WO2018182683A1

WO2018182683A1 - Lithographic registration using a ferromagnetic marker

Info

Publication number: WO2018182683A1
Application number: PCT/US2017/025353
Authority: WO
Inventors: Daniel G. OUELLETTE; Kevin P. O'brien; Christopher J. WIEGAND; Tofizur RAHMAN; Justin S. BROCKMAN; Brian S. Doyle; Mark L. Doczy; Kaan OGUZ; Oleg Golonzka; Tahir Ghani; Angeline K. SMITH
Original assignee: Intel Corp
Current assignee: Intel Corp
Priority date: 2017-03-31
Filing date: 2017-03-31
Publication date: 2018-10-04
Anticipated expiration: 2019-09-30

Abstract

A technique includes registering a lithography tool with a specimen, where the specimen includes a ferromagnetic marker and a layer to be patterned extending over the ferromagnetic marker. Registering the lithography tool includes scanning at least part of the substrate with the optical energy, where the scanning includes directing incident optical energy to a plurality of locations of the layer and acquiring measurements of reflected optical energy associated with the plurality of locations; and determining a location of the ferromagnetic marker based at least in part on the acquired measurements.

Description

LITHOGRAPHIC REGISTRATION USING A FERROMAGNETIC MARKER Background

[0001 ] The fabrication of a semiconductor device may include the patterning of various layers of the IC device. The patterning of a particular layer may involve coating the layer with a light sensitive polymer, called a "photoresist," and using photolithography to selectively expose the photoresist to light to change a solubility of the photoresist according to a geometric pattern. In this manner, the solubility of the photoresist may be increased in regions that are exposed to the light, which allows the photoresist to be developed to remove the soluble regions to create a patterned photoresist that corresponds to the geometric pattern. The patterned photoresist, in turn, protects some parts of the underlying layer and allows the other, exposed parts of the layer to be further processed (e.g., processed using etching, ion implantation, and so forth) for purposes of patterning the layer.

Brief Description of the Drawings

[0002] Fig. 1 is a schematic diagram of a lithography system according to an example implementation.

[0003] Fig. 2 is a schematic diagram of a registration tool of the lithography system illustrating use of the magneto-optical Kerr effect (MOKE) to detect a ferromagnetic marker according to an example implementation.

[0004] Fig. 3 is a flow diagram depicting a lithographic registration process that uses a ferromagnetic marker according to an example implementation.

[0005] Fig. 4 is a flow diagram depicting a process to form a lithographic

registration marker on a substrate according to an example implementation.

[0006] Figs. 5A, 5B, 5C, 5D, 5E and 5F depict structures involved in the fabrication of a substrate containing a ferromagnetic marker according to an example

implementation.

[0007] Fig. 6 is a top view of a ferromagnetic registration marker according to an example implementation. [0008] Fig. 7 is an illustration of a wafer having scribe lines and ferromagnetic registration markers according to an example implementation.

Detailed Description

[0009] For purposes of patterning a semiconductor layer or substrate of a semiconductor device, a lithography system may locate registration markers that are fabricated in the device, so that the patterning is appropriately aligned, or registered, with features (vias, other patterned metal layers or features thereof, semiconductor components, and so forth) of the semiconductor device. For example, the lithograph system may employ photolithography to transfer a pattern to a photoresist using either a mask or a direct pattern transfer process, and registration markers of the semiconductor device may be used to align, or register, the lithography system for the pattern transfer.

[0010] Challenges may exist in registering the lithography system when the layer to be patterned is semi-opaque. In this context, the "semi-opaque" layer refers to an optically absorbing material whose thickness is comparable to or larger than the optical penetration depth at the wavelength that is used for registration. The challenges pertain to detecting registration markers when the registration markers are buried beneath a semi-opaque layer. In this manner, detecting the registration markers may involve optically scanning the semiconductor device with a beam of incident light, so that measurements of the reflected light may be used to identify locations of the registration markers. Detecting a registration marker in this manner may be challenging if the registration marker is buried beneath a semi-opaque material. More specifically, assuming that a portion of the incident device light passes through the semi-opaque material and reaches a given registration marker, the total light reflected from the semiconductor device includes light reflected from the boundary between the marker and the semi-opaque material, and light reflected from the upper surface of the semi-opaque material. The light that is reflected from the upper surface of the semi-opaque material may dominate the total light reflected, thereby making it challenging, if not impractical, to detect the registration marker.

[001 1 ] Alternative ways to register a lithographic system when patterning a semi- opaque material include imaging registration markers from the backside of the wafer using light with photon energy below the bandgap of the wafer; or depositing the semi-opaque material on top of the semiconductor device and registering the system with the topographical pattern on the surface of the deposited material. These methods may have relatively limited resolutions due to the associated long wavelengths or limited contrast. In other instances, the inability to detect registration markers below semi-opaque materials presents a challenge to direct subtractive patterning of the semi-opaque layer. Avoiding this problem can result in complex integrated processes, such as, for example, damascening methods for metal fill.

