Optical coatings for eliminating ghost images in optical metrology tools

Abstract

The present disclosure relates to a metrology measurement system and related methods. In one or more embodiments, a measurement system is provided. The measurement system includes a stage operable to hold an object and a light engine disposed above the stage. The light engine includes a light source directed toward the object, a first lens operable to collimate or focus light from the light source, a reticle tray disposed between the light source and the first lens, and a reticle coupled to the reticle tray. The reticle includes a pattern and an anti-reflective coating disposed on the reticle. The coating is aligned with the pattern.

Description

[Technical Field]

[0001]

[0001] Embodiments of the present disclosure generally relate to optical devices for augmented, virtual, and mixed reality. More specifically, embodiments described herein provide metrology methods and systems. [Background technology]

[0002]

[0002] Virtual reality is generally considered to be a computer-generated simulated environment in which a user has an apparent physical presence. The virtual reality experience is generated in 3D and can be viewed on a head-mounted display (HMD) (e.g., glasses or other wearable display device with near-eye display panels as lenses for displaying a virtual reality environment that replaces the real environment).

[0003]

[0003] However, augmented reality provides an experience where a user not only sees the surrounding environment through the display lenses of glasses or other HMD devices, but also sees images of virtual objects that are generated for display and appear as part of the environment. Augmented reality may include any type of input (e.g., audio input and haptic input), as well as virtual images, graphics, and video that enhance or augment the environment experienced by the user. As an emerging technology, augmented reality presents many challenges and design constraints.

[0004] One such challenge is measuring optical devices to image quality standards. Metrology metrics of manufactured optical devices must be obtained to ensure that image quality standards are met. However, existing measurement systems may not provide the desired field of view and may produce ghost images, commonly referred to as "ghosting." Therefore, what is needed in the art is a measurement system and method for using the measurement system that provides an improved field of view and reduces the occurrence of ghost images. Summary of the Invention

[0005]

[0005] The present disclosure relates to metrology measurement systems and related methods. In one or more embodiments, a measurement system is provided. The measurement system includes a stage operable to hold an object and a light engine disposed above the stage. The light engine includes a light source directed toward the object, a first lens operable to collimate or focus light from the light source, a reticle tray disposed between the light source and the first lens, and a reticle coupled to the reticle tray. The reticle includes a pattern and an anti-reflective coating disposed on the reticle. The coating is aligned to the pattern.

[0006] In one or more embodiments, a reticle is provided, the reticle including a pattern and an anti-reflective coating disposed on the pattern, the coating being opaque.

[0007] In one or more embodiments, a method is provided. The method includes projecting a beam from a light engine toward an optical device. The light engine is disposed within a measurement system. The method also includes passing the beam through a reticle toward the optical device, where the beam undergoes total internal reflection within the optical device. The method also includes absorbing the reflected light with a coating disposed on a pattern of the reticle, detecting one or more images of the beam as it is outcoupled to a detector, and processing the images to extract metrology metrics.

[0008]

[0008] So that the above-mentioned features of the present disclosure can be understood in detail, a more particular description of the present disclosure briefly summarized above can be had by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and therefore should not be considered as limiting the scope of the present disclosure, which may also admit of other equally effective embodiments. [Brief explanation of the drawings]

[0009] [Figure 1A]

[0009] FIG. 1 is a perspective front view of a substrate according to an embodiment described herein. [Figure 1B]

[0010] FIG. 1 is a perspective front view of an optical device according to embodiments described herein. [Figure 2]

[0011] 1 is a schematic cross-sectional view of a measurement system according to embodiments described herein. [Figure 3]

[0012] 3 is a schematic diagram illustrating the configuration of a light engine and detector within the measurement system body of FIG. 2 according to embodiments described herein. [Figure 4]

[0013] FIG. 4 is a schematic diagram of a reticle tray of a measurement system according to embodiments described herein. [Figure 5]

[0014] FIG. 1 is a flow diagram of a method for optical device metrology according to embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0010]

[0015] For ease of understanding, where possible, identical reference numerals have been used to designate identical elements common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further description.

