A surface treatment method of a non-doped high-resistance gallium arsenide wafer

Abstract

This invention discloses a surface treatment method for undoped high-resistivity gallium arsenide wafers, comprising the following steps: The undoped high-resistivity gallium arsenide wafer is placed on a rotating platform and rotated; a cleaning solution is sprayed onto the wafer surface via ultrasonic atomization for etching and cleaning; subsequently, it is rinsed with megasonic-assisted ultrapure water and then dried; in a vacuum chamber, the treated wafer surface is bombarded and planarized using an inert gas cluster ion beam; in the same vacuum chamber or a connected vacuum atmosphere, hydrogen gas is introduced and decomposed to generate atomic hydrogen for further treatment; the wafer is heated and held at a temperature in a vacuum or inert gas atmosphere, and then cooled; through a silicon-free reagent design throughout the process, rotating ultrasonic atomization cleaning replacing traditional immersion cleaning, megasonic-assisted rinsing, and online monitoring technology, the silicon residual concentration on the surface of the undoped high-resistivity GaAs wafer is stably controlled at 1×10¹. 4 Below atoms / cm².

Description

Technical Field

[0001] This invention belongs to the field of semiconductor substrate material surface treatment technology, specifically referring to a surface treatment method for undoped high-resistivity gallium arsenide wafers. Background Technology

[0002] Undoped semi-insulating gallium arsenide (SI-GaAs) is widely used as an epitaxial substrate for optoelectronic devices such as microwave monolithic integrated circuits, high electron mobility transistors, heterojunction bipolar transistors, photodetectors, and lasers due to its high resistivity, good electron mobility properties, and lattice matching with various heterojunction materials. As device feature sizes continue to shrink and integration density increases, the surface quality requirements for substrate wafers are far higher than the flatness requirements of conventional semiconductors.

[0003] Current surface treatment of undoped high-resistivity GaAs wafers typically employs a process route combining chemical mechanical polishing (CMP) and wet cleaning. The industry mainstream uses polishing slurries containing silica sol, followed by ultrasonic cleaning using an ammonia-hydrogen peroxide system to remove silicon residue. However, conventional cleaning can only remove physically adsorbed silicon particles, resulting in low efficiency in removing chemically bonded silicon species. The residual Si after treatment is typically higher than 1×10¹. 5 Atoms / cm², easily degrading the high resistivity of the substrate. Meanwhile, conventional processes also suffer from insufficient planarization precision, subsurface damage, and incompatibility between the passivation layer and MOCVD.

[0004] Therefore, it is necessary to develop a method that can simultaneously achieve extremely low surface silicon residue (<1×10¹). 4 A surface treatment method for undoped high-resistivity GaAs wafers with high density (atoms / cm²), ultra-high flatness (Ra<0.12nm), excellent local thickness uniformity (LTV<1.0µm@20mm×20mm), no residual conductive elements, and compatibility with epitaxial processes is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the needs and problems mentioned in the background above, the present invention provides a surface treatment method for undoped high-resistivity gallium arsenide wafers, thereby at least partially solving the aforementioned problems.

[0006] According to the technical solution of the present invention, a surface treatment method for undoped high-resistivity gallium arsenide wafers is provided, comprising the following steps: Undoped high-resistivity gallium arsenide wafers are placed on a rotating platform and rotated at a speed of 200~500 rpm. The cleaning solution is sprayed onto the wafer surface by ultrasonic atomization for etching and cleaning. Then, the wafer is rinsed with mega-sonic-assisted ultrapure water and dried. In a vacuum chamber, an inert gas cluster ion beam is used to bombard and planarize the surface of the processed wafer. Hydrogen gas is introduced into the same vacuum chamber or in a connected vacuum atmosphere and decomposed to generate atomic hydrogen. The mixture is then treated at a substrate temperature of 200-350°C for 5-15 minutes. In a vacuum or inert gas atmosphere, heat the wafer to 450~550℃ and hold for 30~60 minutes, then cool it.

[0007] Preferably, the cleaning solution comprises, in sequence: Etching solution A: prepared by mixing ammonia, hydrogen peroxide and deionized water in a volume ratio of 1:1:10, with a pH value of 10.5~11.5 and a processing time of 30~60s; Etching solution B: prepared by hydrochloric acid, hydrogen peroxide and deionized water in a volume ratio of 1:1:20, with a pH value of 1.0~2.0 and a treatment time of 30~60s; Etching solution C: prepared by mixing ammonia and deionized water at a volume ratio of 1:5, with a pH value of 10.0~11.0 and a processing time of 10~20s.

[0008] Preferably, the incident angle of the inert gas cluster ion beam is 0° to 15° relative to the normal direction of the wafer surface, and the inert gas is argon.

[0009] Preferably, the flow rate of the hydrogen gas is 50~100 sccm / min, wherein atomic hydrogen is generated by thermal decomposition, microwave decomposition or plasma decomposition; the thermal decomposition can use tungsten wire, platinum wire or tantalum wire as heating element, and the heating temperature is 1500~2000℃.

[0010] Preferably, the cooling is carried out in an argon atmosphere, and the cooling rate does not exceed 5°C / min.

[0011] Preferably, the wafer is subjected to thermal desorption treatment at 450~550℃ for 1~2 hours to remove physically adsorbed impurities on the surface and ensure the adhesion of the subsequent passivation layer.

[0012] Preferably, the megasonic frequency is 800kHz~1.2MHz, the ultrapure water rinsing time is not less than 180s, and the ultrapure water resistivity is ≥18.2MΩ·cm; the drying adopts the Marangoni drying method and gaseous isopropanol is introduced.

