JP2019032378A - Substrate position detection device, exposure apparatus and method for detecting substrate position - Google Patents

Abstract

To perform focus control on a substrate with high accuracy in an exposure apparatus.SOLUTION: An exposure apparatus 10 for projecting pattern light onto a substrate W is provided with a substrate position detection device 20 including a projection part 22 and a detection part 24. The detection part 24 includes a polarizing element 26, a light-receiving part 27 and an imaging optical system 28, in which a polarizing element control part 29 controls polarization of the polarizing element 26. Upon controlling a focus, reflected light of s-polarized light and reflected light of p-polarized light are successively made to enter the light-receiving part 27 by switching polarized light. An image computation part 52 obtains a difference between an image data showing the light intensity distribution of the s-polarized light and an image data showing the light intensity distribution of the p-polarized light, and detects a substrate position from a pixel position where a peak appears.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exposure apparatus, and more particularly to substrate position detection.

  In a projection exposure apparatus (such as a stepper) and a maskless exposure apparatus, light emitted from a light source is imaged on a substrate surface by an illumination optical system and a projection optical system to form a pattern. In these exposure apparatuses, focus detection and focus adjustment are performed before exposure, and the exposure surface is made to coincide with the imaging surface of the projection optical system. In the focus detection method using the triangulation principle, the substrate surface is irradiated with light from an oblique direction, and when the light receiving unit such as a line sensor receives the reflected light, the substrate position is detected from the light receiving position, and the reference position The substrate height is adjusted based on the difference (displacement) from and the focus is adjusted.

  A substrate used in photolithography forms a transparent photoresist layer on a base material such as a silicon wafer. Therefore, when the focus detection light is incident on the substrate from an oblique direction, not only the reflected light from the photoresist surface but also the light transmitted through the photoresist and reflected by the base material enters the light receiving unit. This light becomes a noise component, resulting in a measurement error.

  In order to solve this problem, substrate position detection using a beam splitter is known (see Patent Document 1). In this case, light including both s-polarized light and p-polarized light is irradiated toward the substrate from an oblique direction, and the reflected light is separated into s-polarized light and p-polarized light by a beam splitter. Then, s-polarized light and p-polarized light are incident on separate position sensors. The position of the resist surface is detected based on the light receiving position (pixel position of the light intensity peak) of each position sensor.

JP-A-5-182896

  In an advanced package substrate (FO-PLP or the like), a photoresist layer is formed on a base material on which a redistribution layer is formed by molding a semiconductor chip. Such a substrate has large irregularities on the surface of the base material and is subjected to a roughening treatment. For this reason, when the light for detecting the substrate position is projected, the reflected light is diffusely reflected on the surface of the base material and has a complex and irregular light intensity distribution characteristic having a plurality of peaks.

  For this reason, it is difficult to remove the reflected light component from the base material and extract the reflected light of the photoresist even if it is separated into p-polarized light and s-polarized light by the beam splitter. In addition, since the p-polarized light and the s-polarized light are incident on separate photosensors, a shift occurs in the corresponding positional relationship between the pixels of the photosensors due to an optical system positioning error or the like. An error may occur in detection.

  Therefore, it is required to accurately detect the substrate position regardless of the type of the substrate.

  The substrate position detection apparatus of the present invention is applicable to a maskless exposure apparatus and a projection exposure apparatus (such as a stepper), and a light projecting unit that projects light from an oblique direction onto a substrate having a photoresist layer formed on the surface thereof, A polarizing element that is arranged in the light reflection direction and can select an s-polarized component and a p-polarized component of reflected light, and an s-polarized component and a p-polarized component that pass through the polarizing element by selecting the polarizing element. A light receiving portion for receiving light.

  When the polarization element selects the polarization component, the s-polarization component and the p-polarization component are sequentially incident on the same light receiving unit. Then, the substrate position is detected based on the s-polarized component and the p-polarized component incident on the light receiving unit according to the polarization switching of the polarizing element. For example, it is possible to provide an image calculation unit that calculates the substrate position based on the difference between the light intensity distribution of the s-polarized component incident on the light receiving unit and the light intensity distribution of the p-polarized component incident on the light receiving unit. .

