Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
2002-09-26
2003-11-04
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S306000, C250S309000, C250S310000, C250S399000, C257S048000, C438S011000, C438S014000, C438S015000, C438S018000
Reexamination Certificate
active
06642519
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims benefit of priority under 35USC §119 to Japanese patent application No. 2001-296275, filed on Sep. 27, 2001, the contents of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inspection apparatus and an inspection method of a fine pattern, and more particularly, it concerns an inspection apparatus and an inspection method of a fine pattern in a semiconductor device manufacturing process as well as a managing apparatus and a managing method of a CD-SEM device.
2. Description of the Prior Art
In semiconductor manufacturing processes, in most cases, a dimension inspection of a fine pattern is carried out by a scanning electron microscope device that is referred to as a CD-SEM (Critical Dimension Scanning Electron Microscope) device.
As shown in FIG.
15
A and
FIG. 15B
, the principle of dimension measurements by a CD-SEM device mainly uses the fact that the intensity of a secondary electron signal varies depending on pattern shapes. Specifically, as shown in
FIG. 15A
, assuming that the angle made by a primary beam (electron beam) and a normal component of a pattern side wall which is irradiated with this primary beam is &thgr;, the intensity of a secondary electron signal released from the irradiation point is schematically given by a diffusion reflection model of Lanbert represented by the following formula.
I=I
o
(cos &thgr;)
−n
. [FORMULA 1]
where n represents a diffusion exponent which is a positive number close to 1.
In accordance with this principle, the signal intensity sharply rises in the vicinity of an edge corresponding to a steep portion of a pattern profile. Therefore, in a conventional inspection method of fine patterns using a SEM device, this signal in the vicinity of an edge is analyzed, and the edge position is defined by using a threshold method, for example, peak detection shown in
FIG. 15B
, function modeling and so forth, so that the pattern dimension is calculated as the distance between edges.
However, the secondary electron signal is subjected to various electrical and numeric modulations due to the following reasons. That is, the primary beam tends to expand, the area from which secondary electrons are discharged tends to expand due to diffusion of electrons emitted from the surface in the vicinity of the irradiation point, the beam scanning signal tends to deviate, the relative position between the pattern and the beam tends to vary in an attempt to improve the SN ratio in accumulation of signals, digital errors occur when the signal is AD-converted, etc. Consequently, in an actual operation, signal from edge portions tend to expand. Moreover, the secondary electron signal is susceptible to influences from distortions in a signal caused by a biased surface electrical potential exerted on the sample surface depending on irradiation conditions of the primary beam and from variation in the secondary electron discharging efficiency based on charging effect of a side wall as well as from contrast resulting from materials such as atomic number, density and dielectric constant. As a result, the signal intensity actually obtained is represented by formula (1) on which these many factors are multiplexed.
These influences make the signal in the vicinity of pattern edge broader, with the result that portions, located outside actual pattern edges by few nm through few tens of nm, might be defined as edges in the conventional edge defining system. Moreover, these influences also tend to vary depending on factors, such as the height and width of a pattern, flat face shape thereof, the relationship between the pattern shape and the scanning direction of primary electrons, the irradiation conditions of the primary beam and the material of the pattern. For these reasons, it has been difficult to precisely compare dimensions among a plurality of patterns.
Here, some techniques which can correct some of the factors that modulate the above-mentioned signals in the vicinity of edges have been proposed.
For example, on page 566 in preliminary report No. 2 in the 39th spring joint seminar associated with applied physics in 1992, a method has been proposed in which the expansion of a primary beam is preliminarily measured so that the expansion component is subjected to a de-convolution process from a line profile. However, this method can only correct the effects of expansion in the primary beam.
Moreover, for example, Proc. SPIE vol. 3677, pp669-685 (1999) has proposed a method in which a signal waveform in the vicinity of an edge of a photoresist pattern having an extremely vertical side-wall shape is obtained by a CD-SEM device so that its half-value width is defined as ABW (Apparent Beam Width). In this document, it is preliminarily examined how the ABW changes depending on the above-mentioned various variation factors. Therefore, in principle, it is possible to obtain positional information corresponding to an actual pattern edge position from a signal waveform of a CD-SEM device by using the results thereof. However, practical solutions to such applications have not been proposed. Moreover, the side wall shape of a sample used for examining the ABW is not completely vertical, the resulting errors are contained in the estimation of the ABW.
Furthermore, pp. 640-649 of the same Proc. SPIE vol. 3677 (1999) have disclosed a method in which the signal waveform is estimated through Monte Carlo simulation based upon information such as the pattern cross-sectional shape, beam conditions of a SEM device and the material of a sample so that the signal transmission function is determined so as to make the waveform coincident with a signal waveform to be actually acquired in a reversed manner, and the components of the signal transmission function are lastly removed from the acquired secondary electron signal for each time so as to estimate the cross-sectional shape of the pattern to be inspected. However, in this method, the Monte Carlo calculation is carried out after a physical model on which the signal waveform is generated is set, therefore, in the case when the adopted model is not established, for example, in such a case when a surface of a pattern is charged, a great error has occurred. Moreover, since the Monte Carlo calculation normally takes a very long processing time, this method fails to provide a practical inspection method.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a fine pattern inspection apparatus comprising: a first calculation unit which receives data of a first secondary electron signal obtained by irradiating a plurality of test patterns formed on a test substrate with an electron beam and receives data of an contour shape of a cross-section of each of the test patterns, the test substrate being the same as a substrate on which a pattern to be inspected is formed, the test patterns being formed with different cross-sectional shapes, and which separates the first secondary electron signal into variables of a first function containing the contour shape of the cross-section as arguments, a second function that is defined by a step function depending on respective materials constituting the test patterns and a third function that represents the size of a distortion of the signal; a storing unit which has a first storing area to store the first through third functions obtained from the first calculation unit; and a second calculation unit which receives data of a second secondary electron signal obtained by irradiating the pattern to be inspected with an electron beam, and executes calculations so as to extract components relating to the cross-sectional shape of the pattern to be inspected from the second secondary electron signal by using the first through third functions stored in the storing unit.
According to a second aspect of the invention, there is provided an apparatus connectable to CD-SEM devices and which manages the CD
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Lee John R.
Souw Bernard
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