Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-02-14
2003-01-28
Stafira, Michael P. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
Reexamination Certificate
active
06512579
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the following priority application is herein incorporated by reference:
Japanese Patent Application No. 2000-36396 filed Feb. 15, 2000
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a defect inspection apparatus that inspects defects on a substrate and, in particular, a defect inspection apparatus that inspects for irregularities, scars and the like on a substrate.
2. Related Art
There are apparatuses proposed in the prior art that perform automatic inspection for defects such as irregularities, scars and the like at a surface of an IC wafer or a liquid crystal substrate (hereafter generically referred to as a “substrate”) by using diffracted light originating from a repetitive pattern formed at the surface.
Since the diffraction efficiency at a position where a defect is present differs from diffraction efficiency at a defect-free position at the substrate surface, a difference in brightness manifests in an image formed from the diffracted light from the repetitive pattern, thereby enabling identification of the position of a defect based upon the contrast in the image.
At the position of a defect, for instance, the cross sectional shape of the repetitive pattern may have been changed due to defocusing of the exposure apparatus or a change may have occurred in the film thickness of the resist.
As illustrated in the side elevation in FIG.
12
(
a
), a substrate
101
to undergo inspection is placed on a stage
102
and is illuminated by parallel illuminating light L
11
for inspection. At this time, the illuminating light L
11
enters the substrate at a 90° angle relative to the direction along which the straight lines in a repetitive pattern
101
a
extend (direction X) on the substrate
101
as shown in the top view presented in FIG.
12
(
b
).
Diffracted light L
12
(see FIG.
12
(
a
)) from the substrate
101
illuminated with the illuminating light L
11
is generated at a given position in the repetitive pattern
101
a
at a degree of diffraction efficiency that reflects whether a defect is present in the area or the area is free of defect.
In such an apparatus, in which a light-receiving optical system that receives the diffracted light L
12
is normally fixed, the diffracted light L
12
is guided to the light-receiving optical system by tilting the stage
102
around the axis extending along direction X. The angle setting (tilt angle) at which the stage
102
is tilted is determined in advance in conformance to the diffraction conditions.
The ideal diffraction conditions may be expressed as in the following expression (11) in which &lgr; and &thgr;i respectively represent the wavelength and the angle of incidence of the illuminating light L
11
, &thgr;d and m respectively represent the angle of diffraction and the diffraction order of the diffracted light L
12
, &thgr;t represents the tilt angle of the stage
102
and p represents the pitch of the repetitive pattern
101
a.
(mathematical expression 1)
sin
(
θ
d
-
θ
t
)
-
sin
(
θ
i
+
θ
t
)
=
m
λ
ρ
(
11
)
In expression (11), the angle of incidence &thgr;i, the angle of diffraction &thgr;d and the tilt angle &thgr;t are set in reference to the standard normal line (reference normal line) achieved when the substrate
101
is held in a level state, as illustrated in FIG.
13
. The angle of incidence &thgr;i is positive along the direction looking toward the incidence side and is negative along the direction looking toward the reflection side. The range of the angle of incidence &thgr;i is 0°<&thgr;i<90°.
The angle of deflection &thgr;d and the tilt angle &thgr;t are both negative along the direction looking toward the incidence side and are positive along the direction looking toward the reflection side. The diffraction order m is negative along the direction looking toward the incidence side and is positive along the direction looking toward the reflection side relative to 0-order diffracted light (regular reflected light) at m=0.
However, there are limits to the degree of accuracy at which the substrate
101
can be positioned along the direction of the tilt angle &thgr;t and the degree of accuracy at which the direction of the straight lines of the repetitive pattern
101
a
on the substrate
101
can be positioned at a 90° angle relative to the direction along which the illuminating light L
11
is irradiated for illumination and, thus, there is a problem in that an angular misalignment occurs between the direction along which the diffracted light L
12
originating from the repetitive pattern
101
a
advances (the angle within the YZ plane, i.e., the angle of diffraction &thgr;d and the angle within the XZ plane in
FIG. 12
) and the direction along which the optical axis of the light-receiving optical system extends.
In addition, such an angular misalignment also occurs to a degree corresponding to the extent of an aberration present at an illumination optical system that guides the illuminating light L
11
to the substrate
101
or the light-receiving optical system that receives the diffracted light L
12
. There is an added problem concerning the angular misalignment attributable to an aberration in that the quantity of misalignment varies depending upon the position at which the diffracted light L
12
is generated (the position on the substrate
101
).
Such an angular misalignment may result in some of the diffracted light L
12
advancing outside the pupil of the light-receiving optical system, which will lower the overall contrast or partially lower the contrast of the image formed from the diffracted light L
12
to compromise the reliability of the inspection.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a defect inspection apparatus that achieves highly reliable inspection results by preventing the contrast of the image of the substrate formed from the diffracted light from becoming lowered either in its entirety or in part even when there is an angular misalignment between the direction along which the diffracted light from the substrate advances and the direction of the optical axis of the light-receiving optical system.
In the defect inspection apparatus according to the present invention having an illumination optical system that illuminates a substrate and a light-receiving optical system that receives diffracted light from the substrate to inspect for a defect at the substrate based upon an image of the substrate obtained by the light-receiving optical system, the illumination optical system and the light-receiving optical system have numerical apertures different from each other and the absolute value of the difference between the numerical aperture at the illumination optical system and the light-receiving optical system is set at a value equal to or greater than the degree of the angular misalignment manifesting between the direction along which the diffracted light advances and the direction along which the optical axis of the light-receiving optical system extends.
Thus, even when there is an angular misalignment manifesting between the direction along which the diffracted light advances and the direction along which the optical axis of the light-receiving optical system extends, the quantity of diffracted light passing through the pupil of the light-receiving optical system is sustained at a constant level. As a result, the contrast of the image of the substrate formed from the diffracted light having passed through the pupil of the light-receiving optical system is not lowered, either in its entirety or in part. In other words, the image of the substrate has a contrast that reflects whether or not a defect is present. Consequently, the presence/absence of a defect at the substrate can be inspected based upon the image of the substrate thus obtained.
The absolute value of the difference between numerical apertures is set at a value equal to or grea
Kato Kinya
Oomori Takeo
Nikon Corporation
Stafira Michael P.
LandOfFree
Defect inspection apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Defect inspection apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Defect inspection apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3020616