a) b) c)
120µm
separates
brittle
materials
ONE-STEP PROCESS SEPARATES
WITHOUT CAUSING DEFECTS
MANDY GEBHARDT
Cost, quality, and throughput are major factors in achieving suc- cessful manufacturing in the semiconductor and photovoltaics industry. One important process type is cutting, as different kinds of cutting processes are needed
to separate wafers into dies or cut solar cells into half-cells.
Traditional cutting techniques are mechanical- or laser-based,
both of which are connected with disadvantages such as particle generation because of material removal and
material damages at the cutting edge.
Thermal laser separation
Thermal laser separation (TLS-Dicing)
is a fast, clean, and cost-effective alternative to separate brittle semiconductor materials such as silicon (Si), silicon
carbide (SiC), germanium (Ge), and gallium arsenide (GaAs).
Depending on the application, a
starting point is given by an initial
scribe. Afterwards, the material is
heated by a laser with a well-defined
energy insertion (FIGURE 1a). The heated material expands and
pressure forces occur inside the heated zone, accompanied by
tensile stress around the heated zone. Laser heating is directly
followed by a cooling jet of extremely small amounts (below
10 ml/min) of deionized water spray (FIGURE 1b). This creates
a second cooled zone near the first zone that induces a tangential tensile stress pattern. The resulting tensile stress in the
overlaying region of both stress patterns opens and guides the
crack tip through the material (FIGURE 1c).
TLS-Dicing has many advantages compared to traditional
cutting technologies, including high separation speed; very
smooth side walls free of chipping and micro-cracks and with
superior bending strength; and low cost of ownership because
of no tool wear and almost no consumables.
The process uses two laser sources—a short-pulsed scrib-
ing laser (532nm, or near-infrared [near-IR] wavelength) with
a Gaussian beam profile for the initial scribe and the cleaving
laser. The cleaving is realized by a 200W continuous-wave laser
with a near-IR wavelength.
TLS-Dicing is a kerfless cleaving process,
as almost no particles are generated by TLS
itself. In comparison to traditional technologies, TLS-Dicing is a one-pass process
that separates the whole thickness of the
wafer at once.
Dicing of SiC devices
Because of its wide band gap, high mechanical strength, and high thermal conductivity,
SiC is used in certain power device applications. These devices can operate at higher
voltages, frequencies, and temperatures,
as well as convert electric power at higher
efficiency or lower power losses. At the
same time, SiC is an extremely hard and
brittle material (Mohs scale 9. 2), which can create processing challenges.
Traditional dicing technologies have some disadvantages
concerning process speed and dicing quality. Mechanical
FIGURE 1. The principle of the TLS-Dicing process includes
laser heating (a), water spray cooling (b), and stress-induced
cleaving (c).
FIGURE 2. A SiC die edge after the TLS-
Dicing process shows smooth edges and
no micro-cracks or chipping.
