An Introduction to Semiconductor Manufacturing and Contamination Issues Control
2013 Update: While some of the information on this page is outdated, the experts at Northeastern are working on issues related to the subject matter below.
Studies estimate that contamination is responsible for 75% of the yield loss in integrated circuit fabrication1. Traditionally, surface cleaning research has been focused on front-end-of-the-line (FEOL) processes where the wafer substrate surface is not patterned. However, contamination also occurs during back-end-of-the-line (BEOL) processes with patterned wafer surfaces. The semiconductor industry faces the ongoing challenge of contamination removal.
The need for clean substrates in the fabrication of microelectronic devices has been well recognized since the dawn of solid-state device technology. Particles larger than about ¼ of the minimum line-width may cause fatal device defects. In the past, a 64-Mb 0.25-μm DRAM process flow had 60 to 70 cleaning steps. For 0.18μm CMOS technology about 80 of 400 process steps were cleaning.
As semiconductor device geometry continues to shrink and wafer sizes increase, the limitations of existing cleaning methods on devices yield will become more critical as the size of “killer” particles also shrinks. Physical substrate-independent cleaning processes are highly desirable since they do not have to be modified for different substrates (as in a chemical based cleaning process) and do not have a potential for modifying the surface (such as etching, roughening, etc.). Thus innovative cleaning processes are needed to specifically target removal of strongly adherent, nano-scale particles and contaminants.
Cleaning of deep submicron trenches presents a tremendous challenge in semiconductor manufacturing. Should manufacturers use steady flow or pulsating flow cleaning techniques? What other techniques are even more efficient for semiconductor manufacturing? Most particle removal techniques rely on weakening the adhesion force before or during cleaning for effective removal, so a fundamental phenomenon that needs to be understood is particle adhesion and how it changes during and after the manufacturing process.
There also is a need for reliable and accurate continuous monitoring of impurities in the vacuums or the ultra-pure gases used in most semiconductor processing. Moving the manufacturing process to an aqueous environment is another option.