Method of making an amorphous silicon layer on a polymeric web and articles thereof

Abstract

Described herein is a coated web comprising a polymeric web having a first major surface and an amorphous silicon layer disposed thereon, wherein the amorphous silicon layer comprises (a) a refractive index greater than 3.0 at 1000 nm; (b) an extinction coefficient of less than 0.01 at 1000 nm, and (c) a thickness greater than 500 nanometers, and wherein the coated web has a cross-web curvature of less than 10 m-1. Also described is a continuous process for making such a coated web using plasma enhanced chemical vapor deposition.

Description

PA102588WO02METHOD OF MAKING AN AMORPHOUS SILICON LAYER ON A POLYMERIC WEB AND ARTICLES THEREOFU. S. GOVERNMENT RIGHTS

[0001] This disclosure was made with Government support under Grant NumberFA8650-22-D-5406 awarded by DOD. The Government has certain rights in this disclosure.TECHNICAL FIELD

[0002] A method for depositing a layer of amorphous silicon onto a polymeric web in a continuous fashion is disclosed along with the resulting webs.SUMMARY

[0003] Metasurfaces are thin, engineered sheets comprising subwavelength structures that can control the way light scatters and propagates. Such materials can be used in various applications including optical sensing, thermal imaging, chemical sensing, and free-space wireless communication. Fabricating metasurfaces particularly based on silicon is widely known since silicon-based processes are common and readily available for wafer-based processes. However, there is a desire to fabricate silicon-based metasurfaces in larger part sizes, on flexible substrates, and / or at higher volumes. Thus, there is a need to develop an amorphous silicon layer on a polymeric web that has the necessary optical properties, thickness, and does not substantially curl.

[0004] In one aspect, a coated web is disclosed comprisinga polymeric web having a first major surface and an opposing second major surface; and an amorphous silicon layer disposed on the first major surface,wherein the amorphous silicon layer comprises (a) a refractive index greater than 3.0 at 1000 nm; (b) an extinction coefficient of less than 0.01 at 1000 nm, and (c) a thickness greater than 500 nanometers, and wherein the coated web has a cross-web curvature of less than 10 m’1.

[0005] In another aspect, a method of making an amorphous silicon coated web is disclosed. The method comprising:(a) providing a polymeric web and a vacuum chamber comprising a chilled electrode powered by radio-frequency and a counter electrode;(b) introducing a reactant gas into the vacuum chamber, wherein the reactant gas comprises a gas mixture of a silicon-containing gas and an inert gas;(c) generating a plasma of the gas mixture between the chilled electrode and the counter electrode with the polymeric web therebetween, wherein a portion of the polymeric web is in intimate contact with the chilled electrode and the chilled electrode has a power density of less than 1 W / in2; and(d) continuously depositing a reactive species formed in the plasma onto the polymeric web to form a layer of amorphous silicon on the polymeric web.

[0006] The above summary is not intended to describe each embodiment. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages will be apparent from the description and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

[0008] Fig. 1 is a perspective view of a coated web according to an embodiment of the present disclosure;

[0009] Fig. 2 is a cross-sectional schematic view of a PECVD apparatus according to an embodiment of the present disclosure;

[0010] Fig. 3 is a schematic view of determining the curl angle measurement for a coated web;

[0011] Fig. 4 is a schematic of a template for determining the amount of curl of a coated web;

[0012] Fig. 5 is an SEM image of a cross-section of Example 1; and

[0013] Fig. 6 is an SEM image of a cross-section of Comparative Example 2.

[0014] In the drawings, like reference numerals indicate like elements. While the above-identified drawings, which may not be drawn to scale, set forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.DETAILED DESCRIPTION

[0015] As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” or “the” component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term “and / or” means one or all the listed elements or a combination of any two or more of the listed elements.

[0016] Relative terms such as top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the figures. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way.

[0017] Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certainembodiments,” “in some embodiments” or “in one embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention.

