A plasma-assisted surface hydrophilic or hydrophobic modification method

Abstract

The present invention belongs to the fields of surface modification and semiconductor processing technology, and particularly relates to a plasma-assisted surface hydrophilic or hydrophobic modification method. The method comprises the following four steps: (1) pre-cleaning of a substrate; (2) plasma activation treatment to increase surface free energy; (3) formation of a surface connection layer; and (4) characterization of the surface connection layer. The plasma-assisted surface hydrophilic or hydrophobic modification method provided by the present invention has the advantages of cheap and readily available raw materials, simple operation, environmental friendliness, and compatibility with existing semiconductor manufacturing processes.

Description

Technical Field

[0001] The invention relates to a plasma-assisted surface hydrophilic or hydrophobic modification method, and particularly belongs to the technical fields of surface modification and semiconductor processing. Background Art

[0002] The wettability of a material's surface involves numerous physical and chemical processes, such as adsorption, friction, lubrication, adhesion, and dispersion. Surface wettability plays a crucial role in numerous applications, including catalysis, waterproofing, self-cleaning, lubrication, oil recovery, oil-water separation, mineral processing, coatings, and biomedical materials. Surface wettability is primarily influenced by two factors: surface roughness and surface free energy (also known as surface tension). Regulating surface wettability primarily addresses these two factors.

[0003] Photolithography is a common process in semiconductor integrated circuit manufacturing. Patterning is achieved by spin-coating a layer of photoresist onto a substrate, followed by exposure, development, etching, and demolding. Currently, most photoresists commonly used in industry are hydrophobic, requiring the substrate to be treated with hydrophobicity. Otherwise, adhesion between the photoresist and the substrate is insufficient, leading to easy detachment and lateral over-corrosion, which reduces etching accuracy. For single-crystal Si or Si / SiO2 substrates, hexamethyldisilazane (HMDS) is commonly used for hydrophobic modification to reduce surface free energy. However, HMDS is expensive and difficult to remove, increasing process complexity and production costs. Furthermore, HMDS is highly toxic, flammable, biotoxic, and ecologically unfriendly. Therefore, developing a simple, low-cost, and environmentally friendly hydrophobic modification method would be of great practical value.

[0004] Plasma, as the fourth state of matter besides solid, liquid and gas, is composed of neutral atoms (or atomic groups), ions and electrons, and is in a quasi-electrically neutral state as a whole. Plasma surface treatment is an effective surface treatment method. In the early 21st century, it developed rapidly as a commonly used surface treatment technology in the semiconductor and display industries. Different surface treatment effects can be achieved by using different gas sources to generate plasma. For example, common oxygen plasma treatment usually results in a hydrophilic surface, and CF4 plasma is commonly used for hydrophobic treatment. However, CF4 is a greenhouse gas, and the greenhouse effect it causes is thousands of times that of carbon dioxide. Therefore, the use of cheap, easily available, and environmentally friendly gas sources to achieve hydrophilic and hydrophobic modification of material surfaces is a proposition worthy of study. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a plasma-assisted surface hydrophilic or hydrophobic modification method, which has cheap and easily available raw materials, is simple to operate, is environmentally friendly, and is compatible with existing semiconductor manufacturing processes.

[0006] To achieve the above object, the present invention adopts the following technical solution, which is characterized by comprising the following steps:

[0007] Step 1: Pre-cleaning of the substrate

[0008] A substrate is provided and pre-cleaned to remove surface particles, impure metals, impure oxides, organic contaminants, and other impurities. Specific methods include, but are not limited to, ultrasonic cleaning with distilled water, ethanol, and acetone for 3 to 60 minutes, or soaking in a piranha solution (concentrated sulfuric acid + hydrogen peroxide) for 0.2 to 24 hours.

[0009] The substrate includes but is not limited to silicon wafer, quartz, mica, aluminum oxide, titanium oxide, glass, flexible substrate PET, metal or ceramic, etc.

[0010] The pre-cleaning process described above is different for different substrate materials. The main purpose of pre-cleaning is to remove impurities such as surface particles, impure metals, impure oxides, and organic pollutants.

[0011] Step 2: Plasma activation treatment to increase surface free energy

[0012] The substrate after pre-cleaning in step 1 is subjected to plasma activation treatment. Optionally, the plasma gas source is air or oxygen. Optionally, the plasma treatment conditions are direct treatment mode or indirect treatment mode, with a frequency of 40kHz to 2.45GHz, a power of 1 to 1000W, a gas pressure in the treatment chamber of 1mTorr to 2Torr, and a treatment time of 0.1 to 120min. Preferably, the plasma gas source is air or oxygen, the plasma treatment conditions are direct treatment mode, with a frequency of 13.56MHz or 2.45GHz, a power of 60 to 600W, a gas pressure in the treatment chamber of about 100mTorr to 1Torr, and a treatment time of 1 to 45min. More preferably, the plasma gas source is air, the plasma treatment conditions are direct treatment mode, with a frequency of 13.56MHz, a power of 75 to 150W, a gas pressure in the treatment chamber of about 100mTorr to 750mTorr, and a treatment time of 3 to 25min.

[0013] The plasma activation process can effectively remove chemically adsorbed hydroxyl groups and some hydrocarbons on the substrate surface, increasing the substrate's surface free energy. However, high surface free energy makes the substrate surface unstable, making it prone to adsorbing foreign molecules to reduce its surface free energy.

