A high-temperature volatile protective layer for arsenic gallium wafer water-oxygen metal ion isolation and a preparation method thereof

Abstract

The application discloses a high-temperature volatile protective layer for metal ion isolation of a gallium arsenide wafer and a preparation method thereof. The protective layer is an organic-inorganic hybrid film containing a main polymer material and a functional additive. The main polymer material is grafted with a metal ion capturing group on a molecular chain. The protective layer has a gradient volatile characteristic and can volatilize in stages within a temperature range of 200-400 DEG C. After being treated at 400 DEG C in an inert atmosphere for 30 min, the residue mass on the surface of the gallium arsenide wafer is less than 0.1% of the initial mass. The capture rate of the protective layer to sodium ions is greater than 98%. By chemically bonding a high-selectivity metal ion capturing group to a polymer molecular chain, a transition from passive blocking to active removal is realized.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials and device manufacturing technology, specifically referring to a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions, and its application. Background Technology

[0002] Gallium arsenide (GaAs), a typical III-V compound semiconductor material, is widely used in radio frequency front-end devices (such as high electron mobility transistors (HEMTs) and heterojunction bipolar transistors (HBTs)), optoelectronic devices, and high-speed digital integrated circuits due to its high electron mobility, direct bandgap, and excellent high-frequency characteristics. However, GaAs devices face severe challenges in surface protection during manufacturing.

[0003] First, GaAs material itself has poor chemical stability, and its surface easily forms a natural oxide layer composed of Ga2O3 and As2O3. During subsequent high-temperature processes (such as ohmic contact alloying, typically 350℃-450℃) or plasma etching, the water-oxygen environment exacerbates surface oxidation, leading to an increase in surface state density and causing Fermi level pinning, severely impacting device performance and reliability. Second, mobile metal ions in the process environment (especially alkali metal ions Na) + K + Contamination is another major hidden danger for GaAs devices. Under high-temperature driving, these ions can easily diffuse into the active region, forming leakage channels, leading to threshold voltage drift and decreased reliability of the device.

[0004] Currently, the industry mainly adopts the following two technical solutions to protect GaAs wafers during high-temperature processes: Permanent passivation layer technology: such as SiO2 or SiN grown by plasma-enhanced chemical vapor deposition (PECVD). x Thin films, or spin-coated benzocyclobutene (BCB) polymers, offer good water and oxygen barrier properties, but they contain impurities or pinholes, limiting their ability to block alkali metal ions. More importantly, once deposited, the film is permanent, requiring removal for subsequent processes that expose fresh surfaces (such as metal deposition after backside thinning), increasing process complexity and the risk of introducing damage.

[0005] Temporary protective layer technologies include spin-coated photoresists or polymers such as polymethyl methacrylate (PMMA). These materials can be removed using wet stripping methods with organic solvents after their protective function is complete. However, traditional photoresists have poor thermal stability (typically <200℃) and are prone to flow, decomposition, or even carbonization during high-temperature alloying processes. This not only results in the loss of their protective capabilities but also makes the carbonized residues extremely difficult to remove completely, becoming a new source of contamination. Furthermore, these materials lack the ability to trap metal ions, failing to prevent the diffusion of external ions into the GaAs interior at high temperatures.

[0006] A search of existing technologies reveals that one method discloses a temporary bonding method for GaAs wafers, where the adhesive layer decomposes at high temperatures to achieve wafer separation. However, this method is designed for mechanical support and does not consider the isolation function against water, oxygen, and metal ions. Another prior art discloses a resist composition containing crown ether groups to improve the resolution of photolithography patterns, but its application is limited to photolithography processes and does not address its role as a protective layer at high temperatures or its ability to capture and volatilize metal ions.

[0007] Therefore, developing a novel protective layer that can effectively isolate water, oxygen, and metal ions in harsh high-temperature environments, and that can be cleanly and thoroughly self-removed after the protection task is completed, leaving no residue, is of great significance for improving the performance of GaAs devices and simplifying the process flow. Summary of the Invention

[0008] To address the needs and problems mentioned in the background above, the present invention provides a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions, and its application therein, thereby at least partially solving the aforementioned problems.

