JP5349978B2 - Dimension measuring method and size measuring apparatus using charged particle beam - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure sizes with high accuracy without being affected by the factors of size variation difficult to prevent by only controlling an irradiation amount on an area-by-area basis of beam scanning. <P>SOLUTION: In this method and instrument, a position in a scanning area where a positive heap and a negative heap offset each other is selected as a measuring part, with the positive heap owing to the deposition of contamination caused by a beam while the negative heap owing to the removal of a specimen. Alternately, in the scanning area, a portion not affected or little affected by size variation is selected as a measurement part. In the scanning area, a proper position is selected in measuring sizes. Sizes are measured with high accuracy without being affected by the factors of size variation caused by beam application. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention scans a sample such as a semiconductor device with a charged particle beam, and measures the dimension of the pattern using a signal waveform reflecting the shape of the pattern, such as a secondary electron signal or a reflected electron signal generated by the sample. The present invention relates to a linear dimension measuring apparatus and a dimension measuring method using the same.

  A measurement that scans a charged particle beam over a sample and measures the dimensions of the pattern formed on the substrate using a signal waveform that reflects the shape of the pattern, such as a secondary electron signal or reflected electron signal generated by the sample. The long SEM device is now an indispensable measurement / inspection device in order to perform high-precision fine processing.

  On the other hand, it has been known for a long time that when observation is performed using a surface observation apparatus using a charged particle beam, for example, an electron microscope, contamination adheres to a portion of the sample irradiated with the electron beam. For example, as described in Non-Patent Document 1, contamination is caused by irradiation of charged particles with hydrocarbon-based gas molecules remaining in a vacuum chamber for observing the substrate or released from the substrate itself. It is agglomerated and solidified / deposited in parts, and is generally called contamination. When contamination adheres and accumulates, the pattern becomes thick, and there is a problem that measurement of the pattern dimension cannot be performed accurately.

  With respect to the adhesion of contamination, Patent Document 1 discloses an apparatus provided with a function for limiting a dose amount, that is, a time during which an electron beam is irradiated. That is, in order to minimize the accumulation amount of contamination, a method and apparatus for minimizing the irradiation time of the electron beam or the electron beam irradiation amount on the inspection / measurement target pattern has been proposed.

  In addition, in Patent Document 2, in order to suppress the shrinkage of the pattern, not the contamination, and the dimensional value fluctuation based on the shrinkage, by selectively reducing the magnification in the Y direction, the unit area is reduced. A technique for reducing the amount of beam irradiation is disclosed.

  Further, Patent Document 3 discloses a technique for performing focusing with a pattern different from that of the length measurement target in order to suppress the adhesion of contamination to the measurement target.

WO2003 / 021186 JP 2006-134952 A

"Contamination" (Keiji Yada, Electron Microscope 16 (1981) 2)

  The technology disclosed in each of the above documents reduces contamination of the beam, or prevents the measurement target from performing beam irradiation for adjustment of apparatus conditions (for example, focus adjustment). This is to suppress the occurrence. That is, it is for reducing the irradiation amount in the beam scanning range unit. However, the inventors of this patent application have newly found that there are dimensional value fluctuation factors that are difficult to suppress by simply controlling the irradiation amount in units of beam scanning ranges.

  In the following, a method and an apparatus intended to perform highly accurate dimension measurement regardless of dimension value fluctuation factors that are difficult to suppress by simply controlling the dose in units of the beam scanning range will be described. To do.

  In order to achieve the above object, a position within the scanning range where the positive deposition caused by the adhesion of contamination by the beam and the negative deposition caused by the sample removal are offset is selected as a measurement site or within the scanning region. Proposes a method and an apparatus for selecting a part that is not affected by or less affected by dimensional variation as a measurement site. According to the method and the apparatus, it is possible to select an appropriate position for performing dimension measurement within the scanning region plane.

  According to the above configuration, it is possible to perform highly accurate dimension measurement regardless of the dimension value variation factor caused by beam irradiation.

The schematic block diagram of length measurement SEM. The flowchart explaining the dimension measuring method in a length measurement SEM apparatus. The figure explaining the measurement principle of the pattern dimension by a length measurement SEM apparatus. The figure explaining the principle of adhesion of the contamination to a sample by an electron beam, and the shaving of a sample. The figure explaining an example of the SEM image of a line pattern. The figure explaining the principle of the dimensional value change within a visual field. The figure explaining the determination method of the visual field position in case the some line pattern is arranged. The figure explaining the determination method of the visual field position in case the some hole pattern is arranged. The figure explaining the determination method of the visual field position in case the pattern in which the roughness was formed is arranged. The figure explaining the principle which makes the database the contamination in a visual field, and the distribution information of shaving. The flowchart which shows the process which performs a beam shift and implements dimension measurement based on the information made into database. The flowchart which shows the process which performs a beam shift and implements dimension measurement based on the information made into database. The schematic block diagram of the charged particle beam apparatus provided with the mass spectrometer. The flowchart which shows the process which performs a beam shift and implements dimension measurement based on the information made into database. The figure explaining an example of the visual field position determination method using a FOV setting window. The figure explaining the kind of FOV setting window. The flowchart explaining an example of the visual field position determination method. The figure for demonstrating the visual field position determination method with respect to a line pattern. The figure for demonstrating the visual field position determination method with respect to a hole pattern. The figure explaining the visual field position setting method with respect to the sample in which many patterns were arranged.

  The inventors of the present patent application adhere to and deposit contamination in the periphery of the field of view in the scanning range on the sample by the electron beam, that is, in the field of view by electron beam irradiation, but conversely in the center in the field of view. Has been observed to be thin, that is, the material is removed by the electron beam. This phenomenon is observed by reducing the hydrocarbon gas molecules remaining in the vacuum chamber and improving the so-called vacuum quality. By reducing the hydrocarbon gas in the gas phase, It is understood that this is because hydrocarbon-based gas molecules diffusing water became the main raw material supply for contamination. Depending on the conditions of the sample substrate and the primary electron beam, deposition may occur in the periphery of the irradiated area, but material removal in the central area will not occur, or conversely, no deposition will occur in the peripheral area of the irradiated area. Material removal may occur.

