Analysis of blister formation in spatial ALD Al<inf>2</inf>O<inf>3</inf> for silicon surface passivation

Abstract

Aluminum oxide (Al 2 O 3 ) thin films yield excellent surface passivation of silicon solar cells. However, unwanted delamination, known as blisters, can occur upon annealing. In this research, blistering is linked to hydrogen diffusion in the bulk. Results reveal competition between diffusion lateral and perpendicular to the interface. Therefore, large blister densities coincide with small blister diameters and vice versa. The total blister volume, however, is independent of blister size distribution, but linked to hydrogen diffusion from the Al 2 O 3 bulk. The blister volume was determined using AFM measurements, which show identical blister shapes for different blister sizes. Additionally, no direct relationship between blister formation and minority carrier was found.

Effect of hydrogen diffusion in an In–Ga–Zn–O thin film transistor with an aluminum oxide gate insulator on its electrical properties

“…This result strongly suggests that H in the Al 2 O 3 layer diffuses into the a-IGZO layer, with this causing the passivation of the defects in the a-IGZO layer. Although the Al 2 O 3 layer is known to be an excellent H diffusion barrier, the effusion of H can take place within several nano-meters of alumina during high temperature annealing at about 400 C. 25,26 It is believed that the amount of H which diffused is small because the turnon voltage (V on ) of the a-IGZO TFT was kept at 0 V during the 400 C annealing process. Here, it is noted that H in the SiO 2 passivation layer can also diffuse during the annealing and affect the electrical properties of the a-IGZO TFTs.…”

Large area p-type PERL cells featuring local p+ BSF formed by laser processing of ALD Al2O3 layers

“…In this way the dielectric ablation and the local-BSF are formed simultaneously by laser processing and the firing step to form the local-BSF via Al-Si alloying is not needed anymore. This results in a cell structure equivalent to the traditional Passivated Emitter and Rear Cell (PERC), but the avoidance of the high temperature firing step prevents the occurrence of thermal stability issues related to Al 2 O 3 (such crystallization and blistering [16][17][18][19]) and enhances the rear reflector, thanks to the avoidance of parasitic Si absorption in non-active regions of the device. The method differs from the LaserFired-Contacts technology (LFC [21]) in the fact that the Al dopant atoms do not originate from the Al rear electrode but from the thin ALD Al 2 O 3 layer and in the fact that the laser processing is performed before the Al deposition.…”

Thermal stability of silicon surface passivation by APCVD Al2O3

“…Capacitance-voltage measurements are used to separate changes in charge-assisted and chemical surface passivation. [17][18][19][20]. However, no conclusive correlation between visible blistering and changes in surface passivation has been reported.…”