[0009] According to the technical solution of the present invention, a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions is provided, wherein the protective layer is an organic-inorganic hybrid thin film comprising a main polymer material and functional additives; The molecular chains of the main polymer material are grafted with metal ion capturing groups. The protective layer has gradient volatilization characteristics, and can volatilize in stages within a temperature range of 200-400℃. After treatment at 400℃ in an inert atmosphere for 30 minutes, the mass of the residue on the surface of the gallium arsenide wafer is less than 0.1% of the initial mass. The protective layer has a sodium ion capture rate of greater than 98%.

[0010] Preferably, the main polymer material is a polynorbornene derivative with a number-average molecular weight of 10,000-100,000 g / mol and a molecular weight distribution index of 1.2-2.5.

[0011] Preferably, the metal ion trapping group includes any one of a crypt ether group, a crown ether group, or a calixarene group; The capturing group is grafted onto the polymer backbone via a C1-C6 alkyl linker, and the monomer containing the capturing group accounts for 30%-70% of the total molar amount of the polymer monomer.

[0012] Preferably, the functional additive is a cage-type polysilsesquioxane, and its molar content in the protective layer is 5%-25%, or accounts for 1%-10% of the total solid mass of the protective layer.

[0013] Preferably, the molecular chain ends of the main polymer material are further modified with anchoring groups, including trimethoxysilyl or triethoxysilyl groups, for forming chemical bonds with the surface of gallium arsenide wafers.

[0014] On the other hand, the present invention also provides a method for preparing a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions, comprising the following steps: Step 1, Precursor polymer synthesis: Under inert gas protection, norbornene monomer containing metal ion trapping groups and vinyl-POSS monomer are dissolved in anhydrous organic solvent, and Grubbs second-generation catalyst is added to carry out ring-opening metathesis polymerization. After the reaction is completed, the reaction is terminated, and the solid polymer is obtained by precipitation, washing and vacuum drying. Step 2, preparation of protective layer solution: Dissolve the solid polymer synthesized in Step 1 in a mixed organic solvent to prepare a solution with a mass fraction of 3%-15%, add leveling agent and defoamer, filter to obtain protective layer coating liquid; Step 3, Coating and Pre-baking: Spin-coat the protective layer coating liquid obtained in Step 2 onto the surface of the pretreated gallium arsenide wafer, and then perform gradient heating pre-baking on a hot plate to form a protective layer film. Step 4, High-temperature volatilization: Place the gallium arsenide wafer covered with the protective layer in an annealing furnace, heat it to 350-420℃ in an inert gas atmosphere, and keep it at a constant temperature for 10-30 minutes to allow the protective layer to completely volatilize.

[0015] Preferably, the process parameters for spin coating in step 3 are as follows: first spin coating at a low speed of 300-500 rpm for 5-10 seconds, and then spin coating at a high speed of 2000-4000 rpm for 30-60 seconds, resulting in a dry protective film thickness of 50-500 nm.

[0016] Preferably, the gradient temperature pre-baking treatment in step 3 includes: baking at 80-90℃ for 2-5 minutes in the first stage, baking at 110-130℃ for 3-8 minutes in the second stage, and baking at 140-160℃ for 2-5 minutes in the third stage.

[0017] Preferably, the heating rate in step 4 is 5-20℃ / min, and the flow rate of the inert gas is 2-10slm.

[0018] Thirdly, the present invention also provides an application of a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions, wherein the high-temperature volatile protective layer is used in the manufacturing process of gallium arsenide-based high electron mobility transistors or heterojunction bipolar transistor devices. The applications include serving as a barrier layer against water, oxygen, and metal ions in ohmic contact alloying processes, back-side thinning processes, or temporary protective processes prior to front-side metallization.

[0019] Beneficial effects: 1. Superior ion contamination control: By chemically bonding highly selective metal ion-capturing groups to the polymer molecular chain, a leap from passive blocking to active removal is achieved. During the volatilization of the protective layer, these groups can react with Na+. + K + This process allows for the formation of stable complexes, which are then carried out of the chamber along with the main chain decomposition products. This prevents the diffusion of metal ions into the GaAs active region at high temperatures, thus protecting the Na+ region. + The capture rate exceeds 99.5%, significantly improving the long-term reliability of the device.

[0020] 2. Unique gradient volatilization and zero residue characteristics: Utilizing the synergistic effect of the rigid backbone of polynorbornene and the cage-like structure of POSS, gradient volatilization of the protective layer is achieved. The low-temperature range (<180℃) is stable, meeting the requirements of patterning processes; the medium-temperature range (200-300℃) involves controlled decomposition, releasing trapped ions; and the high-temperature range (>350℃) results in complete volatilization. Ultimately, atomic-level cleanliness is achieved on the GaAs surface, completely avoiding the chemical residue and surface damage problems associated with traditional wet desizing methods.

[0021] 3. Excellent film-forming properties and interfacial adhesion: Through the silane anchoring groups at the ends of the molecular chains, the protective layer forms stable Ga-O-Si covalent bonds with the GaAs surface oxide layer in the initial stage of spin coating, greatly enhancing adhesion and effectively solving the problems of wet-coated films accumulating at the edges of patterns or wrinkling and peeling at high temperatures. Combined with a gradient pre-baking process, a dense, pinhole-free film comparable to ALD deposition can be obtained. In the preferred embodiment, the leakage current density is less than 1×10⁻⁶. -8 In embodiments where anchoring groups are introduced throughout, the leakage current density is below 3.0 × 10 A / cm². -8 A / cm² ensures excellent barrier properties against water and oxygen in high temperature and high humidity environments.

[0022] 4. Simplified Process and Wide Applicability: This protective layer is applied using conventional spin coating equipment, eliminating the need for vacuum equipment such as PECVD or ALD, thus reducing production costs. Its high-temperature volatilization step can be combined with device alloying or annealing processes, eliminating the need for additional resist removal steps and significantly simplifying the process. This protective layer is particularly suitable for back-side thinning processes, temporary protection before front-side metallization, and high-temperature alloying processes in GaAs-based HEMTs and HBTs, which are sensitive to interface states and metal contamination. Detailed Implementation

[0023] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0024] The embodiments of the present invention provide the following technical solutions: In a first aspect, embodiments of the present invention provide a high-temperature volatile protective layer for gallium arsenide wafers. The protective layer is an organic-inorganic hybrid polymer film, comprising a main polymer material and functional additives. The protective layer exhibits gradient volatile characteristics, capable of volatile in stages within a temperature range of 200-400°C. After treatment at 400°C in an inert atmosphere for 30 minutes, the residual mass on the surface of the gallium arsenide wafer is less than 0.1% of the initial mass, and no continuous film layer exists. Simultaneously, the protective layer is resistant to sodium ions (Na+). + The capture rate is greater than 99%.

[0025] Preferably, the protective layer has a thermal weight loss rate of less than 2% in the range of room temperature to 150°C, undergoes main chain breakage and volatilization in the range of 200-300°C, and completes the volatilization of all components in the range of 350-400°C.

[0026] Preferably, the thickness of the protective layer is 50-500 nm, and more preferably 100-200 nm.

[0027] Furthermore, the main polymer material is a polynorbornene (PNB) derivative with metal ion-trapping groups branched on its sides. The polynorbornene derivative is obtained by ring-opening metathesis polymerization (ROMP) of norbornene monomer containing functional side groups, with its number-average molecular weight (Mn) controlled at 10,000-100,000 g / mol and molecular weight distribution index (PDI) of 1.2-2.5.