[0013] Preferably, the process further includes pre-processing the undoped high-resistivity gallium arsenide wafer by performing chemical mechanical polishing (CMP) pre-processing with a chemical mechanical polishing slurry containing silica sol abrasive particles and hydrogen peroxide as an oxidant before placing it on the rotating platform.

[0014] Preferably, the undoped high-resistivity gallium arsenide wafer processed by the method has a subsurface damage layer thickness of no more than 5 atomic layers and a total residual concentration of surface metal ions ≤ 1 × 10¹. 0 Atoms / cm²

[0015] Preferably, the process further includes a low-temperature organic passivation protection step: in a vacuum or inert gas atmosphere, a passivation layer is formed by spraying an organic material with a molecular weight of 200-1000 that is easily pyrolyzed, with a thickness of 5-20 nm; the organic material is polyethylene glycol, polyethylene oxide, or an alkane polymer, which is stable at room temperature; in the subsequent MOCVD process, it is completely vaporized and decomposed in a hydrogen atmosphere at 400-600°C, and discharged from the chamber along with gallium oxide and arsenic oxide.

[0016] Beneficial effects: This invention achieves stable control of the residual silicon concentration on the surface of undoped high-resistivity GaAs wafers at 1×10¹ through a fully silicon-free reagent-free process, replacing traditional immersion cleaning with rotary ultrasonic atomization cleaning, megasonic assisted rinsing, and online monitoring technology. 4 With a density below atoms / cm², this significantly reduces the damage to the high-resistivity properties of the substrate caused by silicon impurities compared to existing CMP processes.

[0017] This invention breaks through the roughness limit that CMP technology cannot stably achieve through a three-step synergistic process of GCIB planarization, atomic hydrogen repair and low temperature annealing, and achieves an ultra-low root mean square roughness of Ra≤0.12nm. At the same time, it reduces the thickness of the subsurface damage layer to less than 5 atomic layers, providing an ideal template surface for subsequent high-quality epitaxial growth.

[0018] This invention utilizes the global uniform planarization capability of GCIB combined with the uniform distribution of the reagent under the action of rotational centrifugation to control the LTV within a 20mm×20mm window to within 1.0µm, which significantly improves the macroscopic flatness of the wafer surface and is beneficial for the photolithography process window of large-size, high-density devices. Detailed Implementation

[0019] 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.

[0020] This invention overcomes the shortcomings of existing technologies and provides a surface treatment method for undoped high-resistivity gallium arsenide wafers. The core technical problems to be solved include: (1) Reduce the residual silicon concentration on the wafer surface to 1×10¹ 4 Below atoms / cm²; (2) Reduce the root mean square roughness of the wafer surface to below 0.12 nm; (3) Control the local thickness uniformity within the 20mm×20mm window to within 1.0µm; (4) Ensure that no conductive elements (including metal ions and silicon elements) are introduced into the wafer surface during the entire processing and after processing. (5) Eliminate or significantly reduce the thickness of the subsurface damage layer; (6) Provide a surface passivation solution that is free of conductive impurities and can be connected in situ with subsequent epitaxial processes.

[0021] To address the aforementioned technical problems, this invention provides a surface treatment method for undoped high-resistivity gallium arsenide wafers. First, a rotating ultrasonic atomization wet cleaning system, free of silicon-containing reagents and metal ions throughout the entire process, is employed to efficiently remove pre-existing particulate matter, organic matter, and metal contaminants from the wafer surface, reducing silicon residue to below the target level. Then, a three-step surface morphology repair process, combining gas cluster ion beam (GCIB) planarization with atomic hydrogen treatment and low-temperature annealing, is used to achieve an atomically smooth surface and repair subsurface damage. Finally, an ultrathin passivation layer free of conductive elements is selectively constructed under ultra-high vacuum conditions to ensure the wafer surface maintains high cleanliness and electrical stability before subsequent processes. Throughout the entire process, all contact materials, gas sources, and reagents undergo rigorous screening to ensure they are free of silicon and metal ions, and an online monitoring system is in place to control conductive element residue throughout the entire process.

[0022] The specific technical solution of this invention includes the following steps: Step 1: Rotary ultrasonic atomization metal-free wet cleaning: An undoped, high-resistivity gallium arsenide wafer is placed on a carrier of a rotating ultrasonic atomization cleaning platform, wafer side facing upwards, and rotated uniformly at a speed of 200–500 rpm. The cleaning solution is atomized into tiny droplets with an average particle size of 1–5 µm using a radio frequency ultrasonic transducer, and sprayed onto the wafer surface at a flow rate of 50–100 ml / min. The droplets spread uniformly under centrifugal force and react chemically with the surface. Excess solution is ejected from the wafer surface during rotation, significantly reducing solution residue.

[0023] The cleaning process sequentially employs three different etching solutions for atomized etching: Etching solution A: An alkaline oxide layer etching solution, prepared by mixing ammonia (NH4OH), hydrogen peroxide (H2O2), and deionized water in a volume ratio of 1:1:10, with a pH value of 10.5~11.5. This etching solution is used to generate oxide layers (Ga2O3 and As2O3) in situ on the GaAs surface, while simultaneously encapsulating and suspending surface-attached contaminant particles. The processing time is 30~60 seconds.

[0024] Etching Solution B: An acidic contaminant removal solution, prepared by mixing hydrochloric acid (HCl), hydrogen peroxide (H₂O₂), and deionized water in a volume ratio of 1:1:20, with a pH of 1.0–2.0. This etching solution selectively dissolves As oxides and exhibits excellent complexing removal capabilities for metallic contaminants (including Fe, Ca, Al, Ti, Zn, Mg, etc.). The processing time is 30–60 seconds.