[0014] Before proceeding to subsequent steps, the plasma-activated substrate should be stored in a low-relative-humidity, high-cleanliness environment for a minimal storage time to prevent contaminants from adsorbing onto the substrate surface and deactivating it. Preferably, the relative humidity should not exceed 45%, the cleanliness level should be no less than Class 100,000, and the storage time should not exceed four days. The optimal storage condition is a vacuum environment; the lower the vacuum pressure, the longer the storage time. For example, a vacuum pressure of 0.1 Pa allows for four days of storage.

[0015] The plasma gas source includes but is not limited to air and / or oxygen.

[0016] The optimal conditions for the plasma treatment process are the optimal conditions on the Tergeo model plasma cleaning machine (also known as plasma surface treatment instrument, plasma treatment machine, plasma activation machine) of PIE. The optimal conditions required for different brands and models of plasma generating equipment and different substrates to be treated may vary.

[0017] Step 3: Forming a surface connection layer

[0018] The substrate after step 2 plasma activation treatment is contacted with a surface modifier (such as ultrapure water, anhydrous ethanol), and the surface modifier dissociates on the activated substrate surface to form a hydrophilic or hydrophobic connecting layer. Optionally, a contact method is that the substrate is soaked for a period of time in a liquid surface modifier, and another contact method is that the substrate is left to stand for a period of time in a gaseous surface modifier. Optionally, heat treatment can be carried out during the contact process to improve the dissociation efficiency of the surfactant and the coverage of the connecting layer on the surface. The substrate after plasma activation treatment is transferred to the process in the surface modifier and should minimize the exposure time in the environment to avoid pollutants being adsorbed on the substrate. The optimal condition is to complete the operation under a clean, vacuum environment.

[0019] The purpose of the process of forming a surface connection layer is to use a selected surface modifier to reduce the surface free energy of the substrate after the plasma activation treatment in step 2. The selected surface modifier undergoes chemical adsorption on the surface of the activated substrate, and the molecules in the form of dissociated adsorption formed on the surface of the substrate are the surface connection layer.

[0020] The surface modifiers include but are not limited to water, C1-C12 alcohols, C1-C12 phenols, C1-C12 amines or C1-C12 halogenated hydrocarbons. Such surface modifiers are characterized by having easily dissociated polar chemical bonds, which can dissociate on the surface of the activated substrate and form relatively stable dissociation products. Depending on the properties of the surface modifiers, surface connection layers with different wettability can be formed.

[0021] The heat treatment has the following purposes: first, to aid the dissociation of the surface modifier through heat, thereby improving the dissociation efficiency; second, to select the dissociation products of the surface modifier through heating, thereby increasing the surface coverage of the target dissociation products. Optionally, the heating temperature is 40-500°C for a heating time of 0.5-120 minutes. Preferably, the heating temperature is 100-400°C for a heating time of 1-60 minutes. More preferably, the heating temperature is 180-230°C for a heating time of 5-30 minutes.

[0022] The substrate in the contact method is immersed in a liquid surface modifier. The soaking time decreases with increasing heating temperature. Optionally, the heating temperature is 40-500°C, and the heating time is 0.5-120 minutes. Preferably, the heating temperature is 100-400°C, and the heating time is 1-60 minutes. More preferably, the heating temperature is 180-230°C, and the heating time is 5-30 minutes. The substrate in the contact method is allowed to stand in a gaseous surface modifier, which is applicable to surface modifiers that are gaseous at room temperature and pressure or that are gaseous by changing temperature and pressure. The standing time decreases with increasing heating temperature and surface modifier pressure. Optionally, the surface modifier pressure is 0.1-1 saturated vapor pressure, the heating temperature is 40-500°C, and the heating time is 0.5-120 minutes. Preferably, the surface modifier gas pressure is 0.5 to 1 saturated vapor pressure, the heating temperature is 100 to 400°C, and the heating time is 1 to 60 minutes. More preferably, the surface modifier gas pressure is 0.8 to 1 saturated vapor pressure, the heating temperature is 180 to 230°C, and the heating time is 5 to 30 minutes.

[0023] The surface connection layer has good stability. Its stability can be maintained for more than 12 hours in an environment with a relative humidity of no more than 45% at room temperature; the vacuum degree at room temperature is less than or equal to 1×10 -3 Its stability can be maintained for more than 10 days in a vacuum chamber of Pa.

[0024] The surface connecting layer formed by selecting different types of surface modifiers can bring different degrees of surface wettability. Its uses include but are not limited to spin coating photoresist on the hydrophobic connecting layer in the photolithography process, increasing the adhesion between the substrate and the film layer with the hydrophobic connecting layer in the coating process, and increasing the surface free energy of the hydrophilic connecting layer in the anti-fog self-cleaning material.

[0025] The heating temperature and the soaking or standing time described in step 3 are optimized based on the required degree of wetting, the type of surface modifier used, and production cost accounting.

[0026] Step 4: Characterization of the surface connection layer

[0027] The wettability of the surface connection layer can be measured by the contact angle of a water droplet on its surface.

[0028] Optionally, the dissociation efficiency of the surface modifier on the substrate surface after plasma activation treatment and the surface coverage of the connecting layer can be characterized by techniques such as sum frequency vibration spectroscopy, infrared spectroscopy, Raman spectroscopy, photoelectron spectroscopy, and atomic force microscopy.

