Special Edition on the Environment

Transcription

1 Special Edition on the Environment Action Plan for Reducing Greenhouse Gases at Semiconductor Manufacturing Factories Masaya IWAMOTO*, Kunihiro YARITA*, Mikio MATSUKI*, Norio TANAKA** Abstract In recent years, environmental problems have expanded from local problems into problems on a global scale, as exemplified by the problem of global warming. Even in developing countries, with industrialization and migration of population to the cities, problems such as pollution, destruction of tropical rainforests, and transition of farmlands to deserts have become major concerns. Among these, global warming, caused primarily by greenhouse gases such as CO 2 (carbon dioxide) which is deeply linked to human life and industrial activity, is a major problem and countermeasures must be found. At semiconductor manufacturing factories, large quantities of energy such as electrical power and fuel oil are consumed in IC manufacturing and these contribute to CO 2 discharge. Likewise, because large quantities of perfluoro compound (PFC) gases, which have a high index of contributing to warming (compared to CO 2, etc.) are used in the manufacturing process, an extremely large burden is placed on the environment in respect to global warming. At our Silicon Solutions Company (SiSC), which handles Oki Electric s semiconductor manufacturing, in order to reduce the discharge quantity of CO 2 as required by our company s environmental objectives (Eco Plan21) we are pursuing programs for energy reduction and for reducing the discharge quantity of greenhouse gases such as PFC s. Domestic activities related to prevention of global warming At the Conference of the Parties [COP] 3-countries which had signed the Third Framework Convention on Climate Change held in Kyoto in 1997, advanced countries agreed on numeric goals for reduction of greenhouse gases and a timetable for accomplishing these goals. As for Japan, it agreed to achieve by 2008 ~ 2012 a 6% reduction compared to In Japan, the government stipulated in the Law for Rationalization of Energy Use, that business operators shall strive to achieve an average annual reduction of 1% or more in their per product usage of energy (i.e. total usage / production volume) and provided guidelines on reducing energy use of the types resulting in CO 2 discharge. Concerning reduction of greenhouse gases, at the World Semiconductor Council (WSC) a common international goal related to reduction of discharge of PFC s, etc. was determined in terms of absolute amounts: by 2010, discharge quantities shall be reduced by 10% or more, compared to the base year of In Japan likewise, in response to the determination reached by WSC, each company has drafted reduction objectives, to be reached by the year 2010 based on autonomous plans, and is working to accomplish them. As for Japan s semiconductor industry, the Japan Electronics and Information Technology Industries Association (the former Electronic Industries Association of Japan) in 1998 established reduction standards in the form of * Silicon Solutions Company, Production Center, Environmental Engineering Team. ** Silicon Solutions Company, Production Center, Environmental Engineering Team, Team Leader. autonomous action plans for the electronic industry relating to control of discharge of HFC, etc. and has submitted these standards to the Ministry of Economy, Trade and Industry (formerly MITI). Present Situation as to Amounts of Electrical Power Consumption and CO 2 Discharge SiSC currently accounts for 90% of the total electrical power consumed by Oki Electric, and for Oki Electric to achieve its goal for CO 2 reduction, SiSC s program for reduction of energy consumption is an important issue. Figure 1 shows SiSC s actual results to date as to the trend in amount of electrical power consumed (on a per product basis) and amount of CO 2 discharged (per product). Per product index (%) Reduction goal Amount of electric power consumed CO 2 discharge amount Figure 1: Trend in SiSC amount of electric power consumed and amount of CO 2 discharged 18

2 December 2001 OKI Technical Review 188 Vol. 68 Discharge quantity of CO2 gas Improvement in utilization efficiency Actual reduction results No countermeasures Reduction plan Technology for breaking down the gas Collection Target level (90% of 1995 results) Alternative gases Figure 2: Roadmap for reducing discharge of greenhouse effect gases New process As can be seen from these results, good progress has been made up to the present. Under the energy reduction program, consumption in 1995 (on a per product basis) was 17.4% lower than that of 1999, while a 16.3% reduction was achieved in CO 2 discharge amount. SiSC s results just up to 1999 already achieved the 10% reduction (per product basis) compared to 1995, which was the Eco Plan 21 objective to be achieved by In addition, related to reducing the discharge quantity of greenhouse gases, based on a survey of our actual results since 1995 as to discharge