|End point detection, plasma etching, laser light polarization, interferometer, optical spectrometer.|
Crystec Technology Trading GmbH
Company Overview Plasma Plasma Etcher Asher Failure Analysis PECVD Si3N4 Si02 Endpoint Graphen E-Beam Sputter
In IC manufacturing, it is necessary to structure layers. In order to do that, layers have to be removed partially. This is done nowadays by dry etching or plasma etching.
|un-etched||incomplete etching||complete etching||over-etching|
First a resist is deposited on top of the layer, then the resist is illuminated and developed. A mask is formed. The mask is protecting some areas, while the unmasked regions will be etched, using plasma. The goal of the etching is to remove this one layer completely in the unmasked areas, but it should not etch the next layer below. In order to achieve this goad you have several possibilities:
The last three methods are called "end point detection" and are available from several manufacturers.
An interferometer is measuring the difference of two or more light paths by overlapping the residual light from both pathes, generating interferance fringes. A monochromatic light source is used and reflected from the surface of the sample. It is overlapped with a reference light beam. Small changes in the range of the light source wavelength can be recognized.
The graph shows the overlapping of two wavelength (green and blue) as well as the residual interferogram (red).
This methode is a combination of interferometry and reflectometry in combination with powerful software to evaluate the measured signal.
The reflected light is a combination of signals from each layer within the sample and
special interference fringes are formed for each sample and can be displayed on a monitor.
The measurement spot can be positioned either on etching material solely or partially on the mask surface.
For end point detection the interference fringe pattern can be simulated for various layers and then compared
during etching with the measured signal.
The method is very effective and can be used for monitor etching and end point detection of samples with two or
more layers. It can be also used to monitor the etch back of dielectric on metal for a number of applications.
The system is installed in front of a window in the plasma etch chamber with incidence view of the wafer being etched. The upper electrode has a hole to allow the measurement. The system consists of an optical head, containing a 670nm laser source, detector and CCD camera, and a rack mounting electronics module. The optical head mounts on a XY and tilt adjustment so that the user can target the laser spot at a particular etch site. The spot size is around 50Ám.
The color of a plasma is determind by the species in the gas. Beside the moleculs and their fractions of the etching gas, also atoms from the etched layer get into the plasma and influence the color and the optical spectrum of the plasma. In some cases, when the etched material changes, the shift of the color is so strong that you can see it with your eyes trough the window of the plasma chamber. In order to measure the light emmission from the plasma, it is possible to use an optical spectrometer.
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