Naoshi Itabashi

Spatial Distribution of SiH3 Radicals in RF Silane Plasma

Infrared diode laser absorption spectroscopy (IRLAS) was applied to the measurement of SiH3 in a RF silane P-CVD chamber with parallel plate electrodes. The spatial distribution of SiH3 radicals between the electrodes was measured to obtain the incident flux density of SiH3 to the electrode surface. The growth rate of a-Si:H was also measured in the same plasma. These data were used to estimate the contribution of SiH3 to a-Si:H thin-film growth.

Measurement of the SiH3 Radical Density in Silane Plasma using Infrared Diode Laser Absorption Spectroscopy

The SiH3 radical is an important precursor in amorphous silicon thin film formation, but its density in silane plasma has never been measured. In this work, we have developed a method for measuring the SiH3 radical density using an infrared diode laser absorption method and have determined the density in a pulsed SiH4/H2 plasma.

Mechanism of Radical Control in Capacitive RF Plasma for ULSI Processing

The radicals of capacitive plasmas actually used in mass production were analyzed using various measurement systems. The composition of radicals in bulk plasma depends on the gas chemistry, the dissociation process, and interaction with the wall. It is revealed that parent gas (C4F8) is dissociated by multiple collision with electrons according to τne , where τ is the residence time, ne is the electron density, σ is the dissociation collision cross section and v is the electron velocity. A high-performance etching process, which can realize 0.09 µm contact holes with aspect ratio of 11, was achieved using a short residence time to suppress the excess dissociation and the control of deposition species through the addition of O2 to C4F8/Ar plasma as well as the reduction of the density of F radicals through the reaction with the Si wall.

Diffusion Coefficient and Reaction Rate Constant of the SiH3 Radical in Silane Plasma

By using infrared diode laser absorption spectroscopy, the rotational temperature and the number density of the SiH3(2A1) radical were measured in a pulsed SiH4/H2 discharge. The decay of the absorption intensity was also measured as a function of the filling gas pressure for the line Q(6, 6)(1- ← 0+) of the SiH3 ν2 fundamental band to determine the effective diffusion coefficients (D(SiH3 in H2) and D(SiH3 in SiH4)) and the reaction rate constant (k) of the SiH3 radical.

SiH3 Radical Density in Pulsed Silane Plasma

The SiH3 radical density in pulsed silane discharge plasma was measured by infrared diode laser absorption spectroscopy (IRLAS) for three buffer gases and also as functions of the sample pressure and the pulse width. They were compared with the SiH and SiH2 radical densities. The growth rate of a-Si:H thin film was compared with the SiH3 radical density on various plasma conditions. These data were employed to discuss the contribution of SiH3 to a-Si:H thin-film growth.

Measurements of the CF radical in DC pulsed CF4/H2 discharge plasma using infrared diode laser absorption spectroscopy

Infrared diode laser absorption spectroscopy (IRLAS) was established as the measurement method for the CF radical density. The absolute density of the CF radical and its pressure dependences were measured in DC pulsed CF4/H2 discharge plasma. Moreover, from the analysis of the decay parts of the observed transient absorption waveforms of the CF radical, the CF radical was shown to be removed mainly by a diffusion process in the present plasma, yielding the diffusion coefficients D(CF in H2) and D(CF in CF4).

A Model Analysis of Feature Profile Evolution and Microscopic Uniformity during Polysilicon Gate Etching in Cl2/O2 Plasmas

A phenomenological model has been developed to simulate the feature profile evolution of polycrystalline silicon (poly-Si) gate etching in Cl2/O2 plasmas. The model takes into account the deposition of etch products, surface oxidation, and the forward reflection of energetic ions on feature sidewalls. To describe the formation of multilayer SiClx or SiClxOy on feature surfaces during etching, the substrates consist of a number of small cells or lattices of atomic size in the computational domain; this model provides a nanometer-scale representation of the feature geometry and the chemical constituents therein. The inelastic or nonspecular reflection of incoming ions from feature surfaces and the penetration of ions into substrates are incorporated into the model by calculating the trajectory of ions through successive binary collisions with substrate atoms. Etching experiments were performed to evaluate and improve the accuracy of the model. To analyze the effects of the control variables of a plasma reactor on profile evolution, the simulated profiles for different gas flow ratios and incident ion energies were compared with the etched profiles obtained in the experiments. The numerical results reproduced the behaviors of profile anomalies such as sidewall tapering and microtrenches at the corner of the feature bottom, upon varying the incident fluxes of O neutrals and etch by-products, and the incident energy of ions. Moreover, the simulated profiles exhibited passivation layers deposited on feature sidewalls, which is a similar geometry to those obtained in the experiments.

FUTURE PROSPECTS FOR DRY ETCHING

An overview of plasma etching, including its basic mechanism, its history, and the problem of trade-offs in its properties, is given as background for a proposal concerning the direction that research aimed at developing future dry- etching techniques should take. Considering the three-level structure of the chemical, physical, and apparatus parameters of plasma etching, we need to develop new plasma souxes with high controllability of the physical parameters. The ideal style is a soft thFee-dimensionally uniform plasma created using a wave- plasma coupling power supply. Also, as device integration continues to advance and special requirements for new-concept devices arise, it may also be necessary to examine processes using post-plasma techniques, where minimizing damage will be especially important. 1. Introduction The integration required for semiconductor-memory devices has approached the giga-bit order in recent years and the scale of fabrication will soon reach the 0.1-pm order. Dry etching, like lithography, is a key technology for fine-pattern delineation. It now has two possible courses of future development. One is to improve current plasma etching techniques, and the other is to stop using plasma and develop new concepts of etching methodology. In this paper, we investigate the future prospects of dry etching, mainly focusing on plasma etching. First, we explain the role of plasma etching in the device fabrication process in terms of the basic mechanism of plasma etching and the desired performance. Next, the essential difficulty in plasma-etching development is discussed from the viewpoint of the structure of etching parameters. In this context, we review the history of plasma etching, mainly at the beginning stages of the research. Then, we propose what we feel are the most feasible future trends in plasma etching, including some important concepts for developing new plasma formation techniques. Finally, the importance and desired aspects of post-plasma etching are briefly discussed.

Desorption induced by electronic potential energy of multiply charged ions

Abstract Particle desorption is investigated in terms of bombardment of a GaAs surface by slow multiply charged Ar ions (charge state q ⩽ 9, kinetic energy E k ⩽ 3 keV). The desorption yield of Ga and As atoms as well as H + ions drastically increased with the charge state of the incident Ar ions, but was changed little by the kinetic energy of the Ar ions. These results demonstrate that desorption reactions at the surface are greatly enhanced by the potential energy of the incident ions. From an analysis of the potential energy dependence of the desorption yield based on the Coulomb explosion model, it is found that the lifetime of multiple holes created by the multiply charged Ar ions is longer than that of a single hole by 2 to 3 orders of magnitude.

Positive Charge Generation at a SiO2/Si Interface due to Bombardment with Metastable Atoms.

The influence of metastable atoms on a SiO2/Si structure is examined to determine the source of damage in ULSI devices during plasma enhanced processes. Holes were generated at the SiO2 surface by the impact of metastable atoms of rare gases. Holes trapped at the interface formed positive charges, and the density of these positive charges increased with the increasing energy of the metastable atoms. The yields of the positive charge generation were between 0.01 and 0.1, which are on the same order as those caused by vacuum ultraviolet photons, and these values are not negligible. Thus, the influence of metastable atoms must be taken into consideration to control the damage that occurs during plasma enhanced processes.