A Hybrid In-die Metrology Solution for High-order Overlay Control and CD Uniformity Improvement

Abstract

Overlay (OVL) and critical dimension uniformity (CDU) are two of the most critical process control steps to enable successful semiconductor manufacturing. A typical overlay control scheme uses an overlay feedback loop by measuring the overlay marks placed on the scribe line of the exposure field and returning scanner corrections through sophisticated data modeling. As the number of overlay marks increases, higher-order overlay correction can be performed, which results in better overlay performance. For CDU control, Scanner DoseMapper (DOMA) or ImageOptimizer (IMO) can provide effective compensation for inter-field and intra-field CD non-uniformity, which relies on the measurement of massive test structures placed on the scribe line using CDSEM or optical CD (OCD). As integrated circuit structures shrink, overlay control and CDU improvement are becoming more challenging. Differences of measurement results in the scribe line vs. product device are becoming more and more significant. In-die metrology can bring more accurate overlay and CD measurements, which leads to better overlay and CDU control. However, this means that a large number of test structures need to be placed in the product chip, or cell to achieve intra-field higher-order overlay correction and intra-field CDU improvement. We propose here a hybrid in-die metrology solution, using the same test structure for in-die overlay and CD measurements, which effectively saves valuable space within the cell.