JP2016021008A - Pattern evaluation method and pattern evaluation device for multi-patterning mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for evaluating positional deviation of plural masks for multi-patterning, while considering effects on wafer transfer due to difference in three-dimensional shapes of patterns.SOLUTION: SEM images of all masks for multi-patterning corresponding to a designated hot spot area are acquired, a pattern side wall angle is measured, and the SEM images of all masks for multi-patterning are synthesized. Then, distance between patterns and a gravity center between patterns are calculated and they are compared with design data for respective patterns, and when positional deviation is equal to or higher than a permissible value, patterns are corrected, or masks are produced again. In addition, even when positional deviation is lower than the permissible value, when difference between masks in the pattern side wall angle is equal to or higher than a permissible value, light exposure simulation of mask patterns is executed, positional deviation is inspected on patterns after light exposure, and when a positional deviation amount is equal to or higher than the permissible value, patterns are corrected, or masks are produced again.SELECTED DRAWING: Figure 1

Description

  The present invention is a pattern evaluation system for a photomask using an electron microscope. When a pattern is exposed on a wafer using a plurality of masks by multi-patterning, the pattern position accuracy between the masks including the effect of the three-dimensional shape of the pattern. The present invention relates to a pattern evaluation method and a pattern evaluation apparatus for a multi-patterning mask.

  In recent years, technological development for coping with miniaturization and complexity of semiconductor devices has been advanced. Currently, EUV lithography using extreme ultraviolet light sources is regarded as the next-generation lithography technology. However, due to insufficient output of the light source, the mass production application that was initially anticipated is postponed, and multi-patterning can be used as an alternative technology. Application is expected.

  Multi-patterning is a process in which pattern data formed on a wafer is divided into three or more pieces and each is formed on a separate mask. The mask pattern exposure transfer to the wafer and the subsequent etching process are performed for the number of masks. This is a technique that enables a fine pattern to be formed on a wafer at a high density by repeatedly performing the process. Masks used for multi-patterning not only require high pattern dimensional accuracy, but also the pattern position accuracy is very important.

  In particular, in a mask for multi-patterning, not only the positional accuracy within one mask surface but also the positional relationship with other mask patterns needs to be controlled with high accuracy.

  Conventionally, the pattern position accuracy in a photomask has been evaluated by drawing a dedicated cross pattern called a monitor pattern on the entire surface of the mask and using a dimension measuring device, and directly measuring the position accuracy of the actual device pattern itself. I did not. Further, the measurement of the pattern position accuracy is intended for a pattern in one mask surface, and there is no means for measuring the position accuracy between a plurality of masks used for multi-patterning.

  Therefore, as a means for measuring the positional accuracy between a plurality of masks, a method described in Patent Document 1 has been proposed. Here, for two masks used for double patterning, SEM images of the coordinate positions that become the hot spot areas are acquired and overlaid, and the distance between the pattern edges is compared with the design value. Whether or not it is a defect is determined. Further, the distance between the pattern edges is calculated from the result of exposure simulation of each mask image, and it is determined whether or not it is a defect based on the deviation from the design value.

Japanese Patent No. 4991499

  Conventionally, since EUV masks reflect EUV light, it is known that changes in the side wall angle of the mask pattern affect the dimensions of the wafer transfer pattern. On the other hand, in the transmission type photomask using ArF light, it has been found that the change in the side wall angle affects the wafer transfer due to the recent high precision and high density of pattern dimensions. In particular, in multi-patterning, a transfer pattern using another mask becomes closer on the wafer, so that the possibility that a dimensional variation of the wafer pattern due to a change in the side wall angle becomes a fatal defect increases.

  However, in the prior art, the mask pattern is regarded as a two-dimensional plane, and three-dimensional effects such as the side wall angle of the pattern are not considered. In advanced semiconductor devices that use multi-patterning with three or more masks, the influence of the sidewall angle of the mask pattern on wafer transfer is even greater, so the positional accuracy between patterns includes the effect of the three-dimensional shape of the pattern. Need to be evaluated.