[0011]

[0016] FIELD OF THE DISCLOSURE Embodiments of the present disclosure generally relate to optical devices for augmented reality, virtual reality, and mixed reality. More specifically, embodiments described herein provide metrology methods and systems. The metrology methods and systems are shown and described herein.

[0012]

[0017] The techniques described herein include using a light engine to project a pattern with light from the light engine. The projected pattern is received by an optical device, undergoes total internal reflection through the optical device, and is output to a sensor in a reflective detector. One or more images of the pattern are detected by the reflective detector. The techniques further include processing the images to extract metrology metrics.

[0013]

[0018] As mentioned above, one challenge encountered when measuring optical devices for image quality standards is the presence of ghost images. One cause of ghost images is the reflection of light from the material used to form the pattern on the reticle. For example, reticles typically implement patterns formed from reflective materials such as metallic materials (e.g., chrome). However, when such reticles are implemented to perform metrology, light may be unintentionally reflected from a measurement object (e.g., a waveguide or other optical device) and returned toward the reticle. The reflected light may then reflect off the pattern disposed on the reticle and return toward the measurement object, resulting in the object receiving a ghost image of the pattern disposed on the reticle.

[0014]

[0019] Thus, in various embodiments, a coating may be placed on the reticle to reduce the amount of light reflected by the pattern, such as by aligning and / or placing the coating over the pattern, as described in further detail in conjunction with Figures 1A-5.

[0015]

[0020] 1A is a perspective front view of a substrate 101 according to embodiments described herein. The substrate includes a plurality of optical devices 100 disposed on a surface 103 of the substrate 101. In some embodiments that can be combined with other embodiments described herein, the optical device 100 is a waveguide coupler utilized in virtual reality, augmented reality, or mixed reality. In some embodiments that can be combined with other embodiments described herein, the optical device 100 is a planar optical device, such as a metasurface.

[0016]

[0021] The substrate 101 can be any substrate used in the art and can be either opaque or transparent to the selected laser wavelength, depending on the application of the substrate 101. The substrate 101 can be made of, but is not limited to, silicon (Si), silicon dioxide (SiO), fused silica, quartz, silicon carbide (SiC), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), silicon nitride (SiN), or a sapphire-containing material. Furthermore, the substrate 101 can have a variety of shapes, thicknesses, and diameters. For example, the substrate 101 can have a diameter of about 150 mm to about 300 mm. The substrate 101 can have a circular, rectangular, or square shape. The substrate 101 can have a thickness between about 300 μm and about 1 mm. Although only nine optical devices 100 are shown on the substrate 101 , any number of optical devices 100 may be disposed on the surface 103 of the substrate 101 .

[0017]

[0022] FIG. 1B is a perspective front view of an optical device 100. The optical device 100 described herein is an exemplary optical device, and it should be understood that other optical devices can be used or modified to achieve aspects of the present disclosure. The optical device 100 includes a plurality of optical device structures 102 disposed on a surface 103 of a substrate 101. The optical device structures 102 can be nanostructures having submicron dimensions (e.g., nano-sized dimensions). Regions of the optical device structures 102 correspond to one or more gratings 104, such as a first grating 104a, a second grating 104b, and a third grating 104c. In one embodiment that can be combined with other embodiments described herein, the optical device 100 includes at least a first grating 104a corresponding to an input coupling grating and a third grating 104c corresponding to an output coupling grating. In another embodiment that can be combined with other embodiments described herein, the optical device 100 also includes a second grating 104b corresponding to an intermediate grating. The optical device structures 102 can be angled or binary. The optical device structure 102 may have other cross-sections, including, but not limited to, circular, triangular, elliptical, regular polygonal, irregular polygonal, and / or irregularly shaped cross-sections.

