Conventional Czochralski Silicon Research Articles

Mechanical strength of Czochralski silicon crystal: Effects of co-doping germanium and nitrogen

Czochralski (CZ) silicon is a base material for manufacturing integrated circuits (ICs). The mechanical strength of CZ silicon determines the processing limitations and often dominates the issues related to packaging and failure of ICs. With the ever-smaller feature size of ICs, the scaling of device dimensions may indirectly lead to increase the stress in silicon substrate, thus increasing the probability of generating dislocations. Consequently, improving the mechanical strength of CZ silicon is of significance for increasing the manufacturing yield of ICs. In this work, we propose a strategy of co-doping germanium (Ge) impurity and nitrogen (N) impurity into CZ silicon to achieve better mechanical strength. In order to explore the feasibility of such a strategy, we comparatively investigate the room-temperature hardness and dislocation gliding behaviors in the temperature range of 600–1200 ℃ in the conventional CZ silicon, Ge-doped CZ silicon, N-doped CZ silicon, as well as N and Ge co-doped CZ silicon. The significant experimental results are described as follows. 1) Ge-doping, N-doping or co-doping of Ge and N hardly influences the hardness and therefore the dislocation gliding behavior at room temperature. 2) The suppressing effect of N-doping on the dislocation gliding is remarkable at 600–1000 ℃ and becomes weakened at the temperatures higher than 1100 ℃, while Ge-doping hardly affects the dislocation gliding at 600–900 ℃ but exhibits a strong suppressing effect on the dislocation gliding at 1000–1200 ℃. 3) Co-doping Ge and N impurities into CZ silicon can take the complementary advantages of both Ge- and N-doping to suppress the dislocation gliding at 600–1200 ℃. It is believed that N-doping can result in the formation of N-O complex-related pinning agents within the dislocation cores to suppress the dislocation gliding at 600–1000 ℃. For Ge-doping, it is supposed that Ge-O complexes acting as the pinning agents can form near the front of a single dislocation when the temperature is as high as 1000 ℃ and above. In a word, it is verified in this work that co-doping Ge and N into CZ silicon can further improve the mechanical strength at the processing temperatures of ICs fabrication.

Effects of co-doping nitrogen and germanium on dislocation gliding in Czochralski silicon: Implication for improving mechanical strength

Improving the mechanical strength of Czochralski (CZ) silicon is of significance for increasing the manufacturing yield of integrated circuits. In this work, we have comparatively investigated the dislocation gliding behaviors in the conventional CZ silicon, nitrogen (N)-doped CZ silicon, germanium (Ge)-doped CZ silicon as well as Ge and N co-doped CZ silicon subjected to the indentations for 30 min at different temperatures in the range of 850–1050 °C with an interval of 50 °C. It is found that the suppressing effect of N-doping on the dislocation gliding is strongest at 950 °C and becomes slightly weakened at higher temperatures, while Ge-doping does not exert a remarkable suppressing effect on the dislocation gliding until the temperature exceeds 950 °C. The co-doping of N and Ge impurities takes both advantages of N- and Ge-doping to suppress the dislocation gliding in CZ silicon at the aforementioned temperatures. More importantly, at 1000 and 1050 °C that are the typical processing temperatures for integrated circuits, the N and Ge co-doping exhibits a stronger suppressing effect on the dislocation gliding in CZ silicon than the single Ge- or N-doping. This indicates that the mechanical strength of CZ silicon in terms of the resistance of dislocation gliding at a high temperature can be further improved by co-doping Ge and N impurities. It is believed that the N-doping can result in the formation of larger grown-in oxygen precipitates and N–O complex-related pinning agents within the dislocations to suppress the dislocation gliding at 850–1050 °C with the strongest suppressing effect at 950 °C, while the suppressing effect of Ge-doping on the dislocation gliding at the temperatures exceeding 950 °C is tentatively ascribed to the formation of Ge–O complexes near the front of the dislocation lines.

Effects of nitrogen doping on vacancy-oxygen complexes in neutron irradiated Czochralski silicon

We have investigated the effect of nitrogen doping on the evolution of vacancy-oxygen (V-O) complexes in neutron irradiated Czochralski (CZ) silicon. During isothermal anneals in the temperature range of 290–330 °C, it is found that both the annihilation rate of VO and generation rate of VO2 are obviously modified with nitrogen doping. Correspondingly, the activation energies for VO annihilation and VO2 generation are 1.84 and 1.23 eV, both smaller (∼ 0.24 eV) than those of the conventional CZ silicon. Moreover, the critical temperatures for total disappearance of VO and VO2 peaks decrease in nitrogen doped CZ silicon, which means that the conversion processes of VO to VO2 and VO2 to VO3 are promoted, respectively. It is suggested that the nitrogen doping in CZ silicon which introduces a tensile stress enhances the diffusion of vacancy and VO complex, promoting the conversion of V-O complexes.

