Optical apparatus and lithographic apparatus using the same

Abstract

An optical element and a lithographic apparatus comprising the same are described herein. The optical apparatus comprises a substrate having an aperture for passing light, a transmissive optical element covering the aperture of the substrate, and an optical contact joint between the substrate and the transmissive optical element, the optical contact joint being spaced apart from the aperture by a sufficient distance such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold. Herein, the optical contact joint geometry e.g. minimizes the contact area and provides a quasi-kinematic (almost exactly constrained) interface between the substrate and the optical element.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 000,587, filed March 27, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to optical devices. For example, the optical devices can be used in lithography equipment or metrology equipment to improve optical-based measurements. Background Technology

[0004] Photolithography projection equipment can be used, for example, in the manufacture of integrated circuits (ICs). In such cases, a patterning apparatus (e.g., a mask) can contain or provide a circuit pattern (“design layout”) corresponding to a single layer of the IC, and this circuit pattern can be transferred onto a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) coated with a layer of radiation-sensitive material (“resist”) by methods such as irradiating the target portion through the circuit pattern on the patterning apparatus. Typically, a single substrate comprises multiple adjacent target portions, and the circuit pattern is transferred sequentially, one target portion at a time, to the multiple adjacent target portions by the photolithography projection equipment. In one type of photolithography projection equipment, the entire circuit pattern on the patterning apparatus is transferred onto a target portion at a time; such equipment is commonly referred to as a wafer stepper. In alternative equipment (commonly referred to as a step-scanning equipment), a projection beam scans across the patterning apparatus along a given reference direction (“scanning” direction) while the substrate is moved synchronously parallel or antiparallel to that reference direction. Different portions of the circuit pattern on the patterning apparatus are transferred progressively onto a target portion. Because, typically, the photolithography projection apparatus will have a magnification factor M (usually <1), the speed F of the substrate movement will be a factor M times the speed at which the projection beam scans the pattern forming apparatus. More information about the photolithography apparatus described herein can be found, for example, in US 6,046,792, which is incorporated herein by reference.

[0005] As noted, microlithography is a central step in IC manufacturing, in which patterns formed on a substrate define the functional elements of the IC, such as microprocessors and memory chips. Similar lithography techniques are also used in the fabrication of flat panel displays, microelectromechanical systems (MEMS), and other devices.

[0006] As semiconductor manufacturing processes have continued to advance, over the past few decades, while the size of circuit elements has been steadily decreasing, the number of functional elements (such as transistors) per device has been steadily increasing, following a trend commonly known as "Moore's Law." In the current state of technology, photolithography projection equipment is used to fabricate layers of devices. This equipment projects a design layout onto a substrate using irradiation from a deep ultraviolet light source, thereby forming individual functional elements with dimensions well below 100 nm (i.e., less than half the wavelength of radiation from the irradiation source (e.g., a 193 nm irradiation source)).

[0007] The process of printing features with dimensions smaller than the classical resolution limit of a photolithography projection device is often referred to as low-k1 lithography, based on the resolution formula CD = k1 × λ / NA, where λ is the wavelength of the radiation used (currently mostly 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the photolithography projection device, CD is the "critical size"—typically the smallest feature size to be printed—and k1 is an empirical resolution factor. From the CD equation, it can be deduced that the minimum printable size of the feature can be reduced in three ways: by shortening the exposure wavelength λ; by increasing the numerical aperture NA; or by decreasing the value of k1.

[0008] To shorten the exposure wavelength and thus reduce the minimum printable size, extreme ultraviolet (EUV) radiation sources have been suggested. EUV radiation is electromagnetic radiation with wavelengths in the range of 5 nm to 20 nm (e.g., in the range of 13 nm to 14 nm, such as in the range of 5 nm to 10 nm (e.g., 6.7 nm or 6.8 nm)). Possible sources include, for example, laser-generated plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

[0009] In embodiments, high light transmittance through the optical reduction system can be desired with minimal or no loss. For example, high light transmittance is desired in UV lithography applications or lithography equipment subsystems. In one aspect, exposure time and overall semiconductor manufacturing time depend on the intensity or magnitude of the light output to the wafer. The optical reduction system (also referred to as a projection system) is intended to output a sharp, focused image of the mask onto the wafer. Such a sharp image ensures the preservation of fine details associated with the target pattern.

[0010] As the exposure wavelength decreases, the optical reduction system comprises optical components (such as lenses) made of materials that are transparent even at low UV wavelengths (such as 193 nm and 157 nm). Examples of such optical materials include calcium fluoride (CaF2) and barium fluoride (BaF2). However, these optical materials have a relatively high degree of intrinsic birefringence (also known as spatial dispersion-induced birefringence). This high intrinsic birefringence is highly direction-dependent. As a result, the optical properties of the optical material (such as transmittance and refractive index) vary non-uniformly over the beam incident on the optical material. In other words, due to the direction dependence of the intrinsic birefringence, some portions of the beam spot may be accelerated or decelerated relative to other portions of the beam spot depending on the polarization of light at different portions of the beam spot. Such intrinsic birefringence is undesirable in applications requiring microlithography, as it can blur or reduce image sharpness or cause loss of light passing through the optical reduction system.

[0011] One method to correct inherent birefringence is to use a single pair of optical elements that rotate relative to each other. For those with... <100> A pair of crystal-oriented lenses, in which the optical axis of the crystal structure of one lens is rotated by an angle relative to the optical axis of the crystal structure of the other lens. This correction of the inherent birefringence is particularly limited in high-quality applications such as photolithography.

[0012] There is a need for a method, or even better, to correct or reduce the birefringence caused by optical elements. This is particularly desirable in optical reduction systems used in low-UV microlithography applications. Summary of the Invention

[0013] In one embodiment, an optical device is provided. The optical device includes: a substrate having an aperture for light to pass through; a transmissive optical element covering the aperture of the substrate; and an optical contact joint located between the substrate and the transmissive optical element. The optical contact joint is spaced a sufficient distance from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold.

[0014] Furthermore, in one embodiment, a measuring device for measuring the properties of an object is provided. The measuring device includes: a light source; and an optical device. The optical device includes: a substrate having an aperture for light to pass through; a transmissive optical element covering the aperture of the substrate; and an optical contact joint located between the substrate and the transmissive optical element. The optical contact joint is spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold. Light passing through the transmissive optical element produces an interference pattern, which is used to extract the measurement results of the object's properties.

