KR20240044792A - Reflective Fourier ptychographic microscopy using deep-ultraviolet - Google Patents

Abstract

The present invention relates to Deep-UltraViolet (DUV) reflective Fourier Ptychographic Microscopy (FPM). The purpose of the present invention is to provide a DUV reflective FPM that uses DUV (deep ultraviolet), rather than visible light, as a light source to lower the diffraction limit of the FPM, thereby achieving much higher resolution than before. Another object of the present invention is to eliminate the need for processing such as DUV coating on optical components on the optical path by introducing a rotating stage for applying a DUV light source, thereby simplifying the configuration and reducing manufacturing costs while achieving the desired performance. The goal is to provide a DUV reflective FPM that allows

Description

ＤＶ Reflective ＦＰＭ {Reflective Fourier ptychographic microscopy using deep-ultraviolet}

The present invention relates to DUV (Deep-UltraViolet) reflective FPM (Fourier Ptychographic Microscopy), and more specifically, to DUV reflective FPM, which further improves resolution in FPM, a large-area, high-resolution measurement technology.

Semiconductor packaging and displays are becoming more ultra-fine and ultra-integrated day by day. According to this trend, increasingly higher levels of resolution are required to measure microscopic defects occurring in semiconductor packaging or displays.

Among the technologies currently used to measure defects, scanning electronic microscopy (SEM) and atomic force microscopy (AFM) have the advantage of having ultra-high resolution of several nm, so they can be used at the laboratory level. However, these technologies require special measurement conditions such as vacuum, create an environment for measurement or post-processing, such as applying a conductive coating to the sample for measurement or cutting a cross section, and also require ultra-high resolution. Although it is high, there is a problem with the measurement speed being significantly low, so there are significant limitations to its use in mass production lines. Optical measurement equipment can be an alternative to SEM and AFM, but due to diffraction limit, the resolution is significantly reduced to at least several hundred nm.

Meanwhile, FPM (Fourier Ptychographic Microscopy) is a phase retrieval method developed by Guoan Zheng in 2013. The existing microscope imaging method focuses the beam through a lens and obtains only the intensity information of the light through a detector, so information about the phase cannot be obtained. In FPM, by injecting light not only vertically but also from various angles, images of various phases, such as bright field images and dark field images, can be obtained, and these images can be used to achieve resolution. ) can be improved.

FPM can calculate phase without using a reference beam like existing digital holographic microscopy. This FPM can calculate the phase without a reference beam, so the system can be compact, and it has the advantage of being resistant to vibration because the signal beam and reference beam are not differentiated. In addition, the existing digital holographic microscope has a small FOV (field of view) and DOF (depth of focus) when using a high NA objective lens to obtain high resolution, whereas FPM replaces the condenser lens with an LED array to achieve high resolution. By enabling an illumination angle, high resolution can be obtained even with a low NA objective lens, which has the advantage of having a wide FOV and DOF. Additionally, since a high illumination angle is achieved with an LED array, there is no need for a mechanical driver.

FPM was initially composed of a transmissive type, that is, a form in which an image is obtained by the light irradiated from a light source passing through the object to be measured and reaching the photodetector, and it can be usefully used in the bio and medical fields to observe transparent objects to be measured such as biological tissue. You can. However, because the measurement object in the semiconductor field is opaque, it is difficult to apply this transmissive FPM. Accordingly, a reflective FPM is being developed and used in which the light emitted from the light source is reflected from the measurement object and reaches the photodetector to obtain an image. It is known that in the case of reflective FPM, very high resolution of about 250 nm or less can be obtained. Korean Patent Registration No. 2315016 (“Reflective FPM using sculptural mirror and screen”, October 14, 2021) clearly discloses the basic structures of such transmissive FPM and reflective FPM.

Until now, FPM has used visible light, but since the diffraction limit is proportional to λ/NA, there is a limit to lowering the diffraction limit, making it difficult to further improve resolution.

Korean Patent Registration No. 2315016 (“Reflective FPM using sculptural mirror and screen”, 2021.10.14.)

