Miki T. Suzuki

Resist stripping in an O2+H2O plasma downstream

Characteristics are reported for a resist stripping process downstream of an oxygen plasma to which water vapor is added. The effects of additive water vapor are an increase in atomic oxygen concentration in the plasma, a decrease in activation energy of ashing reaction, and protection of semiconductor devices from the sodium contamination from the resist. The atomic oxygen concentration was approximately doubled by mixing 10% H2O into the oxygen plasma. The activation energy of the ashing reaction to the resist made from novolak resin decreased from about 0.5 to 0.39 eV by the addition of water vapor of more than 1%. The activation energy of hydrogen abstraction from hydrocarbon molecules by an OH radical was lower than that by a ground state oxygen atom [O(3P)], which was the dominant ashing species in the oxygen plasma downstream, and that by an atomic hydrogen was higher than that by the ground state oxygen atom. Moreover, the activation energy in the downstream ashing of the oxygen plasma added to which was 1% water vapor was lower than that of the oxygen plasma to which 3% hydrogen was added, even though the relative concentration of atomic hydrogen in each plasma was equal. Therefore the decrease in the activation energy was probably due to the OH radical generated in the plasma and the downstream. Sodium atoms in the resist were blocked from entering into the semiconductor devices in the stripping process by use of the O2+H2O plasma downstream. Thus sodium was not removed and remained on the wafer surface after resist stripping. Also, by adding N2 or CF4 to the O2+H2O plasma, we can increase the ashing rate without losing the above characteristics.

Characterization of cleaning technology for silicon surfaces by hot pure water containing little dissolved oxygen

We introduce new cleaning technology using pure water containing little dissolved oxygen (LDO water). To maintain the concentration of dissolved oxygen in water, we performed experiments in a glove box, controlling the ambient between the water and the ambient gas so as to satisfy Henrys law. In the experiment using intentionally contaminated wafers and LDO water containing 1 ppb of dissolved oxygen at room temperature, the amount of residual metallic contaminants, except copper, on a Silicon surface decreased from 1014 atom/cm2 to 1011 atom/cm2 after hot LDO water treatment for 30 min at the boiling point. The cleaning ability depends on the dissolved oxygen concentration, temperature of LDO, and treatment time. The ability to eliminate aluminum during the 30 min hot LDO water treatment was lower than for the other metals. Moreover, the adsorption velocity of aluminum from hot LDO water on the wafer surface was much larger than that of the other metals. Since this hot LDO water treatment simultaneously etched silicon and silicon dioxide with the removal of metal, we also investigated the morphology and chemical structure of the wafer surface after this cleaning process.

Sodium contamination free ashing process using O2+H2O plasma downstream

The effect of O2+H2O plasma downstream ashing on sodium contamination from resists has been studied through measurement of flatband voltage shifts of metal–oxide–semiconductor (MOS) diodes after bias‐stress treatment and measurement by atomic absorption spectroscopy of the amount of sodium in the SiO2 layer after resist stripping. The flatband voltage shift of the MOS diodes on which a resist layer was stripped by the O2+H2O plasma downstream was almost the same as that treated by the O2+H2O plasma downstream without resist and smaller than that where the resist was removed by other dry ashing methods such as O2 plasma and O2 plasma downstream. In addition, the amount of sodium that existed in the SiO2 layer after resist ashing by the O2+H2O plasma downstream was also nearly the same as that in the SiO2 layer as grown. This sodium passivation by the O2+H2O plasma downstream was most effective at the H2O percentage of 40%–60%, and did not depend on wafer temperature below 200 °C or over‐ashing time. These ...

Gate Oxide Deterioration Caused by Organic Contamination onto the Oxide

The breakdown voltage of 10nm thick gate oxlde was deterlorated shonlng lncreased B mode when photoresist uas coated on the gate oxlde and then strlpped, though lt was strlpped uslng HzSOq /HzOz supposed to be damagefree. The thicker the resist was, the lower the oxlde yield was. No deterioratlon rlas observed when At gate llas used. An ashlng added after the stripping recovered the breakdown characterlstlcs ln some degree. Total organic of the wet stripped wafer was 5 times as much as that of reference. lle concluded that the organlc contamlnatlon on the gate oxlde was the cause.

Etching Characteristics During Cleaning of Silicon Surfaces by NF 3 -added Hydrogen and Water-Vapor Plasma Downstream Treatment

Hydrogen and water vapor plasma downstream treatment with the downstream injection of NF 3 removes native oxide from silicon surfaces. In contact hole cleaning, this dry processing is a promising alternative to HF wet treatment, which has a problem of expansion of hole diameter. We examined the etching characteristics of boron-phosphosilicate glass (B-PSG) films, as a typical oxide material for the side-walls of the contact holes and compared the etching depths of B-PSG and thermal oxide films. We found that the etching depths of B-PSG films fell to one third of those of thermal oxide films at lower treatment temperature. This result indicates that the expansion of contact hole diameters can be minimized.