Case studies in energy use to realize ultra-high purities in semiconductor manufacturing

With increasing sophistication of products, there is a general trend towards higher purity (lower tolerances) in materials and parts. The purification of input materials and the need to create low-entropy environments in manufacturing lead to significant energy and materials use - referred to as secondary materialization. In this article we explore secondary materialization in semiconductor manufacturing by characterizing energy use trends for three cases: cleanrooms, producing ultrapure water (UPW), and purifying elemental gases. For purification of water and elemental gases, increasing purity standards are correlated with dramatic increases in energy use. For cleanrooms, while electricity use per square foot tends to increase with increasing air purity, this growth is cancelled by the evolution towards larger wafers and mini-environments. The net result is reductions in energy use per area of wafer processed when moving from 200 mm to 300 mm wafer processing. Given the continuing trend towards higher purity standards and growth in high-tech manufacturing, the high growth in secondary energy use suggests that the characterization and management of energy and materials use for purification deserves increased attention.

I. Introduction

THE increasing sophistication of products induces changes both in manufacturing processes and in the quality of materials used. There is a general trend towards lower tolerances for both physical and chemical properties in materials and parts. Semiconductor manufacturing is the most extreme representative of this trend, which requires raw materials with impurity levels in the parts per billion and cleanroom processing environments with less than 10 particles greater than 0.1µm in size per cubic meter. Purifying water and nitrogen accounts for 5% and 7% of fabrication facility electricity use respectively [1]. Production of silicon wafers is some 160 times more energy intensive per kilogram than the usual industrial grade [2]. The operation of cleanrooms (ventilation, heating, cooling) accounts for 30–46% of electricity consumption in fabrication facilities [1]. This suggests that in addition to purification of input materials, the need to create low-entropy environments when combining materials is also important in understanding energy consumption.