2015 IEEE 65th Electronic Components and Technology Conference (ECTC), 2015
Reliability of gold stud bump bonding must be questioned once process parameters are tweaked and ... more Reliability of gold stud bump bonding must be questioned once process parameters are tweaked and dimensions shrunk to minimize costs for high volume MEMS assembly. 3D mock-up stacks representing a 0.5 x 1.0 mm MEMS die and its read-out integrated circuit were built using thermosonic and thermocompression chip-to-wafer bonding (TSB and TCB) with parameters targeting an optimized throughput. Electrical test circuits, daisy chains and Kelvin structures, were included in the design. Mechanical and electrical characterization was performed on samples directly after bonding and after environmental stressing in the form of thermal cycling and high temperature storage. Bond strength in the range of 40-60 MPa was measured after bonding. No degradation was observed after thermal cycling and an increased strength was measured after high temperature storage. Tilt in the range of 2.2 - 6.6 μm measured using white light interferometry was concluded to be a root cause of a limited yield for TSB. Fractography after shear testing, visual inspection of cross sections and electrical testing supported the hypothesis. On the other hand, tilt was measured to be in the range of 0.3 - 1.3 μm for TCB and this was concluded to be acceptable based on the same inspections and also based on stability of electrical properties measured in situ during environmental stressing. Tilt can be reduced by engineering of bond heads.
2D materials offer excellent possibilities for high performance gas detection due to their high s... more 2D materials offer excellent possibilities for high performance gas detection due to their high surfaceto-volume ratio, high surface activities, tunable electronic properties and dramatic change in resistivity upon molecular adsorption. This paper demonstrates a simple field effect transistor (FET) of molybdenum disulphide (MoS 2) fabricated on a hexagonal boron nitride (hBN) substrate that can detect NO x down to concentrations of 6 ppb and possibly far below at room temperature (RT) with a systematic optimization of the device design and fabrication parameters as well as the device operating conditions. The effects of the substrate, number of MoS 2 layers, channel layout and biasing conditions on the response of MoS 2 FETs to NO x were investigated, providing directions for maximizing the sensitivity. This work also sheds light the issues of recovery and stability and present a methodology for calibration of the sensors which is critical for repeatable and reliable measurements.
Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005., 2005
In this paper, results from investigations of acidic texturing are presented. As-cut, multicrysta... more In this paper, results from investigations of acidic texturing are presented. As-cut, multicrystalline and polished, single crystal Si wafers have been etched in a range of acidic mixtures. The mixtures contained hydrofluoric and nitric acid, with de-ionized water, phosphoric acid or sulphuric acid added as diluents. In the initial phases of the etching process, surface cracks originating from the wafer sawing were transformed into deep and elongated pits. The reflectance of such textures was low. However, as the etching proceeded beyond the damaged surface region, more reflective; hubble-like textures were obtained.
Module-level-processing applies cell processing and/or cell interconnection processes while the s... more Module-level-processing applies cell processing and/or cell interconnection processes while the silicon wafers are attached to a sub-or superstrate, such as the module glass. This thin-film/wafer-hybridsilicon (HySi) approach offers unique possibilities when using ultra-thin silicon wafers that can hardly be processed free-standing. Liquid adhesives are one option for attaching the wafers to the module glass. Here, we analyze the compatibility of a selection of adhesives with module-level processing. The adhesives have to be stable during wet chemical steps and during thermal treatments. A further requirement is that outgassing from the adhesives should be sufficiently low to allow efficient surface passivation by e.g. plasma enhanced chemical vapor deposition. The adhesives have to withstand UVirradiation and thermal exposure in order to fulfill warranty requirements. In this work we develop and apply tests for the screening of adhesives. We find that certain liquid addition-curing 2-part silicones pass all the tests and are thus attractive candidates for module-level-processing.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
The optical properties and etch rates of silicon nitride (SiN x :H) deposited by plasma-enhanced ... more The optical properties and etch rates of silicon nitride (SiN x :H) deposited by plasma-enhanced chemical vapour deposition (PECVD) and their correlation with bond concentrations have been studied. By varying the silane-to-total gas ratio, films with refractive index (n) between 1.92 and 3.00 were deposited. Higher n films had increased absorption and decreased etch rates. Annealing the samples at different temperatures revealed that all films were thermally stable up to 750 1C, above which all experienced a rise in n, attributed mainly to mass densification. The etch rate correlated well the N-H bond concentration for both annealed and as-deposited films.
