Reducing measurement uncertainty drives the use of multiple technologies for supporting metrology

Abstract

Perhaps never before in semiconductor microlithography has there been such an interest in the accuracy of measurement. This interest places new demands on our in-line metrology systems as well as the supporting metrology for verification. This also puts a burden on the users and suppliers of new measurement tools, which both challenge and complement existing manufacturing metrology. The metrology community needs to respond to these challenges by using new methods to assess the fab metrologies. An important part of this assessment process is the ability to obtain accepted reference measurements as a way of determining the accuracy and Total Measurement Uncertainty 1 (TMU) of an in-line critical dimension (CD). In this paper, CD can mean any critical dimension including, for example, such measures as feature height or sidewall angle. This paper describes the trade-offs of in-line metrology systems as well as the limitations of Reference Measurement Systems 2 (RMS). Many factors influence each application such as feature shape, material properties, proximity, sampling, and critical dimension. These factors, along with the metrology probe size, interaction volume, and probe type such as e-beam, optical beam, and mechanical probe, are considered. As the size of features shrinks below 100nm some of the stalwarts of reference metrology come into question, such as the electrically determined transistor gate length. The concept of the RMS is expanded to show how multiple metrologies are needed to achieve the right balance of accuracy and sampling. This is also demonstrated for manufacturing metrology. Various comparisons of CDSEM, scatterometry, AFM, cross section SEM, electrically determined CDs, and TEM are shown. An example is given which demonstrates the importance in obtaining TMU by balancing accuracy and precision for selecting manufacturing measurement strategy and optimizing manufacturing metrology. It is also demonstrated how the necessary supporting metrology will bring together formerly unlinked technology fields requiring new measurement science. The emphasis on accuracy will increase the importance and role of NIST and similar metrology organizations in supporting the semiconductor industry in this effort.

Emerging machine learning strategies for diminishing measurement uncertainty in SPM nanometrology

“…Generally speaking, published studies consider two different inputs for ML processing: (1) quantitative data and (2) image or image-like data. Going back to the history of uncertainty quantification, Banke et al [82] proposed a method for measuring total measurement uncertainty (TMU) related to a source of measurement uncertainty in the calibration of the tip-sample interaction. Aside from that, ML is a promising method for reducing measurement uncertainty in SPM nanometrology via autonomous operation in both data acquisition and the subsequent data analysis processes.…”

Review of reference metrology for nanotechnology: significance, challenges, and solutions

“…Fig. 2 shows results from an earlier IBM study 8 where the RM was a combination of the CDAFM and CDSEM to evaluate a scatterometer measurement system or OCD. The left graph shows the first stage of calibration where the suitability of the CDSEM was evaluated by the CDAFM as the RM.…”

“…4, taken from a 2004 SPIE paper from IBM. 8 The graph of this figure shows an arbitrary ranking from 1 to 9 of three important metrology attributes with 9 being the best-intrinsic relative accuracy, sampling efficiency, and throughput. The x-axis purposely lists the spectrum of measurement technologies from the most automated measurement to the most labor-intensive measurement.…”

Advanced metrology needs for nanoelectronics lithography

“…Since the advent of commercial CD-AFM technology, these tools have gained modest acceptance in semiconductor manufacturing for process development and to support in-line CD metrology. The most common application of CD-AFMs has been to support CD-SEM metrology as a reference for tool matching or as a non-destructive alternative to TEM and SEM cross-sections [9][10][11][12][13]. There has also been significant use of CD-AFMs to study the properties of edges and sidewalls-specifically the line edge roughness (LER) [14,15].…”