JP3634198B2 - Optical aberration measurement method for misregistration inspection apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring optical aberration (Tool Induced Shift: hereinafter referred to as “TIS”) of a misalignment inspection apparatus for inspecting misalignment of a plurality of layers formed on a semiconductor wafer. To the law Related.
[0002]
[Prior art]
A semiconductor device is formed by laminating a plurality of conductive layers (wiring layers) and a plurality of insulating layers on a wafer. In order to achieve high integration of semiconductor devices, it is necessary to minimize the positional deviation between the layers. In general, when inspecting the amount of misalignment between layers, an alignment mark is formed on each layer in a patterning process (photolithography process) of each layer, and the interval between the alignment marks is measured by a misalignment inspection apparatus.
[0003]
By the way, with the further higher integration of semiconductor devices in recent years, TIS of misalignment inspection devices has become a problem. TIS is a measurement error caused by physical asymmetry of the optical system of the misregistration inspection apparatus, and is known to occur when the optical axis of the optical system of the misregistration inspection apparatus is not perpendicular to the wafer surface. ing. TIS can be measured as follows. That is, after placing the wafer on the stage of the misalignment inspection apparatus and measuring the misalignment amount a1 between the layers, the stage is rotated 180 degrees to measure the misalignment amount a2. And TIS is calculated | required by calculating following (1) Formula.
[0004]
TIS = (a1 + a2) / 2 (1)
In order to improve the accuracy of the misregistration inspection apparatus, it is necessary to measure the TIS with high accuracy and adjust the optical system so that the TIS becomes small.
[0005]
In Japanese Patent Laid-Open No. 9-280816, in order to detect an error in the measurement system of the position inspection apparatus, a sample in which a plurality of alignment marks including a plurality of grooves having different depths is used, and a plurality of alignment marks are used. After measuring the distance between them, a method is disclosed in which the stage is rotated 180 degrees, the distance is measured again, and the difference between the measured values is obtained. Japanese Patent Laid-Open No. 9-280816 discloses that the height or depth of an alignment mark is set according to the wavelength of irradiation light.
[0006]
[Problems to be solved by the invention]
However, the invention described in Japanese Patent Laid-Open No. 9-280816 described above relates to a position detection device such as a position alignment device, not a position displacement inspection device, and the amount of position displacement between a plurality of layers in the position displacement inspection device. It is different from what detects.
[0007]
In addition, there are telecentric deviation and coma aberration as factors that cause TIS. However, simply detecting the TIS by rotating the sample cannot individually measure or evaluate the telecentric deviation and coma aberration. Therefore, the optical system of the misalignment inspection apparatus cannot be adjusted efficiently.
[0008]
Further, although a technique for making the position deviation inspection in the wafer process difficult to be affected by TIS is desired, suppression of TIS in the conventional measurement method has not been sufficient. In the misalignment inspection on the actual device wafer, it is necessary to consider an error (Wafer Induced Shift: hereinafter referred to as WIS) generated due to the asymmetry of the inspection mark depending on the wafer process in addition to the TIS. However, in the conventional measurement method, the TIS itself is suppressed, and the misregistration measurement is performed by selecting a mark with a small WIS. However, in this method, the TIS is not completely suppressed and the interaction between the TIS and the WIS is performed. As a result, the measurement value may be greatly distorted or the measurement error may be amplified. For this reason, the amount of displacement on the wafer could not be measured accurately.
[0009]
An object of the present invention is to provide an optical aberration measurement method for a misalignment inspection apparatus that can individually evaluate telecentric displacement and coma aberration, which are the main causes of TIS.
[0011]
[Means for Solving the Problems]
The object is to irradiate a reference sample having first and second inspection marks made of protrusions or grooves with light of wavelength λ, and image the light reflected by the first and second inspection marks with an imaging device. Measuring a first misalignment between the first and second inspection marks based on the acquired image, rotating the reference sample by 180 degrees, and then applying light of wavelength λ to the reference sample The light that is irradiated and reflected by the first and second inspection marks is imaged by the imaging device, and the second positional deviation amount between the first and second inspection marks is calculated based on the acquired image. A method for measuring an optical aberration of a misregistration inspection apparatus, comprising: a measuring step; and a step of calculating an optical aberration of the misregistration inspection apparatus from the first and second misregistration amounts, Measure the second displacement amount Each of the steps includes a step of capturing an image at each focal position by moving the focal position of the imaging device in the height or depth direction of the first and second inspection marks. This is achieved by the optical aberration measurement method of the inspection apparatus.
[0012]
In addition, the object is as follows: (a) a first inspection mark made of a protrusion or groove formed on the substrate, and a second inspection mark made of a protrusion or groove formed adjacent to the first inspection mark. And (b) irradiating the first and second inspection marks of the reference sample with light having a wavelength λ, and Imaging a light reflected from two inspection marks with an imaging device to obtain a first image; and (c) performing signal processing on the first image to determine the positions of the first and second inspection marks. Detecting and measuring a first misalignment amount between the first and second inspection marks; and (d) rotating the stage 180 degrees, and then the first and second of the reference sample. Irradiating light of wavelength λ to the inspection mark of the first and second inspection marks And (e) detecting the positions of the first and second inspection marks by performing signal processing on the second image. Measuring a second misalignment amount between the first and second inspection marks, and (f) calculating an optical aberration of the misalignment inspection apparatus from the first misalignment amount and the second misalignment amount. And a step (c) and a step (d) for measuring the first and second misregistration amounts each of which determines the focal position of the imaging device. And moving the first and second inspection marks in the height or depth direction to capture an image at each focal position, and then, using the first and second positional deviation amounts, A positional deviation detection characterized by executing step (f) of calculating optical aberration. Also achieved by an optical aberration measuring method of the apparatus.
[0013]
In the optical aberration measuring method of the positional deviation inspection apparatus, the height or depth of at least one of the first and second inspection marks is λ / 8 ± 6.25% or 3λ / 8 ± 6. It may be 25%.
[0014]
In the optical aberration measuring method of the positional deviation inspection apparatus, the height or depth of at least one of the first and second inspection marks is λ / 8 ± 6.25%, and the other height or The depth may be 3λ / 8 ± 6.25%.
[0015]
In the optical aberration measurement method of the positional deviation inspection apparatus, the height and depth of the first and second inspection marks may both be 2λ / 8 ± 6.25%. .
[0016]
In addition, the above purpose is to irradiate the wavelength of light λ _i A wavelength λ is applied to a reference sample having n sets of first and second inspection marks made of protrusions or grooves whose height or depth is determined according to (i = 1, 2,..., N). _i The wavelength λ _i The light reflected by the i-th set of first and second inspection marks corresponding to the light of the image is picked up by the imaging device, and the i-th set of first and second inspection marks based on the acquired image Measuring a first misalignment amount between the reference sample and rotating the reference sample by 180 degrees, _i Of the i-th set, the light reflected by the i-th set of the first and second inspection marks is imaged by the imaging device, and the i-th set of the first and second sets based on the acquired image Measuring a second misregistration amount between the inspection marks, and a wavelength λ from the first and second misregistration amounts. _i The step of calculating the optical aberration of the misregistration inspection apparatus for the light of the wavelength, and the wavelength λ of the light irradiated to the reference sample _i And a step of repeating the steps from the step of measuring the first misregistration amount to the step of calculating the optical aberration for all the n sets of first and second inspection marks. In the optical aberration measuring method of the apparatus, the first and second misregistration steps both measure the focal position of the imaging apparatus with the i-th set of first and second inspection marks. It is also achieved by an optical aberration measuring method for a misregistration inspection apparatus characterized by including a step of capturing an image at each focal position by moving in the height or depth direction.
