Method for measuring pattern misalignment

According to one embodiment, a method for measuring pattern misalignment, includes: a first step obtaining image data; a second step specifying a measurement region; a third step calculating a first shift amount (x1, y1); a fourth step determining, after calculating the first shift amount, a first distribution; a fifth step executing a plurality of times the second step, the third step, and the fourth step; a seventh step calculating a second shift amount (x2, y2); an eighth step determining, after calculating the second shift amount, a second distribution; a ninth step executing a plurality of times the sixth step, the seventh step, and the eighth step; and a tenth step calculating a difference (x2−x1, y2−y1) between the second pattern misalignment and the first pattern misalignment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-061122, filed on Mar. 22, 2013; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a method for measuring pattern misalignment.

BACKGROUND

The process for manufacturing a semiconductor device includes e.g. the step of forming an electrode electrically connected to a semiconductor layer through an opening of an insulating film, or the step of forming a conductive via electrically connected to a wiring of each wiring layer of a multilayer wiring structure through an opening of an insulating film. These steps require forming an upper layer pattern in alignment with a lower layer pattern. If the upper layer pattern is formed out of alignment with the lower layer pattern, problems such as wiring failure and increased wiring resistance occur. Thus, after completing the formation of the upper layer pattern, an inspection step for measuring misalignment of the upper layer pattern with respect to the lower layer pattern is required. Marks dedicated to misalignment detection are previously placed on a scribe line for separating semiconductor chips in each of the lower layer and the upper layer. In the step of inspecting misalignment, the misalignment between the mark provided on the lower layer and the mark provided on the upper layer is measured by an optical measurement apparatus. This optical measurement method has short measurement through put and can easily view the mark of the lower layer through the film of the upper layer. Thus, misalignment can be frequently measured in an arbitrary step. However, the problem is that the pattern for measuring alignment needs to be formed larger than the pattern of the semiconductor device. Another problem is that the main pattern in the semiconductor device is not directly measured. In this context, in order to measure misalignment, use of a scanning electron microscope (SEM) secondary electron image (hereinafter referred to as SEM image) is under investigation. The SEM-based measurement method has the advantage of having higher spatial resolution than the optical measurement method, and being able to directly measure the misalignment of the main pattern of the semiconductor device. However, the SEM image is based on the information of a local region. Thus, due to the unevenness of the pattern and the overlapping condition of the upper layer pattern on the lower layer pattern, the accuracy of measuring pattern misalignment is likely to decrease.

DETAILED DESCRIPTION

In general, according to one embodiment, a method for measuring pattern misalignment, includes: a first step obtaining image data of a surface image of a to-be-measured substrate including on its surface a first layer having a first pattern and a second layer provided on the first layer and having a second pattern from the surface side of the substrate, the surface image including an image of the first pattern and an image of the second pattern, and the image data being represented by an X-Y coordinate system; a second step specifying a measurement region in the image data and to specify a first reference region corresponding to the measurement region in design data of the first pattern represented by the X-Y coordinate system; a third step calculating a first shift amount (x1, y1) of the first reference region in the X-Y coordinate system using a pattern matching technique when a portion of the design data of the first pattern in the first reference region is best matched with a portion of the image data corresponding to the image of the first pattern in the measurement region; a fourth step determining, after calculating the first shift amount, a first distribution of spacing between a first contour and a first design contour and to calculate a first standard deviation of the first distribution, the first contour defining the portion of the image data corresponding to the image of the first pattern in the measurement region, and the first design contour defining the portion of the design data of the first pattern in the first reference region; a fifth step executing a plurality of times the second step, the third step, and the fourth step while expanding the measurement region of the second step, and then when it is determined that the first standard deviation for last execution is stabilized, to take the first shift amount (x1, y1) for the last execution as a first pattern misalignment; a sixth step specifying a measurement region in the image data and to specify a second reference region corresponding to the measurement region in design data of the second pattern represented by the X-Y coordinate system; a seventh step calculating a second shift amount (x2, y2) of the second reference region in the X-Y coordinate system using a pattern matching technique when a portion of the design data of the second pattern in the second reference region is best matched with a portion of the image data corresponding to the image of the second pattern in the measurement region; an eighth step determining, after calculating the second shift amount, a second distribution of spacing between a second contour and a second design contour and to calculate a second standard deviation of the second distribution, the second contour defining the portion of the image data corresponding to the image of the second pattern in the measurement region, and the second design contour defining the portion of the design data of the second pattern in the second reference region; a ninth step executing a plurality of times the sixth step, the seventh step, and the eighth step while expanding the measurement region of the sixth step, and then when it is determined that a value of the second standard deviation for last execution is stabilized, to take the second shift amount for the last execution as a second pattern misalignment (x2, y2); and a tenth step calculating a difference (x2−x1, y2−y1) between the second pattern misalignment and the first pattern misalignment as a misalignment of the second pattern with respect to the first pattern.