quantities of the subject gases, in 1998 we drafted a roadmap (Figure 2) for achieving further reductions in discharge quantity through The target level was set, as an autonomous standard, at 90% of the actual usage in As shown in the roadmap, it can be predicted that, without countermeasures, by 2010 the discharge quantity would exceed five times the target level. For that reason, we have made a plan to implement a variety of reduction measures and reach the target level by Actual results up to 2000 have achieved much larger reductions than laid out in the roadmap. Action Plan for Reduction of Greenhouse Gases Here we will introduce our programs for reduction of energy consumption through introduction of the cogeneration system (CGS) which SiSC recently implemented and through reduction in energy for heating and cooling sources, and our program for reduction of PFC gas discharge quantity. 1. Introduction of a cogeneration system The conventional thermal-electric power generation systems of electrical power companies do not utilize the excess heating energy produced when electricity is generated, their energy utilization efficiency is only on the order of 35%. On the other hand, CGS, through multiple effective uses of energy and elimination of power transmission losses, can increase the total utilization effectiveness of energy to 50% or more, thus creating a combination thermal-electric / thermal supply system which can reduce the environmental burden. Figure 3 shows an outline of the dual-source system introduced at Miyazaki Oki Electric (Miyazaki Oki), which is SiSC s mass production factory. It consists of a combination thermal-electric / thermal supply system based on an on-site CGS facility and conventional power purchased from the power company. The CGS facility is comprised of a diesel engine, electrical generator, and exhaust gas steam boiler, and the total electrical generating capacity of the system introduced by Miyazaki Oki is approximately 10,000 KW/Hr. By linking this with the existing system for receiving power company electrical power, a dual-source power supply is created to provide power for production, etc. In addition, utilizing engine exhaust heat at approximately 330 C, steam is produced and supplied to heating and cooling equipment, etc. Table 1 shows the results of evaluation in terms of operation performance and environmental impact due to exhaust gas. Amount of electrical power generated, amount of steam generated, amount of fuel consumed were all about as per the plan. In terms of environmental impact, nitrogen oxides, soot and dust, and sulfur oxides all showed excellent results, coming in under the values originally planned. Table 2 shows the actual results as to reduced energy consumption, and, in terms of the amount of CO 2 discharged through energy conversion, as a percentage of absolute discharge amount, we were able to make a reduction of 3.1%. Thus, at semiconductor factories, in which the large amounts of electrical power are consumed, an important issue is how to utilize energy efficiently and reduce electrical power consumption. Consequently, installation of a system with high efficiency in energy utilization like CGS is an important means of reducing energy consumption and an effective countermeasure in preventing global warming. Fuel Inside the factory grounds Primary fuel ("A" fuel oil) Power station Diesel engines Electrical generators Power transmission lines Exhaust heat recovery/reutilization (utilization of steam, hot water, etc.) Energy utilization rate: Total approx. 40% efficiency: approx. 50% Semiconductor Heat factory Energy utilization rate: approx. 10% Figure 3: Miyazaki Oki dual-source energy supply system 19

3 Operation performance Environmental Burden Item Amount of electrical power generated Amount of steam generated Amount of fuel consumed Nitrogen oxides Soot and dust Sulfur oxides Unit Plan Results Remarks KW/Hr 9,900 9,971 Ton/H L/KWH Vol ppm % of plan g/nm % of plan K value % of plan Table 1: Results as to operation performance and exhaust gas discharge standards Reduction compared to previous year Crude oil equivalent 1.5% CO 2 exhaust amount 3.1% Table 2: Energy reduction effect 2. Reduction of energy for heating and cooling At SiSC, heating and cooling facilities account for approximately 20% of total electrical power usage, so working to reduce energy consumption in this area is an important point. Among heating and cooling facilities, one type of equipment that consumes large amounts of electrical power is refrigeration equipment. These produce chilled water, and provide cooling energy to air conditioning equipment, equipment for making cooling water for production processes, etc. At SiSC, in the winter and interim seasons (spring and fall), the burden on cooling equipment is reduced through effective utilization of natural energy such as outside cool air or cool water. Also, we strive to reduce the energy consumed by refrigeration equipment through updating to high efficiency