Patent Application
20080102259
This disclosure relates to oxide materials, as well as related articles, systems and methods.
Oxides are commonly used in devices and systems where manipulation of electromagnetic (EM) radiation is desired. Examples of EM radiation include the ultra-violet region, the visible region, and the infra-red region. Examples of optical devices include lenses, polarizers, optical filters, antireflection films, optical retarders (e.g., waveplates), and beam splitters (e.g., polarizing and non-polarizing beam splitters).
This disclosure relates to oxide materials, as well as related articles, systems and methods.
In one aspect, the invention features an oxide that includes silicon and a metal and the oxide has a refractive index of at least about 1.8 at a wavelength of 632 nm.
In another aspect, the invention features an oxide compound that includes at least about one atomic percent silicon and at least about twenty atomic percent of a metal.
In a further aspect, the invention features an oxide that includes silicon and a metal. The oxide has a thickness defined by first and second surfaces. The oxide includes a first portion partially defined by the first surface of the oxide and a second portion partially defined by the second surface of the oxide. The first portion is different from the second portion. The first portion has a first average atomic percentage of silicon that is greater than zero, the second portion has a second average atomic percentage of silicon that is greater than zero, and the second average atomic percentage is different from the first average atomic percentage of silicon.
In an additional aspect, the invention features an article that includes a first layer of titanium oxide and a second layer of an oxide comprising titanium and silicon.
In yet another aspect, the invention features an article that includes a substrate and a layer of an oxide supported by the substrate. The oxide includes silicon and a metal. The article is an optical component.
In a further aspect, the invention features an article that includes a substrate and a layer of an oxide supported by the substrate. The oxide includes silicon and a metal and has a refractive index greater than a refractive index of silicon oxide and less than a refractive index of metal oxide. The article is an optical element.
In an additional aspect, the invention features a system that includes an optical element. The optical element includes a substrate and a layer of an oxide that includes silicon and a metal supported by the substrate.
In yet another aspect, the invention features a system that includes an optical element. The optical element includes a substrate and a layer of an oxide supported by the substrate. The oxide includes silicon and a metal and has a refractive index greater than a refractive index of silicon oxide and less than a refractive index of metal oxide.
In a further aspect, the invention features a method that includes forming an approximately amorphous oxide that includes silicon and a metal using gas phase deposition wherein the oxide is formed at a temperature of at least about 190 degrees Celsius.
In an additional aspect, the invention features a method that includes forming an oxide that includes silicon and a metal using atomic layer deposition. The oxide is formed at a temperature of at least about 190 degrees Celsius.
Embodiments can feature one or more of the following.
In certain embodiments, the oxide has a refractive index of at least about 2.0 (e.g., at least about 2.2, at least about 2.5) at a wavelength of 632 nm. In some embodiments, the metal is one of titanium, hafnium, aluminum, niobium, zirconium, tantalum, magnesium, neodymium, tin, vanadium, and yttrium. In certain embodiments, the oxide includes at least about one atomic percent silicon (e.g., at least about five atomic percent silicon). In some embodiments, the oxide includes at most about twenty atomic percent silicon (e.g., at most about ten atomic percent silicon, at most about five atomic percent silicon). In certain embodiments, the oxide includes at least about twenty atomic percent of the metal (e.g., at least about twenty-five atomic percent of the metal). In some embodiments, the oxide includes at most about thirty atomic percent of the metal (e.g., at most about twenty-five atomic percent of the metal).
In some embodiments, the metal is titanium and the oxide includes at least about fifteen atomic percent titanium and at least about one atomic percent silicon. In certain embodiments, the oxide comprises at most about thirty atomic percent titanium. In some embodiments, the oxide comprises at most about ten atomic percent silicon (e.g., at most about five atomic percent silicon).
In certain embodiments, the oxide has first and second surfaces that define a thickness of the oxide, and the thickness of the oxide is at least about 5 nm (e.g., at least about 25 nm, at least about 50 nm, at least about 80 nm, at least about 100 nm. In some embodiments, the oxide is at least about 90 percent amorphous.
In certain embodiments, the oxide has a thickness defined by first and second surfaces, the oxide includes a first portion partially defined by the first surface of the oxide, and the oxide includes a second portion partially defined by the second surface of the oxide. In some embodiments, the first portion is different from the second portion, the first portion has a first average atomic percentage of silicon that is greater than zero, the second portion has a second average atomic percentage of silicon that is greater than zero, and the second average atomic percentage is different from the first average atomic percentage of silicon. In some additional embodiments, the first portion has a first average atomic percentage of silicon that is equal to zero and the second portion has a second average atomic percentage of silicon that is greater than zero. In some additional embodiments, the first portion has a first average atomic percentage of silicon, the second portion has a second average atomic percentage of silicon, and the second average atomic percentage is different from the first average atomic percentage of silicon.
In some embodiments, the difference between the first average atomic percentage and the second average atomic percentage is at least about five percentage (e.g., at least about ten percentage, at least about twenty percentage). In certain embodiments, the first average atomic percentage is at least about one percentage (e.g., at least about three percentage). In some embodiments, the first average atomic percentage is at most about ten percentage (e.g., at most about five percentage). In some embodiments, the second average atomic percentage is at least about ten percentage (e.g., at least about twenty percentage).
In some embodiments, the article can include a third layer of titanium oxide supported by the second layer. In certain embodiments, the article can include a fourth layer of an oxide comprising titanium and silicon supported by the third layer. In some embodiment, the article can include a fifth layer of titanium oxide supported by the fourth layer. In certain embodiments, the article can include a sixth layer of an oxide comprising titanium and silicon supported by the fifth layer.
