JP6044182B2 - Method for determining unevenness of fine patterns - Google Patents

Description

  The present invention relates to a method for determining unevenness of a fine pattern or acquiring three-dimensional information, and more particularly to a method for acquiring unevenness information of a line and space pattern formed on a semiconductor wafer or a photomask.

  A scanning electron microscope (SEM) irradiates a sample with an electron beam from an electron gun, detects secondary electrons and the like generated from the sample by the irradiation of the electron beam, and detects them. A signal is supplied to display means synchronized with the scanning of the electron beam to obtain a scanned image of the sample. For example, when measuring the pattern dimension of a semiconductor device, a method of measuring the dimension by analyzing this image is often employed.

  In a pattern formed on a semiconductor wafer or mask substrate, a portion with a film is called a line, and a portion without a film is called a space. The SEM has a measurement mode for the pattern type of the measurement object, and the measurer needs to select an appropriate measurement mode according to the pattern type. Several methods have been proposed for determining the pattern type of the measurement object. (For example, refer to Patent Document 1).

JP 2009-37985 A

  When the measurer determines the pattern type of the object to be measured, there are line width and space width, brightness, contrast, alignment with CAD data, and the like. However, there is a problem that it is difficult to discriminate the line and space pattern in the case of matching with the CAD data when the width of the line and the space is equal, the brightness and the contrast are about the same, or when the stage movement accuracy of the apparatus is not sufficient. there were.

  Patent Document 1 discloses a method of determining pattern irregularities from the magnitude of the inclination of the signal profile of the line portion and the space portion, and describes that the inclination of the space portion (glass portion) is larger. However, the difference in inclination does not always appear between the line portion and the space portion. In addition, a case where the space portion is not glass, such as an EUV (Extreme Ultra Violet) mask, is not particularly described, and is not suitable as a method for determining pattern irregularities.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fine pattern unevenness determination method capable of accurately determining unevenness of a fine pattern.

According to a first aspect of the present invention, there is provided a method for determining unevenness of a fine pattern of a wafer or a photomask with a scanning electron microscope, irradiating a sample with an electron beam, detecting charged particles emitted from the sample, A step of generating an image of a sample, a step of generating a signal profile by performing image processing on the image, a step of generating a differential profile by performing a first-order differential process on the signal profile, and an edge where the peak of the signal profile stands The step of determining the sandwiched area as a determination target pattern , detecting differential peak values near both edges of the determination target pattern, determining the unevenness of the determination target pattern based on the detection position of the differential peak value, A method for determining unevenness of a fine pattern, comprising:
According to a second aspect of the present invention, in the step of detecting the differential peak value, differential peak values detected respectively inside and outside both edges of the determination target pattern are detected. The method for determining unevenness of a fine pattern as described in 1).
According to a third aspect of the present invention, in the step of determining the unevenness of the fine pattern, the differential peak value detected inside the both edges, and the differential peak value detected outside the both edges, When the differential peak value detected outside is large, the determination target pattern is determined as a line, and when the differential peak value detected outside is small, the determination target pattern is determined as a space. The method for determining unevenness of a fine pattern according to claim 1 or 2, wherein
According to a fourth aspect of the present invention, there is provided a method for determining unevenness of a fine pattern of a wafer or a photomask with a scanning electron microscope, irradiating a sample with an electron beam, detecting charged particles emitted from the sample, A step of generating an image of a sample, a step of generating a signal profile by performing image processing on the image, a step of generating a differential profile by performing a first-order differential process on the signal profile, and an edge where the peak of the signal profile stands the region sandwiched between a target pattern, wherein the step of detecting the corresponding two differential peak value in the position of the edge, the focus position in the Z-axis direction of the scanning electron microscope and the differential peak value of the target pattern And determining the unevenness of the determination target pattern based on the relationship between A.
According to a fifth aspect of the present invention, in the step of generating the sample image, the focus position in the Z-axis direction is changed to generate a plurality of images. This is a pattern unevenness determination method.
According to a sixth aspect of the present invention, in the step of detecting the two differential peak values, the differential peak value detected inside the edge of the judgment target pattern and the outside of the edge of the judgment target pattern are detected. The method according to claim 4 or 5, wherein a differential peak value is detected and stored.
According to the seventh aspect of the present invention, in the step of determining the unevenness of the determination target pattern, the focus position in the Z-axis direction is changed from a focus reference point determined by autofocus of the scanning electron microscope, and the edge A relationship diagram between the differential peak value detected on the inside and the outside and the focus position is created, and the focus position in the Z-axis direction where the differential peak value starts to change small is represented by the relationship diagram inside the edge and the edge position. The method for determining unevenness of a fine pattern according to any one of claims 4 to 6, wherein the unevenness of the determination target pattern is determined by comparison with a relational diagram on the outside.

