Surface modification by hydrogen peroxide plasma

Abstract

The technology described herein relates to surface modification with hydrogen peroxide plasma. In some embodiments, the method includes providing a mixture containing hydrogen peroxide vapor from a source, wherein the concentration of hydrogen peroxide vapor in the mixture is substantially stable over time. The method further includes forming a hydrogen peroxide plasma from the mixture and exposing a material to the hydrogen peroxide plasma in a chamber.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 488,579, filed March 6, 2023, entitled "Hydrogen Peroxide Plasma Surface Modification," which is incorporated herein by reference for all purposes. [Background technology]

[0002] Surface modification of materials to convert hydrophobic surfaces to hydrophilic surfaces is useful in a variety of technical applications and industries.

[0003] For example, semiconductor manufacturing processes may involve the use of silicon substrates that have had their native oxide removed (and the surface terminated with hydrogen atoms), resulting in relatively hydrophobic surfaces. Conventional methods for increasing the hydrophilicity of clean silicon surfaces involve oxidizing the silicon surface using an aqueous solution. For example, an aqueous solution of ammonium hydroxide and hydrogen peroxide has been used to convert a hydrophobic hydrofluoric acid (HF) cleaned silicon surface into a hydrophilic surface.

[0004] In another example, polymeric materials are used as materials for medical applications such as medical implants (e.g., artificial joints) and contact lenses. In some cases, the hydrophilic or hydrophobic characteristics of a polymeric material (e.g., ultra-high molecular weight polyethylene (UHMWPE)) affect biocompatibility. For example, both implant degradation or wear and contact lens comfort have been shown to be related to the affinity of the polymeric material's surface for water. Modifying hydrophobic surfaces to hydrophilic surfaces has also enabled the attachment of antibodies, ligands, or other target molecules to substrates (e.g., acrylic resins and ion exchange materials). Summary of the Invention [Problem to be solved by the invention]

[0005] Some polymers have been treated with plasmas formed using various gases such as Ar, O2, N2, NH3, N2 + H2, and CO2. For example, polystyrene materials have been exposed to argon or oxygen plasmas to functionalize the surface. Some studies have noted that in addition to modifying the surface, the plasma also changes the morphology of the polymer material, e.g., making the surface more rough.

[0006] Coatings have also been used to modify polymeric materials to reduce water and oxygen diffusion in food and electronic packaging applications. These surface modifications include sputtering, chemical vapor deposition, or atomic layer deposition of inorganic oxides such as Al2O3, Ti2O3, or ZnO2. In such cases, modifying hydrophobic polymer surfaces to hydrophilic surfaces has been shown to improve the formation of initiation and interfacial layers between the polymer and inorganic coatings, improving barrier properties and preventing delamination, blistering, or separation. [Means for solving the problem]

[0007] In some embodiments, the technology described herein relates to a method that includes providing a mixture comprising hydrogen peroxide vapor from a source, wherein the concentration of the hydrogen peroxide vapor in the mixture is substantially stable over time; forming a hydrogen peroxide plasma from the mixture; and exposing a material to the hydrogen peroxide plasma in a chamber. [Brief explanation of the drawings]

[0008] [Figure 1A] 1 shows a simplified schematic diagram of an example of a system 100 for generating a hydrogen peroxide plasma and exposing a substrate to the generated hydrogen peroxide plasma, according to some embodiments. [Figure 1B] Table 1 is provided and describes the experimental conditions used in Examples 1-11, including hydrogen peroxide plasma, water plasma, oxygen plasma, and thermal hydrogen peroxide treatments. [Figure 1C]Table 2 is provided and describes the experimental conditions used in Examples 1-11, including hydrogen peroxide plasma, water plasma, oxygen plasma, and thermal hydrogen peroxide treatments. [Figure 1D] Table 3 is presented and describes the experimental conditions used in Examples 12-15, including hydrogen peroxide plasma and oxygen plasma treatments. [Figure 1E] Table 4 is presented and describes the experimental conditions used in Examples 12-15, including hydrogen peroxide plasma and oxygen plasma treatments. [Figure 2] (A) and (B) show measurements of water contact angles (WCA) on silicon surfaces before and after pretreatment according to some embodiments. [Figure 3] 1A and 1B show static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. 1B shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 4] 1A and 1B show static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. 1B shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 5] 1A and 1B show static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. 1B shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 6] 1 shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 7] 1 shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 8] 1 shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 9] 1A and 1B show static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. 1B shows static WCA measurements of silicon surfaces for Examples 1-11, according to some embodiments. [Figure 10]1 shows spectra of the plasma used in Examples 1-9 obtained using optical emission spectroscopy, according to some embodiments. [Figure 11] (A) shows static WCA data for an HDPE substrate with different plasma treatments, according to some embodiments; (B) shows static WCA data for an HDPE substrate with different plasma treatments, according to some embodiments; and (C) shows static WCA data for an HDPE substrate with different plasma treatments, according to some embodiments. [Figure 12] (A) shows static WCA data for a PET substrate with different plasma treatments, according to some embodiments. (B) shows static WCA data for a PET substrate with different plasma treatments, according to some embodiments. (C) shows static WCA data for a PET substrate with different plasma treatments, according to some embodiments. [Figure 13] (A) shows static WCA data for a PVDF substrate with different plasma treatments, according to some embodiments; (B) shows static WCA data for a PVDF substrate with different plasma treatments, according to some embodiments; and (C) shows static WCA data for a PVDF substrate with different plasma treatments, according to some embodiments. [Figure 14] (A) shows static WCA data for a PTEE substrate with different plasma treatments, according to some embodiments. (B) shows static WCA data for a PTEE substrate with different plasma treatments, according to some embodiments. (C) shows static WCA data for a PTEE substrate with different plasma treatments, according to some embodiments. [Figure 15] 1 is a flowchart of a method for modifying the surface of a substrate using a hydrogen peroxide plasma, according to some embodiments. [Figure 16] 1 is a flowchart of a method for modifying the surface of a substrate using a hydrogen peroxide plasma, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present disclosure generally relates to surface modification of materials such as silicon (or other inorganic) substrates or polymeric materials with hydrogen peroxide plasma.

[0010] The systems and methods for hydrogen peroxide plasma surface modification of materials (e.g., silicon substrates or polymeric materials) described herein can include providing hydrogen peroxide from a hydrogen peroxide source to a plasma generating system (e.g., a remote plasma source). The hydrogen peroxide sources described herein can deliver controlled and consistent amounts of hydrogen peroxide vapor, with the concentration of hydrogen peroxide vapor in a carrier gas being substantially stable over time.

[0011] The material whose surface is modified by hydrogen peroxide plasma can be, for example, a substrate formed from silicon or a polymeric material (e.g., plastic, resin, high density polyethylene (HDPE), polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoropolymer, UHMWPE, polyetheretherketone (PEEK), or polyimide). Additional examples of materials whose surfaces can be made more hydrophilic using the systems and methods described herein include all types of silicon, dielectrics, metals (e.g., Ru, Cu, Co), oxides (e.g., SiO2, SiCO3), and the like. x , TiO x , TaO x , ZrO x , HfO x or HZO), or nitrides (e.g., TiN, SiN, GaN, InN, or AlN). In general, the material can be any material on which a layer of hydroxyl groups can be formed on the surface, for example, using a hydrogen peroxide plasma.

[0012] The carrier gas, or inert gas, used to initially form the hydrogen peroxide plasma can be a number of different species, such as a noble gas (e.g., argon, helium, neon, krypton, etc.), nitrogen, compressed dry air (CDA), or hydrogen. The hydrogen peroxide plasma can then be delivered to the chamber, whereupon the surface of the material or substrate can be modified by forming a layer of hydroxyl groups on the surface.

[0013] The systems and methods described herein can be used in a variety of applications where increasing the hydrophilicity of a surface or modifying the surface (e.g., with hydroxyl groups) is required. For example, semiconductor (e.g., Si) surfaces can be made more hydrophilic by exposure to hydrogen peroxide plasma, which can be beneficial in microelectronics processing. In another example, polymeric material surfaces can be modified using hydrogen peroxide plasma, which can be beneficial in biotechnology applications. Some examples of such biotechnology applications are the functionalization of surfaces (e.g., microplates) for use in clinical diagnostics, environmental monitoring, pharmaceutical research and development, materials for liquid chromatography, surface modification and priming for biocompatible implants, and many other areas of basic and applied biotechnology.

[0014] Hydrogen peroxide plasma can modify polymer surfaces from hydrophobic to hydrophilic (or from less hydrophilic to more hydrophilic). Increasing hydrophilicity through conventional treatment with plasma (e.g., composed of oxygen or nitrogen components) occurs through a chemical reaction between the polymer's native surface molecules and reactive ions of the plasma gas, adding functional groups to the polymer structure. As described herein, hydrogen peroxide plasma can modify the surface of a material such that the resulting surface hydrophilicity can be more hydrophilic than the surface after conventional plasma treatment. In some cases, hydroxyl functional groups can be added to the material surface from the hydrogen peroxide plasma, thereby increasing the hydrophilicity of the material surface.

[0015] In some embodiments, the material is exposed to a hydrogen peroxide plasma, where the hydrogen peroxide plasma is generated using hydrogen peroxide vapor delivered to a plasma source using a carrier gas (e.g., argon or other inert gas). In some embodiments, the carrier gas is substantially free of oxygen (e.g., containing less than 10%, 1%, 0.1%, 0.01%, or 0.001% by weight of oxygen). In some embodiments, the hydrogen peroxide vapor delivered to the plasma source is anhydrous or substantially anhydrous (e.g., containing less than 10%, 1%, 0.1%, 0.01%, or 0.001% by weight of water). In some embodiments, the hydrogen peroxide vapor delivered to the plasma source contains less than 60%, less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, less than 1%, less than 0.1%, less than 0.01%, or less than 0.001% water by weight, or between 1% and 60%, or between 1% and 20%, or between 0.001% and 1% water by weight.

[0016] The carrier gas used to deliver hydrogen peroxide to the plasma source can be a number of different species, such as a noble gas (e.g., argon, helium, neon, krypton, etc.), nitrogen, compressed dry air (CDA), or hydrogen. In some cases, using a carrier gas containing hydrogen can beneficially prevent the surface from oxidizing during exposure to the hydrogen peroxide plasma. Without being limited by theory, hydrogen is a reducing agent and can prevent oxidation of the material (e.g., substrate) while allowing a dense layer of hydroxyl groups to change the hydrophilicity of the material surface. In some cases, the carrier gas contains hydrogen and is substantially free of oxygen (as described above), for example, to form a layer of hydroxyl on the surface of the material from the hydrogen peroxide plasma without substantially oxidizing the surface.

[0017] The systems and methods for surface modification of materials (e.g., substrates) using hydrogen peroxide plasma described herein do not involve oxidizing the surface (or minimizing surface oxidation) to increase hydrophilicity, which is advantageous because some processes require a hydrophilic surface on an unoxidized (or minimally oxidized) material. A thick oxide layer on the material can degrade performance, requiring a hydroxylated surface to form a new film or maintain a hydrophilic surface in the material's operating environment.