[0018] As used herein, the term “plasma” means a partially ionized gaseous or fluid state of matter containing reactive species which include electrons, ions, neutral molecules, free radicals, and other excited state atoms and molecules. Visible light and other radiation are typically emitted from the plasma as the species forming the plasma relax from various excited states to lower, or ground, states. The plasma usually appears as a colored cloud in the reaction chamber.

[0019] As used herein, the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise. The phrase “and / or” is used to indicate one or both stated cases may occur, for example A and / or B includes, (A and B) and (A or B).

[0020] As used herein, recitation of ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 10 includes 1.4, 1.9, 2.33, 5.75, 9.98, etc.).

[0021] As used herein, recitation of “at least one” includes all numbers of one and greater (e.g., at least 2, at least 4, at least 6, at least 8, at least 10, at least 25, at least 50, at least 100, etc.).

[0022] As used herein, “comprises at least one of’ A, B, and C refers to element A by itself, element B by itself, element C by itself, A and B, A and C, B and C, and a combination of all three.

[0023] The phrase "comprises at least one of followed by a list refers to comprising any one of the items in the list and any combination of two or more items in the list. The phrase "at least one of followed by a list refers to any one of the items in the list or any combination of two or more items in the list.

[0024] The present disclosure maybe understood with respect to Fig. 1, which depicts one embodiment of the present disclosure, wherein coated web 10, comprises semicontinuous polymeric web 12 with amorphous silicon layer 14 disposed thereon.

[0025] The coated web may be made in a continuous fashion as will be described below, enabling long lengths of material to be fabricated.

[0026] In general, the amorphous silicon layer is present only on one side of the polymeric web as shown in Fig. 1.

[0027] The polymeric web is a material that provides mechanical support to the amorphous silicon layer during processing. Exemplary support materials include polyolefins (such as pol eth lene, polypropylene, cyclic olefin copolymers, etc.), polyesters (such as polyethylene terephthalate (PET)), poly styrene, acrylonitrile butadiene styrene, polyvinyl chloride, poly vinylidene chloride, polycarbonate, polyacrylates. thermoplastic polyurethanes, polyvinyl acetate, polyamide, polyimide, poly(methylmethacrylate), polyethylene naphtlialate, polystyrene acrylonitrile, triacetate cellulose, nylon, silicone-polyoxamide polymers, fluoropolymers, and thermoplastic elastomers. In some embodiments, the polymeric web is a heat stabilized PET. Heat stabilized PET is known in the art and refers to a polyethylene terephthalate that has been treated (for example tentered at high temperature) so that it maintains its shape at high temperatures (e.g., 150 °C).

[0028] In some embodiments, the polymeric web should also be flexible enough to enable continuous processing through rollers, around drums, etc.

[0029] The polymeric web may be semicontinuous, meaning that the web is substantially unbroken in any one direction. In general, the polymeric web will have a length much longer than its width. In some embodiments, the polymeric web has a length of at least 0.5, 1, 2, or even 5 meters. The upper limit to the length of the polymeric web can be kilometers in length and is limited by what can be obtained and / or how much can be held within the apparatus to make the coated web. Typically, the width of the chilled electrode (e.g., drum) dictates the width of the polymeric web, wherein the polymeric web is the same width or smaller than the width of the chilled electrode. In some embodiments, the polymeric web has a width of at least 30, 40, 50, or even 60 cm and at most 1000, 500, 400, 300, 200, 100, 75, or even 65 cm.

[0030] Fig. 1 depicts amorphous silicon layer 14 as a continuous layer across the polymeric web. In some embodiments, the amorphous silicon layer is discontinuous across the polymeric web. For example, the amorphous silicon layer may be patterned across the polymeric web in lines, rows, posts, etc.

[0031] The amorphous silicon layer is a high-performance material, having a high refractive index and low absorption (i.e., low extinction coefficient). Ellipsometry may be used to determine the refractive index and extinction coefficient of the amorphous silicon. In some embodiments, the amorphous silicon layer has a refractive index of at least 3.0, 3.1, 3.2, 3.3, 3.4, or even 3.5 at 1000 nm. In some embodiments, the amorphous silicon layer has a refractive index of at most 4.0, 4.5, or even 5.0 at 1000 nm. In some embodiments, the amorphous silicon layer has extinction coefficient of no more than 0.01, 0.005, 0.001, 0.0005, 0.0001 or even below the detection limit at 1000 nm.