Embodiments will now be described with reference to the drawings. The figures used in describing the embodiments are schematic for ease of description. The shape, dimension, size relation and the like of components in the figures are not necessarily identical to those in practical application, and can be appropriately modified as long as the effects of the embodiments are achieved.

With reference toFIGS. 1 to 11, a method for measuring pattern misalignment according to a first embodiment is described.

FIG. 1is a flow chart of a process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

FIGS. 2 and 3show one step in the process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

FIG. 4is a flow chart of one step in the process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

FIGS. 5 to 8show one step in the process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

FIG. 9shows the relationship between the variation of the spacing between the design contour of design data and the contour of SEM image data on one hand and the number of repetition elements of a pattern in the measurement region on the other.

FIG. 10is a flow chart of one step in the process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

FIG. 11shows one step in the process for measuring pattern alignment using the method for measuring pattern misalignment according to the first embodiment.

As shown inFIG. 1, the process for measuring pattern misalignment using the method for measuring pattern misalignment according to this embodiment includes the wafer loading step (S100), the wafer alignment step (S200), the step of moving to specified coordinates (S300), the step of obtaining SEM image data (S400, first step), the step of matching lower layer design data with the SEM image data (S500), the step of matching upper layer design data with the SEM image data (S600), and the step of calculating misalignment (S700).

By the wafer loading step (S100), a to-be-measured substrate1is set on a measurement stage in a SEM, not shown. The to-be-measured substrate1includes, on its surface, a lower layer (first layer) having a lower layer pattern (first pattern), and an upper layer (second layer) formed on the lower layer and having an upper layer pattern (second pattern). For instance, in the case of forming a multilayer wiring layer, the lower layer is an insulating layer including a plurality of vias electrically connected to the wiring of the upper layer. The upper layer is an insulating layer with a plurality of grooves formed therein so that the wiring is placed above the vias. In the multilayer wiring layer, the lower layer and the upper layer described above are repeated.

Next, as shown inFIG. 2, by the wafer alignment step (S200), the to-be-measured substrate1is positioned so that the origin of the to-be-measured substrate1coincides with the origin of the SEM measurement coordinate system (X-Y coordinate system). Specifically, a registration marker2has been formed on the surface of the to-be-measured substrate1. The position of the to-be-measured substrate1is adjusted using an optical microscope and the like so that this registration marker2is located at a prescribed position of the measurement coordinate system.

Next, as shown inFIG. 3, the stage of the to-be-measured substrate1is moved so that the position irradiated with the electron beam from the electron gun is located at specified measurement coordinates3(S300). Then, the electron beam is applied onto the surface of the to-be-measured substrate1. Thus, SEM image data4represented by the X-Y coordinate system is obtained (S400). The SEM image data4represents a SEM image by the X-Y coordinate system. The SEM image includes an image of the finished lower layer pattern5formed on the lower layer by the process for manufacturing the lower layer pattern, and an image of the finished upper layer pattern6formed on the upper layer by the process for manufacturing the upper layer pattern.

Next, the step of matching lower layer design data with the SEM image data (S500) is performed. As shown inFIG. 4, the step of matching lower layer design data with the SEM image data (S500) includes the step of specifying a measurement region in the SEM image data and specifying a first reference region in the design data of the lower layer pattern (S510, second step), the step of calculating a first shift amount (S520, third step), the step of calculating the variation of the spacing between a first design contour and a first contour (S530, fourth step), and the step of determining whether the variation of the spacing between the first design contour and the first contour is stable (S540, fifth step).