Impact of Carbon Codoping on Generation and Dissociation of Boron–Oxygen Defects in Czochralski Silicon

It has been previously reported that boron–oxygen (B–O) defects in Czochralski (CZ) silicon can be effectively suppressed by carbon codoping. In this work, the kinetics of B–O defect generation and dissociation in carbon-codoped CZ (CCZ) silicon has been investigated. It was found that the activation energy for B–O defect generation in CCZ silicon is 0.56 eV, much larger than that in conventional CZ silicon. However, the activation energy for B–O defect dissociation in CCZ silicon is almost the same as that in conventional CZ silicon, viz. ∼ 1.37 eV. Moreover, the binding energy of B–O defects in both CZ and CCZ silicon is determined to be 0.93 eV. Based on these results, it is believed that carbon atoms in CCZ silicon participate in formation of B–O latent centers before transforming into recombination-active centers under illumination.

Effect of Ge doping on the kinetics of iron–boron pair association and dissociation in photovoltaic silicon

We have investigated the kinetics behaviors of iron–boron pair generation in photovoltaic Czochralski silicon with germanium doping in this paper. It is found that the activation energies of iron–boron pair association and dissociation in germanium-doped silicon are 0.67 and 1.26eV, respectively, both larger than those in conventional CZ silicon. The pre-exponential factors are also increased by one order of magnitude. Experimental results and theoretical calculations both suggest that germanium can not only improve the diffusion barrier of iron, but also increase the capture radius of boron for iron.

Effect of germanium on the kinetics of boron-oxygen defect generation and dissociation in Czochralski silicon

We have investigated the kinetics of boron-oxygen (B–O) defect generation and dissociation in germanium-doped Czochralski (GCZ) silicon. It is found that the activation energies for the B–O defect generation and dissociation in the GCZ silicon are around 0.63 eV and 1.52 eV, respectively, both larger than those in the conventional CZ silicon. The corresponding pre-exponential factors also are enhanced by two orders of magnitude due to Ge doping. It is believed that the Ge cannot only cause a higher energy barrier for oxygen-dimer (O2i) diffusion, due to its modulation on the crystal field in silicon lattice but also enhance the capture cross-section of Bs for O2i, as a result of Ge–B complex formation, as predicted by first-principle calculation. These results are significant for us to understand the mechanism of Ge influencing on the B–O defects in CZ silicon.

Effect of vacancies on oxygen precipitation in germanium-doped Czochralski silicon

The effect of vacancies introduced by rapid thermal annealing (RTA) on the oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. GCZ silicon is annealed at 650–1050 °C to facilitate the precipitation of oxygen. It is observed that the oxygen precipitation in silicon is enhanced by both the vacancies introduced during RTA pretreatment and the doping of germanium. Especially, we find that the enhancement effect of vacancies on the precipitation of oxygen is larger than that of germanium atoms. In contrast to non-RTA pretreatments, RTA pretreatments lead to less significant oxygen precipitation in GCZ silicon than in conventional Czochralski (CZ) silicon at temperatures ranging from 850 to 950 °C. The mechanism for the interaction between vacancies and germanium atoms in CZ silicon is elucidated.

Internal gettering for germanium-doped Czochralski silicon: Treated by rapid-thermal-anneal based processing simulation

Intrinsic gettering (IG) in germanium-doped Czochralski (Cz) silicon wafer has been investigated through a processing simulation of dynamic random access memory fabrication involved with rapid-thermal-anneal (RTA). Compared with that of conventional Cz silicon, both the good quality defect-free denuded zone (DZ) with a slightly narrower width and the gettering region with a slightly higher density of bulk micro-defects (BMDs) could be generated in germanium-doped Cz (GCz) silicon during the device fabrication. These phenomena were interpreted through the generation of denser oxygen precipitates in GCz silicon than Cz silicon, which were considered to be ascribed to the enhancement of precipitate nucleation by the germanium doping. It is therefore believed that the germanium doping could improve the IG capability for Cz silicon wafer.

Copper precipitation in nitrogen-doped Czochralski silicon

Copper (Cu) precipitation behaviors in p-type conventional Czochralski (CZ) and nitrogen-doped Czochralski (NCZ) silicon have been comparatively investigated by means of transmission electron microscopy and optical microscopy. Within the CZ silicon, the Cu precipitates exhibited as spheres with size of about 100 nm and generated stress in the matrix. In this case, they were preferentially delineated as etching pits. On the other hand, within the NCZ silicon, the Cu precipitates were revealed as colonies in which spherelike Cu precipitates with sizes of 10–30 nm assembled on and around the climbing dislocations. As a result, they were preferentially etched as aggregated rods. The formation of Cu precipitate colonies in NCZ silicon was explained in terms of the effect of large grown-in oxygen precipitates on Cu precipitation.

