Local Distribution of Particles Deposited on Patterned Surfaces

Abstract

In many process steps of integrated circuits (IC’s) fabrication, silicon wafers are coming in contact with process liquids such as ultra pure water (UPW) and aqueous and non-aqueous chemical mixtures. During these process steps, liquid-borne particle contamination can deposit on the wafer surface. Particle contamination from UPW is an important factor influencing random yield loss of IC’s [ ]. A number of yield models are used to predict yields including Poisson, Murphy, Seeds, and negative binomial models [ , ]. However, these models are based on the assumption that particles are randomly deposited on the wafer surface [ ].

Particles in Semiconductor Processing

“…It is P d that is the subject of our further investigations as it can have a large impact on yield, if the particle would have a preference to deposit on critical areas. It was shown [11] that particles do deposit on specific areas during the drying sequence of a cleaning procedure.…”

“…This is an important source of particles. If particles are present in the liquids they have plenty of opportunity to end up on the wafer surface (see Figure 3.4) [11]. During the immersion of the wafers into the liquids, hydrodynamic forces act on particles floating on the liquid whereby the particles are ''stamped'' on the wafer surface [12].…”

“…All contamination in the drying liquid will be left on the surface. The final step, drying, does not determine the number of particles left on the wafer, but rather the location on the wafer [11]. Wafers are exposed to liquids during lithography, cleaning, wet etching, galvanic deposition, spin-on layers, and polishing steps.…”

“…Yield models are using this boundary condition (see Section 1.2). It has been shown that particles coming out of a liquid do not deposit randomly [11]. If a surface has mixed areas that are hydrophobic and hydrophilic, particles tend to deposit on the hydrophilic areas, depending on the nature of the particles.…”