The present application claims priority from Japanese patent application serial No. 2007-188986 filed on Jul. 20, 2007, the content of which is hereby incorporated by reference into this application
1. Field of The Invention
The present invention relates to a technology of processing and observing a sample by charged particle beams, and for example to a charged particle beam apparatus to produce a processed surface on a fine sample extracted from a substrate of a semiconductor device by applying microprocessing to a specific portion by FIBs (Focused Ion Beam) and observe the processed surface with a scanning transmission electron microscope (STEM), a transmission electron microscope (TEM), a scanning electron microscope (SEM), or the like.
2. Description of the Related Art
A technology on the combination of an FIB apparatus and an STEM apparatus is disclosed in Japanese Patent Laid-Open No. 2004-228076. It shows that an STEM observation sample produced by FIB processing is placed at the intersection of an ion beam axis and an electron beam axis and can be subjected to additional FIB processing and STEM observation. The ion beam axis and the electron beam axis intersect at acute angles (about 45 degrees in the case shown
Further, Japanese Patent Laid-open No. 2006-127850 describes a technology of realizing: the omission and minimization of the sample rotation or the like during the time between the FIB processing and the STEM observation; and the simplification in the operation of optimizing a sample thickness with an STEM image monitor during processing. According to the technology, an ion beam system, an electron beam system, and a transmitted and scattered beam detection device are disposed around a sample, the illumination axis of the FIB system and the illumination axis of the electron beam system for STEM observation are arranged so as to form nearly right angles to each other, and the sample is placed at the intersection. By so doing, it is possible to carry out both the FIB processing and the STEM observation without the sample displaced.
THE TRC NEWS No. 84, July, 2003 (Kato and Otsuka, Toray Research Center, Inc.) describes a means of three-dimensional structural analysis by FIB processing and SEM observation. Both the illumination axes of the FIB system and the electron beam system intersect with each other at acute angles and it is possible to display an image in the same region with the scanned images of both the beams, namely with the scanning ion microscopic image (the SIM image) and the SEM image. As it is anticipated from the electron beam system, by processing across section by FIBs, it is possible to observe the processed cross section with an SEM without the sample inclined. By repeating the FIB processing and the SEM observation, it is possible to integrate continuous segmented images in the direction of the depth from the processed surface.
The FIB processing and the STEM observation have heretofore been carried out with separate apparatuses in many cases. A thin film sample for an STEM processed with an FIB apparatus had to be once extracted from the FIB apparatus, and thereafter observed with an STEM apparatus. Thin film processing wherein an observed portion was identified by repeating the STEM observation and the additional FIB processing could not meet users' needs sufficiently from the viewpoint of throughput. To cope with the problem, an apparatus integrating FIB processing and STEM observation is announced and the improvement of throughput is attempted.
However, in such a case as to process a sample the exact defective portion and the defect size of which are not known into a thin film while an intended defective portion is retained, drastic improvement in throughput has not been attained yet because of the reasons: (1) a thin film sample larger than an ordinary sample is produced; (2) the repetition of FIB processing and SEM or STEM observation by cross section monitoring is carried out more frequently than usual and thin film processing is carried out while the observation portion is judged; (3) the region of processing itself expands; and others.
The fact that a cross section cannot be observed with an SEM or an STEM during FIB processing is one of the factors that cause throughput to be prevented from improving. Further, in the case of a sample having plural cross sections such as a thin film sample, when the plural cross sections are observed with an SEM or an STEM, displacement operation such as rotation and inclination of the sample or a sample stage is necessary in order to irradiate the cross section to be observed with electron beams. Furthermore, once a sample is displaced, visual field readjustment and focus readjustment are required. From those factors, even an apparatus integrating FIB processing and STEM observation can hardly secure a sufficient throughput.
In the case of three-dimensional structural analysis by FIB processing and SEM observation too, there are similar problems since the FIB processing and the SEM observation are repeated alternately. When the three-dimensional structural analysis is applied to a large region, visual field deviation and focus deviation appear in an SEM observed cross-sectional image as the FIB processing advances, hence it is necessary to adjust the visual field and the focus of the SEM frequently, and such operation is a factor causing the throughput to deteriorate.
Further in recent years, in order to realize a microstructure having high electrical characteristics, a material called a Low-K material that is very susceptible to electron beam irradiation has come to be used much and the cases of destroying or deforming a sample by electron beam irradiation during SEM observation and the like have come to happen frequently. The Low-K material is a low permittivity materials made of, for example, organic polymer or SiOC etc. As measures against the cases, means such as (1) to mitigate damage by cooling a sample, (2) to extremely lower the acceleration voltage of electron beams and reduce irradiation energy, and others have been taken.
