A processing method of a sapphire substrate for high orientation growth of two-dimensional materials

Abstract

This invention belongs to the field of semiconductor polishing technology, specifically relating to a processing method for sapphire substrates used in the high-orientation growth of two-dimensional materials. The method includes: mounting a C-axis [0001] single-crystal sapphire substrate on an angled processing device to process a single-crystal sapphire substrate with a C-axis offset from the A-axis or a C-axis offset from the M-axis; mounting the single-crystal sapphire substrate and a flexible polishing pad on a polishing device, and adding a polyhydroxy functional group compound and deionized water as a polishing fluid; providing charged abrasive particles on the surface of the flexible polishing pad; setting the load and rotation speed of the polishing device to cause relative friction between the single-crystal sapphire substrate and the flexible polishing pad, resulting in the formation of a low-hardness friction reaction layer between the single-crystal sapphire substrate and the polyhydroxy functional group compound in the polishing fluid under the frictional induction of the charged abrasive particles; and uniformly removing the reaction layer through the mechanical action of the charged abrasive particles with a spring-like effect. This invention can greatly improve the processing efficiency of atomic steps on single-crystal sapphire substrates.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor polishing technology, and more specifically, relates to a processing method for sapphire substrates used for highly oriented growth of two-dimensional materials. Background Technology

[0002] Currently, integrated circuits have entered the post-Moore's Law era, and simply improving chip performance through process upgrades is no longer sufficient to meet the demands of the times. Two-dimensional / three-dimensional hybrid devices are considered a crucial research direction for the integrated circuit industry in the post-Moore's Law era. Hybrid-dimensional heterojunctions are one of the "core" technologies for ultra-short channel devices, spintronic devices, energy electronic devices, and optoelectronic devices, and have enormous application prospects in defense, aerospace, quantum chips, neuromorphic computing, full-color displays, and optical storage. High-quality hybrid-dimensional devices require the epitaxial growth of two-dimensional materials into large single-crystal sizes. Research based on crystal nucleation theory and growth mechanisms indicates that achieving large-area atomic steps on the surface of single-crystal sapphire substrates is key to producing large, high-quality two-dimensional heteroepitaxial single crystals.

[0003] Currently, the main methods for preparing large-area atomic steps on the surface of single-crystal sapphire substrates include high-temperature annealing, chemical mechanical polishing (CMP) based on highly corrosive polishing slurries, and plasma polishing. High-temperature annealing requires first processing the sub-nanometer surface through CMP, followed by high-temperature annealing at above 1100℃ for several hours (patent number CN110512287A) to form atomic steps on the substrate surface. This method suffers from problems such as uncontrollable atomic step types, cumbersome steps, high energy consumption, and high equipment requirements. CMP based on highly corrosive polishing slurries suffers from problems such as inconsistent atomic step types on the substrate surface, severe etch pits, and significant environmental pollution. Plasma polishing and other methods suffer from problems such as small processing area, low processing efficiency, and high cost. Summary of the Invention

[0004] The purpose of this invention is to provide a processing method for sapphire substrates used for highly oriented growth of two-dimensional materials, so as to improve the above-mentioned problems.

[0005] The objective of this invention can be achieved through the following methods:

[0006] A method for processing sapphire substrates for highly oriented growth of two-dimensional materials, comprising the following steps:

[0007] S1, mount the C-axis

[0001] single crystal sapphire substrate on the tilt processing equipment to process a single crystal sapphire substrate with the C-axis deviating from the A-axis or the C-axis deviating from the M-axis.

[0008] S2, a single-crystal sapphire substrate and a flexible polishing pad are respectively mounted on a polishing device, and a multi-hydroxyl functional group compound and deionized water are added as polishing fluid; the surface of the flexible polishing pad is provided with charged abrasive grains;

[0009] S3, set the load and speed of the polishing equipment to make the single crystal sapphire substrate and the flexible polishing pad rub against each other. Under the frictional induction of charged abrasive particles, the single crystal sapphire and the polyhydroxy functional group compound in the polishing liquid achieve rapid charge transfer, which promotes the formation of a friction reaction layer with low hardness on the surface of the single crystal sapphire substrate.

[0010] S4 uses the mechanical action of charged abrasive grains with a springy effect to uniformly remove the reaction layer, thereby achieving a large-area atomic step on the surface of a C-axis off-angle single-crystal sapphire substrate.

[0011] Preferably, the flexible polishing pad is composed of a bonded abrasive polishing film and a non-woven fabric composite; the charged abrasive grains are fine-grained abrasive grains with a negative (-) Zeta potential.

