Ge-doped Czochralski 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.

Cellular dislocations patterns in monolike silicon: Influence of stress, time under stress and impurity doping

Besides the well-known local sub-grain boundaries (SGBs) defects, monolike Si ingots grown by Directional Solidification present distributed background cellular dislocation structures. In the present work, the influence of stress level, time under stress, and doping by O and Ge, on the formation of dislocation cells in monolike silicon, is analysed. This is achieved by performing a comparative study of the dislocation structures respectively obtained during crystallisation of pilot scale monolike ingots on Czochralski (CZ) and monolike seeds, during annealing of Float Zone (FZ), CZ, and 1 × 1020 at/cm3 Ge-doped CZ (GCZ) samples, and during 4-point bending of FZ and GCZ samples at 1300 °C under resolved stresses of 0.3, 0.7 and 1.9 MPa during 1–20 h. Synchrotron X-ray White-beam Topography and Rocking Curve Imaging (RCI) are applied to visualize the dislocation arrangements and to quantify the spatial distribution of the associated lattice distortions. Annealed samples and samples bent under 0.3 MPa present dislocation structures corresponding to transient creep stages where dislocations generated from surface defects are propagating and multiplying in the bulk. The addition of the hardening element Ge is found to block the propagation of dislocations from these surface sources during the annealing test, and to retard dislocation multiplication during bending under 0.3 MPa. On the opposite, cellular structures corresponding to the final stationary creep stage are obtained both in the non-molten seeds and grown part of monolike ingots and in samples bent under 0.7 and 1.9 MPa. A comparative discussion is made of the dynamics of formation of these final dislocation structures during deformation at high temperature and monolike growth.

Effect of Germanium Doping on Thermal Evolution of Neutron Irradiation Induced Defects in Czochralski Si

In this paper, the impact of germanium (Ge) doping on thermal evolution of neutron-induced defects in Czochralski (CZ) silicon has been investigated. It is found that more vacancy-oxygen (VO) defects are generated in Ge-doped Czochralski (GCZ) silicon after fast neutron irradiation. This is ascribed to the promoted vacancy production and retarded vacancy annihilation caused by the large-sized Ge atoms, which lead to an increased equilibrium vacancy concentration and VO complex generation. FTIR measurements found the IR bands of vacancy-oxygen-related complexes in GCZ silicon almost copy their counterparts in CZ silicon, which implies that Ge-doping has little influence on the final states of the evolution of VO complexes. This is also verified by the variations of interstitial oxygen concentrations in CZ and GCZ silicon after isothermal annealing at 800 °C for up to 144 h. However, the evolution process may be somewhat retarded in GCZ silicon, which is caused by the continuous vacancy trapping and releasing.

Ge-vacancy complexes in Ge-doped czochralski silicon crystal

The first-principls theory is used to study the interaction between the Ge atom and the vacancies in Ge-doped czochralski silicon. The CASTEP calculation shows the stable structural model of Ge atom and one vacancy, two vacancies and three vacancies through the distance between the Ge atom and vacancy (or the vacancy centers) and the size of the area (or volume). The calculation shows that the Ge atom introduced into the GCZ Si crystal tends to accumulate with the vacancy and then seeds for the Ge-vacancy complexes.

Germanium-doped Czochralski silicon for photovoltaic applications

Germanium (Ge)-doped Czochralski (GCZ) silicon has been grown for photovoltaic (PV) applications. It is found that Ge doping improves the mechanical strength of CZ silicon, resulting in the reduction of breakage during wafer cutting, cell fabrication and module assembly. Boron–oxygen (B–O) defects that lead to the light-induced degradation (LID) of carrier lifetime are effectively suppressed by Ge doping. The decrease in the maximum concentration of B–O defects increases with an increase of Ge concentration. The efficiency of GCZ silicon solar cells and the power output of corresponding PV modules both exhibit smaller loss under sunlight illumination. The current work suggests that GCZ silicon should be potentially a novel substrate for thin solar cells with low LID effect.

