Abstract
This paper constitutes an analysis of the forces of adhesion of small particles to surfaces, most specifically as applied to semiconductor surfaces. The primary forces of adhesion of small, less than 50 μm diam particles on a dry surface are van der Waals forces. These van der Waals forces of adhesion can increase as a function of time due to particle and/or surface deformation which increases the contact area; micron‐size particles can be held to surfaces by forces exceeding 100 dyn, which corresponds to pressures of 109 dyn/cm2 or more. Total forces of adhesion for micron‐size particles exceed the gravitational force on that particle by factors greater than 106. Electrostatic forces only become important and predominate for particles larger than 50 μm diam. Immersion of the adhered particle system can, in some cases, greatly reduce the total adhesion force, first by shielding of the electrostatic and van der Waals attractions, and also by adding double layer repulsion because of dipolar alignment of liquid molecules or dissolved ions at the surfaces. Double layer interactions may, however, also add to the attractive forces if dipoles align properly for attraction. An important consideration is the possibility that if the particles are not removed by the liquid immersion, then a liquid bridge can be formed by capillary action between the particle and surface upon removal from the liquid. This would add a very large capillary force to the total force of adhesion. This capillary force has been shown to remain, in some cases, even when the system is baked at above the liquid boiling point for more than 24h. Removal of these small particles from surfaces is in theory possible but is in practice extremely difficult. It is clear that emphasis should be placed on prevention of particle deposition rather than on counting on achieving subsequent removal.