Flow Pattern Defects Research Articles

Study of Flow Pattern Defects and Oxidation Induced Stacking Faults in Czochralski Single-Crystal Silicon Growth

This paper emphasizes that the furnace pressure, crucible rotation, and pulling rate have important effects on interstitial oxygen (Oi) concentrations and micro-defects during growth in a Czochralski single-crystal silicon (CZ-Si) growth furnace. Since oxygen in a silicon ingot influences minority carrier lifetime, different set-points of furnace pressure and crucible rotation were controlled to achieve different degrees of Oi. The Oi content has a positive correlation with furnace pressure and crucible rotation. Various numbers of micro-defects were generated under the influence of different pulling rates, owing to the transformation from liquid to solid. The sample also underwent Secco etching and a high-temperature wet oxidation to observe defects caused by the Oi concentration and pulling rate, namely, flow pattern defects (FPDs) and oxidation-induced stacking faults (OISFs). Optical microscopy was employed to confirm the surface topography, and for defect number counting, to observe the correlation between the defects and the minority carrier lifetime. The overall results show that the minority carrier lifetime is mainly dominated by OISFs under high Oi content and FPDs under low Oi content. Therefore, growth using a CZ-Si growth furnace should be carried out with low furnace pressure, low crucible rotation, and low pulling rate to reduce micro-defects.

Grown-in microdefects and photovoltaic characteristics of heavily Ge co-doped Czochralski-grown p-type silicon crystals

The minority carrier lifetime (MCL)/flow pattern defect of B and Ge co-doped Czochralski silicon (CZ-Si) was increased/decreased with the initial Ge concentration up to 3 × 10 20 cm −3 and decreased/increased at higher Ge concentrations. Secco etch pit defects were increased in heavily (⩾3 × 10 20 cm −3 ) Ge co-doped CZ-Si (grown at low growth rate), which resulted in a low MCL. The influence of Ge on microdefect variation was relatively lower than the crystal growth rate in heavily Ge co-doped CZ-Si.

An etchant for delineation of flow pattern defects in heavily doped p-type silicon wafers

Secco etchant is conventionally used for delineation of flow pattern defects (FPDs) in lightly-doped Czochralski (Cz) silicon wafers. However, the FPDs in heavily doped p-type silicon wafers cannot be well delineated by Secco etchant. Herein, an etchant based on the CrO3HFH2O system, with an optimized volume ratio of V(CrO3):V(HF)=2:3, where the concentration of CrO3 is 0.25–0.35M, has been developed for delineation of FPDs with well-defined morphologies for the heavily boron (B)-doped p-type silicon wafers.

An Etchant for Delineation of Flow Pattern Defects in Heavily Doped n-type Silicon Wafers

Secco etchant was conventionally used for delineation of flow pattern defects (FPDs) in lightly-doped Czochralski (Cz) silicon wafers. However, the FPDs in heavily doped n-type silicon wafers cannot be well delineated by Secco etchant. Herein, an etchant based on CrO3-HF-H2O system, with an optimized volume ratio of V(CrO3): V(HF)=1:1, where the concentration of CrO3 is 0.25 M, has been developed for delineation of FPDs with well-defined morphologies for the heavily As- or P-doped n-type silicon wafers.

The impact of Ge codoping on the enhancement of photovoltaic characteristics of B-doped Czochralski grown Si crystal

The effect of Ge codoping on minority carrier lifetime in boron (B)-doped Czochralski-silicon (CZ-Si) crystals was investigated. The minority carrier lifetime increased from 110 to 176 µs as Ge concentration was increased from zero to 1 × 1020 cm−3 in B/Ge codoped CZ-Si crystals. Light-induced degradation (LID) experiments showed that B-doped CZ-Si degrades rapidly, while B/Ge codoped CZ-Si degrades more slowly. Moreover, the flow pattern defect (FPD) density of grown-in micro-defects (GMD) in as-grown B/Ge codoped CZ-Si decreased with increasing Ge concentration. From the infrared (IR) absorption studies, it was observed that the interstitial oxygen (Oi) concentration decreased as Ge concentration increased in the crystal. The suppressed LID effect in the B/Ge codoped CZ-Si appears to be related to the low concentration of B-O associated defects, possibly because Ge doping retards the Oi diffusion in addition to the low Oi concentration present (evidenced from IR studies). The mechanism by which the Ge concentration influences the reduction of FPDs and Oi concentration is discussed in terms of Ge-vacancy defect formation during post-growth cooling of the ingots.

