News Article
A CLEAR EDGE: Innovation in vacuum and abatement technology drives savings for fabs
Over the last 15 years vacuum and abatement technologies have made steady gains in performance and efficiency. Incrementally, the advances may escape notice, but when considered together, the benefits are significant. Mike Percy, Business Manager, Semicon Vacuum, Edwards and Michael Boger, Global Market Sector Manager, Semicon, Edwards consider the technological advancements and identify the opportunities to realize cost savings.
Semiconductor manufacturing provides a convincing example of what can be achieved when an industry is built on the premise that "˜good enough never is'. For decades naysayers have warned that fundamental limits will soon prevent further advances in integrated circuit performance, and for decades scientists and engineers have found clever ways to take just one more step. The generations of process vacuum and the abatement of noxious process chemicals and by-products, though perhaps not the most glamorous aspects of the industry, are nonetheless absolutely essential capabilities, and the technologies used to provide them have had to evolve along with the process.
Recent years, in particular, have brought an increasing emphasis on saving energy to reduce manufacturing costs and to minimise the adverse effects of the industry on the environment. The result has been a continuous stream of incremental improvements, and while each has been significant in its own right, it is only in their cumulative effect that their full benefit becomes apparent. We recently had an opportunity to perform an interesting experiment and the results illustrate powerfully the cumulative value of constant innovation.
Greenfield fab development: an ideal case study
A major semiconductor manufacturer undertook the green field development of a new foundry and commissioned Edwards Group to be the exclusive provider of vacuum and abatement systems. This provided Edwards with the opportunity to develop, first hand, a complete list of equipment required for such an undertaking - a list that is not easy to compile otherwise given the complexity of a modern semiconductor fab. The facility was designed to process 40,000 wafers per month. Ultimately, it required nearly 1,500 vacuum pumps and over 260 abatement units -- all connected to nearly 400 process tools. The equipment list allowed us to look back at the various technologies we had introduced over four generations of development, starting 15 years ago (when DRAMs had a 250µm half pitch), and calculate the cost savings accruing to the current generation from each generation past.
Cost savings
In the end, we determined that advancements in abatement technology now deliver more than $17.8M per year in utility cost savings, $15M of which is achieved through over a 90% reduction in water consumption and the remainder from reductions in fuel consumption. Advancements in vacuum pump technology now provide more than $3.3M per year in utility cost savings, the majority through improvements in pump mechanisms and the remainder through green mode operation that cuts energy consumption during idle periods. When new products currently in development come into production, we expect to be able to deliver an additional $1M per year in savings.
Key metrics
As the semiconductor industry continues to evolve, production models have become increasingly sophisticated, allowing manufacturers to measure and predict costs more precisely and promoting cost-of-ownership as a key metric in equipment usage and acquisition decisions. Power consumption is a significant contributor to cost of ownership, particularly in localities where environmental concerns or other factors restrict increases in power generation and distribution. SEMI specification S23 establishes standards for measuring and reporting energy consumption as well as targets for reducing energy usage. Any cost of ownership evaluation of an abatement system must include not only power consumption, but also any treatment and disposal costs for by products and effluents of the system under consideration (for instance, water supply and treatment costs).
In the 15-year period covered by this analysis (1997 to 2012), device sizes have shrunk by an order of magnitude (DRAM half pitch has gone from 250 nm to 2X nm) and new processes and materials have greatly increased the complexity of semiconductor manufacturing. In that same period, process vacuum and abatement systems have evolved through roughly four generations, incorporating major innovations to increase efficiency and reduce operating costs. (In order to generalize this discussion and avoid overly frequent references to Edwards-specific model numbers, the generations are numbered negatively from TØ, the current generation, back through T-1, T-2, T-3 and T-4).
Innovation in vacuum pumps
Several trends are apparent over the four generations of vacuum pumps. Inverters have been added to permit energy efficient operation at varying speeds and enable low energy green mode when the pump is idle. Smaller mechanisms operating at higher speeds have increased efficiency in both power and material consumption. Pump designs have diversified with specific models customized to match the requirements of specific processes. Pumps have incorporated sophisticated thermal management to improve reliability and reduce energy consumption.
Dry pumps
Dry vacuum pumps were introduced for semiconductor manufacturing in the 1980's. Although available in a range of sizes they were all similar in design. With high reliability, oil-free cleanliness and low maintenance requirements, their use proliferated in the industry. In the 1990's (T-4) pumps began to be designed for specific families of processes: one design for clean, light duty, and another design for dirty, harsh duty applications. By T-2, a medium duty pump application was introduced to address intermediate process conditions, such as those for processes such as dielectric material reactive ion etching.
In general, lighter duty pumps are designed with lower power motors with low torque capability for relatively clean applications such as wafer handling and load lock evacuation. Harsh duty pumps have the power and torque required for dirtier deposition processes and may incorporate special measures to prevent pumped gases from forming solids on internal components, or to handle powder and process by-products in the gas flow.
Introduction of inverter-driven motors for heavy-duty pumps
Looking at the evolution of harsh-duty pumps, generation T-3 saw the introduction of inverter-driven motors that not only enabled more efficient operation, but also allowed for the rotational speed of the pump to be increased significantly. By increasing the rotational speed, the physical size of the vacuum pump can be reduced. This reduction relates directly to the amount of material and energy required to manufacture the product. A convenient figure of merit for quantifying this savings is the ratio of peak pumping speed to mass of the pump. For harsh-duty pumps, this figure of merit represented up to 49% savings. Inverters also remove the dependence of pumping performance on the frequency of the electrical supply, a significant feature that can reduce the required time to stabilize a process for customers that operate globally.
