C. Dubois

Phosphorus diffusion from a spin-on doped glass (SOD) source during rapid thermal annealing

Abstract Limiting thermal exposure time using rapid thermal processing (RTP) has emerged as a promising simplified process for microelectronics applications and for manufacturing of terrestrial solar cells in a continuous way. Especially, rapid thermal diffusion (RTD) of phosphorus from doped oxide films (SOD) was extensively used for the emitter formation purpose but few work concerned the diffusion mechanism. Here we investigate more in details the diffusion kinetics of phosphorus after rapid thermal annealing of P-SOD coated silicon samples. The observed enhanced distribution of phosphorus after RTD is discussed based on the dopant sources and processing conditions. Comparisons between experimental profiles and simulation results using up to date phosphorus diffusion models allow us to discriminate between various possible enhancement mechanisms.

Quantification of germanium and boron in heterostructures Si/Si1−xGex/Si by SIMS

Abstract The use of secondary ions mass spectrometry (SIMS) generally leads to very high sensitivity and depth resolution for silicon-based components. Low concentration elements such as dopants, are easy to quantify in silicon, whereas high concentration elements are subject to “matrix effects”, i.e. the intensity does not vary linearly with the concentration. Matrix effects are presently studied in SiGe alloys using two primary beams O 2 + and Cs + and a CAMECA IMS4F instrument. Rapid thermal chemical vapor deposition grown Si/Si 1− x Ge x /Si multilayer structures with x varying from 0 to 23.5% are preliminarily characterized by Rutherford backscattering spectrometry (RBS) in thickness and atomic composition. The linear variation of the SIMS intensity ratio I Ge + / I Si + with the RBS concentration ratio x /(1− x ) is confirmed for both O 2 + and Cs + beams. However, the linearity does not imply the absence of matrix effects. A variation of the ionization yields with Ge concentration and a similar behavior for τ Ge+ and τ Si+ actually lead to an exact compensation of the intensity ratio variation. At any energy, O 2 + experiments systematically over-estimate the real Ge concentration, whereas matrix effects under Cs + beam are weak. For polyatomic MCs + ions, strong matrix effects are observed in Si 1− x Ge x alloys. A quantitative analysis of major constituents and a dopant (boron) is used to determine the depth profiles of a thin base of a SiGe HBT heterostructure. Two different procedures are used depending on the primary beam. Consistent results are obtained for the concentrations of the major elements. The fully autonomous SIMS analysis with the Cs + beam is still penalized by the lack of sensitivity for boron in the secondary positive mode.

Control of the Ti diffusion in Pt/Ti bottom electrodes for the fabrication of PZT thin film transducers

Abstract For the achievement of microactuators based on piezoelectric thin films, a Pt/Ti/Si bottom electrode is widely used. This study presents the experimental results for Ti out-diffusion in Pt and Si for both sputtered Pt/Ti and Pt/TiO x electrodes. These results have been compared before and after a rapid thermal annealing (RTA). The diffusion has been characterized by secondary ion mass spectroscopy (SIMS) analysis using Cs + as a primary ion source. The Pt orientation has been observed by XRD measurements. Ti thin films (20xa0nm) have been sputtered in pure Ar whereas TiO x films have been obtained by reactive sputtering in a mixture of Ar/O 2 (90/10). Finally, the Pt (100xa0nm) has been sputtered without vacuum breaking. After RTA (400°C, 30xa0s, in N 2 ), the Pt film exhibited a (1xa01xa01) orientation for both Ti and TiO x adhesion films. The roughness of the Pt film measured by AFM with TiO x underlayer was 80% less than that of the Pt/Ti bi-layer. The TiO x film, as shown by SIMS analysis, has drastically reduced the diffusion of Ti in both Pt and Si. This phenomenon is accompanied by a very low Pt roughness. These results are analyzed in terms of diffusion and regrowth mechanisms inside the Pt film.

Silicon nitride and oxynitride deposition by RT-LPCVD

Abstract Silicon nitride (Si-N) and oxynitride (Si-O-N) thin films are obtained by low pressure rapid thermal chemical vapor deposition (RT-LPCVD) by using the reaction of diluted silane (SiH 4 /Ar = 10%) with ammonia (NH 3 ) or a mixture of ammonia and nitrous-oxide (N 2 O) at various gas ratios ( R = NH 3 /SiH 4 and R′ = [N 2 O + N 2 O]). Deposition kinetics of silicon nitride films have been studied in the medium to high temperature range (700–850°C) at fixed total pressure of 9.5 mbar and gas flow ratio ( R = 10). Oxynitride deposition rates have been also studied as a function of R′ at fixed temperature and total pressure parameters of 750 °C and 9.5 mbar respectively. Rutherford backscattering spectrometry results showed that the RT-LPCVD Si-N films are silicon-rich and that the composition stoichiometry is mainly controlled by the process parameters, particularly the gas flow ratios. Si 3 N 4 silicon nitride stoichiometry can only be approached for R ≥ 10. Fourier transform spectrometry measurements revealed that the Si-O-N films have a particular structure formed by a mixture of Si-O and Si-N bonds with no apparent separated phases. In addition, in contrast to the few 10 at % usually reported for classical CVD processes, no significant traces of hydrogen bonds (Si-H or N-H) were detected for R ≥ 10. Furthermore, secondary ion mass spectrometry analysis always indicated that Si-N and Si-O-N RT-LPCVD deposited layers are homogeneous along the whole film thickness.

