Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
1997-10-09
2001-02-06
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237500, C356S239300, C356S239700, C356S239800
Reexamination Certificate
active
06184976
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for fabricating semiconductors, and more particularly, to an apparatus and method for measuring an aerial image from which the effects or influences of various defects on a photomask can be inspected.
2. Description of the Related Art
In general, an aerial image that is obtained from a photomask or a reticle (hereinafter commonly referred to as “photomask”) is measured in order to inspect all types of defects exhibited on the photomask to determine the resulting influence of these defects on a pattern formed on the wafers using the photomask.
FIG. 1
is a schematic view of the configuration of a conventional aerial image measuring apparatus. The conventional apparatus for measuring an aerial image includes an optical source
2
for emitting light, e.g., deep ultraviolet (DUV) or I-line, a motor filter
4
having a filter suitable for a wavelength of light irradiated from the optical source
2
, and a condenser lens
10
for condensing light that passed through an illumination aperture
6
and a vision aperture
8
. The illumination aperture
6
controls the numerical aperture (NA) and the coherency of the light. The condensed light is then emitted to a surface of a photomask
50
opposite to the surface on which a chrome pattern
52
is formed.
A charge-coupled device (CCD) camera
30
forms an aerial image by converting light passing through the photomask
50
into an electrical signal. An aerial image measurement system (AIMS)
40
measures the aerial image. The light passing through the photomask
50
is transmitted to the CCD camera
30
via an objective lens
12
, a tube lens
14
, a 7×expanded projection lens
16
and an imaging aperture
20
. An auxiliary lens
22
for observing the numerical aperture (NA) and the coherency is installed between the imaging aperture
20
and the CCD camera
30
. Also, a CCD camera
15
for visible ray observation is installed to observe light focused on the tube lens
14
through the objective lens
12
using an auxiliary outputter (not shown) such as a monitor.
In the conventional aerial image measuring apparatus having such a configuration, light from the optical source
2
is irradiated to the surface of the photomask
50
opposite to the surface on which the chrome pattern
52
is formed so that an aerial image is measured using only the light passing through the photomask.
As a result, the conventional aerial image measuring apparatus can not inspect all types of defects which may exist on the photomask pattern so that the effects or influences of such defects on the photomask can not be accurately determined.
More specifically, the conventional aerial image measuring apparatus measures only an aerial image formed by the light passing through the photomask from the surface of the photomask opposite to the surface on which the chrome pattern is formed. Therefore, one cannot inspect the effects of numerous factors existing over the entire upper surface of the photomask on which the chrome pattern is formed. Such effects that should be inspected include: the reflectivity variation on the surface of an anti-reflection layer coated on the chrome pattern; chrome particles remaining at a repaired portion or its adjacent portion after a defect on the photomask is repaired; an ion beam source, e.g., gallium, in case that the chrome is removed by an ion beam; a damaged portion on the photomask generated after the defect on the photomask is repaired; the thickness variation of the chrome pattern layers formed on the photomask; and contaminants, such as flowable or unflowable particles existing on the chrome pattern formed on the photomask, or other organic materials generated during various processes.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an aerial image measuring apparatus which can inspect various defects existing on the patterns formed on a photomask as well as on the surface of the substrate of the photomask.
It is another object of the present invention to provide an aerial image measuring method which can inspect various defects existing on the patterns formed on a photomask as well as on the surface of the substrate of the photomask.
To achieve these and other advantages, the present invention provides for an aerial image measuring apparatus that inspects defects on the photomask on which predetermined patterns are formed by using an aerial image formed by light passing through a photomask from an optical source. The apparatus according to the present invention includes an optical transmitting section for irradiating light from the optical source to a photomask and forming a transmitted light passing through the photomask. Also, an optical reflecting section irradiates the light from the optical source to the surface of the photomask on which patterns are formed and forms a reflected light reflected by the surface on which the patterns are formed. An aerial image forming device forms an aerial image by converting one of the transmitted light and the reflected light into an electrical signal.
The optical reflecting section includes a beam splitter for splitting the light emitted from the optical source into a transmitted light path along which the transmitted light is advanced and a reflected light path along which the reflected light is advanced, and a reflecting mirror for altering a light path so that the light transmitted along the reflected light path is irradiated to the surface of the photomask on which the patterns are formed.
An on/off device, respectively installed in the transmitted light path and the reflected light path, selectively blocks or passes the light transmitted to each of the transmitted light path and the reflected light path.
The aerial image measuring apparatus according to another embodiment of the present invention inspects defects on a photomask on which predetermined patterns are formed, using an aerial image formed by light emitted from first and second optical sources and passing through the photomask. The apparatus includes an optical transmitting section for irradiating the light emitted from the first optical source to the photomask and forming transmitted light passing through the photomask. An optical reflecting section irradiates the light emitted form the second optical source to the surface of the photomask on which the patterns are formed and forms reflected light reflected from the surface on which the patterns are formed. An aerial image forming device forms an aerial image by converting one of the transmitted light and the reflected light into an electrical signal.
The optical reflecting section includes a reflecting mirror for altering the path of light to irradiate the light emitted from the second optical source to the surface of the photomask on which the pattern is formed.
In another aspect, the present invention provides for a method of measuring an aerial image comprising the steps of providing light emitted from an optical source to a lower surface of the photomask and forming transmitted light passing through the photomask; providing the light emitted from the optical source to the upper surface of the photomask and forming reflected light reflected from the upper surface on which the patterns are formed; selecting one of the transmitted light and the reflected light for analysis; converting the selected light into an electrical signal to form an aerial image; and measuring the aerial image.
According to the present invention, aerial images of the photomask based on the transmitted light as well as the reflected light can be measured. Therefore, the effects or influences of every type of defect on the photomask can be accurately inspected.
REFERENCES:
patent: 5098191 (1992-03-01), Noguchi et al.
patent: 5235400 (1993-08-01), Terasawa et al.
patent: 5737072 (1998-04-01), Emery et al.
patent: 5892579 (1999-04-01), Elyasaf et al.
Park Jin-Hong
Yu Young-hun
Font Frank G.
Jones Volentine, L.L.C.
Merlino Amanda
Samsung Electronics Co,. Ltd.
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