Minority Carrier Lifetime in As-Grown Germanium Doped Czochralski Silicon

The minority carrier lifetime of as-grown germanium-doped Czochralski (GCZ) silicon wafers doped with germanium concentrations [Ge]=1016−1018 cm−3 is investigated in comparison with conventional CZ silicon samples. It is found that the lifetime distribution along the ingot changes with the variation of [Ge]. There is a critical value of [Ge] = 1016 cm−3 beyond which Ge can obviously influence the lifetime of as-grown ingots. This phenomenon is considered to be associated with the competition or combination between the oxygen related thermal donors (TDs) and electrically active Ge-related complexes. The related formation mechanisms and distributions are also discussed.

Effect of annealing atmosphere on the recombination activity of copper precipitates formed by rapid thermal process in conventional and nitrogen-doped Czochralski silicon wafers

The effect of annealing atmosphere of Ar, N2, or O2 on the recombination activity of copper (Cu) precipitates, formed by the rapid thermal process (RTP), in conventional Czochralski (CZ) silicon and nitrogen-doped CZ (NCZ) silicon wafers have been investigated. It was revealed that the recombination activity of Cu precipitates formed under N2, Ar, and O2 atmospheres decreased in turn. Moreover, the RTP under O2 atmosphere led to a higher critical temperature for Cu precipitation in comparison with the RTP under Ar or N2 atmosphere. Furthermore, it was found that the Cu precipitates formed under the same conditions possessed stronger recombination activity in CZ silicon than in NCZ silicon. The above results have been tentatively explained.

Enhanced Formation of Thermal Donors in Germanium Doped Czochralski Silicon Pretreated by Rapid Thermal Annealing

The thermal donor formation at 425oC - 450oC in Ge doped Czochralski (GCZ) silicon having about 1016 cm-3 Ge content pretreated by rapid thermal annealing (RTA) and conventional furnace annealing (CFA) has been investigated using low-temperature infrared spectroscopy (LT-IR). The measurements prove that lightly Ge doping can enhance the formation of thermal double donors in the initial stage of the low temperature annealing after RTA process. Ge induced additional grown-in oxygen precipitates during silicon ingot growth and the abundant self-interstitials during RTA may be the reason for the enhancement. However, after extending the annealing time at the low temperatures, the thermal donor concentration in the GCZ silicon is lower than that in the conventional CZ silicon. In final, the mechanism is also discussed.

Investigation of intrinsic gettering for germanium doped Czochralski silicon wafer

The intrinsic gettering (IG) effects in a germanium-doped Czochralski (GCz) silicon wafer have been investigated through a processing simulation of dynamic random access memory making and an evaluation on IG capability for copper contamination. It has been suggested that both the good quality defect-free denuded zones (DZs) and the high-density bulk microdefect (BMD) regions could be generated in GCz silicon wafer during device fabrication. Meanwhile, it was also indicated that the tiny oxygen precipitates were hardly presented in DZs of silicon wafer with the germanium doping. Furthermore, it was found in GCz silicon wafer that the BMDs were higher in density but smaller in size in contrast to that in conventional Cz silicon wafer. Promoted IG capability for metallic contamination was therefore induced in the germanium-doped Cz silicon wafer. A mechanism of the germanium doping on oxygen precipitation in Cz silicon was discussed, which was based on the hypothesis of germanium-related complexes.

Intrinsic gettering Based on rapid thermal annealing in germanium-doped Czochralski silicon

The intrinsic gettering (IG) effects under different thermal processes involved with rapid thermal annealing (RTA) in Czochralski (CZ) silicon wafers with germanium doping have been investigated. It has been shown that both good quality denuded zones and high-density bulk microdefect regions could be generated in germanium-doped CZ (GCZ) silicon wafers through thermal cycles of RTA treatments plus either low-high temperature two-step annealing or high temperature single-step annealing. Moreover, more oxygen precipitation was formed in GCZ silicon wafers in comparison with conventional CZ silicon wafers, indicating the enhancement of IG capability for CZ silicon wafers by the germanium doping. The phenomena have been considered to be ascribed to the increase of vacancy concentration associated with the presence of germanium, which results in the generation of Ge-V-related complexes in GCZ silicon wafers during RTA treatments.