[0032] The amorphous silicon layer comprises silicon. In some embodiments, the amorphous silicon layer consists of silicon. In some embodiments, the amorphous silicon layer comprises silicon and other elements.

[0033] In some embodiments, the amorphous silicon layer comprises a hydrogenated amorphous silicon, which comprises silicon and hydrogen. In some embodiments, the hydrogenated amorphous silicon comprises at least 0.01, 0.05, 0.1, 0.5, 1, 1.5, or even 2 % and at most 15, 12, 10, 8, 6, 5, 4, 3, or even 2.5 % of hydrogen based on weight (wt). In some embodiments, the amorphous silicon is substantially free of hydrogen, comprising less than 0.01, 0.005, 0.001% of hydrogen based on weight or even below the detection limit (or not observed).

[0034] In some embodiments, the amorphous silicon layer comprises a dopant. Dopants for silicon are known in the art and can include boron, phosphorous, aluminum, nitrogen, indium, and gallium.Typically, the dopants are present in small amounts, generally no more than 0.2, 0.1, 0.05, or even 0.01 wt% based on the weight of the amorphous silicon. In some embodiments, the amorphous silicon is substantially free of dopant, comprising less than 0.01, 0.005, 0.001% of a dopant based on weight or even below the detection limit (or not observed).

[0035] In some embodiments, the amorphous silicon layer comprises low amounts (e.g., less than 0.5, 0.1, 0.05, or even 0.1 wt%) of impurities such as oxygen or carbon.

[0036] In some embodiments, the amorphous silicon layer has a thickness of at least 500, 750, 1000, 1500, or even 2000 nanometers (nm). In some embodiments, the amorphous silicon layer has a thickness of at most 5000, 4000, 3000, 2000, 1500, or even 1000 nm. The thickness may be determined by ellipsometry or measuring a cross-sectioned sample via microscopy (e.g., scanning electron microscopy).

[0037] In some embodiments an inorganic layer is disposed between the substrate and the amorphous silicon layer. The inorganic layer may optionally comprise silicon dioxide, aluminum oxide, chrome oxide, titanium, chrome, or aluminum. This inorganic layer may have a thickness of at least 2, 4, 10, 20, 25, or even 50 nm and at most 500, 400, 300, 200, or even 100 nm.

[0038] The amorphous silicon coated web of the present disclosure may be made in a continuous process using plasma enhanced chemical vapor deposition (PECVD) as described below.

[0039] For example, the cylindrical apparatus disclosed in U. S. Pat. No. 8,460,568 (David, et al.) incorporated by reference herein, can be used to deposit a layer of amorphous silicon onto a web of polymeric material. A simplified apparatus is shown in Fig. 2. Fig. 2 comprises vacuum chamber 200 with polymeric web 12 on unwind roll 212, winding roll 210, drum 220, and rollers 201 and 202.Polymeric web 12 is a roll of a polymer sheet that is unrolled from unwind roll 212 and fed onto drum 220 via roller 201. The polymeric web is deposited with a layer of amorphous silicon and coated web 10 is rolled onto winding roll 210 via roller 202. To form the layer of amorphous silicon, a reactant gas is fed into the vacuum chamber via inlet 260. In some embodiments, multiple inlets are used to input the gas. To achieve the desired thickness of the amorphous silicon layer, in some embodiments, the web is passed repeatedly through the apparatus, by either reversing direction of the rollers or by physically replacing the spent unwind roll 212 with winding roll 210 comprising the coated web and rerunning the apparatus.

[0040] PECVD is a process to create thin films of material by creating a plasma from reactant gas in the reaction chamber. Reactive materials from the plasma then deposit onto a surface (in this instance, the polymeric web and / or coated web).