  ADVANTAGE OF THE INVENTION According to this invention, the unevenness | corrugation determination method of the fine pattern which can determine the unevenness | corrugation of a fine pattern with high precision can be provided. In particular, it is possible to accurately determine the uneven shape in the case where similar patterns are continuous, such as a line and space pattern.

It is a figure explaining the uneven | corrugated determination method of the fine pattern concerning the 1st method of this invention. It is a flowchart which shows the process of the unevenness | corrugation determination method of the fine pattern concerning the 1st method of this invention. It is a figure explaining the uneven | corrugated determination method of the fine pattern concerning the 2nd method of this invention. It is a figure explaining the uneven | corrugated determination method of the fine pattern concerning the 2nd method of this invention. It is a figure explaining the uneven | corrugated determination method of the fine pattern concerning the 2nd method of this invention. It is a flowchart which shows the process of the uneven | corrugated determination method of the fine pattern concerning the 2nd method of this invention. It is a figure which shows the sample concerning an Example typically. It is the signal profile of the sample concerning an Example. It is a differential profile of the sample concerning an Example. It is a cross-sectional profile of AFM of the sample concerning an Example. FIG. 6 is a relationship diagram between a focus position and a differential peak value of a sample according to an example.

  Hereinafter, a method for determining unevenness of a fine pattern according to the present invention will be described in detail with reference to embodiments shown in the drawings. In the following description, the case where the present invention is applied to a line and space pattern formed on a photomask will be described, but the applicable range of the present invention is not limited thereto.

  FIG. 1 is a diagram for explaining a method for determining unevenness of a fine pattern according to the first method of the present invention. FIG. 1A illustrates a line-and-space pattern including a convex portion (line portion) 101 and a concave portion (space portion) 102. FIG. 1B shows a signal profile obtained from the SEM image, and FIG. 1C shows a profile obtained by differentiating the signal profile. Since the signal profile obtained from the SEM image is determined by the amount of secondary electrons emitted from the sample, it has a signal waveform with a peak at the edge portion where many secondary electrons are emitted.

  As shown in FIG. 1B, generally, in the signal profile waveform of the line portion, the tailing on the inner side of the peak (reference numeral 11 in FIG. 1B) gradually decreases to the tailing on the outer side of the peak (FIG. Reference numeral 12) of b) shows a sharpened waveform. The position where the slope of the trailing edge inside the peak is maximum corresponds to the top portion of the pattern edge, and therefore the amount of secondary electron emission largely depends on the shape of the top edge. Depending on the process, the top edge portion may have a rounded shape, and the tailing of the signal profile waveform tends to be gradual. Therefore, the peak value of the differential profile located inside the line portion is small.

  On the other hand, the position where the slope of the tailing outside the peak is the maximum corresponds to the bottom part of the pattern edge, so the secondary electron emission amount depends on the shape of the bottom edge, the material of the line and space parts, and the side wall shielding effect. Dependent. In the case of a photomask, the space is generally made of glass, the amount of secondary electrons emitted is small, and the secondary electrons emitted from the space are not shielded by the side wall and reach the detector. In other words, the brightness of the space portion becomes relatively small. As a result, the contrast between the line portion and the space portion increases, and the trailing slope outside the peak has a sharpened waveform. Therefore, the peak value of the differential profile located outside the line portion is large. Therefore, the unevenness of the pattern can be determined by comparing the magnitudes of the differential peak values of the differential profile.

  The above unevenness determination method will be described with reference to the flowchart of FIG. FIG. 2 is a flowchart showing the processing of the fine pattern unevenness determination method according to the first method of the present invention. First, an image of the pattern is acquired (S1). Next, image processing is performed on the obtained scanned image, a signal profile is generated (S2), the signal profile is differentiated (S3), and a differential profile is generated. Next, differential peak values appearing inside and outside at the left and right edges (both edges) of the determination target pattern are acquired (S4). Next, the magnitudes of the differential peak values are compared, and a detection position where a larger peak value appears is determined (S5). When a large peak appears on the outside as in the pattern 101 in FIG. 1 (E1 and E2 in FIG. 1), the measurement object is determined to be a line (S6). On the other hand, when a large peak appears on the inner side as in the pattern 102 in FIG. 1 (E2 and E3 in FIG. 1), the measurement object is determined to be a space (S7).

