Laser processing method of silicon wafer for solar cell

Abstract

The invention relates to the technical field of photovoltaic equipment and process, in particular to a laser processing method of a silicon wafer for a solar cell, which comprises the following steps of: placing the silicon wafer on an adsorption table, starting a laser transmitter, and transmitting laser A; the laser A is expanded into laser B through a beam expander, the high-speed scanning galvanometer is controlled by a galvanometer motion control card and moves to a designated position, the galvanometer motion control card controls a pulse optical switch of the high-speed laser and triggers a laser pulse packet to be emitted, and the laser pulse packet comprises a plurality of laser sub-pulses D; and the laser pulse packets are respectively guided into the focusing field lens for focusing light beam pulses, and small holes are formed in the surface of the silicon wafer. The damage degree of the edge of a silicon wafer in the machining process is reduced, high monopulse energy including a plurality of D laser sub-pulses is adopted to improve the energy utilization rate of laser, a high-speed scanning galvanometer and a high-response galvanometer motion control card are configured, a single-hole multi-pulse machining scheme can be achieved in the high-speed scanning process, and the machining efficiency is improved. And the uniformity of the machined deep holes is kept.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic equipment and process technology, in particular to a laser processing method for a silicon wafer for a solar cell. Background Art

[0002] The silicon wafer used in solar cells is a semiconductor material that must have an extremely high light absorption rate and be able to absorb a large amount of light energy from the sun and then convert the light energy into electrical energy.

[0003] The structure on the silicon wafer that absorbs light energy is called a light trapping structure. The light trapping structure can reduce reflection and increase light absorption. Generally, the light trapping structure is made by wet method, the morphology is relatively fixed and faces optical limits. It is difficult to make light trapping structure by other methods. Laser is one of the optional methods.

[0004] Reflection loss on the silicon wafer surface is a major problem in solar cells. In order to produce high-efficiency solar cells, reflection must be reduced to 10% or less. The depth of the holes in the light-trapping structure determines the amount of light reflection.

[0005] Existing laser material processing is usually divided into two laser etching methods. One is the unit area etching method. This method is fast, but the energy of each laser beam is low. Usually, it can only process 200nm-300nm light-trapping holes, which cannot meet the low reflection requirements. The other method is to etch single holes one by one, but because the energy of each beam is too large each time, stress concentration occurs on the surface of the silicon wafer, causing damage to the mechanical strength and stability of the silicon wafer, making it difficult to form a thin film on the surface of the silicon wafer, reducing the photoelectric conversion efficiency. Therefore, a laser processing method for silicon wafers for solar cells is urgently needed to solve the above problems. Summary of the invention

[0006] The object of the present invention is to provide a laser processing method for silicon wafers for solar cells, so as to solve the problem that among the two laser etching methods proposed in the above-mentioned background technology, the energy of each laser beam of the method for etching per unit area is relatively low and cannot meet the low reflection requirement, while the energy of each laser beam of the method for etching single holes one by one is too large each time, resulting in stress concentration on the surface of the silicon wafer, causing damage to the mechanical strength and stability of the silicon wafer, making it difficult to form a thin film on the surface of the silicon wafer, thereby reducing the photoelectric conversion efficiency.

[0007] To achieve the above object, the present invention provides the following technical solution: a laser processing method for silicon wafers for solar cells, comprising the following steps:

[0008] 1) Place the silicon wafer on the adsorption table, turn on the laser transmitter, and emit A laser;

[0009] 2) Laser A is expanded into laser B by a beam expander, and then introduced into an optical diffraction device through a reflector group to convert laser B into laser C;

[0010] 3) The C laser enters the high-speed scanning galvanometer vertically. The high-speed scanning galvanometer is controlled by the galvanometer motion control card and moves to the specified position. The galvanometer motion control card controls the pulse light switch of the high-speed laser and triggers the emission of the laser pulse packet, wherein the laser pulse packet contains several D laser sub-pulses;

[0011] 4) The laser pulse packets are introduced into the focusing field mirrors to focus the beam pulses and open small holes on the surface of the silicon wafer.

