Method for coating an optical substrate, and window

Abstract

To provide improved electrically conductive optical coatings for broadband optical components.SOLUTION: A method of coating an optical substrate includes depositing a semiconductor coating over a surface of an optical substrate, where the semiconductor coating has broadband optical transmittance. Portions of the semiconductor coating are doped to form a spatially varied pattern of the doped semiconductor in the semiconductor coating. The method includes annealing the semiconductor coating to cause at least one of: increase of oxygen in undoped areas of the semiconductor coating; and decrease of oxygen in doped areas of the semiconductor coating.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to optical coatings, and more particularly to conductive optical coatings.

Background Art

[0002] Electro-optic (EO) systems require windows to protect sensors and electronic devices from external elements. In addition to rain, dust, etc., often the windows must also block electromagnetic interference (EMI) that would otherwise typically interfere with EO system performance.

[0003] EMI shielding can be achieved by windows that are conductive and optically transparent. There are three conventional types of shielding.

[0004] The first type of EMI shielded window uses semiconductor materials such as silicon or germanium doped with group V elements such as phosphorus, arsine, or antimony to supply additional electrons, thereby imparting electrical conductivity. These windows are opaque to visible wavelengths and are thus not useful for broadband EO systems.

[0005] The second type of shielded window uses a continuous transparent conductive coating. These coatings consist of wide bandgap semiconductors such as indium oxide (In2O3) and zinc oxide (ZnO) that have broadband light transmissivity. The semiconductors are doped to impart electrical conductivity. However, as doping increases to increase electrical conductivity and EMI attenuation, the light transmittance decreases. This effect begins on the long wavelength side where both plasma reflection and free carrier absorption from electrons decrease the transmittance. Traditional transparent and conductive semiconductor coatings are only practical in the range of 0.4 to 2.0 microns, from short wavelength visible to short wavelength infrared (SWIR).

[0006] A third type of shielded window is traditionally required for broadband applications from visible to long-wave infrared (LWIR). A grid of fine metal wires is deposited on the surface of the window. Typical dimensions are 5-micron wide lines with 140-micron spacing. These grid windows allow light transmission over a wide wavelength range, but limit light transmission due to obscuration and scattering.

[0007] Patent Document 1 presents a method for reducing light scattering from a conductive grid. A channel is etched into a window substrate, and an electrically conductive semiconductor is deposited in the channel such that the surface of the window is flat. The semiconductor is transparent to visible and short-wavelength infrared (SWIR) wavelengths, but reflective and absorptive to mid-wavelength infrared (MWIR) and longer wavelengths. Using a semiconductor with a refractive index close to that of the substrate minimizes light scattering from the grid lines. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 9276034 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Conventional techniques have been considered sufficient for their intended purposes. However, there is a persistent need for improved conductive optical coatings, for example, for broadband optical components. This disclosure provides a solution to this problem. [Means for solving the problem]

[0010] A method for coating an optical substrate involves depositing a semiconductor coating onto the surface of the optical substrate, wherein the semiconductor coating has broadband light transmittance. A predetermined portion of the semiconductor coating is doped to form a spatially varied pattern of the doped semiconductor within the semiconductor coating. The method includes annealing to increase the oxygen in the undoped regions of the semiconductor coating, or to decrease the oxygen in the doped regions of the semiconductor coating, or at least one of the above.

[0011] Annealing a semiconductor coating may involve laser annealing it to a predetermined pattern to improve the crystal quality of the transparent conductive oxide (TCO) material of the semiconductor coating and to increase the electrical conductivity within the doped areas of the semiconductor coating.

[0012] Annealing a semiconductor coating may involve annealing in air to activate and diffuse dopants and increase oxygen in the undoped areas of the semiconductor coating. Doping a given portion of a semiconductor coating is Applying a photoresist on top of a semiconductor coating, Selective exposure of photoresist, Developing a photoresist into a predetermined pattern, Doping a semiconductor coating through the aperture of a photoresist, Removing the photoresist so that a semiconductor doped in a predetermined pattern remains on the semiconductor coating, The process involves applying a silicon oxynitride coating to the entire surface of the semiconductor coating, The process involves coating silicon oxynitride with photoresist, exposing the photoresist to light, and developing the photoresist. This may include removing a predetermined portion of silicon oxynitride that is not covered by photoresist, and then removing any remaining photoresist. Annealing a semiconductor coating involves annealing the silicon oxynitride and the semiconductor coating in air to activate and diffuse the dopant and increase the oxygen in the undoped regions of the semiconductor coating.