  The polarizing element is an element that can selectively transmit s-polarized light and p-polarized light, and can be configured by a polarizing element that enables electrical polarization switching, such as a liquid crystal polarization modulator. For example, it is possible to provide a polarizing element control unit that performs polarization switching such as s-polarized light transmission (p-polarized light blocking) and p-polarized light transmission (s-polarized light blocking). On the other hand, a plurality of polarization filters can be switched on the optical path to switch the polarization mechanically. The polarizing element is provided, for example, between an imaging optical system that forms an image of reflected light on the light receiving surface of the light receiving unit and the light receiving unit. The light projecting unit can be configured by, for example, a laser light source.

  In consideration of the refractive index of the photoresist and the difference between the reflectance of the s-polarized component and the p-polarized component with respect to the photoresist, the incident angle α of the light with respect to the substrate may satisfy 50 ° <α <80 °. More preferably, when the Brewster angle on the photoresist surface is B, the incident angle α of light with respect to the substrate should satisfy B <α <80 °. For example, the incident angle α may be set to 65 ° <α <80 ° at which the difference in reflectance between the s-polarized component and the p-polarized component is at or near the maximum.

  According to another aspect of the present invention, there is provided a substrate position detecting method in which light is projected from an oblique direction onto a substrate having a photoresist layer formed on a surface thereof, and reflected light of the light is incident on a polarizing element to generate an s-polarized component and a p-polarized component. The s-polarized component and the p-polarized component that sequentially pass through the polarizing element by the selection of the polarizing element are made incident on the light receiving unit, and the height of the substrate is determined based on the s-polarized component and the p-polarized component received by the light receiving unit. The position is detected.

  According to the present invention, it is possible to accurately adjust the focus of a substrate in an exposure apparatus.

It is a block diagram of the exposure apparatus which is this embodiment. It is the figure which showed the structure of the light projection part of FIG. 1, and a detection part. It is the figure which showed the light intensity part distribution when reflected light is entered into a light-receiving part as it is without polarizing. It is the figure which showed the graph of the reflectance of s polarized light when changing the incident angle to a photoresist, and p polarized light. It is the figure which showed intensity distribution of the light which injects into the light-receiving part 27, when s-polarized light is permeate | transmitted with respect to reflected light (L2, L3) and p-polarized light is interrupted | blocked. It is the figure which showed intensity distribution of the light which injects into the light-receiving part 27, when p polarized light is permeate | transmitted with respect to reflected light (L2, L3) and s polarized light is interrupted | blocked. It is the figure which showed the light intensity distribution when the difference of the light intensity distribution (G1, F1) of FIG. 5 and the light intensity distribution (G2, F2) of FIG. 6 is taken. It is the figure which showed the flow of the focus adjustment process including a board | substrate position detection.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic block diagram of an exposure apparatus according to the first embodiment.

  The exposure apparatus 10 is an exposure apparatus that transfers a mask pattern formed on a reticle 16 to a substrate (work substrate) W according to a step-and-repeat method. A light source (discharge lamp or the like) 12 that emits ultraviolet rays, and an illumination optical system 14 are used. , A projection optical system 18 is provided. The light emitted from the light source 12 becomes parallel light with a uniform illumination light quantity by the illumination optical system 14 and enters the reticle 16. The light source 12 is driven by a light source driving unit (not shown).

  The reticle 16 is made of a quartz material or the like, and is formed with a mask pattern such as a circuit pattern. The reticle 16 is mounted on a reticle stage (not shown) so that the mask pattern is the light source side focal position of the projection optical system 18. The light transmitted through the mask pattern of the reticle 16 is projected as pattern light onto the substrate W by the projection optical system 18. The substrate W is mounted on the exposure stage 30 so that the exposure surface thereof coincides with the image side focal position of the projection optical system 18.

  An XYZ triaxial coordinate system orthogonal to each other is defined for the exposure stage 30 on which the substrate W is mounted. The exposure stage 30 is movable in the XY direction so as to move the substrate W along the focal plane, and also in the Z-axis direction (the optical axis of the projection optical system 18) perpendicular to the focal plane (XY direction). Direction) and can be rotated on an XY coordinate plane. The position coordinates of the exposure stage 30 are measured by a laser interferometer or a linear encoder (not shown).

