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This work proves that blistering is the partial de-lamination of a thick enough Al2O3 layer caused by gaseous desorption in the Al2O3 layer upon thermal treatments above a critical temperature: the Al2O3 layer acts as a gas barrier and bubble formation occurs. First, using an atmospheric pressure rapid thermal processor with an atmospheric pressure ionization mass spectrometry, desorbing species upon heating of Si / Al2O3 samples are identified: evident desorption peaks are observed around 400 °C for all spectra. The spectrum for m/e = 18, an indication of H2O, illustrates that gaseous desorption from Al2O3 and from the Si substrate itself continues up to 600 °C and 700 °C, respectively. Also, it is shown that in the case of a 30 nm Al2O3 layer, blistering starts at same annealing temperatures as gaseous desorption begins. In the case of a thin enough (≤ 10 nm) Al2O3 film, blistering does not show. To complete the proof, elastic recoil detection measurements clearly show that after annealing a thick Al2O3 film above 400 °C the H content is higher near the c-Si interface as compared to the near surface.Fortunately, effective lifetime and capacitance voltage measurements show that 5 to 10 nm Al2O3 layers can still be adequate passivation layers after being annealed in N2 environment at temperatures up to 500-700 °C: (i) interface trap densities (Dit) can remain below 1x10 11 cm -2 and (ii) fixed charge densities (Qf) stay negative and in the order of -3x10 12 cm -2 .Random local Al back surface field (BSF) solar cells, fabricated using a blistered film as rear surface passivation and no additional contact opening step, clearly show that random local BSFs are created upon firing of a blistered rear passivation layer covered by metal. Therefore, it is clear that blistering should be avoided, since it will reduce the overall rear surface passivation.

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