Evgeny Demenev

Quantitative depth profiling of boron and arsenic ultra low energy implants by pulsed rf-GD-ToFMS

In very recent years particular effort is being devoted to the development of radiofrequency (rf) pulsed glow discharges (GDs) coupled to time of flight mass spectrometry (ToFMS) for depth profile qualitative analysis with nanometre depth resolution of technological materials. As such technique does not require sampling at ultra-high vacuum conditions it facilitates a comparatively high sample throughput, related to the reference technique secondary ion mass spectrometry (SIMS). In this work, pulsed rf-GD-ToFMS is investigated for the fast and sensitive characterization of boron and arsenic ultra low energy (ULE) implants on silicon. The possibility of using a simple multi-matrix calibration procedure is demonstrated for the first time for quantification of this type of samples and the validation of the proposed procedure has been carried out through the successful analysis of a multilayered sample with single and couple 11B delta markers. Results obtained with the proposed methodology for boron and arsenic ULE implants, prepared under different ion doses and ion energy conditions, have proved to be in good agreement with those achieved by using complementary techniques including SIMS and grazing incidence X-ray fluorescence. Thus, although further investigations are necessary for more critical evaluation of depth resolution, the work carried out demonstrates that rf-GD-ToFMS can be an advantageous tool for the analytical characterization of boron and arsenic ULE implants on silicon.

Formation of arsenic rich silicon oxide under plasma immersion ion implantation and laser annealing

Samples produced by plasma immersion ion implantation of Arsenic in Silicon using a non-pulsed plasma source and subsequent laser annealing were investigated with respect to As depth distribution, oxide thickness, and As local order using SIMS, XPS, INAA and EXAFS analysis. A surface layer (∼10 nm), was identified as an As-rich Si oxide formed after implantation. The thickness of this layer was found to be larger for samples annealed using a low thermal budget up to a threshold where probably melting occurred. Dopant depth profile was re-distributed whereas the final oxide film of these samples showed thicknesses of a few nm. The retained As dose exhibited an apparent drastic increase. A hypothesis for the processes involved is presented based on experimental evidence.

Solid phase epitaxial re-growth of Sn ion implanted germanium thin films

Doping of Ge with Sn atoms by ion implantation and annealing by solid phase epitaxial re-growth process was investigated as a possible way to create Ge1−xSnx layers. Ion implantation was carried out at liquid nitrogen to avoid nano-void formation and three implant doses were tested: 5×1015, 1×1015 and 5×1014 at/cm2, respectively. Implant energy was set to 45 keV and implants were carried out through an 11 nm SiNxOy film to prevent Sn out-diffusion upon annealing. This was only partially effective. Samples were then annealed in inert atmosphere either at 350°C varying anneal time or for 100 s varying temperature from 300 to 500°C. SPER was effective to anneal damage without Sn diffusion at 350° for samples implanted at medium and low fluences whereas the 5×1015 at/cm2 samples remained with a ∼15 nm amorphous layer even when applying the highest thermal budget.

Formation of arsenolite crystals at room temperature after very high dose arsenic implantation in silicon

Spontaneous growth of arsenolite micro-crystals at room temperature after high fluence, low energy arsenic trihydride implantation in silicon was observed on the wafer surface after exposure to air. The crystals have been identified unambiguously by x-ray absorption and fluorescence spectroscopy. Thermal treatment easily sublimates the crystals at temperatures as low as 200 °C without any relevant in-diffusion of As into the substrate. The deposition of a thin As-rich layer under high fluence implantation conditions is suggested as possible precursor for crystal formation. The same layer can explain the anomalous retained dose increase often observed after annealing.

Silicon defects characterization for low temperature ion implantation and spike anneal processes

In the last years a lot of effort has been directed in order to reduce ion implantation damage, which can be detrimental for silicon device performances. Implantations dose rate and temperature were found to be two important factors to modulate residual damage left in silicon after anneal. In this work high dose rate, low temperature, high dose arsenic and boron implantations are compared to the corresponding low dose rate, room temperature processes in terms of silicon lattice defectiveness and dopant distribution, before and after anneal is performed. The considered implant processes are the one typically used to form a source/drain region in a CMOS process flow in the submicron technology node. A spike anneal process was applied to activate the dopant. Low temperature, high dose rate implantations have found to be effective in reducing silicon extended defects with a negligible effect on the profile of the activated dopant. Experimental set up, results and possible explanation will be reported and discussed in the paper.

Ge nanostructuring by Sn ion implantation

The production of Ge_1-xSn_x alloy nano-structures through high fluence Sn ion implantation at room temperature and subsequent rapid thermal annealing was investigated. Implant energy was set at 45 keV, aiming to produce a <;100 nm thick nano-structured layer. Three high Sn implantation fluences were tested: 5×1015, 1×10¹⁵, 5×10¹⁴ at/cm². First ion implantation was carried out at liquid nitrogen temperature in order to avoid nanostructured Ge film formation and to test further processing in absence of nanostructures. An 11 nm thick SiN_x capping layer was deposited to prevent Sn out-diffusion. The samples were annealed in N₂ atmosphere at 300°C and at 600°C, resulting in the formation of a uniform layer of Ge_1-xSn_x alloy with a tin concentration of x=5.2% and a good degree of crystallinity. The best annealing recipes were then applied to the nano-structured sample in order to produce a Ge_1-xSn_x nanostructured layer. First results show that the same thermal budget used to form the uniform Ge_1-xSn_x alloy layer cannot be easily applied to anneal nano-structures since an early melting was observed.