refrigeration. One example of how effective use of natural energy can reduce energy consumption is a free cooling system based on heat recovery from outside air. A summary configuration is shown in Figure 4. Cooling tower Flow during winter and interim seasons Flow during summer With the free cooling system, energy savings are achieved through reduction in the load on refrigeration. This is accomplished by producing cooling water in the temperature range of 5ºC to 14ºC by using the evaporation heat in a cooling tower as heat energy. However, because the temperature of outside air is utilized, the heat capacity which can be recovered annually varies by geographic region. For example, in a 500RT open-type cooling tower, as shown in Figure 5, between northern and southern locations, as between Miyagi Oki Electric (Miyagi Oki) and Miyazaki Oki, an annual difference in the recoverable heat quantity of 3000 gigacalories was actually recorded. One more effective utilization of natural energy is to recover the temperature difference in industrial water as heat energy and use it to reduce energy consumption. At Miyagi Oki, in winter industrial water is at a temperature of 4 ~ 8ºC and by effectively using this cold water, the burden on the refrigeration can be reduced. Thus, in winter at Miyagi Oki, by utilizing the free cooling system and a system for recovering heat and coldness from industrial water, approximately 80% of the air cooling load can be covered by natural energy. As a result, annual heat recovery of approximately 19,000 gigacalories can be accomplished and roughly 6.3 million KWh of the electrical power consumed by refrigeration can be saved. In contrast, at Oki Miyazaki, whose factory is in the south, the percentage of utilization of natural cooling/heating is low. Nevertheless, through adoption of a free cooling system, annual heat recovery of 3000 gigacalories was possible and the power consumed by refrigeration was reduced by approximately 1 million KWh. Next we will introduce the results of our program to conserve energy through conversion to high efficiency type refrigeration. Recently, even for refrigeration which consume large quantities of electrical power, high efficiency models have become available. As a result, when old-style refrigeration are replaced, it is possible to achieve energy savings by introducing high efficiency type refrigeration which, for the same refrigeration capacity, consume less electrical power. Heat exchanger Refrigeration Cooling water return Cooling water sending Figure 4: Outline of the free cooling system (Gigacalories/year) Miyazaki Tokyo Miyagi Figure 5: Annual recoverable heat capacity by region (open-type cooling tower 500RT) 20

4 December 2001 OKI Technical Review 188 Vol. 68 Item Unit Old-type turbo refrigeration New-type turbo refrigeration Difference Refrigeration capacity USRT Electrical power consumed KW Rated current A Efficiency KW/USRT Table 3: Energy comparison table: old-type vs. new type turbo refrigeration Table 3 shows an energy comparison of old-style refrigeration vs. the latest type of high efficiency refrigeration, with the same 750USRT refrigeration capacity. As a result of introducing the latest type of high efficiency refrigeration whenever old-style refrigeration had to be replaced, SiSC in total achieved an annual energy reduction of approximately 6.5 million KWh, compared to the pre-replacement situation. 3. Reducing the discharge quantity of PFC gases Under WSC, reduction objectives were set for seven kinds of gas which have high Global Warming Potential (GWP) ratings compared to CO 2. The list consists of five kinds of PFC gas tetrafluoromethane (CF 4 ), hexafluoroethane (C 2 F 6 ), octofluropropane (C 3 F 8 ), perfluorocyclobutane (C 4 F 8 ), trifluoromethane (CHF 3 ) and also sulfurhexafluoride (SF 6 ), trifluoronitrogen (NF 3 ). These seven types of gas are required in semiconductor manufacturing for chamber cleaning, primarily in plasma etch and CVD processes. In the semiconductor manufacturing industry, efforts are continuing with the objective of reducing the discharge quantities of these gases primarily through: increasing the efficiency of gas use, breaking down the gases through abatement equipment, recovery and reuse of discharged gas, adoption of alternative gases, and development of new processes. At SiSC, in our work to reduce PFC gas discharge quantities, we are currently focusing on increasing the efficiency of gas usage and breaking down the gases through abatement equipment. It is said that the reason PFC gases have a high level of the greenhouse effect is because their properties remain very stable in air. Consequently, it requires large amounts of energy to break them down and generally equipment utilizing such special s as oxidation by high temperature burning, thermochemical reactions utilizing catalysts, and plasma electric discharge is used. These s of breaking down gases must be studied according to the application and purpose of each greenhouse gas, including