New AFM imaging for an inline LSI process monitor

Hosaka, Sumio; Morimoto, Takafumi; Kuroda, Hiroshi; Minomoto, Yasushi; Kembo, Yukio; Koyabu, Hirokazu

doi:10.1117/12.473488

Cited by 5 publications

(8 citation statements)

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“…As was shown in the mechanical analysis of cantilevers and probe tips 16,17,22 , when a probe tip touches the steep sidewall of a high-aspect-ratio structure, the tip slips on the slope, causing distortions to the measured profile. In a previous studyX 17 P, we determined the relationship between the sidewall angle and the lateral displacement caused by the probe tip slipping on the sidewall.…”

Section: Modeling Of Probe Deflection Caused By Attractive Force Frommentioning

confidence: 95%

“…Here, we explain StepIn™ mode 13,14,15,16,17 . In this method, which is illustrated in Figure 2, after each height sampling point (i.e., measurement pixel), the AFM probe is retracted to a height where the probe tip does not detect short distance forces (such as van der Waals forces and capillary forces) from the sample, and the probe is moved laterally to the next measuring point (1).…”

Section: Introductionmentioning

confidence: 98%

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A novel AFM method for sidewall measurement of high-aspect ratio patterns

et al. 2008

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To use atomic force microscope (AFM) to measure dense patterns of 32-nm node structures, there is a difficulty in providing flared probes that go into narrow vertical features. Using carbon nanotube (CNT) probes is a possible alternative. However, even with its extremely high stiffness, van der Waals attractive force from steep sidewalls bends CNT probes. This probe deflection effect causes deformation (or "swelling") of the measured profile. When measuring 100-nm-high vertical sidewalls with a 24-nm-diameter and 220-nm-long CNT probe, the probe deflection can cause a bottom CD bias of 13.5 nm. This phenomenon is inevitable when using long, thin probes whichever scanning method is used.We have developed a method of deconvolving this probe deflection effect that is well suited to our AFM scanning mode, AdvancedStep-in TM mode. In this scanning mode, the probe is not dragged on the sample surface but approaches the sample surface vertically at each measurement point. The CNT probe deformation is stable because we do not use cantilever oscillation that can cause instability, but we detect static flexure of the cantilever. Consequently, it is possible to estimate the amount of CNT probe deflection by detecting the degree of cantilever torsion. Using this information, we have developed a technique for deconvolving the probe deformation effect from measured profiles. This technique in combination with deconvolution of the probe shape effect makes vertical sidewall profile measurement possible.

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Section: Modeling Of Probe Deflection Caused By Attractive Force Frommentioning

confidence: 95%

Section: Introductionmentioning

confidence: 98%

A novel AFM method for sidewall measurement of high-aspect ratio patterns

et al. 2008

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“…As was shown in a mechanical analysis of cantilevers and probe tips 10,11 , when a probe tip touches a steep sidewall of a high-aspect-ratio structure, the tip slips on the slope, causing errors in height and distorting the measured profile. This effect can be decreased by reducing the force of the probe tip contacting the sample surface.…”

Section: Requirements For High-aspect Ratio Pattern In-line Measurementmentioning

confidence: 95%

“…We have a proprietary AFM scanning method named Step in mode® 7,8,9,10,11,12 . This method is illustrated in Figure 2.…”

Section: Introductionmentioning

confidence: 99%

An advanced AFM sensor for high-aspect ratio pattern profile in-line measurement

et al. 2006

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Design rule shrinkage and the wider adoption of new device structures such as STI, copper damascene interconnects, and deep trench structures have increased the necessity of in-line process monitoring of step heights and profiles of device structures. For monitoring active device patterns, not test patterns as in OCD, AFM is the only non-destructive 3D monitoring tool. The barriers to using AFM in-line monitoring are its slow throughput and the accuracy degradation associated with probe tip wear and spike noise caused by unwanted oscillation on the steep slopes of highaspect-ratio patterns. Our proprietary AFM scanning method, Step in mode®, is the method best suited to measuring high-aspect-ratio pattern profiles. Because the probe is not dragged on the sample surface as in conventional AFM, the profile trace fidelity across steep slopes is excellent. Because the probe does not oscillate and hit the sample at a high frequency as in AC scanning mode, this mode is free from unwanted spurious noises on steep sample slopes and incurs extremely little probe tip wear. To fully take advantage of the above properties, we have developed an AFM sensor optimized for in-line use, which produces accurate profile data at high speeds.The control scheme we have developed for the AFM sensor, which we call "Smart Step-in", elaborately analyses the contact force signal, enabling efficient probe tip scanning and a low and stable contact force. The mechanism of the AFM sensor has been optimized for the higher scanning rate and has improved the accuracy, such as the scanning planarity, position and height accuracy, and slope angle accuracy. Our prototype AFM sensor can scan high-aspectratio patterns while stabilizing the contact force at 3 nN. The step height measurement repeatability was 0.8 nm (3σ). A STI-like test pattern was scanned, and the steep sidewalls with angles of 84° were measured with high fidelity and without spurious noises.

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“…A high aspect ratio probe is bent easily or broken in the worst case. It was difficult to apply conventional AFM methods to critical dimension (CD) metrology for Step-in mode [9][10][11][12] . In the Step-in mode, a probe is scanned only when it is away from a surface of a sample therefore lateral force with scanning does not act on the probe.…”

Section: Introductionmentioning

confidence: 99%

New atomic force microscope method for critical dimension metrology

et al. 2003

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We have developed a new atomic force microscope method that we call Step-in mode. The Step-in mode can realize a high aspect ratio structure observation without tip damage because of its unique probing method. Three types of high aspect ratio probe, a silicon probe sharpened by focused ion beam, a high density carbon probe and a carbon nanotube probe, are analyzed to make clear which probe is appropriate for high aspect ratio structure metrology. It is demonstrated that fine measurement can be carried out with all types of probe and we conclude that the high density carbon probe is the best at the present time. Experimental results show that the pitch repeatability for a standard grating sample is 1.2 nm at 3σ, height repeatability is 1.2 nm at 3σ and width repeatability of a poly-silicon gate with side-wall is less than 3 nm at 3σ. It is also demonstrated that there is no tip damage after taking 1000 profiles of 512 data points in the Step-in mode. The experimental results show that the Step-in mode has a potential for application to critical dimension metrology for a LSI process monitor.

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New AFM imaging for an inline LSI process monitor

Cited by 5 publications

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A novel AFM method for sidewall measurement of high-aspect ratio patterns

A novel AFM method for sidewall measurement of high-aspect ratio patterns

An advanced AFM sensor for high-aspect ratio pattern profile in-line measurement

New atomic force microscope method for critical dimension metrology

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