F. Cazzaniga

Crystal defects and junction properties in the evolution of device fabrication technology

In this paper, the correlation between dislocation density and transistor leakage current is demonstrated. The stress evolution and the generation of defects are studied as a function of the process step, and experimental evidence is given of the role of structure geometry in determining the stress level and hence defect formation. Finally, the role of high-dose implantations and the related silicon amorphization and recrystallization is investigated.

Metal contamination monitoring and gettering

Abstract Some commonly used techniques for metal contamination monitoring by lifetime measurements (surface photovoltage, Elymat and microwave-detected photoconductive decay) are discussed and compared. In order to validate these techniques for the detection and the quantitative evaluation of bulk-diffused contamination, iron and chromium implanted samples have been studied. Though these techniques are very different from each other, we show that for what concerns bulk-diffused impurities they agree very well with each other, provided in the comparison the dependence of carrier lifetime on the injection level is taken into account. In addition, the possibility to extend these techniques to surface characterization (e.g. for the detection of surface-precipitated metals) is studied. Nickel and copper implantated wafers were used to this purpose. Both Elymat and μ-PCD are found to be very sensitive to surface-segregated metals, though under these conditions the correlation between Elymat and μ-PCD data is somewhat different with respect to samples with metals dissolved in the bulk. Finally, some gettering techniques are reviewed and compared for what concerns gettering efficiency. It is pointed out that gettering efficiency is sensitively reduced in high temperature rapid thermal treatments. This fact can be explained by efficiency loss of the segregation mechanism.

Investigation of metal contamination by photocurrent measurements: validation and application to ion implantation processes

In this work we present a systematic study about the metal contamination induced by ion implantation, with the aim to identify contamination mechanisms and possible solutions to the problem. Lifetime measurements have been used in order to evaluate the level of contamination in implented wafers. Lifetime values have been extracted from photocurrent measurments (Elymat technique). Implantations of iron and cromium have been used in order to validate the study of lifetime versus injection level as a technique for the identification of contaminants and for the quantitative evaluation of their concentration. The contamination level in ion implanted wafers has been characterized varying main implantation parameters (species of the implanted ion, dose, current, energy, angle) and surface condition (whether bare or oxidized silicon). Ion implantation is responsible for a a heavy lifetime degradation (i.e. metal contamination), which increases in proportion to implantation dose and comes from the side exposed to the ion beam. The distribution of lifetime over wafer surface provides relevant information. Details of the implanter endstation (e.g., the clamping system) usually show up in wafer maps of lifetime. Results coming from different equipments concur to indicate that contaminants come from material sputtered from the loading disk. This conclusion is confirmed by the dependence of lifetime on implantation energy and tilt angle. The chemical nature of the contaminant can in some cases be identified by injection level spectroscopy. Implantation of heavy ions is mainly responsible for iron contamination; some other impurity (maybe cromium) is detected in boron-implanted wafers. From the point of view of device processing, the problem can be circumvented by implantation through a screening exide. Vice versa gettering techniques remove only a limited fraction of the contaminants introduced during the implantation.

AFM measurement of the grain size in polycrystalline titanium silicides

Abstract In titanium silicide, the transition from the high (C49) to the low resistivity phase (C54) is difficult in small areas. This has been attributed in the literature to the lack of the nucleation sites for phase transition in small areas [1] . The mean grain size is directly related to the nucleation point density and its evaluation is important in obtaining data on nucleation mechanism of a new crystalline phase. TEM and SEM cross sections show that a silicon ridge is formed on the silicon substrate at the silicide grain boundaries, due to the equilibrium between the forces related to the grain–grain and to the grain–silicon interface energies [2] , [3] . AFM measurements have been performed on the interface between silicon and silicide after the removal of the silicide film. The grain boundaries of the silicide were imaged using the silicon ridges, allowing us to obtain unambiguous and statistically relevant data on the grain size.

Phosphorous implantation in silicon through thin SiO2 layers: Oxide damage and postoxidation thermal treatments

A significant increase of HF etching rate and mean surface roughness (monitored by atomic force microscopy) was observed after P ion implantation on thin thermal SiO2 films (150 A). The dependence upon the ion fluence (in the range 3×1012–5×1013 ions/cm2) and energy (in the range 270–500 keV) was analyzed, together with the recovery effect of a postimplantation annealing in N2 atmosphere. Moreover, the impact of P implants on oxides grown by different sequences, considering postoxidation annealing in N2O or N2 atmospheres, was also studied. The effect of ion irradiation was investigated by thermally stimulated luminescence (TSL) above room temperature in order to obtain information on point defects present in the layers. The results showed that postoxidation annealing treatments in N2 atmosphere carried out not only after, but also before ion implantation, were particularly useful in order to lower the concentration of TSL active defects. This can be interpreted as a role of N2 annealing in favoring a str...