In some embodiments, the optical component is a thin film interference filter, an absorption filter, a wire grid light polarizing structure, a rugate filter, a conformal filling of a three-dimensional structure, a conformal film growth on a three-dimensional template structure, an optical lens structure, and/or an interface layer between different parts of an integrated optical component. In certain embodiments, the three-dimensional structure is a trench, a diffraction grating groove, a pillar, a pyramid, a column, and/or a semi-sphere.
In some embodiments, the method uses chemical vapor deposition. In certain embodiments, the method includes depositing silicon atoms, oxygen atoms, and atoms of the metal. The silicon atoms can be deposited separately from the atoms of the metal and from the oxygen atoms. In some embodiments, the method includes exposing a surface to a precursor comprising silicon atoms. In certain embodiments, the method can include exposing silicon atoms to a precursor comprising oxygen atoms and exposing oxygen atoms to a precursor comprising atoms of the metal. In some embodiments, the method includes alternately depositing atoms of silicon, oxygen and the metal. In certain embodiments, the method includes forming a monolayer of oxygen, forming a monolayer of the metal on the monolayer of oxygen, forming a second monolayer of oxygen, the second monolayer of oxygen being on the monolayer of the metal, and forming a monolayer of silicon on the second monolayer of oxygen. In some embodiments, the method includes using atomic layer deposition.
In some embodiments, the oxide is formed at a temperature of at least about 225 degrees Celsius (e.g., at least about 250 degrees Celsius, at least about 300 degrees Celsius).
Embodiments can have one or more of the following advantages.
In some embodiments, a layer of material containing titanium, silicon, and oxygen can be substantially amorphous and have a thickness in excess of about 50 nm. This can be desirable because, in general, amorphous materials may transmit EM radiation better than layers that are partially or mostly crystalline materials. In some embodiments, a substantially amorphous material containing silicon, titanium, and oxygen can be prepared at a temperature in excess of 190° C. For example, in some embodiments a substantially amorphous material containing silicon, titanium, and oxygen can be deposited at a temperature from about 250° C. to about 300° C. This can be advantageous because growing materials at higher temperatures can increase atom packing density, index of refraction and/or make the films more resistant to degradation from environmental changes. In addition high temperature deposition can reduce the stress in the deposited material.
In certain embodiments, an optical article can have an index of refraction that varies as a function of distance from a substrate, referred to as a graded index of refraction. The graded index of refraction can be formed, for example, by varying a ratio of titanium to silicon in a material containing silicon, titanium, and oxygen. This can be desirable because a gradual change in the index of refraction can be useful in various optical articles such as rugate filters.
In some embodiments, the optical properties such as the refractive index, mechanical integrity and/or crystallinity of an optical article can be manipulated or controlled by using one or more silicon oxide materials in which a metal (e.g., titanium) is also present. This can allow for materials to be formed in a predictable fashion that have a desired refractive index and/or other desirable properties.
Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
The disclosure generally relates to materials used to form articles that are sensitive to and can be used to control properties of EM radiation, such as the polarization and/or direction of beams incident on the articles. Examples of EM radiation include the visible region, the ultraviolet region, the infrared region, and the microwave region. In some embodiments, the articles can be sensitive to and/or can be used to control the properties of incident radiation in more than one region of the EM spectrum.
Referring to
Without wishing to be bound by theory, it is believed that having a large difference between the indices of refraction of the two materials can increase the efficiency of the filter. Examples of materials having a high refractive index include TiO2, which has a refractive index of about 2.48 at 632 nm, Ta2O5 which has a refractive index of about 2.15 at 632 nm, and HfO2 which has a refractive index of about 1.9 at 632 nm. Examples of materials having a low refractive index include SiO2 and Al2O3, which have refractive indices of about 1.45 and about 1.65 at 632 nm, respectively.
Referring to
In order to form various types of optical articles, it can be desirable to control the optical transmission characteristics of a material in a predictable fashion. For example, the optical transmission characteristics of a material can vary based on a number of parameters including the refractive index of the material. As described above, in some embodiments it can be desirable to form a material having a known refractive index (e.g., a high refractive index or a low refractive index). In certain embodiments, it can be desirable to form a material having a graded refractive index.
The optical transmission characteristics can vary based on whether the material is substantially amorphous. It is believed that when EM radiation passes through certain materials that are not substantially amorphous, the materials can generate scattering losses.
In order to reduce the scattering losses for such materials, it can be beneficial for the material to be substantially amorphous (e.g., about 95% amorphous or more, about 98% amorphous or more, about 99% or more amorphous).
In some embodiments, in order to reduce the scattering losses, it can be beneficial to limit the maximum size of crystalline domains present in the material. For example, the thickness of layers that crystallize can be limited such that the size of possible crystalline domains is limited. X-ray difractometry XRD can quantify existing crystalline phase.
Material 21 is composed of alternating layers of titanium (e.g., layers 20a, 20b, 20c, 20d, 20e) and oxygen (e.g., layers 22a, 22b, 22c, 22d). Material 21 is shown as a layer of TiO2. While material 21 is shown schematically as an ordered, crystalline layer (to aid in discussion), material 21 can exist in crystalline, substantially amorphous, or mixed form. Further, other types of titanium oxides exist. Other types of titanium oxide include, for example, Ti2O3 and Ti3O5. Titanium oxide layers often grow with tensile stress which can limit the total thickness of the titanium oxide which can be deposited. One method to reduce the tensile stress in a titanium oxide material is to grow the material at an elevated temperature (e.g., a temperature greater than about 200° C., typically 250-350° C.). While growing the titanium oxide at an elevated temperature can be beneficial in reducing stress in the material, titanium oxide layers often exhibit a phase transition from being substantially amorphous to being crystalline at a growth temperature of about 180° C. and above. In general, the amount of crystalline phase increases with temperature and/or with the total thickness of the deposited titanium oxide material. For example, titanium oxide layers having a thickness of above about 80 nm tend to show an increased presence of crystalline phase compared to thinner layers (e.g., layers with a thickness of about 20 nm or less).