  The control unit 50 sequentially transfers the mask pattern of the reticle 16 to each shot area formed on the substrate W in accordance with the step & repeat method. That is, the controller 50 intermittently moves the exposure stage 30 according to the shot area interval, and when the shot area to be exposed is positioned at the projection position of the mask pattern, the control unit 50 drives the light source 12 to emit the pattern light to the shot area. To project.

  Below the projection optical system 18 of the exposure apparatus 10 is provided a substrate position detection device 20 that detects the position of the substrate W in the height direction (z direction) during focus adjustment. The substrate position detection device 20 includes a light projecting unit 22 and a detection unit 24, and the detection unit 24 includes a polarizing element 26, a light receiving unit 27, and an imaging optical system 28. The image calculation unit 52 calculates the position (substrate position) of the surface of the substrate W based on the signal output from the light receiving unit 27. Here, the position on the surface of the substrate W means the position of the surface on the most surface among the photoresist layer, the cover film and the like provided on the surface of the base material. The polarization element control unit 29 switches and controls the polarization of the polarization element 26.

  FIG. 2 is a diagram illustrating the configuration of the light projecting unit 22 and the detecting unit 24 of FIG.

  The light projecting unit 22 includes a light source that emits light, and here is configured by a laser light source. For example, a laser light source that emits red laser light is applicable. The light projecting unit 22 is mounted so that the laser light is incident on the substrate W from an oblique direction of the substrate. The incident angle α is determined within a range of 50 ° to 80 ° as will be described later. For example, the incident angle α can be set to 75 °.

  The detection unit 24 detects light reflected by the substrate W of red laser light. Here, the light receiving unit 27 includes a line sensor in which a plurality of pixels (light receiving elements) are arranged in a line, and is arranged in a direction in which reflected light travels. For example, a CCD or COMS type line sensor can be arranged. The imaging optical system 28 is disposed between the substrate W and the light receiving unit 27 and forms an image of the laser reflected light on the light receiving surface of the light receiving unit 27.

  The polarizing element 26 can select (switchable) one of transmission of s-polarized light component (hereinafter referred to as s-polarized light) and blocking of p-polarized light component (hereinafter referred to as p-polarized light) and blocking of p-polarized light and blocking of s-polarized light. In this case, the polarizing element is constituted by a liquid crystal polarization modulator. However, a structure in which two polarizing filters having different polarizations are mechanically replaced, or a structure in which one polarizing filter is rotated may be employed.

  The substrate W on which the photoresist FD is formed on the surface of the base material BD is composed of an advanced package substrate such as FO-PLP (Fan-Out Panel Level Package) or FO-WLP (Fan-Out Wafer Level Package). ing. On the base material of the advanced package substrate, a semiconductor chip is molded into a resin material, and a plurality of wirings and insulating layers are formed. Therefore, unevenness occurs on the surface of the substrate. Moreover, since the roughening process etc. are also performed, the surface is not smooth.

  The photoresist FD formed in a layer on the base material BD has sensitivity to ultraviolet rays and does not have sensitivity to red laser light incident on the substrate W. Here, a liquid resist, a dry film resist or the like can be used, and a cover film may be attached to the surface of the photoresist.

  In the photoresist FD, a part of laser light (hereinafter referred to as incident light L1) incident on the substrate W is reflected on the surface thereof. The remaining laser light transmitted through the photoresist FD is reflected by the surface of the base material BD. As described above, since the surface of the substrate BD is not smooth, the laser light incident on the substrate BD is irregularly reflected.

  Therefore, when light reflected on the surface of the photoresist FD (hereinafter referred to as reflected light L2) and light irregularly reflected on the surface of the base material BD (hereinafter referred to as reflected light L3) enter the light receiving unit 27 as they are, the light The intensity distribution is a complex intensity distribution.

  FIG. 3 is a diagram showing a light intensity portion distribution when the reflected lights L2 and L3 are incident on the light receiving portion 27 as they are. The horizontal axis indicates the pixel position, and the vertical axis indicates the detected light amount at each pixel position.

  The light intensity distribution (light quantity distribution) detected along the light receiving line of the light receiving unit 27 is a complex intensity distribution in which a plurality of wavelength peaks appear irregularly. From such a light intensity distribution, it is necessary to extract a light intensity component corresponding to the reflected light L2 of the photoresist FD, and to detect the substrate position, that is, the surface position of the photoresist FD from the peak pixel position.