  The present invention has been made to solve these problems, and the first object is to consider the influence on the wafer transfer due to the difference in the three-dimensional shape of the pattern when evaluating the pattern of the mask for multi-patterning, It is to provide a method capable of evaluating misalignment between masks.

Another object of the present invention is to manufacture a high-precision multi-patterning mask by confirming the positional accuracy including the difference in the three-dimensional shape of the pattern.
The present invention is not limited to a multi-patterning mask, and can be applied to a double patterning mask using two masks.

  One aspect of the present invention for solving the above problems is a pattern evaluation method for a multi-patterning mask, the step of designating a hot spot region to be evaluated based on pattern design data, and a hot spot region A step of acquiring SEM images of a plurality of masks used for patterning all of them, a step of measuring pattern sidewall angles of a plurality of masks, a step of combining SEM images of a plurality of masks, and a combined SEM image The step of measuring the distance between each pattern based on the above, the step of calculating the barycentric position of each pattern, the distance between the patterns and the barycentric position are compared with the design data of each pattern, and the positional deviation from the pattern design data A step of calculating the amount, a step of determining whether or not the amount of positional deviation of the pattern is equal to or larger than a positional deviation allowable value, If the amount of positional deviation of the pattern is equal to or larger than the allowable positional deviation value, a plurality of masks are included when the mask corresponding to the pattern is corrected or re-created and when the positional deviation amount of the pattern is smaller than the allowable positional deviation value. Comparing the pattern side wall angle between the plurality of masks to determine whether or not the difference between the pattern side wall angles between the plurality of masks is equal to or greater than the allowable angle difference value, and the difference between the pattern side wall angles between the plurality of masks Whether or not the amount of misalignment between the step of performing the exposure simulation of the pattern patterned by the plurality of masks and the design data of the pattern obtained by the exposure simulation is greater than or equal to the misalignment allowable value. And the exposure simulation when the amount of positional deviation of the pattern obtained by the exposure simulation is greater than the allowable positional deviation And a step of correcting or reengineering of the mask with better obtained pattern, a pattern evaluation method of the multi patterning mask.

  Further, it may further include a step of obtaining a positional deviation allowable value and an angle difference allowable value in advance by simulation for each film type of the mask.

  Further, in the step of combining the SEM images of the plurality of masks, the positions of the SEM images of the plurality of masks may be adjusted and combined based on the design data of the pattern corresponding to the hot spot region.

  Further, in the step of calculating the centroid position for each pattern, the contour line of the pattern in the synthesized SEM image may be extracted, and the average value of the coordinates of each point constituting the contour line may be calculated as the centroid position.

  Another aspect of the present invention is a pattern evaluation apparatus for a mask for multi-patterning, wherein a means for designating a hot spot region to be evaluated is patterned based on pattern design data, and all the hot spot regions are patterned. Means for acquiring SEM images of a plurality of masks used in the above, means for measuring pattern sidewall angles of a plurality of masks, means for combining SEM images of a plurality of masks, and between each pattern based on the combined SEM images Means for measuring the distance; means for calculating the position of the center of gravity for each pattern; means for comparing the distance between the patterns and the position of the center of gravity with the design data of each pattern; and means for calculating the amount of positional deviation from the design data of the pattern; Means for determining whether or not the amount of positional deviation of the pattern is equal to or larger than the allowable positional deviation, and the amount of positional deviation of the pattern is Compare the pattern sidewall angle between multiple masks when the amount of positional deviation of the pattern is less than the allowable positional deviation. And determining whether or not the difference between the pattern side wall angles between the plurality of masks is greater than or equal to the allowable angle difference value, and if the difference between the pattern side wall angles between the plurality of masks is greater than or equal to the allowable angle difference value, Means for performing exposure simulation of a pattern patterned by a plurality of masks, and means for determining whether or not the amount of positional deviation between exposure pattern design data obtained by exposure simulation is equal to or larger than a positional deviation allowable value If the pattern displacement obtained by the exposure simulation is determined to be greater than the allowable displacement, the exposure simulation And means for performing a correction or re-manufacturing a mask corresponding to the obtained pattern Ri is a pattern evaluation apparatus of the multi-patterning mask.

