JP4835481B2 - Resist pattern measuring method and resist pattern measuring apparatus - Google Patents

Description

  The present invention relates to a resist pattern measuring method and a resist pattern measuring apparatus for measuring a resist pattern in a scanning electron microscope for measuring short dimensions.

  With the recent miniaturization of semiconductor LSIs, a scanning electron microscope (hereinafter referred to as CD-SEM (Critical Dimension-Scanning Electron Microscope)) is mainly used as a means for measuring an LSI pattern on a wafer and a photomask pattern as an original of the LSI pattern. )) Is used. In CD-SEM, an electron beam emitted from an electron gun is converged by a condenser lens, and when a secondary electron emitted when it hits a wafer or photomask pattern through an aperture is captured by a detector. Convert to signal and get 2D image. Based on the information of the two-dimensional image, the dimension of the pattern is measured with high accuracy.

  As pattern dimensions become smaller year by year, the measurement accuracy required for CD-SEMs has become stricter. For example, in the technology roadmap of ITRS, the measurement reproducibility accuracy of 0.5 nm or less (3σ) is required after 2007 as the accuracy required for the measuring apparatus. In addition, as the accuracy of photomask patterns progresses, the number of inspection measurement points for confirming whether the pattern is designed as shown in the trend tends to increase. It is done on a daily basis.

  When performing automatic measurement with a CD-SEM, it is necessary to distinguish whether the pattern to be measured in the acquired SEM image is a remaining pattern (Line pattern) or a blank pattern (Space pattern). This is because the pattern in the SEM image has a white band portion at the edge, and the measurement method differs between the Space pattern and the Line pattern. FIG. 8 shows examples of SEM images and measurement methods. In the case of the Space pattern, the inside of the white band is measured, and in the case of the Line pattern, the outside is measured.

  Normally, the user specifies Line / Space in the measurement recipe, but if Line and Space are alternately arranged, the pattern to be measured may be shifted from the center of the SEM image due to variations in stage accuracy. Therefore, it is necessary to determine which pattern corresponds to Line or Space from the acquired image.

In the measurement of the photomask after completion, a method of differentiating the intensity distribution signal for the white band portion of the pattern edge twice and comparing the magnitude of the edge intensity of the signal to distinguish whether the measurement pattern is Line or Space Has been proposed (see Patent Document 1 and Non-Patent Document 1).
JP 2003-100828 A SPIE 6349-152 “A new algorithm for SEM critical dimension measurements for differentiation between lines and spaces in dense line / space patterns without tone dependence”

  However, the above-described method can be applied to a completed photomask, and cannot be applied to resist pattern measurement. In recent years, the accuracy required for patterns has become stricter, and not only the resist pattern exposed and transferred onto the wafer, but also the need to measure the resist pattern during the manufacturing process during photomask manufacturing has increased. ing.

  There is a particular problem in measuring a resist pattern by CD-SEM. The first problem is that, by irradiating an electron beam, the resist itself shrinks and cannot be measured correctly. The second problem is that the contrast of the resist pattern changes due to the influence of the charge, making it impossible to distinguish whether the pattern to be measured is a remaining part (Line pattern) or a removed part (Space pattern). It means that. In particular, the second problem is likely to occur when observing a resist pattern after drawing / development in the photomask manufacturing process, resulting in the phenomenon that the contrast between the resist pattern and the surrounding metal film such as chromium disappears, or even if there is contrast There is a phenomenon in which the light and dark are reversed. This phenomenon makes it impossible to distinguish between Line and Space, causing erroneous measurement in which both are mistakenly measured. FIG. 9A shows an example of an SEM image of a resist pattern. The graph shown in FIG. 5B represents the density distribution of the rectangular area in the SEM image. It can be seen that there is no difference in density between the resist pattern portion and the surrounding portion, and this alone can distinguish between Line and Space.

  The present invention has been made in view of the above problems, and in measurement of a resist pattern by a CD-SEM, a measurement target pattern in an image automatically determines a remaining portion (Line pattern) and a removed portion (Space pattern). An object of the present invention is to provide a resist pattern measuring method and a resist pattern measuring apparatus that can measure correctly and measure a true resist pattern dimension in which a shrink amount of resist is corrected.

