Optical system and projection exposure device

Abstract

The purpose of the present invention is to provide: an optical system capable of improving overlay control technology in a projection exposure device; and the projection exposure device. An optical system 20 is included in a projection exposure device 10, and is disposed between a mask 40 and a wafer W. The optical system 20 comprises a projection system 24 that has a plurality of mirrors which receive first reflection light L1 for exposure obtained by reflecting, by the mask 40, illumination light L0 from a first light source 31, and which guide the first reflection light to the wafer W. The projection system 24: receives second reflection light L3 obtained by reflecting, by the wafer W, first measurement light L2 that is from a second light source 25 and is used for alignment of the position of the wafer W; and guides the second reflection light to the outside of the projection system 24 by the plurality of mirrors.

Description

Optical system and projection exposure apparatus

[0001] This disclosure relates to an optical system and a projection exposure apparatus. This application claims priority to Japanese Patent Application No. 2024-223596 filed in Japan on 18 December 2024 and to Japanese Patent Application No. 2024-229511 filed in Japan on 25 December 2024, the entire disclosures of these applications are incorporated herein by reference.

[0002] Conventional technologies relating to projection exposure apparatus used in semiconductor manufacturing processes are known. For example, Patent Document 1 discloses a positional calibration method for alignment heads in a multi-head alignment system that improves the calibration of multiple alignment heads and enhances overlay accuracy and product yield.

[0003] Japanese Patent Publication No. 2011-023725

[0004] However, the prior art described in Patent Document 1 had room for improvement in the overlay control technology for projection exposure apparatus.

[0005] This disclosure aims to provide an optical system and a projection exposure apparatus capable of improving overlay control technology in projection exposure apparatuses.

[0006] To solve the above problems, an optical system according to one embodiment of the present disclosure is an optical system of a projection exposure apparatus disposed between a mask and a wafer, comprising a projection system having a plurality of mirrors that receive first reflected light for exposure, which is reflected by the mask from illumination light from a first light source, and guide it to the wafer, wherein the projection system receives second reflected light, which is reflected by the wafer from first measurement light from a second light source used for aligning the position of the wafer, and guides it to the outside of the projection system by the plurality of mirrors.

[0007] To solve the above problems, a projection exposure apparatus according to one embodiment of the present disclosure includes: a first light source that irradiates an illumination light onto a mask and exposes a wafer with first reflected light reflected by the mask; a second light source that irradiates the wafer with measurement light used for aligning the position of the wafer; a detection unit that detects the second reflected light reflected by the wafer from the measurement light and outputs alignment information including the measurement pattern for alignment on the wafer; a drive unit that drives the wafer based on the alignment information output from the detection unit; and a control unit that, when exposure by the first light source is being performed, acquires the alignment information from the detection unit and outputs control information based on the alignment information to the drive unit.

[0008] According to an optical system and projection exposure apparatus according to one embodiment of the present disclosure, it is possible to improve the overlay control technology in the projection exposure apparatus.

[0009] This is a first schematic diagram illustrating a part of the configuration of a projection exposure system according to one embodiment of the present disclosure. This is a second schematic diagram illustrating a part of the configuration of a projection exposure system according to one embodiment of the present disclosure. This is the first diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the second diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the third diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the fourth diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the fifth diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is a block diagram illustrating another part of the configuration of the projection exposure apparatus according to one embodiment of the present disclosure. This is the sixth diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the seventh diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the eighth diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is the ninth diagram for illustrating an example of the function of the projection exposure apparatus shown in Figures 1A and 1B. This is a schematic diagram showing an example of the configuration of the mask shown in Figures 1A and 1B. This is a schematic diagram illustrating a part of the configuration of a projection exposure apparatus according to the first modified example of this disclosure. This is the first figure for illustrating an example of the function of a projection exposure apparatus according to the second modified example. This is the second figure for illustrating an example of the function of a projection exposure apparatus according to the second modified example. This is the third figure for illustrating an example of the function of a projection exposure apparatus according to the second modified example.

[0010] The following description will primarily focus on one embodiment of this disclosure, with reference to the attached drawings. The following description of the optical system 20 also applies to projection exposure apparatus 10 and projection exposure system 1 having the optical system 20 to which this disclosure is applied. The numerical values ​​described in the following description and drawings are merely examples and do not limit the scope of this disclosure. The scope of this disclosure should be determined solely based on the claims.

[0011] Figure 1A is a first schematic diagram illustrating a part of the configuration of a projection exposure system 1 according to one embodiment of the present disclosure. Figure 1A schematically shows a part of the configuration of the projection exposure system 1 as viewed from the y direction. Figure 1B is a second schematic diagram illustrating a part of the configuration of a projection exposure system 1 according to one embodiment of the present disclosure. Figure 1B schematically shows a part of the configuration of the projection exposure system 1 shown in Figure 1A as viewed from the x direction, which is orthogonal to the y direction. An example of the configuration and function of the projection exposure system 1 according to one embodiment of the present disclosure will be mainly described with reference to Figures 1A and 1B. The projection exposure system 1 has a projection exposure apparatus 10 and a mask 40 for drawing a circuit pattern on a wafer W. The projection exposure system 1 constitutes, for example, an EUV lithography (Extreme Ultraviolet Lithography) system.

[0012] The projection exposure apparatus 10 has an optical system 20. The optical system 20 includes a first mirror 21, a second mirror 22, a pair of third mirrors 23, a projection system 24, a light source 25, and a detection unit 26. The light source 25 corresponds to the "second light source" described in the claims. The projection system 24 includes a fourth mirror 241 and a fifth mirror 242. In addition to the projection system 24, the projection exposure apparatus 10 has an illumination system 30 including a pair of third mirrors 23. The illumination system 30 includes at least a light source 31 and a pair of third mirrors 23. The light source 31 corresponds to the "first light source" described in the claims.

[0013] Although the detailed configuration of the illumination system 30 of the projection exposure apparatus 10 is omitted in this disclosure, it is possible to apply any conventional configuration that became publicly known before the filing date of this disclosure. The illumination system 30 of the projection exposure apparatus 10 may have, for example, a configuration used in the "innovative EUV lithography advanced semiconductor manufacturing technology that dramatically improves energy efficiency" previously proposed by the applicant. With such a configuration, the illumination system 30 of the projection exposure apparatus 10 may realize a double exposure field.

[0014] In this disclosure, "upstream" corresponds to the direction toward the light source 31 along the optical path of the illumination light L0 and the first reflected light L1 configured in the projection exposure apparatus 10. "Downstream" is the opposite side of the upstream and corresponds to the direction toward the wafer W along the optical path of the illumination light L0 and the first reflected light L1 configured in the projection exposure apparatus 10. The projection exposure apparatus 10 has, in order from upstream to downstream, an illumination system 30 and a projection system 24. The projection exposure apparatus 10 has, in order from upstream to downstream, a light source 31, a pair of third mirrors 23, a fourth mirror 241, and a fifth mirror 242.

[0015] The light source 31 includes, for example, an EUV light source such as a laser plasma. The laser plasma includes, for example, a laser plasma using tin (Tin). The light source 31 irradiates the pair of third mirrors 23 with illumination light L0 having a predetermined spectral width centered on a wavelength of 13.5 nm.

[0016] Each of the pair of third mirrors 23 is positioned furthest downstream in the illumination system 30 and further reflects the guided illumination light L0 toward the mask 40. Each of the pair of third mirrors 23 is, for example, a cylindrical mirror. The pair of third mirrors 23 forms a double exposure field on the mask 40, which includes a first exposure field (scan field) and a second exposure field of the illumination light L0. The first exposure field and the second exposure field are separated from each other.

[0017] Illumination light L0 reflected by each of the pair of third mirrors 23 enters the mask 40. First reflected light L1 reflected by the mask 40 passes between the pair of third mirrors 23 and enters the interior of the projection system 24. In this disclosure, "first reflected light L1" includes illumination light L0 reflected by the mask 40 and diffracted light having structural information of the logic pattern in the mask 40.

[0018] The optical system 20 of the projection exposure apparatus 10 is positioned between the mask 40 and the wafer W. The optical system 20 includes a pair of third mirrors 23 that each receive illumination light L0 from the light source 31 and reflect it back to the mask 40, and a projection system 24 that receives the first reflected light L1 for exposure, which is the illumination light L0 from the light source 31 reflected by the mask 40, and guides it to the wafer W. The projection system 24 has multiple mirrors. For example, the projection system 24 has two mirrors.

[0019] The projection system 24 includes a fourth mirror 241 positioned adjacent to a pair of third mirrors 23, and a fifth mirror 242 positioned on the wafer W side relative to the fourth mirror 241 and having a second optical surface S2 facing the first optical surface S1 of the fourth mirror 241. For example, the fifth mirror 242 is positioned on the side opposite to the pair of third mirrors 23 relative to the fourth mirror 241.

[0020] The central point C between the pair of third mirrors 23, the fourth mirror 241, and the fifth mirror 242 are located on the same straight line. For example, the fourth mirror 241 and the fifth mirror 242 are located on the same central axis A. For example, the optical system 20 is configured such that the central point C between the pair of third mirrors 23, the fourth mirror 241, and the fifth mirror 242 are located on the central axis A, and the central axis A coincides with the central axes of the mask 40 and the wafer W, respectively. The projection system 24 is configured as an in-line projector positioned between the mask 40 and the wafer W.

[0021] The fourth mirror 241 and the fifth mirror 242 may be positioned perpendicular to the central axis A, or they may be positioned at an angle, with their centers located on the central axis A. The mask 40 may be positioned perpendicular to the central axis A. The mask 40 is positioned, for example, to face the projection system 24 directly without tilting. Similarly, the wafer W may be positioned perpendicular to the central axis A. The wafer W is positioned, for example, to face the projection system 24 directly without tilting.

[0022] Each of the fourth mirror 241 and the fifth mirror 242 is, for example, an axisymmetric aspherical mirror. The first optical surface S1 and the second optical surface S2 have substantially the same radius of curvature. In this disclosure, "substantially the same" radii of curvature means that the numerical values ​​of the two radii of curvature are within 1.0%, more preferably within 0.5%, and even more preferably within 0.3%.

[0023] The fourth mirror 241 has a first opening H1 that guides the first reflected light L1 from the outside to the inside of the projection system 24. The first opening H1 includes a first through hole that penetrates the fourth mirror 241 along the thickness direction of the fourth mirror 241. The fifth mirror 242 has a second opening H2 that guides the first reflected light L1 from the inside to the outside of the projection system 24. The second opening H2 includes a second through hole that penetrates the fifth mirror 242 along the thickness direction of the fifth mirror 242.

