| AVS 62nd International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS1-TuA |
| Session: | Novel Materials and Etch Chemistry |
| Presenter: | Daisuke Ogawa, Chubu University, Japan |
| Authors: | D. Ogawa, Chubu University, Japan Y. Nakano, Chubu University, Japan K. Nakamura, Chubu University, Japan |
| Correspondent: | Click to Email |
Next to a great success of blue LEDs, gallium nitride (GaN) is now looking for another success, the application with high-power devices. The wide bandgap of GaN is attractive when considering the integration and fabrication of devices on a substrate. The integration process requires the use of plasma, but the plasma sometimes creates undesirable change on devices, noticed as plasma-induced damages (PID). Therefore, it is important to understand how process plasma creates changes on GaN and what mainly causes the change.
In-situ monitoring is one of ways to understand the damage development of GaN. Towards to the goal, we have used steady-state photoluminescence (PL) emitted from the surface of GaN. The PL represents the optically-transferrable intermediate states that are mainly created with the defects and impurity in GaN. The depth of the PL measurement depends on the wavelength of excitation. Our experiment setup uses 313 nm wavelength for the excitation so that we basically monitored the change of the intermediate states down to ~75 nm below the top surface.
Our in-situ measurements showed that the exposure of argon plasma changed PL spectrum from the GaN; the total PL intensity turned down to 33 % of the original spectrum. We also increased the chuck bias, showing that the total PL intensity decreased even worse. This means that the argon ion affected the change of PL in our system assuming that plasma density stayed the same. We also made ex-situ measurements with X-ray photoelectron spectroscopy (XPS). The measurement showed that the change of atomic distribution was observed down to 4 nm at deepest. In this depth range, gallium and nitrogen atoms dissociated from the surface, and oxygen atoms defused into deeper levels. However, this depth was only ~5 percent of the depth where PL spectrum informs us. This means that the change of PL was caused by the structural change in GaN, such as crystal dislocation.
We also changed the gas that formed the plasma. In general, chlorine gas is utilized to etch GaN. In this measurement, we used the mixture gas of argon and chlorine with the ratio of 2:1. Interestingly, the PL from GaN stayed almost constant even when GaN was exposed into the plasma. We double-checked the etch rate, finding the rate at 100s nm/min. This result indicates that chlorine likely etched GaN without making a major change in the optical intermediate states even though argon could have made some damages during the plasma exposure.
In this presentation, we will show our latest analysis of damage development of GaN that is exposed in plasma, in particular, the plasma that is possibly used in the material process.