[0015] Furthermore, in one embodiment, a photolithography apparatus is also provided. The photolithography apparatus includes: a light source; and an optical device. The optical device includes: a substrate having an aperture for light to pass through; a transmissive optical element covering the aperture of the substrate; and an optical contact joint located between the substrate and the transmissive optical element. The optical contact joint is spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold. Light passing through the transmissive optical element generates an interference pattern, which is used to extract measurement results of characteristics associated with the patterning process. Attached Figure Description

[0016] Embodiments will now be described by way of example only with reference to the accompanying drawings, in which:

[0017] Figure 1A This is a block diagram of an exemplary device employing optical equipment according to an embodiment;

[0018] Figure 1B According to the embodiments Figure 1A Exploded view of the optical equipment used;

[0019] Figure 2 It is an existing optical device according to the embodiments;

[0020] Figure 3 It is an optical device according to the embodiment;

[0021] Figure 4A Schematic representation according to an embodiment Figure 3 The arrangement of the components of the optical device;

[0022] Figure 4B According to the embodiments Figure 3 The cross-section of the optical device;

[0023] Figure 5A This is an exemplary delay generated by non-contact elements (e.g., optical elements that do not contact the substrate) of the optical device according to an embodiment;

[0024] Figure 5B According to the embodiments, it is based on existing optical devices (e.g., Figure 2 Exemplary delays caused by )

[0025] Figure 5C According to the embodiments, by Figure 3 The exemplary delay generated by the optical device;

[0026] Figure 6 The average birefringence associated with different optical devices according to embodiments is shown;

[0027] Figure 7 This is a block diagram of the various subsystems of the lithography system according to an embodiment.

[0028] Figure 8 This is a schematic diagram of a reflective lithography apparatus according to an embodiment;

[0029] Figure 9 According to the embodiments Figure 8 A more detailed view of the device;

[0030] Figure 10 According to the embodiments Figure 8 and Figure 9 A more detailed view of the source collector module SO of the device;

[0031] Embodiments will now be described with reference to the accompanying drawings, which are provided as illustrative examples to enable those skilled in the art to practice these embodiments. It is important to note that the figures and examples below are not intended to limit the scope to a single embodiment, but rather to make other embodiments possible by interchangeing some or all of the elements described or illustrated. Where convenient, the same reference numerals will be used throughout the drawings to refer to the same or similar components. Where some elements of these embodiments can be implemented partially or entirely using known components, only those portions of these known components necessary for understanding these embodiments will be described, and detailed descriptions of other portions of these known components will be omitted so as not to obscure the description of these embodiments. Embodiments shown with a singular number of components in this specification should not be considered limiting; rather, unless expressly stated otherwise herein, the scope is intended to cover other embodiments comprising a plurality of the same components, and vice versa. Furthermore, unless expressly stated otherwise, the applicant does not intend to assign any terminology in this specification or claims an uncommon or special meaning. Additionally, the scope covers present and future known equivalents of components mentioned herein by way of illustration or description. Detailed Implementation

[0032] While this disclosure describes features herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those skilled in the art, upon understanding the teachings provided herein, will recognize additional modifications, applications, and embodiments within their scope, as well as additional areas where the invention will have significant utility.

[0033] To describe the invention more clearly, the following terminology definitions have been consistently maintained throughout this specification.

[0034] The term "optical element" refers to any element that can be used in an optical device or optical system. Optical elements can include, but are not limited to, any type of lens, such as a biconvex lens, a plano-convex lens, a convex-plano lens, a biconcave lens, a plano-concave lens, a concave-plano lens, a shell, or a plate.

[0035] In one example, the optical element can be made of a cubic crystalline material. This cubic crystalline material can be used as an optical element in short-wavelength optical systems, such as wafer steppers or other projection printers for producing smaller features on substrates, such as those used in the semiconductor and semiconductor manufacturing industries. In particular, calcium fluoride is found to have the advantage of being an readily available cubic crystalline material and capable of growing large, high-purity single crystals.

[0036] For the use of cubic crystal materials in optical components for deep ultraviolet lithography systems, the primary concern is the anisotropy of the inherent refractive index within the cubic crystal material; this is known as "intrinsic birefringence." Recently, [J. Burnett, Z. H. Levine, and E. Shipley's "Intrinsic Birefringence in 157 nm materials" (Proc. 2nd Intl. Symp on 157 nm Lithography, Austin, Intl. SEMATECed. R. Harbison, 2001)] reported that cubic crystal materials such as calcium fluoride exhibit an intrinsic birefringence that is inversely proportional to the square of the wavelength of light used in the optical system. This birefringence becomes particularly large when the wavelength decreases below 250 nm, and especially close to 100 nm. Of particular interest is the effect of the intrinsic birefringence at a wavelength of 157 nanometers (nm) (the wavelength of light produced by F2 excimer lasers favored in the semiconductor manufacturing industry).

[0037] Birefringence (or double-refraction) is a property of refractive materials in which the refractive index is anisotropic. For light propagating through a birefringent material, the refractive index varies as a function of the polarization and orientation of the material relative to the direction of propagation. Unpolarized light propagating through a birefringent material will typically be split into two beams with orthogonal polarization states.

[0038] When light travels a unit length through a birefringent material, the difference in refractive index between the two ray paths results in an optical path difference, or delay. Birefringence is a dimensionless quantity, but in photolithography, it is commonly expressed in nm / cm. Birefringence is a material property, while delay is the optical delay between polarization states. The delay of a given ray passing through an optical system can be expressed in nm, or the delay of a given ray passing through an optical system can be expressed in the number of waves of a specific wavelength.

[0039] In one embodiment, stress on the optical element produces a spatially varying birefringence and alters the optical path difference within the optical system. In this embodiment, such stress-induced birefringence or optical path difference may be undesirable because it can affect, for example, measurement accuracy or introduce measurement errors.

[0040] In an embodiment, Figure 1A This is a block diagram of a device S10 employing a lens device OPA according to this disclosure. In the example, the lens device OPA can be used in the sensor S10 (e.g., in...). Figure 7 and Figure 8The horizontal sensor used in the lithography apparatus shown in the figure. Such a lens assembly OPA may produce undesirable changes in birefringence and optical path difference. As mentioned above, birefringence is a property of the optical material that can split light LG propagating through the material into two beams, thereby causing an optical path difference between the two beams.

[0041] Figure 1B The figure shows an exploded view of the lens device OPA. The lens device OPA includes a fused silica window E2 (also referred to as a transmissive optical element) with an optical contact joint. The optical joint can increase the stiffness of the fused silica window E2. In an embodiment, the fused silica window E2 can be relatively thin (e.g., 0.5 mm) to obtain the specified optical properties. In an embodiment, when the window can be thin, a substrate E1 can be used to increase the stiffness of the window E2. The substrate E1 can be an opaque optical element having a thickness of, for example, 3.5 mm. The substrate can include holes (e.g., rectangular slots).

[0042] refer to Figure 2 The window E2 can be supported by the substrate E1 along its outer edge (i.e., outside its light-transmitting aperture AP1). In existing optical components or optical devices, the optical contact portion has a large contact area, such as a surface in contact with the entire surface of the substrate. Alternatively, the optical device can be mounted to a lens system using a ceramic pad and a spring clip located on the pad.

[0043] In exemplary applications, ultraviolet lens sensors (UVLS) have recently encountered problems in system-level checks of Z-level process dependence (ZLPD). In one embodiment, ZLPD is a highly process-dependent (HPD) effect that depends on polarization. In another embodiment, this highly process-dependent effect is a focal length difference across the entire UVLS measurement spot caused by, for example, varying thickness of the oxide layer on the wafer.