[0024] The first reflected light L1, reflected by the mask 40 and passing between the pair of third mirrors 23, passes through the first aperture H1 of the fourth mirror 241 and enters the interior of the projection system 24. The first reflected light L1, having passed through the first aperture H1 and entered the interior of the projection system 24, is reflected by the second optical surface S2 of the fifth mirror 242 and enters the first optical surface S1 of the fourth mirror 241. The first reflected light L1 is further reflected by the first optical surface S1 of the fourth mirror 241 toward the second optical surface S2 of the fifth mirror 242, passes through the second aperture H2 of the fifth mirror 242 and is guided to the wafer W.

[0025] The projection exposure system 1 includes a projection exposure apparatus 10 having the optical system 20 described above, and a mask 40. In Figure 1A, the scanning direction is, for example, along the x-axis. The mask 40 moves, for example, in the left-right direction of the paper plane during scanning. The wafer W moves, for example, in the opposite direction to the mask 40. For example, if the mask 40 moves in the positive x-axis direction, the wafer W moves in the negative x-axis direction. The wafer W moves, for example, in the left-right direction of the paper plane during scanning. The direction perpendicular to the scanning direction is, for example, along the y-axis.

[0026] As described above, the optical system 20 of the projection exposure apparatus 10 guides the first reflected light L1, which is the illumination light L0 from the light source 31 reflected by the mask 40, from the mask 40 toward the wafer W. In addition, the optical system 20 reflects the first measurement light L2 from the light source 25 by the mask 40 and guides it toward the wafer W from the mask 40. Subsequently, the optical system 20 guides the second reflected light L3, which is the first measurement light L2 reflected by the wafer W, toward the mask 40.

[0027] In this disclosure, “first measurement light L2” means, for example, light used for positional alignment of the wafer W. “Alignment” means, for example, the adjustment of the position between one layer and another when the projection exposure apparatus 10 forms multiple layers on the wafer W by overlay control. Alignment includes, as an example, the adjustment of the position of at least one of the x-direction and y-direction of the wafer W.

[0028] The light source 25 of the optical system 20 includes, for example, a light-emitting diode (LED), or a light source such as a semiconductor laser, solid-state laser, liquid laser, or gas laser. The light source 25 irradiates the wafer W with a first measurement light L2 used for position alignment of the wafer W by the projection exposure apparatus 10 via other components of the optical system 20.

[0029] The light source 25 irradiates the wafer W with a first measurement light L2 having an arbitrary wavelength that enables the wafer W to be aligned by the projection exposure apparatus 10. The wavelength of the first measurement light L2 irradiated by the light source 25 is, for example, included in the red region. The light source 25 may be, for example, an LED that irradiates red light as the first measurement light L2, or a He-Ne laser. However, it is not limited to this, and the wavelength of the first measurement light L2 may be included in, for example, other visible regions, near-infrared regions, or other infrared regions.

[0030] The first mirror 21 of the optical system 20 is positioned adjacent to the projection system 24 and receives the first measurement light L2 from the light source 25 and reflects it to the mask 40. The first mirror 21 may be any type of mirror having a predetermined reflectance of approximately 100% at the wavelength of the first measurement light L2.

[0031] The second mirror 22 included in the optical system 20 is disposed between the first mirror 21 and the mask 40, and transmits at least a part of the first measurement light L2 reflected by the first mirror 21 and guides it to the mask 40. In addition, the second mirror 22 receives at least a part of the second reflected light L3 emitted from the projection system 24 and reflected by the mask 40, and reflects it to the detection unit 26. The second mirror 22 may function as a half mirror that transmits a part of the first measurement light L2 from the first mirror 21 while reflecting a part of the second reflected light L3 from the mask 40.

[0032] The detection unit 26 includes, for example, an imaging module such as a camera including a two-dimensional image sensor or a photodetector including a light receiving element such as a photodiode. The two-dimensional image sensor includes, for example, a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor. The detection unit 26 receives the second reflected light L3 based on the first measurement light L2 irradiated on the wafer W by the light source 25, and the second reflected light L3 used for alignment.

[0033] The wavelength band that can be received by the detection unit 26 includes the wavelength band of the second reflected light L3. The detection unit 26 has a detection sensitivity at the wavelength of the second reflected light L3. The wavelength at which the detection unit 26 has a detection sensitivity is included in, for example, the red region. Without being limited thereto, the wavelength may be included in, for example, other visible regions, near infrared regions, or other infrared regions.

[0034] The detection unit 26 detects the second reflected light L3 and outputs an image in which the measurement pattern for alignment based on the reference line SL on the wafer W and the reference pattern RL on the mask 40 corresponding to the measurement pattern overlap. The detection unit 26 outputs an image in which the measurement pattern of the reference line SL and the reference pattern RL overlap to a control unit 14 described later.

[0035] In the present disclosure, the "reference line SL" includes, for example, a scribe line that serves as a boundary line for dividing chip regions on the wafer W. The "measurement pattern" includes, for example, an array pattern indicated by a plurality of scribe lines formed on the wafer W. The "reference pattern RL" includes, for example, an array pattern indicated by a plurality of laminated bodies described later that are formed in a line shape in the black border region of the mask 40.

[0036] The optical system 20 may further include a condensing element 27 such as a lens, which is disposed between the second mirror 22 and the detection unit 26. The condensing element 27 condenses the second reflected light L3 reflected by the second mirror 22 and guides it to the detection unit 26.

[0037] The projection system 24 receives the first measurement light L2 and guides it to the wafer W through a plurality of mirrors, for example, the fourth mirror 241 and the fifth mirror 242. In addition, the projection system 24 receives the second reflected light L3 reflected by the wafer W from the first measurement light L2 of the light source 25 and guides it outside the projection system 24 through a plurality of mirrors, for example, the fourth mirror 241 and the fifth mirror 242. For example, the projection system 24 receives the second reflected light L3 and guides it to the mask 40 through a plurality of mirrors. The projection system 24 arranges the optical paths of the first measurement light L2 and the second reflected light L3 through the plurality of mirrors outside the exposure field by the first reflected light L1. The projection system 24 guides the first measurement light L2 to the reference line SL located in the vicinity outside the exposure field formed by the first reflected light L1 on the wafer W.

[0038] The first aperture H1 of the fourth mirror 241 guides the first measurement light L2 from the outside to the inside of the projection system 24 in addition to the first reflected light L1. The first measurement light L2 reflected by the mask 40 and passing between the pair of third mirrors 23 passes through the first aperture H1 of the fourth mirror 241 and enters the inside of the projection system 24. The first measurement light L2 that enters the inside of the projection system 24 through the first aperture H1 is reflected by the second optical surface S2 of the fifth mirror 242 and enters the first optical surface S1 of the fourth mirror 241. The first measurement light L2 is further reflected by the first optical surface S1 of the fourth mirror 241 toward the second optical surface S2 of the fifth mirror 242, passes through the second aperture H2 of the fifth mirror 242, and is guided to the wafer W.

[0039] The second aperture H2 of the fifth mirror 242 guides the first measurement light L2, in addition to the first reflected light L1, from the inside to the outside of the projection system 24. The second aperture H2 further guides the second reflected light L3 from the outside to the inside of the projection system 24. The second reflected light L3, reflected by the reference line SL of the wafer W, passes through the second aperture H2 of the fifth mirror 242 and enters the inside of the projection system 24. The second reflected light L3 that has entered the inside of the projection system 24 after passing through the second aperture H2 is reflected by the first optical surface S1 of the fourth mirror 241 and enters the second optical surface S2 of the fifth mirror 242. The second reflected light L3 is further reflected by the second optical surface S2 of the fifth mirror 242 toward the first optical surface S1 of the fourth mirror 241, passes through the first aperture H1 of the fourth mirror 241 and is guided to the mask 40. The first opening H1 of the fourth mirror 241 guides the second reflected light L3 from the inside to the outside of the projection system 24.

[0040] The measurement paths of the first measurement light L2 and the second reflected light L3 of red light will be described in more detail with reference to Figures 1A and 1B. In the two-mirror projector system of this disclosure, the mask 40 and the wafer W are arranged parallel to each other, and an optical resonator is formed via the projection system 24, which is an in-line projector. To avoid beam loss to the central second aperture H2, the first measurement light L2 is irradiated onto the wafer W with a small angular offset, as shown in Figure 1A.

[0041] As shown in Figure 1A, the first measurement light L2 follows a closed zigzag path on the xz plane within the projection system 24. On the other hand, as shown in Figure 1B, on the yz plane within the projection system 24, the first measurement light L2 follows the same path as the second reflected light L3, following a simple Z-shaped path. When the telecentric condition (the condition that the first measurement light L2 is perpendicular to the wafer W) is met, the measurement path exits after the reflection of the second reflected light L3 by the mask 40, and the two beams are separated by the second mirror 22, which acts as a half-mirror, as shown in Figure 1B.

[0042] The second reflected light L3 from the wafer W undergoes diffraction at the reference line SL, forming an enlarged image on the mask 40. As will be described later, the mask 40 has corresponding reference patterns RL written at slightly different pitches, generating a moiré pattern. This image is captured by the detection unit 26 via the projection system 24, which functions as a microscope objective lens. The projection exposure apparatus 10 uses the Vernier-Nonius principle to detect the positional error between the mask 40 and the wafer W with nanometer resolution.

[0043] Figure 2 is the first diagram illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Figure 2 conceptually shows the deployed illumination path from the EUV light source 31 to the mask 40 and wafer W, and the deployed measurement path from the red light source 25 to the mask 40 and wafer W. In the actual projection exposure apparatus 10, all the mirrors in the projection system 24 reflect light and change its direction, but in Figure 2, the projection system 24 is virtually represented as something that transmits light like a lens.

[0044] Figure 3 is a second diagram illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Figure 3 conceptually shows the surface of the wafer W in an enlarged view, illustrating the first reflected light L1 and first measurement light L2 incident on the surface, and the second reflected light L3 reflected from the surface. Referring to Figures 2 and 3, the overall light propagation path will be explained for each of the illumination and measurement paths.

[0045] In the illumination path used for exposure, for example, illumination light L0 emitted from an EUV light source 31 is reflected inside the illumination system 30 and further reflected by a pair of third mirrors 23 also included in the illumination system 30. The illumination light L0 reflected by the pair of third mirrors 23 is incident on the mask 40. The first reflected light L1 for exposure, which is the illumination light L0 reflected by the mask 40, passes through the projection system 24 and is guided to the wafer W. The first reflected light L1 is used for exposure to draw a circuit pattern, for example, by irradiating the chip region R1 of the wafer W.

[0046] In the measurement path used for alignment, for example, the first measurement light L2 emitted from the red light source 25 is reflected by the first mirror 21 of the optical system 20, incident on the second mirror 22, and partially transmitted. The first measurement light L2 that has passed through the second mirror 22 is incident on the mask 40. The first measurement light L2 reflected by the mask 40 passes through the projection system 24 and is guided to the wafer W. The first measurement light L2 is irradiated, for example, on the boundary region R2 adjacent to the chip region R1 of the wafer W and is reflected by the reference line SL located in the boundary region R2. The first measurement light L2 is irradiated on the reference line SL located near the outside of the exposure field formed by the first reflected light L1 on the wafer W and is reflected.