  That is, the unevenness determining method according to the first method of the present invention is a method for determining unevenness of a fine pattern of a wafer or a photomask with a scanning electron microscope. A step of detecting particles and generating an image of the sample (S1), a step of generating a signal profile by image processing of the image (S2), a step of differentially processing the signal profile to generate a differential profile (S3) ), Detecting a differential peak value in the vicinity of both edges of the determination target pattern (S4), and determining irregularities of the determination target pattern based on the detection position of the differential peak value (S5, S6). . In the step of detecting the differential peak value in S4, differential peak values detected respectively inside and outside both edges of the determination target pattern are detected. Further, in the step of determining the unevenness of the fine pattern of S5 and S6, the differential peak value detected inside both edges and the differential peak value detected outside both edges are compared and detected outside. When the differential peak value is large, the determination target pattern is determined as a line, and when the differential peak value detected outside is small, the determination target pattern is determined as a space.

  In the above method, the method for determining the unevenness of the pattern by comparing the peak values of the differential profile has been described. However, depending on the pattern and SEM imaging conditions, the peak value may be approximately the same. However, it may not always be possible to determine irregularities by the above method. Hereinafter, a second method for determining the unevenness of the pattern will be described.

  3-5 is a figure explaining the uneven | corrugated determination method of the fine pattern concerning the 2nd method of this invention. As shown in FIG. 3A, in general, the SEM has a wide focal depth range, which is sufficiently larger than the pattern height. Therefore, the scanned image obtained by performing the autofocus process with the SEM can obtain an in-focus image in both the upper surface portion T and the lower surface portion B of the pattern. Next, image processing is performed on the scanned image to obtain a signal profile 21 shown in the upper diagram of FIG. The signal profile at this time has a waveform with a sharp slope both inside and outside the peak corresponding to the pattern edge. Next, the obtained signal profile 21 is differentiated to obtain a differential profile 22 shown in the lower diagram of FIG. Then, a differential peak value 23 corresponding to the upper surface portion T of the differential profile 22 and a differential peak value 24 corresponding to the lower surface portion B are acquired. Next, the acquired data is plotted on a relationship diagram between the focus value and the differential peak value as shown in FIG.

  When the focus position in the Z-axis direction is continuously changed from the state of FIG. 3A, and the upper surface portion T of the pattern edge portion deviates from the focus depth range of the SEM as shown in FIG. The signal profile waveform (inside the signal peak) corresponding to the upper surface portion of the scanned image becomes gentle as shown in the upper diagram of FIG. Therefore, the differential peak value (reference numeral 25 in the lower diagram in FIG. 4B) corresponding to the upper surface portion T of the profile obtained by differentiating this signal profile (see the lower diagram in FIG. 4B) becomes small.

  When the focus position in the Z-axis direction is continuously changed from the state of FIG. 3B, and the lower surface portion B also deviates from the SEM focal depth range as shown in FIG. The differential peak value corresponding to the lower surface portion B is also reduced (see reference numeral 26 in the lower diagram of FIG. 4C).

  As described above, when the process of acquiring the differential peak value from the scanned image obtained by continuously changing the focus position in the Z-axis direction in the vertical direction from the just focus position determined by the autofocus process of the SEM is performed. As shown in FIG. 5A, relationship diagrams 200 and 201 between the focus value and the differential peak value at the upper surface portion T and the lower surface portion B of the pattern edge portion are obtained.

  As described above, when the focus position is continuously changed from the just focus position in the Z-axis direction, either the upper surface or the lower surface of the pattern deviates from the SEM focal depth range first. . When deviating from the range of the focal depth, the differential peak value becomes small as described above, so that the unevenness of the pattern can be determined by comparing the focus values at which the differential peak value starts to decrease.

  In the relationship diagrams 200 and 201 in FIG. 5A, when the focus value is changed in the plus direction from the just focus, the differential peak value starts to change smaller in the relationship diagram 200 first. Assuming that the direction in which the depth of focus moves from the upper surface to the lower surface of the pattern corresponds to a positive change in the focus value, it is determined that the one where the differential peak value starts to change smaller corresponds to the upper surface of the pattern. it can. Therefore, in the illustrated example, it can be determined that the inside of the signal peak constituting the relationship diagram 200 is the upper surface of the pattern, while the outside of the signal peak constituting the relationship diagram 201 is the lower surface of the pattern, and the pattern can be determined to be convex.

  On the other hand, the unevenness of the pattern can also be determined when the focus value is changed in the minus direction from the just focus. When the focus value is changed in the minus direction, in the relationship diagrams 200 and 201, it is the relationship diagram 201 that the differential peak value starts to change smaller first. Assuming that the direction in which the depth of focus range moves from the lower surface of the pattern to the upper surface corresponds to a change in the negative direction of the focus value, it is determined that the one where the differential peak value starts to change smaller corresponds to the lower surface of the pattern. it can.

