CN106735947A - A kind of method of efficiently controllable processing bulk silicon micro-nano structure - Google Patents

Abstract

The invention relates to an efficient and controllable method for processing large-area silicon micro-nano structures, and belongs to the technical field of femtosecond laser applications. The present invention is based on the method of chemical etching-assisted femtosecond laser processing and time-of-flight drilling, effectively utilizes the ultra-fast, super-strong, and ultra-precise processing characteristics of femtosecond laser, and efficiently and controllably processes large-area micro-nano structures in a relatively short period of time ; Specifically, under the action of a single laser pulse, a local modified area is formed on the silicon surface, and the chemical activity of the laser irradiated area drops sharply, so that it can play the role of a mask in the subsequent chemical etching process, thereby realizing maskless high-efficiency Processing of high-quality silicon micro-nanostructures. Compared with the prior art, the present invention omits the step of plating a mask layer on the surface of the processed material, reduces the cost and improves the processing efficiency, and is also convenient for operation and control, and realizes large-area silicon surface micro-nano structures with different shapes and sizes Precise, controllable processing; processing speed is limited only by the laser pulse repetition rate.

Description

A method for efficient and controllable processing of large-area silicon micro-nanostructures

technical field

The invention relates to a method for efficient and controllable processing of large-area silicon micro-nano structures, in particular to a method for efficiently and controllably processing large-area silicon micro-nano structures combined with chemical etching-assisted femtosecond lasers, belonging to the technical field of femtosecond laser applications .

Background technique

Silicon crystal material is currently a more important semiconductor material, mainly due to its high refractive index and its ability to be effectively integrated into complex microelectronic devices. Silicon surface micro-nanostructures with controllable morphology and arrangement have extremely important applications in the fields of microelectronics, photonics, photovoltaics, microfluidics, wetting properties, solar cells, and sensors. Silicon surface micro-nanostructures with different morphologies can be obtained by different processing methods, such as photolithography, nanoimprinting and dry etching.

In recent years, femtosecond laser processing technology has been considered as the most effective processing tool for precision processing micro-nano structures on solid materials due to its advantages of high precision, low recasting layer, no contact, small heat-affected zone, and flexible processing. Micro-nano structures in the form of micro-holes, micro-grooves, micro-protrusions, micro-nano composite structures and nanoparticles can all be processed by femtosecond laser direct writing technology. In addition, in order to better control the processing of micro-nano structure morphology, chemical etching-assisted processing was introduced on the basis of femtosecond laser processing technology. The traditional chemical-assisted femtosecond laser processing technology needs to coat a mask layer of silicon dioxide or silicon nitride on the surface of the processed sample in advance, and the mask layer is partially removed by femtosecond laser irradiation, and then the exposed silicon substrate is engraved. It is etched in the etching solution to form micro-nano structures with different shapes. However, the above-mentioned processing method requires additional processing of the mask layer before processing, which not only increases the cost but also greatly reduces the processing efficiency.

Contents of the invention

The purpose of the present invention is to solve the problems of low processing efficiency and high cost of existing high-quality, high-uniform large-area silicon nano-dot arrays, and proposes an efficient and controllable processing method combined with chemical etching assisted femtosecond laser Methods for areal silicon micro-nanostructures.

The principle of the present invention is to adjust the transient electron density in the laser irradiation area through direct irradiation of femtosecond laser, change the local chemical activity of the material, and then adjust the etching rate of the modified area in the chemical etching process, and combine the femtosecond The laser "time-of-flight drilling method" (Journal of Laser Applications, 4(2), 15-24, 1992) realizes efficient and controllable processing of large-area silicon micro-nano structures.

