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Reducing Risk at 300 mm

By David J. Hemker, Ph.D., Lam Research Corporation

Drivers for the 300 mm transition are the need to reduce costs and increase capital productivity—not the need for new technical capability, although traditional design shrinks will occur concurrently. While the industry continually pushes the limits of technology, it is extremely adverse to risk. This article discusses the means to mitigate the risks of equipment procurement during the 300 mm transition.

Introduction

Minimizing Investment Risk

At 300 mm, IC manufacturers must concurrently manage increased wafer costs often accompanied by smaller geometries implemented in new materials. These tasks, combined with shrinking margins and fierce competition, create a situation where risk and development costs must be minimized in order to justify the transition from 200 mm wafers.

To minimize investment risk, manufacturers must consider initial equipment costs and other areas that are equally important over the long term. These include the state of the industry’s transition to 300 mm wafers and the production readiness of individual tools. Some factors that minimize risk are widely recognized and grouped by the industry under the term “overall equipment effectiveness’ (OEE), and each of these should be evaluated along with yield, which must be high to make the transition feasible. The following discusses each of the factors that reduce investment risk in detail.

Several areas need to be addressed to reduce the 300 mm transition risk. Delivering more mature equipment at release with fully developed 300 mm processes that leverage 200 mm experience is one way.

This allows fabs to ramp quickly—without needing to debug new equipment or rework processes. Offering improved uptime and higher reliability on new tools is also important. Since manufacturers are targeting the same percent yield of good die at 300 mm as they currently achieve at 200 mm, addressing process uniformity and edge exclusion issues will be essential.

Foundries and multi-product manufacturers will need application flexibility. Finally, minimizing 300 mm process equipment footprint and ensuring adaptability to future processes will be important. We can summarize all these requirements under three categories that must be managed to successfully transition to 300 mm: investment risk, technical risk, and obsolescence risk.

Equipment costs The economics of 300 mm equipment costs were debated back in 1998 in a two-part article by authors at Intel and Lam 1. Representing the IC manufacturers’ viewpoint, Intel considered the increase in capital (the relative cost of tools normalized by wafer output) and the increase in footprint (the relative size of the factory, similarly normalized) while transitioning from 200 mm to 300 mm on a factory-wide basis. From Intel’s viewpoint, in order to be economical, the increase in capital costs would have to be 1.3x or less, and the footprint should not increase.

At Lam, we agree that, in the aggregate, 300 mm equipment costs may average a 1.3x increase over 200 mm equivalent equipment. However, to simply apply a 1.3x cost multiplier across all equipment ignores the possibility of broad capability differences among equipment offerings. Additions such as advanced factory automation and in situ sensors may not be available on all tools within an equipment category. Such capabilities should be considered in the cost equation since they impact productivity and yield, which affect overall Spring 2001

Yield Management Solutions

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ed as a fab line, or a new fab line is established, and volume production begins.

A key strategy some manufacturers are implementing is process integration using 200 mm wafers. This approach reduces development costs by saving on expensive 300 mm wafers. Also, some key 300 mm processes, for example, lithography below 180 nm, are not yet widely available. Since chip manufacturers are bringing up initial 300 mm lines with established 200 mm processes, investment risk can be minimized when 300 mm equipment readily adapts to 200 mm and has a footprint equivalent to 200 mm systems. (Figures 1 and 3.)

F i g u re 1. Lam’s na rrower 2 00/300 mm 230 0 footprint conser v e s

Teres System Layout

valuabl e cleanroom sp ace while providin g easy accessi bilit y as c o m p a red to the 2 00 mm Alliance™ footpri nt.

costs. Targeting increased productivity and capability relative to 200 mm, while maintaining a comparable footprint (Figure 1), provides a more comprehensive indicator of value than equipment costs alone.

State of the transition The transition from 200 mm to 300 mm is evolutionary, and the roadmap for production-readiness is short. Twenty-seven 300 mm facilities have been announced since 1999, including both R&D and production, and the number continues to increase (Figure 2). Leveraging 200 mm learning and ensuring equipment maturity will be critical to minimize risk and meet production time lines.

300 mm CMP System Layout

1997 1998 1999 2000 2001 2002 R&D/Pilot Lines in Operation (cumulative)

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Production Lines in Operation (cumulative)

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F i g u re 2. Outlook for th e 300 mm tran sition. (Source : Lam Researc h

F i g u re 3. Lams’ 200 mm Te res™ footprint versus its 200/300 mm

Corporation. Da ta for 2001 an d 2002 a re esti mates).