2015 IEEE 65th Electronic Components and Technology Conference (ECTC), 2015
Reliability of gold stud bump bonding must be questioned once process parameters are tweaked and ... more Reliability of gold stud bump bonding must be questioned once process parameters are tweaked and dimensions shrunk to minimize costs for high volume MEMS assembly. 3D mock-up stacks representing a 0.5 x 1.0 mm MEMS die and its read-out integrated circuit were built using thermosonic and thermocompression chip-to-wafer bonding (TSB and TCB) with parameters targeting an optimized throughput. Electrical test circuits, daisy chains and Kelvin structures, were included in the design. Mechanical and electrical characterization was performed on samples directly after bonding and after environmental stressing in the form of thermal cycling and high temperature storage. Bond strength in the range of 40-60 MPa was measured after bonding. No degradation was observed after thermal cycling and an increased strength was measured after high temperature storage. Tilt in the range of 2.2 - 6.6 μm measured using white light interferometry was concluded to be a root cause of a limited yield for TSB. Fractography after shear testing, visual inspection of cross sections and electrical testing supported the hypothesis. On the other hand, tilt was measured to be in the range of 0.3 - 1.3 μm for TCB and this was concluded to be acceptable based on the same inspections and also based on stability of electrical properties measured in situ during environmental stressing. Tilt can be reduced by engineering of bond heads.
2D materials offer excellent possibilities for high performance gas detection due to their high s... more 2D materials offer excellent possibilities for high performance gas detection due to their high surfaceto-volume ratio, high surface activities, tunable electronic properties and dramatic change in resistivity upon molecular adsorption. This paper demonstrates a simple field effect transistor (FET) of molybdenum disulphide (MoS 2) fabricated on a hexagonal boron nitride (hBN) substrate that can detect NO x down to concentrations of 6 ppb and possibly far below at room temperature (RT) with a systematic optimization of the device design and fabrication parameters as well as the device operating conditions. The effects of the substrate, number of MoS 2 layers, channel layout and biasing conditions on the response of MoS 2 FETs to NO x were investigated, providing directions for maximizing the sensitivity. This work also sheds light the issues of recovery and stability and present a methodology for calibration of the sensors which is critical for repeatable and reliable measurements.
Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005., 2005
In this paper, results from investigations of acidic texturing are presented. As-cut, multicrysta... more In this paper, results from investigations of acidic texturing are presented. As-cut, multicrystalline and polished, single crystal Si wafers have been etched in a range of acidic mixtures. The mixtures contained hydrofluoric and nitric acid, with de-ionized water, phosphoric acid or sulphuric acid added as diluents. In the initial phases of the etching process, surface cracks originating from the wafer sawing were transformed into deep and elongated pits. The reflectance of such textures was low. However, as the etching proceeded beyond the damaged surface region, more reflective; hubble-like textures were obtained.
Module-level-processing applies cell processing and/or cell interconnection processes while the s... more Module-level-processing applies cell processing and/or cell interconnection processes while the silicon wafers are attached to a sub-or superstrate, such as the module glass. This thin-film/wafer-hybridsilicon (HySi) approach offers unique possibilities when using ultra-thin silicon wafers that can hardly be processed free-standing. Liquid adhesives are one option for attaching the wafers to the module glass. Here, we analyze the compatibility of a selection of adhesives with module-level processing. The adhesives have to be stable during wet chemical steps and during thermal treatments. A further requirement is that outgassing from the adhesives should be sufficiently low to allow efficient surface passivation by e.g. plasma enhanced chemical vapor deposition. The adhesives have to withstand UVirradiation and thermal exposure in order to fulfill warranty requirements. In this work we develop and apply tests for the screening of adhesives. We find that certain liquid addition-curing 2-part silicones pass all the tests and are thus attractive candidates for module-level-processing.
Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrate... more Properties and structure of ZnO and ZnO:Al films deposited on c-Si, a-Si:H/Si and glass substrates are studied by various methods. The transmittance of the ZnO:Al was found to be higher when compared to ZnO, and the refractive index lower. X-ray photoelectron spectroscopy (XPS) shows that the screening efficiency in the presence of core holes is enhanced in the Al doped ZnO. The roughness of the ZnO:Al surfaces is strongly substrate dependent. With transmission electron microscopy (TEM) a 2-3 nm thick amorphous interfacial layer was observed independently of substrate and doping. Deposition of ZnO on a-Si:H substrate results in crystallization of the a-Si:H layer independently of Al doping.
The optical properties and etch rates of silicon nitride (SiN x :H) deposited by plasma-enhanced ... more The optical properties and etch rates of silicon nitride (SiN x :H) deposited by plasma-enhanced chemical vapour deposition (PECVD) and their correlation with bond concentrations have been studied. By varying the silane-to-total gas ratio, films with refractive index (n) between 1.92 and 3.00 were deposited. Higher n films had increased absorption and decreased etch rates. Annealing the samples at different temperatures revealed that all films were thermally stable up to 750 1C, above which all experienced a rise in n, attributed mainly to mass densification. The etch rate correlated well the N-H bond concentration for both annealed and as-deposited films.
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Papers by Daniel Wright