[0018] The systems and methods for surface modification of materials (e.g., substrates) using hydrogen peroxide plasma described herein do not involve immersing the substrate in a liquid, which is advantageous because liquid processes may be more difficult to implement in some manufacturing environments than the plasma-based processes described herein. For example, if a material contains pores, vias, holes, and / or deep trenches, such features may have poor wetting properties or tend to trap gases, preventing the liquid from reaching the substrate or material interface.

[0019] In some embodiments, a method for increasing the hydrophilicity of a material includes (a) exposing the material (e.g., a silicon substrate or a polymeric material) to hydrogen peroxide plasma in a chamber; and (b) forming a hydroxyl layer on the surface of the material, wherein the hydroxyl layer increases the hydrophilicity of the material. The hydrogen peroxide plasma can be formed using a hydrogen peroxide source that provides a substantially stable concentration of hydrogen peroxide vapor over time (e.g., in a carrier gas). In some cases, this results in the formation of a dense layer of hydroxyl groups on the substrate surface. Without being limited by theory, some surfaces can be made more hydrophilic by converting H or O bonds between exposed atoms at the surface to hydroxyl bonds. For example, in the case of H-terminated silicon, surface H or O bonds can be converted to hydroxyl bonds to form silanol groups. As the OH / H ratio increases (within a limited range), the silicon surface becomes more hydrophilic.

[0020] In some embodiments, an inert gas plasma is formed (e.g., using argon, helium, neon, krypton, or nitrogen), and then hydrogen peroxide vapor is added to form a hydrogen peroxide plasma. The hydrogen peroxide vapor can be mixed with a carrier gas before being added to the plasma, and the concentration of the hydrogen peroxide vapor from the source can be substantially stable over time. The inert gas and hydrogen peroxide plasma can be formed in a remote plasma source and then transferred to a chamber containing the material (or substrate, or layered structure). The hydrogen peroxide plasma can modify the surface of the material or substrate by forming a layer of hydroxyl groups on the surface of the material. In some cases, multiple surfaces of a material can be modified (e.g., made more hydrophilic) by forming a layer of hydroxyl groups on each surface. For example, the hydrogen peroxide plasma can modify the surface(s) (e.g., make them more hydrophilic) by forming a layer of hydroxyl groups on a rough surface and / or on surfaces containing holes, depressions, and / or other surface features (e.g., variations or perforations). In some cases, a material (or substrate) has a front surface and a back surface, and both the front surface and the back surface of the material (or substrate) can be modified using hydrogen peroxide plasma. In some cases, a layer of hydroxyl groups can be formed on all exposed surfaces of the material or substrate (e.g., including holes, depressions, and other surface penetrations), thereby modifying all exposed surfaces of the material or substrate (e.g., making them more hydrophilic). Thus, the methods described herein can be used to make exposed surfaces of materials more hydrophilic, even when the exposed surfaces include rough surfaces, depressions, and / or holes.

[0021] FIG. 1A shows a simplified schematic diagram of an example of a system 100 for generating a hydrogen peroxide plasma and exposing a substrate to the generated hydrogen peroxide plasma. The system 100 includes a chamber 110, a material 120 (e.g., a substrate or a polymeric material) contained within the chamber 110, an inlet 130 to the chamber 110 for supplying the hydrogen peroxide plasma to the chamber 110, and an outlet 140 from the chamber 110 for removing material from the chamber 110. Some examples of the chamber 110 are a vacuum chamber, an atomic layer deposition reactor chamber, an etching or selective etching reactor chamber, an ashing chamber, a chemical vapor deposition chamber, a surface cleaning reactor chamber, a passivation chamber, and a photolithography process chamber. An optional heater 170 can be used to control the temperature of the material 120 (e.g., a bulk material, a substrate, a layer structure, etc.). A carrier gas (e.g., argon or other inert gas) can flow through hydrogen peroxide source 150 to provide a source of hydrogen peroxide (e.g., gaseous hydrogen peroxide, hydrogen peroxide vapor, substantially anhydrous hydrogen peroxide, or a mixed gas stream containing hydrogen peroxide) to remote plasma source 160. The plasma generated in remote plasma source 160 can then be provided to chamber 110 through inlet 130. Excess carrier gas and other byproducts from the plasma and / or material 120 can be removed from chamber 110 using outlet 140. Hydrogen peroxide source 150 and remote plasma source 160 can provide a controlled hydrogen peroxide plasma to material 120 in chamber 110 for a controlled duration and, optionally, at a controlled temperature. For example, hydrogen peroxide source 150 can provide hydrogen peroxide vapor to remote plasma source 160 at a concentration that is substantially stable over time. System 100 can be used to perform the hydrogen peroxide plasma surface modification methods described herein (eg, methods 1500 and 1600 of FIGS. 15 and 16).

[0022] In some cases, hydrogen peroxide source 150 is coupled to remote plasma source 160 via conduit 180a to provide a substantially stable concentration of hydrogen peroxide vapor to remote plasma source 160, and remote plasma source 160 is coupled to inlet 130 via conduit 180b to provide hydrogen peroxide plasma to chamber 110. In some cases, hydrogen peroxide gas can be delivered from an ampoule (or other container or vessel) within hydrogen peroxide source 150. In some cases, conduits 180a and 180b include appropriate valving and gas controls (not shown). For example, a vacuum pump (not shown) can be coupled to chamber 110 to enable a low-pressure (or vacuum) environment within chamber 110, and remote plasma source 160 (and conduit 180b) can also be maintained at low pressure (or vacuum). In such cases, valves and gas controls coupled to conduits 180a and 180b can be used to control pressure in the components of system 100. Without being limited by theory, hydrogen peroxide plasma may have a short lifetime at pressures of about 1 atmosphere, and therefore a low pressure environment within the remote plasma source, conduit 180b, and chamber 110 may be advantageous.

[0023] In some cases, the remote plasma source 160 can be near or integrated with the chamber 110. For example, the conduit 180b can be short (e.g., less than 10 cm, or less than 1 cm) and the inlet 130 can be near the remote plasma source 160. In some embodiments of the system 100, the conduit 180b can be omitted and the inlet 130 can directly couple the remote plasma source 160 to the chamber 110.

[0024] The hydrogen peroxide source 150 can be filled with high-quality hydrogen peroxide for delivery to the chamber 110. In some cases, the hydrogen peroxide in the hydrogen peroxide source 150 is anhydrous or substantially anhydrous. In practice, it is difficult to remove all of the water from hydrogen peroxide, and in some cases, substantially anhydrous hydrogen peroxide contains less than 60%, 50%, 40%, 30%, 20%, 10%, 1%, 0.1%, 0.01%, or 0.001% water by weight. The mixture of hydrogen peroxide vapor and carrier gas can contain less than 10%, or less than 1%, or less than 1000 ppm, or less than 100 ppm oxygen by weight. In some cases, the hydrogen peroxide source 150 can be filled with a mixed gas and / or vapor that can contain hydrogen peroxide and other species, such as water. In some cases, the hydrogen peroxide in hydrogen peroxide source 150 is mixed with water, and the amount of water in the mixture (or gas mixture) is between 10 ppm and 99%, or between 100 ppm and 75%, or between 100 ppm and 35%, or between 10 ppm and 1%, or between 1% and 99%, or between 30% and 99%, or between 30% and 75%, or less than 10%, less than 2%, less than 0.5%, less than 1000 ppm, less than 100 ppm, or less than 10 ppm by weight. In some cases, the mixture discharged from hydrogen peroxide source 150 may comprise primarily hydrogen peroxide vapor. For example, the mixture discharged from hydrogen peroxide source 150 may comprise hydrogen peroxide vapor and low concentrations (e.g., less than 10%, less than 1%, or less than 0.1%) of water and / or oxygen. In another example, the mixture discharged from hydrogen peroxide source 150 can contain hydrogen peroxide vapor and other components (e.g., water, or a carrier gas) at higher concentrations (e.g., up to 60% or even higher for a mixture of hydrogen peroxide vapor and a carrier gas).

[0025] The ability to deliver a controlled and consistent concentration of hydrogen peroxide vapor to form a hydrogen peroxide plasma is challenging. Additionally, it is difficult to inject a liquid (e.g., in the form of a mist or droplets) into the plasma chamber to generate the plasma. Systems and methods for delivering hydrogen peroxide, particularly systems and methods capable of delivering controlled and consistent concentrations of hydrogen peroxide vapor to form the hydrogen peroxide plasma described herein, are further described in U.S. Pat. Nos. 8,282,708, 9,410,191, 9,545,585, 9,610,550, 10,363,497, and 11,634,816, U.S. Patent Publication Nos. US20200291517A1 and US20200393086A1, U.S. Application No. US18 / 472,551, and International Publication Nos. WO2016 / 164380 and WO2017 / 027581, each of which is incorporated by reference herein in its entirety. Such systems and methods for delivering hydrogen peroxide can be used in the systems and methods described herein, for example, in hydrogen peroxide source 150 in Figure 1A. Several examples of systems and methods for delivering hydrogen peroxide are described herein.

[0026] In some embodiments, the systems and methods described herein include a hydrogen peroxide source configured to provide and maintain a concentration of hydrogen peroxide vapor in a gas mixture that is substantially stable over time (or maintained at a substantially constant or relatively constant value over time). The concentration (or volume fraction) of hydrogen peroxide vapor in a gas mixture can be substantially stable, for example, if the concentration is maintained within 5%, 3%, or 1% of the average value over one hour of delivery time of the gas mixture. The concentration (or volume) of hydrogen peroxide vapor in a gas mixture can be substantially stable, for example, if the concentration has a standard deviation of up to 5%, 3%, or 1% per hour.

[0027] 1A can be configured to provide a substantially stable (or substantially constant) concentration of hydrogen peroxide vapor in a gas mixture over time (e.g., about 1 hour) via the use of a carrier gas or through the use of a vacuum to draw hydrogen peroxide vapor directly from hydrogen peroxide source 150. In some cases, the hydrogen peroxide vapor concentration in the gas mixture is substantially stable over time at a hydrogen peroxide concentration of between 500 parts per million by volume (ppmv) and 4000 ppmv, or between 100 ppmv and 100,000 ppmv, or at ratios greater than 0.1% by volume, greater than 1% by volume, or greater than 2.5% by volume, greater than 10% by volume, 0.1% to 10%, or 0.1% to 2.5%, 1% to 10%, 1% to 2.5%, or 2.5% to 10%, or greater than 1% to 10%.

[0028] In the systems and methods described herein, the hydrogen peroxide source (e.g., hydrogen peroxide source 150 in FIG. 1A) used to deliver hydrogen peroxide vapor to the plasma chamber (or other system component, e.g., a storage container) can utilize a carrier gas to supply hydrogen peroxide vapor from the source to the plasma chamber, or can use a vacuum to draw hydrogen peroxide vapor directly from the hydrogen peroxide source. In some embodiments, the hydrogen peroxide source can include a pre-loaded carrier gas in fluid contact with the vapor phase of a multi-component liquid source (e.g., aqueous hydrogen peroxide solution) and / or a non-aqueous (or anhydrous) hydrogen peroxide solution having a vapor phase separated from the hydrogen peroxide solution by a membrane.

