Effects of plasma processing on the microstructural properties of silicon powders

Abstract

The effects of plasma processing conditions on the microstructural properties of silicon powders are presented. Hydrogenated nanophase silicon powden were preparedming low-pressure and low-temperature square wave modulated RF plasma (1 3.56 MHz) using pure Silane gas. Plasma parameters such as pressure, RF power, plasma modulation frequency, and gas flow rate were varied.In situ analysis by quadrupoiar mass spectroscopy and ex situ analysis of the silicon powders by Fourier transform infrared spectroscopy ( F m ) and thermal desorption spectrometry of hydrogen were performed. The thermal desorption spectrometry results show the fundamental differences behveen the concentrations of hydrogen weakly and strongly bonded in silicon powders as compared to amorphous silicon iiims. Tie mi R anaiysis aiso deiermined ine microstructurai characteristics of powders and hence their volume/surface ratio. This parameter was determined from the balance of Pi probahilities of having one of the HjS[-Si4_j bond arrangements in the powder particles. These results reveal an increase In hydrogen content and a reduction in volume/suriace ratio as the modulation frequency of RF power Increases. in consequence, higher compactness of silicon powders is associated with long particle residence times inside the plasma as a result of ion bombardment TEM analysis indicated a considerable dispersion of particle size and some degree of structure of the silicon powder characterized by intergrain linkage. We point out the dominant presence of hydrogen on the particle surfaces (external voids), which may cause the high reactivity of grains, increasing the degree of intergrain linkage.

Calorimetry of dehydrogenation and dangling-bond recombination in several hydrogenated amorphous silicon materials

“…The usual growing conditions and structure are described elsewhere. 32 Typical particle diameters are much smaller than 100 nm. They have a high hydrogen concentration ͑Ͼ30% ͒ and a residual amount of oxygen that is incorporated when the reaction chamber is opened to the air.…”

Effect of the Nanoparticles on the Structure and Crystallization of Amorphous Silicon Thin Films Produced by rf Glow Discharge

“…4 The microelectronics industry is concerned that the general trend of reduction of the device dimensions may be limited by the particle contamination from the plasma process itself. Nowadays, the undesirable role of the particles during the plasma processing has been questioned because the new properties found in silicon powders 5,6 and in the silicon films 7 grown in the presence of particles can be used in possible future applications as nanostructured materials. [5][6][7][8] In earlier studies on hydrogenated amorphous silicon (a-Si:H) thin films produced by PECVD, the powder formation was correlated to a deterioration of the film quality due to the production of pinholes, roughness, and porosity.…”

“…Nowadays, the undesirable role of the particles during the plasma processing has been questioned because the new properties found in silicon powders 5,6 and in the silicon films 7 grown in the presence of particles can be used in possible future applications as nanostructured materials. [5][6][7][8] In earlier studies on hydrogenated amorphous silicon (a-Si:H) thin films produced by PECVD, the powder formation was correlated to a deterioration of the film quality due to the production of pinholes, roughness, and porosity. 9 Later, however, a study on the increase in the deposition rate and the decrease in the substrate temperature of silicon thin films 10 concluded that the film properties were improved, in spite of the presence of powder during the plasma process.…”

“…5 In these conditions, nanometric particles ͑, 2 nm͒ are produced, they are not all confined within the plasma by the plasma-sheath (because of the charge fluctuation), and they can be incorporated to the growing film. 7,12 In these films, silicon ordered domains (consisting of 3 to 5 Si crystalline planes) were found to be embedded in the amorphous matrix.…”

Enhancement of oxidation rate of a-Si nanoparticles during dehydrogenation

“…3 Transmission electron microscopy observations 11 have revealed that the particles are mostly spherical with mean 20 nm diameter whereas electron diffraction patterns show that they are amorphous. Another important structural characteristic is their high hydrogen content that comes from the silane precursor gas.…”