[0029] The characterization of the surface connection layer can be selected during the process of optimizing process conditions, but is not necessary in the actual production process, so as to save production costs.

[0030] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0031] 1. The plasma-assisted surface hydrophilicity and hydrophobicity modification methods provided by the present invention are based on the following key aspects: first, a substrate with very high surface free energy is obtained through plasma treatment; then, a specific surface modifier is selected to reduce the surface free energy of the substrate through chemical adsorption, thereby forming a relatively stable surface connection layer on the substrate surface. Depending on the properties of the selected surface modifier, different degrees of surface wettability can be provided;

[0032] 2. The plasma-assisted surface hydrophilic and hydrophobic modification method provided by the present invention is compatible with existing semiconductor manufacturing processes and has low equipment modification costs;

[0033] 3. The plasma-assisted surface hydrophilic and hydrophobic modification method provided by the present invention uses the cheapest and most readily available air as the plasma gas source to achieve the purpose of surface activation, greatly simplifying the production process and reducing production costs;

[0034] 4. The plasma-assisted surface hydrophilic and hydrophobic modification method provided by the present invention has a wide variety of optional surface modifiers and is suitable for various application scenarios. The surface hydrophobic modification can be achieved by selecting simple alcohol molecules. It has the advantages of cheap raw materials, easy availability, easy storage, and environmental friendliness, which can simplify the production process and reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings are only for purposes of illustrating particular embodiments and are not to be considered limiting of the invention.

[0036] Figure 1 Schematic diagram of the implementation process of plasma-assisted surface hydrophobic modification with ethanol according to the present invention, with specific conditions corresponding to those in Example 1;

[0037] Figure 2 This is the sum frequency vibration spectrum of the surface connection layer before and after heating in an ethanol atmosphere in Example 1 of the present invention;

[0038] Figure 3 The sum frequency vibration spectrum difference spectrum of the surface connection layer formed by heating at different temperatures under the ethanol atmosphere in Example 1 of the present invention;

[0039] Figure 4 This is a state diagram of the water drop contact angle of the surface connection layer obtained in Example 1 of the present invention;

[0040] Figure 5 The results of sum frequency vibrational spectroscopy measurements of the hydrolytic stability of the silicon-ethoxy surface connecting layer obtained in Example 1 of the present invention are as follows;

[0041] Figure 6 The results of sum frequency vibrational spectroscopy measurements of the thermal stability of the silicon-ethoxy surface connection layer obtained in Example 1 of the present invention are as follows;

[0042] Figure 7 This is a state diagram of the water drop contact angle of the surface connection layer obtained in Example 2 of the present invention;

[0043] Figure 8 The contact angle diagram of the water droplet when the silicon-hydroxy hydrophilic surface connection layer and the surface connection layer are obtained in this embodiment.

[0044] Description of reference numerals:

[0045] 1-substrate, which is specifically a silicon wafer with an oxide layer on the surface in the first embodiment, and is specifically a quartz crystal in the second and third embodiments;

[0046] 2-surface modifier, specifically ethanol in Example 1, specifically methanol, ethanol, tert-butanol in Example 2, and specifically ultrapure water in Example 3;

[0047] 3-surface connection layer, specifically silicon-hydroxyl and silicon-ethoxy in embodiment 1, specifically silicon-hydroxyl and silicon-methoxy, silicon-ethoxy, silicon-tert-butoxy in embodiment 2, specifically silicon-hydroxyl in embodiment 3;

[0048] 4-water droplets;

[0049] The letters PPP- represent that the sum frequency light in the sum frequency vibration spectrum is P polarization, the visible light is P polarization, and the infrared light is P polarization. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0051] The plasma treatment process described in the examples was performed in a PIE Tergeo plasma cleaning machine (also known as a plasma surface treatment apparatus, plasma treatment machine, or plasma activation machine). Different brands and models of plasma generating equipment and substrates to be treated require different optimal conditions.

[0052] Example 1

[0053] Figure 1 The present invention is a schematic diagram of the plasma-assisted surface hydrophobic modification of Si / SiO2 using ethanol. The specific steps are as follows:

[0054] Step 1: Pre-cleaning of the substrate

[0055] The selected substrate 1 is Si(110) with a 500nm thick silicon dioxide oxide layer on the surface. It is ultrasonically cleaned for 10 minutes using distilled water, ethanol, and acetone in turn to remove surface particles and some organic pollutants. Usually, the surface of silicon dioxide has two structures: Si-OH and Si-O-Si. The proportion of the two structures is related to the pre-cleaning method. The substrate 1 selected here has a larger proportion of Si-OH on the surface after the above-mentioned pre-cleaning, such as Figure 1 As shown in (a), the surface is relatively hydrophilic, and the contact angle of water droplets on this surface is as follows Figure 4 (c) shown.

[0056] Step 2: Plasma activation treatment to increase surface free energy

[0057] The substrate 1 pre-cleaned in step 1 is subjected to plasma activation treatment. The plasma gas source selected is air. Preferably, the plasma treatment conditions are direct treatment mode, frequency 13.56 MHz, power 75 W, pressure in the treatment chamber about 250 mTorr, and treatment time 5 min. The air plasma activation treatment dehydrates the Si-OH on the surface of the substrate 1, forming a surface with a Si-O-Si structure, such as Figure 1 As shown in (b), at this time, the surface free energy of the substrate 1 is very high and is in an unstable state, tending to adsorb foreign molecules to reduce its surface free energy.

