A method for regulating nanosecond laser-induced periodic structure on semiconductor surface

Abstract

This invention proposes a simple method for controlling multi-pulse nanosecond laser-induced periodic structures on semiconductor surfaces. The method involves applying a UV nanosecond laser directly and perpendicularly to the surface of a single-side polished semiconductor material, forming small-periodic nanostructures on the surface. The direction of the periodic structures can be controlled by varying the polarization of the incident laser, and the size and depth of the periodic structures can be controlled by varying the laser energy density, number of pulses, and ambient medium. The nanostructures produced on semiconductor surfaces using this method meet the low-cost requirements of industrial large-scale surface processing and can alter the optical, frictional, and wetting properties of the material.

Description

Technical Field

[0001] The present invention relates to a technique for preparing and regulating periodic structures on the surface of semiconductor materials, and in particular to a method for regulating nanosecond laser-induced periodic structures on the surface of semiconductors. Background Art

[0002] Laser-induced periodic surface structures (LIPSS) are periodic striped structures, also known as ripples, produced on a material's surface by laser radiation. These periodic structures can alter the optical, mechanical, and chemical properties of a material and have a wide range of applications in surface functionalization, including controlling wettability and improving friction. The basic units of these periodic structures are micrometer or nanometer in size and are formed through both bottom-up growth and top-down etching. LIPSS is a common physical phenomenon that can occur on the surfaces of various solid materials, such as metals, dielectrics, semiconductors, and ceramics described in patents DE102005043495A1 and US020060173421A1, and in the literature "Borowiec A, Haugen H K. Subwavelength ripple formation on the surfaces of compound semiconductors irradiated with femtosecond laser pulses[J]. Applied Physics Letters, 2003, 82(25): 4462-4464." and "Xing Y, Deng J, Lian Y, et al. Multiple nanoscale parallel grooves formed on Si3N4 / TiC ceramic by femtosecond pulsed laser[J]. Applied Surface Science, 2014, 289(JAN.15): 62-71.". Generally speaking, the formation of LIPSS is affected by irradiation conditions, environmental conditions, and material state. Irradiation conditions include laser energy, pulse number, polarization state, and angle of incidence. Typical environmental conditions include air, vacuum, water, high-refractive-index liquids, and other factors that can alter the properties of the interface. Depending on the light source and material, the resulting LIPSS corresponds to different formation mechanisms, including the generalized scattering and interference model (Sipe model), the capillary wave model, the surface plasmon polariton (SPP) model, and the self-organization model. However, to date, no single theory has effectively explained all the characteristics of LIPSS.

[0003] With the rapid development of ultrashort pulse lasers, the light sources for preparing LIPSS from semiconductor materials silicon and germanium are mostly femtosecond lasers and picosecond lasers. However, the equipment of these lasers is expensive and the operation methods are complicated, making them unsuitable for large-scale processing and production. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for regulating the periodic structure of the semiconductor surface induced by nanosecond laser, which solves the problem of high cost and complicated steps in the prior art of regulating the periodic structure of the semiconductor surface.

[0005] The technical solution for achieving the purpose of the present invention is: a method for regulating nanosecond laser-induced periodic structure on the surface of a semiconductor, the specific steps of which are:

[0006] Pre-treating the semiconductor material, specifically: using an acetone solution to remove grease from the surface of the single-sided polished semiconductor material, and using an ultrasonic cleaning machine to deep clean the semiconductor material;

[0007] The medium and semiconductor are integrated together through a lens mount, and the polished surface of the semiconductor is in contact with the medium. The ultraviolet pulse laser emitted by the nanosecond laser passes through half-wave plate 1, polarization beam splitter prism, half-wave plate 2, convex lens, concave lens, and medium in sequence, and is vertically incident on the surface of the semiconductor material;

[0008] The nanosecond laser sends a set number of ultraviolet pulse laser pulses to form LIPSS on the polished surface of the semiconductor.

[0009] Preferably, the incident laser is linearly polarized light with a pulse width of 5 ns to 10 ns.