[0012] In accordance with example implementations that are described herein, a lithographic registration process enhances the contrast between registration markers and a material that covers the markers to allow the markers to be detected, even if the material is semi-opaque. More specifically, in accordance with systems and techniques that are described herein, the registration markers are ferromagnetic markers, i.e., each marker includes one or multiple ferromagnetic materials. Due to the registration markers exhibiting magnetic properties, the semiconductor device may be scanned with light energy in a process that uses the magneto-optical Kerr effect (MOKE) to identify the locations of the markers, even in the presence of strong reflections from an overlying semi-opaque material.

[0013] In general, the MOKE refers to an optical effect that is exhibited by a ferromagnetic material when reflecting light. Due to the MOKE, a ferromagnetic material changes the polarization state of incident light to produce reflected light that has a changed polarization direction and ellipticity. The degree of change is influenced by the magnetization state (direction and magnitude) of the ferromagnetic material. Therefore, locations of ferromagnetic registration markers may be identified by the change in the polarization state of the incident light, i.e., detecting reflected light that is altered due to the MOKE.

[0014] As a more specific example, Fig. 1 depicts a lithography system 100 in accordance with example implementations. In general, the lithography system 100 includes a pattern transfer tool 104, which is constructed to transfer a pattern to a specimen 150 that is disposed on an adjustable stage 170. As an example, in accordance with some implementations, the specimen 150 may be a semiconductor wafer containing multiple die, which may ultimately form multiple semiconductor devices. The pattern transfer tool 104 may transfer a pattern onto a patterning layer 158 that is formed on top of a non-patterned layer 156 (a semi-opaque metal layer, for example) to be patterned. The pattern transfer may be accomplished in one of many different ways, depending on the particular implementation. For example, in accordance with some implementations, the pattern transfer tool 104 may apply light to a mask to transfer the pattern to the patterning layer 158. In accordance with further example implementations, the pattern transfer tool 104 may directly form the pattern on the patterning layer 158 without the use of a mask.

[0015] In accordance with example implementations, the pattern that is formed by the pattern transfer tool 104 on the patterning layer 158 selectively changes the solubility of the patterning layer 158, and patterning layer 158 may then be developed to form a pattern. Regardless of how the pattern transfer tool 104 transfers the pattern to the patterning layer 158, the pattern is transferred in a specific alignment, or orientation, to correspond with other layers and features of the specimen 150. In accordance with example implementations, the specimen 150 may be a semiconductor wafer, and the specimen 150 may include a semiconductor substrate 155 that is associated with multiple die. Moreover, the non-patterned layer 156 may be a metal layer to form a corresponding patterned metal layer for the die. The die, in turn, contains various layers other than the layer 156 that correspond to various circuits, components and features of the die. To properly align the patterned metal layer 156 with these components/circuits/features, the pattern transfer tool 104 aligns the transferred pattern with one or multiple ferromagnetic markers 154 that have been fabricated on the substrate 155.

[0016] In accordance with example implementations, the ferromagnetic registration markers 154 may be disposed in scribe lines of the wafer so that the markers 154 do not consume die area. In accordance with further example implementations, one or multiple ferromagnetic registration markers 154 may be disposed within die area.

[0017] Depending on the particular implementation, the substrate 155 may be a bulk substrate, a semiconductor-on-insulator substrate or a multi-layered substrate. As specific examples, the substrate 155 may be a germanium substrate; a silicon substrate; a silicon germanium bulk substrate; a germanium; a semiconductor-on- insulator substrate, such as a germanium, silicon or a silicon germanium on oxide substrate; or a substrate formed from one or multiple other materials.

[0018] In accordance with example implementations, the patterning layer 158 may be a positive or a negative photoresist; and the photoresist may be a

photopolymeric, photodecomposable or photocrosslinking photoresist. In

accordance with example implementations, the patterning layer 158 may be a positive photoresist that includes a diazonaphthoquinone-novolac resin. In accordance with further example implementations, the patterning layer 158 may be a negative photoresist that includes SU-8. Other materials may be used for the patterning layer 158, in accordance with further implementations. An antireflective coating may be disposed above or below the patterning layer 158, in accordance with example implementations.

[0019] In accordance with example implementations, one or multiple hardmasks (not shown) may be disposed below the photoresist. As examples, the hardmask may include silicon dioxide, carbon or another material.

[0020] In accordance with example implementations, the non-patterned layer 156 may include one or multiple metals, such as silver, nickel, aluminum, titanium, titanium nitride, molybdenum, hafnium, gold, gold-germanium, nickel-platinum, nickel-aluminum, copper, tantalum, ruthenium, tungsten, an alloy containing any of these metals, or another metal.