[0047] The second reflected light L3, which is the result of the first measurement light L2 being reflected by the wafer W, passes through the projection system 24 and is guided to the mask 40. At this time, the second reflected light L3 is irradiated onto the reference pattern RL formed on the mask 40. The second reflected light L3, which is irradiated onto the reference pattern RL on the mask 40 and reflected by the mask 40, is incident on the second mirror 22 of the optical system 20 and partially reflected. The second reflected light L3 reflected by the second mirror 22 is focused by the light-gathering element 27 and incident on the detection unit 26.

[0048] The illumination path used for exposure and the measurement path used for alignment both pass through the projection system 24 of the optical system 20. The illumination path passes through the projection system 24 in one direction from the mask 40 toward the wafer W. For example, the first reflected light L1 of EUV for exposure propagates in one direction through the projection system 24 from the mask 40 toward the wafer W. On the other hand, the measurement path passes through the projection system 24 bidirectionally between the mask 40 and the wafer W. For example, the first measured light L2 of red light for alignment propagates through the projection system 24 in a first direction from the mask 40 toward the wafer W. For example, the second reflected light L3 of red light for alignment propagates through the projection system 24 in a second direction opposite to the first direction toward the wafer W toward the mask 40.

[0049] Figure 4 is the third figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Referring to Figure 4, the selection of the wavelength of the first measurement light L2 used together with the EUV wavelength of the first reflected light L1 for exposure will be explained in detail. Figure 4 shows the reflectance of the EUV mirror (left vertical axis) and the absorption depth of the silicon wafer (right vertical axis).

[0050] Generally, Mo / Si multilayer coatings function as Bragg reflectors. For example, a Mo / Si multilayer coating reflects EUV light through constructive interference effects within a 3% bandwidth at a central wavelength of 13.5 nm. On the other hand, at longer wavelengths, i.e., in the out-of-band region, the Mo / Si multilayer coating effectively reflects light similarly to a metallic coated mirror of Mo.

[0051] The periodicity of the Mo / Si layer is designed to satisfy the Bragg diffraction condition. Light is reflected primarily due to the higher electron density of Mo atoms, while Si remains relatively transparent. The path difference of each Mo layer must be equal to the EUV wavelength. Therefore, the periodicity is half the wavelength with respect to the angle of normal incidence. A 40-layer bilayer achieves a thickness of 40 × 13.5 / 2 = 270 nm. At longer wavelengths, interference effects disappear, and the entire Mo layer functions as a single metallic block. In this case, light absorption in the Si layer is almost negligible. Visible light is reflected by currents flowing within the skin depth of the conductive surface of Mo. The skin depth is estimated by Equation 1 below.

[0052] (Equation 1) Here, the angular frequency ω at a wavelength of 600 nm is ω = 2πf = 2πc / λ = 3 × 10 １５ The resistivity ρ of Mo is ρ = 53.4 nΩ·m (at 20°C). The permeability μ of Mo is μ = 4π × 10⁻⁶ －７ That is the case.

[0053] Equation 1 shows that δ ≈ 5 nm. Therefore, visible light is thought to be reflected at the top of the Mo layer. It should be noted that the phase of the reflected light is 180° different from that of the incident light. This is because it corresponds to short-circuit reflection in a wave transmission line. At EUV wavelengths, the reflection is caused by Bragg diffraction and should be in phase (or 0°), while individual wavelets have a 180° delay due to Thomson scattering. In summary, EUV reflection and visible light reflection have the same phase, and therefore the optical performance of the EUV mirror system, for example, projection system 24, is the same in both cases.

[0054] Silicon wafers are not completely transparent in visible light, but are partially transparent. Therefore, the projection exposure apparatus 10 can detect scribe lines fabricated beneath the front-end CMOS layer at the start of the process. As shown in Figure 4, the absorption depth is approximately 1 μm in red. This closely matches the thickness of logic semiconductor circuits. For this reason, He-Ne lasers have conventionally been used in photolithography as measurement light for semiconductor manufacturing.

[0055] Today, various diode lasers or LEDs with wavelengths close to He-Ne wavelengths are known. Since speckles associated with coherent light can cause reading errors, the projection exposure apparatus 10 may use a red LED as the light source 25 instead of a He-Ne laser, for example. As shown in Figure 4, since the reflectance R of Mo / Si is about 50% and the absorption depth l of the silicon wafer is about 3 μm, a red LED that emits red light that can penetrate the silicon wafer by about 3 μm may be selected as the light source 25.

[0056] Figure 5A is the fourth figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Figure 5B is the fifth figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Referring to Figures 5A and 5B, the design of the optical paths of the first measurement light L2 and the second reflected light L3 in the optical system 20 will be mainly described.

[0057] As shown in Figure 2, the optical system 20 is conceptually analogous to a TTL (Through The Lens) system. One of the important elements for achieving alignment in TTL is finding a suitable optical path outside the exposure field of the first reflected light L1. Due to the nature of aberration phenomena in the optical system 20, a lower resolution field exists outside the central high resolution field. By combining the broadband capability of the optical system 20 with the EUV mirror described above using Figure 4, the areas outside the EUV exposure field of the first reflected light L1 can be used for visible light measurement by the first measurement light L2 and the second reflected light L3.

[0058] Figure 5A shows an example of simulation results when using the OpTaLix simulator for a projection system 24, which is a two-mirror inline projector. As an example of simulation conditions, the numerical aperture (NA) is 0.3, the object image distance (OID) is 1560 mm, and the magnification is 1 / 4.

[0059] Figure 5B shows the spot diagram of a two-mirror inline projector with a wavelength of 13 nm, an NA of 0.3, and a field width of 13 mm. In Figure 5B, y = 0–6.5 mm is for EUV exposure. y = 6.5–7.5 mm is the visible light measurement field, i.e., the path of red light with a wavelength of 600 nm. It is clearly shown that the Strehl ratio becomes very high because the spot size is smaller than the wavelength of 600 nm. For example, the Strehl ratio is 1.00 at y = 7.5 mm.

[0060] To stably maintain the primary diffraction spot within the two-mirror inline projector, the period, or pitch, of the reference line SL is set to 1.5 μm, allowing the image of the reference line SL to be reproduced as a smooth sine wave. The secondary spot cannot pass through the projector. Considering the projector's magnification, the period of the image at mask 40 is 1.5 × 4 = 6 μm.

[0061] The above explanation mainly focuses on the optical system 20 of the projection exposure apparatus 10. Below, the explanation will mainly focus on the control system used for alignment of the projection exposure apparatus 10.

[0062] Figure 6 is a block diagram illustrating another part of the configuration of a projection exposure apparatus 10 according to one embodiment of the present disclosure. Figure 6 shows an example of the configuration mainly included in the control system of the projection exposure apparatus 10. An example of the configuration and function of the projection exposure apparatus 10 according to one embodiment of the present disclosure will be mainly described with reference to Figure 6. In addition to the light source 31 as the first light source, the light source 25 as the second light source, and the detection unit 26 described above, the projection exposure apparatus 10 further includes a third light source 11, a drive unit 12, a storage unit 13, and a control unit 14.

[0063] The light source 31 of the projection exposure apparatus 10 functions as a first light source that irradiates the mask 40 with illumination light L0 and exposes the wafer W with the first reflected light L1 reflected by the mask 40. The light source 25 functions as a second light source that irradiates the wafer W with a first measurement light L2 used for aligning the position of the wafer W. The detection unit 26 detects the second reflected light L3 that is reflected by the wafer W from the first measurement light L2 and outputs alignment information including a measurement pattern for alignment on the wafer W.

[0064] In this disclosure, “alignment information” includes, for example, an image showing a moiré pattern in which a measurement pattern for alignment based on a reference line SL on a wafer W and a reference pattern RL on a mask 40 corresponding to the measurement pattern overlap. The detection unit 26 outputs the image as alignment information to the control unit 14.

[0065] The third light source 11 includes, for example, an LED, or a light source such as a semiconductor laser, solid-state laser, liquid laser, or gas laser. The third light source 11 irradiates the wafer W with pulsed light used for position alignment of the wafer W by the projection exposure apparatus 10. The wavelength of the pulsed light irradiated by the third light source 11 is, for example, included in the red region. The third light source 11 may be, for example, an LED that irradiates red light as pulsed light. However, it is not limited to this, and the wavelength of the pulsed light may be included in, for example, other visible regions.

[0066] The drive unit 12 includes, for example, an arbitrary drive module that drives the wafer W based on alignment information output from the detection unit 26. The drive module includes, for example, a scan motor and a piezo actuator or voice coil. The stage on which the wafer W is placed, which is directly driven by the drive module, may be movable with friction generated by bearings or the like, or it may be movable with virtually zero friction by an air levitation or magnetic levitation configuration using air bearings or the like.

[0067] The storage unit 13 includes one or more memories. In this disclosure, “memory” includes, but is not limited to, semiconductor memory, magnetic memory, or optical memory. Each memory included in the storage unit 13 may function as, for example, a main memory, an auxiliary memory, or a cache memory. The storage unit 13 stores information necessary to realize the operation of the projection exposure apparatus 10. For example, the storage unit 13 may store a system program, an application program, or embedded software. The storage unit 13 stores information obtained by the operation of the projection exposure apparatus 10.

[0068] The control unit 14 includes one or more processors, one or more programmable circuits, one or more dedicated circuits, or a combination thereof. In this disclosure, "processor" is a general-purpose processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), or a dedicated processor specialized for a specific process, but is not limited to these. "Programmable circuit" is an FPGA (Field-Programmable Gate Array), but is not limited to this. "Dedicated circuit" is an ASIC (Application Specific Integrated Circuit), but is not limited to this. The control unit 14 is communicateably connected to each component constituting the projection exposure apparatus 10 and controls the operation of the entire projection exposure apparatus 10.

[0069] The control unit 14 acquires alignment information from the detection unit 26 when exposure is being performed by the light source 31 as the first light source, and outputs control information based on the alignment information to the drive unit 12. In this disclosure, "control information" includes, for example, position error information used for feedback control in adjusting the position of the wafer W during alignment. For example, the control information includes position error information in at least one of the x and y directions of the wafer W.

[0070] The control unit 14 controls at least one of the movement of the wafer W in the scanning direction and the position of the wafer W in a direction intersecting the scanning direction by outputting control information to the drive unit 12. For example, as shown in Figure 3, the scanning direction of the wafer W corresponds to the x-direction. The direction intersecting the scanning direction of the wafer W corresponds to the y-direction. In this disclosure, "controlling the movement of the wafer W in the scanning direction" means, for example, controlling the velocity or acceleration of the wafer W in the scanning direction. The control unit 14 may control the position of the wafer W in the scanning direction by controlling the movement of the wafer W in the scanning direction.

