JP2004348050A - Photomask, inspection method, and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photomask for inspecting the birefringence of a projection lens. <P>SOLUTION: The photomask is provided with: a transparent substrate 10; a pattern of a light shielding film 11 having a window part and formed on the surface of the transparent substrate 10; a first inspection pattern 13 disposed in the window part and polarizing illumination light into a first polarized state; and a second inspection pattern 14 disposed so as to be separated from the first inspection pattern 13 by a fixed distance in the window part and polarizing the illumination light into a second polarized state different from the first polarized state. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical lithography technique, and more particularly, to a method for inspecting a birefringence of a projection lens of an exposure apparatus.
[0002]
[Prior art]
2. Description of the Related Art In a manufacturing process of a semiconductor device, the wavelength of exposure light of an exposure apparatus has been reduced for forming a fine pattern. In recent years, an argon fluoride (ArF) excimer laser exposure apparatus (wavelength λ = 193 nm) or a fluorine gas (F ₂ 2.) An excimer laser exposure apparatus (wavelength λ = 157 nm) has been developed. The projection lens of the projection optical system used in such a short wavelength exposure apparatus includes fluorite (CaF ₂ ) Is used. Fluorite has a very good transmission of light having a wavelength of 200 nm or less. In particular, the case where the wavelength λ is 157 nm is the only lens material that can be manufactured at low cost at present.
[0003]
However, it has been found that fluorite exhibits birefringence for light having a wavelength of 200 nm or less. In a material exhibiting birefringence, the refractive index changes depending on the polarization state of transmitted light. When a material exhibiting birefringence is used for a lens, the imaging characteristic changes depending on the polarization state of light, and this causes blurring of the image, for example, double image formation. In order to miniaturize a semiconductor device, the birefringence of an optical material used for a projection optical system of an exposure apparatus must be suppressed since the imaging performance is deteriorated. Therefore, efforts have been made to suppress the influence of birefringence by devising the manufacturing process of optical materials and designing and assembling lenses.
[0004]
Inspection of the birefringence of an optical material is generally performed by a method such as a rotation analyzer method or a phase modulation method in which linearly polarized light is incident on the optical material and the polarization state of transmitted light is examined. Non-patent document 1).
[0005]
[Non-patent document 1]
Mochida, Optics, 1989, Vol. 127, p. 127-134
[0006]
[Problems to be solved by the invention]
However, there is no known means for inspecting, after assembling the exposure apparatus, whether the birefringence of the projection lens of the projection optical system of the exposure apparatus is appropriately suppressed so as not to degrade the imaging characteristics. Since the imaging performance of an exposure apparatus is also degraded by factors other than birefringence, for example, aberrations of a projection lens, the presence of birefringence as a factor of image degradation is specified from the amount of deformation of the pattern transferred onto the semiconductor substrate. I can't. Further, it is not easy to incorporate a birefringence measuring device or the like into the optical system of the exposure device.
[0007]
An object of the present invention is to solve such a problem and to provide a photomask capable of inspecting birefringence of a projection lens of an exposure apparatus, an inspection method, and a method of manufacturing a semiconductor device to which the inspection method is applied.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, a first aspect of the present invention includes (a) a transparent substrate, (b) a pattern of a light-shielding film formed so as to have a window on the surface of the transparent substrate, and (c) a window. And a first inspection pattern that polarizes the illumination light to a first polarization state, and (d) is disposed at a position separated by a certain distance from the first inspection pattern in the window. And a second inspection pattern that polarizes the illumination light into a second polarization state different from the first polarization state.
[0009]
According to a second aspect of the present invention, there is provided (a) exposure light polarized in a first polarization state from illumination light of a photomask by a first inspection pattern provided in a window formed in a light shielding film of the photomask. The first inspection pattern is transferred to the resist film applied on the semiconductor substrate by light to form a first transfer pattern, and (b) a predetermined distance from the first inspection pattern in the inspection mark. The second inspection pattern is transferred to the resist film with exposure light polarized to a second polarization state different from the first polarization state by the second inspection pattern formed at the separated position, and the second transfer pattern is formed. And (d) measuring an amount of relative displacement between the first and second transfer patterns.
[0010]
According to a third aspect of the present invention, (a) a photomask for inspection and a semiconductor substrate for inspection coated with a resist film are mounted on each of a plurality of exposure apparatuses. The first inspection pattern is transferred to the resist film with the exposure light polarized in the first polarization state by the first inspection pattern provided in the window formed in the light-shielding film of the photomask. And (c) a second polarization state different from the first polarization state by a second inspection pattern formed at a position separated by a fixed distance from the first inspection pattern in the inspection mark. The second inspection pattern is transferred to the resist film with the exposure light polarized to form a second transfer pattern, and (d) the amount of displacement between the first and second transfer patterns is measured to obtain a reference value and a reference value. And (e) the amount of displacement is below the reference value The optical devices are classified based on the amount of misalignment, and (f) a manufacturing exposure device that can be used in the lithography step of the target manufacturing process is selected from the classified exposure devices, and (g) a manufacturing exposure device. The gist of the present invention is to provide a method of manufacturing a semiconductor device including performing a lithography step using a semiconductor device.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, first to third embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the plane dimension, the ratio of the thickness of each layer, and the like are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. In addition, it goes without saying that parts having different dimensional relationships and ratios are included between the drawings.
[0012]
(First Embodiment)
The exposure apparatus used for explaining the inspection of the projection lens according to the first embodiment of the present invention is a refraction type exposure apparatus (scanner) as shown in FIG. 1, and the reduction ratio is 4: 1. An ArF excimer laser having a wavelength λ = 193 nm is used as the light source 22. The illumination optical system includes a fly-eye lens 23, an illumination aperture 24, a condenser lens 25, and the like. The projection optical system includes a projection lens 26, an aperture stop 30, and the like. The pupil 27 is a plane surrounded by the aperture stop 30. The exposure light reduces and projects the pattern of the photomask 3 placed on the mask stage 28 between the illumination optical system and the projection optical system onto the semiconductor substrate 1 on the substrate stage 29. Note that, for convenience of explanation, a scanner is shown as an exposure apparatus, but a stepper or the like can be used in addition to the scanner. Further, although the reduction ratio is 4: 1, it goes without saying that any reduction ratio may be used. Further, an ArF excimer laser is used as the light source 22, but the F of the wavelength λ = 157 nm is used. ₂ Needless to say, an excimer laser or a krypton fluoride (KrF) excimer laser having a wavelength λ = 248 nm may be used.
[0013]
As shown in FIG. 2, the photomask 3 is provided with a projection lens on each of windows on a matrix of a pattern of a light-shielding film 11 such as chromium (Cr) deposited on the surface of a transparent substrate 10 such as fused quartz. A plurality of inspection marks 12 for inspecting birefringence are arranged. The inspection marks 12 are arranged at substantially equal intervals with respect to the collective exposure area of the exposure apparatus. Although not shown, the photomask 3 also has alignment marks used for positioning on the mask stage 28 of the exposure apparatus.
[0014]
As shown in FIG. 3A, the inspection mark 12 of the photomask 3 is disposed at a first inspection pattern 13 for polarizing illumination light to a first polarization state and at a position concentric with the first inspection pattern 13. And a second inspection pattern 14 that polarizes the illumination light to a second polarization state different from the first polarization state. In the first embodiment, the first inspection mark 13 has a rectangular frame shape and is disposed between the outer light shielding film 11 and the inner first light shielding part 11a. The second inspection pattern 14 has a rectangular frame shape, is located inside the first inspection pattern 13, and is disposed between the first light shielding portion 11a and the second light shielding portion 11b. For example, the first inspection pattern 13 is a square having a side of 80 μm (scale on the photomask 3, the same applies hereinafter) with a width of 8 μm. The second inspection pattern 14 is concentric with the first inspection pattern 13 and has a square of 40 μm on one side of the outer frame and a width of 8 μm. Note that the first and second inspection patterns 13 and 14 are not limited to the dimensions described above, but may be of any size. Although the first and second inspection patterns 13 and 14 are concentric for the sake of simplicity, the center positions thereof may be separated by a certain distance.