[0044] In an embodiment, a high birefringence gradient at the window can be correlated with high ZLPD, for example, through statistical analysis. A large birefringence gradient at the window alters the polarization state of the UVLS wavefront in different ways at different measurement spots. This results in different HPD at each measurement spot. Existing window manufacturing and contact processes cause stress at the window E2 of the optical device OPA1 (e.g., the aperture AP1 of E1), resulting in high birefringence and therefore high ZLPD.

[0045] Some disadvantages of the optical device OPA1 produced by the existing manufacturing process are as follows: High stress in the optical elements caused by the bonding process causes warping of the contacting optical elements. Stress from the optical contacts reaches the region of the optical elements near the aperture AP1, resulting in a high birefringence effect. Such birefringence can lead to a relatively high optical path difference, which increases measurement errors in systems employing the optical device (e.g., OPA1). Incorrect measurements negatively impact UVLS yield because check tests (e.g., ZLPD specifications) may not be met. The HPD effect may be worse due to increased birefringence or increased OPD caused by stressed optical elements.

[0046] According to this disclosure, an optical device is provided such that the contact area of ​​the optical joint and the stress caused by the optical contact joint are minimized at the hole AP1. Figure 3 The figure illustrates an example of an optical device OPA2, wherein a transmissive optical element E2 (e.g., a fused silica window) forms optical contact joints at three designated locations (e.g., L1, L2, and L3). In an embodiment, the placement of the optical contact joints (e.g., at L1, L2, and L3) significantly reduces the birefringence of the window at the aperture AP1. In an embodiment, the placement geometry of the optical contact joints can reduce the birefringence in any thin optical device in contact. The optical device OPA2 having the geometric locations L1, L2, and L3 of the optical contact joints is presented by way of example to describe the features of this disclosure and does not limit the scope of this disclosure.

[0047] According to an embodiment, optical devices (e.g., Figure 3 The OPA2 includes: a substrate E11 having an aperture AP1 for light to pass through; a transmissive optical element E2 covering the aperture AP1 of the substrate E11; and optical contact joints (e.g., at L1, L2, and L3) located between the substrate E11 and the transmissive optical element E2. The optical contact joints (e.g., at L1, L2, and L3) are spaced sufficiently from the aperture AP1 such that the stress in the transmissive optical element E2 from the optical contact joint to the aperture AP1 is below an acceptable stress threshold. In an embodiment, the acceptable stress threshold is associated with the optical properties of the transmissive optical element E2 affected by the stress at the aperture AP1.

[0048] In an embodiment, the aperture AP1 is a rectangular cutout in the substrate E11 through which light can pass (e.g., see...). Figure 1B and Figure 3 ).

[0049] In embodiments, the optical contact joints (e.g., at L1, L2, and L3) are adhesive-free joints between two closely conformal surfaces joined together and held together purely by intermolecular forces. Such a joint differs from joints produced by adhesives, welding, or other joints involving additional material between the two contact surfaces. Such additional material or the joint itself may introduce additional stress into the optical element.

[0050] In an embodiment, the optical contact joints (e.g., at L1, L2, and L3) are formed at selected locations on the substrate E11. The distance of the selected location from the aperture AP1 is a function of the stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3). In an embodiment, one or more of these selected locations are spaced furthest from the aperture AP1, such that the amount of stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3) is minimized at the aperture AP1.

[0051] For example, distances d1, d2, d3, or combinations thereof, used to form the optical contact joint can be selected to minimize stress in the transmissive optical element E2. In an embodiment, the distances d1, d2, and d3 can be the distances furthest from the aperture AP1.

[0052] In an embodiment, the optical contact joints (e.g., at L1, L2, and L3) are spaced apart from the aperture AP1 to constrain the transmissive optical element E2 with six degrees of freedom. In this embodiment, these six degrees of freedom include three translational directions along the x, y, and z axes, and three rotational directions about the x, y, and z axes, respectively.

[0053] In an embodiment, the optical contact joints at selected locations (e.g., at L1, L2, and L3) minimize the birefringence effect caused by light passing through the aperture AP1 and the transmissive optical element E2. In an embodiment, the birefringence effect is the optical path difference (OPD) of the light used to generate the topographic pattern of the substrate E11.

[0054] In an embodiment, such as Figure 4A and Figure 4BAs illustrated in the diagram, selected locations (e.g., L1, L2, and L3) are at least three raised portions of the substrate E11, which form raised surfaces (e.g., RS). The raised surfaces RS, together with the transmissive optical element E2, form the optical contact joint (e.g., at L1, L2, and L3), and the raised surfaces constrain the transmissive optical element E2 within the plane of the raised surfaces RS.

[0055] like Figure 4A and Figure 4B As shown, the raised surface RS creates a recessed surface DS between the transmissive optical element E2 and the raised surface RS surrounding the substrate E11 (see Figure 1). Figure 4B The gap between the transmissive optical element E2 and the recessed surface DS of the substrate E11 (e.g., at L1, L2, and L3) prevents the transmissive optical element E2 from forming an optical contact joint with the recessed surface DS, or prevents the transmissive optical element E2 from naturally connecting to the recessed surface DS.

[0056] In one embodiment, the recessed surface DS of the substrate E11 is relatively rougher than the raised surface RS of the substrate E11. In another embodiment, the recessed surface DS of the substrate E11 is sandblasted. This recessed surface DS prevents thin optical elements (e.g., E2) from being sucked in by the vacuum between the gaps. The vacuum can deform the thin optical element E11 and conform it to the irregular surface of the substrate E11.

[0057] In an embodiment, such as Figure 4BAs shown, the recessed surface DS is created by masking selected areas and acid etching the substrate E11. The gap between the recessed surface DS and the raised surface RS will vary depending on the etching amount. For example, stronger etching results in a larger gap. In an embodiment, the masking of the raised surface RS can be performed on a reduced area at selected locations (e.g., L1, L2, and L3). The fabrication area of ​​the raised surface is determined such that stress caused by contact will be reduced. In an embodiment, the raised surface RS itself does not inherently have low stress. The reduction in the surface area of ​​the raised surface RS reduces the stress caused by contact. Furthermore, the sub-surface deformation removed on the recessed surface DS also reduces the (pre-contact) stress in the substrate E11. In an embodiment, fewer areas have contaminants or contact errors due to such a raised surface RS. Acid etching reduces substrate stress but may worsen surface flatness. However, masking the contact area creates a stress-relieved substrate that can be used for contact without additional polishing. In an embodiment, the use of three spaced-apart contact points (e.g., optical junctions at L1, L2, and L3) further reduces the warping of the window surface and achieves near-precise constraint of the optical element E2 (i.e., neither under-constrained nor over-constrained).

[0058] In an embodiment, the surface roughness of both the transmissive optical element E2 and the substrate E11 is less than 5 nm at the portions forming (e.g., at L1, L2, and L3) the optical contact junction. In an embodiment, the thickness of the substrate E11 is greater than the thickness of the transmissive optical element E2. For example, the thickness of the substrate E11 is between 1 mm and 4 mm, and the thickness of the transmissive optical element E2 is 0.5 mm or less.