[0018]

[0023] During operation, the first grating 104a receives an incident beam of light having an intensity from the light engine. In one embodiment, which can be combined with other embodiments described herein, the light engine is a microdisplay. To direct a virtual image to the intermediate grating (if utilized) or the third grating 104c, the incident beam is split by the optical device structure 102 into a T1 beam having all of the intensity of the incident beam. In one embodiment, which can be combined with other embodiments described herein, the T1 beam undergoes total-internal-reflection (TIR) ​​through the optical device 100 until it contacts the intermediate grating optical device structure 102. The intermediate grating optical device structure 102 diffracts the T1 beam into a T-1 beam, which undergoes TIR through the optical device 100 to the third grating optical device structure 102. The third grating optical device structure 104c outputs the T1 beam to the user's eye. The T1 beam output to the user's eye displays the virtual image generated from the light engine from the user's viewpoint, further increasing the viewing angle through which the user can view the virtual image. In another embodiment, which can be combined with other embodiments described herein, the T1 beam undergoes total internal reflection (TIR) ​​through the optical device 100 until it contacts the optical device structure 102 of the third grating 104c, and is output to display the virtual image generated from the light engine.

[0019]

[0024] To ensure that the optical device 100 meets image quality standards, metrology metrics must be obtained for the manufactured optical device 100. The metrology metrics for each optical device 100 are tested to ensure that predetermined values ​​are achieved. The embodiments of the measurement system 200 described herein provide the ability to obtain multiple metrology metrics with increased throughput. The metrology metrics include one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, a modulation transfer function (MTF) metric, a field of view (FOV) metric, a ghost image metric, and an eyebox metric.

[0020]

[0025] 2 is a schematic cross-sectional view of a measurement system 200 according to an embodiment described herein. The measurement system 200 includes a body 201 with a first opening 203 and a second opening 205 to allow a stage 207 to move therethrough. The stage 207 is operable to move in the X, Y, and Z directions within the body 201 of the measurement system 200. The stage 207 includes a tray 209 operable to hold an optical device 100 (shown herein) or one or more substrates 101 with optical devices 100 thereon.

[0021]

[0026] The measurement system 200 is operable to obtain one or more metrics including one or more of an angular uniformity metric, a contrast metric, an efficiency metric, a color uniformity metric, an MTF metric, an FOV metric, a ghost image metric, or an eyebox metric. The stage 207 and the tray 209 may be transparent such that the metrology metrics obtained by the measurement system 200 are not affected by the translucency of the stage 207 or the tray 209. The measurement system 200 is in communication with a controller 220. The controller 220 is operable to facilitate operation of the measurement system 200.

[0022]

[0027] The measurement system 200 includes an upper portion 204 oriented toward a top surface 222 of the optical device 100 and a lower portion 206 oriented toward a bottom surface 224 of the optical device 100. The upper portion 204 of the measurement system 200 includes an alignment camera 208, a light engine 210, and a reflectance detector 212. The alignment camera 208 is operable to determine a position of a stage 207. The alignment camera 208 is also operable to determine a position of the optical device 100 disposed on the stage 207. The alignment camera 208 includes an alignment camera body 211. The light engine 210 is operable to project light. For example, the light engine 210 is operable to illuminate the first grating 104a of the optical device 100. The light engine 210 includes a light engine body 213. In one embodiment, which can be combined with other embodiments described herein, the light engine 210 projects a pattern onto the first grating 104a. A reflective detector 212 detects the output beam projected from the third grating 104c of the optical device 100. The output beam may be emitted from the top surface 222 or the bottom surface 224 of the optical device 100. The output beam may correspond to a pattern from the light engine 210. One or more images of the pattern are detected by the reflective detector 212. The one or more images of the pattern may be processed by the controller 220 to extract metrology metrics.

