JP4834478B2 - Pattern evaluation method and apparatus - Google Patents

Description

  The present invention relates to a fine pattern inspection method, and more particularly to a method and apparatus for evaluating patterns such as contact holes and line patterns formed on a semiconductor wafer by a photolithography process using an exposure apparatus such as a stepper.

  In a semiconductor manufacturing process, a pattern is formed on a semiconductor wafer by photolithography. In the pattern formation, a reduction projection exposure method using a reduction projection exposure apparatus (hereinafter referred to as a stepper) using a reticle formed with an enlarged dimension of a circuit pattern for several chips is frequently used. In the reduced projection exposure method using a stepper, the resist mask pattern is transferred by exposing the reticle mask pattern to a projected image on the photoresist film of the wafer and developing the exposed photoresist film. Are formed on the wafer. A pattern for several chips formed on the reticle can be transferred by one exposure (shot). This process is stepped and repeated to transfer the pattern onto the wafer.

  As an example, a case where a contact hole is formed on an insulating film of a wafer will be described. First, a photoresist film is formed on the insulating film, and then the photoresist film is exposed and developed using a reticle having a contact hole pattern with dimensions and arrangement according to design values. Thereafter, a contact hole pattern penetrating the insulating film can be formed on the wafer by performing a process such as etching using the photoresist film to which the pattern is transferred as a mask.

Japanese Patent Laid-Open No. 9-33211 JP-A-11-271233 JP-A-10-209230

  By the way, when a pattern is formed on a wafer by a stepper as described above, a fine pattern on an enlarged reticle is subjected to reduced projection exposure on the wafer through a projection optical system. The pattern may differ in size, shape, position, etc. between the surface and the bottom of the exposed layer (photoresist film).

  The cause is first caused by the exposed material such as the wafer and the resist on the wafer. Warpage, distortion, deflection, etc. of the wafer itself are caused by the ambient environment such as the passage of time or temperature after the manufacturing process of the wafer and the like, and affect the interference of exposure light. In addition, the shape of the pattern to be formed varies depending on the properties of the substance used as the resist, the film thickness at the time of applying the resist, and uneven coating. Deviations in the formation position and dimensions of the fine pattern due to these exposed materials with the respective design values on the surface and bottom of the exposure surface (hereinafter collectively referred to as positional displacement) are widespread in a certain area of the wafer. It is often distributed with a certain tendency.

  The second cause is the performance of the optical system itself of the exposure apparatus as schematically shown in FIG. As shown in FIG. 2A, there is no problem in the vicinity of the reticle center, but as shown in FIG. 2B, astigmatism caused by exposure light incident obliquely on the wafer surface at the periphery of the reticle during exposure. Lens aberrations such as aberration and coma correspond to this. The positional deviation resulting from this appears mainly in a certain tendency in the radial direction from the center position within one shot range.

  As a third cause, as a property of the optical system itself of the exposure apparatus, the focal position shift (defocus) caused by the lens of the optical system used for exposure is deformed by the heat during exposure (lens heating). Is mentioned. A fourth cause is the lens optical system of the exposure apparatus. When the lens or the like is tilted in the exposure optical system, the exposure light is incident from the side, so that the exposure pattern within one shot range is displaced in a certain direction.

  Although there is a difference between the design value and the actually formed pattern mainly due to the first to fourth causes, the problem that arises from this is that the position of the pattern formed on the front and bottom surfaces of the photoresist is first. It is possible to shift. Similarly, there is a problem of misalignment between the design value and the pattern of the lower layer or upper layer of the insulator due to the shift of the axis and position of the actually exposed pattern. If the contact hole pattern is misaligned or misaligned, the area of the opening is reduced, resulting in an increase in electrical resistance and ultimately a decrease in semiconductor performance. In some cases, the semiconductor device becomes non-conductive and becomes a fatal defect in the semiconductor device.

  To solve the above problems, a method of evaluating the exposure accuracy by calculating the area of the bottom surface of a fine pattern is currently used. However, exposure is performed based on the amount of pattern displacement, the direction of displacement, or their values. A method for quantitatively evaluating the optical system, wafer, etc. of the apparatus has not been established.

  Therefore, the present invention calculates the positional relationship between the portion corresponding to the surface of the photoresist and the portion corresponding to the bottom surface of the fine pattern in the semiconductor in the form of its displacement vector, and evaluates each fine pattern, and further, one shot unit, chip unit Another object of the present invention is to provide a method for quantitatively evaluating the exposure accuracy in units of wafers, or a method for evaluating each part of the pattern exposure system and detecting an abnormality and warning.