[0059] Figures 5A to 5C The figure illustrates exemplary birefringences produced by different optical device configurations. Figure 5A An exemplary delay R1 (e.g., linear delay R1) is generated by the non-contact elements (e.g., optical elements in contact with the substrate) of the optical device (e.g., OPA1 or OPA2). Figure 5B An exemplary delay R2 (e.g., linear delay R2) is generated by the existing optical device OPA1. Figure 5C It is by ( Figure 3 The exemplary delay R3 (e.g., linear delay R3) produced by the optical device OPA2 suggested in the middle.

[0060] Comparable Figures 5A to 5C This shows the joint with lower stress (e.g., Figure 3 The optical contact joints at L1, L2, and L3 improve birefringence. (Reference) Figure 5B The wavy pattern indicates an irregular surface and internal stress. Figure 5C As shown, more random patterns resemble non-contact windows, resulting in lower stress and smaller surface deformation.

[0061] Figure 6 The figure illustrates the improved birefringence value produced by the proposed optical device OPA2. In the example, when the transmissive optical element (e.g., E2) is coupled to the substrate (e.g., ...), ... Figure 2 When E1 in the middle is in full surface contact. Figure 6 The illustration shows that each of the three different windows produced by the final process demonstrates a 61% reduction in average birefringence when using, for example, a 3-pad design (optical junctions at L1, L2, and L3). For example, based on three samples SP1, SP2, and SP3, the optical device OPA1 has an average birefringence of 0.823 nm / mm, while the optical device OPA2 has an average birefringence of 0.315 nm / mm.

[0062] In an embodiment, a measuring device (e.g., comprising) is provided for measuring the characteristics of an object (e.g., a wafer printed by the photolithography apparatus). Figure 3 The optical device Figure 1A (Horizontal sensor).

[0063] In an embodiment, the measuring device includes: a light source; and an optical device (e.g., including the optical device OPA2). Discussed herein, the optical device includes: a substrate E11 having an aperture AP1 for light to pass through; a transmissive optical element E2 covering the aperture of the substrate E11; and an optical contact joint. The optical contact joint (e.g., at L1, L2, and L3) is formed between the substrate E11 and the transmissive optical element E2. The optical contact joint (e.g., at L1, L2, and L3) is spaced sufficiently from the aperture such that the stress in the transmissive optical element E2 from the optical contact joint (e.g., at L1, L2, and L3) to the aperture is below an acceptable stress threshold. In an embodiment, light passing through the transmissive optical element E2 produces an interference pattern, which is used to extract measurement results of the properties of the object.

[0064] In one embodiment, the characteristic is a height map of the object measured based on the interference pattern, generated by reflecting light from the object and passing the reflected light through the optical device. In the example, the object is a wafer imaged by a photolithography device. The characteristic of the object is alignment data associated with the pattern printed on the wafer imaged by the photolithography device.

[0065] As discussed herein, the optical contact joints (e.g., at L1, L2, and L3) are formed at selected locations on the substrate E11. The distance of the selected location from the aperture is a function of the stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3).

[0066] In an embodiment, one or more of these selected locations are spaced furthest from the aperture, such that the amount of stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3) is minimized at the aperture. In an embodiment, the selected locations are at least three protrusions on the substrate E11 that form a raised surface RS. The raised surface RS, together with the transmissive optical element E2, forms the optical contact joints (e.g., at L1, L2, and L3), and the raised surface constrains the transmissive optical element E2 within the plane of the raised surface RS.

[0067] In an embodiment, the raised surface RS creates a gap between the transmissive optical element E2 and the recessed surface DS surrounding the raised surface RS of the substrate E11. The gap prevents the transmissive optical element E2 from forming an optical contact joint with the recessed surface DS of the substrate E11 (e.g., at L1, L2, and L3) or prevents the transmissive optical element E2 from naturally connecting to the recessed surface DS.

[0068] In this embodiment, the thickness of the substrate E11 is between 1 mm and 4 mm, and the thickness of the transmissive optical element E2 is 0.5 mm or less.

[0069] In one embodiment, the optical contact joints (e.g., at L1, L2, and L3) are spaced apart from the apertures to constrain the transmissive optical element E2 with six degrees of freedom. In another embodiment, the optical contact joints (e.g., at L1, L2, and L3) are formed such that the optical path difference (OPD) of the light is used to generate a topographic map of the substrate E11.

[0070] In this embodiment, the optical device OPA2 can be used in a photolithography device (e.g., Figure 7 and Figure 8 In an embodiment, the photolithography apparatus includes: a light source; and optical devices (e.g., Figure 3The optical device includes: a substrate E11 having an aperture for light to pass through; a transmissive optical element E2 covering the aperture of the substrate E11; and an optical contact joint (e.g., at L1, L2, and L3) located between the substrate E11 and the transmissive optical element E2. The optical contact joint (e.g., at L1, L2, and L3) is spaced sufficiently from the aperture such that the stress in the transmissive optical element E2 from the optical contact joint (e.g., at L1, L2, and L3) to the aperture is below an acceptable stress threshold. Light passing through the transmissive optical element E2 generates an interference pattern, which is used to extract measurements of characteristics associated with the patterning process.

[0071] In one embodiment, the characteristic is a height map of an object patterned by the photolithography apparatus. The characteristic is derived from the interference pattern, which is generated by reflecting light from the object and allowing the reflected light to pass through the optical apparatus.

[0072] In one embodiment, the characteristic is alignment data. The alignment data indicates the alignment between patterns on a specific layer of the object patterned by the photolithography apparatus, or between different layers.

[0073] In an embodiment, the optical contact joints (e.g., at L1, L2, and L3) are formed at selected locations on the substrate F11. The distance of the selected location from the hole is a function of the stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3).

[0074] In an embodiment, one or more of these selected locations are spaced furthest from the aperture, such that the amount of stress in the transmissive optical element E2 caused by the optical contact joints (e.g., at L1, L2, and L3) is minimized at the aperture.

[0075] In an embodiment, the selected locations are at least three raised portions of the substrate E11, which form a raised surface RS. The raised surface RS, together with the transmissive optical element E2, forms the optical contact joint (e.g., at L1, L2, and L3), and the raised surface constrains the transmissive optical element E2 in the plane of the raised surface RS.

[0076] In an embodiment, the raised surface RS creates a gap between the transmissive optical element E2 and the recessed surface DS surrounding the raised surface RS of the substrate E11. This gap prevents the transmissive optical element E2 from forming an optical contact joint with the recessed surface DS of the substrate E11 (e.g., at L1, L2, and L3) or prevents the transmissive optical element E2 from naturally connecting to the recessed surface DS.

[0077] In this embodiment, the thickness of the substrate E11 is between 1 mm and 4 mm, and the thickness of the transmissive optical element E2 is 0.5 mm or less.

[0078] In an embodiment, the optical contact joints (e.g., at L1, L2, and L3) are spaced apart from the holes to constrain the transmissive optical element E2 with six degrees of freedom.

