Mahito Sawada

Novel Shallow Trench Isolation Process from Viewpoint of Total Strain Process Design for 45 nm Node Devices and Beyond

In this paper, a novel shallow trench isolation (STI) process is proposed for 45 nm node technologies and beyond. The major features of this process are the use of a fluorine-doped (F-doped) SiO2 film for gap filling and high-temperature rapid thermal oxidation (HT-RTO) for gate oxidation. Voidless filling of a narrow trench can be realized by F-doped high-density plasma chemical vapor deposition (F-doped HDP-CVD). Moreover, electron mobility degradation caused by STI stress and junction leakage currents can be minimized using F-doped HDP-CVD with HT-RTO. It was also confirmed that compressive stress in the F-doped HDP-CVD sample is smaller in every measurement point around STI than that in the conventional HDP-CVD sample by convergent-beam electron diffraction (CBED). The Si-F bonds in the oxide film play a very important role in stress reduction. By utilizing HT-RTO, Si-F bonds remain and make the SiO2 film in the trench coarse. This technique is a very promising 45 nm node STI scheme with high performance and high reliability.

Effects of Fluorine Stability and Stress in SiOF Films on Film Adhesion

Effects of fluorine stability and stress in SiOF films deposited by high-density plasma process on the generation of blisters were investigated by secondary ion mass spectrometry, thermal desorption spectroscopy (TDS), Fourier transform infrared spectroscopy (FTIR) and four point bending method using Top-SiN/TEOS/SiOF/Bottom-SiN multilayer structure. There are two kinds of fluorine in SiOF films, one is stable fluorine detected by FTIR, and the other is unstable one detected by TDS. Unstable fluorine in SiOF films is easy to diffuse and generates blisters at the interface of Top-SiN/TEOS films. Concentration of unstable fluorine is increased as the O 2 /SiH 4 flow ratio increases and at flow ratios higher than 2.38, blisters are generated. Only the stable fluorine is related with dielectric constant of SiOF film. Hydrogen in gas phase during SiOF-film deposition plays an important role for fluorine stabilization. Compressive stress in SiOF films does not cause blisters.

Hydrogen Ion Drift into Underlying Oxides by RF Bias during High-Density Plasma Chemical Vapor Deposition

High-density plasma chemical vapor deposition (HDP-CVD) is a deposition method of current interest for the gap-filling process of the intermetal dielectric (IMD) in semiconductor circuits. We first demonstrated that hydrogen ions drift into underlying thermal oxides during HDP-CVD with a SiH4–O2–Ar system, and that they degrade the reliability of gate oxides. The characteristics of the oxides were investigated using secondary ion mass spectroscopy (SIMS), thermal desorption spectroscopy (TDS), and capacitance–voltage (C–V) measurements of metal–oxide–semiconductor (MOS) capacitors. The hydrogen ions that are dissociated from SiH4 in plasma penetrate into the HDP-CVD oxides, and some of the hydrogen ions in the HDP-CVD oxides drift into the underlying thermal oxides by rf bias. The drifting hydrogen creates two chemical bonding states and generates hole trap sites in the underlying thermal oxides.

Preparation of Stable F-Doped SiO 2 Thin Films from Si(NCO) 4/SiF 4/O 2 Gas Mixtures Using a Conventional Capacitively Coupled RF Plasma Source

Stable F-doped SiO2 (SiOF) films have been deposited using a simple conventional capacitively coupled RF plasma-enhanced chemical vapor deposition method using H-free tetraisocyanatesilane (Si(NCO)4: TICS) diluted with oxygen, and tetrafluorosilane (SiF4) having Si–F bonds in itself. The SiO2 films deposited only with TICS have poor water resistivity, which originates in the inclusion of the SiNCO structure in the films. This property has been improved by mixing O2 with the source gases. Although F atoms at the top surface of films desorbed upon air exposure, SiOF films deposited with TICS, SiF4 and O2 exhibit excellent water resistivity. A film with F concentration of 6 at.% exhibited a dielectric constant of 3.3, a resistivity of 3.6×1015 Ωcm and a break-down electric field of 7.7 MV/cm. These values are comparable to or better than the reported values for films prepared using tetraethylorthosilicate. These results indicate that the TICS, SiF4 and O2 system can be used to deposit high quality SiOF films using a much simpler method than those requiring complex high density plasma sources.