  Further, the allowable positional deviation value and the allowable angular difference value may be obtained in advance by simulation for each film type of the mask.

  The means for synthesizing the SEM images of the plurality of masks may be synthesized by adjusting the positions of the SEM images of the plurality of masks based on the design data of the pattern corresponding to the hot spot region.

  The means for calculating the center-of-gravity position for each pattern may extract the contour line of the pattern in the synthesized SEM image and calculate the average value of the coordinates of each point constituting the contour line as the center-of-gravity position.

  According to the present invention, it is possible to evaluate the positional accuracy of the actual pattern between the masks for multi-patterning, including the influence due to the difference in the pattern side wall angle. Further, by confirming the positional accuracy including the difference in the three-dimensional shape of the pattern, it becomes possible to manufacture a more highly accurate multi-patterning mask.

The flowchart which shows the process sequence of the pattern evaluation method which concerns on one Embodiment of this invention. Functional configuration diagram of a pattern evaluation apparatus according to an embodiment of the present invention Example of design data for exposure pattern in hot spot area SEM image example of the first to third masks Result of combining three SEM images Measurement example of distance between patterns (a) and calculation example of pattern centroid position (b) Explanatory drawing which shows that a transfer pattern dimension changes with side wall angles.

(Embodiment)
Here, a pattern evaluation method and a pattern evaluation apparatus according to an embodiment of the present invention will be described. FIG. 1 is a flow chart of a pattern evaluation method, and FIG. 2 is a functional configuration diagram of the pattern evaluation apparatus.

<Pattern evaluation method>
First, a pattern evaluation method according to this embodiment will be described with reference to FIGS. First, from the design data of the exposure pattern, a hot spot area where a slight difference in the mask pattern is likely to become a defect on the exposure pattern is designated (S1). An example of the design data of the hot spot area is shown in FIG. The hatching attached to each pattern in the drawing represents the correspondence between the pattern and the mask when the pattern is divided into three masks by the multi-patterning technique. When a pattern is assigned to a plurality of masks, the distance between the patterns is as long as possible on the same mask. Pattern data is allocated to three masks for multi-patterning, and each mask is manufactured.

  Next, an SEM image (hereinafter referred to as an image) of the mask is acquired (S2) in the hot spot region of each mask. 4A to 4C are image examples of hot spot regions of the first to third masks for multi-patterning.

  Next, the side wall angle of the pattern in the hot spot area of each mask is measured (S3). Then, image acquisition and sidewall angle measurement are performed for all the masks for multi-patterning (S4). As a method for measuring the side wall angle, a method for measuring the three-dimensional shape of a pattern using an AFM (Atomic Force Microscope), an irradiation with an electron beam obliquely in a CD-SEM, or a plurality of secondary electron detectors. There is a method of measuring the side wall width of the pattern by using the obtained signal and calculating the side wall angle based on the height information.

  Conventionally, there has been a high need for measuring the sidewall angle in a reflective EUV mask, which is said to have a large influence on the wafer transfer size due to variations in the pattern sidewall angle. Recently, even in the ArF mask which is a transmission type mask, the influence on the wafer transfer due to the variation of the side wall angle of the pattern cannot be ignored. In particular, in the generation in which a mask for multi-patterning is used, the distance between patterns finally formed on the wafer is further shortened, so that the influence of the fluctuation of the sidewall angle becomes relatively large.

  Next, a process of combining images of all masks in the same hot spot area (S5) is performed. This is possible by synthesizing images of the same coordinates in each mask by image processing, but the positional accuracy between the masks depends on the stage accuracy of the SEM apparatus. Therefore, when synthesizing images of each mask with higher accuracy, the design data (S6) of the exposure pattern relating to the hot spot area before division is used, and the pattern of the image of each mask matches the design data of this exposure pattern. Adjust the position so that the images are combined. An example of the synthesized image is shown in FIG.

