JP2003224061A - Misalignment measurement method - Google Patents

Abstract

(57) [Problem] To provide a misalignment measurement method for obtaining a misalignment measurement value most approximate to a true value of misalignment. The present misalignment measuring method uses a misalignment measuring device to determine a pattern formed on an object to be exposed in a previous step and a pattern to be transferred onto the object to be exposed in a subsequent step following the previous step. In measuring the misalignment using the misalignment measurement marks provided on the respective patterns, a misalignment measuring method that is optimal for a misalignment measuring device is found and the misalignment is measured. In the present method, a step of arranging the misalignment measurement marks of the pattern at the misalignment measurement points 32 uniformly distributed on the exposure target W and measuring the misalignment of each misalignment measurement mark by a plurality of types of measurement methods. And a step of obtaining a variation of the misalignment measurement value of each misalignment measurement mark for each measurement technique, and a step of selecting a measurement technique having the smallest variation as an optimal measurement technique for the misalignment measuring apparatus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a misalignment measuring method, and more particularly to a misalignment measuring method for obtaining a misalignment measurement value which is closest to a true misalignment value.

[0002]

2. Description of the Related Art In the process of manufacturing a semiconductor device, a pattern forming layer such as a wiring layer is often patterned to form patterns such as wiring and contact holes. When patterning the pattern formation layer, patterning is usually performed by applying an optical lithography technique. In the photolithography technique, a film of a photosensitive resin (photoresist) is formed on a substrate surface of a semiconductor substrate, exposure light such as ultraviolet rays is irradiated through a mask having a desired pattern, and a photoresist film (hereinafter referred to as a resist film). ) Reduce the size of the mask pattern onto the mask and expose it. Then, by developing, a pattern in which the mask pattern is miniaturized can be transferred onto the resist film.

For example, a case where a contact hole penetrating an insulating film and communicating with a lower wiring under the insulating film is formed will be taken as an example. First, a resist film is formed on the insulating film. Next, exposure light is irradiated through a mask having a pattern of contact holes, and the pattern of the contact holes of the mask is reduced and projected on the resist film for exposure. Then
By developing, an etching mask can be formed on the insulating film by transferring a pattern obtained by miniaturizing the pattern of the contact hole of the mask on the resist film. Then, when the insulating film is etched from above the etching mask, a contact hole which penetrates the insulating film and reaches the lower layer wiring can be opened.

When the above-mentioned contact hole is opened, if the pattern of the lower layer wiring and the pattern of the contact hole are aligned with each other, the contact hole is located just above the lower layer wiring. However, if a pattern shift occurs between the lower layer wiring pattern and the contact hole pattern, the contact hole opens at a position deviated from the lower layer wiring, a contact plug is formed in the contact hole, and the contact plug is formed on the contact plug. When the upper layer wiring is formed, the upper layer wiring and the lower layer wiring are not electrically connected to each other, resulting in a defective product. Therefore, it is most important to match the pattern of the lower layer wiring and the pattern of the contact hole with each other when forming the pattern.

Therefore, in the photolithography process performed in the process of manufacturing a semiconductor device, it is necessary to measure the misalignment between the lower layer wiring and the upper and lower layers (pattern forming layers) forming the contact holes. Conventionally, the misalignment between the layer formed in the previous process and the layer formed in the subsequent process is caused by the misalignment measurement mark provided on the wafer,
It is obtained by measuring the misalignment with the misalignment measurement mark on the mask pattern of the layer formed in the subsequent step with an misalignment measuring machine.

The misalignment measurement marks are, as shown in FIG. 4, on the exposure area where a plurality of misalignment measurement marks cover the four chip forming areas 12A to 12D (matte portion) of the wafer W, or on the exposure area. 4 chip forming area 1
It is provided in a scribe area surrounding 2A to D.
In FIG. 4, the misalignment measurement marks are provided at the center of the wafer W and at four locations around the wafer, a total of five locations.
FIG. 4 is a wafer plan view showing the misalignment measurement points. The misalignment measurement mark 10 is, as shown in FIG. 5, the outer measurement mark 1 provided on the layer formed in the previous step.
4 and the inner measurement mark 16 provided on the layer to be aligned for forming a film on the layer formed in the previous step
It consists of and. The outer measurement mark 14 is formed as a square ring shape, and the inner measurement mark 16 is formed as a square ring shape smaller than the square ring shape of the outer measurement mark 14.