  In the present invention, the formation state of the exposure layer surface (hereinafter referred to as the surface) and the bottom surface of the exposure layer (hereinafter referred to as the bottom surface) and the positional relationship thereof are calculated for the fine pattern to be evaluated, and the relative relationship between them. The positional deviation is calculated as a positional deviation vector and displayed on the screen. When the positional deviation vector exceeds a preset positional deviation allowable range, a warning is issued. The calculated feature quantities are classified according to their trends, and feature analysis is performed in shot units, chip units, and wafer units, thereby enabling evaluation of an exposure system, a wafer, and the like.

  That is, the fine pattern inspection method according to the present invention acquires an image of a fine pattern formed on a thin film in the fine pattern inspection method for inspecting a fine pattern formed on a thin film applied on a substrate through a pattern exposure process. And a step of obtaining a fine pattern shape on the upper surface of the thin film and a fine pattern shape on the lower surface of the thin film from the image, and a step of detecting misalignment between the two fine patterns obtained in the step. . The fine pattern shape can be obtained by detecting the contour of the pattern.

  When the fine pattern is a circular pattern such as a contact hole, a deviation between the center of gravity of the circular pattern on the upper surface of the thin film and the center of gravity of the circular pattern on the lower surface of the thin film is detected as the positional deviation. Further, when the fine pattern is a line pattern, a deviation between the center axis of the line pattern on the upper surface of the thin film and the center axis of the line pattern on the lower surface of the thin film is detected as the positional deviation.

  By displaying an arrow indicating the magnitude and direction of the positional deviation of the fine pattern at the position of the fine pattern, the positional deviation of the pattern can be easily recognized visually. The fine pattern may be displayed as an approximate curve or a discontinuous point or mark.

  The fine pattern inspection method according to the present invention includes a step of detecting the positional deviation at a plurality of positions in a predetermined section, and a step of statistically processing the positional deviation at the plurality of positions to determine the positional deviation characterizing the section. Can further be included. In this case, by displaying an arrow corresponding to the size and direction of the positional deviation that characterizes the section in each section, it is possible to easily recognize the position shift of the overall pattern of the section visually. The section may be a one-shot area or a one-chip area.

  Further, it includes a step of comparing the distribution tendency of misalignment at the plurality of positions with the distribution tendency of misalignment expected when there is an abnormality in the fine pattern forming apparatus, thereby detecting abnormality of the fine pattern forming apparatus. be able to. The fine pattern inspection method according to the present invention also acquires an image of a fine pattern formed on a thin film in the fine pattern inspection method for inspecting a fine pattern formed through a pattern exposure process on a thin film applied on a substrate. The method includes a step, a step of obtaining a shape of a fine pattern from the image, and a step of categorizing the fine pattern according to a feature amount of the shape.

  The fine pattern inspection method includes a step of categorizing the fine pattern at a plurality of positions in one shot or one chip, and a fine process for statistically processing the categorization results at the plurality of positions to characterize the one shot or one chip. And a step of determining a category of the pattern. In statistical processing of categorized results, for example, the number of inspections in each shot or chip is compared with the number of fine patterns belonging to a certain category, and the pattern with the highest ratio is represented by a representative feature at that position. The process is positioned as If the sections of one shot or one chip are colored and displayed according to the category of the fine pattern that characterizes the one shot or one chip, the overall characteristics can be easily grasped visually.

  According to the present invention, for the contact hole and / or line pattern, the edge position corresponding to the surface and the bottom surface of the exposure layer is displayed, and at the same time, the degree of displacement of the pattern on the surface and the bottom surface is displayed as a position displacement vector. When the value exceeds the allowable value, warning and warning can be easily performed and confirmation of the exposure accuracy evaluation of the fine pattern can be easily performed. In addition, for the contact hole and / or line pattern, when the edge position corresponding to the surface or the bottom surface of the exposure layer is displayed, the feature amount of the shape of the exposure pattern is obtained, and the feature amount exceeds the allowable value. By giving a warning, automation and confirmation of exposure accuracy evaluation of a fine pattern can be easily performed. It is also effective to analyze by combining the positional deviation vector and the shape feature amount. Further, the pattern exposure apparatus analyzes the distribution state of the feature amount representing the position deviation vector and / or the shape of the fine pattern with respect to a wider area such as one chip or one shot area or the entire wafer. This makes it possible to collect data that is useful for statistical evaluation of lens aberrations such as thermal stress, astigmatism and coma due to heat treatment over a wide range. Then, by applying the inspection of the fine pattern to an arbitrary plurality of processes, the data can be fed back to the subsequent process.

  According to the present invention, automation and confirmation of exposure accuracy evaluation of a fine pattern can be easily performed. Also, it is possible to detect an abnormality in the optical system of the exposure apparatus or the wafer by evaluating the distribution of the features of the fine pattern in a wider area such as one chip or one shot, or even the entire wafer. .

  Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, a calculation method and a display method of misregistration vectors for individual contact hole patterns and line patterns formed on an exposure layer (photoresist film) of a wafer will be described. Next, a large number of misregistration vectors are analyzed and generally analyzed. A method of deriving a general tendency and analyzing the cause of the positional deviation will be described.