[0025] Etching solution C: An oxide removal solution prepared by mixing ammonia (NH4OH) and deionized water at a volume ratio of 1:5, with a pH of 10.0–11.0. This etching solution is used to remove the thin oxide layer remaining on the wafer surface after step B, exposing a fresh GaAs surface with a stoichiometric ratio close to intrinsic. The processing time is 10–20 seconds.

[0026] The etching solutions A, B, and C mentioned above do not contain any silicon-containing compounds (including but not limited to silica sol, silicates, and siloxanes), nor do they contain sodium. + K + Metal ions are present. The ammonia, hydrochloric acid, and hydrogen peroxide used in the etching solution are all semiconductor-grade high-purity reagents.

[0027] After completing the three-step atomization etching, megasonic-assisted ultrapure water rinsing is immediately performed: using deionized water with a resistivity ≥18.2 MΩ·cm, the wafer surface is rinsed under the assistance of megasonic waves with a frequency of 800 kHz~1.2 MHz for at least 180 seconds, with a deionized water flow rate of at least 2 L / min. The cavitation effect of megasonic waves can effectively remove submicron-sized residual particles without damaging the surface.

[0028] After rinsing, the wafer is dried using the Marangoni drying method: gaseous isopropanol (IPA) is introduced into the wafer surface, and the water film is rapidly removed from the wafer surface by utilizing the Marangoni effect driven by the surface tension gradient. The wafer is then cooled to room temperature in a high-purity nitrogen atmosphere.

[0029] The above-described rotating ultrasonic atomization metal-free wet cleaning method can reduce the total amount of residual metal ions on the wafer surface to ≤1×10¹. 0 Atoms / cm², the residual concentration of silicon element decreased to <1×10¹ 4 Atoms / cm², surface particle count (≥0.2µm) reduced to ≤50 particles / wafer.

[0030] Step 2: Ultra-smooth planarization of gas cluster ion beams: The gallium arsenide wafer, after being cleaned and dried in step one, is transferred to an ultra-high vacuum processing chamber with a base vacuum level better than 1×10⁻⁶. -5 Pa. The wafer surface was planarized using gas cluster ion beam (GCIB) technology.

[0031] The cluster-forming gas used is a high-purity inert gas, preferably argon (Ar, purity ≥ 99.9999%). The gas expands adiabatically through a nozzle to form clusters, which are then ionized and accelerated to form cluster ion beams with specific energies. The process parameters are controlled as follows: Average cluster size: 500~1500 atoms / cluster; Accelerating voltage: 15~30kV; Ion beam incident angle: 0°~15° relative to the normal direction of the wafer surface; Total ion dose: 5 × 10¹ 4 ~5×10¹ 5 ions / cm²; Material removal rate: 10~30nm.

[0032] Under the GCIB treatment conditions, when accelerated atomic clusters collide with the GaAs surface, the kinetic energy they carry (total energy 15~30 keV) is uniformly distributed among hundreds to thousands of atoms within the cluster, resulting in an average energy of only a few electron volts per atom, slightly lower than the bond energy of the Ga-As bond in GaAs. At this energy scale, the atoms in the clusters primarily cause bond activation of surface atoms rather than collisional cascade sputtering. Because surface protrusions have higher collision cross-sections and energy densities, they are preferentially removed; while pits have a lower probability of being impacted, and the energy distribution tends to fill rather than deepen the pits. This preferential smoothing mechanism allows GCIB treatment to significantly reduce surface roughness without introducing additional scratches or subsurface damage.

[0033] After GCIB treatment, the root mean square roughness Ra of the wafer surface is reduced to below 0.25 nm, and the local thickness uniformity LTV within the 20 mm × 20 mm window is less than 1.0 µm.

[0034] Step 3: Repair of surface damage caused by atomic hydrogen: In the same ultra-high vacuum chamber where GCIB planarization has been completed, high-purity hydrogen gas (H2, purity ≥99.9999%) is introduced at a flow rate of 50–100 sccm / min. Atomic hydrogen can be generated in three ways: ① Thermal decomposition: 1500~2000℃ for tungsten / platinum wire, with the substrate temperature controlled at 200~350℃, and the processing time is 5~15min; ② Microwave pyrolysis: 2.45GHz microwave radiation; ③Plasma pyrolysis: Low-pressure hydrogen glow discharge.

[0035] Atomic hydrogen possesses extremely strong reducing and diffusing abilities. During the treatment process, atomic hydrogen diffuses into the subsurface damage region (including lattice distortion, dangling bonds, and microvoids) introduced by GCIB treatment, reacting with the defect structure: It combines with dangling bonds to form As-H or Ga-H bonds, which can be completely decomposed in a hydrogen atmosphere at 400~600℃ during MOCVD process, reducing it to the original GaAs lattice. The oxides (such as Ga2O3 and As2O3) on the reduced surface and subsurface are removed, and the water and volatile byproducts generated are extracted. It promotes the migration and rearrangement of surface atoms, reducing the thickness of the damaged layer to less than 5 atomic layers.

[0036] Atomic hydrogen treatment can further remove trace amounts of carbon and oxygen contaminants that may remain after wet cleaning in step one, and adjust the surface stoichiometry to an ideal state (the (001) face or (111) face terminated by As).

[0037] Step 4: Low-temperature annealing: After the atomic hydrogen treatment is completed, the hydrogen gas supply is stopped, and the chamber vacuum level is maintained at better than 1×10⁻⁶. -4 Pa. The wafer is heated to 450-550°C in an argon (Ar) atmosphere (flow rate 50-100 sccm), held for 30-60 min, and then cooled to room temperature at a rate not exceeding 5°C / min.

