SoLayTec has introduced its InPassion ALD (Atomic Layer Deposition) tool for depositing Al2O3 in mass production. Al2O3 is well known in the PV community for highly effective surface passivation properties and negative fixed charge density, which is required for thinner wafer usage. InPassion ALD tool is capable of processing up to 4,500 wph.
The next generation of silicon-based solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell (front and rear) is required. However, deposition techniques such as PECVD or APCVD make it difficult to accurately control deposition thicknesses in the range of 30nm required for Al2O3. Most solutions now deposit with uniformity in the range of ± 5% wafer-to-wafer, resulting into unwanted wider cell efficiency distribution at the end of line. The use of such technology also results in a high usage of expensive TMAL precursors.
SoLayTec offers the InPassion ALD, which gives the greater flexibility in layer thickness and output. Al2O3 ALD quality and uniformity wafer-to-wafer is claimed to be <4% and the wrap around is less then 1mm. The passivation of low- resistivity p-type silicon by the negative- charge-dielectric Al2O3 is claimed to provide a conversion efficiency of 20.6%. Depending on the number of modules selected (6 or 10) the nominal throughput can differ between 2,160wph or 3,600wph, based on 10nm of Al2O3. The flexibility results in a higher output at lower layer thickness, e.g. when the layer is reduced to 7nm, then the maximum throughput will go up to either 3,000wph respectively 4,500wph. In the event that one module needs to be stopped for service, maintenance or due to an error, the other modules will continue production. Cleaning time of the reactor chamber is claimed to equal only 1 hour per week.
Front and rear side Al2O3 passivation for both p- and n-type cells.
The InPassion ALD systems are delivered including automation, gas cabinet and abatement system. The wafers are floating on air from left to right and pass the injector head without physical contact. Here is the point where the layer is created by spatial ALD under atmospheric pressure. The deposition rate is 1.0nm/second per module