[0071] For example, the control unit 14 outputs control information to two drive units 12, which are used for alignment in the x and y directions, respectively. As shown in Figure 3, the control unit 14 scans the wafer W to one side in the x direction, and then shifts the position of the wafer W by one step to one side in the y direction. Subsequently, the control unit 14 scans the wafer W to the other side in the x direction, and then shifts the position of the wafer W by another step to one side in the y direction. Subsequently, the control unit 14 scans the wafer W to one side in the x direction. The control unit 14 exposes substantially the entire wafer W by repeating the scan in the x direction and the position adjustment in one step at a time in the y direction. However, it is not limited to this, and the control unit 14 may expose substantially the entire wafer W by repeating the scan in the y direction and the position adjustment in one step at a time in the x direction.

[0072] Figure 7 is the sixth figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Referring to Figure 7, we will mainly explain the method for measuring the positional error of the wafer W necessary for feedback control in alignment.

[0073] Figure 7 is a conceptual diagram illustrating a measurement system for lateral (x and y direction) errors in TTL at nanometer resolution. In Figure 7, the central single lens conceptually represents the projection system 24. The diagram mainly illustrates the first reflected light L1 passing from top to bottom through the single lens corresponding to the projection system 24, and the second reflected light L3 passing from bottom to top through the same single lens. The first reflected light L1 from the mask 40 is guided to the wafer W as EUV light via the projection system 24. The first reflected light L1 generates a reticle image on the wafer W and exposes it. The wafer W is scanned, for example, in the x direction, i.e., in a direction perpendicular to the plane of the paper in Figure 7.

[0074] Before the circuit pattern is formed, a scribe line is provided as a reference line SL in the bottom layer of the wafer W. As shown on the left side of Figure 7, the first scribe line, which is used as a reference line SL to detect the position of the wafer W in the y direction, is parallel to the x direction, which is the scanning direction. On the other hand, as shown on the right side of Figure 7, the second scribe line, which is used as a reference line SL to detect the position of the wafer W in the x direction or the scanning speed, is parallel to the y direction, which is perpendicular to the x direction, which is the scanning direction. The line pitch of the first scribe line and the second scribe line is 1.5 μm, as described above.

[0075] On both sides of the x-direction of the second scribe line, which is used to detect the position or scan speed of the wafer W in the x-direction, there are black bars for timing reference. These correspond to the sprocket SP described later, which functions similarly to the sprocket on a film reel.

[0076] The first and second scribe lines are fabricated as follows: First, a series of channels are created on the wafer W by lithography / etching, and then tungsten is sputtered into these channels. A mirror-like tungsten line is created on the wafer W as a reference line SL by CMP (Chemical Mechanical Polishing) surface polishing. This tungsten line efficiently reflects red light, which is the first measurement light L2, resulting in a bright line. The black bars corresponding to the sprocket SP described above represent actual empty areas on the wafer W, where there is no tungsten coating, and where red light penetrates and is absorbed by the wafer W.

[0077] As described above, the penetration depth of the red light used as the first measurement light L2 into the silicon wafer W is approximately 1 μm. Therefore, the projection exposure apparatus 10 can reference the same scribe line in all lithography cycles and maintain the overlay with high precision. In other words, the projection exposure apparatus 10 can perform the front-end CMOS process and the subsequent layer fabrication and connecting wire patterning in advanced semiconductor manufacturing with high-precision overlay.

[0078] The second reflected light L3, reflected by the reference line SL, propagates in the opposite direction to the first reflected light L1 within the projection system 24 through which the first reflected light L1 for exposure passes. The projection system 24, acting as a projector for the EUV mirror, is configured such that, despite the EUV light and red light propagating in opposite directions, its optical performance, including aberrations, is identical for both EUV light and red light. The optical principle is symmetric in both directions, and Maxwell's equations are reversible in time. That is, unless nonlinear materials exist, the optical principle does not depend on the direction of spatial and temporal propagation.

[0079] The second reflected light L3, including diffraction, eventually reaches the mask 40, generating an image containing scribe lines magnified fourfold. The mask 40 has a reference pattern RL corresponding to the measurement pattern of the reference line SL, which is provided at a slightly different pitch than the reference line SL. These two patterns create a moiré pattern. The control unit 14 of the projection exposure apparatus 10 detects a small translation error using the Vernier-Nonius principle.

[0080] Figure 8 is the seventh figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Referring to Figure 8, the translation error detection process performed by the control unit 14 using the Vernier-Nonius principle will be explained in more detail. The control unit 14 calculates control information based on the moiré pattern.

[0081] As shown in Figure 8, a moiré pattern is generated when two periodic lines with different pitches overlap. It is well known that the moiré pattern shifts when the two periodic patterns are misaligned. In this disclosure, a periodicity close to the critical dimension CD is selected.

[0082] (Equation 2) Here, if the second reflected light L3 is red light, for example λ = 632 nm. NA = 0.3. To ensure a margin, the pitch is set to approximately 1.5 μm. In this state, the first diffraction from the reference line SL passes through the projection system 24 and generates an image on the mask 40. For example, if the detection unit 26 includes a CMOS camera, the same NA is used for both the CMOS camera and the optical system 20. Therefore, the control unit 14 represents the image including the reference pattern RL and the measurement pattern of the reference line SL as a sine wave as follows.

[0083] (Equation 3) Here, f １ This is a reference wave corresponding to the reference pattern RL, and f ２ These are waves corresponding to the measurement pattern of the reference line SL. They have slightly different pitches. There is a small position error of δ in the image of the reference line SL. The control unit 14 superimposes the two waves and calculates the linear product as follows.

[0084] (Equation 4) The fourth term represents the interference effect. This term includes high-frequency components and low-frequency components. When the control unit 14 takes the average along the y-axis, that is, sums up all the pixel intensities of the CMOS camera, only the low-frequency (long wavelength) components remain as follows.

[0085] (Equation 5) Here, m is the magnification factor, and m = p ２ / Δp. Δp is the difference between two periods p １ 、p ２ . When the control unit 14 selects two sufficiently close periods p １ 、p ２ , a very high magnification factor can be derived, enabling the detection of position errors at nanometer resolution. This is the essence of the Vernier nonius principle. The control unit 14 sums up all the pixel intensities to detect the center of mass mδ from the CMOS sensor, divides it by m, and obtains the error at nanometer resolution.

[0086] The high-frequency component 1 / p １ + 1 / p ２ ≒ 2 / p １ may cause aliasing patterns in the pixel array of the CMOS camera. To avoid this problem, the CMOS window may be tilted several times.

[0087] FIG. 9 is a eighth diagram for explaining an example of the function of the projection exposure apparatus 10 of FIGS. 1A and 1B. While referring to FIG. 9, a method for controlling the scan speed with nanometer / second accuracy will be mainly described. Similarly in FIG. 9, the projection system 24 is conceptually shown by a single central lens. In addition, the mask 40 is conceptually shown as a transmissive element.

[0088] The drive module of the drive unit 12 includes, for example, a scan motor 121 and an element 122 including a piezo actuator or a voice coil. The projection exposure apparatus 10 functioning as a real-time alignment control system realizes relative position matching at the nanometer level between the mask 40 and the wafer W through real-time error monitoring and feedback to the scan motor 121.

[0089] Here, because the moiré pattern is always moving with the wafer W, the control unit 14 of the projection exposure apparatus 10 cannot easily accurately measure the pattern position without taking any countermeasures. The frame rate of the CMOS sensor of the detection unit 26 is not fixed with high precision, and the delay of line scanning along the pixel array causes the moving object to become a distorted image. To solve the above problems, the projection exposure apparatus 10 further includes a third light source 11 that irradiates pulsed light onto a sprocket SP formed on the wafer W, which determines the output timing of alignment information by the detection unit 26.

[0090] A third light source 11, which is a pulsed laser, and a timing sprocket SP are introduced relative to the scribe line, which is the reference line SL. For example, a pulsed laser diode with a wavelength of 870 nm, a spectral width of 6 nm, a pulse width of 100 ns, a repetition rate of 1 kHz, and several microjoules per pulse is available for the third light source 11. The spectral width of 6 nm means that the laser is not coherent. Therefore, the laser can erase interference patterns and is suitable for measurement applications. The moiré pattern moves 100 μm within a pulse width of 100 ns. This is suitable for measurement applications because it erases the pattern of the 15 μm periodic reference line SL on the CMOS sensor.

[0091] The sprocket SP provides a timing reference for the scan motor 121. As shown in Figure 9, the upper half of the sprocket SP does not have a reference line SL, which is a scribe line, and only the sprocket SP, which provides rough timing information, is positioned. On the other hand, the lower half has a reference line SL positioned as a periodic pattern that provides finer positional errors. The control unit 14 calculates the center of mass by integrating the upper and lower halves. The control unit 14 calculates the error in nanometer resolution of the alignment between the wafer W and the mask 40 by subtracting the second error related to the position of the sprocket SP in the upper half from the first error related to the position of the moiré pattern in the lower half, using the Vernier-Nonius principle.

[0092] As described above, the image output from the detection unit 26 as alignment information includes a first image region IM1 showing a moiré pattern and a second image region IM2 showing only the sprocket SP. The control unit 14 calculates control information by subtracting the second error information based on the sprocket SP in the second image region IM2 from the first error information based on the moiré pattern in the first image region IM1. In this disclosure, "first error information" includes, for example, the first error described above. "Second error information" includes, for example, the second error described above.

[0093] Figure 10 is the ninth figure illustrating an example of the function of the projection exposure apparatus 10 shown in Figures 1A and 1B. Referring to Figure 10, the function of the feedback control system comprising the projection exposure apparatus 10 will be explained in more detail. Similarly in Figure 10, the projection system 24 is conceptually represented by a single lens. In addition, the mask 40 is conceptually represented as a transmission element.

[0094] The feedback control system configured in the projection exposure apparatus 10 includes, for example, a first drive unit 12a used for alignment in the x-direction and a second drive unit 12b used for alignment in the y-direction. The drive module of the first drive unit 12a includes, for example, a scan motor 121a and an element 122a including a piezo actuator or voice coil. The drive module of the second drive unit 12b includes, for example, a scan motor 121b and an element 122b including a piezo actuator or voice coil.

[0095] The feedback control system includes, for example, a first detection unit 26a used for alignment in the x-direction and a second detection unit 26b used for alignment in the y-direction. The first detection unit 26a detects the second reflected light L3 that has been reflected by the reference line SL of the wafer W and has passed through the projection system 24, the mask 40, and the light-gathering element 27. The second detection unit 26b detects the second reflected light L3 that has been reflected by the reference line SL of the wafer W and has passed through the projection system 24, the mask 40, and the light-gathering element 27.

[0096] The first detection unit 26a detects the second reflected light L3 and outputs alignment information including a measurement pattern for x-direction alignment on the wafer W. The control unit 14 acquires an image showing the moiré pattern from the first detection unit 26a as alignment information. Based on the moiré pattern acquired from the first detection unit 26a as alignment information, the control unit 14 calculates the error in the x-direction position as control information. For example, the control unit 14 calculates the control information by subtracting the second error information based on the sprocket SP from the first error information based on the moiré pattern. The control unit 14 uses the Vernier-Nonius principle to calculate the x-error of the alignment between the wafer W and the mask 40 at nanometer resolution.