[0012] Preferably, the material of the charged abrasive particles is one of alumina, silicon oxide, silicon carbide, and silicon nitride; the particle size is W0.5 to W3; and the potential range is -50mV to 0mV.

[0013] Preferably, the nonwoven fabric material is one of polypropylene, polyester, polyester fiber, and viscose fiber; the number of layers of the nonwoven fabric is 0 to 5.

[0014] Preferably, the load application range is 0.3 kg / cm. 3 ~0.6kg / cm 3 .

[0015] Preferably, the rotational speed of the carrier disk of the polishing equipment is in the range of 50 rpm / min to 70 rpm / min. The carrier disk supports the single crystal sapphire substrate and is used to apply a load to the single crystal sapphire substrate.

[0016] Preferably, the polishing disc of the polishing equipment rotates at a speed ranging from 120 rpm / min to 200 rpm / min.

[0017] Preferably, the polyhydroxy functional group compound is one or more of amino acids, serine, citric acid, sorbitol, aminotriacetic acid, and disodium ethylenediaminetetraacetate.

[0018] Preferably, the polyhydroxy functional group compound has a mass percentage of 0.1 wt% to 10 wt% in the polishing solution.

[0019] Preferably, the C-axis deviation angle α of the sapphire substrate satisfies the range of 0.1° < α ≤ 8°; the roughness Ra of the large-area atomic step surface satisfies the range of 0 < Ra ≤ 0.15 nm; the large area S of the large-area atomic step surface satisfies the range of 0.1 mm 2 <S < 5 mm 2 .

[0020] In the present invention, the rapid charge transfer is achieved by the friction of negatively (-) charged abrasive grains to induce sapphire / polyhydroxy functional group compounds, promoting the chemical reaction. Under the induction of the friction of charged abrasive grains, the surface of the sapphire substrate is liable to lose electrons and carry a positive charge, and the polyhydroxy functional group compounds are liable to capture electrons, realizing the rapid transfer of electrons, thereby promoting the rapid formation of the reaction layer on the sapphire surface. The negatively charged abrasive grains generate electrostatic adsorption with the positively charged surface of the sapphire substrate, promoting the rapid removal of the reaction layer.

[0021] The present invention does not require extreme conditions such as acid-base etching solution and high-temperature degradation, and can be applied to the green and efficient processing of large-area atomic steps of single-crystal sapphire substrates with any C-axis deflection angle, greatly improving the processing efficiency of atomic steps of single-crystal sapphire substrates, and playing a great role in promoting the development of the field of high-quality two-dimensional / three-dimensional hybrid dimensional heterojunction devices. Description of the Drawings

[0022] Figure 1 is the processing schematic diagram of the embodiment of the present invention;

[0023] Figure 2 is the surface topography diagram (AFM detection, range: 20×20 um) of the 2-inch C-axis single-crystal sapphire substrate processed in Example 1 of the present invention;

[0024] Figure 3 is the surface topography diagram (white light interferometer detection, range: 53×70 um) of the 2-inch C-axis deflected A-axis direction single-crystal sapphire substrate processed in Example 1 of the present invention by using the present invention;

[0025] Figure 4 is the high-orientation two-dimensional MoS2 CVD epitaxial growth diagram of Example 1 of the present invention. Detailed Embodiments

[0026] The present invention will be described in detail below in conjunction with the drawings and embodiments, but the scope of protection of the present invention is not limited to the following embodiments:

[0027] Example 1

[0028] Please refer to Figures 1 to 4First, a C-axis

[0001] single-crystal sapphire substrate was mounted on an existing semiconductor tilt-controlled processing device (application number: CN115799144A) to process a single-crystal sapphire substrate with a 2° axis offset in the M-axis direction. A 1200S automatic grinding and polishing machine was used as the polishing equipment. A negatively charged silicon oxide-bonded abrasive polishing film (Zate potential -30mV) with a particle size of W0.5 was selected, and a flexible polishing pad was made with three layers of polyester non-woven fabric and an adhesive layer, which was then attached to the polishing pad. The single-crystal sapphire substrate with a C-axis offset was mounted on the carrier disk. A green polishing slurry with a 3wt% weight percentage content was prepared by mixing sorbitol, a polyhydroxy functional group compound, with deionized water, and transported to the surface of the polishing pad using a peristaltic pump. The polishing pressure was set to 0.5 kg / cm². 3 The substrate was polished at 60 rpm and the polishing disk at 160 rpm for 30 minutes on a 2-inch single-crystal sapphire substrate with an initial surface roughness of 8.5 nm and an M-axis tilt angle. The surface roughness reached 0.104 nm, achieving a large-area atomic step surface on the 2°C M-axis tilted single-crystal sapphire substrate with a material removal rate of 8.19 μm / h. CVD epitaxial growth was then performed on the 2°C M-axis tilted single-crystal sapphire substrate to obtain a uniformly oriented two-dimensional MoS2 material.