[0013] It is also intended that annealing a semiconductor coating may include annealing under vacuum to activate and diffuse the dopant and reduce the oxygen within the doped area of ​​the semiconductor coating. Doping a given portion of a semiconductor coating is The semiconductor coating is in an undoped state, and a silicon oxynitride coating is applied to the entire surface of the semiconductor coating. The process involves coating silicon oxynitride with photoresist, exposing the photoresist to light, and developing the photoresist. Removing the portion of silicon oxynitride that is not covered by photoresist, Doping a semiconductor coating through the aperture of a photoresist, This may also include removing the photoresist so that a pattern of doped semiconductor remains on the semiconductor coating. Annealing a semiconductor coating involves annealing the silicon oxynitride and the semiconductor coating in a vacuum to activate and diffuse the dopant and reduce the oxygen within the doped areas of the semiconductor coating.

[0014] The semiconductor coating may contain at least one of In2O3 or ZnO. Doping a predetermined portion of the semiconductor coating to form a spatially varied pattern may include imparting a dopant by ion implantation, spin-on or spray-on solution, or by other means. The doped semiconductor may contain at least one of Sn, Mo, W, Ti, Al, or Ga. The semiconductor coating may have broadband light transmittance in at least the visible and infrared spectra. Depositing the semiconductor coating may include depositing the semiconductor coating in an undoped state. Doping a predetermined portion of the semiconductor coating and annealing the semiconductor coating may include diffusing dopant atoms through the semiconductor coating to the optical substrate. Depositing the semiconductor coating may include depositing the semiconductor coating on the entire surface of the optical substrate. Doping a predetermined portion of the semiconductor coating to form a spatially varied pattern may include doping the surface of the semiconductor coating so that the entire surface of the semiconductor coating is covered with a pattern. A semiconductor coating containing an annealed, activated, and doped semiconductor within the semiconductor coating, and an optical substrate, can be formed to form a window without etching and / or polishing or post-process planarization. The activated and doped semiconductor and the semiconductor coating may have approximately matched refractive indices to reduce light scattering from the pattern. If the refractive index ratio of the doped semiconductor and the semiconductor coating is between 0.82 and 1.22, the interfacial reflection will be less than 1% for perpendicular incidence. For example, the refractive indices of doped and undoped In2O3 at 632.8 nm are approximately 2.00 and 1.77, respectively. A refractive index ratio of 1.13 results in only 0.37% reflection. The method may include making the doped semiconductor electrically conductive.By using a silicon oxynitride process by plasma-enhanced chemical vapor deposition (PECVD) or by using a hydrogen plasma, etc., hydrogen can be added to a doped semiconductor to add electrons and passivate defects, thereby increasing the conductivity.

[0015] A window includes a transparent substrate having a coating thereon. The coating is formed of both a transparent semiconductor and an electrically conductive semiconductor having a lower transparency than the transparent semiconductor. The electrically conductive semiconductor is annealed in a spatially varying pattern within the transparent semiconductor and is distributed.

[0016] These and other features of the disclosed systems and methods will be readily apparent to those skilled in the art from the following detailed description of the preferred embodiments read in conjunction with the drawings.

[0017] To enable those skilled in the art related to the disclosed subject matter to readily understand how to fabricate and use the devices and methods of the disclosed subject matter without undue experimentation, the preferred embodiments are described in detail hereinbelow with reference to specific figures.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional elevation view of an exemplary embodiment of a window or optical component constructed in accordance with the present disclosure, showing a semiconductor coating on an optical substrate. [Figure 2] FIG. 2 is a schematic cross-sectional elevation view of the window or optical component of FIG. 1, showing a portion of a developed photoresist removed to enable doping of the semiconductor coating in a predetermined spatially varying pattern. [Figure 3] FIG. 3 is a schematic cross-sectional elevation view of the window or optical component of FIG. 2, showing a portion of the semiconductor coating having a predetermined spatially varying pattern. [Figure 4]A schematic cross-sectional elevation view of the window or optical component of FIG. 3, showing the removed photoresist and the doped pattern in the semiconductor coating. [Figure 5] A schematic cross-sectional elevation view of the window or optical component of FIG. 4, showing the silicon oxynitride layer deposited on the semiconductor coating. [Figure 6] A schematic cross-sectional elevation view of the window or optical component of FIG. 5, showing the photoresist layer deposited on the silicon oxynitride layer. [Figure 7] A schematic cross-sectional elevation view of the window or optical component of FIG. 6, showing the developed photoresist layer and the removed portion of the silicon oxynitride. [Figure 8] A schematic cross-sectional elevation view of the window or optical component of FIG. 7, showing the removed photoresist. [Figure 9] A schematic cross-sectional elevation view of the window or optical component of FIG. 8, showing the annealing process in air and the dopant atoms diffused through the semiconductor coating to the substrate. [Figure 10] A schematic cross-sectional elevation view of the window or optical component of FIG. 9, showing the removed silicon oxynitride to leave an electrically conductive pattern in the semiconductor coating. [[ID=)19]] [Figure 11] A schematic cross-sectional elevation view of the window or optical component of FIG. 1, showing another embodiment method in which the semiconductor coating is first coated with silicon oxynitride. [Figure 12] A schematic cross-sectional elevation view of the window or optical component of FIG. 11, showing the photoresist layer deposited on the silicon oxynitride. [Figure 13] A schematic cross-sectional elevation view of the window or optical component of FIG. 12, showing the developed photoresist and the removed portion of the silicon oxynitride that enables doping of the semiconductor coating to form a predetermined spatially varying pattern. [Figure 14] A schematic cross-sectional elevation view of the window or optical component of FIG. 13, showing the removed photoresist and the doped pattern in the semiconductor coating. [Figure 15]Figure 14 is a schematic cross-sectional elevation view of a window or optical component, illustrating the annealing process in vacuum for forming an electrically conductive pattern within a semiconductor coating, the electrically conductive pattern after removal of the silicon oxynitride, as shown in Figure 10. [Modes for carrying out the invention]