On the Impact of Heavy Doping on Grown-In Defects in Czochralski-Grown Silicon

The effects of heavy doping of Si on grown-in void size-density distributions and on Flow Pattern Defect (FPD) and Secco Etch Pit Defect (SEPD) density are discussed. Grown-in defects are studied using Scanning Infra Red Microscopy (SIRM) and Secco etching. Doping with 10^20 Ge atoms cm^-3 has a limited effect on the grown-in void size-density distribution but has a clear effect on the FPD density. The observed lower FPD density is most probably related to a decrease of the multiple void density. Co-doping with 10^20 B atoms cm^-3 leads to strong a suppression of the void density by nearly two orders of magnitude in agreement with the reported strong reduction of Crystal Originated Particle (COP) density in low resistivity p-type Si.

On the assumed impact of germanium doping on void formation in Czochralski-grown silicon

The assumed impact of Ge doping on void formation during Czochralski-growth of silicon single crystals, is studied using scanning infrared microscopy. It has been reported that Ge doping leads to a reduction in the flow pattern defect density and of the crystal originated particle size, both suggesting an effect of Ge on vacancy concentration and void formation during crystal growth. The present study however reveals only a marginal-if any-effect of Ge doping on grown-in single void size and density. Double and multiple void formation might however be suppressed partially by Ge doping leading to the observed decrease in flow pattern defect density. The limited effect of Ge doping on single void formation is in agreement with earlier findings that Ge atoms are only a weak trap for vacancies at higher temperatures and therefor should have a smaller impact on the vacancy thermal equilibrium concentration and on single void nucleation than, e.g., interstitial oxygen and nitrogen.

Flow pattern defects in germanium-doped Czochralski silicon crystals

The distribution and etching rate of flow pattern defects (FPDs) in germanium- doped Czochralski (GCZ) silicon (Si) wafers with light and heavy dopants—either boron (B) or phosphorus (P)—have been investigated. In the lightly doped (both B and P) Czochralski (CZ) Si crystals, the FPD densities in GCZ Si decrease with the increase of Ge concentration. In the heavily B-doped GCZ Si crystals, the FPDs are denser compared with the heavily B-doped CZ Si, whereas the reverse is true in the heavily P-doped GCZ Si and CZ Si crystals. It is also shown that the etching rates in the lightly doped CZ Si crystals can be slightly enlarged by the Ge doping. It is proposed that, in lightly doped GCZ Si, Ge doping could consume free vacancies and thus form high-density but small-sized voids, while the stress compensation induced by B and Ge atoms could increase the vacancy concentration in heavily B-doped GCZ Si, leading to sparse and large-sized voids.

Characterization of a Czochralski grown silicon crystal doped with 1020 cm‐3 germanium

AbstractA dislocation‐free silicon single crystal doped with 1020 cm‐3 germanium (Ge) has been grown using the Czochralski (CZ) growth technique. The Ge concentration in the seed‐end and tang‐end of the crystal was 8×1019cm‐3and 1.6×1020 cm‐3, respectively. The effective segregation coefficient of Ge, the distribution of flow pattern defects (FPDs) and the wafer warpage have been characterized. Both the effective segregation coefficient and the equilibrium segregation coefficient of Ge in silicon were evaluated. Then, the density of FPDs was traced from seed‐end to tang‐end of the ingot, a suppression of FPDs by Ge doping was shown. That is probably because the Ge atoms consume free vacancies and thus a higher density of smaller voids is formed. Furthermore, the mechanical strength of wafers has also been characterized by batch warpage analysis. The warpage in the seed‐end was larger than that in the tang‐end of the ingot, showing that the mechanical strength of wafers is enhanced by Ge doping. Such improvement is interpreted by an enhanced dislocation pinning effect associated with the enhanced nucleation of grown‐in oxygen precipitates in the Ge‐doped silicon wafers. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of B and Ge codoping on minority carrier lifetime in Ga-doped Czochralski-silicon

