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First, the LED sapphire substrate processing process First of all, for the sapphire substrate, it has undergone several processes from cutting, rough grinding, fine grinding, and polishing before becoming a qualified substrate. Take 2 inches of sapphire as an example:
1. Cutting: Cutting is performed from a sapphire ingot through a wire cutter to a thickness of about 500um. In this process, diamond wire saws are the most important consumables, currently mainly from Japan, South Korea and Taiwan.
2. Rough throw: The surface of the sapphire after cutting is very rough and needs to be rough thrown to repair the deeper scratch and improve the overall flatness. This step is mainly carried out by using 50~80um B4C plus Coolant, and the surface roughness Ra after grinding is about 1um.
3. Fine polishing: The next step is finer processing, because it is directly related to the yield and quality of the final product. The current standardized 2-inch sapphire substrate has a thickness of 430 um, so the total removal of fine polishing is about 30 um. Considering the removal rate and the final surface roughness Ra, this step is mainly processed by Lapping in a polycrystalline diamond liquid in combination with a resin tin plate.
In order to achieve stability, most sapphire substrate manufacturers use Japanese grinding machines and original polycrystalline diamond liquids. However, with the increase of cost pressure and the improvement of domestic consumables, domestic consumable products can replace the original products and significantly reduce costs.
Speaking of polycrystalline diamond liquid, it may be worthwhile to say a few words. For the micro-powder part of polycrystalline diamond liquid, it is generally required to concentrate the particle size and the shape should be regular, which can provide long-lasting cutting force and uniform surface scratch. Domestic manufacturers that can produce polycrystalline diamond micropowders include Beijing Guoruisheng and Sichuan Jiuyuan, while Guoruisheng can also produce diamond liquid by itself, so it has great advantages in quality and cost. Diamond Innovation in the United States recently introduced "polycrystalline diamonds", which is actually an improvement on ordinary single crystal diamonds. Although the relatively strong structure can provide high cutting force, it is also more likely to cause deeper scratches. .
4. Polishing: Although the scratch caused by polycrystalline diamond is significantly smaller than that of single crystal diamond, it will still leave obvious scratches on the surface of sapphire. Therefore, it will be polished by a CMP to remove all scratches and leave a perfect surface. . The CMP process was originally a process for planarizing germanium substrates, and is now equally applicable to sapphire substrates. The sapphire substrate subjected to the CMP polishing process is subjected to layer inspection, and the qualified product can be delivered to the epitaxial factory for epitaxy.
Second, the back of the sapphire substrate after the thinning process has become a chip epitaxial wafer, the wafer after etching, vapor deposition, electrode fabrication, a protective layer and a series of complex semiconductor manufacturing process, but also cut into capsules The chip, according to the size of the chip, a 2-inch epitaxial wafer can be cut into thousands to tens of thousands of CHIP. As mentioned above, the thickness of the epitaxial wafer is around 430 um. Due to the hardness and brittleness of sapphire, it is difficult to process it by ordinary cutting processes. The current common process is to thin the epitaxial wafer from 430um to around 100um, and then use laser to cut.
1. Grinding process:
Although the processing quality is good for the epitaxial film in Lapping mode, the removal rate is too low, and the maximum can only reach about 3um/min. If Lapping is used in the whole process, only the processing takes about 2 hours, and the time cost is too high. . The current solution is to add Grinding's process before Lapping, and achieve the purpose of rapid thinning through the cooperation of the diamond grinding wheel and the thinning machine.
2. After the Lapping process is thinned, use 6um of polycrystalline diamond liquid combined with resin copper plate to achieve higher removal rate and repair the deeper scratch left by the Grinding process. Generally, the cracks in the cutting process are not removed due to the deep scratches in the Grinding process, so the requirements for the diamond liquid are also high.
In addition to the lobes, some chip manufacturers in order to increase the brightness of the chip, after the Lapping process will also be copper plated on the back side of the epitaxial wafer, at this time put forward higher requirements on the surface after Lapping. Although some scratches do not cause lobes, they can affect the effect of back plating. At this point, 3 um polycrystalline diamond solution or smaller nuance can be used for the Lapping process to achieve better surface quality.
LED sapphire substrate and chip back thinning process
Abstract In the LED process, although the sapphire substrate is challenged by Si and GaN substrates, considering the cost and yield, sapphire still has advantages in the past two years. It is foreseeable that the development direction of the sapphire substrate is large size and patterning. (PSS). ...
In the LED process, although the sapphire substrate is challenged by Si and GaN substrates, considering the cost and yield, sapphire still has advantages in the past two years, and it is expected that the development direction of the sapphire substrate will be large size and patterning ( PSS). Because sapphire hardness is second only to diamonds, it is very difficult to reduce and flatten the surface of the sapphire. In the gradual exploration, the industry has formed a set of roughly the same process for thinning and flattening the sapphire substrate.