Nobuaki Makino

Dry Etching Characteristics of Si-based Materials Using CF4/O2 Atmospheric-Pressure Glow Discharge Plasma

We etched materials used for semiconductor manufacturing processes, such as poly-Si films, SiN films, SiO2 films and photoresists, using atmospheric-pressure glow discharge plasmas, where CF4 gas was added to the O2 gas in the discharge and downflow regions. High etching rates of 2.3 µm/min for the poly-Si and SiN films, 1.0 µm/min for the SiO2 films and 7.0 µm/min for photoresist were obtained in the discharge region. Furthermore, a reasonably high etching rate of 0.82 µm/min for poly-Si films was also confirmed in the downflow region. The etching characteristics obtained under atmospheric-pressure glow discharge plasmas and low-pressure glow discharge plasmas in the discharge region were very similar. However, in the downflow region, the etching rates of SiN and SiO2 films were substantially reduced compared to those in the discharge region. These etching mechanisms were also modeled based on analytical data and the results of the etching evaluation.

A highly selective photoresist ashing process for silicon nitride films by addition of trifluoromethane

A highly selective photoresist ashing process was developed for the fabrication of thin-film transistor liquid-crystal displays (TFT-LCDs). This ashing process utilizes downflow plasma consisting of a carbon trifluoromethane/oxygen (CHF3/O2) gas mixture at a low temperature. The etching selectivity of photoresist films to silicon nitride (SiN) film increased when using the CHF3/O2 gas mixture plasma, as compared to that when using the carbon tetrafluoride/oxygen (CF4/O2) gas mixture plasma. At the CHF3 gas flow rate of 30 sccm, a high etching selectivity ratio of about 1080 for the photoresist films to the SiN films was achieved at room temperature. On the basis of surface analysis results for SiN films and plasma analysis results for the CHF3/O2 gas mixture, a mechanism for the high etching selectivity of the photoresist films was proposed. Reaction products that were formed on SiN films by the CHF3/O2 gas mixture plasma obstructed the etching of SiN films by fluorine (F) radicals, resulting in the high selectivity. It was found that the CHF3/O2 gas mixture plasma reacted with SiN, resulting in the formation of a protective reaction product that is considered to be an ammonium salt such as (NH4)2SiF6.

Analysis Technique of Organic Contaminants on the Surface of the Polyimide Film of Liquid Crystal Displays

The presence of organic contaminants on the polyimide film surface causes picture nonuniformity in liquid crystal displays (LCDs). In order to determine the reason for this phenomenon, chemical identification of these contaminants is very important. We consider that the IR-Johnson method is useful for identifying unknown organic contaminants. This paper defines the surface sensitivity for this method. The spectrum for four-layer (about 100-A-thick) Ba icosanoate LB film was observed by this method, and it was found that this spectrum has no polyimide peak. Analysis by the IR-Johnson method is effective for identification of unknown organic contaminants approximately 100 A thick on polyimide films. The same samples were analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). It was shown that the mass spectra for TOF-SIMS were supplementary data for this identification.

Characterization of ion-induced sodium migration in various kinds of silicon oxide films

Abstract The migration behavior of Na in SiO 2 films during SIMS depth profiling was characterized, and effects of the chemical structure and defects in the film on Na migration were investigated. Several types of SiO x N y samples were prepared and the relationship between Na migration behavior and the type of the films was determined. It is clarified that not only defects formed by ion-implantation but also porousness of the film accelerate the Na migration during SIMS analysis and it is suggested that reducing Na migration in such low-density SiO 2 film is quite difficult. On the other hand, it was shown that Si–N bonds in the film are effective in suppressing the migration of Na. Thus the Na migration during SIMS analysis is affected by the structure of the film, and there is the possibility of obtaining information on the chemical structure of the films.

Stabilization of amorphous structure in silicon thin film by adding germanium

The stabilization of the amorphous structure in amorphous silicon film by adding Ge atoms was studied using Raman spectroscopy. Amorphous Si1−xGex (x = 0.0, 0.03, 0.14, and 0.27) films were deposited on glass substrates from electron beam evaporation sources and annealed in N2 atmosphere. The change in the amorphous states and the phase transition from amorphous to crystalline were characterized using the TO, LO, and LA phonons in the Raman spectra. The temperature of the transition from the amorphous phase to the crystalline phase was higher for the a-Si1−xGex (x = 0.03, 0.14) films, and the crystallization was hindered. The reason why the addition of a suitable quantity of Ge atoms into the three-dimensional amorphous silicon network stabilizes its amorphous structure is discussed based on the changes in the Raman signals of the TO, LO, and LA phonons during annealing. The characteristic bond length of the Ge atoms allows them to stabilize the random network of the amorphous Si composed of quasi-tetrahe...