The measurement of edge roughness has become a hot issue in the semiconductor industry. Especially the contact roughness is being more critical as design rule shrinks. Major vendors offer a variety of features to measure the edge roughness in their CD-SEMs. For the line and space patterns, features such as Line Edge Roughness (LER) and Line Width Roughness (LWR) are available in current CD-SEMs. However the features currently available in commercial CD-SEM cannot provide a proper solution in monitoring the contact roughness. We had introduced a new parameter R, measurement algorithm and definition of contact edge roughness to quantify CER and CSR in previous paper. The parameter, R could provide an alternative solution to monitor contact or island pattern roughness. In this paper, we investigated to assess optimum number of CD measurement (1-D) and fitting method for CER or CSR. The study was based on a circular contact shape. Some new ideas to quantify CER or CSR were also suggested with preliminary experimental results.
Proc. SPIE. 5752, Metrology, Inspection, and Process Control for Microlithography XIX
KEYWORDS: Electronics, Sensors, Electron microscopes, Control systems, Image analysis, Scanning electron microscopy, Image quality, Critical dimension metrology, Semiconducting wafers, Electron transport
Contact patterns that have high aspect ratio (HAR) are inevitable as the design rule has been shrunk in semi-conductor fabrication processes. HAR contacts have serious troubles to monitor the Critical Dimension (CD) of the contact bottom images with Scanning Electron Microscope (SEM). Because we can not see the bottom images anymore with general methods as the contact is getting deep. We must be able to extract secondary electrons from the contact bottom to monitor the bottom images in the contact patterns. One possible solution that we may suggest is using positive charges on the wafer surface as a driving force for secondary electrons from the contact bottom. If the positive charges are generated on the wafer surface, an electric field will be created between the contact bottom and the wafer surface. The electric field will drive the secondary electrons from the contact bottom to the wafer surface, which makes the contact bottom images. High surface voltage can be acquired when the electron energy and the magnification in pre-charge are smaller, but it requires longer charging time. High probe current can help the charging time in this case, though it may cause some damages on the wafer. After all, optimized determination is required considering the charging time and the surface voltage at various aspect ratios. In addition, there is one thing that we must consider. When the charged contact pattern is exposed to electrons at high magnification, the surface voltage on the wafer surface tends to be stabilized at lower voltage which causes fading away of the contact bottom images. Therefore, electron exposure must be minimized at high magnification by setting the focus a little away from the observation point and so on.
The measurement of edge roughness has become a hot issue in the semiconductor industry. Major vendors offer a variety of features to measure the edge roughness in their CD-SEMs. However, most of the features are limited by the applicable pattern types. For the line and space patterns, features such as Line Edge Roughness (LER) and Line Width Roughness (LWR) are available in current CD-SEMs. The edge roughness is more critical in contact process. However the measurement of contact edge roughness (CER) or contact space roughness (CSR) is more complicated than that of LER or LWR. So far, no formal standard measurement algorithm or definition of contact roughness measurement exists. In this article, currently available features are investigated to assess their representability for CER or CSR. Some new ideas to quantify CER and CSR were also suggested with preliminary experimental results.