JP2005337919A - Position detection apparatus, position detection method, exposure apparatus, and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a position detection apparatus and a position detection method allowing to perform position detection of a mark having a low stepped pattern with high precision. <P>SOLUTION: The position detection apparatus comprises an optical system which introduces light from a mark provided in an object to be subjected to position detection, a photoelectric detector which detects light from the mark photoelectrically, and a detection system which detects the position of the mark on the basis of an output signal of the photoelectric detector. The position of the mark is detected under a focus state in which when a predetermined reference pattern having a pair of facing edge sections is detected, signal intensity values of the output signals of the photoelectric detector for the parts corresponding to the edge sections respectively become nearly equal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a position detection apparatus, a position detection method, an exposure apparatus, and an exposure method, and in particular, a position detection apparatus used in a lithography process or the like for manufacturing a microdevice such as a semiconductor element, an imaging element, a liquid crystal display element, and a thin film magnetic head. The present invention relates to a position detection method, an exposure apparatus, and an exposure method.

  In general, when a device such as a semiconductor element is manufactured, a plurality of layers of circuit patterns are formed on a wafer (or a substrate such as a glass plate) coated with a photosensitive material. Therefore, an exposure apparatus for exposing and transferring a circuit pattern onto a wafer includes an alignment apparatus for performing relative alignment (alignment) between the mask pattern and each exposure area of the wafer on which the circuit pattern is already formed. Is provided. In recent years, with the miniaturization of circuit pattern line widths, high-precision alignment has been required.

  Conventionally, as this type of alignment apparatus, as disclosed in JP-A-4-65603, JP-A-4-273246, and the like, an off-axis type and imaging type alignment apparatus is known. The position detection system of this imaging type alignment apparatus is also called an FIA (Field Image Alignment) position detection apparatus. In the FIA-based position detection device, an alignment mark (wafer mark) on a wafer is illuminated with light having a wide wavelength bandwidth emitted from a light source such as a halogen lamp. Then, an enlarged image of the wafer mark is formed on the image sensor via the imaging optical system, and the position of the wafer mark is detected by performing image processing on the obtained imaging signal.

In general, in the case of an alignment mark having a pattern with a low step and a small difference in reflectance between the mark portion and the surrounding area, the contrast of the alignment mark image obtained in the best focus state is lower than that obtained in a predetermined defocus state. In view of this, JP-A-7-183186, JP-A-9-6017, JP-A-10-50592 and the like disclose an alignment mark image by detecting an alignment mark of a low step pattern under a predetermined defocus state. A technique for improving the contrast is disclosed. With the recent progress in manufacturing technology related to semiconductor elements, it has become necessary to detect the position with high accuracy even with an alignment mark having an asymmetric low step pattern.
JP-A-4-65603 JP-A-4-273246 Japanese Patent Laid-Open No. 7-183186 Japanese Patent Laid-Open No. 9-6017 Japanese Patent Laid-Open No. 10-50592 International Publication WO03 / 074966 Pamphlet

  In the conventional technology that detects the position of the low step pattern at the best focus position, if the alignment mark is an asymmetrical low step pattern, the alignment mark image is also asymmetrically distorted. As a result, the position detection accuracy may deteriorate. Further, when an error remains in the imaging optical system, for example, when the imaging aperture stop is displaced with respect to the optical axis of the optical system, the alignment mark image is asymmetrically distorted and similarly positioned. The detection accuracy may deteriorate.

  In this regard, as disclosed in the above-mentioned Patent Document 6 relating to the international application filed by the applicant of the present application, the diffracted light of a specific order among the diffracted light from the mark reaching the photoelectric detector A technique has been proposed in which the position of a mark is detected in a predetermined optical state in which a phase difference is given so that the phase difference is approximately 90 degrees. According to this technology, the above-mentioned problems of the prior art can be almost solved. However, in actual sites (manufacturing factories, etc.), the mark to be detected is not limited to a low step pattern in terms of design specifications or process, but varies. Therefore, in some cases, the detection accuracy is not improved but may be deteriorated.

  The present invention has been made in view of the above-described problems, and provides a detection situation in which the waveform of a detection signal is asymmetric when the mark is asymmetric or when there is a residual error in the imaging optical system of the mark. It can be improved without changing the structure on the mark side and the detection device side, and a detection situation where a more symmetrical output signal waveform is obtained can be created, and a mark with a low step pattern can be detected with high accuracy. An object is to provide a position detection device and a position detection method.

  It is another object of the present invention to provide a position detection method and a position detection apparatus capable of detecting a mark position with high accuracy and speed in a flexible manner in response to actual situations.

  It is another object of the present invention to provide an exposure apparatus and an exposure method that can manufacture high-precision, high-quality microdevices and the like with high throughput.

  Hereinafter, in the description shown in this section, the present invention will be described in association with the member codes shown in the drawings representing the embodiments. However, each constituent element of the present invention is limited to the members shown in the drawings attached with these member codes. Is not to be done.

  According to the first aspect of the present invention, an optical system (7-14, 17) for guiding light from a mark (WM) provided on an object (W) whose position is to be detected, and photoelectric detection of light from the mark. And a detection system (18) for detecting the position of the mark based on an output signal of the photoelectric detector to detect a predetermined reference pattern. There is provided a position detection device that detects the position of the mark under a focus state in which the symmetry of the output signal of the photoelectric detector obtained is substantially symmetric.

  The waveform of a signal obtained by photoelectrically detecting a pattern often breaks in symmetry. This loss of symmetry changes continuously according to the focus state (relative positional relationship between the optical system and the mark in the optical axis direction of the optical system), so that a predetermined reference pattern can be detected in various focus states. Thus, it is possible to specify the focus state in which this symmetry is the best. In the present invention, since the mark is detected under the specified focus state, even if it is an asymmetrical low step mark or there is a residual error in the optical system, it is substantially symmetrical and A mark image with substantially good contrast can be obtained, and the mark position can be detected with high accuracy.