The purpose of the present invention is achieved through the following technical solutions:

A method for efficiently and controllably processing large-area silicon micro-nano structures combined with chemical etching-assisted femtosecond lasers, the specific steps are as follows:

Step 1, using a microscopic objective lens to focus the femtosecond laser beam;

Step 2, adjusting the laser energy: using the half-wave plate-polarizer combination to adjust the laser energy so that the laser pulse energy is lower than the ablation threshold of the surface of the processed material, and the laser pulse energy can be continuously adjusted;

Step 3, fix the processed material on the mobile platform, adjust the mobile platform to focus the femtosecond laser pulse on the surface of the processed material;

Step 4, using the "time-of-flight drilling method" to realize large-area and efficient processing under the condition of femtosecond laser single pulse;

In step five, the processed material processed by the femtosecond laser in step four is placed in a chemical solution at a constant temperature and at a specific concentration, and after an etching time t, a high-quality silicon micro-nano structure with a smooth and uniform surface is obtained.

Preferably, by controlling the laser flux and etching time, the micro-nano structures with different shapes and sizes meeting the application requirements can be obtained, and the distance between adjacent structures can be controlled by controlling the pulse laser repetition frequency and scanning speed.

Preferably, the processing material in step three is N-type undoped single crystal silicon with 100 crystal orientation.

Preferably, the etching solution is a potassium hydroxide (KOH) solution with a concentration of 25wt%, a constant temperature of 55°C, and an etching time t between 30s and 120s.

Beneficial effect

Compared with the existing silicon nano-dot array processing technology, a method for efficiently processing large-area silicon nano-dot array structures combined with chemical etching-assisted femtosecond laser proposed by the present invention has the following characteristics:

1. The present invention forms a local modification area through femtosecond laser single pulse irradiation, and this modification area can be directly used as a mask in the etching process, omitting the step of coating the mask layer on the surface of the processed sample, reducing the cost while improving improved processing efficiency;

2. Use chemical solution to etch the processed materials after femtosecond laser processing, which is convenient for operation and control compared to coating the surface of processed samples with a mask layer;

3. The processing speed is only limited by the laser pulse repetition frequency. If the upper limit of the laser repetition frequency and the displacement speed of the processed material is higher, the processing efficiency can be further improved in theory;

4. By adjusting the femtosecond laser energy, it is possible to achieve precise and controllable processing of micro-nano structures on large-area silicon surfaces with different shapes and sizes, so as to meet the application requirements of different occasions.

Description of drawings

FIG. 1 is a schematic structural diagram of a device for efficiently processing a large-area silicon nano-dot array structure combined with chemical etching-assisted femtosecond laser according to the present invention.

FIG. 2 is a schematic diagram of steps of a method for efficiently processing a large-area silicon nano-dot array structure combined with chemical etching-assisted femtosecond laser according to the present invention.

Reference signs: 1-femtosecond laser system, 2-half-wave plate, 3-polarization beam splitter, 4-continuous attenuation plate, 5-mirror, 6-mechanical shutter, 7-dichroic mirror, 8-focusing display Micro-objective lens, 9-processing material, 10-six-dimensional precision displacement platform, 11-dichroic mirror A, 12-plano-convex lens, 13-CCD image sensor, 14-imaging lighting source.

detailed description

The preferred embodiments of the present invention will be further described below in conjunction with the accompanying drawings and examples.

In this embodiment, the device for realizing the present invention includes: a femtosecond laser system 1, a half-wave plate 2, a polarization beam splitter prism 3, a continuous attenuation plate 4, a mirror 5, a mechanical shutter 6, a dichroic mirror 7, and a focusing microscope objective lens 8. The six-dimensional precision displacement platform 10, the water bath heating device required for chemical etching, and the glass beaker vessel carrying the etching solution.

Its connections are shown in Figure 1 and Figure 2. The femtosecond laser system 1, the half-wave plate 2, the polarization beam splitter prism 3, and the continuous attenuation plate 4 are placed in parallel and coaxially in sequence, and the reflector 5 and the continuous attenuation plate 4 are coaxial and placed at 45° to each other; the mechanical shutter 6 and the reflector 5 are coaxial and mutually form 45°, the center of the dichroic mirror 7 is located at the focus position of the central axis of the mechanical shutter 6 and the central axis of the focusing microscope objective lens 8, and is placed at 45°; the laser optical axis passes through the dichroic mirror 7 The reflection passes through the focusing microscope objective lens 8 and the center of the processing material 9 in sequence. In order to facilitate the real-time monitoring of the processing process by the operator, an imaging lighting source and an image sensor are added to the above-mentioned device, and the two form a frontal imaging system to perform real-time imaging of the processing process; the lighting source is located above the six-dimensional precision displacement platform, and the illuminating light emitted by it Transmit dichroic mirror A11 and dichroic mirror 7 sequentially, and irradiate the processing material 9 on the six-dimensional precision displacement platform 10 through the focusing microscopic objective lens 8. After being reflected by the processed material 9, it passes through the focusing microscopic objective lens The color mirror 7 is reflected by the dichroic mirror A11 and then focused by the plano-convex lens 12 into the CCD image sensor 13 to form a real-time observation image.

