Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-01-14
2001-09-04
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C250S358100
Reexamination Certificate
active
06285199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a device and method for optimally detecting a surface condition of different types of wafers by automatically selecting filters to appropriately cut off a certain amount of reflected ray from impinging on an imaging sensor to process wafers with different surface properties.
2. Discussion of Related Art
FIG. 1
shows elements of a conventional device for detecting the surface condition of a wafer. Referring to
FIG. 1
, the conventional device comprises an Xe-lamp
1
for emitting a constant emissive ray, a filtering lens
3
for filtering the emissive ray from the Xe-lamp
1
within a band of 400~700 nm, a reticle
5
for adjusting the focus of the emissive ray transmitted through the filtering lens
3
, a half mirror
7
for directing the filtered ray to a beam splitter
17
and to a mirror
8
, the beam splitter
17
for splitting the ray reflected from the half mirror
7
to each PCD (Position Charge Device) sensor
13
and
15
, the PCD sensors
13
and
15
determining the optimal points of automatic focus for the ray, amplifiers
19
and
21
for respectively amplifying signals output from the PCD sensors
13
and
15
, an image processing device
23
for comparing the signals output from the amplifiers
19
and
21
to each other to determine the best optimal point of automatic focus for the wafer
27
, a piezo driving device
25
for controlling a piezo member
29
to provide the best optimal focus point for the wafer
27
according to a signal output from the image processing device
23
, and the piezo driving device
25
for controlling the piezo member
29
. The piezo member
29
is placed on a side of the stage on which the wafer
27
is placed for three-dimensionally controlling the position of the stage.
The conventional device further comprises the mirror
8
, an objective lens
9
for magnifying a ray reflected from a wafer
27
and directing it to the mirror
8
, and a CCD (Charge Coupled Device) sensor
11
for representing surface condition of the wafer
27
based on the reflected ray output from the objective lens
9
. The output of the CCD sensor
11
is processed by the image processing device
23
to determine any abnormality on the surface of the wafer
27
.
An operation of the conventional device of
FIG. 1
is as follows.
Referring to
FIG. 1
, an emissive ray is projected from the Xe-lamp
1
in the direction of the stage where the wafer
27
is placed. The emissive ray is filtered by the lens
3
to a wave band of 400~700 nm suitable for detecting particles. The filtered ray is reflected by the half mirror
7
. The beam splitter
17
splits the reflected ray into two beams which are respectively directed to two PCD sensors
13
and
15
. The amplifiers
19
and
21
respectively amplify the outputs of the PCD sensors
13
and
15
.
The image processing device
23
determines the best optimal point of automatic focus for the wafer
27
by finding the intersection position of electrical signals output from the two PCD sensors
13
and
15
, and generates a control signal to the piezo driving device
25
. The piezo driving device
25
controls the piezo member
29
based on the control signal so that the Xe-lamp
1
projects light on the wafer
27
at the optimal point of automatic focus. That is, in accordance with a driving signal output from the piezo driving device
25
, the piezo member
29
displaced at one side of the stage having the wafer
29
thereon is moved to achieve the optimal point of automatic focus for the light impinging on the wafer
27
.
At the same time, the ray emitted from the Xe-lamp
1
and reflected from the wafer
27
passes through the objective lens
9
and is reflected by the mirror
8
. Then this ray impinges on the CCD sensor
11
, and is visualized subsequently to identify the pattern of the surface of the wafer
27
. The CCD sensor
11
generates digital signals representing any abnormality (e.g., particles, dents, etc.) on the surface of the wafer
27
. The principle of the CCD sensor
11
is to detect any displacement of the wafer surface by reading and analyzing light-receiving spots (photo-diode) of the reflected ray. The image processing device
23
processes the output of the CCD sensor
11
to detect an abnormality on the surface of the wafer
27
.
In the conventional device of
FIG. 1
, the emissive ray from the Xe-lamp
1
is reflected at the surface of the wafer
27
, and then transferred to the CCD sensor
11
so that the wafer surface can be examined. However, since the reflection rate at the surface of each wafer differs from each other, wafer abnormality will be detected only if the reflection rate of the wafer is high. Otherwise, surface abnormality of the wafer can not be detected effectively since the processing of a weak reflective ray by the CCD sensor can result in inaccurate detection results. Therefore, conventional detection devices and methods are not reliable when detecting the surface condition of different types of wafers.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a device and method for detecting particles on a wafer that substantially obviate one or more of the problems due to the limitations and disadvantages of the related art.
Therefore, it is an object of the present invention to provide a device and method for effectively detecting the surface condition of different types of wafers based on the reflection rates of the wafers.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purposes of the present invention, as embodied and broadly described, a device for detecting surface conditions of wafers, comprising a light generating unit for impinging light on a wafer to generate a reflected light; a combining unit, including a plurality of filters having different light cut-off ratios, for receiving the reflected light and outputting a varied amount of the reflected light; and a detection unit for receiving the varied amount of the reflected light from the combining unit and processing the received light to detect a surface condition of the wafer.
Furthermore, the present invention is directed to a method for detecting surface conditions of wafers, comprising the steps of impinging light on a wafer to generate a reflected light; generating a varied amount of the reflected light selectively using a plurality of filters having different light cut-off ratios; and processing the varied amount of the reflected light to detect a surface condition of the wafer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4352017 (1982-09-01), Duffy et al.
patent: 4929081 (1990-05-01), Yamamoto et al.
patent: 5289260 (1994-02-01), Miyazaki et al.
Hyundai Electronics Industries Co,. Ltd.
Karlsen Ernest
Tang Minh
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