Nanoscale strain characterisation of modern microelectronic devices

PhD ThesisSources of stress and strain in modern microelectronics can be either beneficial to the electrical performance or detrimental to the mechanical integrity and ultimately lifetime of the device. Strain engineering is commonplace in state-of-the-art device fabrication as a means to boost performance in the face of device scaling limitation. The strain present in the device is directly related to the improvement factor and as such precise measurements and good understanding are of utmost importance due to the many thermal processing steps that can induce or cause relaxation of the strain. Front-end-of-line (FEOL) strain characterisation is becoming increasingly challenging due to the small volumes of material and nanoscale feature sizes being analysed. In this work, an extensive survey of strain characterisation techniques was undertaken. Narrow sSOI stripes were profiled using conventional Raman spectroscopy. Unlike with previous studies, it was shown that it is possible to achieve nanoscale measurements using current techniques. This study was supported by ANSYS FE simulation. The review of the literature briefly investigates the possibility of EBSD as a strain measurement tool. It is possible to calculate not just an absolute strain value as achievable with Raman spectroscopy, but the strain tensor. However, this is a difficult and complex process and not necessary for use in industry. This study proposes the possibility of a more simple method that would provide a good calibration technique to confirm Raman measurements. SERS and TERS are explored in detail as the most promising techniques when dealing with device scaling. Currently, SERS is a destructive technique not suitable for use in a highly cost driven industry such as semiconductor manufacturing. While it theoretically gives improved surface selectivity over conventional Raman spectroscopy, there is no improvement to the xy spatial resolution. With Si and SiGe samples, this study concludes there is also often no surface selectivity with either technique and the mechanisms behind the enhancement are not understood to the point of being able to implement the techniques in a process line. However, where a non-destructive technique is desired, outlined in this study is a method of achieving the SERS effect without sacrificing the sample. Aggressive scaling has forced the dimensions of the interconnecting wires that give the devices functionality to the deep submicron range. Copper, Cu has been introduced as a replacement to the traditionally used aluminium, Al because of its superior electrical and mechanical properties and scalability. However, as these wires begin to approach the dimensions of thin foils, the microtexture of the wires becomes significantly different from their bulk counterparts. This can affect the mechanical integrity of the interconnects and this has an impact on the reliability of the device. Failure mechanisms such as blistering, cracking and peeling caused by stress and strain are not uncommon and traditional methods of characterising residual stress in the thin films is no longer applicable to these narrow wires. The mechanical properties and microtexture of thin copper films annealed at temperatures comparative to those found in device manufacturing were characterised in some detail. EBSD was used to determine the grain size and structure of the films before nanoindentation confirmed properties such as hardness and elastic modulus. These results pave the way for investigation of strain applied along deep-submicron interconnects to lead to further understanding of what causes failure mechanisms from interconnecting wires

Development of mechanical reliability testing techniques with application to thin films and piezo MEMS components

This work focuses on the development of a method for probing the mechani- cal response of thin film materials based on miniature tensile testing. A number of mechanisms that may compromise the performance and potentially limit the operational lifetime of MEMS devices which incorporate functional ferroelectric ceramics were also identified and investigated. Reliability of piezo MEMS com- ponents was studied at a wafer and at a device level through the development of appropriate techniques based on miniature tensile testing, time- resolved mi- cro RAMAN spectroscopy and laser Doppler vibrometry. Micro tensile testing was further used for the extraction of the elastic properties of various thin film materials. A miniature tensile stage was developed in common with DEBEN UK for the mechanical characterization of functional thin film materials like PZT and ZnO ceramics, which are commonly used in MEMS fabrication. The stage is of- fered with a piezo electric motor which can be fitted with interchangeable heads. These can be combined with di.erent types of mounting jaws, enabling both con- ventional tensile testing and compression testing to be performed. Strains and displacements were measured in- situ using an optical, non destructive method based on CCD imaging. The elastic constants of polymer (LCP), LCP-Au bi- layers and electroplated Ni were defined in good agreement with the literature. However yield of successfully released ceramic samples was rather poor so a col- laboration with IMTEK at Germany was established. Using their facilities batch processing of a large number of wafers was possible. Cont/d.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of mechanical reliability testing techniques with application to thin films and piezo MEMS components

