Yoshio Ohshita

Evaluation of Cu adhesive energy on barrier metals by means of contact‐angle measurement

The adhesive energies at Cu/SiO2, Cu/TiN, and Cu/TiW interfaces were investigated by measuring the contact angles of Cu particles to the substrate. To form the Cu particles, thin Cu films deposited on each substrate were annealed at 500 °C for 50 h. The adhesive energies are determined to be 0.8, 1.8, and 2.2 N/m for the SiO2, TiN, and TiW, respectively. The Cu particle on TiW film shows the highest adhesion. When TiW is used as a barrier metal, fine Cu lines are fabricated by reactive ions etching without peeling. On the other hand, Cu lines on the TiN film are peeled during the etching. This is consistent to the evaluation result that TiW has higher adhesive energy than TiN.

Low‐temperature and selective growth of β‐SiC using the SiH2Cl2/C3H8/H2/HCl gas system

β‐SiC is grown on a Si (100) substrate by the chemical vapor deposition method using the SiH2Cl2/C3H8/H2/HCl/ gas system. The addition of HCl to the SiH2Cl2/C3H8/H2 gas system makes it possible to grow stoichiometric β‐SiC at the low temperature of 1000 °C. Moreover, β‐SiC selective deposition on a Si (100) surface, with no nucelation on a SiO2 surface, is achieved in more than 1.5% HCl concentration. The mechanism of low‐temperature selective β‐SiC growth due to HCl addition is discussed.

Lower‐temperature plasma etching of Cu films using infrared radiation

The etching of Cu films is achieved at lower temperature (150 °C) with Cl2 plasma by IR light radiation. Anisotropic fine Cu patterns are obtained. The etch rate is 4000 A/min and there are no microloading effects. It is considered that the etching temperature lowering and the anisotropy are realized by the IR light enhancement of CuClx desorption.

TI CONCENTRATION EFFECT ON ADHESIVE ENERGY AT CU/TIW INTERFACE

Changes in adhesive energy at Cu/TiW interfaces caused by varying the Ti concentration were evaluated by means of contact angle measurement. The adhesive energy was evaluated by applying the Young–Dupre equation to the contact angle. Copper particles were fabricated by annealing thin Cu film deposited on the TiW film. The adhesive energies at the Cu/TiW interface were evaluated as 1.5, 2.1, and 2.6 N/m for a Ti concentration of 0, 10, and 20 wt. %, respectively. The adhesive energies were found to increase almost linearly as the Ti concentration was increased. These results were applied to prevent TiW/Cu/TiW interconnects fabricated by using infrared-assisted reactive ion etching from peeling at the Cu/TiW interface. In annealing Cu films on TiW substrates at 600 °C in a vacuum, it was found that the Cu peeled from the TiW when the Ti concentration was 10 wt. %, but it stuck to that at 20 wt. %. The effect of Ti on the adhesion strength was also studied from the results of molecular calculation by using t...

Reactants in SiC chemical vapor deposition using CH3SiH3 as a source gas

Abstract The growth mechanism of SiC CVD using CH3SiH3 (1% CH3SiH3 diluted by 99%H2) as a source gas is studied by the experiment with macro/microcavity method. It is found that there are two types of the important reactants: one is the slightly active source gas CH3SiH3 itself, which reacts directly with the SiC surface. The other is the CH3SiH, which is produced by the thermal decomposition of CH3SiH3 in the gas phase, it is radical and its sticking coefficient is almost 1. Under the kinetic control conditions, the reaction of CH3SiH3 with SiC surface and the decomposition of CH3SiH3 in the gas phase determine the growth rate.

Charge transfer adsorption in silicon vapor‐phase epitaxial growth

Silicon vapor‐phase epitaxial growth with SiH2Cl2 is theoretically studied. The optimized geometries and total energies of the species, generated from SiH2Cl2, are calculated by using an ab initio molecular orbital method. The charge transfer of the interaction between a silicon surface and SiCl2 is considered. Based on the computational result that SiCl−2 has the lower total energy that SiCl2, a new adsorption mechanism, named charge transfer adsorption, is proposed. By using this charge transfer adsorption followed by the surface reaction at the hollow bridge site, the epitaxial growths on the silicon (001), (111), and (110) surfaces are discussed. The epitaxial growths take place in different ways for these three surfaces because of the specific locations of the hollow bridge sites.

Surface reaction mechanism of SiCl2 with carrier gas H2 in silicon vapor phase epitaxial growth

In Si vapor phase epitaxial growth, the rate determining process is considered to be the surface reaction of SiCl2 thermally generated by the decomposition of SiH2Cl2 with the carrier gas H2. Therefore, the mechanism is studied by using both experimental techniques and ab initio molecular orbital calculations. The experimental results are explained well by the Rideal-Eley model rather than the Langmuir-Hinshelwood model. No meta-stable state is found from the ab initio MO calculations and the reaction rate is simply governed by how thermally active the H2 molecules are.

Low temperature and selective growth of β‐SiC using the SiH2Cl2/i‐C4H10/HCl/H2 gas system

β‐SiC is grown on a silicon substrate by the chemical vapor deposition method using the SiH2Cl2/i‐C4H10/H2/HCl gas system. Stoichiometric β‐SiC films are obtained with high growth rate at a low temperature of 900 °C. Highly (111) oriented β‐SiC polycrystal is grown on a Si(111) substrate. Moreover, using the above‐mentioned gas system, β‐SiC selective growth is attained on a Si substrate, with no nucleation on the SiO2 area. This letter discusses the i‐C4H10 effects and selective growth condition.

Prebaking and silicon epitaxial growth enhanced by UV radiation

UV light irradiation effects on prebaking and silicon epitaxial growth is studied. An ArF excimer laser, a KrF excimer laser, and a Hg‐Xe lamp are used as light sources. The epitaxial growth is carried out using a SiH2Cl2/H2 system under reduced pressure. ArF radiation and Hg‐Xe radiation are found to be effective for volatilizing native SiO2 on silicon‐substrate surfaces even at low temperatures. When a substrate surface is irradiated with these UV radiations during prebaking and epitaxial growth, epilayer surface morphology and crystalline quality are much improved. Furthermore, the epitaxial growth rate seems to be enhanced photothermally by excimer laser radiations, and photochemically by Hg‐Xe radiation.

TiSi2/Si interface instability in plasma-assisted chemical vapor deposition of titanium

The heterointerface between a Si(1 0 0) substrate and a TiSi2 layer becomes rough when the substrate temperature during the formation of the TiSi2 layer by plasma-assisted chemical vapor deposition using the TiCl4/H2/Ar gas system is between 650 and 750°C. In this temperature range, the Si substrate is etched and pits that have (1 0 0) and (1 1 1) vicinal surfaces can be observed at the heterointerface. At higher or lower temperatures, however, a smooth interface is created. This morphological instability appears to be due to the processes of Cl desorption from the surface during the Ti deposition.