Ring‐Like Defect Formation in N‐Type Czochralski‐Grown Silicon Wafers during Thermal Donor Formation

Abstract

This article presents experimental and simulation studies on the formation of recombination‐active ring‐like defects during thermal donor (TD) formation at 450 °C in n‐type Czochralski‐grown silicon wafers. With increasing anneal duration from 1 to 24 h, the resistivity and interstitial oxygen concentration of samples decrease, consistent with the formation of TDs. However, after a subsequent TD annihilation treatment, the resistivity recovers completely, while the interstitial oxygen concentration recovers only partially. Furthermore, the wafers exhibit ring‐like defects in photoluminescence images after the TD generation and remain persistent even after annihilation treatment. By applying a tabula rasa (TR) treatment prior to TD generation anneals, the net loss of interstitial oxygen is reduced, and the incubation time of the ring‐like defects is extended in comparison to as‐grown wafers. Finally, to investigate the possibility of low‐temperature precipitation, simulation of oxygen precipitation (OP) kinetics during the 450 °C annealing steps is performed using an enhanced effective diffusivity of oxygen. These simulations demonstrate that OP can occur simultaneously during TD formation, resulting in recombination‐active ring‐like defects.

Comprehensive Model for Charge Carrier Recombination in Czochralski‐Grown Silicon Due to Oxygen Precipitation in Industrial Solar Cell Manufacturing

“…Consequently, in our model all OPs present after a HT process are nucleated at the beginning of that process. In other publications, [39][40][41] the retardation in nucleation is implicitly considered, due to very slow formation of oxygen particles consisting of only several O atoms. Section 5 gives a more detailed discussion of this topic.…”

“…In any case, it is clear that the model proposed in this work requires the implementation of a time-lag, along the lines of Inoue et al, [22] in order to reproduce the experimental findings. As mentioned above, other publications [39][40][41] considered the retardation in nucleation implicitly, due to very slow formation of oxygen-particles consisting of only several O atoms.…”

“…Furthermore, the time-lag in nucleation is explicitly considered, which was, to our knowledge, not implemented in OP modeling so far. In contrast with published numerical simulations [39,40] and own previous work, [41] this model is easily implemented without recurring to specialized numerical simulation tools.…”

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.…”

The Effect of Pull Speed and Heat Treatment on Thermal Donors in Czhocralski Silicon

“…60 years later, the details of the processes by which the defects are generated and eliminated are not completelyv clear. However, several authors [6][7][8] and most recent [9][10][11] have studied the phenomenon. A comprehensive review on diffusion mechanisms of oxygen in silicon has been published.…”