George W. Banke

Characteristics of accuracy for CD metrology

The evaluation of a critical dimension (CD) metrology tool foes beyond determining precision. A year ago at this conference, a paper was presented which described the efforts of the SEMATECH metrology group to describe the characteristics of a CD metrology SEM. In that referenced paper there was a description of accuracy, or characteristics of accuracy, that needed evaluation as well. In this paper these characteristics are further developed. Tool evaluation for accuracy requires well characterized artifacts. Constructing these share many of the same hurdles as constructing true standards. Evaluation artifacts must have properties that vary similarly to the products to be measured in the manufacturing line. They also must be characterized by a reference measurement system (RMS) sufficiently well to make the result of an evaluation reflect upon the tool under investigation and not the RMS. This paper details the construction of such an artifact using SEM measurements of cross sections as part of the RMS and the use of this artifact in the evaluation of several CD SEMs. Application of this project to SEMATECH evaluation artifacts currently under construction is also discussed.

New apparent beam width artifact and measurement methodology for CD-SEM resolution monitoring

The Apparent Beam Width (ABW) total system resolution metric is part of the International SEMATECH CDSEM specification and bench marking activities. It is also used in our own CDSEM specification, evaluations, and tool maintenance activities. Our first set of ABW artifacts, constructed a few years ago, need retirement for several reasons, including: (1) their materials and dimensions no longer represent current manufacturing line samples and (2) their line edge variation is too large for current and future ABW applications. The construction and testing of a new ABW artifact will be discussed in this paper. The use of ABW as a monitor for total system resolution requires a unique set of sample characteristics, which include near vertical sidewalls, minimal top corner rounding, minimal line edge roughness (LER), and good line edge uniformity across the artifact set. Several process iterations were performed using the latest photolithographic processes whilst including numerous measurement evaluations in order to achieve these characteristics. A sampling methodology has been formulated to take advantage of the good within-field, field-to-field, and wafer-to-wafer uniformities of the artifacts. In addition to driving resolution improvements ABW also serves as a metric for tool-to-tool matching in a manufacturing environment.

Toward a unified advanced CD-SEM specification for sub-0.18-μm technology

The stringent critical dimension control requirements in cutting edge device facilities have placed significant demands on metrologists and upon the tools they use. We are developing a unified, advanced critical dimension scanning electron microscope specification in the interests of providing a unified criterion of performance and testing. The specification is grounded on standard definitions and strong principles of metrology. The current revision is to be published as a SEMATECH document. A new revision, now in progress, will embody the consensus of a vendor/user conference.

Monitoring printing fidelity with image correlation measurements on the CD SEM

A promising use for image and waveform correlation measurements now possible on modern CDSEMs is to monitor pattern fidelity in printing for multiple structural dimensions. This work explores some ofthese possibilities specifically for image correlation. Two different CDSEM-based pattern recognition engines and off-line image correlation with several image enhancement techniques are examined. The printing fidelity of an unassisted cross as a function of stepper focus and dose is studied because the variations of the structural details demonstrate many of the issues of concern in lithography today. Strategies for extracting the most information with the least beam writing are also explored. In some examples the pattern recognition score is directly interpretable in terms ofprinting fidelity. With additional calibration overhead associated with a particular lithography process, scores can be interpreted in terms ofprinting variables such as defocus and dose. The conflict in goals for using image correlation for navigation versus monitoring pattern fidelity is also discussed.