[0017]
In addition, the above purpose is as follows: (a) The wavelength λ of the irradiated light _i A reference sample having n sets of first and second inspection marks composed of protrusions or grooves whose height or depth is determined in accordance with (i = 1, 2,..., N) is used as a stage of a displacement inspection apparatus. (B) a wavelength λ on the first and second inspection marks of the reference sample; _i The wavelength λ _i Imaging the light reflected from the i-th set of the first and second inspection marks corresponding to the light of the first image with an imaging device to obtain a first video, and (c) signal processing the first video Detecting the positions of the first and second inspection marks of the i-th set and measuring a first positional deviation amount between the first and second inspection marks of the i-th set; (D) after rotating the stage by 180 degrees, the wavelength λ is applied to the first and second inspection marks of the i-th set of the reference sample. _i And (e) the second image obtained by imaging the light reflected from the i-th set of the first and second inspection marks with the imaging device, and (e) the second image. Is processed to detect the positions of the first and second inspection marks of the i-th set, and the second positional deviation amount between the first and second inspection marks of the i-th set is measured. (F) calculating an optical aberration of the misregistration inspection apparatus from the first and second misregistration amounts, and (g) a wavelength λ of light irradiated on the reference sample. _i And (b) to (f) are repeated for all of the n sets of first and second inspection marks, and the method for measuring optical aberrations of a misregistration inspection apparatus, In each of the steps (c) and (e) of measuring the first and second misregistration amounts, the focus position of the imaging device is set to the height or depth of the i-th set of first and second inspection marks. Performing a step (f) of calculating an optical aberration of the misregistration inspection apparatus from the first and second misregistration amounts after the step of moving in the vertical direction and capturing an image at each focal position. It is also achieved by the optical aberration measuring method of the misregistration inspection apparatus characterized by the above.
[0018]
In the optical aberration measurement method of the positional deviation inspection apparatus, an average value of optical aberrations calculated for each of the n sets of first and second inspection marks may be calculated.
[0019]
In the optical aberration measurement method of the positional deviation inspection apparatus, the height or depth of any one of the i-th set of the first and second inspection marks is set to λ. _i /8±6.25% or 3λ _i /8±6.25 may be set.
[0020]
In the optical aberration measuring method of the misregistration inspection apparatus, the height or depth of at least one of the i-th set of first and second inspection marks is λ. _i /8±6.25%, and the other height or depth is 3λ _i /8±6.25% may be set.
[0021]
In the optical aberration measurement method of the positional deviation inspection apparatus, the height or depth of the first and second inspection marks of the i-th set is set to 2λ. _i /8±6.25% may be set.
[0026]
The operation will be described below.
[0027]
In the present invention, a reference sample having first and second inspection marks made of protrusions or grooves is used, and the focal position of the imaging device is moved in the height direction or depth direction of the first and second inspection marks. Then, the positions of the first and second inspection marks are detected, and the optical aberration at each focal position is calculated.
[0028]
According to the experiments by the present inventors, it has been found that if the TIS is detected at each focal position by moving the focal position as described above, the TIS changes depending on the focal position. At this time, if the telecentric deviation is large, the TIS changes linearly when the focal position of the imaging apparatus is moved. On the other hand, when the coma aberration is large, the TIS changes in a curve (dome shape) when the focal position of the imaging apparatus is moved in one direction. Therefore, the telecentric deviation and the coma aberration can be distinguished from the state of change of TIS. Thereby, the adjustment and quality control of the optical system of the misregistration inspection apparatus can be performed efficiently.
[0029]
When the wavelength of the irradiation light is λ, the value of TIS increases when the height or depth of at least one of the first and second inspection marks is λ / 8 or 3λ / 8. In particular, when one height or depth of the first and second inspection marks is λ / 8 and the other height or depth is 3λ / 8, the value of TIS is the largest. Accordingly, when the focus position is moved with the height or depth of at least one of the first and second inspection marks set to λ / 8 or 3λ / 8, and the TIS is measured at each focus position, the illumination is detected from the change in TIS. The telecentric distortion of the system can be evaluated effectively.
[0030]
Further, when the height and depth of the first and second inspection marks are both 2λ / 8 and the focal position is moved and TIS is measured at each focal position, the influence of coma appears most prominently in TIS. . Therefore, when the influence of coma aberration is strengthened, it is preferable that the height and depth of the first and second inspection marks are both 2λ / 8. The height or depth of the first and second inspection marks is allowed within a range of about ± 1/16 (= 6.25%) from the above values.
[0031]
In order to measure TIS with higher accuracy, it is preferable to measure the TIS by changing the wavelength of light irradiated to the reference sample, and obtain the average value of the TIS measured at each wavelength. In this case, a plurality of sets of inspection marks having different heights or depths are used according to the wavelength of light. Thereby, TIS can be measured with higher accuracy.
[0032]
Further, when the step of the inspection mark is D and the wavelength of the irradiation light is λ, the TIS is the smallest when the relationship of D = nλ / 4 (n = 1, 2,...) Is satisfied. Therefore, by selecting the inspection wavelength λ for the positional deviation inspection according to the step D of the inspection mark, the positional deviation amount can be measured with high accuracy while suppressing the influence of TIS.
[0033]
Further, since the relationship between the step D and the wavelength λ has periodicity, when the main scale step and the sub-scale step satisfy a certain relationship, that is, the main scale step is defined as M. _m , The step of the vernier is M _s Λ / 4 = M _m / N _m = M _s / N _s (N _m , N _s = 1, 2,...), The TIS is minimized in the measurement of both the main scale and the sub scale at the wavelength λ. Therefore, the main step difference M with respect to the inspection wavelength λ. _m And vernier step M _s Can satisfy the above-mentioned relationship, it is possible to perform highly accurate displacement measurement while simplifying the displacement inspection process.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
The optical aberration measuring method of the misalignment inspection apparatus according to the first embodiment of the present invention will be described with reference to FIGS.
[0035]
FIG. 1 is a schematic diagram showing a misalignment inspection apparatus used in the optical aberration measuring method according to the present embodiment, FIG. 2 is a diagram for explaining the inspection mark and the output of the CCD camera, and FIGS. 3 and 4 are grooves for the inspection mark. FIG. 5 is a schematic diagram showing a change in TIS when the focal position is moved in the depth direction of the inspection mark, and FIG. 6 shows the depth of the first inspection mark. FIG. 7 to FIG. 9 show the results of actual measurement of TIS values when λ / 8 and the height of the second inspection mark is 2.7λ / 8 to 5.5λ / 8. FIGS. FIG. 10 to FIG. 14 are sectional views showing examples of reference samples, FIG. 14 is a flowchart showing an optical aberration measuring method of the misregistration inspection apparatus according to the present embodiment, FIG. 15 and FIG. FIG. 16 shows an optical aberration measurement method according to this embodiment. Is a diagram showing the relationship between the TIS and the focal position measured by.
[0036]
[1] Overall configuration of misalignment inspection device
FIG. 1 is a schematic view showing a misalignment inspection apparatus used in the optical aberration measuring method according to the present embodiment.
[0037]
As shown in FIG. 1, the misalignment inspection apparatus includes a light source 11, a light guide 12, an irradiation lens group 13, a beam splitter 14, an objective lens group 15, a stage 16, an eyepiece lens group 17, and a CCD (Charge Coupled Device) camera 18. And a signal processing unit 19.
[0038]
As the light source 11, a xenon lamp or a semiconductor laser is used. The light emitted from the light source 11 is guided to the illumination lens group 13 through the light guide 12. The illumination lens group 13 is composed of one or a plurality of lenses, and makes light emitted from the light guide 12 substantially parallel light. The beam splitter 14 reflects the light passing through the illumination lens group 13 in the direction of the stage 16. The light reflected by the beam splitter 14 passes through the objective lens group 15 composed of one or a plurality of lenses and irradiates the wafer 10 placed on the stage 16 from the vertical direction. The wafer 10 is previously formed with alignment marks for detecting misalignment between layers. In addition, the stage 16 can be rotated at an arbitrary angle with a direction perpendicular to the surface of the stage 16 as an axis.