issues such as the corresponding process and the type and quantity of the gases mixed in the process. In this regard, Table 4 shows the results of a comparison of the characteristics, such as treatment capacity, treatment performance, etc. for each gas breakdown. Breakdown : Energy By-products Other "Oxidation by burning" Fuel Second air needed for burning "Chemical reaction" Chemical agent (catalyst) Requires exchanging chemical agents and filling chamber with agents Plasma Breakdown effectiveness (CF 4) 95% 95% 95% Treatment capacity Large Medium Small Space Large Medium Small Ability to treat flammable gases (Multi-layer chemical agents) Difficult Ability to treat Somewhat Somewhat corrosive gases difficult difficult Ability to treat (chemical) Not possible Somewhat deposition by-products (requires pre-processing) difficult Later-stage Multi-layer chemical agent Later-stage treatment Later-stage treatment treatment Requires O 2 /H 2O for treatment Table 4: Comparison of greenhouse gas breakdown s These breakdown s can be evaluated for each manufacturing process, based on the above results. For CVD equipment, it can be concluded that for simultaneous treatment of dangerous flammable gases and deposition materials and for treating large volumes of exhaust gases, including purge gases, breakdown by means of oxidation by burning (which enables complete processing) is effective, in terms of both efficiency and safety. In contrast, in cases, such as etching equipment, where in a small amount of exhaust gas, the gas to be treated (broken down) has the same properties, it can be said that breakdown by the plasma or the chemical reaction using a chemical agent that has a comparatively small environmental impact would be effective. In regard to space requirements, in cases where a large amount of space cannot be used, such as cases where gas treatment equipment has to be added to an existing production line, the plasma is effective, because the required equipment can be installed in a small space. In contrast, in cases where adequate space is available, a large-scale oxidation by burning would be effective because it enables bulk treatment of large volumes of gas. Table 5 shows the reduction % s actually achieved through 2000, with the target level of 1.0 set at 90% of the actual discharge amount for 1995, for all of SiSC. From these results through 2000, it can be seen that, primarily through programs of improving utilization efficiency and breaking down gases through abatement equipment, an unexpectedly high 57% reduction in discharge amount, compared to the assumed discharge amount in the case of no gas treatment was achieved. In the future, to achieve the goals through year 2010, additional programs will be needed. 21

5 Discharge amount not targeted for treatment Discharge amount to be treated Reduction achieved (%) *1.0 = the absolute discharge amount in 1995 Table 5: Actual results in reducing greenhouse gases Programs at SiSC for reducing greenhouse gases in the future Concerning energy conservation, in the future also, we will have to pursue a variety of programs to achieve our goal to achieve annual average reduction in energy usage of 1%. To do that, programs which address the field of manufacturing equipment, where (compared to the field of facilities) few energy reduction programs are being conducted, will become important. Thus our plans address energy conservation as related to manufacturing equipment which involves the process group, facilities group, and also the equipment makers. In addition, the facilities engineering group is introducing the following energy conservation program for on-going study on an independent basis. 1 Recovery and re-use of unutilized energy 2 Full-scale introduction of CGS 3 High efficiency energy use through introduction of ice thermal storage 4 Improvement in efficiency of clean room air conditioning recycling energy Concerning reduction of PFC gas discharge quantity, the key thing for accomplishing our roadmap is to promote programs which involve both the process group and the facilities group. As its immediate theme, the process group is proceeding with the prompt introduction of programs, such as alternative gases, new processes, etc. for reduction of discharge quantity, cooperating with outside organizations, equipment makers, and materials makers. In addition, facilities group is continuing their work on breaking down greenhouse gases by means of abatement equipment, and, as a technology for the future, the group is continuing its study and evaluations aimed at introducing PFC gas recovery and reuse techniques. Conclusion In recent years, many global environmental problems have come to surround our company. Even beyond global warming, these include atmospheric pollution, noise and vibration, water quality contamination, waste disposal, resource depletion, etc. Based on recognition of corporate obligation, we want to maintain a keen awareness of these problems and take corrective actions to deal with them. 22