  According to the second aspect of the present invention, the position detection detects the position of the mark based on the waveform signal obtained by photoelectrically detecting the light from the mark (WM) provided on the object (W) to be position-detected. In the method, the position of the mark is determined under a focus state in which signal strengths of portions corresponding to the edge portions of the waveform signal obtained by photoelectrically detecting a predetermined reference pattern having a pair of opposite edge portions are substantially equal. A position detection method including a detection step (S2 to S4) for detection is provided.

  A waveform of a signal obtained by photoelectrically detecting a pattern having a pair of opposing edge portions is a portion corresponding to one edge portion (hereinafter referred to as a left edge waveform portion for convenience) and a portion corresponding to the other edge portion ( In the following description, for the sake of convenience, there is often a difference in signal intensity. This difference continuously changes in accordance with the focus state (relative positional relationship between the optical system and the mark in the optical axis direction of the optical system). Therefore, by detecting a predetermined reference pattern in various focus states, It is possible to specify a focus state in which the signal strengths of the edge waveform portion and the right edge waveform portion are substantially equal. In the present invention, since the mark is detected under the specified focus state, even if it is an asymmetrical low step mark or there is a residual error in the optical system, it is substantially symmetrical and A mark image with substantially good contrast can be obtained, and the mark position can be detected with high accuracy.

  According to the third aspect of the present invention, a signal obtained by photoelectrically detecting light from the mark (WM) provided on the object (W) to be position-detected via the optical system (7-14, 17). In the position detection method of detecting the position of the mark based on the detection step (S2 to S4) for detecting the position of the mark under a focus state determined based on the signal, and prior to the detection step, the mark A position detection method is provided that includes step information regarding a step amount of the line portion and a determination step (S1) for determining whether to perform the detection step based on the step information.

  In the present invention, since it is determined whether or not to perform the detection step based on the step information regarding the step amount of the mark, for example, the detection that is detected under the predetermined focus state when the step amount is small. If the step is large and the level difference is large, position detection can be performed under normal focus conditions without performing the detection step. Detection can be performed. In addition, since such a determination is made, highly accurate detection can be performed without significantly reducing the overall throughput.

  According to the fourth aspect of the present invention, an optical system (7-14, 17) for guiding light from a mark (WM) provided on an object (W) whose position is to be detected, and photoelectric detection of light from the mark. And a detection system (18) for detecting the position of the mark based on the output signal of the photoelectric detector, the output signal of the photoelectric detector There is provided a position detection device having a determination unit that determines whether or not to detect the position of the mark by the detection system based on step information regarding the step amount of the mark under a focus state determined based on the focus state. . Effects similar to those of the invention according to the third aspect of the present invention can be obtained.

  According to a fifth aspect of the present invention, an illumination system (IL) that illuminates a mask (R) on which a pattern is formed, and a projection optical system (PL) that projects a pattern image of the mask onto an object (W) There is provided an exposure apparatus comprising the position detection devices (1 to 18) according to the first or fourth aspect of the present invention. Since the position detection apparatus according to the present invention capable of detecting the low step mark with high accuracy is provided, the mark position can be detected with high accuracy, and as a result, a high-precision and high-quality microdevice can be manufactured.

  According to a sixth aspect of the present invention, in an exposure method for exposing an object (W) through a mask (R) pattern, the object is detected using the position detection method according to the second or third aspect of the present invention. There is provided an exposure method including a step of detecting the position of. Since the step of detecting the position of the mark using the position detection method according to the present invention capable of detecting the low step mark with high accuracy is provided, the mark position can be detected with high accuracy. Devices and the like can be manufactured.

  According to the present invention, even when the mark is asymmetrical or when there is a residual error in the imaging optical system of the mark, the position of the mark of the low step pattern can be detected with high accuracy and speed. There is an effect.

  In addition, there is an effect that the mark position can be detected with high accuracy while flexibly responding to the situation at the actual site and suppressing a decrease in throughput as much as possible.

  Furthermore, there is an effect that high-precision and high-quality microdevices can be manufactured with high throughput.

  Embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a view schematically showing a configuration of an exposure apparatus provided with a position detection apparatus according to an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating an example of a wafer mark or a reference mark formed of a step pattern formed on a process wafer or a reference wafer (details will be described later).

  In the present embodiment, the present invention is applied to an FIA-based position detection device for detecting the position of a photosensitive substrate in an exposure device for manufacturing a semiconductor element. In FIG. 1, the Z axis is parallel to the optical axis AX0 of the projection optical system PL of the exposure apparatus, and the X axis is in the direction parallel to the plane of FIG. 1 in the plane perpendicular to the Z axis. In the vertical plane, the Y axis is set in the direction perpendicular to the paper surface of FIG.

The illustrated exposure apparatus includes an exposure illumination system IL for illuminating a reticle R as a mask (projection original) with appropriate exposure light. The light source of the illumination system IL is not particularly limited, but an ultra-high pressure mercury lamp (g-line (wavelength 436 nm), i-line (wavelength 365 nm)), KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), or An F ₂ laser (wavelength 157 nm) or the like is used. The reticle R is supported on the reticle stage 30 substantially parallel to the XY plane, and a circuit pattern to be transferred is formed in the pattern area PA. The light transmitted through the reticle R reaches the wafer W as a photosensitive substrate via the projection optical system PL, and a pattern image of the reticle R is projected onto the wafer W.