[0038] The low-temperature annealing step serves the following purpose: Complete the final saturation of dangling bonds in the surface and near-surface regions; promote the desorption of residual atomic hydrogen and reaction byproducts from the lattice; release thermal stress or residual stress that may be introduced during GCIB and atomic hydrogen treatment; further smooth the surface through thermally activated atomic migration, stabilizing the surface roughness at Ra≤0.12nm; confirm that the subsurface damage layer is completely eliminated or reduced to a negligible level (≤5 atomic layers).

[0039] Step 5: Thermal desorption treatment: The wafer is subjected to thermal desorption treatment at 450~550℃ for 1~2 hours to remove physically adsorbed impurities on the surface and ensure the adhesion of the subsequent passivation layer.

[0040] Step Six: Passivation Protection of Low Molecular Weight Organic Compounds at Room Temperature After low-temperature annealing, an organic passivation layer is prepared on the wafer surface by spraying under an inert gas (high-purity N2) atmosphere: polyethylene glycol (PEG) with a molecular weight of 200~1000 is selected as the passivation material, 1%~5% anhydrous ethanol solution is prepared, and it is uniformly sprayed at room temperature. After natural evaporation, a dense passivation layer with a thickness of 5~20nm is formed.

[0041] This passivation layer is stable at room temperature, isolating moisture and preventing oxidation. Subsequently, it is fed into an MOCVD chamber where it is completely vaporized and decomposed into small-molecule hydrocarbons in a hydrogen atmosphere at 400–600°C. These hydrocarbons are discharged along with gallium oxide and arsenic oxide, leaving no residual contamination. After reduction CMP cleaning, the silicon residue on the GaAs surface is consistently below 1 × 10¹. 4 Atoms / cm²

[0042] Example 1 I. Preparation of Raw Materials and Equipment: Wafer specifications: Undoped high-resistivity gallium arsenide (SI-GaAs) wafer, 100mm (4 inches) in diameter, crystal orientation (100), resistivity > 1×10⁻⁶. 7 Ω·cm, initial surface roughness Ra≈0.6~0.8nm, initial residual Si concentration approximately 5×10⁻⁶ 16 ~1×10 17 atom / cm².

[0043] Cleaning equipment: Rotary ultrasonic atomization cleaning platform (equipped with radio frequency ultrasonic transducer, frequency 1.6MHz; rotating stage, speed adjustable from 0 to 600 rpm; 3 liquid atomization nozzles; mega-sound rinsing nozzle, frequency adjustable from 0.5 to 2.0MHz; Marangoni drying system).

[0044] Ultra-high vacuum processing system: GCIB chamber (equipped with cluster ion source, accelerating voltage 0~50kV; sample stage can be tilted and rotated; background vacuum <1×10⁻⁶ kV). -5 Pa); microwave atomic hydrogen source (2.45GHz microwave radiation pyrolysis); annealing heating stage (maximum temperature 800℃).

[0045] Reagents and gases: Etching solution A: Semiconductor grade NH4OH (29%), H2O2 (30%), ultrapure water (18.2 MΩ·cm), volume ratio 1:1:10.

[0046] Etching solution B: Semiconductor-grade HCl (37%), H2O2 (30%), and ultrapure water, in a volume ratio of 1:1:20.

[0047] Etching solution C: Semiconductor-grade NH4OH (29%), ultrapure water, volume ratio 1:5.

[0048] Ultrapure water: resistivity ≥18.2MΩ·cm, TOC <1ppb, dissolved oxygen <5ppb.

[0049] The water used for rinsing the megaphonic signal is the same as that used for ultrapure water.

[0050] CMP polishing slurry: silica sol (particle size 80nm, solid content 10%) + H2O2.

[0051] GCIB working gas: High-purity Ar (99.9999% purity).

[0052] Atomic hydrogen gas: high-purity H2 (purity 99.9999%).

[0053] Annealing protective gas: High-purity Ar (99.9999% purity).

[0054] Organic passivation: PEG (molecular weight 400) anhydrous ethanol solution.

[0055] Carrier and chamber wall materials: PFA (perfluoroalkoxy resin) or stainless steel coated with a 100nm Al2O3 film.

[0056] II. Handling methods: Step 1: Rotary ultrasonic atomization metal-free wet cleaning: Loading and initial adjustment: Place the GaAs wafer on the PFA carrier of the rotating ultrasonic atomizing cleaning platform with the polished side of the wafer facing upward.

[0057] Close the chamber door and purge with high-purity N2 for 2 minutes to remove air from the chamber.

[0058] Set the rotation speed to 300 rpm.

[0059] Etching solution A atomization etching: Preparation of etching solution A: In the chemical solution tank A of the cleaning platform, add ultrapure water, NH4OH and H2O2 in sequence, stir and mix evenly, pH 11.

[0060] Turn on the ultrasonic atomizing transducer and adjust the atomization power to make the average droplet size 3µm.

[0061] Etching solution A is sprayed onto the rotating wafer surface through a nozzle at a flow rate of 75 mL / min.

[0062] Processing time: 45s. During this time, the liquid medicine is evenly spread and thrown off under centrifugal force, and excess liquid medicine is collected in the waste liquid tank.

[0063] Turn off the supply of etching solution A, and continue to rotate the wafer for 15 seconds to dry the surface residue.

[0064] Etching solution B atomization etching: Switch to chemical tank B. Etching solution B is HCl:H2O2:H2O=1:1:20 (volume ratio) with pH 1.5.

[0065] It is also sprayed at a flow rate of 75 mL / min and a droplet size of 3 µm.

[0066] Processing time: 45s.