[0019] Here, references are made to the drawings. In the drawings, similar reference numerals identify similar structural features or embodiments of the subject disclosure. For illustrative and illustrative purposes, rather than limiting, a partial drawing of an exemplary embodiment of a window or optical component according to the present disclosure is shown in Figure 1, which is collectively designated by reference numeral 100. Other embodiments of windows or optical components according to the present disclosure or embodiments thereof are provided in Figures 2–15, as described. Using the systems and methods described herein, spatially varied electrical conductivity of transparent oxide coatings for optical components and windows can be provided. This can be used for electromagnetic interference (EMI) shielding, spatially varied sheet resistance, or smart window applications or any other suitable applications.

[0020] Transparent conductive oxides (TCOs), such as indium tin oxide (ITO) and aluminum zinc oxide (AZO), are important coating materials for a wide variety of products requiring optical and electrical conductivity. Indium oxide (In2O3) and zinc oxide (ZnO), with their broad bandgap semiconductors, exhibit broadband optical transmittance. The materials can be doped to provide electrical conductivity. However, as doping increases and electrical conductivity increases, optical transmittance decreases. This effect begins on the longer wavelength side, where plasma reflection and absorption of free carriers from electrons both reduce transmittance. Typical conductive oxide coatings generally exhibit transmittance only within the wavelength range of 0.4 to 2.0 microns. This disclosure describes a method for spatially controlling the conductivity and transmittance of a transparent oxide thin film in different regions of the coating.

[0021] A method for coating an optical substrate 102 includes depositing a semiconductor coating 104 on the surface of the optical substrate 102, for example, on the entire surface of the optical substrate 102. Depositing the semiconductor coating 104 may include depositing the semiconductor coating 104 in an undoped state and in the presence of oxygen. Alternatively or additionally, the oxide semiconductor may be annealed in air to provide excess oxygen within the semiconductor coating 104. The semiconductor coating 104 has broadband light transmittance as a transparent conductive oxide (TCO) material and may include, for example, In2O3, ZnO, etc., and has an electrical sheet resistance greater than 2000 ohms / square. Therefore, the semiconductor coating may have broadband light transmittance in at least the visible and infrared spectra.

[0022] A predetermined portion of the semiconductor coating 104 is doped to form a spatially varied pattern of the doped semiconductor within the semiconductor coating, as further described below. Doping a predetermined portion of the semiconductor coating to form a spatially varied pattern may include imparting a dopant by ion implantation of donor atoms. Any other suitable technique, such as spin-on or spray-on dopant solutions, may be used without departing from the scope of this disclosure. The doped semiconductor may include at least one of Sn, Mo, W, Ti, Al, or Ga. Hydrogen may serve as an electron donor and may also passivate defects.

[0023] This method involves annealing the semiconductor coating 104, thereby diffusing dopant atoms through the semiconductor coating to increase oxygen in the undoped regions of the semiconductor coating, or to decrease oxygen in the doped regions of the semiconductor coating. Each of these is described below.

