碳化矽基板之氮化鋁金氧半電容器暨稀釋一氧化二氮之氧化機制之研究

Abstract

碳化矽被視為有前瞻性的功率元件半導體材料，同時適合應用於高溫、高壓環境操作，同時擁有寬能隙、高崩潰電場以及高導熱係數的物理特性。但是對於碳化矽金氧半場效電晶體而言，通道遷移率太低是一個影響電晶體效能的重要問題，由於二氧化矽介電層與碳化矽的介面有相當多的介面能態，使得通道中的載子被這些介面能態捕捉，也容易因為很強的庫倫散射導致等效遷移率降低，因此降低介面能態密度是必要的目標。 在近來的文獻中，使用氮元素去修補介面能態密度是常見且有效的方式。在本論文中，我們使用了原子層沉積技術沉積氮化鋁在二氧化矽上，氮化鋁沉積在二氧化矽上能些微地改善介面能態，是因為在沉積氧化鋁時的氮擴散到碳化矽的表面，但氮化鋁的厚度並不影響介面能態。氮遠程電漿處理與乾氧氧化相比，可以些微地改善介面能態，另外氨氣電漿處理的介面能態稍微比氮氣電漿還要低。 另一方面，使用一氧化氮或是一氧化二氮氧化是一個有效降低介面能態密度的方法，但碳化矽基板上的稀釋一氧化二氮的氧化機制尚未被研究發表，本論文探討了稀釋一氧化二氮在碳化矽基板上的氧化機制。一氧化二氮分解過程中的第一個反應是碰撞反應，此反應式中包含了碰撞對象。在我們的稀釋一氧化二碳氧化結果當中，碰撞對象是氮氣分子而且在低於1200 °C的一氧化二氮分解中扮演了一個很重要的角色。在稀釋一氧化二氮氧化中增加氮氣的流速會提高一氧化二氮的分解，所以增加了氧化速率。此外，氮氣與一氧化二氮的碰撞比一氧化二氮與一氧化二氮碰撞更有效率去造成更多有效的碰撞。因此比較低的一氧化二氮對氮氣的比例會有比較厚的氧化層厚度。在1300 °C時，因為一氧化二氮的熱分解主導了分解化學反應，一氧化二氮對氮氣的比例與流速幾乎不會影響養化速率，但也因為在高溫時一氧化二氮分解完全，鈍化效果更加有效降低介面能態密度。 上述研究，對於控制氧化製程，改善氧化層品質，提供重要資訊。

Silicon carbide (SiC) is a foreseen semiconductor material for power device. It is suitable for high temperature and high power applications due to its wide bandgap, high breakdown field, and high thermal conductivity. However, low channel carrier mobility is a critical issue for SiC MOSFET. There are a lot of interface states at the SiO2/SiC interface which can capture carriers from channel. They also make channel carriers suffer from strong coulomb scattering in operation. This effect results in the reduction of effective channel mobility. Therefore, interface state density (Dit) must be reduced to enhance the channel carrier mobility. Recently, reports indicate that nitrogen is an effective method for interface state passivation. In this thesis, we deposit aluminum nitride (AlN) by atomic layer deposition (ALD) on SiO2 firstly. The AlN deposition on SiO2 slightly reduces the Dit due to the nitrogen diffusion to the SiC surface during the AlN deposition process although the thickness of AlN may not affect the Dit. Besides, nitrogen remote plasma treatment can slightly improve the Dit compared with dry oxidation. And the Dit of sample with NH3 plasma treatment is slightly lower than that with N2 plasma treatment. On the other hand, oxidation by nitric oxide (NO) and nitrous oxide (N2O) is an effective method to reduce Dit. But the oxidation mechanism of SiC in diluted N2O has not been reported in literature. In this thesis, we investigate the oxidation mechanism of 4H-SiC in diluted N2O ambient. The first step of the N2O decomposition process is a collision reaction, which includes the collision partner M. The M is N2 in our experiments which plays a critical role in the N2O decomposition process at temperature below 1200 °C. Increasing the N2 flow rate enhances the N2O decomposition thus increases the oxidation rate. Additionally, the collision of N2 with N2O is more efficient to create more successful collision than the collision of N2O with N2O. Therefore, the lower the N2O/N2 ratio is, the thicker the oxide thickness is. At 1300 °C, the N2O/N2 ratio and total flow rate hardly affect the oxidation rate. It is considered that the thermal decomposition of N2O dominates the decomposition chemistry. Since the decomposition is more completed, the passivation effect will be more effective at high temperature so that the Dit is reduced. These results are helpful for oxidation process control and useful to obtain high quality gate dielectric.