  In the present embodiment, the s-polarized light and the p-polarized light of the reflected light L2 and L3 are alternately incident on the light receiving unit 27 by switching the polarization direction blocked by the polarizing element 26 (polarization switching). Then, the peak pixel position of the reflected light L2 of the photoresist FD is detected by taking the difference between the light intensity distributions of s-polarized light and p-polarized light. This will be described below.

  FIG. 4 is a graph showing the reflectance of s-polarized light and p-polarized light when the incident angle to the photoresist is changed.

  It is known that the light L1 incident on the photoresist FD from an oblique direction has different reflectance between p-polarized light and s-polarized light, and the magnitude of the difference varies depending on the incident angle. When the refractive index n of the photoresist FD is 1.5 to 1.6, the reflectance of s-polarized light and p-polarized light is represented by lines P1 and P2. The Brewster angle B at which the reflectance of p-polarized light becomes zero is 60 ° here.

  When the incident angle is between 50 ° and 80 °, the s-polarized light has a higher reflectance than the p-polarized light. Therefore, the reflected light L2 incident on the light receiving unit 27 has a large s-polarized component. On the other hand, since the reflected light L3 from the base material BD becomes irregular reflection as described above, there is not much difference between the s-polarized light and the p-polarized light in the reflected light L3, and is included in the same degree.

  Therefore, if the reflected light L3 of the base material BD is separately obtained by separating it into s-polarized light and p-polarized light, and subtracting this, it is possible to remove most of the components of the reflected light L3. On the other hand, since most of the reflected light L2 of the photoresist FD is s-polarized light and has little p-polarized component, the reflected light L2 is obtained separately by separating it into s-polarized light and p-polarized light. The component of L2 remains. If the peak pixel position of the light intensity distribution of the reflected light L2 can be extracted, the substrate position can be obtained.

  FIG. 5 is a diagram showing an intensity distribution of light incident on the light receiving unit 27 when s-polarized light is transmitted and p-polarized light is blocked with respect to the reflected light (L2, L3).

  In FIG. 5, the light intensity distribution by the reflected light L2 of the photoresist FD is represented by G1, and the light intensity distribution by the reflected light L3 of the base material BD is represented by F1. For the sake of explanation, the light intensity distributions G1 and F1 are drawn with different waveforms. However, in the actual light intensity distribution, as is apparent from FIG. 4, the light intensity distributions (spectrums) of the photoresist FD and the substrate BD are shown. The distribution curve does not appear separately.

  The light intensity distribution G1 by the photoresist FD that is not irregularly reflected is symmetric with respect to the peak wavelength. On the other hand, the light intensity distribution F1 of the substrate BD that diffusely reflects is a complex intensity distribution having a plurality of peaks.

  FIG. 6 is a diagram showing an intensity distribution of light incident on the light receiving unit 27 when the p-polarized light is transmitted with respect to the reflected light (L2, L3) and the s-polarized light is blocked.

  Since most of the reflected light L2 from the photoresist FD is an s-polarized component, the light intensity distribution G2 has a light intensity distribution whose peak is sufficiently smaller than the light intensity distribution G1 shown in FIG. On the other hand, the light intensity distribution F2 of the reflected light L3 from the base material BD is not much different in its distribution characteristics (light intensity at each pixel position) and peak size compared to the light intensity distribution F1 in FIG.

  FIG. 7 is a diagram showing the light intensity distribution when the difference between the light intensity distribution (G1, F1) in FIG. 5 and the light intensity distribution (G2, F2) in FIG. 6 is taken. Here, the light intensity distribution of the photoresist FD is indicated by G3, and the light intensity distribution of the substrate BD is indicated by F3.

  As shown in FIG. 7, the light intensity distribution F <b> 3 of the base material BD has a small light intensity distribution due to the difference. On the other hand, the light intensity distribution G3 of the photoresist FD is a light intensity distribution having a larger peak than that. By removing the reflected light L3 of the base material BD that becomes a noise component and detecting the peak pixel position PT of the reflected light L2 of the photoresist FD, the surface position of the photoresist FD, that is, the substrate position can be detected.