In the step of specifying a measurement region in the SEM image data and specifying a first reference region in the design data of the lower layer pattern (S510), as shown by the dashed line inFIG. 5, a measurement region4ais specified in the SEM image data4. A first reference region7ais provided in the lower layer pattern design data7. The first reference region7ais a quadrangular region corresponding to the measurement region4ain the SEM image data4. The lower layer pattern design data7includes data of the contour of the design lower layer pattern8represented by the X-Y coordinate system (hereinafter referred to as first design contour). The contour of the finished lower layer pattern5in the SEM image data4(hereinafter referred to as first contour) has been formed by a lithography process based on the first design contour of the design lower layer pattern8described above.

In the step of calculating a first shift amount (S520), as shown inFIG. 6, the first reference region7aof the lower layer pattern design data7is superposed on the measurement region4aof the SEM image data4. By a pattern matching technique such as the template matching technique, the first reference region7ais shifted on the measurement region4ain the X-Y coordinate system so that the design lower layer pattern8in the first reference region7aof the lower layer pattern design data7is best matched with the finished lower layer pattern5in the measurement region4aof the SEM image data4. The shift amount at this time is calculated as a first shift amount (x1, y1). The pattern matching technique can be a technique other than the template matching technique.

Next, the step of calculating the variation of the spacing between the first design contour and the first contour (S530) is performed. This step calculates the variation of the spacing between the first design contour of the design lower layer pattern8and the first contour of the finished lower layer pattern5when the design lower layer pattern8of the first reference region7adescribed above is best matched with the finished lower layer pattern5of the measurement region4a.

Specifically, as shown inFIG. 7, attention is focused on one of the repetition elements of the design lower layer pattern8and one of the repetition elements of the finished lower layer pattern5superposed thereon. A normal is drawn from a prescribed point of the first design contour of the aforementioned repetition element of the design lower layer pattern8to the first contour of the aforementioned repetition element of the finished lower layer pattern5. The length of this normal is taken as the spacing between the first design contour of the design lower layer pattern8and the first contour of the finished lower layer pattern5. At each of a plurality of points of the first design contour of one repetition element of the design lower layer pattern8, the length of the normal described above is calculated. This calculation of the length of the normal is performed on each repetition element of the design lower layer pattern8in the first reference region7a. Thus, for the number of repetition elements of the design lower layer pattern8occupying the first reference region7a, a first distribution of the spacing between the first design contour of the design lower layer pattern8and the first contour of the finished lower layer pattern5is obtained. The standard deviation a of this first distribution is calculated and taken as the variation of the spacing between the first design contour and the first contour.

In the step of determining whether the variation of the spacing between the first design contour and the first contour is stable (S540), as shown inFIG. 8, the measurement region4aand the first reference region7acorresponding thereto are expanded. In conjunction therewith, the step of specifying a measurement region in the SEM image data and specifying a first reference region in the design data of the lower layer pattern (S510), the step of calculating a first shift amount (S520), and the step of calculating the variation of the spacing between a first design contour and a first contour (S530) are performed a plurality of times. Here, the expansion of the measurement region4aand the expansion of the first reference region7arefer to increasing the number of repetition elements of the design lower layer pattern8in the first reference region7a.

FIG. 9shows a result of calculating the variation of the spacing between the first design contour and the first contour while expanding the measurement region4a(simply denoted as variation of contour spacing inFIG. 9). The variation of contour spacing is represented by 3σ. The size of the measurement region4ais represented by the number of repetition elements of the design lower layer pattern8included in the measurement region4aor the first reference region7a. The contour spacing is represented by the number of pixels of the image processing apparatus, with the actual numerical value omitted.

With the expansion of the measurement region4aand the first reference region7a, the variation of contour spacing significantly decreases and then starts to increase. When the number of repetition elements is 200 or more, the variation of contour spacing is stabilized. In the region where the variation of contour spacing is unstable, the shift amount of the first reference region7acalculated by the pattern matching technique has low reliability in measurement accuracy. Thus, when the variation of contour spacing is stable, the first shift amount (x1, y1) is calculated by the pattern matching technique and taken as a first pattern misalignment (x1, y1).

The determination of whether the variation of contour spacing is stable is performed e.g. as follows. The above process is executed a plurality of times. The value of the first standard deviation of the spacing between the first design contour and the first contour for the execution of the last time is calculated. The average value of the first standard deviations for the executions of a plurality of most recent times is calculated. When the difference between these values becomes a prescribed value or less, it is determined that the first standard deviation is stabilized. In the case ofFIG. 9, the first standard deviation for the number of repetition elements being 200 was calculated. The average value of the first standard deviations for the number of repetition elements being 195-199 was calculated. The difference between these values was 0.1 pixels or less. Thus, it was determined that the first standard deviation was stabilized.