  Based on the above phenomenon, the inventor of the present application is able to adjust the amount of contamination by selecting the pattern measurement site within the field of view, that is, as a result of the influence of contamination, It was found that measurement values can be acquired from values to-values. In other words, if the material removal described above is considered as negative deposition, the deposition amount is the sum of adhesion and removal. The value is positive if the deposition is the main component, and the value is negative if the removal is the main component. Thus, the deposition is zero at the zero position, both positive and negative. Based on the above, the following knowledge for achieving the above object was obtained.

  That is, in order to suppress the influence based on contamination, etc., the position where the deposition amount of adhesion and removal becomes zero, for example, the region where contamination adheres (positive deposition) and material removal (negative deposition). We propose to select the measurement position of the boundary position of the region where the phenomenon occurs and to perform pattern measurement, and to provide the function. As described above, depending on the conditions of the sample substrate and the primary electron beam, there may be cases where material removal does not occur, or conversely, adhesion does not occur. Is the boundary position between the area where the contamination adheres and the substrate surface, or the boundary position where material removal occurs from the substrate surface. Hereinafter, in this specification, the position where the amount of deposition combined with adhesion and removal becomes zero is defined as the boundary position between the area where contamination adheres and the area where material removal occurs.

  According to the above method, it is possible to eliminate the influence of contamination deposition caused by electron beam irradiation and material removal by the beam, and a value close to the true inspection / measurement result can be obtained. As a result, it is possible to measure and inspect a fine pattern with high accuracy.

  Hereinafter, a measurement method and apparatus capable of performing stable measurement regardless of positive and negative deposition will be described in detail with reference to the drawings.

  Note that the measurement method described below is effective for measurement / inspection apparatuses using various charged particle beams, but in the following embodiments, an electron beam type dimension measurement apparatus and a length measurement SEM will be described. As already described, a length measuring SEM using a scanning electron microscope (SEM) has become an indispensable device for pattern dimension management in semiconductor manufacturing processes.

  FIG. 1 is a schematic configuration diagram of a length measurement SEM. The length measurement SEM includes an electron optical system 1100, a vacuum chamber 1200 provided with a stage mechanism system, a wafer transfer system (not shown), an evacuation system (not shown), a process control unit 1300 that performs apparatus control and signal processing. Consists of

  The electron optical system 1100 includes an electron gun 1101, an alignment coil 1107 that aligns the emission of the primary electron beam 1102 from the electron gun 1101, a condenser lens 1103 that focuses the primary electron beam 1102, and the astigmatism of the primary electron beam 1102. An astigmatism correction coil 1108 for correction, deflectors 1105 and 1106 for deflecting the primary electron beam 1102 two-dimensionally, an objective lens 1104 and an objective lens aperture 1109 are included. The wafer 1201 is placed on the XY stage 1202 and travels in the XY directions according to a command from the stage controller 1301, and can be stopped at an arbitrary position. The secondary electron detector 1110 detects secondary electrons generated by irradiating the wafer 1201 with a primary electron beam, and converts them into electrical signals. Thereby, a secondary electron beam image (SEM image) can be obtained.

  In the above configuration, the primary electron beam emitted from the electron gun 1101 is focused by the condenser lens 1103 and the objective lens 1104, and is irradiated onto the wafer 1201 placed on the XY stage 1202 as a minute spot. When the electron beam is irradiated, secondary electrons and reflected electrons corresponding to the material and shape of the sample are generated from the irradiated portion. The primary electron beam 1102 is two-dimensionally scanned using the deflectors 1105 and 1106, the generated secondary electrons are detected by the secondary electron detector 1206, converted into an electrical signal, and further converted into an electric signal by the A / D converter 1211. Can be obtained as a two-dimensional digital image. In this embodiment, the secondary electron image is described. However, the present invention can be similarly used for a reflected electron image.

  The stage controller 1301 controls the XY stage 1202 based on a command from the processing control unit 1300. The deflection / focus control unit 1302 and the acceleration voltage control unit 1303 also control the deflectors 1204 and 1205 to perform image magnification setting and focus control, and control the acceleration voltage based on a command from the processing control unit 1300. . The obtained SEM image is subjected to measurement processing by the processing control unit 1300. The processing control unit 1300 has a database 1304 for storing the obtained images and measurement data, and includes a computer 1305 for operating the apparatus, displaying results, and setting conditions (creating recipes).

  The recipe can be created by an external computer that stores the design data of the semiconductor device or can access the design data of the semiconductor device to an external storage medium. In this embodiment, the control device that controls the SEM and the computer that performs measurement based on the signal obtained by the SEM are described as separate units. However, the present invention is not limited to this. Control of the apparatus and measurement processing may be performed collectively by a computer, or SEM control and measurement processing may be performed together by each control apparatus. The following description relates to the description of the dimension measuring method and the dimension measuring apparatus, and also relates to the apparatus condition setting method such as SEM and the apparatus condition setting apparatus.

  In addition, the computer or the control device (hereinafter also referred to as an image processing device) stores a program for executing a measurement process, and the measurement is performed according to the program. Furthermore, a computer or an external computer stores photomask (hereinafter also simply referred to as a mask) and wafer design data used in the semiconductor manufacturing process. This design data is expressed in, for example, the GDS format or the OASIS format, and is stored in a predetermined format. The design data can be of any type as long as the software that displays the design data can display the format and can handle the data as graphic data. The design data may be stored in a storage medium provided separately from the data management device.

  A computer or the like can set measurement points and beam scanning positions on design data, and the settings are stored and saved as a recipe. In addition, the computer or the like includes a storage medium that stores information related to a positive deposition area and / or a negative deposition area described later. The information may be acquired by calculation using a method described later, or information previously acquired by another device may be acquired via an information transmission medium.

