1 Introduction
The goal of every HB LED manufacturer is to get more light output with less money. In the face of strong competition and numerous technical obstacles, it is essential that all production steps advance to produce the best results. Optimized plasma etching provides several ways to improve device output and reduce manufacturing costs, resulting in a double profit.
2. Graphical sapphire substrate
Sapphire is still the substrate of choice for growing HBLED structures. However, there are two problems with sapphire growth: sapphire does not have a perfect lattice match, and light extraction is reduced by having two parallel reflecting surfaces. In the future, these two problems will be solved. Since 2005, some companies have etched graphics on sapphire before they grow. This can improve the light extraction performance of a finished device by more than 98%.
Sapphire is a very stable substance with a melting point of 2054 degrees, making it difficult to perform plasma etching. However, there is still a temperature upper limit for the photoresist used to achieve very specific pattern formation before being reduced to the usual 150 degrees. PR is the mask of choice for this process. The final "dome" shape depends on the completion of all mask removal, and its shape is closely related to the relative etch rate of sapphire and mask. PR has also become the first choice because it simplifies the production process and reduces the overall cost per lumen.
In order to etch the material, the combination of Cl2, BCl3, Ar is often used for higher etch rates achieved with higher plasma sources. However, this increases the thermal load of the sample, and therefore, the use of PR as a mask maintains a high etch rate, and it is necessary to effectively cool the wafer sample.
The silicon industry is accustomed to fastening a single wafer to a temperature-controlled workbench and introducing a heat transfer medium, usually helium, between the workbench and the wafer. “Backside Cooling†has become the standard method for single wafer temperature control. HBLED manufactures a small batch of substrates in urban areas that are delivered to the etch tool on the conveyor board. For patterned sapphire substrate etches, HBLED devices still primarily manufacture 2" or 4" wafers, which can significantly reduce cost, making it a viable way to process as many wafers as possible in a single run. The etching of a large number of photoresist films requires that the temperature of each wafer be controlled. This requires understanding how to transfer heat from the plasma from the sample to the cooled electrode. The backside cooling of helium is the key, and it is important to understand how to effectively cool each wafer Deo to ensure success. This technology has a batch scale from 20*2 inches up to 43*2 inches with an etch rate between 50 nm/min and 100 nm/min, depending on the PR mask and PSS shape requirements.
Figure 1 Typical dome PSS characteristics
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