[0029] The hydrogen peroxide sources described herein are uniquely capable of providing controlled concentrations of hydrogen peroxide vapor that are substantially stable over time. According to Raoult's Law, when the vapor phase of a liquid solution is continuously swept by a carrier gas, the more volatile components evaporate faster than the less volatile components, resulting in a dynamic (or changing) concentration of the components in the liquid solution, and similarly, a dynamic (or changing) concentration of the components in the vapor generated from the liquid solution. As the evaporation of more volatile components continues, the solution becomes more concentrated with less volatile components, which in some cases (e.g., aqueous hydrogen peroxide solutions) may require a stable solution or convert it into a highly concentrated hazardous substance. The hydrogen peroxide sources of the systems and methods described herein overcome such limitations and are configured to deliver a stable concentration of hydrogen peroxide vapor over time, for example, by using a pre-loaded carrier gas in fluid contact with the vapor phase of a multi-component liquid source and / or by using a non-aqueous (or anhydrous) hydrogen peroxide solution with a vapor phase separated from the hydrogen peroxide solution by a membrane.

[0030] In some embodiments, the hydrogen peroxide source of the systems and methods described herein can include: (a) a multi-component liquid source (e.g., containing aqueous hydrogen peroxide or a solution containing hydrogen peroxide and a solvent) having a vapor phase separated from the liquid source, optionally by a membrane; (b) a pre-filled carrier gas source in fluid contact with the vapor phase, the pre-filled carrier gas comprising the carrier gas and at least one component of the liquid source; and (c) a device for delivering a gas stream containing at least one component of the liquid source. The membrane can be permeable to hydrogen peroxide, particularly a substantially gas-impermeable membrane, e.g., a perfluorinated ion-exchange membrane such as a NAFION® membrane. In some embodiments, the device delivering the process gas-containing gas stream is an outlet of the headspace containing the vapor phase and is connected directly or indirectly to the plasma chamber, allowing the process gas-containing gas stream to flow from the headspace to the plasma chamber. Methods for delivering hydrogen peroxide from such sources include adjusting operating conditions, such as the temperature and pressure of the pre-charged carrier gas, the flow rate of the carrier gas, the concentration of the liquid source, and the temperature and pressure of the liquid source, so that hydrogen peroxide can be accurately and safely delivered as a process gas.

[0031] In some embodiments, the hydrogen peroxide source of the systems and methods described herein can include: (a) a hydrogen peroxide source and a gas phase provided by the hydrogen peroxide source, wherein the hydrogen peroxide source contains hydrogen peroxide at an initial concentration and the gas phase contains hydrogen peroxide and water; (b) a carrier gas in fluid contact with the gas phase, thereby forming a hydrogen peroxide gas stream, whereby the formation of the hydrogen peroxide gas stream increases the concentration of hydrogen peroxide in the hydrogen peroxide source to a second concentration higher than the initial concentration; (c) a fill tube that replenishes the hydrogen peroxide source with an aqueous hydrogen peroxide solution containing hydrogen peroxide at a third concentration lower than the second concentration; and (d) a device that delivers the hydrogen peroxide gas stream to the material to be modified, wherein the delivered hydrogen peroxide gas stream contains a substantially stable steady-state concentration of hydrogen peroxide. For example, maintaining the hydrogen peroxide vapor concentration in the gas mixture within 3% of the mean value or with a standard deviation of up to 5% over a one-hour period would be considered substantially stable (or relatively constant).

[0032] In some embodiments, the hydrogen peroxide source of the systems and methods described herein can include (a) a non-aqueous (or anhydrous) hydrogen peroxide solution having a vapor phase separated from the hydrogen peroxide solution by a membrane; (b) a carrier gas or vacuum in fluid contact with the vapor phase; and (c) a device for delivering a gas stream containing hydrogen peroxide from the source to the plasma chamber (or other system component, e.g., a storage vessel). The membrane can be, for example, a perfluorinated ion-exchange membrane such as a NAFION™ membrane. In some embodiments, the device delivering the hydrogen peroxide-containing gas stream is an outlet of the headspace containing the vapor phase and is connected directly or indirectly to the plasma chamber, allowing the hydrogen peroxide-containing gas stream to flow from the headspace to the plasma chamber. By adjusting the operating conditions of the systems and devices, e.g., the temperature and pressure of the carrier gas or vacuum, the concentration of the hydrogen peroxide solution, and the temperature and pressure of the hydrogen peroxide solution, hydrogen peroxide vapor can be delivered precisely and safely in the gas mixture. In some embodiments, the amount of hydrogen peroxide in the vapor phase delivered to the plasma chamber can be controlled by applying energy, such as thermal energy, rotational energy, or ultrasonic energy, to the hydrogen peroxide solution. In some cases, a method of operating such a hydrogen peroxide source can include: (a) providing a non-aqueous hydrogen peroxide solution having a vapor phase separated from the hydrogen peroxide solution by a membrane; (b) contacting a carrier gas or vacuum with the vapor phase; and (c) delivering a gas stream containing substantially anhydrous hydrogen peroxide to the plasma chamber.

[0033] The multi-component solutions and / or non-aqueous hydrogen peroxide solutions of the above-described sources can be, for example, non-aqueous solutions containing alcohols, polyalcohols, phenols, lactones, amides, esters, polyesters, ethers, carboxylic acids, polycarboxylic acids, sulfonic acids, sulfinic acids, phosphonic acids, phosphinic acids, organic solvents, inorganic solvents, aromatic compounds, polyaromatic compounds; heterocyclic compounds including polyheterocyclic compounds, fluorinated ethers, fluorinated alcohols, fluorinated sulfonic acids, fluorinated carboxylic acids, polycarboxylic acids, fluorinated phosphonic acids, deep eutectic solvents, such as those described in U.S. Pat. No. 3,557,009, incorporated herein by reference, and combinations thereof that do not contain substantial amounts of water. Examples of solvents for such multi-component solutions and / or non-aqueous hydrogen peroxide solutions include diethyl phthalate, propylene carbonate, triethyl phosphate, polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetate-polyvinylpyrrolidone copolymer, mellitic acid, benzenehexol, tetrahydrobenzoquinone, 1,8-octanediol, 2,6-dichlorophenol, acridine, 8-hydroxyquinoline, benzilic acid, 1,4-dioxane, amyl acetate, DMF, DMSO, dimethylacetamide, 2-ethyl-1-hexanol, furfuryl alcohol, 2-octanol, 2-methyl-2-heptanol, and combinations thereof.

[0034] In some embodiments, the hydrogen peroxide source of the systems and methods described herein can include a storage device for a process solution containing hydrogen peroxide. The storage device can include: a housing having a wick disposed therein; a process solution contained within the housing and in fluid contact with the wick such that the solution is adsorbed onto the wick, thereby diluting the solution in the wick; and a headspace contained within the housing and separated from the process solution by the wick. The process solution contains hydrogen peroxide and, optionally, one or more other components (e.g., water, a solvent, or any of the liquids described herein). In some cases, the process solution contains anhydrous hydrogen peroxide. In various embodiments, the housing is configured to allow a carrier gas to flow through the headspace or to convey a vacuum through the headspace to generate a gas stream containing the vapor phase of the process solution and deliver the gas stream to the plasma chamber (or other system component, e.g., a storage vessel). In some embodiments, the amount of process solution in the apparatus is between about 30% and 1900% by weight of the process solution / core composite, or between about 30% and 800% by weight of the process solution / core composite, or between about 30% and 100% by weight of the process solution / core composite.

[0035] In some embodiments, the core material of the above-described devices is 100 to 1000 mm 2 / g。 In various embodiments, the core is configured to adsorb more than 42% by weight (or "w / w") hydrogen peroxide, or more than 50% w / w hydrogen peroxide, or more than 100% w / w, or more than 200% w / w, or more than 800% w / w, or more than 1000% w / w, or more than 1900% w / w hydrogen peroxide. In some embodiments, the concentration of the hydrogen peroxide solution is less than 30% w / w. In some embodiments, the concentration of the hydrogen peroxide solution is stable over time, for example, for a period of about 1 hour or more, or 100 hours or more. In some embodiments, the concentration of hydrogen peroxide vapor emitted from the device is stable over time, for example, for about 1 hour.

[0036] In some embodiments, the core material is formed as a fabric, a powder, one or more bricks, one or more blocks, one or more beads, one or more particles, one or more extrudates, or one or more pellets. In some embodiments, the core material is a nonwoven fabric that has been treated with a mechanical finishing process such as spunbonding, needlebonding, perforated bonding, carding, and any combination thereof. In some embodiments, the nonwoven fabric is a polytetrafluoroethylene (PTFE) fabric. In some embodiments, the core material is formed as a mesh. In some embodiments, the core material is selected from the group consisting of alumina, aluminum oxide, titanium dioxide, silica, silicon dioxide, quartz, activated carbon, carbon molecular sieves, carbon pyrolyzate, polytetrafluoroethylene (PTFE), polyester (PE), polyethylene terephthalate (PET), polyethylene / polyethylene terephthalate copolymer, polypropylene (PP), rayon, zirconium oxide, zeolite, high silica zeolite, polymethylpentene (PMP), polybutylene terephthalate (PBT), polyethylene / polypropylene copolymer, hydrophilic high density polyethylene (HDPE), hydrophobic high density polyethylene (HDPE). The mesh substrate may be formed from materials such as polyethylene (HDPE), hydrophilic UHMW polyethylene, hydrophobic UHMW polyethylene, perfluoroalkoxyalkane (PFA), polyvinylidene fluoride (PVF), silk, Tencel, sponge materials, polyethylene glycol (PEG), polyvinyl alcohol (PVA), and / or polyvinylpyrrolidone (PVP), polypyridine, polyacrylate, polyacrylic acid, polyacrylic acid / acrylate copolymer, polycarbonate, polyacrylamide, polyacrylate / acrylamide copolymer polymer, cellulosic material, and any combination thereof. In some embodiments, the mesh substrate is spirally wound within the housing.

[0037] In some embodiments, the storage device includes a separator disposed adjacent to the mesh, wherein the separator is configured to support and separate the layers of spiral mesh. In certain embodiments, the separator is formed from PTFE.

[0038] In some embodiments, the core material is a hydrogel selected from the group consisting of polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polypyridine, and any combination thereof. In various embodiments, the hydrogel is a 20% PEG hydrogel or a 40% PEG hydrogel. In some embodiments, the hydrogel may be encased in a PTFE mesh and / or may further include a separator disposed adjacent to the mesh.

[0039] In some embodiments, a method for delivering hydrogen peroxide vapor using a hydrogen peroxide source described herein includes contacting a process solution containing hydrogen peroxide with a wick in a closed enclosure such that the solution is adsorbed onto the wick, thereby diluting the process solution within the wick; exposing the wick to a carrier gas or vacuum, thereby forming a gas stream containing a vapor phase of the process solution; and delivering the gas stream to a plasma chamber (or other component of the system). The enclosure may be configured to allow a carrier gas to flow through a headspace contained within the enclosure or to allow a vacuum to be drawn through the headspace, and the headspace may be separated from the process solution by the wick.