[0041] The reaction chamber is held under a vacuum (also referred to herein as vacuum chamber) to remove any atmospheric gases and / or contaminants that might interfere with the purity of the deposited layer. In some embodiments, the vacuum chamber is held at a pressure of at least 1, 2, 4, 5, 10, 15, or even 20 mTorr (millitorr) and at most 50, 40, or even 30 mTorr.

[0042] Drum 220 is a chilled electrode that rotates. Typically, drum 220 is made of an electrically and thermally conductive material having a dielectric surface. Generally, polymeric web 12 is in intimate contact (i.e., touching) with drum 220 to cool the web, preventing the polymeric web from becoming compromised during the PECVD process. In some embodiments, the chilled electrode is held at a temperature of no more than room temperature (i.e., between 20 to 25 °C). In some embodiments the chilled electrode is held at a temperature of no more than 30, 20, or even 10 °C. The chilled electrode is described as a drum or cylinder above in discussion of Fig. 2, but other configurations may be considered.

[0043] The reactant gas is introduced into the vacuum chamber via inlet 260. The reactant gas comprises the gas to form the amorphous silicon layer and optionally an inert carrier gas. Gases used toform the amorphous silicon layer include silicon-containing compounds such as silane (SiH4), disilane, or trisilane. Optional inert carrier gases include argon, helium, or in some cases even nitrogen. In some embodiments, the ratio of the silicon-containing gas (e.g., SiH4) to the inert gas (e.g., argon) is no more than 10, 7, 5, 4, 3, 2, or even 1 wt%. In some embodiments, the reactant gas is substantially free (i.e., less than 0.1, 0.05, or even 0.01 wt %) of dihydrogen. Ideally, the vacuum chamber is free of gases that can impact the refractive index of the resulting amorphous silicon layer such as oxygen or carbon. The reactant gas may be introduced at sufficient flow rates to achieve an operating pressure between 5 and 500 mTorr. The flow rates may be varied based on the size of the reaction chamber, number of gas inlets, and surface area of the chilled electrode. In some embodiments, the flow rate is at least 500, 1000, 2000, or even 3000 standard cubic centimeters per minute (sccm). In some embodiments, the flow rate is at most 10000, 8000, 6000, 5000, 4000, 3000, 2500, or even 2000 sccm.

[0044] A plasma of the reactant gas is generated between the chilled electrode, which is powered by a radio-frequency, and a counter electrode. As shown Fig. 2, the housing of the vacuum chamber is grounded forming counter electrode 240. Thus, the polymeric web passes between the chilled electrode and the counter electrode.

[0045] A potential is applied between drum (i.e., working electrode) 220 and counter electrode 240, generating a plasma of the reactant gas, which then causes a reactive species from the plasma to deposit upon the polymeric web, creating the amorphous silicon layer. To achieve a high-performance material, the chilled electrode should have a power density of no more than 1, 0.9, 0.8, 0.7, 0.6, or even 0.5 W / in2(square inch), which is determined based on the applied power used and the surface area of the chilled electrode.

[0046] Ideally, the amorphous silicon layer is homogeneous, meaning that it is a uniform, single layer of silicon. In some embodiments, the deposition may result in different domains (or densities) of silicon form resulting in a non-uniform or striated layer, for example, as shown in Fig. 6.

[0047] As shown in the experimental section below, to achieve a high-performance, homogeneous layer, the process conditions should be optimized. Ideally, the reactant gas should be inputted close to the chilled electrode, however further distances may be used, so long as the power and gas flow conditions are kept lower. Because PECVD results in a thin film of deposited material, a number of passes may be required to achieve a layer of amorphous silicon having a thickness greater than 500 nm. A balance must be achieved between high processing rates (i.e., high deposition rates) and generating an ideal, high density amorphous silicon layer. If both the power and gas flow are too high, then the coated web can suffer from too much curl.