  Subsequently, the pattern position accuracy is evaluated using the synthesized image. The pattern position accuracy is confirmed by the distance between the patterns and the deviation of the center of gravity position. First, in the synthesized image, the distance between the patterns is measured by measuring the distance between the edges of adjacent patterns (S7). FIG. 6A shows an example in which the position where the distance between patterns is measured is indicated by an arrow. Next, the center of gravity position of each pattern is calculated from the synthesized image (S8). The center of gravity position of the pattern is calculated by extracting the contour line of the pattern image and averaging the x coordinate and y coordinate of each point constituting the contour line for every x coordinate and y coordinate. FIG. 6B shows the result of calculating the barycentric coordinates of each pattern and displaying the positions with black circles.

  Next, the distance between the patterns and the position of the center of gravity are compared with the design data of each exposure pattern (S9), and the amount of positional deviation from the design data of the exposure pattern is calculated. Thereafter, it is determined whether or not the amount of pattern misalignment is greater than or equal to an allowable value (S10). Since this allowable value varies depending on the technology node in which the mask is used and the film type of the photomask, it is calculated in advance using an optical exposure simulator or an exposure test evaluation mask. If a positional deviation greater than the allowable value is found, the target mask is corrected or recreated (S15).

Here, when the amount of pattern displacement is smaller than the allowable value, the side wall angles between the masks are compared (S11). Also in the ArF optical mask, it has been found that the pattern size exposed on the wafer varies depending on the side wall angle of the opening pattern portion. As shown in FIG. 7, even when the mask pattern dimensions defined at the boundary between the glass substrate (102) and the light shielding film (103) are the same, the side wall angles (θ ₁ , θ ₂ ) of the light shielding film This is because the amount of transmitted exposure light (101) differs and the size (P ₁ , P ₂ ) of the resist pattern (104) on the wafer changes. Therefore, in the mask for multi-patterning, when the pattern sidewall angle is different between the masks, the wafer pattern may be changed even if the pattern dimension between the masks is the same.

  Therefore, it is determined whether the side wall angle difference between the masks is equal to or greater than an allowable value (S12). Since this allowable value varies depending on the technology node and the film type of the photomask, it is calculated in advance using a light exposure simulator. If the side wall angle difference between the masks is greater than or equal to the allowable value, there is a high possibility that a defect will occur after wafer exposure due to the difference in the side wall angle. It is determined whether or not the amount of positional deviation between the pattern obtained by the simulation and the design data of the exposure pattern is not less than an allowable value (S14). If it is equal to or greater than the allowable value, the target mask is corrected or recreated (S15).

  If the side wall angle difference between the masks is smaller than the allowable value, or if the displacement of the simulation pattern is smaller than the allowable value, the pattern evaluation is performed assuming that there is no problem in the positional deviation between the masks of the multi-patterning in the investigated hot spot area. Complete (S16).

<Pattern evaluation device>
Next, a pattern evaluation apparatus that performs pattern evaluation will be described with reference to FIG. The operation of this pattern evaluation apparatus will be described in detail. First, the design data storage function (F1) is a function for storing the design data of the exposure pattern, and the pattern data of the designated area is taken out from here. The position of the hot spot region is designated by the mask coordinate designation function (F2), and each image of the designated coordinates of each multi-patterning mask is obtained by the SEM image acquisition function (F3). The SEM image acquisition function uses a mask CD-SEM for length measurement. Further, the side wall angle of the pattern is measured using the side wall angle measuring function (F9) at the designated coordinates of each multi-patterning mask.

  Next, the position of each image of the multi-patterning mask is aligned by the alignment function (F4). At this time, the original design data is called from the design data storage function, and each image is aligned based on the design data of the exposure pattern. Then, each image of the multi-patterning mask is synthesized into one image by using the image synthesis function (F5). When combining images of each mask with higher accuracy, use the exposure pattern design data related to the hot spot area before division, and adjust the position so that the pattern of each mask image matches the design data of this exposure pattern. And combine the images.

  Next, the synthesized image is input to the inter-pattern distance measurement function (F6), and the distance between adjacent patterns in the synthesized image is calculated. Further, the synthesized image is input to the center-of-gravity position calculation function (F7), the contour line of each pattern in the synthesized image is extracted, and the average value is calculated for each of the x and y coordinates for the coordinate data constituting the contour line. The center of gravity coordinates are obtained. As a method for extracting a contour line from an image, there are a method for performing a combination of general image processing such as smoothing, binarization, and differentiation processing, a contour line extracting method disclosed in Japanese Patent No. 4085635, and the like. is there.

