Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1998-09-30
2001-10-09
Anderson, Bruce (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S397000
Reexamination Certificate
active
06300629
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to particle beam imaging and measurement equipment, such as a scanning electron microscope. The invention has particular applicability for in-line inspection of semiconductor wafers during manufacture of high-density semiconductor devices with submicron design features.
BACKGROUND ART
Current demands for high density and performance associated with ultra large scale integration require submicron features, increased transistor and circuit speeds and improved reliability. Such demands require formation of device features with high precision and uniformity, which in turn necessitates careful process monitoring, including frequent and detailed inspections of the devices while they are still in the form of semiconductor wafers.
Conventional in-process monitoring techniques employ a particle beam apparatus, such as a scanning electron microscope (SEM), for defect review. The SEM scans the surface of a specimen with an energetic particle beam; e.g., an electron beam having an energy of about 400 eV to about 1 keV. The impact of the particle beam on the surface of the specimen causes electrons of the particle beam to be deflected, or “backscattered”, by atoms of the specimen with energies close to that of the particle beam (i.e., about 400-1000 eV). These deflected electrons are referred to as backscattered electrons. Electrons released from the surface of the specimen due to the impact of the particle beam, with energies of about 50-100 eV, are referred to as secondary electrons. It is well known that since the backscattered electrons are deflected by atoms of the specimen, they provide information relating to the material composition of the specimen (e.g., density information). On the other hand, the secondary electrons are released from the specimen corresponding to the slope of the surface of the specimen, so secondary electrons provide topographical information, i.e., the distribution of secondary electrons will vary with the slope of the surface of the specimen. Thus, images of a semiconductor wafer under review showing material contrast can be generated after detecting backscattered electrons, and images of the wafer showing the bottoms of trenches and contact holes, as well as particles and other surface features, can be generated after detecting secondary electrons. Furthermore, certain attributes of a defect may be apparent only in an image generated by a mix of both backscattered and secondary electrons.
FIG. 1
depicts a prior art SEM for producing such images, wherein a primary beam
11
is directed at a wafer
12
to produce backscattered electrons BSE and secondary electrons SE, which are detected by a single detector
13
. Backscattered electrons BSE tend to deflect from wafer
12
at acute angles, while secondary electrons SE are dispersed at many angles. Secondary electrons SE which impinge detector
13
simultaneously with backscattered electrons BSE are selectively repelled by an electrode in the form of a grid
14
provided near the entry side of detector
13
to produce the desired images of wafer
12
.
In practice, a switch
15
, typically a potentiometer, is manually adjusted to negatively bias grid
14
such that an image of the desired combination of backscattered and secondary electrons is produced. For example, a negative potential of about the same energy as secondary electrons SE is applied to grid
14
via switch
15
to repel most secondary electrons SE, thus allowing easier detection of backscattered electrons BSE, which are not significantly repelled by the negative bias on grid
14
because they are of a substantially higher energy. Then, grid
14
is switched off and an image is generated from secondary electrons SE, since when grid
14
is not biased, mostly secondary electrons impinge on detector
13
.
The detection apparatus of
FIG. 1
suffers from the disadvantage of not providing simultaneous viewing of images generated as a result of the detection of backscattered electrons BSE and secondary electrons SE; that is, the two or more respective images are normally produced sequentially (by varying the potential on grid
14
), so that only one image can be seen by the operator at a time.
SUMMARY OF THE INVENTION
Simultaneous viewing of several images would provide information regarding different attributes of a specimen. For example, one image may show material characteristics, another may show topographical features of a given site on a wafer, and still another a combination of attributes. Simultaneous viewing would facilitate comparison of images of defect sites and reference sites, identification of defects, and classification of defects, since attributes of a defect may appear in one type of image and not in any other. There exists a need for a SEM having a single detector which simultaneously displays images generated from the detection of backscattered and secondary electrons.
According to the present invention, the above stated needs and others are met by a particle beam apparatus for imaging of a specimen, the particle beam apparatus comprising a particle source for providing a primary beam for impinging on the specimen to release secondary electrons therefrom and to provide backscattered electrons to be deflected by the specimen; a detector for detecting the backscattered and the secondary electrons; an electrode disposed between the detector and the specimen chargeable to a plurality of potentials for directing a path of the secondary electrons; an imager responsive to the detector for generating images based on the secondary electrons and the backscattered electrons; and a charge controller for automatically controlling the potential on the electrode such that the imager simultaneously generates a plurality of different images.
Another aspect of the present invention is a method for imaging a specimen, which method comprises directing a particle beam onto the specimen to release secondary electrons therefrom and to deflect backscattered electrons of the particle beam therefrom; detecting the backscattered and the secondary electrons; directing the path of the secondary electrons relative to the detector; consecutively producing a plurality of images based on the detected electrons; and displaying the plurality of images substantially simultaneously.
Additional features and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
REFERENCES:
patent: 4560872 (1985-12-01), Antonovsky
patent: 4831266 (1989-05-01), Frosien et al.
patent: 5043583 (1991-08-01), Robinson
patent: 5424541 (1995-06-01), Todokoro et al.
patent: 5466940 (1995-11-01), Litman et al.
patent: 5608218 (1997-03-01), Sato
patent: 5644132 (1997-07-01), Litman et al.
patent: 6084238 (2000-07-01), Todokoro et al.
Anderson Bruce
Applied Materials Inc.
McDermont Will and Emery
LandOfFree
Defect review SEM with automatically switchable detector 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 review SEM with automatically switchable detector, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Defect review SEM with automatically switchable detector will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2596088