Identification of some key parameters for photoelectric laser stimulation of IC: an experimental approach (original) (raw)
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Picosecond laser drilling of silicon with applied voltage
SN Applied Sciences, 2018
The short pulse duration of a picosecond laser (ps) leads to high peak power and ablates materials with much reduced thermal effects. Commercial ps lasers generate high-repetition-rate pulses and become more accepted as a major tool for material removal applications. However, most of the commercial ps lasers emit pulses at infrared (IR) wavelengths with photon energy close to the Si band gap energy of 1.1 eV. The corresponding optical absorption coefficient is low. To improve the laser beam absorption in Si, several methods have been investigated. For instance, it is reported that the material removal efficiency has been improved by raising the substrate temperatures during laser drilling due to the enhancement of the Si absorption coefficient. However, such approach may result in reduction in machining accuracy due to thermal expansion of the substrate. In this paper, we propose a new method by applying a direct current (DC) across a silicon substrate during the ps laser drilling process. The externally applied voltage potential would lead to more aligned movement of free electrons and therefore increase electrical current flow in the silicon substrate. The hypothesis of this study is that more free electrons are made available in the Si substrate for collisions with the laser photons, which increases the Si absorption coefficient of the laser beam. It was found that the material removal is markedly improved with the assistance of the electrical current flow. The entrance hole diameter increased by 14% and the exit hole diameter increased by 90% when the current in the Si substrate was subjected to a fixed current of 0.5 A. However, a larger amount of material debris covering an enlarged surface area was observed under the applied DC voltage. The possible reasons for such observations are discussed based on the enhanced laser energy absorption as the result of the presence of electrical current in the Si substrate.
Microelectronics Reliability, 2012
This paper presents the electrical model of a PMOS transistor in 90nm technology under 1064nm Photoelectric Laser Stimulation. The model was built and tuned from measurements made on test structures. It permits to simulate the effect of a continuous wave laser on a PMOS transistor by taking into account the laser's parameters (i.e. spot size and location, or power) and the PMOS' geometry and bias. It offers a significant gain of time by comparison with experiments and makes possible to build 3D photocurrent cartographies generated by the laser on the PMOS.
Proceedings of the 20th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA), 2013
This paper presents the electrical model of an NMOS transistor in 90nm technology under 1064nm Photoelectric Laser Stimulation. The model was built and tuned from measurements made on test structures and from the results of physical simulation using Finite Element Modeling (TCAD). The latter is a useful tool in order to understand and correlate the effects seen by measurement by given a physical insight of carrier generation and transport in devices. This electrical model enables to simulate the effect of a continuous laser wave on an NMOS transistor by taking into account the laser's parameters (i.e. spot size and power), spatial parameters (i.e. the spot location and the NMOS' geometry) and the NMOS' bias. It offers a significant gain of time for experiment processes and makes it possible to build 3D photocurrent cartographies generated by the laser on the NMOS, in order to predict its response independently of the laser beam location.
Laser ablation of Silicon for the Buried Contact Solar Cells application
Creating grooves to make the metal buried is one of the important steps in the production of a buried contact solar cell. Various techniques are used to ablate the material such as photolithography, diamond scratching, chemical etching, and laser ablation. Laser ablation is an ultra-fast, easy, and reliable method to ablate material from a silicon wafer. Thus, in the present study, I have developed a onedimensional laser heating model of the nanosecond laser to predict the temperature profile. Further, the effects of different laser parameters such as the average laser power, repetition rate of the pulse, and width of the pulse are also observed on the temperature generated during the laser matter interaction. From the study it is found that the surface temperature increases with power, whereas with increase in pulse width and pulse repetition rate, the surface temperature decreases. Furthermore, with an 80% decrease in power, a 70% reduction in surface temperature is observed and with an 80% reduction in pulse width, a 30% increase in surface temperature is observed. A 30% increase in the repetition rate of the pulse leads to the surface temperature being halved. These indicates that laser power has the highest influence on surface temperature followed by pulse repetition rate and pulse width.