  Next, the calculated distance data between the patterns and the barycentric coordinate data are input to the exposure pattern design data comparison function (F8), and the distance between the patterns in the exposure pattern design data and the difference from the barycentric coordinates are calculated. The amount of pattern position deviation is assumed. The result is input to the determination function (F10), and it is determined whether the pattern displacement amount is larger than a preset allowable value.

  If the amount of pattern displacement is greater than or equal to the allowable value, the evaluation result output function (F13) displays the number of the mask having a pattern with a large displacement and the fact that the mask needs to be corrected or recreated. On the other hand, when the pattern positional deviation amount is smaller than the allowable value, the processing is divided depending on the difference in the side wall angle between the masks. Since this allowable value varies depending on the technology node in which the mask is used and the film type of the photomask, it is calculated in advance using an optical exposure simulator or an exposure test evaluation mask.

  The side wall angle difference between the masks is calculated from the side wall angle of each mask calculated by the side wall angle measurement function (F9), and if this is smaller than the allowable value, the hot spot area evaluated this time by the evaluation result output function (F13) Indicates that there is no problem in the pattern position accuracy. However, if the side wall angle difference is greater than or equal to the allowable value, the wafer pattern dimension may change due to the difference in the side wall angle between the masks. Therefore, the exposure evaluation of the pattern of each mask is performed using the exposure simulation function (F11). carry out. Since this allowable value varies depending on the technology node and the film type of the photomask, it is calculated in advance using a light exposure simulator.

  The exposure simulation result is input to the exposure pattern evaluation function (F12), and the positional deviation is evaluated with the pattern after exposure of each mask. If the amount of displacement is greater than or equal to the allowable value, the evaluation result output function (F13) indicates that the mask needs to be corrected or recreated. Display that there is no.

  With the pattern evaluation apparatus having the above functions, it is possible to verify the pattern position accuracy between the masks of the multi-patterning mask, which has been difficult to evaluate so far, including the influence of the sidewall angle.

  The present invention can be used for manufacturing a high-precision multi-patterning mask.

S1 Process for designating hot spot area S2 Process for acquiring SEM image of mask S3 Process for measuring side wall angle of pattern S4 Process for performing image acquisition and side wall angle measurement for all target masks S5 Composite image of all masks Process S6 Design data of hot spot area S7 Process of measuring distance between patterns S8 Process of calculating center of gravity position of pattern S9 Process of comparing distance and center of gravity of pattern with design data S10 Pattern misalignment as allowable value Processing to compare S11 Processing to compare the side wall angle between the masks S12 Processing to compare the side wall angle difference between the masks with the allowable value S13 Exposure simulation processing S14 Processing to compare the positional deviation of the simulation result with the allowable value S15 Modify the target mask Re-fabrication process S16 Complete pattern evaluation End F1 Design data saving function F2 Mask coordinate specification function F3 SEM image acquisition function F4 Position alignment function F5 Image composition function F6 Pattern distance measurement function F7 Center of gravity position calculation function F8 Design data comparison function F9 Side wall angle measurement function F10 Judgment function F11 exposure simulation function F12 exposure pattern evaluation function F13 evaluation result output function 101 exposure light 102 glass substrate 103 light shielding film 104 resist pattern 105 target layer 106 substrate

Claims (8)

