Isahiro Hasegawa

SiO2 Tapered Etching Employing Magnetron Discharge of Fluorocarbon Gas

SiO2 tapered etching has been studied with special emphasis on the substrate temperature. A tapered etching profile was formed accompanying a polymer deposition on the side wall, and a high etching rate was obtained by lowering the substrate temperature. The polymer film deposited on the side wall was easily removed together with photoresist by O2 plasma ashing to yield a very smooth side wall in the via hole without any residual films. Experiments on polymer deposition revealed that the polymerization at as low a temperature as -70°C gives a fluorine-rich polymer film with poor durability in a plasma environment, and the etchants for SiO2 are released by ion bombardments at the interface between the polymer and the underlying SiO2 to enhance SiO2 etching.

Mechanism of Oxidation of Si Surfaces Exposed to O2/Ar Microwave-Excited Plasma

Plasma oxidation of 200-mm-diameter Si wafer surface at low temperature (400 °C) with use of high-density microwave plasma in O2/Ar gas was investigated. Dependence of the time-averaged oxidation rate on the percentage O2 showed a maximum value of 0.95 nm/min at a few % O2 in Ar. However, the measured O radical density was considerably low in this condition, and hence the O radical is not considered to be a key species in the plasma oxidation. A good correlation was found between the oxidation rate and the electron density; the oxidation rate averaged for 10 min discharge is proportional to the square root of the electron density measured near the Si wafer. The experimental results are basically explained by the Jorgensen-Mott model: in a presence of electron flux from plasma, the O2 molecule adsorbed on SiO2 surface is dissociated into negative ions which are transported to the SiO2–Si interface.

Negative Ion Transfer Model of Low-Temperature Oxidation of Silicon Surface by High-Density Microwave Plasma

High-quality thin SiO2 layer is rapidly formed at low temperature (~400 °C) by oxidation of silicon wafer using high-density microwave plasma in argon containing a few % O2. The oxidation rate is proportional to the square root of electron density but hardly correlates with the measured O radical density. Secondary ion mass spectrometry (SIMS) depth analysis of SiO2 layer with 18O as an isotope tracer suggests that predominant mobile species in the oxide layer is not neutral oxygen atom but oxygen negative ion, possibly O2-, as proposed by Jorgensen and Mott. The time evolution of oxidation process calculated in a negative ion transfer model well explains the experimental observation and accounts for the square root dependence on the electron density.

Influence of Al Surface Modification on Selectivity in Via-Hole Etching Employing CHF3 Plasma

The Al etching characteristics in CHF3 plasma have been studied. The etching rate increased drastically with decreasing pressure. Analysis of the surface exposed to CHF3 plasma revealed that the Al surface was not covered with a fluorocarbon film, but was fluorinated. It has become evident that Al fluoride is sputtered much faster than Al. That is, fluorination of the surface results in the high etching rate of Al in a CHF3 plasma. Furthermore, the surface analyses of Si, Al, W and Ni exposed to CHF3 plasma made it clear that fluorocarbon films are formed on the materials whose etching products have high vapor pressure, and are not formed on the materials whose vapor pressure for the etching products is very low. The continuous fluorine consumption which is caused by evaporation of etching products through the fluorocarbon film, leads to formation of fluorocarbon film.

Measurements and Simulations of Particles in a Plasma Chemical Vapor Deposition Chamber

In a plasma chemical vapor deposition (CVD) chamber, particles generated during the deposition process adhere to the wafer after the process ends. Since it is important to remove particles efficiently in the discharge step after the deposition process, we determined the optimal conditions by using particle motion simulation. The electrostatic force, ion drag force, and gas drag force produced by neutrals, which particles receive in plasma, are calculated from plasma and gas flow simulations. The particles vibrate in response to the downward ion drag force and the upward electrostatic force, while moving to the wafer edge due to the gas flow. In the discharge step, the baseline condition and another condition (the side power condition) where the electric field is perpendicular to the wafer were compared using 50 particles set at random positions. The number of remaining particles was 15.0 under the baseline condition and 2.8 under the side power condition. In the experimental results corresponding to both conditions, the number was found to be reduced to 23.3% by adjusting the conditions. The simulation results are in good agreement with the experimental results.