CHALCOGENIDE HYBRID ORGANIC/INORGANIC POLYMERS FILMS AND COATINGS AND THE USE THEREOF

Abstract

The present invention provides certain CHIP films and coatings, as well as the preparation and uses thereof. Chalcogenide hybrid organic/inorganic polymers or CHIPs may be suitable for use in antireflection coatings for use with infrared optics, for example as applied to lenses for infrared cameras. The coatings may be applied with spin coating and have a thickness related to the quarter wavelength of the desired infrared wavelengths.

Claims

1. An antireflective (AR) coating comprising one or more chalcogenide hybrid organic/inorganic polymers (CHIPS), where the antireflection coating is applied to a substrate.

2. The coating of claim 1, wherein infrared light in the 700-5000_nm wavelength spectrum is preferentially transmitted through the coating as compared to the incident light.

3. A method of applying a coating of claim 1 to a substrate, the method comprising contacting the coating with the surface of the substrate.

4. The method of claim 3, wherein said coating is applied to the surface by spin coating.

5. The method of claim 3, wherein the substrate is silicon, glass, plastic, inorganic oxides, germanium surface, an inorganic transmissive device component, a lens, or optical device component.

6. A high refractive index inorganic transmissive material operating in the near and short-wave infrared regions (NIR through MWIR) comprising an antireflective coating of claim 1.

7. A lens or optical system in a camera, wherein one or more components of the optical system comprises the coating of claim 1.

8. The antireflective (AR) coating of claim 1, wherein the substrate comprises a high refractive index infrared optical material comprising germanium, silicon, or zinc selenide.

9. The antireflective (AR) coating of claim 1, wherein the coating has a thickness in the range of 0.1 to 0.4 of the ratio of at least 25% of the range of the wavelengths of the incident light divided by the refractive index of the coating.

10. The antireflective (AR) coating of claim 1, wherein the coating is a single layer, multiple layers, or a textured layer.

11. The method of claim 3, wherein the material comprises glass, silicon, and germanium.

12. The antireflective (AR) coating of claim 1, wherein the one or more CHIPS are prepared from one or more monomers comprising sulfur monomers derived from elemental sulfur, and elemental selenium (Se.sub.8) or selenium sulfide, or a combination thereof.

13. The antireflective (AR) coating of claim 1, wherein the one or more CHIPS comprises poly(sulfur-random-(1,3-diisopropenylbenzene) (poly(S-r-DIB)) copolymers.

14. The antireflective (AR) coating of claim 13, wherein the one or more CHIPS comprises at least 50% sulfur monomers.

15. The antireflective (AR) coating of claim 1, wherein the comprising one or more chalcogenide hybrid organic/inorganic polymers (CHIPS) comprises poly(sulfur-random-selenium-random-1,3 diisopropenylbenzene) (poly(S-r-Se-r-DIB)) terpolymers.

16. The antireflective (AR) coating of claim 15, wherein the one or more CHIPS comprises about 5-50 wt % of elemental sulfur (S.sub.8).

17. The antireflective (AR) coating of claim 15, wherein the one or more CHIPS comprises about 5-50 wt % of elemental selenium (Se.sub.8).

18. The antireflective (AR) coating of claim 1, wherein the coating has a thickness in the range of 0.2 to 0.3 of the ratio of at least 25% of the range of the wavelengths of the incident light divided by the refractive index of the coating.

19. The antireflective (AR) coating of claim 1, wherein the one or more CHIPS are prepared from one or more monomers comprising sulfur monomers derived from (i) elemental sulfur; (ii) elemental selenium (Se.sub.8); and (iii) one or more comonomers each selected from a group consisting of amine comonomers, thiol comonomers, sulfide comonomers, alkynyly unsaturated comonomers, epoxide comonomers, nitrone comonomers, aldehyde comonomers, ketone comonomers, thiirane comonomers, ethylenically unsaturated comonomers, styrenic comonomers, vinylic comonomers, methacrylate comonomers, acrylonitrile comonomers, allylic monomers, acrylate monomers, vinylpyridine monomers, isobutylene monomers, maleimide monomers, norbornene monomers, monomers having at least one vinyl ether moiety, and monomers having at least one isopropenyl moiety.