[0079] As used in this invention, the terms "mask" or "patterning apparatus" can be broadly interpreted to refer to a general patterning apparatus that can be used to impart a patterned cross-section to an incident radiation beam, the patterned cross-section corresponding to a pattern to be generated in a target portion of the substrate. In this context, the term "optical valve" may also be used. Examples of such patterning apparatuses, besides classic masks (transmissive or reflective; binary, phase-shifting, hybrid, etc.), include:

[0080] - Programmable mirror arrays. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle underlying such a device is that, for example, the addressed regions of the reflective surface reflect incident radiation as diffracted radiation, while the unaddressed regions reflect incident radiation as non-diffracted radiation. With the use of suitable filters, the non-diffracted radiation can be filtered out from the reflected beam, leaving only the diffracted radiation; thus, the beam becomes patterned according to the addressing pattern of the matrix-addressable surface. Suitable electronic devices can be used to perform the desired matrix addressing. More information on such mirror arrays can be obtained, for example, from U.S. Patent Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference.

[0081] - Programmable LCD array. An example of such a construction is given in U.S. Patent No. 5,229,872, which is incorporated herein by reference.

[0082] As a brief introduction, Figure 7The figure illustrates an exemplary photolithography projection apparatus 10A. The main components are: a radiation source 12A, which may be a deep ultraviolet excimer laser source or other types of sources including extreme ultraviolet (EUV) sources (as discussed above, the photolithography projection apparatus itself does not need to have the radiation source); an illumination optics that defines partial coherence (denoted as sigma) and may include optics 14A, 16Aa, and 16Ab that shape the radiation from the source 12A; a pattern forming apparatus 14A; and a transmission optics 16Ac that projects an image of the pattern formed by the pattern forming apparatus onto a substrate plane 22A. An adjustable filter or aperture 20A at the pupil plane of the projection optics can limit the range of beam angles incident on the substrate plane 22A, wherein the maximum possible angle defines the numerical aperture NA of the projection optics as sin(θmax).

[0083] During system optimization, the system's quality factor can be represented as a cost function. The optimization process boils down to finding the set of parameters (design variables) that minimize the cost function. The cost function can have any suitable form depending on the optimization objective. For example, the cost function can be the weighted root mean square (RMS) of the deviations of certain characteristics (estimated points) of the system relative to expected values ​​(e.g., ideal values) of those characteristics; the cost function can also be the maximum value of these deviations (i.e., the worst-case deviation). The term "estimated point" as used herein should be interpreted broadly to include any characteristic of the system. Due to the practicality of the system's implementation, the system's design variables can be restricted to a finite range and / or be interdependent. In the case of photolithography projection equipment, these constraints are often associated with the physical properties and characteristics of the hardware (such as tunability range) and / or manufacturability design rules of the patterning apparatus, and the estimated point can include physical points on the resist image on the substrate, as well as non-physical characteristics (such as dose and focal length).

[0084] In a photolithography projection apparatus, a source provides illumination (i.e., light); a projection optics device guides and shapes the illumination onto a substrate via the patterning apparatus. Here, the term "projection optics device" is broadly defined as any optical component that can modify the wavefront of the radiation beam. For example, a projection optics device may include at least some of components 14A, 16Aa, 16Ab, and 16Ac. A spatial image (AI) is the distribution of radiation intensity at the substrate level. A resist layer on the substrate is exposed, and the spatial image is transferred to the resist layer as a potential "resist image" (RI). The resist image (RI) can be defined as the spatial distribution of the solubility of the resist in the resist layer. The resist image can be calculated using a resist model based on the spatial image; an example of such a scheme can be found in commonly assigned U.S. Patent Application Serial No. 12 / 315,849, the entire disclosure of which is hereby incorporated by reference. The resist model relates only to the properties of the resist layer (e.g., the effects of chemical processes occurring during exposure, PEB, and development). The optical properties of the photolithography projection apparatus (e.g., the properties of the source, the patterning apparatus, and the projection optics) define the spatial image. Since the patterning apparatus used in the photolithography projection apparatus can be modified, it is desirable to separate the optical properties of the patterning apparatus from the optical properties of the rest of the photolithography projection apparatus, including at least the source and the projection optics.

[0085] In this document, the terms “radiation” and “beam” are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., with wavelengths of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and EUV (extreme ultraviolet radiation, e.g., with wavelengths in the range of 5 nm to 20 nm).

[0086] Additionally, the photolithography projection apparatus may be of the type having two or more substrate stages (and / or two or more pattern forming apparatus stages). In such a "multi-platform" apparatus, additional stages can be used in parallel, or one or more other stages can be used for exposure while preparatory steps are performed on one or more stages. For example, a dual-platform photolithography projection apparatus is described in US 5,969,441, which is incorporated herein by reference.

[0087] Figure 8An exemplary photolithography projection apparatus LA is schematically depicted. The photolithography projection apparatus LA includes: a source collector module SO; an illumination system (illuminator) IL configured to modulate a radiation beam B (e.g., EUV radiation); a support structure (e.g., a mask stage) MT configured to support a pattern forming apparatus (e.g., a mask or stencil) MA and connected to a first positioner PM configured to accurately position the pattern forming apparatus; a substrate stage (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted by the pattern forming apparatus MA to the radiation beam B onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0088] The irradiation system may include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0089] The support structure MT holds the patterning apparatus MA in a manner dependent on the orientation of the patterning apparatus, the design of the lithography equipment, and other conditions (such as whether the patterning apparatus is kept in a vacuum environment). The support structure can hold the patterning apparatus using mechanical, vacuum, electrostatic, or other clamping techniques. The support structure can be a frame or a stage, which may be fixed or movable as needed. The support structure ensures that the patterning apparatus (e.g., relative to the projection system) is in the desired position.

[0090] The term "patterning apparatus" should be interpreted broadly to refer to any apparatus that can be used to impart a pattern to the cross-section of a radiation beam in order to generate a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a specific functional layer in a device (such as an integrated circuit) generated in the target portion.

[0091] The pattern forming apparatus may be reflective (e.g., in...). Figure 8In lithography equipment (LA), patterns are either transmissive or transmissive. Examples of pattern forming apparatuses include masks, programmable mirror arrays, and programmable LCD panels. Masks are well-known in lithography and include mask types such as binary masks, alternating phase-shift masks, attenuation phase-shift masks, and various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect the incident radiation beam in different directions. The tilted mirrors impart a pattern to the radiation beam reflected by the mirror matrix.

[0092] The projection system, such as the illumination system, may include various types of optical components suitable for the exposure radiation used or other factors (such as the use of vacuum), such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof. Because other gases may absorb excessive radiation, it may be desirable to use a vacuum for EUV radiation. A vacuum environment can therefore be provided throughout the beam path by means of vacuum walls and a vacuum pump.

[0093] As depicted here, the device LA is a reflective type (e.g., employing a reflective mask). It should be noted that because most materials are absorbent in the EUV wavelength range, the mask can have a multilayer reflector comprising multiple stacks of, for example, molybdenum and silicon. In one example, the multilayer reflector has 40 pairs of molybdenum and silicon layers, each layer being a quarter wavelength thick. Even smaller wavelengths can be produced using X-ray lithography. Since most materials are absorbent at both EUV and X-ray wavelengths, the patterned sheets of absorbing material on the morphology of the patterning apparatus (e.g., a TaN absorber on top of a multilayer reflector) define features that will be printed in (positive resist) or not printed in (negative resist) areas.

