PECVD System for Dynamic Deposition on 40×40 cm² Substrates
Motivation and Objectives
The objective is to transfer the developments for small-area solar cells to medium-sized solar panels (40×40 cm²) by means of industrial processes. For this, continuous PECVD coating by means of a linear plasma source is also being developed as an alternative method to conventional PECVD. We intend to produce films from amorphous (a-Si:H) and microcrystalline (µc-Si:H) silicon at high growth rates without compromising the homogeneity or quality of the materials properties (film thickness, crystallinity, optoelectronic properties). VON ARDENNE GmbH, the FAP GmbH research and application laboratory, the Technical University of Dresden (TU Dresden) and Forschungszentrum Jülich are cooperating in this project and thus pooling their experience. We are working on an in-line concept for a cost-effective industrial manufacturing procedure. This includes the preparation of solar cells without interrupting the vacuum between the deposition of contact and semiconductor layers.
We apply an alternative deposition technique – continuous PECVD using a VHF (very high frequency) linear plasma source – in particular for producing µc-Si:H films. This involves moving the glass substrate in front of the plasma source. This concept has the advantage that surfaces greater than 1 m2 can be coated homogeneously. In contrast to static deposition in the VHF regime, which produces standing waves, homogeneity is facilitated by the one-dimensional electrode.
The PECVD chambers are part of a larger in-line system, which was originally designed for sputtering processes only. The PECVD part consists of a load chamber, a static PECVD chamber (for reference films and doped films, RF 13.56 MHz) and a dynamic PECVD chamber with a VHF linear source (60 MHz). The linear source is used to develop intrinsic a-Si:H and µc-Si:H films at high deposition rates on 40×40 cm² substrates. It should be possible to homogeneously coat substrates with a width of up to 3 m with µc-Si:H. The purpose of our system is industry-oriented process development for large-scale applications.
Current Research Topics
Our objective is to develop a linear VHF plasma source for depositing µc-Si:H at a high rate (local deposition rate > 1 nm/s) without compromising material homogeneity or quality. The deposition process and plasma source are developed simultaneously. This development combines the expertise in the field of dynamic coating available at TU Dresden as well as know-how in the deposition of high-quality films at high pressure and at high capacity at Jülich.
Furthermore, we examine the influence of the speed of operation on the properties of the films and carry out a comparison with statically deposited materials and solar cells. The influence of the gas flow configuration and the dwell time on the deposition is also studied. We need to work out the difference between the chambers (static coating and dynamic coating) in this respect.