  The invention according to claim 1 of the present invention is a resist pattern measuring method for measuring a resist pattern of a wafer or a photomask, and an image input step of acquiring at least two resist pattern images from the resist pattern of the wafer or photomask; The resist measurement step of measuring the inner dimension and the outer dimension of the pattern edge from each resist pattern image, and the measured values of the inner dimension and the outer dimension are compared to determine whether the resist pattern image is a remaining part or a removed part. And a measurement result output step of outputting each measurement result of the inner dimension and the outer dimension of the resist pattern subjected to the pattern determination.

  The resist pattern measurement method according to the present invention can automatically determine whether a measurement pattern is a remaining part (Line pattern) or a cut-out part (Space pattern) in measuring a resist pattern.

  According to a second aspect of the present invention, in the measurement result output step, a shrink amount of the resist by measurement is obtained from each measured value of the inner dimension and the outer dimension of each resist pattern image, and based on the shrink amount. And a true value calculating step for calculating the true value of the resist pattern before measurement.

  The resist pattern measuring method according to the present invention makes it possible to measure the true value of a pattern dimension obtained by correcting the shrinkage (reduction) of the resist.

  According to a third aspect of the present invention, there is provided a resist pattern measuring apparatus for measuring a resist pattern of a wafer or a photomask, and an image input means for acquiring at least two resist pattern images from the resist pattern of the wafer or the photomask. A resist measuring means for measuring an inner dimension and an outer dimension of a pattern edge from each resist pattern image, and comparing each measured value of the inner dimension and the outer dimension to determine whether the resist pattern image is a remaining part or a removed part. And a measurement result output means for outputting each measurement result of the inner dimension and the outer dimension of the resist pattern subjected to the pattern determination.

  The resist pattern measuring apparatus according to the present invention can automatically determine whether a measurement pattern is a remaining part (Line pattern) or a removed part (Space pattern) in measuring a resist pattern.

  In the invention according to claim 4 of the present invention, the measurement result output means obtains a shrink amount of the resist by measurement from each measured value of the inner dimension and the outer dimension of each resist pattern image, and based on the shrink amount. And a true value calculating means for calculating the true value of the resist pattern before measurement.

  The resist pattern measuring apparatus according to the present invention can measure the true value of the pattern dimension obtained by correcting the shrinkage (reduction) of the resist.

  According to the present invention, in the measurement of a resist pattern, it becomes possible to automatically determine the line / space distinction of the measurement pattern, and to measure the true value of the pattern dimension corrected for the resist shrinkage (reduction). Is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a resist pattern measuring apparatus 10 according to an embodiment of the present invention. In this figure, reference numeral 1 denotes an image input unit for inputting an observation image of a resist pattern to be measured. An image processing unit 2 performs pre-measurement processing such as noise removal processing on the input resist pattern image. The image processed at this time is displayed on three image display units (such as a monitor) and stored in a bitmap format in four image data storage units.

  Next, the measurement processing unit 5 performs pattern dimension measurement on the stored resist pattern image, and the obtained measurement result is stored in the numerical data storage unit 6. 7 uses the measurement result to determine whether the resist pattern is a removed portion (hereinafter referred to as a “space pattern”) or a remaining portion (hereinafter referred to as a “line pattern”), and to determine the true value of the resist pattern dimension. Processing to calculate is performed. Finally, the result is output to the result display unit 8 including a file, a printer, a monitor, and the like.

  Here, with reference to FIG. 2, the operation of the above-described resist pattern measuring apparatus 10 will be described in order. First, a first resist pattern image is acquired for measuring a resist pattern from an LSI pattern on a wafer or a photomask serving as an original of the LSI pattern (step S1). Next, a measurement process is performed on the first resist pattern image (step S2). As shown in FIG. 3A, the measurement process is performed by measuring the inner dimension 1 and the outer dimension 1 with the white band portion of the pattern edge as a boundary. Subsequently, a second resist pattern image is acquired for the resist pattern at the same location (step S3), and measurement processing is performed (step S4). As in step S2, the measurement process is performed by measuring the inner dimension 2 and the outer dimension 2 with the white band portion of the pattern edge as a boundary, as shown in FIG. 3B.

