Plasma etching has been widely used to etch the materials in the fabrication of semiconductor devices. For further development of integrated semiconductor devices, more precise control of the etching process is required. Thus, we have developed a mass-analyzed ion beam apparatus; energy controlled single species ions are irradiated onto the surface under an ultra-high vacuum condition, and thus we can study the roles of individual reactive ion irradiation without gas phase reactions or neutral radicals irradiation. We have investigated the desorption products and etching yields for silicon and silicon dioxide by CFx+ (x=1, 2, 3) ion bombardments. Desorbed products could be detected with a quadrupole mass spectrometer by the pulse ion beam method, and we estimate the kinetic energy of desorbed products from the time delay of waveform of incident ion pulse. Etching yields of CFx+ increased with increasing ion energy and with increasing number of fluorine atoms in the ions. Above 1000 eV, etching yields is gradually saturated. Below 500 eV, etching yields abruptly dropped with decreasing ion energy, and fluorocarbon films grew on the surfaces. These results suggest that the etching reactions are affected by chemical reactivity of the incident ions.
In an interconnect structure of advanced large scale integrated (LSI) circuits, Cu diffusion leads to migration failure, known as stress migration and electro migration. In order to prevent these failures and to improve interconnect reliability, interface properties should be improved between Cu and a barrier layer. Among various interface properties, adhesion strength can be measured easily and be used as a representative interface property related to reliability. This paper show the relationship of interface adhesion strength with wettability, energy, and diffusivity. Then the effects of the adhesion strength on SM and EM reliability are discussed. Finally, key factors to improve the adhesion strength are proposed, together with our recent experimental evidences.
Broadening effect in SIMS depth profiling, attributed to diffusion and segregation, was explored for In with O2+ bombardment at low energies (180 eV-5 keV) and over a wide range of impact angles, from normal (0o) to glancing incidence (70o). The effect depended on the oxidation level of the oxide layer generated by the oxygen bombardment. The oxidation level was controled by the sputtering yield and the yields below 0.3 atoms/O2+ enhanced the effect. At the yields above 0.3 atoms/O2+, the atomic mixing strongly influenced on the effect. The use of glancing incidence reduced the effect. However, another unfavorable effect, i.e., the ripple formation was observed at glancing incidence. The “critical angles” were around 40o. The bombardment at about 40o is effective for more accurate depth profiling.
By applying Scanning Nonlinear Dielectric Microscopy (SNDM), we succeeded in clarifying the position of the electrons/holes in the gate SiO2-Si3N4-SiO2 (ONO) film of the Metal-ONO-Semiconductor type flash memories, After the write-erase cycling operation, the electrons were found in the Si3N4 part of the ONO film. The holes, on the other hand, were found in the Si3N4 film as well as at the bottom of the SiO2 film. This indicates that the electrons and holes are apparently neutralized but exist separately. We also succeeded in clarifying that electrons exist in the poly-Si layer of the floating gate of a flash memory. We confirmed that SNDM is one of the most useful methods for observing the charge in flash memories.
We introduce scanning capacitance force microscopy (SCFM), a newly developed dopant profiling method, and a 3-dimensional wiring procedure enabling evaluation of dopant profile under metal-oxide-semiconductor field-effect-transistor (MOSFET) operation. The principle of the SCFM is based on measurement of an electrostatic force (ESF) that is induced by bias voltage of angular frequency ω between a tip and a sample. The focused ion beam (FIB) technique was employed to evaluate dopant profile for the cross-section of MOSFET devices under the device operation. Local etching, deposition, and formation of small wiring for the specified MOSFET were successively carried out with the FIB, and the variation of dopant profiling was clearly shown with applying voltage to the MOSFET. These techniques are expected to be utilized for the failure analysis and the development of next-generation devices.
Synthesis of singlewalled and doublewalled carbon nanotubes by hot-filament chemical vapor deposition using alcohol as carbon source has been attempted. Cobalt particles obtained by scratching a polycrystal cobalt plate with a sheet of sandpaper were used as catalyst for carbon nanotube growth. Catalyst temperature was mainly 700oC, and the vapor pressure of alcohol was mainly 80 Torr. Products were evaluated by transmission electron microscope, Raman spectroscopy and thermogravimetric analysis. Nevertheless the size of cobalt particles extended from 2 nm to 80 nm, single and doublewalled carbon nanotubes were synthesized with a high yield of above 80%. To synthesize such thin tubes, it is important to use methanol as carbon source and to make the synthesis duration short. However, neither single nor doublewalled carbon nanotubes were synthesized at all by using ethanol instead of methanol.
We have developed a scanning electron microscope (SEM) equipped with a chemical vapor deposition system to investigate the growth processes and bundling processes of single-walled carbon nanotubes (SWNTs). The SWNT growth and in-situ SEM observation were performed on planar and micro-pillar-patterned substrates. Even an isolated SWNT could be observed using the enhanced secondary electron emission due to electron-beam-induced-current on insulator, or when it was suspended between pillar structures. On the planer substrate, SWNT grows upward from the surface in the initial growth stage, but falls to the surface in the later stage. On the patterned substrate, it forms a bridge between pillars in the initial growth stage, and then bundles with other SWNTs in the later stage. Understanding the growth mechanism of SWNTs is essential for the control of their diameter and chirality of them, and useful for the assembly of new SWNT architectures.
We demonstrate an extremely efficient chemical vapour deposition synthesis of single-walled carbon nanotubes where the activity and lifetime of the catalysts are enhanced by an addition of water into the ambient of the CVD furnace. We call the growth mode as super growth. The enhanced catalytic activity of super growth results in massive growth of super-dense and vertically-aligned single-walled nanotubes forests with heights up to 2.5 millimeters. In addition, these SWNT forests were easily separated from the catalysts, producing the most pure SWNT material (over 99.98%) ever made, amazingly through an all-dry process without any purification. Moreover, patterned highly organized intrinsic single-walled nanotube structures were successfully fabricated. The super growth simultaneously addresses many critical problems such as scalability, purity, and cost, and opens up innumerable opportunities ranging from fundamental research to real applications.
Light-modulated scanning tunneling spectroscopy (LM-STS), a potential method that provides us with the technique to investigate spatially resolved carrier dynamics such as surface photovoltage is discussed. With the results obtained for a GaAs(110) p-n junction as an example, the basic principle and experimental techniques of LM-STM are introduced.