Mari Nozoe

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.

Detecting Defects in Cu Metallization Structures by Electron-Beam Wafer Inspection

A technique using an electron-beam to inspect wafers with Cu interconnects was developed. It can detect defects such as voids or incomplete contact failures with resistances of more than 10 7 Ω by utilizing the voltage contrast of a secondary electron image. The technique is performed by controlling the charging voltage of the interconnect while the electron-beam is irradiating the wafer. The charging voltage was found to depend on the conditions of the incident electron-beam, including the incident energy. To investigate the generation of voltage contrast in a Cu via chain, the electronic characteristics of detected defects were measured with probes. It was found that the resistance of a defect measured during electron irradiation and that measured with probes agree well. The contrast of a secondary electron image depends on the resistance of the differential voltage between the ends of a defect during electron-beam irradiation. To detect voids with high sensitivity, the differential voltage between the ends of a defect should be kept between 1 and 2 V, because the resistance of the defect suddenly decreases when the differential voltage is increased beyond a certain point.

Evaluation of EUV mask defect using blank inspection, patterned mask inspection, and wafer inspection

The key challenge before EUVL is to make defect-free masks, for which it is important to identify the root cause of defects, and it is also necessary to establish suitable critical mask defect size for the production of ULSI devices. Selete has been developing EUV mask infrastructures such as a full-field actinic blank inspection tool and 199nm wavelength patterned mask inspection tool in order to support blank/mask supplier in reducing blank/mask defects which impact on wafer printing. In this paper, by evaluating the printability of programmed phase defects and absorber defects exposed by full-field scanner EUV1, we demonstrate that defect detection sensitivities of ABI (actinic blank inspection) and PI (patterned mask inspection) are higher than that of WI (wafer inspection) in HP32nm. The evaluations were done by comparing the detection sensitivities of full-field actinic blank inspection tool, 199nm wavelength patterned mask inspection tool, and wafer EB inspection tool. And then, based on the native defect analysis of blank/mask, we ascertained that actinic blank inspection and patterned mask inspection developed at Selete, are effective in detecting killer defects both at the main pattern and at light-shield border area.

Evaluation of extreme ultraviolet mask defect using blank inspection, patterned mask inspection, and wafer inspection

The key challenge before extreme ultraviolet lithography is to make defect-free masks, for which it is important to identify the root cause of defects, and it is also necessary to establish suitable critical mask defect size for the production of ULSI devices. We have been developing extreme ultraviolet (EUV) mask infrastructures such as a full-field actinic blank inspection tool and 199 nm wavelength patterned mask inspection tool in order to support blank/mask supplier in reducing blank/mask defects which impact wafer printing. In this paper, by evaluating the printability of programmed phase defects and absorber defects exposed by full-field scanner EUV1, we demonstrate that defect detection sensitivities of actinic blank inspection and patterned mask inspection are higher than that of wafer inspection in HP32nm. The evaluations were done by comparing the detection sensitivities of full-field actinic blank inspection tool, 199 nm wavelength patterned mask inspection tool, and electron beam (EB) wafer inspection tool. And then, based on the native defect analysis of blank/mask, we ascertained that actinic blank inspection and patterned mask inspection are effective in detecting killer defects both at the main pattern and at the light-shield border area.

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.

Application of review-SEM to high-resolution inspection for 3xnm nodes

As the pattern size shrinkage, it becomes more important to control the critical size of various pattern shapes at a semiconductor production line. Recently, in a semiconductor process with 20 nm nodes size or less the common optical and even EB inspection tool have considerable limitation to detect critical physical defects. From these backgrounds, we have developed the high-sensitivity fixed point inspection tool based on Review-SEM as the product accomplishment judgment tool for below 10nm size defects on critical size devices. We examined the basic performance of this inspection tool, optimized inspection parameters including beam condition and image processing. Then, the defect detection performance was evaluated using various real advanced memory device containing various critical defects. In this paper, we report these results and show the effectiveness of this inspection tool to the advanced memory devices.

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.

Advanced surface inspection techniques for SOI wafers

In this paper, it is described that (1) Various type of SOI wafers have each optimum laser illumination mode, (2) Using this optimum laser illumination, 0.1 - 0.3 micrometer particle detection sensitivity has been achieved. (3) By measuring the noise element of scattered light from SOI surface, failure mode can be determined. The performance of the particle detection for each type of wafer and the result of surface roughness failure is also discussed.