[0058] Step 3: Forming a surface connection layer

[0059] The substrate 1 after the plasma activation treatment in step 2 was transferred to a vacuum chamber and evacuated to 1×10 -4 Pa, so that the surface modifier is vaporized, and then 6.7kPa 2-deuterated ethanol (CH3CD2OH) is filled into the chamber at room temperature as the surface modifier 2. The surface modifier 2 dissociates on the surface of the substrate 1 with high surface free energy to form a surface connection layer 3 of Si-OH and Si-OCD2CH3 structure, as shown in FIG. Figure 1 As shown in (c), the sum frequency vibration spectrum of the surface Si-OCD2CH3 connection layer was measured after vacuuming. Figure 2 As shown in the square curve, in the figure ~2945cm -1 and ~2985cm -1The inverted peaks correspond to the Fermi resonance peak and antisymmetric stretching peak of the methyl group in the ethoxy OCD2CH3, respectively, and the peak area is approximately proportional to the surface coverage. Since the proportions of the two structures of Si-OH and Si-OCD2CH3 on the surface are similar after ethanol dissociates at room temperature, the surface is still relatively hydrophilic at this time. 6.7kPa 2-deuterated ethanol (CH3CD2OH) is filled into the chamber again as a surface modifier 2, and then the substrate 1 is heated. Heating can improve the dissociation efficiency of ethanol on the surface of substrate 1. At the same time, the Si-OCD2CH3 structure is very stable during the heating process, and the Si-OH structure will be dehydrated, releasing Si-O-Si sites for chemical adsorption of ethanol molecules, thereby increasing the coverage of the Si-OCD2CH3 surface connection layer. The heating conditions were optimized by heating at 200℃ for 8min, 300℃ for 1min, and 400℃ for 1min in sequence. The sum frequency vibration spectra of the surface connection layers formed under the three conditions were used as difference spectra, as shown below. Figure 3 As shown in the difference spectrum, the peak areas of the Fermi resonance peak and the antisymmetric stretching peak of the methyl group in OCD2CH3 are very small, indicating that heating at 300℃ for 1min and 400℃ for 1min has no significant effect on increasing the coverage. Therefore, the more preferred heating condition is 200℃ for 8min. Finally, cool to room temperature and evacuate. Figure 1 As shown in (c), a high coverage silicon-ethoxy connecting layer 3 is formed on the surface of the substrate 1, and the sum frequency vibration spectrum of the surface Si-OCD2CH3 connecting layer is measured as follows Figure 2 As shown in the regular triangle curve, the peak areas of the Fermi resonance peak and antisymmetric stretching peak of the methyl group in OCD2CH3 are significantly increased compared with room temperature, indicating that the silicon-ethoxy coverage is indeed improved.

[0060] Step 4: Characterization of the surface connection layer

[0061] During the heating process described in step 3, the sum frequency vibration spectrum of the surface connection layer is measured to help optimize the heating conditions. The sum frequency vibration spectrum of the silicon-ethoxy connection layer on the substrate surface is measured before and after heating under vacuum to characterize the coverage of the silicon-ethoxy group. The hydrolytic stability and thermal stability of the high-coverage silicon-ethoxy surface connection layer formed in step 3 are characterized by sum frequency vibration spectrum. The substrate is removed from the vacuum chamber, and a water droplet 4 is placed on its surface to test the contact angle of the water droplet on the surface connection layer.

[0062] The optimal conditions for the plasma treatment process described in this embodiment are the optimal conditions for processing the substrate 1 on the Tergeo model plasma cleaning machine of PIE. The optimal conditions required for using different brands and models of plasma generating equipment and different selected substrates 1 may vary.

[0063] The reason why the surface modifier 2 described in this embodiment uses 2-deuterated ethanol instead of ethanol is to facilitate the measurement and analysis of sum frequency vibration spectrum.

[0064] The gas pressure of the surface modifier 2 described in this embodiment specifically refers to the preferred gas pressure of the surface modifier 2 when the surface modifier 2 is 2-deuterated ethanol and the substrate 1 is Si(110) with a 500 nm thick oxide layer. The optimal gas pressure of the surface modifier 2 varies under different conditions.

[0065] The heating conditions described in this embodiment are optimized using sum frequency vibrational spectroscopy, with the goal of achieving a high coverage silicon-ethoxy linker layer using the lowest possible temperature and the shortest possible heating time, thereby saving energy and reducing process costs.

[0066] Figure 2 This is the sum frequency vibration spectrum of the silicon-ethoxy surface connection layer before and after heating in an ethanol atmosphere in this embodiment. The coverage of the silicon-ethoxy surface connection layer after heating at 200°C for 8 minutes, 300°C for 1 minute, and 400°C for 1 minute is much higher than the coverage of the silicon-ethoxy surface connection layer formed at room temperature. Preferably, heating during the formation of the surface connection layer helps to improve its coverage.