[0039]
The light reflected in the vertical direction by the wafer 10 passes through the objective lens group 15 and passes through the beam splitter 14. Then, it passes through an eyepiece lens group 17 composed of one or a plurality of lenses and forms an image on the CCD element surface of the CCD camera 18. The CCD camera 18 converts the received light into an electrical signal and outputs it to the signal processing unit 19. The signal processing unit 19 performs signal processing on the signal transmitted from the CCD camera 18 and detects the position of each alignment mark. Then, the distance between the alignment marks is measured to determine the amount of misalignment between the layers.
[0040]
When measuring the TIS of the misalignment inspection apparatus, a reference sample on which a predetermined inspection mark is formed is placed on the stage 16 instead of the wafer 10.
[0041]
[2] Principle
(1) Inspection signal asymmetry due to optical axis tilt
2A and 2B are diagrams for explaining the inspection mark and the output of the CCD camera. FIG. 2A is a cross-sectional view showing an example of the inspection mark used for TIS measurement of the misalignment inspection apparatus, and FIGS. ) Is a schematic diagram showing a signal output from the CCD camera 18.
[0042]
As shown in FIG. 2A, it is assumed that a groove having a rectangular cross section is formed as the inspection mark 21 in the reference sample 20. Assuming that the reference sample 20 is irradiated with light from the direction perpendicular to the surface, the CCD camera 18 outputs a symmetrical signal with respect to the center of the groove, as shown in FIG. However, when the optical axis of the light that irradiates the reference sample 20 is tilted, the signal output from the CCD camera 18 is not symmetrical with respect to the center of the groove, as shown in FIG. For this reason, when the position of the inspection mark 21 is determined by the signal processing unit 19, the position shifted from the center of the groove is recognized as the position of the inspection mark 21, which causes TIS to increase.
[0043]
(2) Relationship between height or depth of inspection mark and light intensity
3 and 4, the horizontal axis indicates the position on the reference sample surface, and the vertical axis indicates the light intensity detected by the CCD camera 18 (relative value when the light intensity of the surface of the flat portion of the reference sample is 1). FIG. 5 is a diagram showing the relationship between the depth of a groove as an inspection mark and the light intensity. However, the depth of the groove was changed by λ / 16, where λ is the wavelength of the irradiation light (centroid wavelength). As is clear from FIGS. 3 and 4, when the groove depth is λ / 16 to 3λ / 16, the light intensity at the left edge portion of the groove is lower than the light intensity at the right edge portion of the groove. . When 2λ / 16 (= λ / 8), the difference between the light intensity at the left edge portion and the light intensity at the right edge portion is the largest. When the depth of the groove is 5λ / 16 to 7λ / 16, the light intensity at the left edge portion of the groove is higher than the light intensity at the right edge portion of the groove. At 6λ / 16 (= 3λ / 8), the difference between the light intensity at the left edge portion and the light intensity at the right edge portion is the largest. Further, when 4λ / 16 (= 2λ / 8), the light intensity at the left edge portion of the groove is substantially equal to the light intensity at the right edge portion of the groove.
[0044]
Therefore, when TIS measurement is performed using two inspection marks (first and second inspection marks), the depth of one groove is λ / 8 and the depth of the other groove is 3λ / 8. It can be seen that TIS can be detected with high sensitivity. Similarly, when a projection is used instead of a groove as an inspection mark, the height of one projection is set to λ / 8, and the height of the other projection is set to 3λ / 8. Can be detected. Thus, when the height or depth of the inspection mark is λ / 8 or 3λ / 8, the influence of the telecentric deviation of the irradiation system can be evaluated.
[0045]
Further, when the height of the inspection mark is 2λ / 8, the influence of coma appears remarkably on the curve indicating the relationship between the focal position and TIS. Therefore, when evaluating the influence of coma aberration of the optical system, it is preferable to set the height or depth of the inspection mark to 2λ / 8.
[0046]
(3) Change in TIS when the focal position is moved
In the present invention, the TIS is measured by moving the focus position of the imaging device (CCD camera) in the height direction of the inspection mark.
[0047]
FIG. 5 is a schematic diagram showing changes in TIS when the focal position is moved in the depth direction of the inspection mark, with the focal position on the horizontal axis and TIS on the vertical axis. In the case of a telecentric shift, as shown in FIG. 5A, the TIS changes (increases or decreases) substantially on a straight line as the focal position moves. The greater the telecentric deviation, the greater the slope of the straight line.
[0048]
On the other hand, in the case of coma aberration, as shown in FIG. 5B, the TIS changes into a curved shape (dome shape) as the focal position moves. The greater the coma aberration, the greater the difference between the TIS at the center and the TIS at the periphery.
[0049]
As described above, when the focus position is moved in the height or depth direction of the inspection mark, the TIS changes, and the telecentric deviation and the coma aberration can be individually evaluated according to the change state of the TIS.
[0050]
FIG. 6 shows the result of actual measurement of the TIS value when the depth of the first inspection mark is λ / 8 and the height of the second inspection mark is 2.7λ / 8 to 5.5λ / 8. FIG. However, the first inspection mark was formed by etching a silicon (Si) substrate, and the second inspection mark was formed of a photoresist. Then, TIS in two directions (X direction and Y direction) parallel to the surface of the silicon substrate and perpendicular to each other was measured.
[0051]
As a result, as shown in FIG. 6, the value of TIS changes in accordance with the change in the height of the second inspection mark, and the maximum value of TIS is obtained when the height of the second inspection mark is approximately 3λ / 8. It became.
[0052]
[3] Inspection mark
(1) Examples of inspection marks (I)
FIG. 7 is a cross-sectional view showing an example (I) of an inspection mark used for TIS measurement. The reference sample 10 a is made of a silicon substrate 31. On the silicon substrate 31, a projection is formed as a first inspection mark (main scale) 32, and a groove is formed as a second inspection mark (second scale) 33.
[0053]
Hereinafter, a method for forming the inspection mark shown in FIG. 7 will be described.
[0054]
First, a photoresist is applied on the silicon substrate 31 to form a photoresist film. Thereafter, exposure and development are performed to pattern the photoresist film into a predetermined shape. Then, the silicon substrate 31 is etched to a depth of λ / 8, for example, using the photoresist film as a mask. As a result, the portion masked by the photoresist film remains as a protrusion. This protrusion becomes the first inspection mark 32. Thereafter, the photoresist film used for forming the first inspection mark 32 is removed.
[0055]
Next, a photoresist is applied on the silicon substrate 31 to form a photoresist film. Thereafter, exposure and development are performed to pattern the photoresist film into a predetermined shape. Then, the silicon substrate 31 is etched using the photoresist film as a mask to form, for example, a groove having a depth of 3λ / 8. This groove portion becomes the second inspection mark. Thereafter, the photoresist film used for forming the second inspection mark 33 is removed. Thereby, the reference sample 10a is completed.
[0056]
In the above example, the height of the first inspection mark 32 is λ / 8 and the depth of the second inspection mark 33 is 3λ / 8. However, the height of the first inspection mark 32 is 3λ / 8. The depth of the second inspection mark 33 may be λ / 8.
[0057]
(2) Example of inspection mark (II)
FIG. 8 is a cross-sectional view showing an example (II) of an inspection mark used for TIS measurement. The reference sample 10 a has a first inspection mark 34 formed by etching the silicon substrate 31 and a second inspection mark 35 made of a protrusion of a resist film formed inside the inspection mark 34.
[0058]
Hereinafter, a method for forming the inspection mark shown in FIG. 8 will be described.