Boron gettering on cavities induced by helium implantation in Si

Abstract In this paper, we shed light on the strong interaction between the cavity layer induced by helium implantation and boron. First of all, we evidence the impact of He gettering step on a boron-diffused profile. In order to study the boron–cavity interaction, we had used uniformly boron-doped wafers implanted with helium at high dose and anneal using usual furnace annealing (FA) as well as rapid thermal annealing. Then, to avoid any precipitation phenomena, conditions were chosen to not exceed the boron solid solubility value. Our experimental results exhibit a large trapping of boron within the cavity layer. This trapping occurs since the early stage of the annealing. These results enable us to have better understanding of this He gettering step as well as its interaction with boron atoms, which are of great interest for device.

Diffusion of low-dose implanted aluminum in silicon in inert and dry O2 ambient

Redistribution of a high-energy (3 MeV) low-dose (5×1013u200acm−2) implanted aluminum profile in silicon under inert and dry O2 is investigated in the temperature range (900–1100u200a°C). The chemical profiles were measured by secondary ion mass spectroscopy and the effective diffusivities were extracted from the experimental data from fitting with calculated profiles obtained by numerical resolution of Fick’s law. It is found that the aluminum diffusion is significantly enhanced during thermal oxidation. The diffusivity enhancement decreases with the temperature. Comparison with boron data suggests that the mechanism of aluminum diffusion in silicon is similar to that of boron.

Thermal redistribution of Al implanted in Si: evidences for interactions with extended defects

Abstract Al was implanted at 180 keV to a dose of 4.5xa0×xa010 14 cm −2 . Various anneals were performed in the temperature range (900–1100°C), for times varying from 15 min up to several hours. The SIMS measurements reveal anomalous redistribution of the aluminium profiles. The bulk side of the profiles diffuses normally at a rate in agreement of the Al intrinsic diffusivity, but two peaks of apparently immobile atoms are formed near the surface. Cross observations by Transmission Electronic Microscopy (TEM) prove that there is no Al precipitation, and reveal the existence of two extended defects bands, the position of which is perfectly correlated with Al peaks. This strongly suggests that these peaks are due to Al trapping on the extended defects. First simulations also support this assumption.

Depth resolution in SIMS study of boron δ-doping in epitaxial silicon

Abstract Microelectronic needs accurate analysis of very thin layers as delta doped structures. By secondary ion mass spectrometry (SIMS) with O2+ ion beam, we analyse mono-delta of boron in silicon located at 30 nm under the surface and then a multi-delta of boron in silicon located just under the surface ( ≈ 10 nm). For the mono-delta, we study modifications of the SIMS profiles within the projected range of primary ion beam Rp. From the dependence of FWHM within Rp, we deduce the real thickness of pseudo-delta thin layers by assuming a convolution process for SIMS measurements. This assumption is well confirmed by the analysis of a boron tri-delta doped layers.

Depth resolution in SIMS study of a Fe-Ti multilayer structure

Abstract Depth profiles of Fe-Ti multilayer structure composed of 29 alternate Fe and Ti layers (68 and 84 A thick) were obtained by secondary ion mass spectrometry under 5.5 and 3 keV O2+ bombardment. The effect of oxygen flooding on the in-depth resolution and matrix effects was investigated. Without oxygen flooding during ion bombardment, induced roughness has been developed. With oxygen flooding at 10−5 Torr, the layers are easily visible, the depth resolution is constant with the depth and the Ti signal is representative of the composition profile in the multilayer sandwich (no matrix effects on Ti intensities).

Growth and physical properties of in situ phosphorus-doped RTLPCVD polycrystalline silicon thin films

Abstract In situ phosphorus-doped (P-doped) polysilicon (poly-Si) thin films are obtained by rapid thermal low pressure chemical vapor deposition (RTLPCVD) in a single chamber RTP machine by using diluted silane (SiH4/Ar=10%) and phosphine (PH3=200 ppm). Deposition kinetics of poly-Si films were studied in the 600–850°C temperature range at fixed total pressure of 2 mbar and gas flow rate (100 sccm). Activation energy of 1.82 eV was calculated in the surface reaction deposition regime. Dopant activation has been obtained sequentially by RTO at 1000°C in pure O2 atmosphere. This later process permits to both activate the phosphorus dopant and forms an ultrathin polyoxide which blocks dopant outdiffusion. Secondary ion-mass spectrometry (SIMS) analysis showed flat P-dopant profiles throughout the film thickness with a P concentration varying from 5.5×1020 to 2.4×1019 at/cm3 when the deposition temperature increases in the 600–850°C range. Grazing incidence X-ray diffraction (XRD) has been used to study the structural properties of the poly-Si layers. It appeared particularly that the amorphous to crystalline temperature transition occurs at around 650°C. Finally, four-point probe measurements showed that sheet resitivities in the mΩ cm range can be routinely achieved for in situ P-doped RTLPCVD poly-Si films.