TWI849033B - Optical elements - Google Patents

Abstract

Disclosed herein are optical elements and methods for making the same. Such optical elements may comprise a first layer disposed on a substrate, a second layer disposed on the first layer, a terminal layer disposed on the second layer, and a cap layer disposed on the terminal layer. The cap layer may comprise boron, boron nitride, or boron carbide. Such optical elements may be made using a method comprising depositing a first layer using vapor deposition such that the first layer is disposed on a substrate, depositing a second layer using vapor deposition such that the second layer is disposed on the first layer, depositing a terminal layer using vapor deposition such that the terminal layer is disposed on the second layer, and depositing a cap layer comprising boron, boron nitride, or boron carbide using vapor deposition such that the cap layer is disposed on the terminal layer.

Description

Optical components

The present invention generally relates to semiconductor lithography. More particularly, the present invention generally relates to capping layers for EUV optics.

The evolution of semiconductor manufacturing places higher demands on yield management and especially on metrology and inspection systems. Critical dimensions continue to shrink, but the industry needs to reduce the time to achieve high-yield, high-value production. Minimizing the total time from detecting a yield problem to fixing it determines the return on investment for semiconductor manufacturers.

The manufacture of semiconductor devices, such as logic and memory devices, typically involves processing semiconductor wafers using a number of processes to form the various features and multiple layers of the semiconductor devices. For example, photolithography is a semiconductor process that involves transferring a pattern from a reticle to a photoresist disposed on a semiconductor wafer. Additional examples of semiconductor processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices can be fabricated on a single semiconductor wafer in a configuration and then separated into individual semiconductor devices.

Extreme ultraviolet lithography (EUV) is an emerging lithography technology in semiconductor manufacturing. EUV systems generally consist of a laser plasma light source and reflective optical devices, which generally include a molybdenum (Mo) silicon (Si) multilayer (Mo:Si) in a controlled ambient environment.

Optical devices for EUV radiation generally consist of a multi-layer stack of molybdenum and silicon, typically a few nanometers thick. Optical performance is severely degraded by oxidation of the silicon and molybdenum layers during operation and carbon accumulation on the top surface. A capping layer (or layers) is applied to prevent oxidation of the silicon and to allow removal of carbon contamination. Boron is well suited for this purpose because it forms a stable interface with silicon, is resistant to oxidation, has low EUV absorption, and can be deposited in continuous layers using low-temperature sputtering processes or high-temperature chemical vapor deposition.

Existing ruthenium-based coatings are not resistant to oxidative cleaning methods such as ultraviolet ozone (UVO) and plasma. Atomic hydrogen (H) must be used to clean ruthenium-based coatings, which requires large flows of hydrogen (H ₂ ). This significantly increases the cost, design complexity, and safety risks of the optical system.

Existing metal oxide capping layers such as titanium dioxide ( _TiO2 ), zirconium oxide ( _ZrO2 ) and niobium pentoxide ( _Nb2O5 ) are resistant to oxidative cleaning, but absorb EUV light more than boron. Therefore, they must be less than about _3nm thick. This does not provide adequate protection for the underlying silicon from oxidation during EUV exposure.

Therefore, improved capping layers for EUV optics are needed.

This article discloses a boron-based capping layer for EUV optics and a method for making the same.

In one embodiment, an optical element may include a first layer disposed on a substrate, a second layer disposed on the first layer, a terminal layer disposed on the second layer, and a cover layer disposed on the terminal layer. There may be a single first layer and a single second layer, or there may be multiple first layers or multiple second layers.

In another embodiment, a method of manufacturing an optical element is provided. The method may include depositing a first layer, depositing a second layer, depositing a terminal layer, and depositing a cap layer. The first layer may be deposited using vapor deposition and may be deposited so that it is disposed on a substrate. The second layer may be deposited using vapor deposition and may be deposited so that it is disposed on the first layer. The terminal layer may be deposited using vapor deposition and may be deposited so that it is disposed on the second layer. There may be a single first layer and a single second layer, or there may be multiple first layers or multiple second layers. The cover layer may be deposited using vapor deposition and may be deposited such that it is disposed over the termination layer.

The method may further include depositing a diffusion barrier. The diffusion barrier may be deposited using vapor phase deposition and may be deposited such that the diffusion barrier is disposed on the terminal layer and the cover layer is disposed on the diffusion barrier.

The method may further include depositing a terminal cover layer using vapor deposition. The terminal cover layer may be deposited such that the terminal cover layer is disposed on the cover layer.

The coating may include boron, boron nitride or boron carbide or any combination thereof.

The cover layer can be deposited using magnetron sputtering.

The optical element may constitute an extreme ultraviolet lithography system including the optical element. Alternatively, the optical element may constitute a detection system including the optical element.

The capping layer may include boron. The capping layer may have or may be deposited to a thickness in the range of from 5 nm to 30 nm (inclusive).

The capping layer may include boron nitride. The capping layer may have or may be deposited to a thickness in the range of from 2 nm to 10 nm (inclusive).

The capping layer may include boron carbide. The capping layer may have or may be deposited to a thickness in the range of from 2 nm to 25 nm (inclusive).

The optical element may further include a diffusion barrier. The diffusion barrier may be disposed on the terminal layer and the cover layer may be disposed on the diffusion barrier.

The diffusion barrier may include carbon.

The optical element may include a terminal covering layer. The terminal covering layer may be disposed on the covering layer.

The terminal coating may include ruthenium, titanium dioxide, zirconium dioxide or niobium oxide or any combination thereof.