20. The antireflective (AR) coating of claim 1, wherein the one or more CHIPS are prepared from one or more monomers comprising sulfur monomers derived from (i) elemental sulfur; (ii) elemental selenium (Se.sub.8); and (iii) one or more norbornene monomers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The features and advantages of the present invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:

[0073] FIG. 1 shows CHIPs antireflection coating on an infrared optical material (comprising Ge, Si, ZnSe), an exemplary embodiment of a transmissive surface. In some embodiments, the transmissive surface may be glass or any other surface to which the coating can adhere.

[0074] FIG. 2 shows spin coating process for depositing CHIPs anti-reflection coating. The liquid coating material is applied to a substrate (such as native silicon), which is then spun at a high rate of speed to achieve a uniform thin film. The higher the spin speed the thinner the resulting film.

[0075] FIG. 3 shows the thickness of the spun coat AR film as a function of the spin-coating speed, for the poly (S-r-DIB) 50/50 copolymer in solution

[0076] FIG. 4 shows Reflectance spectrum of silicon wafer coated with varying thicknesses of poly (S-r-DIB)

[0077] FIG. 5 shows Reflectance spectrum of silicon wafer coated with varying thicknesses of poly (S-r-DIB). Same as FIG. 6, but now just showing a few of the results and better evidencing the thickness dependence of the antireflection coating effectiveness.

[0078] FIG. 6 shows Reflectance spectrum of silicon wafer coated with varying thicknesses of poly (S-r-DIB). Same as FIG. 6 but using a different scale on the x-axis.

[0079] FIG. 7 shows a plot of refractive index vs. wavelength for the CHIPs terpolymers having varying S/Se compositions.

EXAMPLES

Example 1

[0080] Preparation of poly(sulfur-random-selenium-random-1,3 diisopropenylbenzene) (poly(S-r-Se-r-DIB)) terpolymers.

[0081] To a 11 mL glass vial equipped with a magnetic stir bar was added sulfur (S8, 1.5 g, 46.78 mmol) and heated to T=160° C. in a thermostated oil bath until a clear orange colored molten phase was formed. The vial was then transferred to an adjacent T=150° C. in a thermostated oil bath where selenium (Se, 0.6 g, 7.59 mmol) was then directly added to the molten sulfur medium. 1,3-Diisopropenylbenzene (DIB, 0.9 g (0.97 mL)) was then directly added to the molten sulfur-selenium medium via syringe. The resulting mixture was stirred at T=150° C. for 1 to 1 ½ hours, which resulted in vitrification of the reaction media. The product was then taken directly from the vial using a metal spatula and removal of the magnetic stir bar for determination of yields after allowing the reaction mixture to cool to room temperature.

Example 2 (Preparation of AR Coating, Generally)

Overview

[0082] The simplest AR Coating is one that consists of a single thin layer whose thickness is one quarter the wavelength where AR is desired, divided by the refractive index of the AR coating. The reflection is minimized when the index of refraction of the AR is sqrt(ns), where ns is the substrate index, if the incident medium is air. Therefore, for high index materials (e.g., Si, Ge, etc.) a good AR coating is one with high index with the substrate.

[0083] For example, it was found that using silicon for the substrate, with an n of 3.48 at 1554 nm, and poly(sulfur-r-diisopropenylbenzene) (poly(s-r-DIB)) for the AR coating, with an n of 1.719 at 1554 nm; the square root of the refractive index of Silicon (1.865) closely matches that of poly(S-DIB) film making it a good candidate for single film AR coatings on silicon.

Preparation of Substrate

[0084] Silicon wafer (100 mm diameter, P type/Boron doped, 1-0-0 orientation, 1-20 ohm-cm resistivity, 525±25 μm thick, Prime grade, Single side polished, 2 SEMI FLATS) was cleaved along the crystalline axes using a diamond tip scribe pen into a 1 inch×1 inch sample.

