Hidetoshi Nishiyama

New voltage-contrast imaging method for detection of electrical failures

A new voltage contrast imaging method using single scan of high current electron beam has been developed. This method achieved the automatic inspection system, which detects electrical failures in acceptable amount of time. The sensitivity of the system is evaluated using open failure of via holes. First, the image contrast of poly-Si deposited on defective via holes is measured. Then the cross section of the defects is examined to obtain the correlation between contrast and the thickness of resistive residue at the bottom of the defective via holes. The result shows that this imaging method is capable of detecting 2 nm oxide remaining at the bottom of via.

Open-contact failure detection of via holes by using voltage contrast

We used two techniques to determine the sensitivity of a scanning-electron-microscope-based wafer-inspection system in detecting open-contact failures. (1) The correlation between the contact resistance and the brightness of the voltage-contrast image as captured by the system was obtained experimentally. (2) A voltage-contrast simulation was developed and applied to derive a correlation between resistance and brightness from these results. A close agreement between the experimental results and the calculated values was obtained. We succeeded in clarifying the determinants of the sensitivity of open-contact-failure detection. The brightness, over part of its range, appears to be proportional to log(R*Ip) where R is the resistance and Ip is the irradiating electron-beam current. This relationship indicates that the sensitivity of open-contact failure detection is determined by Ip. Control of Ip can be used to improve the voltage contrast, and this, in turn, can improve the sensitivity of detection.

An energy analyzer for high-speed secondary electrons accelerated in inspection SEM imaging

An energy analyzer has been developed to evaluate sample charging and voltage-contrast (VC) in a retarding-type scanning electron microscope (SEM) for inspecting semiconductor devices for defects. Since secondary electrons (SEs) are accelerated by the strong retarding field, a high degree of accuracy is needed to evaluate the energy of SEs. The energy analyzer consists of several electrodes for forming suitable electrostatic lens fields. Evaluation results showed that energy resolution of 2 eV for SE incident energy of 9.5 keV was attained and that evaluations of charging voltages on patterned samples were performed quantitatively.

Quantitative scanning electron microscope measurement of resistance of incomplete contact holes in ultralarge scale integrated devices

A method for measuring quantitative resistance of incomplete contact holes in ultralarge scale integrated devices-which uses the brightness of voltage contrast in scanning electron microscope (SEM) images-was proposed. The voltage contrast between a contact hole and the surrounding SiO2 surface was observed by both high and low electron-beam-current SEMs and compared with the resistance of that contact hole measured by a nanoprober. The relationship between the SEM-image brightness and the contact-hole resistance was analyzed theoretically by voltage-contrast simulation based on time-differential equations. It was found that the brightness, within 0<log(RIp)<3, is proportional to log(RIp), where R is the contact resistance and Ip is the irradiating electron-beam current. It is thus concluded that resistance of incomplete contact holes can be determined quantitatively by utilizing the relationship between SEM-image brightness and the contact-hole resistance.

Advanced inspection technique for deep-submicron and high-aspect-ratio contact holes

We developed a technique using electron beams for inspecting contact holes immediately after dry etching and detecting incomplete contact failures. Wafers with deep-submicron contact holes that had high aspect ratios of 10 could be detected during practical inspection time by controlling the charging effect on the wafer surfaces. Measurements of the energy distribution in the secondary electrons exhausted from the bottom of the holes indicated that they were accelerated by the charge-up voltage on the wafer surfaces. Our analysis showed that high-density electron beams must be used to charge the surfaces when the aspect ratio is high. The minimum thickness of the residual SiO 2 that could be detected at the bottom of the contact holes was 2 nm using an aspect ratio of 8. Applying this mechanism to optimize the dry etching process in semiconductor manufacturing showed that we could achieve reliable process control.

Defect inspection on CMP process and its application

A high-throughput high-sensitivity defect-detection technique has been developed for manufacturing 0.15-0.25- micrometers LSI devices. It incorporates a high-resolution detection systems using multi-channel detectors and a high- resolution imaging system using spatial filtering and collimated focused-beam illumination. A new algorithm called correlated local area statistical threshold enables this technique to achieve a sensitivity of 0.15 micrometers on front- end processes and 0.3 micrometers on back-end processes and a high throughput.