  FIG. 1 is a schematic view showing an example of a fine pattern inspection apparatus used in the method of the present invention. FIG. 1 shows a scanning electron microscope as a typical fine pattern inspection apparatus. The electron gun 1 energizes and heats the heating filament 2 to obtain an electron beam 8. The electron beam 8 drawn out by the Wehneld 4 is accelerated by the anode 5, focused by the condenser lens 6, scanned by the deflection coil 7 to which the deflection signal is applied from the deflection signal generator 15, and is sampled by the objective lens 9. Focused on a sample 11 placed in 10. In this way, the electron beam 8 is scanned one-dimensionally or two-dimensionally on the sample 11 on which a fine pattern is engraved. By irradiation with the electron beam 8, secondary electrons corresponding to the shape of the sample 11 are generated near the surface of the sample 11 and detected by the secondary electron detector 17. The detected secondary electrons are amplified by the amplifier 18 and become a luminance modulation signal of the CRT 14. The CRT 14 is synchronized with the deflection signal generator 15, and the luminance modulation signal reproduces a secondary electron image generated from the surface portion of the sample 11 by the electron beam 8 irradiated in synchronization. By the above procedure, information on the fine pattern formed on the sample surface can be acquired. The secondary electron image displayed on the CRT 14 is taken by the camera 13 as necessary.

  FIG. 3 is a flowchart for calculating the positional deviation vector of the fine pattern based on the image information of the fine pattern obtained as described above. In the following, a method for detecting a misregistration vector and a display method for a case where a fine pattern to be misregistration detection is a contact hole pattern formed in an exposure layer (photoresist film) will be described. Here, the fine pattern image is obtained by the scanning electron microscope, but the fine pattern image may be obtained by means other than the scanning electron microscope such as an optical microscope.

  First, in step 11, an image of a fine pattern acquired with a scanning electron microscope or the like is displayed on the image display device, and an arbitrary one of contact hole patterns is designated by operating a mouse cursor or the like. In step 12, polar coordinate conversion is performed on the image of the selected contact hole pattern, and a plurality of cross-sectional waveform information (profiles) are generated at a certain angle in the radial direction from the center of the contact hole pattern. Each is subjected to differentiation, threshold processing, and the like to calculate edge candidates. With the above operation, a plurality of edge candidates are calculated for each angle direction. From these edge candidates, an edge corresponding to the exposed layer surface of the contact hole pattern (hereinafter referred to as an outer circle) and an edge corresponding to the bottom surface of the exposed layer (hereinafter referred to as an inner circle) are detected. Edge information obtained as a profile is abundant due to factors such as the complexity and miniaturization of the structure of the fine pattern itself, and further improvement in performance of the inspection apparatus, making it difficult to detect an edge corresponding to a desired position. However, the portions corresponding to the edges of the outer circle and the inner circle described above have abundant edge information, and exist at a substantially constant distance (that is, a circle) from the center of the hole pattern in all angle directions. Therefore, by calculating more edge candidates when calculating edge candidates, and calculating outer circles and inner circles using the edge information, edge detection corresponding to the desired position can be performed.

  In step 13, the center of gravity is calculated for each of the inner circle and the outer circle detected in step 12, and these are set as M1 and M2. Here, the position information of the outer circle and the inner circle is expressed by the center of gravity. However, for example, the intersection of the major axis and the minor axis of the circle may be used as the position information of the circle. However, it is necessary to always use a certain standard in a series of fine pattern inspections. In step 14, a vector from the center of gravity M1 of the inner circle to the center of gravity M2 of the outer circle is calculated as a contact hole positional deviation vector. At this time, an allowable range of the positional deviation of the fine pattern is set in advance by visually observing an image picked up by an inspection apparatus or the like. It should be noted that the allowable range of misalignment is preferably set at its maximum and minimum values based on two criteria, for example, direction and size. Similarly, the major and minor diameters of the outer circle and the inner circle, or the permissible range of the area and the area ratio of the outer circle and the inner circle are also set. Then, it is determined whether or not the calculated positional deviation vector exceeds an allowable value.

  On the image display device, the outer circle and inner circle calculated for the selected contact hole are circles formed by connecting edge candidates having edge information corresponding to the respective circles calculated for each fixed angle, and the step The screen is displayed as shown in FIG. 4 by an arrow connecting the misregistration vector calculated in 14 in the direction from M1 to M2. Here, the positive direction of the positional deviation amount is set as the direction from M1 to M2, but if a constant reference is always used, the direction from M2 to M1 may be set as the positive direction.

