Yoshitaka Iwazaki

Evaluation of GeO desorption behavior in the metal/GeO2/Ge structure and its improvement of the electrical characteristics

The relation between germanium monoxide (GeO) desorption and either improvement or deterioration in electrical characteristics of metalGeO(2)Ge capacitors fabricated by thermal oxidation has been investigated. In the metalGeO(2)Ge stack, two processes of GeO desorption at different sites and at different temperatures were observed by thermal desorption spectroscopy measurements. The electrical characteristics of as-oxidized metalGeO(2)Ge capacitors shows a large flat-band voltage shift and minority carrier generation due to the GeO desorption from the GeO(2)Ge interface during oxidation of Ge substrates. On the other hand, the electrical properties were drastically improved by a postmetallization annealing at low temperature resulting in a metal catalyzed GeO desorption from the top interface.

Low-temperature fabrication of ultrathin ZrO2/Si structure using metal deposition followed by oxygen annealing

Metal deposition followed by oxygen annealing has been carried out for the fabrication of ZrO2/Si structures. Using this method, 200°C oxygen annealing enables the oxidation of Zr metal and 220°C annealing enables the surface potential control of Si in metal–insulator–semiconductor (MIS) structures, even if the dielectric constant of ZrO2 has been shown to be 11.8. High-quality ZrO2 films with a dielectric constant of ~20 can be achieved by 300°C annealing with an interfacial layer of 0.9 nm thickness. For these films, no degradation of leakage characteristics was observed after the thermal budget corresponding to that of impurity activation at 850°C for 30 min. Consequently, using this method, a high-quality ZrO2/Si structure that has good chemical stability under a high thermal budget could be fabricated at a low temperature.

HfO2/Si and HfSiO/Si Structures Fabricated by Oxidation of Metal Thin Films

Hafnium metal deposition followed by oxidation, either on bare silicon or SiO2/Si substrates, was performed for the fabrication of high-k/Si gate stacks with small equivalent oxide thickness values. HfO2/Si structures were fabricated without substrate heating but with the electron cyclotron resonance (ECR) plasma oxidation of Hf metal deposited on bare Si substrates by DC magnetron sputtering. These HfO2/Si structures have ideal abrupt interface without interfacial layer (IL)-SiO2 and silicide layers, as determined by an X-ray photoelectron spectroscopy (XPS) measurements. A direct stacking was induced by the characteristic film growth of ECR plasma in a buried interfacial region. On the other hand, on SiO2/Si substrates, the HfSiO/Si structures were successfully fabricated by thermal treatment for both the interdiffusion of Hf metal and SiO2, and the oxidation of the layer. The HfSiO/Si structures show small leakage currents because of high barrier heights and have no hafnium silicide layer.

Effects of Structural Transformation of Metal-GeO2 Interface on Electrical Properties

The relations between physical structural transformations and improvement of electrical properties of metal/GeO 2 /Ge systems using low temperature oxidation and the post metal deposition annealing (PDA) have been investigated. In metal/GeO 2 /Ge systems, we found that the electrical properties were drastically improved by the oxidation and the PDA. The oxidation at low temperature achieves no C-V hysteresis because of suppression of GeO desorption. on the other hand, according to results of X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS), the improvement mechanism of electrical properties of metal/GeO 2 /Ge structures after the PDA was clearly shown as follows. Once the metals were deposited on the GeO 2 , GeO x layer was formed at the surface region of the GeO 2 due to reduction of the oxide by the metals. The sub-oxide layer at the interface causes a large negative flat-band voltage (V FB ) shift on the capacitance-voltage (C-V) characteristics of the metal/GeO 2 /Ge structures. Then, during the PDA process at low temperature, the sub-oxide layer is disappeared with desorbing as germanium monoxide (GeO) gas, and the V FB shifts of the metal/GeO 2 /Ge systems were drastically improved and also their accumulation capacitances were increased because of disappearance of the sub-oxide layer.

Thermal Stability of HfO2 Films Fabricated by Metal Organic Chemical Vapor Deposition

The effect of impurities in HfO2 films fabricated by metal organic chemical vapor deposition (MOCVD) on high-temperature annealing was investigated. Thermal desorption spectroscopy (TDS) shows that residual impurities such as carbon are desorbed from HfO2 films with mass number of 28, expected to be carbon monoxide (CO), during high-temperature annealing. The deterioration of the electrical properties of HfO2 with high-temperature annealing is caused by such desorption. For HfO2 films from which many molecules of the mass number 28 are desorbed, the deterioration, indicated by events such as an increase in leakage current and flat-band voltage shifts caused by 850 °C and 30 min annealing, occurs markedly. The suppression of such desorption caused by the decrease in the number of residual impurities in the films leads to an improvement of the thermal stability of HfO2 films during high-temperature annealing. Furthermore, in the fabrication of HfO2 films using MOCVD, an intermittent introduction of an MO source and oxygen decreases the number of residual impurities compared with conventional MOCVD. Consequently, the stability of HfO2 films against the thermal budget was improved.