[0048] The density of the amorphous silicon layer may be determined by using Wavelength Dispersive X-ray Fluorescence (WDXRF) and the thickness of the layer for example, by measuring the cross-section thickness via Scanning Electron Microscopy (SEM). WDXRF analysis can determine the presence of silicon. Using the net intensity of the silicon k-alpha peak reported as the kilocounts per second (keps) and the thickness of the amorphous silicon layer reported in nanometers (nm), the density can be determined (reported as keps / nm). In some embodiments, the density of amorphous silicon layer is atleast 0.080, 0.082, 0.083, 0.084, 0.085, 0.088, 0.090, 0.092, or even 0.095 kcps / nm. In some embodiments, the density of amorphous silicon layer is at most 0.14, 0.13, 0.12, 0.11, 0.10, or even 0.095 kcps / nm. Ideally, higher densities are preferred.

[0049] In some embodiments, the deposition rate of the amorphous silicon is at least 10, 12, 15, 18, or even 20 nm / min. In some embodiments, the deposition rate of the amorphous silicon is at most 25, 24, 22, or even 20 nm / min.

[0050] Ideally, the resulting coated webs of the present disclosure have minimal curl. Curl is defined as the tendency of a web to deviate from a generally flat or planar orientation when there are no external forces on the web. Herein, curl is determined based on angle and amount of curl and is reported as the cross-web curvature.

[0051] The angle of curl of a sample is determined by cutting a circle from the web and marking the machine direction of the web. The center of the circle is aligned onto a template such as shown in Fig. 3 and the major curl axis is noted, where curled coated web 30 is placed on template 300. The machine direction of coated web 30 designated by arrow 305 is aligned with MD on the template. The major curl axis of coated web 30 is designated by dashed line 306, which is the axis perpendicular to the tightest curl of the web. In Fig. 3, the major curl axis corresponds to a curl angle of 37°. The curl angle is reported as 0, which in the case of coated web 30 would be 37°.

[0052] The amount of curl is determined by cutting a strip of sample from the web, along the major curl axis (for example line 306 in Fig. 3), which is designated as the minor curl strip. A second strip of sample is cut perpendicular to the major curl axis and is the major curl strip. Each strip is placed on a Kappa gauge as shown in Fig. 4. Kappa Gauge 490 comprises two posts 495 spaced w distance apart, wherein w is determined based on the length of the strip to be measured. Strip of sample 40 is centered on the Kappa gauge held between the two posts. The arc formed by strip of sample 40 is fitted to imaginary circle 480 with a radius r. This is done for both stripes. Kmajor is 1 / r for the tightest curl (i.e., smallest r), while K is 1 / r for the least curled sample (i.e., larger r).

[0053] The cross-web curvature (Kcross-web) is calculated using Equation 1The coated webs of the present disclosure should have a cross-web curvature of less than 10, 9, 8, 7, 6, or even 5 m'1with the ideal cross-web curvature being 0.

[0054] In some embodiments, the coated webs of the present disclosure may be further processed to make infrared (IR) metasurfaces. IR metasurfaces are planar devices composed of subwavelength structures (i.e., meta-atoms) and can steer the polarization, phase, and amplitude of electromagnetic waves at the wavelengths between 0.700 micrometers and 300 micrometers. Their ability to control the properties of electromagnetic waves, particularly polarization, in the longer IR wavelength region allows these materials to play an important role for various applications including optical sensing, thermal imaging, and free-space wireless communication.EXAMPLES

[0055] Unless otherwise noted, all parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, and all reagents used in the examples were obtained, or are available, from general chemical suppliers such as, for example, Sigma-Aldrich Company, Saint Louis, Missouri, or may be synthesized by conventional methods.

