Optics: measuring and testing – Inspection of flaws or impurities – Transparent or translucent material
Reexamination Certificate
1999-04-02
2001-03-20
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Transparent or translucent material
C356S237400
Reexamination Certificate
active
06204918
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a surface inspecting apparatus for measuring precisely the position of a foreign matter present on a surface.
PRIOR ART
Of conventional surface inspecting apparatuses, those are known in which the surface of an object of inspection is subjected to a spiral scan or a linear luster scan with the use of an irradiating light beam and a foreign matter present on the reflecting surface is detected according to the level of received-light signals derived from reflected light beams from the surface.
In the prior art apparatuses, when the direction in which a light beam is continuously moved is called the main scanning direction and the direction in which the light beam is intermittently moved is called the sub-scanning direction, it becomes necessary to make the pitch of movement of the beam finer in the sub-scanning direction if it is desired that the position of the object of inspection in the sub-scanning direction be measured with high resolution.
However, when the pitch of movement in the sub-scanning direction is made finer, such a difficulty arises that the tact time is prolonged and the time required for measurement becomes longer.
SUMMARY OF THE INVENTION
An object of the invention is to provide a surface inspecting apparatus capable of measuring the position, in the sub-scanning direction, of a foreign matter, as the object of inspection, with high resolution without making finer the pitch of movement of the beam in the sub-scanning direction and prolonging the tact time.
A surface inspecting apparatus according to the invention is a surface inspecting apparatus capable of accurately measuring the position of a foreign matter (a comprehensive term embracing a dust, flaw, particle and the like) present on the surface of such a material as a semiconductor wafer.
A surface inspecting apparatus of the invention comprises, for example, a light source, an irradiating optical system for throwing an irradiating light beam from the light source onto the surface of an object of inspection, a light receiving optical system for receiving a scattered light beam reflected from the surface of the object of inspection irradiated by the irradiating optical system, a photosensing portion for forming a surface data signal from the scattered light beam received by the light receiving optical system, a displacement portion for providing the surface of the object of inspection and the irradiating optical system, plus the light receiving optical system, with displacement relative to each other, continuously in the main scanning direction and intermittently in the sub-scanning direction, and a foreign matter detecting portion for detecting a foreign matter present on the surface of the object of inspection on the basis of the maximum level of the surface data signal and obtaining the position, in the sub-scanning direction, of the foreign matter present on the surface of the object of inspection on the basis of at least two adjoining surface data signals in the sub-scanning direction.
Preferably, the foreign matter detecting portion is adapted to obtain the position of a foreign matter present on the surface of the object of inspection on the basis of the levels of at least two adjoining surface data signals in the sub-scanning direction.
Further, the foreign matter detecting portion is adapted to obtain the position, in the main scanning direction and the sub-scanning direction, of the foreign matter present on the surface of the object of inspection on the basis of the levels of at least two adjoining surface data signals in the sub-scanning direction on the presumption that the intensity distribution of the irradiating light beam of the irradiating optical system is in conformity with a specific curve.
Further, the foreign matter detecting portion is adapted to obtain the position, in the sub-scanning direction, of the foreign matter present on the surface of the object of inspection on the basis of the levels of at least two adjoining surface data signals in the sub-scanning direction on the presumption that the intensity distribution of the irradiating light beam of the irradiating optical system is in conformity with a Gaussian curve, according to Formula 1 as mentioned below:
x
=
{
(
D
2
/
8
)
ln
(
I1
/
I2
)
-
p
2
}
/
2
p
Formula
1
In Formula 1, D is the beam diameter, p is the scanning pitch, n is the scanning number of the beam, In is the peak level of the n-th received-light signal, and In+1 is the peak level of the (n+1)-th received-light signal.
In a preferred embodiment of the invention, the foreign matter detecting portion is adapted to obtain the position, in the main scanning direction and the sub-scanning direction, of the center of the foreign matter present on the surface of the object of inspection on the basis of positional data of at least two adjoining surface data signals in the sub-scanning direction.
Further, the foreign matter detecting portion is adapted to obtain the position, in the main scanning direction and the sub-scanning direction, of the foreign matter present on the surface of the object of inspection by obtaining the position of the center of gravity of the object of inspection from the starting position and the ending positions of at least two adjoining surface data signals in the sub-scanning direction.
Further, the foreign matter detecting portion is adapted to obtain the position, in the main scanning direction and the sub-scanning direction, of the center of the foreign matter present on the surface of the object of inspection on the basis of a change in the surface data signal in the main scanning direction.
Further, the foreign matter detecting portion is adapted to obtain a sectional area caused by the foreign matter from changes in the main scanning direction of the surface data signals of adjoining surface data signals and, thereupon, to obtain the position, in the main scanning direction and the sub-scanning direction, of the center of the foreign matter present on the surface of the object of inspection on the basis of the obtained sectional area.
Description will be made taking a surface inspecting apparatus of a semiconductor wafer as an example. In measuring a foreign matter, such as a dust, a flaw, or the like, present on the surface of the semiconductor, there are various ways of beam scanning. In any of these beam scanning methods, the point where the scattered light beam by a foreign matter exceeds a threshold is stored as a Start, the point where the light beam falls below the threshold is recorded as an End, and a Peak of the scattered light beam by the foreign matter is recorded between the Start and the End, and these Start, End, and Peak are treated as data of one foreign matter. For example, a scattered light beam by a foreign matter is detected by an A/D sensor with a high resolving power and the point where the beam exceeds a threshold is stored as a Start, a Peak of the scattered light beam by the foreign matter is recorded, and the point where the beam falls below the threshold is recorded as an End, and these are treated as data of one foreign matter.
Preferably, an A/D clock counter may be used to record the accurate coordinate of each point (Start, Peak, and End) as data. As additional data, the coordinate of the scanning direction and the current scanning number are stored.
When data of one foreign matter are detected at two or more times of scanning, a Gaussian correction (to be described later in detail) is made by utilizing the peak data (the maximum values of the data) in the scanning and, thereupon, an ideal peak position of the foreign matter is obtained by calculation. The thus obtained coordinate of the peak position is recorded as the real coordinate of the foreign matter. And, the value of the data at the obtained peak position is recorded as the real peak data of the foreign matter.
Another method is like this. When data of one foreign matter are detected in two or more times of scanning, the position of the center of gravity
Isozaki Hisashi
Sato Takuji
Shida Yutaka
Foley & Lardner
Font Frank G.
Kabushiki Kaisha Topcon
Stafira Michael P.
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