[0067] After turning off, spin dry for 15 seconds.

[0068] Etching solution C atomization etching: Switch to chemical tank C. Etching solution C is NH4OH:H2O=1:5 (volume ratio) with pH10.5.

[0069] Flow rate 75 mL / min, droplet size 3 µm.

[0070] Processing time: 15s.

[0071] After turning off, spin dry for 15 seconds.

[0072] Megasonic-assisted ultrapure water rinsing: Stop rotating and move the Megasonic rinsing nozzle to a position 2-5mm directly above the wafer.

[0073] Turn on the megohm generator, set the frequency to 1.0MHz, and the power to 2W / cm².

[0074] The wafer surface was rinsed with ultrapure water at a flow rate of 2 L / min for 200 s. During rinsing, the wafer was slowly rotated at 50 rpm to ensure uniform rinsing.

[0075] Turn off the siren, continue rinsing with ultrapure water for 30 seconds, and then stop the water supply.

[0076] Marangoni drying: Keep the wafer rotating at 50 rpm.

[0077] High-purity N2 (flow rate 10 L / min) and gaseous isopropanol (IPA, flow rate 500 sccm, obtained by evaporating liquid IPA heated to 80°C) are simultaneously sprayed onto the wafer surface through a gas nozzle.

[0078] The Marangoni effect (surface tension gradient) is used to quickly remove the water film from the wafer surface, with a drying time of about 30 seconds.

[0079] Stop rotating and cool to room temperature (approximately 25°C) in an N2 atmosphere.

[0080] Post-cleaning inspection (optional, use monitoring wafer): TXRF testing revealed approximately 6 × 10¹³ atoms / cm² of residual silicon and ≤ 8 × 10⁻⁶ total metal ion residue. 9 atom / cm².

[0081] Surface particle counter (≥0.2µm): ≤50 particles / wafer.

[0082] Step 2: Ultra-smooth planarization of gas cluster ion beams: Transfer to UHV Chamber: The dried wafer is transferred to the GCIB processing chamber via a vacuum transfer tube (passing through a buffer chamber in between), maintaining a vacuum level of <5×10⁻⁶ throughout the transfer process. -5Pa, to avoid air pollution.

[0083] GCIB process parameter settings: working gas: Ar, flow rate 200 sccm.

[0084] Cluster formation: Gas expands adiabatically through a nozzle (0.5 mm diameter) into a vacuum, forming neutral clusters, which are then ionized by electron bombardment (electron energy 100 eV) to obtain single charges.

[0085] Cluster size selection: By monitoring time-of-flight mass spectrometry and adjusting nozzle temperature and back pressure, the average cluster size is made to be 1000 atoms / cluster.

[0086] Accelerating voltage: 22kV (total cluster energy 22keV, average energy of a single atom 22eV).

[0087] Ion beam incident angle: 8° (relative to the wafer surface normal).

[0088] Total ion dose: 2×10¹ 5 ions / cm².

[0089] Scanning method: Ion beam fixed, wafer stage scans in the XY direction, scanning speed 50mm / s, covering the entire wafer area.

[0090] Expected material removal: 20 nm (based on in-situ monitoring using a quartz crystal micro-sky or pre-experimental calibration).

[0091] Perform GCIB processing: Heat the wafer to room temperature (no additional heating is required, but ion beam bombardment may raise the surface temperature to 50~80°C).

[0092] Turn on the ion source and perform scanning and bombardment according to the parameters described above.

[0093] After the treatment is complete, turn off the ion source and wait 1 minute for the chamber pressure to recover.

[0094] Step 3: Repair of surface damage caused by atomic hydrogen: Atomic hydrogen generation and conditions: Keep the wafer in the GCIB chamber (or move it to a dedicated atomic hydrogen processing chamber via a transfer tube; this embodiment uses the same chamber but switches the gas system).

[0095] High-purity H2 was introduced at a flow rate of 75 sccm, and the chamber pressure was stabilized at 5 × 10⁻⁶. - Approximately 2 Pa.

[0096] Microwave pyrolysis at 2.45 GHz was activated to produce atomic hydrogen.

[0097] The wafer stage is heated to raise the wafer temperature to 280°C (measured by thermocouple contact with the back of the wafer).

[0098] Processing time: 10 minutes.

[0099] Reaction process: Atomic hydrogen reacts with dangling bonds and oxides on the surface and subsurface of GaAs to generate volatile products such as H2O, AsH3, and GaH3, which are then extracted by a vacuum pump.

[0100] During processing, the wafer is kept rotating slowly at 20 rpm to ensure uniformity.

[0101] End and evacuation: Turn off the tungsten filament power supply and stop the H2 flow.

[0102] Continue evacuating until the base pressure is <1×10⁻⁶. -4 Pa, while the wafer is naturally cooled to below 100°C for 15 minutes.

[0103] Step 4: Low-temperature annealing: Annealing conditions: In the same chamber (or moved to a dedicated annealing station), high-purity Ar is introduced as a protective gas at a flow rate of 75 sccm, and the pressure is maintained at approximately 1 × 10⁻⁶. - ¹Pa.

[0104] The wafer was heated to 500°C at a heating rate of 10°C / min.

[0105] Keep warm at 500℃ for 45 minutes.

[0106] After the heat preservation is completed, the temperature is reduced to 200℃ at a rate of 5℃ / min, and then allowed to cool naturally to below 50℃.

[0107] Turn off Ar traffic.

[0108] Annealing process: completes dangling bond saturation, eliminates residual stress, further smooths surface atomic rearrangement, and reduces Ra to 0.09 nm.