As shown in FIG. 6, the misalignment measuring machine 30 includes a light source 18, a beam splitter 20 for changing the optical path of the irradiation light from the light source 18, and irradiation light received from the beam splitter 20 on a wafer chuck 22. A lens 24 for reducing and projecting onto the held wafer W, and a CCD camera 26 for receiving reflected light from the wafer W via the lens 24 and the beam splitter 20 and detecting a misalignment measurement mark.
Have and.

The misalignment measuring machine 30 is a CCD camera 2
6, the measurement mark 1 outside the misalignment measurement mark 10
4 and the inner measurement mark 16 are picked up and output as image data to the image processing device, and then the positions of the outer measurement mark 14 and the inner measurement mark 16 are obtained as detection waveforms as shown in FIG. The difference between the midpoint positions of the mark 14 and the inner measurement mark 16 is measured as a misalignment value. In FIG. 7, the two thin peaks inside the detected waveform indicate the position of the inner measurement mark 16, and the two outer thick peaks indicate the position of the outer measurement mark 14. Hereinafter, the thin peak is referred to as the CCD detection waveform of the inner measurement mark, and the thick peak is referred to as the CCD detection waveform of the outer measurement peak.

When measuring the misalignment using the misalignment measuring machine 30, a recipe for measuring misalignment (measurement method)
There are various types. For example, as shown in FIG. 8A, the CC of the outer measurement mark used for measuring the detected waveform is used.
There is a recipe (hereinafter referred to as a first recipe) for setting a position measurement window on the outer waveform of the D detection waveform and the outer waveform of the CCD detection waveform of the inner measurement mark. Also, FIG.
As shown in (b), a recipe for setting windows on the inner waveform of the CCD detection waveform of the outer measurement mark and the outer waveform of the CCD detection waveform of the inner measurement mark used for measuring the detection waveform (hereinafter referred to as the second recipe and There is). Further, as shown in FIG. 8C, a recipe for setting a window for the entire waveform of the CCD detection waveform of the outer measurement mark used for measuring the detection waveform and the outer waveform of the CCD detection waveform of the inner measurement mark (hereinafter, referred to as There is a third recipe). Furthermore, recipes of other methods can be adopted.

In the conventional misalignment measuring method, the misalignment of one misalignment measurement mark provided at any of a plurality of misalignment measuring points provided on the wafer is measured by various recipes, and the most misalignment is measured. A recipe with less variation in measured values is selected as the optimum recipe. For example, the misalignment of one misalignment measurement mark is measured a plurality of times using the above-mentioned first to third recipes, and the measurement reproducibility of each recipe, that is, 3σ, the range (Range), etc. A recipe with a small value or range value is selected as the optimum recipe, and misalignment measurement is performed. Here, 3σ is 3 of the standard deviation value of the measurement values measured multiple times.
The range means the absolute value of the difference obtained by subtracting the maximum value from the minimum value of the measurement values measured multiple times.

[0011]

However, in the conventional misalignment measuring method described above, it is possible to reduce erroneous measurement, but whether the absolute value of the misalignment measurement value is accurate, that is, the true value. There remains a question as to whether the difference between and is small. Therefore, an object of the present invention is to provide a misalignment measurement method that obtains a misalignment measurement value that most closely approximates the true misalignment value.

