Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
2000-04-10
2004-02-24
Ahmed, Samir (Department: 2623)
Image analysis
Applications
Manufacturing or product inspection
C356S237500
Reexamination Certificate
active
06697517
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for detecting the presence of defects, such as particles on a substrate surface. More particularly, the invention utilizes a combination of a light source and a detector to illuminate a substrate surface and detect scattered energy therefrom.
BACKGROUND OF THE RELATED INVENTION
Semiconductor processing generally involves the deposition of material onto and removal (“etching”) of material from substrates. Typical processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), etching and others. During the processing and handling of substrates, the substrates often become contaminated by particulates that can lodge themselves in the features of devices formed on substrates. Sources of contamination include wear from mechanical motion, degradation of seals, contaminated gases, other contaminated substrates, flaking of deposits from processing chambers, nucleation of reactive gases, condensation during chamber pumpdown, arcing in plasma chambers and so forth. As the geometries of device features shrink, the impact of contamination increases. Thus, current semiconductor manufacturing routinely includes inspection of substrates for particles to identify “dirty” processes or equipment.
In general, there are two commercial methods for detecting particle contamination on a substrate surface, one being an X-Y surface scan and another being a rotary type scan. In each case, an actuating mechanism, or stage, is used to move a substrate relative to light sources, such as laser diodes.
FIG. 1
is a perspective view of an exemplary inspection apparatus
10
. A substrate
11
is positioned on a stage
13
capable of moving in an X-Y plane. In the case of a rotary type inspection device, the stage
13
is also capable of rotation about an axis. A light source
12
emits light beam
14
onto the substrate
11
and irradiates the surface. The light beam
14
is focused as a spot by condenser lens
15
to define an inspected area of the substrate
11
. Particles, device patterns, and other protrusions on the upper surface of the substrate
11
cause the incident light beam
14
to scatter in various directions, as shown by arrows
16
, according to the light incidence angle and geometry of the protrusions. The scattered light
16
is received by a collector lens
18
and then transmitted to a detector
20
positioned in proximity to the substrate
11
. The detector
20
is typically a Photo-Multiplier Tube (PMT), a charge-coupled device (CCD) or other light sensitive detector. The detector
20
converts the scattered light
16
into a signal corresponding to the detected protrusions on the substrate surface. The signal is routed to a processing unit
22
to generate data regarding various parameters of interest such as the size and location of the detected protrusions. This approach, wherein scattered light from a surface under observation is detected, is known as “Dark Field Illumination.” Dark Field Illumination implies that only light scattered by protrusions on the substrate surface is detected and light which is merely reflected by the planar substrate surface is disregarded.
One disadvantage with conventional inspection systems is the prohibitive size and cost of the systems. Current systems are typically expensive stand-alone platforms that occupy additional clean-room space. As a result of the large area, or “footprint,” required by the stand-alone inspection platforms, the cost of owing and operating such a system is high. One reason for the size of the inspection systems is the desire for highly sensitive equipment capable of detecting sub-micron particles. In order to achieve such sensitivity, vibration due to the various moving components of the platform such as the stage, which interfere with the inspection techniques, must be eliminated. Thus, the inspection platforms are stabilized using a massive base comprising, granite slab, for example, to minimize the effects of vibration. To accommodate the wide range of motion of the stage and the massive base, conventional platforms occupy a large footprint in a fabrication facility (fab), thereby increasing the cost of operation of the overall fab.
Another problem with current inspection devices is the negative impact on throughput, or productivity. As described above, a stage moves a substrate through an X-Y plane to position the substrate relative to the light source. Conventional inspection platforms, such as the one in
FIG. 1
, illuminate only a small portion, or spot, on the substrate being inspected. The substrate is then moved repeatedly by the stage to expose the entire surface of the substrate to the light source. Consequently, conventional platforms drastically increase overhead time associated with chip manufacturing. One attempt to reduce the overhead time and increase throughput in a reticle inspection using a stage is shown in U.S. Pat. No. 5,663, 569 which utilizes optics capable of shaping the light beam into a line, or slit, to allow for single-pass inspection. The slit dimensions are adjusted to accommodate the width of the object under inspection so that the object need only be scanned in a single direction once. However, the light source is positioned to obliquely irradiate the reticle, thereby producing a non-uniform spot pattern. Specifically, the light source is offset to one side of the reticle such that the reticle moves past the light source during a scan as opposed to toward or away from the light source. As a result, the light produces a more intense pattern on the portion of the reticle closer to the light source while a less intense pattern is produced farther away from the light source.
Throughput is further diminished because the current inspection systems are stand-alone platforms that require substrates to be removed from the vacuum environment of the processing system and transferred to the separate inspection platform. Thus, production is effectively halted during transfer and inspection of the substrates. Further, because such an inspection method is conducive only to periodic sampling due to the negative impact on throughput, many contaminated substrates are processed before inspection and detection of problems occurs. The problems with substrate inspection can be compounded in cases where the substrates are re-distributed from a given batch making it difficult to trace the contaminating source.
It would be preferable to have an inexpensive in situ inspection method and apparatus incorporated into existing processing systems capable of detecting particles on substrates. Further, the preferred inspection apparatus should be capable of being retrofitted to existing processing systems. The inspection apparatus should be positioned to allow inspection of each substrate before and/or after processing. Impact to throughput should be minimized by inspecting substrates “on-the-fly” during transfer between typical processing steps without the need for a separate inspection platform and stage.
Another problem with particle detection systems is the noise produced by chip patterns formed on substrates. During inspection by conventional illumination techniques, the patterns act as micro-mirrors causing the light to reflect in various directions. As a result, the patterns may produce misleading information, i.e., the patterns may indicate the presence of foreign particles where none are found. In order to allow particle detection of patterned substrates various methods and apparatus have been implemented in the art.
U.S. Pat. No. 5,463,459, entitled “Method and Apparatus for Analyzing the State of Generation of Foreign Particles in Semiconductor Fabrication Process,” provides a method of detecting foreign particles on a substrate by “eliminating” the patterns formed on the substrate. For example, corresponding portions of adjacent chips are compared to determine differences. The chips are illuminated with a light source to cause reflection of the light which is detected by detection equi
Ahmed Samir
Applied Magerials, Inc.
Moser Patterson & Sheridan
LandOfFree
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