Photovoltaic energy conversion devices are on a rapidly accelerating growth path driven by increasing government and
societal pressure to use renewable energy as part of an overall strategy to address global warming attributed to
greenhouse gas emissions. Initially supported in several countries by generous tax subsidies, solar cell manufacturers
are relentlessly pushing the performance/cost ratio of these devices in a quest to reach true cost parity with grid
electricity. Clearly this eventual goal will result in further acceleration in the overall market growth. Silicon wafer
based solar cells are currently the mainstay of solar end-user installations with a cost up to three times grid electricity.
But next-generation technology in the form of thin-film devices promises streamlined, high-volume manufacturing and
greatly reduced silicon consumption, resulting in dramatically lower per unit fabrication costs. Notwithstanding the
modest conversion efficiency of thin-film devices compared to wafered silicon products (around 6-10% versus 15-20%), this cost reduction is driving existing and start-up solar manufacturers to switch to thin-film production. A key
aspect of these devices is patterning large panels to create a monolithic array of series-interconnected cells to form a low
current, high voltage module. This patterning is accomplished in three critical scribing processes called P1, P2, and P3.
Lasers are the technology of choice for these processes, delivering the desired combination of high throughput and
narrow, clean scribes. This paper examines these processes and discusses the optimization of industrial lasers to meet
their specific needs.
Photovoltaics has in the last five years enjoyed unprecedented growth and acceptance as part of the worldwide energy mix. Innovations in both wafered silicon and various thin-film PV technologies anticipated in the next 5-10 years promise to lower the cost of PV power to parity with that supplied by the grid. When that occurs, the growth of the industry will be pulled even more strongly by market demand. A challenge in meeting this growth will be the availability of automated production equipment that can streamline the solar cell manufacturing process. Laser processing offers the potential to provide several facets of that high-volume manufacturing solution. This paper provides an overview of PV technologies, discusses current and emerging laser processes for PV manufacturing, and highlights some of the challenges for laser technology and systems that must be met to fulfill this promise.
Semiconductor manufacturing, is dominated by the relentless demand for electronic products with greater performance, minimized dimensions, increased sophistication, and higher speed, all at reduced process cost. Logic device manufacturers need to satisfy this demand by producing integrated circuits that meet the predicted density increase encapsulated in Moore's law. This has led to the use of low-κ dielectrics. For memory devices, thinner wafers are used to enable close stacking of multiple dies in a single low-profile package. And in a third market segment, newer photonic devices are using novel materials such as GaAs, SiC, GaN and sapphire. Traditional mechanical methods are struggling to meet the singulation needs in all three of these device types. Yet at the same time, market realities dictate that the effective cost for increased processing power, novel photonic performance, and higher memory density all continue to fall. As a result, laser-based methods are being adopted in all three areas. In this overview paper, we examine the drivers for each of these market segments and see how laser technology is meeting the singulation demands of current and future devices.
A necessary step in the fabrication of many different flat panel display types is the selective removal of a thin layer of indium tin oxide (ITO) or other transparent conductor from the substrate to create circuit patterns. The conventional method of performing this patterning utilizes photolithography. Specifically, an image of the desired pattern is projected on to a photoresist coated substrate, and this substrate is then developed and etched with wet chemicals. However, it is possible to use a laser to directly ablate ITO without damaging the substrate, and thus eliminate all the expense, time and environmental concerns associated with a multi-step wet chemical process. First generation laser based systems for ITO patterning were too slow to be competitive with traditional means, however, laser manufacturers are focused on developing sources that enable the required process speed, and also possess desirable characteristics in
terms of lifetime, maintenance downtime, and overall cost-of ownership. This paper examines the requirements for an optimum laser source to service this emerging laser application.
Lasers continue to gain ground in materials processing applications for microelectronics manufacturing. Printed circuit boards, IC wafers, substrates for blue/green LEDs, and various components in flat panel displays are all being processed with lasers. Some of these operations, such as microvia drilling in high-density circuit boards, are well established; others are under evaluation or in early stages of development. This paper summarizes the status of a number of key applications that currently or potentially add value to the complex manufacturing processes for state-of-the-art microelectronic devices. Particular attention is paid to flat panel display manufacturing, where the worldwide massproduction ramp currently underway is demanding innovative techniques that provide the speed, quality, or flexibility needed to reduce manufacturing costs.
Laser processing of glass components is of significant commercial interest for the optoelectronics and telecommunications industries. In this paper, we present laser processing techniques using microsecond, nanosecond, and femtosecond lasers for machining of glass. Surface structures, mainly groove geometries, are generated with a diode-pumped solid-state nanosecond pulsed UV laser operating at 266 nm, a Q-switched CO2 laser operating at 9.25 μm, a CO2 laser operating at 10.6 μm and the femtosecond pulsed laser operating at 800 nm. Grooves are cross-sectioned and viewed with a focused ion beam (FIB) microscope. The resultant material structures are examined with respect to the differences in time scale and the appropriateness of each laser type for particular processes.
As the demand for semiconductor devices based upon ever-thinner silicon substrates continues to increase, mechanical techniques suitable for dicing wafers appear to be approaching their practical limits. Recent advances in power scaling have now enabled reliable ultraviolet-wavelength lasers to be considered to offer a flexible solution to this dilemma. This paper presents new data on the machining of thin silicon wavers using a high average power 355-nm wavelength pulsed laser. In particular, the concept of pulse repetition-rate scaling of the effective cutting speeds was investigated to determine the preferred direction for further laser development efforts.
This paper presents a new CO2 laser technology for precision microfabrication applications. The laser produces short (microsecond) pulses at very high pulse repetition frequencies (PRFs). In contrast, most commercial CO2-laser micromachining applications employ one of two type of CO2 lasers: RF-excited with external pulse modulation, and TEA lasers. The laser technology presented here produces pulses sharing some of the characteristics of the TEA CO2 laser, but is capable of delivering them at much higher PRFs (20-100 kHz). Microfabrication applications to date are primarily microdrilling in common electronic circuit board and IC packaging materials, including unreinforced, glass-fiber reinforced, and particle-filled epoxies. These materials are processed using pulse energies lower than those generally used by conventional CO2 laser designs, and at speeds typically 1.5 to three times as fast as achieved by conventional CO2 laser drills.
Laser drilling has emerged in the last five years as the most widely accepted method of creating microvias in high-density electronic interconnect and chip packaging devices. Most commercially available laser drilling tools are currently based on one of two laser types: far-IR CO2 lasers and UV solid-state lasers at 355 nm. While CO2 lasers are recognized for their high average power and drilling throughput, UV lasers are known for high precision material removal and their ability to drill the smallest vias, with diameters down to about 25 –30 micron now achievable in production. This paper presents an overview of techniques for drilling microvias with the lasers.
Laser drilling has emerged in the last five years as the most widely accepted method of creating microvias in high- density electronic inter connect and chip packaging devices. Most commercially available laser drilling tools are currently based on one of two laser types: far-IR CO2 lasers and UV solid state lasers at 355 nm. While CO2 lasers are recognized for their high average power and drilling throughput, UV lasers are known for high precision material removal and their ability to drill the smallest vias, with diameters down to about 25-30 micrometers now achievable in production. This paper presents a historical overview of techniques for drilling microvias with UV solid state lasers. Blind and through via formation by percussion drilling, trepanning, spiralling, and image projection with a shaped beam are discussed. Advantages and range of applicability of each technique are summarized. Drivers of throughput scaling over the last five years are outlined and representative current-generation performance is presented.
Laser micromachining has been a part of the manufacturing process for semiconductors and microelectronics devices for several decades. More recent applications such as the drilling of microvia holes in high-density electronic packages have recently entered broad industrial use for high-volume production. In such applications, process stability and throughput are key drivers of commercial success. Particularly in the UV, where solid-state laser power is growing rapidly but is still limited to less than 10 watts, innovations that permit the available laser power to be applied at the work surface more efficiently are of interest. Within the last two years, the use of beam shapers to create round laser spots with near-uniform irradiance at the work surface has been demonstrated. Shaping the irradiance profile has been shown to both increase process speed and improve the quality of the drilled holes, which range in diameter between 20 and 150 micrometers . This paper gives an historical overview of laser via drilling, presents the Gaussian-to-flattop beam shaping optics used in the microvia laser drills, and discusses the process results obtained.
The use of lasers in microelectronics is production for trimming, ablating, drilling and general micromachining continues to grow. As one example, traditional laser trimming techniques for passive and active microelectronic circuits have been used for nearly thirty years to improve yields and/or device performance. The majority of these processes have been accomplished using the fundamental wavelengths of the Nd:YAG laser source. However, recent technological advances in microelectronics laser processing, mainly for hybrid integrated circuits (HIC), dynamic random access memories (DRAM) and printed wiring boards (PWB) have resulted in new process techniques. Several new technologies, such as alternative wavelength processing and shaped, uniform laser spots have produced better processing quality, higher reliabiltiy, and greater yields. This paper will review the past, present and future of laser micromachining in microelectronics.
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