Method for coating an optical substrate and window

Abstract

To provide an improved conductive optical coating for a broadband optical component.SOLUTION: A method of coating an optical substrate includes depositing a semiconductor coating over a surface of the optical substrate, the semiconductor coating having a broadband optical transmittance. Predetermined portions of the semiconductor coating are doped to form a spatially varied pattern of doped semiconductor in the semiconductor coating. The method includes annealing the semiconductor coating to at least one of increase oxygen in an undoped region of the semiconductor coating or decrease oxygen in a doped region of the semiconductor coating.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to optical coatings, and more particularly to conductive optical coatings. [Background technology]

[0002] Electro-optic (EO) systems require windows to protect sensors and electronics from the elements. In addition to rain, dust, etc., windows often must also block electromagnetic interference (EMI), which would otherwise hinder EO system performance.

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

[0004] The first type of EMI shielded window uses a semiconductor material such as silicon or germanium doped with a Group V element such as phosphorus, arsine, or antimony to provide additional electrons and thereby electrical conductivity. These windows are opaque to visible wavelengths and therefore not useful for broadband EO systems.

[0005] The second type of shielded window uses continuous transparent conductive coatings. These coatings are made of wide-bandgap semiconductors, such as indium oxide (In2O3) and zinc oxide (ZnO), which have broadband optical transparency. The semiconductors are doped to impart electrical conductivity. However, as doping increases, increasing electrical conductivity and EMI attenuation, optical transmittance decreases. This effect begins at longer wavelengths, where plasma reflection and free-carrier absorption from electrons both decrease transmittance. Traditional transparent conductive semiconductor coatings are only practical in the 0.4-2.0 micron range, from short-wavelength visible to short-wavelength infrared (SWIR).

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

[0007] US Patent No. 5,949,999 presents a method for reducing light scattering from a conductive grid. Channels are etched into a window substrate, and an electrically conductive semiconductor is deposited within the channels so that the window surface is flat. The semiconductor is transparent to visible and short-wavelength infrared (SWIR) wavelengths, but is 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. 9,276,034 Summary of the Invention [Problem to be solved by the invention]

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

[0010] A method for coating an optical substrate includes depositing a semiconductor coating over a surface of the optical substrate, the semiconductor coating having broadband optical transmittance. Predetermined portions of the semiconductor coating are doped to form a spatially varied pattern of doped semiconductor within the semiconductor coating. The method includes annealing to at least one of increase oxygen within undoped regions of the semiconductor coating or decrease oxygen within doped regions of the semiconductor coating.

[0011] Annealing the semiconductor coating can include laser annealing in a predetermined pattern to improve the crystalline quality of a transparent conductive oxide (TCO) material of the semiconductor coating and increase electrical conductivity within doped regions of the semiconductor coating.

[0012] Annealing the semiconductor coating can include annealing in air to activate and diffuse the dopant and increase oxygen in undoped regions of the semiconductor coating. applying a photoresist over the semiconductor coating; selectively exposing the photoresist; developing the photoresist into a predetermined pattern; doping a semiconductor coating through the openings in the photoresist; removing the photoresist to leave a doped semiconductor on the semiconductor coating in a predetermined pattern; depositing a coating of silicon oxynitride over the entire surface of the semiconductor coating; applying a photoresist onto the silicon oxynitride, exposing the photoresist, and developing the photoresist; removing predetermined portions of the silicon oxynitride not covered by the photoresist, and then removing any remaining photoresist; Annealing the semiconductor coating includes annealing the silicon oxynitride and the semiconductor coating in air to activate and diffuse the dopants and increase oxygen in the undoped regions of the semiconductor coating.

[0013] It is also contemplated that annealing the semiconductor coating may include annealing under vacuum to activate and diffuse the dopants and reduce oxygen in the doped regions of the semiconductor coating. depositing a coating of silicon oxynitride over the entire surface of the semiconductor coating while the semiconductor coating is undoped; applying a photoresist onto the silicon oxynitride, exposing the photoresist, and developing the photoresist; removing portions of the silicon oxynitride not covered by the photoresist; doping a semiconductor coating through the openings in the photoresist; removing the photoresist to leave a patterned doped semiconductor on the semiconductor coating; Annealing the semiconductor coating includes annealing the silicon oxynitride and the semiconductor coating in a vacuum to activate and diffuse the dopants and reduce oxygen in the doped regions of the semiconductor coating.

