A Study Of Interfacial Properties Of GaAs MOS Capacitors Using Hf-baesd Gate Dielectrics

Based on Moore’s Law, the shrink of feature size contributes to the increasing integrated level of Integrated Circuit. However, Si-based devices reached their limits with a lot of problems about reliability. For the continuation of Moore’s Law, Ga As, a high-electron-mobility substrate, is used to replace Si. Besides, high-k dielectric is getting increasing attentions. It is noted that the lattice mismatch between high-k dielectric and Ga As results in a large interface trap density, which will severely reduce the carriers’ mobility. As a result, it is a huge challenge for Ga As MOSFET to be used in a practical way.The dielectric deposited by Atomic Layer Deposition(ALD) has the characteristics of high desification, low surface roughness, high precision of thickness, etc, compared with the traditional depositons(Such as MOCVD and MBE). Based on the basic principles and characteristics of ALD, as well as the fabrication of back-side ohmic contact, the fabrication processes of Ga As MOSCAPs, with Hf Al O(4:1), Hf O2/Al2O3 and Hf O2 as the gate dielectrics, are introduced.The interface trap densities of Hf Al O(4:1), Hf O2/Al2O3 and Hf O2 are extracted by Terman method with 1MHz C-V curve. It is found that Hf O2/Al2O3 has the smallest interface trap density(around 8.12×1012e V-1cm-2), while the interface trap density of Hf Al O(4:1) is smaller than that of Hf O2. The result of XPS indicates that the amount of As2O3 and As2O5 of all three samples, treated with PDA at 500℃, is small. It is becausethe precursor of Al2O3 is capableof reducing the As2O3.Besides, during the PDA, As2O3 with higher Gibbs free energy is converted into Ga2O3,which makes Ga2O3 become the main component of interface trap.And Al2O3 is more effective than Hf O2 in preventing the As-O and Ga-O from regrowing,due to the fact that O2 and H2 O has smaller diffusion coefficient than that of Hf O2. As a result, Hf O2/Al2O3 has smaller interface trap density than that of Hf Al O(4:1), and the interface trap density of Hf O2 is the largest.I-V testsof three samples are introduced, in order to estimate the quality of gate dielectrics. The result indicates that the gate leakage current of Hf O2/Al2O3 is larger than that of Hf Al O(4:1). It is because Hf O2/Al2O3 has a large number of border trapsbetween HfO2 and Al2O3. These border traps act as the “slow interface trap” and contribute to the increase of gate leakage current.And the gate leakge current of Hf O2 sample is the largest, due to its extremely large interface trap density.The interface trap density of Hf Al O(4:1) issmallerthan that of Hf O2. Besides, Hf Al O(4:1) has the smallest equivalent oxide thickness, dispersion and gate leakage current. As a result,Hf Al O(4:1) has relatively low interface trap, as well as high reliability.All these advantages make Hf Al O(4:1) a good candidate as the gate dielectric for Ga As MOSFET.