  Next, a basic procedure when pattern measurement on a wafer is performed using a length measurement SEM will be described. The flowchart is shown in FIG. First, the processing control unit 1300 acquires the position coordinates on the wafer of the pattern to be measured (201). Usually, it is performed by a recipe or command created in advance. Next, based on a command from the processing control unit 1300, the stage controller 1301 generates a movement target and moves the XY stage 1202 (202). After the stage is stopped, an image is acquired and image adjustment such as focus adjustment is performed, but image adjustment may be performed at the temporary target table position before positioning is completed in order to increase throughput (202). Since the pattern to be measured is on the order of nanometers, the positioning accuracy of the stage 1202 is very strict, and positioning is completed with a certain error. Therefore, after the positioning is completed, an image is acquired at a magnification lower than the measurement magnification (203), and matching with a representative actual pattern image recorded in the processing control unit 1300 is performed, so that the target dimension measurement location can be obtained. An accurate position is obtained (204), and the dimension measurement location is moved to the center of the screen by beam shift (205). Recently, a technique using a design shape as a pattern for matching is being adopted. The magnification is increased, and the movement of the dimension measurement location to the center of the screen is repeated by matching and beam shifting (206). However, if the stage stop accuracy is sufficiently accurate, step 206 is skipped. Next, dimension measurement is performed at the magnification at which measurement is finally performed (207). Specifically, the image is acquired with the beam conditions, magnification, and frame addition number set in the recipe, the edge of the line profile at the dimension measurement point is extracted, the dimension is obtained from the edge information, and the data is stored. (208). For example, when an image for a line pattern 301 as shown in FIG. 3A is acquired and the measurement location is an arrow 302, a profile of secondary electrons corresponding to the cross section of the pattern (FIG. 3B). Can be obtained as shown in FIG. The edge portions 303 and 304 are extracted from the secondary electron profile to determine the line pattern dimensions.

  As already described, when pattern measurement is performed by such a measurement apparatus and method, the accumulation of contamination makes the pattern thicker, so that accurate measurement of the pattern dimension cannot be performed. The discrepancy with the true pattern dimension becomes larger as the pattern dimension becomes finer.

  The inventors have found that the contamination is deposited in the electron beam scanning range on the sample, i.e., in the field of view, with a lot of contamination deposited on the periphery of the field of view, and the contamination decreases toward the center of the field of view. On the other hand, we found a phenomenon that the pattern was observed to be thin in the center. FIG. 4A is an SEM image obtained by scanning a planar sample with an electron beam for 10 minutes, and FIG. 4B is a three-dimensional profile obtained by measuring the portion scanned with the electron beam by AFM. FIG. 4C shows a two-dimensional cross-sectional profile of the AFM corresponding to the arrow 401.

  A large amount of contamination 402 is deposited on the periphery in the field of view scanned with the electron beam, the contamination 402 decreases toward the center in the field of view, and scraping 403 is observed in the center, and the substrate material is removed. That is, it can be seen that shaving due to the beam is occurring. That is, it can be seen that contamination 402 is deposited from the outer peripheral portion toward the central portion (positive deposition) and shaving 403 (negative deposition) is caused by the beam, and there is a region that is not affected by both of them at the boundary. .

  Next, FIG. 5 shows the result of observing a line pattern having a width of 55 nm and a pitch of 100 nm with a length measurement SEM. In order to make the phenomenon easy to see, the sample was scanned with an electron beam for 5 minutes to obtain an SEM image. In the outer peripheral portion 501 in the image, the line size was 59 nm, the central portion 502 was 51 nm, and the boundary portion 503 was 55 nm. That is, the thickness was measured to be about 4 nm thick at the outer peripheral portion 501, and conversely, the thickness was measured to be about 4 nm thin at the center portion.

  Based on the discovery of such a phenomenon, a method and an apparatus capable of performing highly accurate measurement regardless of the phenomenon will be described below. As already described, depending on the conditions of the sample substrate and the primary electron beam, the contamination 402 may be deposited around the irradiation region, but the shaving 403 will not occur at the center, or conversely, the deposition may be performed around the irradiation region. In some cases, the scraping 403 at the center portion may occur without the occurrence of 402. Hereinafter, in the present specification, the position where the total deposition amount including adhesion and removal is zero is defined as the boundary position between the area where contamination adheres and the area where material removal occurs.

  A first embodiment for performing appropriate measurement and inspection will be described with reference to FIG. Usually, the acquisition position of the dimension data is positioned at the center of the scanning range of the primary electron beam, that is, the center in the field of view (FOV). On the other hand, in this embodiment, the scanning range of the primary electron beam, that is, the boundary line between the contamination deposition region and the material removal region in the visual field, or the boundary region is positioned as the acquisition position of the dimension measurement data.

  Note that material removal may not occur depending on the conditions of the primary electron beam. In this case, the boundary area between the contamination deposition area and the substrate surface in the visual field is set as the acquisition position of the dimension measurement data.

  When the dimension measurement target is a line pattern as shown in FIG. 6A, the uneven distribution in the field of view by electron beam scanning is a deposition region (positive deposition) 601 due to contamination and a shaved region (negative deposition) due to the beam. By 602, for example, as shown in FIG. In the SEM image obtained in this way, the true line pattern dimension has a negative (−) value in the A portion and a positive (+) value in the D portion, but in the C portion. Since it hits the boundary 603 between the region that becomes + and the region that becomes-, a value with little difference can be obtained. In B, since the left side of the line is + but the right side is-, the measurement result can be a true value and a value with a small error. As shown in the flow of FIG. 2, conventionally, the image is moved by beam shift so that the measurement data acquisition portion is positioned at the center of the image, and the center of the image, that is, the portion A is set as the acquisition position of the dimension measurement data. That is, in this case, a result smaller than the true line pattern dimension is obtained. Here, in the present invention, the measurement is performed with a function of controlling the dimension measurement data acquisition position so that it can be positioned not in the center of the visual field but in the C part and the D part, thereby being affected by contamination and shaving due to the beam. Therefore, it is possible to obtain a value close to the true inspection / measurement result.