[0023]

[0028] The lower portion 206 of the measurement system 200 includes a code reader 214 and a transmission detector 216. The code reader 214 and the transmission detector are positioned on the opposite side of the stage 207 from the alignment camera 208, the light engine 210, and the reflection detector 212. The code reader 214 is operable to read a code on the optical device 100, such as a quick response (QR) code or a barcode on the optical device 100. The code read by the code reader 214 may include identification information and / or instructions for obtaining one or more metrology metrics of the optical device 100. The transmission detector 216 detects an output beam projected from the third grating 104c through a bottom surface 224 of the optical device 100. In one embodiment, which can be combined with other embodiments described herein, the transmission detector 216 is coupled to a transmission detector stage 226. The transmission detector stage 226 is operable to move the transmission detector 216 in the X, Y, and Z directions. The transmission detector stage 226 is operable to adjust the position of the transmission detector 216 to enhance detection of the output beam projected from the third grating 104c.

[0024]

[0029] During operation, metrology metrics are obtained by illuminating the first grating 104a of the optical device 100 with the light engine 210. The light engine 210 projects a pattern onto one or more optical devices 100. The incident light undergoes TIR until the light is output (e.g., reflected or transmitted) from the optical device 100. The pattern is captured as one or more images by the reflectance detector 212. The one or more images may correspond to red, green, and blue channels. The one or more images may also correspond to one or more different metrology metrics. In various embodiments, the one or more images are full-field images.

[0025]

[0030] 3 is a schematic diagram of an arrangement 300 of a light engine 210 and a reflectance detector 212 within a body 201 of a measurement system 200 (FIG. 2) according to embodiments described herein. The light engine 210 includes a light source 302, a first lens 306, and a reticle tray 400. The reflectance detector 212 includes a second lens 310 and a sensor 312. The light source 302, the first lens 306, the reticle tray 400, and the second lens 310 are disposed within the body 201.

[0026]

[0031] The light source 302 is operable to project a first light beam 341. The first light beam 341 can be white light corresponding to a range of wavelengths. In one or more embodiments that can be combined with other embodiments described herein, the light source 302 is an LED. In another embodiment that can be combined with other embodiments described herein, the wavelength range is 390 nm to 750 nm, corresponding to white light.

[0027]

[0032] The reticle tray 400 is operable to move in one or more of the X, Y, and Z directions. Thus, the reticle tray 400 can be adjusted so that light is projected through the reticle 322. The reticle tray 400 is adjusted in the Z direction to improve the quality of the projected pattern. For example, adjusting the reticle tray 400 in the Z direction can change the angle and intensity of light incident on the reticle 322. The reticle tray 400 is positioned between the object 350 and the light source 302. The object 350 can be the optical device 100 and / or an optical device substrate.

[0028]

[0033] First lens 306 is positioned between reticle tray 400 and object 350. First lens 306 collimates or focuses first light beam 341 toward object 350. In one embodiment, which can be combined with other embodiments described herein, first lens 306 is an eyepiece.

[0029]

[0034] The optical device 100 is placed on a tray 209. The optical device 100 includes a first grating 104a and a third grating 104c. The first grating 104a corresponds to the input coupling grating of the optical device 100. The third grating 104c corresponds to the output coupling grating of the optical device 100.

[0030]

[0035] A second lens 310 is positioned between the third grating 104c and a sensor 312 of the reflectance detector 212. The second lens 310 focuses light toward the sensor 312. The sensor 312 is used to measure an attribute of the object 350.

[0031]

[0036] The reticle tray 400 includes a reticle 322. The reticle tray 400 can include one or more reticles 322. The reticle 322 includes one or more patterns (e.g., the pattern 410 shown in FIG. 4), as described in more detail below. In one or more embodiments, the reticle 322 is a transparent substrate having an opaque pattern 410. In some embodiments, the pattern 410 of the reticle 322 includes a metallic material, such as chromium, aluminum, or silver. A coating 330 is further disposed on the reticle 322.

