The use of carbon nanotubes (CNT) as probes for atomic force microscopy (AFM) has been studied worldwide for more than a decade; however, the industries have not widely accepted CNT probes in their day-to-day operation. In this work, we present a series of studies on the metrology performance of CNT probes in semiconductor industry. A total of 54 CNT probes were studied for tip geometry, and 11 probes were tested on production wafers from a variety of IC manufacturers. Five out of the 11 probes were further evaluated for tip lifetime in semiconductor manufacturing environments. Statistical measurement data and tip shape characterization results provide insights on the applications of CNT probes in microlithography process control.The recent advancements in AFM scan algorithms that enable the control and use of CNT probes were also discussed in this paper. Sidewall measurement data using tilted CNT probes, and the AFM image of a CNT probe showing a comparable resolution to that of transmission electron microscopy (TEM) were presented for the first time. The combination of advanced AFM system and CNT probes has proven to perform challenging metrology in 65 nm node and beyond.

We present 3-dimensional atomic force profiler (AFP) measurements on die-scale flatness (20 mm x 20 mm) after copper and STI CMP. True metrology is achieved for patterned wafers. Wafers are vacuummounted on a flat chuck, as they would be in a stepper, so wafer warpage and strain-related non-planarity are not present. The results of this new technique are compared against current measurement techniques. For logic, memory and System-on-a-chip, we discuss the implications of wafer planarity going into subsequent photolithography steps.

The need for absolute accuracy is increasing as semiconductor-manufacturing technologies advance to sub-65nm nodes, since device sizes are reducing to sub-50nm but offsets ranging from 5nm to 20nm are often encountered. While TEM is well-recognized as the most accurate CD metrology, direct comparison between the TEM data and in-line CD data might be misleading sometimes due to different statistical sampling and interferences from sidewall roughness. In this work we explore the capability of CD-AFM as an accurate in-line CD reference metrology. Being a member of scanning profiling metrology, CD-AFM has the advantages of avoiding e-beam damage and minimum sample damage induced CD changes, in addition to the capability of more statistical sampling than typical cross section metrologies. While AFM has already gained its reputation on the accuracy of depth measurement, not much data was reported on the accuracy of CD-AFM for CD measurement. Our main focus here is to prove the accuracy of CD-AFM and show its measuring capability for semiconductor related materials and patterns. In addition to the typical precision check, we spent an intensive effort on examining the bias performance of this CD metrology, which is defined as the difference between CD-AFM data and the best-known CD value of the prepared samples. We first examine line edge roughness (LER) behavior for line patterns of various materials, including polysilicon, photoresist, and a porous low k material. Based on the LER characteristics of each patterning, a method is proposed to reduce its influence on CD measurement. Application of our method to a VLSI nanoCD standard is then performed, and agreement of less than 1nm bias is achieved between the CD-AFM data and the standard's value. With very careful sample preparations and TEM tool calibration, we also obtained excellent correlation between CD-AFM and TEM for poly-CDs ranging from 70nm to 400nm. CD measurements of poly ADI and low k trenches are also reported, and both show good correlation to in-line CD-SEM results.

No abstract

No abstract