[0028] The metal ion trapping group is selected from any one of the following: azacrown ether group, cryptether group, calixarene group. Preferably, the trapping group is p-Na. +The monomer possesses a highly selective [2.2.2]-cryptoether group or an aza-18-crown-6 group. The trapping group is grafted onto the norbornene monomer via a C1-C6 alkyl linker. The norbornene monomer containing the functional side group accounts for 30%-70% of the total molar amount of the polymerized monomer.

[0029] Furthermore, the functional additive is a cage-like polysilsesquioxane (POSS), used to adjust the evaporation rate and film-forming properties of the protective layer. The POSS is a monofunctional POSS with reactive functional groups such as vinyl or epoxy groups, introduced into the protective layer through copolymerization or blending. When introduced through copolymerization, vinyl-POSS participates in ROMP polymerization as a comonomer, with a molar content of 5%-25% in the polymer. When introduced through blending, the proportion of POSS in the total solid mass of the protective layer is 1%-10%.

[0030] Furthermore, the molecular chain ends of the host polymer material are modified with anchoring groups for forming chemical bonds with the gallium arsenide wafer surface. The anchoring groups are selected from trimethoxysilyl or triethoxysilyl groups. This anchoring is achieved during polymer synthesis by introducing a chain transfer agent or terminator containing the corresponding group.

[0031] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned high-temperature volatile protective layer, comprising the following steps: Precursor polymer synthesis steps: Under inert gas protection, norbornene monomer containing metal ion trapping groups and vinyl-POSS monomer are dissolved in anhydrous organic solvent, and Grubbs second-generation catalyst is added. The ring-opening metathesis polymerization reaction is carried out at 30-50℃ for 4-8 hours. After the reaction is completed, vinyl ether is added to terminate the reaction. The reaction solution is precipitated in methanol, filtered, washed and vacuum dried to obtain solid polymer.

[0032] The anhydrous organic solvent is selected from anhydrous toluene, dichloromethane, or tetrahydrofuran.

[0033] The molar ratio of norbornene monomer containing metal ion trapping groups to vinyl-POSS monomer is 1:0.1-0.5.

[0034] The molar ratio of the catalyst to the total monomer is 1:200-1000.

[0035] The vacuum drying conditions are: temperature 40-60℃, vacuum degree <-0.1MPa, and time 12-24h.

[0036] Protective layer solution preparation steps: Dissolve the solid polymer synthesized in step 1 in a mixed organic solvent to prepare a solution with a mass fraction of 3%-15%; then add 0.01%-0.1% leveling agent and 0.01%-0.1% defoamer based on the total mass of the solution to the solution, stir and mix evenly, and filter through a 0.22μm filter to obtain the protective layer coating solution.

[0037] The mixed organic solvent is a mixture of mesitylene and cyclohexanone in a volume ratio of (9-6):(1-4).

[0038] The leveling agent is a polyacrylate or a fluorocarbon surfactant (e.g., FC-4430).

[0039] The defoamer is a polysiloxane-based defoamer.

[0040] Coating and pre-baking steps: After pre-treating the gallium arsenide wafer, the protective coating liquid obtained in step 2 is spin-coated onto the wafer surface, and then a gradient heating pre-baking treatment is performed on a hot plate to form a dense protective film.

[0041] The gallium arsenide wafer pretreatment includes: ultrasonic cleaning with acetone, isopropanol and deionized water in sequence, then soaking in dilute hydrochloric acid prepared by mixing 37% concentrated hydrochloric acid and deionized water at a volume ratio of 1:10 for 1-5 minutes to remove the natural oxide layer on the surface, and finally drying with high-purity nitrogen.

[0042] The spin coating process parameters are as follows: first, spin coating at a low speed of 300-500 rpm for 5-10 seconds, and then spin coating at a high speed of 2000-4000 rpm for 30-60 seconds.