[0032]

[0037] In various embodiments, coating 330 is an anti-reflective coating. Coating 330 is disposed over one or more patterns 410 of reticle 322. In some embodiments, coating 330 is disposed over less than all of the reticle, such as by aligning coating 330 with one or more patterns 410. Additionally, in some embodiments, coating 330 may be disposed over one or more patterns 410.

[0033]

[0038] In one or more embodiments, coating 330 is a multi-layer coating. For example, coating 330 can include first layer 303 and second layer 305. While coating 330 is shown as having first layer 303 and second layer 305, other embodiments are contemplated. In various embodiments, coating 330 includes two or more layers. For example, coating 330 can include first layer 303, second layer 305, and third layer. Coating 330 has a thickness of about 10 nanometers to about 10 micrometers (e.g., about 50 nanometers to about 5 micrometers, e.g., about 100 nanometers to about 1 micrometer). In various embodiments, first layer 303 and / or second layer 305 include a metallic material. The metal can include one or more of gold (Au), platinum (Pt), aluminum (Al), silver (Ag), chromium (Cr), and / or titanium (Ti). In various embodiments, first layer 303 and / or second layer 305 are dielectric layers. The dielectric layers may include one or more of silicon oxide (SiOx), titanium oxide (TiOx), niobium oxide (NbOx), zirconium oxide (ZrOx), tantalum oxide (TaOx), silicon nitride (SiN), magnesium fluoride (MgF2), and / or silicon. In various embodiments, coating 330 may be formed by alternating metal and dielectric layers as first layer 303 and second layer 305. In some embodiments, coating 330 includes three or more layers, e.g., four or more layers (e.g., two metal layers alternating with two dielectric layers), e.g., six or more layers (e.g., three metal layers alternating with three dielectric layers), alternating between the metal and dielectric layers.

[0034]

[0039] In various embodiments, coating 330 has a refractive index of less than 6. In some embodiments, coating 330 has a refractive index of about 1 to about 4.2, such as about 1.2 to about 4.

[0035]

[0040] In various embodiments, the coating 330 reduces the amount of reflected light 343 that reflects from one or more patterns 410 of the reticle 322 and back toward the optical device 100. For example, the coating 330 may include an opaque material that absorbs light and does not reflect light toward the optical device 100. In some embodiments, the material of the coating 330 is selected based on the type of material used to form the pattern 410. For example, if the pattern 410 is formed by the deposition of a metallic material on the reticle 322, the coating 330 may be an oxide of the metallic material. In a specific example, if the pattern 410 includes chromium, the first layer 303 and / or the second layer 305 of the coating 330 may include chromium oxide.

[0036]

[0041] The material of coating 330 is selected so that as reflected light 343 passes through coating 330 toward pattern 410, the reflected light 343 is absorbed by coating 330 and reduced by 20% or less. For example, if reflected light 343 is incident on coating 330 at 100% intensity, reflected light 343 is reflected from pattern 410 through coating 330 at an intensity of about 20% or less (e.g., about 15% or less, e.g., about 5% or less). By implementing alternating layers (e.g., alternating metal and dielectric layers), reflected light 343 is more effectively absorbed by coating 330 rather than being reflected toward optical device 100.

[0037]

[0042] In some embodiments, which can be combined with other embodiments described herein, the first layer 303 comprises the same metal material as the pattern 410, and the second layer 305 is a dielectric layer.

[0038]

[0043] As described above, when reflected light 343 is received by optical device 100 and output from third grating 104c, reflected light 343 causes a ghost image (e.g., of pattern 410) to be received by sensor 312. As will be described in more detail below, the implementation of coating 330 on reticle 322 reduces the occurrence of ghost images.