[0109] Step 5: Thermal desorption treatment: The annealed wafer is then subjected to a vacuum (<1×10⁻⁶) -7 The wafer (Pa) is directly transferred to the processing chamber without exposure to the atmosphere. It is heated to 500°C and held for 1 hour to remove physically adsorbed impurities and ensure a clean surface. It is then cooled to room temperature.

[0110] Step Six: Passivation Protection of Low Molecular Weight Organic Compounds at Room Temperature Under a high-purity N2 atmosphere, a 3% PEG400 ethanol solution was sprayed, and a film of about 10 nm was formed at room temperature; it was then stored at room temperature before being sent to MOCVD.

[0111] Example 2 The difference from Example 1 is as follows: Step 1: Rotation speed 200 rpm; Etching solutions A and B each 60 s, etching solution C 20 s; Atomization flow rate 50 mL / min, droplet size 1 µm; Megohm frequency 800 kHz, rinsing 180 s.

[0112] Step 2: Cluster average size 500 atoms / cluster, accelerating voltage 15kV, incident angle 0°, total dose 5×10¹ 4 ions / cm², removal amount 10nm.

[0113] Step 3: Raise the wafer temperature to 200℃ for 15 minutes, with an H2 flow rate of 50 sccm.

[0114] Step 4: Heat the wafer to 450°C at a heating rate of 10°C / min, and hold at 450°C for 60 minutes.

[0115] Step five is cancelled.

[0116] Example 3 The difference from Example 1 is as follows: Step 1: Rotation speed 500 rpm; Etching solutions A and B each 30 s, etching solution C 10 s; Atomization flow rate 100 mL / min, droplet size 5 µm; Megohm frequency 1.2 MHz, rinsing 240 s.

[0117] Step 2: Cluster average size 1500 atoms / cluster, accelerating voltage 30kV, incident angle 15°, total dose 5×10 15 ions / cm², removal amount 30nm.

[0118] Step 3: Raise the wafer temperature to 350℃ for 5 minutes, with an H2 flow rate of 100 sccm.

[0119] Step 4: Heat the wafer to 550°C at a heating rate of 10°C / min, and hold at 550°C for 30 minutes.

[0120] Step 5: Organic passivation layer thickness 1.5nm (15 sprays), densification temperature 400℃, time 5min.

[0121] Example 4 The difference from Example 1 is as follows: Step 1: Rotation speed 400 rpm; Etching solutions A and B each 40 s, Etching solution C 15 s; Atomization flow rate 80 mL / min, droplet size 2 µm; Megohm frequency 1.0 MHz, Rinse for 200 s.

[0122] Step 2: Cluster average size 800 atoms / cluster, accelerating voltage 20kV, incident angle 5°, total dose 1×10⁻⁶ 15 ions / cm², removal amount 15nm.

[0123] Step 3: Raise the wafer temperature to 250℃ for 12 minutes, with an H2 flow rate of 100 sccm.

[0124] Step 4: Heat the wafer to 480°C at a heating rate of 10°C / min, and hold at 480°C for 50 minutes.

[0125] Step five is cancelled.

[0126] Example 5 The difference from Example 1 is as follows: Step 1: After atomizing and etching C, add a pure water atomization rinse (ultrapure water, flow rate 75 mL / min, 30 seconds), and then perform a megasonic rinse twice (180 seconds each time, with a 30-second interval between rinses).

[0127] Step 5: Organic passivation layer thickness 0.5nm.

[0128] Example 6 Step 2: Cluster average size 1200 atoms / cluster, accelerating voltage 35kV, incident angle 0°, total dose 3×10 15 ions / cm².

[0129] Step 3: Raise the wafer temperature to 300℃ for 8 minutes, with an H2 flow rate of 100 sccm.

[0130] Step 4: Heat the wafer to 520°C at a heating rate of 10°C / min, and hold at 520°C for 40 minutes.

[0131] Step five is cancelled.

[0132] Example 7 The difference from Example 1 is as follows: Step 4: Heat the wafer to 550°C at a heating rate of 10°C / min, and hold at 550°C for 60 minutes.

[0133] Step 5: Organic passivation layer thickness 1.2nm, densification temperature 360℃, time 10min.

[0134] Example 8 The difference from Example 1 is as follows: Step 1: Etching solutions A and B each for 30 seconds, and etching solution C for 10 seconds.

[0135] Step 2: Total dose 4×10 15 ions / cm².

[0136] Step 5: Cancel.

[0137] Example 9 The difference from Example 1 is as follows: An additional pre-polishing step (replacing conventional silicon-containing CMP) was added: Before cleaning, a silicon-free chemical mechanical polishing slurry (1 wt% H2O2, pH adjusted to 5.0 with citric acid) was used, with a non-woven fabric polishing pad, pressure of 150 g / cm², rotation speed of 50 rpm, and time of 5 min, removing approximately 50 nm. Then, the same cleaning process as in Example 1 was performed.

[0138] Step five is cancelled.

[0139] Comparative Example 1 Traditional process: CMP uses silica sol + H2O2 polishing slurry; cleaning is conventional RCA + ultrasonic cleaning, leaving 8×10¹ silicon residue. 5 atom / cm², verifying that conventional cleaning methods do not completely remove chemically bonded silicon.

[0140] Comparative Example 2 The cleaning steps are exactly the same as in Example 1 (rotary ultrasonic atomization metal-free cleaning).

[0141] After cleaning, instead of GCIB and atomic hydrogen treatment, CMP fine polishing was performed using a silicon-free polishing solution (NaClO / H2O2, the same as the pre-polishing solution in Example 9): pressure 100g / cm², rotation speed 40rpm, time 15min, removing 100nm.

[0142] Then anneal at 500°C for 45 minutes (same as in Example 1).