[0040] In some embodiments, the hydrogen peroxide vapor delivery system includes a process solution provided within a housing, where the process solution contacts a wick disposed within the housing such that the solution is adsorbed onto the wick, thereby diluting the process solution within the wick. The chemical supply system may also include a carrier gas or vacuum in fluid contact with the gas phase within the headspace of the process solution, thereby forming a mobile gas stream within the headspace. The chemical delivery system may further include a device in fluid communication with the housing and used to deliver the gas stream to the plasma chamber (or other components of the system). In some embodiments, the housing allows a carrier gas to flow through the headspace contained within the housing, or allows a vacuum to be drawn through the headspace.

[0041] The hydrogen peroxide sources of the methods and systems described herein, including process solutions and wicks, may further include the use of various components to contain and control the flow of gases and liquids used therein. For example, the methods and systems may include one or more mass flow controllers, valves, check valves, filters, pressure gauges, gas sensors, regulators, tachometers, and pumps. The methods and systems provided herein may also include various heaters, thermocouples, and temperature controllers to control the temperatures of various system components and method steps.

[0042] In some embodiments, the systems and methods described herein include a hydrogen peroxide source (such as those described above) configured to provide and maintain a molar ratio of water to hydrogen peroxide that is substantially stable over time (or maintained at a substantially constant or relatively constant value over time). A substantially stable molar ratio of water to hydrogen peroxide in a gas mixture over time can be, for example, if the molar ratio (or the concentration of hydrogen peroxide to the concentration of water) is maintained within 1%, 3%, or 5% of the mean value over one hour of delivery of the gas mixture. A substantially stable molar ratio of water to hydrogen peroxide in a gas mixture over time can be, for example, if the molar ratio has a standard deviation of 1%, 3%, or up to 5% over one hour. For example, the hydrogen peroxide source 150 in FIG. 1A can be configured to provide a substantially constant concentration of hydrogen peroxide vapor and water in the gas mixture by using a carrier gas or by using a vacuum to draw hydrogen peroxide vapor directly from the hydrogen peroxide source 150. The concentrations of hydrogen peroxide vapor and water can be any of those described herein.

[0043] Conditions within the chamber 110 during exposure of the material 120 (e.g., a substrate or a polymeric material) to the hydrogen peroxide plasma can affect the degree to which the surface of the material (e.g., a bulk material, a substrate, or a layered structure) becomes hydrophilic. In some cases, the pressure within the chamber can be between 1 mTorr and 1000 Torr, between 0.1 Torr and 10 Torr, or about 0.5 Torr, or about 5 Torr. The flow rate of gas into the remote plasma source 160 (or the flow rate of gas into the chamber 110, or the flow rate of carrier gas through the hydrogen peroxide source 150) can be between 10 sccm and 200 Lpm, or between 10 sccm and 10 Lpm, or between 10 sccm and 1 Lpm, or between 500 sccm and 5000 sccm. The flow rate of the gas (e.g., hydrogen peroxide vapor) can be substantially stable over time, and the variation in flow rate over time can also be small (e.g., with a standard deviation of up to 5%, or up to 3%, or up to 1% over the process time). The process time, or duration of exposure of material 120, can be from 1 minute to 10 minutes, or from 10 seconds to 100 minutes. The temperature of material 120 can be from 20°C to 300°C, or from 100°C to 300°C, or from 150°C to 200°C, or from 20°C to 150°C, depending in part on the melting point or glass transition temperature of material 120.

[0044] System 100 or a similar system can be used in any of the methods or processes described herein. For example, water plasma can be generated using remote plasma source 160 instead of hydrogen peroxide plasma. In such cases, hydrogen peroxide source 150 can be replaced with a water source. In another example, oxygen plasma can be generated using remote plasma source 160 instead of hydrogen peroxide plasma. In such cases, hydrogen peroxide source 150 can be omitted, and oxygen gas can be provided directly to remote plasma source 160. In another example, material 120 can be exposed to a thermal hydrogen peroxide treatment instead of hydrogen peroxide plasma. In such cases, remote plasma source 160 can be omitted, and hydrogen peroxide vapor can be provided directly to chamber 110 from hydrogen peroxide source 150. [Example]

[0045] Hydrogen peroxide plasma was used to treat several types of materials, including semiconductor substrates and polymeric materials, and the results were compared with other types of treatments. Figures 1B and 1C show Tables 1 and 2, respectively, which describe the experimental conditions used in Examples 1-11, including hydrogen peroxide plasma, water plasma, oxygen plasma, and thermal hydrogen peroxide treatments. Figures 1D and 1E show Tables 3 and 4, respectively, which describe the experimental conditions used in Examples 12-15, including hydrogen peroxide plasma and oxygen plasma treatments.

[0046] Table 1 shows examples of hydrogen peroxide plasma generation using a system similar to that shown in Figure 1A. The method for Tests A-D involved generating an argon plasma with an initial flow of argon (500 sccm flow rate). Subsequently, a carrier gas listed in Table 1 was passed through a hydrogen peroxide source (e.g., hydrogen peroxide source 150 in Figure 1A) to introduce a substantially stable concentration of hydrogen peroxide vapor and carrier gas into the plasma. The final pressure of the hydrogen peroxide plasma with carrier gas was approximately 5 Torr for all conditions in Table 1. The hydrogen peroxide used in Tests A-D was substantially anhydrous, as described herein. Tests A and B resulted in stable hydrogen peroxide ignition, while Tests C and D did not. The total carrier gas flow rate was held constant at 5000 sccm for these tests. These tests demonstrate that stable hydrogen peroxide plasma can be generated using argon carrier gas and that some oxygen can be added to the argon carrier gas. However, oxygen carrier gas, or argon and oxygen mixtures with too much oxygen, did not produce stable plasma in Tests C and D.

[0047] Table 2 shows the experimental conditions for Examples 1-11, in which hydrogen peroxide plasma, water plasma, oxygen plasma, or thermal hydrogen peroxide treatment was used to modify the surface of the material, which in these examples was a silicon substrate. Examples 1-8 used hydrogen peroxide plasma (Examples 1-5) or water plasma (Examples 6-8) with different carrier gases to modify the silicon surface using a system similar to that shown in FIG. 1A with a hydrogen peroxide source 150. Example 9 used oxygen plasma using a system similar to that shown in FIG. 1A (with the hydrogen peroxide source 150 omitted). Examples 10-11 used thermal hydrogen peroxide treatment to modify the silicon surface, in which a system similar to that shown in FIG. 1A (with the exception of the remote plasma source 160) was used to expose the silicon substrate to hydrogen peroxide vapor (not hydrogen peroxide plasma) at an elevated temperature. The temperatures of the silicon substrates in Examples 1-11 are shown in Table 2, and the duration of exposure to treatment was 5 minutes in each of these examples.

[0048] The extent of surface modification of the silicon substrates of Examples 1-11 was evaluated using static water contact angle (WCA) measurements. In static WCA measurements, a larger contact angle indicates a more hydrophobic surface, while a smaller contact angle indicates a more hydrophilic surface. For example, Figures 2A and 2B show static WCA measurements of silicon surfaces before and after pretreatment, and the contact angle of a water droplet on the surface is shown in Figure 2B. Additionally, Figures 3A-3B, 4A-4B, 5A-5B, 6-8, and 9A-9B show static WCA measurements of the silicon surfaces of Examples 1-11, as well as some static WCA measurements (after exposure to hydrogen peroxide plasma or thermal treatment, i.e., "resulting contact angles"). All contact angle measurements and contact angles described herein are "static water contact angle (WCA) measurements" and "static water contact angles (WCA)," and they may also be referred to as "WCA measurements," "contact angle measurements," or "contact angles." All contact angle measurements described herein refer to static contact angle measurements.

[0049] In Examples 1-11, the silicon surface was pretreated to substantially remove the native oxide layer before the silicon substrate was exposed to the processing conditions (e.g., hydrogen peroxide plasma or hydrogen peroxide vapor) described in Examples 1-11. The pretreatment involved immersing the silicon substrate in a buffered HF etchant for 30 seconds. Figure 2A shows the WCA measurement before immersion, and Figure 2B shows the WCA measurement after native oxide removal. Before pretreatment, the silicon surface was relatively hydrophilic due to the presence of native oxide, as indicated by the small WCA measured in Figure 2A. After pretreatment, the contact angle was near 90° (approximately 85° in the example shown in Figure 2B), indicating a substantially hydrophobic surface for the unprocessed silicon without significant native oxide (e.g., a substantially hydrogen-terminated surface). All processing conditions in Examples 1-11 were performed on silicon substrates that had undergone a pretreatment similar to that shown in Figure 2B, so the contact angles obtained in the examples can be compared to the initial (or control) contact angles shown in Figure 2B.

[0050] 3A and 3B show WCA measurements for Examples 1 and 2, in which silicon substrate surfaces were modified using hydrogen peroxide plasma with argon carrier gas at substrate temperatures of 150°C and 200°C, respectively. In both of these examples, the contact angles of the silicon substrates were small, as evidenced by the relatively flat water film across the substrate surface, indicating that the hydrogen peroxide plasma with argon carrier gas in these examples effectively modified the silicon substrate surface, rendering it substantially hydrophilic. The contact angle of the silicon substrate after exposure to hydrogen peroxide plasma in Example 2 (at a substrate temperature of 200°C) was approximately 4.0°, which was significantly more hydrophilic than the unprocessed silicon substrate (which was substantially hydrophobic, with a contact angle of approximately 85°, as shown in FIG. 2B).

[0051] Figures 4A and 4B show WCA measurements for Examples 6 and 7, in which silicon substrate surfaces were modified using water plasma with argon carrier gas at substrate temperatures of 150°C and 200°C, respectively. The contact angles of the silicon substrates in both of these examples were relatively small, indicating that the water with argon carrier gas in these examples also modified the silicon substrate surface to be more hydrophilic than the unprocessed silicon substrate. However, the contact angles of Examples 6 and 7, which used water plasma, were larger than the contact angles of the substrates in Examples 1 and 2, which used hydrogen peroxide plasma. The contact angle of the silicon substrate in Example 7 after exposure to water (substrate temperature of 200°C) was approximately 6.5°, which was larger than the contact angle of the silicon substrate in Example 4 (substrate temperature of 200°C), which was approximately 4.0°. Although the contact angle of the silicon substrate after exposure to water in Example 7 was significantly more hydrophilic than the unprocessed silicon substrate (which was essentially hydrophobic, with a contact angle of approximately 85°, as shown in FIG. 2B), the water plasma still did not perform as well as the hydrogen peroxide plasma, which is consistent with the higher concentration of hydroxide species in the hydrogen peroxide plasma than in the water plasma (e.g., as shown in the spectra in FIG. 10 and described in more detail below).

