Epitaxial Growth of High Quality n-type Silicon Foils in a Quasi-inline APCVD Reactor

Abstract

Reduction of solar cell fabrication costs is still of importance and can be achieved by going towards thinner silicon wafers. The aim is to achieve thicknesses in the range of100μm and below while avoiding further kerf loss. The approach using porous silicon as a sacrificial detachment layer and as a seed layer for epitaxial growth can accomplish that goal [1]. Several research groups have already shown the high potential of this technique[2]. Most processes have been conducted in microelectronic-grade batch or single-wafer reactors, questioning the industrial feasibility of this concept. In this work n-type silicon wafers, epitaxially grown in a quasi-inline Atmospheric Pressure Chemical Vapour Deposition (APCVD) reactor, will be presented. The wafers were characterized using confocal white light microscopy, quasi steady state photo conductance decay (QSSPC), microwave detected photo conductance decay (MWPCD) and spreading resistance profiling (SRP) measurements. The first batch of n-type wafers showed mean effective carrier lifetimes exceeding 100 μs on 45 x 45 mm2 and locally more than 300 μs. A detailed analysis on the thickness distribution, bulk lifetime and surface recombination velocity, affecting the effective carrier lifetime was conducted. For the second batch of n-type wafers mean effective carrier lifetimes of over 260 μs on 25 x25 mm2 and locally over 500 μs were determined. This corresponds to a local bulk lifetime of over 800 μs and shows the high material quality of epitaxial layers grown in our developed APCVD reactors.