  In order to extract the light intensity distribution of the reflected light L2 of the photoresist FD based on the difference between the s-polarized image data and the p-polarized image data, first, the s-polarized light intensity reflected by the photoresist FD is calculated using the photoresist. It is necessary to make it sufficiently larger than the p-polarized light reflected by the FD. At the same time, the difference between the s-polarized light that passes through the photoresist FD and is reflected by the substrate BD and the p-polarized light that passes through the photoresist FD and is reflected by the substrate BD needs to be as small as possible.

  Here, referring again to FIG. 4, the curve P1 representing the reflectance of the s-polarized light increases as the incident angle α increases, and exponentially increases from around the incident angle of 50 °. . On the other hand, the curve P2 representing the reflectance of p-polarized light gradually approaches a Brewster angle of 60 ° where the reflectance is zero, and when the Brewster angle exceeds 60 °, the reflectance increases greatly.

  When the incident angle is smaller than 50 °, the difference in reflectance between s-polarized light and p-polarized light is small. In this case, since the difference between the s-polarized light and the p-polarized light is not large in the reflected light L3 from the substrate BD, by taking the difference, some of the peaks of the reflected light L3 from the substrate BD that are noise components are all small. Become. However, since the reflectance of s-polarized light is as small as 15% or less, the peak of the light intensity distribution G3 (see FIG. 7) of the photoresist FD does not become sufficiently large.

  On the contrary, when the incident angle exceeds 80 °, the increase rate of the reflectance of p-polarized light exceeds the increase rate of the reflectance of s-polarized light, and the difference between the reflectances of s-polarized light and p-polarized light is reduced. This means that the difference in the light intensity between the s-polarized light and the p-polarized light of the reflected light L2 from the photoresist FD becomes small. If the difference between the image data is taken, the peak of the light intensity distribution G3 of the photoresist FD is extracted. The harder it gets.

  For this reason, the incident angle α is set in a range of 50 ° <α <80 ° where the difference between the reflectance of s-polarized light and the reflectance of p-polarized light is relatively large. When the Brewster angle B exceeds 60 °, the difference in reflectance increases, so it is preferable that the range is set to 60 ° <α <80 °.

  In particular, when the reflectance of s-polarized light is in the range of about 30% to 60%, the light intensity of s-polarized light reflected by the photoresist FD becomes sufficiently large, while the light of s-polarized light and p-polarized light reflected by the base material BD. Since the difference in intensity does not become so large, the incident angle α is preferably set to 65 ° <α <80 °.

  FIG. 8 is a diagram showing a flow of focus adjustment processing including substrate position detection. The focus adjustment process is performed for each substrate or shot area before pattern exposure.

  The light projecting unit 22 is operated to irradiate the substrate W with laser light (S101). At this time, by switching the polarization element 26, the s-polarized light is transmitted and the p-polarized light is blocked, and then the p-polarized light is transmitted and the s-polarized light is blocked (S102, S103). In the light receiving unit 27, reflected light of s-polarized light transmission and p-polarized light light is sequentially incident, and pixel signals corresponding to the light intensity distribution are sequentially output as image data. The image data is temporarily stored in a memory or the like not shown in FIG. The reflected light may be transmitted in the order of p-polarized light and s-polarized light.

  The image calculation unit 52 performs image data difference processing (S104). Then, a pixel position where the light intensity reaches a peak is extracted from the difference image data (S105). The pixel position corresponding to the reference (focused) substrate position is determined in advance, and focus adjustment is performed according to the difference (deviation) between the reference pixel position and the detected pixel position (S106). .

  As described above, according to the present embodiment, in the exposure apparatus 10 that projects pattern light onto the substrate W, the substrate position detection device 20 including the light projecting unit 22 and the detection unit 24 is provided. The detection unit 24 includes a polarizing element 26, a light receiving unit 27, and an imaging optical system 28, and the polarizing element 26 is controlled by a polarizing element control unit 29. At the time of focus adjustment, s-polarized reflected light and p-polarized reflected light enter the light receiving unit 27 in order by switching the polarizing element 26. The image calculation unit 52 obtains the difference between the image data indicating the light intensity distribution of s-polarized light and the image data indicating the light intensity distribution of p-polarized light, and detects the substrate position from the pixel position where the peak appears.

