If money makes the world go round, then perhaps electronics provide a gravitational pull – something of a central part of modern civilisation.
A broad business and a lucrative market, electronics encompasses a vast array of applications and processes throughout the manufacturing chain. From semiconductors to solar cells and packaging to performance TFT-LCD systems, a diverse selection of industrial, electronic, process, high purity and specialty gases are put to good effect in this busy business.
When thinking of the electronics industry the most commonly referred to gases tend to be silane, nitrogen trifluoride (NF3), ammonia and high purity nitrogen. There are also an assortment of carrier gases which fulfil an equally significant role within the electronics and semiconductor industry, with each gas used in a varying degree or quantity.
According to The Linde Group’s 2007 Annual Report, demand for electronic gases in the semiconductor and solar cell industries continues to outpace global GDP growth by more than two times.
This demand is driven by the use of gases across the whole electronics manufacturing chain, with four key elements that comprise this sector – notably electronic gases, high purity core gases, services,
High purity air gases are fundamental, as nitrogen is utilised as a carrier gas for reactive agents and both nitrogen and argon are used in applications requiring an inert environment or atmosphere.
Oxygen is employed in the oxidation of silicon, while growth in helium use is increasingly arising from its prevalent service in the electronics field as its good thermal conductivity and high diffusibility find application in the manufacturing of fibre optic cables and semiconductors, laser technology and space systems.
In other stages of the manufacturing process gases such as silane, dichlorosilane and trichlorosilane are used in processes such as epitaxy in chemical vapour deposition (CVD), to deposit layers of silicon directly onto a single crystal silicon substrate.
Of such demand in electronics at present is silane, that Japan’s KK Gas Review recently reported of the market dynamics for this somewhat chemically complex, colourless gas.
In terms of the volume consumed, there is said to be growth in the existing markets for use in the semiconductor and liquid crystal areas, while photovoltaic (PV) power generation systems account for 10% of the silane market.
The expansion in the volume of gas consumed in accordance with the increasingly larger size of the glass substrate stands out especially so, in the liquid crystal field. If demand for use within PV power systems goes into full swing, supply capacity is unlikely to keep up with demand.
The developing trends in the market for silane and other electronic gases are influenced by a number of aspects including process changes and the development of new methods.
Steve Pilgrim, Global Marketing Manager for Linde Electronics, explains, “Changes in gas use over the years are largely attributable to process changes, industry growth, and environmental factors. Much of the volume growth in more common gases has been driven by the emergence of new electronic sectors like LCD, while the growth in the complexity of te portfolio has been driven by the relentless pursuit of ever higher performing chips by the semiconductor industry. That pursuit is now close to the realms of science fiction, as we talk about layers whose thickness is measured in single atoms and a range of materials that spand most of the periodic table.”
“For instance, the development of metalisation processes led to the introduction of tungsten hexafluoride, a high priced material that requires special cylinder materials to be used to maintain purity.”
“The move from batch deposition processes in quartz furnace tubes that were wet cleaned off-line, to single wafer deposition chamber type tools has led to the development of in situ chamber cleaning, which spawned the NF3 demand. Environmental factors have led to the reduction in use of many halocarbons. As device geometries shrink many new materials are being developed by gas companies, even though many are not gas based,” he added.
The electronics industry is then, both diverse and developing. As technology advances, so too do the trends for gas usage and consumption, with the semiconductor industry swallowing a large amount of the gas consumption in electronics.
There are more than five hundred steps to manufacture a state-of-the-art semiconductor, all using gases to varying degrees. More than twenty different gases are known to be used in semiconductor manufacture, playing a versatile role in a wide range of steps in the process chain.
Electronic gases are applied for layer deposition, etching, doping, layer removal and cleaning process chambers, while gases such as nitrogen, argon, helium, hydrogen, ammonia, sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3) are consumed in vast quantities.
Describing where these gases and more can be found in the semiconductor industry, Linde’s Pilgrim comments, “There are four main areas in semiconductor processing that use significant quantities of gases - doping, deposition, etching, and cleaning. Forty-plus different gases might be used by a typical fab (compared to 15-20 for LCD’s or solar cell).”
“Inerting uses large volumes of nitrogen and other inert gases. The purity of these inert gases is critical as the silicon wafers, and entire fabric of the production system, are exposed to these gases for long periods of time, probably longer than the more active gases.”
Typical gases used in the doping process, as Pilgrim points out, are arsine, phosphine, diborane and boron trifluoride, used to modify the local electrical properties of the semiconductor material to create microscopic transistors.
The process of plasma etching (involving various layers), relies largely on the consumption of inert fluorocarbons such as halocarbons, trifluoromethane and hexafluoroethane, while deposition utilises ammonia, silane and silicon compounds, nitrous oxide, and tungsten hexafluoride among others.
Finally, in the process area of CVD chamber cleaning and ultra levels of cleanliness, gases such as nitrogen trifluoride and the more environmentally friendly fluorine (F2) are employed to remove any contaminants or stray molecules – in a practice which is of immense importance to the success of the manufacturing process.
The use and supply of nitrogen trifluoride has, in fact, been of such a trend that production capacities by some of the gas majors have had to increase to keep-up with demand. Air Products had announced capacity increases in December 2007, expanding production in the markets of Schulfkill County and Korea by 28% to reach 3,200 tpy in the first half of 2009.
Commenting on this market dynamic, Pilgrim said, “The initial demand for NF3 led to a period of severe shortage and high prices. The principal suppliers all added capacity and brought the supply & demand back into balance. Within semiconductors, silane supply has never really been an issue, aside from the obvious safety need for safe handling. The growth in solar cell manufacturing is about to change this again.”
Burning bright – solar cells
If there had been a few murmurs of concern regarding the supply and demand of silane, nitrogen trifluoride and other such gases, this issue could be set to resurface again in the future as the world sees the light and there is more and more adoption of the solar cell industry.
While growth of around 8% per year until 2010 is expected in traditional semiconductor segments such as microchips and flat panel displays, the annual anticipation for the solar sector lies at around 30%.
According to Linde’s 2007 Annual Report, industry experts expect that from 2012, photovoltaic producers will spend more on gases than flat-screen manufacturers. Furthermore, from 2017 these are set to overtake the chip sector.
This growth in the solar cell industry is affirmed by Pilgrim as he says, “I think the key thing to note is that the industry is not new, but the latest process development (thin film cells) is going to need large volumes of H2 & Silane to deposit the film, and CVD chamber cleaning gases (traditionally NF3, but increasingly F2 on cost and environmental grounds) to cope with the predicted demand.”
“A medium sized thin film solar fab represents a large investment in gas & supply chain infrastructure by the supplier, often in ‘new’ geographies as far as use of some of these gases is concerned, such as Spain and India. In the short term, just as in the earlier NF3 case, demand is likely to outstrip supply, especially for silane, before gas companies make the required investments,” he added.
Although only a handful of different gases are used in solar cell manufacturing, compared with semiconductor production, the volumes required are quite considerably larger and if the expectedly rapid rise of solar power takes place, this could present quite a demand for electronic gases.
As energy alternatives are constantly sought for a sustainable future, solar energy is prospering around the world and experiencing a particular upturn in Spain, Italy and India – driven by the local climate.
Spain’s first thin-film solar cell production facility is under development, while Germany leads the field along with Japan and a project has been launched in Austria to build the nation’s first PV cell plant. Just as in Europe, new production plants are believed to be emerging in India and throughout East Asia.
Thin-film solar cell technology is, perhaps, the hottest new trend at present, providing increased gases demand and attracting investment from the gases industry and beyond.
Similar to the production of microchips, the process of producing crystalline solar cells is based on silicon wafers and therefore consumes a large degree of silicon. With the new wave of thin-film solar cells however, this is no longer a wafer-based process and instead, the silicon is deposited in several thin layers onto other substrate materials such as glass, foil, or ceramic.
The key benefit of thin film cells is that they can be manufactured in much larger sizes, offering potentially much lower cost, which will widen their application into areas such as electricity-generating panels on the exterior of buildings.
This versatility and greater efficiency lends itself to the strong growth in this area, as do a number of environmental factors.
“Growth is rapid at the moment. If the holy grail of ‘grid parity’ is achieved for solar, the growth could be extraordinary. As cell efficiency increases and costs reduce, this milestone is expected to be within grasp over the coming years. Both leading gas materials companies like Linde, and production equipment manufacturers like Applied Materials and Oerlikon are investing significant sums to develop cost reducing technologies,” explains Pilgrim.
The solar cell industry is prospering at present and looks set to boom further in the future, but what other trends could be on the horizon?
Speaking loosely of the possible developments to come in this wired industry, Pilgrim suggests, “New gases? Looking into my crystal ball - carbon nanotubes are a potentially interesting development for use as interconnects in microcircuits. Not sure if they would be grown in situ, or in bulk elsewhere and deposited.....either way a lot of new carbon source gases may be needed.$quot;
$quot;Plus as I said earlier, the gas companies are evolving into broader materials suppliers, developing non-traditional materials to enable technology development, especially in semiconductors.”
The process of integrated circuit packaging or simply ‘packaging’ as it’s known, is the final stage of the semiconductor fabrication chain and a significant consumer of gases too.
The packaging stage of production generally refers to the technology of mounting or interconnecting of devices, such as the soldering of components to circuit boards for example.
While this could seem as merely applying the finishing touches to a complex, gas-consuming semiconductor process, there is often much more to this and certainly a glowing demand for various gases.
Steve Pilgrim comments, “The soldering of finished components to circuit boards was the first application in this area, requiring large volumes of N2 for inerting. Recent developments at the silicon die packaging stage have led to the development of new processes such as solder bumping (solder balls or bumps applied to the die or to the package) requiring more sophisticated inerting & reducing atmospheres.”
“Changes to interconnect processes & materials, such as copper wire bonding, are also driving the growth in more rigorously controlled packaging atmospheres. Furthermore, to drive miniaturisation and multi-functionality, silicon die are now being stacked several layers high within the chip packaging, requiring vertical interconnection as well as 2D. The need to make holes in the die to permit these connections, as well as the desire to thin the silicon as much as possible for space reduction, means that new applications are opening up for silicon etching gases.”
“N2 volumes are significant, and in many cases are supplied by pipeline from a central gas plant to multiple manufacturers within the same science park. For example, Linde operates an N2 pipeline in Suzhou, China.”