Recent advances in key technologies of high power LED MOCVD

Author: Dr. Rainer Beccard, Marketing Director Vice President, AIXTRON AG

Due to the exciting application of new applications, LED technology is rapidly advancing. For notebook computers, desktop computer monitors and large screen TV backlight device is a key application of today's high brightness LED, to create a large number of LED to create demand. In addition to quantity, this LED must also meet stringent requirements on performance and cost. Therefore, the production technology is very important to the success of LED manufacturers, beyond any time.

One of the key manufacturing technologies of high brightness LED is MOCVD. Because of the vertical structure of LED by MOCVD growth, this technology not only determine the quality and performance of the LED, and determine LED manufacturing yield and cost to a great extent. Therefore, the optimization of MOCVD productivity and reduction of operating cost is a key target for MOCVD system manufacturers. Accurate parametric analysis of the productivity and cost of MOCVD processes is a prerequisite for any improvement efforts. Through this analysis, we find that the yield (per unit time of the wafer area produced) and the yield are key features.

Improved yield (4 inches and 6 inches) by employing larger wafer sizes

All LED (blue, green or white LED) is the main part of the GaN/InGaN/AlGaN material as the foundation. So far, most of the LED are manufactured in 2 inch sapphire substrate. Therefore, in recent years, any progress in MOCVD yield is obtained by increasing the loading capacity of the MOCVD reactor. The most popular MOCVD system in the current growth of GaN/InGaN/AlGaN planetary reactor and close coupled showerhead reactor, respectively supply 42 pieces of 2 inch and 31 2 inch wafer two (Figure 1). These translate into impressive high yield and low cost of ownership. However, this is further improved by transforming into larger wafer sizes. At this time, some major LED manufacturers have begun to turn 4 inches, and most other manufacturers intend to carry out the same changes. Since the MOCVD tool already has the ability to grow a large size wafer, the decision is easy.

Fig. 1 CRIUS? CCS (31x2) and AIX 2800G4 HT (42x2)

In the MOCVD system mentioned above, the transition from 2 inches to 4 inches (or even 6 inches) can be accomplished simply by replacing some of the components in the MOCVD reactor. However, the reaction chamber and the main component will remain the same, so the need to adjust the hardware and process is reduced to the school by doing this, such as planetary reactor from a 42x2 set into a 11x4 or "6x6" type. Although the cost of this conversion is relatively low, it has obvious benefits in terms of yield. In order to obtain a quantitative understanding, it is helpful to calculate the total wafer area of the full crystal circle load with different wafer diameters. 42x2 "configuration is equivalent to 851 cm2. Conversion to 11x4 "or 6x6" produced 891 cm2 and a wafer area of 1094 cm2, respectively. The relative increase in yield can be calculated from these figures. In addition, it must be taken into account that a few millimeters outside of the outside are usually excluded from the available wafer area. If you choose a larger wafer area, then the total area of the total area of the wafer area was significantly lower. Table 1 shows the results of this calculation.

However, the increase in productivity discussed above is not the only measure to increase the productivity of the MOCVD system. At the same time, the uniformity of epitaxial wafers must be improved to ensure that the LED process has a maximum chip yield level. From the design of the MOCVD reactor, this must be translated into specific requirements. Since the uniformity of MOCVD RUN is mainly determined by the good control of the gas phase dynamics and the consistent temperature distribution, it is necessary to choose a robust design in order to properly control the two parameters.

One of the key devices to determine the dynamics of the gas phase in a planetary reactor is the nozzle. In order to achieve maximum stability and the ability to adjust the maximum uniformity, the development of a special nozzle. The three beam nozzle has three separate water injection zones, which are not only allowed to be injected into group III and group V independently, but also provide an additional purge flow above (Fig. 2). This laminar flow of gas to avoid any type of re circulation, so that there is no sediment. In addition, by adjusting the upper air flow to allow fine tuning of the growth uniformity. The nozzle is designed to ensure that the injected geometry remains stationary and the gas is injected in a strictly horizontal manner. This means that no mechanical adjustment is required to obtain a prominent and repeatable uniformity.

Figure 2. The three beam nozzle used in the AIX 2800G4 HT reactor

In order to obtain repeatable growth temperature and uniform temperature distribution across the wafer load. This heating method does not show any long-term movement or sudden movement of the temperature setting. During the design and development of the MOCVD reactor, extensive numerical simulations are used to determine the best uniformity and stability of the heaters in all relevant process systems.

The growth results obtained at 4 "and 6" wafers fully confirm this. For example, the growth of a "4" wafer in the 11x4 configuration is shown in figure 3.

Figure 3 uniformity of PL in a AIX 2800G4 HT reactor with a blue MQW structure grown in the 11x4 configuration and in the 11x4 configuration. Uniformity (standard deviation) is 0.8 nm

Convert to 6x6 "configuration provides similar uniformity. It is important to pay attention to wafer warpage, which is the stress effect caused by the difference of lattice mismatch and the thermal expansion coefficient of different layers. This will be impressive