Laser induced plasma can be used for rapid optical diagnostics of electronic, optical, electro-optical, electromechanical and other structures. Plasma monitoring and diagnostics can be realized during laser processing in real time by means of measuring optical emission that originates from the pulsed laser-material interaction. In post-process applications, e.g., quality assurance and quality control, surface raster scanning and depth profiling can be realized with high spatial resolution (~10 nm in depth and ~3 μm lateral). Commercial instruments based on laser induced breakdown spectrometry (LIBS) are available for these purposes. Since only a laser beam comes in direct contact with the sample, such diagnostics are sterile and non-disruptive, and can be performed at a distance, e.g. through a window. The technique enables rapid micro-localized chemical analysis without a need for sample preparation, dissolution or evacuation of samples, thus it is particularly beneficial in fabrication of thin films and structures, such as electronic, photovoltaic and electro-optical devices or circuits of devices. Spectrum acquisition from a single laser shot provides detection limits for metal traces of ~10 μg/g, which can be further improved by accumulating signal from multiple laser pulses. LIBS detection limit for Br in polyethylene is 90 μg/g using 50-shot spectral accumulation (halogen detection is a requirement for semiconductor package materials). Three to four orders of magnitude lower detection limits can be obtained with a femtosecond laser ablation – inductively coupled plasma mass spectrometer (LA-ICP-MS), which is also provided on commercial basis. Laser repetition rate is currently up to 20 Hz in LIBS instruments and up to 100 kHz in LA-ICP-MS.
Nanosecond pulsed laser ablation of silicon in liquids
Applied Physics A, 2009
Laser fluence and laser shot number are important parameters for pulse laser based micromachining of silicon in liquids. This paper presents laser-induced ablation of silicon in liquids of the dimethyl sulfoxide (DMSO) and the water at different applied laser fluence levels and laser shot numbers. The experimental results are conducted using 15 ns pulsed laser irradiation at 532 nm. The silicon surface morphology of the irradiated spots has an appearance as one can see in porous formation. The surface morphology exhibits a large number of cavities which indicates as bubble nucleation sites. The observed surface morphology shows that the explosive melt expulsion could be a dominant process for the laser ablation of silicon in liquids using nanosecond pulsed laser irradiation at 532 nm. Silicon surface's ablated diameter growth was measured at different applied laser fluences and shot numbers in both liquid interfaces. A theoretical analysis suggested investigating silicon surface etching in liquid by intense multiple nanosecond laser pulses. It has been assumed that the nanosecond pulsed laser-induced silicon surface modification is due to the process of explosive melt expulsion under the action of the confined plasma-induced pressure or shock wave trapped between the silicon target and the overlying liquid. This analysis allows us to determine the effective lateral interaction zone of ablated solid target related to nanosecond pulsed laser illumination. The theoretical analysis is found in excellent agreement with the experimental measurements of silicon ablated diameter growth in the DMSO and the water interfaces. Multiple-shot laser ablation threshold of sil-icon is determined. Pulsed energy accumulation model is used to obtain the single-shot ablation threshold of silicon. The smaller ablation threshold value is found in the DMSO, and the incubation effect is also found to be absent.
Proceedings, 2012
This study responds to our need to optimize failure analysis methodologies based on laser/silicon interactions, using the functional response of an integrated circuit to local laser stimulation. Thus it is mandatory to understand the behavior of elementary devices under laser stimulation, in order to model and anticipate the behavior of more complex circuits. This paper characterizes and analyses effects induced by a static photoelectric laser on a 90 nm technology PMOS transistor. Comparisons between currents induced in short or long channel transistors for both ON and OFF states are made. Experimental measurements are correlated to Finite Elements Modeling Technology Computer Aided Design (TCAD) analyses. These physical simulations give a physical insight of carriers generation and charge transport phenomena in the devices.