[0014] The semiconductor coating may include at least one of In2O3 or ZnO. Doping predetermined portions of the semiconductor coating to form a spatially varied pattern may include applying the dopant by ion implantation, a spin-on or spray-on solution, or other methods. The doped semiconductor may include at least one of Sn, Mo, W, Ti, Al, or Ga. The semiconductor coating may have broadband optical transmittance in at least the visible and infrared spectra. Depositing the semiconductor coating may include depositing the semiconductor coating while the semiconductor coating is undoped. Doping predetermined portions 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 over the entire surface of the optical substrate. Doping predetermined portions of the semiconductor coating to form a spatially varied pattern may include doping the surface of the semiconductor coating such that the entire surface of the semiconductor coating is covered with the pattern. The semiconductor coating, including the annealed activated and doped semiconductor within the semiconductor coating, and the optical substrate can be formed into a window without etching and / or polishing or post-process planarization. The activated and doped semiconductor and the semiconductor coating can have approximately matched refractive indices to reduce light scattering from the pattern. When the ratio of the refractive indices of the doped semiconductor and the semiconductor coating is between 0.82 and 1.22, the interface reflection will be less than 1% at 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 a 0.37% reflection. The method can include making the doped semiconductor electrically conductive.Hydrogen can be added to doped semiconductors, such as by using a plasma-enhanced chemical vapor deposition (PECVD) silicon oxynitride process or a hydrogen plasma, to increase conductivity by adding electrons and passivating defects.

[0015] The window includes a transparent substrate having a coating on the transparent substrate, the coating being formed of both a transparent semiconductor and an electrically conductive semiconductor having a transparency less than that of the transparent semiconductor, the electrically conductive semiconductor being annealed and distributed in a spatially varied pattern within the transparent semiconductor.

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

[0017] Preferred embodiments thereof will be described in detail hereinafter with reference to certain figures so that those skilled in the art to which the subject disclosure pertains will readily understand, without undue experimentation, how to make and use the subject disclosed apparatus and methods. [Brief explanation of the drawings]

[0018] [Figure 1] 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] 2 is a schematic cross-sectional elevation view of the window or optical component of FIG. 1 showing a photoresist layer deposited on the semiconductor coating. [Figure 3] 3 is a schematic cross-sectional elevation view of the window or optical component of FIG. 2 showing portions of the developed photoresist that have been removed to allow doping of the semiconductor coating in a predetermined spatially varying pattern. [Figure 4]4 is a schematic cross-sectional elevation view of the window or optical component of FIG. 3 showing the photoresist removed and the doped pattern in the semiconductor coating. [Figure 5] 5 is a schematic cross-sectional elevation view of the window or optical component of FIG. 4, showing a silicon oxynitride layer deposited on the semiconductor coating. [Figure 6] 6 is a schematic cross-sectional elevation view of the window or optical component of FIG. 5, showing a photoresist layer deposited on the silicon oxynitride layer. [Figure 7] 7 is a schematic cross-sectional elevation view of the window or optical component of FIG. 6 showing the developed photoresist layer and portions of the silicon oxynitride removed. [Figure 8] 8 is a schematic cross-sectional elevation view of the window or optical component of FIG. 7, showing the photoresist removed. [Figure 9] 9 is a schematic cross-sectional elevation view of the window or optical component of FIG. 8 illustrating the annealing process in air and the dopant atoms diffusing through the semiconductor coating to the substrate. [Figure 10] 10 is a schematic cross-sectional elevation view of the window or optical component of FIG. 9 showing the silicon oxynitride removed to leave an electrically conductive pattern in the semiconductor coating. [Figure 11] 2 is a schematic cross-sectional elevation view of the window or optical component of FIG. 1 illustrating another embodiment method in which the semiconductor coating is first coated with silicon oxynitride. [Figure 12] 12 is a schematic cross-sectional elevation view of the window or optical component of FIG. 11 showing a photoresist layer deposited on the silicon oxynitride. [Figure 13] 13 is a schematic cross-sectional elevation view of the window or optical component of FIG. 12 showing portions of the developed photoresist and silicon oxynitride removed to allow doping of the semiconductor coating in a predetermined spatially varying pattern. [Figure 14] 14 is a schematic cross-sectional elevation view of the window or optical component of FIG. 13 showing the photoresist removed and the doped pattern in the semiconductor coating. [Figure 15]15 is a schematic cross-sectional elevation view of the window or optical component of FIG. 14 illustrating an annealing process in vacuum to form an electrically conductive pattern in the semiconductor coating, the electrically conductive pattern being as shown in FIG. 10 after removal of the silicon oxynitride. DETAILED DESCRIPTION OF THE INVENTION

