Silicon carbide is a third-generation semiconductor material with excellent performance, characterized by good optical properties, chemical inertness, excellent physical properties, including bandgap width, high breakdown voltage, high thermal conductivity and high temperature resistance, etc., often as a new generation of high-frequency, high-power devices as the substrate material, widely used in high-end manufacturing areas, such as a new generation of electronic industrial equipment,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 a 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 ionization removal, belonging to the non-traditional sense of the cold processing treatment.
In the silicon carbide semiconductor wafer back-channel process, the need for individual 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, and small material loss.
01. Laser wafer marking applications
In the silicon carbide waferproduction process, in order to have thedistinction, traceability and other functions, the need for eachwere unique bar code marking. The traditionalmarking method is 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 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 ultraviolet laser is more inclined to cold processing, marking clearer and more effective, suitable for marking higher requirements of materials and processes. Laser through the external optical path for transmission, 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.
Silicon carbide wafer nanosecond UV laser marking effect, character height 1.62mm, character width 0.81mm, depth 50μm, surrounding protrusion height 5μm.
02. Laser Back Gold Removal Process
After completing the production of a number of chips on the whole silicon carbide wafer, it is necessary to cut and slice it to get an independentinto the back-end sealing and testing process. Silicon carbide chips need to be gold-plated (drain) on the backside during the production process, so the backside gold and silicon carbide substrate materials need to be cut and separated together during cutting and slicing.
For the silicon carbide wafer slicing process, the traditional processing method for diamond knife wheel cutting, this mechanical grinding process has the advantage of 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 ofmaterials, 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 is a 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 are gradually increasing in the application.
Back gold removal laser process generally use nanosecond or picosecond ultraviolet laser as a light source, with the appropriate focusing cutting head and precision motor motion platform to collimated way to process, generally remove the back gold thickness of 10 μm or less, the removal of the width of not less than half of the front channel. 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 the 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.
Picosecond UV laser backing gold removal effect on silicon carbide wafer with backing gold, front side trench width is 100μm, backing gold removal width is more than 50μm, and removal depth is about 3μm.
03. Laser Invisible Modified Cutting Process
The next process after the completion of the back gold removal process is laser invisible modified cutting, the principle is to use the focusing objective lens to focus a specific wavelength of the laser beam on the material to be processed inside the formation of a certain width of the modified layer, and the upper and lower surfaces of the material are not damaged, and then under the action of the external force through the expansion of cracks to carry out the cracks, to get the required particle chip.
For silicon carbide wafers with gold backing removed, the removal surface may cause a decrease in laser transmission due to gold backing residue or silicon carbide damage, making it difficult to achieve a good stealth cutting effect, so the laser needs to be incident from the channel surface for cutting. Laser stealth cutting of silicon carbide generally uses a picosecond infrared laser as the light source, and the near-infrared wavelength can better penetrate through the silicon carbide and focus on the material to form a modified zone.
The thickness of silicon carbide wafers varies from 100μm to 400μm depending on therequirements and the process, and usually a single invisible cut does not have a large enough re-modeling zone to complete a high-quality lobe, so it is necessary to move the focal point position for multiple invisible cuts. In this process, due to the large refractive index of the silicon carbide material to the laser and at the same time need to ensure that can not hurt the upper and lower surfaces, moving the focus of the Z-axis precision requirements are very high, usually need to add the focus of the function of the followers, the focus of the processing surface caused by the ups and downs caused by the change in detection and real-time compensation.
Silicon carbide is a hard material that is difficult to slice, so a mechanical cleaver is used to slice the sample after the invisible cutting is completed.
In recent years with the development of technology and innovation, silicon carbidemarket is increasing, the production of chips in the process available to the laser processing of the field is also gradually increasing, Huagong laser grasp the opportunities for the development of the industry, in-depth research and development of silicon carbide wafers laser processing technology and its applications, has been around the wafer marking, back gold removal, laser invisible texture modification cutting and other related processes to launch a series of "Laser + Intelligent Manufacturing" solutions, and for the industry to develop a long-term cooperation plan for industry, academia, research and use, for the expansion of the laser intelligent equipment market, the realization of high-end equipment localization is very important. Translated with www.DeepL.com/Translator (free version)