[0052] 5A and 5B show WCA measurements for Examples 5 and 4, in which silicon substrate surfaces were modified using a hydrogen peroxide plasma with a mixed argon and oxygen carrier gas at a substrate temperature of 200°C. Example 5 used a carrier gas containing 270 sccm of oxygen mixed with argon, while Example 4 used a carrier gas containing 1000 sccm of oxygen mixed with argon. Although the contact angles obtained in Examples 4 and 5 were significantly lower than those of the pretreated silicon substrate (which was essentially hydrophobic, having a contact angle of approximately 85°, as shown in FIG. 2B), adding oxygen to the hydrogen peroxide plasma resulted in less hydrophilic silicon substrates compared to Examples 1 and 2. These examples demonstrate that the contact angle increases as more oxygen is added to the carrier gas, and that the presence of oxygen in the hydrogen peroxide plasma results in a less hydrophilic surface compared to the similar Example 2, which used an oxygen-free argon carrier gas.

[0053] Figure 6 shows WCA measurements for Example 3, in which a silicon substrate surface was modified using a hydrogen peroxide plasma with a carrier gas mixture of argon and oxygen at a substrate temperature of 150°C. Example 3 used a carrier gas containing 1000 sccm of oxygen mixed with argon. Similar to Examples 4 and 5, this example showed that the addition of oxygen to the carrier gas increased the contact angle, and that the presence of oxygen in the hydrogen peroxide plasma reduced the surface hydrophilicity, even at temperatures as low as 150°C, compared to conditions using an oxygen-free argon carrier gas.

[0054] FIG. 7 shows the WCA measurements for Example 8. In this measurement, a silicon substrate surface was modified using water plasma with a carrier gas mixture of argon and oxygen at a substrate temperature of 200°C. Example 8 used a carrier gas containing 340 sccm of oxygen mixed with argon. Although the contact angle obtained in Example 8 was significantly lower than that of the pretreated silicon substrate (which was essentially hydrophobic and had a contact angle of approximately 85°, as shown in FIG. 2B), this example showed that the contact angle increased as oxygen was added to the water plasma carrier gas. As with the examples using hydrogen peroxide plasma, these examples showed that the presence of oxygen in the water plasma made the surface less hydrophilic than when water plasma with argon carrier gas was used without oxygen mixing (as shown by the resulting smaller contact angle in Example 7).

[0055] 8 shows the WCA measurements of Example 9, in which a silicon substrate surface was modified using oxygen plasma at a substrate temperature of 200°C. This example showed that the oxygen plasma modified the silicon surface to be more hydrophilic than the pretreated silicon substrate (which was substantially hydrophobic and had a contact angle of about 85°, as shown in FIG. 2B). However, the oxygen plasma in this example resulted in a surface that was less hydrophilic than when the silicon surface was modified using hydrogen peroxide plasma with an argon carrier gas (e.g., as shown by the resulting smaller contact angle in Example 2).

[0056] 9A and 9B show WCA measurements for Examples 10 and 11, in which silicon substrate surfaces were modified by exposing the substrates to a gas stream containing hydrogen peroxide vapor in a carrier gas at substrate temperatures of 150°C and 300°C, respectively. These examples demonstrate that the thermal hydrogen peroxide treatment modified the silicon surface to be more hydrophilic than the pretreated silicon substrate (which was essentially hydrophobic and had a contact angle of approximately 85°, as shown in FIG. 2B). Furthermore, the thermal hydrogen peroxide treatment at 300°C (Example 11) resulted in a significantly more hydrophilic silicon surface than the thermal hydrogen peroxide treatment at 150°C (Example 10). However, the contact angle obtained after the thermal hydrogen peroxide treatment for Example 11 was 11.5°, significantly higher than the resulting contact angle of 4.0° observed after the hydrogen peroxide plasma exposure for Example 2. Furthermore, the substrate temperature was 300°C for Example 11 (thermal hydrogen peroxide) but only 200°C for Example 2 (hydrogen peroxide plasma). Thus, the thermal hydrogen peroxide treatment in these examples resulted in a less hydrophilic surface than when the silicon surface was modified with hydrogen peroxide plasma using an argon carrier gas (as indicated, for example, by the lower contact angles obtained in Examples 1 and 2).

[0057] To summarize the results of Examples 1-11, all conditions resulted in surface modification of the silicon substrate to be more hydrophilic than the pretreated silicon substrate. The most hydrophilic silicon surfaces in Examples 1-11 were produced using hydrogen peroxide plasma with argon carrier gas at substrate temperatures of 150°C and 200°C (Examples 1 and 2). Water plasma with argon carrier gas (Examples 6 and 7) resulted in higher contact angles (less hydrophilic surfaces) than hydrogen peroxide plasma with argon carrier gas (Examples 1 and 2). Adding oxygen to the hydrogen peroxide plasma carrier gas (Examples 3, 4, and 5) resulted in even higher contact angles (more hydrophobic surfaces) compared to hydrogen peroxide plasma with argon carrier gas but without oxygen (Examples 1 and 2). Adding oxygen to the water plasma also increased the resulting contact angle (Example 8 compared to Examples 6 and 7). Thermal hydrogen peroxide treatments at substrate temperatures of 150°C and 200°C (Examples 10 and 11) also resulted in higher contact angles (less hydrophilic surfaces) than when hydrogen peroxide plasma with argon carrier gas was used (Examples 1 and 2), with the 200°C condition (Example 11) resulting in a surface that was significantly more hydrophilic than the 150°C condition (Example 10).

[0058] Figure 10 shows the spectra of the plasmas used in Examples 1-9 obtained using an optical emission spectroscopy method. A hydroxyl peak is observed at approximately 309 nm. These spectra show the presence of hydroxyl group peaks in water plasma (i.e., "H2O + Ar"), hydrogen peroxide plasma generated using argon carrier gas (i.e., "H2O2 + Ar"), and hydrogen peroxide plasma generated using a mixed carrier gas of argon and oxygen (i.e., "H2O2 O2 + Ar"). No significant hydroxyl peak was observed in the mixed plasma of oxygen and argon (i.e., "O2 + Ar").

[0059] The spectra shown in Figure 10 indicated that the hydrogen peroxide plasma generated with argon carrier gas had a higher hydroxyl content than the water plasma generated with argon carrier gas. Without being limited by theory, this may be because the bond dissociation energy for forming -OH is higher for water (5.17 eV) than for hydrogen peroxide (2.22 eV), resulting in a lower hydroxyl content in the water plasma than in the hydrogen peroxide plasma. The resulting contact angles were also lower (and more hydrophilic) after exposure to hydrogen peroxide plasma than after exposure to water plasma (both using argon carrier gas). Without being limited by theory, this is consistent with the layer of hydroxide groups formed on the surface of the substrate increasing the hydrophilicity of the substrate.

[0060] The spectra shown in Figure 10 also indicate that there is a greater hydroxyl content in the hydrogen peroxide plasma generated using a carrier gas mixture of argon and oxygen than in the hydrogen peroxide plasma generated using only argon carrier gas. Surprisingly, the use of hydrogen peroxide plasma generated with an argon carrier gas (Examples 1 and 2) produced a more hydrophilic surface than the use of hydrogen peroxide plasma generated with a carrier gas mixture of argon and oxygen (Examples 3, 4, and 5). This result was not easily predictable and was therefore a counter-intuitive phenomenon discovered through the careful experimentation described above.

[0061] Without being limited by theory, the spectra suggest that oxygen in the plasma produces oxygen radical peaks (e.g., peak 1010) not seen in water or hydrogen peroxide without substantial amounts of oxygen (e.g., with argon carrier gas). Oxygen radicals can penetrate silicon and create a thicker oxide layer. When SiO2 is formed, oxygen radicals can also convert surface silicon atoms from two hydroxyl groups to a single bridging oxygen atom. SiO2 becomes less hydrophilic as the surface hydroxyls are removed and converted to a single oxygen atom. Furthermore, similar mechanisms can occur with other types of materials, e.g., other inorganic or organic materials. For example, organic materials can be oxidized by forming a bond between a carbon atom and an oxygen atom (e.g., supplied from excited oxygen species in the plasma), or organic materials can be hydroxylated by forming a bond between a carbon atom and a hydroxyl group (e.g., supplied from excited hydroxyl species in the plasma). In general, a surface can be hydroxylated when a hydroxyl group is attached to the surface by any means, e.g., by forming a covalent bond to the atom or by being physisorbed or chemisorbed to the surface. Oxygen plasma can also damage organic surfaces by converting hydrocarbons into CO (or CO gas), which volatilizes and leaves the surface, which can cause pitting, increase surface roughness, and / or change the overall morphology of the material.

[0062] For purposes where higher hydroxyl density is desired (e.g., for bonding to hydroxyls or reducing surface energy), adding oxygen to the plasma can reduce the overall hydroxyl density by overcoming the hydroxyls that can form at the surface. Therefore, for even higher hydroxyl density, oxygen-free water vapor or hydrogen peroxide plasma can be used. Furthermore, hydrogen peroxide plasma can be used to produce surfaces with higher hydroxyl density than water plasma, as shown by the larger hydroxyl peak 1005 in the optical emission spectroscopy experiments in Figure 10, and resulted in the most hydrophilic surfaces in the experimental results (Examples 1 and 2). The present system and method uniquely uses hydrogen peroxide plasma (e.g., with a low oxygen content) to increase the hydrophilicity of a surface by forming a hydroxylated surface, and can do so without significant oxidation and damage to the material near the surface. In some cases, as described herein, exposing a material to hydrogen peroxide plasma (e.g., with a low oxygen content) does not substantially increase surface roughness.

[0063] The experimental spectra obtained in the presence of oxygen in the plasma (i.e., "O2 + Ar" and "HO2 + O2") shown in Figure 10 contain peaks 1010 not observed in the spectra of oxygen-free plasmas ("HO + Ar" and "HO2 + Ar"). Without being limited by theory, the spectra in Figure 10 appear to indicate that the oxygen in the plasma creates oxygen radical peaks (e.g., peak 1010) not seen in plasmas containing water mixed only with argon or hydrogen peroxide. When bonded to a silicon surface, the oxygen radicals not only penetrate the surface and create a relatively thick oxide layer, but also convert the silicon surface from two hydroxyls to a single bridging oxygen atom (forming SiO2 and / or siloxanes (i.e., Si=O)). The resulting SiO2 and / or siloxane surfaces are less hydrophilic due to the removal of the surface hydroxyls and their conversion to a single oxygen atom. While a surface with a high hydroxyl density can advantageously reduce surface energy and make the surface more hydrophilic, in the examples described herein, the addition of oxygen to the plasma appeared to adversely reduce hydroxyl density, thereby making the surface more hydrophobic. Without being limited by theory, this may be because the radicals generated by the molecular oxygen added to the water plasma or hydrogen peroxide plasma outcompete the hydroxyls provided by either the water vapor or hydrogen peroxide gas to form SiO2 and / or siloxanes on the surface, thereby reducing the overall surface hydroxyl density and adversely increasing the surface energy. Without being limited by theory, a similar reaction may occur on the surface of other materials, such as polymeric materials, where oxygen radicals in the plasma bond with surface atoms and mobilize surface hydroxyl groups, reducing the hydrophilicity of the surface. Without being limited by theory, furthermore, a higher hydroxyl concentration on a surface can increase the surface area for absorption of water molecules. This can make the surface even more hydrophilic, since the more water molecules that attach to a surface, the more hydrophilic it becomes.