[0094] refer to Figure 8 The irradiator IL receives an extreme ultraviolet (EUV) radiation beam from the source collector module SO. Methods for generating EUV radiation include, but are not limited to, converting a material into a plasma state having at least one element (e.g., xenon, lithium, or tin) with one or more emission lines in the EUV range. In one such method, often referred to as laser-generated plasma (“LPP”), plasma can be generated by irradiating a fuel with a laser beam, the fuel being, for example, a droplet, beam, or cluster of a material having a line-emitting element. The source collector module SO may be a laser comprising a laser beam for providing excitation of the fuel. Figure 8(Not shown) is part of an EUV radiation system. The resulting plasma emission uses output radiation, such as EUV radiation, collected by a radiation collector disposed within the source collector module. For example, when a CO2 laser is used to provide a laser beam for fuel excitation, the laser and the source collector module can be separate entities.

[0095] In these cases, the laser is not considered part of the lithography apparatus, and the radiation beam is delivered from the laser to the source collector module by means of a beam delivery system including, for example, suitable directional mirrors and / or beam expanders. In other cases, such as when the source is a discharge-generated plasma EUV generator (often referred to as a DPP source), the source can be part of the source collector module.

[0096] The irradiator IL may include adjusters for adjusting the angular intensity distribution of the radiation beam PB. Typically, at least the outer radial range and / or inner radial range (often referred to as σ-outer and σ-inner, respectively) of the intensity distribution in the pupil plane of the irradiator can be adjusted. Additionally, the irradiator IL may include various other components, such as faceted fields and pupil reflector devices. The irradiator can be used to adjust the radiation beam to achieve a desired uniformity and intensity distribution in its cross-section.

[0097] The radiation beam B is incident on and patterned by the patterning apparatus (e.g., a mask) MA, which is held on the support structure (e.g., a mask stage) MT. After being reflected from the patterning apparatus (e.g., the mask) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto the target portion C of the substrate W. The substrate stage WT can be accurately moved, for example, to position different target portions C in the path of the radiation beam B, by means of a second locator PW and a position sensor PS2 (e.g., an interferometer device, a linear encoder, or a capacitive sensor). Similarly, the first locator PM and another position sensor PS1 can be used to accurately position the patterning apparatus (e.g., the mask) MA relative to the path of the radiation beam B. The patterning apparatus (e.g., the mask) MA and the substrate W can be aligned using patterning apparatus alignment marks M1, M2 and substrate alignment marks P1, P2.

[0098] The described device LA can be used in at least one of the following modes:

[0099] 1. In step mode, while keeping the support structure (e.g., mask stage) MT and the substrate stage WT substantially stationary, the entire pattern imparted to the radiation beam B is projected onto the target portion C in one pass (i.e., single static exposure). The substrate stage WT is then moved along the X and / or Y directions, allowing exposure of different target portions C.

[0100] 2. In scanning mode, while simultaneously scanning the support structure (e.g., mask stage) MT and the substrate stage WT, a pattern imparted by the radiation beam B is projected onto the target portion C (i.e., single dynamic exposure). The velocity and orientation of the substrate stage WT relative to the support structure (e.g., mask stage) MT can be determined by the (reduced) magnification and image inversion characteristics of the projection system PS.

[0101] 3. In another mode, a support structure (e.g., a mask stage) MT that sustains the programmable patterning apparatus is held substantially stationary, and a pattern imparted by the radiation beam is projected onto the target portion C while the substrate stage WT is moved or scanned. In this mode, a pulsed radiation source is typically employed, and the programmable patterning apparatus is updated as needed after each movement of the substrate stage WT or between successive radiation pulses during scanning. This mode of operation can be readily applied to maskless lithography utilizing programmable patterning apparatuses (such as programmable mirror arrays of the type mentioned above).

[0102] Figure 9 The device LA is shown in more detail, including the source collector module SO, the irradiation system IL, and the projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within the enclosure structure 220 of the source collector module SO. The plasma 210 emitting EUV radiation can be formed by a discharge-generated plasma source. EUV radiation can be generated by a gas or vapor, such as xenon, lithium vapor, or tin vapor, in which a very hot plasma 210 is generated to emit radiation in the EUV range of the electromagnetic spectrum. For example, the very hot plasma 210 is generated by a discharge that causes at least partial ionization of the plasma. For efficient radiation generation, Xe, Li, Sn vapor, or any other suitable gas or vapor, such as one with a partial pressure of 10 Pa, may be required. In an embodiment, an excited tin (Sn) plasma is provided to generate EUV radiation.

[0103] Radiation emitted by the thermal plasma 210 is transferred from the source chamber 211 to the collector chamber 212 via an optional gas barrier or contaminant trap 230 (also referred to in some cases as a contaminant barrier or vane trap) positioned in or behind an opening in the source chamber 211. The contaminant trap 230 may include a channel structure. The contaminant trap 230 may also include a gas barrier, or a combination of a gas barrier and a channel structure. As is known in the art, the contaminant trap or contaminant barrier 230 further shown herein includes at least a channel structure.

[0104] The collector chamber 211 may include a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation passing through the collector CO may be reflected off the grating spectral filter 240 and then focused along the optical axis indicated by the dashed line "O" at a virtual source point IF. The virtual source point IF is often referred to as the intermediate focus, and the source collector module is arranged such that the intermediate focus IF is located at or near the opening 221 in the enclosure structure 220. The virtual source point IF is an image of the plasma 210 emitting radiation.

[0105] Subsequently, the radiation traverses the illumination system IL, which may include a faceted field mirror assembly 22 and a faceted pupil mirror assembly 24. The faceted field mirror assembly 22 and the faceted pupil mirror assembly 24 are arranged to provide a desired angular distribution of the radiation beam 21 at the patterning apparatus MA, and a desired uniformity of radiation intensity at the patterning apparatus MA. Upon reflection of the radiation beam 21 at the patterning apparatus MA, held by the support structure MT, a patterned beam 26 is formed, and the patterned beam 26 is imaged onto the substrate W, held by the substrate stage WT, via the projection system PS through reflective elements 28 and 30.

[0106] The illumination optics unit IL and projection system PS can typically contain more elements than are shown. The grating spectral filter 240 may be optional, depending on the type of lithography equipment. Additionally, more mirrors than are shown in the figure, for example, in the projection system PS, there may be additional mirrors besides those shown. Figure 9 In addition to the reflective element shown, there are 1 to 6 additional reflective elements.

[0107] Collector optics CO (e.g.) Figure 9The image shown is depicted as a nested collector with grazing incidence reflectors 253, 254, and 255, the nested collector being merely an example of a collector (or collector mirror). The grazing incidence reflectors 253, 254, and 255 are arranged symmetrically about the optical axis O, and this type of collector optics CO is preferably used in conjunction with a plasma source generated by discharge (often referred to as a DPP source).