[0015]
As shown in FIG. 3B, the AA cross section of the first inspection pattern 13 has a line and space (a plurality of linear light shielding portions 15 disposed between the light shielding films 11 on the surface of the transparent substrate 10). (L / S) pattern. The material of the light shielding portion 15 is a conductor, for example, Cr. Further, as shown in FIG. 3C, the BB cross section of the second inspection pattern 14 includes a plurality of linear light-shielding portions 16 arranged between the first light-shielding portions 11a on the surface of the transparent substrate 10. FIG. The period P of the L / S pattern of the first and second inspection patterns 13 and 14 is shorter than the wavelength λ of the light source 22 of the exposure apparatus, for example, 150 nm. The ratio between the line width and the space interval of each of the light shielding portions 15 and 16 in the period P direction is approximately 1: 1. The light-shielding portions 15 and 16 are arranged so that their longitudinal directions are orthogonal to each other. For example, the periodic direction of the L / S pattern of the first inspection pattern 13 is the horizontal direction (x-axis direction) on the paper of FIG. 3A, and the periodic direction of the L / S pattern of the second inspection pattern 14 is Is the vertical direction (y-axis direction) on the paper.
[0016]
A periodic structure grating shorter than the wavelength of the illumination light functions as a polarizer, and is called a wire grid polarizer (for example, Kikuta and Iwata, Transactions of the Institute of Electronics, Information and Communication Engineers, vol. J83-C, 2000, p173-181). The period P of the L / S pattern of the first and second inspection patterns 13 and 14 is shorter than the wavelength of the illumination light emitted from the light source 22 of the exposure apparatus. Therefore, the first and second inspection patterns 13 and 14 function as a wire grid polarizer for the illumination light incident on the photomask 3. The wire grid polarizer has a characteristic that a component whose vibration plane of the electric field of the illumination light coincides with the periodic direction of the L / S pattern passes therethrough and reflects a component whose vibration plane of the electric field coincides with the longitudinal direction of the L / S pattern. Have. The illumination light passing through the first inspection pattern 13 is linearly polarized light polarized in the x-axis direction, while the illumination light passing through the second inspection pattern 14 is linearly polarized light polarized in the y-axis direction. . Since the illumination light incident on the photomask 3 is non-polarized light, both the x-axis and y-axis polarized light components are present. Thus, according to the photomask 3 according to the first embodiment, the linearly polarized light polarized in the first and second directions orthogonal to each other, for example, the x-axis and the y-axis directions, from the unpolarized illumination light. Is emitted.
[0017]
Next, a method of inspecting birefringence according to the first embodiment will be described. For example, as shown in FIG. _i When unpolarized light is incident on a transparent material at an incident angle θ, the refraction angle θ usually follows Snell's law. _o Refraction and enter the transparent material. Since the transparent material 6 that exhibits birefringence has a different refractive index depending on the direction of oscillation of the electric field of light (hereinafter referred to as polarization direction), the light is split into two light beams in the transparent material 6. That is, the transparent material 6 is converted to the refraction angle θ. _o And the refraction angle θ _e An extraordinary ray that is transmitted at the point occurs. Both the ordinary ray and the extraordinary ray exit from the transparent material 6 at the exit angle θ. As a result, as shown in FIG. _i From the original position p by the ordinary ray on the image plane 7 _o And the position p due to the extraordinary ray _e The light beam also reaches the object, resulting in double copying. Here, the ordinary ray and the extraordinary ray are each linearly polarized light, and the vibration planes of the electric field of the light are orthogonal to each other. The refractive index of the transparent material 6 for ordinary rays and extraordinary rays is n _o , N _e Assuming that the refractive index of air is 1, the following relationship is established.
[0018]
sin θ _o = (Sinθ) / n _o , Sin θ _e = (Sinθ) / n _e ... (1)
Here, for normal incidence, the refraction angle θ _o And θ _e Are both 0 degrees, no light splitting is observed. Also, the refractive index n _o , N _e Is small, the refraction angle θ _o And θ _e Are almost equal, making it difficult to observe the splitting of light rays.
[0019]
In order to inspect the birefringence of the transparent material 6, the position p of the image on the object plane 5 as shown in FIG. _i , The imaging position p split at the image plane 7 _o And p _e Should be observed. However, the birefringence of the transparent material used in the exposure apparatus is small, and the splitting of the light beam is not so large that a normal mask pattern is separated at the image forming position. Therefore, the images of the ordinary ray and the extraordinary ray after passing through the transparent material are displaced and overlapped, and it is difficult to observe the imaging positions of the ordinary ray and the extraordinary ray separately, and cannot be applied to the inspection of birefringence.
[0020]
In the first embodiment, birefringence inspection is performed by making orthogonal linearly polarized light incident on a transparent material. Linearly polarized light, when incident on a transparent material exhibiting birefringence, is split into two light beams whose polarization directions are orthogonal to each other. The orthogonal polarization directions are called the fast axis and the slow axis. The fast axis and the slow axis are specific to the transparent material, and are determined by, for example, the crystal axis direction of the transparent material or the direction of the stress applied to the transparent material. Light whose polarization direction is the fast axis has a high speed and a small phase change during a unit distance. On the other hand, light whose polarization direction is the slow axis has a low speed and a large phase change during a unit distance. In the first embodiment, the former is an ordinary ray and the latter is an extraordinary ray. However, the relationship may be reversed depending on the birefringence characteristics of the transparent material. Light transmitted through the transparent material has a phase difference due to a speed difference. The emitted light is a superposition of an ordinary ray and an extraordinary ray vibrating at different phases, that is, elliptically polarized light. When the polarization direction of the incident light is parallel to the fast axis direction or the slow axis direction, the polarization state of the light beam does not change.
[0021]
As described above, the illumination light of the photomask 3 is, for example, linearly polarized light that passes through the first and second inspection patterns 13 and 14 and is orthogonal to the first and second directions. As shown in FIG. 5, the first polarized light Lp1 and the second polarized light Lp2 transmitted through the first and second inspection patterns 13 and 14 are shifted from the orthogonal fast axis and slow axis. And For example, the amplitude A1o of the ordinary ray Lp1o of the fast axis component of the first polarized light beam Lp1 in FIG. 5A is larger than the amplitude A1e of the extraordinary ray Lp1e of the slow axis component, and the amplitude A1e of FIG. The amplitude A2o of the ordinary ray Lp2o of the fast axis component of the second polarized light beam Lp2 is smaller than the amplitude A2e of the extraordinary ray Lp2e of the slow axis component.
[0022]
As shown in FIG. 6A, the first polarized light beam Lp1 emitted from the first inspection pattern 13 of the photomask 3 becomes an ordinary light beam Lp1o and an extraordinary light beam Lp1e in the projection lens 26 that exhibits birefringence. Split. The split ordinary ray Lp1o and extraordinary ray Lp1e are refracted on the exit surface of the projection lens 26 and projected to different positions p1o and p1e on the surface of the semiconductor substrate 1. Further, as shown in FIG. 6B, the second polarized light beam Lp2 emitted from the second inspection pattern 14 is split into the ordinary light beam Lp2o and the extraordinary light beam Lp2e in the projection lens 26 exhibiting birefringence. . The split ordinary ray Lp2o and extraordinary ray Lp2e are projected to different positions p2o and p2e on the surface of the semiconductor substrate 1. Here, since the optical paths of the ordinary rays Lp1o and Lp2o of the first and second polarized light rays Lp1 and Lp2 are almost the same, the positions p1o and p2o projected on the surface of the semiconductor substrate 1 are almost the same. Similarly, since the optical paths of the extraordinary rays Lp1e and Lp2e are almost the same, the positions p1e and p2e are almost the same.
[0023]
As shown in FIG. 7, the light intensity distribution formed on the semiconductor substrate 1 is asymmetrical as shown by the solid line because the light intensity distribution of the extraordinary ray Lp1e or Lp2e overlaps with the ordinary ray Lp1o or Lp2o indicated by the dotted line. Shape. As shown in FIG. 6, the optical paths of the ordinary rays Lp1o and Lp2o of the first and second polarized light rays Lp1 and Lp2 are the same, and the optical paths of the extraordinary rays Lp1e and Lp2e are also the same. However, as shown in FIG. 5, the amplitude A1o of the ordinary ray Lp1o is larger than the amplitude A1e of the extraordinary ray Lp1e in the first polarized ray Lp1, and the amplitude A2o of the ordinary ray Lp2o is abnormal in the second polarized ray Lp2d. It is smaller than the amplitude A2e of the light beam Lp2e. Therefore, the light intensity distribution of the first polarized light beam Lp1 in FIG. 7A is different from that of the second polarized light beam Lp2 in FIG. 7B in that the light intensity of the ordinary light beam Lp1o is shifted toward the extraordinary light beam Lp1e. Has a small distribution shape. The photoresist applied to the surface of the semiconductor substrate 1 is exposed to a light intensity exceeding a threshold value Ith. Accordingly, as shown in FIG. 7, the first and second inspection patterns 13 and 14 are projected and the respective center positions cp1 and cp2 of the first and second transfer patterns 33 and 34 formed on the resist film 31. Deviates from the respective center positions p1o and p2o of the original image formation by the ordinary rays Lp1o and Lp2o by displacements D1 and D2 to the left side of the paper surface, respectively. In the light intensity distribution, the displacement D2 is larger than the displacement D1 because the second polarized light Lp2 is more shifted to the extraordinary light side than the first polarized light Lp1. Note that the period P of the L / S pattern of the first and second inspection patterns 13 and 14 is shorter than the wavelength of the illumination light, and is not resolved on the semiconductor substrate 1. Therefore, the first and second transfer patterns 33 and 34 become openings.