This work focuses on the development of a method for probing the mechani- cal response of thin film materials based on miniature tensile testing. A number of mechanisms that may compromise the performance and potentially limit the operational lifetime of MEMS devices which incorporate functional ferroelectric ceramics were also identified and investigated. Reliability of piezo MEMS com- ponents was studied at a wafer and at a device level through the development of appropriate techniques based on miniature tensile testing, time- resolved mi- cro RAMAN spectroscopy and laser Doppler vibrometry. Micro tensile testing was further used for the extraction of the elastic properties of various thin film materials. A miniature tensile stage was developed in common with DEBEN UK for the mechanical characterization of functional thin film materials like PZT and ZnO ceramics, which are commonly used in MEMS fabrication. The stage is of- fered with a piezo electric motor which can be fitted with interchangeable heads. These can be combined with di.erent types of mounting jaws, enabling both con- ventional tensile testing and compression testing to be performed. Strains and displacements were measured in- situ using an optical, non destructive method based on CCD imaging. The elastic constants of polymer (LCP), LCP-Au bi- layers and electroplated Ni were defined in good agreement with the literature. However yield of successfully released ceramic samples was rather poor so a col- laboration with IMTEK at Germany was established. Using their facilities batch processing of a large number of wafers was possible. Cont/d.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Holographie électronique en champ sombre (une technique fiable pour mesurer des déformations dans les dispositifs de la microélectronique)

Les contraintes font maintenant partie des boosters de la microélectronique au même titre que le SOI (silicium sur isolant) ou le couple grille métallique / diélectrique haute permittivité. Appliquer une contrainte au niveau du canal des transistors MOSFETs (transistors à effet de champ à structure métal-oxyde-semiconducteur) permet d'augmenter de façon significative la mobilité des porteurs de charge. Il y a par conséquent un besoin de caractériser les déformations induites par ces contraintes à l'échelle nanométrique. L'holographie électronique en champ sombre est une technique de MET (Microscopie Électronique en Transmission) inventée en 2008 qui permet d'effectuer des cartographies quantitatives de déformation avec une résolution spatiale nanométrique et un champ de vue micrométrique. Dans cette thèse, la technique a été développée sur le microscope Titan du CEA. Différentes expériences ont été réalisées afin d'optimiser la préparation d'échantillon, les conditions d'illumination, d'acquisition et de reconstruction des hologrammes. La sensibilité et la justesse de mesure de la technique ont été évaluées en caractérisant des couches minces épitaxiées de Si_{1-x}Ge_{x}/Si et en effectuant des comparaisons avec des simulations mécaniques par éléments finis. Par la suite, la technique a été appliquée à la caractérisation de réseaux recuits de SiGe(C)/Si utilisés dans la conception de nouveaux transistors multi-canaux ou multi-fils. L'influence des phénomènes de relaxation, tels que l'interdiffusion du Ge et la formation des clusters de b-SiC a été étudiée. Enfin, l'holographie en champ sombre a été appliquée sur des transistors pMOS placés en déformation uniaxiale par des films stresseurs de SiN et des sources/drains de SiGe. Les mesures ont notamment permis de vérifier l'additivité des deux procédés de déformation.Strain engineering is now considered as one of the most important boosters of microelectronics among other technologies such as SOI (Silicon On Insulator) and high- metal gates. By applying a stress in the channel of MOSFET (Metal Oxyde Semiconductor Field Effect Transistor) devices, the charge carriers mobility can be significantly increased. Consequently, there is now a need for a strain metrology at the nanometer scale. Dark-field electron holography is a TEM (Transmission Electron Microscopy) technique invented in 2008 that allows to map strain with micrometer field-of-view and nanometer spatial resolution. In this thesis, the technique was developed on the CEA Titan microscope. First, different developements were carried out concerning the sample preparation, the illumination/acquisition conditions and the reconstruction of the holograms. The sensitivity and the accuracy of the technique were evaluated through the characterization of Si_{1-x}Ge_{x} layers epitaxied on Si and by comparing the results with mechanical finite element simulations. Then, the technique was applied to the study of annealed SiGe(C)/Si superlattices that are used in the construction of new 3D architectures such as multichannel or multiwires transistors. The influence of the different relaxation mechanisms on the strain especially Ge interdiffusion and b-SiC clusters formation was investigated. Finally, dark-field electron holography was applied to the characterization of uniaxially strained pMOS transistors by SiN liners and recessed SiGe sources and drains. The measurements allowed to confirm the strain additivity of the two processes.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF