Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
1998-09-03
2002-03-05
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S307000
Reexamination Certificate
active
06353222
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to using scanning electron microscopy (SEM) to study defects in wafer structures. Wafer structures are articles having a plurality of very thin layers on a wafer. An example of a wafer structure is an integrated circuit fabricated on a semiconductor wafer.
More particularly, this invention relates to a method of obtaining defect depth information which can be used to help determine the layer of a wafer structure in which a defect is located. In other words, the invention ultimately involves classifying and determining the depth of a defect. Defect depth information may include contour height information.
The invention is advantageous in that, by determining the depth of a defect, a corresponding processing step may be identified for further scrutiny.
2. Background
Until the present invention, the study of defects in wafer structures has focused on determining whether the particular wafer structure is faulty and, if so, whether the wafer structure should be discarded or kept. This conventional approach will now briefly be described.
Many steps are typically required in producing a wafer structure. The sizes involved are very small, however, and it is not unusual for a defect to occur. An example of such a defect, which will be mentioned many times in this discussion, is the accidental introduction of an undesired particle. Many other defects are possible, as is well known to those acquainted with this field, and the invention is to be understood to relate to all detectable defects. For the sake of focusing attention on the invention, however, the particle defect will provide an easily-understandable example of a defect. A particle is an example of a protrusion defect. Protrusion defects “stick up” from the surface. Another kind of defect is a recess defect, like a pit or a scratch. Recess defects recede into the surface.
It will be appreciated that a protrusion defect may include a particle or other unwanted structure on top of a surface, or a bump that is a manifestation of a particle/unwanted structure below a surface. Since the production of wafer structures involves many layers, it may be more common for a protrusion defect to be manifested as a bump which reflects a sub-surface particle, instead of as a particle itself on top of a surface.
Because defects occur, inspections are necessary. Inspecting only the finished product is economically impractical, for several reasons. One reason is that a defect that occurs early in the manufacturing process might be obscured by the layers deposited in subsequent steps. Another reason is that, if a defect in a wafer structure can be detected earlier, then the further devotion of time and resources to that particular wafer structure can be avoided.
Although the inspection of only the finished wafer structure is economically impractical, so too is the inspection of the wafer structure after each manufacturing or process step. The production of wafer structures typically involves hundreds of steps, and inspecting after each step would unacceptably slow production. Furthermore, each inspection adds to the cost of the final wafer structure, and an inspection after each step would make the end product prohibitively expensive.
In view of the foregoing, inspections are normally performed after only critical steps. Every different wafer structure product will necessarily have somewhat different critical steps, and persons versed in the production of wafer structures already understand how to select which steps are critical and which are not, and how to balance such a selection against the economic considerations. Practical considerations also take a role in determining when inspections are to be performed. For example, where automated robotic processing is involved, it may be the case that several steps are performed automatically and that access to the wafer structure is not possible until a final step. Thus, a critical step in such a system might be the final step in a series of automatically performed steps.
After each critical step in the manufacturing process, the wafer structure is inspected. In particular, the wafer structure may be placed in an inspection station for initial defect detection.
One example of an inspection station is an optical inspection station, such as that described in U.S. Pat. No. 5,699,447 to Alumot et al., hereby incorporated by reference. This inspection station for initial defect detection may be referred to as a first optical review station, or as a first optical inspection station.
The first optical inspection station performs a die to die or a cell to cell inspection and flags x,y coordinates for cells or dies differing from the others. Although no two dies/cells will be perfectly identical, an optical inspection station such as that described above has a threshold. Where the differences exceed the threshold, the die/cell is flagged. The comparison is statistical in nature, and lends itself to computer processing.
The optical inspection station provides a notification of the flagged locations that contain differences that are supposed by the optical inspection station to be defects (i.e., the differences that exceed the threshold). This notification typically takes the form of a defects map.
A defects map provides, for each supposed defect in the wafer structure, the location of the supposed defect. To be more precise, the defects map treats the wafer structure as a plane and provides planar coordinate information (i.e., x and y coordinates) so that the supposed defects can be located for further inspection. The inspection equipment of the optical inspection station is therefore useful for detecting the possible presence of defects.
After a critical step, when the defects map indicates a supposed defect, the wafer structure then must be reviewed in more detail. To review the wafer structure in more detail, the wafer structure typically is given a more detailed optical review (as mentioned in U.S. Pat. No. 5,699,447).
The defect determination possible from this second optical review is more detailed than that possible at the first optical inspection station. At this optical review station, the supposed defect of the wafer structure is studied. In particular, the supposed defect location coordinates are used to bring the supposed defect directly under the optics of the station.
Using the optical review station, there is typically made a more accurate determination as to whether there is a defect, such as a particle, in the wafer structure. Given the limited level of detail possible at the first optical inspection station, it may happen that no actual defect is noted by the second optical review station at the location where a supposed defect was indicated. In other words, the second optical inspection station may be used to differentiate between actual defects and falsely detected defects.
Optical inspection stations have been described above in relation to making a determination as to the existence of a defect. Another known station which may be used for review is a scanning electron microscope (SEM). An example of a SEM may be seen in U.S. Pat. No. 5,659,172 to Wagner et al., which is incorporated by reference. A SEM also may be used to determine the presence or absence of a defect at a location indicated by a defect map. In particular, a conventional SEM provides an SEM image of an area containing a suspected defect, the image forming the basis for a defect determination.
The present inventor has determined that the above-identified approach using only optical review or using a combination of optical and SEM review leaves much to be desired in the prevention of future defects. This deficiency in the conventional approach will now be described.
It will be recalled that not all of the manufacturing process steps, for economic reasons, are critical steps. There are normally several steps, and perhaps many steps, carried out before each critical step. The manufacturing process steps may thus be thought of as being grouped in m
Nguyen Kiet T.
Sughrue Mion Zinn MacPeak & Seas PLLC
LandOfFree
Determining defect depth and contour information in wafer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Determining defect depth and contour information in wafer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Determining defect depth and contour information in wafer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2867588