[0021 ] In accordance with further example implementations, the non-patterned layer 156 may be a material other than a metal. For example, in accordance with further example implementations, the non-patterned layer 156 may be a

semiconductor that is semi-opaque at ultraviolet (UV) wavelengths, although the semiconductor may be more transparent at longer wavelengths. For example, in accordance with further example implementations, the non-patterned layer 156 may include one or multiple of the following semiconductor materials: doped and undoped silicon; doped and undoped silicon germanium; silicon carbide; silicon nitride; doped and undoped gallium arsenide; aluminum gallium arsenide; and aluminum nitride.

[0022] In accordance with example implementations, the ferromagnetic registration marker 154 may include one or more of the following ferromagnetic materials: cobalt; cobalt iron; manganese-doped indium oxide; maganese-doped indium arsenide; manganese-doped indium antimonide; boron maganese-doped indium arsenide; manganese-doped gallium arsenide; chromium doped aluminum nitride; nickel;

cobalt iron boron; gadolinium; iridium manganese; iron nickel (permalloy); as well as other ferromagnetic materials.

[0023] In accordance with example implementations, the ferromagnetic registration marker 154 may include an anisotropic ferromagnetic material that has its preferred magnetic orientation, or magnetic easy axis (i.e., the axis energetically favorable direction of spontaneous magnetization), in the plane of the wafer (i.e., orthogonal to the normal of the wafer). Such anisotropic ferromagnetic materials include one or more of the following: iron; cobalt; nickel; cobalt iron; iron nickel (permalloy);

gadolinium; manganese aluminum; cobalt manganese silicon; copper manganese aluminum; aluminum nickel cobalt; samarium cobalt; manganese-doped indium oxide; maganese-doped indium arsenide; manganese-doped indium antimonide; boron maganese-doped indium arsenide; manganese-doped gallium arsenide;

chromium doped aluminum nitride; as well as other materials.

[0024] In accordance with further example implementations, the ferromagnetic registration marker 154 may include a layered material having two or more

constituents, with one or more repeated units, having a preferred magnetic

orientation (easy axis) perpendicular to the plane of the wafer. As examples, the multilayered material may include one or more of the following: cobalt/platinum; cobalt/palladium; cobalt/nickel; magnesium oxide/cobalt iron boron; magnesium oxide/iron boron; magnesium oxide/manganese cobalt aluminum; as well as other multi-layer materials.

[0025] In accordance with example implementations, the lithography system 100 includes a registration tool 190 that optically scans the specimen 150 and uses the MOKE for purposes of identifying the locations of ferromagnetic registration markers 154. More specifically, in accordance with example implementations, the optimal scanning includes projecting an incident light beam 192 onto the specimen 150 and spatially varying the light to scan a given region of the specimen 150 for

ferromagnetic registration markers 154. When light from the incident light beam 192 interacts with a ferromagnetic registration marker 154, the MOKE introduces a polarization change and/or phase shift in light 194 that is reflected from the specimen 150. Therefore, by observing incident beam locations for which the reflected light 194 exhibits the MOKE-induced polarization change and/or phase shift, the registration tool 190 may identify the locations of the ferromagnetic registration markers 154. The registration tool 190 may then communicate data 180 representing the identified marker positions to the pattern transfer tool 104 so that the tool 104 may take the appropriate actions (adjust the stage 170, for example) to align the pattern transfer in accordance with the marker positions.

[0026] Referring to Fig. 2, as a more specific example, in accordance with some implementations, the registration tool 190 may include an optical source 202 that generates light that travels through adjustable polarization optics 204. In accordance with some implementations, the adjustable polarization optics 204 may include a linear polarizer 206 and a quarter wave plate, or retarder 208.

[0027] The light from the adjustable polarization optics 204 produces the light beam 192 that passes through the patterning layer 158 and is incident upon an upper surface 212 of the non-patterned layer 156. As a more specific example, in accordance with some implementations, the adjustable polarization optics 204 may, for example, produce s-polarized light, which is incident on the upper surface 212 of the non-patterned layer 156. It is noted that although light may be reflected from the upper surface of the patterning layer 158, this may practically be eliminated by an anti-reflection coating (not shown). Light reflects from the upper surface 212 of the non-patterned layer 156 to produce a corresponding reflected light component 214. As indicated at reference numeral 216, some of the incident light beam 192 propagates through the non-patterned layer 156 and reflects from an optical interface 218 between the non-patterned layer 156 and the exemplary ferromagnetic registration marker 154.

[0028] In accordance with example implementations, the non-patterned layer 156 is formed from a semi-opaque material that has a transmissivity constraint: the properties of the layer 156 and its thickness 236 are such that a fraction (e.g., 10^"3) of light that is incident on the upper surface 212 of the layer 156 reflects from the optical interface 218 and is transmitted back through layers 156 and 158, as indicated by optical components 219 and 221.

