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上获得SiO_2当量氧化层厚度(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。首先，采用分子束沉积(MBD)技术在硅衬底上制备了各种高介电常数薄膜，包括ZrO_2、HfO_2、CeO_2、Y_2O_3、La_2O_3、Pr_2O_3、Sm_2O_3等，并进行了表征。对于HfO_2和La_2O_3薄膜，EOT值分别为0.88 nm和1.5 nm。研究还发现，La_2O_3薄膜易受空气湿度的影响而损坏。因此，为了抑制这种损伤，在沉积La_2O_3薄膜后立即制作了栅电极。利用这一技术，我们用La_2O_3栅绝缘体制作了MOSFET，其EOT为0.88 nm。制作的器件证实了晶体管的正常工作。其次，发展了金属有机化学气相沉积(MOCVD)技术在硅衬底上生长HfO_2薄膜。用不含氧和氯的Hf[N(CH3)2]4和Hf[N(C2H5)2]4和常规的Hf(O-t-C4H9)4作为Hf前驱体。用O2或H2O作为氧化剂气体。我们通过交替引入Hf前驱体和氧化剂气体在硅衬底上制备了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只有1.8 nm，在1V下的漏电流密度小于10^&lt；-5&gt；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.