  In the above description, the case where the direction in which the range of the focal depth moves from the upper surface to the lower surface of the pattern is assumed to correspond to a change in the positive direction of the focus value is described. . In other words, assuming that the direction in which the depth of focus moves from the lower surface of the pattern to the upper surface corresponds to a change in the focus value in the plus direction, the direction in which the differential peak value starts to change smaller corresponds to the lower surface of the pattern. It can be judged. In general, since the relationship between the focus movement direction and the focus value is known by the device, it is only necessary to change the pattern unevenness determination criteria depending on the device used as appropriate, and the focus position can be easily controlled by the focus value. Can do.

  In addition, when it is difficult to determine the falling portion of the differential peak value as shown in FIG. 5B, the pattern unevenness is determined by approximating the data with a curve and the focus value corresponding to the inflection point. That's fine. Assuming that the direction in which the range of the focal depth moves from the upper surface to the lower surface of the pattern corresponds to a positive change in the focus value, the smaller focus value corresponds to the upper surface of the pattern.

  The second unevenness determination method will be described with reference to the flowchart of FIG. FIG. 6 is a flowchart showing the processing of the fine pattern unevenness determination method according to the second method of the present invention. First, an autofocus process is performed to set a just focus state (S11). Next, a plurality of images are acquired by continuously changing the focus position in the Z-axis direction (S12). Next, image processing is performed on the plurality of images, and signal profiles are respectively generated (S13). Next, the signal profile is differentiated (S14), and a differential profile is generated. Next, differential peak values appearing inside and outside the edge are acquired and stored together with the focus position (S15). A similar process is performed on a plurality of images, and a relationship diagram between the differential peak value and the focus position is created (S16). Next, pattern irregularities are determined from the relationship diagram (S17). As described above, as described above, when the focus value is changed, the differential peak values appearing on the inner side and the outer side of the edge are compared, and the determination is made because the differential peak value starts to change smaller.

  That is, the unevenness determination method according to the second method of the present invention is a method for determining unevenness of a fine pattern of a wafer or a photomask with a scanning electron microscope. A step of detecting particles and generating an image of the sample (S11, S12), a step of image-processing the image to generate a signal profile (S13), and a step of differentially processing the signal profile to generate a differential profile; (S14), a step of detecting two differential peak values corresponding to the position of the edge of the determination target pattern (S15), and the relationship between the differential peak value and the focus position in the Z-axis direction of the scanning electron microscope And (S16, S17) for determining unevenness of the pattern. In the step of generating an image of the sample in S12, the focus position in the Z-axis direction is changed to generate a plurality of images. In the step of detecting two differential peak values in S15, the differential peak value detected inside the edge of the determination target pattern and the differential peak value detected outside the edge are detected and stored. Further, in the step of determining the unevenness of the determination target pattern in S16 and S17, the focus position in the Z-axis direction is changed from the focus reference point determined by the autofocus of the scanning electron microscope, and the detection is performed on the inside and outside of the edge. A relationship diagram between the differential peak value and the focus position is created (S16), and the focus position in the Z-axis direction where the differential peak value starts to change slightly is compared between the relationship diagram inside the edge and the relationship diagram outside the edge. Then, the unevenness of the determination target pattern is determined (S17).

  Hereinafter, specific examples of the fine pattern unevenness determination method of the present invention will be described. First, an embodiment of the fine pattern irregularity determination method according to the first method of the present invention will be described.

  FIG. 7 is a diagram schematically illustrating a sample according to the example. As a sample measured in this example, a sample in which the line portion of the pattern was composed of MoSi and the space portion was composed of Qz was used.

  First, an autofocus process was performed on the line and space pattern of the sample to obtain a scanned image. It is determined whether the patterns P1 and P2 in FIG. 7 are lines or spaces, respectively. Next, image processing was performed to generate a signal profile (FIG. 8). Next, the signal profile was differentiated (FIG. 9). In the differential profile, at the left and right edges of the pattern P1, it can be seen that the outer peak values (61 and 64 in FIG. 9) are larger than the inner peak values (62 and 63 in FIG. 9). Therefore, this pattern P1 was determined to be a line. On the other hand, at the left and right edges of the pattern P2, it can be seen that the inner peak values (64 and 65 in FIG. 9) are larger than the outer peak values (63 and 66 in FIG. 9). Therefore, this pattern P2 was determined to be a space. Thereafter, the line and space pattern was measured using an AFM to obtain a profile shape (FIG. 10). FIG. 10 shows that the pattern P1 is a convex line and the pattern P2 is a concave space, and it was confirmed that the unevenness determination of the present invention was correctly performed.