[0029] Thus, as graphically depicted in Fig. 1 , in response to the incident light beam 192, the reflected light 194 toward the registration tool 190 has two

components: a significantly higher intensity optical component 214 due to the reflection from the upper surface 212 of the semi-opaque non-patterned layer 156; and a relatively significantly lower intensity optical component 220 due to the reflection from the optical interface 218 between the layer 156 and the ferromagnetic registration marker 154.

[0030] It is noted that in accordance with further example implementations, the layer that introduces the dominant reflection may not be an upper non-patterned layer (such as layer 156). For example, in accordance with further implementations, a non-patterned layer that overlays the ferromagnetic registration marker 154 may be transparent, but a reflective layer may be disposed beneath the registration marker 154. For these implementations, the MOKE may be used to selectively detect the reflection from the ferromagnetic registration marker 154 against the background reflection from the layer below.

[0031 ] Referring back to the example implementation that is depicted in Fig. 2, in accordance with example implementations, as compared to the incident light beam 192, the optical component 219 has a polarization rotation (a change in ellipticity, generally) and a phase shift that is proportional to the magnetization of the ferromagnetic marker 154. In accordance with example implementations in which the incident light beam 192 is s-polarized, the ferromagnetic registration marker 154 may introduce a p-polarized component to the reflected component 219. Therefore, by detecting p-polarized light (for this example), the registration tool 190 may detect whether the incident light beam 192 has reflected from a ferromagnetic registration mark 154.

[0032] As depicted in Fig. 2, in accordance with example implementations, the registration tool 190 may include adjustable polarization optics 224 that receives the reflected light 194 and produces an optical signal 225 that represents whether (by its presence or absence, for example) the reflected light 194 exhibits properties consistent with part of the light 194 being reflected from a ferromagnetic registration marker 154. In this manner, in accordance with example implementations, the adjustable polarization optics 224 is a filter that is constructed to pass through light to an optical detector 230 in response to the light being altered by the MOKE. For the example above in which the incident light beam 192 is s-polarized light, the adjustable polarization optics 224 may filter the light so that the optics 224 passes through light that is p-polarized (i.e., passes through light resulting from the MOKE changing the s-polarized light to p-polarized light).

[0033] In accordance with example implementations, the adjustable polarization optics 224 may include an adjustable quarter waveplate, or compensator 228, and a polarizer, or analyzer 226. Moreover, in accordance with example implementations, the compensator 228 and analyzer 226 may operate to form the optical signal 225 (which may then be detected by detector 230) in response to the optical component 220 having a predefined polarization and/or phase shift.

[0034] In accordance with some implementations, the registration tool 190 includes a controller 290, which controls the adjustable polarization optics 204 and adjustable polarization optics 224 for purposes of controlling the polarization and/or phase of the incident beam 192 and detecting the polarization and/or phase of the optical component 220 of the reflected light 194. As a more specific example, in

accordance with some implementations, the controller 290 may control the polarizer 206, retarder 208, compensator 228 and analyzer 226 to rotate these components to nullify all reflections (e.g., produce a null optical signal 225 at the detector 230 except, when the optical component 220 has a shifted ellipticity and/or phase due to the MOKE). [0035] In accordance with example implementations, the registration tool 190 may include focusing and beam directing optics 270, which are controlled by the controller 290 for purposes of scanning the specimen 150 in a two-dimensional (2-D) search pattern with the incident beam 192 to locate one or multiple ferromagnetic registration markers 154. In this manner, the focusing and beam directing optics 270 may include, for example, apertures, lenses, mirrors, and so forth. In a similar manner, the registration tool 190 may include focusing and beam directing optics 280, which the controller 290 adjusts in coordination with the focusing and beam directing optics 270 for purposes of directing the reflected beam 194 to the polarization optics 224.

[0036] Thus, referring to Fig. 3 in conjunction with Fig. 2, in accordance with example implementations, a technique 300 may be used to register a lithography tool with a specimen that includes a ferromagnetic registration marker and includes a layer to be patterned, which extends over the marker. The technique 300 includes scanning (block 304) at least part of a specimen with optical energy, including directing optical energy to a plurality of locations of the specimen and acquiring measurements of the reflected optical energy associated with the plurality of locations. The technique 300 includes determining (block 308) the location of the ferromagnetic marker based at least in part on the acquired measurements.

[0037] Referring back to Fig. 2, in accordance with example implementations, the optical source 202 may be a non-coherent source or a coherent source, such as a laser. Moreover, depending on the particular implementation, the optical source 202 may provide visible, infrared or ultraviolet (UV) wavelengths that are used by the registration tool 190 for registration marker detection. Depending on the particular implementation, the registration tool 190 may employ broadband or monochromatic illumination and detection.