[0056] The following abbreviations are used in the Example Section: % = percent, °C = degrees Celsius, cc = cubic centimeter, ft = feet, g = gram, gsm = gram per square meter, in = inch, nm = nanometer, pm = micron = micrometer, mm = millimeter, min = minute, hr = hour, MHz = mega Hertz, rev = revolution, m = meter, mTorr = milli Torr, Pa = Pascal, sccm = standard cubic centimeters per minute, W = Watt, and kcps = kilocounts per second.Table 1. Materials ListAbbreviation DescriptionSiH4 / Ar mixture 5 mole% Silane in argon mixture gas (UHP compressed) obtained from Airgas, Roseville, MNPET film 1 heat-stabilized polyester (PET) film, 5 mil (0.127mm) thickness, singleside primed obtained under the trade designation MELINEX ST504 from DuPont Teijin Films, Chester, VAPET film 2 heat-stabilized polyester (PET) film, 7 mil (0.178 mm) thickness, singleside primed obtained under the trade designation MELINEX ST504 from DuPont Teijin Films, Chester, VA

[0057] Method to Coat Amorphous Silicon Layer

[0058] An amorphous silicon layer was deposited using a home-built parallel plate capacitively coupled plasma reactor chamber as described in U. S. Patent No. 6,696, 157 (David et al.). The reactor chamber has a central cylindrical powered electrode with a surface area of 1921.7 in2(1.24 m2). After placing the PET film substrate on the powered electrode, the reactor chamber was pumped down to a base pressure of less than 1.3 Pa (2 mTorr). The powered electrode was cooled at a temperature below 25°C during the deposition. A mixture of silane and argon was introduced into the chamber at the flow rates detailed below. Deposition was carried out using a plasma enhanced CVD method by coupling radio frequency power into the reactor at a frequency of 13.56 MHz with an applied power and deposition time(s) detailed below. The targeted thickness for the layer was reached by translating the film samples through the reaction zone at speeds detailed below. To achieve the desired thickness, the film samples may be passed through the reaction zone multiple times by reversing the direction of the rollers. After completing the deposition, the process gas flow, applied power, and film translation were stopped, and the reactor chamber was returned to atmospheric pressure. Additional information regarding materials and processesfor applying cylindrical plasma enhanced chemical vapor deposition (PECVD) and further details around this kind of reactor can be found in U. S. Patent No. 8,460,568 (David et al.).

[0059] Wavelength Dispersive X-ray Fluorescence (WDXRF) Method

[0060] Wavelength dispersive X-ray fluorescence measurements were collected with a Supermini200 WDXRF instrument from Rigaku Corporation (Woodlands, TX). Samples were measured in vacuum using the manufacturer-standard settings to measure the net intensity of the silicon k-alpha peak, reported as kcps (kilocounts per second).

[0061] Ellipsometry Method

[0062] Spectroscopic ellipsometry (SE) measurements were collected with a dual-rotating compensator ellipsometer (RC2 from J. A. Woollam Co., Lincoln, NE) at 790 wavelengths between 200-1000 nm. Measurements were collected in reflection at angles of 65, 70, 75 and 80°. The resulting data was analyzed or modeled in CompleteEase software available from J. A. Woollam Co. The substrates were modeled using a biaxial description (multiple B -spline functions) of PET as measured from a reference substrate (PET 1). The deposited coatings were modeled using oscillator models. Reported is the refractive index, n, at 1000 nm, the extinction coefficient, k, at 1000 nm, the thickness of the amorphous silicon layer determined by the software and whether or not a single layer (S) or multiple layers (M) were present, which was determined based on whether or not the data was able to be modeled as a single layer.

[0063] Scanning Electron Microscopy (SEM) Method

[0064] For cross-section analysis of the coated web, samples were freeze fractured with liquid nitrogen. The cross-sectioned sample was mounted on aluminum examination stubs and coated with AuPd by DC sputtering in a deposition system (Desk IV available from Denton Vacuum, Moorestown, NJ) to ensure conductivity. AuPd coated samples were examined with a microscope (S4700 Field Emission Scanning Electron Microscope available from Hitachi, Ltd., Tokyo, Japan). Where applicable, feature dimensions were measured in ImageJ using the reference scale bar generated by the microscope.

[0065] Curl Method (or curvature of sheets)

[0066] The curl angle was determined as described in the description above using a 3 in (7.6 cm) diameter circle. The amount of curl was measured on 150 mm by 15 mm strips cut along the major and minor curl axis with a Kappa Guage as described above with a distance w of 115.5 mm between posts to determine Kmajorand K minor. The cross-web curvature was calculated using Equation 1.