100: Substrate

101: First level

102: Second level

103: Sequence

104: Terminal layer

105: Diffusion barrier

106: Covering layer

107: Terminal covering layer

110: Optical components

120: Optical components

130:Optical components

140:Optical components

201:Deposition Steps

202:Deposition step

203: Repeat

204:Deposition Steps

205:Deposition Steps

206:Deposition Steps

207:Deposition Steps

210: Methods

220:Methods

230:Methods

240:Methods

300: Drawing

301:Curve

302:Curve

303:Curve

304: Lower limit R _Crit

305: Upper limit R _Crit

400: Drawing

401:Graph

402:Graph

403:Graph

500:System

501: Optical-based subsystem

502: Sample

503: Light source

504:Optical components

505: Lens

506: Carrier

507: Collector

508: Components

509: Detector

510: Collector

511: Components

512: Detector

513: Beam splitter

514: Processor

515: Electronic data storage unit

In order to more fully understand the nature and purpose of the present invention, reference should be made to the following detailed description in conjunction with the accompanying drawings, in which: FIG. 1A shows an optical element having a protective covering layer; FIG. 1B shows an optical element having a protective covering layer; FIG. 1C shows an optical element having a protective covering layer; FIG. 1D shows an optical element having a protective covering layer; FIG. 2A shows a method of forming an optical element having a protective covering layer; FIG. 2B shows FIG. 2C shows a method of forming an optical element having a protective covering layer; FIG. 2D shows a method of forming an optical element having a protective covering layer; FIG. 3 shows a plot of the reflectivity of a typical optical element as a function of the thickness of the covering layer; FIG. 4 shows a calculated transmission of an illustrative optical system; and FIG. 5 shows an optical system according to an embodiment of the present invention.

Cross-references to related applications

This application claims priority to U.S. Provisional Application No. 62/788,330 filed on January 4, 2019, the entire contents of which are incorporated herein by reference.

Although the present invention will be described in terms of specific embodiments, other embodiments (including embodiments that do not provide all of the benefits and features described herein) are also within the scope of the present invention. Various structural, logical, process step and electrical changes may be made without departing from the scope of the present invention. Therefore, the scope of the present invention is defined solely by reference to the scope of the attached patent application.

This document discloses a range of values. A range specifies a lower limit and an upper limit. Unless otherwise specified, a range includes all values up to the minimum value (lower limit or upper limit) and the range between the values of the range.

Unless otherwise indicated, all ranges provided herein include all values within the range to the tenth decimal place.

EUV optics is severely degraded by oxidation and carbon (C) accumulation of constituent silicon and molybdenum layers. Boron (B) based materials such as pure boron (B), boron nitride (BN), and boron carbide ( _B4C ) can be deposited in dense thick layers that form strong bonds with silicon to resist oxidation and enable carbon contamination removal during EUV exposure. Boron carbide has long been used as a thin (<2nm) buffer layer between other materials to prevent diffusion. Therefore, a protective layer or capping layer containing boron for EUV optics is disclosed herein, which may be greater than about 2nm to about 4nm thick.

Boron-based protective layers are highly resistant to oxidation and can be used as a cap or buffer layer to prevent silicon oxidation, and can form a passivation layer of boron carbide on a surface to reduce further carbon contamination. It can be cleaned to the atomic level by molecular hydrogen, hydrogen plasma, UVO or other ultraviolet (UV) activated oxidation cleaning, vacuum ultraviolet (VUV) activated oxidation cleaning or EUV activated oxidation cleaning, oxygen plasma or other plasma. It has a lower EUV absorption than most other capping materials. This allows a thicker protective layer. The unique optical properties of boron interact with the constructive interference of EUV optics to produce enhanced reflectivity for boron layer thicknesses between 8nm and 12nm. The boron-based protective layer can be used as a distributed spectral purity filter to suppress out-of-band reflectivity in the range of about 130nm to about 430nm, which is comparable to the 13.5nm reflectivity of ruthenium (Ru) covered optics.

The unique optical properties of boron interact with the constructive interference of EUV optics to cause reflectivity to increase with increasing boron thickness between about 7 nm and about 10 nm. The resulting local reflectivity maximum between about 9 nm and about 10 nm is only 3.5% below the absolute maximum. Similar resonance effects do not occur or result in much lower local maximum reflectivity for metal oxide or ruthenium capping materials.

The out-of-band reflectivity of a typical ruthenium-coated molybdenum silicon multilayer in the range of about 200nm to about 400nm is comparable to the in-band reflectivity at 13.5nm. Boron coverage greater than 5nm reduces this ratio of out-of-band reflectivity to in-band emissivity by more than a factor of ten to reduce the amount of unwanted light reaching the detector.

Embodiments disclosed herein include a boron-based protective capping layer for EUV optics and a method for making the same. The boron-based protective capping layer may be a component of an EUV lithography system including an optical element.

As shown in FIG. 1A , an embodiment of the present invention may be an optical element 110 for use in EUV lithography. The optical element 110 may include a first layer 101 and a sequence 103 of a second layer 102 disposed on the first layer 101, which is disposed on a substrate 100. There may be only one of each of the first layer 101 and the second layer 102 in the sequence 103, or there may be n first layers 101 and n second layers 102 in the sequence 103. A terminal layer 104 may be disposed on the sequence 103, if there is only a single second layer 102, the terminal layer 104 may be disposed on the second layer 102; if there are n second layers 102, the terminal layer 104 may be disposed on the nth second layer 102. A cover layer 106 may be disposed on the terminal layer 104. In this example, the sequence of layers on the substrate of the optical element 110 may be: (i) one or more first layers 101 and second layers 102, (ii) the terminal layer 104, and (iii) the cover layer 106.

As shown in FIG. 1B , an embodiment of the present invention may be an optical element 120 for use in EUV lithography. The optical element 120 may be similar to the optical element 110 , but it may additionally include a diffusion barrier 105 . In this manner, the optical element 120 may include a first layer 101 and a sequence 103 of a second layer 102 disposed on the first layer 101 , which is disposed on a substrate 100 . There may be only one of each of the first layer 101 and the second layer 102 in the sequence 103 , or there may be n first layers 101 and n second layers 102 in the sequence 103 . A terminal layer 104 may be disposed on the sequence 103. If there is only a single second layer 102, the terminal layer 104 may be disposed on the second layer 102; if there are n second layers 102, the terminal layer 104 may be disposed on the nth second layer 102. A cover layer 106 may be disposed on the terminal layer 104, but the diffusion barrier 105 is disposed between the terminal layer 104 and the cover layer 106, so that the diffusion barrier 105 is disposed on the terminal layer 104 and the cover layer 106 is disposed on the diffusion barrier 105. In other words, the optical element 120 may include a diffusion barrier 105 disposed on the terminal layer 104, such that the cover layer 106 is disposed on the diffusion barrier 105. In this example, the layer sequence on the substrate of the optical element 120 may be: (i) one or more first layers 101 and second layers 102, (ii) the terminal layer 104, (iii) the diffusion barrier 105, and (iv) the cover layer 106.

As shown in FIG. 1C , an embodiment of the present invention may be an optical element 130 for use in EUV lithography. The optical element 130 may be similar to the optical element 110, but it may additionally include a terminal capping layer 107. In this manner, the optical element 130 may include a first layer 101 and a sequence 103 of a second layer 102 disposed on the first layer 101, which is disposed on a substrate 100. There may be only one of each of the first layer 101 and the second layer 102 in the sequence 103, or there may be n first layers 101 and n second layers 102 in the sequence 103. A terminal layer 104 may be disposed on the sequence 103. If there is only a single second layer 102, the terminal layer 104 may be disposed on the second layer 102; if there are n second layers 102, the terminal layer 104 may be disposed on the nth second layer 102. A cover layer 106 may be disposed on the terminal layer 104. A terminal cover layer 107 may be disposed on the cover layer 106. In this example, the sequence of layers on the substrate of the optical element 130 may be: (i) one or more first layers 101 and second layers 102, (ii) terminal layer 104, (iii) cover layer 106, and (iv) terminal cover layer 107.

As shown in FIG. 1D , an embodiment of the present invention may be an optical element 140 for use in EUV lithography. Optical element 140 may be similar to optical element 110, but it may additionally include a diffusion barrier 105 and a terminal capping layer 107. In this manner, optical element 140 may include a first layer 101 and a sequence 103 of a second layer 102 disposed on the first layer 101, which is disposed on a substrate 100. There may be only one of each of the first layer 101 and the second layer 102 in the sequence 103, or there may be n first layers 101 and n second layers 102 in the sequence 103. A terminal layer 104 may be disposed on the sequence 103. If there is only a single second layer 102, the terminal layer 104 may be disposed on the second layer 102; if there are n second layers 102, the terminal layer 104 may be disposed on the nth second layer 102. A cover layer 106 may be disposed on the terminal layer 104, but the diffusion barrier 105 is disposed between the terminal layer 104 and the cover layer 106, so that the diffusion barrier 105 is disposed on the terminal layer 104 and the cover layer 106 is disposed on the diffusion barrier 105. In other words, the optical element 120 may include a diffusion barrier 105 disposed on the terminal layer 104, such that the cover layer 106 is disposed on the diffusion barrier 105. A terminal cover layer 107 may be disposed on the cover layer 106. In this example, the layer sequence on the substrate of the optical element 140 may be: (i) one or more first layers 101 and second layers 102, (ii) terminal layer 104, (iii) diffusion barrier 105, (iv) cover layer 106, and (v) terminal cover layer 107.

Other embodiments of the present invention are methods for manufacturing an optical element for use in EUV lithography.

As shown in FIG. 2A , an embodiment of the present invention may be a method 210 for fabricating an optical element for use in EUV lithography. The method 210 may be used, for example, to fabricate the optical element 110. The method 210 may include a deposition step 201 of depositing a first layer such that the first layer may be disposed on a substrate, which may be accomplished using, for example, vapor deposition. This may be followed by a deposition step 202 of depositing a second layer such that the second layer may be disposed on the first layer, which may be accomplished using, for example, vapor deposition. Additional first and second layers up to and including n first layers and n second layers may be deposited as appropriate. Thus, for n desired first layers and n desired second layers, there may be m repetitions 203 of depositing first layers and second layers, where m=n-1. In this manner, each additional mth first layer after the initial first layer may be disposed on the previous m-1th second layer, up to n first layers and n second layers. This may be followed by a deposition step 204 of depositing a terminal layer such that the terminal layer may be disposed on the second layer. It should be noted that when there may be only one second layer, the terminal layer may be deposited such that it may be disposed on the second layer, and when there are n second layers, the terminal layer may be deposited such that it may be disposed on the nth second layer. This may be followed by a deposition step 206 of a capping layer such that the capping layer may be disposed on the terminal layer. In this example, when completed, the sequence of layers on the substrate produced according to method 210 may be: (i) one or more first layers and second layers, (ii) a terminal layer, and (iii) a capping layer.

As shown in FIG. 2B , an embodiment of the present invention may be a method 220 for fabricating an optical element for use in EUV lithography. Method 220 may be similar to method 210, but it may additionally include a deposition step 205 for depositing a diffusion barrier. Method 220 may be used, for example, to fabricate optical element 120. Method 220 may include a deposition step 201 of depositing a first layer such that the first layer may be disposed on a substrate, which may be accomplished using, for example, vapor deposition. This may be followed by a deposition step 202 of depositing a second layer such that the second layer may be disposed on the first layer, which may be accomplished using, for example, vapor deposition. Additional first and second layers may be deposited up to and including n first layers and n second layers. Thus, for n desired first layers and n desired second layers, there may be m repetitions 203 of depositing first and second layers, where m=n-1. In this manner, each additional mth first layer after the initial first layer may be placed on the previous m-1th second layer, up to n first layers and n second layers. This may be followed by a deposition step 204 of depositing a terminal layer such that the terminal layer may be placed on the second layer. It should be noted that when there may be only one second layer, the terminal layer may be deposited so that it may be disposed on the second layer, and when there are n second layers, the terminal layer may be deposited so that it may be disposed on the nth second layer. This may be followed by a deposition step 206 of depositing a cover layer so that the cover layer may be disposed on the terminal layer, but before the deposition step 206, the deposition step 205 may be performed. The deposition step 205 may include depositing a diffusion barrier so that the diffusion barrier may be disposed on the terminal layer, and after the deposition step 206, the cover layer may be disposed on the diffusion barrier. In this example, when completed, the sequence of layers on the substrate produced according to method 210 may be: (i) one or more first layers and second layers, (ii) a termination layer, (iii) a diffusion barrier, and (iv) a capping layer.

As shown in FIG. 2C , an embodiment of the present invention may be a method 230 for fabricating an optical element for use in EUV lithography. Method 230 may be similar to method 210, but it may additionally include a deposition step 207 for depositing a terminal capping layer. Method 230 may be used, for example, to fabricate optical element 130. Method 230 may include a deposition step 201 of depositing a first layer such that the first layer may be disposed on a substrate, which may be accomplished using, for example, vapor deposition. This may be followed by a deposition step 202 of depositing a second layer such that the second layer may be disposed on the first layer, which may be accomplished using, for example, vapor deposition. Additional first and second layers may be deposited up to and including n first layers and n second layers. Thus, for n desired first layers and n desired second layers, there may be m repetitions 203 of depositing first and second layers, where m=n-1. In this manner, each additional mth first layer after the initial first layer may be placed on the previous m-1th second layer, up to n first layers and n second layers. This may be followed by a deposition step 204 of depositing a terminal layer such that the terminal layer may be placed on the second layer. It should be noted that when there may be only one second layer, the terminal layer may be deposited so that it may be disposed on the second layer, and when there are n second layers, the terminal layer may be deposited so that it may be disposed on the nth second layer. This may be followed by a deposition step 206 of depositing a cover layer so that the cover layer may be disposed on the terminal layer. This may be followed by a deposition step 207 of depositing a terminal cover layer so that the terminal cover layer may be disposed on the cover layer. In this example, when completed, the sequence of layers on the substrate produced according to method 210 may be: (i) one or more first layers and second layers, (ii) a terminal layer, (iii) a cap layer, and (iv) a terminal cap layer.

As shown in FIG. 2D , an embodiment of the present invention may be a method 240 for fabricating an optical element for use in EUV lithography. Method 240 may be similar to method 210, but it may additionally include a deposition step 205 for depositing a diffusion barrier, and a deposition step 207 for depositing a terminal capping layer. Method 240 may be used, for example, to fabricate optical element 140. Method 240 may include a deposition step 201 of depositing a first layer such that the first layer may be disposed on a substrate, which may be accomplished using, for example, vapor deposition. This may be followed by a deposition step 202 of depositing a second layer such that the second layer may be disposed on the first layer, which may be accomplished using, for example, vapor deposition. Additional first and second layers may be deposited up to and including n first layers and n second layers. Thus, for n desired first layers and n desired second layers, there may be m repetitions 203 of depositing first and second layers, where m=n-1. In this way, each additional mth first layer after the initial first layer may be placed on the previous m-1th second layer, up to n first layers and n second layers. This may be followed by a deposition step 204 of depositing a terminal layer such that the terminal layer may be placed on the second layer. It should be noted that when there may be only one second layer, the terminal layer may be deposited so that it may be disposed on the second layer, and when there are n second layers, the terminal layer may be deposited so that it may be disposed on the nth second layer. This may be followed by a deposition step 206 of depositing a cover layer so that the cover layer may be disposed on the terminal layer, but before the deposition step 206, the deposition step 205 may be performed. The deposition step 205 may include depositing a diffusion barrier so that the diffusion barrier may be disposed on the terminal layer, and after the deposition step 206, the cover layer may be disposed on the diffusion barrier. A terminal capping layer may then be deposited such that the terminal capping layer may be disposed on the capping layer in a deposition step 207. In this example, when completed, the sequence of layers on the substrate produced according to method 210 may be: (i) one or more first layers and second layers, (ii) a terminal layer, (iii) a diffusion barrier, (iv) a capping layer, and (v) a terminal capping layer.

Deposition step 201 may be, for example, deposition of a first layer 101 as shown in FIGS. 1A to 1D. Deposition step 202 may be, for example, deposition of a second layer 102 as shown in FIGS. 1A to 1D. Repetition 203 may be, for example, formation of a sequence 103 as shown in FIGS. 1A to 1D. Deposition step 204 may be, for example, deposition of a termination layer 104 as shown in FIGS. 1A to 1D. Deposition step 205 may be, for example, deposition of a diffusion barrier 105 as shown in FIGS. 1B and 1D. Deposition step 206 may be, for example, deposition of a capping layer 106 as shown in FIGS. 1A to 1D. The deposition step 207 may be, for example, the deposition of a terminal capping layer 107 as shown in FIG. 1C and FIG. 1D .

Deposition according to any of the methods described herein may in particular be vapor deposition, physical vapor deposition, chemical vapor deposition, sputtering or magnetron sputtering.