[0043] The gradient temperature pre-baking treatment includes: a first stage of baking at 80-90℃ for 2-5 minutes; a second stage of baking at 110-130℃ for 3-8 minutes; and a third stage of baking at 140-160℃ for 2-5 minutes.

[0044] Thirdly, embodiments of the present invention also provide a method for high-temperature process protection of gallium arsenide wafers using the above-mentioned high-temperature volatilization protective layer, which further includes a high-temperature volatilization step after completing the process steps requiring protection: Gallium arsenide wafers with a protective layer on their surface are placed in an annealing furnace and heated to 350-420°C at a heating rate of 5-20°C / min under an inert gas atmosphere (such as high-purity nitrogen or argon). The temperature is held constant for 10-30 minutes, with the gas flow rate maintained at 2-10 slm to carry the decomposition products out of the chamber. After that, the wafers are allowed to cool naturally and then removed. At this point, there is no protective layer residue on the wafer surface, and subsequent processes can be carried out directly.

[0045] Examples 1-9 below all utilize the high-temperature volatile protective layer described in the first aspect of this invention, are prepared according to the preparation method described in the second aspect, and are finally applied and tested according to the method described in the third aspect. Key process parameters for each example are shown in Table 1.

[0046] Table 1 Example 1 Precursor polymer synthesis: Under nitrogen protection, norbornene monomer containing [2.2.2]-cryptoether groups and vinyl-POSS monomer were dissolved in anhydrous toluene at a molar ratio of 1:0.3 (the monomer containing the trapping group accounted for 50 mol% of the total monomers). Grubbs second-generation catalyst (catalyst to monomer molar ratio 1:500) was added, and the reaction was carried out at 40 °C for 6 h. The reaction was terminated by adding vinyl diethyl ether. The reaction solution was precipitated in methanol, filtered, washed, and dried under vacuum at 50 °C for 18 h to obtain a solid polymer (Mn=45,000, PDI=1.8). A chain transfer agent containing trimethoxysilane was introduced during the polymerization process for end-modification.

[0047] Preparation of protective layer solution: Dissolve the synthesized polymer in a mixed solvent of mesitylene / cyclohexanone (volume ratio 7:3) to prepare an 8wt% solution; add 0.05% leveling agent FC-4430 and 0.03% polysiloxane defoamer based on the total mass of the solution, stir and mix evenly, and filter through a 0.22μm filter.

[0048] Coating and Pre-baking: The gallium arsenide wafer was ultrasonically cleaned sequentially with acetone, isopropanol, and deionized water, then immersed in a 1:10 dilute hydrochloric acid solution for 3 minutes and dried with high-purity nitrogen. The protective coating solution was spin-coated at 400 rpm for 8 seconds, followed by high-speed spin-coating at 3000 rpm for 45 seconds. Gradient pre-baking was performed on a hot plate: 90℃ for 3 minutes → 130℃ for 5 minutes → 160℃ for 3 minutes, forming a 150 nm thick protective film.

[0049] High-temperature volatilization: Place the wafer covered with the protective layer in an annealing furnace, and heat it to 400°C at a rate of 10°C / min under a high-purity nitrogen atmosphere (flow rate 5 slm), hold it at the same temperature for 30 min, and then allow it to cool naturally.

[0050] Example 2 The difference from Example 1 is that the capturing group is replaced with aza-18-crown-6, and the remaining steps are the same as in Example 1.

[0051] Example 3 The difference from Example 1 is that the capturing group is replaced with calix[4] aromatic hydrocarbon, and the rest of the steps are the same as in Example 1.

[0052] Example 4 The difference from Example 1 is that the molar ratio of the capturing group monomer was adjusted to 30%.

[0053] Example 5 The difference from Example 1 is that the molar ratio of the capturing group monomer was adjusted to 70%.

[0054] Example 6 The difference from Example 1 is that the POSS content was adjusted to 5 mol%.

[0055] Example 7 The difference from Example 1 is that the POSS content was adjusted to 25 mol%. Example 8 The difference from Example 1 is that no anchoring group was introduced in the synthesis.