  Next, an embodiment of the fine pattern unevenness determination method according to the second method of the present invention will be described.

  In the pattern P1 shown in FIG. 7, a scanned image was acquired while changing the focus position by ± 0.05 μm in the Z-axis direction from the just focus position determined by the autofocus process. Next, a signal profile was generated for each scanned image (FIG. 8), and a differential profile was obtained (FIG. 9). FIG. 11 shows the relationship between the differential peak value and the focus value at the left edge of the pattern P1. The data group D1 represents a change in the differential peak value of the inner waveform of the edge peak of the signal profile, and the data group D2 represents a change of the differential peak value of the outer waveform.

  From the result of FIG. 11, since it is difficult to determine the focus position at which the differential peak value starts to change small, the data was approximated by a quadratic curve. When the focus position at the inflection point of each quadratic curve was obtained, the inner waveform of the edge peak (data group D1) was -41.053 μm, and the outer waveform of the edge peak (data group D2) was −40.815 μm. Met. In the SEM apparatus used in this example, it is known that the change in the focus value in the plus direction corresponds to the movement of the focus position from the upper surface to the lower surface, and therefore the smaller focus value corresponds to the upper surface of the pattern. . Therefore, since the inner waveform of the edge peak can be determined to be the upper surface of the pattern, it can be determined that the outer waveform of the edge peak is the lower surface of the pattern. That is, it is found that the left edge of the pattern P1 is a rising edge from the lower surface of the pattern to the upper surface, and the right edge is derived as a falling edge. From the above, it can be determined that the pattern P1 is a convex line. When the same process was performed on the pattern P2, it was determined that the pattern P2 was a concave space.

  Since the unevenness determination method for fine patterns according to the present invention can determine the line and space of a pattern, it is expected to be used in a field where it is required to correctly measure the dimensions of the pattern.

  101 ... Convex part (line part), 102 ... Concave part (space part), P1 ... Convex shape (line), P2 ... Concave shape (space)

Claims (7)

In the method of determining the unevenness of the fine pattern of the wafer or photomask with a scanning electron microscope,
Irradiating the sample with an electron beam, detecting charged particles emitted from the sample, and generating an image of the sample;
Image processing the image to generate a signal profile;
Generating a differential profile by performing a first-order differential process on the signal profile;
A region sandwiched between edges where the peak of the signal profile stands is a determination target pattern, and a step of detecting differential peak values near both edges of the determination target pattern;
Determining unevenness of the determination target pattern based on the detection position of the differential peak value;
A method for determining unevenness of a fine pattern, comprising:   2. The fine pattern unevenness determination method according to claim 1, wherein in the step of detecting the differential peak value, differential peak values detected respectively inside and outside both edges of the determination target pattern are detected.   In the step of determining the unevenness of the fine pattern, the differential peak value detected inside the both edges is compared with the differential peak value detected outside the both edges, and detected outside. The determination target pattern is determined to be a line when the differential peak value is large, and the determination target pattern is determined to be a space when the differential peak value detected outside is small. 3. A method for determining unevenness of a fine pattern according to 2. In the method of determining the unevenness of the fine pattern of the wafer or photomask with a scanning electron microscope,
Irradiating the sample with an electron beam, detecting charged particles emitted from the sample, and generating an image of the sample;
Image processing the image to generate a signal profile;
Generating a differential profile by performing a first-order differential process on the signal profile;
Detecting said a region sandwiched between the edge peak stands signal profile as a target pattern, corresponding two differential peak value in the position of the edge of said target pattern,
Determining the unevenness of the determination target pattern from the relationship between the differential peak value and the focus position in the Z-axis direction of the scanning electron microscope;
A method for determining unevenness of a fine pattern, comprising:   5. The method for determining unevenness of a fine pattern according to claim 4, wherein in the step of generating an image of the sample, the focus position in the Z-axis direction is changed to generate a plurality of images. In the step of detecting the two differential peak values, a differential peak value detected inside the edge of the determination target pattern and a differential peak value detected outside the edge of the determination target pattern are detected and stored. The method for determining unevenness of a fine pattern according to claim 4 or 5.   In the step of determining the unevenness of the determination target pattern, the differential peak value detected inside and outside the edge by changing the focus position in the Z-axis direction from a focus reference point determined by autofocus of the scanning electron microscope And the focus position in the Z-axis direction in which the differential peak value starts to change small are compared between the relationship diagram inside the edge and the relationship diagram outside the edge, The method for determining unevenness of a fine pattern according to any one of claims 4 to 6, wherein the unevenness of the determination target pattern is determined.

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