[0010] Preferably, the incident laser is an ultraviolet wave with a wavelength of 350nm to 360nm.

[0011] Preferably, the medium is a liquid or a gas that does not chemically react with the semiconductor material.

[0012] Preferably, the medium is air or water.

[0013] Preferably, the focal length of the convex lens is f1 = 50 mm, and the focal length of the concave lens is f2 = -25 mm.

[0014] Preferably, when the medium is air, the laser pulse energy density ranges from 0.69 to 0.90 times the melting threshold, corresponding to a number of pulses of N = 40 to 100; or the laser pulse energy density ranges from 0.52 to 0.90 times the melting threshold, corresponding to a number of pulses of N = 150 to 250.

[0015] Preferably, when the medium is water, the range of the laser pulse energy density is 0.84 times the melting threshold, corresponding to the number of pulses N=15; or the range of the laser pulse energy density is 0.72~0.84 times the melting threshold, corresponding to the number of pulses N=20~50; or the range of the laser pulse energy density is 0.61~0.84 times the melting threshold, corresponding to the number of pulses N=100~200; or the range of the laser pulse energy density is 0.72~0.86 times the melting threshold, corresponding to the number of pulses N=300~400.

[0016] Preferably, the semiconductor is single crystal germanium with a crystal orientation of <p100>

[0017] Compared with the existing technology, the present invention has the following significant advantages: 1) the present invention belongs to laser direct writing technology and is a non-contact processing method; 2) the LIPSS generated on the semiconductor surface by the method of the present invention can change the optical properties, wetting properties and biocompatibility of the material; 3) the present invention uses a relatively simple device to control the direction and period size of the LIPSS stripes; 4) the present invention is tolerant to the environmental requirements of laser processing and does not require vacuum conditions; 5) the present invention is suitable for forming LIPSS on the surface of microfluidic and microhydraulic devices; 6) the nanosecond laser used in the present invention is low in cost, simple to operate, and has stable output energy.

[0018] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the experimental setup for regulating nanosecond laser-induced periodic structures on semiconductor surfaces.

[0020] Figure 2 Schematic diagrams of atomic force microscopy results of LIPSS generated on the surface of single crystal germanium, (a) schematic diagram of atomic force microscopy results of Example 1; (b) schematic diagram of atomic force microscopy results of Example 2.

[0021] Figure 3 Graph showing the relationship between the direction of the LIPSS stripes induced on the surface of single crystal germanium in Example 1 and the polarization direction of the incident laser, (a) the laser polarization direction is horizontal; (b) the laser polarization direction is vertical.

[0022] Figure 4 This is a schematic diagram showing the results of the LIPSS period induced on the surface of single crystal germanium in Example 1 changing with the laser energy density and the number of pulses.

[0023] Figure 5 This is a schematic diagram showing the results of how the depth of LIPSS induced on the surface of single crystal germanium in Example 1 changes with laser energy density and pulse number. DETAILED DESCRIPTION

[0024] like Figure 1 As shown, a method for regulating nanosecond laser-induced periodic structures on semiconductor surfaces is described. The LIPSS parameters formed by this invention are closely related to the laser parameters used and environmental factors. By changing the incident laser parameters and environmental factors, the direction, period, and depth of LIPSS can be controlled. The energy density of the laser single pulse used is less than the material ablation threshold, so it will not cause cracks, ablation pits with high surface roughness, or ring-shaped ablation morphology. The specific steps are:

[0025] The semiconductor material is pre-treated, specifically: the single-side polished semiconductor material is first removed from the surface grease by using an acetone solution, and then deep cleaned by an ultrasonic cleaning machine.

[0026] The dielectric and semiconductor material are integrated together via a lens mount, with the polished surface of the material in contact with the dielectric. The lens mount is affixed to a three-dimensional translation stage with an accuracy of 10μm in all directions. Ultraviolet pulsed laser light emitted by a nanosecond laser passes sequentially through half-wave plate 1, a polarizing beam splitter prism, half-wave plate 2, a convex lens, a concave lens, and the dielectric before being perpendicularly incident on the surface of the semiconductor material. All optical components are concentric and coaxial. After the semiconductor material surface absorbs the laser energy, LIPSS forms on the polished surface.