[0056] Example 9 The difference from Example 1 is that an 80nm thick protective film is formed.

[0057] Comparative Example 1 A 150 nm SiO2 thin film was deposited on the surface of a GaAs wafer using a conventional PECVD process at a deposition temperature of 250 °C. This comparative example represents existing permanent passivation layer technology.

[0058] Comparative Example 2 A benzocyclobutene (BCB) polymer was coated onto the surface of a GaAs wafer using a spin-coating process and cured at 250°C to form a 150 nm thin film. This comparative example represents existing spin-coating permanent / semi-permanent passivation layer technologies.

[0059] Comparative Example 3 An AZ series photoresist with a thickness of 150 nm was coated onto the surface of a GaAs wafer using a spin-coating process, followed by pre-baking at 110°C. This comparative example represents existing temporary protective layer technology.

[0060] The protective layer samples prepared in Examples 1-9 and Comparative Examples 1-3 were subjected to the following performance tests: Volatile residue test: Thermogravimetric analysis (TGA) was used to heat the sample to 400℃ at a rate of 10℃ / min under a nitrogen atmosphere, and the temperature was held for 30 min to calculate the percentage of residual mass.

[0061] Na + Capture rate test: The sample was immersed in 100 ppm Na + After soaking in standard solution for 30 min and drying with nitrogen, the GaAs wafer was annealed at 380℃ under a nitrogen atmosphere for 15 min. Secondary ion mass spectrometry (SIMS) was used to measure the Na+ content on the surface and near-surface (depth 0-50 nm) of the GaAs wafer before and after annealing. + Concentration, calculate capture rate.

[0062] Leakage current density test: A metal-insulator-semiconductor (MIS) structure was fabricated, and the leakage current density was tested under an electric field of 1 MV / cm.

[0063] Device gain degradation rate test: The GaAs HBT device with protective layer was annealed at 380℃ in nitrogen atmosphere for 15 min. The change rate of device current gain β before and after annealing was tested to evaluate the effect of protective layer on device performance. The results are shown in Table 2 below.

[0064] Table 2 In conclusion: 1. Comparison of volatility characteristics: The volatilization residue rates of Examples 1-9 were all below 0.2%, especially Examples 1, 4, 5, and 7, which were all below 0.06%, indicating that the protective layer of the present invention can achieve near-complete volatilization at high temperatures, reaching the design goal of zero residue. Among them, Example 7 (POSS content 25%) had the lowest residue rate (0.03%), indicating that appropriately increasing the POSS content helps to promote complete volatilization.

[0065] Comparative Example 1 (SiO2) is completely non-volatile, Comparative Example 2 (BCB) is basically non-volatile after curing (residual rate 98.5%), and Comparative Example 3 (photoresist) carbonizes at high temperature with a residual rate as high as 12.3%. These permanent residues will become new sources of pollution and affect subsequent processes.

[0066] 2. Comparison of metal ion capture capabilities: Na in Examples 1-7 and 9 + The capture rates were all above 98%, especially in Examples 1, 5, and 7, which reached over 99.5%, fully demonstrating the effectiveness of the design concept for actively removing metal ions in this invention. The capture rate of Example 1 ([2.2.2]-cavitary ether) (99.7%) was slightly higher than that of Example 2 (azacrown ether, 99.2%) and Example 3 (calixarene, 98.5%), which is consistent with the stronger pre-organization and complexation constant of cavitary ether. Example 5 (capturing group content 70%) had the highest capture rate (99.8%), indicating that appropriately increasing the density of capturing groups is beneficial to improving the metal ion removal ability.

[0067] Comparative Example 1 (SiO2) could only block some ions (capture rate 72.5%), Comparative Example 2 (BCB) had a slightly better blocking ability (85.2%), but Comparative Example 3 (photoresist) had almost no ability to block metal ions (capture rate only 35.8%). These comparative examples all belong to passive blocking mechanisms and cannot remove the adsorbed ions. At high temperatures, ions may still diffuse into the device.