[0038] In accordance with example implementations, the registration tool 190 may use normal or non-normal incidence angles, i.e., incidence angles in the range of zero to ninety degrees. Moreover, in accordance with example implementations, the registration tool 190 may map the location of the ferromagnetic registration markers 154 using polar, transverse and/or longitudinal geometries defined by whether the magnetization of the ferromagnetic registration marker 154 is aligned out of the plane of the specimen; in the plane of the specimen and perpendicular to the angle of optical incidence; or in the plane of the specimen and parallel to the angle of optical incidence.

[0039] In accordance with some implementations, the registration tool 190 may use two imaging modes: a coarse imaging mode; and a fine imaging mode. For example, in accordance with some implementations, the registration tool 190 may contain a camera, which the tool 190 enables for use as the detector 230 for the coarse imaging mode. The camera may have a relatively wide field of view (a field of view of 100 microns, for example) for purposes of coarsely detecting the positions of the ferromagnetic registration markers 154. In this manner, in the coarse imaging mode, the controller 290 may first configure the registration tool 190 to scan the specimen 150 to identify the coarse locations of the ferromagnetic registration markers 154. The controller 290 may then reconfigure the registration tool 190 for the fine imaging mode to precisely identify the marker locations. For example, in accordance with some implementations, for the fine imaging mode, the registration tool 190 may contain a laser having a spot size near the diffraction limit for fine alignment, so that the tool 190 may enable the use of the laser for the fine imaging mode. Thus, using the coarse marker positions found in the coarse imaging mode, the controller 290 may control the beam positioning in the fine imaging mode to focus the fine imaging in regions that correspond to the coarse marker positions.

[0040] The registration tool 190 may include various other features, depending on the particular implementation. For example, in accordance with some

implementations, the registration tool 190 may include a magnet 290 (Fig. 2) for purposes of providing a magnetic field to magnetize the ferromagnetic registration markers 154. In accordance with some implementations, the magnet 290 may be a permanent magnet. However, in accordance with further example implementations, the magnet 290 may be an electromagnet, which the controller 290 controls to apply a variable magnetic field to the ferromagnetic registration markers 154 for purposes of modulating or reversing their magnetizations for an improved signal-to-noise ratio (SNR). As another example of features of the registration tool 190, in accordance with some implementations, the adjustable polarization optics 204 may include a photoelastic modulator for purposes of enabling lock-in detection for an improved SNR. In this manner, in accordance with some implementations, the polarizer 206 may include a photoelastic modulator, the analyzer 226 may include a photoelastic demodulator, and the reference signal for the modulator may be received by the demodulator for purposes of demodulating the reflected signal from the

ferromagnetic registration markers 154.

[0041 ] In accordance with some implementations, a process 400 that is depicted in Fig. 4 may be used for purposes of forming, or fabricating, ferromagnetic registration markers on a semiconductor substrate. Figs. 5A, 5B, 5C, 5D, 5E and 5F illustrate structures that may be created as part of the process 400. Pursuant to block 404 of the process 400, a patterning layer 504 is formed on a substrate 508, as illustrated by a structure 500 of Fig. 5A. Pursuant to block 408 of the process 400, the patterning layer 504 may then be developed, as depicted in a structure 510 of Fig. 5B, to form an opening 512 corresponding to a region of the substrate 508 in which a ferromagnetic registration marker is to be formed. In accordance with example implementations, the substrate 508 may be part of a wafer, and the opening 512 may be disposed in a region 515 of the wafer, which is associated with a scribe line.

[0042] Pursuant to block 412 of the technique 400, the substrate 508 may then be etched, as depicted in a structure 520 of Fig. 5C, to form a channel 522 for the ferromagnetic material. In accordance with example implementations, the channel 522 may be fully contained in a saw street, or scribe line, of a wafer. In this regard, in accordance with some implementations, the ferromagnetic registration markers may be deployed in the scribe lines of a wafer so that when the wafer is diced, the ferromagnetic registration markers are removed and die area is not consumed by the ferromagnetic registration markers. In accordance with further example

implementations, one or multiple ferromagnetic registration markers may be formed in areas of the wafer, other than areas that correspond to the scribe lines. For example, in accordance with some implementations, an integrated circuit that is fabricated using magnetic markers as disclosed herein may contain one or multiple ferromagnetic registration markers or markers from this process. Thus, many implementations are contemplated, which are within the scope of the appended claims.

[0043] Fig. 5D depicts a structure 524 in which the patterning layer 504 (Fig. 5C) has been removed. Pursuant to the process 400, a ferromagnetic material 534 may be deposited (block 416) in the channel 522, and polishing (not shown) may then be performed to produce a structure 530 that is depicted in Fig. 5E. A metal layer 544 to be patterned may then be deposited (block 420), such that the metal layer 554 overlays and contacts the ferromagnetic material 534, as illustrated by a structure 540 in Fig. 5F.