[0108] Alternatively, the source collector module SO can be as follows: Figure 10 The diagram shows a portion or component of the LPP radiation system. A laser (LAS) is arranged to deposit laser energy into a fuel, such as xenon (Xe), tin (Sn), or lithium (Li), thereby generating a highly ionized plasma 210 with an electron temperature of tens of eV. High-energy radiation generated during the deexcitation and recombination of these ions is emitted by the plasma, collected by a near-normal incident collector optics (CO), and focused onto the opening 221 of the enclosure structure 220.

[0109] Other aspects of the invention will be described with reference to the following numbered aspects:

[0110] 1. An optical device, comprising:

[0111] A substrate having a hole for allowing light to pass through;

[0112] A transmissive optical element, the transmissive optical element covering the aperture of the substrate; and

[0113] An optical contact joint is located between the substrate and the transmissive optical element, and the optical contact joint is spaced at a sufficient distance from the hole, such that the stress in the transmissive optical element from the optical contact joint to the hole is below an acceptable stress threshold.

[0114] 2. The optical device according to aspect 1, wherein the optical contact joint is formed at a selected location on the substrate, wherein the distance of the selected location from the hole is a function of the stress induced by the optical contact joint in the transmissive optical element.

[0115] 3. The optical device according to aspect 2, wherein one or more of the selected portions are spaced furthest from the aperture, such that the amount of stress caused by the optical contact joint in the transmissive optical element is minimized at the aperture.

[0116] 4. The optical device according to aspect 3, wherein the selected portion is at least three protruding portions of the substrate, the protruding portions forming a protruding surface, the protruding surface forming the optical contact joint together with the transmissive optical element, and the protruding surface constraining the transmissive optical element in the plane of the protruding surface.

[0117] 5. The optical device according to aspect 4, wherein the raised surface creates a gap between the transmissive optical element and a recessed surface of the substrate surrounding the raised surface, the gap preventing the transmissive optical element from forming an optical contact joint with the recessed surface of the substrate or preventing the transmissive optical element from naturally connecting to the recessed surface.

[0118] 6. The optical device according to aspect 5, wherein the recessed surface of the substrate is relatively rougher than the raised surface of the substrate.

[0119] 7. The optical device according to aspect 6, wherein the recessed surface of the substrate is sandblasted.

[0120] 8. The optical device according to any one of aspects 5 to 7, wherein the recessed surface is produced by masking the selected portion and acid etching the substrate, the masking reducing the area of ​​the raised surface of the selected portion, such that the stress caused by contact is reduced compared to the stress at the recessed surface.

[0121] 9. The optical device according to any one of aspects 6 to 8, wherein the surface roughness of both the transmissive optical element and the substrate is less than 5 nm at the portion forming the optical contact junction.

[0122] 10. The optical device according to any one of aspects 1 to 9, wherein the hole is a rectangular cut in the substrate.

[0123] 11. The optical device according to any one of aspects 1 to 10, wherein the thickness of the substrate is greater than the thickness of the transmissive optical element.

[0124] 12. The optical device according to aspect 11, wherein the thickness of the substrate is between 1 mm and 4 mm, and the thickness of the transmissive optical element is 0.5 mm or less.

[0125] 13. The optical device according to any one of aspects 1 to 12, wherein the optical contact joint is separated from the aperture so as to constrain the transmissive optical element with six degrees of freedom.

[0126] 14. The optical device according to aspect 13, wherein the six degrees of freedom include:

[0127] Translations along the three directions of the x-axis, y-axis, and z-axis, respectively.

[0128] The three directions of rotation about the x-axis, y-axis and z-axis respectively.

[0129] 15. The optical device according to any one of aspects 1 to 14, wherein the optical contact joint is an adhesive-free joint between two closely conformal surfaces joined together and held together purely by intermolecular forces.

[0130] 16. The optical device according to any one of aspects 1 to 15, wherein the acceptable stress threshold is associated with the optical properties of the transmissive optical element affected by stress at the aperture.

[0131] 17. The optical device according to any one of aspects 1 to 16, wherein the optical contact joint at the selected location minimizes the birefringence effect caused by light passing through the aperture and the transmissive optical element.

[0132] 18. The optical device according to aspect 17, wherein the birefringence effect is the optical path difference (OPD) of light used to generate the topographic pattern of the substrate.

[0133] 19. A measuring device for measuring the properties of an object, comprising:

[0134] Light source; and

[0135] Optical device, the optical device comprising:

[0136] A substrate having a hole for allowing light to pass through;

[0137] A transmissive optical element, the transmissive optical element covering the aperture of the substrate; and

[0138] An optical contact joint is provided, located between the substrate and the transmissive optical element, and spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold.

[0139] In this process, light passing through the transmissive optical element generates an interference pattern, which is used to extract measurement results of the object's properties.

[0140] 20. The measuring apparatus according to aspect 19, wherein the characteristic is based on a height map of the object measured by the interference pattern, and the interference pattern is generated by reflecting light from the object and passing the reflected light through the optical device.

[0141] 21. The measuring apparatus according to aspect 20, wherein the object is a wafer imaged by a photolithography apparatus.

[0142] 22. The measuring apparatus according to aspect 21, wherein the characteristics of the object are alignment data associated with a pattern printed on a wafer imaged by the photolithography apparatus.

[0143] 23. The measuring device according to aspect 19, wherein the optical contact joint is formed at a selected location on the substrate, wherein the distance of the selected location from the hole is a function of the stress induced by the optical contact joint in the transmissive optical element.

[0144] 24. The measuring device according to aspect 22, wherein one or more of the selected portions are spaced furthest from the aperture, such that the amount of stress caused by the optical contact joint in the transmissive optical element is minimized at the aperture.

[0145] 25. The measuring apparatus according to aspect 23, wherein the selected portion is at least three raised portions of the substrate, the raised portions forming raised surfaces, the raised surfaces forming the optical contact joint together with the transmissive optical element, and the raised surfaces constraining the transmissive optical element in the plane of the raised surfaces.

[0146] 26. The measuring apparatus according to aspect 24, wherein the raised surface creates a gap between the transmissive optical element and a recessed surface of the substrate surrounding the raised surface, the gap preventing the transmissive optical element from forming an optical contact joint with the recessed surface of the substrate or preventing the transmissive optical element from naturally connecting to the recessed surface.

[0147] 27. The measuring apparatus according to any one of aspects 19 to 26, wherein the thickness of the substrate is between 1 mm and 4 mm, and the thickness of the transmissive optical element is 0.5 mm or less.

[0148] 28. The measuring device according to any one of aspects 19 to 27, wherein the optical contact joint is spaced apart from the aperture so as to constrain the transmissive optical element with six degrees of freedom.

[0149] 29. The measuring apparatus according to aspect 28, wherein the optical contact joint is formed such that the optical path difference (OPD) of the light is used to generate a topographic map of the substrate.

[0150] 30. A photolithography apparatus, comprising:

[0151] Light source; and

[0152] Optical device, the optical device comprising:

[0153] A substrate having a hole for allowing light to pass through;

[0154] A transmissive optical element, the transmissive optical element covering the aperture of the substrate; and

[0155] An optical contact joint is provided, located between the substrate and the transmissive optical element, and spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold.

[0156] In this process, light passing through the transmissive optical element generates an interference pattern, which is used to extract measurement results of characteristics associated with the patterning process.