  The wafer W is supported on the Z stage 32 through the wafer holder 31 so as to be substantially parallel to the XY plane. The Z stage 32 is configured to be driven in the Z direction by the stage control system 34 along the optical axis AX0 of the projection optical system PL. The Z stage 32 is further supported on the XY stage 33. Similarly, the XY stage 33 is configured to be driven two-dimensionally in the XY plane perpendicular to the optical axis AX0 of the projection optical system PL by the stage control system 34.

  In the exposure apparatus having such a configuration, it is necessary to optically align (align) the pattern area PA on the reticle R and each exposure area (shot area) on the wafer W prior to the projection exposure. Therefore, a wafer mark (wafer alignment mark) WM having a pattern as schematically shown in FIG. 2 is formed on the wafer W which is an object whose position is to be detected. The wafer mark WM may have a step structure as shown in FIG. The position detection apparatus of this embodiment is used to detect the position of the wafer mark WM, and thus detect the position of the wafer W.

  Specifically, as the wafer mark WM, a wafer mark WMX in the X direction as a one-dimensional mark having periodicity in the X direction, and a Y-direction wafer mark WMY (not shown) as a one-dimensional mark having periodicity in the Y direction. ) Is formed on the wafer W. In the present embodiment, two independent one-dimensional marks having periodicity in the X direction and the Y direction are employed as the wafer marks WM, but two-dimensional marks having periodicity in the X direction and the Y direction are used. Marks can also be adopted.

  The wafer mark is not limited to such a mark having substantially the same width of the line portion and the space portion, but is a so-called fine groove mark (a mark in which the width of the line portion is set narrower than the width of the space portion or the same). Or a segment mark (a mark in which a plurality of ultrafine patterns are arranged at a narrow pitch and the width between the patterns is set to be equal to or less than the resolution limit of the imaging optical system). .

  Reference is again made to FIG. The position detection apparatus according to the present embodiment includes a light source 1 for supplying illumination light having a wide wavelength bandwidth (for example, a wavelength of 530 nm to 800 nm). As the light source 1, a light source such as a halogen lamp can be used. Illumination light supplied from the light source 1 enters an incident end of a light guide 2 such as an optical fiber via a relay optical system (not shown). Illumination light propagating through the inside of the light guide 2 and exiting from the exit end thereof is restricted through an illumination aperture stop 3 having, for example, a circular opening (light transmission part), and then enters the condenser lens 4. To do.

  The illumination light that has passed through the condenser lens 4 enters the illumination relay lens 6 through the illumination field stop 5. The illumination light that passes through the illumination relay lens 6 passes through the half prism 7 and then enters the first objective lens 8. The illumination light that has passed through the first objective lens 8 is reflected downward (in the −Z direction) in the figure by the reflecting surface of the reflecting prism 9 and then illuminates the wafer mark WM formed on the wafer W.

  As described above, the light source 1, the light guide 2, the illumination aperture stop 3, the condenser lens 4, the illumination field stop 5, the illumination relay lens 6, the half prism 7, the first objective lens 8, and the reflection prism 9 are incident on the wafer mark WM. An illumination system for illumination is configured. Reflected light (including diffracted light) from the wafer mark WM with respect to the illumination light is incident on the half prism 7 via the reflective prism 9 and the first objective lens 8. The light reflected upward (in the + Z direction) in the drawing by the half prism 7 forms an image of the wafer mark WM on the index plate 11 via the second objective lens 10.

  The light that has passed through the index plate 11 enters the XY branch half prism 14 via the relay lens system (12, 13). The light reflected by the XY branch half prism 14 enters the Y direction CCD 15, and the light transmitted through the XY branch half prism 14 enters the X direction CCD 16. An imaging aperture stop 17 is disposed in the parallel optical path of the relay lens system (12, 13).

  As described above, the reflecting prism 9, the first objective lens 8, the half prism 7, the second objective lens 10, the indicator plate 11, the relay lens system (12, 13), the imaging aperture stop 17 and the half prism 14 are provided with illumination light. An imaging optical system for forming a mark image based on the reflected light from the wafer mark WM is configured. Further, the Y-direction CCD 15 and the X-direction CCD 16 constitute a photoelectric detector for photoelectrically detecting a mark image formed through the imaging optical system.

  Thus, a mark image is formed together with the index pattern image of the index plate 11 on the imaging surfaces of the Y-direction CCD 15 and the X-direction CCD 16. Output signals from the Y-direction CCD 15 and the X-direction CCD 16 are supplied to a signal processing system 18. Further, the position information of the wafer mark WM obtained by signal processing (waveform processing) in the signal processing system 18 is supplied to the main control system 35. The main control system 35 outputs a stage control signal to the stage control system 34 based on the position information of the wafer mark WM from the signal processing system 18.

  The stage control system 34 appropriately drives the XY stage 33 in accordance with the stage control signal to align the wafer W. A command for the illumination aperture stop 3 and a command for the imaging aperture stop 17 are supplied to the main control system 35 via an input means 36 such as a keyboard. Based on these instructions, the main control system 35 may drive the illumination aperture stop 3 via the drive system 19 or drive the imaging aperture stop 17 via the drive system 20.

Although the mark shown in FIG. 2 has an ideal shape. A mark formed through an actual process may be asymmetrically distorted. FIG. 3 is a diagram schematically showing an example of an asymmetric low step pattern. Referring to FIG. 3, for example, an insulating layer 40 made of SiO ₂ (silicon oxide) is formed on a wafer W made of silicon, and a plurality of line portions 41 made of W (tungsten) are formed in the insulating layer 40. . Here, the plurality of line portions 41 have a shape that is elongated in a straight line along the Y direction, and are arranged according to a predetermined pitch along the X direction. The surfaces of the insulating layer 40 and the plurality of line portions 41 are planarized by a CMP (Chemical Mechanical Polishing) method, and an aluminum layer 42 is formed on the surfaces of the insulating layer 40 and the line portions 41.