  In the above description, the data acquisition position of the measurement target pattern is positioned in the boundary line defined between the positive deposition area and the negative deposition area or in the boundary area set around the boundary line. As described above, the example of moving the FOV position has been described. However, it is not always necessary to set a boundary line in data processing. For example, the FOV center or the FOV outline is set to a predetermined distance position (within a distance range). The data acquisition position may be positioned. Further, when a part of the data acquisition position is superimposed on the boundary line or the like, it may be determined that the proper FOV positioning has been performed, or the data acquisition position (acquisition range) of the predetermined boundary line region may be determined. It may be determined that proper FOV positioning has been performed when everything is included or when a portion of the data acquisition range is greater than or equal to a predetermined value.

  Moreover, if the above-described algorithm is used to correct the measurement position or the visual field position defined by the recipe creator of the scanning electron microscope, the recipe creator determines the measurement conditions without being aware of the presence of contamination. It becomes possible.

  Next, a second embodiment will be described with reference to FIG. When the patterns 706 are densely arranged as shown in FIG. 7A, an average value of pattern dimensions may be obtained for a plurality of line patterns in the field of view, and dimension management may be performed based on the average value. The present embodiment is particularly effective for measuring the average value of such dimensions. Here, an example in which the average value of the six lines 706 is obtained at the dimension measurement data acquisition position E is shown. FIG. 7A is a diagram for explaining an example of the relationship between the six lines 706 and the visual field range 704. FIG. 7B illustrates the visual field range position when the dimension measurement data acquisition position E is arranged at the center of the visual field. FIG. 7C is a diagram for explaining the positional relationship between the dimension measurement data acquisition position E and the visual field range position in the present embodiment. As described with reference to FIG. 6, the line pattern size is distributed due to the deposition by contamination and the beam shaving, and the size is thick in the region 701 and thin in the region 702. Here, as illustrated in FIG. 7B, the dimension measurement data acquisition position E of the measurement target pattern is moved by beam shift so as to be positioned at the center of the image, and the dimension measurement data is acquired. The result is smaller than the line pattern dimension. In contrast to this, in the present embodiment illustrated in FIG. 7C, the dimension measurement data acquisition position E is not the center in the field of view, but the boundary line 703 (contamination deposition amount (positive deposition) and the amount of shaving by the beam (negative). It is characterized in that it is positioned at the sum of the deposition) or the portion where the average value is substantially zero (FIG. 7B). As a result, the average value of the dimension as the measurement result can be obtained as a value close to the true inspection / measurement result without being affected by contamination or beam shaving.

  In the FOV position determination method illustrated in FIG. 7, the dimensions of a plurality of measurement target patterns are included in both a region where deposits are deposited by charged particle beam irradiation and a region where material on the sample is removed by charged particle beam irradiation. The field of view of the charged particle beam is set so that the measurement data acquisition position is superimposed and the dimension measurement data acquisition position is positioned at a position where the influence of deposition and the effect of material removal are offset. That is, the FOV position is determined so that the data acquisition position E is arranged at a position where the negative accumulation and the positive accumulation are substantially canceled. In the example of FIG. 7, the FOV position is formed by the first FOV position (FIG. 7B) where the center of the circle formed by the boundary line 703 and the data acquisition position E overlap and the boundary line 703. And the second FOV position where the line segment of the data acquisition position E circumscribes the circle.

  The first FOV position is a region where the data acquisition position E section passes through the center of the circle where negative deposition is expected to be the most, and theoretically the longest distance, the region where negative deposition is expected (boundary line This is a position where the data acquisition position E part overlaps the inside. On the other hand, the second FOV position is a place where there is theoretically no negative deposition and positive deposition is expected except for a portion circumscribing the boundary line. Therefore, it is desirable to set the FOV between the first FOV position and the second FOV position in order to bring the measured value closer to the true value by using both positive and negative depositions.

  If an algorithm that automatically moves the FOV is applied based on the above rules, even an FOV that is set unconsciously can be measured under measurement conditions with very little measurement error. It becomes.

  FIG. 18 is a diagram for explaining another algorithm for determining the position of the FOV. FIG. 18 is a diagram illustrating a filter that stores information on positive and negative deposition amounts in the FOV in a matrix format. The filter 1801 stores information on the deposition amount of each region in a matrix format of n × m (9 × 9 in this example).

  For example, an operator of a length measurement SEM sets measurement conditions on design data of a semiconductor device or the like, and registers the setting information as a recipe. In order to measure the average value of the line widths of three line patterns 1802, 1803, and 1804 as illustrated in FIG. 19, a measurement position 1805 is set. In this case, since information on the deposition amount is stored in each small region, the deposition stored in the region related to the measurement position 1805 (in the case of FIG. 18, the eight small regions on which the measurement position 1805 overlaps). The FOV position may be determined so that the measurement position is set at a position where the total value of the quantities is closest to zero.

  By setting the measurement range, the range in which the total amount of deposition is to be calculated is found. Therefore, by searching for the position in the filter 1801 where the total of the range is closest to zero, A small number of FOV positions can be automatically determined. The above technique is particularly effective when the deposition occurs to some extent with stability.

  In the above example, the accumulation amount is described as an example of information stored in each small area. However, the present invention is not limited to this, and for example, the variation amount, variation rate, or error rate of the measured value is set to each small region. Information stored in the area may be used. Any kind of information can be used as long as the influence of the accumulation can be found as a result of finding the canceled position. In the case of the change rate, for example, the change rate (for example, 1.1, 0.9, etc.) of each small area when the true value is 1.0 is stored, and the result of the addition average is 1.0. Or the FOV position may be determined so as to be closest to 1.0.

  Next, a third embodiment will be described using a hole pattern as shown in FIG. 8 as an example. In the line patterns described in the first and second embodiments, the dimension is thick in the contamination deposition region in the field of view, while the dimension is thin in the scraped region by the beam. In the contamination accumulation region, the size is small, and in the shaving region by the beam, the size is large. FIG. 8A is a diagram for explaining the positional relationship between the hole pattern and the visual field range 804. FIG. 8B is a diagram illustrating the field-of-view range 805 of the SEM image with respect to the dimension measurement data acquisition position F in the present embodiment.

