|
Metal-Insulator-Metal（MIM） capacitors have been widely used in RF ICs,as the VLSI technology is developing rapidly,MIM capacitors are required highly to replace traditional insulators such as SiO2 and Si3N4.In this these,three kinds of high-k materials such as HfO2,Al2O3 and Nb2O5 are studied for MIM capacitor applications.We compare the performance of MIM capacitors with different bottom electrodes,the electrodes are prepared by sputtering TaN,Ta,and HfN on SiO2 bottom,then deposit HfO2 using ALD technique.HRTEM,Capacitor-Voltage and Current-Voltage measurements are used to investigate electrical properties of MIM capacitors and the related mechanisms.During the deposition process of HfO2 material,Ta bottom electrode easily form TaxOy,oxidation layer increase the thickness of insulator,on the other hand,it increase the density of interlayer defect, cause poor performance of VCC character.However,TaN and HfN bottom electrodes have stable chemical character that can avoid the formation of oxidation layer during ALD process,thus MIM capacitors with these electrode show higher capacitor density, lower VCC and higher breakdown electric field,then we analysis the leakage current mechanism of three capacitors.High-k Nb2O5 dielectrics are deposited using atomic layer deposition（ALD） technique with Nb（OC2H5）5 and water as its precursors.With XPS measurement and ellipsometer,analysis deposition rate of ALD Nb2O5,chemical components and refractive index.Deposition rate is 0.07-0.09 nm/cycle,higher defect density are found in film deposit under 300℃.Besides that,the film is amorphous without any post process,but crystal structure form after anneal under 500℃.Finally,VCC mechanism of MIM capacitors with Al2O3 and HfO2 are studied. Simulation based on two prevalent models.The main mechanism that affect VCC mechanism of Al2O3 based capacitors is free carrier mechanism,relating to leakage current.But for HfO2 based MIM capacitors,VCC mechanism are different with film thickness decrease.For 55 nm HfO2,VCC mechanism is electrode polarization mechanism,cause by oxygen vacancy;for 12nm HfO2,both mechanism are participant.
|