  Next, determination of Line / Space of the resist pattern image is performed by using each dimension value in Step S2 and Step S4 (Step S5). The determination of Line / Space of the resist pattern image is made by comparing the first and second values of the inner dimension (or outer dimension) using the fact that the resist shrinks due to the irradiation of the electron beam by the CD-SEM. Do. That is, it is determined whether the measurement target pattern is Line / Space depending on whether the result of subtracting the inner dimension 1 from the inner dimension 2 is positive or negative. For example, when the result of subtracting the inner dimension 1 from the inner dimension 2 is negative, the measurement target pattern is determined to be a line pattern. In this case, the outer dimension is the resist dimension of the Line pattern. On the other hand, when the result of subtracting the inner dimension 1 from the inner dimension 2 is positive, the measurement target pattern is determined to be a Space pattern. In this case, the inner dimension is the resist dimension of the Space pattern.

  After performing the Line / Space determination of the measurement target pattern, a process for calculating the true value of the resist pattern dimension is performed (step S6). FIG. 4 shows a graph in which the pattern shrinks (reduces) when the resist pattern (line pattern) is measured 10 times. From this graph, it can be seen that the pattern dimension changes almost linearly according to the number of measurements. Since the true value of the resist pattern dimension is before such shrinkage occurs, it is sufficient to subtract the shrinkage from the first measurement result. Therefore, the true value of the resist pattern dimension may be calculated by calculating the shrink amount of the resist pattern from the difference between the two measurement results and correcting the first measurement value by the shrink amount as shown in FIG. That is, Δwidth, which is the shrink amount, is calculated from width2−width1, and the true value of the resist pattern dimension is obtained from width1−Δwidth.

  As described above, according to the resist pattern measuring apparatus of the present embodiment, it becomes possible to automatically determine the Line / Space distinction of the measurement pattern, and the trueness of the pattern dimension obtained by correcting the resist shrinkage (reduction). The value can be measured.

[Example 1]
Here, Example 1 of the resist pattern measuring method of the present invention is shown. FIG. 6 is an SEM image of a certain resist pattern. It is unknown whether this resist pattern is Line / Space. Therefore, first, the first resist pattern image is acquired, and the inner dimension 1 and the outer dimension 1 are measured. Then, a second resist pattern image is acquired and the inner dimension 2 and the outer dimension 2 are measured. The measurement results were as follows.

1st sheet inner dimension 1 = 355.7 nm, outer dimension 1 = 408.6 nm
2nd sheet inner dimension 2 = 355.2 nm, outer dimension 2 = 407.4 nm

  Comparing the measurement results of the first sheet and the second sheet, it can be seen that the second sheet is smaller. Therefore, the resist pattern in FIG. 6 is determined to be a line pattern. Since the outer dimension is applied to the measurement of the Line pattern, the true value is calculated from the outer dimensions 1 and 2 by the following procedure.

Δwidth = outside dimension 2−outside dimension 1
= 407.4 nm-408.6 nm = -1.2 nm
True value = outside dimension 1−Δwidth
= 408.6 nm-(-1.2 nm) = 409.8 nm

[Example 2]
Next, as Example 2, a measurement example using a Line / Space pattern (see FIG. 7) in which Line patterns and Space patterns are alternately arranged will be described. Also in this case, at the time of obtaining the resist pattern image, it is not known which is the Line / Space pattern. First, a first resist pattern image is acquired, and an inner dimension A1 and an outer dimension A1, and an inner dimension B1 and an outer dimension B1 are measured. Next, a second resist pattern image is acquired, and the inner dimension A2 and the outer dimension A2, and the inner dimension B2 and the outer dimension B2 are measured. The result was as follows.