  As illustrated in FIG. 8A, when the dimension measurement data is acquired by controlling the dimension measurement data acquisition position F of the pattern to be measured so as to be positioned at the center of the image, the true value is obtained. A measurement value larger than the hole pattern dimension will be obtained. On the other hand, as shown in FIG. 8B, the dimension measurement data acquisition position E is not the center in the field of view, but the sum of the amount of contamination deposition (positive deposition) and the amount of shaving by the beam (negative deposition). By positioning it at the portion 803 that becomes zero, it is possible to obtain a true inspection / measurement result, that is, a value close to the hole diameter, without being affected by contamination or beam shaving.

  FIG. 19 is a diagram for explaining an example in which the filter described in FIG. 18 is applied to the dimension measurement of the hole pattern 1902. As in the example of FIG. 18, the dimensions of the patterns arranged continuously are not measured, and it is only necessary to know the dimensions between the length measuring boxes 1903 and 1904, so that two places of the length measuring boxes 1903 and 1904 are What is necessary is just to arrange | position on the boundary line between a positive deposition area | region and a negative deposition area | region. Therefore, instead of using the filter 1901, the FOV position may be determined by a method in which the two length measurement boxes 1903 and 1904 are simply brought close to the boundary line.

  Next, a fourth embodiment will be described with reference to FIG. Due to the miniaturization of the line pattern, the roughness of the line edge may affect device characteristics such as the gate threshold voltage. For this purpose, the dimension measuring apparatus sometimes performs roughness measurement. Specifically, as shown in FIG. 9A, the roughness of the line edge is measured by acquiring dimensions at a constant pitch over the longitudinal direction region 902 of the line pattern 901. FIG. 9B shows the uneven distribution in the longitudinal direction of the line in the visual field. As already described in the description up to the third embodiment, conventionally, the dimension measurement data acquisition position of the pattern to be measured is positioned at the center in the field of view 903. That is, when performing line edge roughness measurement, the center of the longitudinal direction region 902 of the line pattern 901 is positioned at the center in the visual field 903. In this example, most of the measurement region 902 is a region where the line is thin, and therefore the roughness is measured to be a small value with respect to the true value. Next, the position of the visual field 907 with respect to the measurement region 902 according to the present embodiment is shown in FIG. 9C, and the uneven distribution in the longitudinal direction of the line in the visual field 907 is shown in FIG. 9D. In the present embodiment, for example, the beam shift amount is calculated so that the sum of the amount of contamination deposition (positive deposition) in the longitudinal direction of the roughness measurement region 902 and the amount of scraping by the beam (negative deposition) becomes approximately zero, A feature is that the measurement region 902 is positioned in the area 907. As a result, more accurate roughness measurement can be performed.

  According to the above-described embodiment, in the process of recognizing the pattern to be measured by pattern matching (FIG. 2, 204), moving the image by beam shift and putting the measurement object in the field of view of the SEM (FIG. 2, 205), Rather than controlling the beam shift so that it is positioned at the center of the image, the beam shift amount is set so that the measurement target part of the pattern is located in the boundary area between the deposition area due to contamination in the field of view and the shaving area due to the beam. It has a function to control and performs measurement. Furthermore, when measuring an average value or roughness of a plurality of line patterns, the measurement site is positioned within the field of view so that the sum of the amount of contamination accumulated in the measurement region and the amount of shaving due to the beam is approximately zero. As a result, a value close to the true inspection / measurement result can be obtained without being affected by contamination or beam shaving.

  Next, a fifth embodiment will be described with reference to FIG. FIG. 20 illustrates a sample in which a large number of hole patterns are arranged, and is a diagram for explaining a technique for measuring an average value of pattern dimensions on the sample. In the present embodiment, a method of selecting a measurement target for obtaining an average value of a large number of arranged patterns will be described.

  FIG. 20 illustrates a method of selecting a pattern to be used for calculation of an average value by a FOV setting window 2001 having a boundary line 2002 on a sample image (or design data) in which a large number of hole patterns are arranged. Yes. The FOV setting window 2001 can be set to an arbitrary position on the SEM image or design data, and the SEM scanning position is set based on the setting. The FOV setting window 2001 also displays a boundary line 2002, a boundary area upper limit 2003, and a boundary area lower limit 2004. A boundary region upper limit 2003 and a boundary region lower limit 2004 indicate a range in which a dimensional variation value based on deposition can be regarded as substantially zero, or is acceptable as a measurement error.

  In this embodiment, an example will be described in which the boundary region upper limit 2003 and the boundary region lower limit 2004 are used as the boundary line region, and a pattern in which the pattern area is superimposed on the region by 50% or more is selected as the average value calculation target pattern. However, the present invention is not limited to this. For example, a pattern existing within a predetermined distance from the boundary line 2002 may be selected, or a pattern partially overlapping in the predetermined area may be selected. good. Any kind of selection method can be used as long as it is a selection method that selects a pattern in which dimensional variation based on deposition can be regarded as substantially zero.

  As described above, in the method (ACD (Averaged Critical Dimension)) for measuring the average value of the dimensions of a plurality of similar patterns, the influence of positive and negative depositions is selected by selecting the pattern to be used for the average value calculation as described above. It is possible to carry out a small amount of highly accurate measurement and calculation.

  When the number of patterns used for average value measurement is determined in advance, a predetermined number of patterns may be selected from patterns existing on or near the boundary line 2002. In this case, if a predetermined number is selected in the order of distance from the boundary line 2002, a pattern with less influence of positive and negative deposition can be selected. On the other hand, when the number of patterns existing in the vicinity of the boundary line 2002 is less than the predetermined number, the operator displays the information to that effect on the display device, so that the operator can set the recipe setting conditions (magnification, field position, device conditions). Etc.) can be reviewed.

  Next, a sixth embodiment will be described with reference to FIG. FIG. 15 is a diagram illustrating the FOV setting window 1501 as in FIG. In this embodiment, in the state where a plurality of arbitrary measurement points are set on the design data, the plurality of measurement points are on the boundary line 1507 or in the vicinity of the boundary line (for example, the boundary area upper limit 1508 and the boundary area lower limit 1509). In this example, the position of the FOV setting window 1501 is adjusted so as to be positioned.