  If it is determined in step 14 that the size, direction, etc. of the positional deviation vector are within the preset allowable range of positional deviation, the process proceeds from step 14 to step 15 where the outer circle, inner circle, and The displacement vector is displayed on the screen in white, which means that it is within the allowable range. If the size, direction, etc. of the misregistration vector exceeds the preset misregistration tolerance, the process proceeds to step 16 to indicate a warning for the outer circle, inner circle and misregistration vector of the contact hole. Display in red.

  In addition to the positional deviation vector, whether or not the contact hole is permitted may be determined based on the shapes of the outer and inner circles of the contact hole. As shown in FIG. 5, typical categories related to the shape of the outer circle and inner circle include circularity (perfect circle, ellipse), ratio of major axis to minor axis, absolute value of area, or outer circle and inner circle. Area ratio etc. can be considered. In this case, each category is classified into levels according to the ratio of large, medium, small, or a reference value, and an allowable range for each category is set at the same time. Then, it is calculated which level of the set category the shape of the outer circle or inner circle of the contact hole of interest belongs to and compared with the allowable range.

  When the shape of the contact hole exceeds the allowable range, a warning is given by displaying the contact hole displayed on the image display device in color. FIG. 6 is a display example when the shape of the contact hole exceeds the allowable range. FIG. 6A shows a display example when the major axis of the outer circle is longer than the allowable maximum value, the difference from the allowable value is indicated by an arrow, and the outer circle is displayed in a color such as red indicating a warning. FIG. 6B shows a display example when the major axis of the outer circle is shorter than the allowable minimum value, the difference from the allowable value is indicated by an arrow, and the circle corresponding to the outer circle is indicated by a color such as red indicating a warning. indicate. FIG. 6C is a display example when the area of the outer circle is smaller than the allowable minimum value, and a warning is given by displaying the inside of the outer circle in light red. Although FIG. 6 shows an example in which the shape is evaluated for the outer circle of the contact hole, the same evaluation can be performed for the inner circle of the contact hole.

  Next, with reference to the flowcharts of FIGS. 7 and 3, a detection method and a display method of a positional deviation vector when the fine pattern to be detected for positional deviation is a line pattern formed on an exposure layer will be described. First, in step 11 of FIG. 3, an image of a line pattern to be inspected is acquired by a fine pattern inspection apparatus such as a scanning electron microscope or an optical microscope. Next, in step 12, a fixed detection range 21 is set for the acquired line pattern image as shown in FIG. 7A, and an edge is detected within the detection range 21 as shown in FIG. 7B. Detection is performed to detect line edges on the surface and bottom surface of the exposure layer (photoresist film). Next, the process proceeds to step 13, and as shown in FIG. 7B, the center axis L1 of the line edge on the photoresist bottom surface and the center axis L2 of the line edge on the photoresist surface are obtained. FIG. 7C is a cross-sectional view taken along the line AA in FIG. Then, as shown in FIG. 7D, a perpendicular line extending from the center of the axis L1 to the axis L2 in the detection range 21 is obtained as a positional deviation vector (L1-L2) of the line pattern.

  Also in this case, an allowable value of the positional deviation amount is set in advance by visual inspection or the like with an inspection device, and in step 14, the positional deviation vector calculated in step 13 is compared with the preset allowable value. Do. If it is determined in step 14 that the calculated displacement vector size is larger than the preset displacement tolerance value, the process proceeds to step 16 to display the edge of the line pattern and the displacement vector in red. Warning. If the size of the positional deviation vector is smaller than a preset positional deviation allowable value, the process proceeds to step 15, and the edge of the line pattern and the positional deviation vector are displayed on the screen in white.

  In the line pattern, as in the case of the contact hole pattern, the shape of each of the exposed layer (photoresist film) surface and the bottom surface is categorized to determine whether the line pattern is allowed or not. May be. As a typical category of the line pattern, as shown in FIG. 8, there is a shape or a line width. An allowable range is set for the shape and width of the line pattern, and when there is a line pattern that exceeds the allowable range, the line pattern is displayed in color in red or the like to call attention.

  Next, an evaluation method for a fine pattern such as a plurality of contact hole patterns and line patterns exposed by a stepper, particularly an evaluation method for an area corresponding to one shot of a reticle or one chip will be described. Here, an example will be described in which a fine pattern is evaluated using two pointers of a displacement vector and a shape.

  As shown in FIG. 9, generally, a plurality of chips 31a, 31b, 31c,. First, image information for one shot of the exposure pattern is acquired by an inspection apparatus such as a scanning electron microscope. Contact hole patterns or line patterns are selected at a plurality of positions within one shot range, shape information is acquired for each pattern, and the position of each contact hole pattern or line pattern is obtained by the method described with reference to the flowchart of FIG. A shift vector is calculated. At this time, in order to realize the chip comparison together with the shot comparison, in each chip 31a, 31b, 31c,... In one shot, at the representative locations in the chip such as the four corners 32a to 32d and the center 32e. It is preferable to select a sample pattern for calculating the displacement vector. It is desirable to select a large number of sample patterns evenly in the chip area so as not to significantly reduce the inspection throughput. Also, the sample pattern acquisition location is the same for each chip.