[0097] The control unit 14 outputs the calculated control information to the scan motor 121a of the first drive unit 12a. This allows the control unit 14 to perform feedback control of the scanning speed of the wafer W in the x-direction, for example. For instance, the control unit 14 operates the scan motor 121a and element 122a of the first drive unit 12a by outputting this control information. The first drive unit 12a moves the stage ST on which the wafer W is placed in the x-direction, which is the scanning direction, at a speed based on the control information from the control unit 14.

[0098] The second detection unit 26b detects the second reflected light L3 and outputs alignment information including a measurement pattern for y-direction alignment on the wafer W. The control unit 14 acquires an image showing the moiré pattern from the second detection unit 26b as alignment information. Based on the moiré pattern acquired from the second detection unit 26b as alignment information, the control unit 14 calculates the y-direction position error as control information. For example, the control unit 14 uses the Vernier-Nonius principle to calculate the y-error of the alignment between the wafer W and the mask 40 at nanometer resolution.

[0099] The control unit 14 outputs the calculated control information to the scan motor 121b of the second drive unit 12b. This allows the control unit 14 to perform feedback control of the wafer W's position in the y-direction, for example. For instance, the control unit 14 operates the scan motor 121b and element 122b of the second drive unit 12b by outputting this control information. Based on the control information from the control unit 14, the second drive unit 12b adjusts the position of the stage ST on which the wafer W is placed in the y-direction.

[0100] Figure 11 is a schematic diagram showing an example of the configuration of the mask 40 in Figures 1A and 1B. Referring to Figure 11, we will mainly explain an example of the configuration of the reference pattern RL formed on the mask 40. In Figure 11, for ease of understanding, the scale relationships between the components of the mask 40 and the wafer W are illustrated in a manner that differs from the actual scale.

[0101] The mask 40 is constructed as a laminate in which a conductive back film 41, a glass layer 42, a multilayer reflective portion 43, a capping layer 44, and an absorber 45 are stacked in that order. In the laminate, the back film 41 and the glass layer 42 have a total thickness d4. In the laminate, the multilayer reflective portion 43 and the capping layer 44 have a total thickness d5. In the laminate, the absorber 45 has a total thickness d6.

[0102] In the mask 40, the region EX used for exposure is located in the center with a width d1. A reference pattern RL with a width d2 is formed on each side of region EX. The reference pattern RL is formed in the black border region BL located on each side of region EX. The areas in the black border region BL where the reference pattern RL is not formed have a width d3.

[0103] The width d1 is, for example, 104 mm. The width d2 is, for example, 0.6 mm. At width d2, a reference pattern RL is formed, which includes multiple laminates with a pitch of 6 μm and a period of 100. The width d3 is, for example, 2 mm. The thickness d4 is, for example, 6.35 mm. The thickness d5 is, for example, about 200 nm. The thickness d6 is, for example, about 60 nm.

[0104] Similarly, on wafer W, a measurement pattern based on multiple reference lines SL is formed on each side of the region EX used for exposure. In this measurement pattern, the multiple reference lines SL are formed, for example, with a pitch of 1.5 μm and a period of 100.

[0105] According to the optical system 20 and projection exposure apparatus 10 of the above embodiment, the overlay control technology in the projection exposure apparatus 10 can be improved. The optical system 20 has a projection system 24 having a plurality of mirrors that receive a first reflected light L1 for exposure and guide it to the wafer W. The projection system 24 receives a second reflected light L3 that is reflected by the wafer W from a first measurement light L2 used for aligning the position of the wafer W, and guides it to the outside of the projection system 24 with a plurality of mirrors. As a result, the optical system 20 can be made to have a simple structure by using the same configuration for exposure and alignment.

[0106] The optical system 20, having a total internal reflection optical system based on multiple mirrors, can be configured so that short-wavelength EUV light for exposure and visible or infrared light for measurement pass through the same projection system 24 with identical optical performance. Optical performance includes, for example, properties such as NA, aberration, distortion, or geometric offset. The Mo / Si multilayer coating on the mirrors of the optical system 20 reflects EUV light through interference effects while functioning as a Mo metal-coated mirror in the longer wavelength range. This function is extremely beneficial for advanced semiconductor manufacturing.

[0107] The optical system 20 enables real-time alignment and overlay control during the step-and-scan lithography process. The projection exposure apparatus 10 includes a detection unit 26 that detects the second reflected light L3 and outputs alignment information including a measurement pattern for alignment, and a control unit 14 that acquires the alignment information from the detection unit 26 and outputs control information based on the alignment information to the drive unit 12. As a result, the projection exposure apparatus 10 can detect positional errors in real time by allowing visible light to pass through the projection system 24, carrying an image of the reference line SL, which is a scribe line, from the wafer W, and comparing it with a reference pattern RL on the mask 40.

[0108] The projection lithography apparatus 10 can correct errors in real time by providing feedback to the drive unit 12 that drives the wafer stage ST, similar to autonomous vehicles or noise-canceling headphones. The projection lithography apparatus 10 can appropriately control the overlay even if there are random errors related to the CMP process, etching, etc. The projection lithography apparatus 10 can easily correct positional drift in the projection system 24, for example, due to mirror heating, because it causes the same drift in the EUV and visible regions.

[0109] In lithography for advanced semiconductor manufacturing, high-precision wafer alignment and overlay control with nanometer resolution are required. Overlay is a critical parameter that affects the yield, performance, and reliability of the final integrated circuit. The projection exposure apparatus 10 enables accurate overlay measurement and a rigorous control mechanism throughout the entire IC manufacturing process.

[0110] Unlike conventional technologies, the projection exposure apparatus 10 generates a moiré pattern by aligning the forward path of the first measurement light L2 from the mask 40 to the wafer W and the return path of the second reflected light L3 from the wafer W to the mask 40. This enables the projection exposure apparatus 10 to achieve nanometer-precision alignment of the mask 40 and the wafer W.

[0111] Unlike conventional technologies, in the projection lithography apparatus 10, friction of the stage ST on which the wafer W is placed does not affect the accuracy of the overlay. Therefore, conventional mechanical bearings can be used in the stage ST of the projection lithography apparatus 10. Compared to conventional technologies that mount multiple magnetic coils on the wafer stage, the projection lithography apparatus 10 is much lighter and can improve the scanning speed. Therefore, the projection lithography apparatus 10 can improve throughput and increase productivity.

[0112] For example, conventional technologies such as twin-scan systems are scanner technologies based on innovative frictionless magnetic levitation bearings, sophisticated error feedback using multiple laser sensors, and overall error feedback in the litho-cycle. This essential tool is also one of the cost factors of advanced lithography tools. Even with such advanced systems, random errors related to chemical etching or CMP surface polishing processes could cause malfunctions. The projection exposure apparatus 10 can solve these problems as well.

[0113] The projection exposure apparatus 10 allows for virtually the same level of mechanical tolerances as conventional systems, eliminating the need for a large balance mass and multiple laser rangefinders. Therefore, the projection exposure apparatus 10 can significantly reduce the cost of the scanner. As mentioned above, the projection exposure apparatus 10 can use conventional mechanical bearings in the stage ST instead of magnetic levitation bearings. Therefore, the projection exposure apparatus 10 can save the cost of a large permanent magnet array that can weigh up to approximately one ton.

[0114] Because the projection lithography system 10 is single-scan and small in size, the vacuum chamber can be made much smaller and lighter. The projection lithography system 10 does not require an extremely quiet environment and can be installed in a typical factory. The projection lithography system 10 can significantly reduce overall costs. The projection lithography system 10 can also promote Moore's Law by narrowing the line rule without significantly increasing production costs.

[0115] The optical system 20, projection exposure apparatus 10, and projection exposure system 1 also enable improved energy efficiency. For example, the projection system 24 of the optical system 20 has two mirrors. This allows for a cost-effective solution that meets performance requirements using technology available within a reasonable timeframe. By focusing on low NA lithography with an in-line two-mirror configuration, it is possible to reduce costs and save power consumption.

[0116] For example, a multilayer mirror absorbs more than 30% of the EUV light power at each reflection. In conventional projection exposure apparatuses, for example, six mirrors are arranged in the projection optical system and four mirrors in the illumination optical system. The transfer of light power from the EUV light source to the wafer is very low. On the other hand, a projection exposure apparatus 10 according to one embodiment of the present disclosure realizes a two-mirror projector having a simplified projection system 24 using two mirrors in series, and can dramatically improve the light power transfer efficiency.

[0117] For example, the projection lithography apparatus 10 can increase the efficiency of the two-mirror projector by approximately 13 times compared to conventional technology, and reduce the power consumption required to generate EUV light power by 92%. This reduces AC power consumption from approximately 1 MW to approximately 80 kW. Furthermore, the cooling water flow rate in the drive laser system is also significantly reduced. The design of the EUV light source is simplified, reducing investment and maintenance costs, and improving the reliability of the projection lithography apparatus 10. At this power level, the projection lithography apparatus 10 can also prevent debris from the plasma light source and protect expensive masks and mirrors by placing a transparent window of thin film, similar to the pellicle of a mask, at an intermediate focus in the illumination system 30.

[0118] Existing EUV tools typically have slower scanning speeds than optical scanners due to the weaknesses of EUV light sources, such as insufficient intensity. However, by using the projection exposure apparatus 10 according to one embodiment of this disclosure, the EUV light power to the wafer W can be increased, resulting in faster scanning speeds and improved productivity.

[0119] The two-mirror projector can also be mounted in a tube similar to those used in ultraviolet lithography lenses. In the projection exposure apparatus 10, highly accurate mirrors are sealed within the tube, providing several advantages such as mechanical stability, ease of assembly, alignment, and replacement, and excellent sealing to protect against dust contamination. As a result, capital and maintenance costs are reduced, and the reliability of the projection exposure apparatus 10 is improved.

[0120] It will be apparent to those skilled in the art that this disclosure can be implemented in other predetermined forms besides the embodiments described above without deviating from its spirit or essential features. Therefore, the prior description is illustrative and not limiting. The scope of the disclosure is defined not by the prior description but by the added claims. Any modifications within their equivalent scope are included therein.

[0121] For example, the shape, pattern, size, arrangement, orientation, type, and number of each component described above are not limited to those shown in the above description and drawings. The shape, pattern, size, arrangement, orientation, type, and number of each component may be configured arbitrarily as long as they can realize their function. The components of the optical system 20, projection exposure apparatus 10, and projection exposure system 1 shown are functional concepts, and the specific form of each component is not limited to those shown.