[0067] Figure 3 The difference spectrum of the sum frequency vibration spectrum of the surface connection layer formed by heating at 200°C for 8 minutes, 300°C for 1 minute, and 400°C for 1 minute in an ethanol atmosphere in this embodiment is drawn. In the difference spectrum of the sum frequency vibration spectrum of the surface connection layer formed by heating at 300°C for 1 minute and 400°C for 1 minute and the surface connection layer formed by heating at 200°C for 8 minutes, the peak areas of the Fermi resonance peak and the antisymmetric stretching peak of the methyl group in OCD2CH3 are very small, indicating that heating at 300°C for 1 minute and 400°C for 1 minute has no significant effect on increasing the coverage. More preferably, the heating condition is 200°C for 8 minutes. In this embodiment, a 10.6μm laser is used to heat the substrate 1 from the back side. This non-contact heating method can avoid contamination caused by contact heating.

[0068] The purpose of the water drop contact angle test of the surface connection layer described in this embodiment is to correlate the wettability and surface coverage of the silicon-ethoxy surface connection layer and to guide the optimization of process conditions.

[0069] Figure 4 Graph showing the water drop contact angle of the surface connection layer obtained in this embodiment. Figure 4 (a) is a graph showing the contact angle of a water droplet on the silicon-ethoxy surface connection layer formed after heating at 200°C for 8 minutes, 300°C for 1 minute, and 400°C for 1 minute. The contact angle is at least 90°, which is comparable to the effect of the hydrophobic modification using HMDS in the existing process. For comparison, when the surface modifier 2 is replaced with methanol in the above process, the contact angle of a water droplet on the silicon-methoxy surface connection layer is shown in FIG. Figure 4 (b) shows that it is Figure 4The silicon-ethoxy surface connection layer shown in (a) is more hydrophilic, with a contact angle of about 52°. Figure 4 (c) is a diagram showing the contact angle of a water droplet on a substrate that has only undergone step 1 pre-cleaning and has no surface connection layer, with a contact angle of approximately 65°.

[0070] The hydrolytic and thermal stabilities of the silicon-ethoxy surface bonding layer described in this example were characterized by sum frequency vibrational spectroscopy.

[0071] Figure 5 The sum frequency vibration spectrum measurement results of the hydrolysis stability of the silicon-ethoxy surface connecting layer obtained in this embodiment are as follows: Figure 5 As shown in the square curve, after standing in 2kPa D2O at room temperature for 14 hours, the sum frequency vibration spectrum of the silicon-ethoxy surface connection layer is as follows Figure 5 As shown in the equilateral triangle curve, the measurement results show that the peak areas of the Fermi resonance peak and the antisymmetric stretching peak of the methyl group in the ethoxyl group OCD2CH3 are slightly reduced, indicating that a small portion of the surface silicon-ethoxy groups are replaced by water to form silicon-hydroxyl groups, indicating that the silicon-ethoxy surface connection layer is not completely stable in an aqueous atmosphere, which provides a method for removing the silicon-ethoxy surface connection layer. In addition, it also shows that the silicon-ethoxy surface connection layer is relatively stable at room temperature and will not be replaced by water vapor in the air in a short time under atmospheric conditions. In this embodiment, D2O is used instead of H2O to facilitate the measurement and analysis of sum frequency vibrational spectroscopy.

[0072] Figure 6 The sum frequency vibration spectrum measurement results of the thermal stability of the silicon-ethoxy surface connection layer obtained in this embodiment are as follows: Figure 6 As shown in the square curve, heating is carried out under vacuum at 100℃ for 1 hour, 200℃ for 1 hour, and 300℃ for 1 hour. The corresponding sum frequency vibration spectra of the silicon-ethoxy surface connection layer are as follows: Figure 6 As shown in the middle circular curve, the regular triangle curve, and the inverted triangle curve, the measurement results show that after heating under the above conditions, the peak area changes of the Fermi resonance peak and the antisymmetric stretching peak of the methyl group in the surface ethoxy OCD2CH3 are very small, indicating that the thermal stability of the silicon-ethoxy surface connection layer in a vacuum environment is very good.

[0073] Example 2

[0074] The specific steps of this embodiment are as follows:

[0075] Step 1: Pre-cleaning of the substrate

[0076] The selected substrate 1 is a quartz crystal, with 3 pieces in total. All of them were ultrasonically cleaned for 15 minutes using distilled water, ethanol, and acetone in turn to remove surface particles and some organic pollutants. Usually, the surface of silicon dioxide has two structures: Si-OH and Si-O-Si. The proportion of the two structures is related to the pre-cleaning method. The surface of the substrate 1 selected here is relatively hydrophilic after the above pre-cleaning. The water drop contact angle state of the surface is as follows: Figure 8 As shown in (b), the contact angle is about 60°.

[0077] Step 2: Plasma activation treatment to increase surface free energy

[0078] After the pre-cleaning step 1, substrate 1 is subjected to plasma activation treatment. Oxygen is used as the plasma source gas. Preferably, the plasma treatment conditions are direct treatment mode, with a frequency of 13.56 MHz, a power of 75 W, a chamber pressure of approximately 250 mTorr, and a treatment time of 5 minutes. Oxygen plasma activation treatment dehydrates Si-OH groups on the surface of substrate 1, forming a Si-O-Si structure. At this point, the surface free energy of substrate 1 is very high, making it unstable and prone to adsorbing foreign molecules to reduce its surface free energy.