[0143] No organic passivation.

[0144] Comparative Example 3 The first four steps are exactly the same as in Example 1 (including cleaning, GCIB, atomic hydrogen, and annealing).

[0145] The final step: Instead of organic passivation, the wafer is immersed in a 10% (NH4)2S solution (commercial grade, containing Na). + The impurities were removed (approximately 5 ppm), incubated at room temperature for 5 minutes, then rinsed with deionized water and dried with N2.

[0146] Vacuum desorption and densification annealing are not performed.

[0147] The wafers processed in Examples 1-9 and Comparative Examples 1-3 were transferred to the sample outlet chamber under vacuum, filled with high-purity N2 to atmospheric pressure, and then removed for the following tests. The results are shown in Table 1 below: Si Residue Detection: The surface of the treated wafer is analyzed using a total reflectance X-ray fluorescence spectrometer. The wafer is placed on a sample stage, and X-rays are incident on the wafer surface at an angle below the critical angle, exciting surface atoms to produce characteristic fluorescent X-rays. The spectra are collected by an energy-dispersive detector, and qualitative and quantitative analysis is performed by analyzing the energy position and intensity of the characteristic peaks of each element. No special sample preparation is required before detection, making it a non-destructive testing method.

[0148] Detection conditions: The X-ray source uses a W target or a Mo target, the incident angle is set below the critical angle, the measurement time is usually 300~600s, and the measurement area covers multiple points at the center and edge of the wafer.

[0149] Surface particle count detection: A laser surface particle detection system is used to scan the entire surface of the processed wafer. The wafer rotates at a fixed angular velocity on a rotating platform, while the laser beam scans radially, forming a spiral scanning trajectory across the entire wafer surface. When the laser beam irradiates surface particles, the scattered light generated by the particles is collected. By detecting the intensity of the scattered light, the particle size and quantity can be determined. The lower limit for particle size is typically set to 0.2 μm.

[0150] Detection conditions: A 488nm or 532nm laser source is used, with adjustable incident and scattering angles. The measurement mode is full wafer scanning, recording the number and coordinate distribution of particles ≥0.2μm.

[0151] Surface roughness Ra measurement: The processed wafer surface is scanned using an atomic force microscope to acquire a three-dimensional topographic image. The root mean square roughness (RMS / Rq) and arithmetic mean roughness (Ra) are calculated using software. The wafer is cut to a suitable size (typically 10mm × 10mm) before measurement.

[0152] Measurement conditions: Scanning range 5µm×5µm, scanning frequency 0.5~1.0Hz, 512 or 1024 sampling points per line. Three to five regions at different locations on the wafer surface were randomly selected for testing, and the average value was taken as the final Ra value.

[0153] LTV (Local Thickness Variation) Detection: A laser Fizeau interferometer is used to detect the surface morphology of the wafer and calculate the local thickness variation. The wafer is vacuum-adsorbed onto a high-precision measuring fixture. An interference cavity is formed between the plane reference mirror and the wafer surface. The height deviation of each point on the wafer surface relative to the reference plane is measured using the principle of equal thickness interference. The range of local thickness variation within a 20mm × 20mm window is calculated by an algorithm.

[0154] Measurement conditions: The light source is a single-mode frequency-stabilized helium-neon laser (wavelength 632.8nm), the measurement mode is phase-shift interferometry, the data acquisition point density is at least 500×500 points, the window size for calculating LTV is 20mm×20mm, the step scan covers the entire wafer (usually sampling in the central area), and the measurement environment temperature is controlled at 20±0.5℃.

[0155] Lattice integrity testing: High-resolution X-ray dual-crystal diffractometer was used for testing. The (004) diffraction peak corresponding to the (001) crystal plane of the GaAs single crystal was selected for rocking curve scanning. The wafer was fixed on the sample stage, and the detector was fixed at the 2θ angle position (corresponding to the GaAs (004) diffraction angle, which is about 66° for CuKα radiation source). The sample was rocked near the Bragg angle (ω scan), and the diffraction intensity change curve with the incident angle was recorded to obtain its peak half-width at half-maximum (FWHM).

[0156] Measurement conditions: The X-ray source was CuKα (wavelength λ = 0.15406 nm), tube voltage was 40 kV, tube current was 40 mA, and a quad-crystal Ge(220) asymmetric monochromator was used to obtain a highly parallel incident beam. The ω scanning range was within ±100 arcseconds of the Bragg angle, and the scanning step size was 1 arcsecond. Three to five measurement points were selected in different regions of the wafer surface to perform rocking curve scanning.

[0157] Subsurface damage layer observation: Thin slices were cut from the wafer using a focused ion beam polishing system, and the observation directions included cross-sectional and plan-view views. The slice thickness required that the electron beam could penetrate (typically <100 nm). Near-surface region observation was performed under a high-resolution transmission electron microscope: High-resolution images were taken along the

[110] or

[110] zone axis, and the extent of the damage layer was determined based on the contrast difference near the surface. Simultaneously, selected area electron diffraction was used to analyze the structural integrity of the damaged region.

[0158] Sample preparation method: Using the FIB dual-beam system, a protective layer (Pt or C) is first deposited on the surface of the area to be tested. Then, a thin film with a thickness of about 100 nm is milled from both sides using a Ga ion beam with a gradually decreasing beam current. The film is then transferred to a copper mesh carbon support film by a nanorobot. Finally, a low-energy ion beam (2~5kV) is used for cleaning to reduce the surface amorphous layer.