1st sheet inner side A1 = 951.5 nm, outer side A1 = 998.6 nm,
Inner B1 = 1002.9 nm, outer B1 = 1050.9 nm
2nd sheet inner side A2 = 950.9 nm, outer side A2 = 997.0 nm
Inner B2 = 1004.1 nm, outer B2 = 1051.8 nm

  Comparing the measurement results of the first and second sheets, it can be seen that the pattern A is smaller on the second sheet and the pattern B is larger on the second sheet. Accordingly, in the resist pattern of FIG. 7, it is determined that the pattern A is Line and the pattern B is Space. Since the outer dimension is applied to the measurement of the line pattern, the true value is calculated from the outer dimensions A1 and A2 by the following procedure.

Δwidth = outside dimension A2-outside dimension A1
= 997.0 nm-998.6 nm = -1.6 nm
True value = outside dimension A1-Δwidth
= 998.6 nm-(-1.6 nm) = 1000.2 nm

  On the other hand, since the inner dimension is applied to the measurement of the Space pattern, the true value is calculated from the inner dimensions B1 and B2 by the following procedure.

Δwidth = inside dimension B2—inside dimension B1
= 1004.1 nm-1002.9 nm = 1.2 nm
True value = inside dimension B1-Δwidth
= 1002.9 nm- (1.2 nm) = 1001.7 nm

  The present invention can be applied to the measurement of resist patterns by CD-SEM.

It is a block diagram which shows the structure of the resist pattern measuring apparatus which concerns on embodiment of this invention. It is a flowchart explaining operation | movement of the resist pattern measuring apparatus which concerns on embodiment of this invention. FIG. 6A is a graph showing an example of density distribution measurement of a first resist pattern image, and FIG. 5B is a graph showing an example of density distribution measurement of a second resist pattern image according to an embodiment of the present invention. It is a graph which shows the shrink of the resist pattern which concerns on embodiment of this invention. It is a schematic diagram which calculates the true value of the resist pattern which concerns on embodiment of this invention. It is a figure which shows the example of a measurement of the resist pattern which concerns on Example 1 of this invention. It is a figure which shows the example of a measurement of the resist pattern which concerns on Example 2 of this invention. It is a figure explaining the conventional SEM image example and the measuring method of a resist pattern. The conventional (a) is a SEM image example of a resist pattern, and (b) is a graph showing a density distribution measurement example of a resist pattern image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image input part 2 Image processing part 3 Image display part 4 Image data storage part 5 Measurement processing part 6 Numerical data storage part 7 Data analysis part 8 Result display part 10 Resist pattern measurement apparatus

Claims (4)

In a resist pattern measuring method for measuring a resist pattern of a wafer or a photomask,
An image input step of obtaining at least two resist pattern images from the resist pattern of the wafer or photomask;
A resist measurement step of measuring the inner and outer dimensions of the pattern edge from each resist pattern image;
A pattern determination step of comparing each measured value of the inner dimension and the outer dimension to determine whether the resist pattern image is a remaining part or a removed part;
A resist pattern measurement method comprising at least a measurement result output step of outputting each measurement result of the inner dimension and the outer dimension of the resist pattern subjected to the pattern determination.   In the measurement result output step, the shrink amount of the resist by measurement is obtained from the measured values of the inner dimension and the outer dimension of each resist pattern image, and the true value of the resist pattern before the measurement is calculated based on the shrink amount. The resist pattern measuring method according to claim 1, further comprising a true value calculating step. In a resist pattern measuring apparatus for measuring a resist pattern of a wafer or a photomask,
Image input means for obtaining at least two resist pattern images from the resist pattern of the wafer or photomask;
A resist measuring means for measuring inner and outer dimensions of the pattern edge from each resist pattern image;
Pattern determination means for comparing the measured values of the inner dimension and the outer dimension to determine whether the resist pattern image is a remaining part or a removed part;
A resist pattern measuring apparatus comprising at least measurement result output means for outputting measurement results of the inner dimension and the outer dimension of the resist pattern whose pattern has been determined.   The measurement result output means calculates a resist shrink amount by measurement from each measured value of the inner dimension and the outer dimension of each resist pattern image, and calculates a true value of the resist pattern before the measurement based on the shrink amount. 4. The resist pattern measuring apparatus according to claim 3, further comprising a true value calculating means.