Optical device

Abstract

To provide an optical device which can remove measurement noise due to a lower layer other than a measurement object.SOLUTION: An optical device 100 comprises: a light source 101; an illumination side pinhole 102 which is arranged on an optical path of the light source 101 and a sample; a lens 110 which narrows down measurement light in the order from the sample side toward an imaging plane; an imaging side pinhole 111; a lens 112 which forms parallel light; and an image sensor 113. The illumination side pinhole 102 and the imaging side pinhole 111 are arranged such that the pinhole centers respectively match the optical axis, and the imaging side pinhole 111 removes reflection light equal to or less than two layers from the surface of the sample.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an optical device, for example, an optical device for measuring shape errors of a three-dimensional structure formed on a wafer in a semiconductor manufacturing process. [Background technology]

[0002] In the semiconductor manufacturing process, it is necessary to measure the shape of three-dimensional structures formed on a wafer, which affects device performance. The dimensions of the semiconductor device patterns to be measured today exceed the resolution of ordinary optical microscopes, making shape measurement with an optical microscope difficult. Therefore, to directly measure the shape, it is necessary to use a method with higher resolution, such as an electron microscope, but the problem is that the measurement time is extremely long. Optical measurement techniques and equipment such as scatterometry, which do not directly resolve the shape of the object being observed but instead use responses such as reflectance to determine the average shape of the illuminated area, have become indispensable for the mass production of semiconductor devices in terms of measurement speed.

[0003] On the other hand, as device patterns become finer, the measurement accuracy required is becoming higher. There is a demand for highly sensitive detection of error signals that have decreased due to the miniaturization of patterns.

[0004] Patent Document 1 proposes a method in which a detector is placed in the pupil conjugate plane (Fourier transform plane) of the objective lens, rather than in an image of a device pattern formed on a wafer as in a normal optical microscope, to detect the diffraction pattern appearing on the pupil plane and changes in the distribution intensity within the pupil plane, thereby enabling highly sensitive measurement of critical dimensions (CD) and pattern overlay measurements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 8,054,467 Summary of the Invention [Problem to be solved by the invention]

[0006] Semiconductor devices are made up of a variety of stacked patterns through hundreds of manufacturing processes. Device pattern dimensions are becoming finer not only in the planar direction but also in three dimensions, and the distance between each stacked pattern in the depth direction is also becoming shorter. Semiconductor devices also use many light-transmitting materials, and when performing optical measurements, signals from other patterns than the one being measured are mixed in, causing measurement noise and reducing measurement sensitivity. This becomes more pronounced as the distance between stacked patterns becomes shorter.

[0007] CD metrology, which measures the dimensions of devices, has the problem that signals from underlying patterns other than the process pattern being measured near the surface become measurement noise and reduce measurement accuracy.

[0008] In addition, in overlay measurement, a pattern dedicated to overlay measurement, which is larger in size than the device pattern, was previously formed outside the device pattern and measured, but as device patterns become finer, the error between the measurement results of the dedicated measurement pattern and the actual device overlay has become large, and overlay measurement using the device pattern is now required. In overlay measurement, the overlay error of patterns of about the top two layers is measured, so the signal of the lower layer pattern becomes noise, which causes a problem of reducing measurement accuracy.

[0009] It is believed that Patent Document 1 detects unnecessary information from layers below the device that are out of focus of the optical system. [Means for solving the problem]

[0010] An optical device in one embodiment comprises a light source, an illumination-side pinhole arranged on the optical path between the light source and the sample, a lens that narrows the measurement light, an image-side pinhole, a lens that collimates the light, and an image sensor, in that order from the sample side toward the image plane, the illumination-side pinhole and the image-side pinhole are arranged so that their pinhole centers coincide with the optical axis, and the image-side pinhole removes two layers or less of reflected light from the surface of the sample.

[0011] According to an embodiment of the optical device, it is possible to remove light reflected from a lower layer pattern that is defocused due to the Confocal effect.

[0012] In one embodiment of the optical device, the image-side pinhole may include, in order from the sample side toward the image plane, a ring-shaped filter and a pinhole.

[0013] According to an embodiment of the optical device, diffracted light at the edge of the pinhole can be removed.

[0014] In one embodiment, the image-side pinhole may further include a ring-shaped filter on the image-plane side of the pinhole.

