Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2001-09-24
2004-08-24
Wells, Nikita (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S307000
Reexamination Certificate
active
06781125
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus system used as observation, analysis and evaluation means in research and development and manufacturing of an electronic device such as a semiconductor device, liquid crystal device and a magnetic head, a micro-electronic device or the like which require observation and analysis of not only a surface of an object to be observed but also an inner section near the surface.
In manufacturing of a semiconductor device such as a semiconductor memory typified by a dynamic random access memory, a microprocessor and a semiconductor laser, and electronic parts such as a magnetic head, a product property is inspected for quality control of a product during a manufacturing process or at completion of the process. In the inspection, measurement of manufacturing dimension, defect inspection of a circuit pattern, or analysis of foreign materials are carried out. For that purpose, various means are prepared and used.
Particularly, when there is a wrong portion within the product, a minute processing and observation apparatus is increasingly used which comprises a combination of a focused ion beam (FIB) apparatus and an electron microscope. This apparatus is disclosed in JP-A-11-260307 specification. In the specification, disclosed is a technique of carrying out section processing of a sample by an FIB apparatus and observing an exposed section by an electron microscope disposed slantingly above the sample.
As another technique of observing the sample section, invented and used is a method of taking out of a processing and observation apparatus a minute sample, which is a cut-out minute area of micron orders including an observation region, and moving the minute sample to a separately prepared apparatus to be reprocessed into an optimum shape and observed and analyzed. This method is disclosed in JP-A-5-52721 specification. This is a method of cutting out part of a sample and observing its section, where a tip of a probe driven by a manipulator is positioned on a minute sample cut by an FIB, the probe and minute sample are connected by a deposition gas, and the minute sample is transferred in the connected condition.
SUMMARY OF THE INVENTION
The above described conventional methods have the following problems.
First, to observe a section of a hole or groove of the sample formed by FIB processing, a sample stage is inclined to thereby observe a section of an inner wall of the hole or groove in a slanting direction. In that case, an adjustment range of inclination of the sample stage is limited by constraints in structure due to a working distance of an FIB apparatus, presence of an objective lens, or size of a sample stage, and larger inclination cannot be allowed. Thus, vertical observation of the section of the inner wall of the hole or groove is impossible. The vertical observation of the section is indispensable in confirmation of processing properties such as dry etching, planarization, thin film forming, or the like in process development or the like of semiconductor device manufacturing, but the above described known apparatuses cannot cope with the vertical observation.
Second, a reduction in resolution resulting from the slant observation becomes a serious problem. When slantingly emitting an electron beam to a wafer surface from above and to observe a section of an inner wall of a hole or groove, observation resolution in a direction perpendicular to the wafer surface, that is, of the section of the inner wall of the hole or groove is reduced. A reduction rate reaches approximately 15% at an angle of 30°, and 30% at an angle of around 45°, which is most frequently used. Miniaturization of recent semiconductor devices has reached the limit, and measurement of the dimension or shape with accuracy below a few nano meters is required. Required observation resolution is less than 3 nm, which falls a technical limit area of a scanning electron microscope. In addition, with high resolution of such degree, depth of focus is extremely shallow and focusing is achieved only in a range below some ten percent of 1 &mgr;m, so that an appropriate observation range of a vertical section of the device at the time of slant observation is often less than half of a required area. This problem can be solved by vertical observation. The vertical observation enables superior observation in focus on the whole observation area.
Third, the observation section exists on a wall surface of a minute hole or groove formed in the wafer, so that numeral density of secondary electrons coming out of the hole are reduced in comparison with those on the surface of the wafer. Thus, secondary electron detecting efficiency is reduced and it causes a reduction in S/N of a secondary electron image, inevitably resulting in a reduction in accuracy of the section observation.
Miniaturization of LSI patterns progresses at a rate of 30% reduction every a few years without stop, and higher resolution is increasingly required in the observation apparatus. Moreover, even if surface distribution of an atomic property X-ray excited by emitting an electron beam is measured by an X-ray detector to carry out elementary analysis (EDX analysis), enlargement of an X-ray generation area due to the electron beam entering into the sample causes surface resolution of analysis to be approximately 1 &mgr;m though the electron beam has a diameter equal or less than 0.1 &mgr;m, which is insufficient for analysis of the LSI element section having a minute structure.
Fourth, cases where the vertical observation of the section is indispensable include evaluation of workmanship of etching, implantation of grooves or holes, planarization or the like in wafer process. In order to accurately measure a dimension and shape of a processed section, a sample of a chip size including a section to be observed has been determined and observed by a scanning electron microscope for general purpose in the past. However, accompanying with miniaturization progress of devices and enlargement of diameter of the wafer, sometimes failure is resulted since it is considerably difficult to accurately break an element circuit pattern at a position to be observed. However, failure in creating an evaluation sample is not allowed because of poor supply capacity or increased price of the wafer for evaluation.
Fifth, with the technique disclosed in JP-A5-52721 specification, it is possible to obtain sufficient level of observation and analysis accuracy such as resolution, but the sample has to be manufactured in the conventional apparatus, taken out of the apparatus, and introduced into the separately prepared observation and analysis apparatus, thus there is a problem of requiring hours of time for taking out the minute sample, processing, observation and analysis. Further, in a case where the sample exposed to the air is degraded by oxidation or moisture adsorption, it is difficult to avoid the degradation. Section observation of the semiconductor device has been recently considered to be important as an advantageous inspection technique in manufacturing the semiconductor, and a desirable throughput in that case at present is observation and analysis of more than a few positions per hour, and processing at much higher speed will be desired in the future. Contrary to the desire, the problem of extremely low throughput of the conventional method has not been solved.
In view of the above problems, the present invention has its object to provide a method and apparatus for processing and observing a minute sample, which can vertically observe an inner section of the sample to be observed, and can carry out observation and analysis with high resolution, high accuracy and high throughput without degradation resulting from exposure to the air and without failure.
Another object of the present invention is to provide a minute sample processing apparatus which requires minimum capacity of a vacuum container and a reduced occupying area and has high operability even when the apparatus is intended for a large sample.
Fukuda Muneyuki
Kashima Hideo
Koike Hidemi
Mitsui Yasuhiro
Shichi Hiroyasu
Hitachi , Ltd.
Hughes James P.
Kenyon & Kenyon
Wells Nikita
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