  In general, when the surfaces of the insulating layer 40 and the plurality of line portions 41 are flattened using the CMP method in the above-described steps, the surface of the line portions 41 is asymmetrically recessed and corresponds to the surface portion of the line portion 41. The surface portion of the aluminum layer 42 is also asymmetrically recessed. In the present embodiment, the aluminum layer 42 as the reflective layer is used as the wafer mark WMX in the X direction. As a result, in the wafer mark WMX, the concave portion (the surface portion of the aluminum layer 42 corresponding to the surface portion of the line portion 41) and the convex portion (the surface portion of the aluminum layer 42 corresponding to the surface portion of the insulating layer 40) have a pitch direction ( It is constituted by asymmetric low step patterns formed asymmetrically with respect to (X direction). The same applies to the wafer mark WMY in the Y direction.

  4A to 4C are diagrams showing signal waveforms obtained when an asymmetric step pattern is detected on the Gaussian image plane. When a step pattern asymmetric with respect to the central axis as shown in FIG. 4C is detected via an ideal imaging optical system having no residual error as shown in FIG. 4B, FIG. As shown in A), an asymmetric (distorted) signal waveform with respect to the central axis is obtained. This distortion is asymmetrically distributed with respect to the optical axis between the plus-order diffracted light and the corresponding minus-order diffracted light in the diffracted light collected by the imaging optical system and reaching the CCDs (photoelectric detectors) 15 and 16. Is one of the main factors. As a result, the mark image causes an asymmetric distortion detection error. In this case, a detection result including an error corresponding to the asymmetry of the step pattern is obtained.

  5 and 8 are diagrams showing signal waveforms obtained when a symmetric pattern is detected on the Gaussian image plane through an imaging optical system having a residual error. As shown in the wafer mark indicated by WM in FIG. 5, the stepped pattern symmetrical to the central axis is shifted in position (optical axis shift) with respect to the optical axis as shown in FIG. When detected via the imaging optical system, as shown in FIG. 8, a signal waveform that is asymmetric (distorted) with respect to the central axis is obtained as in FIG. As shown in FIG. 5, this distortion is caused by the fact that a part of the higher-order diffracted light (third-order diffracted light in the figure) out of the diffracted light from the object plane OP (wafer mark WM) is located at the position of the imaging aperture stop 17. This is because it is blocked by the deviation and does not reach the image plane IP (CCD). Also in this case, a detection result including an error corresponding to the residual error of the imaging optical system is obtained.

  FIG. 6 shows the difference between the detection error (measurement position deviation) and the pattern step amount when the pattern (mark) is detected in the best focus state (that is, the focus state in which the mark coincides with the object plane of the imaging optical system). It is a figure which shows the result of having simulated the relationship. In the same figure, as apparent from the line indicated by the reference AEO (Aperture Stop Opticality for Optical Axis), the positional deviation of the imaging aperture stop 17 remains. It can be seen that the detection error increases rapidly when the pattern is lowered. The figure also shows the relationship between the step amount and the detection error with respect to coma aberration as another error factor of the position detection device (in the figure, indicated by the symbol Coma). Since the detection error due to the remaining coma aberration does not depend on the step amount of the mark, here, focusing on the positional deviation of the imaging aperture stop, the detection error associated therewith is reduced.

  FIG. 7 is a graph showing the relationship between the mark level difference, image contrast (Iac), asymmetry (ΔI), and asymmetry (Q). The detection waveform for a pattern having a pair of edge portions (normal line pattern) corresponds to the edge portion as shown in FIG. 8 when the mark itself is asymmetric or when there is an error in the imaging optical system. The signal intensity of the portion (hereinafter, referred to as the left edge waveform portion and the right edge waveform portion) is asymmetric in the left and right edge waveform portions. The signal intensity of one of the left and right edge waveform parts (the signal edge having the larger signal intensity, here the right edge waveform part) is Iac (contrast of the image), and the difference in signal intensity between the left and right edge waveform parts is ΔI (asymmetric amount). , ΔI / Iac is defined as Q (degree of asymmetry).

In FIG. 6 described above, the detection error rapidly increases when the pattern is lowered, because the deterioration of the contrast (Iac) of the image as the mark step θ decreases.
Iac∝1-cos θ (1)
Whereas the relationship of image asymmetry (ΔI) degradation is
Asymmetry degree Q representing the degree of asymmetry is a phenomenon that occurs because ΔI∝sinθ changes.
Q = ΔI / Iac∝sinθ / (1-cosθ) = 1 / tan (θ / 2) (2)
This is because the degree of asymmetry Q rapidly deteriorates when the step θ becomes smaller.

  As described above, generally, when diffracted light reaching the CCD (photoelectric detector) becomes asymmetric with respect to the optical axis, the mark image is also asymmetrically distorted, and the waveform of the detection signal is also asymmetrical, resulting in a detection error (measurement error). .

  This point will be described in more detail. When the mark is detected and defocused from the best focus state, wavefront aberration (phase shift) symmetrical to the optical axis occurs. Here, the magnitude of the defocus amount is ΔZ, the center wavelength of the light from the mark is λ, the pitch of the mark is P, and the order of the diffracted light is N (N = 0, ± 1, ± 2,...) Then, the magnitude ΔW (radian) of the generated phase shift is expressed by the following equation (3).