[0015] According to an embodiment of the optical device, diffracted light at the edge of the pinhole can be further removed.

[0016] In one embodiment of the optical device, the image-side pinhole may have a shape in which a pinhole is formed in a transparent material, and the thickness of the substrate may be such that a half-wavelength phase shift occurs with respect to the illumination wavelength.

[0017] According to an optical device of one embodiment, the diffracted light is irradiated to a position outside the pupil of the image sensor by the image-side pinhole, so that measurement noise can be reduced.

[0018] An optical device according to one embodiment may include an illumination pupil shape controller having a light-shielding portion at the center of the optical axis, on the sample side of the illumination-side pinhole, and may further include a calculation processing unit that removes the influence of the pinhole by subtracting a pinhole diffracted light component from the imaging pupil plane light amount distribution obtained from the image sensor.

[0019] In one embodiment of the optical device, the arithmetic processing unit may be configured to predict a distribution other than that of the light shielding portion from the light distribution on the imaging pupil plane obtained from the image sensor, which is at a position conjugate to the light shielding portion of the illumination pupil shape controller, and calculate a pinhole diffracted light component.

[0020] In one embodiment, the arithmetic processing unit may obtain the distribution prediction of the area other than the light-shielding area by performing an interpolation process between the light-shielding areas.

[0021] According to the optical device of one of these embodiments, the diffracted light at the edge of the pinhole can be removed by calculation. Effect of the Invention

[0022] According to the optical device of the present invention, measurement noise caused by layers below other than the measurement target can be eliminated. [Brief description of the drawings]

[0023] [Figure 1] 1 is a side view showing a schematic configuration of an optical device according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a photometry section of an optical device 100 according to a first embodiment; [Diagram 3] FIG. 13 is a diagram showing an example of diffracted light due to a pinhole. [Figure 4] 4A to 4C are diagrams illustrating an example of noise removal by an image-side pinhole 111 in the optical device according to the first embodiment. [Diagram 5] 2 is a cross-sectional view showing an example of an image-side pinhole 111 in the optical device according to the first embodiment. FIG. [Figure 6] FIG. 2 is a diagram illustrating an example of an illumination pupil shape controller 104 in the optical device according to the first embodiment. [Figure 7] 4 is a diagram illustrating an example of pupil distribution processing of the optical device according to the first embodiment. FIG. [Figure 8] 13 is a diagram showing an example of noise removal by an image-side pinhole 111 in the optical device according to the second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] (Embodiment 1) Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a side view showing a schematic configuration of an optical device according to the first embodiment. In Fig. 1, the optical device 100 includes a light source 101, an illumination-side pinhole 102, a first lens 103, an illumination pupil shape controller 104, an illumination-side polarization controller 105, a beam splitter 106, an objective lens 107, an image-side polarization controller 108, a second lens 110, an image-side pinhole 111, a third lens 112, and an image sensor 113.

[0025] The light source 101 is configured to generate light to be irradiated onto the sample 150. For example, the light source 101 is preferably a laser light source.

[0026] The illumination-side pinhole 102 uses the light emitted from the light source 101 as a point light source. The illumination-side pinhole 102 is, for example, a pinhole having a circular transmission portion on the central optical axis of the light source.

[0027] The first lens 103 is a lens that converts the light transmitted through the illumination side pinhole 102 into parallel light.

[0028] Illumination pupil shape controller 104 controls the beam shape of light from first lens 103. By providing a light-shielding portion in the illumination pupil shape controller 104, it becomes possible to perform interpolation to remove pinhole diffraction in processing after image detection. For example, illumination pupil shape controller 104 is an annular filter with a light-shielding portion in the center.

[0029] The illumination side polarization controller 105 transmits a predetermined polarization of the light from the illumination pupil shape controller 104 .

[0030] The beam splitter 106 reflects the light from the illumination-side polarization controller 105 and directs it to an objective lens 107. The beam splitter 106 also transmits the light reflected from the sample to an imaging-side polarization controller 108.

[0031] The objective lens 107 focuses the light from the beam splitter 106 on the surface of the measurement target sample 150. The objective lens 107 also refracts the light reflected from the sample 150 and directs it towards the beam splitter 106.