The femtosecond laser 1 produces an ultrashort pulse femtosecond laser with a center wavelength of 800nm. The laser pulse flux can be adjusted in a large range by using the combination of the half-wave plate 2 and the polarization beam splitter 3, and then the continuous attenuation plate 4 can be used to further continuously change The laser flux changes the direction of the laser beam through the reflector 5, and the mechanical shutter 6 is used to control whether the laser beam passes or not, thereby controlling whether the laser beam can be processed; use the focusing microscope objective lens 8 to focus the Gaussian beam to realize High-resolution processing that breaks through the diffraction limit; the processing material 9 is fixed on the six-dimensional precision displacement platform 10, and the imaging illumination source 14 above the processing optical path generates white light for illumination, and the illumination light passes through the dichroic mirror A11 and the dichroic mirror 7 And the focusing objective lens 8 reaches the surface of the processing material, and then the illumination light reflected by the processing material 9 returns along the original path, and enters the CCD image sensor 13 for imaging after being reflected by the dichroic mirror A11. monitor. After the femtosecond laser irradiates the surface of the processed material 9 to form a large-area modified nanostructure region, it is placed in a constant temperature alkaline solution, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), tetramethylammonium hydroxide ( TMAH) solution, etc., for chemical etching, so that large-area, high-quality silicon micro-nano structures can be obtained.

Example

The femtosecond laser system in this embodiment adopts the laser produced by American Spectra Physics Company, the laser center wavelength is 800nm, the pulse width is 35fs, the repetition frequency is adjustable at 1KHz, the single pulse maximum energy is 3mJ, and the light intensity distribution is Gaussian , linearly polarized.

The processing material 9 is N-type non-doped single crystal silicon with crystal orientation 100, and its size is 10mm×10mm×1mm. Of course, those skilled in the art know that the actual processed object is not limited to single crystal silicon, it can be any other substance whose chemical properties can be changed by laser irradiation.

A method for efficiently processing large-area silicon micro-nano structures combined with chemical etching-assisted femtosecond laser proposed by the present invention, the processing optical path diagram and the schematic diagram of the experimental steps are shown in Figure 1 and Figure 2 respectively, and the specific processing steps are as follows:

Step 1: Use the femtosecond laser system 1 to generate femtosecond pulsed laser. Either use the half-wave plate 2 and the polarization beam splitter 3 to adjust the single pulse laser flux to 0.14J/cm ² , or use the continuous attenuation plate 4 to adjust the laser flux to reach corresponding value. Whether the laser beam can be processed is controlled by controlling the opening and closing of the mechanical shutter 5 .

Step 2: The Gaussian beam in Step 1 is vertically incident into a 20×focusing microscope objective lens 8 (Olympus, NA=0.45), and the laser spot diameter after focusing is about 2.2 μm.

Step 3: Fix the monocrystalline silicon sample 9 with 100 crystal orientations on the six-dimensional precision displacement platform 10, and use a computer program to control the movement of the six-dimensional precision displacement platform 10 up and down, so that the surface of the processed sample 9 is in the femtosecond laser focus plane . The front imaging system is formed by means of the imaging illumination light source 14 and the image sensor 13 to observe the processing process in real time.

