Hiroshi Yanazawa

Adhesion model and experimental verification for polymer—SiO2 system

Abstract The adhesion of polymer films to the SiO 2 surface is strongly influenced by ambient conditions. In a dry environment, polymer films adhere to SiO 2 surfaces through London dispersion force, whereas in liquid media the effect of liquid penetration must also be considered. These interactions are evaluated in terms of the surface free energies and wettability of SiO 2 , and polymer films. A series of experiments has been carried out utilizing surface conversion techniques to alter the surface of thin SiO 2 films. Using these experiments, a model has been developed to describe the organic polymer—SiO 2 adhesion.

Hydrophobic Conversion of the Chemical-Vapor-Deposited SiO2 Surface

The surface silanol groups of SiO2 react with alcohols and other organic compounds to form alcoxyl groups in situ and their surfaces change into hyprophobic. These surface treatments were applied to the Chemical-Vapor-Deposited SiO2 films, which are widely used in semiconductor devices for passivation and insulation. The properties of the CVD-SiO2 surfaces treated with various alcohols, phenol and silane derivatives were investigated by measuring the contact angle against H2O. The alcoxyl groups were quantitatively evaluated by mass-spec-trometry. It was found that the properties of the treated surface depend on the structure and number of the alcoxyl groups formed, and that the hydrophobic natures of the CVD-SiO2 surfaces can be precisely controlled through these surface treatments.

A Novel Method of Removing Impurities from Multilevel Interconnect Materials

A novel method of removing impurities from dielectric films has been developed. The removal of water and charges is accomplished by humidification and wet pretreatment followed by charge extraction with CO2 supercritical fluid (SCF). Films treated in this manner exhibit intrinsic properties, which are usually masked by moisture and impurities.

Precision Evaluation in Kr Adsorption for Small BET Surface Area Measurements of Less Than 1 m2

A volumetric Kr-adsorption apparatus using a precise capacitance manometer has been developed. A specially designed adsorption cell (CVC: constant volume adsorption cell) utilizing a vacuum jacket (Joyner et al., 1949) is adopted to keep the adsorption cell volume constant regardless of the variation in liquid nitrogen level throughout the experiment. Using the CVC, the pressure change in accordance with liquid N2 supply cycle has been minimized to less than 0.01 Pa compare to about 1 Pa for conventional cell. Time dependent change of the adsorption cell volume and repeatability in its measurements have been demonstrated in detail using helium gas. Good linearity of the BET plot of the Kr adsorption isotherm on several hundred cm2 samples are demonstrated in the relative pressure range from 0.05 to 0.35.

Analysis of Leakage Current of Low-k Materials for Use as Interlayer Dielectric

The relationship between mobile charge and leakage current was investigated. Both leakage paths and change of charge distribution were taken into account. The difference in flat-band voltage between the applied high and low frequencies reflects the number of mobile charges. Films with a large difference were found to exhibit a large leakage current at high temperatures. Thus, we can conclude that the leakage current arises mainly from the mobile charges in a film.

Analysis of leakage current in Cu/SiO2/Si/Al capacitors under bias-temperature stress

An investigation was carried out of the conduction mechanism by which leakage current arises in Cu/SiO2/Si/Al capacitors under bias-temperature (BT) stress. C–V measurements on the capacitors before and after BT stress revealed that the stress reduces the capacitance of the Si depletion layer and induces the formation of interface states at the SiO2/Si interface. Secondary ion mass spectroscopy (SIMS) measurements on samples after BT stress showed the presence of Cu not only in the oxide, but also at the SiO2/Si interface. These results indicate that BT stress causes Cu ions to drift through the SiO2 film as far as the Si substrate. The good linearity of the ln (I/E) versus E1/2 curve suggests that current conduction is due to Poole–Frenkel emissions. The origin of the Poole–Frenkel current is also discussed based on a study of how BT stress at a negative bias affects the gate current of the capacitors.

Optimization of SiON Film Compositions for Encapsulation of Refractory Metal Gate GaAs Metal‐Semiconductor Field Effect Transistor

The composition of the SiON film were optimized to be used as an anneal encapsulation based on the GaAs metal-semiconductor field effect transistor (MESFET) characteristics. The SiON films investigated in the present study were deposited by plasma-enhanced chemical vapor deposition. The refractive indexes of the SiON films with various compositions were found to be useful indicators of film composition. By varying the ratio of the source gases, SiH 4 and N 2 O, we could control the composition to range from SiO 2 to Si 3 N 4 corresponding to refractive indexes from 1.47 to 2.02. MESFET characteristics were evaluated in terms of the Schottky diode ideality factor n, which was found to be highly dependent on the film composition: when we used a SiON film with a refractive index below 1.53, which corresponds to an O-rich composition, the n value exceeded 1.4. This indicates an unstable interface between the GaAs and the SiON. When we used the N-rich SiON, however, such as SiON with a refractive index 1.6, the n value was 1.25. These results are discussed from the viewpoint of interface reaction between GaAs and SiON, which we investigated by using Auger electron spectroscopy.

Surface Conversion for Antisticking to Reduce Patterning Defects in Photolithography

After an exhaustive reevaluation of the contact printing processes, photoresist sticking to the photomask surface is identified as the principal cause of patterning defects and a preventive measure is developed. This process, called surface conversion for antisticking (SURCAS), facilitates a reduction in defect density by about one‐fourth compared to conventional contact printing. This technique opens the way for improvement of current LSI fabrication, and moreover should be useful in ultrafine pattern lithography down to 1 μm in the near future.

High Resolution, High Precision I-Line Stepper Processing

Currently, the integrated MOS dynamic RAM has as many as 256 thousand memory cells per chip based on 2 pm photolithography. Figure 1 shows the history and the prospects for progress in microfabrication technology. Feature size versus year, as reported by Bossung in 1978, is shown, as developed from independent analysis by Moore, Noyce and Gnostic concept. Circles numbered 1 and 2 show that 64K- and 256K-bit RAMs were developed in 1981 and 1984, and that their feature sizes were 3μm and 2μm, respectively. It is significant that the predictions and the real developments are so close. Furthermore, since the basic process for 3 M-bit RAMs based on 1.3μm microlithography has already been reported in conference, it is highly likely that they will become commercially available around 1987, as predicted by the circle numbered 3 based on 1.3μm microlithography.

Evaluation of hydrophobic SiO2 surfaces prepared by fluorinated organosilane treatments

A surface conversion technique was developed to make the SiO2 surface extremely hydrophobic. Two kinds of fluorine-substituted organosilanes, (heptafluoroisopropoxy)propyl methyl dichlorosilane and trifluoropropylmethyl dichlorosilane, were utilized as the conversion agents. The hydrophobicity was evaluated in terms of the London dispersion force component of the surface free energy (Fowkess γd s) by measuring the contact angles of CH2I2, hexadecane, and H2O. The values of γd s for the converted surface are 15 and 21 mJ/m2 for the former and the latter conversion reagent, respectively. These surfaces were found to have resistance to 60 min hydrolysis in boiling water and pyrolysis in air up to 450°C.