The first layer(s) 101 (which may also refer to one or more first layers deposited using deposition step 201) may include, for example, silicon (Si).

The second layer(s) 102 (which may also refer to one or more second layers deposited using deposition step 202) may include, for example, molybdenum (Mo).

The terminal layer(s) 104 (which may also refer to a terminal layer deposited using deposition step 204) may include, for example, silicon (Si).

Diffusion barrier 105 (which may also be referred to as a diffusion barrier deposited using deposition step 205) may include, for example, carbon or another suitable material or combination of materials.

The capping layer 106 (which may also refer to a capping layer deposited using the deposition step 206) may include boron, boron nitride (BN), or boron carbide ( _B4C ). When the capping layer 106 includes boron, it may have a thickness in the range of 5 nm to 30 nm (including 5 nm and 30 nm). When the capping layer 106 includes boron nitride, it may have a thickness in the range of 2 nm to 10 nm (including 2 nm and 10 nm). Alternatively, when the capping layer 106 includes boron nitride, it may have a thickness in the range of 4 nm to 10 nm (including 4 nm and 10 nm). When the capping layer 106 includes boron carbide, it may have a thickness in the range of 2 nm to 25 nm (including 2 nm and 25 nm). Alternatively, when the capping layer 106 includes boron carbide, it may have a thickness in the range of from 4 nm to 25 nm (inclusive). These thickness ranges may refer to the final deposition thickness on the entire capping layer 106 or may refer to a target thickness or thickness tolerance for the capping layer 106. In one embodiment, when referring to a target thickness, there may be a finished target thickness of the capping layer 106 with different actual thicknesses, but the average or target thickness of the material falls within the scope of the composition material of the capping layer 106. In this way, the actual thickness at any given point on the capping layer 106 may be higher or lower than the average or target thickness. In another embodiment, when thickness tolerances are referred to, there may be a finished thickness of the cover layer 106 having different thicknesses, but the range boundaries given herein are tolerance levels or minimum and maximum thicknesses of the cover layer 106. In this way, the actual thickness at any given point on the cover layer 106 may fall within the given range of thicknesses. Further embodiments may require a target thickness of the cover layer 106 to fall within a range specified by the composition material and bounded by the minimum and maximum values described.

Alternatively, the capping layer 106 may include any combination of boron, boron carbide, and boron nitride. In one example, the capping layer may include a boron carbide capping layer, a boron capping layer, and a boron nitride capping layer.

The terminal capping layer 107 (which may also refer to a terminal capping layer deposited using deposition step 207) may include, for example, ruthenium (Ru), titanium dioxide ( _TiO2 ), zirconium dioxide ( _ZrO2 ) or niobium oxide. Niobium oxide may refer to different oxidation states of niobium, which particularly includes niobium monoxide (NbO), niobium dioxide ( _NbO2 ) or _niobium pentoxide ( _Nb2O5 ).

The first layer 101, the second layer 102, the terminal layer 104, the diffusion barrier 105, the cover layer 106, and the terminal cover layer 107 may include materials with different physical properties, depending on the application. For example, the materials may have different porosities, densities, and uniformities depending on the application and the deposition process used. In some embodiments, the porosity, density, and uniformity are optimized and other materials may contribute to the optimization of one or more of the porosity, density, and uniformity. There may also be an impurity tolerance specified based on the application and detection needs. Such an impurity tolerance may be determined based on material or manufacturer settings, among other things.

To demonstrate the possibility of boron as a capping layer, simulations were performed using the IMD software and the optical constants at 13.5 nm that have been measured for boron, silicon, molybdenum and boron carbide and calculated for titanium dioxide, ruthenium and boron nitride. FIG. 3 depicts a plot 300 showing the reflectivity R of a typical Mo:Si multilayer optical device as a function of the thickness of the capping layer of different capping materials, namely, ruthenium (curve 301), titanium dioxide (curve 302) and boron (curve 303). The non-monotonic dependence of R on the capping thickness is due to the constructive interference inherent in multilayer optical devices.

An alternative capping layer should not reduce the reflectivity of a standard 2.2nm ruthenium-capped multi-layer mirror by more than a certain critical amount ΔR _Crit . For the simulation shown in FIG3 , ΔR _Crit = 3.5% (between lower limit R _Crit (304) and upper limit R _Crit (305)) was used, which is a typical representation of acceptable losses. This limits the thickness of the ruthenium cap and the titanium dioxide cap to 4.5nm and 2.2nm, respectively. This thickness of titanium dioxide may not be sufficient to protect the underlying silicon from oxidation during years of EUV exposure.

A critical boron thickness of 4.2 nm should provide adequate protection against oxidation based on the performance of existing 5 nm coatings on Si-based detectors. If a greater reflectivity loss of 5% is an acceptable tradeoff for more than doubling the capping thickness, a 9.8 nm boron layer can be used to exploit the local maximum in the boron curve 303 shown in FIG3 .

Similar calculations show that 4nm to 5nm layers of pure boron nitride and boron carbide also have acceptable reflectivity loss. Since boron carbide is known to be an effective diffusion barrier and boron nitride is known to be highly resistant to oxidation and oxygen diffusion, the following structure can be used (bottom-up) to obtain the best balance of stability over time, oxidation resistance, and reflectivity: silicon/boron carbide/boron/boron nitride.

