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Large-Diameter LED Has A Higher Yield

Each step in the manufacturing process of an LED chip has a yield loss, from the preparation of substrates through chip packaging. The yield losses at each step add up and contribute to a significant portion of the final chip cost. There is therefore a great deal of focus currently on improving yield in all of these areas.

Switching to large-diameter LED manufacturing has been linked to yield improvement in a number of stages of the manufacturing process. The potential benefits come both directly as the larger wafer size is a more uniform surface for epitaxy and indirectly through the use of better manufacturing equipment and techniques. While yield can be a complex subject, we will briefly look at some highlights of the possible benefits.

One of direct yield benefits of larger wafers comes during epitaxy. In the MOCVD chamber, any physical disturbances, such as wafer edges, can disturb the gas flow and reduce yield. Larger wafers can help here because there are fewer edges and more undisturbed surface area. The resulting higher yield during this expensive step is an important advantage.

The second component of improved yield comes from access to modern process control and automation tools, which are designed around large-diameter wafers and have been perfected in IC manufacturing. Today’s commonly used small-diameter manufacturing techniques use manual processes, requiring many human interactions, and lack sophisticated tracking that could spot yield issues. Many experts have pointed to a general need to move from a research-style production environment to a true mass production environment. Let’s look in a little more detail at what this means.

Automation primarily refers to the use of machines to handle and transport wafers – removing the human element. Wafers can be moved faster and with less damage through automated machines instead of being hand carried. The benefit is a combination of fewer skilled operators required, less loss of wafers due to mishandling, and quicker movement through the manufacturing steps.
In addition to more automation, the use of more modern tools brings better process control. Process control is the use of data analysis to detect and predict problems that cause yield losses in any area of the production process. This involves a tracking and analysis of the substrate throughout the process, extending back to the crystal growth stage. Process control also takes into account the analysis data recorded by the various production tools.

The use of process control is often cited as a necessary step in advancing the LED industry. As with automation, the tools needed for implementing process control are designed around large-diameter substrates, so the benefit to switching goes beyond just more LED chips.


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