Effects of germanium doping on the behavior of oxygen and carbon impurities and impurity-related complexes in Si

Abstract The production and annealing of oxygen and carbon related defects in electron-irradiated Ge-doped Czochralski silicon have been studied by means of IR spectroscopy. The results demonstrate that the role of Ge changes with increasing Ge content. At low Ge concentrations, much less than 1020 cm−3, Ge atoms act as temporary traps for vacancies preventing their annihilation with self-interstitials. At high Ge concentrations, Ge atoms form clusters which tend to attract vacancies and self-interstitials, enhancing their mutual annihilation. As a result, for low Ge concentrations the production of oxygen-related defects (VO) and carbon-related defects (CiOi, CiOi(SiI), CiCs) tend to increase as a function of Ge content, while for high Ge concentrations tend to decrease. The annealing of the oxygen-related defects VOn (1≤n≤6) is also affected by the Ge presence. The ratio of the VO defects that convert to VO2 is reduced in Ge doped material. However, this ratio increases for the conversions VOn→VOn+1 (3≤n≤5), respectively. The annealing temperature of VO defect and the growth temperature of VO2 defect decrease versus Ge content. On the other hand, the thermal stability of the carbon-related defects was found to be insensitive to the presence of Ge. It was also found that the carbon precipitation process shows some marked differences in irradiated Ge-doped Si, in comparison with the undoped material.

Ge-vacancy pair in Ge-doped Czochralski silicon

The potential configurations of Ge-vacancy pairs in a Ge-doped Czochralski Si (GCz-Si) crystal have been identified through first-principles theory using a total-energy pseudopotential method. The Ge atoms in the GCz-Si lattice are suggested to aggregate with the vacancy/vacancies to generate the Ge-related complexes. The total energy of the GCz-Si lattice configuration containing multivacancies decreases with the reduction of bond lengths among the vacancies and decreases with the reduction of bond lengths between the Ge atom and the vacancies. It is suggested that the Ge atom introduced in the GCz-Si crystal tends to accumulate with the vacancy and then seeds for the Ge-vacancy pairs.

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.

Stress-dependent transformation of interstitial oxygen in processed Ge-doped Cz-Si

The effect of stress induced by enhanced hydrostatic pressure (HP, up to 1.2GPa) applied at processing at up to 1400K, on the transformation of interstitial oxygen (Oi) in Ge-doped Czochralski silicon (Cz-Si:Ge, cGe=7×1017cm−3) was investigated by spectroscopic, X-ray and electrical methods.While the presence of Ge results in reduced generation of thermal donors (TDs) in Cz-Si:Ge annealed under 105Pa, the same processing under HP at 675–750K produces TDs in a concentration up to about 1015cm−3. The treatment under HP at 1270–1400K stimulates agglomeration of interstitial oxygen; the HP-dependent generation of different oxygen-containing defects is observed. The effect of HP on transformation of oxygen in Ge-doped Cz-Si is related, among others, to stress-induced activation of germanium to act as a component of nuclei for precipitation of Oi’s.

Defects in Ge-doped Cz-Si annealed under high stress

The effect of stress induced by enhanced hydrostatic pressure (HP, up to 1.1 GPa) at annealing up to 1400 K of Ge-doped Czochralski silicon (Cz-Si:Ge) on a creation of thermal donors (TDs) and of oxygen-related defects is investigated by spectroscopic (FTIR) photoluminescence and electrical methods. While the presence of Ge results in reduced generation of TDs in Cz-Si:Ge annealed at 723 K under 10 5 Pa, HP applied at 698–748 K produces TDs in a much enhanced concentration. The treatments under 1.1 GPa at 1070–1270 K result in increasing, for up to 20%, precipitation of oxygen. An explanation of the HP effect on a creation of defects in Cz-Si:Ge is proposed.

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.

Dislocation behavior in heavily germanium-doped silicon crystal

Dislocation-free heavily Ge-doped Czochralski (CZ)-Si crystal growth using a heavily Ge-doped Si seed has been investigated. Dislocations due to thermal shock were suppressed in a seed 7×7 mm 2 in cross-section when Ge concentration in the seed exceeded 9×10 19 atoms/cm 3. When Ge concentration in the grown crystal was 5.7×10 20 atoms/cm 3, cellular growth occurred, and this concentration was a limit for heavily Ge-doped Si single crystal growth with a growth rate of about 1 mm/min. Resistivity in the crystal results in B or P doping could be controlled precisely in spite of using a heavily Ge-doped Si seed for growing a dislocation-free CZ-Si crystal without Dash necking.