[0012]

In order to achieve the above-mentioned object, a method for measuring misalignment according to the present invention comprises a pattern formed on an object to be exposed in a pre-process and a pattern formed in a post-process following the pre-process. When measuring the misalignment with the pattern to be transferred on the exposed body using the misalignment measuring machine based on the misalignment measuring marks provided on each pattern, we found the optimum misalignment measuring method for the misalignment measuring machine. , A method of measuring misalignment, in which pattern misalignment measurement marks are arranged at evenly distributed misalignment measurement points on the exposed object, and misalignment of each misalignment measurement mark is measured by a plurality of types. Method, the step of obtaining the deviation of the misalignment measurement value of each misalignment measurement mark for each measurement method, and the measurement method with the smallest deviation It is characterized by a step of selecting as the optimum measurement techniques misalignment measuring machine.

Practically, the variation of the misalignment measurement value is displayed as 3σ, and the measurement method with the smallest 3σ is selected as the optimum measurement method. In the step of measuring the misalignment by a plurality of kinds of measuring methods, the misalignment of the misalignment measuring mark is measured once by a plurality of kinds of measuring methods. As a result, the maximum effect can be achieved with the minimum effort.

The optimization method of the alignment measurement according to the present invention is
By selecting the optimum measurement method for the misalignment measuring machine, instead of the conventional method of improving the measurement accuracy of the measuring machine by setting the optimization recipe using the measurement reproducibility and reducing erroneous measurements. This is a measurement method that improves the absolute value measurement accuracy (difference from the true value) of the misalignment measuring machine.
The method of the present invention can be applied to an optical misalignment measuring machine, although it can be applied to any misalignment measuring machine.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described specifically and in detail with reference to the accompanying drawings. Embodiment Example This embodiment example is an example of an embodiment of a misalignment measuring method according to the present invention, and FIG. 1 is a wafer plan view showing positions of misalignment measuring points. In this embodiment example, first,
Dispersion is evenly distributed over the entire surface of the wafer W, and misalignment measurement points are set. For example, as shown in FIG. 1, the misalignment measuring points 32 are provided on every other chip forming area 12 of the wafer W or on a scribe area surrounding every other chip forming area 12. At the misalignment measurement point 32, an outer measurement mark provided on the pattern of the layer formed in the previous step is arranged.

Next, as shown in FIG. 7, the inner measurement mark provided in the mark pattern is positioned inside the outer measurement mark, and the mask of the layer formed in the subsequent step is placed on the layer formed in the previous step. Align with. The misalignment of the misalignment measurement marks at each misalignment measurement point 32 is measured once by each of various recipes, and the σ of the misalignment measurement values by the respective recipes at all the misalignment measurement points in the X and Y directions, that is, 3σX. , And 3σY.

For example, in this embodiment, the misalignment of the misalignment measurement mark at the misalignment measurement point 32 on the wafer W shown in FIG. 1 is measured once by each of the above-described first to third recipes. , 3σX and 3σY are obtained for each of the first to third recipes. 3σX and 3σY of each recipe are as shown in Table 1.

[0018] From Table 1, the values of both 3σX and 3σY of the second recipe are the smallest, so the second recipe is certified as the optimum recipe for the use misalignment measuring machine, and thereafter, the misalignment measurement is performed using this recipe. I do. By applying this embodiment to the recipe selection of the misalignment measuring machine, the absolute value accuracy (difference from the true value) of the misalignment measuring machine is improved.

In order to evaluate the method of the present embodiment by the magnitude of the difference from the true value, the method of the present embodiment is applied to the recipe selection when measuring the aberration of the projection lens of the exposure apparatus,
The result of the method of the present embodiment and the measurement result of the aberration measuring machine were compared. The aberration measuring machine is a high-precision measuring machine with a high absolute value accuracy developed as a dedicated machine for measuring the aberration of the projection lens, and the measurement result of the aberration measuring machine can be regarded as a true value. The measurement results are shown in FIG. The measurement results of the first to third recipes are as shown in FIGS. 2B, 3D and 3E, respectively. FIG. 2C shows the height of contour lines representing the magnitude of the aberrations of FIGS. 2A, 3D and 3E. Figure 2
(A) and (b) and FIGS. 3 (d) and (e), respectively,
The magnitude of the lens aberration is shown by a contour graph, and the magnitude of the aberration is indicated by λ. The original photographs of FIGS. 2A to 2C and FIGS. 3D and 3E are separately submitted as reference photographs 1 to 5, respectively.