  The positional deviation vector calculated for each contact hole pattern or line pattern is displayed with an arrow from the position of the center of gravity of each contact hole pattern or line pattern, for example. If the calculated positional deviation vector exceeds the allowable range, a warning is given in red. The categorization shown in FIG. 10 is performed on the position shift vector at each sample position in one shot or chip area calculated here. For the entire one shot range, the size (large, medium, small) of the entire displacement vector shown in FIG. 10A and the direction (upper, upper right, Categorize by 8 directions (right, lower right, lower, lower left, left, upper left, etc.).

  Further, the categorization is performed on the displacement vector of the contact hole pattern or the line pattern (sample pattern) acquired at a representative location in one chip or one shot according to the directionality and size deviation. For example, as shown in FIG. 10 (c), the directionality is determined by whether the displacement vector at each sample position is in the same direction, outward, inward, or in an irregular direction. Characterize by whether or not. As shown in FIG. 10D, for example, as shown in FIG. 10D, the deviation of the size of the positional deviation vector is categorized so as to be uniform, large only in the peripheral part, large in the central part, and locally large. Each feature amount is associated with the region from which the feature is extracted. Note that the categorizing method is not limited to the four types shown in FIG. 10, and other feature amounts may be used as long as they can represent the tendency of the positional deviation vector within one shot range.

A positional deviation vector representing one shot range or the entire chip range is calculated as follows. In a certain k-th chip range, for example, k1 contact holes and patterns and k2 line patterns are set as sample patterns for calculating a displacement vector, and processing as described in the flowchart of FIG. To calculate the displacement vector of the contact hole pattern calculated as SH ₁ , SH ₂ ,. . . . SH _k1 , the line pattern misregistration vectors as SL ₁ , SL ₂ ,. . . . , SL _k2 , the displacement vector VCk representing the chip can be calculated by the following [Equation 1]. Note that when the design value is different for each pattern, the size of the calculated displacement vector is also different, so adjustment is performed using the coefficients α and β. The calculation of the positional deviation vector representing each shot range can be performed in the same manner.

  Further, the results of categorizing the contact hole and line pattern shape performed as shown in FIG. 5 or FIG. 8 are collected in one shot range or chip range, and for example, the shape of the shape corresponding to the region corresponding to the largest category is obtained. It is a representative value.

  From the characterization regarding the magnitude and distribution status of the displacement vector within one shot range calculated in this way, and the results of categorization regarding the shape of the contact hole or line pattern, the first cause to the fourth cause described above. Possible to suggest abnormalities.

  FIG. 11 is a diagram showing the tendency of positional deviation within one shot when the pattern projection optical system has lens aberration. For example, as shown in FIG. 11A, when a plurality of misalignment vectors are inward of the radial direction from the center within one shot range, or the shape of the contact hole is in the central direction as shown in FIG. When it is deformed vertically, or when it is horizontally deformed in the center direction as shown in FIG. 11C, an abnormality caused by lens aberration of the exposure apparatus is considered. Therefore, when such a feature is seen, a warning that lens aberration may appear in the projection optical system of the stepper is displayed as an image.

  FIG. 12 is a diagram showing a tendency of positional deviation when the projection optical system has an axial deviation or a lens inclination. As shown in FIG. 12, when a plurality of positional deviation vectors are directed in one direction within the range of one shot, an abnormality caused by the axial deviation of the projection optical system can be considered. Therefore, when such a feature is found, a warning is given by means such as displaying a message to that effect.

  FIG. 13 is an explanatory diagram of a line pattern formed when defocusing due to lens heating occurs. FIG. 13A shows a line pattern formed at the time of best focus, and FIGS. 13B and 13C show a line pattern formed at the time of defocus. In FIGS. 13A to 13C, the left diagram is a view of the line pattern as viewed from above, and the left diagram is a schematic sectional view thereof. FIG. 13B shows a line pattern when the defocus direction is the + direction (when the focal position is above the exposure surface). At this time, the line pattern has a shape in which the upper part is thin and the skirt is widened. Become. FIG. 13C shows a line pattern when the defocus direction is in the negative direction (when the focal position is below the exposure surface). At this time, the line pattern has a narrow upper part and a widened skirt. The part becomes unclear. As described above, when the shape of the line pattern is thin or the hem portion is unclear, an abnormality caused by defocus is considered, and a warning to that effect is displayed. Since the lens heating is caused by heat accumulation in the lens due to continuous exposure for a long time, the characteristics of the lens to be used can be known by examining the time-series change of the pattern shape.