We investigated the effects of B/Ge codoping on the minority carrier lifetime in gallium (Ga)-doped Czochralski-silicon (CZ-Si) crystals. Minority carrier lifetime decreased from 28 to 0.1 μs when the B concentration was increased from 1×1015 to 1×1017 cm−3 in Ga/B codoped CZ-Si crystals. The minority carrier lifetime increased from 30 to 76 μs with increasing Ge concentration from 1×1017 to 2×1020 cm−3 in Ga/Ge codoped CZ-Si crystals. Light-induced degradation experiments showed that Ga/B codoped CZ-Si degraded rapidly, while Ga/Ge codoped CZ-Si showed no degradation. Moreover, the flow pattern defect density related to grown-in microdefects in as-grown Ga/Ge codoped CZ-Si decreased with increasing Ge concentration. The experimental results are explained using a defect reaction model based on the formation of Ge-vacancy-oxygen dimer complexes in the CZ-Si crystal during postgrowth cooling.

Microstructure of flow pattern defects in boron-doped Czochralski-grown silicon

The morphology and microstructure of flow pattern defects (FPDs) in lightly boron-doped Czochralski-grown silicon (Cz-Si) crystals were investigated using optical microscopy and atomic force microscopy. The experimental results showed that the morphology of FPDs was parabola-like with several steps. Single-type and dual-type voids were found on the tip of FPDs and two heaves exist on the left and right sides of the void. All the results have proved that FPDs were void-type defects. These results are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high-temperature annealing.

Micro-defects in Ge doped Czochralski grown Si crystals

With the reduction in size of the features of ultra large-scale integrated (ULSI) circuits, micro-defects such as voids in Czochralski (Cz) silicon (Si) crystals play more important roles in the reliability and yield of these devices. As one of the tetravalent atoms, the behavior of germanium (Ge) doped in Cz Si crystals has attracted considerable attention in recent years. In this presentation, recent processes in the study of voids in Ge doped Cz (GCZ) Si crystals are reviewed. The grown-in characteristics of voids in GCZ wafer, including flow pattern defects (FPDs) and crystal originated particles (COPs), suggested that Ge can suppress large voids resulting in denser and smaller voids. Meanwhile, it has been found that the density of voids can be decreased by Ge doping and they can be eliminated easily in GCZ Si crystals through high temperature annealing. It is therefore speculated that the gate oxide integrity (GOI) of semiconductor devices can be improved by Ge doping. The mechanism of the effect of Ge on voids is discussed to explain the experimental results.

Effect of annealing atmospheres on the void defects in large-diameter CZSi single crystals

The influence of rapid thermal annealing (RTA) atmospheres on the flow pattern defects (FPDs) was studied in this paper. Ar, N 2, N 2/O 2(9%), N 2/O 2(14%) and O 2 were used as the atmosphere of RTA, respectively. The experimental results showed that the FPDs density on the wafers reduced after RTA process at 1195 °C for 5 min in every atmospheres, but the decrease of FPDs depends greatly on the annealing atmosphere. In N 2/O 2 mixed atmosphere, the FPDs density decreased with the increase of O 2 percent in the N 2/O 2 mixed atmosphere and is the lowest in O 2 atmosphere. In addition, the densities of FPDs after RTA decreased obviously on the surface and in the region of 20 μm depth from the surface as well. The influence mechanism of annealing atmospheres on the void annihilation was also discussed according to the behavior of the vacancies and interstitial atoms affected greatly by the atmosphere of RTA.

Effect of high temperature rapid thermal annealing on flow pattern defects in heavily Sb-doped CZSi

Flow pattern defects(FPDs) in as-grown and rapid thermal annealed heavily Sb-dop ed silicon wafers was investigated. The experimental results show that the dens ity of FPDs can be reduced after high temperature annealing, and H2 is the most effective annealing atmosphere. The mechanism of elimination of FPDs is also discussed from the relationship between heavily doping Sb and interstit ial oxygen concentration. The heavily doping Sb influences not only the distribu tion of initial oxygen concentration in CZSi wafer, but also the formation and h eat behavior of grown-in void defects.

