Design optimization for a kinematic coupling for use in vacuum with minimum particle generation

Abstract

In the semiconductor industry, integrated circuits with nanometre scale structures are manufactured on silicon wafers. Particle contamination on the topside of the wafer can result in the defectivity of the entire die. In the ever-increasing efforts to create smaller structures onto a wafer particle contamination becomes more restrictive to prevent the defectivity of the die. In order to reduce the risk of particle contamination the wafer is placed in a vacuum environment. But further risks exist, during the grasping and positioning of the wafer new particles are generated and are able to transport to critical surfaces. This study investigates what guidelines need to be followed for the design of a kinematic coupling for use in a vacuum, whilst keeping particle generation as low as possible. The guidelines can be used to determine an optimal kinematic coupling design for any arbitrary object shape, size and mass. First of all, it is determined that abrasive wear, adhesive wear, contact stresses and outgassing are the predominant factors that have an effect on particle generation and influence the design of a kinematic coupling. The first guideline optimizes the constraint method of the kinematic coupling. Here, the guideline states that each constraint needs to be able to translate parallel to the surface of the object, doing so minimizes abrasive and adhesive wear. This can be achieved by suspending the contact points by using, for example, (folded) leaf springs. The second guideline encompasses the contact point shape and size. To equally distribute contact stresses, a spherical indenter shape should be chosen. Here, the radius of the indenter is chosen to be as small as possible to prevent adhesive wear. The third and last guideline optimizes the position of the contact points placed on the object. These positions influence the positioning repeatability, an algorithm is introduced that can calculate the optimal position for the contact points to maximize this repeatability. Also, the stability of the grasp is determined in terms of maximum allowable external disturbance forces.