Multicrystalline Silicon

Multicrystalline silicon solar panels have been dominating the photovoltaic market in recent years, so Multicrystalline silicon grown by directional solidification method has probably been the most prevalent material in the photovoltaic market. The market is at the inversion point to switch from a buyer’s market to a seller’s market.

The new trend with seed-assisted growth such as Quasi-Mono and High Performance Multicrystalline silicon also looks promising. The above-mentioned processes all require good temperature control.

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The Challenge

Ideally, the temperature distribution inside the silicon is of most interest but not very practical. The top surface of the silicon is typically measured but the stray radiation from the heaters can affect the measurement. In the seed-assisted growth, the bottom of the crucible is typically measured. It is desired to measure through the crucible as close as possible to the bottom layer temperature where seed/seeds are placed. Because the crucible is typically made of quartz and coated with Si₃N₄, a good understanding of the optical properties of the quartz and the Si₃N₄ is required.

Our Solution

Lumasense offers the following solutions:

Measurement inside a closed-end tube. The pyrometer measures the very bottom tip of the blind tube, which reaches thermal equilibrium with the environment inside the furnace.
Measurement through an open-end tube onto the molten silicon. Carefully designed optics minimizes the effect of the heaters, so the temperature reading would not be strongly related to that of the top heater.
Measurement on/through the bottom of the crucible to infer the seed layer temperature. The Lumasense pyrometer is optimized to measure as close as possible to the seed layer.