[0024]
The photomask 3 is set on the mask stage 28 of the exposure apparatus shown in FIG. 1, and the surface of the semiconductor substrate 1 coated with the positive photoresist is exposed by projection. The illumination light incident on the photomask 3 from the light source 22 is non-polarized light and illuminates the surface of the photomask 3 vertically. The inspection mark 12 is projected on the resist film by the first and second polarized light beams Lp1 and Lp2 emitted from the first and second inspection patterns 13 and 14. After the projection exposure, the semiconductor substrate 1 is developed to form an inspection resist pattern 32 on which the inspection mark 12 is transferred on the surface of the semiconductor substrate 1 as shown in FIG. The inspection resist pattern 32 has first and second transfer patterns 33 and formed on the resist film 31 corresponding to the first and second inspection patterns 13 and. The respective center positions C1 and C2 of the patterns of the first and second transfer patterns 33 and 34 are shifted, for example, to the upper left in the drawing by the birefringence of the projection lens 26. Since the polarization states of the first and second polarized light beams Lp1 and Lp2 are different, for example, the first and second polarized light beams Lp1 and Lp2 are formed on the resist film 31 on the semiconductor substrate 1 as shown in FIG. The center position C1 of the first transfer pattern 33 and the center position C2 of the second transfer pattern 34 are shifted by Δx. The center positions C1 and C2 of the first and second transfer patterns 33 and 34 are shifted by Δy in the vertical direction (y-axis direction) of the drawing.
[0025]
With respect to the inspection resist pattern 32 formed on the semiconductor substrate 1, for example, measurement of the center positions C1 and C2 of the first and second transfer patterns 33 and 34 using an optical misalignment inspection apparatus is performed. Done. The measured positional shift amount 中心 (Δx) between the center positions C1 and C2 of the first and second transfer patterns 33 and 34. ² + (Δy) ² ｝ ^1/2 Is compared with a reference value to determine whether or not the projection lens 26 has birefringence.
[0026]
In the inspection of birefringence according to the first embodiment, the first and second polarized light beams Lp1 and Lp2 which cross the illumination light of the photomask 3 by the first and second inspection patterns 13 and 14 of the inspection mark 12 at right angles. And make the light enter the projection lens 26. When the projection lens 26 exhibits birefringence, the ratio of the fast axis component and the slow axis component of the first and second polarized light beams Lp1 and Lp2 is different. Accordingly, the pattern centers of the first and second transfer patterns 33 and 34 in which the first and second inspection patterns 13 and 14 are transferred to the photoresist are shifted. As described above, according to the method of inspecting birefringence according to the first embodiment, the position of the center position of the first and second transfer patterns 33 and 34 is measured to measure the amount of misalignment, and thus the integrated pattern is incorporated in the exposure apparatus. The birefringence of the projection lens 26 can be inspected.
[0027]
In the case where a plurality of element lenses made of a birefringent material are included in the element lenses constituting the projection lens 26, the light beam is split each time it passes through the element lens exhibiting birefringence. In general, the directions of the fast axis and the slow axis of each element lens with respect to the traveling direction of the light beam are different. Accordingly, the maximum number of rays passing through the n element lenses exhibiting birefringence is 2 ⁿ Split into linearly polarized light. Even in such a case, as in the case of a single element lens, the amount of displacement of the inspection resist pattern 32 transferred to the photoresist can be measured, so that the inspection of birefringence can be performed by the above method.
[0028]
Further, one of the first and second inspection patterns 13 and 14 of the inspection mark 12 may not be a wire grid polarizer. In that case, transmitted light from a pattern that is not a wire grid polarizer splits into ordinary and extraordinary rays of approximately the same amplitude. Therefore, although the amount of displacement is small and the sensitivity is lowered, it is needless to say that the inspection of birefringence can be performed.
[0029]
In the first embodiment, illumination light for vertically illuminating the surface of the photomask 3 is used, and the light passes through the vicinity of the center of the pupil 27 of the projection lens 26 and reaches the substrate. In order to inspect the birefringence of the optical path passing through the end of the pupil 27 of the projection lens 26, as shown in FIG. 9, illumination light for obliquely illuminating the surface of the photomask 3 using an illumination aperture 24a is used. The illumination aperture 24a has an illumination hole 42 provided at a position shifted from the center of the light shielding plate 41, as shown in FIG. The illumination light that has passed through the illumination aperture 24a from the fly-eye lens 23 has its optical path bent by the condenser lens 25 and illuminates the photomask 3 obliquely. Therefore, the exposure light emitted from the photomask 3 passes through the end of the pupil 27 of the projection lens 26 and exposes the semiconductor substrate 1. In this way, by using the illumination aperture 24a, it becomes possible to inspect the birefringence of the optical path passing through the end of the pupil 27 of the projection lens 26.
[0030]
Next, a method for manufacturing a semiconductor device using a plurality of exposure apparatuses inspected by the inspection method for birefringence according to the first embodiment will be described with reference to the flowchart shown in FIG.
[0031]
(A) First, the photomask 3 for birefringence inspection shown in FIG. 2 is installed in a plurality of exposure apparatuses to be inspected used in the manufacturing process of the semiconductor device. In step S101, the first and second inspection patterns 13 and 14 of the inspection mark 12 of the photomask 3 are transferred to the resist film applied to the semiconductor substrate 1 for inspection by the exposure apparatus to be inspected.
[0032]
(B) In step S102, the amount of positional deviation of the first and second transfer patterns 33 and 34 (see FIG. 8) of the inspection resist pattern 32 transferred onto the semiconductor substrate 1 is measured using a misalignment inspection device. .
[0033]
(C) In step S103, the presence / absence of birefringence of the projection lens is determined by comparing the amount of displacement measured from the exposure apparatus to be inspected with a reference value.
[0034]
(D) If it is determined that the displacement amount of the exposure apparatus to be inspected is larger than the reference value, the projection lens of the exposure apparatus to be inspected is adjusted in step S104. After the adjustment, steps S101 to S103 are repeated again. If the displacement does not fall below the reference value only by adjusting the projection lens, repair such as replacement of the projection lens is performed.
[0035]
(E) When it is determined that the displacement amount of the exposure apparatus to be inspected is equal to or less than the reference value, the exposure apparatus is determined to be an exposure apparatus that can be used in a lithography step in a semiconductor device manufacturing process. The inspections in steps S101 to S104 are repeated for a plurality of exposure apparatuses to be inspected, and in step S105, a plurality of available exposure apparatuses are classified based on the imaging performance based on the amount of displacement.
[0036]
(F) In step S106, a usable exposure apparatus is selected, and a lithography process for a semiconductor device is performed. For example, an exposure apparatus classified into an imaging performance equal to or smaller than an allowable dimensional error of a pattern formed in a manufacturing process is selected from the classified available exposure apparatuses.
[0037]
2. Description of the Related Art In an exposure apparatus used for manufacturing a semiconductor device having a fine pattern, even if the dimensional accuracy in specifications is the same, there is a machine difference between the exposure apparatuses due to a manufacturing error of the exposure apparatus. Depending on the exposure apparatus used in the lithography process, the performance of the manufactured semiconductor device varies. According to the first embodiment, the birefringence of the projection lens 26 incorporated in the exposure apparatus is inspected, and the exposure apparatuses are classified according to the imaging performance. The lithography process can be performed by selecting an exposure apparatus capable of achieving a dimensional accuracy equal to or less than an allowable dimensional error required for a semiconductor device manufacturing process. Therefore, it is possible to manufacture a semiconductor device in which variation in performance is suppressed.