ΔW = (1/2) × (N · λ / P) ² × ΔZ × (2π / λ) (3)

In addition, when only the 0th-order diffracted light and the + 1st-order diffracted light reach the photoelectric detector and the −1st-order diffracted light does not reach the photoelectric detector due to the pattern asymmetry or the optical axis shift of the imaging aperture stop, they are formed on the photoelectric detection surface. The intensity distribution I of the pattern image is defined as follows: d is the step amount between the line portion and the space portion of the pattern, X is the position coordinate in the pitch direction of the pattern, C ₀ is the Fourier amplitude of the _0th-order diffracted light, and ± 1 When the Fourier amplitude of the diffracted light is C _1, it is expressed by the following equation (4).

I = 2C ₀ ² + 2C ₁ ² + (C ₀ −2C ₁ ² ) cos θ
+ 2C ₁ sin θ (cosXsinΔW + sinXcosΔW) (4)
here,
θ = 2d × (2π / λ)
It is. Therefore, in the best focus state where the defocus amount is ΔZ = 0, the phase difference between the 0th-order diffracted light and the first-order diffracted light is ΔW = 0, and the intensity distribution I of the pattern image is expressed by the following equation (5).

I = 2C ₀ ² + 2C ₁ ² + (C ₀ −2C ₁ ² ) cos θ + 2C ₁ sin θsinX (5)

That is, in the best focus state where the defocus amount is ΔZ = 0, the term of the odd function sin of X appears in the expression (5) representing the intensity distribution I of the pattern image, thereby causing asymmetry in the pattern image. On the other hand, when defocusing is performed by a predetermined defocus amount ΔZ ₀ so that the phase difference between the 0th-order diffracted light and the 1st-order diffracted light is ΔW = π / 2, the intensity distribution I of the pattern image is expressed by the following formula ( 6). The defocus amount ΔZ ₀ where the phase difference between the 0th-order diffracted light and the 1st-order diffracted light is ΔW = π / 2 is expressed by the following equation (7).

I = 2C ₀ ² + 2C ₁ ² + (C ₀ −2C ₁ ² ) cos θ + 2C ₁ sin θcosX (6)
ΔZ ₀ = (1/2) × (P2 / λ) (7)

  That is, in a predetermined defocus state in which the phase difference between the 0th-order diffracted light and the 1st-order diffracted light is ΔW = π / 2, the term of the odd function sin of X is expressed in Equation (6) representing the intensity distribution I of the pattern image. Since the term of the even function cos of X appears and the term of the even function cos of X appears, the asymmetry of the pattern image disappears and a symmetric pattern image is obtained. In this case, the contrast of the obtained pattern image is also good.

  As described above, when detecting an asymmetric low step pattern mark based on the 0th-order diffracted light and the 1st-order diffracted light from the mark, the phase difference between the 0th-order diffracted light and the 1st-order diffracted light is 90 degrees (π / 2). When a predetermined defocus state is set, a completely symmetrical image with good contrast can be obtained.

  In the above description, for the sake of simplicity, it is assumed that the mark is detected based on the 0th-order diffracted light and the 1st-order diffracted light from the mark. In many cases, photoelectric detection is also configured. Also in this case, when a mark having an asymmetric low step pattern is detected in a predetermined defocus state in which the phase difference between the highest order diffracted light and the zeroth order diffracted light is 90 degrees out of the diffracted light from the mark reaching the photoelectric detector. Thus, it is possible to obtain a mark image that is substantially symmetrical and has a substantially good contrast. Further, in general, among the diffracted lights from the mark reaching the photoelectric detector, the phase difference between one diffracted light of a specific order or a plurality of diffracted lights of a specific order and zero-order diffracted light is approximately 90 degrees. When a mark having an asymmetrical low step pattern is detected in a predetermined optical state in which a phase difference is added to the mark image, it is possible to obtain a mark image that is substantially symmetric and has a substantially good contrast.

  In order to perform mark detection in such a focus state that the phase difference between the 0th-order diffracted light and the high-order diffracted light is 90 degrees, in this embodiment, the signal intensity of the left edge waveform portion and the right edge waveform portion in FIG. A focus state in which is substantially equal is specified, and a mark is detected in the focus state. Note that this focus state is usually a defocused state from the Gaussian image plane, but may be substantially coincident with the Gaussian image plane.

  Hereinafter, a specific method for specifying such a focus state (a focus state in which the left and right edge waveform portions in FIG. 8 are substantially equal) will be described.

  First, a step data collection process is performed using a reference wafer (tool wafer). On the reference wafer, a plurality of reference patterns having different step amounts from one another are formed in advance. The reference pattern is a near-ideal pattern with good symmetry, and here is a line-and-space pattern having a configuration as shown in FIG. 2 formed by etching a silicon wafer. The reflectances of the line portion of the reference pattern and the space portion around the line portion are set to be substantially equal. Each step amount of each reference pattern can be formed (used) in the exposure process, and from a suitable step amount (about 200 nm in the example of FIG. 7) to which the step change starts to affect the accuracy to the minimum step amount. Are selected at an appropriate pitch. It is desirable that the width of the line portion and the width of the space portion (that is, the arrangement pitch) of the reference pattern are substantially the same as the wafer mark formed on the process wafer. When there are a plurality of types of wafer marks formed on the process wafer, a reference pattern corresponding to each of them is formed on the reference wafer at once, or formed on another reference wafer and replaced as appropriate. It should be used.

