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Foundries look again at older production

Although 300mm foundry capacity is expanding fast, many applications in power and mixed-signal are finding new life in older 200mm fabs.

Last month, Singapore-based foundry Systems on Silicon Manufacturing (SSMC) celebrated its tenth anniversary of silicon manufacture with the news that it was to spend $30m - split roughly 50/50 between research and development (R&D) and manufacturing. The investment is meant to keep SSMC's production lines relevant in a business now dominated by plants that process larger wafers and which should be more cost-effective.

'We are putting in place a vision that ensures SSMC is in a good position for the next decade or two,' says Jagadish CV, the CEO of SSMC.

Jointly owned by NXP Semiconductor and Taiwanese foundry TSMC, SSMC was one the last big 200mm digital logic-oriented fabs to be constructed, opening just ahead of the dotcom crash. During the 1990s, 200mm production lines overtook their 6in or 150mm predecessors that had, in turn, displaced 4in wafer fabs from the 1970s as the most advanced.

The reason for this shift is simply one of cost-effectiveness. As long as you have the volume to support the increasing number of dice that you can inscribe on larger wafers, the bigger the wafer, the cheaper the chips.

After the recovery from what was then the semiconductor industry's worst slump, 300mm production with 0.13m copper processes had pretty much taken over from manufacture on 200mm lines. Because of the decisions made by production-equipment makers, who did not see the point in trying to maintain parallel product lines, the 200mm fab owners were stuck with 0.15m and larger line widths and aluminium metal interconnect.

Rather than throw in the towel, SSMC changed direction, concentrating on 'ABCD' products - analogue, bipolar, complementary metal-oxide semiconductor (CMOS) and double-diffused metal-oxide semiconductor (DMOS) processes. It covers applications as diverse as 'smart power' - digital control combined with power-supply circuitry, which is where the DMOS transistors come in - and radio-frequency (RF) products, in contrast to the mainly digital products turned out by fabs that use 300mm wafers.

'Many of the products they produce are not line width-driven, such as lighting control. All of them require high voltages and high-voltage circuits don't scale well, so there is no advantage in moving to 40nm,' says Ren Penning de Vries, senior vice president and CTO of NXP.

But the company did not just stick with the 0.18m processes that were available when the fab opened in 2000. By pushing the equipment SSMC had, the foundry was able to introduce a 0.14m process in the first half of the decade. This has gradually expanded from being a 5V-maximum technology to one that can handle voltages up to 100V, suitable for power electronics.

By the end of the year, SSMC expects to have a 0.11m process running - using pretty much the same equipment the company has used for its other operations - and is looking at introducing ultra-low leakage variants, similar to the process for 0.18m line widths, called 180ULL, that TSMC launched recently.

'We have even been challenged to do 90nm. Those types of opportunity do exist,' says Jagadish.

The extension to 0.11m is thanks to the same techniques that have helped make it possible to draw features as small as 40nm using light that has a wavelength four or five times larger.

'For many, many years, people have declared lithography to be dead. But it continues,' says Richard Thurston, vice president and general counsel of TSMC, and a director of SSMC. 'The same thing has happened here.'

Why go to the extent of pushing older equipment to build more advanced processes when there are 300mm fabs out there with similar processes? For a customer like Geoff Lees, general manager of NXP's microcontroller division, manufacturing on 200mm makes more sense for microcontroller production on a cost-per-die basis.

'The economics of 300mm tend to drive a different strategy,' says Lees, talking late last year about his plans for the microcontroller business.

Production on 200mm lines makes it easier to produce a wider range of peripherals and memory options for 32bit microcontrollers, which, individually, tend to be medium-volume products because they go into industrial and automotive systems. Move to 300mm, and you have to strip out a lot of the variety or eat the die cost of producing large memory arrays and then simply fuse half of it out to produce the 'cheaper' low-end versions.

Although there is potential to extend the process roadmap to 90nm at SSMC, the main focus will be on applications such as automotive and lighting, where the demand is for higher voltages. In microcontrollers, 90nm makes it possible to reduce the size of on-chip memory which can reach into the megabytes on 32bit designs. However, Lees cautions that circuits such as power management units don't scale well and make it hard to churn out low-end, low-memory devices on 90nm because of the relative size of the power unit and other analogue peripherals.