[0038]
(Modification of First Embodiment)
As shown in FIG. 12, a photomask 3a according to a modification of the first embodiment of the present invention differs from the first embodiment in having an inspection mark 12 and an inspection mark 12a. The first inspection mark 13 of the inspection mark 12 has a rectangular frame shape, is arranged between the outer light shielding film 11 and the inner first light shielding portion 11a, and polarizes the illumination light to the first polarization state. I do. The second inspection pattern 14 has a rectangular frame shape, is inside the first inspection pattern 13, is disposed between the first light-shielding portion 11a and the second light-shielding portion 11b, and emits illumination light to the first light-shielding portion 11a. Polarize to a second polarization state orthogonal to the polarization state. The first inspection mark 13a of the inspection mark 12a has a rectangular frame shape, is disposed between the outer light-shielding film 11 and the inner first light-shielding portion 11c, and polarizes the illumination light to the third polarization state. I do. The second inspection pattern 14a has a rectangular frame shape, is located inside the first inspection pattern 13a, is disposed between the first light-shielding part 11c and the second light-shielding part 11d, and emits illumination light to the third light-shielding part 11d. The light is polarized to a fourth polarization state orthogonal to the polarization state. The first and second inspection patterns 13a and 14a of the inspection mark 12a are each inclined by 45 ° with respect to the mutually orthogonal L / S patterns of the first and second inspection patterns 13 and 14 of the inspection mark 12. The difference is that the L / S patterns are arranged as described above. The other configuration is the same as that of the first embodiment, and a duplicate description will be omitted.
[0039]
With only the inspection mark 12 similar to the pattern shown in FIG. 3 in the first embodiment, the first and second polarized light beams Lp1 and Lp2 are oriented at approximately 45 ° with respect to the fast axis and the slow axis. When they are oriented, the light intensities of the ordinary ray and the extraordinary ray become equal. If the light intensities of the ordinary ray and the extraordinary ray are equal, the shifts of the center positions of the first and second transfer patterns 33 and 34 are almost equal, and it is determined that there is no birefringence.
[0040]
In the photomask 3 a according to the modification of the first embodiment, for example, the L / S patterns of the first and second inspection patterns 13 and 14 of the inspection mark 12 are arranged in parallel in the y-axis and x-axis directions. If so, the L / S patterns of the first and second inspection patterns 13a and 13b of the inspection mark 12a are arranged obliquely at 45 ° counterclockwise and 45 ° clockwise from the y-axis, respectively. When the inspection marks 12 and 12a are used, the first and second polarized light beams Lp1 and Lp2 are oriented at approximately 45 ° with respect to the fast axis and the slow axis in one of the inspection marks, and the ordinary light and the extraordinary light are used. Even if the light intensities of the other inspection marks are almost equal, the light intensities of the ordinary ray and the extraordinary ray will be different in the other inspection mark. Therefore, the amount of displacement can be measured from at least one of the inspection resist patterns to which the first inspection patterns 13, 13a and the second inspection patterns 14, 14a of the inspection marks 12, 12a have been transferred.
[0041]
According to the photomask 3a according to the modified example of the first embodiment of the present invention, it is possible to inspect the birefringence of the projection lens with higher accuracy.
[0042]
(Second embodiment)
As shown in FIG. 13A, the photomask 3b according to the second embodiment of the present invention includes a first inspection mark 52 disposed on the light shielding film 51 and having a light transmitting portion, and a first inspection mark. 52 has a second inspection mark 62 arranged corresponding to 52. In the second embodiment, the photomask 3b is different from that of the first embodiment, and the same exposure apparatus is used.
[0043]
The first inspection mark 52 includes first and second inspection patterns 53 and 54 of concentric square frame-shaped L / S patterns. For example, the frame-shaped L / S patterns are arranged parallel to the x-axis or the y-axis, respectively. In the second embodiment, the outer circumference of the first inspection pattern 53 is 100 μm on one side, and the outer circumference of the second inspection pattern 54 is 50 μm on one side.
[0044]
For example, in the DD cross section of a part of the first inspection pattern 53, a plurality of linear light-shielding portions 58a to 58j are interposed between the light-shielding films 51 on the surface of the transparent substrate 50, as shown in FIG. It has a plurality of first L / S patterns 58 arranged in parallel, and a plurality of light shielding portions 57a to 57c arranged in parallel between the first L / S patterns 58. Further, the first L / S pattern 58 is a pattern that is not resolved on the semiconductor substrate, as described later, and thus can be regarded as a light transmitting portion. Therefore, the first L / S pattern 58 and the light shielding portions 57a to 57c arranged in parallel with each other can be regarded as the second L / S pattern 57. The pitches of the first and second L / S patterns are Ps and Pt, respectively. The second inspection pattern 54 also has first and second L / S patterns 58 and 57 having the pitches Ps and Pt, but the direction of the first L / S pattern 58 is changed as shown in FIG. Are different. In the first inspection pattern 53 shown in FIG. 14A, the first L / S pattern 58 has a periodic direction in the x-axis direction, and the second L / S pattern 57 has a frame-shaped light shielding portion 57a to 57a. 57d. In the second inspection pattern 54 shown in FIG. 14B, the periodic direction of the first L / S pattern 58 is the y-axis direction, and the frame-shaped light shielding portions 57e to 57e of the second L / S pattern 57 are formed. It is located between 57h. Thus, the periodic directions of the first L / S patterns 58 of the first and second inspection patterns 53 and 54 are orthogonal to each other. The period Ps of the first L / S pattern 58 is shorter than the wavelength λ of the light source 22 of the exposure apparatus in FIG. Therefore, the first L / S pattern 58 functions as a wire grid polarizer. The ratio of the width of the light shielding portions 58a to 58j to the space width between the light shielding portions 58a to 58j in the period Ps direction is approximately 1: 1. Therefore, for example, the illumination light that has passed through the first inspection pattern 53 is a linearly polarized light that is polarized in the x-axis direction, while the illumination light that has passed through the second inspection pattern 54 is a linearly polarized light that is polarized in the y-axis direction. It becomes polarized light.
[0045]
The period Pt of the second L / S pattern 57 is
M * λ / {NA * (1-σ)} ≦ Pt ≦ 3 * M * λ / {NA * (1 + σ)} (1)
Are set so as to satisfy the three light beam interference conditions. Here, M is the reduction ratio of the exposure apparatus, NA is the numerical aperture on the exit side of the projection lens, λ is the wavelength of the illumination light, and σ is the coherence factor. The “three-beam interference condition” is a condition under which an image of the L / S pattern is formed by interference between the zero-order diffracted light and the ± first-order diffracted light. Note that diffraction occurs in the periodic direction of the second L / S pattern 57. For example, when M = 4, λ = 193 nm, NA = 0.65, and σ = 0.25, the range of the period Pt that satisfies the three-beam interference condition is 1584 nm to 2850 nm. In the second embodiment, the period Pt is set to 2000 nm, but it is needless to say that the period Pt may be any value as long as the range satisfies the above three light beam interference conditions. The ratio of the pattern width of the first L / S pattern 58 to the line width of the light-shielding portions 57a to 57h arranged between the first L / S patterns 58 is approximately 1: 1.
[0046]
The second inspection mark 62 is provided on the light-shielding film 51 on the transparent substrate 50, as shown in FIGS. 13A and 13C. The first light shielding portion 63 has a square frame shape, and is disposed between the first and second transparent portions 61a and 61b. The second light-shielding portion 64 has a square frame shape, is located inside the first light-shielding portion 63, and is disposed between the second and third transparent portions 61b and 61c. For example, the outer periphery of the first transparent portion 61a is a square having a side of 100 μm. The first light-shielding portion 63 has a square shape with one side of 80 μm on the outer periphery of the frame shape and a width of 8 μm. The second light-shielding portion 64 is concentric with the first light-shielding portion 63, and has a square shape with one side of the outer periphery of the frame shape of 40 μm and a width of 8 μm. In the second embodiment, the center of the second inspection mark 62 is arranged at a distance of 200 μm in the x-axis direction from the center of the corresponding first inspection mark 52. When the second inspection mark 62 is moved by 200 μm in the x-axis direction so as to be aligned with the first inspection mark 52, the outer periphery of the frame shape of the first and second light shielding portions 63 and 64 is the first inspection mark 52. Are designed to be located near the center of the first L / S pattern 58 between adjacent light shielding portions 57a to 57l.