However, the means (1) requires time for cooling and exchanging samples and the throughput of processing lowers enormously. Further, the damage caused by electron beam irradiation appears locally and the observed portion deforms even though the sample stage is cooled unless a cooling path is sufficiently secured. A drawback of the means (2) is that the image resolution of an SEM lowers by lowering the acceleration voltage of electron beams and the microstructure is hardly recognized.
An object of the present invention is to process a sample by charged particle beams and monitor the processed cross section with a high throughput.
The present invention relates to observing a cross-sectional structure during FIB processing as a secondary particle image generated from a sample by using ion beams shaving the cross section.
The present invention makes it possible to observe a cross section by ion beams used for processing.
The present inventors have earnestly studied and obtained the following knowledge.
In order to produce an accurate sample while an intended defective region is retained even though the location and size of the defect in the sample is unknown, it is necessary to produce at least two cross sections and advance the processing of the sample while the processing and the monitoring of the processed cross sections are carried out. A high throughput in processing and monitoring of a processed cross section may be obtained by: observing a cross-sectional structure during FIB processing as a secondary particle image generated from a sample by using ion beams shaving the cross section; and thereby making it possible to carry out both the processing and the observation at the same time. By so doing, it is possible to obtain a high throughput also in the process of repeating the processing and the monitoring of the processed cross sections and analyzing the structure of the sample.
At the final stage of shaving a cross section, a fabrication area forms a shape of a strip and usually an observed image also has a strip shape. The end point of the processing has heretofore been judged by the average brightness of a whole observed image. Consequently, although the process of advancing cross-sectional processing from the surface toward the sample substrate has roughly been obtained, the structure of the cross section has hardly been obtained. To cope with the problem, the combined use of an SEM has been studied. In the present invention, the observation is arranged so as to be displayed expansively in the direction of the short side of the strip shape and the cross-sectional structure is arranged so as to be obtained only by FIBs during processing.
In general, a processed cross section is formed by FIB processing so as to incline at an angle of several degrees to the incident angle of ion beams in consideration of the relationship between a local angle of the ion beams incoming to a sample and a sputtering efficiency (J. Vac. Sci. Technol. B9(5), September/October 1991, pp 2636). In the present invention, a cross-sectional structure can be displayed by: using the physical phenomenon; setting a strip-shaped fabrication area at an inclined portion; and displaying the processing monitor expansively in the short side direction. Although the image resolution deteriorates worse than the beam diameter since the beams are applied from a direction oblique to, nearly parallel with, the cross section, it is possible to display an image that is sufficient in obtaining a cross-sectional structure such as the existence of a wiring structure. The cross-sectional structure is observed by using the function and, when an intended cross section is not attained yet, the fabrication area shifts in the direction of the cross section and the processing and the judgment of the cross-sectional structure are repeated. By so doing, it is possible to attain an intended cross section without the combined use of an SEM.
A region requiring high resolution observation with an SEM, an STEM, or a TEM is only a part of a sample and hence the other region not requiring high resolution observation is subjected to the aforementioned FIB processing observation and, when another region requiring high resolution observation appears, the FIB processing observation is switched to SEM, STEM, or TEM observation. By so doing, it is possible to reduce stage shift and switching operation between FIB processing and SEM, STEM, or TEM observation.
Even in the case of using three-dimensional structural analysis by FIB processing and SEM observation and a material that is very susceptible to electron beam irradiation, a region requiring high resolution observation with an SEM, an STEM, or a TEM is only a part of a sample. Consequently, the other region not requiring high resolution observation is subjected to the aforementioned FIB processing observation and, when another region requiring high resolution observation appears, the FIB processing observation is switched to SEM, STEM, or TEM observation. By so doing, it is possible to: reduce the visual field readjustment and the focus readjustment of an SEM observed cross-sectional image that is required as the FIB processing advances; and also reduce the amount of electron beams applied to a material that is very susceptible to electron beam irradiation.
In the present invention, it is possible to produce an accurate sample with a high throughput while an intended region is retained even though the exact defective portion of the sample is not known in the process for producing the sample such as a thin film while processing and monitoring of a processed cross section are repeated. Further, in the process for repeating processing and monitoring of a processed cross section and applying three-dimensional structural analysis to a sample too, the throughput of the analysis can be improved. Moreover, it is possible to observe a cross section infinitely close to a true appearance even with a material that is very susceptible to electron beam irradiation.