[0059]
First, a photoresist is applied on the silicon substrate 31 to form a photoresist film. Thereafter, exposure and development are performed to pattern the photoresist film into a predetermined shape. Then, the silicon substrate 31 is etched using the photoresist film as a mask to form a groove having a depth of λ / 8. This groove portion becomes the first inspection mark 34. Thereafter, the photoresist film used for forming the first inspection mark 34 is removed.
[0060]
Next, a photoresist is applied on the silicon substrate 31 slightly thicker than 3λ / 8 to form a photoresist film. Thereafter, exposure and development are performed to pattern the photoresist film, leaving the photoresist film only inside the first inspection mark 34. Then, the photoresist film is post-baked by heating at a predetermined temperature. By this post-bake, the thickness of the photoresist film is slightly reduced to approximately 3λ / 8. This photoresist film becomes the second inspection mark 35. Thereby, the reference sample 10a is completed.
[0061]
In the above example, the depth of the first inspection mark 34 is λ / 8 and the thickness of the second inspection mark 35 is 3λ / 8. However, the depth of the first inspection mark 34 is 3λ / 8. The height of the second inspection mark 35 may be λ / 8. In order to evaluate the influence of coma aberration, the depth of the first inspection mark 34 and the height of the second inspection mark 35 are both set as shown in the example (III) of the inspection mark in FIG. 2λ / 8 is desirable.
[0062]
(3) Other examples of inspection marks
10 to 13 are diagrams showing other examples of the reference sample. The reference sample in FIG. 10 includes a silicon substrate 40, SiO 2 ₂ A film 41, a tungsten (W) film 42, an aluminum film 43, and a resist film 44 are included. SiO ₂ The film 41 is formed on the silicon substrate 40, and the tungsten film 42 is made of SiO. ₂ The film is buried in a groove selectively formed in the film 41. The tungsten film 42 is formed with a groove, and the aluminum film 43 is made of SiO. ₂ The film 41 and the tungsten film 42 are covered. Grooves are formed in the aluminum film 43 in a shape corresponding to the grooves of the tungsten film 42. This groove becomes the first inspection mark. A resist film 44 is selectively formed inside the groove of the aluminum film 43. This resist film 44 becomes the second measurement pattern.
[0063]
Similarly to the reference sample of FIG. 10, the reference sample of FIG. ₂ The film 41, the tungsten film 42, the aluminum film 43, and the resist film 45 are included. However, the second inspection mark is the opening 46 of the resist film 45.
[0064]
The reference sample of FIG. 12 includes a silicon substrate 40, a tungsten film 47, and SiO. ₂ The film 48, the aluminum film 49, and the resist film 50 are included. SiO ₂ The film 48 is selectively formed on the silicon substrate 40, and the tungsten film 47 is formed of SiO. ₂ It is formed on the silicon substrate 40 so as to cover the film 48. An aluminum film 49 is formed on the tungsten film 47. The aluminum film 49 and the tungsten film 47 are made of SiO. ₂ Projections are formed for the film. The projection of the aluminum film 49 becomes the first inspection mark. A resist film 50 is selectively formed on the aluminum film 49. This resist film 50 becomes the second measurement pattern.
[0065]
The reference sample of FIG. 13 is similar to the reference sample of FIG. 12 in that the silicon substrate 40, the tungsten film 47, and the SiO 2 ₂ The film 48, the aluminum film 49, and the resist film 51 are included. However, the second inspection mark is the opening 52 of the resist film 51.
[0066]
For the reference sample, various materials other than the above-described silicon substrate can be used. Further, the first and second inspection marks are not limited to the structure described above.
[0067]
[4] Optical aberration measurement method
The optical aberration measuring method of the misalignment inspection apparatus according to the first embodiment of the present invention will be described with reference to FIG.
[0068]
First, in step S11, a reference sample 10a having a first inspection mark 32 and a second inspection mark 33 formed by etching a semiconductor substrate as shown in FIG. 7 was prepared. The height of the first inspection mark 32 is λ / 8.
[0069]
Next, the reference sample 10a was placed on the stage 16 of the misalignment inspection apparatus shown in FIG. 1, and the TIS in the X direction and the Y direction were measured. That is, in step S12, the reference sample 10a was irradiated with the light emitted from the light source 11, and the process proceeds to step S13 where the CCD camera 18 images the reference sample 10a. At this time, the center position in the height direction of the first inspection mark 32 is set as the origin, and the focal position f is set at the origin. ₀ Together. Then, the output of the CCD camera 18 is signal-processed by the signal processor 19 to detect the positions of the first and second inspection marks, and the first inspection mark 32 and the second inspection mark 33 between the first inspection mark 33 and the second inspection mark 33 are detected. The amount of displacement of 1 was measured. After that, the focal position f ₀ Is moved within a range of ± 500 nm in steps of 100 nm from the origin to detect the position of the first inspection mark 32 at each focal position, and the first inspection mark 32 and the second inspection mark 33 The first misalignment amount was measured. However, the position of the second inspection mark 33 is the focal position f. ₀ Was the position when detected by aligning with the origin.
[0070]
Thereafter, after the stage 16 is rotated by 180 °, the center position in the height direction of the first inspection mark 32 is set as the origin, and the focal position f is set at the origin in the same manner as described above. ₀ Together. Then, the output of the CCD camera 18 is signal-processed by the signal processing unit 19 to detect the positions of the first inspection mark 32 and the second inspection mark 33. After that, the focal position f ₀ Is moved within a range of ± 500 nm in steps of 100 nm in the height direction from the origin, and each focal position f ₀ Then, the position of the first inspection mark 32 was detected, and the second displacement amount between the first inspection mark 32 and the second inspection mark 33 was measured. Also at this time, the position of the second inspection mark 33 is the focal position f. ₀ Was the position when detected by aligning with the origin.
[0071]
Then, the process proceeds to step S14, and the TIS at each focal position is calculated by the above-described equation (1). The result is shown in FIG. In this example, the change in the TIS in the X direction is relatively small, but the change in the TIS in the Y direction decreases almost linearly with the change in the focal position in the height direction. Therefore, in this example, although the telecentric deviation in the X direction is small, it can be seen that the telecentric deviation in the Y direction is relatively large.
[0072]
If it is determined that the telecentric deviation is large, the light source 11 (lamp house) may be improved by rotating the light source 11 with respect to the optical axis or moving the light source 11 in the optical axis direction.
[0073]
However, if adjustment is made so that the TIS is reduced by the above method while the coma aberration remains large, variations in TIS occur in the actual exposure process. In the case of coma aberration, the TIS size changes when the step state (height difference) changes, but the TIS shift direction does not change. In the case of a telecentric shift, the TIS size changes when the step state changes. This is because the direction changes. Since the step is not uniform in an actual wafer, adjusting the telecentric shift so as to eliminate the influence of coma aberration in a certain step state changes the TIS depending on the step state. Therefore, when the coma aberration is larger than a certain level, it is necessary to replace the lens with one having a smaller coma aberration and then adjust the telecentric deviation.
[0074]
If the TIS is large even though the telecentric deviation is relatively small, the influence of coma aberration can be considered. When measuring coma aberration individually, the height (or depth) of the first and second inspection marks is set to 2λ / 8, and the TIS may be measured by changing the focal position in the same manner as described above.
[0075]
The focal position f ₀ The TIS may be obtained by detecting the positions of the first inspection mark 32 and the second inspection mark 33 each time the is moved. FIG. 16 is a diagram showing the results of obtaining TIS in this way. This figure also shows that there is a telecentric deviation in the X direction.
[0076]
As described above, according to the present embodiment, the focal position f ₀ Is moved in the height direction of the first inspection mark 32 to measure the TIS at each focal position, so that the influence of the telecentric deviation and the influence of the coma aberration can be individually evaluated. Thereby, the management and quality control of the manufacturing process of the misalignment inspection apparatus are facilitated, and the misalignment inspection apparatus with a small TIS can be provided.