Therefore, the present invention was conceived to solve the problems of the prior art as described above, and the purpose of the present invention is to lower the diffraction limit of FPM by using DUV (deep ultraviolet) rather than visible light as a light source, thereby reducing the The goal is to provide a DUV reflective FPM that allows for higher resolution. Another object of the present invention is to eliminate the need for processing such as DUV coating on optical components on the optical path by introducing a rotating stage for applying a DUV light source, thereby simplifying the configuration and reducing manufacturing costs while achieving the desired performance. The goal is to provide a DUV reflective FPM that allows

The DUV reflective FPM (100) of the present invention for achieving the above-mentioned purpose is a light source when, in reflective FPM (Fourier Ptychographic Microscopy), the direction in which light travels is forward and the opposite direction is backward. (111), a rotating stage 112 that is formed in the form of a mask that changes at a predetermined period and allows only a portion of the light coming from the light source 111 to pass through, and is disposed in front of the rotating stage 112 to transmit only light of the DUV (Deep UltraViolet) wavelength. A light generating unit 110 including a DUV filter 113 that passes through; a light transmitting unit 120 that forms an optical path so that the light output from the light generating unit 110 travels to a predetermined location; An optical measurement unit 130 that obtains an image of the measurement object 500 by irradiating the light transmitted by the light transmitting unit 120 to the measurement object 500 using an objective lens 132; It includes, and the mask shape that changes at a predetermined period of the rotation stage 112 may be a form that implements the role of an LED ring in which a plurality of LEDs arranged in a ring shape are turned on/off at a predetermined period.

At this time, the rotation stage 112 passes only the light corresponding to the center line (L1) and the peripheral line (L2) among the light coming from the light source 111, and the position of the peripheral line (L2) is at the center line (L1). It may be formed to rotate around the center at a predetermined period.

In addition, the rotation stage 112 includes a rotating body 112a that rotates at a predetermined period about the optical axis, and a fixed body that is fixedly stacked with the rotating body 112a and rotatably supports the rotating body 112a. (112b), a rotation center hole 112c formed at the center of the rotation body 112a, a single spaced spaced around the rotation center hole 112c by a predetermined distance r from the rotation center hole 112c. A rotation peripheral hole (112d), a fixed center hole (112e) formed at the center of the fixed body (112b), and the fixed center hole (112e) is spaced around the fixed center hole (112e) by the separation distance (r). It may include a plurality of fixed peripheral through holes 112f arranged at radial equal intervals from each other.

In addition, the rotation stage 112 forms a fixed center line L1 as the position where the rotation center hole 112c and the fixed center hole 112e are formed is always open and light always passes through. The position where the rotating peripheral through hole 112d, which rotates at a determined period, overlaps with any one selected from the plurality of fixed peripheral through holes 112f is in a periodically open state and the peripheral line L2 rotates periodically as light passes periodically. can be formed.

Additionally, the separation distance (r) of the rotating stage 112 may be determined depending on the focal length and numerical aperture (NA) of the objective lens 132.

Additionally, the light source 111 is preferably a plasma light source.

In addition, the light transmitting unit 120 includes a first mirror 121 and a second mirror that change the optical path by reflecting the light of the center line L1 and the peripheral line L2 coming from the light generating unit 110. (122), a first lens 123 arranged to adjust the distance between the center line (L1) and the peripheral line (L2) by refracting the light reflected through the first and second mirrors (121) and (122), and It may include a second lens 123.

In addition, the light measuring unit 130 is a beam splitter that reflects the light transmitted from the light transmitting unit 120 and sends it to the measurement object 500, and transmits the light reflected from the measurement object 500. (131), an objective lens 132 that focuses and irradiates the light reflected from the beam splitter 131 onto the measurement object 500, and a tube lens that focuses the light passing through the beam splitter 131. (133), it may include a photodetector 134 that detects the light focused from the tube lens 133 and acquires an image of the measurement object 500.

According to the present invention, by lowering the diffraction limit of FPM by using DUV (deep ultraviolet) rather than visible light as a light source, there is a great effect of achieving much higher resolution than before.

On the other hand, when using an optical system consisting of a beam steering mirror and various optical components used in the conventional visible light FPM, or when creating an LED array using DMD, if only the light source is changed to DUV, all of the light in the optical path is changed. Because DUV coating must be applied to the mirror, there may be a problem that the cost increases significantly. However, in the present invention, a rotating stage was introduced to optimize the application of the DUV light source. The application of this rotating stage eliminates the need for DUV coating on optical parts, which has the effect of minimizing economic losses in device configuration. there is.