Evolution of flow pattern defects in boron-doped 〈1 0 0〉 Czochralski silicon crystals during secco etching procedure

Flow pattern defects (FPDs) is one kind of grown-in defects in large diameter Czochralski silicon (Cz-Si) crystals. The evolution of FPDs in lightly doped Cz-Si crystals during secco etchant (50% HF: 0.15 mol L −1K 2Cr 2O 7=2:1) etching process, was studied in detail firstly. The results also showed that the outline of FPDs became larger and the void on the tip of FPDs changed into a shallow hole with the increasing of etching time. A parabola model was firstly put forward to explain the evolution of FPDs in Cz-Si wafers during the procedure. Furthermore, the microstructure of FPDs was observed by optical microscopy and atomic force microscopy, the results showed that the outline of FPDs was parabola with several steps and two heaves were firstly found on the left and right sides of the void on the tip of FPDs. All the results provide forceful evidence to that FPDs is one kind of void-type as-grown defects. These are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high temperature annealing processes.

Investigation of flow pattern defects in as-grown and rapid thermal annealed CZSi wafers

The flow pattern defects (FPDs) in as-grown and rapid thermal annealed 〈1 0 0〉 boron-doped CZSi wafers were investigated in this paper. The experimental results showed that a hole occurred on the apex of FPDs observed by atomic force microscope. The changes in the number and the size of the FPDs in as-grown and annealed wafers were measured by optical microscope after etching in Secco etchant. The size of FPDs became smaller, the density of FPDs reduced above 1100°C annealing and became very low above 1200°C annealing in an Ar atmosphere; the hole on the apex became shallower and larger. This mechanism was discussed.

Effect of oxygen precipitation on voids in bulk silicon

The effect of oxygen precipitation on flow pattern defects (FPDs) relative to voids in bulk silicon was investigated. FPDs and voids were measured after different annealing time, and with various interstitial oxygen contents and bulk stacking faults (BSFs). It was found that, during annealing, interstitial oxygen in bulk silicon precipitated, however the FPDs density remained constant. The density of BSFs increased with annealing time at 1100 °C. After annealing, the morphology of voids was found to be octahedral with the oxide films inside them, the same as as-grown samples. Therefore, it is concluded that the interstitial silicon atoms released during oxygen precipitation did not enter the voids because of the resistance of the oxide films inside the voids, but condensed into stacking faults. The dissolution of the oxide films is believed to be the principal cause for the annihilation of voids.

Germanium effect on void defects in Czochralski silicon

The effect of germanium (Ge) on void defects in lightly Ge-doped Czochralski (GCZ) silicon (Si) crystals has been investigated. Three GCZ Si crystals with different Ge concentrations (10 15–10 18 cm −3) and one conventional Czochralski (CZ) Si crystal were grown under almost the same growth conditions. It is found that the density of flow pattern defects (FPDs) related to void defects in the as-grown GCZ Si decreases with the increase of Ge concentration. The voids in the GCZ Si could be eliminated more easily during annealing at the high temperatures of 1050–1200°C. It is concluded that Ge can suppress the formation of voids during Si crystal growth. Thus, GCZ Si can be expected to use widely in modern microelectronic industry.

The Annihilation of the Flow Pattern Defects in Czochralski Silicon Crystal by High Temperature Heat Treatment

A Czochralski silicon crystal was annealed at 1350°C to dissolve the vacancy-type grown-in defects. The faster dissolution rate of the grown-in defects was observed in the bulk of the silicon wafer than near the surface. This suggests that the presence of a higher concentration of silicon interstitials hinders the dissolution of the grown-in defects, which are composed of the vacancy clusters with the surrounding silicon oxide film. This expectation was confirmed by the observation that the dissolution rate of the grown-in defects near the surface of the silicon wafer in the oxygen atmosphere was slower than that in the argon atmosphere. This is in contrast with the previous argument that the presence of the excess silicon interstitials leads to a faster dissolution rate of vacancy-type defects. © 2002 The Electrochemical Society. All rights reserved.

Classification of etch pits at silicon wafer surface using image-processing instrument

An image-processing instrument with an algorithm for the classification of etch pits such as flow pattern defects (FPDs), small pits (SPs) and large pits (LPs) revealed on silicon wafer surfaces after preferential etching was developed. In comparison with the usual human inspection, this instrument has the merit to obtain two-dimensional distributions of these pits in the wafer. Using this instrument, the pit distribution in two wafers taken from Czochralski (CZ) silicon grown at different growth rate was obtained. It was found that (i) the distributions of FPDs, SPs and LPs differed in each wafer, and (ii) the etch pit density changed with the growth rate of CZ silicon.