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KR-102963910-B1 - NEAR INFRARED OPTICAL INTERFERENCE FILTERS WITH IMPROVED TRANSMISSION

KR102963910B1KR 102963910 B1KR102963910 B1KR 102963910B1KR-102963910-B1

Abstract

The interference filter comprises a layer stack comprising at least: layers of nitrogen-doped amorphous hydrogenated silicon (a-Si:H,N ) , and a plurality of layers of one or more dielectrics, such as SiO₂ , SiO₆x₀ , SiO₆x₀Ny₀ , a dielectric having a higher refractive index in the range of 1.9 to 2.7, etc. The interference filter is designed to have a passband center wavelength in the range of 750-1000 nm. Nitrogen doped in the a-Si:H,N layer provides improved transmission in the passband without significantly lowering the refractive index observed in a-Si:H, which has similar transmission. The dielectric layers having a higher refractive index in the range of 1.9 to 2.7 provide a smaller angular shift compared to a similar interference filter using SiO₂ as the low refractive index layer.

Inventors

  • 스프레이그, 로버트
  • 바이, 쉥유안

Assignees

  • 마테리온 코포레이션

Dates

Publication Date
20260512
Application Date
20160218
Priority Date
20150218

Claims (10)

  1. As an interference filter: at least: Layers of nitrogen-doped amorphous hydrogenated silicon (a-Si:H,N); and The above-mentioned layer stack comprises a plurality of dielectric layers having a refractive index less than that of a-Si:H,N, wherein one or more dielectric layers comprise dielectric layers having a refractive index in the range of 1.9 to 2.7, and one or more dielectric layers further comprise silicon dioxide ( SiO2 ) layers. Here, the interference filter has at least one passband having a center wavelength in the range of 750-1000 nm, and Here, at least one of the one or more dielectrics comprises a silicon suboxide (SiO x ) where x is not exactly 2, an interference filter.
  2. delete
  3. In claim 1, An interference filter, wherein a first layer of one or more dielectrics is arranged on a first plane of one layer of a-Si:H, and a second layer of one or more dielectrics is arranged on a second plane of one layer of a-Si:H.
  4. In claim 1 or 3, The interference filter described above further comprises a transparent substrate supporting the layer stack.
  5. In claim 4, The above transparent substrate is an interference filter comprising a glass substrate.
  6. In claim 4, An interference filter, wherein the layer stack comprises a first layer stack on one side of the transparent substrate and a second layer stack on the opposite side of the transparent substrate.
  7. In claim 6, An interference filter, wherein the first layer stack defines a low-pass filter having a low-pass cutoff wavelength, and the second layer stack defines a high-pass filter having a high-pass cutoff wavelength, wherein at least one passband is defined between the high-pass cutoff wavelength and the low-pass cutoff wavelength.
  8. As an interference filter: at least: Layers of nitrogen-doped amorphous hydrogenated silicon (a-Si:H,N); and The above-mentioned layer stack comprises a plurality of dielectric layers having a refractive index less than that of a-Si:H,N, wherein one or more dielectric layers comprise dielectric layers having a refractive index in the range of 1.9 to 2.7, and one or more dielectric layers further comprise silicon dioxide ( SiO2 ) layers. Here, the interference filter has at least one passband having a center wavelength in the range of 750-1000 nm, and an interference filter having a-Si:H,N with a hydrogen atomic concentration of 4% to 8% and a nitrogen atomic concentration of 2% to 12%.
  9. As an interference filter: at least: Layers of nitrogen-doped amorphous hydrogenated silicon (a-Si:H,N); and The above-mentioned layer stack comprises a plurality of dielectric layers having a refractive index less than that of a-Si:H,N, wherein one or more dielectric layers comprise dielectric layers having a refractive index in the range of 1.9 to 2.7, and one or more dielectric layers further comprise silicon dioxide ( SiO2 ) layers. Here, the interference filter has at least one passband having a center wavelength in the range of 750-1000 nm, and an interference filter in which a-Si:H,N has a nitrogen atomic concentration of 3% to 7%.
  10. A method for manufacturing an interference filter of claim 1, wherein at least one of one or more dielectrics is silicon-based, and the method comprises: A step of sputtering silicon from a target onto a filter substrate; and During sputtering, (i) a process gas comprising hydrogen and nitrogen for depositing a-Si:H,N to form each a-Si:H,N layer; and (ii) a method for manufacturing an interference filter comprising the step of alternating at least one of a process gas containing oxygen for depositing SiO x to form at least one layer of a silicon-based dielectric, a process gas containing oxygen and nitrogen for depositing silicon oxynitride (SiO x N y ), or a process gas containing nitrogen for depositing silicon nitride (Si 3 N 4 ).