  Next, the reference wafer is loaded onto the wafer stage, and for each reference pattern having a different step amount, the defocus amount from the Gaussian image plane is changed in stages, and the waveform of the output signal (FIA signal) of the CCD is as follows. A defocus amount at which the left and right edge waveform portions in FIG. 8 are substantially equal (hereinafter, sometimes referred to as an optimal defocus amount or an optimal focus state for convenience) is specified. Based on the data collected in this data collection step, step data (step information) including each step amount and the corresponding optimum defocus amount is created as a table, for example, and stored. It should be noted that the change of the defocus amount when collecting the step data may be performed in both the plus direction and the minus direction with respect to the Gaussian image plane, but the left and right edge waveforms in FIG. 8 accompanying the change of the defocus amount. The relative change (change in ΔI) of the part may be collected for only one of the patterns appearing symmetrically in the plus direction and the minus direction.

  In the above example, the reference pattern having a duty ratio of 1: 1 as shown in FIG. 2 is used, but the optical system as shown in FIG. 9A resolves each edge. It may be a narrow groove pattern. Also in this case, the pattern is symmetrical, and the line portion and the space portion have substantially the same reflectance. In that case, the defocus amount is determined such that the symmetry of the waveform in FIG. 9B is substantially symmetric as shown in FIG. 9C.

  In the actual process wafer alignment step (wafer mark detection step for alignment), the step amount of the wafer mark (alignment mark) formed on the process wafer as the measurement target (exposure target) is acquired, Referring to the step data, the optimum defocus amount corresponding to the step amount is obtained, and the position of the wafer mark is detected in a state where the defocus is made from the Gaussian image plane by the amount corresponding to the optimum defocus amount. .

  This makes it possible to obtain an output signal having a symmetrical waveform even when the imaging aperture stop is shifted or when the wafer mark is an asymmetrical low step pattern, and the contrast becomes good. Mark position detection accuracy can be improved. In addition, the change in the detected waveform is small with respect to the change in the focus position (the change based on the positioning accuracy) when the mark detection is actually performed. That is, the focus dependency of the detection result is reduced, and stable and highly accurate position detection is possible.

  If the step amount of the wafer mark is known by design or actual measurement in an actual process, it can be input by an operator or acquired from a preset process data (recipe). However, a step amount measuring device for actually measuring the step amount of the wafer mark may be provided, and this may be obtained by actually measuring the wafer mark before detecting it.

  In some cases, the step data corresponding to the step amount of the wafer mark does not necessarily exist. In this case, the step data closest to the step amount of the wafer mark may be selected or a part of the step data may be selected. Alternatively, all may be interpolated with an appropriate interpolation function to obtain the corresponding defocus amount. In this interpolation, two points including the step amount of the wafer mark may be linearly interpolated, or another point may be used for linear or curved interpolation.

  Note that defocusing from the Gaussian image plane during measurement of the wafer mark in the exposure process may be performed in one of the plus direction and the minus direction to detect the position of the wafer mark, and this may be used as the measurement result. Alternatively, the average of the positions of the wafer marks detected in both cases may be used as the measurement result.

  In the above description, the reference wafer is moved in the optical axis direction with respect to the imaging optical system at the time of collecting the step data so as to obtain the optimum defocus amount, and also at the time of measuring the wafer mark in the exposure process. The process wafer is moved and defocused in the optical axis direction with respect to the imaging optical system, but the photoelectric detector (the photoelectric detection surface of the CCD) is moved in the optical axis direction of the imaging optical system, or a lens. (8, 10, 12, 13, etc. in FIG. 1) may be moved in the optical axis direction.

  Further, in the above-described embodiment, the step data is collected using the reference wafer on which the reference pattern is formed. However, a fiducial mark for baseline measurement that is permanently installed on the wafer stage on which the wafer is mounted. The reference pattern may be formed on a plate (FM plate), or the reference pattern may be formed on another member and permanently installed on the wafer stage, or may be installed interchangeably.

  In the above-described embodiment, the wafer mark is incidentally illuminated. However, the present invention is not limited to this, and the present invention can also be applied to a position detection apparatus that transmits and illuminates the wafer mark. In the above-described embodiment, separate CCDs are used for X-direction mark detection and Y-direction mark detection. However, both X-direction mark detection and Y-direction mark detection may be performed by one CCD. .

  By the way, in the above description, the process is performed under a focus state in which the signal intensities of the left and right edge waveform portions of the reference wafer in FIG. The wafer mark of the wafer is detected (hereinafter, since the focus state is usually a defocused state from the Gaussian image plane, it may be referred to as “position detection in the defocused state of the present invention” for convenience) . However, in actual manufacturing sites, the accuracy required for detecting the position of the wafer mark (hereinafter sometimes referred to as “required accuracy”) varies, and when high accuracy is required, Although position detection in the defocus state is extremely effective, when position accuracy is not so required, position detection in the conventional best focus state is performed without performing position detection in the defocus state of the present invention. Doing so may be advantageous in terms of throughput. Similarly, in an actual manufacturing site, the pattern step amount varies from small to large, and the position detection in the defocused state of the present invention is extremely effective when the step amount is relatively small. However, when the step amount is relatively large, there may be a case where the detection error is smaller when the detection is performed in the conventional best focus state.

  In order to cope with such a case, the present embodiment takes the following measures. This will be described with reference to the flowchart shown in FIG.

  Referring to FIG. 10, there is a determination step S1 for determining whether or not to perform position detection in the defocused state of the present invention based on a predetermined condition as will be described later. In the determination step S1, for example, it is determined whether or not to perform position detection in the defocused state of the present invention based on the required accuracy required for position detection of the wafer mark WM. That is, when the required accuracy is higher than the predetermined reference accuracy, the process proceeds to an acquisition step S2 for acquiring the corresponding defocus amount from the step data in order to perform position detection in the defocus state of the present invention. On the other hand, when the required accuracy is lower than the predetermined reference accuracy, the position detection according to the present invention is not performed, and the conventional best focus state is achieved in accordance with the prior art disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-324746. The process proceeds to a focus detection step S10 for performing position detection.