[0047]
The illumination light of the photomask 3b passes through the first and second inspection patterns 53 and 54 of the first inspection mark 52, becomes linearly polarized light, and is diffracted. Linearly polarized 0th-order diffracted light DL, + 1st-order diffracted light DL ₊ And -1st order diffracted light DL ₋ Are incident on the projection lens 26. As shown in FIG. 14, since the periodic directions of the first and second L / S patterns 57 and 58 of the first and second inspection patterns 53 and 54 are different, the polarization direction and the diffraction direction of the diffracted light are different. Are also different. For example, in the first inspection pattern 53 located outside the first inspection mark 52, as shown in FIGS. 15A and 15B, an arrow is displayed on the pupil plane 80 corresponding to the pupil 27 of the projection lens 26. Is the x-axis direction. The diffraction direction of the first inspection pattern 53 follows the periodic direction of the second L / S pattern 57, and in two regions facing each other along the x-axis, from the left side to the right side of the drawing, the −1st-order diffracted light DL ₋ , 0th-order diffracted light DL and + 1st-order diffracted light DL ₊ , And in the region facing along the y-axis, from the upper side to the lower side of the drawing, the −1st-order diffracted light DL ₋ , 0th-order diffracted light DL and + 1st-order diffracted light DL ₊ It becomes the y-axis direction as shown in FIG. In the second inspection pattern 54 located inside the first inspection mark 52, as shown in FIGS. 15C and 15D, the polarization direction in the pupil plane 80 is the y-axis direction. The diffraction direction of the second inspection pattern 54 follows the periodic direction of the second L / S pattern 57, and in two regions facing each other along the x-axis, from the left side to the right side of the drawing, the −1st-order diffracted light DL ₋ , 0th-order diffracted light DL and + 1st-order diffracted light DL ₊ In the x-axis direction, and in the region facing along the y-axis, from the upper side to the lower side of the drawing, the −1st-order diffracted light DL ₋ , 0th-order diffracted light DL and + 1st-order diffracted light DL ₊ It becomes the y-axis direction as shown in FIG. As described above, according to the second embodiment, not only the vicinity of the center of the projection lens 26 but also the vicinity of the end of the pupil plane 80 are obtained by the 0th-order diffracted light and the ± 1st-order diffracted light obtained by diffracting mutually orthogonal polarized light beams. Inspection of birefringence becomes possible.
[0048]
As shown in FIG. 16, the illumination light L of the photomask 3b is the 0th-order and ± 1st-order diffracted lights DL, DL polarized by the first inspection mark 52 shown in FIG. ₊ And DL ₋ It becomes. When the projection lens 26 exhibits birefringence, the ordinary rays DLo and DLo of the 0th-order and ± 1st-order diffracted lights incident on the projection lens 26, respectively. ₊ And DLo ₋ And the extraordinary rays DLe, DLe of the 0th and ± 1st diffraction orders, respectively. ₊ And DLe ₋ Divided into If the birefringence is not very large, the splitting of the light beam is very small, but the difference in the phase velocity of the light beam appears as an error in the wavefront. As a result, the wavefront created by the ordinary ray after passing through the lens is different from the wavefront created by the extraordinary ray after passing through the lens. The interference of the diffracted light occurs between the light beams having the same polarization direction and does not occur between the light beams having the same polarization direction. That is, ordinary rays and abnormal rays interfere with each other to form an image, and no interference occurs between the ordinary rays and the extraordinary rays. Therefore, the ordinary rays DLo and DLo of the 0th-order and ± 1st-order diffracted lights, respectively, are placed on the semiconductor substrate 1. ₊ And DLo ₋ Interfering waves and extraordinary rays DLe, DLe of the 0th-order and ± 1st-order diffracted lights, respectively ₊ And DLe ₋ Is formed. The light intensity distribution as a whole is a superposition of the intensities of the ordinary ray interference wave and the extraordinary ray interference wave. Therefore, if the position of the peak of the wave is defined as the image forming position, the image forming position is any position between the peak position pbo of the ordinary ray interference wave and the peak position pbe of the extraordinary ray interference wave. The imaging position is determined by the magnitude relationship between the intensity of the ordinary ray interference wave and the intensity of the extraordinary ray interference wave, and is close to the position of the peak of the interference wave having the high intensity.
[0049]
As described above, the polarization directions of the diffracted light are orthogonal to each other in the first inspection pattern 53 located outside the first inspection mark 52 and the second inspection pattern 54 located inside. Therefore, the intensity ratio between the ordinary ray and the extraordinary ray formed from the light passing through the first inspection pattern 53 and the intensity ratio between the ordinary ray and the extraordinary ray formed from the light passing through the second inspection pattern 54 are different. . That is, the magnitude relationship between the intensity of the ordinary ray interference wave formed from the light passing through the first inspection pattern 53 and the intensity of the extraordinary ray interference wave is determined by the relationship between the intensity of the ordinary ray interference wave formed from the light passing through the second inspection pattern 54. The magnitude relationship between the intensity of the extraordinary ray interference wave and the intensity of the extraordinary ray interference wave is different. As a result, there is a relative displacement between the projection pattern corresponding to the first inspection pattern 53 and the projection pattern corresponding to the second inspection pattern 54. Occurs. As described above, according to the photomask 3b according to the second embodiment, since the ± 1st-order diffracted light passes through the vicinity of the pupil 27, the birefringence of the central part of the projection lens 26 and the vicinity of the pupil 27 is measured. It becomes possible.
[0050]
When the projection lens 26 exhibits birefringence, the phases of the ordinary ray and the extraordinary ray are different. Further, there is a phase difference between the ordinary ray and the extraordinary ray of the 0th-order and ± 1st-order diffracted lights.
[0051]
Generally, in interference between light beams having a phase difference from each other, an interference wave is distorted or the position of the wave is shifted in a horizontal direction. This phenomenon is called lens aberration. Aberration is a wavefront error in the pupil plane, and is represented by a two-dimensional function defined in the pupil plane. Aberration is one of the indices indicating the imaging characteristics of the projection lens 26, and when an image is formed by a lens having a large aberration, the image is deformed or blurred.
[0052]
Since the ordinary ray and the extraordinary ray of the projection lens 26 exhibiting birefringence have different phases, it can be considered that the interference wave generated by each of the ordinary ray and the extraordinary ray behaves according to different lens aberrations. Consider the interference of the 0th order and ± 1st order diffracted light of the ordinary ray or the extraordinary ray. Using the 0th-order diffracted light passing through the center of the pupil plane as a phase reference, the phase difference between the -1st-order diffracted light and the + 1st-order diffracted light is φ _-1 And φ ₊₁ It expresses. At this time, the lateral shift amount of the interference wave is
Δxs = (φ _-1 −φ ₊₁ ) * Pt (2)
(See, for example, Optical Review, 2000, Vol. 7, p525-534).
[0053]
As described above, in a lens exhibiting birefringence, a lateral shift may occur between the interference wave generated by the ordinary ray and the interference wave generated by the extraordinary ray.
[0054]
On the other hand, the projection lens 26 generally has aberration. This aberration has nothing to do with birefringence, and the influence on the imaging characteristics does not depend on the polarization state of the exposure light. Due to this aberration, a lateral shift of the imaging position occurs between the transfer patterns transferred from the second L / S pattern 57 of each of the first and second inspection patterns 54. That is, since the lateral displacement of the imaging position is caused by both the birefringence of the projection lens 26 and the aberration of the projection lens 26, the cause cannot be specified even if the absolute value of the lateral displacement is measured. However, if the relative displacement between the image forming positions of the first and second inspection patterns 53 and 54 is measured, the influence of only the birefringence can be extracted. That is, the optical path through which the polarized light incident from the second L / S pattern 57 of the first and second inspection patterns 53 and 54 passes through the inside of the projection lens 26 is substantially except for the case where the birefringence is extremely large. It is common. Therefore, the effects of aberrations independent of birefringence on the two polarized lights are common. Since the aberration causes a wavefront error equal to the light projecting the first and second inspection patterns 53 and 54, the relationship between the image forming positions does not change even when the aberration exists, and the measured relative position shift. The amount is zero.
[0055]
Therefore, if the relative displacement occurs between the first and second transfer patterns 73 and 74, and the displacement amount indicates a significant value, it can be determined that the projection lens 26 has birefringence.