[0067] Examples 1-6 (Ex 1-6) and Comparative Examples 1-5 (CE 1-5)

[0068] An amorphous silicon layer was deposited as described in “Method to Coat an Amorphous Silicon Layer.” SiH4 / Ar mixture was introduced into the chamber at the designated gas flow rate and power density as shown in Table 2. The designated PET Film was passed through the reaction zone for the designated number of passes at 1 ft / min (30 cm / min). The chamber was configured with the inlet gas manifolds located close (less than 3 inches (76 mm) away) or distant (greater than 3 inches (76 mm) away) to the drum. For each sample, the WDXRF, Ellipsometry, and SEM methods were done. Shown in Table 2 below is the PET film used, number of passes through the reaction zone, the location of the gas manifold to the drum, the power density, and gas flow rates used for each sample. Also shown in Table 2is the corresponding Ellipsometry measurements, the calculated density, and deposition (dep) rate for the amorphous silicon layer. The calculated density for the amorphous silicon layer was determined by using the kcps results from WDXRF and dividing by the thickness of the amorphous silicon layer as determined by SEM. The deposition rate of the amorphous silicon was determined by dividing the thickness of the amorphous silicon layer as determined by SEM by the residence time, wherein the residence time was the number of passes through the reaction zone multiplied by the film length in the reaction zone and divided by the speed. The film length in the reaction zone was calculated as the length of the polymeric web contacting the chilled electrode (i.e., distance from roller 201 to 202 in Fig. 2).Table 2Sample PET No. of manifo Power Gas Ellipsometry Density Dep rate Film passes Id density flow n k Thickness layer (kcps / nm) (nm / min)(W / in2) (sccm) (nm)Ex 1 2 9 close 0.52 2000 3.38 < 0.001 648 S 0.105 12.02 Ex 2 2 9 close 0.52 3000 3.42 < 0.001 996 S 0.115 15.03 Ex 3 2 9 close 0.52 3500 3.34 < 0.001 1112 s 0.116 15.85 Ex 4 2 9 close 0.52 4000 3.33 < 0.001 1021 s 0.096 20.10 Ex 5 1 9 close 0.52 4000 3.38 < 0.001 1004 s 0.084 17.75 CE 1 2 9 close 1.04 4000 3.21 < 0.001 1525 s 0.085 28.04 Ex 6 1 10 distant 0.52 2000 3.38 < 0.001 1038 s 0.086 14.21 CE 2 1 6 distant 0.52 4000 No fit M 0.088 26.57 CE 3 1 4 distant 2.08 4000 No fit M 0.097 46.67 CE 4 1 6 distant 0.78 4000 No fit M 0.087 31.43 CE 5 1 10 distant 0.31 4000 No fit M 0.074 29.14

[0069] Each of the samples and an untreated PET Film 1 were tested for Curl. The values used to determine curl and the cross-web curvature are reported in Table 3.Table 3Sample K 0 Cross-web(m-1) (m-1) (degree) curvature (m-1)Ex 1 5.5 9 -60 8.1Ex 2 4 7 -80 6.9Ex 3 4.5 6.5 65 6.1Ex 4 7 7 55 7Ex 5 1 19 30 5.5CE 1 10 12 -30 10.5Ex 6 1 25 35 8.90CE 2 1 12.5 9 12.22CE 3 1 8.5 10 8.27CE 4 0.5 7 5 6.95CE 5 0.75 6 -85 -0.96PET Film 1 0.25 -6 -85 -5.95

[0070] Shown in Fig. 5 is the SEM image of Ex 1. Shown in Fig. 6 is the SEM image of CE 2. As shown in the images, Fig. 5 shows a smooth cross-sectional image of the amorphous silicon layer, while Fig. 6 shows a rougher looking cross-sectional image, consistent with multiple domains of amorphous silicon formed.

[0071] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes. To the extent that there is any conflict or discrepancy between this specification as written and the disclosure in any document mentioned or incorporated by reference herein, this specification as written will prevail.