  Further, in the determination step S1, it may be determined whether or not to perform position detection in the defocus state of the present invention based on the pattern information of the wafer mark WM. That is, when the step amount of the wafer mark WM is equal to or smaller than the predetermined threshold value, the process proceeds to the acquisition step S2 in order to perform position detection in the defocus state of the present invention. The pattern information (step information) used at this time may be a step value (similar to a so-called design value) that is uniquely determined in accordance with setting information such as a process by the user, or You may use the actual value actually measured with the level | step difference measuring device. On the other hand, when the step amount of the wafer mark WM exceeds a predetermined threshold value, the focus detection step S10 is performed in order to perform the conventional position detection in the best focus state without performing the position detection in the defocus state of the present invention. Migrate to Note that the threshold value regarding the step amount (the above-mentioned predetermined threshold value) can be about 50 nm in FIG. 6 where the detection error begins to deteriorate rapidly, or about 100 nm with some margin. .

  As described above, the degree of asymmetry Q of the image changes according to Q∝1 / tan (θ / 2). Therefore, in the case of epi-illumination, the step θ at which the degree of asymmetry suddenly increases is θ ≦ θ. When λ / 10, the process proceeds to the acquisition step S2 to perform position detection in the defocus state of the present invention. When θ> λ / 10, position detection in the conventional best focus state is performed. Therefore, the process may proceed to the focus detection step S10. Here, the step θ is a phase difference added to light that illuminates the mark due to a difference in height between the line portion of the mark and the surrounding space portion. Therefore, in the case of transmitted illumination, when θ ≦ λ / 5, the process proceeds to the acquisition step S2 to perform position detection in the defocused state of the present invention, and when θ> λ / 5, In order to perform position detection in the conventional best focus state, the process proceeds to the focus detection step S10. Note that λ is the center wavelength of the illumination light that illuminates the mark.

  Furthermore, in the determination step S1, it may be determined whether or not to perform position detection in the defocus state of the present invention based on the waveform information of the photoelectric detection signal obtained from the wafer mark WM in the best focus state. . That is, for example, when the contrast of the waveform obtained in the best focus state is relatively low or the symmetry of the waveform is relatively poor, the process proceeds to the acquisition step S2 in order to perform position detection in the defocus state of the present invention. If the contrast of the waveform obtained in the best focus state is relatively high or the symmetry of the waveform is relatively good, the conventional focus is not performed without performing position detection in the defocus state of the present invention. The process proceeds to the detection step S10. In this case, as the determination of the symmetry of the waveform, for example, a threshold value is set for the non-target level Q of the image or the non-target level ΔI of the image as a condition regarding the amount of collapse of the waveform signal obtained by photoelectrically detecting the mark. Based on this, it is possible to determine whether to perform position detection in the defocus state of the present invention or to perform position detection in the conventional best focus state.

  In addition, for example, depending on whether it is expected that only an optical image having a relatively low contrast can be obtained on the basis of the pattern information related to the material and film thickness (and thus the refractive index and the absorptivity) of the pattern. It may be determined whether position detection in the defocus state is performed or position detection in the conventional best focus state is performed.

In the acquisition step S2, first, a step amount of a mark on a process wafer as a processing target is acquired. Since the step amount is input by an operator or the like as described above, or obtained by actual measurement, it is obtained. Next, the step data is searched based on the acquired step amount, and the corresponding optimum defocus amount ΔZ ₀ is acquired. Then, in the setting step S3, by driving the wafer stage (32, 33) in accordance with the defocus amount [Delta] Z ₀ obtained, the wafer W (and hence the wafer marks WM) set to a predetermined defocus state. Thereafter, the process proceeds to detection step S4, and the position of the wafer mark WM is detected based on the output signal of the photoelectric detector (15, 16) in the defocus state set in the setting step S3. In order to detect the positions of a plurality of (for example, six or eight) wafer marks WM arranged on the wafer W according to a so-called EGA (Enhanced Global Alignment) technique, the wafer stage (32, 33) is used. The setting step S3 and the detection step S4 are repeated a plurality of times while being driven two-dimensionally along the XY plane.

  In the above description, whether to perform position detection in the defocus state of the present invention or position detection in the conventional best focus state is determined based on various conditions. It can also be used to determine whether to perform position detection in the defocused state described in the references listed in the prior art section or to perform position detection in the conventional best focus state.

  The embodiment described above is described for facilitating understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment includes all design changes and equivalents belonging to the technical scope of the present invention.

  For example, in the above-described embodiment, the present invention is applied to a position detection apparatus including an imaging optical system that forms an image based on light from a wafer mark. However, the present invention is not limited to this. In general, the present invention can also be applied to a position detection apparatus having an optical system for guiding light from a wafer mark.

  Further, the present invention is not limited to an exposure apparatus used for manufacturing a semiconductor element or a liquid crystal display element, but also an exposure apparatus and reticle used for manufacturing a plasma display, a thin film magnetic head, and an imaging element (CCD, etc.), or In order to manufacture a mask, the present invention can also be applied to an exposure apparatus that transfers a circuit pattern to a glass substrate or a silicon wafer. In other words, the present invention can be applied regardless of the exposure method and application of the exposure apparatus.

  Furthermore, although the case where the present invention is applied to an exposure apparatus has been described in the above embodiment, the present invention measures the position of a transport apparatus, a measurement apparatus, an inspection apparatus, a test apparatus, and other marks to align an object. Applicable to all devices to be performed.