To demonstrate the effectiveness of the boron capping layer as a distributed spectral purity filter, FIG. 4 depicts a plot 400 of the calculated transmission for a pictorial 4-mirror system having boron and ruthenium coatings, i.e., for 2.2 nm ruthenium (depicted by plot 401), 9.8 nm boron (depicted by plot 402), and 4.4 nm boron (depicted by plot 403). For a typical coverage of 2.2 nm ruthenium, the system transmission in the range 200 nm to 400 nm is comparable to the in-band reflectivity at 13.5 nm. The transmission in the range 130 nm to 430 nm is reduced by a factor of 10 to 100 by using the boron capping layer, with thicker boron resulting in greater suppression. This thickness trend is reversed in the 50nm to 130nm range; therefore, a trade-off must be made between the suppression of these two bands.

An embodiment of a system 500 is shown in FIG. 5 . The system 500 includes an optics-based subsystem 501 . Generally, the optics-based subsystem 501 is configured to generate an optics-based output of a sample 502 by directing light to a sample 502 (or causing light to scan the sample 502 ) and detecting light from the sample 502 . In one embodiment, the sample 502 includes a wafer. The wafer may include any wafer known in the art. In another embodiment, the sample includes a zoom mask. The zoom mask may include any zoom mask known in the art.

In an embodiment of system 500 shown in FIG. 5 , an optical-based subsystem 501 includes an illumination subsystem configured to direct light to a sample 502. The illumination subsystem includes at least one light source. For example, as shown in FIG. 5 , the illumination subsystem includes a light source 503. In one embodiment, the illumination subsystem is configured to direct light to the sample 502 at one or more incident angles that may include one or more oblique angles and/or one or more normal angles. For example, as shown in FIG. 5 , light from the light source 503 is directed through the optical element 504 and then the lens 505 to the sample 502 at an oblique incident angle. The oblique incident angle may include any suitable oblique incident angle, which may vary depending on, for example, the characteristics of the sample 502.

The optics-based subsystem 501 can be configured to direct light to the sample 502 at different incident angles at different times. For example, the optics-based subsystem 501 can be configured to change one or more characteristics of one or more components of the illumination subsystem so that light can be directed to the sample 502 at an incident angle different from the incident angle shown in FIG. 5. In one such example, the optics-based subsystem 501 can be configured to move the light source 503, the optical element 504, and the lens 505 so that light is directed to the sample 502 at a different oblique incident angle or a normal (or near-normal) incident angle.

In some examples, the optical-based subsystem 501 may be configured to direct light to the sample 502 at more than one incident angle simultaneously. For example, the illumination subsystem may include more than one illumination channel, one of which may include a light source 503, an optical element 504, and a lens 505 (as shown in FIG. 5 ) and another of the illumination channels (not shown) may include similar elements, which may be configured differently or identically or may include at least one light source and possibly one or more other components (such as those further described herein). If this light is directed to the sample simultaneously with the other light, one or more characteristics (e.g., wavelength, polarization, etc.) of the light directed to the sample 502 at different incident angles may be different, so that the light resulting from illuminating the sample 502 at different incident angles can be distinguished from each other at the detector(s).

In another example, the illumination subsystem may include only one light source (e.g., light source 503 shown in FIG. 5 ) and light from the light source may be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Light in each of the different optical paths may then be directed to the sample 502. Multiple illumination channels may be configured to direct light to the sample 502 at the same time or at different times (e.g., when different illumination channels are used to illuminate the sample sequentially). In another example, the same illumination channel may be configured to direct light with different characteristics to the sample 502 at different times. For example, in some instances, optical element 504 can be configured as a spectral filter and the properties of the spectral filter can be changed in various ways (e.g., by swapping out spectral filters) so that light of different wavelengths can be directed to sample 502 at different times. The illumination subsystem can have any other suitable configuration known in the art for directing light with different or the same characteristics to sample 502 sequentially or simultaneously at different or the same incident angles.

In one embodiment, light source 503 may include a broadband plasma (BBP) source and an extreme ultraviolet lithography (EUV) source. In this manner, the light generated by light source 503 and directed to sample 502 may include broadband light or ultraviolet light. However, the light source may include any other suitable light source, such as a laser. The laser may include any suitable laser known in the art and may be configured to generate light of one or more of any suitable wavelengths known in the art. In addition, the laser may be configured to generate monochromatic or near-monochromatic light. In this manner, the laser may be a narrowband laser. Light source 503 may also include a polychromatic light source that generates light of multiple discrete wavelengths or bands.

Light from optical element 504 may be focused by lens 505 onto sample 502. Although lens 505 is shown in FIG. 5 as a single refractive optical element, it should be understood that lens 505 may actually include a plurality of refractive and/or reflective optical elements that focus a combination of light from the optical elements onto the sample. The illumination subsystem shown in FIG. 5 and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarization components, spectral filter(s), spatial filter(s), reflective optical element(s), apodizer(s), beam splitter(s) (such as beam splitter 513), aperture(s), and the like, which may include any such suitable optical elements known in the art. Additionally, the optical-based subsystem 501 may be configured to change one or more of the elements of the illumination subsystem based on the type of illumination used to produce the optical-based output. Such optical elements may have a first layer, a second layer, a terminal layer, and a cover layer as described herein and depicted, for example, in FIG. 1A. Such optical elements may additionally have a diffusion barrier, a terminal cover layer, or both, as described herein and depicted, for example, in FIGS. 1B-1D. The layers and barriers described herein may be formed using, for example, one of the methods described herein and depicted in FIGS. 2A-2D as appropriate.

The optical-based subsystem 501 may also include a scanning subsystem configured to cause light to scan the sample 502. For example, the optical-based subsystem 501 may include a stage 506 on which the sample 502 is placed during the generation of the optical-based output. The scanning system may include any suitable mechanical and/or robotic assembly (including the stage 506) that can be configured to move the sample 502 so that the light can scan the sample 502. Additionally or alternatively, the optical-based subsystem 501 may be configured so that one or more optical elements of the optical-based subsystem 501 perform a certain optical scan of the sample 502. The light can scan the sample 502 in any suitable manner, such as along a serpentine path or a spiral path.

