Grantee Research Project Results
Final Report: Exhaust Gas Monitoring for Process Control and Pollution Reduction in Semiconductor Manufacturing
EPA Contract Number: 68D01037Title: Exhaust Gas Monitoring for Process Control and Pollution Reduction in Semiconductor Manufacturing
Investigators: Spartz, Martin
Small Business: MKS Instruments Inc.
EPA Contact:
Phase: I
Project Period: April 1, 2001 through September 1, 2001
Project Amount: $69,889
RFA: Small Business Innovation Research (SBIR) - Phase I (2001) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
Perfluorocarbons (PFCs) such as C2F6, CF4, CHF3, C3F8, and other fluorinated compounds such as SF6 and NF3 are widely used as etch gases in semiconductor manufacturing. The industry consumes millions of pounds of PFCs, and the amount is increasing rapidly. However, PFC emissions have a harmful environmental impact (including a contribution to global warming) and can last in the atmosphere for up to 50,000 years. The On-Line Products Division of MKS Instruments, Inc., intends to develop technology to control PFC emissions by reducing greenhouse gas usage during wafer fabrication and during nonproduction operation of the fabrication tool. Several options for reducing the emissions of PFCs are being considered, including: (1) optimizing the process; (2) reducing the nonproduction operation of the fabrication tool; (3) using alternative etch gases; (4) recovering and recycling the unused PFCs; and (5) postprocess abatement (combustion). This program has focused on a method to investigate and optimize the first three approaches by monitoring etch exhaust gas composition through Fourier transform infrared (FT-IR) spectroscopy. Measurements during a series of both traditional and nontraditional wet clean recoveries were performed to demonstrate the abilities of FT-IR for process monitoring and control. A wet clean is the process by which a plasma etch reactor is manually cleaned to remove contaminants that build up during production wafer etching. The conservative "recipe" for recovery from the clean can last for more than 3 hours and consume at least 25 wafers; therefore, any approaches to actively control the recovery process can result in significant savings in both time and materials, and will assure the end user that the chamber is ready to accept production wafers. In addition to these measurements and analyses, consideration was given to how an advanced process control (APC) system based on exhaust can be implemented.Summary/Accomplishments (Outputs/Outcomes):
Based on the exhaust gas measurements obtained during this project, in which more than 36 compounds were measured simultaneously, it appears that a more efficient, less time-consuming, and more environmentally friendly recovery process should be possible if active endpoint-detection based on exhaust gas composition is implemented. Several key species measured with FT-IR were seen to vary systematically over the course of the initial chamber clean, while other species showed systematic variation from one wafer to the next during the conditioning wafer phase of the recovery process. These species, which behaved consistently over multiple recoveries, will provide the information necessary to determine when to stop the chamber clean and when to stop running seasoning wafers.To further demonstrate the utility of FT-IR for process optimization and investigation into alternative etch gases, a series of wet clean recoveries were performed using NF3 as the plasma clean gas instead of SF6. This change is of interest to the U.S. Environmental Protection Agency and end users for several reasons:
- The global warming potential of SF6 is two to four times greater than that of NF3 (SF6 is being outlawed in Europe).
- NF3 may require a shorter recovery step, thus reducing the amount of material consumed as well as reducing the overall time to condition the chamber.
- NF3 produces mostly gas-phase products, so there is less chance for solid formation on the wall of the chamber, thus reducing the potential for particulates generated during the cleaning process to contaminate the wafer.
- If a semiconductor fabrication does not have scrubbers on the exhaust lines, NF3 emissions will be significantly less harmful to the atmosphere than the SF6 emissions.
A preliminary study with NF3 using identical recipe steps to the SF6 recovery process was performed, and the stabilization of the chamber during the initial chamber clean appears to be faster. Further tests during the following months should help clarify the benefits of NF3, and the FT-IR measurements are seen as a key element in the transition to this chemistry.
Conclusions:
This project has developed the framework for an advanced process control method based on monitoring exhaust gas composition through FT-IR spectroscopy to investigate and minimize semiconductor etch chamber emissions. These exhaust measurements make it possible to: (1) optimize various etch and chamber conditioning processes; (2) reduce the nonproduction operation of the fabrication tool; and (3) use alternative etch gases. As a demonstration of this approach, exhaust gas composition was measured during a series of both traditional and nontraditional wet clean recoveries. During the recovery from this process, a series of SF6/O2/Cl2 plasmas are struck in the chamber without a wafer, followed by a series of bare and polysilicon wafer etches and chamber cleans. The conservative "recipe" for this recovery was developed to ensure consistent conditioning of the chamber in preparation for etching of production wafers. Because the entire conditioning procedure after completion of the wet clean can last for more than 3 hours and consume at least 25 wafers, any method to actively control the recovery process results in significant savings in both time and materials during the recovery process, and should guarantee that the chamber is ready to accept production wafers.In addition to these measurements and analyses, consideration was given to how an APC system based on exhaust could be implemented. The APC system to be developed incorporates four innovative components:
- An auxiliary FT-IR sensor for infrared process exhaust gas (PEG) monitoring (developed by On-Line Technologies, Inc., and utilized in Phase I by MKS and Lam Research Corporation to monitor a Lam TCP-9400SE Alliance etcher).
- An etch chemistry model (ECM) that relates the PEG monitor data to etch rate parameters.
- An equipment model for endpoint detection, chamber matching, and run-to-run control, which relates the etch rate parameters to the tool-state operating parameters.
- An operations model for fault detection and classification (FDC) and maintenance management.
The proposed technology will improve operating efficiency, product quality, environmental compliance, process development, process qualification, and yield learning.
Finally, the potential for commercialization of this technology was examined. The benefits of the technology could be enormous for emission reductions and improved manufacturing efficiency. According to SEMATECH, the average overall equipment effectiveness (OEE) for semiconductor microelectronics manufacturing equipment is only 43 percent. During the nonproductive time, the tool is running test wafers and being tuned up and operated for troubleshooting. This nonproductive tool time creates emissions and wastes valuable production capacity. If an advanced control and FDC system costing $50,000 can increase OEE from 43 percent to 65 percent, it can increase the value of a $2,000,000 tool by $1,000,000 and reduce energy consumption and emissions by up to 50 percent. In addition, improvements in development and yield learning times also can reduce emissions. With the high benefit-to-cost ratio, sales of such systems are expected to reach more than $1 billion by 2004.
Supplemental Keywords:
greenhouse gases, perfluorocarbons, PFCs, engineering, chemistry, EPA, monitoring, emissions reduction, exhaust gas measurement., RFA, Scientific Discipline, Air, Waste, Ecosystem Protection/Environmental Exposure & Risk, climate change, Chemistry, Monitoring/Modeling, Environmental Monitoring, Environmental Engineering, Engineering, Engineering, Chemistry, & Physics, Incineration/Combustion, monitoring, exhaust gases, green house gas concentrations, PFCs, combustion, exhaust, exhaust gas, perflurocarbons (PFCs)The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.