Lifetime control in silicon power P-i-N diode by ion irradiation: Suppression of undesired leakage
Introduction
Nowadays, the irradiation with alphas in combination with high-energy electrons is a dominant technique for setting the carrier lifetime in silicon P-i-N diodes [1]. It is widely accepted that the optimum position of the narrow and heavily damaged region produced by alphas, where carrier recombination is enhanced locally, is close to the anode junction [2], [3]. Unfortunately, if high irradiation fluences are necessary, high concentration of defects (vacancy complexes) produced in this region drastically increases device leakage [4] and causes parasitic doping [3]. One way to eliminate this drawback is to modify the shape of the lifetime profile within the device. The goal may be, for example, decreasing of the peak defect concentration or/and placement of the majority of the defects to the position where they are not harmful, e.g. outside the space charge region (SCR) of the anode junction. Another possibility is the suppression of vacancy complexes generation using local irradiation by lighter projectiles (low energy electrons) [5], [6] or application of lifetime killing based on more appropriate recombination centers, e.g. platinum atoms. However, in this case, an adequate method capable of axial profile shaping comparable to irradiation techniques should be developed [7], [8], [9].
In this paper, we compare the traditional local lifetime reduction by alpha-particle irradiation with lifetime killing using a wide defect peak (or its part) produced by proton irradiation with relatively high-energy (>7 MeV). The impact of both techniques on device parameters is evaluated for two types of post-irradiation annealing, which were used for radiation defect stabilization: the low temperature annealing at 220 °C, which is usually applied on wafer devices, and annealing at 350 °C which is used for chip devices soldered into modules.
Section snippets
Experimental
The device under test was a planar 100 A/1700 V P+PN−N+ chip diode produced on the low-doped 〈100〉-oriented FZ n-type silicon substrate. The diode contact area was 11×5.2 mm2. The doping profile of the diode and concentration profiles of recombination centers, which were introduced for lifetime reduction, are shown in Fig. 1. The reference local lifetime reduction was done by standard irradiation with alphas at fluences ranging from 2×1010 to 1×1012 cm−2. The alpha's range was set into two
Recombination centers
C-DLTS spectra of majority carrier (electron) traps measured on diodes irradiated with alpha particles and protons into region B are shown in Fig. 2, Fig. 3, respectively. The figures contain spectra recorded after irradiation on not annealed (n.a.) samples, and on diodes which were subsequently annealed at 220 and 350 °C. Table 1 collects the identification parameters of resolved levels labeled E1–E7, T1, T2 and their attribution to particular lattice defects. Only deep levels given by pure
Conclusions
The effect of local lifetime reduction in the power chip P+N−N+ diode using high-energy proton and standard alpha particle irradiation was compared from the point of device leakage current. It is shown that applied irradiation with protons provides 3–10 times lower leakage compared to standard alphas for equivalent reduction of the reverse recovery current maximum. This is explained by lower production of divacancies which are responsible for the carrier generation in the depletion regime.
Acknowledgements
This work was supported by the EC-Access to Research Infrastructure Action of the Improving Human Potential Program project HPRI-1999-00039, by the Grant Agency of the Czech Republic under the grant number 102/03/0456 and the Research Programme no. MSM 6840770014. Authors also acknowledge ABB Switzerland Ltd, Semiconductors for diode preparation, FZ Rossendorf for ion irradiation.
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