[0122] In the above embodiment, the projection system 24 was described as arranging the optical paths of the first measurement light L2 and the second reflected light L3 through a plurality of mirrors outside the exposure field of the first reflected light L1, but it is not limited to this. The projection system 24 may arbitrarily arrange the optical paths of the first measurement light L2 and the second reflected light L3 through a plurality of mirrors, as long as it can realize both exposure and alignment functions.

[0123] In the above embodiment, the projection system 24 is described as directing the first measurement light L2 to a reference line SL located near the outside of the exposure field formed by the first reflected light L1 on the wafer W, but it is not limited to this. The projection system 24 may direct the first measurement light L2 to another reference line SL different from the scribe line on the wafer W, or to any other mark different from the reference line SL.

[0124] In the above embodiment, the projection system 24 was described as receiving the second reflected light L3 and guiding it to the mask 40 with a plurality of mirrors, but it is not limited to this. When the projection system 24 guides the received second reflected light L3 to the outside of the projection system 24 with a plurality of mirrors, it may guide it to a location different from the mask 40. In this case, the reference pattern RL may be placed in place of, or in addition to, the mask 40, at the location to which the second reflected light L3 is guided.

[0125] In the above embodiment, the projection system 24 was described as receiving the first measurement light L2 and guiding it to the wafer W with multiple mirrors, but it is not limited to this. The projection system 24 only needs to guide the second reflected light L3 from at least the wafer W to the outside of the projection system 24, such as the mask 40, and does not need to receive the first measurement light L2. In this case, the first measurement light L2 may be guided to the wafer W along any other optical path that does not pass through the projection system 24.

[0126] In the above embodiment, the optical system 20 was described as having a first mirror 21 positioned adjacent to the projection system 24 and receiving the first measurement light L2 from the light source 25 and reflecting it to the mask 40, but it is not limited to this. The optical system 20 does not have to have the first mirror 21. The optical system 20 may guide the first measurement light L2 to the mask 40 in any other configuration that does not use the first mirror 21.

[0127] In the above embodiment, the detection unit 26 was described as detecting the second reflected light L3 and outputting an image in which the measurement pattern for alignment based on the reference line SL and the reference pattern RL on the mask 40 corresponding to the measurement pattern overlap, but it is not limited to this. The detection unit 26 may output any other information that can be used for alignment.

[0128] In the above embodiment, the optical system 20 was described as having a second mirror 22 positioned between the first mirror 21 and the mask 40, which receives the second reflected light L3 emitted from the projection system 24 and reflected by the mask 40, and reflects it to the detection unit 26. However, the optical system 20 is not limited to this. The optical system 20 does not have to have a second mirror 22. The optical system 20 may also guide the second reflected light L3 to the detection unit 26 in any other configuration that does not use a second mirror 22.

[0129] In the above embodiment, the optical system 20 was described as having a pair of third mirrors 23 that each receive illumination light L0 from the light source 31 and reflect it to the mask 40, but it is not limited to this. The optical system 20 does not have to have a pair of third mirrors 23. The optical system 20 may guide the illumination light L0 to the mask 40 in any other configuration that does not use a pair of third mirrors 23.

[0130] In the above embodiment, the projection system 24 of the optical system 20 was described as having two mirrors, but it is not limited to this. The projection system 24 may have three or more mirrors.

[0131] In the above embodiment, the fifth mirror 242 was described as being positioned on the opposite side of the pair of third mirrors 23 relative to the fourth mirror 241, but this is not limited to that. The fifth mirror 242 may be positioned on the wafer W side relative to the fourth mirror 241, and the position of the pair of third mirrors 23 relative to the fourth mirror 241 is not limited to the position shown in Figure 1A, etc. The pair of third mirrors 23 are not limited to being located outside the projection system 24, but may be located inside the projection system 24. The pair of third mirrors 23 may be located between the fourth mirror 241 and the fifth mirror 242.

[0132] In the above embodiment, the fourth mirror 241 and the fifth mirror 242 were described as being located on the same central axis A, but this is not limited to this. For example, if the center C between the pair of third mirrors 23, the fourth mirror 241, and the fifth mirror 242 are located on the same straight line, the central axes of the fourth mirror 241 and the fifth mirror 242 do not necessarily coincide.

[0133] In the embodiments described above, the fourth mirror 241 and the fifth mirror 242 were described as axially symmetric aspherical mirrors, but are not limited thereto. The fourth mirror 241 and the fifth mirror 242 do not have to be axially symmetric. The fourth mirror 241 and the fifth mirror 242 may be other types of mirrors other than aspherical mirrors that can achieve the functions of the present disclosure.

[0134] In the above embodiment, the first optical surface S1 and the second optical surface S2 were described as having substantially the same radius of curvature, but this is not limited to this. The first optical surface S1 and the second optical surface S2 may have different radii of curvature.

[0135] In the above embodiment, the fourth mirror 241 was described as having a first opening H1 that guides the first reflected light L1 and the first measured light L2 from the outside to the inside of the projection system 24, but it is not limited to this. The fourth mirror 241 is not limited to the configuration of the first opening H1, such as a first through hole, and may have any other configuration that can guide the first reflected light L1 and the first measured light L2 from the outside to the inside of the projection system 24. For example, the fourth mirror 241 may have a transparent window or the like.

[0136] In the above embodiment, the fifth mirror 242 was described as having a second opening H2 that guides the first reflected light L1 and the first measured light L2 from the inside to the outside of the projection system 24, and the second reflected light L3 from the outside to the inside of the projection system 24, but it is not limited to this. The fifth mirror 242 is not limited to the configuration of the second opening H2, such as a second through hole, and may have any other configuration that is capable of guiding the first reflected light L1 and the first measured light L2 from the inside to the outside of the projection system 24, and the second reflected light L3 from the outside to the inside of the projection system 24. For example, the fifth mirror 242 may have a transparent window or the like.

[0137] In the embodiments described above, each of the pair of third mirrors 23 was described as a cylindrical mirror, but is not limited thereto. Each of the pair of third mirrors 23 may be any other type of mirror capable of achieving the functions of the present disclosure.

[0138] In the above embodiment, the pair of third mirrors 23 formed a first exposure field and a second exposure field of illumination light L0 on the mask 40, and the first exposure field and the second exposure field were described as being separated from each other, but this is not limited to the above. The exposure fields on the mask 40 are not limited to a double-line configuration and may consist of at least one of other numbers, other shapes, and other arrangements.

[0139] In the above embodiment, the control unit 14 of the projection exposure apparatus 10 controls at least one of the movement of the wafer W in the scanning direction and the position of the wafer W in a direction intersecting the scanning direction by outputting control information to the drive unit 12, but it is not limited to this. The control unit 14 may control the state of the wafer W in any other manner necessary for overlay control.

[0140] In the above embodiment, the alignment information was described as including an image showing a moiré pattern formed by the overlapping of the measurement pattern and the reference pattern RL on the mask 40 corresponding to the measurement pattern, but it is not limited to this. The alignment information may also include an image showing information other than the moiré pattern, or it may include any other information that can be used for alignment, rather than an image.

[0141] In the above embodiment, the control unit 14 of the projection exposure apparatus 10 was described as calculating control information based on the moiré pattern, but it is not limited to this. The control unit 14 may also calculate control information based on any information included in the alignment information acquired from the detection unit 26.

[0142] In the above embodiment, the projection exposure apparatus 10 was described as having a third light source 11 that irradiates pulsed light onto a sprocket SP formed on the wafer W for determining the output timing of alignment information by the detection unit 26, but it is not limited to this. The projection exposure apparatus 10 does not have to have a third light source 11.

[0143] In the above embodiment, the image was described as including a first image region IM1 showing a moiré pattern and a second image region IM2 showing only the sprocket SP, but it is not limited to this. The image may include at least one image region in any other configuration.

[0144] In the above embodiment, the control unit 14 of the projection exposure apparatus 10 was described as calculating control information by subtracting second error information based on the sprocket SP of the second image area IM2 from first error information based on the moiré pattern of the first image area IM1, but it is not limited to this. The control unit 14 may calculate control information by any other method.

[0145] Figure 12 is a schematic diagram illustrating a part of the configuration of a projection exposure apparatus 10 according to a first modification of the present disclosure. In the above embodiment, alignment was described as including, but is not limited to, adjustment of the position of the wafer W in at least one of the x and y directions. Alignment may further include, in addition to adjustment of the position of the wafer W in at least one of the x and y directions, adjustment of the position of the wafer W in the z direction. Referring to Figure 12, an example of the configuration and function of the projection exposure apparatus 10 related to the alignment of the wafer W in the z direction, for example, the vertical direction, will be mainly described.

[0146] The projection exposure apparatus 10 may further include a spectrometer 50, a light guide component 60, a first optical element 70, and a second optical element 80 in order to achieve vertical alignment of the wafer W. The spectrometer 50 may also include a fourth light source 51 and a light receiving unit 52. The first optical element 70 and the second optical element 80 may be included in the optical system 20. That is, the optical system 20 may further include the first optical element 70 and the second optical element 80.

[0147] The spectroscopic unit 50 may be configured as a single unit in which, for example, the fourth light source 51 and the light receiving unit 52 are arranged together inside a single housing. The spectroscopic unit 50 is located outside the housing V, such as a vacuum chamber, in which the projection system 24 is housed. One end of the spectroscopic unit 50 is connected to the other end of a light guide component 60 located inside the housing V. The spectroscopic unit 50 irradiates the inside of the projection system 24 with the second measurement light L4 from the fourth light source 51 via the light guide component 60, and the second measurement light L4 that returns from inside the projection system 24 as interference light via the light guide component 60 is received by the light receiving unit 52. The spectroscopic unit 50 may also function as a displacement meter using spectral interference.

[0148] The fourth light source 51 of the spectroscopic unit 50 includes, for example, any light source capable of emitting a coherent second measurement light L4 while having a broadband emission spectrum. This light source includes, for example, an SLD (Super Luminescent Diode). The fourth light source 51 irradiates the inside of the projection system 24 with the second measurement light L4 used for aligning the vertical position of the wafer W by the projection exposure apparatus 10. The fourth light source 51 irradiates the first optical element 70 with the second measurement light L4 via the light guide component 60, and further irradiates the wafer W and the second optical element 80 with the second measurement light L4, which has been branched into two optical paths by the first optical element 70.

[0149] The fourth light source 51 irradiates the wafer W with a second measurement light L4 having an arbitrary wavelength that enables vertical alignment of the wafer W by the projection exposure apparatus 10. The wavelength of the second measurement light L4 irradiated by the fourth light source 51 may include, for example, substantially the entire visible region. The fourth light source 51 may irradiate, for example, white light as the second measurement light L4. However, it is not limited to this, and the wavelength of the second measurement light L4 may include, for example, a part of the visible region, the near-infrared region, or other infrared regions.