[0012] Preferably, the diameter of the B laser=the diameter of the A laser*N (1.5 to 4 times).

[0013] Preferably, the A laser has a spot size of 2 mm to 8 mm, a wavelength of 300 nm to 1200 nm, and a pulse width of 300 femtoseconds to 30 picoseconds.

[0014] Preferably, the B laser is Gaussian light, and the C laser is flat-top light.

[0015] Preferably, the single pulse energy of the A laser is 0.3 mj-5 mj, and the energy of each D laser sub-pulse is 0.03 mj-0.1 mj.

[0016] Preferably, the time interval between the D laser sub-pulses is 1ns-1ms.

[0017] Preferably, the focusing field lens includes a telecentric field lens and a non-telecentric field lens, and has a size of 50mm×50mm-240mm×240mm.

[0018] Preferably, the small hole has a diameter of 10 μm-300 μm and a depth of 10 μm-300 μm.

[0019] Preferably, a dust extraction device is provided on one side of the adsorption table, and the dust extraction device includes a dust extraction hood and a dust outlet connector, and the dust outlet connector can be an external dust receiving mechanism.

[0020] Preferably, a cooling device is installed under the adsorption table, and the cooling device includes a water inlet joint and a water outlet joint, and the water inlet joint and the water outlet joint can be externally connected to a water pipe.

[0021] Compared with the prior art, the present invention has the following beneficial effects: by changing the spot shape from Gaussian to flat top, the energy density of the focused spot is made more uniform, the energy density at the edge of the Gaussian spot is reduced to be too low, and the degree of damage to the edge of the silicon wafer during processing is reduced. A high single pulse energy (0.3mj-5mj) containing several D laser sub-pulses is used to improve the energy utilization rate of the laser. A high-speed scanning galvanometer (>5m / s) and a high-response (<10ns) galvanometer motion control card are configured, wherein the galvanometer motion control card adopts a high-speed photoelectric grating closed-loop control module, which can provide real-time feedback on the movement position of the galvanometer and dynamically trigger the laser pulse (PSO). Therefore, a single-hole multi-pulse processing scheme can be realized during high-speed scanning, and the uniformity of deep hole processing can be maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a front view structural schematic diagram of the present invention;

[0023] Figure 2 It is a schematic diagram of Gaussian light and flat top light of the present invention.

[0024] In the figure: 1. adsorption table; 2. laser transmitter; 3. laser A; 4. beam expander; 5. laser B; 6. reflector assembly; 7. optical diffraction device; 8. laser C; 9. high-speed scanning galvanometer; 10. focusing field lens; 11. dust extraction device; 111. dust extraction hood; 112. dust outlet connector; 12. cooling device; 121. water inlet connector; 122. water outlet connector. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technical personnel in this field without creative work are within the scope of protection of the present invention.

[0026] See also Figure 1-Figure 2 The present invention provides a technical solution: a laser processing method for silicon wafers for solar cells, comprising the following steps:

[0027] 1) Place the silicon wafer on the adsorption table 1, turn on the laser emitter 2, and emit A laser 3;

[0028] 2) A laser 3 is expanded into B laser 5 by beam expander 4, and then introduced into optical diffraction device 7 by reflector group 6, so as to convert B laser 5 into C laser 8;

[0029] 3) The C laser 8 vertically enters the high-speed scanning galvanometer 9, which is controlled by the galvanometer motion control card and moves to a specified position. The galvanometer motion control card controls the pulse light switch of the high-speed laser to trigger the emission of the laser pulse packet, wherein the laser pulse packet contains a number of D laser sub-pulses (not shown in the figure);

[0030] 4) The laser pulse packets (not shown in the figure) are respectively introduced into the focusing field lens 10 to focus the beam pulses and open small holes on the surface of the silicon wafer.

[0031] It should be noted that the generation of laser pulse packets is achieved by selecting multiple high-frequency sub-pulses with the same repetition frequency as the seed source through a controlled optical switch to form a pulse packet or pulse train output.

[0032] Furthermore, the diameter of the B laser 5 = the diameter of the A laser 3 * N (1.5 to 4 times).

[0033] Furthermore, the spot size of the A laser 3 is 2 mm-8 mm, the wavelength is 300 nm-1200 nm, and the pulse width is 300 femtoseconds-30 picoseconds.

[0034] Furthermore, the B laser 5 is Gaussian light, and the C laser 8 is flat-top light.

[0035] It should be noted that the energy distribution of Gaussian light presents a Gaussian distribution, that is, the energy at the center point is the strongest and then gradually weakens. Its cross-section is usually circular or approximately circular. Gaussian light beams are easily affected by diffraction and defocusing during transmission, resulting in spot expansion.

[0036] The energy distribution of flat-top light is in the shape of a flat top. The energy distribution of the entire laser beam is basically uniform, and there is no obvious center point with the strongest energy. Its cross-section is usually rectangular or approximately rectangular. The flat-top beam is relatively more stable during transmission and is not easily affected by diffraction and defocusing.

[0037] Furthermore, the energy of a single pulse of the A laser 3 is 0.3 mj-5 mj, and the energy of each D laser sub-pulse (not shown in the figure) is 0.03 mj-0.1 mj.

[0038] Furthermore, the time interval between the D laser sub-pulses (not shown in the figure) is 1 ns-1 ms.

[0039] Furthermore, the focusing field lens 10 includes a telecentric field lens and a non-telecentric field lens, and has a size of 50 mm×50 mm-240 mm×240 mm.

[0040] It should be noted that the differences between telecentric field lenses and non-telecentric field lenses in the light path and the angle of the main ray are: the main ray of the telecentric field lens is parallel to the optical axis. No matter where the object is, the main ray entering the lens (the ray that passes through the center of the aperture among the rays emitted from each point on the surface of the object) is parallel to the optical axis, and the light enters the sensor vertically, avoiding imaging distortion caused by changes in object height or tilt.

[0041] The chief ray of a non-telecentric field lens is inclined to the optical axis. The light enters the lens at a certain angle. When the distance of the object changes, the angle of the chief ray will change. When the height or position of the object changes, the imaging position and size may shift due to the change in the light angle.

[0042] Furthermore, the diameter of the small hole is 10 μm-300 μm, and the depth is 10 μm-300 μm.

[0043] Furthermore, a dust extraction device 11 is provided on one side of the adsorption table 1. The dust extraction device 11 includes a dust hood 111 and a dust outlet connector 112. The dust outlet connector 112 can be an external dust collecting mechanism. When the energy density W>0.5mj / 0.01mm2, the molecular bonds of the material are stimulated to break, thereby being vaporized into a powder state, and finally the dust is collected by the dust extraction device 11 with the dust hood 111.

[0044] Furthermore, a cooling device 12 is installed under the adsorption table 1, and the cooling device 12 includes a water inlet joint 121 and a water outlet joint 122. The water inlet joint 121 and the water outlet joint 122 can be connected to an external water pipe. The water inlet joint 121 receives low-temperature water, and the water outlet joint 122 outputs high-temperature water after work.

[0045] Embodiment 1: Place a silicon wafer on an adsorption table 1, turn on the laser emitter 2, emit A laser 3, A laser 3 is shot into a beam expander 4, beam expander 4 expands the beam into B laser 5, B laser 5 is shot onto a reflector group 6, the number of reflector groups 6 is greater than or equal to 2, after passing through the last reflector, it is introduced into an optical diffraction device 7, the optical diffraction device 7 can convert Gaussian light into a flat-top light, at this time the flat-top light can be called C laser 8, C laser 8 vertically enters a high-speed scanning galvanometer 9, the high-speed scanning galvanometer 9 is controlled by a galvanometer motion control card and moves to a specified position, the galvanometer motion control card controls the pulse light switch of the high-speed laser, triggers the emission of a laser pulse package, wherein the laser pulse package contains a number of D laser sub-pulses, the laser pulse packages are respectively introduced into a focusing field lens 10 to focus the light beam pulse, and a small hole is opened in the silicon wafer, this embodiment is provided with an optical diffraction device 7.

