LASER END POINT DETECTORS
As the North American distributor and service provider for
Intellemetrics
products, we sell, install and integrate dry etch laser end point detectors and
optical thickness monitors throughout the United States and Canada.
Our dry etch laser end point detectors are
specialized interferometers adapted for etching applications. They have a superb modeling
capability that predicts the reflection curve from the wafer before the etch.
Dry etch processing is a fundamental
step in many semiconductor processing schemes. The continued development of higher packing
densities and the increased use of trench structures have placed ever more demanding
requirements on the technique used to terminate the etch process.
Our dry etch laser end point detector, the LEP300, uses the laser reflection method to
rise to this challenge. It the first in the industry to use sophisticated modeling and
predictive data filter techniques to extract the ultimate in rate and thickness data from
the etch process.
The LEP300 allows users to terminate etches in
individual quantum wells, including III-V materials. Si etch versions are available with
IR laser sources and can be modulated to give high noise rejection for clear output data. |
Specifications | System
Layout
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How It Works
The basic innovation Intellemetrics brings to the laser end point detector is curve
facility based on modelling expertise licensed from the University of Glasgow. Laser end
point detection is based on the phenomenon of interference occurring when laser light is
reflected off a substrate covered with one or more thin overlying semi-transparent films.
The return reflected light varies cyclically with changes in thickness and this signal
behavior is used to determine the process end-point.
There are two basic approaches to using the technique. In
the first, "masked etch," a structure is defined by an overlaying mask and the
main interference occurs between rays reflected off the mask and the etched film surface.
In the second, "planar etch," the mask open area is large compared to the laser
spot size and the dominant interference mechanism is between reflection within the film
itself. The LEP300 addresses both the mask and planar etch requirements and provides compensation
measures for erosion of the mask itself during the monitoring process.
Earlier instruments relied on comprehensive calibration
runs to determine the signal behavior that should be identified with the end of the etch
process. While the LEP300 can still be used in this mode, the major innovation is use of
modelling software to predict the behavior of the reflected laser signal by modelling the
physical structure. This approach was pioneered by Glasgow University researchers to etch
very thin layers in multiple layer stack structures, with a reported etch resolution of 20
nm.
To use the modelling software, the user inputs information
on the mask material — the "open area" of the mask, such as the material of
the thin films and the substrate. The properties of these materials are stored in
libraries and used, along with user-defined data, to predict the behavior of the reflected
light. The next step is for the user to define the various stages of the etch process,
including the end point. This is done graphically by "dragging" vertical lines
on the modelled data so that the user is immediately aware of the likely signal behavior
at each important step. The end point itself can be set by reference to the continuously
updated etch thickness and/or a logical combination of the behavior of the signal and its
first and second derivatives.
Benefits
The
immediate advantage of the LEP300's signal
prediction capability is that the user is always
aware of what the signal is likely to do — even
before the etch process actually begins. A more
subtle but equally important advantage is that the
predicted signal behavior is used to process the
acquired data, achieve a high level of noise
rejection, and ensure the continuous update of
rate and thickness
information.
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