Patent Application
20110180707
The present application claims priority from Japanese application JP 2010-014995 filed on Jan. 27, 2010, the content of which is hereby incorporated by reference into this application.
The present invention relates to a microsampling apparatus for isolating and sampling a small object on a workpiece substrate, and also relates to a sampling method thereof.
In electronic device manufacturing/fabrication processes, it is required to continue to mass-produce nondefective products. Due to the fact that the number of products is extra-large, the occurrence of a defect leads to a decrease in product yield or to stoppage of a production line(s), which will greatly affect the commercial profit. For this reason, efforts are made to eliminate defective products and promote cause investigation. Practically, the identification of very small foreign matter that causes detection is carried out by a variety of analyses. In such analyses, the sampling and isolation of foreign matter from a substrate becomes important in order to improve the analytical precision. In cases where the isolation is impossible, it is unavoidable to analyze both the substrate and the foreign matter simultaneously, resulting in an extreme degradation of the signal-to-noise (S/N) ratio of an aimed signal. For instance, although it is considered that the use of the micro Fourier transform infrared ray (FT-IR) spectroscopy is effective for the analysis of small organic foreign matter residing on electronic devices, this micro FT-IR spectroscopy is typically about 10 μm in spatial resolution and thus suffers from a demerit which follows: when an attempt is made to analyze a foreign object with its size of several micrometers, the information of those other than the foreign matter occupies a major part, resulting in the information of the foreign matter per se hiding in the background, which leads to the lack of an ability to identify the foreign matter. However, if it is possible to isolate the foreign matter, only the information of the target foreign matter is obtainable, resulting in an appreciable increase in analysis precision.
For the sampling and isolation of such micro-foreign matter, commercially available micromanipulator systems are usually used.
In prior known microsampling systems of the type using an optical microscope, because of the use of this optical microscope, when performing the sampling of an object with its size less than or equal to 10 μm as an example, a sampling instrument or tool used therefor is shifted in position toward outside of the range of observation due to the occurrence of out-of-focus to be caused by shallowness of the focal depth of a lens. This leads to increased difficulty in operation.
One solution to the above-stated problem is to use a scanning electron microscope (SEM) which is larger in focal depth than optical microscopes. Observation and fabrication processing are performed using the SEM equipment in a way as disclosed, for example, in JP-A-11-271636, JP-A-2001-198896, and JP-A-2001-88100.
However, in view of the fact that the SEM is designed to use charged particles, a specimen or “sample” made of an electrically insulative material can be electrified by the irradiation of an electron beam in the process of observing and/or sampling such insulator specimen. The electrification can sometimes cause degradation of the quality of an observation image and also the occurrence of quantitative and qualitative deteriorations of signals of secondary electrons and reflected electrons or the like along with undesired scattering of a constituent material(s) of the insulator specimen.
These problems become more noticeable as the insulator specimen becomes higher in electrical resistivity. This is caused by the fact that charged particles with the reverse polarity tend to stay on-site, which are generated by the release of either electrical changes of charged particles being irradiated onto an insulator specimen or secondary electrons produced from the insulator specimen. Traditionally, for those problems arising from the electrification, the following techniques or schemes have been employed either independently or in a combined manner.
(a) Lessening the dose of an electron beam.
(b) Forming a conductive thin-film on the surface of a specimen.
(c) Irradiating a beam of charged particles that are opposite in polarity to the charge electrified.
Unfortunately, the above-stated methods (a) to (c) are faced with problems which follow.
Use of the method (a) would result in a decrease in signal amount of secondary electrons, which leads to a likewise decrease in observation performance.
Use of the method (b) results in an unwanted change in composition of the specimen of interest. This causes undesired mixture of an extra signal as derived from the conductive thin-film during analysis after the sampling, thereby complicating the analyzation of a result.
When using the method (c), it is a must to irradiate a specific amount of charged particles which amount is carefully determined to negate or “cancel out” the charge to be generated; however, the surface potential varies with time, letting the signal amount of secondary electrons become unstable. Consequently, preliminary experimentation for determining a suitable irradiance level of charge is needed. Furthermore, in case the charged particles to be irradiated are ions, surface sputtering can often take place with a risk of the cutting of interatomic bonding.
It is therefore a first object of the present invention to achieve, in a sampling apparatus having an observation system of the type using charged particles, reduction of electrification of an electrically insulative specimen at any given positions on the specimen, thereby to assure observation performance.
It is a second object of this invention to perform, in the sampling apparatus having the charged particle-using observation system, sampling of a specimen while suppressing specimen scattering otherwise occurring due to electrification.
To attain either one of the foregoing objects, a microsampling apparatus which has a mechanism for enabling observation of a specimen and for contacting a potential-controllable terminal made of an electrically conductive material with a sampling area and a sampling method thereof are provided. The mechanism is generally made up of an operation mechanism for precisely controlling, during the observation, a conductive terminal for contact with a surrounding part of the sampling area and movement of this terminal, a potential control mechanism for applying a voltage to the terminal, and a mechanism for connecting the terminal to the ground or “earth” and also to the potential control mechanism. By contacting the terminal with either the specimen or a part in close proximity thereto, those charged particles that are created in the observation and sampling processes are forced to escape via an earth lead. A conceptual diagram of this mechanism is shown in
The operation of bringing the terminal into contact with the specimen or its nearby part is performed with the aid of a control device having a coarse motion control mechanism and a fine or “micro” motion control mechanism.
