Silicon is one of the most important semiconductor materials and the basic material in the field of modern microelectronics, and it has been widely used in microelectronics and photovoltaic industries which are closely related to our daily life. Because the traditional silicon wafer cutting technology has some serious problems such as insufficient cutting accuracy, low efficiency, and serious pollution, the laser processing has been paid more and more attention in silicon wafer cutting applications in about recent fifteen years. Therefore, it is extremely important to develop the laser silicon wafer cutting procedure for the improvement of the laser silicon wafer processing technology. An algorithm named as constrained interpolation profile has been invented in computational fluid dynamics. It is actually a semi-Lagrangian method to solve hyperbolic partial differential equations, and has the advantages of the stable results, compact process, and low dissipation, etc. Focused Gaussian laser beams with the same energy of 200 μJ and pulse widths of 100 fs, 20 ps, and 0.5 ns, respectively, were irradiated on the surface of a silicon wafer. The physical properties of density, temperature, and pressure in both time and space domains were obtained by means of the algorithm of constrained interpolation profile in the laser processing simulation. The mechanisms of laser silicon wafer processing were studied in detail by analyzing the changes in physical properties of silicon material. The conclusions of this paper might be useful in the optimization of a silicon wafer cutting process by the use of a pulsed laser.
Laser processing plays a key role in treating a lot of materials. The mechanism of laser stealth dicing (SD) is based on irradiation of a laser beam which is focused inside the brittle material. The laser beam scans along the predetermined path, so that the characteristics of the interior brittle material can be changed, the stress layer can be therefore formed. Finally, an external force is applied to separate the brittle material. Since only the limited interior region of a wafer is processed by the laser irradiation, the damages and debris contaminants can be avoided during the SD process. SD has the advantages of a high speed for thinner wafers without any chipping, the smooth section without dust and slag, and completely dry process, which has been widely used in large scale integrated circuits and microelectronic manufacturing systems. However, further studies on the simulation analyze and parameter optimization have kept to be rear for SD so far. In this study, an approach named as constrained interpolation profile (CIP) was adopted, which has the advantages of compactness, stability, and low dissipation in computational fluid dynamics compared with other simulation procedures. We have finished a theoretical simulation to obtain the physical features of the temperature, pressure, density of the silicon substrate at different focal depth where a nanosecond pulsed laser is irradiated, then we found a suitable focal depth with a good dicing quality by analyzing these physical features.
Laser drilling has been more and more widely used in laser machining process. Therefore, optimizing the quality of laser drilling becomes extremely important. We know that laser drilling can be achieved by using high power density of a laser. As light waves with different waveforms represent the different energy distributions in time domain, we believe that the quality of laser drilling should be related to the laser waveform. At present, a laser used in the laser processing usually hasthe waveform with a Gaussian or a Lorentzian distribution. In this study, we numerically simulated the punching quality of a pulsed laser with the Gaussian distribution and a pulsed laser with the top-flat distribution (we called it as a square-shaped laser pulse) at the same energy. It mainly refers to the changes of density, temperature, and pressure of the target materials under the same energy for different waveforms. The constrained interpolation profile algorithm has been used to simulate the machining process. Until now, there are few studies on the features of laser drilling with different waveforms in time domain. This paper provides a new method to optimize the quality of laser drilling.
Laser processing plays a key role in treating a lot of materials. The visible nanosecond laser processing based on a tripartite-interaction system has been proved to be an effective method of processing materials with high optical transparency, which has the advantages of low cost, high efficiency, and simplicity over the direct processing by using a femtosecond laser. However, further studies on the theoretical mechanism and parameter optimization keep to be rear for the hybrid tripartite-interaction laser processing. In this study, we have carried out the confirmatory experiment and numerical simulation of laser processing with a tripartite-interaction system, which includes a visible nanosecond laser (19 ns@532 nm), a piece of transparent glass, and a copper foil. The experiment indicates that drilled holes can be obtained on the glass sheets by using the visible nanosecond laser. The numerical results, which have been obtained by an approach named as constrained interpolation profile, reveal that the processing mechanism is based on the heat conduction, generation of stress and ablation between the glass and the copper foil. Our results could to be useful for the development of visible nanosecond laser processing in industrial applications.
It has always been difficult to process a metal film with high reflectivity in the field of manufacture, industry, medicine, and military, etc. Since much of the laser energy can be reflected especially when the reflectance of the target film surface is high, it is hard to process such a metallic film by laser radiation as the energy absorbed by the film material is very little. In this paper, we used a nanosecond pulsed laser to scribe some patterns on a smooth titanium (Ti) film, and investigated the surface morphology of a Ti film ablated by different laser spot sizes and laser energy. In our experiments, it has been found that the Ti film can be efficiently processed although the surface reflectance of the Ti film is about 57% at the wavelength of 532 nm. We also see that the processing range of the Ti film will decrease when the diameter of a laser beam increases. The experimental results show that the ablated status of the surface of a Ti film for a just-focus beam is much better than that for a defocus beam under the same laser power. Furthermore, the higher the laser power, the larger the processed area. By using the optimal parameters we obtained, we also produced some hole matrices and line patterns on a glass-based Ti film by employing a short pulsed laser. The processed samples were observed with a reflecting microscope and a transmitting microscope, respectively. Our research results can play an important role in the selection of laser parameters for laser processing of some materials with a high reflectivity.
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