Investigation of the Grain Boundary Character and Dislocation Density of Different Types of High Performance Multicrystalline Silicon

Abstract

Wafers from three heights and two different lateral positions (corner and centre) of four industrial multicrystalline silicon ingots were analysed with respect to their grain structure and dislocation density. Three of the ingots were non-seeded and one ingot was seeded. It was found that there is a strong correlation between the ratio of the densities of (coincidence site lattice) CSL grain boundaries and high angle grain boundaries in the bottom of a block and the dislocation cluster density higher in the block. In general, the seeded blocks, both the corner and centre block, have a lower dislocation cluster density than in the non-seeded blocks, which displayed a large variation. The density of the random angle boundaries in the corner blocks of the non-seeded ingots was similar to the density in the seeded ingots, while the density in the centre blocks was lower. However, the density of CSL boundaries was higher in all the non-seeded than in the seeded ingots. It appears that both of these grain boundary densities influence the presence of dislocation clusters, and we propose they act as dislocation sinks and sources, respectively. The ability to generate small grain size material without seeding appears to be correlated to the morphology of the coating, which is generally rougher in the corner positions than in the middle. Furthermore, the density of twins and CSL boundaries depends on the growth mode during initial growth and thus on the degree of supercooling. Controlling both these properties is important in order to be able to successfully produce uniform quality high-performance multicrystalline silicon by the advantageous non-seeding method.

Impurity control in high performance multicrystalline silicon

“…We believe that the gentler transition between melting and growth phase in I1‐HPQ compared to the other ingots, possibly combined with a slower response to the initiation of the cooling in the bottom due to more thermal insulation of the thicker remaining seed layer has a profound influence on the dislocation density. The differences in thermal conditions during this phase appear to be the only realistic explanation to this phenomenon, and we believe this occurs as a result of less generation of grain boundary dislocation sources due to lower melt supercooling .…”

Characterization of Grain Boundary‐Engineered Aluminum–Magnesium Alloys

“…[ 15 ] As the film grew, the high deposition rate increased the temperature at the free surface where new growth was occurring, [ 23 ] promoting even greater boundary mobility and diffusion [ 24,25 ] and activating more boundary annihilation toward the top of the sample, yielding fewer CSL boundaries. [ 26 ] Furthermore, it is also possible that the Σ3 and Σ7 boundaries possessed similar energies when they appeared together, as has been previously observed by Tschopp et al, [ 27,28 ] as the GB plane orientation can produce large variations in GB energy even for boundaries with the same Σ value. [ 29,30 ]…”

X-ray Based in Situ Investigation of Silicon Growth Mechanism Dynamics—Application to Grain and Defect Formation

“…The latter can be either arranged in cellular patterns, in the entire cm-Si ingot and are known as background dislocations [8] or generated on the top of the seeds [9,10], at their junctions on precipitates [10] and propagate vertically along the growth direction [9,[11][12][13][14][15][16] generating the formation of sub-grain boundaries. HP mc-Si technique is based on a very different approach aiming at obtaining small-size and uniform grains at the initial stage of solidification with random angle and coherent grain boundaries [6,17]. This results in low density of dislocation clusters thanks to blocking mechanisms by which dislocations that nucleate at the beginning of the crystallization process cannot propagate further along the growth of the ingot.…”

“…This results in low density of dislocation clusters thanks to blocking mechanisms by which dislocations that nucleate at the beginning of the crystallization process cannot propagate further along the growth of the ingot. Recent work by Stokkan et al [17] highlighted the necessity to control the first nucleation events to improve the crystalline quality. It is worth noting that in the other main process in the market, Czokralski (Cz), which aims at the of the fabrication of monocrystalline ingots the issue of dislocations and structural defects remains a main concern especially when one wants to improve the method (higher volumes, faster process, reusable crucibles and seeds, etc.)…”