It is believed that introducing at least some silicon into a titanium oxide material to form a material composed of silicon, titanium, and oxygen (such as material 25) can alter the refractive index and/or certain other characteristics (e.g., whether the material is substantially amorphous) of the material. It is believed that the refractive index and/or certain other characteristics can be altered by varying the ratio of the atomic percent of titanium to the atomic percent of silicon in the material.
In comparison to material 21, in material 25 some of the titanium atoms have been selectively substituted with silicon atoms. Specifically, relative to material 21, in material 25, fifty percent of the titanium atoms have been substituted by silicon atoms such that material 25 includes multiple layers of titanium (e.g., layers 24a, 24b, and 24c), multiple layers of silicon (e.g., layers 28a and 28b), and multiple layers of oxygen (e.g., layers 26a, 26b, 26c, 26d). It is believed that substituting at least some of the titanium with silicon during the growth of material 25 can modify the internal material stress and/or the refractive index of material 25 while maintaining low optical losses for material 25. It is also believed that substituting at least some of the titanium with silicon during the growth of material 25 can increase the temperature at which a transition of the material containing silicon, titanium, and oxygen from being substantially amorphous to crystalline occurs. Thus, it is believed that in comparison to material 21, material 25 can be deposited at higher temperatures and/or greater thicknesses while remaining substantially amorphous.
It is believed that, by selectively substituting at least some of the titanium in a titanium oxide material with silicon to form a material containing silicon, titanium, and oxygen, a substantially amorphous material (e.g., a material in which little or no crystalline or crystal grain structure exist) can be formed having a thickness of at least about 5 nm (e.g., at least about 10 nm, at least about 20 nm, at least about 40 nm, at least about 50 nm, at least about 80 nm, at least about 100 nm, at least about 120 nm, at least about 150 nm). Various methods can be used to determine if the material is substantially amorphous. For example, in some embodiments, X-Ray difraction (XRD) can identify and quantify specific material phase(s) present in the material layers. In another example, optical measurements with transmitted light can be used to determine if the material is substantially amorphous. The optical measurements will show reduced transmission due to scattering when a non-amorphous, e.g., crystalline, structure exists. The transmission can be observed with spectrophotometer or tunable laser source and detector. In an additional example, visual inspection of a wafer under oblique incidence of light (e.g., a light source with strong blue light content such as Xenon or Halogen lamp) can be used to determine if the material is substantially amorphous. If the material has a crystalline structure, the material will appear hazy or milky.
In some embodiments, such a substantially amorphous material containing silicon, titanium, and oxygen can have an index of refraction of about 1.8 or greater at a wavelength of 632 nm (e.g., about 2.0 or greater at a wavelength of 632 nm, about 2.1 or greater at a wavelength of 632 nm, about 2.2 or greater at a wavelength of 632 nm, about 2.3 or greater at a wavelength of 632 nm).
In some embodiments, a substantially amorphous material containing silicon, titanium, and oxygen can be formed at temperatures above about 190° C. (e.g., above about 200° C., above about 220° C., above about 240° C., above about 250° C., above about 260° C., above about 280° C., above about 300° C., above about 320° C.). In some embodiments, such a material can have an index of refraction of about 1.8 or greater at a wavelength of 632 nm (e.g., about 2.0 or greater at a wavelength of 632 nm, about 2.1 or greater at a wavelength of 632 nm, about 2.2 or greater at a wavelength of 632 nm, about 2.3 or greater at a wavelength of 632 nm).
It is also believed that varying the atomic ratio of titanium to silicon in a material containing silicon, titanium, and oxygen can modify the refractive index of the resulting material.
In general, the refractive index of the material containing silicon, titanium, and oxygen decreases as the proportion of silicon in the material increases. The index of refraction is bounded by the index of refraction of TiO2 (as indicated by arrow 56) and the index of refraction of SiO2 (as indicated by arrow 58). Thus, for a material containing titanium, silicon and oxygen, the index of refraction varies from about 2.45 to about 1.45 as measured using a wavelength of 632 nm. SiO2 has a lower refractive index than TiO2, therefore, the greater the ratio of silicon atoms to titanium atoms the lower the index of refraction of the material containing titanium, silicon and oxygen will be. Thus, the refractive index of the material containing titanium, silicon and oxygen can be controlled by modifying a proportion of silicon relative to titanium in the material containing titanium, silicon and oxygen.
In some embodiments, the material containing silicon, titanium, and oxygen can include at least about 1 atomic percent silicon (e.g., at least about 2 atomic percent silicon, at least about 5 atomic percent silicon, at least about 10 atomic percent silicon, at least about 15 atomic percent silicon) and/or at most about 20 atomic percent silicon (e.g., at most about 15 atomic percent silicon, at most about 10 atomic percent silicon, at most about 5 atomic percent silicon). For example, in certain embodiments, the material containing silicon, titanium, and oxygen can include from about 1 atomic percent to about 10 atomic percent silicon (e.g., from about 1 atomic percent to about 5 atomic percent silicon, from about 1 atomic percent to about 3 atomic percent silicon, from about 1 atomic percent to about 2 atomic percent silicon).
