Growth of high permittivity dielectrics by high pressure sputtering from metallic targets

Resumen

In this thesis, the fabrication of metal insulator semiconductor (MIS) structures using high permittivity (¿) dielectrics grown from metallic targets by means of high pressure sputtering (HPS) was analyzed. The key novelty of this work consisted on the development of a two step deposition process: first, a thin metallic film was sputtered in an Ar atmosphere and, afterwards, this film was in situ oxidized in a mixed Ar/O2 plasma. The main objective was the fabrication of GdScO3 (a high ¿ dielectric that presents interesting and promising properties) from metallic Gd and Sc targets. Since co sputtering is not possible, a nanolaminate of these materials was necessary. With the aim of determining the growth properties and the interfacial quality of the binary oxides (Gd2O3 and Sc2O3), an initial study of those materials was performed. Using this two step fabrication process, amorphous and stoichiometric Gd2O3 layers were obtained. With a shorter oxidation performed at 20 W, MIS devices were fabricated with an equivalent oxide thickness (EOT) of 2.2 nm showing good electrical behavior. The effective ¿ value was 11, due to a GdSiOx interfacial layer formation after the forming gas anneal (FGA). For the Sc2O3 case, MIS devices with reasonable electrical characteristics and with 1.6 nm of EOT were obtained. The ¿ was 9, again related to a silicate formation at the interface. Once these binary oxides were analyzed, Gd0.9Sc1.1O3 films were fabricated. After a FGA at 600 ºC, amorphous and homogeneous layers were obtained. However, MIS devices presented better leakage current density and lower hysteresis after a FGA at 500 ºC. The permittivity value obtained was 32, very promising for future CMOS generations. During this work, it was also studied the effect of using different gate electrodes, studying Al (a material that reacts with the dielectric, increasing the EOT and, thus, reducing the ¿ value), Pt (a noble metal which does not react and it was used to study the bare properties of the insulator) and Ti (that is an oxygen scavenger which reduces the interlayer thickness and, therefore, permits achieving a lower EOT). In this thesis it was demonstrated the compatibility of the scavenging effect of the Ti electrodes with the three analyzed dielectrics. A reduction in the EOT value was observed for all the samples with Ti (as compared with Pt). Besides, it was found that an appropriate choice of the Ti thickness and the FGA temperature were key parameters to achieve a controlled scavenging, that decreases the interlayer thickness without compromising the interfacial state density, Dit, and without degrading the dielectric. Finally, MIS capacitors were fabricated on a high electron mobility semiconductor, such as InP. This way, it would be possible to increase the n metal oxide semiconductor field effect transistor (n MOSFET) current. MIS devices grown with Gd2O3 as dielectric showed a full accumulation depletion inversion sweep even before the FGA and without surface passivation treatments. This implied an unpinned Fermi level. However, a high Dit was obtained, which indicated the necessity of a surface passivation treatment performed before the high ¿ dielectric deposition. Besides, the scavenging effect with this semiconductor was also demonstrated.