In this work, we present the results of the replacement of silver screen printing on heterojunction crystalline silicon (c-Si) solar cells with a copper metallization scheme that has the potential to reduce the manufacturing cost while improving their performance. We report for the first time silverfree heterojunction c-Si solar cells on 6-in. wafers. The conversion efficiency reached is a record 22.1% for c-Si technology for this wafer size (V oc ¼ 729 mV, J sc ¼ 38:3 mA/cm 2 , FF ¼ 79:1%). The total power generated is more than 5 W for 1-sun illumination, which is a world record. Heatdamp reliability tests show comparable performance for mini-modules fabricated with copper metalized as for conventional silver screen printed heterojunction c-Si solar cells. #
A new approach is presented for resist strip after high-dose implantation of ultra-shallow extensions with minimal loss in the S/D area. For our work, solvents are selected in combination with physical force to remove the resist because of their excellent selectivity towards the sensitive USJ implanted substrates. To enable a more gentle physically enhanced strip of the crusted resist with less risk for damage and less residues left, a short oxidizing pre-and/or post-treatment has to be introduced. Wet O 3 -based cleans have limited efficiency while UV/O 3 -exposure and particularly a short plasma step are found to be beneficial. The effect of such an oxidizing treatment on the crusted resist and its removal is presented as well as the effect on highly doped substrates. It is shown that especially after NMOS implantation, a short oxidizing step results in better dopant retention during activation anneal due to the grown oxide.
Following Moores scaling law, the transistor source and drain area become shallower and higher doped regions. As a consequence the limitations of substrate and dopant loss during cleaning become more stringent. For a better understanding, highly B, As and P doped blanket substrates, either prepared by ion implantation or by EPI growth, are studied. Substrate and dopant loss as a function of time and different HF etching conditions is monitored by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and additional techniques like Spectroscopic Ellipsometry (SE), .... It is shown that in general, the Si etching is dependent of the position of the Fermi level. More remarkably, the junction (4 nm) of a non-annealed heavily As or P doped substrate is completely removed after less than 20 min of etching in HF. This process is related to enhanced etch rates because of the amorphization of the substrate.
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