[0039]

[0044] During operation, the light source 302 projects a first light beam 341 through a reticle 322 in a reticle tray 400, generating a projected pattern 342 corresponding to pattern 410 ( FIG. 4 ). The projected pattern 342 is received by the first lens 306, which collimates or focuses the projected pattern 342 onto an object 350. In one or more embodiments, the object 350 is the optical device 100 of FIG. 1 . For example, the first lens 306 collimates the projected pattern 342, which is then received by the first grating 104 a. The projected pattern 342 then undergoes TIR within the optical device 100 and is output from the third grating 104 c as output light 345.

[0040]

[0045] The output light 345 is directed to a second lens 310, which focuses the output light 345 onto a sensor 312 of the reflectance detector 212.

[0041]

[0046] In various embodiments, a portion of the first light beam 341 is reflected from the optical device 100 as reflected light 343. The reflected light 343 returns from the optical device 100 through the first lens 306 and is absorbed by the coating 330, which prevents the light from being reflected back toward the first grating 104a. Thus, the coating 330 reduces ghost images and improves measurement accuracy.

[0042]

[0047] 4 is a schematic diagram of a reticle tray 400 of measurement system 200 according to embodiments described herein. Reticle tray 400 includes one or more reticle apertures 409. One or more reticles 322 are disposed within reticle apertures 409. Reticle 322 may include one or more patterns 410 to be projected onto first grating 104a of optical device 100. Reticle 322 includes coating 330 (FIG. 3) and / or transparent region 430 where pattern 410 is not disposed.

[0043]

[0048] 3, the one or more patterns 410 may include one or more rectangular patterns 410a, line patterns 410b, circular patterns 410c, or one or more other shapes or combinations thereof. The one or more patterns 410 provide a reference of known size and shape so that any changes to the pattern 410 as the projected pattern 342 (FIG. 3) passes through the grating of the optical device 100 can be detected.

[0044]

[0049] In some embodiments, each of the patterns 410 of the reticle 322 may correspond to a different metrology metric determined by the measurement system 200. For example, one or more patterns 410 may be implemented to measure different types of geometric distortion.

[0045]

[0050] In some embodiments, which may be combined with other embodiments described herein, a single pattern may be implemented to measure multiple metrology metrics. In some embodiments, which may be combined with other embodiments described herein, a metrology metric may require multiple patterns to be used. Thus, one or more reticles 322 may be used to obtain different metrology metrics of the optical device 100. The reticle tray 400 is not limited to one reticle 322. In some embodiments, the reticle tray 400 is operable to hold multiple reticles 322 (such as three or more reticles 322). For example, an array of reticles 322 may be placed on the reticle tray 400.

[0046]

[0051] In some embodiments, the coating 330 is aligned with the one or more patterns 410 such that the coating 330 is positioned between the one or more patterns 410 and the measurement object. By aligning the coating 330 with the one or more patterns 410 such that the areas of the reticle 322 not covered by the one or more patterns 410 remain transparent, the first light beam 341 can pass through the reticle 322 to form the projected pattern, but the reflected light 343 either passes through the transparent areas 430 of the reticle 322 or is absorbed by the coating 330, thereby reducing reflections and ghost images.

[0047]

[0052] 5 is a flow diagram of a method 500 of optical device metrology according to embodiments described herein. Method 500 may be utilized to project a pattern onto first grating 104a of optical device 100. Method 500 may be utilized in conjunction with configuration 300 of light engine 210. In one embodiment, which may be combined with other embodiments described herein, light engine 210 is operative to be disposed on a rotational stage such that light engine 210 can be rotated and / or tilted as needed during method 500.

[0048]

[0053] In step 501, a pattern is projected. The pattern is projected via light engine 210. As shown in FIG. 3, a first light ray 341 may be projected by light source 302. The first light ray 341 may be directed to reticle 322. The first light ray 341 passes through reticle 322 and enters first lens 306 from light source 302, which collimates the light. The first light ray 341 corresponds to a wavelength or range of wavelengths.

