FEATURED ARTICLE Dicing of Thin Si Wafers BY CHRISTIAN FORNAROLI
Currently, electrical semiconductor components such as LEDs, solar cells or transistors are commonly produced in a batch process. This way, many identical components can be processed in parallel on one big wafer; subsequently, each chip has to be singulated. Mechanical sawing with diamond blades has been used for a long time, but as the wafer material gets thinner and the chip size smaller, this classical process can be replaced by laser-based dicing processes. In particular, the mechanical load and the relatively large kerf width are serious disadvantages of a mechanical dicing process. A reduction of the kerf width leads to a much higher yield of chips per wafer and, therefore, to
The experiments were carried out with a Coherent HyperRapid 50 at a wavelength of = 532 nm, an average power of up to 22 W @ 400 kHz and pulse duration of = 6 ps. In Scanlab IntelliScan 14DE Galvo scanner and focused onto a spot diameter of 14 μm by a 100 mm f-Theta lens. The laser source and the entire beam path are installed in a Kugler MICROGANTRY Nano3x with aerodynamic bearings for highest cutting depth attainable.
At a pulse repetition frequency of 400 kHz, the scanning speed was set to 2500 mm/s, which means a temporal pulse overlap – 0.75, 5.5 and 10 J/cm² – for up to 1000 repeats. In general μm cannot be
with a Picosecond Laser Ablation Process
J/cm² the cutting depth amounts to almost 20 μm after 400 pulse energy of 3.1 μJ, the cutting depth after 1000 repetitions is 105 μm.
Although the depth is increased, the progress is again degressive. Even an additional few thousand repetitions will not lead to the desired cutting depth of 120 μ μm after 1000 passes. The 120 μm are even obtained after 400 repetitions which means an effective cutting speed (scanning speed / number of passes) of 6 mm/s. The groove width also strongly depends on the pulse energy. For low pulse energy, the width amounts to less than 15 μm, or medium and high μm.
Altogether the cutting depth development is logarithmically shaped with different saturation levels, dependent on the repetitions even cause damage: cracks and melting zones in the chips. Figure 2 shows light microscope pictures of ablation experiment was conducted, the wafer was cleaved perpendicular to the cutting direction, thus exposing the cutting geometry. The Big differences occur in terms of the depth attained. At a high
Figure 1. Progress of the groove depth and width at different J/cm²), light blue (5.5 J/cm²), orange (10 J/cm²)
10
LIATODAY FOCUS: SCIENCE & RESEARCH SEPTEMBER/OCTOBER 2014
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32