'It's hard to get a tiny die at 90nm,' says Lees.

Finding niches

By concentrating on automotive and lighting, Jagadish hopes to extend the operational life of SSMC out as far as 2025. At the moment, 6 per cent of SSMC's wafers go into automotive. 'The board has set a direction for that to go to 20 per cent,' he says.

'The other applications we are looking at are in the low-energy market, such as fluorescent lighting,' says Jagadish, who has the aim of building a presence in niches such as cold-cathode fluorescent lighting (CCFL), which is one alternative to the tungsten bulbs that are being banned by governments in Europe and elsewhere.

'This 'more than Moore' aspect very much distinguishes SSMC from many of the 8in fabs out there,' says Thurston, who pointed to changes in the chipmaking economy that are putting a new focus on older process technologies.

'Scalability is the key issue. If Moore's Law had plenty of room to run, then you would go the newer generations more readily. But Moore's Law is hitting the wall and companies are discovering that scalability doesn't necessarily matter,' Thurston adds. 'We are seeing a resurgence in 'mainstream' business. We are seeing that, with each of these older generations, starting with 0.18m, applications in RF or automotive can get a lot more of our technology.

'We have these ageing fabs. Let's make them more profitable and give our engineers more than a 300mm roadmap.'

De Vries notes: 'The base technology is available. It's now about building upon this base technology. We see it as very much application driven. Many things are changing and they often require dedicated solutions, with the ability to sense the ambient environment or improve the efficiency of solar cells.'

TSMC is not just reworking its older 200mm fabs. The company held the groundbreaking ceremony for a new fab and research centre in Hsinchu that will concentrate on LED lighting and solar cells. The company is spending NT$5.5bn ($170m) to build phase one of the lighting research centre. It's a move that will see TSMC expand from being a front-end foundry to a supplier of packaged lighting products.

The unit is headed by Rick Tsai, president of new business, who up to last year was CEO of TSMC before chairman Morris Chang stepped in to take up the reins of the company's core business.

Tsai said at the groundbreaking: 'We will enter the market next year by offering LED light sources and light engines.'

The LED fab will be built in two phases. In phase one, equipment will start moving in during the fourth quarter of 2010 with plans to go to full production as early as the first quarter of 2011. TSMC will decide whether to press ahead with phase two based on the results of the first phase.

Although $170m is a significant amount of investment in process technologies used for LED production, it is a tiny fraction of TSMC's overall planned capital spend for 2010 of close to $5bn - most of that money will go into 40nm and 28nm capacity expansion on 300mm lines. But lighting by itself could be a huge market as production costs come down and device lifetimes improve.

The key question is whether, for markets such as lighting, because the volumes could be so huge, manufacturers will move to 300mm production over time even for these 'older' technologies to get the benefits of scale or trade lower capital spending for higher production cost to get very high long-term return on capital employed (ROCE) scores.

Texas Instruments (TI) has already begun with its plan to use equipment from defunct memory maker Qimonda to create a 300mm fab dedicated to analogue rather than digital processes.

'It will be the first facility to run analogue wafers on 300mm,' says Kevin Ritchie, senior vice president of technology and manufacturing at TI.

The company spent $170m to pick up much of the production equipment for which Qimonda originally paid more than $1bn and is moving it from Virginia to Richardson, Texas to fill out the facility TI calls RFAB.

For very high volume parts - analogue die sizes are generally much smaller than those of complex digital parts made on 300mm - TI could use the efficiencies of scale to lower its production costs relative to manufacturing on 200mm wafers. The downside is that the masks used to draw features on to the surface of the wafer are generally more expensive to make for 300mm wafers, which limits the variety of devices that a 300mm fab can make.

Initially, TI will make analogue chips using a 0.25m process that supports both bipolar and CMOS transistors. The company expects to move to 0.18m and 0.13m processes at RFAB over time.

Moves such as this demonstrate that the boundary between types of wafer fab are becoming more fluid as foundries and integrated device manufacturers find new ways to eke value out of the equipment they bought.

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