Subfab sync increases energy savings
Studies show that 40% of wafer processing facility energy is consumed in the subfab. Reducing subfab energy consumption per wafer pass without compromising environmental, health and safety (EHS) standards is desirable and achievable. Synchronization of discrete subfab components and integration with process tool interfaces demonstrates >20% energy and carbon equivalence reduction.
P. Chandler, A. Neuber, P. Fisher, Applied Materials, Santa Clara, CA USA
Industry studies  show that a significant component of wafer fabrication facility operating expense is the subfab ancillary equipment for wafer processing. Reducing the energy and related utility consumption of these subfab components is a practical method to reduce overall wafer processing cost and improve the wafer manufacturing environmental footprint at the same time.
Subfab components such as vacuum pumps, point-of-use (POU) abatement and heat removal devices are included in the wafer processing cost calculations and the overall carbon footprint of the process tool. Many subfab components must operate continuously with virtually no downtime and without impacting the processing tools they support.
The primary function of vacuum pumps and POU abatement equipment is to control exhaust and waste gas emissions from wafer manufacturing tools, mitigating critical EHS concerns. As such, these subfab components are typically designed to manage worst-case risk scenarios.
For example, silane presents a major safety risk in wafer processing. Current subfab engineering design practice is to dilute silane to <1% in an inert purge gas, such as nitrogen. Inert dilution ensures that accidental leaks should not result in a pyrophoric reaction, but requires more abatement energy to offset the inert cold gas diluent and achieve acceptable destruction of waste process gases.
In a conventional subfab environment, equipment is independently arrayed and runs at a constant high energy level. A new technique, designed to significantly reduce energy consumption, is to integrate subfab critical components, such as process vacuum pumps, point of use abatement, pipeline heaters and gas delivery systems into a single integrated mainframe and central control system.
Integrated subfab control of critical components, synchronized to wafer processing tool operation permits recipe level control ('RLC') of energy consumption. Figure 1 illustrates a central subfab machine controller screen.
|Figure 1. Central subfab machine control screen.|
Recipe level control monitors the gas sequence and flow on all the individual gas delivery circuits in the process tool platform. For example, a 300mm multi chamber deposition process tool can have 42 individual gas delivery lines. Data points of gas type, duration, flow rate and process chamber state are converted into instructions to reduce vacuum inert purging, abatement fuel flow, and abatement inert purge flow.
Energy consumption is significantly reduced (over 20% in the subfab) through synchronization of subfab components with the operational state of the process chamber. Figure 2a illustrates the available energy savings for process vacuum pumps and abatement technologies.
From our experience on improving subfab efficiencies, we found it is critical that target process gas species are abated during energy saving modes of operation. For example, the transition between idle, inert idle, deposition, chamber clean, and chamber operation states must be synchronized to eliminate the EHS risk of hazardous gases escaping into the environment.
|Figure 2. a) Vacuum pump energy savings; b) Abatement energy savings.|
Figure 2b illustrates the critical synchronization of process tool operational state with subfab abatement energy. Subfab design investment in active fuel and electrical energy control systems have been shown to deliver fast transition states – typically <8s.
Figure 3 test data demonstrates safe abatement during energy saving mode. The plasma clean process was performed using plasma activation of nitrogen trifluoride (NF3) in a 300mm process tool. Fuel flow response time and final system gaseous emissions were monitored and quantitative measurements taken in accordance to the industry protocol, using quadrupole mass spectroscopy (QMS) and Fourier transform infrared spectroscopy (FTIR).
|Figure 3. Process gas abatement synchronization in energy saving idle mode.|
Results from the synchronization validation demonstrate that consistent abatement of process gases used in the chamber cleaning and seasoning during the transition from idle, to clean, to process operational states, are achievable.
Complex multichamber operation requires dynamic subfab critical component control, synchronization with recipe level control and validated fast transition response timing from abatement. Systemization of the subfab mechanical and electrical components controlled by a single cluster machine can realize >20% energy savings without EHS impact.
In addition to energy efficiencies achievable with subfab/process tool integration and synchronization, an integrated subfab strategy offers significant savings in installation cost and floor space. Typically, a traditional set of subfab components requires >40 discrete connections for installation and is a complex, customized process that can take several days to complete. An integrated subfab system can reduce the number of connections of forelines, exhaust, water and power lines, communication cables and racking by >50%, reducing installation time to <24 hours.
Greater complexity in process tools is driving a substantial increase in the number of subfab support systems, forcing costly expansions of subfab areas. New, fully integrated subfab solutions feature compact assembly of major components and peripherals, which eliminates redundancies, optimizes serviceability, and greatly reduces the subfab footprint for each tool.
Integrated subfab component systems synchronized to process tools can offer IC manufacturers significant cost savings and carbon reduction of >20% compared to current baselines with discrete components and mechanical switch interface. Consolidating multiple discrete subfab components and connections into a single integrated unit requires system engineering to a single cluster controller to sense tool loading. A recipe-level control interface from the process tool to the integrated subfab system enables critical inert dilution and abatement energy matching to wafer processing gas environmental, health and safety requirements.
1. ITRS estimate, average 35k wspm fab and ISMI, 2009; http://itrs.public.net.
Phil Chandler has 20 years of experience as an air pollution abatement engineer and is primarily responsible for the selection and development of air pollution abatement and emissions measurements for Applied's global operations in semiconductor, solar and display manufacturing. He is the Global Head of Environmental Products at Applied Materials, 3050 Bowers Ave., Santa Clara, CA 95054 USA; email Phil_Chandler@amat.com.
Paul Fisher received a BS degree in metallurgical engineering from the U. of Nevada, Reno, and is the general program manager for subfab solutions for Applied Global Services, Applied Materials.
Andreas Neuber received his PhD from the Technical U. of Dresden and is managing director, environmental services, FabVantage, Applied Global Services, at Applied Materials.