In some embodiments, the material containing silicon, titanium, and oxygen can include at least about 15 atomic percent titanium (e.g., at least about 20 atomic percent titanium, at least about 25 atomic percent titanium, at least about 30 atomic percent titanium) and/or at most about 32 atomic percent titanium (e.g., at most about 30 atomic percent titanium, at most about 25 atomic percent titanium, at most about 20 atomic percent titanium). In certain embodiments, the material containing silicon, titanium, and oxygen can include from about 25 atomic percent to about 32 atomic percent titanium (e.g., from about 28 atomic percent to about 32 atomic percent titanium, from about 30 atomic percent to about 32 atomic percent titanium).
In some embodiments, the ratio of the atomic percentage of titanium to the atomic percentage of silicon in a material containing titanium, silicon, and oxygen can be at least about 1.0 (e.g., at least about 2, at least about 5, at least about 7, at least about 9, at least about 12, at least about 15) and/or at most about 200 (e.g., at most about 150, at most about 100, at most about 50). In some embodiments, in a material containing silicon, titanium, and oxygen having a ratio of the atomic percent of titanium to the atomic percent of silicon greater than 1, the material can have a refractive index of at least about 1.8 at a wavelength of 632 nm (e.g., at least about 1.9 at a wavelength of 632 nm, at least about 2.0 at a wavelength of 632 nm, at least about 2.1 at a wavelength of 632 nm, at least about 2.2 at a wavelength of 632 nm, at least about 2.3 at a wavelength of 632 nm, at least about 2.4 at a wavelength of 632 nm).
In general, a material containing silicon, titanium, and oxygen can be prepared as desired. In some embodiments, a material containing silicon, titanium, and oxygen can be prepared using atomic layer deposition (ALD). Referring to
ALD system 100 includes a reaction chamber 110, which is connected to sources 150, 160, 170, 180, and 190 via a manifold 130. Sources 150, 160, 170, 180, and 190 are connected to manifold 130 via supply lines 151, 161, 171, 181, and 191, respectively. Valves 152, 162, 172, 182, and 192 regulate the flow of gases from sources 150, 160, 170, 180, and 190, respectively. Sources 150 and 180 contain a first and second precursor, respectively, while sources 160 and 190 include a first reagent and second reagent, respectively. For example, if a material containing titanium, silicon and oxygen is being deposited, sources 150 and 180 can contain titanium and silicon precursors while sources 160 and 190 can contain an oxygen providing reagent. Source 170 contains a carrier gas, which is flowed through chamber 110 during the deposition process transporting precursors and reagents to substrate 120, while transporting reaction byproducts away from the substrate. Precursors and reagents are introduced into chamber 110 by mixing with the carrier gas in manifold 130. Gases are exhausted from chamber 110 via an exit port 145. A pump 140 exhausts gases from chamber 110 via an exit port 145. Pump 140 is connected to exit port 145 via a tube 146.
ALD system 100 includes a temperature controller 195, which controls the temperature of chamber 110. During deposition, temperature controller 195 elevates the temperature of substrate 120 and multilayer material 101 deposited on substrate 120 above room temperature. In general, the substrate temperature should be sufficiently high to facilitate a rapid reaction between precursors and reagents, but should not cause precursor pre-decomposition nor damage the substrate. In some embodiments, the substrate temperature can be about 500° C. or less (e.g., about 400° C. or less, about 300° C. or less, about 200° C. or less, about 150° C. or less, about 125° C. or less). In some embodiments, the substrate temperature can be about 150° C. or greater (e.g., about 180° C. or greater, about 200° C. or greater, about 250° C. or greater, about 300° C. or greater).
Deposition process parameters are controlled and synchronized by an electronic controller 199. Electronic controller 199 is in communication with temperature controller 195; pump 140; and valves 152, 162, 172, 182, and 192. Electronic controller 199 also includes a user interface, from which an operator can set deposition process parameters, monitor the deposition process, and otherwise interact with system 100.
The introduction of the oxygen providing precursor (202) followed by the titanium providing precursor (204) is repeated for a predetermined number of cycles, P (206). This forms a layer of titanium oxide (e.g., composed of alternating layers of titanium and oxygen) on the surface of substrate 120.
After the predetermined number of cycles, P, system 100 introduces an oxygen providing precursor (208). The introduction of the oxygen providing precursor forms a monolayer of chemisorbed oxygen providing reactant on the surface of the most recently deposited titanium monolayer. The residual precursor is purged from chamber 110 by the continuous flow of carrier gas through the chamber. Subsequently, the system introduces a silicon providing precursor into chamber 110 (210). Examples of silicon providing precursors include tetrabutoxysilane, tres(tertpentory)sil and, silicon halides (SiCl4), terasiso-cyanatosilane, tetrakis(dimethylamids)silane, and tris(dimethlamido)silane. The silicon providing precursor reacts with the monolayer of chemisorbed oxygen providing reactant to form a monolayer of silicon on the layer of oxygen. The residual precursor is purged from chamber 110 by the continuous flow of carrier gas through the chamber. The introduction of the oxygen providing precursor (208) followed by the silicon providing precursor (210) is repeated for a predetermined number of cycles, Q (212).