The optics-based subsystem 501 further includes one or more detection channels. At least one of the one or more detection channels includes a detector that is configured to detect light from the sample 502 due to illumination of the sample 502 by the subsystem and to generate an output in response to the detected light. For example, the optics-based subsystem 501 shown in FIG5 includes two detection channels: one detection channel is formed by a collector 507, an element 508, and a detector 509 and the other detection channel is formed by a collector 510, an element 511, and a detector 512. As shown in FIG5, the two detection channels are configured to collect and detect light at different collection angles. In some examples, two detection channels are configured to detect scattered light, and the detection channels are configured to detect light scattered from the sample 502 at different angles. However, one or more of the detection channels may be configured to detect another type of light (e.g., reflected light) from the sample 502.

As further shown in FIG. 5 , two detection channels are shown as being positioned in the paper and the illumination subsystem is also shown as being positioned in the paper. Thus, in this embodiment, the two detection channels are positioned in (e.g., centered in) the incident plane. However, one or more of the detection channels may be positioned outside the incident plane. For example, the detection channel formed by the collector 510, the element 511, and the detector 512 may be configured to collect and detect light scattered from the incident plane. Thus, such a detection channel may generally be referred to as a "side" channel, and such a side channel may be centered in a plane substantially perpendicular to the incident plane.

Although FIG. 5 shows an embodiment of an optical-based subsystem 501 including two detection channels, the optical-based subsystem 501 may include a different number of detection channels (e.g., only one detection channel or two or more detection channels). In one such example, the detection channel formed by the collector 510, the element 511, and the detector 512 may form a side channel as described above, and the optical-based subsystem 501 may include an additional detection channel (not shown) formed as another side channel positioned on the opposite side of the incident surface. Thus, the optical-based subsystem 501 may include a detection channel including a collector 507, an element 508, and a detector 509 and centered in the incident plane and configured to collect and detect light at (several) scattering angles normal or close to normal to the surface of the sample 502. Thus, this detection channel may generally be referred to as a "top" channel, and the optical-based subsystem 501 may also include two or more side channels configured as described above. Thus, the optical-based subsystem 501 may include at least three channels (i.e., one top channel and two side channels), and each of the at least three channels has its own collector, each collector being configured to collect light at a different scattering angle than each of the other collectors.

As further described herein, each of the detection channels included in the optics-based subsystem 501 can be configured to detect scattered light. Thus, the optics-based subsystem 501 shown in FIG. 5 can be configured for dark field (DF) output generation of the sample 502. However, the optics-based subsystem 501 can also or alternatively include (several) detection channels configured for bright field (BF) output generation of the sample 502. In other words, the optics-based subsystem 501 can include at least one detection channel configured to detect light reflected from a mirror surface of the sample 502. Thus, the optics-based subsystem 501 described herein can be configured for DF-only, BF-only, or both DF and BF imaging. Although each of the collectors is shown in FIG. 5 as a single refractive optical element, it should be understood that each of the collectors may include one or more refractive optical grains and/or one or more reflective optical elements.

The one or more detection channels may include any suitable detector known in the art. For example, the detectors may include photomultiplier tubes (PMTs), charge coupled devices (CCDs), time delay integration (TDI) cameras, and any other suitable detectors known in the art. The detectors may also include non-imaging detectors or imaging detectors. In this manner, if the detectors are non-imaging detectors, each of the detectors may be configured to detect specific properties of the scattered light (such as intensity), but may not be configured to detect such properties that vary depending on position within the imaging plane. Thus, the output generated by each of the detectors included in each of the detection channels of the optically-based subsystem may be a signal or data, but not an image signal or image data. In such examples, a processor (such as processor 514) may be configured to generate an image of sample 502 from the non-imaging output of the detector. However, in other examples, the detector may be configured as an imaging detector configured to generate an imaging signal or image data. Thus, the optically-based system may be configured to generate an optical image or other optically-based output described herein in a variety of ways.

It should be noted that FIG. 5 is provided herein to generally illustrate a configuration of an optical-based subsystem 501 that may be included in or may produce an optical-based output used by the system embodiments described herein. The configuration of the optical-based subsystem 501 described herein may be modified to optimize the performance of the optical-based subsystem 501 typically performed when designing a commercial output acquisition system. In addition, the system described herein may be implemented using an existing system (e.g., by adding the functionality described herein to an existing system). For some of these systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the system described herein may be designed as an entirely new system.

Processor 514 may be coupled to components of system 500 in any suitable manner (e.g., via one or more transmission media that may include wired and/or wireless transmission media) so that processor 514 can receive output. Processor 514 may be configured to use the output to perform a number of functions. System 500 may receive instructions or other information from processor 514. Processor 514 and/or electronic data storage unit 515 may electronically communicate with a wafer inspection tool, a wafer metrology tool, or a wafer review tool (not shown), as appropriate, to receive additional information or send instructions. For example, processor 514 and/or electronic data storage unit 515 may electronically communicate with a SEM.

The processor 514, other system(s), or other subsystem(s) described herein may be part of a variety of systems including a personal computer system, video computer, mainframe computer system, workstation, network equipment, Internet equipment, or other devices. The subsystem(s) or system may also include any suitable processor known in the art, such as a parallel processor. In addition, the subsystem(s) or system may include a platform with high-speed processing and software as a stand-alone or networked appliance.

The processor 514 and the electronic data storage unit 515 may be disposed in the system or another device or otherwise be part of the system 500 or another device. In one example, the processor 514 and the electronic data storage unit 515 may be part of an independent control unit or located in a centralized quality control unit. Multiple processors 514 or electronic data storage units 515 may be used.

