T Mcwaid

Methods divergence between measurements of micrometer and sub-micrometer surface features

Measurements of micrometer and sub-micrometer surface features have been made using a stylus profiler, an STM, an AFM and a phase-measuring interferometric microscope. The differences between measurements of the same surface feature as obtained with the different instruments illustrate the problem of methods divergence. Measurements are compared in an effort to point out, and explain, the observed methods divergence.

Increasing the value of atomic force microscopy process metrology using a high‐accuracy scanner, tip characterization, and morphological image analysis

Atomic force microscopes are being used increasingly for process metrology. As a case study, the measurement by atomic force microscope of a soda lime glass optical disk patterned using optical lithography and reactive plasma etching is examined. The atomic force microscope used for this measurement has a highly accurate scanner system. The X, Y, and Z axes are calibrated using laser interferometry. To determine the shape of the tip used a commercially available tip calibration artifact was imaged both before and after the measurement. The image was corrected for the tip shape using mathematical morphology. The value of the atomic force microscope measurement is defined to be the impacts of the metrology on the product or process. It is shown that the value of atomic force microscopy process metrology on an optical disk is increased by using an accurate scanner, tip characterization, and morphological image analysis; however, the cost per measurement is increased as well. In general, the characteristics o...

Progress on accurate metrology of pitch, height, roughness, and width artifacts using an atomic force microscope

NIST personnel (J.S. and T.M.) visited 23 IC manufacturing companies and equipment suppliers during 1994 to determine semiconductor industry needs for scanned probe metrology. NIST has initiated projects addressing some of the need identified. When complete these projects will enable improved metrology using the scanned probe microscope. Industry needs include pitch, height, angle, and width calibration artifacts, and understanding of the effect of humidity on AFM measurements, and tip metrology techniques. To meet these needs we have designed and built a Calibrated Atomic Force Microscope (C-AFM) with interferometric position control. This AFM is capable of making accurate measurements. We present the operational characteristics of the instrument, accurate X, Y, and Z pitch measurements on a commercially available artifact, measurements on a prototype surface roughness artifact, and a promising technique by which to make accurate linewidth measurements.

Effects of thin films on interferometric step height measurements

Optical profiling instruments utilizing phase-shifting interferometry offer one the opportunity to obtain a large amount of surface texture data quickly without damaging the measured surface. Unfortunately, the presence of dissimilar surface materials or even spatial variations in the subsurface morphology can result in spurious optical measurements. This paper presents equations that can be used to calculate the reflection of electromagnetic radiation from thin film structures. These equations are utilized to determine what minimum metal overcoat thickness will ensure accurate optical step height measurements. Interferometric and stylus- based measurements of three thin film steps are presented and discussed. An opaque metal overcoat is found to be essential to the accurate optical measurement of step heights.

Measurement of a CD and sidewall angle artifact with two-dimensional CD AFM metrology

Despite the widespread acceptance of SEM metrology in semiconductor manufacturing, there is no SEM CD standard currently available. Producing such a standard is challenging because SEM CD measurements are not only a function of the linewidth, but also dependent on the line material, sidewall roughness, sidewall angle, line height, substrate material, and the proximity of other objects. As the presence of AFM metrology in semiconductor manufacturing increases, the history of SEM CD metrology raises a number of questions about the prospect of AFM CD artifacts. Is an AFM CD artifact possible? What role would it play in the manufacturing environment? Although AFM has some important advantages over SEM, such as relative insensitivity to material differences, the throughput and reliability of most AFM instruments is not yet at the level necessary to support in-line CD metrology requirements. What, then, is the most useful relationship between AFM and SEM metrology? As a means of addressing some of these questions, we have measured the CD and sidewall angle of 1.2 micrometer oxy-nitride line on Si using three different techniques: optical microscopy (with modeling), AFM, and cross sectional TEM. Systematic errors in the AFM angle measurements were reduced by using a rotational averaging technique that we describe. We found good agreement with uncertainties below 30 nm (2 sigma) for the CD measurement and 1.0 degrees (2 sigma) for the sidewall angles. Based upon these results we suggest a measurement procedure which will yield useful AFM CD artifacts. We consider the possibility that AFMs, especially when used with suitable CD artifacts, can effectively support SEM CD metrology. This synergistic relationship between the AFM and SEM represents an emerging paradigm that has also been suggested by a number of others.

Instrument for calibrating atomic force microscope standards

To facilitate the use of AFMs for manufacturing we have initiated a project to develop and calibrate artifacts which can in turn be used to calibrate a commercial AFM so that subsequent AFM measurement are accurate and traceable back to the wavelength of light. We plan to calibrate our artifacts using a specially designed AFM system which we call the Calibrated AFM (C-AFM). The C-AFM has been constructed as much as possible out of commercially available components. We use a flexure stage driven by piezoelectric transducers for scanning; a heterodyne interferometer to measure the X-Y position of the sample; a capacitance sensor to measure the Z position of the sample; and a commercially available AFM control system. The control system has two feedback loops which read from the X and Y interferometers, respectively, and adjust the piezoelectric voltages to keep the X-Y scan position accurate. The critical electromechanical and metrology issues involved in the construction and operation of such a system are discussed in detail.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.