[0157] 31. The photolithography apparatus according to aspect 30, wherein the characteristic is a height map of an object patterned by the photolithography apparatus, wherein the characteristic is derived based on the interference pattern, the interference pattern being generated by reflecting light from the object and passing the reflected light through the optical apparatus.

[0158] 32. The lithography apparatus according to aspect 31, wherein the feature is alignment data, wherein the alignment data indicates alignment between patterns on a particular layer or alignment between different layers of the object patterned by the lithography apparatus.

[0159] 33. The photolithography apparatus according to any one of aspects 30 to 32, wherein the optical contact joint is formed at a selected location on the substrate, wherein the distance of the selected location from the hole is a function of the stress induced by the optical contact joint in the transmissive optical element.

[0160] 34. The photolithography apparatus according to aspect 33, wherein one or more of the selected portions are spaced furthest from the aperture, such that the amount of stress caused by the optical contact joint in the transmissive optical element is minimized at the aperture.

[0161] 35. The photolithography apparatus according to aspect 34, wherein the selected portion is at least three raised portions of the substrate, the raised portions forming raised surfaces, the raised surfaces forming the optical contact joint together with the transmissive optical element, and the raised surfaces constraining the transmissive optical element in the plane of the raised surfaces.

[0162] 36. The photolithography apparatus according to aspect 31, wherein the raised surface creates a gap between the transmissive optical element and a recessed surface of the substrate surrounding the raised surface, the gap preventing the transmissive optical element from forming an optical contact joint with the recessed surface of the substrate or preventing the transmissive optical element from naturally connecting to the recessed surface.

[0163] 37. The photolithography apparatus according to any one of aspects 30 to 36, wherein the thickness of the substrate is between 1 mm and 4 mm, and the thickness of the transmissive optical element is 0.5 mm or less.

[0164] 38. The photolithography apparatus according to any one of aspects 30 to 37, wherein the optical contact junction is spaced apart from the aperture so as to constrain the transmissive optical element with six degrees of freedom.

[0165] While the concepts disclosed herein can be used for imaging on substrates such as silicon wafers, it should be understood that the disclosed concepts can be used with any type of lithography imaging system, such as a lithography imaging system for imaging on substrates other than silicon wafers.

[0166] The foregoing description is intended to be exemplary and not restrictive. Therefore, those skilled in the art will understand that modifications as described can be made without departing from the scope of the appended claims.

Claims

1. An optical device, comprising: A substrate having a hole for allowing light to pass through; A transmissive optical element that covers the hole in the substrate; as well as An optical contact joint is located between the substrate and the transmissive optical element, the optical contact joint being spaced a sufficient distance from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold, wherein the optical contact joint is formed at a selected location on the substrate, the selected location being at least three protruding portions of the substrate forming a raised surface, and the masking of the raised surface is performed on a reduced area at the selected location.

2. The optical device according to claim 1, wherein, The distance of the selected location from the hole is a function of the stress caused by the optical contact joint in the transmissive optical element.

3. The optical device according to claim 2, wherein, One or more of the selected locations are spaced furthest from the hole, such that the amount of stress caused by the optical contact joint in the transmissive optical element is minimized at the hole.

4. The optical device according to claim 3, wherein, The raised surface together with the transmissive optical element forms the optical contact joint, and the raised surface constrains the transmissive optical element in the plane of the raised surface.

5. The optical device according to claim 4, wherein, The raised surface creates a gap between the transmissive optical element and the recessed surface of the substrate surrounding the raised surface, the gap preventing the transmissive optical element from forming an optical contact joint with the recessed surface of the substrate or preventing the transmissive optical element from naturally connecting to the recessed surface.

6. The optical device according to claim 5, wherein, The recessed surface of the substrate is relatively rougher than the raised surface of the substrate.

7. The optical device according to claim 6, wherein, The recessed surface of the substrate is sandblasted.

8. The optical device according to any one of claims 5 to 7, wherein, The recessed surface is created by masking the selected area and acid etching the substrate. The masking reduces the area of ​​the raised surface at the selected area, thereby reducing the stress caused by contact compared to the stress at the recessed surface.

9. The optical device according to any one of claims 6 to 7, wherein, The surface roughness of both the transmissive optical element and the substrate is less than 5 nm at the portion forming the optical contact junction.

10. The optical device according to any one of claims 1 to 7, wherein, The hole is a rectangular cut in the substrate.

11. The optical device according to any one of claims 1 to 7, wherein, The thickness of the substrate is greater than the thickness of the transmissive optical element.

12. The optical device according to claim 11, wherein, The thickness of the substrate is between 1 mm and 4 mm, and the thickness of the transmissive optical element is 0.5 mm or less.

13. The optical device according to any one of claims 1 to 7 and 12, wherein, The optical contact joint is separated from the hole so as to constrain the transmissive optical element with six degrees of freedom.

14. The optical device according to claim 13, wherein, The six degrees of freedom include: Translations along the three directions of the x-axis, y-axis, and z-axis, respectively. The three directions of rotation about the x-axis, y-axis and z-axis respectively.

15. The optical device according to any one of claims 1 to 7, 12 and 14, wherein, The optical contact joint is a glue-free joint between two closely conformal surfaces that are joined together and held together purely by intermolecular forces.

16. The optical device according to any one of claims 1 to 7, 12 and 14, wherein, The acceptable stress threshold is associated with the optical properties of the transmissive optical element affected by stress at the aperture.

17. The optical device according to any one of claims 2 to 7, wherein, The optical contact joint at the selected location minimizes the birefringence effect caused by the light passing through the hole and the transmissive optical element.

18. The optical device according to claim 17, wherein, The birefringence effect is the optical path difference (OPD) of the light used to generate the topographic pattern of the substrate.

19. A measuring device for measuring the properties of an object, comprising: light source; and Optical device, the optical device comprising: A substrate having a hole for allowing light to pass through; A transmissive optical element, the transmissive optical element covering the aperture of the substrate; and An optical contact joint is provided, located between the substrate and the transmissive optical element, and spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold. The light passing through the transmissive optical element generates an interference pattern, which is used to extract measurement results of the characteristics of the object. The optical contact joint is formed at a selected location on the substrate, the selected location being at least three protruding portions of the substrate, the at least three protruding portions forming a protruding surface, and the masking of the protruding surface is performed on a reduced area at the selected location.

20. A photolithography apparatus, comprising: light source; and Optical device, the optical device comprising: A substrate having a hole for allowing light to pass through; A transmissive optical element, the transmissive optical element covering the aperture of the substrate; and An optical contact joint is provided, located between the substrate and the transmissive optical element, and spaced sufficiently from the aperture such that the stress in the transmissive optical element from the optical contact joint to the aperture is below an acceptable stress threshold. In this process, the light passing through the transmissive optical element generates an interference pattern, which is used to extract measurement results of characteristics associated with the patterning process. In this process, the optical contact joint is formed at a selected location on the substrate, the selected location being at least three protruding portions of the substrate, the at least three protruding portions forming a protruding surface, and the masking of the protruding surface is performed on a reduced area at the selected location.

Images