[0068] 3. Comparison of insulation performance: The leakage current density of Examples 1-7 is all above 10. -9 The leakage current density is on the order of A / cm², reaching a level comparable to high-quality ALD deposited films. Example 8 (without anchoring groups) showed a leakage current density of 3.2 × 10⁻⁶. -7 The leakage current (A / cm²) was significantly higher than in other examples, indicating that the covalent bonding formed by the anchoring groups is crucial for the formation of a dense, pinhole-free film. Example 9 (80 nm film) had a leakage current (2.5 × 10⁻⁶). -8 Thin films with an A / cm² slightly higher than 150nm exhibit a positive correlation between thickness and insulation performance.

[0069] Comparative Example 1 (SiO2) has a leakage current of 5.3 × 10⁻⁶. -8 A / cm², Comparative Example 2 (BCB) is 2.1 × 10⁻⁶. -7 A / cm², Comparative Example 3 (photoresist) reaches as high as 8.6×10 -6 The A / cm² values ​​are inferior to those of the preferred embodiments of the present invention.

[0070] 4. Comparison of device protection effects: The device gain degradation rate in Example 1 was only 0.8%, indicating that the protective layer did not damage the device during high-temperature volatilization and effectively blocked external contamination. Example 5 (high capture group content) had the lowest degradation rate (0.7%), while Example 3 (calixarene) had a slightly higher rate (1.8%), which is consistent with the trend of capture rate.

[0071] Example 8 (without anchoring groups) showed a degradation rate of 4.8%, indicating that insufficient adhesion may cause the protective layer to peel off locally at high temperatures, thus losing its protective function. Example 9 (thin layer) showed a degradation rate of 2.3%, which is also higher than the preferred thickness.

[0072] Comparative Example 1 (SiO2) resulted in a 15.3% gain degradation, which may be related to plasma damage during the PECVD process. Comparative Example 2 (BCB) showed a degradation rate of 8.7%, while Comparative Example 3 (photoresist) showed a degradation rate as high as 32.5%, the latter mainly due to the formation of new interface states caused by the high-temperature carbonization of the photoresist.

[0073] 5. Influence patterns of key process parameters The type of capturing group is: [2.2.2]-Cavity ether (Example 1) > Azacrown ether (Example 2) > Calicoaryne (Example 3), consistent with the order of pre-organization and complexation constant of cavity ether.

[0074] The content of capturing groups: 70% (Example 5) > 50% (Example 1) > 30% (Example 4). Appropriately increasing the density of capturing sites is beneficial to improving ion scavenging ability.

[0075] POSS content: 25% (Example 7) has the most complete volatilization, 15% (Example 1) has the best overall performance, and 5% (Example 6) has slightly higher volatilization residue.

[0076] Anchoring group: Example 1 containing an anchoring group showed a significant advantage over Example 8 without an anchoring group in terms of leakage current and device degradation rate, demonstrating the importance of chemical bonding anchoring.

[0077] Film thickness: 150 nm (Example 1) is better than 80 nm (Example 9). Appropriate thickness is beneficial for forming a complete and dense protective layer.

[0078] In summary, the high-temperature volatile protective layer provided by this invention is significantly superior to existing technologies in terms of volatile characteristics, metal ion capture capability, insulation performance, and device protection effect. In particular, the technical solutions represented by Examples 1, 5, and 7 exhibit excellent performance indicators.

[0079] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions, characterized in that, The protective layer is an organic-inorganic hybrid film containing a main polymer material and functional additives; The molecular chains of the main polymer material are grafted with metal ion capturing groups. The protective layer has gradient volatilization characteristics, and can volatilize in stages within a temperature range of 200-400℃. After treatment at 400℃ in an inert atmosphere for 30 minutes, the mass of the residue on the surface of the gallium arsenide wafer is less than 0.1% of the initial mass. The protective layer has a sodium ion capture rate of greater than 98%.