[0032] The imaging side polarization controller 108 transmits a predetermined polarization of the light from the beam splitter 106 (light reflected from the sample).

[0033] The second lens 110 is a lens that converges the light from the image-side polarization controller 108 so that the light is focused at the position of the image-side pinhole 111 .

[0034] The image-side pinhole 111 is disposed on a sample conjugate plane in the optical axis direction. The illumination-side pinhole 102 and the image-side pinhole 111 are disposed so that the pinhole centers coincide with the optical axis. The image-side pinhole 111 removes two or fewer layers of reflected light from the surface of the sample.

[0035] The third lens 112 is a lens that converts the light from the image-side pinhole 111 into parallel light. The image sensor 113 is an image sensor that detects light from the third lens 112. The image sensor 113 is set on the pupil plane.

[0036] With the above configuration, the optical device 100 measures the surface of a sample. Next, the operating principle of the optical device 100 will be described.

[0037] First, a laser light source is used as the light source 101, and an illumination-side pinhole 102 is placed immediately after emission to form a point light source. The light beam diverging from the point light source is collimated by a first lens 103, and after passing through an illumination pupil shape controller 104 and an illumination-side polarization controller 105, a point light source image is formed on an observation sample (wafer) by an objective lens 107. The reflected light from the sample passes through the objective lens 107 and a beam splitter 106, then passes through an imaging-side polarization controller 108, and an intermediate image is formed by a second lens 110. An imaging-side pinhole 111 is placed at the intermediate image position. The light beam passing through the imaging-side pinhole 111 is collimated by a third lens 112, and observed by an image sensor 113 placed on the pupil plane.

[0038] Next, the principle of cutting off light reflected from a portion two layers or less from the surface of the sample to be measured will be described. Fig. 2 is a schematic diagram of a photometry portion of the optical device 100 according to the first embodiment. Since the reflected light from the sample 150 will be described in Fig. 2, the light source 101, the illumination side pinhole 102, the first lens 103, the illumination side polarization controller 105, and the illumination pupil shape controller 104 are omitted. Furthermore, since the configuration of cutting off light reflected from a portion two layers or less from the surface of the sample to be measured will be described in Fig. 2, the imaging side polarization controller 108 is omitted.

[0039] For example, when the sample 150 has a layered structure such as a semiconductor device, not only the light reflected from the surface of the sample (solid line) but also the light reflected from an underlying pattern not being measured (dotted line) travels through the optical system from the objective lens 107 to the second lens 110.

[0040] In conventional methods, light reflected from underlying patterns that are not the measurement target reaches the image sensor, and the obtained pupil distribution is affected by the underlying patterns, resulting in measurement noise.

[0041] The optical device 100 of the first embodiment has an image-side pinhole 111 on the sample conjugate plane to remove light reflected from an underlying pattern that is defocused due to the Confocal effect. For example, when the sample is a semiconductor device, only the pattern to be measured is detected by the image sensor 113, enabling measurement with higher sensitivity.

[0042] Next, the image-side pinhole 111 will be described in detail. Fig. 3 is a diagram showing an example of diffracted light by a pinhole. As shown in Fig. 3, an in-focus light ray 211 passes through the pinhole 201 because the position of the pinhole 201 is the focal point. On the other hand, a defocus light ray 212 that is removed near the edge of the pinhole generates diffracted light due to the pinhole edge. This diffracted light generates an intensity distribution due to diffracted light that is unrelated to the distribution on the pupil plane due to the sample structure, and becomes measurement noise when it reaches the image sensor.

[0043] An example of this noise removal is shown in Fig. 4. Fig. 4 is a diagram showing an example of noise removal by image-side pinhole 111 of the optical device according to the first embodiment. Fig. 4 also shows a cross-sectional view of image-side pinhole 111. In Fig. 4, image-side pinhole 111 includes, from the object side, annular filter 301 and pinhole 302.

[0044] The ring filter 301 has a circular light blocking portion 311 on the central optical axis, a ring-shaped light transmitting portion 312, and a light blocking portion 313 having a circular hole.

[0045] The pinhole 302 has a circular transmitting portion and is disposed on the image plane. The circular light blocking portion of the ring filter 301 and the circular light transmitting portion of the pinhole 302 are arranged so as to coincide on the central optical axis.