It is a figure which shows schematically the structure of the exposure apparatus provided with the position detection apparatus which concerns on embodiment of this invention. It is a figure which shows typically the structure of a wafer mark or a reference pattern. It is a figure which shows roughly an example of an asymmetrical low level | step difference pattern. It is a figure which shows the signal waveform obtained when an asymmetrical level | step difference pattern is detected through the imaging optical system without a residual error. It is a figure for demonstrating the principle which a signal waveform distorts asymmetrically by the shift | offset | difference of an imaging aperture stop. It is a figure which shows the relationship between the level | step difference amount of a pattern, and a detection error. It is a figure which shows the relationship between the level | step difference amount of a pattern, the contrast (Iac) of an image, an asymmetry amount ((DELTA) I), and an asymmetry degree (Q). It is a figure which shows the waveform of a detection signal when a mark itself is asymmetric or when there is an error in an imaging optical system. It is a figure explaining the mark comprised by the fine groove pattern, and its signal waveform. It is a flowchart which shows the detection process of the mark position of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Halogen lamp 2 Light guide 3 Illumination aperture stop 5 Illumination field stop 7 Half prism 8 First objective lens 9 Reflective prism 10 Second objective lens 11 Indicator plate 14 XY branch half prisms 15 and 16 CCD
17 imaging aperture stop 18 signal processing system 30 reticle stage 31 wafer holder 32 Z stage 33 XY stage 34 stage control system 35 main control system 36 keyboard IL exposure illumination system R reticle PA pattern area PL projection optical system W wafer WM wafer mark

Claims (17)

An optical system for guiding light from a mark provided on an object to be position-detected, a photoelectric detector for photoelectrically detecting light from the mark, and detecting the position of the mark based on an output signal of the photoelectric detector In a position detection device comprising a detection system,
A position detection apparatus for detecting the position of the mark under a focus state in which the symmetry of the output signal of the photoelectric detector obtained by detecting a predetermined reference pattern is substantially symmetric.   The position detection device according to claim 1, wherein the reference pattern has a pair of opposing edge portions, and the symmetry is such that signal strengths of portions corresponding to the edge portions are substantially equal.   The position detection apparatus according to claim 1, wherein the reference pattern is a pattern in which the reflectance of the line portion and the non-line portion around the line portion is substantially equal to each other. In a position detection method for detecting the position of the mark based on a waveform signal obtained by photoelectrically detecting light from a mark provided on an object to be position-detected,
Detection for detecting the position of the mark under a focus state in which signal intensities corresponding to the edge portions of the waveform signal obtained by photoelectrically detecting a predetermined reference pattern having a pair of opposing edge portions are substantially equal to each other. A position detection method comprising a step.   The position detection method according to claim 4, wherein the reference pattern is a pattern in which the reflectance of the line portion and the non-line portion around the line portion is substantially equal to each other.   The position detection method according to claim 4, further comprising a determination step of determining whether or not to perform the detection step based on a predetermined condition determined in advance.   The position detection method according to claim 6, wherein the predetermined condition is a condition related to accuracy required for detection of the position of the mark.   The position detection method according to claim 6, wherein the predetermined condition is a condition related to a step amount of the mark.   The position detection method according to claim 8, wherein in the determination step, it is determined that the detection step is performed when the step amount is 100 nm or less.   In the determination step, the wavelength of illumination light for illuminating the mark is λ, and the phase difference between the light from the line portion of the mark and the non-line portion around the line portion is θ, and the case of epi-illumination 9. The position detection method according to claim 8, wherein the detection step is determined to be performed when θ ≦ λ / 10 and when θ ≦ λ / 5 in the case of transmitted illumination.   The position detection method according to claim 6, wherein the predetermined condition related to the determination step is a condition related to symmetry of a waveform signal obtained by photoelectrically detecting the mark. In a position detection method for detecting the position of the mark based on a signal obtained by photoelectrically detecting light from the mark provided on an object to be position-detected via an optical system,
A detection step of detecting the position of the mark under a focus state determined based on the signal;
Prior to the detection step, the method includes a step of acquiring step information regarding the step amount of the mark and determining whether to perform the detection step based on the step information.   In the determination step, the wavelength of illumination light for illuminating the mark is λ, and the phase difference between the light from the line portion of the mark and the non-line portion around the line portion is θ, and the case of epi-illumination 13. The position detection method according to claim 12, wherein the detection step is determined to be performed when θ ≦ λ / 10, and in the case of transmitted illumination, when θ ≦ λ / 5. An optical system for guiding light from a mark provided on an object to be position-detected, a photoelectric detector for photoelectrically detecting light from the mark, and detecting the position of the mark based on an output signal of the photoelectric detector In a position detection device comprising a detection system,
Judgment means for judging whether or not to detect the position of the mark by the detection system based on step information on the step amount of the mark under a focus state determined based on an output signal of the photoelectric detector. A position detection device comprising: An illumination system for illuminating the mask on which the pattern is formed;
A projection optical system that projects a pattern image of the mask onto an object;
The position detection device according to claim 1, 2, 3 or 14,
An exposure apparatus comprising: Prior to detecting the position of the mark on the object, as the predetermined reference pattern, a plurality of types of reference patterns having different step amounts and having a pair of edge portions are prepared. Photoelectrically detecting the reference pattern of each, obtaining a focus state in which the signal intensity of the portion corresponding to each of the edge portions is substantially equal, storing the obtained respective focus state for each reference pattern,
When detecting the position of the mark on the object, an optimal focus state for the mark is determined based on the information on the structure of the mark, the information on the structure of the reference pattern, and the plurality of stored focus states. The position detection method according to claim 4 or 5, wherein the position of the mark is detected under the specified focus state. In an exposure method for exposing an object through a mask pattern,
An exposure method comprising a step of detecting the position of the object using the position detection method according to any one of claims 4 to 13 and 16.

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