As can be seen from FIGS. 2 and 3, the measurement result by the second recipe selected as the optimum recipe by applying the method of this embodiment, that is, the measurement result shown in FIG. It is the closest to the measurement result of the machine. That is, it can be evaluated that the measurement result of the second recipe is the closest to the true value.

In the above-described embodiment, the optical misalignment measuring machine is taken as an example to describe the misalignment measuring method according to the present invention. However, the inventive method is not limited to the misalignment measuring machine, and may be, for example, By applying it to other measuring machines such as a long SEM and a film thickness measuring machine, it is possible to improve the absolute value measurement accuracy of the measuring machine.

[0022]

According to the present invention, the misalignment measurement marks of the pattern are arranged at the misalignment measurement points which are uniformly dispersed on the object to be exposed, and the misalignment of each misalignment measurement mark is measured by a plurality of types. A step of measuring by the method, a step of obtaining the deviation of the misalignment measurement value of each misalignment measurement mark for each measurement method, and a step of selecting the measurement method having the smallest deviation as the optimum measurement method for the misalignment measuring machine. By configuring the misalignment measuring method with, it is possible to improve the absolute value measurement accuracy of misalignment measurement. By applying the method of the present invention to length measurement SEM, film thickness measurement, etc., the absolute value measurement accuracy of measurement can be improved.

[Brief description of drawings]

FIG. 1 is a wafer plan view showing positions of misalignment measurement points.

FIG. 2A and FIG. 2B are diagrams respectively showing a lens aberration measurement result by a lens aberration measurement dedicated machine and a lens aberration measurement result by a second recipe. FIG. 2C is a table showing the heights of contour lines representing the magnitudes of the aberrations of FIGS. 2A, 3D and 3E.

3 (d) and 3 (e) are diagrams showing lens aberration measurement results according to a first recipe and a second recipe, respectively.

FIG. 4 is a wafer plan view showing misalignment measurement points.

FIG. 5 is a schematic diagram showing a configuration of a misalignment measurement mark.

FIG. 6 is a schematic diagram showing a configuration of a misalignment measuring machine.

FIG. 7 is a diagram showing a detection waveform of a misalignment measurement mark of the misalignment measuring machine.

8A to 8C are diagrams showing detection waveforms of misalignment measurement marks, respectively.

[Explanation of symbols]

10 ... Misalignment measurement mark, 12 ... Chip forming area, 14 ... Outer measurement mark, 16 ... Inner measurement mark, 18 ... Light source, 20 ... Beam splitter, 24 ...
... Lens, 26 ... CCD camera, 30 ... misalignment measuring device, 32 ... misalignment measuring point.

Claims (4)

[Claims] 1. A misalignment between a pattern formed on an object to be exposed in a previous step and a pattern transferred onto the object to be exposed in a subsequent step subsequent to the previous step. A method for measuring the misalignment by finding an optimum misalignment measuring method for the misalignment measuring machine when measuring with the misalignment measuring machine based on the misalignment measuring mark, and measuring the misalignment uniformly on the exposed object. Steps for arranging the pattern misalignment measurement marks at the misalignment measurement points dispersed in the above, and measuring the misalignment of each of the misalignment measurement marks by a plurality of types of measurement methods, and the misalignment measurement value of each misalignment measurement mark. Variation for each measurement method, and the measurement method with the smallest variation is selected as the optimum measurement method for the misalignment measuring machine. A method for measuring misalignment, comprising the steps of: 2. The misalignment measuring method according to claim 1, wherein the deviation of the misalignment measurement value is displayed as 3σ. 3. The misalignment of the misalignment measurement mark is measured once each by the plural kinds of measuring methods in the step of measuring the misalignment by a plurality of kinds of measuring methods. Alternatively, the misalignment measuring method described in 2. 4. The misalignment measuring method according to claim 1, wherein an optical misalignment measuring machine is used as the misalignment measuring machine.