[0049]

[0054] 3, in some embodiments, which may be combined with other embodiments described herein, the reticle 322 is selected based on one or more determined metrology metrics. A pattern corresponding to one of the patterns 410 is projected onto the first grating 104a of the optical device 100. The patterns 410a, 410b, 410c may be directed onto the first grating 104a through the first lens 306.

[0050]

[0055] In step 502, one or more images of a pattern are detected. The one or more images of the pattern are captured by the sensor 312. The pattern is subjected to TIR until an output (e.g., reflected or transmitted) is captured by the reflectance detector 212 as one or more images. The one or more images are processed to extract metrology metrics. In various embodiments, the images are full-field images. The one or more images may be processed by the controller 220 (shown in FIG. 2). The controller 220 may be a remote controller 220 operable to receive the one or more images. The controller 220 may include a central processing unit (CPU) configured to process computer-executable instructions stored in a memory. The computer-executable instructions may include algorithms configured to extract metrology metrics. For example, the controller 220 may be configured to perform embodiments of the method 500 described herein, such as processing the one or more images to determine values ​​of metrology metrics corresponding to each pattern captured in the one or more images. One skilled in the art will appreciate that one or more elements of the controller 220 may be remotely located and accessed over a network.

[0051]

[0056] In step 503, steps 501 and 502 are repeated for a subsequent reticle 322 and / or pattern 410 placed on top.

[0052]

[0057] Advantages of the present disclosure include the reduction of detected ghost images by incorporating coatings on the reflective surfaces of the reticle 322.

[0053]

[0058] While the foregoing is directed to embodiments of the present disclosure, other embodiments of the disclosure may be devised without departing from the basic scope thereof, the scope of which is determined by the claims that follow.

Claims

1. a stage operable to hold an object; a light engine disposed above the stage; 1. A measurement system comprising: a light source directed towards the object; a first lens operable to collimate or focus light from said light source; a reticle tray disposed between the light source and the first lens; a reticle coupled to the reticle tray; the reticle comprising: Patterns and an anti-reflective coating disposed on the reticle and aligned with the pattern; a measurement system,

2. The measurement system of claim 1 , wherein the coating comprises a multi-layer coating.

3. The measurement system of claim 1 , wherein the coating is configured to absorb light reflected from the object.

4. The measurement system of claim 1 , wherein the coating is disposed between the pattern and the object.

5. The measurement system of claim 1 , wherein the coating is opaque.

6. The measurement system of claim 1 , wherein the object comprises one or more optical devices disposed on a substrate.

7. The measurement system of claim 6 , wherein the one or more optical devices include a waveguide.

8. The measurement system of claim 1 , wherein the pattern comprises a metal.

9. The measurement system of claim 8 , wherein the coating comprises an oxide of the metal.

10. Patterns and an opaque anti-reflective coating disposed over the pattern; and Including, the reticle.

11. The reticle of claim 10 , wherein the pattern comprises a metal.

12. The reticle of claim 11 , wherein the anti-reflective coating comprises an oxide of the metal.

13. The reticle of claim 10 , wherein the anti-reflective coating comprises a multi-layer coating.

14. The reticle of claim 10 , wherein the pattern and the anti-reflective coating are disposed on a first surface of the reticle.

15. projecting a beam from a light engine disposed within the measurement system toward an optical device; passing the beam through a reticle towards an optical device, where the beam undergoes total internal reflection within the optical device; absorbing reflected light with a coating disposed on the reticle pattern; detecting one or more images of the beam as it is output to a detector; processing the image to extract metrology metrics; A method comprising:

16. The light engine comprises: The main body and a light source disposed within the body; a first lens operable to collimate or focus light from said light source; a reticle tray containing the reticle, the reticle tray being positioned between the light source and the first lens; 16. The method of claim 15, comprising:

17. The method of claim 15 , wherein the coating is opaque.

18. The method of claim 15 wherein the coating is a multi-layer coating.

19. The method of claim 15 , wherein the pattern comprises a metal.

20. The method of claim 15 , wherein the coating comprises an oxide.

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