[0056]
In the method of inspecting birefringence according to the second embodiment, the photomask 3b is set on the mask stage 28 of the exposure apparatus shown in FIG. 1 and is projected and exposed on the semiconductor substrate 1 coated with a positive photoresist. At this time, double exposure is performed on the same semiconductor substrate 1 while changing the relative positions of the photomask 3b and the semiconductor substrate 1. In the second exposure, the semiconductor substrate 1 is moved in the x-axis direction so that the second inspection mark 62 is projected onto the position on the semiconductor substrate 1 where the first inspection mark 52 is projected in the first exposure. Is shifted by 200 μm. The illumination light of the exposure apparatus is non-polarized light and illuminates the surface of the photomask 3b vertically.
[0057]
After the double exposure, the first and second inspection marks 52 and 62 are transferred to the resist film 71 on the semiconductor substrate 1 by developing the semiconductor substrate 1 as shown in FIGS. 17A and 17B. The inspection resist pattern 72 thus formed is formed. The projected images of the first inspection pattern 53 located outside the first inspection mark 52 and the second inspection pattern 54 located inside the first inspection mark 52 are subjected to the second exposure, and the corresponding first images of the second inspection mark 62 are exposed. The portions other than the light-shielding portion 63 and the second light-shielding portion 64 are exposed by the first to third transparent portions 61a to 61c. Therefore, in the inspection resist pattern 72, a first transfer pattern 73 corresponding to the first inspection pattern 53 and a second transfer pattern 74 corresponding to the second inspection pattern 54 are formed in the opening 75. . Here, the first and second transfer patterns 73 and 74 are L / S resist patterns to which the second L / S pattern 57 has been transferred, respectively. As described above, in the first and second inspection patterns 53 and 54, the polarization directions of the diffracted light are orthogonal. Accordingly, a displacement of Δx in the x-axis direction and Δy in the y-axis direction occurs between the centers C1 and C2 of the first transfer pattern 73 and the second transfer pattern 74 according to the birefringence of the projection lens 26.
[0058]
For the inspection resist pattern 72 formed on the semiconductor substrate 1, the center positions C1 and C2 of the first and second transfer patterns 73 and 74 are measured using, for example, an optical misalignment inspection apparatus. The amount of displacement of the measured center positions C1 and C2 ｛(Δx) ² + (Δy) ² ｝ ^1/2 Is compared with a reference value to determine whether or not the projection lens 26 has birefringence.
[0059]
As described above, according to the birefringence inspection method according to the second embodiment, it is possible to inspect the birefringence of the optical path at the center and the end of the projection lens 26 incorporated in the exposure apparatus.
[0060]
(Third embodiment)
As shown in FIG. 18A, the photomask 3c according to the third embodiment of the present invention includes a first inspection mark 52a having a light transmitting portion disposed in a light shielding film 51, and a first inspection mark 52a. Has the second inspection mark 62 arranged corresponding to each of the inspection marks 52a. The first inspection mark 52a includes first and second inspection patterns 53a and 54a of L / S patterns in the form of concentric square frames. For example, the frame-shaped L / S patterns are arranged parallel to the x-axis or the y-axis, respectively. In the second embodiment, the outer circumference of the first inspection pattern 53a is 100 μm on one side, and the outer circumference of the second inspection pattern 54a is 50 μm on one side.
[0061]
For example, the first inspection pattern 53a is arranged such that one end thereof is in contact with the light-shielding film 51 on the surface of the transparent substrate 50, as shown in the FF section of FIG. A plurality of first L / S patterns 68 in which a plurality of first L / S patterns 68 j are arranged, and a second L / S in which a plurality of linear light-shielding portions 67 a and 67 b are arranged between the plurality of first L / S patterns 68. It has a pattern 67. The width of the first L / S pattern 68 is the same as the width of the light shielding portions 67a and 67b. For example, in the area where the first L / S pattern 68 is arranged, the transparent substrate 50 is dug in a substantially half area on the left side of the paper surface of FIG. 89 are provided. Here, the digging depth of the transparent substrate 50 of the phase shift section 89 is set such that the phase difference of the transmitted light is 180 degrees with respect to the non-phase shift section 88 in which the light shielding sections 68f to 68j are arranged. It is. The periods of the first and second L / S patterns 68 and 67 are Ps and Pb, respectively. The period Ps is set to 150 nm as in the first and second embodiments. Therefore, the first L / S pattern 68 functions as a wire grid polarizer.
[0062]
As shown in FIG. 19, the direction of the first L / S pattern 68 is different between the first and second inspection patterns 53a and 54a. In the first inspection pattern 53a shown in FIG. 19A, the first L / S pattern 68 has a periodic direction in the x-axis direction, and the second L / S pattern 67 has a frame-shaped light-shielding portion 67a to 67a. 67d. In the second inspection pattern 54a shown in FIG. 14B, the first L / S pattern 68 has a periodic direction in the y-axis direction, and the frame-shaped light-shielding portions 67e to 67e of the second L / S pattern 67. It is located between 67h. Further, a phase shift section 89 and a non-phase shift section 88 are arranged in the first L / S pattern 68 of each of the first and second inspection patterns 53a and 54a. The longitudinal directions of the phase shift section 89 and the non-phase shift section 88 are parallel to the second L / S pattern 67. The phase shift section 89 is arranged such that the periodic direction of the second L / S pattern 67 is located on the left side of the paper surface of FIG. 19 in the region of the x-axis direction, and is located above the paper surface in the region of the y-axis direction.
[0063]
As described above, the periodic directions of the first L / S patterns 68 of the first and second inspection patterns 53a and 54a are orthogonal to each other. Therefore, for example, the illumination light that has passed through the first inspection pattern 53a is a linearly polarized light that is polarized in the x-axis direction, while the illumination light that has passed through the second inspection pattern 54a is a linearly polarized light that is polarized in the y-axis direction. It becomes polarized light.
[0064]
The period Pb of the second L / S pattern 67 is
M * λ / {NA * (1-σ)} ≦ Pb ≦ 2 * M * λ / {NA * (1 + σ)} (3)
Are set to satisfy the two-beam interference condition. Here, the “two-beam interference condition” is a condition under which an image of the L / S pattern is formed by interference with either the 0th-order diffracted light or the ± 1st-order diffracted light. The ratio of the width in the periodic direction of the light-shielding portions 67a and 67b, the phase shift portion 89, and the non-phase shift portion 88 is approximately 2: 1: 1. Therefore, when the photomask 3c is illuminated, for example, among the ± 1st-order diffracted lights generated by passing through the second L / S pattern 67, the intensity of the −1st-order diffracted light becomes 0, and the two luminous fluxes of the 0th-order and + 1st-order diffracted lights (For example, see Japanese Patent No. 3297423).
[0065]
In the second embodiment, the inspection is performed under the three-beam interference condition that is symmetric with respect to the axis. For example, when the birefringence of the projection lens 26 has the axial symmetry, the position shift due to the ± 1st-order diffracted light cancels out. Refraction detection becomes difficult. In the third embodiment, birefringence inspection is performed under an asymmetric two-beam interference condition using the photomask 3c on which the first L / S pattern 68 having the phase shift portion 89 and the non-phase shift portion 88 is arranged. Is different from the second embodiment, and the other points are the same.
[0066]
For example, as shown in FIGS. 20A and 20B, the pattern surface of the photomask 3c is set in the exposure apparatus with the pattern surface facing the projection lens 26. Between the light shielding films 67a and 67b of the second L / S pattern 67, the phase shift portions 89 and the non-phase shift portions 88 of the first L / S pattern 68 are arranged in order from the left side of FIG. . The illumination light L of the photomask 3c is composed of 0th and + 1st order diffracted lights DL and DL polarized by the first inspection mark 52a. ₊ It becomes. When the projection lens 26 exhibits birefringence, the 0th-order and + 1st-order diffracted lights DL, DL incident on the projection lens 26 ₊ Are ordinary rays DLo and DLo of the 0th and + 1st order diffracted light, respectively. ₊ And extraordinary rays DLe, DLe of the 0th and + 1st order diffracted light ₊ Divided into If the birefringence is not very large, the splitting of the light beam is very small, but the difference in the phase velocity of the light beam appears as an error in the wavefront. As a result, the wavefront created by the ordinary ray after passing through the lens is different from the wavefront created by the extraordinary ray after passing through the lens. On the other hand, the interference of diffracted light occurs between light beams having the same polarization direction, and does not occur between light beams having the same polarization direction. Ordinary rays DLo and DLo of the 0th and + 1st order diffracted lights are placed on the semiconductor substrate 1. ₊ And the extraordinary rays DLe, DLe of the 0th and + 1st order diffracted lights ₊ Is formed. Ordinary rays DLo, DLo of 0th and + 1st order diffracted light ₊ And the extraordinary rays DLe and DLe of the 0th and + 1st order diffracted light ₊ Are different from each other, the positions of the ordinary ray interference wave and the extraordinary ray interference wave are shifted. The light intensity distribution is the sum of the intensities of the two interference waves, and if the position of the wave peak is defined as the image position, the image position is the position pco of the ordinary ray interference wave and the position of the peak of the extraordinary ray interference wave. The imaging position at any position between pce is determined by the magnitude relationship between the intensity of the ordinary ray interference wave and the intensity of the extraordinary ray interference wave, and is close to the position of the peak of the interference wave having a high intensity. .