In addition, according to the present invention, the economic effect can be further increased by using a plasma light source rather than an excimer laser among DUV light sources, which has no speckle noise, has sufficiently high output, and is much cheaper. . In addition, because the plasma light source is much more compact than the excimer laser, it has the great effect of miniaturizing the device and applying it directly to the product mass production line to realize a simultaneous manufacturing and measurement process that measures defects in real time during production. .

1 is a configuration diagram of a DUV reflective FPM of the present invention.
Figure 2 is a detailed view of an embodiment of the rotating stage of the present invention.
Figure 3 is a comparative diagram of a conventional LED ring and a rotating cage of the present invention.
Figure 4 is an example image acquired by the DUV reflective FPM of the present invention.

Hereinafter, the Deep-UltraViolet (DUV) reflective Fourier Ptychographic Microscopy (FPM) according to the present invention having the above-described configuration will be described in detail with reference to the attached drawings.

Figure 1 is a configuration diagram of the DUV reflective FPM of the present invention. As shown in FIG. 1, the DUV reflective FPM 100 of the present invention may largely include a light generating unit 110, a light transmitting unit 120, and a light measuring unit 130. At this time, in the case of the light transmitting unit 120 and the light measuring unit 130, the light transmitting unit 120 forms an optical path so that the light output from the light generating unit 110 travels to a predetermined location. The light measuring unit 130 irradiates the light transmitted by the light transmitting unit 120 to the measurement object 500 using the objective lens 132 to create an image of the measurement object 500. It plays an acquisition role and is not much different from the conventional reflective FPM in terms of role and composition.

However, unlike the conventional FPM, the present invention uses DUV (deep ultraviolet), that is, light with a wavelength of 193 nm, rather than visible light, as a light source, lowering the diffraction limit of the FPM, making it possible to obtain much higher resolution than before. For this purpose, a new configuration was introduced to the light generating unit 110. More specifically, in the present invention, the light generator 110 includes a light source 111 that emits continuous high-output light, a rotating stage 112, and a DUV filter 113, thereby enabling DUV to be used. The optical measurement device is realized very effectively and economically. Below, each part will be described in more detail. At this time, the direction in which light travels is called forward, and the opposite direction is called backward.

First, the light source 111 and the DUV filter 113 will be described. The light source 111 serves to generate light. At this time, in the present invention, the DUV filter 113 is used to pass only light of the DUV wavelength among the light emitted from the light source 111, so the light source 111 It does not need to generate light of a specific wavelength, that is, DUV.

As explained earlier, FPM to date has used visible light, but since the diffraction limit is proportional to λ/NA, there is a limit to lowering the diffraction limit, making it difficult to further improve resolution. Accordingly, there have been attempts to use light outside the visible light range, especially DUV, but there are several limitations to directly applying DUV to the conventional FPM, which was based on visible light, as follows. First, in most conventional FPMs, LEDs that generate light in the visible light range are used as light sources, but there is currently no high-output LED that generates light in the DUV range among LEDs. In addition, when using an optical system consisting of a beam steering mirror and various optical components used in conventional visible light FPM, or when creating an LED array using DMD, if only the light source is changed to DUV, all of the light in the optical path is changed. Because DUV coating must be applied to the mirror, there may be a problem that the cost increases significantly.

In addition, one of the widely used light sources that generate light of a specific wavelength is the excimer laser. Although the excimer laser has the advantage of high output, it generates pulsed light rather than continuous light, and is very expensive and difficult to handle. The downside is that it is difficult. In addition, in the case of coherent sources such as lasers, speckle noise occurs, so an additional process to remove this is required.

In the present invention, since it is not necessary to generate light of a specific wavelength, it is sufficient to generate light of appropriate high output. Therefore, in the present invention, a plasma light source can be used as the light source 111. Plasma light sources have sufficiently high output but are much cheaper than excimer lasers, and since they have only partial coherence like LEDs, there is no inversion noise and no additional post-processing is required. In addition, because the plasma light source is much more compact than the excimer laser, for example, when applying the FPM of the present invention to a product mass production line, the volume of the device itself can be much smaller and lighter, making it much more advantageous for field application. . That is, in the present invention, by applying a plasma light source to the light source 111, not only can sufficient performance as desired be achieved while achieving economic effects, but also the advantage of greatly expanding the application range of the device can be obtained.