Te res footprint.

Ready for production

Overall equipment effectiveness

Manufacturers are very conservative when introducing new equipment and technology. First, R&D develops and characterizes unit processes (e.g., CVD, CMP, or etch). Then the processes are introduced on a pilot line to integrate the unit process into the overall process flow. Finally, the pilot line is expand-

Another important component of investment risk is overall equipment effectiveness (OEE), which includes capital investment, footprint, productivity, and uptime.

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Cost of ownership (CoO) is defined as the capital and operational costs required for a given level of produc-

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tivity, expressed as the number of good die per wafer per unit time. The capital investment portion of CoO is reflected in the selling price of the tool and is directly related to the supplier’s development costs. Suppliers can employ modeling to reduce their development costs, then pass the savings on to customers to lower their CoO. For example, gas flow can be modeled throughout the operating pressure range and thermal modeling can be used to understand and control important surface chamber temperatures. Plasma modeling can help optimize the chamber design and the coil configuration for transformer coupled plasma™ product lines.

A common platform and common modules will also reduce production costs and CoO. The commonality reduces fab investment in parts inventory and maintenance training. Sensor development costs can also be shared across equipment types. For example multiwavelength interferometry, originally developed for endpoint detection (EPD) for CMP, can be extended to CMP thickness measurement, then adapted for etch-todepth endpoint monitoring.

Balancing ease of serviceability with footprint for 300 mm is a particular challenge for suppliers, and advanced, streamlined, modular designs, as described above, are needed. The keys to enhancing 300 mm productivity (wafers/hour) are improving wafer transfer efficiency (less dead time during transfer in and out of load and vacuum transfer chambers) and reducing process times (with good etch rate, efficient endpoint detection, and good CMP removal rate, among others).

Yield Minimizing investment risk for 300 mm includes the assurance that yield will be sufficient to reduce per-die costs enough to justify the transition. Employing CoO formulas, manufacturers are targeting the same percent yield of good die per wafer on 300 mm as they currently achieve at 200 mm. To meet this aggressive goal, equipment suppliers will need to ensure uniformity across the larger 300 mm surface area. They will also need to monitor the wafer’s edge more closely because of the larger number of die in that region.

Minimizing Technology Risk

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technology risk. Other means of assuring against technical obsolescence in a tool include its ability to process several device generations, its demonstrated process flexibility, and its maturity at the time of purchase.

Supplier-manufacturer collaboration To minimize technology risk, a new 300 mm tool should be adaptable to at least the next two to three technology generations. Customers have a range of individual, fast-changing roadmaps, and many future equipment requirements are yet unknown. To accomplish this extendibility, significant versatility must be built in, and direction from customers is needed.

The responsibility for process development has moved toward suppliers in recent years, while chip manufacturers focus on integration issues. With the 300 mm equipment generation, we are beginning to see manufacturers working with suppliers to establish required process equipment capabilities. A mutual sharing of product roadmaps and greater trust is now emerging that will result in lower development costs and equipment that is better targeted to manufacturing needs.

With mutual agreement on key parameters requiring independent control, flexibility can then be designedin-giving process engineers the right adjustable “knobs” to allow adaptation for future process development.

Next-generation readiness Drivers for the 300 mm transition are the need to reduce costs and increase capital productivity2-not the need for new technical capability, although traditional design shrinks will occur concurrently.

For example, early adopters of 300 mm are using process flows developed for 180 nm. Other leaders are planning volume production at 130 nm by mid-2001, most likely starting on a 200 mm fab line. They can then rely on a good comparison with their baseline that was established with 200 mm wafers.

Their goal is to have fully integrated processes for the next-generation interconnect technology (copper and low-κ interlevel dielectric) for 150 nm and 130 nm.

The shrink is required for this next-generation interconnect technology to be fully cost effective. Beyond this, there will be other next-generation technologies, such as metal gate technology with a high-κ gate dielectric.

Strong collaboration between the supplier and manufacturer is one of the best assurances of minimizing

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We are seeing chip manufacturers take one of three approaches to prepare for the 300 mm transition: 1. Initially performing R&D for advanced processes at 200 mm on the dual-capability equipment, then later scaling to 300 mm. This allows manufacturers to take advantage of the most advanced materials and lithography, which are available only at 200 mm, and also to gain experience on new equipment.