[0044] Referring to Fig. 6, in accordance with example implementations, the ferromagnetic material of the ferromagnetic registration marker 154 may be patterned. For example, referring to Fig. 6, in accordance with some

implementations, the ferromagnetic registration marker 154 may be patterned in elongated strips 610 to form two optical gratings. In this manner, a first grating may have elongated members 610-1 , 610-2, 610-3, 610-4, 610-5 and 610-6, which are parallel to each other and extend along a given direction. Moreover, in accordance with example implementations, the ferromagnetic registration marker 154 may contain another optical grating having elongated members 610-7, 610-8 and 610-9, which are parallel to each other and extend along a direction that is orthogonal to the direction along which the axis along which the elongated members 610-1 , 610-2, 610-3, 610-4, 610-5 and 610-6 extend. In general, the members 610 are large enough to distinguish optically (members having a feature size greater than 400 nm, for example). The use of the optical grating permits software controlling the alignment process to look for a color change or overall photon count as the integrated circuit is being scanned for the ferromagnetic registers markers 154. In this manner, if the registration tool observes a repeated structure, such as the elongated marks of a particular optical grating, then the registration tool may determine that a registration marker has been located.

[0045] Fig. 7 depicts a portion 700 of a wafer illustrating placement of

ferromagnetic registration markers, in accordance with an example

implementation. As shown, the wafer may include die regions 720 and regions 710 corresponding to saw streets, or scribe lines, which separate the die regions

720. One or multiple ferromagnetic registration markers 154 may be disposed in the scribe line regions 710, as depicted in Fig. 7.

[0046] The optical detection of buried magnetic registration markers may be described by standard multilayer optical methods, such as the Jones matrix formalism and effective medium modeling. Each material interface (e.g.,

air/photoresist, photoresist/overlayer, overlayer/marker) may be characterized by reflection and transmission intensities and phases for s- and p- polarized light.

[0047] Absorption within a material, such as a semi-opaque overlayer, occurs as an exponential decrease in optical intensity with optical path length: the intensity is reduced by a factor 1/e after traveling a distance equal to the penetration depth. The penetration depth is a material parameter, which depends on the refractive index and extinction coefficient at the wavelength(s) used for registration. The reflection and transmission intensities are derived from the differences in refractive indices and extinction coefficients of the materials on either side of the interface.

[0048] The total reflection of s- and p- polarized light from the specimen consists of the coherent summation of all reflections from each optical interface, less the absorption occurring in each layer. Multiple internal reflections in each layer can modify the reflected intensity by constructive or destructive interference.

[0049] At the buried interface between an overlayer and a magnetic registration marker, the Kerr effect mixes s- and p- polarized light to a degree which is

dependent on the direction and magnitude of the magnetization and of the incident light. The polarization state of the reflected light may be modified in both angle and ellipticity in proportion to the magnitude of the magnetization of the marker.

[0050] In the case of a semi-opaque overlayer, only a small fraction of the total reflected light intensity is influenced by the buried registration marker. This light can still be detected by virtue of the MOKE polarization change and the sensitive polarization optics of the lithography apparatus.

[0051 ] It is noted that other optical effects which are distinct from the Kerr-effect can also mix s- and p- polarized light, for example, birefringence or dichroism in transparent overlayers. These effects can be distinguished from the Kerr signal, as only the latter is modulated by the magnetic registration markers.

[0052] For a given overlayer material and thickness, the MOKE registration wavelength can be selected to improve signal to noise ratio by reducing absorption, or improving reflection and transmission coefficients. The technique accommodates overlayers whose thickness is comparable to or larger than the penetration depth. However, practical constraints for signal to noise may place a limitation on the overlayer thickness.

[0053] In an example implementation, the semi-opaque overlayer is a transition metal such as Ru, Ta, or Cu, having ultra-violet penetration depth of order 10-20 nm, deposited with a thickness of a few 10s of nanometers.

[0054] The following examples pertain to further implementations.

[0055] Example 1 includes a method that includes registering a lithography tool with a specimen, where the specimen includes a ferromagnetic marker and a layer to be patterned extending over the ferromagnetic marker. Registering the lithography tool includes scanning at least part of the specimen with optical energy, where scanning includes directing incident optical energy to a plurality of locations of the specimen and acquiring measurements of reflected optical energy associated with the plurality of locations. Registering the lithography tool includes determining a location of the ferromagnetic marker based at least in part on the acquired

measurements.

[0056] In Example 2, the subject matter of Example 1 may optionally include the ferromagnetic marker producing a change in a polarization state of the incident optical energy and determining the location of the ferromagnetic marker may include detecting the change in the polarization state of the incident optical energy.

