Systematic survey and property control of high-dielectric-constant thin films for gate insulators of next generation MOSFETs

本研究的目的是在硅衬底上制备SiO_2等效氧化层厚度（EOT）小于2 nm的高介电常数（high-k）薄膜，用于下一代MOSFET的栅绝缘层应用。首先，利用分子束沉积技术在Si衬底上制备了ZrO_2，HfO_2，CeO_2，Y_2O_3，La_2O_3，Pr_2O_3，Sm_2O_3等高介电常数薄膜，并对其进行了表征。HfO_2和La_2O_3薄膜的EOT值分别为0.88 nm和1.5 nm。La_2O_3薄膜易被空气中的湿度破坏。因此，为了抑制这种损伤，一旦沉积La_2O_3膜就制造栅电极。利用这种技术，我们用EOT为0.88 nm的La_2O_3栅绝缘体制备了MOSFET。对于所制造的器件，确认了正常的晶体管操作。其次，发展了金属有机化学气相沉积（MOCVD）技术在Si衬底上生长HfO_2薄膜。Hf[N（CH_3）_2]_4和Hf[N（C_2H_5）_2）]_4以及常规的Hf（O-t-C_4H_9）_4被用作Hf前体。O_2或H_2O作为氧化剂气体。我们采用交替引入Hf前驱体和氧化剂气体的方法在Si衬底上制备了HfO_2薄膜，发现用H_2O制备的HfO_2薄膜的残余杂质浓度和漏电流密度都比用O_2制备的HfO_2薄膜低得多。用Hf[N（C_2H_5）_2]_4和H_2O生长的HfO_2薄膜的EOT小至1.8 nm，在1 V下的漏电流密度小于10^<-5>A/cm^2。

The objective of this study is to obtain high-dielectric-constant (high-k) thin films on Si which have an SiO_2 equivalent oxide thickness (EOT) of less than 2 nm for gate insulator application of next generation MOSFETs. First, various high-k thin films, such as ZrO_2, HfO_2, CeO_2, Y_2O_3, La_2O_3, Pr_2O_3, Sm_2O_3 and so on, were fabricated on Si substrate by the molecular beam deposition (MBD) technique and characterized. For HfO_2 and La_2O_3 thin films, EOT values of 0.88 nm and 1.5 nm were obtained, respectively. It was also found that the La_2O_3 film was easily damaged by the humidity in the air. Hence, to suppress this damage, gate electrodes were fabricated as soon as the La_2O_3 film was deposited. With this technique, we fabricated MOSFETs using a La_2O_3 gate insulator which had an EOT of 0.88 nm. Normal transistor operation was confirmed for the fabricated devices. Next, metalorganic chemical vapor deposition (MOCVD) technique was developed for HfO_2 thin films growth on Si substrates. Hf[N(CH_3)_2]_4 and Hf[N(C_2H_5)_2)]_4 which contain no oxygen nor chlorine as well as conventional Hf(O-t-C_4H_9)_4 were used as Hf precursors. Either O_2 or H_2O was used as an oxidant gas. We fabricated HfO_2 thin films on Si substrates by alternatively introducing Hf precursor and oxidant gas and found that the residual impurity concentrations and leakage current density are much lower for the HfO_2 films fabricated with H_2O than HfO_2 films fabricated with O_2. An EOT of the HfO_2 films grown with Hf[N(C_2H_5)_2]_4 and H_2O was as small as 1.8 nm and the leakage current density of the films at 1 V is less than 10^<-5> A/cm^2.