[0064] Examples 12-15 involved plasma treatment of polymeric materials. Table 3 shows the experimental parameters for Examples 12-15, in which four types of polymeric substrates were each exposed to three different plasma conditions to determine the effect on surface hydrophilicity. In these examples, HDPE, PET, PVDF, and PTFE were each exposed to three different plasmas (O, H, O / N, and H, O / O plasma) at four different pressure and power combinations, resulting in a total of 12 experimental conditions for each polymeric material. The static water contact angle (WCA) results from Examples 12-15 are shown in Table 3 and are illustrated in Figures 11A-14C.

[0065] Table 4 shows the pressure and power conditions for each of Examples 12 to 15. In Example 12, an HDPE substrate was exposed to oxygen plasma under the following conditions: low-high pressure and power (LH: 200 mTorr, 100 watts), high-high pressure and power (HH: 375 mTorr, 100 watts), low-low pressure and power (i.e., LL: 200 mTorr, 50 watts), and high-low pressure and power (i.e., HL: 375 mTorr, 50 watts). In Example 12, the HDPE substrate was also exposed to H2O2 / N2 plasma under LH, HH, LL, and HL conditions. In Example 12, the HDPE substrate was also exposed to H2O2 / O2 plasma under LH, HH, LL, and HL conditions. In Example 13, a PET substrate was exposed to the same type of plasma under the same pressure and power combinations as in Example 12. In Example 14, a PVDF substrate was exposed to the same type of plasma at the same pressure and power combination. In Example 15, a PTEE substrate was exposed to the same type of plasma at the same pressure and power combination.

[0066] In Examples 12-15, approximately 1" x 1" specimens of four polymers, HDPE, PET, PVDF, and PTFE, were first cleaned with isopropyl alcohol, rinsed with deionized (DI) water, and dried in a vacuum oven at 40°C for at least 1 hour. The specimens were then loaded into a plasma chamber configured for exposure to O2, H2O2 / N2, or H2O2 / O2 plasma and treated for 5 minutes according to the power and pressure settings shown in Table 4. A system similar to system 100 of FIG. 1A was used for Examples 12-15, in which hydrogen peroxide was supplied from hydrogen peroxide source 150, hydrogen peroxide plasma was formed in remote plasma source 160, and the hydrogen peroxide plasma was introduced into chamber 110 where material 120 was exposed to the hydrogen peroxide plasma. Oxygen and nitrogen were supplied as gases. O2 plasma was generated by bypassing hydrogen peroxide source 150. Using the systems and methods described herein, hydrogen peroxide gas was generated from a hydrogen peroxide source (e.g., 150 in FIG. 1A). The hydrogen peroxide concentration in the gas emitted from the source remained substantially stable over time at about 2250 ppm, and the moisture content of the gas was about 1130 ppm.

[0067] 11A-11C show experimental WCA measurements from the HDPE substrate of Example 12 in an untreated state and after different plasma treatments, respectively. The untreated HDPE surface has a WCA between 85° and 90° and is therefore relatively hydrophobic. In some cases, "hydrophobic" can be defined as having a WCA range of 65° to 150°, and "hydrophilic" can be defined as having a WCA range of less than 65°. As used herein, a superhydrophobic surface has a WCA greater than 150°, and a superhydrophilic surface has a WCA of less than about 10°, or less than about 5°, or less than about 1°, or about 0°.

[0068] Figures 11A-11C show that exposure to plasmas formed from all three gas blends resulted in enhanced hydrophilicity of the HDPE surface under all plasma treatment conditions. However, the amount of hydrophilic improvement varied among conditions.

[0069] Figure 11A shows the WCA results for an untreated HDPE substrate and an HDPE substrate after four plasma treatments using neat (or "pure") O as the inlet gas. As is known in the art, "neat" (or "pure") oxygen can have some impurities. For neat oxygen plasma treatment, a process pressure of 375 mTorr resulted in a less hydrophilic (more hydrophilic) surface compared to 200 mTorr, while the power settings (50 W or 100 W) made less difference.

[0070] Figure 11B shows the WCA data for HDPE specimens plasma-treated with H2O2 vapor in a nitrogen carrier gas. The lowest measured WCA occurred at a low pressure of 200 mTorr, in this case, and the pressure setting again had a greater effect on WCA than the power setting. These results show that the WCA value for H2O2 / N2 plasma treatment at 200 mTorr (both conditions had a WCA of approximately 46.5°) was 8° lower than the WCA value obtained using undiluted O2 plasma at 375 mTorr, indicating that hydrogen peroxide-nitrogen mixed plasma is more effective than oxygen plasma at creating a hydrophilic surface on HDPE.

[0071] Figure 11C shows WCA data for HDPE specimens plasma-treated using a hydrogen peroxide plasma with oxygen carrier gas (i.e., oxygen was used to draw hydrogen peroxide vapor from the source vessel as the plasma's input mixture). The H2O2 / O2 plasma treatment conditions produced a variety of results. The lowest measured WCA value among the four conditions was at 50 watts power and 375 mTorr pressure, while the highest was at 100 watts power and 375 mTorr pressure. Using oxygen as the carrier gas, the even lower power setting of 50 watts was more effective than 100 watts and 200 mTorr, and significantly more effective than 100 watts and 375 mTorr. However, the highest WCA value was 53.0° at 50 watts and 375 mTorr when N was used as the carrier gas (see Figure 11B), whereas the highest WCA value was 59.5° at 100 watts and 375 mTorr when O was used as the carrier gas (Figure 11C), and only one test condition with O as the carrier gas produced a WCA value below 47°. For these H2O2 plasma parameters, using oxygen as the carrier for the H2O2 vapor did not result in lower WCA values ​​than using nitrogen.

[0072] The WCA results for Example 12 (Figures 11A-11C) show that H2O2 / N2 plasma treatment produced the most hydrophilic surface for HDPE. That is, the 200 mTorr and 50 watt conditions produced HDPE with a WCA of 46.31°, compared to a WCA of 87.71° for untreated HDPE. For comparison, the best oxygen plasma conditions in Example 12 produced a WCA of 52.0°, and the best H2O2 / O2 plasma conditions in Example 12 produced a WCA of 46.5°. Thus, while all plasma treatments were able to increase the hydrophilicity of HDPE, H2O2 / N2 plasma produced the most hydrophilic HDPE surface. These WCA results indicate that abundant available oxygen did not improve H2O2 plasma performance, and that improving HDPE wettability (i.e., hydrophilicity) was the primary indicator.

[0073] FTIR spectra were also obtained using attenuated total reflectance (ATR) from the HDPE specimens of Example 12 in the untreated state and after different plasma treatments. The FTIR data can describe what changes occurred at the molecular level on the sample surface (e.g., at a depth of less than 2 microns). All of the treated specimens of Example 12 had both peak shifts and broadening consistent with C=O stretching.

[0074] For example, the FTIR spectrum of HDPE treated with H2O2 / N2 plasma shows a peak at 966 cm -1 Without being limited by theory, this absorbance may be caused by out-of-plane fluctuations of C-H, indicating the formation of double carbon bonds that were not present in untreated HDPE. -1 The maximum peak at approximately 966 cm was produced by the 100 watt and 200 mTorr H2O2 / N2 plasma treatment, which coincided with one of the smallest measured WCA values ​​of less than 47°. Without being limited by theory, -1 The formation of this peak at 1000 cm can be evidence that the polyethylene molecule is modified by plasma treatment to create a double-bonded carbon with a single hydrogen atom that is readily available for reaction and functionalization, provided sufficient oxidizing agent is made available. In some cases, after oxygen exposure, the CO absorbance appears between 1100 and 1000 cm in the FTIR spectrum. -1 It will become clear in the field.

[0075] Figures 12A-12C show the WCA results from the PET substrate of Example 13 after different plasma treatments. Similar to the HDPE substrate of Example 12, 1" x 1" specimens were immersed in isopropyl alcohol, rinsed with deionized water, and dried in a vacuum oven at 40°C. After washing, WCA measurements were performed before plasma treatment. PET is less hydrophobic than HDPE, resulting in pre-treatment WCA values ​​of approximately 70.0° to 72.0°. All of the plasma treatments in Example 13 made the PET substrates more hydrophilic, and the achieved WCA was also lower than that of the HDPE substrate of Example 12.

[0076] Figure 12A shows that for O plasma, three treatment conditions (both 200 mTorr and 375 mTorr pressure conditions at 100 watts) resulted in WCAs ranging from approximately 26.0° to 28.0°. One condition (375 mTorr and 50 watts) was less effective, resulting in a WCA of 35.0°.

[0077] Figure 12B shows the WCA results for a PET substrate after exposure to a plasma generated from H2O2 vapor with nitrogen carrier gas. Conditions of 100 watts and 200 mTorr produced a nearly superhydrophilic surface, with a WCA of 10.0°. The H2O2 / N2 plasma again produced the lowest WCA values ​​measured for any PET plasma condition, with the two most effective treatments obtained at 100 watts and the least hydrophilic results occurring at 50 watts and 375 mTorr.

[0078] Figure 12C shows the WCA results for a PET substrate after exposure to a plasma generated from H2O2 vapor with oxygen carrier gas. While the WCA was lower than the oxygen plasma results, it did not produce a surface with a WCA as low as the best H2O2 / N2 plasma condition investigated. The pressure and power conditions showed some similar trends to the H2O2 / N2 plasma results in Figure 12B. Another nearly superhydrophilic WCA value (12.5°) was again obtained at 200 mTorr and 100 watts.

[0079] Regardless of the gas / vapor mix, the least effective treatment conditions for all tests of PET in Example 13 were 50 watts and 375 mTorr, a consistency not observed in the HDPE treatments of Example 12.

[0080] FTIR measurements were also performed on the PET substrate of Example 13. A portion of the plasma-treated sample was analyzed at 2970 cm -1 A CH symmetric stretching vibration was observed at 2923 cm, which may be due to the four hydrogen atoms attached to the benzene ring structure. However, in the untreated and oxygen plasma treated specimens, -1 and 2854 cm -1The absence of CH2 asymmetric stretching optical absorption and symmetric stretching optical absorption in SiO2 suggests that the plasma treatment with H2O2 / N2 caused unique changes at the molecular level. Furthermore, for example, the lowest measured WCA value was 2923 cm -1 The 100 watt and 200 mTorr H2O2 / N2 plasma treatment showed the largest peak at 2923 cm3, and had the highest WCA value. -1 The peak at 2923 cm is the smallest under conditions of 50 watts and 375 mTorr. -1 It was observed that the magnitude of the peak at 1000 nm corresponds to the degree of wettability. Without being limited by theory, the symmetric C-H stretch associated with the benzene ring does not show a decrease in magnitude, so it is not expected that the ring is opened by the plasma treatment. Rather, the ester groups in the PET monomer may be modified and / or the terminal chains of the polymer PET may be modified by the plasma.