[0046] 4, an in-focus light ray 311 passes through an annular filter 301 and a pinhole 302. A defocus light ray 312 is diffracted by the annular filter 301, and emits diffracted light 323. However, the diffracted light 323 is blocked by the light-blocking portion of the pinhole 302. As a result, the diffracted light is largely cut off by the image-side pinhole 111.

[0047] As a specific configuration of the image-side pinhole 111, a glass plate may be provided between the annular filter 301 and the pinhole 302. FIG. 5 is a cross-sectional view showing an example of the image-side pinhole 111 of the optical device according to the first embodiment. In FIG. 5, the image-side pinhole 111 includes the annular filter 301, the pinhole 302, and a glass plate 303. The annular filter 301 and the pinhole 302 have light-shielding portions formed by Cr coating the glass plate 303. The shape of the transmitting portion is the same as that of FIG. 4.

[0048] Next, a principle of noise removal by illumination pupil shape controller 104 will be described. Fig. 6 is a diagram showing an example of illumination pupil shape controller 104 of the optical device according to the first embodiment. As shown in Fig. 6, illumination pupil shape controller 104 is an annular filter having a light blocking portion 701 at the center. Note that the illumination pupil shape controller may use a spatial modulator such as a Digital Micromirror Device (DMD).

[0049] The distribution of the remaining diffracted light is calculated using this central light blocking portion 701. Fig. 7 is a diagram showing an example of pupil distribution processing of the optical device according to the first embodiment. In graphs 801-804, the horizontal axis represents the distance from the central optical axis, and the vertical axis represents the light intensity.

[0050] 7, first, the central optical axis of the light beam is blocked by a light blocking plate by the illumination pupil shape controller 104. Therefore, as shown in graph 801, the light intensity near the central optical axis becomes 0. The intensity image 811 of the light beam appears.

[0051] When the reflected light from the sample reaches the image sensor 113, it has a distribution as shown in graph 802. As shown in graph 802, an intensity distribution due to the diffracted light from the image-forming pinhole appears near the central optical axis where the light does not actually reach. The intensity image 812 of the light beam appears.

[0052] Then, from the distribution of graph 802, optical device 100 extracts only the intensity (solid line portion of graph 803) of the portion blocked by illumination pupil shape controller 104 (center and outer periphery near the optical axis). The result is intensity image 813 of the light flux. Then, interpolation is performed from the extracted intensity distribution (dotted line portion of graph 803). The distribution obtained by interpolation is regarded as the pupil distribution due to the diffracted light from the image-formation side pinhole. This pupil distribution due to the diffracted light from the image-formation side pinhole looks like intensity image 821.

[0053] Then, the optical device 100 subtracts the pupil distribution due to the obtained diffracted light from the image-side pinhole from the original distribution to obtain a signal only from the measurement sample. In Fig. 7, the solid line and dotted line of graph 803 are subtracted from graph 802 to obtain graph 804. Also in Fig. 7, intensity image 821 is subtracted from intensity image 812 to obtain intensity image 814. These processes are executed by a calculation processing circuit (not shown).

[0054] This pupil distribution is then used to perform processing such as Reflectometry, Ellipsometry, Polarimetry, or Scatterometry, which can simultaneously measure all angles of incidence and azimuth, in which the position within the pupil plane corresponds to the angle of incidence and azimuth of the illumination on the sample, and calculate the measured value of the sample structure.

[0055] (Embodiment 2) 8 is a diagram showing an example of noise removal by the image-side pinhole 111 of the optical device according to the second embodiment. In FIG.

[0056] The light shielding plate 901 has a circular hole at the central optical axis. The light shielding plate 901 is designed so that the phase of the incident light is shifted by a half wavelength between the hollow portion inside the pinhole and the outer base. In other words, the light shielding plate 901 has a thickness that causes a half wavelength phase shift with respect to the light emitted by the light source 101. For example, the light shielding plate 901 is preferably made of quartz.

[0057] The light incident on the vicinity of the end of the image-formation side pinhole 111 has a phase shift of half a wavelength, so that the light traveling in a straight line is cancelled out, and the light is diffracted in a direction in which the phase is aligned, and is irradiated to a position outside the pupil of the image sensor 113 .