Next, the step of matching upper layer design data with the SEM image data (S600) is performed. As shown inFIG. 10, the step of matching upper layer design data with the SEM image data (S600) includes the step of specifying a measurement region in the SEM image data and specifying a second reference region in the design data of the upper layer pattern (S610, sixth step), the step of calculating a second shift amount (S620, seventh step), the step of calculating the variation of the spacing between a second design contour and a second contour (S630, eighth step), and the step of determining whether the variation of the spacing between the second design contour and the second contour is stable (S640, ninth step). These steps perform the same operation as the step of specifying a measurement region in the SEM image data and specifying a first reference region in the design data of the lower layer pattern (S510, second step), the step of calculating a first shift amount (S520, third step), the step of calculating the variation of the spacing between a first design contour and a first contour (S530, fourth step), and the step of determining whether the variation of the spacing between the first design contour and the first contour is stable (S540, fifth step), respectively, included in the step of matching lower layer design data with the SEM image data (S500).

In the step of specifying a measurement region in the SEM image data and specifying a second reference region in the design data of the upper layer pattern (S610), as shown by the dashed line inFIG. 11, a measurement region4ais specified in the SEM image data4. A second reference region9ais provided in the upper layer pattern design data9. The second reference region9ais a quadrangular region corresponding to the measurement region4ain the SEM image data4. The upper layer pattern design data9includes data of the contour of the design upper layer pattern10represented by the X-Y coordinate system (hereinafter referred to as second design contour). The contour of the finished upper layer pattern6in the SEM image data4(hereinafter referred to as second contour) has been formed by a lithography process based on the second design contour of the design upper layer pattern10described above.

In the step of calculating a second shift amount (S620), the upper layer pattern design data9ais superposed on the measurement region4aof the SEM image data4. By a pattern matching technique such as the template matching technique, the second reference region9ais shifted on the measurement region4ain the X-Y coordinate system so that the design upper layer pattern10in the second reference region9aof the upper layer pattern design data9is best matched with the finished upper layer pattern6in the measurement region4aof the SEM image data4. The shift amount at this time is calculated as a second shift amount (x2, y2). The pattern matching technique can be a technique other than the template matching technique.

Next, the step of calculating the variation of the spacing between the second design contour and the second contour (S630) is performed. This step calculates the variation of the spacing between the second design contour of the design upper layer pattern10and the second contour of the finished upper layer pattern6when the design upper layer pattern10of the second reference region9adescribed above is best matched with the finished upper layer pattern6of the measurement region4a. The specific calculation method is the same as that of the step of calculating the variation of the spacing between the first design contour and the first contour (S530), and thus the description thereof is omitted. By this step, for the number of repetition elements of the design upper layer pattern10occupying the second reference region9a, a second distribution of the spacing between the second design contour of the design upper layer pattern10and the second contour of the finished upper layer pattern6is obtained. The standard deviation σ of this second distribution is calculated and taken as the variation of the spacing between the second design contour and the second contour.

Next, the step of determining whether the variation of the spacing between the second design contour and the second contour is stable (S640) is performed. This is performed similarly to the step of determining whether the variation of the spacing between the first design contour and the first contour is stable (S540), and thus the description thereof is omitted. By this step, when the variation of the spacing between the second design contour and the second contour is stable, the second shift amount (x2, y2) is calculated by the pattern matching technique and taken as a second pattern misalignment (x2, y2).

Next, the step of calculating misalignment (S700) is performed. In this step, the difference (x2−x1, y2−y1) between the second pattern misalignment (x2, y2) calculated by the step of matching upper layer design data with the SEM image data (S600) and the first pattern misalignment (x1, y1) calculated by the step of matching lower layer design data with the SEM image data (S500) is calculated as the misalignment of the upper layer pattern (second pattern) with respect to the lower layer pattern (first pattern).

In the method for measuring pattern misalignment according to this embodiment, the main pattern of the semiconductor device is directly observed by SEM. Thus, the misalignment measurement has high spatial resolution. This facilitates correction for the misalignment of the lithography process. Furthermore, in pattern matching, pattern misalignment is measured in the state in which the variation of contour spacing of the pattern is stable. Thus, the reliability of the measurement is improved.