Surface morphology of nitrided thin thermal SiO2 studied by atomic force microscopy

In this work the surface morphology of nitrided silicon dioxide is extensively studied using atomic force microscopy. Nitridation is obtained by thermal annealing in nitriding atmosphere in conventional furnace, immediately after thermal oxidation of silicon substrates. The characterisation performed concerns the oxide surface, as well as the region where nitrogen is incorporated, the latter exposed using a diluted HF solution. Significant differences in the morphology of the nitrided layer are observed, which are a function of the nitridation process applied. They allow us to correlate the morphology to the nitrogen incorporation mechanisms that have occurred.

Impact of plasma treatment time on MOCVD-TiN properties and on the electrical performance of deep contacts

MOCVD-TiN deposition from TDMAT precursor consists of two steps: a deposition and a plasma treatment in hydrogen. The effects of different plasma treatment times are tested on high aspect ratio contacts, finding an increase in the number of high resistance contacts for short plasma treatments. Moreover, the W nucleation layer thickness on MOCVD-TiN is impacted by the plasma time: for a short treatment a thin nucleation layer is found. Various investigations are performed on different MOCVD-TiN layers, comparing samples exposed to the air and samples in-situ capped by Ti to prevent oxygen contamination. It is shown that the plasma treatment influences the film morphology.

The Role of the Interstitial Oxygen in the Recovery and Evolution of the Boron Implantation Damage

The recovery of the boron implantation damage can be very difficult. Depending on the energy and the dose many dislocations are generated at the projected range of the boron implantation. The morphology of these dislocations depends on the silicon substrate. In this work we demonstrate that the interstitial oxygen concentration ([Oi]) is related with the dislocation dimension, density end morphology. Particularly long dislocation dipoles were generated by the boron implantation in substrate with interstitial oxygen, and their density is connected with the [Oi] concentration.

Effects of Ion Metal Plasma (IMP) Titanium Deposition on Ti Silicide Formation

Titanium disilicide obtained by direct interaction between Si and a deposited Ti layer is a choice for low- resistance gate interconnections and source and drain areas. The properties of the TiSi 2 film can be influenced by many factors; such as substrate nature and doping, the depositing Ti layer, structure dimensions [1][2][3][4]. This work is addressed to study the properties of TiSi 2 film as obtained from titanium deposited by Ion Metal Plasma (IMP), which has recently been introduced in high aspect ratio contact and via applications. Its suitability for titanium silicide formation is investigated here in comparison to standard PVD deposition. The study was carried out on flat and patterned samples. Titanium silicide formed on mono- Si substrates were characterized as a function of RTP temperature in terms of sheet resistance, tilm morphology, crystallography and phase evolution. It was found that the TiSi 2 film obtained from IMP- Ti is very similar to the one obtained from PVD standard deposition. However, for annealing below 700°C, an increase in the sheet resistance of the TiSi 2 C49 phase from IMP- Ti compared to the one from PVD- Ti was found, and is explained by different silicide grain size. Analyses performed on patterned samples with doped silicon and poly- Si lines show similar electrical results for TiSi 2 from IMP and PVD deposition; however, fbr p + poly-Si lines, the IMP samples displayed correct TiSi 2 formation down to 0.18µm line width, while the PVD wafers showed discontinuous results at these minimum feature sizes.

Ultrathin NO/N 2 O Oxynitride Dielectric For Advanced Flash Memory Application: Single Wafer and Batch Technology

In this paper a systematic investigation of nitrided oxides obtained by Rapid Thermal Oxidation/Nitridation (RTO/RTN) in AMAT Centura System is reported. Two different aspects were considered: first the comparison between single wafers and batch technology, second the different possible oxide architecture achievable with RTO/RTN system (i.e. RTO + RTN, RTN + RTO, RTN + RTO + RTN). Both morphological and patterned wafers were processed. Physical and chemical characterizations were carried out by means of SIMS, XPS, ELYMAT, AFM and Etching Rate studies. Morphological results were then correlated to electrical data obtained on MOS capacitors. The film obtained performing a NO RTN nitridation of the native oxide followed by a ISSG (In Situ Steam Generation) oxidation exhibited very promising electrical properties that made it an appealing candidate as gate dielectric in CMOS and Flash memories applications.