Application Note
AK_22_AN
Structuring of Chrome Films by Chlorine
Based Reactive Ion Etching (RIE)
Applications in large area plasma processing
Recently plasma based dry etching processes have taken on greater significance for a large number of applica-tions in surface
technologies. The most important challenges in these efforts are the development of large area high density plasma sources
with an excellent homogeneity and a rugged system design which fulfills industry standards for throughput and maintenance.
Scaling of equipment and source technology covering larger sample areas is an important target in product development.
At the same time challenging demands in process technology have to be solved. Structures below the µm-range has to be
etched with a good etch homogeneity across large area. Excellent optical properties of the structures and perfect edge
contrast have to be achieved. Dependent on the applications, different materials like metals, ceramics or oxides are used.
Applying recent developments in large area plasma processing, structures down to a CD (Critical Dimension) of 100 nm can
be processed by reactive ion etching (RIE). These high demands have to be fulfilled homogeneously on large substrates with
certain selectivity between different materials. An example of application is the structuring of thin chrome films by RIE (Reactive
Ion Etching). The chrome films are commonly deposited on LTE glass materials. Often such glass substrates are large and
heavy. So there are additional requirements on the handling within the RIE equipment. Structuring of the chrome film is done by
chlorine based RIE process using an additional photo mask.
Modular AK platform for industrial large area RIE
The AK platform of MicroSystems (Fig. 1) provides a state of the art solution for scalable large area plasma processing. A
modular system layout allows for an optimum adaptation for industrial high-end applications in reactive ion etching (RIE) as
well as in plasma enhanced chemical vapor deposition (PECVD).
The basis of the AK platform is a patented high density linear microwave plasma source. Arranging these linear sources in
an array (Fig. 2) allows for an effective and homogeneous excitation of high density plasma over a wide pressure range. The
sources are scalable in length up to 1.30 m, and, by the number of sources in the array, an adaptation to different sample
sizes is possible.
Fig.1: AK 1000 for large area Chlorine based Chromium RIE
with automatic load-lock system
Fig.2: Arrangement of an array of linear microwave plasma
sources for sample face-up processing with RF biased sample
The chrome etching application described below is performed on an AK 1000 which is the largest of the AK series. Due to the
chlorine operation the system is completely made of aluminum and for safety and throughput reasons fitted with a fully robotic
loaded automatic load-lock system. The robot and automatic loading are mandatory also for handling the heavy samples with
a weight up to maximum 20 kg. The CD in the chrome patterns requires a turbo-pump and a low process pressure of a few
10-3 mbar. All the AK systems are clean room compatible down to ISO 5.
The AK 1000 allows the processing of a 550mm square sample area. Thereby the standard sample orientation is face-up. To
avoid any particle contamination on sensible optical surfaces a face-down orientation was designed also (Fig.3).
Therefore the upper sample electrode has a special clamping mechanism for defined sample carriers. This substrate electrode is
powered by an independent 13.56 MHz RF bias. Additionally an electrode cooling is applied to ensure a stabil substrate
temperature. The sample faces the 6 microwave plasma sources mounted in the chamber bottom part.
300
200
y-direction [mm]
400
100
0
0
100
200
300
400
x-direction [mm]
29,0-32,0 nm
Fig.3: Real source arrangement of AK 1000 in sample
face-down process configuration
32,0-35,0 nm
Fig.4: Chrome removal profile across a substrate area
of 450 mm square achieving ± 5% (3 σ) homogeneity
Results on patterning of chrome structures by chlorine based Reactive Ion Etching
Chrome films of 50 to 100 nm thickness deposited on massive LTE glass material are structured by an RIE process. The samples
measure 510 mm square with a weight of 12.5 kg. Sample loading and etching are performed with the chrome film face-down.
The RIE of chrome films is using a chlorine based
chemistry with an additional oxygen admixture. The
variable admixture of the process gases is typically adjusted to
Cl2:O2 = 5:1. To achieve a defined structure in the chrome film a
phote resist mask of a thickness of < 500nm is used. The selectivity
between photo resist and chrome amounts to about 0.8:1.0.
34
0
2.5
5.0
7.5
µm
10.0
12.5
Fig.5: AFM Image (top) and line scan image (bottom) of
RIE etched chrome structures
Meyer Burger (Germany) AG - BU MicroSystems, [email protected], http://microsystems.meyerburger.com
An der Baumschule 6-8, 09337 Hohenstein-Ernstthal, Germany, Phone: +49 3723 671 234
Technical data are subject to change / 01-2014
For efficient process performance in a second process step the
resist mask gets immediately stripped by an O2 plasma etch
process.
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Depentend on the geometry of the photoresist and the
selectivity of the etching process, chrome structures with
steep sidewall angles are achieved. The variability of the
etched geometries ranges from single lines with a width of some
micrometers right up to grids with a lattice constant of 500 nm at a
1:1 ratio between structure and trench (Fig. 5).
nm
-156
To guarantee a uniform etch performance, the substrate
temperature is kept constantly below 70°C during the whole
process. Both the etch rate and the homogeneity can be
influenced and optimized by the gas flow and the process
pressure. Typically etch rates of 5 to 50 nm/min with a homogeneity
better ± 5% is possible (Fig. 4).