Since the processing and observation of a cross section can be simultaneously carried out by ion beams used for the processing, it is possible to reduce: stage transfer for monitoring the cross section during processing; SEM visual field adjustment; and SEM focus adjustment. Further, since the processing and observation are carried out by ion beams incoming perpendicularly to the sample surface, the location where a cross section is formed is not restricted. Consequently, however an intended region is placed, vertically, transversely, or obliquely, as long as at least two cross sections are formed and processing and monitoring are repeated, it is possible to retain the intended region without fail. Also when plural processed cross sections are monitored, it is not necessary to move a stage in order to monitor a cross section except the case of high-resolution observation using an SEM, an STEM, or a TEM. In addition, it is not necessary to readjust the focus of ion beams since the position of a sample is not changed. In the present invention, unnecessary stage transfer, accompanying beam adjustment, SEM, STEM, or TEM observation for cross section monitoring can be avoided and hence it is possible to carry out with a high throughput the process accompanying continuous or intermittent processing and the monitoring of a processed cross section, for example aforementioned production of a thin film sample and three-dimensional structural analysis. Further, information on a cross section that has not been obtained during FIB processing can be obtained and the information on a cross section can be obtained not only as discrete data but also as continuous motion picture data.
Further, since an intended cross section can be formed without the combined use of an SEM, it is possible to carry out FIB cross section processing and thin film processing while damage and deformation in a cross section of a sample susceptible to electron beam irradiation are inhibited. A cross section to which the FIB processing is applied in a vacuum is clean and has no impurities such as an adsorption gas and hence, by installing an FIB, an SEM, an STEM, or the like in an identical vacuum chamber, it is possible to observe at a high resolution an unlimitedly clean surface having: extremely small damage and deformation in the sample susceptible to electron beam irradiation; and scarce adsorption gas.
(1) to form cross sections (A) 9 and (B) 10 in nearly parallel with the beam irradiation direction 12 by the irradiation of ion beams 11;
(2) to set a strip-shaped fabrication area 13 at the region where the cross sections are contained and process the region from the beam irradiation direction 12; and
(3) to display the secondary particle image 15 during processing at least so as to expand the strip shape in the direction of the short side.
On the display device 6, as shown in
Since a cross section formed by FIB processing has an angle 18 of about 3 to 6 degrees from the beam irradiation direction 12, the cross section in the scanning area 19 of the ion beams can be observed as a secondary particle image 15 during processing even by the ion beams 11 incoming perpendicularly to the sample surface. The outline of a cross-sectional structure is obtained by displaying the strip-shaped secondary particle image in an expanded manner and it is possible to judge the cross-sectional structure by the ion beams incoming perpendicularly to the sample surface without a stage inclined. By so doing, it is possible to reduce or omit: the operation of interrupting processing in order to observe a cross section, switching the ion beams 11 from the ion beams for processing to ion beams for observation, and displacing (in X, Y, and Z directions, rotation, inclination, etc.) a sample stage 4 to a location where the cross section can be observed; the operation of interrupting processing and displacing the sample 3 to another apparatus such as an SEM or an STEM; or both the operations. Further, in the present invention, since the cross-sectional structure is observed at the same time with processing, switching from processing to observation is unnecessary. By those effects, it is possible to considerably improve the operation efficiency of processing and observation requiring accurate judgment of processing end in order to surely retain an intended defective portion while the defective portion is searched particularly in a sample the accurate defective portion of which is unknown. Although the case of processing and observing two cross sections is shown in the present embodiment, the number of the cross sections is not particularly limited and the orientations of the cross sections can be set arbitrarily. Further, a cross section is not necessarily planar but may be round. In a conventional case, since processing and observation are carried out alternately, the observation data of a cross section come to be discrete data such as images or the like. In the present embodiment, since processing and observation are carried out simultaneously, it is possible to obtain the observation data of a cross section not only as discrete data such as images but also as continuous data such as motion picture data.
The plural pieces of image data obtained and stored with the charged particle beam apparatus 101 are corrected so that the dimensional ratio of length to width may conform to the actual dimensional ratio of the sample 3 and aligned in the processing direction 31 of the cross sections. Then image data obtained and stored with another electron beam apparatus 102 is added to the data group, the linkage between adjacent images is complemented, and thereby the three-dimensional data (B) 33 of the sample 3 are constructed. In the case of the present embodiment, the data is produced by synthesizing a scanning ion microscopic image (an SIM image) formed by ion beams 11 and a transmission electron microscopic image (a TEM image). The data obtained with another electron beam apparatus 102 may be a secondary electron image or a reflected electron (backscattered electron) image. The data obtained with the charged particle beam apparatus 101 may be motion picture data.
In the present embodiments, it is possible to produce an accurate sample with a high throughput without an intended region lost in the process for producing a sample such as a thin film while processing and monitoring of a processed cross section are repeated even with a sample the accurate defective position of which is not known. Further, it is possible to improve analysis throughput in a process of repeating processing and monitoring of a processed cross section and analyzing the three-dimensional structure of the sample. Furthermore, it is possible to observe a cross section extremely close to the true feature even with a material very susceptible to electron beam irradiation.
Number | Date | Country | Kind |
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2007-188986 | Jul 2007 | JP | national |
Number | Date | Country | |
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Parent | 12175940 | Jul 2008 | US |
Child | 13601893 | US |