[0159] Table 1 As shown in Table 1 above, all examples satisfy the condition that residual Si < 1 × 10¹. 4 atom / cm². Comparative Example 1, due to the use of a silicon-containing polishing slurry, had a Si residue as high as 8 × 10¹. 5This exceeds the limits of the present invention by more than an order of magnitude. Although the Si residue in Comparative Examples 2 and 3 met the standards, other indicators were defective.

[0160] Surface roughness Ra: All examples were ≤0.12 nm, with Examples 3 and 7 reaching 0.07 nm. Comparative Example 1 had a roughness of 0.58 nm, and Comparative Example 2 had a roughness of 0.35 nm, neither of which could reach 0.12 nm, proving that the GCIB+ atomic hydrogen combination is the key to achieving an atomically smooth surface.

[0161] Local thickness uniformity (LTV): All examples had LTV <1.0µm, with Example 6 achieving the best result of 0.55µm. Comparative Examples 1 and 2 showed LTVs as high as 2.4µm and 1.8µm, respectively, indicating that traditional CMP and annealing alone cannot effectively control flatness within small windows, while GCIB has a significant global smoothing effect.

[0162] Metal ion residue: all examples were controlled to be within 1×10¹ 0 Within this range, Example 5 is as low as 2×10 9 Comparative Example 1 showed a higher level of metal residue (5 × 10⁻⁶). 11 Comparative Example 3, due to the use of a passivation solution containing Na, had a Na residue of 2 × 10⁻⁶. 12 This severely damages the intrinsic high-resistivity characteristics.

[0163] Subsurface damage: In the examples, it can be completely eliminated at the lowest level (Example 3) and at the highest level, not exceeding 5 atomic layers. Comparative Examples 1 and 2 have 50 nm and 20 nm damage layers, respectively, which affect the quality of subsequent epitaxy.

[0164] Overall Assessment: The embodiments provided by this invention outperform the comparative examples in all key indicators. In particular, Examples 6 and 7 show outstanding performance in their respective focuses (optimal LTV, lowest Ra). Comparative Example 1 represents traditional silicon-containing CMP, where both Si and LTV fail; Comparative Example 2, although without silicon, lacks GCIB, resulting in substandard roughness and LTV; Comparative Example 3 introduces metal ion contamination.

[0165] 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 surface treatment method for undoped high-resistivity gallium arsenide wafers, characterized in that, Includes the following steps: Undoped high-resistivity gallium arsenide wafers are placed on a rotating platform and rotated at a speed of 200~500 rpm. The cleaning solution is sprayed onto the wafer surface by ultrasonic atomization for etching and cleaning. Then, the wafer is rinsed with mega-sonic-assisted ultrapure water and dried. In a vacuum chamber, an inert gas cluster ion beam is used to bombard and planarize the surface of the processed wafer. Hydrogen gas is introduced into the same vacuum chamber or in a connected vacuum atmosphere and decomposed to generate atomic hydrogen. The mixture is then treated at a substrate temperature of 200-350°C for 5-15 minutes. In a vacuum or inert gas atmosphere, heat the wafer to 450~550℃ and hold for 30~60 minutes, then cool it.

2. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The cleaning solution includes, in order: Etching solution A: prepared by mixing ammonia, hydrogen peroxide and deionized water in a volume ratio of 1:1:10, with a pH value of 10.5~11.5 and a processing time of 30~60s; Etching solution B: prepared by hydrochloric acid, hydrogen peroxide and deionized water in a volume ratio of 1:1:20, with a pH value of 1.0~2.0 and a treatment time of 30~60s; Etching solution C: prepared by mixing ammonia and deionized water at a volume ratio of 1:5, with a pH value of 10.0~11.0 and a processing time of 10~20s.

3. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The incident angle of the inert gas cluster ion beam is 0° to 15° relative to the normal direction of the wafer surface, and the inert gas is argon.

4. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The flow rate of the hydrogen gas is 50~100 sccm / min, wherein atomic hydrogen is generated by thermal decomposition, microwave decomposition or plasma decomposition; the thermal decomposition can use tungsten wire, platinum wire or tantalum wire as heating element, and the heating temperature is 1500~2000℃.

5. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The cooling is carried out in an argon atmosphere, and the cooling rate does not exceed 5°C / min.

6. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, It also includes thermal desorption treatment of the wafer at 450~550℃ for 1~2 hours to remove physically adsorbed impurities on the surface and ensure the adhesion of the subsequent passivation layer.

7. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The megasonic frequency is 800kHz~1.2MHz, the ultrapure water rinsing time is not less than 180s, and the ultrapure water resistivity is ≥18.2MΩ·cm; the drying adopts the Marangoni drying method and gaseous isopropanol is introduced.

8. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, It also includes the pre-processing of the undoped high-resistivity gallium arsenide wafer by chemical mechanical polishing with a chemical mechanical polishing slurry containing silica sol abrasive particles and hydrogen peroxide as an oxidant before it is placed on the rotating platform.

9. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, The undoped high-resistivity gallium arsenide wafer processed by the method has a subsurface damage layer thickness of no more than 5 atomic layers and a total residual concentration of surface metal ions ≤ 1 × 10¹. 0 Atoms / cm² 10. The surface treatment method for undoped high-resistivity gallium arsenide wafers according to claim 1, characterized in that, It also includes a low-temperature organic passivation protection step: in a vacuum or inert gas atmosphere, an organic material with a molecular weight of 200~1000 and easy thermal decomposition is sprayed to form a passivation layer with a thickness of 5~20nm; the organic material is polyethylene glycol, polyethylene oxide or alkane polymer, which is stable at room temperature; in the subsequent MOCVD process, it is completely vaporized and decomposed in a hydrogen atmosphere at 400~600℃, and discharged from the chamber along with gallium oxide and arsenic oxide.

Images