[0027] Furthermore, the irradiation time of the nanosecond laser is determined by the number of pulses required. The combination of a half-wave plate and a polarization beam splitter effectively regulates the energy of the incident laser light. The angular difference between half-wave plates 1 and 2 controls the polarization direction of the incident laser light. The combination of convex and concave lenses forms a telephoto system, which corrects aberrations.

[0028] In a further embodiment, when the medium is air, Figure 2 As shown in (a), the LIPSS generated on the surface of the semiconductor material has isotropic properties, its grating structure is consistent, and has an average period slightly larger than the incident wavelength. The laser pulse energy density ranges from 0.69 to 0.90 times (number of pulses N = 40 to 100) and 0.52 to 0.90 times (number of pulses N = 150 to 250) the melting threshold.

[0029] When the medium is water, Figure 2 As shown in (b), the size of the LIPSS period generated on the surface of the semiconductor material is related to environmental factors. Due to the large refractive index of the liquid, the LIPSS period generated in water will be smaller than the LIPSS period generated in the air. The laser pulse energy density ranges from 0.84 times the melting threshold (number of pulses N = 15), 0.72 to 0.84 times (number of pulses N = 20 to 50), 0.61 to 0.84 times (number of pulses N = 100 to 200), and 0.72 to 0.86 times (number of pulses N = 300 to 400).

[0030] like Figure 3 As shown in the figure, the direction of LIPSS is related to the polarization direction of the incident laser. Specifically, the direction of LIPSS stripes is always perpendicular to the polarization direction of the incident laser. The laser energy density that can produce a uniform LIPSS morphology depends on the type of material to be processed, laser pulse width, laser wavelength, number of pulses, environmental factors, etc. Figure 4 and Figure 5 As shown in Figure 3, the period and depth of LIPSS vary with the laser energy density and the number of pulses.

[0031] In a further embodiment, the incident laser is linearly polarized light with a pulse width of 5 ns to 10 ns.

[0032] In a further embodiment, the incident laser is an ultraviolet wave with a wavelength of 350nm to 360nm.

[0033] In a further embodiment, the medium is air and water which do not chemically react with the semiconductor.

[0034] In a further embodiment, the semiconductor material is single crystal germanium with a crystal orientation of <p100>.

[0035] In a further embodiment, the graduation accuracy of the half-wave plate is 2°, the focal length of the convex lens is f1 = 50 mm, and the focal length of the concave lens is f2 = -25 mm.

[0036] Example 1

[0037] The technical solution of the present invention is described in detail by taking the process of regulating LIPSS on the surface of a typical semiconductor germanium as an example.

[0038] (1) A linearly polarized laser with a wavelength of 355 nm and a pulse width of 7 ns was selected as the light source, and the laser was incident normally from the polished side of the germanium substrate.

[0039] (2) A single-sided polished germanium substrate with a size of 15 mm × 15 mm × 0.5 mm was used.

[0040] (3) The medium selected is air.

[0041] (4) The scale accuracy of the selected half-wave plate is 2°.

[0042] (5) A convex lens with a focal length of f1 = 50 mm and a concave lens with a focal length of f2 = -25 mm are selected to form a combined lens with a beam optimization function, and the combined focus is located 25 mm from the polished surface.

[0043] (6) Laser energy density F on the material surface = 60.1 mJ / cm 2 ~104.2mJ / cm 2 , the number of action pulses N = 40 ~ 250.

[0044] This embodiment is suitable for generating periodic fringe structures with a period of 366nm to 386nm and a depth of 11nm to 40nm on the surface of semiconductor single crystal germanium. The size and depth of the periodic structure are adjusted by the laser energy density and the number of pulses, respectively. The direction of the periodic structure is controlled by controlling the polarization direction of the incident laser, so that the LIPSS fringe direction is always perpendicular to the laser polarization direction.