[0077]
In addition to TIS, there is a factor called WIS (Wafer Induced Shift) as a factor of measurement error of the misregistration inspection apparatus. WIS occurs due to the asymmetry of the inspection mark depending on the wafer process. In the present embodiment, the telecentric deviation and the coma aberration can be individually evaluated, and the TIS can be reduced on the basis thereof, so that the influence of WIS can also be evaluated.
[0078]
[Second Embodiment]
The optical aberration measuring method of the misalignment inspection apparatus according to the second embodiment of the present invention will be described with reference to FIGS. The same components as those in the optical aberration measuring method of the misalignment inspection apparatus according to the first embodiment shown in FIGS. 1 to 16 are denoted by the same reference numerals, and description thereof is omitted or simplified.
[0079]
FIG. 17 is a diagram showing a misalignment inspection apparatus used in the optical aberration measuring method according to the present embodiment, FIGS. 18 and 19 are diagrams showing spectra of irradiated light that has passed through a filter, and FIG. 20 is a method for calculating a centroid wavelength. FIG. 21 is a flowchart showing the optical aberration measuring method of the misregistration inspection apparatus according to the present embodiment, FIGS. 22 and 23 are sectional views showing examples of the reference sample, and FIG. 24 is the focal position in the reference sample of FIG. FIG. 25 is a graph showing the result of examining the relationship between the TIS and the TIS by changing the depth of the first inspection mark. FIG. 25 shows the relationship between the focal position and the TIS in the reference sample of FIG. FIG. 26 is a diagram showing the results of measuring TIS by changing the depth of the first inspection mark of the reference sample shown in FIGS. 22 and 23. FIG.
[0080]
[1] Overall configuration of misalignment inspection device
A misregistration inspection apparatus used in the optical aberration measuring method according to the present embodiment will be described with reference to FIG.
[0081]
In the misalignment inspection apparatus according to the present embodiment, a xenon lamp is used as the light source 11. A filter 31 that controls the wavelength of light output from the light source 11 is disposed between the light source 11 and the light guide 12. A plurality of filters 31 having different transmission wavelengths are prepared. Then, as in the first embodiment, the focus position is moved in the height or depth direction of the inspection mark for each filter 31, and the TIS is measured at each focus position. Thereafter, the filter 31 is changed to change the wavelength of the irradiation light, and similarly, the focus position is moved in the height or depth direction of the inspection mark, and the TIS is measured at each focus position. In this way, the TIS at each focal position is measured, and the average value of the TIS at each focal position is obtained.
[0082]
[2] Spectrum of irradiated light and centroid wavelength
FIG. 18 and FIG. 19 are diagrams showing the spectrum of irradiated light, with the horizontal axis representing wavelength and the vertical axis representing intensity. However, in FIGS. 18 and 19, the vertical axis represents the output of the CCD camera 18 and depends on the spectrum of the light output from the light source 11, the spectral characteristics of the filter 31, and the sensitivity characteristics of the CCD camera 18.
[0083]
In this embodiment, when each filter 31 is used, the height or depth of the inspection mark is set according to the barycentric wavelength of the irradiation light. For example, assuming that the spectrum of light is as shown in FIG. 20, the center-of-gravity wavelength is determined as the center-of-gravity wavelength by obtaining the wavelength c where the area between ac and the area between cb are equal in the figure.
[0084]
[3] Optical aberration measurement method
FIG. 21 is a flowchart showing the optical aberration measuring method according to the present embodiment. First, in step S21, a reference sample 10a is prepared. In the reference sample 10a, a plurality of sets of first and second inspection marks whose height or depth is set according to the irradiation light are formed. For example, let λ _i Assuming (i = 1, 2,..., N), n sets of first and second inspection marks are formed on the reference sample. When the TIS is to be examined with high sensitivity, the height or depth of any one of the i-th set of first and second inspection marks is set to λ. _i / 8, the other height or depth is 3λ _i / 8. When the influence of coma aberration is to be examined, the height or depth of the i-th set of first and second inspection marks is set to 2λ. _i / 8.
[0085]
Next, in step S22, the wavelength of the reference sample is λ. _i The focus position is adjusted to the intermediate position in the height direction of the i-th set of first inspection marks. Then, the positions of the first inspection mark and the second inspection mark are detected, and the amount of misalignment between the first inspection mark and the second inspection mark is measured. Thereafter, the process proceeds to step S23 where the focal position is moved by, for example, 100 nm in the first inspection mark height direction, and the amount of positional deviation between the first inspection mark and the second inspection mark at each focal position is determined. taking measurement. Next, the stage of the misalignment inspection apparatus is rotated by 180 ° to adjust the focal position to the intermediate position in the height direction of the first inspection mark. Then, the positions of the first and second inspection marks are detected, and the amount of displacement between the first inspection mark and the second inspection mark is measured. Thereafter, the focal position is moved by, for example, 100 nm in the height direction of the first inspection mark, and the amount of positional deviation between the first inspection mark and the second inspection mark at each focal position is measured.
[0086]
Next, the process proceeds to step S24, and the TIS at each focal position is calculated by the equation (1).
[0087]
Next, the process proceeds to step S25, and it is determined whether or not the filter 25 is changed. In the case of replacing the filter 25, the process proceeds to step S26, the filter 25 is replaced, and then the process returns to step S22 to repeat the above processing. When the filter 25 is not replaced in step S25, the process proceeds to step S27, and the average value of TIS calculated in step S25 is calculated.
[0088]
In the present embodiment, the light output from the light source 11 is passed through the filter 31 to obtain light with centroid wavelengths of 545 nm, 595 nm, 675 nm, 600 nm, 630 nm, and 465 nm, as shown in FIGS. Then, the TIS at each focal position is measured by moving the focal position with the light of each wavelength in the same manner as in the first embodiment. Thereafter, an average value of TIS at each focal position is obtained, and telecentric deviation and coma aberration are evaluated from the relationship between the focal position and the average value of TIS at each focal position.
[0089]
In the present embodiment, the TIS is measured by changing the wavelength of the irradiation light, and the TIS of the optical system is evaluated based on the average value. Therefore, the TIS can be evaluated more accurately.
[0090]
[4] Reference sample structure and TIS
FIG. 22 is a view showing a reference sample 60 in which a groove is formed by etching the silicon substrate 61 and a protrusion made of a resist film is formed inside the groove. In this reference sample 60, the groove is used as the first inspection mark 62, and the resist film is used as the second inspection mark 63. The depth of the first inspection mark 62 is X, and the height of the second inspection mark 63 is Y.
[0091]
FIG. 23 is a view showing a reference sample 70 in which a groove is formed by etching the silicon substrate 71. In this reference sample 70, the groove is a first inspection mark 72, and the portion surrounded by the groove is a second inspection mark 73. Therefore, the depth of the first inspection mark 72 and the height of the second inspection mark 73 are both X.
[0092]
FIG. 24 is a diagram showing a result of measuring TIS by changing the focal position by setting the X value of the reference sample 60 shown in FIG. 22 to λ / 8, 2λ / 8, and 3λ / 8. However, the height Y of the second inspection mark 63 is constant. FIG. 25 is a diagram showing a result of measuring TIS by changing the focal position by setting the X value of the reference sample 70 shown in FIG. 23 to λ / 8, 2λ / 8, and 3λ / 8. Further, FIG. 26 is a diagram showing the relationship between the value of X and TIS for the reference samples 60 and 70 shown in FIGS. As can be seen from FIGS. 24 to 26, the reference sample 60 having the structure shown in FIG. 22 can measure the TIS with higher sensitivity than the reference sample 70 having the structure shown in FIG.