[0058] As described above, according to the optical device of the second embodiment, the diffracted light is irradiated onto a position outside the pupil of the image sensor by the image-formation side pinhole, so that measurement noise can be reduced.

[0059] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, the image-side pinhole 111 may also include a ring-shaped filter on the image-forming side of the pinhole 302. That is, the image-side pinhole 111 may include, from the object side, a ring-shaped filter, a pinhole, and a ring-shaped filter.

[0060] Each element that performs signal processing of the image sensor 113 can be configured in hardware with a CPU, memory, and other circuits, and in software with a program loaded into memory, etc. Therefore, it will be understood by those skilled in the art that these functional blocks can be realized in various forms by hardware alone, software alone, or a combination thereof, and is not limited to any one of them.

[0061] The above-mentioned program can be stored and provided to a computer using various types of non-transitory computer-readable media. The non-transitory computer-readable media includes various types of tangible recording media. Examples of the non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)). The program may also be provided to a computer by various types of temporary computer-readable media. Examples of the temporary computer-readable media include electrical signals, optical signals, and electromagnetic waves. The temporary computer-readable media can provide the program to a computer via a wired communication path such as an electric wire and an optical fiber, or via a wireless communication path. [Explanation of symbols]

[0062] 100 Optical equipment 101 Light source 102 Illumination side pinhole 103 First Lens 104 Illumination pupil shape controller 105 Lighting side polarization controller 106 Beam splitter 107 Objective Lens 108 Imaging side polarization controller 110 2nd lens 111 Image side pinhole 112 Third lens 113 Image Sensor 150 samples 201, 302 Pinhole 301 Ring Filter 303 Glass Plate 701 Shading part 901 Shading plate

Claims

1. a light source; and an illumination-side pinhole disposed on an optical path between the light source and the sample; a first lens that converts the light transmitted through the illumination side pinhole into a parallel light; a beam splitter that reflects the parallel light toward a sample and transmits the light reflected from the sample as a measurement light; and an objective lens that collects the parallel light reflected by the beam splitter on a surface of the sample and directs the light reflected from the sample toward the beam splitter; The measuring device includes, in order from the sample side toward the image forming surface, a second lens for narrowing down the measurement light, an image forming side pinhole, a third lens for collimating the light, and an image sensor; the illumination-side pinhole and the image-side pinhole are arranged such that their pinhole centers coincide with the optical axis; the image-side pinhole is disposed at a position conjugate with a focal position of the objective lens so as to remove reflected light from other than the surface of the sample; The image-side pinhole of the optical device includes, in order from the sample side toward the image plane, a ring filter and a pinhole.

2. The optical device according to claim 1 , wherein the image-side pinhole further comprises a ring-shaped filter on the image-plane side of the pinhole.

3. A light source; an illumination side pinhole disposed on an optical path between the light source and a sample; a first lens that converts the light transmitted through the illumination side pinhole into a parallel light; a beam splitter that reflects the parallel light toward a sample and transmits the light reflected from the sample as a measurement light; and an objective lens that collects the parallel light reflected by the beam splitter on a surface of the sample and directs the light reflected from the sample toward the beam splitter; The measuring device includes, in order from the sample side toward the image forming surface, a second lens for narrowing down the measurement light, an image forming side pinhole, a third lens for collimating the light, and an image sensor; the illumination-side pinhole and the image-side pinhole are arranged such that their pinhole centers coincide with the optical axis; the image-side pinhole is disposed at a position conjugate with a focal position of the objective lens so as to remove reflected light from other than the surface of the sample; an illumination pupil shape controller having a light blocking portion at a center of an optical axis is provided between the first lens and the beam splitter; The optical device further includes an arithmetic processing unit that removes the influence of a pinhole by subtracting a pinhole diffracted light component from the imaging pupil plane light amount distribution obtained from the image sensor.

4. 4. The optical device according to claim 3, wherein the arithmetic processing unit predicts a distribution other than that of a light shielding portion from a light intensity distribution at a position conjugate with the light shielding portion of the illumination pupil shape controller, among the imaging pupil plane light intensity distributions obtained from the image sensor, and calculates pinhole diffracted light components.

5. The optical device according to claim 4 , wherein the calculation processing unit obtains the distribution prediction for the portion other than the light-shielding portion by performing an interpolation process between the light-shielding portions.

Images