[0081] A corresponding decrease in the amplitude of the CO stretching vibration was also observed in the FTIR spectra of the plasma-treated PET samples of Example 13 (Figures 12A-12C). The untreated, O plasma-treated, and H2O2 / N2 plasma-treated specimens under 50 watts and 375 mTorr conditions exhibited the highest peak intensity (approximately 1101 cm). -1 and 1124 cm -1 ), indicating the presence of many more intact CO bonds in the polymer. This is consistent with the WCA data, which showed that among the peroxide treatments, the H2O2 / N2 plasma condition at 375 mTorr and 50 watts produced the least hydrophilic PET surface. Undiluted O2 plasma at 100 watts and 200 mTorr had the lowest WCA values ​​measured with the pure oxygen treatment method, but was not as effective at reacting with CO bonds in PET as H2O2 in an N2 carrier, and no decrease in CO optical absorption was observed in the FTIR spectra of PET substrates after plasma treatment using H2O2 with O2 as a carrier. When oxygen was used as the carrier gas for hydrogen peroxide plasma, the CO optical absorption was even greater than in the untreated sample.

[0082] To summarize the WCA results for Examples 12 and 13, plasma treatment using undiluted oxygen and hydrogen peroxide vapor in both N2 and O2 carrier gases rendered all HDPE and PET surfaces more hydrophilic. Overall, plasma treatment resulted in PET achieving greater hydrophilicity than HDPE, which was also more hydrophilic than HDPE before treatment. (Without being limited by theory, this may be because it is known that the wettability of a polymer increases directly with oxygen content, with materials with higher O / C ratios being more hydrophilic.) The smallest measured WCA value (10.28°) was obtained for PET using H2O2 vapor in N2 carrier gas at an RF power of 100 Watts and a pressure of 200 mTorr. For H2O2 / N2 plasma treatment, the surface wettability (or hydrophilicity) of HDPE was greatest at a pressure of 200 mTorr, regardless of the RF power setting. Nevertheless, for PET, the surface wettability was greatest when the plasma was treated at 100 Watts, regardless of the process pressure. Based on the WCA values ​​of Examples 12 and 13, using oxygen as a carrier gas to deliver HO to the plasma from a hydrogen peroxide container (described herein) did not perform as well as or provide additional benefits beyond those of using a nitrogen carrier gas.

[0083] Figures 13A-13C show WCA results from the PVDF substrate of Example 14 after different plasma treatments. As with the previous polymer substrates of Examples 12 and 13, WCA measurements were performed on specimens before and after various plasma treatments. PVDF was relatively hydrophobic, with pre-treatment WCA values ​​of approximately 79.0° to 82.0°. While the achieved WCA of PVDF was not as low as that of HDPE or PET (Examples 12 and 13), all of the plasma treatments in Example 14 rendered the PVDF substrate more hydrophilic. Pressure and power did not significantly affect WCA for the oxygen plasma conditions in Figure 13A. Figure 13B shows a trend in pressure and power for WCA after H2O2 / N2 plasma treatment, with the 200 mTorr and 100 watt conditions resulting in the lowest measured WCA (61.80°) for any of the PVDF substrates of Example 14. The H2O2 / O2 plasma in Figure 13C showed higher WCA under all conditions compared to the H2O2 / N2 plasma in Figure 13B. These results indicate that the H2O2 / N2 plasma can significantly improve the hydrophilicity of PVDF and reduce the WCA from approximately 82.0° to approximately 62.0°.

[0084] Figures 14A-14C show the WCA results from the PTFE substrate of Example 15 after various plasma treatments. As with the previous polymer substrates in Examples 12-14, WCA measurements were performed on the specimens before and after the various plasma treatments. PTFE was the most hydrophobic polymer substrate examined, with pre-treatment WCA values ​​ranging from approximately 99.0° to 106.5°. The post-treatment WCA for PTFE was also the highest among the polymer substrates examined in Examples 12-15, although all of the plasma treatments in Example 15 were able to make the PTFE substrate more hydrophilic. Some trends can be seen in the WCA of each plasma with respect to pressure and power. The WCA obtained using the H2O2 / N2 plasma, shown in Figure 14B, again exhibited the lowest WCA measured on PTFE. At 375 mTorr and 100 watts, the WCA was 80.5°, lower than any of the conditions on PTFE in Example 15. The H2O2 / O2 plasma in Figure 14C showed higher WCA under all conditions compared to the H2O2 / N2 plasma in Figure 14B. These results indicate that the hydrophilicity of PTEE can be significantly improved using H2O2 / N2 plasma, reducing the WCA from approximately 99.0° to approximately 80.5°.

[0085] In Examples 1-11, which used silicon substrates, and Examples 12-15, which used polymer substrates, the most hydrophilic surfaces were produced using hydrogen peroxide plasma with nitrogen carrier gas. In Examples 1-15, both hydrogen peroxide plasma formed using oxygen carrier gas and oxygen plasma treatment produced surfaces that were less hydrophilic than those produced by hydrogen peroxide plasma using nitrogen carrier gas. Therefore, without being limited by theory, oxygen radicals present in the plasma may contribute to the reduced hydrophilicity. Oxygen radicals not only form oxides on the surface but also penetrate into the treated material (i.e., into the portion of the material near the surface), thereby creating a thicker oxide layer (i.e., not just a monolayer on the surface). Oxides and other oxygen ligands produced by oxygen radicals that are less hydrophilic than hydroxyls reduce available hydroxyl sites.

[0086] In some embodiments of the systems and methods described herein, a surface of a material (e.g., silicon or a polymer) is exposed to (or treated with) a hydrogen peroxide plasma, and the surface and / or near-surface portions of the material are not oxidized (or are minimally oxidized by the plasma).

[0087] The spectral changes detected by FTIR-ATR in plasma-treated specimens (e.g., Examples 12 and 13) were subtle and difficult to quantify. Qualitatively, in the FTIR spectra, -1 , 1101cm -1 , and 1021 cm -1 The CO stretching vibration at position attenuated going from untreated to O2 plasma-treated and was minimized by H2O2 plasma treatment without added O2. This may indicate the conversion of the CO compound to a C-hydroxyl bond. The small peak observed in the plasma-exposed material indicated possible hydrophilic bonding to the surface.

[0088] method

[0089] FIG. 15 is a flowchart of a method 1500 for modifying the surface of a material using hydrogen peroxide plasma. Method 1500 can be performed using system 100 or a similar system. In block 1510, hydrogen peroxide plasma is formed. The hydrogen peroxide plasma can be formed in a chamber. For example, a mixture of hydrogen peroxide vapor and a carrier gas can be added to the plasma chamber. In some cases, forming the hydrogen peroxide in the chamber can include forming the hydrogen peroxide plasma with a remote plasma source and then introducing the hydrogen peroxide plasma into the chamber. The carrier gas can include many different species, such as an inert gas (e.g., a noble gas, argon, helium, etc.), nitrogen, CDA, hydrogen, or a mixture thereof. The mixture of hydrogen peroxide vapor and carrier gas can include less than 10% by weight water and less than 1% by weight oxygen (or can include any of the hydrogen peroxide materials described herein). As described herein, the concentration of hydrogen peroxide vapor in the mixture can be substantially stable over time. In some cases, the hydrogen peroxide can be anhydrous. The mixture of hydrogen peroxide vapor and carrier gas can optionally have less than 60% water by weight, or less than 10% water by weight, or less than 0.1% water by weight. The mixture of hydrogen peroxide vapor and carrier gas can optionally have less than 1% oxygen by weight, or can be substantially oxygen-free. In block 1520, a material (e.g., a silicon material, a material with or without an additional layer, or a polymeric material) is exposed to a hydrogen peroxide plasma to modify the surface of the material. Optionally, the material is exposed to the hydrogen peroxide plasma in a chamber. The hydrogen peroxide plasma can modify the material surface by forming a layer of hydroxyl groups on the material surface. Optionally, a dense layer of hydroxyl groups is formed on the material surface. Method 1500 can be used to increase the hydrophilicity of a material. For example, WCA measurements of the material can show a decrease in contact angle as a result of performing method 1500. Optionally, performing method 1500 can result in the formation of hydroxyl groups on the surface(s) of the material, rendering one or more surfaces of the material more hydrophilic.In some cases, after performing method 1500, one or more surfaces of the material have a WCA of less than about 15°, or less than about 10°, or less than about 5°.

[0090] FIG. 16 is a flowchart of a method 1600 for modifying the surface of a material using hydrogen peroxide plasma. Method 1600 can be performed using system 100 or a similar system. In optional block 1610, an inert gas plasma is formed, for example, in a chamber. In some cases, the inert gas plasma can be formed using a remote plasma source, and then the inert gas plasma can be introduced into the chamber. In block 1620, a hydrogen peroxide vapor mixture is provided from a source (e.g., hydrogen peroxide source 150 of FIG. 1A). The hydrogen peroxide vapor mixture can primarily comprise hydrogen peroxide vapor. For example, the mixture can include hydrogen peroxide vapor and low concentrations (e.g., less than 10%, or less than 1%, or less than 0.1%) of water and / or oxygen. In another example, the mixture can include hydrogen peroxide vapor and other components (e.g., water or a carrier gas) at higher concentrations (e.g., up to 60% or even higher for a mixture of hydrogen peroxide vapor and a carrier gas). The concentration of hydrogen peroxide vapor in the mixture provided from the source can be substantially stable over time. In block 1630, a hydrogen peroxide plasma is formed, for example, in a plasma source coupled to the chamber. If an inert gas plasma is first formed, the hydrogen peroxide plasma can then be formed in step 1630 by adding a mixture of hydrogen peroxide vapor and a carrier gas to the inert gas plasma. In some cases, the hydrogen peroxide plasma can be formed in a remote plasma source, and then the hydrogen peroxide plasma can be introduced into the chamber. The carrier gas can include many different species, such as an inert gas (e.g., a noble gas, argon, helium, etc.), nitrogen, CDA, hydrogen, or a mixture thereof. The hydrogen peroxide vapor and carrier gas in the source (and the stream derived from the source) can contain less than 10% water by weight and less than 1% oxygen by weight (or can contain any of the hydrogen peroxide materials described herein). In some cases, the hydrogen peroxide can be anhydrous. The mixture of hydrogen peroxide vapor and carrier gas can be substantially oxygen-free in some cases.However, because hydrogen peroxide decomposes into water and oxygen within the plasma, some oxygen may be present in the resulting plasma. In block 1640, a material is exposed to a hydrogen peroxide plasma (e.g., in a chamber). The material can be a silicon or polymer material (e.g., plastic, UHMWPE, or PEEK). In optional block 1650, the surface of the material is modified with a layer of hydroxyl groups. In some cases, a dense layer of hydroxyl groups forms on the material surface. Method 1600 can be used to increase the hydrophilicity of a material. For example, WCA measurements of the material can show a decrease in the contact angle of the material as a result of performing method 1600.