[0045] Example 2

[0046] The technical solution of the present invention is described in detail by taking the process of regulating LIPSS on the surface of a typical semiconductor germanium as an example.

[0047] (1) A linearly polarized laser with a wavelength of 355 nm and a pulse width of 7 ns was selected as the light source, and the laser was incident normally from the polished side of the germanium substrate.

[0048] (2) A single-sided polished germanium substrate with a size of 15 mm × 15 mm × 0.5 mm was used.

[0049] (3) The medium selected is water.

[0050] (4) The scale accuracy of the selected half-wave plate is 2°.

[0051] (5) A convex lens with a focal length of f1 = 50 mm and a concave lens with a focal length of f2 = -25 mm are selected to form a combined lens with a beam optimization function, and the combined focus is located 25 mm from the polished surface.

[0052] (6) Laser energy density F on the material surface = 22.9 mJ / cm 2 ~31.7mJ / cm 2 , the number of action pulses N = 15 ~ 400.

[0053] This embodiment is suitable for generating a periodic stripe structure with a period of 262nm to 279nm and a depth of 4.3nm to 8.1nm on the surface of semiconductor single crystal germanium, and adjusting the size and depth of the periodic structure by laser energy density and number of pulses.

Claims

1. A method for regulating nanosecond laser-induced periodic structure on a semiconductor surface, characterized in that: The specific steps are: Pre-treating the semiconductor material, specifically: using an acetone solution to remove grease from the surface of the single-sided polished semiconductor material, and using an ultrasonic cleaning machine to deep clean the semiconductor material; The medium and semiconductor are integrated together through a lens mount, with the polished surface of the semiconductor in contact with the medium. Ultraviolet pulsed laser light emitted by a nanosecond laser passes through a half-wave plate 1, a polarization beam splitter prism, a half-wave plate 2, a convex lens, a concave lens, and the medium in sequence, and is vertically incident on the surface of the semiconductor material. The ultraviolet pulsed laser light serves as the incident laser light. The polarization direction of the incident laser light is controlled by the angle difference between the half-wave plate 1 and the half-wave plate 2. The combination of the convex and concave lenses forms a telephoto system to correct aberrations. The medium is a liquid or gas that does not chemically react with the semiconductor material. The focal length of the convex lens is f1 = 50 mm, and the focal length of the concave lens is f2 = -25 mm. The nanosecond laser sends a set number of ultraviolet pulse laser pulses to form LIPSS on the polished surface of the semiconductor.

2. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 1, characterized in that: The incident laser is linearly polarized light with a pulse width of 5ns to 10ns.

3. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 1, characterized in that: The incident laser is an ultraviolet wave with a wavelength of 350nm to 360nm.

4. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 1, characterized in that: The medium is air or water.

5. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 4, characterized in that: When the medium is air, the range of the incident laser pulse energy density is 0.69 to 0.90 times the melting threshold, and the corresponding number of pulses is N = 40 to 100; or the range of the incident laser pulse energy density is 0.52 to 0.90 times the melting threshold, and the corresponding number of pulses is N = 150 to 250.

6. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 4, characterized in that: When the medium is water, the range of the incident laser pulse energy density is 0.84 times the melting threshold, corresponding to the number of pulses N=15; or the range of the incident laser pulse energy density is 0.72~0.84 times the melting threshold, corresponding to the number of pulses N=20~50; or the range of the incident laser pulse energy density is 0.61~0.84 times the melting threshold, corresponding to the number of pulses N=100~200; or the range of the incident laser pulse energy density is 0.72~0.86 times the melting threshold, corresponding to the number of pulses N=300~400.

7. The method for controlling nanosecond laser-induced semiconductor surface periodic structure according to claim 1, characterized in that: The semiconductor is single crystal germanium, and the crystal orientation is <p100> 。< / p100>

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