2. Integrating the 200/300 mm equipment directly into 200 mm production lines since the equipment is competitive at 200 mm. This strategy provides learning on new equipment that will significantly shorten the ramp for future 300 mm lines, where process scaling is straightforward. This also reduces capital investment risk, should these manufacturers delay transitioning to 300 mm.

3. Employing the versatile equipment directly in 300 mm pilot lines.

Because the difference between the 200- and 300 mm systems is minimal-a few parts changes and a straightforward scale-up of recipes-customers learning on the 200 mm equipment are extremely confident about the 300 mm equipment. Also, fewer 300 mm wafers will be needed to qualify processes 3. Regardless of the strategy employed, by the time manufacturers are ready for high-volume 300 mm production, they will have gained extensive experience with the equipment and processes.

Process flexibility

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Tool maturity Achieving tool maturity and reliability by working with customers prior to shipping the first production units is essential. Marathon internal testing, securing key beta sites and addressing all problems that arise, and leveraging proven technologies all lead to the required maturity. During the current transition to larger wafers, suppliers were afforded the time to establish maturity, and this advantage should pay off for manufacturers as they ramp product. Offering built-in 200 mm capability is another way to attain maturity, since it aids in uncovering problems that often do not appear until volume production. Gaining experience at 200 mm is also less costly than learning on 300 mm.

Minimizing Obsolescence Risk

Obsolescence risk, a subset of investment risk, is inherent in technology-driven competition. The challenge for suppliers is to be ready for the unknown-to develop equipment with broad capabilities, while still controlling costs. The ability to easily adapt chambers to different processes reduces the threat of obsolescence and may reduce the number of specialized systems needed.

The 300 mm generation will also require more sensors for equipment and wafer state monitoring, for factory automation, to leverage increased connectivity (intermachine, intra-machine, fab-wide, fab-to-fab, and fabto-tool-supplier), and to enable sophisticated diagnostics tools. Some of the needed technologies are available and being integrated on equipment. Other technologies are still in development. Process equipment designed with “plug and play” capability will ease the

Process flexibility is essential for minimizing technology risk since the requirements of future technology generations are not fully known in advance. Flexibility is also essential for foundries and multi-product manufacturers. Suppliers will need to adopt proven, flexible technologies, such as a dual frequency confined (DFC) plasma source for dielectric etch.

Designing-in process versatility has led to the development of more than 40 integrated process sequences on Lam’s 200/300 mm-capable etch equipment. An example is etching a low-κ dual damascene via first stack in situ (in the same chamber) (Figure 4). Flexibility also enables processes commonly run in separate chambers, such as an ARC-open hard-mask etch and STI4, to be integrated and simplified, which improves both productivity and process results.

F i g u re 4. A low- κ dual damascene via f irst stack etch in situ (i n the same chamber).

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integration of important new technologies as they become available and reduce the risk of obsolescence.

Process conversion Processes become obsolete. For example, many fabs will be replacing aluminum metallization with copper, eliminating the need for aluminum etch chambers. A modular design should be incorporated into new equipment to enable conversion to new processes, when possible. For example, when fabs move to damascenepatterned copper, they will no longer require aluminum etch chambers for interconnect. Being able to convert obsolete chambers—for example, Lam’s 200/300 metal etch chamber converts to a polysilicon etch chamber— will protect capital investment.

In situ sensors To reduce the risk of mis-processing costly 300 mm wafers, in situ EPD and process- and wafer-state metrology are needed to enable equipment to signal when processes are within tolerance or completed, or when equipment is failing. Key technologies now available and being integrated on equipment to enable better process control include broadband optical emission spectroscopy (OES) and bias compensation electrical EPD. OES—The industry-standard EPD method for plasma etch has become OES, which depends on detecting the change in light emission at a characteristic wavelength as the underlying layer is reached. The output of a broadband OES can also provide a process “fingerprint.”

Figure 5 shows a broadband OES spectrum of a baseline

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process of record (red curve). The blue spectrum shows the impact of a small change in power to the process.

The spectra are a sensitive monitor of tool and wafer state that can help predict the potential for problems and avoid them.

On Lam’s 200/300 mm etch systems, a similar technology enables real-time interferometry for monitoring etch steps. This eliminates the uncertainty of timed etch. However, if the exposed area at endpoint is small relative to the total wafer area, as with etching small vias, these methods may not be applicable.