Claims

What is claimed is:

1. A coated web comprisinga polymeric web having a first major surface and an opposing second major surface; and an amorphous silicon layer disposed on the first major surface,wherein the amorphous silicon layer comprises (a) a refractive index greater than 3.0 at 1000 nm; (b) an extinction coefficient of less than 0.01 at 1000 nm, and (c) a thickness of at least 500 nanometers, andwherein the coated web has a cross-web curvature of less than 10 m’1.

2. The coated web of claim 1, wherein the opposing second major surface is substantially free of amorphous silicon.

3. The coated web of any one of the previous claims, wherein the polymeric web comprises polyolefins (such as polyethylene, polypropylene, cyclic olefin copolymers, etc.), polyesters (such as polyethylene terephthalate (PET)), polystyrene, acrylonitrile butadiene styrene, polyvinyl chloride, polyvinylidene chloride, polycarbonate, polyacrylates, thermoplastic polyurethanes, polyvinyl acetate, polyamide, polyimide, poly(methylmethacrylate), polyethylene naphthalate, polystyrene acrylonitrile, triacetate cellulose, nylon, silicone-polyoxamide polymers, fluoropolymers, thermoplastic elastomers, or combinations thereof.

4. The coated web of any one of the previous claims, wherein the amorphous silicon layer comprises a dopant, hydrogen, or combinations thereof.

5. The coated web of any one of claims 1-3, wherein the amorphous silicon layer is substantially free of hydrogen, a dopant, or combinations thereof.

6. The coated web of any one of the previous claims, wherein the amorphous silicon layer comprises less than 0.5 wt% of oxygen and carbon.

7. The coated web of any one of the previous claims, wherein the amorphous silicon layer has a refractive index greater than 3.2 at 1000 nm.

8. The coated web of any one of the previous claims, wherein the amorphous silicon layer has an extinction coefficient of less than 0.001 at 1000 nm.

9. The coated web of any one of the previous claims, wherein the amorphous silicon layer has a thickness of at least 1 micrometer.

10. The coated web of any one of the previous claims, wherein the coated web has a cross-web curvature of less than 8 m’1.

11. The coated web of any one of the previous claims, wherein the amorphous silicon layer is discontinuous.

12. A method of making an amorphous silicon coated web, the method comprising:(a) providing a polymeric web and a vacuum chamber comprising a chilled electrode powered by radio-frequency and a counter electrode;(b) introducing a depositing a reactant gas into the vacuum chamber, wherein the reactant gas comprises a gas mixture of a silicon-containing gas and an inert carrier gas;(c) generating a plasma of the gas mixture between the chilled electrode and the counter electrode with the polymeric web therebetween, wherein a portion of the polymeric web is in intimate contact with the chilled electrode and the chilled electrode has a power density of no more than 1 W / in2; and(d) continuously depositing a reactive species formed in the plasma onto the polymeric web to form a layer of amorphous silicon on the polymeric web.

13. The method of claim 12, wherein the chilled electrode is held at a temperature of no higher than room temperature.

14. The method of claim 12, wherein the chilled electrode is held at a temperature of at most 30°C.

15. The method of any one of claims 12-14, wherein the reactant gas is substantially free of dihydrogen.

16. The method of any one of claims 12-15, wherein the silicon-containing gas is silane, disilane, trisilane, or combinations thereof.

17. The method of any one of claims 12-16, wherein the inert gas comprises argon.

18. The method of any one of claims 12-17, wherein the chilled electrode is a cylinder.

19. The method of any one of claims 12-18, wherein the polymeric web comprises a heat stabilized PET.

20. The method of any one of claims 12-19, wherein the layer of amorphous silicon is at least 500 nanometers thick.

21. The method of any one of claims 12-20, wherein the layer of amorphous silicon has a refractive index of at least 3.0 at 1000 nm.

22. The method of any one of claims 12-21, wherein the layer of amorphous silicon has an extinction coefficient of less than 0.01 at 1000 nm.

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