The process of repeating the titanium cycle P times (206) followed by repeating the silicon cycle Q times (212) is repeated R times (214) to form a bulk layer of a material containing titanium, silicon and oxygen having a desired thickness. As described above, the index of refraction of the bulk layer of a material containing titanium, silicon and oxygen will be greater than the index of refraction of bulk SiO2 and less than the index of refraction of bulk TiO2. The index of refraction of the material containing silicon, titanium, and oxygen is related to the ratio of P to Q. For example, as the ratio of P to Q increases the refractive index of the deposited material containing titanium, silicon and oxygen increases and as the ratio of P to Q decreases the refractive index of the material containing titanium, silicon and oxygen decreases.
In some embodiments, it is desirable to grow a bulk material containing silicon, titanium, and oxygen having a relatively high index of refraction. In order to grow a material containing silicon, titanium, and oxygen with a high index of refraction, typically less than 50% of the titanium atoms will be substituted with silicon atoms such that P will be greater than Q. For example, a ratio of P to Q can be at least about 2 (e.g., at least about 3, at least about 4, at least about 5, at least about 10, at least about 20, at least about 40). For example, in some embodiments, a ratio of P to Q can be 120:6, 140:6, 200:6, or 240:6.
Although the oxygen-providing precursor is introduced into the chamber before the silicon or titanium providing precursor during each cycle in process 200 described above, in other examples the oxygen-providing precursor can be introduced after the silicon or titanium providing precursor. The order in which the oxygen-providing precursor and the silicon or titanium providing precursor are introduced can be selected based on their interactions with the exposed surfaces. For example, where the bonding energy between the titanium or silicon precursor and the surface of the substrate on which the material is grown is higher than the bonding energy between the oxygen providing precursor and the surface, the silicon or titanium providing precursor can be introduced before the oxygen providing precursor. Alternatively, if the binding energy of the oxygen providing precursor is higher, the oxygen providing precursor can be introduced before the silicon or titanium providing precursor. While process 200 described above includes introducing an oxygen providing precursor followed by a silicon providing precursor to deposit a monolayer of oxygen and a monolayer of silicon, other methods for depositing low index materials based on metal-silicates. For example, a precursor that includes both oxygen and silicon can be used to selectively deposit monolayer of oxygen and a monolayer of silicon upon the introduction of a single precursor. Examples of such precursors include tris(tert-butoxy)silanol ((tBuO)3SiOH), or tris(tert-pentoxy)silanol, or tris(isopropxy)silanol, or bis(tert-butoxy)(isopropoxy)silanol, or bis(isopropoxy)(tert-butoxy)silanol, or bis(tert-pentoxy)(isopropoxy)silanol bis(isopropoxy)(tert-pentoxy)silanol, or bis(tert-pentoxy)(tert-butoxy)silanol bis(tert-butoxy)(tert-pentoxy)silanol. Examples of such silicon precursors and their use are described, for example, in U.S. Pat. No. 6,969,539.
In some embodiments, when precursors such as tris(tert-butoxy)silanol are used, the introduction of the tris(tert-butoxy)silanol is preceded by the introduction of the metal providing precursor. The metal-providing precursor acts as a catalyst for the Silanol to attach a Si and O atoms using a single precursor. For example, a process can include introducing a TMA pulse which deposits Al-2(CH)3 on a surface of a wafer. Subsequent to the TMA pulse, silanol is introduced. The Silanol removes the two CH3 molecules by converting them to CH4 and Si and O are attached. A similar reaction can be performed using TiCl4 is used instead of TMA.
While embodiments described above show a bulk material comprised of silicon, titanium, and oxygen with a constant composition throughout the material, in some embodiments it can be beneficial to form a material having a composition that varies.
When material 250 is formed, different portions of material 250 have different chemical compositions and therefore, different indices of refraction. For example, material 250 can have a total thickness defined by surface 254 of substrate 252 and a surface 255 of material 250 (as indicated by arrow 280). The material can be formed such that different portions of material 250 have different atomic percentages of silicon and titanium. A first portion 283 of material 250 can be at least partially defined by surface 254 of substrate 252 and have a thickness, t1 (as indicated by arrow 282). A second portion 285 of material 250 can be at least partially defined by surface 255 of layer 250 and can have a thickness, t2, (as indicated by arrow 284). A third portion 287 of material 250 can be disposed between first portion 283 and second portion 285 and have a thickness t3 (as indicated by arrow 286).
In order to form a material having a graded index of refraction, the average atomic percentage of silicon of portion 283, portion 285, and portion 287 will be different In material layers for which the index of refraction decreases as a function of the distance from surface 254 of substrate 252, the average atomic percentage of silicon of portion 283 will be greater than the average atomic percentage of silicon of portion 285 and the average atomic percentage of silicon in portion 287 will be less than the average atomic percentage of silicon in portion 285 and greater than the average atomic percentage of silicon in portion 283. In material layers for which the index of refraction increases as a function of the distance from the surface of substrate 252, the average atomic percentage of silicon of portion 283 will be lower than the average atomic percentage of silicon of portion 285 and the average atomic percentage of silicon in portion 287 will be greater than the average atomic percentage of silicon in portion 285 and less than the average atomic percentage of silicon in portion 283.
