B. Pivac

Infrared study of Si-rich silicon oxide films deposited by plasma-enhanced chemical vapor deposition

A single chamber system for plasma-enhanced chemical vapor deposition was employed to deposit different films of SiOx:N,H with 0.85⩽x⩽1.91, which are studied here by Fourier transform infrared transmission spectroscopy. The sample composition was determined by Rutherford backscattering spectrometry, nuclear reaction, and elastic recoil detection analysis. Moreover, physical properties such as thickness uniformity, deposition rate, density, wet and dry etch rates, and stress are determined. A quantitative study of Si–OH, N–H, and Si–H bonds was performed and interpreted on the basis of the random bonding model; in addition, the presence of NH2, Si–O–Si, H2SiO2, and Si–N groups was detected. The effect of sample annealing at 600 and 900 °C was studied and two species of Si–H bonds were identified, one more stable and the other one easily releasable. A reordering effect of annealing was also detected as a reduction of the amorphous network stress and as the increase of the bond angle in the Si–O–Si groups up...

In situ Cr gettering in polycrystalline silicon sheets obtained by edge-defined film-fed growth

Gettering of Cr during the growth of silicon sheets from a Cr‐doped melt is observed when the solid/liquid interface region is exposed to CO or CO2 gases. The gettering occurs within a region about 1‐μm wide at the surface of the crystal, where a large accumulation of carbon and oxygen is detected. Mechanisms for carbon and oxygen participation in forming gettering sites for Cr are examined.

Polarization effect on infrared absorption of oxygen precipitates in silicon

High‐spatial resolution Fourier transform infrared spectroscopy permitted us to study the effects of incident light polarization on the absorption band related to aggregates of SiO2 disk‐shaped precipitates present in annealed (100) Czochralski silicon samples. This is the first report documenting the strong dependence of such a band intensity on light polarization. Experimental results were compared with the simulation obtained using the effective medium theory. From this comparison we deduce that the precipitates only lie on the planes among {100} which are parallel to the wafer surface. This result can be related to the difference between the 〈100〉 direction and those crystallographically equivalent, introduced by the ingot growth process.

Stoichiometry of oxygen precipitates in silicon

Abstract We studied oxygen precipitation in silicon upon brief sample annealing at 1100°C by high resolution Fourier transform infrared technique. This technique permits the detection of small agglomerates of disc-shaped precipitates formed in the bulk of annealed silicon wafers. Precipitates are characterized by a peak at 1230 cm -1 in the infrared absorption spectrum. It is further demonstrated that only the disc-shaped precipitates can contribute to the absorption band mentioned. Moreover, the exact wavenumber position of the peak can give additional information about the chemical composition of the oxide constituting the discs.

Infrared characterization of oxygen precipitates in silicon wafers with different concentrations of interstitial oxygen

Abstract The study of the optical behavior of oxygen in silicon is presented, based on infrared absorption measurements performed at liquid helium temperature. A total of six groups of silicon wafers characterized by different initial concentrations of interstitial oxygen from ∼2×1017 to ∼1018 atoms cm−3 were analysed. The experimental conditions were chosen so as to distinguish the contributions from interstitial and precipitated oxygen, while the thermal treatment of the samples was studied in order to cause the growth of the grown-in precipitates. The relative concentrations of platelet and spheroid precipitates grown after the thermal treatment of the wafers are discussed.

EPR study of He-implanted Si

Abstract Electron paramagnetic resonance has been used to study the influence of thermal treatments on defect evolution in helium-implanted Czochralski single-crystal silicon. It is shown that the thermal treatment induces helium migration and capturing by vacancy clusters that transform into pressurized bubbles. Such transformation produces a strain field, which in turn affects the dangling bond’s lineshape in its vicinity. It is shown that the strain field causes asymmetry of dangling bond lineshape that is proportional to the strain field. This selects the electron paramagnetic resonance as a convenient technique for the monitoring of the early phases of bubble formation.

Non-doping light impurities in silicon for solar cells

The impurities present in silicon for solar cells directly influence its electrical characteristics and therefore solar cells performance. Light non-doping impurities like oxygen, carbon, hydrogen, and nitrogen are of particular importance since they exhibit both a positive and a negative impact when present in silicon substrates. In this overview we illustrate the positive and negative effects of impurities on silicon material properties. It is also shown that their contemporary presence leads to a mutual interaction and hence to the formation of more complex structures.

Homogeneity of carbon microdistribution in edge-defined film-fed grown polycrystalline silicon

Abstract Edge-defined film-fed grown polycrystalline silicon sheets are known to contain carbon impurities in a state of extremely high supersaturation. During very rapid growth, carbon is incorporated with an unusually high effective segregation coefficient close to unity; therefore it is of interest to study its microdistribution over the sheet. We performed a scanning IR absorption microanalysis over macroscopic distances in order to evaluate the homogeneity of carbon microdistribution in as-received samples grown in an inert or oxidizing atmosphere, as well as on samples annealed for 72 h in air at different temperatures, up to 1150 °C. As-received samples revealed a very good homogeneity of carbon distribution, which is not even disturbed by the presence of oxygen. However, the homogeneity of carbon microdistribution was found to be significantly disturbed upon annealing. This must be taken into consideration when studying the electrical characteristics of solar cells produced from such material upon various thermal treatments.

DLTS and EPR study of defects in H implanted silicon

Abstract Single crystal CZ Si samples were implanted with hydrogen ions to the dose of 2E16 He ions/cm 2 at room temperature and subsequently annealed in vacuum in the temperature interval from 100 to 900 °C. The aim of the experiment was to determine the conditions for bubble formation within the solid film, which may have important technological application. Defects produced in such samples were studied by deep-level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR) spectroscopy. It is shown that high dose hydrogen implantation produces vacancy-related and silicon selfinterstitial clusters. The latter are thought to be responsible for the formation of the weak displacement field. The annealing at higher temperatures creates multivacancy-related clusters responsible for the strong displacement field formation.

Evaluation of the precipitate contribution to the infrared absorption in interstitial oxygen measurements in silicon

The spurious contribution of oxide precipitates to the infrared absorption of interstitial oxygen in silicon is determined from spectra collected at 7 K for samples with different initial interstitial oxygen Oi concentration subjected to a three-step thermal treatment. These data can be used to correct the residual Oi values determined at room temperature following the standard procedure from the intensity of the 1107 cm−1 absorption band. The error in residual Oi is found to reach values on the order of 2×1017 atoms/cm3 for samples with initial Oi content higher than 6.5×1017 atoms/cm3.