Evolution of the topographical and chemical signatures of plasma-treated surfaces along the staging time pathway

Plasma treatment is a widely used process in the semiconductor and electronics industries for surface preparation, via contamination removal and surface activation, promoting interfacial adhesion resulting in improved wire bondability and decreased occurrence of delamination at the interface. Due to the sensitivity of the surface to its immediate environment, the activated surface gradually lose its wettability. Thus, the positive plasma treatment effect diminishes over time, prompting the critical question about the duration wherein the surface is active. In the jargon of assembly process control, this duration is defined as the staging time; the total time from plasma treatment to the completion of the next process step, i.e., wirebond or molding. In this study, we monitor the topographical and chemical evolution of the surface prior to plasma treatment, immediately after plasma treatment, and at certain time points up to 72 h after plasma treatment, with the aim of correlating a measurable parameter such as contact angle (CA) to the topography (roughness) and chemical nature (oxide thickness and functionality) of the surface. Using scanning electron microscopy (SEM) and non-contact atomic force microscopy (NC-AFM), sessile drop contact angle meter, and sequential electro-reduction analysis (SERA), we show that the improvement of wettability imparted by the plasma treatment process arises from the stability of the surface topography (physical) and the promotion of the Cu2O layer (chemical). The loss of surface activation is possibly due to the reduction of the Cu2O layer, resulting from its conversion to CuO.