The conductive terminal for suppression of the electrification is constituted from a structure having a needle-like shape or any other suitable shapes resembling thereto. It should be noted that although one example of the shape and structure of the terminal is shown in
According to this invention, it is possible to achieve the sampling of an insulator specimen on an insulative substrate even in the state that an electron beam is irradiated thereonto.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
Currently preferred embodiments of this invention will be described with reference to the accompanying views of the drawings below.
One important feature of a microsampling apparatus in accordance with this embodiment is that the apparatus has a terminal for electrification suppression and specimen sampling to thereby enable execution of the sampling of an electrically insulative specimen while at the same time performing electron microscope (EM) observation. More specifically, the microsampling apparatus performs observation and cutting processes while suppressing the electrification and performs electrostatic sampling of an insulative micro-specimen which is slightly electrified.
A process of sampling the micro insulator specimen 2 in this embodiment will be set forth with reference to a flow chart of
While the electron beam is being irradiated with respect to the insulator at this time, the electron beam becomes higher in irradiation density when the observation is done at a high magnification of 10,000-fold which is necessary for precise positioning, resulting in dominant appearance of the influence of electrification on the surface, i.e., distortion of a secondary electron image in a desired observation area, a change in contrast, and scattering of the micro insulator specimen 2.
Here, as shown in
Next, an explanation will be given of the isolation of the micro insulator specimen 2 (at step 104 of
In the case where diamond and sapphire which are high in hardness are used for the cutting tool 3, these are electrically insulative materials so that electrification takes place as a result of the electron beam irradiation. Therefore, the micro insulator specimen 2 that was isolated and put on the cutting tool 3 is electrified and, in some cases, scatters due to repulsion or “repelling” between the electrified specimen 2 and the cutting tool 3. The polarity and quantity of such electrification is determined by a release ratio of secondary electrons to the electron irradiation amount. An example is that the specimen is electrostatically charged to have the positive polarity in a case where the amount of secondary electrons produced is greater than the electron irradiation amount. Accordingly, the terminal 4 which was in contact with the substrate 1 is moved to thereby transfer the micro insulator specimen 2 on the cutting tool 3 to the terminal 4 (at step 105). At this time, a negative voltage is applied to the terminal 4 by a potential control mechanism 13, thereby electrostatically sampling a slightly positively electrified foreign object. The voltage potential of the terminal 4 is adequately varied in a way depending upon the electrification polarity of the specimen 2. A sampling step is shown in
An explanation will next be given of a method for picking up foreign matter which is negatively electrifiable upon irradiation of an electron beam. The steps 101 to 103 of the above-stated embodiment are the same. At step 104, the diamond-made cutting tool 3 provided at the manipulator 7 is used to cut and isolate a foreign object (specimen 2) from the substrate 1 in a similar way to the embodiment 1. The micro insulator specimen 2 which is mounted on the cutting tool 3 is electrified to have the negative polarity. At step 105, the terminal 4 that was brought into contact with the substrate 1 is driven to move toward the micro insulator specimen 2 on the cutting tool 3; then, a positive voltage is applied to the terminal 4 by the potential control mechanism 13 so that the negatively electrified foreign object 2 is electrostatically picked up at the end of the terminal 4. As the electrification quantity of the foreign object 2 depends upon the material and shape of this foreign matter, there is a case where the foreign object 2 does not readily transfer to the terminal 4. If this is the case, the voltage being applied to the terminal 4 is gradually increased in potential, thereby achieving application of a voltage which is potentially high enough to force the foreign matter 2 to move to the terminal 4.
Next, an explanation will be given of an example having as the foreign matter pickup mechanism a tweezers-shaped grasp/holding mechanism consisting essentially of two arms. The micro-specimen grasp/hold mechanism is a tool or instrument for plucking up a very small thing with its size being on the order of submicrometers, which tool is built in the manipulator 7 and operates to pick up a small thing by utilizing the phenomenon that the voltage application to an electrostatic actuator causes the micro specimen grasp/hold mechanism to become narrower in distance between ends thereof.
In this embodiment, there will be explained (1) a merit of cutting performance in the case of the grasp/hold mechanism being used and (2) a merit of scattering prevention in the case of the grasp/hold mechanism being used. (1) A specimen large in brittleness sometimes breaks or wrecks during cutting, resulting in failure to perform sampling. By surely grasping such brittle specimen by the grasp/hold mechanism in advance, it is possible to readily perform the sampling. (2) In cases where the micro insulator specimen 2 that was cut behaves to scatter dynamically rather than electrostatically after the cutting process, the micro insulator specimen 2 can disappear out of an observer's eyesight. To avoid this and for the purposes of prevention of such flying, the micro insulator specimen 2 is plucked by the micro specimen grasp/hold mechanism, and then the cutting process is performed. This makes it possible to prevent unwanted scattering.
In this embodiment, the apparatus has the micro-specimen grasp/hold mechanism in place of the terminal 4 as used in the embodiments 1 and 2. This grasp/hold mechanism is controllable in its potential by the potential control mechanism 13. Regarding a procedure of the sampling, its vacuum evacuation and electron beam irradiation steps are the same as the steps 101 and 102 of the embodiment 1. After the electron beam irradiation, the foreign object 2 is picked up and held by the micro-specimen grasp/hold mechanism. At this time, electrical charge carriers that are electrified to the specimen 2 are forced by the grasp/hold mechanism to escape to thereby suppress electrification. Thereafter, in a similar way to the step 104 of the embodiment 1, the cutting tool 3 is used to cut the specimen 2. At this time, the cutting-applied specimen 2 is firmly seized by the grasp/hold mechanism; so, the sampling is completed by letting this mechanism return to its standby position without having to perform the step 105 of the embodiment 1.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-014995 | Jan 2010 | JP | national |
