Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

Abstract

Light and elevated temperature induced degradation (LeTID) kinetics in float-zone silicon are investigated by varying the initial sample state, composed of different base material, base doping, SiN x :H films, and subsequent firing, and/or annealing steps. The approach of deliberately changing the initial sample state is shown to allow for specific studies of influences of LeTID kinetics. Bulk-and surface-related degradations are examined separately and the influence on the kinetics of bulk-and surface-related degradation is illustrated by a four-state and three-state model, respectively. In case of bulk-related degradation, an increase in defect density because of the firing step is shown, whereas the annealing step has an inverse effect. Both temperature stepsindividually and combined-influence the transition rates of bulkrelated degradation and regeneration by presumably changing the distribution of a defect precursor. For surface-related degradation, the firing step reduces the transition rate from the initial to the degraded state. In addition, the influence of a comparably humid atmosphere and the absence of UV light are found to be negligible. Index Terms-Bulk-related degradation (BRD), crystalline silicon, defect density, float zone (FZ), light and elevated temperature induced degradation (LeTID), surface-related degradation (SRD). I. INTRODUCTION L IGHT and elevated temperature induced degradation (LeTID) is a degradation phenomenon first found especially in mc-Si in 2012 [1]. Recently, a similar or the same phenomenon was discovered in Cz-Si [2], [3] and float-zone (FZ) Si [4], [5]. Compared with other degradation effects like boron-oxygen-related (BO) degradation [6], higher treatment temperatures >50°C are needed to investigate the effect on experimentally viable time scales [1], [7]. Besides LeTID, which is a bulk-related degradation (BRD), a second degradation phenomenon is visible and can be identified as a This work was supported by the German Federal Ministry for Economic Affairs and Energy under Contracts 0324226A and 0324001.

Temporary Recovery of the Defect Responsible for Light- and Elevated Temperature-Induced Degradation: Insights Into the Physical Mechanisms Behind LeTID

“…The sinks that are best controlled in silicon wafer processing are the dopant atoms. In a recent study, Hammann et al [50] demonstrated that in otherwise similarly processed p-type FZ samples with different base resistivity, the maximum [LD] was much larger for samples with higher doping. This observation can directly be explained by our theory.…”

Electrical Characterization of Thermally Activated Defects in n-Type Float-Zone Silicon

“…These defects are found to be activated by heat-treatments in the temperature range from 450 to 700 °C [16]. Unlike the lightinduced degradation in FZ silicon which was mainly identified in p-type material (except that a recent study observed a weak degradation in 200 Ω•cm n-type FZ silicon [17]), these thermally activated defects can have a substantial impact in both n-type and p-type FZ silicon [16], [18]. After formation, these defects can be permanently annihilated by an annealing at temperature above 1000 °C for 30 mins.…”

Insights into the Hydrogen‐Related Mechanism behind Defect Formation during Light‐ and Elevated‐Temperature‐Induced Degradation

“…[16], this dependence on the equilibrium could also explain findings, where a lower LeTID extent was observed on wafers with lower doping concentration. [26] Considering the temporary recovery, B-H pairs would need to dissociate, with the dissociated hydrogen binding to LD to form the recombination-inactive LP. Even though, on a fundamental level, a complex dissociates more likely with increasing temperature, the important factor for this reverse reaction is the concentration of H þ .…”