[0024] First, annealing the semiconductor coating 104 may include thermal annealing and / or laser annealing to a predetermined pattern to improve the crystalline quality of the TCO material of the semiconductor coating 104 and increase the electrical conductivity within the doped regions of the semiconductor coating 104. Annealing the semiconductor coating 104 may also include annealing in air to activate and diffuse the dopant and increase the oxygen within the undoped regions of the semiconductor coating 104. Doping a predetermined portion of the semiconductor coating 104 may include applying a photoresist 106 onto the semiconductor coating as shown in Figure 2. The photoresist is selectively exposed and developed into a predetermined spatially varied pattern. That is, any pattern can be used, but in Figure 3, the spatial variation of the pattern includes a wider opening in the photoresist 106 at the left opening compared to the right opening in the photoresist 106. The method includes doping the semiconductor coating 104 through an opening 105 in the photoresist 106, as indicated by the downward arrow in Figure 3. Referring to Figure 4, the photoresist 106 is removed, for example, using a solvent, leaving a pattern of doped semiconductor 108 within the semiconductor coating 104. A coating of silicon oxynitride 110 is deposited onto the entire surface of the semiconductor coating 104 using plasma chemical vapor deposition (PECVD), as shown in Figure 5. Hydrogen in the PECVD process increases conductivity by adding electrons and passing on defects in the oxide semiconductor. Hydrogen plasma may be used similarly. While silicon oxynitride is used as an example herein, those skilled in the art will readily recognize that any other suitable protective film may be used without departing from the scope of this disclosure. Another photoresist 112 is applied on top of the silicon oxynitride 110, as shown in Figure 6. This photoresist 112 is exposed to and developed on an inverted pattern of the first photoresist 106, and the portions of silicon oxynitride not covered by the photoresist are removed, for example, using diluted hydrofluoric acid (HF:H2O), as shown in Figure 7. Remove the remaining photoresist 112 as shown in Figure 8, and prepare the substrate for annealing.This method includes annealing the semiconductor coating 104, which involves annealing the silicon oxynitride 110 and the semiconductor coating 104 in air, as shown in Figure 9, thereby activating and diffusing the dopant and increasing the oxygen in the undoped regions of the semiconductor coating 104. The sheet resistance of undoped In2O3 can be increased from less than 100 Ω per square to more than 2000 Ω per square by increasing the oxygen through air annealing. The remaining portion of the silicon oxynitride 110 is then removed from the substrate as shown in Figure 10, and the activated and annealed dopant in the doped region 108 forms a predetermined electrically conductive pattern within the semiconductor coating 104.

[0025] Doping a predetermined portion 108 of the semiconductor coating 104 and annealing the semiconductor coating 104 may involve diffusing the doped semiconductor through the semiconductor coating 104 to the optical substrate 102. That is, the dopant diffuses throughout the entire thickness of the semiconductor coating 104, as shown in Figure 10. The upper surface of the semiconductor coating 104 may be entirely covered with a pattern, which may vary spatially to achieve any desired electrical conductivity as a function of the two-dimensional position on the window or optical component 100. Thus, the optical component or window 100 may be formed to have a window with a conductive coating having broadband transparency without etching and / or without polishing or post-process planarization. The activated and doped semiconductor portion 108 and the semiconductor coating 104 may have approximately matched refractive indices to reduce light scattering from the pattern. If the ratio of the refractive indices of the doped semiconductor and the semiconductor coating is between 0.82 and 1.22, the interfacial reflection will be less than 1% for normal incidence. For example, the refractive indices of doped and undoped In2O3 at 632.8 nm are approximately 2.00 and 1.77, respectively. A refractive index ratio of 1.13 results in only 0.37% reflection.

[0026] As shown in Figure 10, the resulting window or optical component 100 includes a transparent substrate, i.e., an optical substrate 102 having a semiconductor coating 104 having an electrically conductive portion 108, which is made of both a transparent semiconductor and an electrically conductive semiconductor.

[0027] Referring here to Figures 11-15, another method is described in which, after depositing the semiconductor coating 104 as shown in Figure 11, a coating of silicon oxynitride 110 is applied to the entire surface of the semiconductor coating in an undoped state. A photoresist 106 is applied to the silicon oxynitride 110 as shown in Figure 12, and the photoresist 106 is exposed and developed. The developed photoresist 106 protects a predetermined portion of the silicon oxynitride 110, and removes the unprotected portion of the silicon oxynitride 110, exposing a predetermined portion 108 of the semiconductor coating 104 as shown in Figure 13. The semiconductor coating 104 is doped through openings 105 in the photoresist 106, as indicated by the downward arrow in Figure 13. Optionally, the photoresist 106 may be removed before doping, or otherwise, after doping as shown in Figure 14, leaving a pattern of doped semiconductor portions 108 within the semiconductor coating 104. As shown in Figure 15, annealing the silicon oxynitride 110 and the semiconductor coating 104 under vacuum activates and diffuses the dopant, reducing the oxygen in the doped region, i.e., portion 108, of the semiconductor coating 104. The oxygen vacancies contribute electrons, increasing the conductivity of the oxide semiconductor. Without the addition of dopant atoms, the sheet resistance of In2O3 can be reduced from above 2000 Ω per square to below 100 Ω per square by reducing oxygen through vacuum annealing. The silicon oxynitride 110 can then be removed to obtain the structure shown in Figure 10.