  FIG. 14 is a diagram illustrating an example of a tendency that appears in the misregistration vector when the wafer itself is deformed or there is resist unevenness. If the wafer itself warps, bends, or unevenly coats the applied photoresist film, it will have a significant effect on the axial misalignment of the entire wafer. By examining the above, it becomes possible to evaluate the elements caused by the wafer. As shown schematically in FIG. 14, abnormalities caused by uneven coating of the wafer itself or the photoresist film are often distributed over a certain range of the wafer 30. Therefore, by paying attention to certain characteristics and analyzing the distribution in the wafer, it is possible to suggest the occurrence of an abnormality due to the wafer itself or photoresist coating unevenness.

  Next, a description will be given of a method for displaying on the screen information on positional deviation vectors and shapes for fine patterns such as contact holes and line patterns. One or a plurality of areas are designated for each chip in the wafer, and a positional deviation vector is obtained in the designated area, and the positional deviation vector for each chip or shot is calculated in the same manner as in [Equation 1]. Characterize. When displaying information on positional deviations of fine patterns, a figure in which the wafer is divided into shot areas or a figure in which specific shot areas are divided into chip areas is displayed on the display device, and each shot area on the wafer is specified or specified. The calculated displacement vector is displayed in color for each chip area in the shot. Similar to the processing in the flowchart of FIG. 3, if the positional deviation vector exceeds the allowable range for each shot unit or for each chip unit, a warning is given with a noticeable color such as red.

  FIG. 15 is an explanatory diagram of a format for storing positional deviation vectors and feature amount data calculated for each pattern on the wafer. The data is a tree structure having a hierarchy of wafers, shots, chips, and in-chip patterns. The record of each pattern in the chip includes the x and y coordinates of the pattern, pattern information (whether the pattern is a line pattern, a contact hole, etc.), the feature amount such as the size, direction, and shape information of the positional deviation vector in the pattern. have. The chip unit holds an average of each piece of pattern information belonging to the chip as a chip record. Similarly, in the case of shot units, an average of information held by chips in the shot is held as a record. Also, each data holds the ID of the area one level higher as “parent”, the ID of the area derived from the same parent as “sibling”, and the ID of the next lower level as “child” is doing. For example, the chip “3” holds information of “1” as a parent, “4” as a sibling, and “7” and “8” as children.

  FIGS. 16 and 17 show examples in which various feature quantities related to the positional deviation vector obtained by the above-described method are statistically processed and displayed on the display device. FIG. 16 shows a wafer screen, and FIG. 17 shows a shot screen.

  The wafer screen displays shot unit information as shown in FIG. In the wafer map, the shot unit is divided by a square or the like, and the feature amount and the position deviation vector of the entire shot range are displayed. Numbers 1 to 16 are assigned to each shot range, and the numbers correspond to coordinates in the wafer. Each shot range 1 to 16 on the wafer map is displayed by color according to the color corresponding to the feature amount representing the shot (the most feature amount in the shot) A to D, and the shot is superimposed on each shot range. A displacement vector representing the range is displayed. In the table at the bottom of the screen, the distribution of feature quantities related to the shape of the fine pattern is displayed numerically. The numbers in the table represent the number of appearances of each feature amount in each shot range. The total number of each feature amount is displayed on the right side of the table, and when there is a feature in the appearance tendency, it is displayed in the evaluation column. A typical tendency is analyzed in advance, and when the actual evaluation is applicable, it is displayed as (1) and (2), and an explanatory text is displayed in the lower part of the screen regarding the fine tendency.

  As shown in FIG. 17, the shot screen displays information in units of chips in the shot. A wafer map is simultaneously displayed on the shot screen, and a position on the wafer map corresponding to the currently displayed shot is displayed. Further, each chip 1 to 8 in the shot is color-coded and displayed by a color corresponding to a feature amount (the most feature amount in the chip) A to D representing the chip, and is superimposed on the position of each chip. A displacement vector representative of the chip is displayed. In the table at the bottom of the screen, the distribution of feature quantities related to the shape of the fine pattern is displayed numerically. The total number of each feature amount is displayed on the right side of the table, and when there is a feature in the appearance tendency, it is displayed in the evaluation column. A typical tendency is analyzed in advance, and when the actual evaluation is applicable, it is displayed as (1) and (2), and an explanatory text is displayed in the lower part of the screen regarding the fine tendency. In the case of the illustrated example, the feature amount B is evaluated as being abnormal, and the chip 1 column is displayed in light red.

  The display screen shown in FIG. 16 or FIG. 17 changes depending on the feature amount of interest (the layout is the same). For example, if the feature amount is “A: circular feature” illustrated in the upper part of FIG. 5, the items of feature amounts A, B, C, D,... In FIG. Horizontal, oblique (1), oblique (2) characters are entered. When there are five categories, the number of items is five (A to E), and the corresponding display colors are five. Each shot or chip area is colored and displayed with the color of the characteristic quantity representing the area (the largest characteristic quantity in the area). In addition, the “feature value” part of the table is like a button, and each time you press it, the categorization of FIG. 5 is, for example, first “circular feature”, once pressed “flatness”, once again pressed As shown in “Area”, it changes in order, and the numerical value in the table and the display color of the shot area in the wafer map or the chip area in the shot change accordingly.