[0150] The light-receiving unit 52 of the spectroscopic unit 50 includes, for example, a spectrometer that spectrally separates the second measurement light L4 that has returned from inside the projection system 24 via the light guide component 60 into wavelengths, and a photodetector that includes an imaging module such as a camera including a two-dimensional image sensor or a light-receiving element such as a photodiode. The two-dimensional image sensor includes, for example, a CCD sensor or a CMOS sensor. The spectrometer includes, for example, a diffraction grating. The light-receiving unit 52 receives interference light based on the second measurement light L4 irradiated into the inside of the projection system 24 by the fourth light source 51 and outputs spectral information of the interference light.

[0151] The wavelength range that the light-receiving unit 52 can receive includes the wavelength range of the second measurement light L4. The light-receiving unit 52 has detection sensitivity at the wavelengths of the second measurement light L4. The wavelengths at which the light-receiving unit 52 has detection sensitivity may include, for example, substantially the entire visible region. However, it is not limited to this, and such wavelengths may include, for example, a part of the visible region, the near-infrared region, or other infrared regions.

[0152] The spectroscopic unit 50 may calculate the position error in the z-direction as control information, using an inverse Fourier transform or the like, based on the spectroscopic information acquired by the light receiving unit 52. The spectroscopic unit 50 may output the calculated control information to a scan motor or other drive unit that drives the wafer W in the z-direction. This allows the spectroscopic unit 50 to perform feedback control of the position of the wafer W in the z-direction, for example. For example, the spectroscopic unit 50 may operate the scan motor or other drive unit by outputting the control information. The drive unit may adjust the position in the z-direction of the stage ST on which the wafer W is placed based on the control information from the spectroscopic unit 50.

[0153] The light guide component 60 includes, for example, an optical fiber. The light guide component 60 guides the second measurement light L4 emitted from the fourth light source 51 of the spectroscopic unit 50 to the first optical element 70 located inside the projection system 24. The light guide component 60 guides the second measurement light L4, which has been reflected by the wafer W and the second optical element 80 and interfered with each other at the first optical element 70, as interference light to the light receiving unit 52 of the spectroscopic unit 50.

[0154] The first optical element 70 includes, for example, an arbitrary optical element that splits the second measurement light L4 emitted from the light guide component 60 into two optical paths. The optical element includes, for example, a half mirror, a beam splitter, or a prism. The first optical element 70 splits the second measurement light L4 from the fourth light source 51, which is used for aligning the vertical position of the wafer W, into two optical paths toward the wafer W and the second optical element 80. The first optical element 70 may, for example, split the second measurement light L4 into two optical paths in a 50:50 ratio of intensity, or it may split it into two optical paths in other ratios.

[0155] The first optical element 70 may be positioned on the focal plane F located inside the projection system 24. In addition, the first optical element 70 may be located on the central axis A. The first optical element 70 may be located on the same central axis A as the wafer W and directly above the wafer W. The optical path of the second measurement light L4 from the first optical element 70 to the wafer W may be configured to be straight along the vertical direction. Similarly, the optical path of the second measurement light L4 from the first optical element 70 to the second optical element 80 may be configured to be straight along the horizontal direction.

[0156] The Fourier image at the focal plane F located between the first optical plane S1 and the second optical plane S2 is, for example, an image having a defect in the center due to the first aperture H1 and the second aperture H2, and four bright spots located outside the center and arranged symmetrically with respect to the center. In this disclosure, the "four bright spots" correspond to, for example, the zeroth Bragg spot obtained by the Fourier transform of the pattern on the mask 40, which is additionally obtained to the bright spot equal to the origin when the illumination light L0 converges and is Fourier transformed. The projection system 24 guides the first reflected light L1 to the wafer W by, for example, symmetrical off-axis illumination from four directions.

[0157] The second optical element 80 includes, for example, an arbitrary optical element that reflects one of the second measurement light L4 branches off at the first optical element 70 back towards the first optical element 70. This optical element includes, for example, a mirror or a corner cube. The second optical element 80 may also reverse the optical path of one of the second measurement light L4 branches off at the first optical element 70 by 180°, so that the optical path of the second measurement light L4 from the second optical element 80 to the first optical element 70 is linear along the horizontal direction.

[0158] In the system described above, the fourth light source 51 of the spectroscopic unit 50 irradiates the light guide component 60 with a second measurement light L4 used for aligning the vertical position of the wafer W. The second measurement light L4 emitted from the fourth light source 51 propagates inside the light guide component 60 and is guided into the projection system 24 housed in the housing V. The second measurement light L4 emitted from the light guide component 60 propagates linearly along the horizontal direction to the first optical element 70.

[0159] A portion of the second measurement light L4 incident on the first optical element 70 is reflected by the first optical element 70, passes through the second aperture H2 in a straight optical path along the vertical direction, and is guided to the wafer W. A portion of the second measurement light L4 is incident on the wafer W from directly above on the central axis A. The remaining portion of the second measurement light L4 incident on the first optical element 70 passes through the first optical element 70 and is guided to the second optical element 80 in a straight optical path along the horizontal direction. The second measurement light L4 reflected from the wafer W and returning to the first optical element 70 and the second measurement light L4 reflected from the second optical element 80 and returning to the first optical element 70 interfere with each other in the first optical element 70 and are guided to the light receiving unit 52 via the light guide component 60.

[0160] The optical system 20 according to the first modified example described above includes a first optical element 70 that splits the second measurement light L4 into two optical paths toward the wafer W and the second optical element 80, and a second optical element 80 that reflects one of the second measurement light L4 split by the first optical element 70 toward the first optical element 70. As a result, the optical system 20 can contribute to the vertical alignment of the wafer W based on the principle of a Michelson interferometer. The optical system 20 can improve the overlay control technology in the projection exposure apparatus 10.

[0161] The first optical element 70 is positioned at the focal plane F located inside the projection system 24. This allows the optical system 20 to position the first optical element 70 at a location corresponding to the defect in the focal plane F where a Fourier image with a defect in the center due to the first aperture H1 and the second aperture H2 is formed. Therefore, the optical system 20 can reduce the influence of the first optical element 70 on the reticle image generated on the wafer W by exposure of the first reflected light L1.

[0162] The first optical element 70 is positioned on the central axis A and can therefore function as a shield on the central axis A. For example, in the two-mirror projector shown in Figure 12, there is a portion of the first reflected light L1 that travels in a straight line along the central axis A from the first aperture H1 to the second aperture H2. Therefore, the optical system 20 can block this portion of the first reflected light L1 with the first optical element 70, thereby reducing background noise based on the portion of the first reflected light L1.

[0163] In the first modified example described above, the positional relationship between the first optical element 70 and the second optical element 80 for achieving vertical alignment of the wafer W is not limited to that shown in Figure 12. For example, the first optical element 70 may be positioned horizontally between the end of the light guide component 60 and the central axis A. In this case, the second optical element 80 may be positioned directly below the first optical element 70. Further mirrors may be positioned on the central axis A to reflect the optical path of the second measurement light L4 that has passed through the first optical element 70 back toward the wafer W at a right angle.

[0164] The configuration for achieving vertical alignment of the wafer W is not limited to the first modified example described above. The optical system 20 may have at least one optical element in any other number, arrangement, orientation, or type that can achieve vertical alignment of the wafer W.

[0165] In the first modified example described above, the first optical element 70 is positioned at the focal plane F located inside the projection system 24, but this is not limited to this. The first optical element 70 may be positioned at a location different from the focal plane F located inside the projection system 24.

[0166] In the first modified example described above, the first optical element 70 is positioned on the same central axis A as the wafer W, but this is not limited to this. The first optical element 70 may be positioned at a location different from the central axis A.

[0167] Figure 13A is the first figure illustrating an example of the function of the projection exposure apparatus 10 according to the second modification. Figure 13A shows the optical path around the mask 40 in detail. Figure 13B is the second figure illustrating an example of the function of the projection exposure apparatus 10 according to the second modification. Figure 13B shows how four illumination spots are formed in the focal plane F within an aperture partially restricted by shadows from a pair of third mirrors 23. Figure 13C is the third figure illustrating an example of the function of the projection exposure apparatus 10 according to the second modification. Figure 13C shows how the field projected onto the wafer W appears as a double line.

[0168] In the above embodiment, the mask 40 and wafer W were described as moving in opposite directions by scanning, but this is not limited to this. The mask 40 and wafer W may remain stationary. In this case, the projection exposure apparatus 10 according to the second modification may function as a stepper instead of a scanner together with the mask 40 and wafer W.

[0169] For example, the illumination system 30 of the projection exposure apparatus 10 according to the second modification was intended for use in scanner mode in the above embodiment, but it may also be designed to function effectively in stepper mode. For example, the illumination system 30 of the projection exposure apparatus 10 may scan a pair of third mirrors 23 with the mask 40 and wafer W fixed in place. By scanning the pair of third mirrors 23, the illumination system 30 may sequentially guide illumination light L0 to different positions on the stationary mask 40 to form a predetermined exposure field. The projection exposure apparatus 10 may transfer the pattern on the mask 40 to the wafer W by stepwise repeating the above operation by the illumination system 30.

[0170] As shown in Figure 13A, illumination light L0 from the light source 31 is guided to a pair of third mirrors 23 via other components of the illumination system 30. As the pair of third mirrors 23 are scanned and moved in a predetermined direction, the illumination light L0 is directed onto two exposure fields (a) moving in that predetermined direction on the mask 40. １ +a ２、 b １ +b ２) is formed. At this time, the mask 40 is fixed. Therefore, the projection exposure apparatus 10 achieves switching of the exposure position solely by optical means based on scanning of a pair of third mirrors 23 in stepper motion. This point differs significantly from the scanner method in the above embodiment.

[0171] The rectangular drawing area R represents, for example, a unit exposure field that is illuminated at each step in a stepper operation. The drawing area R is, for example, (a １ +a ２ ) field and (b １ +b ２ This indicates a rectangular or square exposure field that is ultimately formed by combining two line fields. The drawing area R indicates the range in which the pattern is transferred all at once by the illumination light L0, and is formed as a rectangular or square exposure field. The projection exposure apparatus 10 can form the entire two-dimensional pattern on the wafer W with high precision by precisely overlapping the drawing area R in multiple stages.

[0172] In Figure 13B, the illumination distribution at the entrance pupil formed on the focal plane F is schematically shown. In the projection exposure apparatus 10 according to the second modified example, four spots are arranged by quadrupole off-axis illumination. The Fourier image at the focal plane F located between the first optical plane S1 and the second optical plane S2 is, for example, an image having a defect B in the center due to the first aperture H1 and the second aperture H2, and four bright spots arranged symmetrically with respect to the center outside the center.

[0173] As shown in Figure 13C, the first reflected light L1 reflected by the mask 40 is irradiated onto the wafer W via the fourth mirror 241 and fifth mirror 242 of the projection system 24. In stepper mode, the wafer W is fixed in the same state as the mask 40, and the illumination positions of the two line fields are switched by scanning the pair of third mirrors 23.