  In recent years, OPC (Optical Proximity Correction) processing has been performed in order to transfer a designed pattern onto a wafer in lithography. The proximity effect in pattern formation is more conspicuous as the pattern is transferred closer to the resolution limit of the lens of the reduction projection type exposure apparatus, and complicated correction is required. There are many places on the photomask where such correction is performed, and proper evaluation of these is the key to improving the accuracy of OPC.

  Even when such a large number of measurement objects exist on the sample, measurement conditions for performing high-accuracy measurement with little influence of positive and negative deposition by determining the visual field position using the FOV setting window 1501 Can be set. FIG. 15 illustrates an example in which an FOV setting window 1501 is used to determine a visual field position for measuring five measurement points 1502 to 1506. As one aspect thereof, a search using the FOV setting window 1501 is performed on the design data of the semiconductor device, and five measurement points are included between the boundary region upper limit 1508 and the boundary region lower limit 1509, or the measurement points It is conceivable to select a visual field position that is partially overlapped as a visual field position for measurement. In addition, a search using the FOV setting window 1501 is performed on the design data, and the visual field position where the added value of the distance between the boundary line 1507 and the five measurement points is minimized is determined as the visual field position for measurement. Can be selected. In this case, if the minimum addition value exceeds a predetermined value, this fact is displayed as information, so that it is possible to grasp a state where a large divergence occurs between the measurement point and the boundary line. It becomes possible. In addition, not only the added value but also a distance threshold is set for each individual measurement point, and when the threshold value is exceeded, the information is displayed, for example, a state where only one point is separated from the boundary line Can be easily grasped.

  As described above, even when there are a large number of measurement points, it is possible to find a visual field position with little influence of positive and negative deposition by performing a search using the FOV setting window 1501.

  FIG. 16 is a diagram for explaining types of FOV setting windows. (A) is a method for selecting a measurement range between a decrease in size due to negative deposition inside the boundary line region (region close to the center of the circle) and an increase in size due to positive deposition outside the boundary line region. It is a window. (B) is a window for selecting the inside of the positive deposition region as a measurement range when negative deposition does not occur much while the influence of positive deposition is dominant. (C) is a window for selecting the outside of the negative deposition region as the measurement range when the negative deposition does not occur much while the influence of the negative deposition is dominant.

  By using these windows in accordance with the sample conditions and the apparatus conditions of the measuring apparatus, it becomes possible to automatically determine the visual field position for measurement with little influence of deposition.

  FIG. 17 is a flowchart for explaining a process of automatically determining the FOV position in accordance with the measurement point set on the design data. After setting measurement points on the design data (S1701), sample information and apparatus information are input (S1702). The input of the sample information or the like is for reading out a FOV setting window corresponding to a sample or apparatus condition stored in advance. However, when there is no corresponding FOV setting window, an arbitrary FOV setting window is applied. In some cases, this step is not necessary.

  The boundary line position (area) is set on the pre-registered or arbitrary FOV setting window, but when there is no such setting or when setting the arbitrary boundary line position (area) In the FOV, such setting is performed in S1703. Next, an FOV position where the measurement point is positioned at the boundary line position (area) is searched (S1704). When there are a plurality of measurement points, all the measurement points are positioned at the boundary line position (area) or satisfy the relationship between the boundary line and the measurement point as described above. If the condition is satisfied, the information is set as a recipe (S1706). If the condition is not satisfied, the FOV position is reset or reset. If it is determined that the setting is not possible, information indicating that the setting is impossible is transmitted (S1707).

  According to the processing illustrated in FIG. 17, it is possible to automatically determine the FOV position for performing measurement with little influence of positive and negative deposition.

  Next, a seventh embodiment will be described with reference to FIGS. In the present embodiment, a method for acquiring the uneven distribution in the field of view caused by contamination deposition and beam shaving in the examples shown in FIGS. 6 to 9 will be described.

  Conditions for measuring the actual pattern with the flat sample pattern in advance, such as the substrate material, acceleration voltage, probe current, voltage, number of frames added, and the number and magnification of autofocus performed until the final magnification is reached. In addition, the SEM image and the cross-sectional shape by AFM of the site scanned with the electron beam are acquired. For example, as shown in FIG. 10, data such as positional information in the field of view of the boundary 1003 between the contamination deposition region 1001 and the beam scraping region 1002, the contamination deposition amount 1005 and the beam scraping amount 1006, and the like are stored in a database in advance. Store it.

  In the flowchart shown in FIG. 11, first, in-field unevenness information in accordance with the measurement conditions is acquired from the database (FIGS. 1 and 1304), and the processing controller 1300 determines coordinates corresponding to the boundary of the unevenness distribution in the field of view at the measurement magnification. calculate. Next, the process proceeds to (201) and after the position coordinates on the wafer of the pattern to be measured are obtained. The final pattern positioning is performed by beam matching by obtaining the exact position of the target dimension measurement location by pattern matching, but the movement position by the beam shift of the dimension measurement location that was the center in the image is In this embodiment, the position corresponds to the boundary of the uneven distribution in the visual field calculated in the step 1011 (1015). It is desirable that a data table is prepared for each measurement condition in the database. Considering the possibility that the unevenness distribution due to the accumulation of contamination and the shaving by the beam fluctuates due to the change in the apparatus state, it is desirable to periodically acquire the SEM image and the cross-sectional shape of the AFM and update the data.