[0067]
In the above description, a combination of the 0th-order and + 1st-order diffracted light is used. For example, as shown in FIGS. 21A and 21B, the pattern surface of the photomask 3d is set in the exposure apparatus with the pattern surface facing the projection lens 26. Contrary to the case where a combination of the 0th-order and + 1st-order diffracted light is used between the light shielding films 67a and 67b of the second L / S pattern 67, the non-phase shift portion 88 of the first L / S pattern 68 and the phase The shift units 89 are arranged in order from the left side of the paper of FIG. The illumination light L of the photomask 3d is divided into 0-order and -1st-order diffracted lights DL and DL polarized by the first inspection mark 52a. ₋ It becomes. When the projection lens 26 exhibits birefringence, the 0th-order and -1st-order diffracted lights DL, DL incident on the projection lens 26 ₋ Are the ordinary rays DLo and DLo of the 0th and -1st order diffracted light, respectively. ₋ And the extraordinary rays DLe, DLe of the 0th and -1st order diffracted light ₋ Divided into Ordinary rays DLo and DLo of the 0th-order and -1st-order diffracted light are placed on the semiconductor substrate 1. ₋ And the extraordinary rays DLe, DLe of the 0th and -1st order diffracted light ₋ Is formed. The light intensity distribution is the sum of the two interference waves, and the imaging position is any position between the peak position pdo of the ordinary ray interference wave and the peak position pde of the extraordinary ray interference wave. The imaging position is determined by the magnitude relationship between the intensity of the ordinary ray interference wave and the intensity of the extraordinary ray interference wave, and is close to the position of the peak of the interference wave having the high intensity.
[0068]
In the third embodiment, the birefringence is inspected by two light beams that pass through an asymmetric optical path using one of the axially symmetric ± first-order diffracted lights. Inspection becomes possible.
[0069]
Also, due to the aberration of the projection lens, the interference wave between the 0th-order diffracted light and the + 1st-order or -1st-order diffracted light is shifted laterally even under the two-beam interference condition. For example, the lateral shift amount Δxt of the interference wave due to the 0th and + 1st order diffracted light is
Δxt = (φ ₊₁ + Δz) * Pt (4)
(See, for example, Optical Review, 2001, Vol. 8, p184-190). Here, Δz is the defocus amount on the surface of the semiconductor substrate 1. As in the second embodiment, lateral displacement due to aberration occurs in the same direction with respect to the first and second inspection patterns 53a and 54a. On the other hand, since the displacement due to birefringence is different between the first and second inspection patterns 53a and 54a, a relative displacement occurs. Therefore, according to the third embodiment, the birefringence of the projection lens can be inspected separately from the aberration.
[0070]
In the birefringence inspection method according to the third embodiment, the photomask 3c is set on the mask stage 28 of the exposure apparatus shown in FIG. 1 and is projected and exposed on the semiconductor substrate 1 coated with a positive photoresist. At this time, double exposure is performed on the same semiconductor substrate 1 while changing the relative position between the photomask 3c and the semiconductor substrate 1. In the second exposure, the semiconductor substrate 1 is moved in the x-axis direction so that the second inspection mark 62 is projected so as to be superimposed on the position on the semiconductor substrate 1 where the first inspection mark 52a is projected in the first exposure. Is shifted by 200 μm. The illumination light of the exposure apparatus is non-polarized light and illuminates the surface of the photomask 3c vertically.
[0071]
After the double exposure, the semiconductor substrate 1 is developed, so that the first and second inspection marks 52a and 62a are overlaid on the resist film 71 on the semiconductor substrate 1 and transferred as shown in FIG. A resist pattern 72a is formed. The projected images of the first inspection pattern 53a located outside the first inspection mark 52a and the second inspection pattern 54a located inside the first inspection mark 52a are subjected to the second exposure, and the first light-shielding portion of the second inspection mark 62 is exposed. The portions other than the portion corresponding to 63 and the second light shielding portion 64 are exposed by the first to third transparent portions 61a to 61c. Therefore, in the inspection resist pattern 72a, first and second transfer patterns 73a and 74a corresponding to the first and second inspection patterns 53a and 54a are formed in the opening 75. As described above, the polarization directions of the diffracted lights are orthogonal to each other in the first and second inspection patterns 53a and 54a. Therefore, a displacement of Δx in the x-axis direction and Δy in the y-axis direction occurs between the centers C1 and C2 of the first transfer pattern 73a and the second transfer pattern 74a according to the birefringence of the projection lens 26.
[0072]
For the inspection resist pattern 72a formed on the semiconductor substrate 1, the center positions C1, C2 of the first and second transfer patterns 73a, 74a are measured using, for example, an optical misalignment inspection apparatus. The amount of displacement of the measured center positions C1 and C2 ｛(Δx) ² + (Δy) ² ｝ ^1/2 Is compared with a reference value to determine whether or not the projection lens 26 has birefringence.
[0073]
As described above, according to the birefringence inspection method according to the third embodiment, it is possible to inspect the birefringence of the optical path at the center and the end of the projection lens 26 incorporated in the exposure apparatus. In addition, by using an asymmetric two-beam interference condition, it becomes possible to inspect the projection lens 26 that exhibits birefringence that is axisymmetric.
[0074]
In the above description, the phase shift portion 89 of the first L / S pattern 68 is formed by excavating the transparent substrate 50. However, any structure having a phase difference of 180 degrees with respect to the non-phase shift unit 88 can be used. For example, as shown in FIG. 23A, the phase shift portion 89a may be formed by embedding a transparent film 90 having a different refractive index in a dug portion of the transparent substrate 50. The light shielding films 68a to 68j are formed after the transparent film 90 is embedded. Further, as shown in FIG. 23B, after forming the light shielding portions 68a to 68j, the transparent film 90a may be selectively deposited on the phase shifter portion 89b. Further, as shown in FIG. 23C, the light shielding films 68a to 68j may be formed after the transparent film 90b is selectively deposited on the phase shifter 89c. The transparent films 90a and 90b may be made of the same material as the transparent substrate 50 or a transparent material having a different refractive index from that of the transparent substrate 50.
[0075]
(Other embodiments)
As described above, the first to third embodiments of the present invention have been described. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples, and operation techniques will be apparent to those skilled in the art.
[0076]
As described in the modification of the first embodiment of the present invention, if the first and second polarized light beams are oriented at approximately 45 ° with respect to the fast axis and the slow axis, the ordinary ray And the intensity of the extraordinary ray become equal, making it impossible to inspect birefringence. In the modification of the first embodiment, as shown in FIG. 12, an inspection mark 12a in which the L / S pattern of the wire grid polarizer of the first and second inspection patterns 13a and 14a is inclined by 45 ° is used. However, it goes without saying that, for example, the inspection mark 12 may be used after being rotated by 45 °. Further, as is clear from the above description, the position displacement amount is largest when the first and second polarized light beams are directed in the directions of the fast axis and the slow axis. Therefore, it goes without saying that the use of a photomask in which the inspection marks 12 rotated at various angles are arranged can further facilitate the inspection of birefringence. Further, similarly to the above, it is needless to say that the present invention can be applied to the first and second inspection marks 52 and 62 or 52a and 62 according to the second or third embodiment.