A pattern evaluation method for a multi-patterning mask,
A process for designating a hot spot area to be evaluated based on pattern design data;
Acquiring SEM images of a plurality of masks used to pattern all of the hot spot regions;
Measuring a pattern sidewall angle of the plurality of masks;
Synthesizing SEM images of the plurality of masks;
Measuring a distance between each pattern based on the synthesized SEM image;
Calculating a barycentric position for each pattern;
Comparing the distance between the patterns and the position of the center of gravity with the design data of each pattern to calculate a positional deviation amount from the design data of the pattern;
Determining whether the positional deviation amount of the pattern is equal to or greater than a positional deviation allowable value;
A step of correcting or recreating a mask corresponding to the pattern when the amount of positional deviation of the pattern is equal to or larger than the positional deviation allowable value;
When the positional deviation amount of the pattern is smaller than the positional deviation tolerance value,
Comparing the pattern sidewall angle between the plurality of masks and determining whether the difference in pattern sidewall angle between the plurality of masks is greater than or equal to an allowable angle difference; and
When the difference in pattern side wall angle between the plurality of masks is not less than the angle difference tolerance,
Performing an exposure simulation of a pattern patterned by the plurality of masks;
Determining whether a positional deviation amount of the pattern obtained by the exposure simulation and the design data of the pattern is equal to or greater than the positional deviation allowable value;
A step of correcting or recreating a mask corresponding to the pattern obtained by the exposure simulation when the amount of positional deviation of the pattern obtained by the exposure simulation is equal to or larger than the allowable value of the position deviation. Mask pattern evaluation method.   2. The pattern evaluation method for a multi-patterning mask according to claim 1, further comprising a step of obtaining, in advance, the positional deviation allowable value and the angle difference allowable value by simulation for each film type of the mask.   The step of synthesizing SEM images of the plurality of masks is performed by adjusting positions of the SEM images of the plurality of masks based on design data of the pattern corresponding to the hot spot region. Pattern evaluation method for multi-patterning mask.   2. The step of calculating a centroid position for each pattern extracts a pattern outline in the combined SEM image, and calculates an average value of coordinates of each point constituting the outline as the centroid position. The pattern evaluation method of the mask for multi-patterning as described in 2. A pattern evaluation apparatus for a multi-patterning mask,
A means for designating a hot spot area to be evaluated based on pattern design data;
Means for acquiring SEM images of a plurality of masks used to pattern all of the hot spot regions;
Means for measuring a pattern sidewall angle of the plurality of masks;
Means for synthesizing SEM images of the plurality of masks;
Means for measuring the distance between each pattern based on the synthesized SEM image;
Means for calculating a center-of-gravity position for each pattern;
Means for comparing the distance between the patterns and the position of the center of gravity with the design data of each exposure pattern, and calculating a positional deviation amount of the pattern from the design data;
Means for determining whether or not a positional deviation amount of the pattern is equal to or larger than a positional deviation allowable value;
Means for displaying that it is necessary to correct or recreate a mask corresponding to the pattern when the amount of positional deviation of the pattern is equal to or greater than the tolerance for positional deviation;
When the positional deviation amount of the pattern is smaller than the positional deviation tolerance value,
Comparing the pattern sidewall angle between the plurality of masks and determining whether the difference in pattern sidewall angle between the plurality of masks is greater than or equal to an allowable angle difference; and
When the difference in pattern side wall angle between the plurality of masks is greater than or equal to the allowable angle difference,
Means for performing an exposure simulation of a pattern patterned by the plurality of masks;
Means for determining whether a positional deviation amount of the pattern obtained by the exposure simulation and the design data of the pattern is equal to or greater than the positional deviation allowable value;
When it is determined that the positional deviation amount of the pattern obtained by the exposure simulation is equal to or larger than the allowable positional deviation value, it is displayed that the mask corresponding to the pattern obtained by the exposure simulation needs to be corrected or recreated. And a pattern evaluation apparatus for a multi-patterning mask.   The multi-patterning mask pattern evaluation apparatus according to claim 5, wherein the positional deviation allowable value and the angle difference allowable value are obtained in advance by simulation for each film type of the mask.   The means for combining the SEM images of the plurality of masks adjusts the positions of the SEM images of the plurality of masks based on the design data of the pattern corresponding to the hot spot region, and combines the SEM images. Pattern evaluation apparatus for multi-patterning masks.   The means for calculating a centroid position for each pattern extracts a pattern outline in the synthesized SEM image and calculates an average value of coordinates of each point constituting the outline as the centroid position. A pattern evaluation apparatus for a mask for multi-patterning according to claim 1.

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