In the present invention, sufficient high output is secured by using the light source 111 as a plasma light source, and only DUV can be easily extracted from the light emitted from the light source 111 by using the DUV filter 113. Here, there is one more element required for the light source in FPM, which is that the angle of the light from the light source must be able to change in various ways. As explained earlier, because visible light was used in the past, it was possible to easily realize the operation of irradiating light at various angles by arranging a plurality of LEDs that generate visible light in a ring shape and selectively turning them on or off. . However, as explained earlier, since there are no LEDs that generate DUV in existence, it is impossible to construct an LED ring, and since the plasma light source generates light with a large numerical aperture (large NA), a separate device is required to create a beam form suitable for FPM. There must be.

In the present invention, this problem is solved by using the rotating stage 112. To briefly explain, the rotation stage 112 of the present invention is formed in the form of a mask that changes at a predetermined period and serves to pass only a portion of the light coming from the light source 111. At this time, the shape of the mask that changes at a predetermined period of the rotation stage 112 becomes a form that implements the role of an LED ring in which a plurality of LEDs arranged in a ring shape are turned on/off at a predetermined period. To be more specific, as shown in FIG. 1, the rotation stage 112 basically passes only the light corresponding to the center line (L1) and the peripheral line (L2) among the light coming from the light source 111. I order it. However, at this time, the position of the peripheral line (L2) is formed to rotate at a predetermined period around the center line (L1), and for this purpose, the rotation stage 112 is also configured to rotate as a mask.

Figure 2 shows a detailed view of an embodiment of the rotating stage of the present invention. As shown in Figure 2, the rotating stage 112 of the present invention may include a rotating body 112a and a fixed body 112b, each of which has several holes formed to allow light to pass through. do.

The rotating body 112a rotates at a predetermined period around the optical axis. At this time, a rotation center hole 112c and a rotation peripheral hole 112d are formed in the rotation body 112a. As shown in FIG. 2, the rotation center hole 112c is formed at the center of the rotation body 112a. In addition, a single rotation peripheral hole 112d is formed on the rotation body 112a, and is arranged around the rotation center hole 112c to be spaced apart from the rotation center hole 112c by a predetermined distance r. . At this time, the separation distance (r) is determined according to the focal length and numerical aperture (NA) of the objective lens 132.

The fixed body 112b is fixedly arranged to be stacked with the rotating body 112a and rotatably supports the rotating body 112a. At this time, a fixed center hole 112e and a fixed peripheral hole 112f are formed in the fixed body 112b. As also shown in FIG. 2, the fixing center hole 112e is formed at the center of the fixing body 112b. In addition, a plurality of the fixing peripheral through-holes 112f are formed on the fixing body 112b, and are spaced around the fixing center through-hole 112e by the distance r from the fixing center through-hole 112e and radially radiate from each other. They are placed at equal intervals.

When the rotating body 112a and the fixed body 112b formed in this way are stacked on each other, the positions where the rotating center through hole 112c and the fixed center through hole 112e are formed are always open. In other words, light can always pass through and its position is fixed and does not change. That is, when the rotation stage 112 is disposed in front of the light source 111, the position where the rotation center hole 112c and the fixed center hole 112e are formed are always open and fixed as light always passes through. It is possible to form a central line (L1).

Meanwhile, since the rotating body 112a rotates at a predetermined period, the rotation peripheral hole 112d also rotates at a predetermined period. When the rotating peripheral through hole 112d is positioned to overlap with one selected among the plurality of fixed peripheral through holes 112f while rotating, this position becomes open at this moment and allows light to pass through. That is, the position where the rotation peripheral through hole 112d, which rotates at a predetermined period, overlaps with any one selected among the plurality of fixed peripheral through holes 112f is periodically opened, and as light passes periodically, it rotates periodically. A peripheral line (L2) can be formed.

Figure 3 shows a comparative diagram of a conventional LED ring and a rotating stage of the present invention.