The difference in the average atomic percentage of silicon of portion 283 compared to the average atomic percentage of silicon of portion 285 can be at least about one percentage (e.g., at least about 5 percentage, at least about 10 percentage, at least about 20 percentage, at least about 30 percentage, at least about 40 percentage, at least about 50 percentage, at least about 60 percentage, at least about 70 percentage, at least about 80 percentage, at least about 90 percentage, at least about 95 percentage). The atomic percentage of silicon in layer 287 will be between the atomic percentage of silicon in layer 283 and atomic percentage of silicon in layer 285. The average atomic percent silicon for the portion having the lesser atomic percentage of silicon (e.g., portion 283 if the refractive index increases) as a function of the distance from surface 254 of substrate 252 or portion 285 if the refractive index increases as a function of the distance from surface 254 of substrate 252) can be at least about 1 atomic percent of (e.g., at least about 3 atomic percent, at least about 5 atomic percent, at least about 10 atomic percent) silicon and/or at most about 20 atomic percent (e.g., at most about 15 atomic percent, at most about 10 atomic percent) silicon. For example, the average atomic percentage of the portion having the lesser atomic percentage of silicon can have an atomic percent from about 1 atomic percent to about 20 atomic percent (e.g., from about 1 atomic percent to about 10 atomic percent, from about 1 atomic percent to about 5 atomic percent, from about 5 atomic percent to about 10 atomic percent).
The average atomic percent silicon of the portion having the greater atomic percentage of silicon (e.g., portion 283 if the refractive index increases as a function of the distance from surface 254 of substrate 252 or portion 285 if the refractive index decreases as a function of the distance from surface 254 of substrate 252) can be at least about 10 atomic percent (e.g., at least about 15 atomic percent, at least about 20 atomic percent, at least about 25 atomic percent) silicon, and/or at most about 30 atomic percent (e.g., at most about 25 atomic percent, at most about 20 atomic percent) silicon. For example, the average atomic percent silicon of the portion having the greater atomic percentage of silicon be from about 10 atomic percent to about 30 percent (e.g., from about 10 atomic percent to about 30 atomic percent, from about 20 atomic percent to about 30 atomic percent, from about t25 atomic percent to about 30 atomic percent).
In some embodiments it can be beneficial to form a material having an index of refraction that varies according to an approximately periodic function. For example, in some embodiments the material can have an index of refraction that varies according to a function with a constant period (e.g., a sine or cosine function). For example, starting from the substrate, the index of refraction can increase until it reaches maximum and then decrease until the index of refraction reaches the initial index value. The index of refraction in the material continues to decrease until it reaches its lowest value and then increases until it reaches the start value. The total optical design of the material will include multiple periods as described above. In another example, starting from the substrate, the index of refraction can decrease until it reaches a minimum and then increase until the index of refraction reaches the initial index value. The index of refraction in the material continues to increase until it reaches its highest value and then decreases until it reaches the start value. The total optical design of the material will include multiple periods as described above. In some embodiments, the index of refraction can vary between a maximum of about 1.48 and a minimum of about 2.44.
In some additional embodiments, the material composition can vary to form a material having an index of refraction that varies according to a function with a varying period (e.g., a chirped function).
In some embodiments, the percentage of the titanium atoms substituted with silicon atoms during the growth of the material can increase as the distance from substrate 252 increases.
In some embodiments, the percentage of the titanium atoms substituted with silicon atoms decreases as the distance from substrate 252 increases.
While in the examples described above in relation to
While embodiments described above relate to a bulk layer of material that includes titanium, silicon and oxygen, in some embodiments a multi-layer stack of materials can include alternating layers of different materials. For example,
The thickness of the titanium oxide layers 302a, 302b, 302c, and 302d and the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can be selected as desired. The thickness of the titanium oxide layers 302a, 302b, 302c, and 302d can be at least about 5 nm (e.g., at least about 8 nm, at least about 10 nm, at least about 12 nm, at least about 15 nm, at least about 20 nm). The maximum thickness of the titanium oxide layers 302a, 302b, 302c, and 302d can also be selected as desired. For example, the maximum thickness of the titanium oxide layers 302a, 302b, 302c, and 302d can be selected to limit the absorption or scattering loss for the material and/or to maintain an amorphous material. In some embodiments, the thickness of the titanium oxide layers 302a, 302b, 302c, and 302d can be at most about 30 nm (e.g., at most about 25 nm, at most about 20 nm, at most about 15 nm).
In general, the thickness of layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can be selected as desired. In some embodiments, the thickness of the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can be less than the thickness of the titanium oxide layers 302a, 302b, 302c, and 302d. It is believed that if the thickness of the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d is significantly smaller than the wavelength of visible light (e.g., less than about 400 nm) the light “sees” an effective index of refraction that characterizes the total material with one bulk value for the index of refraction. The thickness of the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can also be selected to inhibit or reduce the tendency of the titanium oxide layers to crystallize.
The thickness of the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can be at least about 0.2 nm (e.g., at least about 0.5 nm, at least about 0.75 nm, at least about 1 nm, at least about 1.5 nm, at least about 1.75 nm, at least about 2 nm, at least about 2.5 nm) and/or at most about 3 nm (e.g., at most about 2.5 nm, at most about 1.5 nm, at most about 1.0 nm, at most about 0.75 nm). In some embodiments, the thickness of the layers of material containing titanium, silicon and oxygen 304a, 304b, 304c, and 304d can be from about 0.2 nm to about 3 nm (e.g., from about 0.2 nm to about 2 nm, from about 0.2 nm to about 1.5 nm, from about 0.2 nm to about 1 nm, from about 0.2 nm to about 0.75 nm, from about 0.2 nm to about 0.5 nm).
