ADE for TOPCON cells

Latest TOPCON cell results from Fraunhofer ISE, using ADE for poly-Si wrap around removal

Atmospheric Pressure Dry Etching of Polysilicon Layers for Highly Reverse Bias‐Stable TOPCon Solar Cells

DOI: 10.1002/solr.202100481

ABSTRACT:

" Single-sided etching (SSE) of a-Si/poly-Si is typically considered a challenge for realizing a cost–efficient TOPCon production sequence, as there is a certain degree of unwanted wrap–around for various poly-Si deposition technologies such as LPCVD, PECVD and APCVD. To date, alkaline or acidic wet-chemical solutions in either inline or batch configurations are used for this purpose. In this work, we propose an alternative SSE process using an inline dry etching tool, which applies molecular fluorine (F2) as the etching gas under atmospheric pressure conditions. The developed etching process performs complete etching of both as–deposited amorphous silicon (a–Si) and annealed polycrystalline silicon (poly–Si) layers, either intrinsic or doped, and with measured etch rates of > 3 μm/min at 10% F2 concentration allows etching of typical layer thickness of 200 nm in just a few seconds. The etching process is also configured to perform excellent edge isolation, while maintaining a low wrap–around etching (drear<500 μm) at the opposing-side. The etching process is successfully transferred to the industrial TOPCon solar cell architecture, yielding high parallel resistances (Sshunt,avg. > 1500 kΩ cm²) and low reverse current density (Jrev,avg<0.8 mA/cm²) measured at a bias voltage of -12 V, and independently certified conversion efficiencies of up to 23.3%."