The upper diagram of Figure 3 shows the operation of the LED ring used in a conventional FPM. LED 1 arranged in the center is always on, and LEDs 2 to 9 arranged radially at equal intervals around it turn on and off according to time. , LED 3, … Turns on in order. Accordingly, beams of various angles can be realized as light sources, and high-resolution images can be obtained by obtaining and processing images from each.

The lower view of FIG. 3 shows the operation of the rotation stage 112 of the present invention. POS 1, the central position, is always open and corresponds equally to the operation of LED 1, which is always on. When the rotating body 112a rotates, the position becomes open when the rotation peripheral through hole 112d and the fixed peripheral through hole 112f overlap. In other words, locations that are selectively open depending on time are POS 2, POS 3, … They change in order, with LED 2, LED 3, etc. turning on selectively depending on the time. It corresponds equally to the sequentially changing movements.

As such, in the present invention, the rotation stage 112 can be used to implement exactly the same operation of the LED ring used in the conventional FPM. Of course, the detailed configuration of the rotation stage 112 of the present invention is not limited to FIG. 2, and as shown in FIG. 3, any structure that can implement the operation of the LED ring can be modified and designed.

As described above, the configuration of the light transmitting unit 120 and the light measuring unit 130 is not significantly different from the operation of the components corresponding to the light transmitting unit and the light measuring unit in the conventional FPM, and is briefly described below. Let me just explain.

First, the light transmitting unit 120 is a first mirror that changes the optical path by reflecting the light of the center line (L1) and the peripheral line (L2) coming from the light generating unit 110, as shown in FIG. (121) and the second mirror 122, which are arranged to adjust the gap between the center line (L1) and the peripheral line (L2) by refracting the light reflected through the first and second mirrors (121) and (122). It may include a first lens 123 and a second lens 123. Of course, this does not limit the present invention, and additional mirrors or lenses may be provided if the optical path is configured differently as needed. To elaborate, assuming that a DUV light source is directly applied to a conventional FPM, there is a risk that the manufacturing cost of the device will increase significantly as DUV coating must be applied to all of the various parts forming this optical path. However, in the present invention, the operation of the LED ring is implemented using the rotating stage 112, and the light thus produced is passed through the DUV filter 113 to create a DUV beam suitable for use in FPM, so the light Since there is no need to apply DUV coating to the optical components included in the transmission unit 120, the risk of increasing device manufacturing costs can be fundamentally eliminated.

Next, as shown in FIG. 1, the light measuring unit 130 reflects the light transmitted from the light transmitting unit 120 and sends it to the measurement object 500, and the measurement object 500 A beam splitter 131 that transmits the light reflected from the beam splitter 131, an objective lens 132 that focuses and irradiates the light reflected from the beam splitter 131 to the measurement object 500, and the beam splitter 131. It may include a tube lens 133 that focuses the light passing through and a photodetector 134 that detects the light focused in the tube lens 133 to obtain an image of the measurement object 500. Since the operations and roles of each part are not significantly different from those of optical components corresponding to a typical conventional FPM, further explanation is omitted here.

Figure 4 is an example of an image acquired by the DUV reflective FPM of the present invention. As shown in each image, in the order of top → bottom / left → right, the first image is an image acquired when only POS 1 is open (i.e., only LED 1 in the LED ring is turned on), and the second image is obtained when only POS 1 is open. Image acquired when POS 1 and 2 are open (i.e. LEDs 1 and 2 in the LED ring are on), the third image is when POS 1, 2 and 3 are open (i.e. LEDs 1 and 2 in the LED ring are on). Image acquired when 3 corresponds to the on state), … am. As shown, it can be intuitively confirmed that the resolution of the image increases significantly as images acquired at various angles are further processed.

In other words, it is confirmed by the experimental results of FIG. 4 that in the present invention, when the operation of the LED ring is implemented using the rotation stage 112 and measured in the FPM method, the image can be successfully acquired and the resolution can be improved. Accordingly, it is also clearly confirmed that resolution can be improved by lowering the diffraction limit by applying DUV, which has not been used as measurement light for FPM in the past.

The present invention is not limited to the above-described embodiments, and its scope of application is diverse, and anyone skilled in the art can understand it without departing from the gist of the invention as claimed in the claims. Of course, various modifications are possible.