[0093]
[Third Embodiment]
A misregistration inspection method according to a third embodiment of the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same component as the position shift inspection apparatus by 2nd Embodiment shown in FIG. 17, and description is abbreviate | omitted or simplified.
[0094]
FIG. 27 is a schematic cross-sectional view showing an example of an inspection mark for explaining the step dependency of TIS, FIG. 28 is a graph showing the relationship between TIS and inspection wavelength, and FIG. 29 shows a misalignment inspection method according to this embodiment. FIG. 30 is a schematic sectional view showing an example of an inspection mark formed on the inspection wafer.
[0095]
In the present embodiment, the misalignment inspection method shown in FIG. 17 is used as an example of the misalignment inspection method capable of performing the misalignment inspection on the actual device wafer with high accuracy while minimizing the interaction between TIS and WIS. I will explain. In the present embodiment, the case where the step D of the inspection mark is not clear is particularly handled.
[0096]
[1] Principle
As shown in FIG. 27, on the inspection wafer 80, there is a main scale made of a groove having a depth D on a silicon substrate 81 and a sub scale made of a resist film 82 having a predetermined thickness inside the main scale groove. Assume that an inspection mark is formed. At this time, if the wavelength λ of the inspection light by the misalignment inspection apparatus is changed and TIS is measured for each wavelength, the value of TIS changes. That is, the value of TIS changes depending on the step D of the inspection mark and the wavelength λ of the inspection light. FIG. 28 is a graph showing the wavelength dependence of the inspection light of the TIS size measured using the structure of FIG. The horizontal axis represents the depth D formed on the silicon substrate 81 by the amount (D / λ) normalized by the inspection wavelength λ. As shown in the figure, the TIS periodically changes with respect to the inspection wavelength λ, and the step D is
D = nλ / 4 (n = 1, 2,...) (2)
TIS is minimized when the relationship is satisfied.
[0097]
Accordingly, the wavelength λ of the inspection light is selected according to the step D of the inspection mark, that is,
λ = 4D / n (n = 1, 2,...) (3)
By using the inspection light having the wavelength λ, it is possible to perform the positional deviation inspection while suppressing the influence of TIS.
[0098]
In the first and second embodiments, the optical aberration measurement is performed at the inspection wavelength where the influence of TIS appears greatly in order to measure TIS with high accuracy. Conversely, the inspection wavelength that can suppress the influence of TIS is selected. By doing so, it is possible to perform a highly accurate displacement inspection while suppressing the influence of TIS.
[0099]
[2] Misalignment inspection method
First, an inspection wafer 90 to be inspected is placed on the stage 16 of the misalignment inspection apparatus shown in FIG. The inspection wafer 90 is an actual device wafer in the manufacturing process. For example, an inspection mark as shown in FIG. 30 is formed on the inspection wafer 90. That is, on the silicon substrate 91, SiO ₂ A film 92, an aluminum film 93, and a resist film 94 are sequentially formed, and SiO 2 ₂ The main scale is configured by selectively removing a part of the film 92, and the vernier is configured by a resist film 94 formed in a region inside the main scale. For example, SiO ₂ Such an inspection mark is used when measuring the displacement of the resist pattern for processing the wiring layer made of the aluminum film 93 in the contact hole formed in the film 92.
[0100]
Next, using the inspection marks formed on the inspection wafer 90, the TIS in the X direction and the Y direction in the misalignment inspection apparatus is measured. The TIS measurement is for determining the measurement light wavelength in the subsequent misalignment inspection process. In the misalignment inspection method according to the present embodiment, TIS measurement is performed a plurality of times while changing the wavelength of the inspection light, and the wavelength having the smallest influence of TIS is found.
[0101]
That is, first, in step S31, the number n of wavelengths of inspection light is designated. The number n of wavelengths is appropriately set according to the number of filters 25, the number of base lines of the light source 11, and the like. Further, the number n of wavelengths may be selected so that an arbitrary wavelength interval (for example, an interval of 10 nm) is obtained in an arbitrary wavelength band (for example, about 400 to 800 nm which is a visible light region).
[0102]
Next, in step S32, the wavelength of the i-th inspection light is set. For example, when the wavelength is changed by the filter 25, the barycentric wavelength of the transmitted light obtained by the i-th filter is set by the above-described method. For example, if the same filter 25 as in the second embodiment is used, the center-of-gravity wavelength of the inspection light is 545 nm, 595 nm, 675 nm, 600 nm, 630 nm, or 465 nm. In this case, the number n of wavelengths specified in step S31 is 6.
[0103]
Next, TIS is measured with the inspection light having the wavelength λ set in step S33, and the TIS at that time is calculated in step S34. For the measurement and calculation of TIS, for example, the inspection method according to the first embodiment is used.
[0104]
Next, in step S35, it is determined whether or not the measurement is finished. When the measurement is completed, that is, when i = n, the process proceeds to step S36 described later. When the measurement is not completed, that is, when i <n, 1 is added to i in step S38 and the process returns to step S32, and the TIS is measured with the light of the (i + 1) th wavelength in the same manner as described above. Thus, the 1st to nth TIS are measured.
[0105]
Next, in step S36, a centroid wavelength (optimal centroid wavelength) that gives the smallest TIS is determined from the measured n TIS values.
[0106]
Next, in step S37, the displacement of the inspection wafer is measured using the optimum center-of-gravity wavelength obtained in step S36. When the wavelength is changed by the filter 25, the positional deviation of the inspection wafer 90 is measured using the filter 25 whose center of gravity wavelength is closest to the optimum center of gravity wavelength. The optimum center-of-gravity wavelength is a wavelength that satisfies the above-described relationship of λ = 4D / n. Therefore, the influence of TIS can be suppressed by performing the displacement inspection with this wavelength.
[0107]
Note that the difference in level is usually different between the main scale and the sub-scale. Therefore, it is desirable to detect the position of the main and sub-scales at different inspection wavelengths. That is, for the main scale, the optimum center-of-gravity wavelength for the main scale is obtained, and the position of the inspection mark is detected based on the wavelength. For the sub-scale, the optimum center-of-gravity wavelength for the vernier is obtained and the inspection mark is obtained based on the wavelength. The position deviation between the two is calculated from these results. By doing so, it is possible to more accurately inspect the amount of displacement between the main scale and the sub-scale while suppressing the influence of TIS. However, even when the optimum center-of-gravity wavelength is specified for only one scale, the effect of suppressing TIS is obtained, although the effect is inferior to the case of specifying the optimum center-of-gravity wavelength for both the main scale and the sub scale. It is done.
[0108]
As described above, according to the present embodiment, since the misregistration amount is measured using the inspection light having the wavelength that minimizes the TIS, the misregistration amount can be inspected while suppressing the influence of the TIS. Further, since the influence of TIS can be suppressed, the positional deviation inspection on the actual device wafer can be performed with high accuracy while minimizing the interaction between TIS and WIS.
[0109]
[Fourth Embodiment]
A misregistration inspection method according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 31 is a flowchart showing the misalignment inspection method according to this embodiment.
[0110]
In this embodiment, the misregistration inspection apparatus shown in FIG. 1 is used for another misregistration inspection method capable of performing the misregistration inspection on the actual device wafer with the minimum interaction between TIS and WIS. An example will be described.
[0111]
[1] Principle
In the misregistration inspection method according to the third embodiment, a method is shown in which measurement is performed a plurality of times while changing the inspection wavelength, the optimum center-of-gravity wavelength giving the minimum TIS is obtained, and then the misregistration amount is measured. However, the step of the inspection mark is often known on the actual device wafer. For example, in the example of the inspection mark shown in FIG. ₂ The step of the vernier is defined by the film thickness of the resist film 94, and these parameters are controlled to predetermined values in the manufacturing process. These steps are determined according to the device structure, characteristics, and the like, and the steps of the main scale and the sub-scale cannot be controlled according to the wavelength of the inspection light of the misalignment inspection apparatus. Therefore, when the step of the inspection mark is known in this way, it is desirable to select the wavelength of the inspection light according to the step of the inspection mark from the relationship between the TIS and the wavelength of the inspection light as shown in FIG. .
