The accelerated reduction in feature size and the use of Damascene and advanced etching of gate electrodes is greatly challenging critical dimension and defect review metrology. These issues are discussed in the International Technology Roadmap for Semiconductors' Metrology Roadmap. Scanning electron microscopes (SEM) now require 3D imaging and metrology capability and other methods such as scatterometry and CD-AFM provide sidewall angle. Recent evaluation of the depth of field of SEM is below the typically expected micron range. In addition, improving precision, which is directly tied to resolution, can be done only at the expense of either beam voltage or depth of filed field. This greatly limits the application of CD-SEM to sub 70 nm technology generations (logic gates of 45 nm) unless a breakthrough in technology is achieved. Other methods also face challenges. Scatterometry is being extended to provide more than just the typical flat sidewall angle for advanced gate geometries. Metal gates seem to be a tremendous challenge considering that the relative transparency of poly silicon allows scatterometry an advantage. In this paper, the limitations of SEM, scatterometry, and AFM will be discussed in terms of future measurement requirements. An attempt to include new materials, such as porous low k interconnects, in this discussion will also be done.
This paper summarizes three studies of the semiconductor industry conducted at SEMATECH and MIT's Sloan School of Management. In conjunction they lead to the conclusion that rapid problem solving is an essential component of profitability in the semiconductor industry, and that metrology-based control is instrumental to rapid problem solving. The studies also identify the need for defect attribution. Once a source of a defect has been identified, the appropriate resources--human and technological--need to be brought into the physically optimal location for corrective action. The Internet is likely to enable effective defect attribution by inducing collaboration between different companies.
Realizing optimum integrated circuit yield has always been a formidable challenge for the semiconductor device manufacturer. With continuing reduction in minimum feature size, ongoing introduction of new materials and device architectures and inclusion of diverse functional blocks in the chip design, this challenge will continue to grow with each successive process technology node. The key focus areas that must be optimized to meet this challenge include: design for manufacturing and design for test; process technology development and transfer; modeling of random and systematic defect limited yields; detection and characterization of yield detracting defects; and integrated yield management for rapid defect sourcing. This paper will provide an overview of the tools and methods used in the industry today and outline future needs for achieving optimum yields with special emphasis on the focus areas listed above.
As integrated circuit fabrication processes continue to increase in complexity, it has been determined that data collection, retention, and retrieval rates will continue to increase at an alarming rate. At future technology nodes, the time required to source manufacturing problems must at least remain constant to maintain anticipated productivity as suggested in the International Technology Roadmap for Semiconductors. Strategies and software methods for integrated yield management have been identified as critical for maintaining this productivity. Integrated yield management must use circuit design, visible defect, parametric, and functional test data to recognize process trends and excursions so that yield-detracting mechanisms can be rapidly identified and corrected. This will require the intelligent merging of the various data sources that are collected and maintained throughout the fabrication environment.
Images of semiconductor defects are maintained in semiconductor yield management systems to diagnose problems that arise during the manufacturing process. A semiconductor-specific content-based image retrieval system was developed by Oak Ridge National Laboratory under the auspices of International SEMATECH (ISMT) during 1998 - 1999. The system uses commercial databases to store image information and uses a customized indexing technology to rapidly retrieve similar images. Additional defect information (position, wafer ID, lot, etc) has now been incorporated into the system through the use of additional database tables. During Fall 2000, the system was deployed in two ISMT member company fabs to demonstrate the utility of this approach in managing large databases of images and to show causal relationships between image appearance and wafer information such as processing layer, wafer lot, analysis dates, etc. This paper summarizes the results of these field tests and shows the utility of this approach through data analysis conducted on approximately one month of historical defect data.
With respect to the two major challenges in micromeasurement, which are high resolution and small object size, digital micro-holo-interferometry is proposed in this paper to provide quantitative information on load-induced variations of microstructures under testing. As primarily measured properties, the obtained deflection-load relationship enables subsequent accurate determination of strain and stress. More importantly, properties of materials in the micro level, which are known different greatly from those of identical bulky ones, can be evaluated based on these experimental input data for computational simulations. Developed upon the in-line configuration and incorporated with long distance microscope, the proposed system can achieve higher imaging performance and resolution capacity. Studies demonstrate that it is capable of realizing accurate measurement to microstructures with lateral dimensions of at least 8 microns. Its applications in characterization of microstructures are experimentally investigated on a micro cantilevered beam as an example. The load-induced deflection is obtained and validated with numerical simulated results based on finite element analysis.
There exist many techniques for the measurement of micro and nano surfaces and also several conventional ways to represent the resulting data, such as pseudo color or isometric 3D. This paper addresses the problem of building complete 3D micro-object models from measurements in the submicrometric range. More specifically, it considers measurements provided by an atomic-force microscope and investigates their possible use for the modeling of small 3D objects. The general approach for building complete virtual models requires to measure and merge several data sets representing the considered object observed under different orientations, or views.
Digital Holography makes it possible to reconstruct the phase distribution of wavefields directly. By application of interferometric technics the observed interference phase contains the information about the shape of the object under test and/or its deformation after loading. These data can be used to investigate the materials' behavior of microcomponents. However, the observed mod2(pi) -interference phase must be unwrapped and the absolute phase values have to be transformed into 3D-coordinates and displacement components. To this purpose a multi-wavelength procedure was developed that avoids the complicated spatial unwrapping procedure. Moreover an adapted calibration technique is used to calculate the metrological data from the distorted phase field. In combination with special loading techniques and physical models of the loading behavior of components with beam geometry some important material parameters such as the Young's modulus, the Poisson ratio and the thermal expansion coefficient of microcomponents can be measured. The paper describes the measuring technology and shows some examples of microcomponent testing.