[0091] In some cases, the flow rate of the inert gas used to form the inert gas plasma in block 1610 is significantly lower than the flow rate of the combined hydrogen peroxide and carrier gas used to form the hydrogen peroxide plasma in block 1630. In some cases, the flow rate of the inert gas used to form the inert gas plasma in block 1610 can be half, one-fifth, one-tenth, one-twentieth, or one-hundredth of the flow rate of the combined hydrogen peroxide and carrier gas used to form the hydrogen peroxide plasma in block 1630.

[0092] In some cases, the material is added to the chamber and then the hydrogen peroxide plasma is subsequently introduced into the chamber. For example, in some cases, it may be beneficial to allow the gas flow pattern within the chamber to stabilize before adding the hydrogen peroxide plasma to the chamber.

[0093] In some cases of method 1600, the material is a substrate or a layered structure, including a thin film. In some cases of method 1600, the surface(s) of the material exposed to the hydrogen peroxide plasma do not form plasma-derived SiO or siloxanes, e.g., due to the low oxygen content in the hydrogen peroxide vapor and carrier gas. For example, in some cases, after block 1640, the surface(s) may not contain SiO or siloxanes, or may not contain measurable amounts of SiO or siloxanes (e.g., using a surface characterization technique such as X-ray photoelectron spectroscopy (XPS)). In some cases of method 1600, the surface(s) may not form plasma-derived C-O or C=O bonds, e.g., due to the low oxygen content in the hydrogen peroxide vapor and carrier gas. For example, in some cases, after block 1630, the surface(s) may not contain C-O or C=O bonds, or may not contain measurable amounts of C-O or C=O bonds (e.g., using a surface characterization technique such as XPS).

[0094] In some cases, it may be difficult to measure bonding properties at the surface, for example, if the concentration at the surface is below the detection level of a surface analytical technique. In some cases, after performing a method described herein (e.g., Method 1500 or 1600), the surface of the material does not substantially form SiO resulting from exposing the material to hydrogen peroxide plasma. In some cases, after performing a method described herein (e.g., Method 1500 or 1600), the surface of the material does not substantially form C-O or C=O bonds resulting from exposing the material to hydrogen peroxide plasma. In some cases, after performing a method described herein (e.g., Method 1500 or 1600), a portion of the material near the surface is not substantially oxidized by exposing the material to hydrogen peroxide plasma. As used above, the phrase "not substantially" indicates that the concentration of the above-described species is below the detection level of a surface analytical technique. For example, if the concentration of SiO at the surface of the material is below the detection limit after exposing the material to hydrogen peroxide plasma, the surface of the material does not substantially form SiO resulting from exposing the material to hydrogen peroxide plasma. Without being limited by theory, replacing hydroxyl groups on a material surface with SiO2, siloxane, C-O bonds, or C=O bonds increases the surface energy and makes the material surface less hydrophilic.

[0095] Furthermore, the surface may be modified by the ambient atmosphere upon removal from the plasma chamber. Therefore, special equipment (e.g., integrated characterization tools) may be required to avoid exposure to the atmosphere and obtain accurate measurements of the bonding properties at the surface after exposing the material to hydrogen peroxide plasma, as described herein (e.g., methods 1500 or 1600). For example, heat, humidity, atmospheric contaminants, and even volatile components of the plastic box or bag containing the sample may modify the surface after it is removed from the treatment chamber and exposed to the external environment. Furthermore, in some cases, even in a low-pressure (or vacuum) environment, the properties of the surface may change over time. For example, the hydroxylated surfaces of some polymeric materials may degrade (or become less hydrophilic) over time due to reactions with the molecules of the polymer itself. Therefore, to obtain an accurate measurement of the effect of hydrogen peroxide plasma treatment on a material surface, it may be necessary to measure the hydrophilicity of the surface within a certain time period (e.g., within an hour, within 10 minutes, or within a few seconds), depending on the atmosphere and conditions to which it is exposed, as well as the type of material.

[0096] Embodiment

[0097] Clause 1. A method comprising: providing a mixture comprising hydrogen peroxide vapor from a source, wherein a concentration of the hydrogen peroxide vapor in the mixture is substantially stable over time; forming a hydrogen peroxide plasma from the mixture; and exposing a material to the hydrogen peroxide plasma in a chamber.

[0098] Clause 2. The method of clause 1, wherein exposing the material to the hydrogen peroxide plasma in the chamber increases the hydrophilicity of the surface of the material.

[0099] Clause 3. The method of clause 1, wherein the material is a substrate or a layered structure including a thin film.

[0100] Clause 4. The method of clause 1, wherein the material is a substrate comprising silicon.

[0101] Clause 5. The method of clause 4, wherein the method further comprises immersing the substrate in a buffered HF solution prior to said exposing the substrate to the hydrogen peroxide plasma.

[0102] Clause 6. The method of clause 1, wherein the material comprises a polymer material, ultra-high molecular weight polyethylene (UHMWPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), or polyetheretherketone (PEEK).

[0103] Clause 7. The method of clause 1, wherein the surface of the material does not substantially form SiO2 from said exposing said material to said hydrogen peroxide plasma.

[0104] Clause 8. The method of clause 1, wherein the surface of the material does not substantially form C-O bonds, C=O bonds, or CO2 gas from said exposing said material to said hydrogen peroxide plasma.

[0105] Clause 9. The method of clause 1, wherein the surface of the material is not substantially oxidized by said exposing said material to said hydrogen peroxide plasma.

[0106] Clause 10. The method of clause 1, wherein the roughness of the material is not substantially increased by said exposing said material to said hydrogen peroxide plasma.

[0107] Clause 11. The method of clause 1, wherein the mixture contains less than 60% water by weight at the source.

[0108] Clause 12. The method of clause 1, wherein the mixture contains less than 10% water by weight at the source.

[0109] Clause 13. The method of clause 1, wherein the mixture contains less than 0.1% water by weight at the source.

[0110] Clause 14. The method of clause 1, wherein the mixture contains less than 1% oxygen by weight at the source.

[0111] Clause 15. The method of clause 1, wherein the mixture further comprises a carrier gas, the carrier gas comprising one or more of an inert gas, hydrogen, or nitrogen.

[0112] Clause 16. The method of clause 1, wherein providing the mixture comprising the hydrogen peroxide vapor from the source further comprises drawing the mixture directly from the source using a vacuum.

[0113] Clause 17. The method of clause 1, further comprising introducing the material into the chamber prior to exposing the material to the hydrogen peroxide plasma in the chamber.

[0114] Clause 18. The method of clause 1, wherein said exposing said material to said hydrogen peroxide plasma in said chamber causes a surface of said material to have a static water contact angle of less than about 15 degrees.

[0115] Clause 19. The method of clause 1, wherein the exposed surface of the material comprises a roughened surface, depressions, or holes, and wherein exposing the material to the hydrogen peroxide plasma in the chamber makes the exposed surface of the material more hydrophilic.

[0116] Clause 20. The method of clause 1, wherein the material is exposed to the hydrogen peroxide plasma for about 5 minutes and the pressure in the chamber is about 5 Torr during the exposure.

[0117] Clause 21. The method of clause 1, further comprising forming an inert gas plasma before forming the hydrogen peroxide plasma, and forming the hydrogen peroxide plasma from the mixture comprises adding the mixture to the inert gas plasma.

[0118] Reference has been made in detail to the disclosed embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided for the purpose of illustrating the technology, not limiting it. Indeed, while the specification has described in detail certain embodiments of the invention, it will be understood that those skilled in the art, upon gaining an understanding of the foregoing, will readily conceive of modifications, variations, and equivalents to these embodiments. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield yet a still further embodiment. It is therefore intended that the present subject matter encompass all such modifications and variations within the scope of the appended claims and their equivalents. These and other modifications and variations to the invention may be practiced by those skilled in the art without departing from the scope of the invention, which is more particularly set forth in the appended claims. Moreover, those skilled in the art will understand that the foregoing description is illustrative only and is not intended to limit the invention.

[0119] Although the invention has been described with reference to the above examples, it will be understood that modifications and variations are encompassed within the scope of the invention. Accordingly, the invention is limited only by the scope of the following claims.

Claims

1. 1. A method comprising: providing a mixture comprising hydrogen peroxide vapor from a source, wherein the concentration of the hydrogen peroxide vapor in the mixture is substantially stable over time; forming a hydrogen peroxide plasma from the mixture; exposing a material to the hydrogen peroxide plasma in a chamber.

2. The method of claim 1 , wherein the exposing the material to the hydrogen peroxide plasma in the chamber increases the hydrophilicity of the surface of the material.

3. The method of claim 1 , wherein the material is a substrate or a layered structure including a thin film.

4. The method of claim 1 , wherein the material is a substrate comprising silicon.

5. 5. The method of claim 4, wherein the method further comprises immersing the substrate in a buffered HF solution prior to said exposing the substrate to the hydrogen peroxide plasma.

6. The method of claim 1 , wherein the material comprises a polymeric material, ultra-high molecular weight polyethylene (UHMWPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), or polyetheretherketone (PEEK).

7. The surface of the material is SiO 2 resulting from the exposure of the material to the hydrogen peroxide plasma. ２ The method of claim 1 , wherein substantially no

8. The surface of the material contains C—O bonds, C═O bonds, or CO bonds resulting from the exposure of the material to the hydrogen peroxide plasma. ２ The method of claim 1 , wherein substantially no gas is formed.

9. 10. The method of claim 1, wherein a near-surface portion of the material is not substantially oxidized by the exposure of the material to the hydrogen peroxide plasma.

10. The method of claim 1 , wherein the roughness of the material is not substantially increased by the exposure of the material to the hydrogen peroxide plasma.

11. The method of claim 1 , wherein the mixture comprises less than 60% water by weight at the source.

12. The method of claim 1 , wherein the mixture comprises less than 10% water by weight at the source.

13. The method of claim 1 , wherein the mixture contains less than 0.1% water by weight at the source.

14. 10. The method of claim 1, wherein the mixture contains less than 1% by weight of oxygen at the source.

15. The method of claim 1 , wherein the mixture further comprises a carrier gas, the carrier gas comprising one or more of an inert gas, hydrogen, or nitrogen.

16. 10. The method of claim 1, wherein said providing said mixture comprising said hydrogen peroxide vapor from said source further comprises drawing said mixture directly from said source using a vacuum.

17. The method of claim 1 , further comprising introducing the material into the chamber prior to exposing the material to the hydrogen peroxide plasma in the chamber.

18. 10. The method of claim 1, wherein said exposing said material to said hydrogen peroxide plasma in said chamber causes a surface of said material to have a static water contact angle of less than about 15 degrees.

19. 10. The method of claim 1, wherein the exposed surface of the material comprises a roughened surface, depressions, or holes, and wherein exposing the material to the hydrogen peroxide plasma in the chamber makes the exposed surface of the material more hydrophilic.

20. 10. The method of claim 1, wherein the material is exposed to the hydrogen peroxide plasma for about 5 minutes and the pressure in the chamber is about 5 Torr during the exposure.

21. 10. The method of claim 1, further comprising forming an inert gas plasma before forming the hydrogen peroxide plasma, wherein forming the hydrogen peroxide plasma from the mixture comprises adding the mixture to the inert gas plasma.

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