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In semiconductor fabrication industries, photomask cleaning with no pattern damage is a critical issue, especially for advanced technology nodes. Thus, optimization of cleaning techniques adopted for photomask cleaning or development of new cleaning technique is always of great interest to meet process requirements. In this book chapter, the sources of contaminants on photomask and their impact on imprinted images are first discussed. Then a critical review is presented on the wide spectrum of cleaning techniques and strategies that are adopted for the removal of particulate contaminants and organics from the photomask. The applicability of each technique and its limitations are also examined. Because extreme ultraviolet lithography (EUVL) is considered to be a next-generation lithography, a separate section is devoted to EUVL mask-cleaning techniques.

Chemical mechanical planarization (CMP) has emerged as a critical step in integrated circuit fabrication for achieving global surface planarization of various thin films in the front- and back-end processing. This has led to the development of novel and advanced post-CMP cleaning techniques that can effectively remove different types of contaminants (e.g., particulate, organic, metallic, etc.) from surfaces. There is an increasing effort toward improving the fundamental understanding of the interfacial phenomena and the underlying physical and mechanical mechanisms that drive the post-CMP cleaning process. In this chapter, a review of batch- and single-wafer brush and megasonic cleaning processes with emphasis on the effect of different process variables on particle removal is provided. The first few sections briefly describe the forces that drive particle adhesion and removal in a post-CMP cleaning process. The last part of the chapter focuses on the typical chemical formulations and the role of additives in post-CMP cleaning of silicon dioxide, tungsten, and copper films.

Publisher Summary This chapter focuses on the laser particle removal applications in the semiconductor industry. In the laser techniques, a laser beam with short pulse duration is used as a source of energy for nanoparticle detachment. In the case of particles with nanometer-scale characteristic diameters, the intermolecular forces dominate many other forces, especially those that are proportional to the volume (e.g., inertia and gravity) and surface (e.g., hydrodynamic and electrostatic forces) of the particle. As the feature size in nano-manufacturing is continuing to shrink and the number of particles on a surface to be removed is decreasing, the re-deposition-free particle removal requirements are inevitably becoming more stringent as yield remains a critical concern in nano-manufacturing, such as in the semiconductor industry. Advances in nanotechnology products have also been driving nano-particle removal research and development. The most common cleaning techniques employed in various high technology industries include brush scrubbing, ultrasonic and megasonic cleaning, centrifugal spray cleaning, vapor phase cleaning, fluid jet cleaning, and cryogenic cleaning. These techniques are often effectively employed for removal of large numbers of micro/nano-scale particles when particle re-deposition is not an issue. The major concerns of the current wet cleaning techniques with respect to semiconductor substrates are threefold: (i) material loss; (ii) contamination issues due to chemical residues (e.g., haze defects); and (iii) possibility of damage to features present elsewhere from the particle defects on the substrate, since conventional cleaning processes target the entire substrate; in other words, precision cleaning is not possible.

Publisher Summary This chapter describes the megasonic cleaning. Megasonic cleaning is a type of acoustic cleaning, related to ultrasonic cleaning. It is a gentler cleaning mechanism, less likely to cause damage, and is currently used extensively in wafer cleaning in semiconductor manufacturing. Similar to ultrasonic cleaning, megasonics utilizes a transducer, usually composed of piezoelectric crystals to create megasonic energy. The difference between ultrasonic cleaning and megasonic cleaning lies in the frequency that is used to generate the acoustic waves. Ultrasonic cleaning uses lower frequencies; it produces random cavitation. Megasonic cleaning uses higher frequencies at and above 1000 kHz; it produces controlled cavitation. An important distinction between the two methods is that the higher megasonic frequencies do not cause the violent cavitation effects found with ultrasonic frequencies. Megasonic cleaning is widely used for removing particles from wafer surfaces, as well as from critical component surfaces in other high-technology products, but its underlying mechanism is not clearly understood even by many of the practitioners. Unlike ultrasonics, which can function very effectively as a “physical” cleaner, with water and surfactant only, a megasonic cleaner typically relies upon strong chemistry to optimize cleaning. From an environmental point of view, this is not entirely desirable, but deploying megasonics very likely results in a reduction in chemical usage and in processing time, both highly desirable outcomes.