[0112]
Further, as described above, there is a periodicity between the TIS and the wavelength of the inspection light. Therefore, if the wavelength of the light when measuring the main scale and the light of the wavelength when measuring the vernier satisfy the period, the measurement light in the measurement of the main scale and the measurement of the vernier There is no need to change the wavelength.
[0113]
That is, the inspection wavelength λ that gives the smallest TIS for the main scale _m Is
M _m = N _m λ _m / 4 (n _m = 1, 2, ...) (4)
The inspection wavelength λ that gives the smallest TIS for the vernier _s Is
M _s = N _s λ _s / 4 (n _s = 1, 2, ...) (5)
Therefore, in the equations (4) and (5), λ = λ _m = Λ _s As
λ / 4 = M _m / N _m = M _s / N _s (N _m , N _s = 1, 2, ...) (6)
If there is a wavelength λ that satisfies the condition, TIS can be minimized for both the main scale and the sub-scale.
[0114]
For example, in the misalignment inspection mark shown in FIG. _m Is 300nm, vernier step M _s Is 1000 nm, n _m = 3, n _s = 10, that is, when the wavelength λ = 400 nm, the relationship is satisfied.
[0115]
When there are a large number of wavelengths λ that satisfy the relationship of equation (6), it is desirable to select the least common divisor. Moreover, it is desirable that the wavelength λ can be in the visible light range (about 400 to 800 nm).
[0116]
[2] Misalignment inspection method
First, an inspection wafer 90 to be inspected is placed on the stage 16 of the misalignment inspection apparatus shown in FIG. The inspection wafer 90 is an actual device wafer in the manufacturing process. For example, an inspection mark as shown in FIG. 30 is formed on the inspection wafer 90. That is, on the silicon substrate 91, SiO ₂ A film 92, an aluminum film 93, and a resist film 94 are sequentially formed, and SiO 2 ₂ The main scale is configured by selectively removing a part of the film 92, and the vernier is configured by a resist film 94 formed in a region inside the main scale.
[0117]
Next, in step S41, the main scale step M defined by the device process. _m And the step M of the vernier _s Enter. Main scale step M _m And vernier step M _s The value measured beforehand by other means may be used, or the target film thickness in the process may be used.
[0118]
Next, in step S42, it is calculated whether there is an inspection wavelength that can be measured while minimizing the TIS for both the main scale and the sub-scale. That is, the step of the main scale is M _m , The step of the vernier is M _s Then, it is calculated whether or not there is a wavelength λ that satisfies the relationship of the expression (6).
[0119]
If there is a wavelength λ that satisfies the relationship of equation (6) in step S42, the process proceeds to step S47. On the other hand, if there is no wavelength λ satisfying the relationship of the expression (6), the process proceeds to step S43.
[0120]
When the process proceeds to step S47, first, the wavelength λ satisfying the relationship of the equation (6) is set as the barycentric wavelength of the inspection light. Next, the inspection wafer 90 is irradiated with inspection light having the center-of-gravity wavelength λ, image signal processing is performed on the main scale and the vernier, and the position of the main and vernier is detected.
[0121]
On the other hand, when the process proceeds to step S43, first, in step S43, the optimum center-of-gravity wavelength λ with respect to the main scale is calculated based on the above equation. _m Ask for. Next, in step S44, the center-of-gravity wavelength λ _m The inspection wafer 90 is irradiated to the inspection wafer 90, image signal processing for the main scale is performed, and the position of the main scale is detected. Next, in step S45, the optimum center-of-gravity wavelength λ for the vernier based on the above equation _s Ask for. Next, in step S46, the center of gravity wavelength λ _s The inspection wafer 90 is irradiated to the inspection wafer 90, image signal processing for the vernier is performed, and the position of the vernier is detected.
[0122]
Next, in step S48, based on the positions of the main scale and the sub-scale obtained in step S44 and step S46 or step S47, the amount of misalignment between them is calculated. By doing so, it is possible to inspect the amount of misalignment between the main scale and the sub-scale while suppressing the influence of TIS.
[0123]
As described above, according to the present embodiment, the step of the inspection mark is provided in advance, and the wavelength of the inspection light that minimizes the TIS is set based on the step, so that the misalignment inspection process can be easily performed. . Further, since the main-scale inspection light and the vernier inspection light are shared, the misalignment inspection process can be simplified. Further, as in the case of the third embodiment, the displacement amount can be inspected while suppressing the influence of TIS, and since the influence of TIS can be suppressed, the interaction between TIS and WIS is minimized. It is possible to suppress the positional deviation on the actual device wafer with high accuracy.
[0124]
【The invention's effect】
As described above, according to the present invention, the focus position is moved in the height or depth direction of the inspection mark, and the TIS at each focus position is calculated. The influence of aberration can be individually evaluated. Thereby, the optical system of the misalignment inspection apparatus can be adjusted efficiently, and a misalignment inspection apparatus with a small TIS can be manufactured. In addition, since a misalignment inspection apparatus with a small TIS can be provided, the influence of WIS can be evaluated, and a reference sample having an inspection mark with a small influence of WIS can be provided.
[0125]
In addition, since the misregistration amount is measured by selecting light having a wavelength corresponding to the step of the inspection mark, the misregistration amount can be inspected with high accuracy while suppressing the influence of TIS. Therefore, it is possible to perform the displacement inspection on the actual device wafer with high accuracy while minimizing the interaction between TIS and WIS.
[0126]
Also, when the main scale step and the sub-scale step satisfy a certain relationship, that is, the main scale step is defined as M. _m , The step of the vernier is M _s Λ / 4 = M _m / N _m = M _s / N _s (N _m , N _s = 1, 2,...), The misalignment inspection is performed with the light of wavelength λ, so that the measurement can be performed while minimizing the TIS for both the main scale and the sub scale. Therefore, it is possible to perform the positional deviation inspection with high accuracy and simplify the processing.
[Brief description of the drawings]
FIG. 1 is a diagram showing a misalignment inspection apparatus used in an optical aberration measuring method according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing an example of arrangement of inspection marks used for TIS measurement of a misalignment inspection apparatus and signals output from a CCD camera.
FIG. 3 is a diagram (part 1) illustrating a relationship between a depth of an inspection mark and light intensity.
FIG. 4 is a diagram (part 2) illustrating the relationship between the depth of an inspection mark and the light intensity.
FIG. 5 is a schematic diagram showing a change in TIS when the focal position is moved in the depth direction of an inspection mark.
FIG. 6 shows the results of actual measurement of TIS values when the depth of the first inspection mark is λ / 8 and the height of the second inspection mark is 2.7λ / 8 to 5.5λ / 8. It is a graph.
FIG. 7 is a schematic sectional view (No. 1) showing a structure of an inspection mark used for TIS measurement.
FIG. 8 is a schematic cross-sectional view (part 2) showing the structure of an inspection mark used for TIS measurement.
FIG. 9 is a schematic cross-sectional view (part 3) showing the structure of an inspection mark used for TIS measurement.
FIG. 10 is a schematic sectional view (No. 1) showing the structure of a reference sample.
FIG. 11 is a schematic cross-sectional view (part 2) showing the structure of the reference sample.
FIG. 12 is a schematic cross-sectional view (part 3) showing the structure of the reference sample.
FIG. 13 is a schematic cross-sectional view (part 4) showing the structure of the reference sample.
FIG. 14 is a flowchart showing an optical aberration measuring method of the misalignment inspection apparatus according to the first embodiment of the present invention.