The percentage of the total thickness of the material (as indicated by arrow 308) comprised of the material containing titanium, silicon and oxygen (e.g., a sum of the thicknesses of layers 304a, 304b, 304c, and 304d divided by the total thickness of the material) can be selected as desired. In some embodiments, the percentage of the total thickness of the material composed of material containing titanium, silicon and oxygen can be from about 2 percent to about 10 percent (e.g., from about 2 percent to about 8 percent, from about 2 percent to about 5 percent, about 2 percent, about 3 percent, about 4 percent, about 5 percent). In general, by varying the ratio of titanium oxide material to the material containing silicon, titanium, and oxygen the index of refraction can be modified to meet optical design requirements (e.g., to obtain a particular refractive index).
In some embodiments, it is believed that layers 304a, 304b, 304c, and 304d can exhibit compressive stress while titanium oxide layers 302a, 302b, 302c, and 302d can be exhibit tensile stress. In general, titanium oxide layers tend to grow with tensile stress. Layers 304a, 304b, 304c, and 304d exhibit different properties than the titanium oxide layers due to the substitution of some Titanium atoms with Silicon atoms (e.g., when grown under some conditions the TiSiO material may exhibit compressive strain). It is believed that the introduction of several (e.g., about 2 to 8) TiSiO monolayers in a TiO2 material between every 100 to 150 monolayers of TiO2 can reduce the overall stress of the material stack. Without wishing to be bound by theory, it is believed that a correctly chosen strain in layers 304a, 304b, 304c, and 304d can reduce the tendency of the titanium oxide layers 302a, 302b, 302c, and 302d to crystallize. Without wishing to be bound by theory, it is believed that a correctly chosen compressive strain in the layers 304a, 304b, 304c, and 304d and a correctly chosen tensile strain in the layers 302a, 302b, 302c, and 302d can result in a substantially relaxed material stack.
In some embodiments, the thickness of the titanium oxide layers 302a, 302b, 302c and/or the thickness of layers 304a, 304b, 304c, and 304d can vary as a function of distance from the surface of the substrate. By varying the thickness of the titanium oxide layers 302a, 302b, 302c and/or the thickness of layers 304a, 304b, 304c, and 304d a material with a varying index of refraction can be formed.
For example, in certain embodiments, the thickness of layers 304a, 304b, 304c, and 304d is constant and the thickness of the titanium oxide layers 302a, 302b, 302c increases as a function of distance from the substrate. This results in an increasing index of refraction. In certain additional embodiments, the thickness of the thickness of layers 304a, 304b, 304c, and 304d is constant and the thickness of the titanium oxide layers 302a, 302b, 302c decreases as a function of distance from the substrate. This results in a decreasing index of refraction.
In certain embodiments, the thickness of the titanium oxide layers 302a, 302b, and 302c is constant and the thickness of layers 304a, 304b, 304c, and 304d increases as a function of distance from the substrate. This results in a decreasing index of refraction. In certain additional embodiments, the thickness of the titanium oxide layers 302a, 302b, 302c is constant and the thickness of layers 304a, 304b, 304c, and 304d decreases as a function of distance from the substrate. This results in an increasing index of refraction.
While in the embodiments described above in relation to
While in the embodiments described above in relation to
While in the embodiments described above, a material containing titanium, silicon and oxygen has been described as being formed of a titanium oxide in which some of the titanium has been substituted by silicon to form the material, other materials can be formed using a similar process. In general, the refractive index and/or material properties of a metal oxide can be altered by selectively substituting at least some of the metal atoms with silicon atoms. Exemplary metal oxides include hafnium oxide, aluminum oxide, niobium oxide, zirconium oxide, tantalum oxide, magnesium oxide, neodymium oxide, tin oxide, vanadium oxide, yttrium oxide. The index of refraction of the silicates of hafnium, aluminum, niobium, zirconium, tantalum, magnesium, neodymium, tin, vanadium, and yttrium formed when some of the metal atoms are substituted by silicon atoms can vary between the index of refraction of silicon oxide and the index of refraction of the metal oxide.
In some embodiments, a third material atom is introduced into the material containing silicon, titanium, and oxygen. For example if a material with higher oxidation state such as tantalum (or niobium) is introduced (in Ta2O5 the oxidation state of tantalum is 5) as a partial substitute to some of the titanium or silicon of the material containing titanium, silicon and oxygen then the material intrinsic stress properties can be additionally modified by the presence of the additional excess electronic bond. Therefore by using silicon substitution of titanium atoms optical properties of the material can be tailored, and by using tantalum or niobium substitution of titanium atoms intrinsic stress properties of the material can be modified.
The materials described above can be used to form various optical articles. For example, in some embodiments, the substrate can include one or more structured surface that is coated with a material using ALD. Referring to
Other examples of structured surfaces that may be coated using ALD include grating structures, such as ruled gratings and surface relief gratings, cylindrical surfaces, such as the surface of an optical fiber or an inner surface of a hollow waveguide (e.g., having a circular, square or rectangular cross section). A further example is a cleaved surface of an optical fiber. For example, some telecommunications applications utilize design schemes in which a cleaved fiber is positioned very close to a lens or an optical article. Coating an AR material onto a cleaved surface using ALD can reduce reflections at the surface. Multiple cleaved surfaces can be coated in a single ALD run.
Optical articles formed using the methods disclosed herein can be used in a variety of optical systems. Referring to
In some embodiments, ALD may be used to integrate optical articles in an optical system. For example, discrete IR filter 610 in imaging system 600 can be replaced with a filter coated directly onto one or more surfaces of the lenses in an imaging system. For example, referring to
In a further embodiment,
Ray divergence is illustrated by rays 860 and 870, which originate from a common source point and are imaged to a common point 851 on detector 850. The propagation angles of rays 860 and 870 with respect to an optical axis 899 of imaging system 800 are Φ1 and Φ2, respectively. The divergence of the rays is the difference between Φ1 and Φ2. In some embodiments, rays of imaged EM radiation have a maximum divergence of about 20 degrees or less at IR filter 810 (e.g., about 15 degrees or less, about 10 degrees or less, about 8 degrees or less). Accordingly, the blue shift experienced by the system's marginal rays compared to rays propagating along axis 899 can be about 20 nm or less (e.g., about 15 nm or less, about 12 nm or less, about 10 nm or less).