Bias Compensation EPD—Bias compensation endpoint sensing (a sensitive, non-optical, EPD method) has been developed to address some of the limitations of OES and timed etch. For the small exposed areas, which are required for certain dielectric etch applications, this electrical technique provides a higher signal-to-noise ratio than optical emission. The endpoint has been detected for exposed areas less than 0.01%5 of the total wafer area, when the nitride at the bottom of an etched via is barely exposed. The endpoint signal is generated at the wafer level rather than by a change in the plasma species. This provides earlier endpoint detection than optical emission.

Factory automation, connectivity, and diagnostics Since 300 mm fabs will be automated, advanced process control (APC) and factory automation capability must be built in or easily ported. Within-tool and external connectivity for data transfer must conform to standards. The system must be adaptable to existing industry standards and advanced standards that are still in flux-as well as to mechanical and electrical interfaces and protocols that are sometimes competing.

Integrating widely accepted standards, such as Internet TCP/IP communication links ensures future scalability and adaptability. Specifically, using Internet protocols enables a remote PC browser to view tool operation and diagnose problems-or perform “e-diagnostics.”

F i g u re 5. The impact of a small change i n p ower ( blue cur ve) is comp a red to a bas eline process of re c o rd (red cur ve).

An open-architecture approach reduces the risk of obsolescence by easing the integration of new technologies to enable greater connectivity and speed for accessing, analyzing, and monitoring critical data. Key diagnostics being developed include advanced fault detection and analysis, predictive maintenance capability, integration of metrology and other off-board sensors, and advanced modeling to increase overall OEE.

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Conclusion

In the inherently high-risk, capital-intensive, semiconductor industry, equipment suppliers and semiconductor manufacturers must work together to achieve their mutual goals of minimizing risk and costs. This includes sharing responsibility for process development as well as jointly assessing the requirements for new equipment capability in order to manage today’s aggressive technology roadmaps. Innovative approaches are needed now more than ever to manage risk in ways that will benefit both suppliers and IC manufacturers.

Working closely with customers in developing 300 mm equipment, we identified overall risk reduction as the primary challenge in the 300 mm transition. To support risk management, we recommend four broad strategies for equipment development: • Employ extendible, production-proven, technologyincluding current process technologies and securing as much production experience as possible.

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Similar strategies implemented by suppliers in other equipment sectors will reduce overall transition risk and help ensure a successful 300 mm generation for both suppliers and manufacturers.

References 1. D. Seligson and J. Bagley, “Two sides of the debate on 300 mm tool costs,” Solid State Te c h n o l o g y, 41(7), July 1998, p. 344.

2. D. Seligson, “Planning for the 300 mm Transition,” Intel Technology Journal, 4th Quarter 1998.

3. N. Bright, “300 mm Begins: Etch Tool Readiness,” Semiconductor International, 23(8), July 2000, p. 136.

4. S. Lassig, C.S. Xu, A.J. Miller; S. Kamath, A. Romano, T. Kudo, “An Integrated Etch Approach as STI Evolves for the 100 nm Regime,” Solid State Te c h n o l o g y, July 2000, p.

157.

5. E.A. Hudson and F.C. Dassapa, “Sensitive Endpoint Detection for Dual Damascene Via Etch,” Plasma Etching Processes for Sub-Quarter Micron Devices, Electrochemistry Society Proceedings, Vol. 99-30, p. 295.

Trademarks

• Provide adaptable equipment-minimizing capital investment risk since timing for 300 mm and new materials and process ramps vary by manufacturer.

Equipment that is independent of technology roadmaps-that is, equally capable and competitive at 200 and 300 mm with straightforward process scaling and extendible to 100 nm and beyond-will reduce this risk.

• Enable versatile advanced process performanceincluding integrated in situ process capability to allow manufacturers flexibility in choosing processes and materials for 100 nm and beyond.

• Leverage 200 mm volume learning-taking advantage of the most advanced lithography and high volume production that is available only at 200 mm to reduce 300 mm production ramp risk. This also eliminates the risk of 300 mm timing.

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TCP is a registered trademark of Lam Research Corporation, Fremont, Calif.

About the Author

A 12-year veteran of the semiconductor industry, Dr. David Hemker joined Lam Research Corporation (Fremont, Calif.) in 1998. As vice president of new product development, he directs next-generation etch product, process, and 300 mm development. Previously, Dr. Hemker was vice president of technology for PMT/Trikon, managing research and development, technology, and engineering. He also spent five years in various technology roles at Applied Materials. He received his Ph.D. and MS degrees in chemical engineering from Stanford University, holds five patents, and has authored more than 25 published technical papers on semiconductor processing and thin-film applications.