  Although not shown here, a screen in the range of one chip is also prepared. The one-chip range screen is a screen similar to the one-shot range screen, and a pattern displacement vector is displayed at the position of each sample pattern in one chip. In addition, the shot screen is displayed at the same time so that the position of the currently displayed chip in the shot can be seen at a glance.

  FIG. 18 is a diagram illustrating the relationship between the wafer screen, the shot screen, and the chip screen. On the wafer screen in FIG. 18A, for example, when the mouse cursor is clicked on the shot range 2 where a large displacement vector is displayed, the shot is displayed in an enlarged manner as shown in FIG. 18B. Move to the screen. On the shot screen, an average positional deviation vector in the chip is displayed for each chip in the shot. Furthermore, on the shot screen, for example, when the mouse cursor is clicked on the chip 7 on which a large displacement vector is displayed, the chip is enlarged and displayed as shown in FIG. 18C. The deviation vector distribution is displayed. In this way, it is possible to identify a particularly prominent point. It is also possible to return to the original shot screen by double-clicking the chip screen and to return to the wafer screen by double-clicking the shot screen. The database structure shown in FIG. 15 is used when moving the wafer screen and the shot screen and when moving from the shot screen to the chip screen. For example, when moving from the screen of shot 1 to the chip screen, the chip screen is generated using the information of chips 3 and 4.

  FIG. 19 is a flowchart for explaining the entire procedure of the fine pattern inspection method according to the present invention. First, in step 21, a wafer as an object to be inspected is loaded into an inspection apparatus such as a scanning electron microscope or an optical microscope. Next, in step 22, a shot (or chip) for investigating the positional deviation of the fine pattern or the feature of the shape of the fine pattern is designated in the wafer, and the process proceeds to step 23, where the position in the shot (or chip) is determined. Specify the deviation calculation position.

  Next, in step 24 to step 28, the positional deviation vector is calculated and the positional deviation vector is characterized for the designated fine pattern. In step 29, it is determined whether or not the calculated positional deviation vector or the feature amount of the shape is within an allowable range. If the positional deviation is within the allowable range, the process proceeds to step 30 to display the positional deviation vector or fine pattern in a normal color. If it exceeds, the process proceeds to step 31 to display a warning by displaying the misalignment vector or fine pattern in red or the like.

  Next, the process proceeds to step 32, and statistical trend analysis is performed on the characteristics regarding the distribution status of the large number of misregistration vectors calculated at steps 24 to 28 or the shape of the fine pattern. Subsequently, the process proceeds to step 33, in which it is determined whether the tendency of the feature amount analyzed in step 32 suggests an abnormality of the exposure apparatus or the wafer. In the determination process of step 33, for example, a combination of a positional deviation vector distribution pattern and a known abnormality cause as shown in FIGS. 11 (a), 12 and 14, or FIGS. 11 (b) and 11 (c). FIG. 13 shows a combination of the pattern shape feature amount distribution pattern and the known abnormality cause as a table, and the tendency of the feature amount obtained in step 32 is checked against the table to determine the cause of the abnormality. Perform a search. If it is determined in step 33 that the positional deviation vector distribution pattern or pattern shape feature amount distribution exists in the table and an abnormality of the exposure apparatus or wafer is suggested, the process proceeds to step 34 to display a message or the like about the cause of the abnormality. And warn you.

Schematic which shows an example of the fine pattern inspection apparatus used for the method of this invention. Explanatory drawing of an example of the exposure abnormality resulting from the performance of optical system itself of exposure apparatus. The flowchart of position shift vector calculation. The figure which shows the example of the screen display method of the outer circle of a contact hole, an inner circle, and a position shift vector. The figure which shows the example of the categorization regarding the shape of a contact hole. The figure which shows the example of a display of the warning when the major axis, minor axis, or area of the outer circle and / or inner circle of a contact hole exceeds an allowable value. The figure which shows the example of the screen display method of the exposure layer surface pattern of a line pattern, a bottom face pattern, and a position shift vector. The figure which shows the example of the categorization of the exposure layer surface pattern of a line pattern, and a bottom face pattern. The figure which shows the example of selection of the sample fine pattern for position shift vector calculation in each chip | tip within 1 shot range. The figure which shows the example of the categorization of the positional offset vector calculated in multiple positions. The figure which shows the position shift tendency of the fine pattern resulting from a lens aberration, and the deformation | transformation tendency of a shape. The figure which shows the tendency of position shift generation | occurrence | production in case there exists an axis shift and the inclination of a lens in a projection optical system. Explanatory drawing of the line pattern formed when the defocus by lens heating has generate | occur | produced. The figure which shows the example of the distribution tendency of the position shift vector resulting from a deformation | transformation of a wafer itself, or resist application nonuniformity. The figure which shows the example of the database structure of the positional offset vector and the feature-value calculated by each pattern on a wafer. The figure which shows the example of the screen display of the positional offset vector and feature-value evaluation in a wafer unit. The figure which shows the example of the screen display of the position shift vector in 1 shot, and feature-value evaluation. The figure which shows the relationship between a wafer screen, a shot screen, and a chip | tip screen. The flowchart explaining the whole procedure of the fine pattern inspection method by this invention.