Step 4: Use the "time-of-flight drilling method" to adjust the femtosecond laser repetition rate to 200Hz, and control the six-dimensional precision displacement platform 10 to move at a constant speed through a computer programming program. The moving speed is set at 2mm/s, which can realize single-pulse processing Large-area nano-dot array with a spacing of 10 μm between adjacent nano-dots. By analogy, controlling the six-dimensional precision displacement platform to automatically and rapidly perform periodic fold-line scanning processing can realize high-efficiency processing of large-area silicon nano-dot local modification areas.

Step 5: Put the KOH solution with a concentration of 25wt% into a water bath heating device for heating, stop heating when the temperature reaches 55°C and keep the temperature constant at 55°C, place the silicon sample irradiated by the femtosecond laser in Step 4 Etching in an etching solution at a constant temperature for 60 s, and then ultrasonically cleaning with acetone, alcohol, and distilled water for 5 min, respectively, can obtain a high-quality, high-uniform large-area silicon nano-dot array structure. Those skilled in the art know that the etching solution KOH is selected based on the chemical characteristics of the processed sample single crystal silicon, and for other materials, an appropriate etching solution can be selected according to the chemical characteristics of the corresponding materials.

Micro-nano structures with different shapes and sizes that meet the requirements of use can be obtained by controlling the laser flux and etching time, such as ring-like silicon column structures, flat-topped silicon column structures, and silicon nano-dot structures. By controlling the pulse laser repetition rate, The scanning speed controls the spacing of adjacent structures. On the premise that the scanning speed is sufficiently large, the higher the pulse frequency is, the higher the processing efficiency will be. In this embodiment, when a pulsed laser flux of 0.14 J/cm ² and a chemical etching time of 60 s are used, the silicon nanodots obtained through single pulse laser processing have a diameter of about 313 nm and a height of about 200 nm. When the laser repetition frequency is 200 Hz and the moving speed of the precision displacement platform 10 is 2 mm/s, it takes only about 85 minutes to uniformly process 100, 200, and 1 nanometer dots on a single crystal silicon sample 9 with a size of 1 cm × 1 cm. Quality nano-dot array structure, the distance between adjacent nano-dots is 10 μm. When increasing the laser energy, using a pulsed laser flux of 0.40J/cm ² and a chemical etching time of 60s, the diameter of the flat top-shaped silicon column structure obtained by using a single pulse laser is about 1.20μm, and the height is about 250nm. Further increase the laser energy, when using a pulsed laser flux of 0.93J/ ^cm2 and a chemical etching time of 60s, a ring-like silicon column structure can be obtained under single-pulse laser processing conditions, and the outer ring diameter is about 1.70 μm, the height of the outer ring is about 220nm, the diameter of the inner ring is about 1.37μm, and the height is about 230nm. Similarly, on the premise that adjacent structures do not overlap, the spacing between adjacent micro-nano structures in a large-area array structure can be controlled by adjusting the laser pulse repetition frequency and scanning speed. For example, the repetition frequency is 200Hz and the scanning speed is 2mm. /s, the distance between them is 10 μm; when the repetition rate remains unchanged and the scanning speed becomes 1 mm/s, the distance between adjacent micro-nano structures becomes 5 μm.

In order to process micro-nano structures with different shapes and sizes, different etching times can be selected, but the etching time t should be in the range of 30s to 120s, because if the etching time is too short, no microstructures can be formed on the surface of the processed material. Nano structure; the etching time is too long, the masking effect of the modified area with reduced chemical activity decreases sharply with the increase of etching time, the surface of the obtained micro-nano structure is partially etched, the surface roughness increases sharply, and the surface The mass decreases and so does the height. Therefore, within the etching time range of 30s<t<120s, a micro-nano structure with high surface quality and a height between 100nm and 300nm can be obtained.