[0079] Step 3: Forming a surface connection layer

[0080] The three substrates 1 after plasma activation treatment in step 2 are immersed in methanol, ethanol, and tert-butyl alcohol surface modifier 2 respectively. Figure 7 As shown, after immersion at room temperature for 40 hours, the surface modifier 2 dissociates on the surface of the substrate 1 with high surface free energy, forming a surface connection layer 3 with Si-OH and silicon-methoxy, silicon-ethoxy, and silicon-tert-butoxy structures respectively.

[0081] Step 4: Characterization of the surface connection layer

[0082] The substrate 1 is taken out from the surface modifier 2, and a water drop 4 is dropped on the surface of the substrate to measure the contact angle of the water drop on the surface connection layer.

[0083] The plasma treatment conditions described in this embodiment are the optimal conditions for processing the substrate 1 on the Tergeo model plasma cleaning machine of PIE. The optimal conditions required for using different brands and models of plasma generating equipment and different selected substrates 1 may vary.

[0084] The immersion time of the substrate 1 in the surface modifier 2 described in this embodiment specifically refers to the preferred immersion time when the surface modifier 2 is methanol, ethanol, or tert-butanol at room temperature and the substrate 1 is a quartz crystal. The optimal immersion time varies in different situations.

[0085] The purpose of the water drop contact angle test of the surface connection layer described in this embodiment is to compare the wettability of the surface connection layer obtained by selecting different surface modifiers 2 and to guide the optimization of process conditions.

[0086] Figure 7 Graph showing the water drop contact angle of the surface connection layer obtained in this embodiment. Figure 7 (a) is the contact angle diagram of the water droplet on the Si-OH and silicon-methoxy surface connection layer obtained by the above process, with a contact angle of about 48°. Figure 7 (b) is a state diagram of the water drop contact angle of the Si-OH and silicon-ethoxy surface connection layers obtained by the above process, with a contact angle of about 50°. Figure 7 (c) is a diagram showing the contact angle of a water droplet on the Si-OH and silicon-tert-butoxy surface connection layers obtained by the above process, with a contact angle of about 37°. Figure 7 (a) Figure 7 (b) Figure 7 (c) The order of contact angles for water droplets is, from smallest to largest, silicon-tert-butoxy surface linking layer < silicon-methoxy surface linking layer < silicon-ethoxy surface linking layer. The water droplet contact angle is related to both the surface coverage of the silicon-alkoxy layer (greater coverage, stronger hydrophobicity) and the steric hindrance caused by the alkane chains in the silicon-alkoxy layer. In principle, the greater the number of carbon atoms in the alkane chain, the greater the steric hindrance, which prevents direct contact between the water droplet 4 and the surface of the substrate 1. This results in a larger contact angle, but also greater steric hindrance, as repulsion between alkane chains hinders increased surface coverage of the silicon-alkoxy layer.

[0087] Example 3

[0088] The specific steps of this embodiment are as follows:

[0089] Step 1: Pre-cleaning of the substrate. The selected substrate 1 is a quartz crystal. Distilled water, ethanol, and acetone are used for ultrasonic cleaning for 5 minutes to remove surface particles and some organic pollutants. Usually, the surface of silicon dioxide has two structures: Si-OH and Si-O-Si. The proportion of the two structures is related to the pre-cleaning method. The surface of the substrate 1 selected here is relatively hydrophilic after the above pre-cleaning. The water drop contact angle state of the surface is as follows: Figure 8 (b) shown. ;

[0090] Step 2: Plasma Activation Treatment to Increase Surface Free Energy. Substrate 1 cleaned in Step 1 is subjected to plasma activation treatment, using oxygen as the plasma source gas. Preferably, the plasma treatment conditions are direct treatment mode, with a frequency of 13.56 MHz, a power of 75 W, a chamber pressure of approximately 250 mTorr, and a treatment time of 5 minutes. Oxygen plasma activation treatment dehydrates Si-OH groups on the surface of substrate 1, forming a Si-O-Si structure. At this point, the surface free energy of substrate 1 is very high, making it unstable and prone to attracting foreign molecules to reduce its surface free energy.

[0091] Step 3: Forming a surface connection layer

[0092] The substrate 1 after the plasma activation treatment in step 2 is immersed in the ultrapure water surface modifier 2, such as Figure 8 As shown, after immersion at room temperature for 40 hours, the surface modifier 2 dissociates on the surface of the substrate 1 with high surface free energy to form a surface connection layer 3 with a Si-OH structure.

[0093] Step 4: Characterization of the surface connection layer

[0094] The substrate 1 is taken out from the surface modifier 2, and a water drop 4 is dropped on the surface of the substrate to measure the contact angle of the water drop on the surface connection layer.

[0095] The optimal conditions for the plasma treatment process described in this embodiment are the optimal conditions for processing the substrate 1 on the Tergeo model plasma cleaning machine of PIE. The optimal conditions required for using different brands and models of plasma generating equipment and different selected substrates 1 may vary.

[0096] The immersion time of the substrate 1 in the surface modifier 2 described in this embodiment specifically refers to the preferred immersion time at room temperature when the surface modifier 2 is ultrapure water and the substrate 1 is a quartz crystal. The optimal immersion time varies in different situations.

