In the paper, we show the example of the non-thermal chemistry over the nano-metal/semiconductor interface caused by the non-equiliblium low pressure RF plasma exposure. The process is directed to the new fablication scheme of high-k dielectric thin film for MOSFETs with fewer process steps, lower impurity, and minimised EOT (equivalent oxide thickness). In the process, high density hafnium metal nano particle with 4 nm diameter is formed on SiO2/Si surface and subsequent nitrogen plasma exposure (~10 min.) leads to the growth of HfSiON high-k dielectric film with SiN interfacial layer.

 

Current ULSI technology requires the use of hafnium related high-k dielectrics with ~3 nm thick for MOSFET to lower the power consumption. HfSiON is the most applicable chemistry for the high-k material with proper energy band alignment, large area uniformity, and thermal stability. The direct formation of HfSiO film from the Hf overlayer and underlying SiO2 utilizing the thermal interfacial reaction was previously proposed [1]. The process demonstrates remarkably low inpurity in the film due to the lack of carbon in contrast to the case of MOCVD processes. In our

case, 2.5 nm thick Hf metal layer is deposited with e-beam deposition source on SiO2/Si(100) surface uniformly. The morphology obtained with the in-situ non-contact AFM measurement revealed the surface consists of the high density array of Hf nano particles with the size of 4 nm in diameter. The exposure of atomic nitrogen and ions from the non-equiliblium plasma enables the introduction of N into the film and increases the interfacial reaction rate of Hf and SiO. Within the first 1 min., the Hf nano particles are oxynitrided with the N atoms from the plasma and the O atoms supplied from the lower interface judging from the XPS analysis. The following plasma exposure (~10min.) enables the diffusion of Si atoms into the higk-k film from the underlying SiO layer. The Si content in the film increases with the exposure time and becomes comparable to the Hf content with 35 min. exposure. The XPS spectrum shows the Si incorporated is mostly nitrided in the film. The spectrum also indicates the interfacial SiO layer is nitrided and this leads to the minimized EOT of the high-k stack structure.

 

[1] H. Watanabe, Appl. Phys. Lett. 85, 449 (2004).