[0057] In Example 3, the subject matter of Examples 1 -2 may optionally include the layer to be patterned including a metal.

[0058] In Example 4, the subject matter of Examples of 1 -3 may optionally include acquiring measurements of the reflected optical energy including acquiring a first set of measurements associated with a relatively larger field of view and acquiring a second set of measurements associated with a relatively smaller field of view than the relatively larger field of view; and registering the lithography tool includes performing a relatively coarse alignment of the lithography tool specimen based at least in part on the first set of measurements and performing a relatively finer alignment of the lithography tool than the coarse alignment based at least in part on the second set of measurements.

[0059] In Example 5, the subject matter of Examples 1 -4 may optionally include applying a magnetic field to alter a magnetization of the ferromagnetic material.

[0060] In Example 6, the subject matter of Examples 1 -5 may optionally include applying a magnetic field to vary magnetization of the ferromagnetic material during the scanning.

[0061 ] In Example 7, the subject matter of Examples 1 -6 may optionally include registering the lithography mask by processing the measurements to detect a magneto-optical Kerr effect that is exhibited by the ferromagnetic marker.

[0062] In Example 8, the subject matter of Examples 1 -7 may optionally include acquiring the measurements including controlling optical components associated with the incident optical energy and the measurements to nullify optical reflections that are not associated with a magneto-optical Kerr effect.

[0063] In Example 9, the subject matter of Examples 1 -8 may optionally include the substrate including a plurality of dies and a scribe line, and the ferromagnetic marker being disposed in the scribe line.

[0064] Example 10 includes an apparatus that includes an optical source to generate light; polarization optics; first beam directing optics; second beam directing optics; an optical filter; a detector; and a controller that is coupled to the detector. The polarization optics polarize the light according to a predefined polarization state; the first beam directing optics direct the polarized light to a surface of a layer to receive lithographic patterning, where the metal layer is formed on a substrate; and the second beam directing optics receive light reflected as a result of the light directed to the surface. The optical filter provides an optical signal representing light associated with the magneto-optical Kerr effect; and the detector detects the optical signal provided by the optical filter. The controller controls the first and second beam directing optics to scan at least part of the surface to identify locations of magnetic markers for lithographic registration.

[0065] In Example 1 1 , the subject matter of Example 10 may optionally include the polarization optics including a photoelastic modulator and a filter including a photoelastic demodulator.

[0066] In Example 12, the subject matter of Examples 10-1 1 may optionally include a magnet to apply a modulating magnetic field to the substrate.

[0067] In Example 13, the subject matter of Examples 1 1 -12 may optionally include the optical source including an incoherent optical source or a coherent optical source.

[0068] In Example14, an apparatus includes a semiconductor substrate; a magnetic material formed on the substrate to form an optical grating; an unpatterned layer; and a patterning layer. The unpatterned layer is formed over and contacts the magnetic material, and the patterning layer is formed over and contacts the unpatterned layer.

[0069] In Example 15, the subject matter of Example 14 may optionally include the unpatterned material including a magnetic material.

[0070] In Example 16, the subject matter of Examples 14-15 may optionally include a scribe line, and the magnetic material may be disposed in the scribe line.

[0071 ] In Example 17, the subject matter of Examples 14-16 may optionally include the unpatterned layer including a metal.

[0072] In Example 18, the subject matter of Examples 14-17 may optionally include the metal including one of the following: silver, nickel, aluminum, titanium, titanium nitride, molybdenum, hafnium, gold, gold-germanium, nickel-platinum, nickel- aluminum, copper, tantalum, ruthenium or tungsten. [0073] In Example 19, the subject matter of Examples 14-18 may optionally include the patterning layer including a positive photoresist or a negative photoresist.

[0074] In Example 20, the subject matter of Examples 14-19 may optionally include the magnetic material including cobalt; cobalt iron; manganese-doped indium oxide; maganese-doped indium arsenide; manganese-doped indium antimonide; boron maganese-doped indium arsenide; manganese-doped gallium arsenide; chromium doped aluminum nitride; nickel; cobalt iron boron; gadolinium; iridium manganese; or iron nickel.

[0075] In Example 21 , the subject matter of Examples 14-20 may optionally include the semiconductor substrate being part of a wafer and the magnetic material including an anisotropic magnetic material having a magnetic easy axis in a plane of the wafer.

[0076] In Example 22, the subject matter of Examples 14-21 may optionally include the semiconductor substrate being part of a wafer and the magnetic material including an anisotropic magnetic material having a magnetic easy axis orthogonal to the plane of the wafer.

