Improved hot-zone for manufacturing low-oxygen silicon ingots for passivated emitter and rear cell

Abstract

In the silicon wafers, interstitial oxygen and vacancies make oxygen precipitation in the cell process. The oxygen precipitates become combination centers for minority carriers, and it is resulted in decrease of minority carrier life-time (MCLT) and cell efficiency. In order to grow ingots with low oxygen concentration, we locally optimized hot-zone in the ingot grower. We have designed new hot-zone for commercial 8.3-in. diameter ingot growth using 24-in. quartz crucible and old grower. The average oxygen reduction is about 3 ppma at the top position of ingot, which is similar to the simulation result of oxygen distribution. Despite the inside temperature of grower rises, the concentration of oxygen was suppressed to 15 ppma or less as in a normal heater. As a result, it is possible to grow a low-oxygen ingot that can suppress the light induced degradation (LID), which can fundamentally help improve the efficiency of a high efficiency passivated emitter and rear cell (PERC).

Reduction of oxygen concentration in 300 mm diameter n-type Czochralski silicon crystal growth using an optimized heating zone with dual side-heaters

“…1,2 At the same time, oxygen impurities will affect the quality of Cz-Si by forming effective recombination centers such as thermal donors, ring like defects, oxygen precipitates and so on. [3][4][5][6] Thus, controlling the oxygen concentration in Cz-Si is of great significance for the electrical performance of silicon solar cells, which has become a hot research topic in the PV industry since 2012. Several available methods have been tried in the silicon crystal growth process, including heating zone and growth condition optimization, such as the installation of a heat shield, the applications of a higher argon gas flow or magnetic field, the optimization of the heater structure, and so on.…”

Novel Way to Assess the Validity of Czochralski Growth Simulations

“…Mostly due to their long minority carrier lifetime, Czochralski (Cz) Si wafers are widely used as substrates for high efficiency cells. Numerous upgrades of Cz growth furnaces (e.g., new hot zone designs) and alternative processes (continuous growth, recharging, larger feedstock sizes, etc) allow to improve Cz competitiveness . To optimize the throughput and the ingot quality, it is common for growth engineers to use finite element softwares (CGSim, Fluent, or FEMAG/Cz to cite a few) to estimate how modifications in the furnace alter the residual mechanical stress, the growth rate and the electricity uptake, or the defect spatial distribution .…”

“…Numerous upgrades of Cz growth furnaces (e.g., new hot zone designs) and alternative processes (continuous growth, recharging, larger feedstock sizes, etc) allow to improve Cz competitiveness. [2,3] To optimize the throughput and the ingot quality, it is common for growth engineers to use finite element softwares (CGSim, Fluent, or FEMAG/Cz to cite a few) to estimate how modifications in the furnace alter the residual mechanical stress, [4] the growth rate and the electricity uptake, [4,5] or the defect spatial distribution. [5,6] A key quantity governing all these outputs is the temperature (T) distribution within the ingot and its evolution throughout the pulling process (T versus time, called "thermal history").…”