[0097] The purpose of the water drop contact angle test of the surface connection layer described in this embodiment is to compare the wettability of the substrate 1 using ultrapure water as the surface modifier 2 to form a silicon-hydroxyl surface connection layer and the substrate 1 without a surface connection layer, so as to guide the optimization of the process conditions.

[0098] Figure 8 3 is a diagram showing the contact angle of a water droplet with and without the silicon-hydroxy hydrophilic surface connection layer obtained in this embodiment. Figure 8 (a) is a state diagram of the water droplet contact angle of the silicon-hydroxyl hydrophilic surface connection layer obtained by the above process, and the contact angle is about 18°. For comparison, Figure 8(b) shows the contact angle of a water droplet without a surface connection layer, which is approximately 60°. The surface of substrate 1 with the silicon-hydroxyl connection layer has a higher surface free energy than the untreated substrate 1, making it more hydrophilic.

[0099] Example 4

[0100] The specific steps of this embodiment are as follows:

[0101] Step 1: Pre-cleaning of the substrate

[0102] Substrate 1, made of aluminum, was ultrasonically cleaned for 12 minutes using distilled water, ethanol, and acetone, respectively, to remove surface particles and some organic contaminants. Aluminum typically forms an oxide layer on its surface, which often contains a significant number of hydroxyl groups. Substrate 1, after the aforementioned pre-cleaning, was relatively hydrophilic, with a contact angle of approximately 53°.

[0103] Step 2: Plasma activation treatment to increase surface free energy

[0104] After the pre-cleaning in step 1, the substrate 1 is subjected to a plasma activation treatment. Air is used as the plasma source gas. Preferably, the plasma treatment conditions are a direct treatment mode, with a frequency of 13.56 MHz, a power of 40 W, a pressure in the treatment chamber of approximately 410 mTorr, and a treatment time of 12 minutes. The air plasma activation treatment dehydrates the Al-OH groups on the surface of the substrate 1, forming an Al-O-Al structure on the surface. At this point, the surface free energy of the substrate 1 is very high, making it unstable and prone to adsorbing foreign molecules to reduce its surface free energy.

[0105] Step 3: Forming a surface connection layer

[0106] The substrate 1 after plasma activation treatment in step 2 is immersed in the ethanol surface modifier 2 and immersed at 80°C for 2 hours. The surface modifier 2 dissociates on the surface of the substrate 1 with high surface free energy to form a surface connection layer 3 of Al-OH and Al-ethoxy structures respectively.

[0107] Step 4: Characterization of the surface connection layer

[0108] The substrate 1 was taken out from the surface modifier 2, and the water drop contact angle of the surface connection layer was measured to be about 85°.

[0109] The plasma treatment conditions described in this embodiment are the optimal conditions for processing the substrate 1 on the Tergeo model plasma cleaning machine of PIE. The optimal conditions required for using different brands and models of plasma generating equipment and different selected substrates 1 may vary.

[0110] The immersion time of the substrate 1 in the surface modifier 2 described in this embodiment specifically refers to the preferred immersion time when the surface modifier 2 is ethanol and the substrate 1 is metal aluminum at 80° C. The optimal immersion time varies in different situations.

[0111] Example 5

[0112] The specific steps of this embodiment are as follows:

[0113] Step 1: Pre-cleaning of the substrate

[0114] The selected substrate 1 is mica, which was ultrasonically cleaned for 5 minutes using distilled water, ethanol, and acetone in turn to remove surface particles and some organic pollutants. Mica is an aluminum silicate containing metals such as potassium, aluminum, magnesium, iron, and lithium. The surface of mica is usually composed of Si-OH, Al-OH, Si-O-Si, and Al-O-Al structures. The surface of the substrate 1 selected here is relatively hydrophilic after the aforementioned pre-cleaning. The contact angle of water droplets on the surface is as follows: Figure 8 As shown in (b), the contact angle is about 60°. The contact angle is about 48°.

[0115] Step 2: Plasma activation treatment to increase surface free energy

[0116] After pre-cleaning in step 1, substrate 1 is subjected to plasma activation treatment, using air as the plasma source gas. Preferably, the plasma treatment conditions are direct treatment mode, with a frequency of 13.56 MHz, a power of 60 W, a pressure in the treatment chamber of approximately 750 mTorr, and a treatment time of 25 minutes. Air plasma activation treatment dehydrates Si-OH and Al-OH on the surface of substrate 1, forming a surface with Si-O-Si and Al-O-Al structures. At this point, the surface free energy of substrate 1 is very high, making it unstable and prone to adsorbing foreign molecules to reduce its surface free energy.

[0117] Step 3: Forming a surface connection layer

[0118] The substrate 1 after plasma activation treatment in step 2 is immersed in the dodecanol surface modifier 2 and immersed at 250°C for 30 minutes. The surface modifier 2 dissociates on the surface of the substrate 1 with high surface free energy to form surface connection layers 3 of Si-OH, Al-OH, Si-ethoxy structure, and Al-ethoxy structure respectively.

[0119] Step 4: Characterization of the surface connection layer

[0120] The substrate 1 was taken out from the surface modifier 2, and the water drop contact angle of the surface connection layer was measured to be about 102°.

[0121] The plasma treatment conditions described in this embodiment are the optimal conditions for processing the substrate 1 on the Tergeo model plasma cleaning machine of PIE. The optimal conditions required for using different brands and models of plasma generating equipment and different selected substrates 1 may vary.