Explanation of symbols

1: electron gun, 2: heating filament, 4: Wehneld, 5: anode, 6: condenser lens, 7: deflection coil, 8: electron beam, 9: objective lens, 10: sample chamber, 11: sample, 13: camera , 14: CRT, 15: deflection signal generator, 17: secondary electron detector, 18: amplifier, 21: detection range, 30: 1 shot range, 31a to 31n: chip, 32a to 32d: representative in chip Place

Claims (10)

In a pattern evaluation method for evaluating a pattern formed in a sample including a plurality of chips,
Detect the electrons obtained based on the electron beam irradiation on the sample,
Based on the detected electrons, for each chip on the sample, or for each shot of the projection exposure apparatus, the size of the deviation between the upper surface and the lower surface of the contact hole formed on the resist film in the chip or shot,及beauty to detect the direction of this upper surface and the lower surface of the displacement,
Each said chip, or displays the detected deviation of the size of each shot, the information about the direction of及beauty those upper surface and the lower surface of the displacement,
The shift is the shift of the center of gravity on the upper surface of the contact hole and the center of gravity on the lower surface of the contact hole, or the intersection of the major axis and minor axis of the ellipse on the upper surface of the contact hole and the major axis of the ellipse on the lower surface of the contact hole. A pattern evaluation method characterized by being a deviation between the intersection of the axis and the minor axis . The pattern evaluation method according to claim 1 ,
A pattern evaluation method, wherein an arrow indicating the magnitude and direction of displacement of the contact hole is displayed at the position of the contact hole. The pattern evaluation method according to claim 1 , further comprising:
Detecting the shift at a plurality of positions in a predetermined section;
Statistically processing misalignment at the plurality of positions to determine misalignment characterizing the section;
A pattern evaluation method comprising: The pattern evaluation method according to claim 3 ,
A pattern evaluation method, wherein an arrow corresponding to the magnitude and direction of a shift characterizing the section is displayed on the section. In pattern evaluation method according to claim 3 or 4, further
A pattern for detecting an abnormality of the hole pattern forming apparatus, comprising a step of comparing the distribution tendency of the deviation at the plurality of positions with a distribution tendency of deviation expected when the hole pattern forming apparatus has an abnormality. Evaluation methods. In a pattern evaluation apparatus that evaluates a pattern formed in a sample including a plurality of chips,
An electron detection means for detecting electrons obtained based on irradiation of the sample with an electron beam;
Based on the detected electrons, for each chip on the sample, or for each shot of the projection exposure apparatus, the size of the deviation between the upper surface and the lower surface of the contact hole formed on the resist film in the chip or shot, a deviation detecting means for detecting the direction of及beauty those upper surface and the lower surface of the displacement,
Each said chip, or the detected shift in the size of each shot, and display means for displaying information about the direction of及beauty those upper surface and the lower surface of the displacement,
Equipped with a,
The shift is the shift of the center of gravity on the upper surface of the contact hole and the center of gravity on the lower surface of the contact hole, or the intersection of the major and minor axes of the ellipse on the upper surface of the contact hole and the major axis of the ellipse on the lower surface of the contact hole. a pattern evaluation apparatus according to claim Zuredea Rukoto between the intersection of the minor axis. The pattern evaluation apparatus according to claim 6 ,
The pattern evaluation apparatus, wherein the display means displays an arrow indicating the magnitude and direction of displacement of the contact hole at the position of the contact hole. The pattern evaluation apparatus according to claim 6 ,
The deviation detecting means detects the deviation at a plurality of positions in a predetermined section,
The pattern evaluation apparatus further comprises means for statistically processing the position shifts at the plurality of positions to obtain a shift characterizing the section. The pattern evaluation apparatus according to claim 8 ,
The pattern evaluation apparatus, wherein the display unit displays an arrow corresponding to a magnitude and direction of a shift characterizing the section on the section. In the pattern evaluation apparatus according to claim 8 or 9 ,
And a means for comparing the distribution tendency of deviation at the plurality of positions with the distribution tendency of deviation expected when there is an abnormality in the hole pattern forming apparatus, and detecting abnormality of the hole pattern forming apparatus, Pattern evaluation device.

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