[0028] This disclosure relates to transparent conductive oxides (TCOs) or oxide semiconductors in which there is an increase or decrease in oxygen in selected regions during the annealing process. These oxygen changes decrease or increase the electron concentration and conductivity of the semiconductor, respectively. The sheet resistance of undoped In2O3 can be changed from above 2000 Ω per square to below 100 Ω per square, and vice versa, by decreasing or increasing oxygen.

[0029] The methods and systems of the present disclosure described above and shown in the drawings provide optical coatings having excellent properties, including spatially controlled electrical conductivity, for broadband windows and optical components. Although the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily recognize that changes and / or modifications to preferred embodiments may be made without departing from the scope of the subject disclosure. [Explanation of Symbols]

[0030] 100…Optical component or window 102...Optical board 104... Semiconductor coating 105…Opening 106... Photoresist 108... Doped semiconductor portion 110... Silicon oxynitride 112... Photoresist

Claims

1. A method for coating an optical substrate, A semiconductor coating having broadband light transmittance is deposited on the surface of the optical substrate, A first photoresist is applied to the semiconductor coating and developed into a first pattern, thereby doping a predetermined portion of the semiconductor coating to form a spatially varied pattern of the semiconductor doped within the semiconductor coating. A protective layer is formed on the semiconductor coating by applying a protective material to the entire surface of the semiconductor coating, applying a second photoresist on the protective material, developing it into a second pattern which is an inverted pattern of the first pattern, and selectively removing the portion of the protective material not covered by the second photoresist. Annealing the semiconductor coating to increase the oxygen in the undoped region of the semiconductor coating, To have, a method.

2. The method according to claim 1, wherein annealing the semiconductor coating comprises laser annealing it to a predetermined pattern to improve the crystal quality of the transparent conductive oxide (TCO) material of the semiconductor coating and to increase the electrical conductivity of the doped region of the semiconductor coating.

3. The method according to claim 1, wherein annealing the semiconductor coating comprises annealing it in air to activate and diffuse the dopant and increase the oxygen in the undoped regions of the semiconductor coating.

4. The method according to claim 1, wherein the protective material comprises silicon oxynitride.

5. The aforementioned semiconductor coating is In ２ O ３ The method according to claim 1, comprising at least one of the following: or ZnO.

6. The method according to claim 1, wherein doping a predetermined portion of the semiconductor coating to form a spatially varied pattern includes imparting a dopant by ion implantation.

7. The method according to claim 1, wherein the doped semiconductor comprises at least one of Sn, Mo, W, Ti, Al, or Ga.

8. The method according to claim 1, wherein the semiconductor coating has broadband light transmittance in at least the visible and infrared spectra.

9. The method according to claim 1, wherein the deposition of the semiconductor coating includes depositing the semiconductor coating in an undoped state.

10. The method according to claim 1, wherein doping a predetermined portion of the semiconductor coating and annealing the semiconductor coating includes diffusing dopant atoms through the semiconductor coating to the optical substrate.

11. The method according to claim 1, wherein depositing the semiconductor coating includes depositing the semiconductor coating on the entire surface of the optical substrate.

12. The method according to claim 1, wherein doping a predetermined portion of the semiconductor coating to form a spatially varied pattern includes doping the surface of the semiconductor coating such that the entire surface of the semiconductor coating is covered with the pattern.

13. The method according to claim 1, wherein the semiconductor coating, which includes an annealed, activated, and doped semiconductor within the semiconductor coating, and the optical substrate are formed to form a window without etching.

14. The method according to claim 1, wherein the semiconductor coating, which includes an annealed, activated, and doped semiconductor within the semiconductor coating, and the optical substrate are formed to form a window without polishing or post-process planarization.

15. The method according to claim 1, wherein the activated and doped semiconductor and the semiconductor coating have refractive indices that are approximately matched to reduce light scattering.

16. The method according to claim 1, further comprising making the doped semiconductor electrically conductive.

17. The method according to claim 1, further comprising adding hydrogen to the doped semiconductor by a silicon oxynitride process using plasma chemical vapor deposition (PECVD) or by hydrogen plasma.

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