FIG. 15 is a graph showing the relationship between the TIS measured by the optical aberration measuring method according to the first embodiment and the focal position; the focal position is fixed, the position of the second detection mark is detected; The measurement result when it is moved and the first detection mark is detected is shown.
FIG. 16 is a graph showing the relationship between the TIS measured by the optical aberration measuring method according to the first embodiment and the focal position, in which the positions of the first and second detection marks are detected by moving the focal position. The measurement results are shown.
FIG. 17 is a diagram showing a misalignment inspection apparatus used in the optical aberration measuring method according to the second embodiment of the present invention.
FIG. 18 is a diagram (part 1) illustrating a spectrum of irradiation light when irradiation light output from a light source passes through a filter;
FIG. 19 is a diagram (part 2) illustrating a spectrum of irradiation light when irradiation light output from a light source passes through a filter;
FIG. 20 is a diagram illustrating the definition of the barycentric wavelength of irradiation light.
FIG. 21 is a flowchart showing an optical aberration measuring method of the misalignment inspection apparatus according to the second embodiment of the present invention.
FIG. 22 is a view showing a reference sample in which a groove formed in a silicon substrate is used as a first inspection mark and a second protrusion made of a resist film formed inside the groove is used as a second inspection mark.
FIG. 23 is a diagram showing a reference sample in which a groove formed in a silicon substrate is used as a first inspection mark and an inner portion of the groove is used as a second inspection mark.
24 is a graph showing the result of examining the relationship between the focal position of the reference sample having the structure shown in FIG. 22 and TIS by changing the depth of the first inspection mark.
FIG. 25 is a graph showing the results of examining the relationship between the focal position of the reference sample having the structure shown in FIG. 23 and TIS by changing the depth of the first inspection mark.
FIG. 26 is a graph showing a result of measuring TIS by changing the depth of the first inspection mark of the reference sample having the structure shown in FIGS. 22 and 23;
FIG. 27 is a schematic cross-sectional view showing an example of an inspection mark for explaining the step dependency of TIS.
FIG. 28 is a graph showing the relationship between TIS and the wavelength of inspection light.
FIG. 29 is a flowchart showing a misalignment inspection method according to a third embodiment of the present invention.
30 is a schematic cross-sectional view showing an example of an inspection mark formed on an inspection wafer. FIG.
FIG. 31 is a flowchart showing a misalignment inspection method according to a fourth embodiment of the present invention.
[Explanation of symbols]
10 ... wafer
10a ... reference sample
11 ... Light source
12. Light guide
13 ... Irradiation lens group
14 ... Beam splitter
15 ... Objective lens group
16 ... Stage
17 ... Eyepiece group
18 ... CCD camera
19 ... Signal processing section
20 ... reference sample
21 ... Inspection mark
25 ... Filter
31 ... Silicon substrate
32 ... First inspection mark
33 ... Second inspection mark
34 ... First inspection mark
35 ... Second inspection mark
36 ... First inspection mark
37 ... Second inspection mark
40 ... Silicon substrate
41 ... SiO ₂ film
42. Tungsten film
43. Aluminum film
44. Resist film
45. Resist film
46 ... Opening
47 ... Tungsten film
48 ... SiO ₂ film
49. Aluminum film
50. Resist film
51. Resist film
52. Opening
60 ... reference sample
61 ... Silicon substrate
62 ... 1st inspection mark
63 ... Second inspection mark
70 ... reference sample
71 ... Silicon substrate
72. First inspection mark
73 ... Second inspection mark
80 ... Inspection wafer
81 ... Silicon substrate
82. Resist film
90 ... Inspection wafer
91 ... Silicon substrate
92 ... SiO ₂ film
93 ... Aluminum film
94. Resist film

Claims (9)

An image obtained by irradiating a reference sample having first and second inspection marks made of protrusions or grooves with light having a wavelength λ, and imaging the light reflected by the first and second inspection marks with an imaging device. Measuring a first misalignment amount between the first and second inspection marks based on
After rotating the reference sample by 180 degrees, the reference sample is irradiated with light of wavelength λ, the light reflected by the first and second inspection marks is imaged by the imaging device, and based on the acquired image Measuring a second positional deviation amount between the first and second inspection marks;
A method of measuring an optical aberration of the misregistration inspection apparatus, comprising calculating an optical aberration of the misregistration inspection apparatus from the first and second misregistration amounts,
In each of the steps of measuring the first and second misregistration amounts, the image at each focal position is obtained by moving the focal position of the imaging device in the height or depth direction of the first and second inspection marks. A method for measuring an optical aberration of a misregistration inspection apparatus, comprising the step of: In the optical aberration measuring method of the misalignment inspection apparatus according to claim 1,
Optical of a misalignment inspection apparatus, wherein the height or depth of at least one of the first and second inspection marks is λ / 8 ± 6.25% or 3λ / 8 ± 6.25% Aberration measurement method. In the optical aberration measuring method of the misalignment inspection apparatus according to claim 1,
The height or depth of at least one of the first and second inspection marks is λ / 8 ± 6.25%, and the other height or depth is 3λ / 8 ± 6.25%. An optical aberration measurement method for a misregistration inspection apparatus. In the optical aberration measuring method of the misalignment inspection apparatus according to claim 1,
An optical aberration measuring method for a misregistration inspection apparatus, wherein the height or depth of each of the first and second inspection marks is 2λ / 8 ± 6.25%. A reference sample having n sets of first and second inspection marks each including a protrusion or a groove whose height or depth is determined according to the wavelength λ _i (i = 1, 2,..., N) of the light to be irradiated. Is irradiated with light of wavelength λ _{i, and} the light reflected by the i-th set of first and second inspection marks corresponding to the light of wavelength λ _i is imaged by the imaging device, and based on the acquired image Measuring a first misalignment amount between the i-th set of first and second inspection marks;
After rotating the reference sample by 180 degrees, the reference sample is irradiated with light of wavelength λ _i , and the light reflected by the i-th set of first and second inspection marks is imaged by the imaging device, Measuring a second misalignment amount between the i-th set of first and second inspection marks based on the acquired image;
Calculating an optical aberration of a misregistration inspection apparatus for light of wavelength λ _i from the first and second misregistration amounts;
The steps from the step of measuring the first positional deviation amount by changing the wavelength λ _{i of} the light irradiating the reference sample to the step of calculating the optical aberration include the n sets of first and second inspection marks. A method for measuring an optical aberration of a misregistration inspection apparatus having a process of repeating all of
In each of the steps of measuring the first and second misregistration amounts, the focal position of the imaging device is moved in the height or depth direction of the i-th set of first and second inspection marks. A method for measuring an optical aberration of a misregistration inspection apparatus, comprising a step of capturing an image at each focal position. In the optical aberration measuring method of the misregistration inspection apparatus according to claim 5,
An optical aberration measurement method for a misregistration inspection apparatus, wherein an average value of optical aberrations calculated for each of the n sets of first and second inspection marks is calculated. In the optical aberration measuring method of the misregistration inspection apparatus according to claim 5,
The height or depth of either one of the i-th set of first and second inspection marks is λ _i /8±6.25% or 3λ _i /8±6.25. Method for measuring an optical aberration of a misalignment inspection apparatus. In the optical aberration measuring method of the misregistration inspection apparatus according to claim 5,
The height or depth of at least one of the i-th set of first and second inspection marks is λ _i /8±6.25%, and the other height or depth is 3λ _i / 8 ± 6. 25. A method for measuring an optical aberration of a misregistration inspection apparatus, characterized by being 25%. In the optical aberration measuring method of the misregistration inspection apparatus according to claim 5,
An optical aberration measuring method for a misalignment inspection apparatus, wherein the height or depth of each of the i-th set of first and second inspection marks is 2λ _i /8±6.25% .

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