[0077] While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Claims

What is claimed is: 1 . An apparatus comprising:

an optical source to generate light;

polarization optics to polarize the light according to a predefined polarization state;

first beam directing optics to direct the polarized light to a surface of a layer to receive lithographic patterning, wherein the metal layer is formed on a substrate;

second beam directing optics to receive light reflected as a result of the light directed to the surface;

an optical filter to provide an optical signal representing light associated with the magneto-optical Kerr effect;

a detector to detect the optical signal provided by the optical filter; and a controller coupled to the detector, the controller to control the first and second beam directing optics to scan at least part of the surface to identify locations of magnetic markers for lithographic registration.

2. The apparatus of claim 1 , wherein the polarization optics comprises a photoelastic modulator, and the filter comprise a photoelastic demodulator.

3. The apparatus of claim 1 or 2, further comprising an electromagnet to apply a modulating magnetic field to the substrate.

4. The apparatus of claim 1 , 2 or 3, wherein the optical source comprises an incoherent optical source or a coherent optical source.

5. An apparatus comprising:

a semiconductor substrate;

a magnetic material on the substrate to form an optical grating;

an unpatterned layer on and contacting the magnetic material; and a patterning layer on and contacting the unpatterned layer.

6. The apparatus of claim 5, wherein the unpatterned layer comprises a magnetic material.

7. The apparatus of claim 5 or 6, wherein the apparatus comprises a scribe line, and the magnetic material is disposed in the scribe line.

8. The apparatus of claim 5, 6 or 7, wherein the unpatterned layer comprises a metal.

9. The apparatus of claim 8, wherein the metal comprises silver, nickel, aluminum, titanium, titanium nitride, molybdenum, hafnium, gold, gold-germanium, nickel-platinum, nickel-aluminum, copper, tantalum, ruthenium or tungsten.

10. The apparatus of claim 5, 6, 7, 8 or 9, wherein the magnetic material comprises cobalt; cobalt iron; manganese-doped indium oxide; maganese-doped indium arsenide; manganese-doped indium antimonide; boron maganese-doped indium arsenide; manganese-doped gallium arsenide; chromium doped aluminum nitride; nickel; cobalt iron boron; gadolinium; iridium manganese; or iron nickel.

1 1 . The apparatus of claim 5, 6, 7, 8, 9 or 10, wherein the semiconductor substrate is part of a wafer, and the magnetic material comprises an anisotropic magnetic material having a magnetic easy axis in a plane of the wafer.

12. The apparatus of claim 5, 6, 7, 8, 9 or 10, wherein the semiconductor substrate is part of a wafer, and the magnetic material comprises an anisotropic magnetic material having a magnetic easy axis orthogonal to the plane of the wafer.

13. The apparatus of claim 5, 6, 7, 8, 9, 10, 1 1 or 12, wherein the patterning layer comprises a positive photoresist or a negative photoresist.

14. A method comprising:

registering a lithography tool with a specimen, wherein the specimen comprises a ferromagnetic markenand a layer to be patterned extending over the ferromagnetic marker, and registering the lithography tool comprises:

scanning at least part of the specimen with optical energy, wherein the scanning comprises directing incident optical energy to a plurality of locations of the specimen and acquiring measurements of reflected optical energy associated with the plurality of locations;

determining a location of the ferromagnetic marker based at least in part on the acquired measurements.

15. The method of claim 14, wherein the ferromagnetic marker produces a change in a polarization state of the incident optical energy, and determining the location of the ferromagnetic marker comprising detecting the change in the polarization state of the incident optical energy.

16. The method of claim 14 or 15, wherein the layer comprises a metal.

17. The method of claim 14, 15 or 16, wherein:

acquiring measurements of the reflected optical energy comprises acquiring a first set of measurements associated with a relatively larger field of view and acquiring a second set of measurements associated with a relatively smaller field of view than the relatively larger field of view; and

registering the lithography tool comprises performing a relatively coarse alignment of the lithography tool with the specimen based at least in part on the first set of measurements and performing a relatively finer alignment of the lithography tool than the coarse alignment based at least in part on the second set of measurements.

18. The method of claim 14, 15, 16 or 17, wherein registering the lithography tool further comprises applying a magnetic field to alter a magnetization of the ferromagnetic material.

19. The method of claim 14, 15, 16, 17 or 18, wherein registering the lithography tool further comprises applying a magnetic field to vary a magnetization of the ferromagnetic material during the scanning.

20. The method of claim 14, 15, 16, 17, 18 or 19, wherein registering the lithography tool further comprises:

processing the measurements to detect a magneto-optical Kerr effect exhibited by the ferromagnetic marker.

21 . The method of claim 14, 15, 16, 17, 18, 19 or 20, wherein acquiring the measurements comprises controlling optical components associated with the incident optical energy and the measurements to nullify optical reflections not associated with the magneto-optical Kerr effect.

22. The method of claim 14, 15, 16, 17, 18, 19, 20 or 21 , wherein the substrate comprises a plurality of dies and a scribe line, and the ferromagnetic marker is disposed in the scribe line.