[0019] Reference will now be made to the drawings, in which like reference numerals identify like structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a window or optical component according to the present disclosure is shown in FIG. 1 and generally designated by reference character 100. Other embodiments of windows or optical components according to the present disclosure or aspects of the present disclosure are provided in FIGS. 2-15, as noted. The systems and methods described herein can be used to provide spatially controlled or spatially varied electrical conductivity of transparent oxide coatings for optical components and windows. This can be used for electromagnetic interference (EMI) shielding, spatially varied sheet resistance for smart window applications, or any other suitable application.

[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 transparency and electrical conductivity. Wide-bandgap semiconductors, indium oxide (In2O3) and zinc oxide (ZnO), have broadband optical transparency. Materials can be doped to provide electrical conductivity. However, as doping increases to enhance electrical conductivity, optical transmittance decreases. This effect begins at longer wavelengths, where plasma reflection and free-carrier absorption from electrons both decrease transmittance. Typical conductive oxide coatings are generally transparent only within the 0.4-2.0 micron wavelength range. This disclosure describes a method for spatially controlling the conductivity and transmittance of transparent oxide thin films in different regions of the coating.

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

[0022] Predetermined portions of the semiconductor coating 104 are doped to form a spatially varied pattern of doped semiconductor within the semiconductor coating, as described further below. Doping predetermined portions of the semiconductor coating to form a spatially varied pattern may include applying dopants 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 the present 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 passivate defects.

[0023] The method includes annealing the semiconductor coating 104, thereby diffusing dopant atoms through the semiconductor coating to at least one of increasing oxygen in undoped regions of the semiconductor coating or decreasing oxygen in doped regions of the semiconductor coating, each of which is described below.

[0024] First, annealing the semiconductor coating 104 may include thermal annealing and / or laser annealing in a predetermined pattern to improve the crystalline quality of the TCO material of the semiconductor coating 104 and increase electrical conductivity in the doped regions of the semiconductor coating 104. Annealing the semiconductor coating 104 may include annealing in air to activate and diffuse the dopants and increase oxygen in the undoped regions of the semiconductor coating 104. Doping predetermined portions of the semiconductor coating 104 may include applying a photoresist 106 over the semiconductor coating as shown in FIG. 2. The photoresist is selectively exposed and developed into a predetermined spatially varying pattern. That is, while any pattern can be used, in FIG. 3, the spatial variation of the pattern includes wider openings 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 openings 105 in the photoresist 106, as indicated by the downward arrows in FIG. 3. Referring to FIG. 4, the photoresist 106 is removed, for example, using a solvent, leaving a pattern of doped semiconductor 108 in the semiconductor coating 104. A coating of silicon oxynitride 110 is deposited over the entire surface of the semiconductor coating 104 using plasma-enhanced chemical vapor deposition (PECVD), as shown in FIG. 5. Hydrogen in the PECVD process increases conductivity by adding electrons and passivating defects in the oxide semiconductor. Hydrogen plasma can also be used. While silicon oxynitride is used as an example herein, those skilled in the art will readily recognize that any other suitable protective film can be used without departing from the scope of this disclosure. Another photoresist 112 is applied over the silicon oxynitride 110, as shown in FIG. 6. This photoresist 112 is exposed and developed in a reverse pattern to the first photoresist 106, and the portions of the silicon oxynitride not covered by the photoresist are removed, for example, using dilute hydrofluoric acid (HF:HO), as shown in FIG. 7. The remaining photoresist 112 is removed as shown in FIG. 8, preparing the substrate for annealing.The method includes annealing the semiconductor coating 104, including annealing the silicon oxynitride 110 and the semiconductor coating 104 in air, to activate and diffuse the dopants and increase the oxygen in the undoped regions of the semiconductor coating 104, as shown in Figure 9. The sheet resistance of undoped In2O3 can be increased from less than 100 ohms per square to over 2000 ohms per square by increasing the oxygen with an air anneal. The remaining portions of the silicon oxynitride 110 are then removed from the substrate, as shown in Figure 10, and the activated and annealed dopants in the doped regions 108 form a predetermined electrical conductivity pattern in the semiconductor coating 104.