[0077]
Further, in the first to third embodiments, the first and second inspection patterns of the inspection mark use concentric squares. However, the shape of the inspection mark may be, for example, a rectangle or a polygon. Of course, it is not limited to. Further, the first and second inspection patterns need not be concentric. When the center positions of the first and second inspection patterns are different, the reference distance between the center position of each of the first and second inspection patterns is determined in advance from the layout data of the mask pattern or the transfer pattern by the exposure device that does not show birefringence. Ask for it. The difference between the distance between the center positions of the first and second transfer patterns and the obtained reference distance may be used as the positional deviation amount. Also, the first and second inspection patterns need not be frame-shaped but may be box-shaped, for example.
[0078]
As described above, the present invention naturally includes various embodiments and the like not described herein. Therefore, the technical scope of the present invention is determined only by the invention specifying matters according to the claims that are appropriate from the above description.
[0079]
【The invention's effect】
According to the present invention, it is possible to provide a photomask for inspecting birefringence of a projection lens incorporated in an exposure apparatus, an inspection method, and a method for manufacturing a semiconductor device to which the inspection method is applied.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exposure apparatus according to a first embodiment of the present invention.
FIG. 2 is a perspective view illustrating an example of a photomask according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a configuration of a photomask according to the first embodiment of the present invention.
FIG. 4 is a diagram illustrating an example of birefringence of a transparent material.
FIG. 5 is a diagram illustrating an example of a polarization direction of a polarized light beam according to the first embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of an imaging characteristic of a polarized light beam according to the first embodiment of the present invention.
FIG. 7 is a diagram illustrating a relationship between a polarized light beam and light intensity on a semiconductor substrate according to the first embodiment of the present invention.
FIG. 8 is a diagram showing a transfer pattern of the inspection mark on the semiconductor substrate according to the first embodiment of the present invention.
FIG. 9 is a schematic configuration diagram of another exposure apparatus according to the first embodiment of the present invention.
FIG. 10 is a schematic configuration diagram of an illumination aperture used in another exposure apparatus according to the first embodiment of the present invention.
FIG. 11 is a flowchart used to explain the method for manufacturing the semiconductor device according to the first embodiment of the present invention.
FIG. 12 is a diagram illustrating a photomask according to a modification of the first embodiment of the present invention.
FIG. 13 is a diagram illustrating an example of a configuration of a photomask according to a second embodiment of the present invention.
FIG. 14 is a diagram illustrating a combination of L / S patterns of first and second inspection patterns of a photomask according to a second embodiment of the present invention.
FIG. 15 is a diagram illustrating diffracted light passing through a pupil plane according to the second embodiment of the present invention.
FIG. 16 is a diagram illustrating an example of three-beam interference according to the second embodiment of the present invention.
FIG. 17 is a diagram showing a transfer pattern of an inspection mark on a semiconductor substrate according to a second embodiment of the present invention.
FIG. 18 is a diagram illustrating an example of a configuration of a photomask according to a third embodiment of the present invention.
FIG. 19 is a diagram illustrating a combination of L / S patterns of first and second inspection patterns of a photomask according to a third embodiment of the present invention.
FIG. 20 is a diagram illustrating an example of two-beam interference according to the third embodiment of the present invention.
FIG. 21 is a diagram illustrating another example of two-beam interference according to the third embodiment of the present invention.
FIG. 22 is a diagram showing a transfer pattern of an inspection mark on a semiconductor substrate according to a third embodiment of the present invention.
FIG. 23 is a diagram illustrating another example of the configuration of the photomask according to the third embodiment of the present invention.
[Explanation of symbols]
1 semiconductor substrate
3, 3a-3d Photomask
5 Object plane
6 Transparent material
7 Image plane
10,50 transparent substrate
11,51 Light shielding film
11a, 11c, 63 1st light shielding part
11b, 11d, 64 Second light shielding unit
12, 12a Inspection mark
13, 13a, 53, 53a First inspection pattern
14, 14a, 54, 54a Second inspection pattern
15, 16, 57a to 57h, 58a to 58j, 67a to 67h, 68a to 68j
22 light source
23 Fly Eye Lens
24, 24a Lighting aperture
25 Condenser lens
26 Projection lens
27 eyes
28 Mask Stage
29 Substrate stage
30 aperture stop
31, 71 resist film
32, 72, 72a Inspection resist pattern
33, 73, 73a First transfer pattern
34, 74, 74a Second transfer pattern
41 Shade plate
42 Illumination hole
43 Exposure mark
52, 52a First inspection mark
57, 67 Second L / S pattern
58, 68 First L / S pattern
61a first transparent part
61b 2nd shade part
61c Third light shield
62 Second inspection mark
75 Opening
80 Eye plane
88 Non-phase shift section
89, 89a to 89c Phase shift unit
90, 90a, 90b Transparent film

Claims (19)

A transparent substrate,
A pattern of a light-shielding film formed so as to have a window on the surface of the transparent substrate,
A first inspection pattern disposed in the window, for polarizing illumination light to a first polarization state;
A second polarization unit that is disposed at a position separated by a fixed distance from the first inspection pattern in the window unit and polarizes the illumination light to a second polarization state different from the first polarization state; A photomask comprising an inspection pattern. The photomask according to claim 1, wherein the first polarization state is linearly polarized light. 3. The photomask according to claim 1, wherein the second polarization state is such that the first polarization state and the polarization plane are orthogonal to each other. 4. The said 1st and 2nd test | inspection pattern is a line and space pattern which has a period of less than the wavelength of the said illumination light, and the light-shielding part of the said line and space pattern is a conductor. 4. The photomask according to any one of 3. Each of the first and second inspection patterns includes a first line-and-space pattern having a period equal to or less than the wavelength of the illumination light and a plurality of the first line-and-space patterns between a plurality of light-shielding portions. The photomask according to any one of claims 1 to 3, comprising a second line-and-space pattern disposed on the photomask. The photomask according to claim 5, wherein the cycle of the second line and space pattern satisfies a three-beam interference condition. The first line and space pattern is arranged in a phase shift portion and a non-phase shift portion provided between the light shielding portions, and a cycle of the second line and space pattern satisfies a two-beam interference condition. The photomask according to claim 5, wherein: A resist film applied on a semiconductor substrate with exposure light polarized in a first polarization state by a first inspection pattern provided in a window formed in a light shielding film of the photomask from illumination light of the photomask Transferring the first inspection pattern to form a first transfer pattern,
Polarized to a second polarization state different from the first polarization state by a second inspection pattern formed at a position separated by a fixed distance from the first inspection pattern in the window portion. Transferring the second inspection pattern to the resist film with exposure light to form a second transfer pattern,
An inspection method comprising measuring a relative displacement amount of the first and second transfer patterns. The inspection method according to claim 8, wherein the first polarization state is linearly polarized light. The inspection method according to claim 8, wherein the second polarization state is linear polarization orthogonal to the polarization of the first exposure light. The inspection method according to claim 8, wherein the illumination light is incident on the photomask at an angle. The inspection method according to any one of claims 8 to 10, wherein the transfer of the first and second transfer patterns is performed under three light beam interference conditions. The inspection method according to claim 8, wherein the transfer of the first and second transfer patterns is performed under two light beam interference conditions. A photomask for inspection and a semiconductor substrate for inspection coated with a resist film are mounted on each of the plurality of exposure apparatuses,
From the illumination light of the photomask, the resist film is exposed to the first light by the first inspection pattern provided in the window formed in the light shielding film of the photomask. Transferring the inspection pattern to form a first transfer pattern,
Polarized to a second polarization state different from the first polarization state by a second inspection pattern formed at a position separated by a fixed distance from the first inspection pattern in the window portion. Transferring the second inspection pattern to the resist film with exposure light to form a second transfer pattern,
Measuring a relative displacement amount of the first and second transfer patterns and comparing with a reference value;
Classifying the exposure apparatus in which the displacement amount is equal to or less than the reference value based on the displacement amount,
Select a manufacturing exposure apparatus that can be used in the lithography step among the manufacturing steps targeted from the classified exposure apparatus,
A method for manufacturing a semiconductor device, comprising: performing the lithography step using the manufacturing exposure apparatus. The method according to claim 14, wherein the first polarization state is linearly polarized light. 16. The method according to claim 14, wherein the second polarization state is a polarization orthogonal to the polarization of the first exposure light. 17. The method according to claim 14, wherein the illumination light is incident on the photomask at an angle. 17. The method of manufacturing a semiconductor device according to claim 14, wherein the transfer of the first and second transfer patterns is performed under three light beam interference conditions. 17. The method of manufacturing a semiconductor device according to claim 14, wherein the transfer of the first and second transfer patterns is performed under two light beam interference conditions.

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