The above-mentioned invention proposes a method for efficiently and controllably processing large-area silicon micro-nano structures in combination with chemical etching assisted femtosecond laser. , that is, in this embodiment, the femtosecond laser is used to act on the surface of the single crystal silicon with 100 crystal orientations. Due to the characteristics of ultrafast and super strong characteristics of the femtosecond laser, the redistribution of the free electron density excited in the material during the laser action affects the processed The chemical properties of the material make the processed material change from single crystal silicon state to amorphous silicon state after laser action, and the chemical activity drops sharply. Due to the difference in chemical activity between the processed area and the unprocessed area, the etching rate during the chemical etching process is quite different, so that the local processed area with ultra-low chemical activity plays the role of an etching mask during the etching process. The processing area reacts violently with the KOH solution, and the reaction rate between the processing area and KOH is low and negligible. Finally, a large-area high-quality micro-nano structure is formed to realize high-efficiency processing without a mask.

Since this embodiment is under the condition of a single-pulse femtosecond laser, the "time-of-flight drilling method" is used to process a large-area high-quality nano-dot array structure. According to the processing principle of the "time-of-flight drilling method", the repetition frequency of the femtosecond laser determines the processing speed of nano-dots, that is, when the repetition frequency is 200Hz, the processing speed of nano-dots is 200 per second. When the moving speed of the six-dimensional precision platform is allowed, increasing the femtosecond laser repetition rate can increase the processing speed of nano-dots and further improve the efficiency of large-area processing. In addition, compared with the traditional method of adding a mask layer on the surface of the material to assist etching, the present invention proposes a maskless processing method, that is, using a femtosecond laser to control the chemical properties of the material, so that the processing area has the ability to etch The role of the mask layer, so the process of processing the mask layer can be omitted, the processing cost is reduced, the processing process is simplified, and the overall processing efficiency is improved. It is a simple, Efficient and practical processing method.

In order to illustrate the content and implementation method of the present invention, this specification provides a specific embodiment. The purpose of introducing details in the examples is not to limit the scope of the claims, but to facilitate the understanding of the method described by the invention. Those skilled in the art should understand that various modifications, changes or substitutions to the steps of the preferred embodiment are possible without departing from the spirit and scope of the present invention and its appended claims. Therefore, the present invention should not be limited to what is disclosed in the preferred embodiments and drawings.

Claims (6)

1. it is a kind of efficiently controllable processing bulk silicon micro-nano structure method, it is characterised in that comprise the following steps：

Step one, femtosecond laser beam is focused on using microcobjective；

Step 2, adjusts laser energy：Using half-wave plate-polarizer combination regulation laser energy so that pulsed laser energy is low Can be continuously adjusted in the ablation threshold on rapidoprint surface, and pulsed laser energy；

Step 3, rapidoprint is fixed on a mobile platform, and regulation mobile platform makes femto-second laser pulse focus on processing material Material surface；

Step 4, utilizes " flight time punch method ", realizes the large area highly-efficient processing under the conditions of femtosecond laser pulse；

Step 5, the chemical solution that the rapidoprint after femtosecond laser processing in step 4 is placed under the certain concentration of constant temperature In, after etched time t, obtain that surface is smooth and uniform high quality silicon micro-nano structure.

2. it is according to claim 1 it is a kind of efficiently controllable processing bulk silicon micro-nano structure method, it is characterised in that：Institute State micro-nano structure including but not limited to class annular silicon column structure, flat-top shape silicon column structure and silicon nano dots structure.

3. it is according to claim 1 it is a kind of efficiently controllable processing bulk silicon micro-nano structure method, it is characterised in that：It is logical Crossing control laser flux, etch period can be met the different-shape of use requirement and the micro-nano structure of size, and The spacing of adjacent structure can be controlled by controlling pulse laser repetition rate, sweep speed.

4. it is according to claim 1 it is a kind of efficiently controllable processing bulk silicon micro-nano structure method, it is characterised in that：Step Rapidoprint described in rapid three is that the N-type of 100 crystal orientation undopes monocrystalline silicon.

5. it is according to claim 1 it is a kind of efficiently controllable processing bulk silicon micro-nano structure method, it is characterised in that：Step Chemical solution described in rapid five is alkaline solution.

6. according to a kind of method of any described efficiently controllable processing bulk silicon micro-nano structures of claim 1-5, its feature It is：Chemical solution described in step 5 is the potassium hydroxide solution of concentration 25wt%, and temperature is 55 DEG C, and etch period t is between 30s To between 120s.