Innovations in nanotechnology are empowering scientists to deepen their understanding of physical, chemical and biological mechanisms. Powerful and precise characterization systems are essential to meet researchers’ requirements. SEEC (Surface Enhanced Ellipsometric Contrast) microscopy is an innovative advanced optical technique based on ellipsometric and interference fringes of Fizeau principles. This technique offers live and label-free topographic imaging of organic, inorganic and biological samples with high Z resolution (down to 0.1nm thickness), and enhanced X-Y detection limit (down to 1.5nm width). This technique has been successfully applied to the study of nanometric films and structures, biological layers, and nano-objects. We applied SEEC technology to different applications explored below.
The purpose of this paper is to define standard methods for effective and efficient image-based dimensional metrology for microlithography applications in the manufacture of integrated circuits. This paper represents a consensual view of the co-authors, not necessarily in total agreement across all subjects, but in complete agreement on the fundamentals of dimensional metrology in this application. Fundamental expectations in the conventional comparison-based metrology of width are reviewed, with its reliance on calibration and standards, and how it is different from metrology of pitch and image placement. We discuss the wealth of a priori information in an image of a feature on a mask or a wafer. We define the estimates of deviations from these expectations and their applications to effective detection and identification of the measurement errors attributable to the measurement procedure or the metrology tool, as well as to the sample and the process o fits manufacture. Although many individuals and organizations already use such efficient methods, industry-wide standard methods do not exist today. This group of professionals expects that, by placing de facto standard meth-odologies into public domain, we can help reduce waste and risks inherent in a "spontaneous" technology build-out, thereby enabling a seamless proliferation of these methods by equipment vendors and users of dimensional metrology. Progress in this key technology, with the new dimensional metrology capabilities enabled, leads to improved perform-ance and yield of IC products, as well as increased automation and manufacturing efficiency, ensuring the long-term health of our industry.
Foot (bottom corner) characterization of a trench or a line in semiconductor processing is of high interest to set and follow processes. The scanning probe microscopes (SPM) available at the present time are not capable of obtaining this measurement. Conventional atomic force microscopes (AFM) are not able to measure the shape of the foot of a trench or a line due to scanning algorithm and probe shape. Even CD-AFM performed with 2 dimensional servo code and boot shaped tips is limited in its ability to make this measurement if the corner is sharper than the radius of the corner of the boot tip used for measurement. We use an extra sharp probe (full cone angle 5 degrees or less) and a technique to tilt the sample to get at the foot of the structure to be measured. We are able to scan this corner of the structure and are able to characterize it by various techniques such as surface roughness. In addition, sidewall, line and line edge roughness can be addressed using the same technique. This characterization can be performed automatically and set as a production control.
As dimensions get smaller and circuits get more complex, the demand for comprehensive measurements of reticule geometries increases. 3D characterization of phase shift mask (PSM) is required to understand the quality of the transferred image. To avoid anomalies between the measurements, the structures on both mask/reticule and wafer should be measured using the same technique. The technique used should be insensitive to differences in the intrinsic characteristics of the materials (chromium on quartz, resist on conductive or non-conductive layers). Scanning probe microscopy (SPM) is ideally suited to make these characterizations on both masks/reticule and wafers. It quantitatively profiles lines and trenches in three dimensions. SPM is a nondestructive technique, allowing for the preservation of the integrity of mask and wafers. The profiles of features on a phase shift mask (PSM) are measured with SPM. Some undesirable effects such as micro loading versus structure size during quartz etch, positive slope of the quartz sidewall, and CD differential between chromium and quartz are characterized. Some of the corresponding features on the wafer are measured with SPM and the correlation between the mask anomalies and their effect on wafer features are established.
Decreasing dimensions of features in semiconductor device manufacturing makes it imperative to control the sidewall, line and line-edge roughness. The roughness contributes to the variation in critical dimension (CD) and it might affect device functions and reliability. Roughness of vertical surfaces is needed in order to understand its effect on the performance, especially in the case of structures such as optical wave-guides. One of the ways to measure the sidewall, line and line-edge roughness is to use a scanning probe microscope. By using specific techniques in operating the scanning probe microscope and special analysis, we obtain the sidewall, line and line-edge roughness. We also use high-resolution image of the sidewall to characterize its roughness with various techniques including spatial frequency analysis. Both qualitative and quantitative evaluations are demonstrated. These measurements are made with an automated tool in a non-destructive fashion and are useful in production control.
ULSI processing for the manufacture of devices such as DRAMs involves fabrication of several high aspect ratio structures. The determination and control of depth of these structures is crucial for device performance. We report the utilization of Atomic Force Microscopy to characterize 0.2 micrometers ground rule products. Features with 2.1 micrometers depth and 0.2 micrometers top nominal top width dimensions can be consistently measured. TO accomplish this a recently developed Deep Trench scan mode is employed and used in conjunction with new Super Angle Tapered CD and Super Angle COne tips. New analysis algorithms are developed to extract eh data in a repeatable from width decreased sensitivity to changes in tip size, top shape, and sample.
Focus exposure matrices (FEMs) are a critical tool for evaluating the performance of lithographic processes. Any change in any process component, including critical dimension (CD) targets, chemistry, optics, or processing times requires that an FEM be run to verify process performance. Scheduled FEMs are also used as part of regular process monitoring. The CD-AFM is a powerful tool in evaluating FEMs. Unlike standard AFMs it quantitatively profiles lines and trenches in three dimensions. Further, none of the tedious and time consuming sample preparation required by cross-sectional TEM or SEM is needed; since samples need not be cleaved, profiles can conveniently be measured anywhere on the wafer and in any order. A CD-FEM is used to characterize an FEM wafer and the results are compared with those obtained with electron microscopy. First, the CD-AFM is calibrated, which includes the characterization of the tip geometry. Then, the measurements on the FEM wafer is made and the results computed taking the tip width into account. The measurements thus obtained are compared with SEM measurements.
Ever-smaller dimensions and more complex circuits demand ever more accurate and precise characterization of mask geometry. Feature must be characterized non-destructively for attributes that include width, undercut, centering, shorting, rounding, optical proximity correction (OPC) and seriff formation. Once characterized, the transfer function of these mask features to wafer features must be determined. The CD-AFM is a uniquely powerful tool for performing these measurements on masks and wafers. It is non-destructive and provides data unobtainable with standard AFMs or electron microscopes. Unlike standard AFMs, it quantitatively profiles lines and trenches in three dimensions. It does not require any of the tedious and time- consuming sample preparation required by cross-sectional TEM or SEM. Another advantage of the CD-AFM is that the samples need not be cleaved and profiles can conveniently be measured anywhere on the wafer and in any order. CD-AFM is used to characterize the mask and techniques for setting the lithographic process are developed. The CD-AFM is calibrated, which includes the characterization of CD-AFM tip-geometry. The effect of tip-geometry on measurement-precision and accuracy are analyzed. Measurement throughput is explored including the benefits of automated data acquisition and analysis.