Generations T-2 and T-1 also saw the introduction of additional process specific modifications, such as thermal management, which ensures precise control of internal temperatures to allow tighter mechanical tolerances and prevent gas condensation on critical pump components. Green mode, a selectable operating mode that reduces input power to the pump when in an idle state, saw introduction at T-2.
Load lock pumps - reducing scale & co-location
Light duty pumps are widely used to evacuate load locks, where they pump only air or nitrogen. In this application, the most important performance criterion is chamber evacuation time, the time it takes to reduce the pressure in the chamber from atmospheric to process levels. Load lock pumps have developed along two parallel axes. The first axis began with the introduction in T-3 of small, low vibration pumps that could be mounted directly beneath process tools on the same floor.
Eliminating the long pipe run from the tool to the sub-fab, where T-4 pumps were installed, permitted much smaller pumps to achieve the same evacuation performance. This, plus further improvements in small pumps that could be installed on or close to the tool (T-2 to TØ), reduced power consumption, physical volume, and mass by roughly 86%, while at the same time achieving a reduction in pump down time of 47%.
Introduction of inverters & increasing rotational speed
The second axis of development for load lock pumps followed a path similar to that of harsh-duty pumps: adding motor inverters, specialization in pumping mechanism design, and increasing rotational speeds. These changes resulted in equally dramatic improvements (T-3 to TØ), reducing power consumption, volume and mass by 79% and shortening evacuation time by 14%.
Gas a batement systems
The majority of abatement systems deployed in semiconductor manufacturing use heat generated through combustion to destroy noxious compounds in the exhaust gas stream. In the 15 years considered in this discussion, these systems also went through four generations of improvements, beginning at T-4 with the basic thermal processing unit which burned natural gas and used a continuous flow of water to scrub solid and gaseous combustion products from the exhaust stream. T-3 saw the addition of water recirculation, which reduced water consumption by 91% and generated significant savings in both water supply and water treatment costs.
At T-2 a new combustor design increased the destruction and removal efficiency (DRE) of the system while reducing fuel costs by 39%. More inlets for process gases allowed the system to support up to six process tools simultaneously. (Since the gases are not mixed until they reach the combustor there is no requirement for compatibility or sequencing of the exhaust flows.) T-1 and TØ introduced green mode to reduce fuel consumption during idle periods, and automated monitoring and control of numerous system functions to increase system reliability and lengthen maintenance intervals.
Foundry cost modeling
To estimate the aggregate annual savings accruing from the effects of each generation of changes, engineers modeled the vacuum and abatement requirements of a state of the art fab based on the equipment list generated for the green field development of a major new foundry. The facility was designed to start 40,000 wafers per month. The final equipment list included approximately 1,500 vacuum pumps and 260 abatement units, supporting 400 process tools. Table 1 shows the assumptions used for utility and other costs. Figures 1 and 2 show the overall utility costs and process specific utility costs (respectively) for each generation of vacuum pumps. Figures 3 and 4 show the same information for each generation of gas abatement system.
Improving the efficiency of the installed base
Improvements in efficiency are not limited to equipment installed in new facilities. Upgrades to existing vacuum and abatement systems can provide significant utility savings. Figure 5 shows increases in energy efficiency for two different sizes of harsh duty pump, 80 m3/h and 600 m3/h pumping speeds, achieved by upgrading the motors to optimize performance around a tighter input voltage range and targeted operating vacuum level. The upgrades improved efficiency by 10 and 24 percentage points (respectively), and together reduce energy consumption by
570 watts.
Even larger improvements in efficiency, from 30% to 50%, can be achieved by upgrading gas abatement systems to current burner technology. The new burner can be used in most deposition and etch applications, except those using CF4 as a process of cleaning gas. The upgrade can be performed quickly and easily in the field.
If installed during required annual maintenance, when the burner is regularly replaced, the upgrade adds only about an hour of additional time. Depending on local fuel costs, the upgrade can pay for itself in as little as one year.
Conclusion
The semiconductor industry never stands still. Neither can its equipment suppliers. This study demonstrates the value delivered by constant attention to improving efficiency, with annual savings totaling nearly $21M at a fab with a 40k wafer start capacity. For larger-scale fabs, or across a major manufacturer, these efficiency savings can multiply into a very significant sum, and is thus increasingly a topic of conversation at many customers, especially at the time of planning increased capacity, or upgrading lines.
Sitting across the table as a supplier, ongoing success requires continuous innovation to reduce product operating costs and environmental impact through improvements in energy efficiency and reductions in material consumption. It is equally important to support existing customers by addressing the same issues for installed systems with practical and economical upgrade paths. The R&D capability and expertise required to deliver such improvements is considerable, and only really available to the largest of vacuum players in the industry.
At Edwards, the experience gained in large-scale projects such as the Greenfield fab has been invaluable, providing numerous insights into the challenges, and rewards available at our biggest customers and placing some actual dollar values on the outcome. When combined with current industry developments such as EUV and 450mm, the pace of change is relentless, along with the pursuit of ever increasing efficiencies to support our customers and their businesses.
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