Non-contact, high precision interferometric techniques like phase shifting interferometry (PSI), vertical scanning interferometry (VSI) and a VSI and PSI combination are commonly used for surface topography measurement. In order to obtain quality object surface data these techniques rely on both high fringe contrast and maximum intensity, which occur when the beams reflected from the reference and object surfaces are of equal intensity and when the fringe maxima are close to the saturation level of the detector. However, these conditions are difficult to attain when testing objects that have both high and low reflectance within the tested area such as ball grid arrays on a low-reflective substrate or a silver step on a glass substrate. Our proposals allow for obtaining better quality data when testing samples that have both high and low reflectivity areas. Separate modifications are suggested first for samples with different areas of reflectivity that are significantly separated in the vertical direction and second for samples with different reflectivity areas separated by less than about 10 microns in the vertical direction.
Manufacturing of semiconductor devices is an extremely complicated, time consuming, multi-stage process. In order to maintain acceptable yield levels, the production line must be continuously monitored. Scanning Electron Microscopes (SEMs) are employed by all advanced wafer fabrication lines (fabs) for imaging and review of sub- micron defects which may result in faulty circuits. Designed to greatly enhance the functions of a defect review SEM, the Applied Materials SEMVision cXTM is a fully automated defect review and classification system, that is able to generate a novel type of defect image, and to use the information in these images for automatic defect classification. A unique technology that was developed for this purpose is Multiple Perspective SEM Imaging (MPSITM), an electron detection method in which multiple detectors that differ in their spectral and spatial response, are employed such that multiple images (perspectives) containing complementary information are generated simultaneously.
A comprehensive defect analysis scheme has been described here incorporating defect monitoring, classification and review tools. The integration scheme is presented pictorially, and described in detail in the body of this paper. This paper will also describe CMP defects gathered using this new defect detection methodology.
Non-contact optical methods can be used for sub micron surface thermal characterization of active semiconductor devices. Point measurements were first made, and then real time thermal images were acquired with a specialized PIN- array detector. This method of thermal imaging can have spatial resolution better than the diffraction limit of an infrared camera and can work in a wide range of ambient temperatures. The experimentally obtained thermal resolution is on the order of 50 mK.
We demonstrate a through the substrate, numerical aperture increasing lens (NAIL) technique for high-resolution inspection of silicon devices. We experimentally demonstrate a resolution of 0.2 micrometers , with the ultimate diffraction limit of 0.14 micrometers . Absorption limits inspection in silicon to wavelengths greater than 1 micrometers , placing an ultimate limit of 0.5 micrometers resolution on standard subsurface microscopy techniques. Our numerical aperture increasing lens reduces this limit to 0.14 micrometers , a significant improvement for device visual inspection (patent pending). The NAIL technique yields a resolution improvement over standard optical microscopy of at least a factor of n, the refractive index of the substrate material, and up to a factor of n 2. In silicon, this constitutes a resolution improvement between 3.6 and 13. This is accomplished by increasing the numerical aperture of the imaging system, without introducing any spherical aberration to the collected light. A specialized lens made of the same material as the substrate is placed on the back surface of the substrate. The convex surface of this lens is spherical with a radius of curvature, R. The vertical thickness of the lens, D, should be selected according to D equals $ (1 + 1/n)-X and the substrate thickness X.
Silicon wafers that are fabricated by the Czochralski technique contain pyramidal pits, which are referred to in more general terms as crystal-originated particles (COPs). Because wafer inspection systems now benefit from the predictability of scattering from particles of known size, shape, and composition, it is of interest to achieve the same level of predictability for surface breaking defects such as pits. A model, valid for s-polarization and a high incidence angle, is based on the Fraunhoffer approximation for the diffraction from a square aperture, which neglects edge effects due to surface current accumulation at the periphery. Measurements and the model show that (using the prescribed optics configuration) a characteristic peak occurs between 20 and 45 degrees in the forward scatter region that increases in magnitude and moves forward with increasing pit size. Wafer inspection system designers can use this kind of information to improve their instruments' ability to distinguish between surface contaminants and COPs and to correctly gauge the size of COPs. Further work is underway to improve the fit between the model and the data and to extend its range of applicability.
An X-ray microtomography (or micro-CT) is an instrument for high-resolution 3D reconstruction of objects internal microstructure without destruction or time consuming specimen preparation. By using modern technology in x-ray sources and detectors several micro-CT systems were created as a simply usable desktop instrument. First micro-CT system is a laboratory instrument, giving true spatial resolution over a ten million times more detailed (in the term of volume parts) than the medical CT-scanners. The instrument contains a sealed microfocus X-ray source, a cooled X-ray digital CCD-camera and a Dual Pentium computer for system control and 3D-reconstructions running under Windows NT.
In this paper, the principle of our depth-image based surface measurement sensor using the single-stripe pattern is introduced. The mathematical model of depth measurement based on structured-light method is given. According to the analysis of the depth measurement error of our sensor, the design rules of our sensor is put forward so as to achieve the aim of enhancing the surface measurement precision of our sensor. The designed example of our sensor is given.