[0025] Doping predetermined portions 108 of the semiconductor coating 104 and annealing the semiconductor coating 104 may include diffusing the doped semiconductor through the semiconductor coating 104 and into the optical substrate 102. That is, the dopant diffuses throughout the entire thickness of the semiconductor coating 104, as shown in FIG. 10 . The top surface of the semiconductor coating 104 may be entirely covered with a pattern, and the pattern may vary spatially to achieve any desired electrical conductivity as a function of two-dimensional position on the window or optical component 100. Thus, the optical component or window 100 may be formed without etching and / or polishing or post-process planarization to result in a window with an electrically conductive coating with broadband transparency. The activated and doped semiconductor portions 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 interface reflection will be less than 1% at 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 a reflection of only 0.37%.

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

[0027] 11-15, an alternative method is described in which, after the semiconductor coating 104 is deposited as shown in FIG. 11, a coating of silicon oxynitride 110 is applied over the entire surface of the semiconductor coating while the semiconductor coating remains undoped. Photoresist 106 is applied over the silicon oxynitride 110 as shown in FIG. 12, and the photoresist 106 is exposed and developed. The developed photoresist 106 protects predetermined portions of the silicon oxynitride 110 and removes the unprotected portions of the silicon oxynitride 110, exposing predetermined portions 108 of the semiconductor coating 104 as shown in FIG. 13. The semiconductor coating 104 is doped through openings 105 in the photoresist 106, as indicated by the downward arrows in FIG. 13. Optionally, the photoresist 106 is removed before doping; otherwise, the photoresist 106 can be removed after doping, leaving doped semiconductor portions 108 in a pattern within the semiconductor coating 104, as shown in FIG. 14. Annealing the silicon oxynitride 110 and semiconductor coating 104 under vacuum activates and diffuses the dopants, reducing the oxygen in the doped regions or portions 108 of the semiconductor coating 104, as shown in FIG. 15. 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 over 2000 Ω per square to less than 100 Ω per square by reducing the oxygen through vacuum annealing. The silicon oxynitride 110 can then be removed to arrive at the structure shown in FIG. 10.

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

[0029] The methods and systems of the present disclosure, as described above and illustrated in the drawings, provide optical coatings with superior properties, including broadband windows and spatially controlled electrical conductivity for optical components. While 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 may be made to the preferred embodiments without departing from the scope of the subject disclosure. [Explanation of symbols]

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

Claims

1. 1. A method of coating an optical substrate, comprising: depositing a semiconductor coating having broadband optical transmittance over a surface of the optical substrate; doping predetermined portions of the semiconductor coating to form a spatially varying pattern of doped semiconductor within the semiconductor coating; Enriching oxygen in undoped regions of the semiconductor coating; or reducing oxygen in the doped region of said semiconductor coating; annealing the semiconductor coating to at least one of: A method comprising:

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

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

4. Doping a predetermined portion of the semiconductor coating comprises: applying a photoresist over said semiconductor coating; selectively exposing the photoresist; developing the photoresist into a predetermined pattern; doping the semiconductor coating through the openings in the photoresist; removing the photoresist to leave the doped semiconductor in the pattern on the semiconductor coating; depositing a coating of silicon oxynitride over the entire surface of the semiconductor coating; applying a photoresist onto the silicon oxynitride, exposing the photoresist, and developing the photoresist; removing portions of the silicon oxynitride not covered by photoresist, and then removing any remaining photoresist; Including, 10. The method of claim 1, wherein annealing the semiconductor coating comprises annealing the silicon oxynitride and the semiconductor coating in air to activate and diffuse dopants and increase oxygen in undoped regions of the semiconductor coating.

5. 10. The method of claim 1, wherein annealing the semiconductor coating comprises annealing under vacuum to activate and diffuse dopants and reduce oxygen in doped regions of the semiconductor coating.

6. Doping a predetermined portion of the semiconductor coating comprises: depositing a coating of silicon oxynitride over the entire surface of the semiconductor coating while the semiconductor coating is undoped; applying a photoresist onto the silicon oxynitride, exposing the photoresist, and developing the photoresist; removing portions of the silicon oxynitride not covered by photoresist; doping the semiconductor coating through the openings in the photoresist; removing the photoresist to leave the doped semiconductor in the pattern on the semiconductor coating; Including, 10. The method of claim 1, wherein annealing the semiconductor coating comprises annealing the silicon oxynitride and the semiconductor coating in a vacuum to activate and diffuse dopants and reduce oxygen in undoped regions of the semiconductor coating.

7. The semiconductor coating is In ２ O ３ or ZnO.

8. 10. The method of claim 1, wherein doping predetermined portions of the semiconductor coating to form a spatially varying pattern comprises applying dopants by ion implantation.

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

10. The method of claim 1 , wherein the semiconductor coating has broadband optical transmittance in at least the visible and infrared spectra.

11. The method of claim 1 , wherein depositing the semiconductor coating comprises depositing the semiconductor coating in an undoped state.

12. The method of claim 1 , wherein doping the predetermined portion of the semiconductor coating and annealing the semiconductor coating comprises diffusing dopant atoms through the semiconductor coating to the optical substrate.

13. The method of claim 1 , wherein depositing the semiconductor coating comprises depositing the semiconductor coating over the entire surface of the optical substrate.

14. 2. The method of claim 1, wherein doping predetermined portions of the semiconductor coating to form a spatially varied pattern comprises doping a surface of the semiconductor coating such that the surface is entirely covered with the pattern.

15. 10. The method of claim 1, wherein the semiconductor coating, which includes an annealed, activated, and doped semiconductor within the semiconductor coating, and the optical substrate are formed into a window without etching.

16. 10. The method of claim 1, wherein the semiconductor coating, including the annealed activated and doped semiconductor within the semiconductor coating, and the optical substrate are formed into a window without polishing or post-process planarization.

17. 10. The method of claim 1, wherein the activated and doped semiconductor and the semiconductor coating have refractive indices that are closely matched to reduce light scattering.

18. The method of claim 1 further comprising rendering the doped semiconductor electrically conductive.

19. 10. The method of claim 1, further comprising adding hydrogen to the doped semiconductor by a plasma enhanced chemical vapor deposition (PECVD) silicon oxynitride process or by a hydrogen plasma.

20. 1. A window comprising a transparent substrate having a coating, the coating being made of both a transparent semiconductor and an electrically conductive semiconductor having a transparency less than that of the transparent semiconductor, the electrically conductive semiconductor being annealed and distributed in a spatially varying pattern within the transparent semiconductor.

21. 21. The window of claim 20, wherein the electrically conductive semiconductor is laser annealed.

22. 21. The window of claim 20, wherein the transparent semiconductor coating comprises a transparent conductive oxide (TCO) material, the electrically conductive semiconductor comprises a semiconductor material doped to impart electrical conductivity, and the doped semiconductor comprises at least one of Sn, Mo, W, Ti, Al, or Ga.

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