Abstract
An overlay error was analyzed by the least square circle method and error factors were revealed in 3D microfabrication technology using surface-activated bonding. Ten-layered thin-film stacking structures were fabricated with several batches and the overlay errors determined by the shifts of the center coordinates of the layers were examined. It was found that the overlay errors were classified into three factors : (1) intra-cell random error of σ1 = 34 nm; (2) inter-cell random error of σ2 = 98 nm; and (3) inter-cell systematic error of 32 nm/mm. The dominant causes of the intra-cell random error were the patterning error of the thin films on a donor substrate 32.6 nm, and the measurement error 9.5 nm. The major causes of the inter-cell random error were the positioning error of XY stage 73.6 nm and the fluctuation of Z stage in XY directions 46 nm, each induced by the vibration of vacuum pump. The inter-cell systematic error was observed in spite of an alignment operation between the donor substrate and XY stage. An alignment simulation was revealed that the systematic error was developed by the random error of alignment mark coordinates acquired in the alignment operation. It was also demonstrated that the inter-cell systematic error was reduced down to 9 nm/mm by applying an average reading method of the alignment mark coordinates.
