Laser Applications in Silicon Carbide Semiconductor Wafer Processing
Time：
2022-11-17
来源：
Silicon carbide is an excellent performance of the third generation of semiconductor materials, with good optical properties, chemical inertia, excellent physical properties, including band gap width, high breakdown voltage, high thermal conductivity and high temperature resistance, etc., often as a new generation of high-frequency, high-power devices substrate materials, widely used in high-end manufacturing areas, such as a new generation of electronic industrial equipment, aerospace and so on. Particularly prominent is the rise in recent years and growing new energy automotive industry, it is estimated that in 2025 China's new energy vehicle annual output of nearly 6 million, the demand for power chips for 1000-2000 / car, of which more than 50% for the silicon carbide chip.
In the interaction between laser and silicon carbide material, continuous laser, long pulse laser and even nanosecond short pulse laser and material reaction is mainly thermal effect, its processing principle is high power density laser beam focused on the surface of the material for heating, melting processing. The picosecond, femtosecond ultrashort pulse laser focused on the material surface is based on material ionisation removal, belonging to the non-traditional sense of the cold processing treatment.
Silicon carbide semiconductor wafers in the back-channel process, the need for a single wafer marking, cutting, slicing, packaging and other steps, and ultimately become a complete commercial chip, in which the wafer marking, cutting process has gradually begun to use the laser processing equipment to replace the traditional mechanical processing equipment to deal with the advantages of high efficiency, good results, small loss of material and so on.
First, laser wafer marking applications
In the silicon carbide wafer chip production process, in order to have the chip distinction, traceability and other functions, the need for each chip were unique barcode marking. Traditional chip marking methods are generally ink printing or mechanical needle engraving, etc., low efficiency, large amount of consumables and other shortcomings. Laser marking as a non-contact processing methods, with small damage to the chip, high processing efficiency, the process of no consumables advantages, especially in the wafer more and more thin and light on the processing of quality and precision requirements of the trend of its advantages are more obvious.
Laser wafer marking laser is usually selected according to user needs or material characteristics, for silicon carbide wafers generally use nanosecond or picosecond ultraviolet laser. Nanosecond UV lasers are less expensive, suitable for most wafer materials, and are more widely used. Picosecond UV lasers are more inclined to cold processing, marking clearer and more effective, suitable for marking higher requirements of materials and processes. Laser transmission through the external optical path, beam expansion into the galvanometer scanning system, and ultimately through the field mirror focused on the surface of the material, marking content according to the processing map file by the galvanometer scanning to achieve.
Second, the laser back gold removal process
In the whole piece of silicon carbide wafer to complete a number of chip production needs to be cut, slice, and then get an independent chip into the back-channel sealing process. Silicon carbide chips need to be gold-plated (drain) on the backside during the production process, and thus the backside gold and silicon carbide substrate materials need to be cut and separated together during the cutting and slicing process.
Silicon carbide wafer slicing process, the traditional processing method for the diamond knife wheel cutting, the advantages of this mechanical grinding process is very mature technology, market share is very high, the shortcomings of the processing efficiency is low, the processing process of consumables (pure water, tool wear, etc.) the use of large amounts of chip materials, such as high losses. Especially the back gold removal part, due to the ductility of the metal, the knife wheel cutting speed needs to be reduced to a very low and easy to have the metal curled in the blade and thus affect the cutting quality. Laser processing belongs to non-contact processing, the process does not require consumables, high processing efficiency, good processing quality, based on these advantages in the back gold removal and cutting and slicing of the two processes in the application of the gradual increase.
Back gold removal laser processing process generally use nanosecond or picosecond ultraviolet laser as a light source, with the appropriate focusing cutting head and precision motor motion platform in a collimated manner for processing, generally remove the thickness of the back of the gold in the 10μm or less, the removal of the width of the front groove is not less than half. The silicon carbide wafer is inverted (the front side with grooves is facing down, and the back gold side is facing up) on a transparent adsorption jig, and the lower CCD grabs the wafer grooves through the transparent jig for alignment, and then the laser on top of the jig focuses on the back gold side of the wafer corresponding to the location of the grooves for back gold removal processing.
Silicon carbide wafer with back gold, picosecond UV laser back gold removal effect, the front channel width of 100 μm, back gold removal width greater than 50 μm, removal depth of about 3 μm.
Third, the laser invisible texture modification cutting process
Back gold removal process completed the next process for the laser invisible texture modification cutting, the principle is to use the focusing objective lens will be a specific wavelength of the laser beam focused on the material to be processed in the interior, the formation of a certain width of the texture layer, and the material up and down the
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Laser Applications in Silicon Carbide Semiconductor Wafer Processing
Silicon carbide is a high-performance third-generation semiconductor material with good optical properties, chemical inertness and excellent physical properties, including wide bandgap, high breakdown voltage, high thermal conductivity and high-temperature resistance, often used as a new generation of high-frequency, high-power device substrate materials, widely used in high-end manufacturing areas
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