  By making the s-polarized reflected light and the p-polarized reflected light incident on the light receiving unit 27 in time series using the polarizing element 26, the reflected light L2 from the photoresist FD and the reflected light from the base material BD that diffusely reflects. The light in which the light intensity distribution of the light L3 appears can be detected as it is. In addition, with the single light receiving unit 27, there is no problem in uniquely associating the pixel position of the peak wavelength with the substrate position, and the substrate position can be detected with high accuracy.

  In this embodiment, since the polarization element 26 performs polarization switching control by voltage (electricity), s-polarized light and p-polarized light can be incident on the light receiving unit 27 with almost no time difference, and the substrate position can be detected quickly. It becomes. On the other hand, the polarizing element 26 is provided between the imaging optical system 28 and the light receiving unit 27. Accordingly, the detection unit 24 equipped with the polarizing element 26, the light receiving unit 27, and the imaging optical system 28 can be configured as a compact integrated device. At the same time, since only the reflected light passing through the imaging optical system 28 is polarized by the polarizing element 26, the light intensity distribution is obtained based on the reflected light in which the influence of the irregularly reflected light component that appears strongly near the surface of the substrate W is suppressed. Is possible.

  A plurality of substrate position detection devices may be provided to detect a plurality of positions on the substrate. For the light projecting unit 22, a light source other than a laser such as an LED may be used. The polarizing element 26 may be disposed on the substrate side with respect to the imaging optical system 28. The substrate position detection apparatus 20 can be applied not only to a projection exposure apparatus such as a stepper but also to other exposure apparatuses such as a maskless exposure apparatus.

DESCRIPTION OF SYMBOLS 10 Exposure apparatus 20 Substrate position detection apparatus 22 Light projection part 24 Detection part 26 Polarization element (liquid crystal polarization modulator)
27 Light Receiving Unit 28 Imaging Optical System 29 Polarizing Element Control Unit 52 Image Calculation Unit W Substrate FD Photoresist BD Base Material

Claims (10)

A light projecting unit that projects light from an oblique direction onto a substrate having a photoresist layer formed on the surface;
A polarizing element that is arranged in the reflection direction of the light and is capable of selecting an s-polarized component and a p-polarized component of the reflected light of the light;
A light receiving unit that receives the s-polarized component and the p-polarized component that have passed through the polarizing element by selection of the polarizing element;
A substrate position detecting apparatus, wherein a height position of a substrate is detected based on the s-polarized component and the p-polarized component.   The substrate position detection apparatus according to claim 1, wherein an incident angle α of light with respect to the substrate satisfies 50 ° <α <80 °.   3. The substrate position detecting apparatus according to claim 1, wherein the incident angle [alpha] of light with respect to the substrate satisfies B <[alpha] <80 [deg.], Where B is the Brewster angle on the photoresist surface.   4. The substrate position detection apparatus according to claim 1, wherein an incident angle α of light with respect to the substrate satisfies 65 ° <α <80 °. 5.   An image calculation unit that calculates a height position of the substrate based on a difference between the light intensity distribution of the s-polarized component incident on the light receiving unit and the light intensity distribution of the p-polarized component incident on the light receiving unit; 5. The substrate position detecting device according to claim 1, further comprising a substrate position detecting device.   6. The polarizing element according to claim 1, wherein the polarizing element is provided between an imaging optical system that forms an image of the reflected light on a light receiving surface of the light receiving unit and the light receiving unit. Substrate position detection device.   The substrate position detecting apparatus according to claim 1, wherein the polarizing element includes a liquid crystal polarization modulator.   The substrate position detecting device according to claim 1, wherein the light projecting unit is a laser light source.   An exposure apparatus comprising the substrate position detection apparatus according to claim 1. Light is projected from an oblique direction onto a substrate having a photoresist layer formed on the surface,
The reflected light of the light is incident on a polarizing element to select an s-polarized component and a p-polarized component,
The s-polarized component and the p-polarized component that sequentially pass through the polarizing element by the selection of the polarizing element are incident on a light receiving unit,
A substrate position detection method, comprising: detecting a height position of a substrate based on the s-polarized component and the p-polarized component received by the light receiving unit.

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