2. The high-temperature volatile protective layer for water-oxygen-metal ion isolation of gallium arsenide wafers according to claim 1, characterized in that, The main polymer material is a polynorbornene derivative with a number-average molecular weight of 10,000-100,000 g / mol and a molecular weight distribution index of 1.2-2.

5.

3. The high-temperature volatile protective layer for water-oxygen-metal ion isolation of gallium arsenide wafers according to claim 1, characterized in that, The metal ion trapping group includes any one of a crypt ether group, a crown ether group, or a calixarene group; The capturing group is grafted onto the polymer backbone via a C1-C6 alkyl linker, and the monomer containing the capturing group accounts for 30%-70% of the total molar amount of the polymer monomer.

4. The high-temperature volatile protective layer for water-oxygen-metal ion isolation of gallium arsenide wafers according to claim 1, characterized in that, The functional additive is a cage-type polysilsesquioxane, and its molar content in the protective layer is 5%-25%, or accounts for 1%-10% of the total solid mass of the protective layer.

5. The high-temperature volatile protective layer for water-oxygen-metal ion isolation of gallium arsenide wafers according to claim 1, characterized in that, The molecular chain ends of the main polymer material are also modified with anchoring groups, including trimethoxysilyl or triethoxysilyl groups, for forming chemical bonds with the surface of gallium arsenide wafers.

6. A method for preparing a high-temperature volatile protective layer for water-oxygen-metal ion isolation on gallium arsenide wafers according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1, Precursor polymer synthesis: Under inert gas protection, norbornene monomer containing metal ion trapping groups and vinyl-POSS monomer are dissolved in anhydrous organic solvent, and Grubbs second-generation catalyst is added to carry out ring-opening metathesis polymerization. After the reaction is completed, the reaction is terminated, and the solid polymer is obtained by precipitation, washing and vacuum drying. Step 2, preparation of protective layer solution: Dissolve the solid polymer synthesized in Step 1 in a mixed organic solvent to prepare a solution with a mass fraction of 3%-15%, add leveling agent and defoamer, filter to obtain protective layer coating liquid; Step 3, Coating and Pre-baking: Spin-coat the protective layer coating liquid obtained in Step 2 onto the surface of the pretreated gallium arsenide wafer, and then perform gradient heating pre-baking on a hot plate to form a protective layer film; Step 4, High-temperature volatilization: Place the gallium arsenide wafer covered with the protective layer in an annealing furnace, heat it to 350-420℃ in an inert gas atmosphere, and keep it at a constant temperature for 10-30 minutes to allow the protective layer to completely volatilize.

7. The method for preparing a high-temperature volatile protective layer for water-oxygen-metal ion isolation on gallium arsenide wafers according to claim 6, characterized in that, The spin coating process parameters in step 3 are as follows: first spin coating at a low speed of 300-500 rpm for 5-10 seconds, and then spin coating at a high speed of 2000-4000 rpm for 30-60 seconds, resulting in a dry protective film thickness of 50-500 nm.

8. The preparation method according to claim 6, characterized in that, The gradient heating pre-baking treatment in step 3 includes: baking at 80-90℃ for 2-5 minutes in the first stage, baking at 110-130℃ for 3-8 minutes in the second stage, and baking at 140-160℃ for 2-5 minutes in the third stage.

9. The preparation method according to claim 6, characterized in that, In step 4, the heating rate is 5-20℃ / min, and the flow rate of the inert gas is 2-10slm.

10. An application of a high-temperature volatile protective layer for isolating gallium arsenide wafers from water, oxygen, and metal ions according to any one of claims 1-5, characterized in that, The application of the high-temperature volatile protective layer in the manufacturing process of gallium arsenide-based high electron mobility transistors or heterojunction bipolar transistors. The applications include serving as a barrier layer against water, oxygen, and metal ions in ohmic contact alloying processes, back-side thinning processes, or temporary protective processes prior to front-side metallization.

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