[0174] According to the projection exposure apparatus 10 of the second modified example described above, a high-precision scanning mechanism using a mechanical stage mechanism is not required for each of the mask 40 and the wafer W. The projection exposure apparatus 10 eliminates the need for a scanning mechanism to precisely synchronize the mask 40 and the wafer W, enabling pattern formation on the wafer W with a simple configuration. In addition, even if distortion remains on the image plane in the projection system 24, the projection exposure apparatus 10 can cancel out such distortion in advance by correcting the mask 40 at the design stage before exposure.

[0175] Some embodiments of the present disclosure are illustrated below. However, it should be noted that embodiments of the present disclosure are not limited to these. [Note 1] An optical system for a projection exposure apparatus disposed between a mask and a wafer, comprising a projection system having a plurality of mirrors that receive first reflected light for exposure, which is reflected by the mask from illumination light from a first light source, and guide it to the wafer, wherein the projection system receives second reflected light, which is reflected by the wafer from a first measurement light from a second light source, used for aligning the position of the wafer, and guides it to the outside of the projection system by the plurality of mirrors. [Note 2] The optical system according to Note 1, wherein the projection system has optical paths for the first measurement light and the second reflected light through the plurality of mirrors located outside the exposure field formed by the first reflected light. [Note 3] The optical system according to Note 2, wherein the projection system guides the first measurement light to a reference line located near the outside of the exposure field formed by the first reflected light on the wafer. [Note 4] An optical system according to any one of Notes 1 to 3, wherein the projection system receives the second reflected light and guides it to the mask with the plurality of mirrors. [Note 5] An optical system according to any one of Notes 1 to 4, wherein the projection system receives the first measurement light and guides it to the wafer with the plurality of mirrors. [Note 6] An optical system according to any one of Notes 1 to 5, further comprising a first mirror arranged adjacent to the projection system, which receives the first measurement light from the second light source and reflects it to the mask. [Note 7] An optical system according to Note 6, further comprising a detection unit that detects the second reflected light and outputs an image in which the alignment measurement pattern based on a reference line on the wafer and the reference pattern on the mask corresponding to the measurement pattern overlap. [Note 8] The optical system described in Note 7, further comprising a second mirror positioned between the first mirror and the mask, which receives the second reflected light emitted from the projection system and reflected by the mask, and reflects it back to the detection unit.[Note 9] An optical system according to any one of Notes 1 to 8, further comprising a pair of third mirrors that each receive the illumination light from the first light source and reflect it to the mask, wherein the projection system has two mirrors, a fourth mirror positioned adjacent to the pair of third mirrors, and a fifth mirror positioned on the wafer side relative to the fourth mirror and having a second optical surface facing the first optical surface of the fourth mirror, wherein the center between the pair of third mirrors, the fourth mirror, and the fifth mirror are located on the same straight line. [Note 10] An optical system according to Note 9, wherein the fourth mirror and the fifth mirror are located on the same central axis. [Note 11] An optical system according to Note 9 or 10, wherein the fourth mirror has a first aperture that guides the first reflected light and the first measurement light from outside to inside the projection system, and the fifth mirror has a second aperture that guides the first reflected light and the first measurement light from inside to outside the projection system, and guides the second reflected light from outside to inside the projection system. [Note 12] An optical system according to any one of Notes 1 to 11, further comprising: a first optical element that branches the second measurement light from a fourth light source, which is used for aligning the vertical position of the wafer, into two optical paths toward the wafer and the second optical element; and a second optical element that reflects one of the branches of the second measurement light toward the first optical element. [Note 13] An optical system according to Note 12, wherein the first optical element is located at a focal plane located inside the projection system and is located on the same central axis as the wafer.[Note 14] A projection exposure apparatus comprising: an optical system described in any one of Notes 1 to 13; a first light source that irradiates the mask with illumination light and exposes the wafer with first reflected light; a second light source that irradiates the wafer with first measurement light used for aligning the position of the wafer; a detection unit that detects the second reflected light and outputs alignment information including the measurement pattern for alignment on the wafer; a drive unit that drives the wafer based on the alignment information output from the detection unit; and a control unit that, when exposure by the first light source is being performed, acquires the alignment information from the detection unit and outputs control information based on the alignment information to the drive unit. [Note 15] A projection exposure apparatus described in Note 14, wherein the control unit controls at least one of the movement of the wafer in the scanning direction of the wafer and the position of the wafer in a direction intersecting the scanning direction by outputting the control information to the drive unit. [Note 16] A projection exposure apparatus according to Note 14 or 15, wherein the alignment information includes an image showing a moiré pattern in which the measurement pattern and a reference pattern on the mask corresponding to the measurement pattern overlap. [Note 17] A projection exposure apparatus according to Note 16, wherein the control unit calculates the control information based on the moiré pattern. [Note 18] A projection exposure apparatus according to Note 16 or 17, further comprising a third light source that irradiates pulsed light onto a sprocket formed on the wafer for determining the output timing of the alignment information by the detection unit. [Note 19] A projection exposure apparatus according to Note 18, wherein the image includes a first image region showing the moiré pattern and a second image region showing only the sprocket. [Note 20] A projection exposure apparatus as described in Note 19, wherein the control unit calculates the control information by subtracting the second error information based on the sprocket in the second image region from the first error information based on the moiré pattern in the first image region.

[0176] 1 Projection exposure system 10 Projection exposure apparatus 11 Third light source 12 Drive unit 121 Scan motor 122 Element 12a First drive unit 121a Scan motor 122a Element 12b Second drive unit 121b Scan motor 122b Element 13 Memory unit 14 Control unit 20 Optical system 21 First mirror 22 Second mirror 23 Third mirror 24 Projection system 241 Fourth mirror 242 Fifth mirror 25 Light source (second light source) 26 Detection unit 26a First detection unit 26b Second detection unit 27 Light-gathering element 30 Illumination system 31 Light source (first light source) 40 Mask 41 Backside film 42 Glass layer 43 Multilayer reflector 44 Capping layer 45 Absorber 50 Spectroscopic unit 51 Fourth light source 52 Light receiving section 60 Light guide component 70 First optical element 80 Second optical element A Central axis B Defect BL Black border area C Center area EX Area F Focal plane H1 First aperture H2 Second aperture IM1 First image area IM2 Second image area L0 Illumination light L1 First reflected light L2 First measurement light (measurement light) L3 Second reflected light L4 Second measurement light R Drawing area R1 Chip area R2 Boundary area RL Reference pattern S1 First optical surface S2 Second optical surface SL Reference line SP Sprocket ST Stage V Housing W Wafer d1, d2, d3 Width d4, d5, d6 Thickness

Claims

1. An optical system for a projection exposure apparatus, disposed between a mask and a wafer, comprising a projection system having a plurality of mirrors that receive first reflected light for exposure, which is reflected by the mask from illumination light from a first light source, and guide it to the wafer, wherein the projection system receives second reflected light, which is reflected by the wafer from a first measurement light from a second light source used for aligning the position of the wafer, and guides it to the outside of the projection system by the plurality of mirrors.

2. The optical system according to claim 1, wherein the projection system is configured such that the optical paths of the first measurement light and the second reflected light through the plurality of mirrors are located outside the exposure field of the first reflected light.

3. The optical system according to claim 2, wherein the projection system guides the first measurement light to a reference line located near the outside of the exposure field formed by the first reflected light on the wafer.

4. An optical system according to any one of claims 1 to 3, wherein the projection system receives the second reflected light and guides it to the mask with the plurality of mirrors.

5. An optical system according to any one of claims 1 to 4, wherein the projection system receives the first measurement light and guides it to the wafer with the plurality of mirrors.

6. An optical system according to any one of claims 1 to 5, further comprising a first mirror positioned adjacent to the projection system, which receives the first measurement light from the second light source and reflects it to the mask.

7. The optical system according to claim 6, further comprising a detection unit that detects the second reflected light and outputs an image in which the alignment measurement pattern based on the reference line on the wafer and the reference pattern on the mask corresponding to the measurement pattern overlap.

8. The optical system according to claim 7, further comprising a second mirror disposed between the first mirror and the mask, which receives the second reflected light emitted from the projection system and reflected by the mask, and reflects it back to the detection unit.

9. An optical system according to any one of claims 1 to 8, further comprising a pair of third mirrors that each receive the illumination light from the first light source and reflect it to the mask, wherein the projection system has two mirrors, a fourth mirror positioned adjacent to the pair of third mirrors, and a fifth mirror positioned on the wafer side relative to the fourth mirror and having a second optical surface facing the first optical surface of the fourth mirror, the center between the pair of third mirrors, the fourth mirror, and the fifth mirror are located on the same straight line.

10. The optical system according to claim 9, wherein the fourth mirror and the fifth mirror are located on the same central axis.

11. An optical system according to claim 9 or 10, wherein the fourth mirror has a first aperture that guides the first reflected light and the first measuring light from outside to inside the projection system, and the fifth mirror has a second aperture that guides the first reflected light and the first measuring light from inside to outside the projection system, and guides the second reflected light from outside to inside the projection system.

12. An optical system according to any one of claims 1 to 11, further comprising: a first optical element that splits a second measurement light from a fourth light source, which is used for aligning the vertical position of the wafer, into two optical paths toward the wafer and the second optical element; and a second optical element that reflects one of the branches of the second measurement light toward the first optical element.

13. The optical system according to claim 12, wherein the first optical element is located at a focal plane within the projection system and is located on the same central axis as the wafer.

14. A projection exposure apparatus comprising: a first light source that irradiates a mask with illumination light and exposes a wafer with first reflected light reflected by the mask; a second light source that irradiates the wafer with measurement light used for aligning the position of the wafer; a detection unit that detects the second reflected light reflected by the wafer from the measurement light and outputs alignment information including the measurement pattern for alignment on the wafer; a drive unit that drives the wafer based on the alignment information output from the detection unit; and a control unit that, when exposure by the first light source is being performed, acquires the alignment information from the detection unit and outputs control information based on the alignment information to the drive unit.

15. A projection exposure apparatus according to claim 14, wherein the control unit controls at least one of the movement of the wafer in the scanning direction of the wafer and the position of the wafer in a direction intersecting the scanning direction by outputting the control information to the drive unit.

16. A projection exposure apparatus according to claim 14 or 15, wherein the alignment information includes an image showing a moiré pattern in which the measurement pattern and a reference pattern on the mask corresponding to the measurement pattern overlap.

17. A projection exposure apparatus according to claim 16, wherein the control unit calculates the control information based on the moiré pattern.

18. A projection exposure apparatus according to claim 16 or 17, further comprising a third light source that irradiates pulsed light onto a sprocket formed on the wafer for determining the output timing of the alignment information by the detection unit.

19. A projection exposure apparatus according to claim 18, wherein the image includes a first image region showing the moiré pattern and a second image region showing only the sprocket.

20. A projection exposure apparatus according to claim 19, wherein the control unit calculates the control information by subtracting a second error information based on the sprocket of the second image region from a first error information based on the moiré pattern of the first image region.

Images