Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2000-07-10
2001-12-18
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S237400
Reexamination Certificate
active
06331888
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of surface inspection for inspecting a foreign matter (“foreign matter” herein is a comprehensive term embracing a dust, flaw, and the like) present on the surface of an object of inspection such as a wafer and an apparatus for carrying out the method.
PRIOR ART
Such a method for surface inspection has so far been known in which a light beam from a light source is thrown on the surface of an object of measurement through an optical system and a scattered light beam reflected from the surface of the object of measurement is sensed by a photoelectric converting element, while the object of measurement and the optical system are provided with relative displacement, whereby a foreign matter on the surface of the object of measurement is inspected and the position coordinates of the foreign matter are recorded. As the converting element, a photomultiplier for example is in use.
An object of measurement such as a wafer has an effective range of measurement. Foreign matter/flaw is inspected within the effective range.
A photomultiplier having a high sensitivity is quite capable of measuring a scattered light beam from a foreign matter on the wafer. However, the region outside the effective range, i.e., a circumferential range, is frequently dirty. Therefore, a great amount of scattered light is generated in the circumferential range, not to be compared with that in the effective range. Because the circumferential range has an edge portion of the wafer, an extremely great amount of scattered light is produced there.
However, conventional apparatuses for foreign matter inspection measure the circumferential range and the effective range on the basis of the signal from the same photomultiplier. Therefore, when a great amount of scattered light is produced in the circumferential range, a saturation phenomena due to the characteristic of a photomultiplier occurs. Because of this, it sometimes becomes impossible for such an apparatus to continue the measurement for a certain period of time.
For example, such a state in which the measurement becomes impossible is shown in
FIG. 17. A
light beam from a light source is thrown on the surface of an object of measurement through an optical system and a scattered light beam reflected from the surface of the object of measurement is sensed by a photoelectric converting element, while the object of measurement and the optical system are provided with relative displacement, and a scanning light beam is continuously directed to a plurality of objects of measurement, whereby a foreign matter on the surface of the object of measurement is inspected. While the effective range is inspected, there arises no problem. However when the scanning light beam enters the circumferential range of the wafer, i.e., enters the circumferential range beyond the effective range, a great amount of scattered light is produced as shown at the bottom of
FIG. 3 and
, thereby, the photomultiplier is put into the saturated state and it is made impossible to perform the measurement for a certain period of time thereafter. This state is shown as the photomultiplier's dead zone in FIG.
17
.
Since there is the above described problem arising from the principle of the photomultiplier, it has been unavoidable in the conventional method of surface inspection with the use of a photomultiplier that the dead zone is produced by the effect of the strong scattered light beam from the edge portion of the wafer. Especially when there is present a U or V notch or the like in the wafer, accurate surface inspection becomes difficult. In fact, accurate measurement of the edge is impossible.
Let it be supposed, while the conventional method for surface inspection with the use of a photomultiplier as shown in
FIG. 17
is used, that another sensor is also used for inspecting the surface of the wafer. Then, even if measurement data of the wafer surface are stored, the processing may become useless as shown in
FIG. 18
when position coordinates are not accurate or they are not recorded at all.
Therefore, various forms of data processing are being performed on the measurement data in the circumferential range.
Whichever data processing method may be used, it is difficult, from principle, to perform accurate measurement. As for the measurement of the coordinates in the circumferential range, no accurate measurement method has yet been established.
Even if another sensor is used only for measurement of the circumferential range, the measurement and data processing may have to be made separately from that of the sensor used for measurement in the effective range. Thus, it is theoretically impossible to accurately match the position coordinates obtained by both the sensors.
Such a method may be considered as to employ another low-sensitivity sensor for sensing reflected light by regular reflection of an inspecting light beam and subject the obtained data to the same processing as that for foreign matter inspection, to thereby accurately measure the circumferential range. However, even if the data in the circumferential range are accurately measured by the employment of another sensor sensing the reflected light by regular reflection of the inspecting light beam, the quantity of the pertinent coordinate data will become too huge to be processed in the same way as in the processing of the foreign matter data and a large volume of memory will become necessary. This follows a serious problem of cost increase for processing data and constructing hardware.
When pixel processing is made without having coordinate data, since coordinate data are absent even if data are present, it is impossible to obtain accurate measurement data in the circumferential range.
Such a method and apparatus for surface inspection, in which an inspecting light beam is thrown on the surface of an object of inspection through an optical system, a scattered light beam reflected from the surface of the object of inspection is sensed, the object of inspection and the optical system are provided with relative displacement in the meantime such that the inspecting light beam makes a spiral scan, and thereby a foreign matter on the surface of the object of inspection is inspected, is known. In such a conventional method and apparatus for surface inspection on the spiral scan system, the detection of the foreign matter signal is performed by making sampling along the scanning direction of the inspecting light beam at each of divided sections at predetermined intervals (divided for example by an encoder signal) and by detecting the largest signal therein and recording only such data. The method to store only the maximum data in each of the divided sections is called “pixel system”.
FIG. 2
shows a processing method on a conventional pixel system. In the section A, the data Da takes on the maximum value. In the section B, the data Db takes on the maximum value. According to a known software processing method on the pixel system, it is determined that there is one foreign matter or there are two foreign matters in this case. For example, in the case where they are judged to be continuous by software, the number becomes one. In the case where they are judged discontinuous, the number becomes two.
FIG. 7
shows a method on another conventional pixel system of surface inspection, in terms of determination of the existence of continuity.
The determination in the scanning direction in
FIG. 7
is made as follows. Namely, in the section A, the data Da takes on the maximum value and, in the section B, the data Db takes on the maximum value. Depending on the software processing method on the pixel system, the number of the foreign matters becomes one or two. In the case of software judging them to be continuous, the number becomes one. In the case of software judging them to be discontinuous, the number becomes two.
In the state of inspection shown in
FIG. 7
, determination of the existence of continuity in the direction of feed indicated by the arrow is made as shown in FIG.
8
Foley & Lardner
Kabushiki Kaisha Topcon
Pham Hoa Q.
LandOfFree
Method and apparatus for surface inspection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for surface inspection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for surface inspection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2590025