[0122] The immersion time of the substrate 1 in the surface modifier 2 described in this embodiment specifically refers to the preferred immersion time at 250° C. when the surface modifier 2 is dodecanol and the substrate 1 is mica. The optimal immersion time varies in different situations.

[0123] The above description is only an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modification, equivalent replacement, improvement, expansion, etc. made within the spirit and principle of the present invention are included in the scope of protection of the present invention.

Claims

1. A plasma-assisted surface hydrophilic or hydrophobic modification method, characterized in that The following steps are involved: Step 1: Pre-cleaning of the substrate: clean the substrate; The substrate in step 1 is one or more of silicon wafer, quartz, mica, aluminum oxide, titanium oxide, and glass; Step 2: plasma activation treatment to increase the surface free energy of the substrate; The substrate after pre-cleaning in step 1 is subjected to plasma activation treatment. The plasma treatment conditions are direct treatment mode, frequency 40 kHz~2.45 GHz, power 1~1000 W, gas pressure in the treatment chamber 1 mTorr~2 Torr, and treatment time 0.1~120 min; The plasma gas source is one or both of air and oxygen; Step 3, forming a surface connection layer; contacting the substrate after the plasma activation treatment in step 2 with a surface modifier, so that the surface modifier dissociates on the surface of the activated substrate to form a hydrophilic or hydrophobic connecting layer; The surface modifier described in step 3 includes one or more of water and C1-C12 alcohols, and forms a hydrophilic or hydrophobic connection layer on the surface of the substrate.

2. The modification method according to claim 1, wherein: The frequency is 13.56 MHz or 2.45 GHz, the power is 60-600 W, the gas pressure in the processing chamber is about 100 mTorr-1 Torr, and the processing time is 1-45 minutes.

3. The modification method according to claim 2, wherein: The frequency is 13.56 MHz, the power is 75-150 W, the gas pressure in the processing chamber is about 100 mTorr-750 mTorr, and the processing time is 3-25 minutes.

4. The modification method according to claim 1, wherein: The main purpose of the pre-cleaning in step 1 is to remove particles, impurity metals, impurity oxides or organic contaminants from the substrate surface; The pre-cleaning process in step 1 is to use distilled water, ethanol, and acetone for ultrasonic cleaning in sequence; or, soak in piranha solution.

5. The modification method according to claim 1, wherein: The plasma treatment conditions described in step 2 vary depending on the brand and model of plasma generating equipment and the substrates being treated.

6. The modification method according to claim 1, wherein: The substrate after the plasma activation treatment should be stored in an environment with low relative humidity and high cleanliness before proceeding to subsequent steps, and the storage time should be minimized to avoid contaminants being adsorbed on the substrate surface and causing surface inactivation.

7. The modification method according to claim 1, wherein: One contact method between the substrate and the surface modifier is to immerse the substrate in a liquid surface modifier; or, another contact method is to allow the substrate to remain stationary in a gaseous surface modifier.

8. The modification method according to claim 1 or 7, characterized in that: Heating during the contact process of the surface modifier helps to improve the dissociation efficiency of the surfactant and the coverage of the connecting layer on the surface; The substrate is contacted with the surface modifier by immersing the substrate in the liquid surface modifier. The heating temperature is 40-500° C. and the heating time is 0.5-120 min. Alternatively, the substrate in the contact method is allowed to stand in a gaseous surface modifier: this is applicable to surface modifiers that are gaseous at room temperature and pressure or that are made gaseous by changing the temperature and pressure; the standing time decreases with increasing heating temperature and surface modifier pressure; the surface modifier pressure is 0.1 to 1 saturated vapor pressure, the heating temperature is 40 to 500°C, and the heating time is 0.5 to 120 min.

9. The modification method according to claim 8, characterized in that: The soaking process: the heating conditions are a heating temperature of 100-400° C. and a heating time of 1-60 min; Alternatively, the heating conditions during the static process are as follows: the surface modifier gas pressure is 0.5 to 1 saturated vapor pressure, the heating temperature is 100 to 400° C., and the heating time is 1 to 60 min.

10. The modification method according to claim 9, characterized in that: The soaking process: the heating temperature is 180-230°C, and the heating time is 5-30 minutes; Alternatively, the heating conditions during the static process are as follows: the surface modifier gas pressure is 0.8 to 1 saturated vapor pressure, the heating temperature is 180 to 230° C., and the heating time is 5 to 30 min.

11. The modification method according to claim 1, wherein: The surface modifiers are selected in different types or treated with different plasma conditions. The surface connection layer formed will bring different degrees of surface wettability. Its uses include spin coating photoresist on the hydrophobic connection layer in the photolithography process, increasing the adhesion between the substrate and the film layer in the coating process, or increasing the surface free energy of the hydrophilic connection layer in the anti-fog self-cleaning material.

12. The modification method according to claim 1, characterized in that: Characterization of the surface connection layer: The wettability of the surface connection layer is measured by the contact angle of a water drop on its surface; The dissociation efficiency of the surface modifier on the substrate surface after plasma activation treatment and the surface coverage of the connecting layer are characterized by one or more of sum frequency vibration spectroscopy, infrared spectroscopy, Raman spectroscopy, photoelectron spectroscopy, and atomic force microscopy techniques.

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