Efficiency Engineering Leads To Operational Cost Reduction
Approximately 40% of the operational costs of a new wafer fab are due to capital investment, and another 30% can be attributed to the supply and disposal of materials and energy. Consequently, activities that support the continuous reduction of material and energy consumption and disposal will improve cost of ownership and therefore the financial performance of a fab (Gälli et al.).
During the processing of GaAs wafers, wet cleaning and wet etching are used. These processes require large amounts of ultra-pure water and expensive chemicals, and produce wastewater containing arsenic compounds that must be treated at high cost.
In dry etching some of the process gases used are perfluorinated carbons (PFCs) or related compounds, which results in exhausts containing these gases, their reaction products and arsenic compounds. In GaAs device fabrication the epitaxy process alone often contributes to more than 50% of the wafer cost. This includes the costs for energy as well as chemicals and gases such as trimethyl gallium, arsine and hydrogen. Many of these and their related compounds are toxic, pyrophoric or explosive, and therefore require specific investments for their safe delivery and handling, as well as for the emission control of exhaust, wastewater and solid waste. As a result, efficiency improvements include both the consumption of material and energy as well as the resulting emissions, making the management of reduction programs crucial.
The continual introduction of new processes and materials also creates new costs in supply, disposal, safety and health. To foresee and understand these costs in the context of the entire fab is also therefore an ongoing and critical management task.
The efficiency engineering approach
In a compound semiconductor fab the supply and disposal demands of production determine the capacity of the facility. Within the fab, individual facility systems influence each other. If production needs more ultra-pure water, the consumption of raw water, nitrogen, electricity, chemicals, and heating and cooling energy, will also increase to a certain extent, since these materials are used in the ultra-pure water plant.
This simple example illustrates the importance of thinking in terms of systems rather than considering plants or media individually. The financial consequences of any planned changes can only be assessed if cost transparency is achieved.
Cost transparency is a key factor in achieving the optimal financial performance of a wafer fab. This is where efficiency engineering comes in. The following five elements are the basis for efficiency enhancement of a compound semiconductor fab:
• transparency of mass, energy and cost flows;
• monitoring of equipment performance;
• benchmarking of production and facility efficiency;
• cost-reduction programs to optimize efficiency;
• planning of future developments.
Combining these elements with the overall efficiency goals set by the fab management will result in a continuous improvement process that is fully compatible with the ISO 14001 strategy of establishing an environmental management system.
The methodologies for efficiency engineering are mass- and energy-flow analyses, which are based on the principles of mass and energy conservation. By assigning costs to the media, a cost-flow analysis can be achieved.
Mass-, energy- and cost-flow analyses are used to optimize the entire fab based on input and output considerations. The bottom-up approach starts with the individual equipment and may end at the level of the entire fab (figure 1). In the efficiency engineering approach the fab is viewed as the sum of the processes which have a potential for improvement.
Cost-saving potentials can be classified according to their potential for implementation. Short-term optimization may be implemented immediately without interference to the manufacturing processes. Examples include reducing excessive consumption, changing the segregation of waste streams, and reusing/recycling material and energy.
Long-term optimization includes improvements that often require minor adaptations of processes and equipment. These improvements need to be evaluated and will only be implemented if they are financially attractive. Some improvements might become relevant when assessing cost of ownership for new process equipment. Improvements affecting process equipment and process design require the integration of the tool manufacturer.
M+W Zander s approach is the application of efficiency engineering throughout the entire life cycle of a fab, including design, construction and facility management. This leads to an increase in productivity and a reduction in the total cost of ownership.