[0085] Sample was cleaned using Acetone/IPA rinse (rinsed with acetone, blow dried with nitrogen, rinsed with IPA, blow dried with nitrogen) until the sample visually looks free of any debris or dust.

[0086] Sample was placed in Oxygen Plasma Cleaner (Plasma-Preen Plasma Cleaning/Etching System) under vacuum (−25 kPa) with oxygen (<5 scfh) for 5 minutes.

Preparation of Polymer Solution

[0087] 50/50 S-DIB was synthesized using inverse vulcanization process yielding a glassy red polymer.

[0088] The polymer was crushed into fine powders using a mortar and pestle.

[0089] 1 g of this powder was precisely weighed using a weighing scale and added to a glass vial (25 mL capacity).

[0090] 8 mL of chlorobenzene was measured and added with a syringe to the glass vial containing 50/50 S-DIB.

[0091] A small magnetic stir bar was added to the vial as well.

[0092] The glass vial containing the polymer and solvent was kept on a preheated hotplate at 115° C. while closing the cap.

[0093] The solution was allowed to mix for ˜15 minutes at 115° C. with 500 rpm stirring, until all the polymer is dissolved in the solvent.

[0094] The final solution is a red colored homogeneous solution, which is then allowed to cool down to room temperature.

Preparation of AR Coatings

[0095] The clean silicon sample is placed on the vacuum chuck of the Laurell spin coater. The spin process used is as follows:

[0096] Step 1—500 rpm rotation/5 secs,

[0097] Step 2—3000 rpm*/30 secs

[0098] Polymer solution was filled in a 3 mL syringe. Any air bubbles in the syringe was removed. A 0.2 μm pore size, 13 mm diameter, PTFE membrane syringe filter was screwed on the syringe. The syringe was turned upside down to let the air bubbles come to the top and was passed through the syringe. Some liquid was passed through to wet the membrane and to get rid of any remaining air bubbles.

[0099] Polymer was dispensed on the center of the substrate until the solution fills ⅔ of the substrate.

[0100] Spinner was turned on to allow the film to uniformly cover the substrate. Spinning at high speed also evaporates the solvent out of the film. The spin process used is as follows:

[0101] Step 1—500 rpm rotation/5 secs,

[0102] Step 2—3000 rpm*/30 secs.

*Varying spin speed were used to obtain different thicknesses of the films (220-370 nm)

[0103] The spun film was checked for uniformity and the sample was placed on a preheated hotplate at 130° C. for 3 mins to get rid of any remaining solvent in the film.

[0104] After 3 minutes, sample was taken off the hotplate resulting in a uniformly thin S-DIB coating on silicon substrate.

Example 3

[0105] The data in FIG. 3 was generated using the following procedure:

[0106] Film thickness was measured using Dektak which measures the variation in film thickness using stylus profilometry. The film is scanned over the set distance and set time, using a stylus capable of measuring film uniformity by tracking the motion of the cantilever and monitoring the force applied on the stylus. Two scratches were created on the sample, removing the film and exposing the bare polished Si. This creates a geometry where the base is the Si substrate, and there is a platform existing as tall as the film. A stylus can then probe over the grooves, tracking the region with no film and then goes over to the film and then back to no film. The film height can then be derived by the difference in z values between the base Si substrate and the S-r-DIB platform. The process was repeated at 3 different positions on the sample and the measurement was averaged. The resulting film thickness is an average of the three points.

Example 4

[0107] The data in FIGS. 4, 5, and 6 was generated using the following procedure:

[0108] The performance of the anti-reflection coating was verified using a Cary 7000 UV-Vis-NIR spectrophotometer. The Cary Universal Measurement Accessory (UMA) proved to be a useful tool in taking these measurements. The UMA allows the user to control the orientation of the sample relative to the input beam, and the position of the detector in relation to the sample. In our case, the coated Si sample was oriented at 5.5° from the input beam, and the detector was located at position 11° . The angle of 5.5° was used on the sample under test so that the input beam was as close to normal as possible on the sample without being blocked by the detector that would measure the reflected light. The detector was oriented at 11° in order to collect the specularly reflected light that would naturally result from Fresnel reflection of the silicon.