Processor 514 may be implemented by any combination of hardware, software, and firmware. In addition, the functions described herein may be performed by a single unit or distributed among different components, each of which may in turn be implemented by any combination of hardware, software, and firmware. Program code or instructions for processor 514 to implement various methods and functions may be stored in a readable storage medium (such as a memory in electronic data storage unit 515 or other memory).

If the system 500 includes more than one processor 514, different subsystems may be coupled to each other so that images, data, information, instructions, etc. may be sent between subsystems. For example, a subsystem may be coupled to additional subsystem(s) via any suitable transmission medium, which may include any suitable wired and/or wireless transmission medium known in the art. Two or more of such subsystems may also be effectively coupled by a common computer-readable storage medium (not shown).

Processor 514 may be configured to use the output of system 500 or other output to perform a number of functions. For example, processor 514 may be configured to send output to an electronic data storage unit 515 or another output medium. Processor 514 may be further configured as described herein.

If the system includes more than one subsystem, the different subsystems may be coupled to each other so that images, data, information, instructions, etc. may be sent between the subsystems. For example, a subsystem may be coupled to (several) additional subsystems via any suitable transmission medium, which may include any suitable wired and/or wireless transmission medium known in the art. Two or more of these subsystems may also be effectively coupled by a common computer-readable storage medium (not shown).

Processor 514 may be configured according to any of the embodiments described herein. Processor 514 may also be configured to use the output of system 500 or to use images or data from other sources to perform other functions or additional steps.

The various steps, functions and/or operations of system 500 and the methods disclosed herein are implemented by one or more of the following: electronic circuits, logic gates, multiplexers, programmable logic devices, ASICs, analog or digital controls/switches, microcontrollers, or computing systems. Program instructions for implementing methods (such as the methods described herein) can be transmitted via or stored on a carrier medium. The carrier medium can include an output medium, such as a read-only memory, a random access memory, a magnetic or optical disk, a non-volatile memory, a solid-state memory, a magnetic tape, and the like. A carrier medium can include a transmission medium, such as a wire, cable, or wireless transmission link. For example, the various steps described in the present invention may be implemented by a single processor 514 or alternatively multiple processors 514. Furthermore, different subsystems of the system 500 may include one or more computational or logical systems. Therefore, the above description should not be interpreted as a limitation of the present invention, but is merely illustrative.

Various advantages are presented by embodiments of the present invention. These embodiments include boron-based protective capping layers for EUV optics, namely: using a thick (between 5nm and 30nm) boron layer to protect EUV optics; using a boron layer having a thickness greater than or equal to 5nm and optimized at the local reflectivity maximum of a multi-layer mirror to protect EUV optics; using a thick (between about 2nm and about 25nm) boron carbide layer to protect EUV optics; using a thick (between about 2nm and about 10nm) boron nitride layer to protect EUV optics; using a stack of silicon/boron carbide/boron/boron nitride (bottom-up) to protect EUV optics; and using a boron capping layer as a distributed spectral purity filter. Such embodiments may provide advantages including, among other things, reduced costs and risks in designing, manufacturing, and operating EUV lithography equipment. Additionally, the boron-based capping layer provides easier cleanability and enhanced durability over multiple cycles. The embodiments of the boron-based capping layer disclosed herein on the ruthenium-based capping layer achieve this easier cleanability due to different crystal structures and sizes and other chemical differences.

The various embodiments disclosed herein and the steps of the methods described in the embodiments are sufficient to implement the methods of the present invention. Therefore, in one embodiment, the method consists essentially of a combination of the steps of the methods disclosed herein. In another embodiment, the method consists of these steps.

Although the present invention has been described with respect to one or more specific embodiments, it should be understood that other embodiments of the present invention may be made without departing from the scope of the present invention.

100: Substrate

101: First level

102: Second level

103: Sequence

104: Terminal layer

106: Covering layer

110: Optical components

Claims (9)

An optical element comprises: a first layer disposed on a substrate, wherein the first layer comprises silicon; a second layer disposed on the first layer, wherein the second layer comprises molybdenum, and wherein the molybdenum of the second layer is directly disposed on the silicon of the first layer; a terminal layer disposed on the second layer, wherein the terminal layer comprises silicon, and wherein the silicon of the terminal layer is directly disposed on the molybdenum of the second layer; and a capping layer. layer), which includes boron, boron nitride, or boron carbide, wherein the covering layer is disposed on one side of the terminal layer relative to the second layer, and wherein the boron, the boron nitride, or the boron carbide of the covering layer is directly disposed on the silicon of the terminal layer. The optical element of claim 1 further comprises: an extreme ultraviolet lithography system including the optical element, or a detection system including the optical element. An optical element as claimed in claim 1, wherein the capping layer comprises boron and has a thickness ranging from 5 nm to 30 nm (including 5 nm and 30 nm). An optical element as claimed in claim 1, wherein the covering layer comprises boron nitride and has a thickness ranging from 2nm to 10nm (including 2nm and 10nm). An optical element as claimed in claim 1, wherein the covering layer comprises boron carbide and has a thickness ranging from 2 nm to 25 nm (including 2 nm and 25 nm). As in claim 1, the optical element, wherein the coating layer includes a boron carbide coating layer, a boron coating layer, and a boron nitride coating layer. The optical element of claim 1 further comprises a terminal covering layer disposed on the covering layer. An optical element as claimed in claim 7, wherein the terminal covering layer comprises ruthenium, titanium dioxide, zirconium dioxide, or niobium oxide. An optical element as claimed in claim 1, wherein an outer surface of the covering layer relative to the terminal layer is the farthest point of the optical element from the substrate.