Description

Near Infrared Optical Interference Filters with Improved Transmission This application claims priority to U.S. provisional patent application No. 62/117,598, filed on February 18, 2015, under the title "NEAR INFRARED OPTICAL INTERFERENCE FILTERS WITH IMPROVED TRANSMISSION". The entire contents of U.S. provisional patent application No. 62/117,598, filed on February 18, 2015, are incorporated herein by reference. The following concerns optical technology, optical filter technology, and related technologies. Known transmission interference filters utilize a stack of alternating layers of silicon and silicon dioxide ( SiO2 ). These devices are known to be used within the short-wave and mid-wave infrared ranges up to approximately 1100 nm, and both silicon and SiO2 are transparent in this range. Lower wavelength thresholds (corresponding to the upper photon energy threshold) are controlled by the onset of absorption by silicon, which has a bandgap of approximately 1.12 eV in its crystalline form. The main advantage of silicon in these devices is its high refractive index. The spectral profile of an optical interference filter depends, among other things, on the angle of illumination. As the angle increases, the filter shifts to shorter wavelengths. This angular shift depends on the materials used and their distribution. A higher refractive index results in a smaller angular shift. In the case of narrow band filters, when used in an optical system, the amount of angular shift limits the useful bandwidth of the filter. In systems with large acceptance angles, a filter configured to produce a small angular shift can have a narrower passband than one composed of a material with a lower refractive index, and thus can achieve greater noise rejection. It is also known that hydrogenating silicon is used to utilize alternating layers of hydrogenated amorphous silicon (a-Si:H) and SiO2 to extend device operation to the near-infrared range. By hydrogenating silicon, material loss and refractive index are reduced. With this approach, high-performance interference filters operating in the 800-1000 nm range can be achieved. Some improvements are disclosed here. FIG. 1 is a schematic diagram showing a sputtering deposition system for manufacturing a near-infrared optical interference filter having improved transmission and/or reduced angular shift as disclosed herein. Figure 2 is a schematic diagram showing the effect of hydrogenation on the optical properties (transmission and refractive index) of amorphous hydrogenated silicon (a-Si:H). Figure 3 is a schematic diagram showing the effect of nitrogen addition on the optical properties (transmission and refractive index) of a-Si:H at a fixed hydrogenation level. Figure 4 is a schematic diagram showing an interference filter properly manufactured using the sputtering deposition system of Figure 1. As previously mentioned, since hydrogenation of silicon reduces absorption losses (both intrinsic silicon and induced disturbances) sufficiently to provide acceptable filter transmission characteristics in the passband, interference filters comprising a layer-by-layer stack having a silicon hydride (a-Si:H) layer are used for operation in the near-infrared (800-1250 nm). Referring briefly to Fig. 2, this approach for the near-infrared is recognized here as having significant disadvantages. As can be seen in Fig. 2, for a fixed wavelength of infrared (e.g., in the 800-1100 nm range), increasing the hydrogenation of a-Si:H (i.e., increasing the hydrogen content of a-Si:H) reduces losses, but also reduces the refractive index of a-Si:H as schematically illustrated in Fig. 2. The performance of narrowband interference filters for high numerical aperture optical systems is a trade-off between obtaining low angular shift and high transmission in the near-infrared region where material properties change rapidly. High transmission corresponds to a low extinction coefficient (obtainable with a large amount of hydrogen), while a small angular shift is achieved by a high refractive index (obtainable with a small amount of hydrogen). Referring briefly to FIG. 3, the disclosed improvement relates to adding a controlled amount of nitrogen to the a-Si:H layer of a Si-based interference filter for use in the near-infrared (800-1100 nm) range. In other words, this improvement involves replacing a-Si:H with a-Si:H,N. As schematically illustrated in FIG. 3, for a fixed wavelength in the infrared range (e.g., 800-1100 nm) and a given (fixed) level of hydrogenation, the addition of nitrogen increases transmission with a reduced concomitant reduction in the refractive index. The effect of nitrogen addition on the refractive index is much less than that of hydrogenation, especially for nitrogen fractions in the nitrogen range of 10% or less. Thus, this modification enables the fabrication of a near-infrared interference filter operating in the 800-1100 nm range with improved control of angular shift, peak t