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Plasma etching of high-brightness LED programme

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Center stage:

  * Optimization of plasma etching to improve LED output


  Solution:


  *LED graphical Sapphire substrates


  *LED plasma etching method


  1, preparation of high-brightness LED plasma etching technology


  Each HBled manufacturer's target is to spend less money for more light output. Face strong competition and numerous technical obstacles, it is essential that all the production steps forward have to yield the best results. Optimization of plasma etching provides several methods to improve the device's output and lower manufacturing costs, in order to achieve a double profit.


  2, graphical Sapphire substrates


  Now Sapphire substrate selection remains growth HBLED structure. However, there are also two Sapphire growth issues: Sapphire does not have a perfect lattice match, extract reduced because there are two parallel reflector. Resolving these two issues in the future, since 2005, just prior to the growth of the company are etched on Sapphire graphics. This can make a finished product light extraction device performance improvements over 98%.


  Sapphire is a very stable substance, melting point at 2,054 degrees, making it difficult to make plasma etching. However, before the reduce to the usual 150 degrees, to achieve very specific patterns of forming photoresist there is still a high temp. PR is the process of selecting the mask, the ultimate "dome-shaped relies on all of mask removal is complete, its shape and Sapphire and mask etch rate are closely related. Thanks to simplify the production process, reducing the overall cost per lumen, PR has also become the first choice.


  To etch materials, Cl2, BCl3, Ar combination is often used at high plasma source achieving high etch rate. However, this increases the heat load of specimens and, therefore, use PR as a mask to maintain high etch rate of wafer sample is necessary for effective cooling.


  Single crystal silicon is used to round tight temperature control platform, and introduces a heat transfer medium between the Workbench and wafer, usually helium. "Back of the helium cooling has become a standard method for temperature control of single crystal. HBLED manufacturing currently smaller batches in the urban area of substrate, delivered to the carrier plate etching tools on. For graphical Sapphire substrate etching, HBLED devices still makes 2-inch or 4 inch wafers, so you can significantly reduce costs, it runs in a way to handle as many wafers are feasible. A large number of optical delay film wafer etching requirements of each wafer temperature control, which you need to know how to transfer heat from the specimen to a cooling from the plasma electrode. Helium cooling is a key on the back, at the same time to learn how to make each wafer deao efficient cooling to ensure success. The technology of lot sizes from 20*2 up to 43*2 inches to inches, etch rates between 50nm/and 100nm/, the rate depends on the PR and PSS mask shape requirements.


  3, GaN etch


  GaN Gao Jian and chemical stability of bonding strength, its melting point and bond energy but also it has a very high degree of 2,500 wet etching acid or alkali etching agent capabilities. To date, due to the lack of suitable wet etching technology, enables people to develop the appropriate HBLED dry etching processes of production have had a great interest. This must be a single batch to a large number of wafer etching. Late in the 1990 of the 20th century, plasma etch batch sizes from 4*2 inch 55*2 inch wafers up to today or 3*8 inches, its appeal, the question is now disappearing before it can process large batches. With wafer sizes from 2 inches to 4 English followed by a 6-inch upward migration, this problem has been resolved. GaN etch main field of application is light and high aspect ratio structures in contact etching etching.


  4, light contact etching


  When etch into the contact layer, minimum is of crucial importance to semiconductor plasma caused by injuries, or is likely to increase contact resistance. Etching process requires careful optimization to maximize throughput, while maintaining the performance of the device. Surface etching of high-quality smooth surface often.


  Unoptimized etching process may result in GaN etching of dislocation, which in turn lead to increased surface pitting and contact resistance. Similarly, PR is the mask option in this step, because it is the most simple way to handle. Reportedly due to the typical batch of etch rate up to 140nm/of temperature limit, PR use could reduce the use of power.


  5, isolation of deep etching


  When you need depth up to 7 microns, etch-rate is the key to this process. This step is etched into the role of active devices between the Sapphire substrate at the bottom. Because Sapphire is not electrically conductive, in physically separate isolation device before. If you use PR mask, major challenges of this moment erosion step is heat, because high plasma density for high etch rate is achieved. This means that single crystals of fastening problems, the usual method is to use static electricity suckers. You can use the medium hard mask, it will be possible to achieve high etch rate batch, in which case consistency determines the output of the entire batch.


  6, Photonic Crystal Graphics


  Using quasi crystals, called Photonic Crystal array of graphical HBLED light-emitting surface to enhance the light extraction capabilities. Its extreme performance as shown in Figure 3, 600nm corrosion has been etched 4 microns deep, enabling high aspect ratio structures greater than 6:1. Vertical profiles of corrosion challenge here is to keep to ensure that the optical properties of Photonic crystals.


  7, equipment


  In order to meet the requirement of high etch rate and low damage, the industry has developed several high density plasma sources: inductively coupled plasma (ICP), transformer coupled plasma (TCP), high density plasma (HDP). All technology provides a fixed sample-driven, independent plasma source for high plasma density, without increasing the sample of DC bias. DC bias has proven to be more sensitive to surface and plasma damage, so this is a critical system characteristics.

 
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