional array of mesh pixels, and classifying the intensity signal output of each pixel by a predetermined threshold;
An inspection apparatus for a resist hole pattern, wherein the quality of a resist hole formed in the resist is determined from the shape or area of an aggregate of pixel regions having the same classification for the divided pixels. In an inspection method for inspecting a resist pattern by irradiating an electron beam onto a semiconductor surface on which a resist pattern is formed, analyzing a signal intensity distribution of secondary electrons output from the resist surface,
A resist pattern inspection method characterized by superimposing a design pattern of a semiconductor and an image of an observation pattern of a scanning electron microscope apparatus to monitor the formation state of the observation pattern with an amount of deviation from the design.   7. The method for inspecting a resist pattern according to claim 6, wherein when the observation pattern of the scanning electron microscope apparatus is a hole pattern, it is a region having the lowest secondary electron beam intensity in the pattern. A means for irradiating the semiconductor surface on which the resist pattern is formed while scanning with an electron beam; a detecting means for detecting a secondary electron beam outputted from the resist surface; And a resist pattern inspection apparatus comprising means for comparing an observation pattern of a region having the lowest secondary electron beam intensity with a design pattern.