Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2003-06-24
2004-07-20
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S305000, C250S309000, C250S310000, C250S492100, C250S492210, C378S044000, C378S045000, C378S049000, C356S237400
Reexamination Certificate
active
06765205
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an instrument system, including an electron microscope, for use in observation, analysis, and evaluation in the course of research/development and manufacture of electronic devices and micro-devices, such as a semiconductor device, liquid crystal device, and magnetic head.
In the case of manufacturing devices, such as a semiconductor memory, there are situations where foreign particles generated in the course of the manufacturing process are mixed therein. Examples of the foreign particles include foreign species particles attributable to process material represented by the residue of etching operations and the residue of a resist, the wall material of process vessels, the material for fixedly holding a wafer, and the material used for a vacuum gas line, etc. Adhesion of such foreign particles to a wafer results in the generation of defective items at times.
It is important from the viewpoint of improving the yield in the manufacture of various devices to analyze the respective elemental composition of the foreign particles that have adhered to a wafer, and to search for the sources of the foreign particles on the basis of their kinds, thereby removing the causes of generation thereof.
As means for obtaining information on the elemental compositions of specimens, there is a known technique of irradiating the specimen with an electron beam, thereby detecting X-rays that are generated. The X-rays comprise a characteristic X-ray emitted when electrons of atoms on the surface of, and in the vicinity of the surface of, specimens fall from an excited state into a lower energy state, and a continuous X-ray at an energy level below the energy of an incident electron beam due to braking radiation, whereby incident electrons are braked before emission. The characteristic X-ray has energy inherent to respective elements, indicated by K, L, and M lines, respectively, depending on the excited state of the characteristic X-ray. Accordingly, the elemental composition of specimens can be found by analyzing the energy at peaks appearing in a spectrum. This method is called energy dispersive X-ray spectroscopy (EDX or EDS). Instruments for performing this method, supplied by companies such as Oxford Instrument, EDAX, TermoNORAN Instrument, and so forth, are available on the market, and they are capable of providing both qualitative analysis and quantitative analysis. Users can find the elemental composition of specimens by analyzing obtained spectra by means of qualitative analysis and quantitative analysis, respectively.
Another example of a method of identifying the elemental composition of specimens from X-ray spectra is disclosed in JP-A No. 108253/1988 (example 1). This publication describes a method in which respective characteristic X-ray spectra (reference spectra) of a plurality of known substances are registered in a memory, and by checking the X-ray spectrum of an unknown substance against the reference spectra registered in the memory, the unknown substance is identified.
An example of the inspecting of foreign particles on the surface of a wafer by use of the method described is disclosed in JP-A No.14811/1996 (example 2). In this example, there is a configuration wherein the locations of foreign particles are determined by observation of images dependent on the magnitude of reflection electron signals, and, by checking the X-ray spectra of the foreign particles against reference spectra, the elemental compositions of the foreign particles can be identified.
Still another method is disclosed in JP-A No. 321225/2000 (example 3). This publication describes a method wherein the net X-ray spectrum of a foreign particle is found on the basis of an X-ray spectrum of a portion of the surface of a wafer having the foreign particle, and an X-ray spectrum of the rest of the surface of the wafer having no foreign particle, (background spectrum), and the elemental composition of the foreign particle is found by checking the net X-ray spectrum of the foreign particle against a database.
Further, JP-A No. 68518/2001 discloses a method of generalizing information on foreign particles, found by the method described above, and registering the same into predetermined categories, thereby specifying causes of defects.
An electron beam, even if focused in a narrow region, is subjected to interaction with the substance inside a specimen upon impacting on the specimen, thereby undergoing scattering. The magnitude of a scattering region is dependent on the element which serves as the constituent of the specimen and the acceleration voltage of the electron beam.
FIGS. 18A through 18D
are views of the results of a calculation using a Monte Carlo method, showing electron beam scattering conditions when electron beams with acceleration voltage at 15 kV and 5 kV, respectively, are irradiated to specimens of silicon (Si) and tungsten (W), respectively. In the case of the specimen being silicon, the magnitude of a scattering region of the electron beam is about 4 &mgr;m, if the acceleration voltage is 15 kV, and it is about 0.4 &mgr;m, if the acceleration voltage is 5 kV. Due to the excitation of the electron beams, X-rays are generated substantially in these regions, respectively. This means that the X-ray spectra as observed reflect information on not only the irradiation points of the electron beams, but also the substances contained in the respective scattering regions. Accordingly, the space resolving power in elemental analysis is determined not by the size of an electron beam, but by the magnitude of the scattering region.
Since the processing sizes of semiconductor elements that have attained miniaturization have lately reached sub-micron levels, the sizes of foreign particles causing degradation in the characteristics of the elements have also become smaller.
FIG. 19
is a view showing a semiconductor device structure as it appears during a manufacturing process, having respective scattering regions of the electron beams, inside the Si, as shown in
FIGS. 18A and 18B
. In the case of EDX analysis of a small foreign particle, an electron beam passes through the foreign particle and scatters inside the substrate. Accordingly, an X-ray spectrum as observed contains information on both the foreign particle and the substrate (background), causing difficulty with the analysis. For a substrate in the middle of a manufacturing process, in particular, patterns, that is, an oxide film, electrodes, a dielectric film, and so forth, are formed on the substrate; and, in a case where flakes from those substances constitute foreign particles, the foreign particles need to be distinguished from those substances.
Further, if the acceleration voltage is lowered in order to reduce the effect of the background, that is, to reduce the size of the scattering region, the characteristic X-rays that can be excited are restricted, in which case, elements need to be identified with overlapping characteristic X-ray peaks. Such an instance will be described with reference to FIG.
20
.
FIG. 20
is a graph showing X-ray spectra of a titanium (Ti) foreign particle 50 nm thick, that is present on the surface of a silicon wafer. The X-ray spectra were obtained by two electron beams having an acceleration voltage of 15 kV and 5 kV, respectively. In the case of the acceleration voltage at 15 kV, a Ti-K line peak is observed at 4.51 keV of X-ray energy; however, in the case of the acceleration voltage at 5 kV, such a peak is not observed because such a characteristic X-ray cannot be excited. In this case, the presence of a titanium element is determined by a Ti-L line that is observed at 0.45 keV of X-ray energy. However, since there exist K-line peaks of oxygen and nitrogen, respectively, in this region of X-ray energy, the characteristic X-ray peaks are observed in an overlapped state, if those elements are present, causing difficulty with the analysis.
Further, in the case of lowering the acceleration voltage, the quantity of X-rays being generated decreases, although the
Kubo Toshiro
Kurosaki Toshiei
Ochiai Isao
Suzuki Naomasa
Hitachi High-Technologies Corporation
Lee John R.
Vanore David A.
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