[0109] Before each measurement, a baseline using air was taken using the spectrometer. This ensured that an accurate reflection spectrum of the sample would be measured. Unpolarized light was used in this application. The polished side of the Si wafer was AR coated, and this side faced the incoming light. The backside was not polished, and light transmitted through the Si sample would scatter and not interfere with the collected reflection data. Measured data demonstrated a dramatic decrease in Fresnel reflection on the Si substrate due to the Quarter Wave Anti Reflection coating. The plot contains the S-r-DIB films with varying thicknesses, resulting in different spectral reflectance dependence. For reference, silicon substrate with no film was used which shows typical ˜30% reflectance off the surface. Adding the AR coating on the surface reduces this reflectance to less than 1% which demonstrates the excellent performance of the AR coatings. Adding multiple layers of the S-r-DIB film will lead to reducing the reflectance even further down.

Example 5

[0110] The data in FIG. 7 was generated using the following procedure:

[0111] Refractive index of the different polymers were measured using the Metricon Prism coupler.** The exact theory of measurement can be found in this link below https://www.metricon.com/model-2010-m-overview (last visited Sep. 30, 2019, which is incorpooraated by reference; see below for excerpt)

[0112] The instrument contains four different lasers with wavelengths 633 nm, 816 nm, 1305 nm, and 1554 nm. The S-DIB and other polymers were melt casted and used for measurement using the process described above. The index was measured in bulk mode for different wavelengths.

[0113] Theory of Measurement (excerpt from https://www.metricon.com/model-2010-m-overview (last visited Sep. 30, 2019, which is incorpooraated by reference)**

[0114] The sample to be measured is brought into contact with the base of a prism by means of a pneumatically-operated coupling head, creating a small air gap between the film and the prism (see diagram A). A laser beam strikes the base of the prism and is normally totally reflected at the prism base onto a photodetector. At certain discrete values of the incident angle, called mode angles, photons can tunnel across the air gap into the film and enter into a guided optical propagation mode, causing a sharp drop in the intensity of light reaching the detector:

[0115] To a rough approximation, the angular location of the first mode (dip) determines film index, while the angular difference between the modes determines the thickness, allowing thickness and index to be measured completely independently.

[0116] Measurements are made using a computer-driven rotary table which varies the incident angle, and locates each of the film propagation modes automatically. As soon as two of the mode angles are found, film thickness and index can be calculated. The entire measurement process is fully automated and requires approximately twenty seconds.

[0117] The number of modes supported by a film of given index increases with film thickness. For most film/substrate combinations, a thickness of 100-200 nm is required to support the first mode, while films in the one-micron range can support as many as four or five modes. If the film is thick enough to support two or more propagation modes (typically 300-500 nm), the Model 2010/M calculates thickness and index for each pair of modes, and displays the average and standard deviation of these multiple estimates.

[0118] The standard deviation calculation, unique to the prism coupling technique, is an indication of measurement self-consistency and a powerful means of confirming the validity of the measurement.

[0119] Measurements of thickness and index can be made on most samples with thickness up to 10-15 microns. For thickness above 15 microns, index is still measurable using the bulk measurement technique (see below) although thickness and index for many samples is often measurable at thicknesses up to 150-200 microns.

[0120] When acting as a refractometer to measure index of bulk materials (Diagram B above), the sample is also clamped against the prism and index is determined by measuring the critical angle θ.sub.c for the sample/prism interface. Films thicker than 10-15 microns usually show a clear critical angle knee and can be measured as bulk materials. Flexible materials are easily measured and a cell is available for liquid measurements. Unlike most conventional refractometers, which are single-wavelength (typically 589 nm), the 2010/M can be equipped with as many as five lasers, allowing easy measurement of dispersion across a wide wavelength range.

[0121] By changing the polarization state of the laser, index anisotropy (birefringence) can be measured in x, y, and z directions for both thin films and bulk materials.