  In addition, there are a wide variety of materials used in recent semiconductor devices, and some of them include, for example, organic materials that emit a very large amount of gas. In the vacuum chamber after measuring a wafer using such a material, that is, a wafer with a large amount of outgassing, a large amount of residual hydrocarbon gas remains, affecting the measurement of the next wafer There is. Considering the possibility of fluctuations in the unevenness distribution due to contamination accumulation and beam shaving due to the influence of the previous process, the database contains unevenness on the next wafer, especially for wafers using materials with high gas release. It is desirable to memorize the result of variation to the distribution. Specifically, a wafer using a material that releases a large amount of gas in advance is retained in the vacuum chamber together with the time required to measure the actual pattern, and then the flat sample pattern is introduced into the vacuum chamber and the actual pattern. In addition to the conditions for measuring the SEM image, the cross-sectional shape by the AFM of the site scanned with the electron beam is acquired, and the uneven distribution is stored as a database. In the measurement, first, wafer information of the previous process is acquired, and when the previous wafer is a wafer with a large amount of outgassing, the uneven distribution of the unevenness considering the effect of the stored previous wafer is considered instead of the normal uneven distribution. By using the measurement result, the influence of the previous wafer can be eliminated.

  Some recent resist materials shrink by a primary electron beam. For such a resist material, it is desirable to store and store the shrink amount of the resist by the primary electron beam in a database, and to correct the uneven distribution during measurement. In actual pattern measurement, the unevenness distribution due to contamination accumulation and beam shaving is corrected for the amount of resist shrink, and the dimensional measurement position is positioned within the field of view, so that contamination, beam shaving, resist shrink, All effects can be eliminated. Regarding the measurement of the shrink amount of the resist, it is desirable to match conditions such as the primary electron beam conditions such as the acceleration voltage, the probe current, the voltage, the frame addition number, the resist pattern dimension, and the thickness.

  In addition, as a method for obtaining the boundary between another contamination accumulation region and a shaving region by a beam, a method using image contrast is also effective. For example, the accumulation region of contamination in FIG. 4C corresponds to the dark part of the SEM image (FIG. 4A), and the etching region in FIG. 4C is the SEM image (FIG. 4A). It corresponds to the bright part. Also in the line pattern of FIG. 5, the surrounding dark part and the bright part of the central part can be observed in the image, and the dark part has a thick dimension (FIGS. 5 and 501) and a small dimension in the bright part (FIGS. 5 and 502). ). This is because the secondary electron emission efficiency varies depending on the material, and the SEM image has a contrast. That is, there is a contrast difference between the amorphous carbon portion where the contamination is deposited and the substrate, in this case, Si. For example, the flowchart shown in FIG. 12 is obtained by adding contrast information acquisition (1012) to the flow described in FIG. For example, after the high-magnification image is captured, the contrast information of the image is acquired, and the processing controller 1300 calculates the coordinates corresponding to the boundary between the light and dark portions. Based on this, the beam shift amount is determined so that the position coordinates for obtaining the dimension data are calculated based on the contrast information and become the position corresponding to the boundary of the bright and dark part (1015).

  In this embodiment, the example in which the contrast information of the image is acquired after the high-magnification image is captured has been described. However, the same result can be obtained if the process is before beam shift or dimension measurement. The method for acquiring the contrast information can also be used for diagnosis of the state of the apparatus. For example, the coordinates corresponding to the boundary of the light and dark part are stored in the database (FIG. 1, 1301), and the variation in the width of the bright part when the same pattern is measured is graphed. When a trend that the light part becomes narrower is seen, this indicates that the hydrocarbon gas is increasing in the device, that is, the vacuum quality is lowered, and the device It is possible to schedule a maintenance period. It is also possible to continue to use the apparatus with an image quality that exceeds a certain level.

  Next, another embodiment for obtaining the boundary between the contamination accumulation region and the shaving region due to the beam will be described. As described above, the cause of contamination is that hydrocarbon gas molecules remaining in the vacuum chamber for observing the substrate or released from the substrate itself are aggregated in the part irradiated with charged particles and solidified. It will be converted into a deposit. Therefore, the incidence frequency of the hydrocarbon gas molecules in the sample in the vacuum chamber and the amount of contamination deposition are in a proportional relationship. The present embodiment is characterized in that the frequency of incidence of hydrocarbon-based gas molecules on the sample is used as an index of contamination deposition, that is, an area for forming a dark part in the SEM image field. Here, since the incidence frequency of hydrocarbon-based gas molecules to the sample is proportional to the partial pressure of the hydrocarbon-based gas, a mass analyzer capable of measuring the partial pressure is used. As shown in FIG. 13, the vacuum chamber 1200 is provided with a mass analyzer 1401, and information on the total amount of hydrocarbon-based gas partial pressure, for example, a mass number of 50 to 300 is sent to the processing control unit 1300 in real time. In the database in advance, the total amount of residual hydrocarbon gas and contamination accumulation information, specifically, flat sample pattern, substrate material, acceleration voltage, probe current, voltage, frame addition number, final magnification Acquire and store the relationship between the SEM image that matches the conditions when measuring the actual pattern, and the cross-sectional shape by the AFM of the part scanned with the electron beam, such as the number and magnification of the autofocus performed until reaching Keep it. In the flowchart shown in FIG. 14, first, the total amount Pcarbon of residual hydrocarbon gas in the vacuum chamber 1200 is obtained (1013), and then the value of the total amount of residual hydrocarbon gas, pattern measurement conditions (substrate material, acceleration voltage, In-field unevenness information corresponding to the probe current, voltage, number of frames added, number of times of autofocus performed until reaching the final magnification, magnification, etc.) is acquired from the database (FIGS. 12, 1304).

  As a result, the processing control unit 1300 can calculate the coordinates corresponding to the boundary of the uneven distribution in the field of view at the measurement magnification. In this case, since the change in the residual hydrocarbon gas in the vacuum chamber is monitored by the mass analyzer 1401, the apparatus state is monitored in real time. That is, the quality of the vacuum is lowered, and it is possible to schedule a maintenance time for the apparatus. In addition, it is possible to obtain an effect that it is possible to continuously use the apparatus with an image quality of a certain level or more.

  In the above-described embodiment, the example in which the FOV position is determined such that the influence of deposition or the like is reduced with respect to the measurement point has been described. However, the correction coefficient of the dimension value is stored in each small area of the FOV setting window. Alternatively, the true value may be calculated by multiplying the dimension value obtained at each measurement point by a correction coefficient stored in the small area to which each measurement point belongs.