100: DUV reflective FPM
110: light generating unit
111: light source 112: rotating stage
112a: rotating body 112b: fixed body
112c: Rotation center through hole 112d: Rotation peripheral through hole
112e: Fixed center through hole 112f: Fixed peripheral through hole
113: DUV filter
120: Light transmission unit
121: first mirror 122: second mirror
123: first lens 124: second lens
130: Optical measurement unit
131: Beam splitter 132: Objective lens
133: tube lens 134: photodetector
500: Measurement object

Claims (8)

In reflective FPM (Fourier Ptychographic Microscopy), when the direction in which light travels is called forward and the opposite direction is called backward,
A light source 111, a rotating stage 112 that is formed in the form of a mask that changes at a predetermined period and allows only a portion of the light coming from the light source 111 to pass, and is disposed in front of the rotating stage 112 and emits a DUV (Deep UltraViolet) wavelength. A light generator 110 including a DUV filter 113 that allows only light to pass through;
a light transmitting unit 120 that forms an optical path so that the light output from the light generating unit 110 travels to a predetermined location;
An optical measurement unit 130 that acquires an image of the measurement object 500 by irradiating the light transmitted by the light transmitting unit 120 to the measurement object 500 using an objective lens 132;
Includes,
The mask shape that changes at a predetermined period of the rotation stage 112 is,
A DUV reflective FPM, characterized in that a plurality of LEDs arranged in a ring shape implement the role of an LED ring in which a plurality of LEDs are turned on/off at a predetermined cycle.
The method of claim 1, wherein the rotation stage 112 is:
Among the light coming from the light source 111, only the light corresponding to the center line (L1) and the peripheral line (L2) passes through, and the position of the peripheral line (L2) is formed to rotate at a predetermined period around the center line (L1). Features DUV reflective FPM.
The method of claim 2, wherein the rotation stage (112) is:
A rotating body 112a that rotates at a predetermined period around the optical axis,
A fixed body (112b) that is fixedly arranged to be stacked with the rotating body (112a) and rotatably supports the rotating body (112a),
A rotation center hole (112c) formed at the center of the rotation body (112a),
A single rotation peripheral aperture (112d) disposed around the rotation center aperture (112c) spaced apart from the rotation center aperture (112c) by a predetermined distance (r),
A fixed center hole (112e) formed at the center of the fixed body (112b),
A plurality of fixed peripheral through holes (112f) are spaced apart from the fixed center through hole (112e) by the distance (r) around the fixed center through hole (112e) and are arranged at radial equal intervals from each other.
DUV reflective FPM comprising:
The method of claim 3, wherein the rotation stage 112 is:
The positions where the rotation center hole 112c and the fixed center hole 112e are formed are always open and light always passes through them, forming a fixed center line L1,
The position where the rotation peripheral through hole 112d, which rotates at a predetermined period, overlaps with one selected among the plurality of fixed peripheral through holes 112f is in a periodically open state and the peripheral line L2 rotates periodically as light passes periodically. ) DUV reflective FPM, characterized in that forming.
The method of claim 3, wherein the rotation stage 112 is:
DUV reflective FPM, wherein the separation distance (r) is determined according to the focal length and numerical aperture (NA) of the objective lens 132.
The method of claim 1, wherein the light source 111 is:
DUV reflective FPM characterized by being a plasma light source.
The method of claim 1, wherein the light transmitting unit 120,
A first mirror 121 and a second mirror 122 that change the optical path by reflecting the light of the center line (L1) and the peripheral line (L2) coming from the light generator 110,
A first lens 123 and a second lens ( 123)
DUV reflective FPM comprising:
The method of claim 1, wherein the light measurement unit 130,
A beam splitter 131 that reflects the light transmitted from the light transmitting unit 120 and sends it to the measurement object 500, and transmits the light reflected from the measurement object 500,
An objective lens 132 that focuses and irradiates the light reflected from the beam splitter 131 onto the measurement object 500,
A tube lens (133) that focuses the light passing through the beam splitter (131),
A photodetector 134 that detects the light focused from the tube lens 133 and acquires an image of the measurement object 500.
DUV reflective FPM comprising:

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