[0029] Example 2

[0030] A C-axis

[0001] single-crystal sapphire substrate was mounted on an existing semiconductor tilt-controlled processing device (application number: CN115799144A) to process a single-crystal sapphire substrate with a 4° axis offset in the A-axis direction. A 1200S automatic grinding and polishing machine was used. A negatively charged (-) alumina-bonded abrasive polishing film with a particle size of W1 (Zate potential of -20mV) was used, and a flexible polishing pad was made with two layers of polypropylene non-woven fabric and an adhesive layer, which was then attached to the polishing pad. The sapphire substrate with the C-axis offset was mounted on a carrier disk. A green polishing slurry with a weight percentage of 4 wt% was prepared by mixing glycine (a polyhydroxy functional group compound) with deionized water and pumped onto the surface of the polishing pad using a peristaltic pump. The polishing pressure was set to 0.4 kg / cm². 3 A 2-inch C-axis-biased A-axis single-crystal sapphire substrate with an initial surface roughness of 5 nm was polished for 30 minutes at a disk rotation speed of 70 rpm and a polishing disk rotation speed of 180 rpm, achieving a surface roughness of 0.12 nm and realizing a large-area atomic step surface on the 4℃ C-axis-biased A-axis single-crystal sapphire substrate. CVD epitaxial growth was then performed on the 4℃ C-axis-biased A-axis single-crystal sapphire substrate to obtain a uniformly oriented two-dimensional MoS2 material.

[0031] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention.

Claims

1. A method for processing sapphire substrates for highly oriented growth of two-dimensional materials, characterized in that, Includes the following steps: S1, mount the C-axis [0001] single crystal sapphire substrate on the tilt processing equipment to process a single crystal sapphire substrate with the C-axis deviating from the A-axis or the C-axis deviating from the M-axis. S2, a single-crystal sapphire substrate and a flexible polishing pad are respectively mounted on a polishing device, and a multi-hydroxyl functional group compound and deionized water are added as polishing fluid; the surface of the flexible polishing pad is provided with charged abrasive grains; S3, set the load and speed of the polishing equipment to make the single crystal sapphire substrate and the flexible polishing pad rub against each other. Under the frictional induction of charged abrasive particles, the single crystal sapphire substrate and the polyhydroxy functional group compound in the polishing liquid achieve rapid charge transfer, which promotes the formation of a friction reaction layer with low hardness on the surface of the single crystal sapphire substrate. S4. The reaction layer is uniformly removed by the mechanical action of charged abrasive grains with a spring-back effect, thereby achieving large-area atomic steps on the surface of the C-axis off-angle single-crystal sapphire substrate; the flexible polishing pad is composed of a fixed abrasive polishing film and non-woven fabric; the charged abrasive grains are fine-grained abrasive grains with a negative (-) Zeta potential; wherein, the material of the charged abrasive grains is one of alumina, silica, silicon carbide, and silicon nitride; the grain size is W0.5~W3; the potential range is -50mV-0mV; the non-woven fabric material is one of polypropylene, polyester, polyester fiber material, and viscose fiber; the number of layers of the non-woven fabric is 0 to 5 layers; the load application range is 0.3kg / cm 3 ~0.6kg / cm 3 ; the rotational speed range of the carrier plate of the polishing equipment is 50rpm / min~70rpm / min, the carrier plate carries the single-crystal sapphire substrate and is used to apply a load to the single-crystal sapphire substrate; the rotational speed range of the polishing plate of the polishing equipment is 120rpm / min~200rpm / min; the C-axis off-angle α of the sapphire substrate satisfies the range 0.1°<α≤8°; the roughness Ra of the large-area atomic step surface satisfies the range 0<Ra≤0.15nm; the large area S of the large-area atomic step surface satisfies the range 0.1mm 2 <S<5mm 2 .

2. The processing method according to claim 1, characterized in that, The polyhydroxy functional group compound is one or more of amino acids, serine, citric acid, sorbitol, aminotriacetic acid, and disodium ethylenediaminetetraacetate.

3. The processing method according to claim 1, characterized in that, The polyhydroxy functional group compound has a mass percentage of 0.1 wt% to 10 wt% in the polishing solution.

Images