402 Contamination 403 Scraping 601, 1001 Contamination deposition region 602, 1002 Scraping region 603 Region boundary 701, 702 Region 703 Boundary line 803 Partial 1003 Contamination deposition region and beam scraping region boundary 1100 Electron optical system 1101 Electron gun 1102 Primary electron beam 1103 Condenser lens 1104 Objective lens 1105, 1106 Deflector 1107 Alignment coil 1108 Astigmatism correction coil 1109 Objective lens stop 1110 Secondary electron detector 1111 A / D converter 1200 Vacuum chamber 1201 Wafer (substrate)
1202 XY stage 1300 processing control unit 1301 stage controller 1302 deflection / focus control unit 1303 acceleration voltage control unit 1304 database 1305 computer 1401 mass analyzer

Claims (20)

In a dimension measuring method of scanning a charged particle beam on a measurement target pattern formed on a sample and measuring a dimension of the measurement target pattern,
The charged particle beam is positioned so that a measurement position of the measurement target pattern is positioned between a region where deposits are deposited by the charged particle beam irradiation and a region where material on the sample is removed by the charged particle beam irradiation. And measuring the dimension of the pattern to be measured based on the scanning of the charged particle beam into the set field of view. In claim 1,
The determination of the visual field position is performed based on information relating to the deposition region of the deposit in the visual field acquired in advance. In claim 2,
Information on the deposition region of the deposit is obtained when the charged particle beam is irradiated on a flat sample. In claim 1,
Dimension that acquires information on a boundary between a region where the deposit is deposited and a region where the material on the sample is removed from contrast information of an image obtained when the sample is irradiated with a charged particle beam Measuring method. In claim 1,
Measure the amount of residual carbonized gas in the vacuum region irradiated with the charged particle beam,
Based on the acquired information on the amount of residual carbonaceous gas, the region where the deposit is deposited, or the region where the deposit is deposited by the charged particle beam irradiation, and the material on the sample by the charged particle beam irradiation A dimension measuring method, comprising: determining a boundary between a region to be removed. In a dimension measurement method for scanning a plurality of measurement target patterns formed on a sample with a charged particle beam and measuring the dimensions of the plurality of measurement target patterns,
While the area where deposits are deposited by the charged particle beam irradiation and the area where the material on the sample is removed by the charged particle beam irradiation, the dimension measurement data acquisition positions of the plurality of measurement target patterns overlap. The charged particle beam visual field position is set so that the dimension measurement data acquisition position is positioned at a position where the influence of the deposition and the influence of the removal of the material are offset. A dimension measuring method comprising measuring a dimension of the measurement target pattern based on scanning of a charged particle beam. In claim 6,
The determination of the visual field position is performed based on information relating to the deposition region of the deposit in the visual field acquired in advance. In claim 7,
Information on the deposition region of the deposit is obtained when the charged particle beam is irradiated on a flat sample. In claim 6,
Dimension that acquires information on a boundary between a region where the deposit is deposited and a region where the material on the sample is removed from contrast information of an image obtained when the sample is irradiated with a charged particle beam Measuring method. In claim 6,
Measure the amount of residual carbonized gas in the vacuum region irradiated with the charged particle beam,
Based on the acquired information on the amount of residual carbonaceous gas, the region where the deposit is deposited, or the region where the deposit is deposited by the charged particle beam irradiation, and the material on the sample by the charged particle beam irradiation A dimension measuring method, comprising: determining a boundary between a region to be removed. In a dimension measuring apparatus for measuring a dimension of a measurement target pattern based on a signal acquired by scanning a charged particle beam to the measurement target pattern formed on a sample,
The charged particle beam is positioned so that a measurement position of the measurement target pattern is positioned between a region where deposits are deposited by the charged particle beam irradiation and a region where material on the sample is removed by the charged particle beam irradiation. And a control device for setting the visual field position, and the control device measures the size of the measurement target pattern based on scanning of the charged particle beam into the set visual field. . In claim 11,
The control device includes a storage medium that stores information related to a deposition region of the deposit. In claim 12,
The dimension measuring apparatus is characterized in that the information related to the deposition region of the deposit is acquired when the charged particle beam is irradiated to a flat sample. In claim 11,
Obtaining information on a boundary between a region where the deposit is deposited and a region where the material on the sample is removed based on contrast information of an image obtained when the sample is irradiated with a charged particle beam. Dimension measuring device. In claim 11,
The region where the deposit is deposited or the charged particle beam irradiation based on the information on the residual carbonaceous gas amount obtained from a measuring device that measures the residual carbonaceous gas amount in the vacuum region irradiated with the charged particle beam And determining a boundary between a region where deposits are deposited by the step and a region where material on the sample is removed by the charged particle beam irradiation. In a dimension measuring apparatus for measuring a dimension of a measurement target pattern based on a signal acquired by scanning a charged particle beam to the measurement target pattern formed on a sample,
While the area where deposits are deposited by the charged particle beam irradiation and the area where the material on the sample is removed by the charged particle beam irradiation, the dimension measurement data acquisition positions of the plurality of measurement target patterns overlap. A control device that sets a field-of-view position of the charged particle beam so that the dimensional measurement data acquisition position is positioned at a position where the influence of the deposition and the influence of the material removal are offset, A dimension measuring apparatus for measuring a dimension of the measurement target pattern based on scanning of the charged particle beam into the set visual field. In claim 16,
The control device includes a storage medium that stores information related to a deposition region of the deposit. In claim 17,
The dimension measuring apparatus is characterized in that the information related to the deposition region of the deposit is acquired when the charged particle beam is irradiated to a flat sample. In claim 16,
Obtaining information on a boundary between a region where the deposit is deposited and a region where the material on the sample is removed based on contrast information of an image obtained when the sample is irradiated with a charged particle beam. Dimension measuring device. In claim 16,
The region where the deposit is deposited or the charged particle beam irradiation based on the information on the residual carbonaceous gas amount obtained from a measuring device that measures the residual carbonaceous gas amount in the vacuum region irradiated with the charged particle beam And determining a boundary between a region where deposits are deposited by the step and a region where material on the sample is removed by the charged particle beam irradiation.

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