Oxygen Precipitation of Nitrogen-Doped Czochralski Silicon Subjected to Multi-Step Thermal Process

The effect of nitrogen on oxygen precipitation in nitrogen- doped Czochralski (NCZ) silicon subjected to the simulated CMOS process was investigated. It was found that nitrogen could enhance oxygen precipitation in silicon during the multi- step thermal process. And the denuded zone in NCZ silicon was formed near the surface, through it was not as wide as that in conventional Czochralski (CZ) silicon. It was also found that the loss rates of oxygen concentration in the NCZ silicon pre- annealed by rapid thermal process (RTP) were higher than those in the CZ silicon. In addition, during the multi-step process the oxygen concentrations in the CZ silicon and NCZ silicon after the multi-step pre-annealing, which could create denuded zone, changed slightly.

Effect of Nitrogen Doping on Oxygen Precipitate Profiles in Czochralski Silicon Wafer

The effect of nitrogen doping on the profiles of oxygen precipitates in Czochralski (CZ) silicon subjected to conventional annealing and rapid thermal annealing (RTA) has been investigated. After conventional high-low-high three-step annealing (1150 °C, 4 h + 650 °C, 128 h + 1050 °C, 16 h), it was found that an M-like oxygen precipitate profile existed in the cross section of a nitrogen-doped CZ silicon (NCZ-Si) wafer; however, this was not the case in conventional CZ silicon (CZ-Si) wafers. In contrast to conventional annealing, after rapid thermal annealing (RTA) followed by a low-high two-step annealing (800 °C, 8 h + 1050 °C, 16 h), an M-like oxygen precipitate profile existed in the cross section of the CZ-Si wafer but not in the NCZ-Si wafer. It is suggested that not only vacancies but also nitrogen doping have an influence on the oxygen precipitate profile. In addition, the relevant mechanism is discussed.

Effect of ramping anneals under inert or oxidizing ambient on the formation of oxygen precipitate denuded zone in nitrogen‐doped Czochralski silicon wafers

AbstractThe formation of an oxygen precipitate denuded zone in nitrogen‐doped Czochralski (NCZ) silicon and conventional CZ silicon subjected to ramping anneals under Ar or O2 ambient has been investigated. It is revealed that the nitrogen doping is able to homogenize substantially the density of bulk micro‐defects associated with oxygen precipitation in the silicon wafers with different thermal histories and initial oxygen contents. The oxygen precipitate denuded zone is only formed in specimens subjected to the ramping anneal under Ar ambient. It is believed that the ramping anneal under Ar ambient could be an alternative intrinsic gettering process for NCZ silicon wafers, while it is not very appropriate for conventional CZ silicon wafers. Furthermore, it is somewhat unexpected that oxygen precipitation during the ramping anneal under O2 ambient is not suppressed but slightly enhanced in comparison with that during the ramping anneal under Ar ambient, the reason for which is tentatively explained. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhancement effect of germanium on oxygen precipitation in Czochralski silicon

Oxygen precipitation in germanium (Ge)-doped Czochralski (CZ) silicon has been investigated through a series of isothermal anneals at temperatures ranging from 550to950°C. It is found that the nucleation of oxygen precipitates can be enhanced in a wide temperature range and the onset temperature for precipitate nucleation can be increased by the germanium doping. Furthermore, it is also revealed that the oxygen precipitates with a higher density and smaller sizes can be formed in germanium-doped CZ silicon in comparison with those in conventional CZ silicon. These two phenomena are ascribed to the reduction in the critical radius for oxygen precipitation and the increase in the concentration of heterogeneous nuclei due to the germanium doping.

Effects of rapid thermal processing on oxide precipitation in conventional and nitrogen‐doped Czochralski silicon

AbstractIn this paper, the effects of vacancies introduced by rapid thermal processing (RTP) on nucleation and growth of oxide precipitates in Czochralski (Cz) silicon are elucidated. Moreover, the nitrogen and vacancy enhancement roles in oxide precipitation are differentiated through designing specific annealing schemes. Furthermore, it is pointed out that the RTP‐based internal gettering process for a nitrogen‐doped Cz silicon wafer should be different from that for a conventional Cz silicon wafer in order to strengthen the intrinsic gettering capability. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of light germanium doping on thermal donors in Czochralski silicon wafers

In this paper, the effect of light Germanium (Ge-) doping on thermal donors (TDs) in Czochralski silicon (CZ-Si) has been investigated by four-point probe and low-temperatures Fourier transform infrared (FTIR) spectrometer. After 650 °C, 30 min annealing to eliminate the grown-in TDs, conventional CZ-Si and germanium-doped CZ-Si (GCZ-Si) samples were further subjected to isothermal annealing at about 450 °C to generate TDs. It was found that Ge-doping suppressed the formation of TDs. Moreover, the low temperature FTIR absorption spectra of the TDs in GCZ-Si were found to agree quite well with that of TDs in CZ-Si, which was not the case for the heavily Ge-doped silicon. Therefore, it is considered that the light Ge-doping suppresses the formation of TDs but does not affect the microscopic structure of TDs.