[0046] Embodiment 2: Place a silicon wafer on the adsorption table 1, turn on the laser emitter 2, emit A laser 3, A laser 3 enters the beam expander 4, beam expander 4 expands the beam into B laser 5, B laser 5 is shot at the reflector group 6, the number of reflector groups 6 is greater than or equal to 2, after passing the last reflector, B laser 5 vertically enters the high-speed scanning galvanometer 9, the high-speed scanning galvanometer 9 is controlled by the galvanometer motion control card and moves to the specified position, the galvanometer motion control card controls the pulse light switch of the high-speed laser, triggers the emission of laser pulse packets, wherein the laser pulse packets contain a number of D laser sub-pulses, the laser pulse packets are respectively introduced into the focusing field lens 10 to focus the light beam pulses, and small holes are opened in the silicon wafer, and this embodiment does not have an optical diffraction device 7.

[0047] Example 3: The focused laser pulse directly acts on the surface of the silicon wafer. When the energy density w>0.5mj / 0.01mm 2 When the dust is discharged, the molecular bonds of the material are stimulated to break, thereby being gasified into a powder state, and finally being absorbed by the dust extraction hood 111 on the dust extraction device 11 and collected at the dust outlet joint 112.

[0048] Embodiment 4: In order to reduce the thermal impact of efficient processing, the adsorption platform 1 is also equipped with a cooling device 12. The water inlet joint 121 in the cooling device 12 is connected to low-temperature water. After cooling the silicon wafer on the adsorption table 1, high-temperature water is discharged from the water outlet joint 122. This is repeated to ensure thermal stability during the processing.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. Technical personnel in this industry should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A laser processing method for silicon wafers for solar cells, characterized in that: The steps include: 1) Place the silicon wafer on the adsorption table, turn on the laser transmitter, and emit A laser; 2) Laser A is expanded into laser B by a beam expander, and then introduced into an optical diffraction device through a reflector group to convert laser B into laser C; 3) The C laser enters the high-speed scanning galvanometer vertically. The high-speed scanning galvanometer is controlled by the galvanometer motion control card and moves to the specified position. The galvanometer motion control card controls the pulse light switch of the high-speed laser and triggers the emission of the laser pulse packet, wherein the laser pulse packet contains several D laser sub-pulses; 4) The laser pulse packets are introduced into the focusing field mirrors to focus the beam pulses and open small holes on the surface of the silicon wafer.

2. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The diameter of the B laser=the diameter of the A laser*N (1.5 to 4 times).

3. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The A laser has a spot size of 2mm-8mm, a wavelength of 300nm-1200nm, and a pulse width of 300 femtoseconds-30 picoseconds.

4. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The B laser is Gaussian light, and the C laser is flat-top light.

5. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The single pulse energy of the A laser is 0.3mj-5mj, and the energy of each D laser sub-pulse is 0.03mj-0.1mj.

6. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The time interval between the D laser sub-pulses is 1ns-1ms.

7. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The focusing field lens includes a telecentric field lens and a non-telecentric field lens, and the size is 50mm×50mm-240mm×240mm.

8. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: The diameter of the small hole is 10 μm-300 μm, and the depth is 10 μm-300 μm.

9. The laser processing method for a silicon wafer for solar cells according to claim 1, characterized in that: A dust extraction device is arranged on one side of the adsorption table, and the dust extraction device comprises a dust extraction hood and a dust outlet connector, and the dust outlet connector can be connected to an external dust receiving mechanism.

10. The laser processing method for silicon wafer for solar cells according to claim 1, characterized in that: A cooling device is installed below the adsorption table, and the cooling device includes a water inlet joint and a water outlet joint. The water inlet joint and the water outlet joint can be connected to an external water pipe.

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