In another embodiment,
While particular examples of optical articles have been described above, oxide materials as described herein can be used in other optical articles. Examples of such optical articles include thin film interference filters, absorption filters, wire grid light polarizing structures, rugate filters, conformal filling of three-dimensional structures (e.g., trenches, diffraction grating grooves), conformal material growth on three-dimensional template structures (e.g., pillars, pyramids, columns, semi-spheres), optical lens structures, interface layers between different parts of an integrated optical component.
Imaging systems, such as those discussed previously, may be used in electronic devices, such as digital cameras and digital camcorders. In some embodiments, the imaging systems may be used in digital cameras in cellular telephones.
The following examples are illustrative and not intended as limiting.
A material was formed by depositing a material on a SBSL 7 type of substrate, which was obtained from Ohara Corporation. The material was a layer of material containing titanium, silicon and oxygen in having about equal amounts of titanium and silicon.
To deposit the material, the substrate was placed in an ALD reaction chamber. Air was purged from the chamber. Nitrogen was flowed through the chamber, maintaining the chamber pressure at about 0.5 Torr. The chamber temperature was set to 300° C. and left for about 2 hours for the substrate to thermally equilibrate. Once thermal equilibrium was reached, the valve to the TiCl4 was opened for 0.5 seconds, introducing TiCl4 into the chamber. The chamber was allowed to purge by the nitrogen flow for 2 seconds before the valve to the tris(tert-butoxy)silanol was opened for 1.2 seconds, introducing Silanol into the chamber. The chamber was then allowed to purge for 2 seconds. This cycle of a dose of TiCl4, followed by a dose of Silanol was repeatedly introduced, resulting in a layer of material containing titanium, silicon and oxygen being formed on the exposed surfaces of the substrate. No additional oxygen delivering precursor was used. This cycle was repeated 1000 times, resulting in a material containing titanium, silicon and oxygen layer having a thickness of about 100 nm.
A multilayer stack of materials was formed by depositing multilayer stacks on SBSL 7 type of substrate, which was obtained from Ohara Corporation. The multilayer stack of materials included alternating layers of a high index material and a lower index material (e.g., as shown schematically in
To deposit the material, the substrate was placed in an ALD reaction chamber. Air was purged from the chamber. Nitrogen was flowed through the chamber, maintaining the chamber pressure at about 0.5 Torr. The chamber temperature was set to 300° C. and left for about 2 hours for the substrate to thermally equilibrate. Once thermal equilibrium was reached, an initial pulse of water vapor was introduced into the chamber by opening the valve to the water supply for 1 second. After the valve to the water supply was closed, the chamber was purged by the nitrogen flow for 2 seconds. Next, the valve to the TiCl4 was opened for 0.4 seconds, introducing TiCl4 into the chamber. The chamber was again allowed to purge by the nitrogen flow for 2 seconds before another dose of water vapor was introduced. Alternating doses of water vapor and TiCl4 were introduced between purges, resulting in a layer of TiO2 being formed on the exposed surfaces of the substrate. This cycle was repeated 200 times, resulting in TiO2 layer having a thickness of 8 nm
Subsequently, a pulse of TiCl4 was introduced into the chamber by opening the valve to the TiCl4 was opened for 0.5 seconds. The chamber was again allowed to purge by the nitrogen flow for 2 seconds before the valve to the tris(tert-butoxy)silanol was opened for 1.2 seconds, introducing Silanol into the chamber. The chamber was purged for 2 seconds after that. This cycle of a dose of TiCl4, followed by a dose of Silanol was repeatedly introduced, resulting in a layer of material containing titanium, silicon and oxygen being formed on the exposed surfaces of the substrate. This cycle was repeated 6 times, resulting in a 0.6 nm thick layer of a material containing titanium, silicon and oxygen being formed on the titanium layer.
Additional layers of titanium oxide and a material containing titanium, silicon and oxygen were deposited using the steps outlined above to provide a multilayer stack on the exposed substrate surfaces. The thickness of each layer and number of deposition cycles used to deposit each layer are summarized in Tables I-III.
Referring to
Referring to
A material was formed by depositing a material on a SBSL 7 type of substrate, which was obtained from Ohara Corporation. To deposit the material, the substrate was placed in an ALD reaction chamber. Air was purged from the chamber. Nitrogen was flowed through the chamber, maintaining the chamber pressure at about 0.5 Torr. The chamber temperature was set to 300 and left for about 2 hours for the substrate to thermally equilibrate. Once thermal equilibrium was reached, an initial pulse of water vapor was introduced into the chamber by opening the valve to the water supply for 1 seconds. After the valve to the water supply was closed, the chamber was purged by the nitrogen flow for 2 seconds. Next, the valve to the TiCl4 was opened for 0.5 seconds, introducing TiCl4 into the chamber. The chamber was again allowed to purge by the nitrogen flow for 2 seconds before another dose of water vapor was introduced. This cycle of providing an oxygen precursor followed by a titanium precursor was repeated for a predetermined number of times (as shown in
Referring to
As shown in
Other embodiments are in the claims.
