Articles you may be interested inEffect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults in nitrogen-doped Czochralski silicon Silicon crystals doped with nitrogen from the melt contain shallow thermal donors ͑STDs͒ detected both optically and electrically. Annealing samples at 600 and 650°C results in a saturated STD concentration that depends on the nitrogen concentration approximately by a square-root law. This indicates the involvement of only one nitrogen atom in every STD species. The model of STDs consistent with the present data is the NO m complex of a nitrogen interstitial and m oxygen atoms; the concentration of every STD species reaches the equilibrium value during annealing. The temperature dependence of the equilibrium reaction constant allows us to estimate the average number of oxygen atoms m of the STD complexes as 3.
The generation of Thermal Donors in Si is a nucleation process controlled by several mobile On clusters. The rate-limiting transitions are found to be O1 O2 and O4 O5. The individual transition rates G12 and G45, and also G23 and G34 are deduced from the experimental data. From the transient variation of the generation rate G(t), the equilibrium concentration of the dimers is found, and with it the dimeric diffusivity is also defined. In samples pre-treated at high T, the G(t) dependence has a maximum, due to quenched-in fast-diffusing oxygen monomers (FDMs). The concentration and diffusivity of FDMs were determined.
This work was initially intended to examine the effect of rapid thermal annealing (RTA) on the generation of thermal donors (TD) in silicon in the temperature range 450 to 500ЊC. RTA preanneals made at 1200ЊC in nitrogen were reported 1 to retard TD generation at 450ЊC for about 5 h, and so it was thought interesting to look at the temperature dependence of this retardation. Such an RTA-induced retardation was not found in the present study, however. The difference in the TD kinetics between as-grown and RTA samples was not significant, in accord with other recent data. 2 Instead of the expected retardation we observed another striking effect: it was noticed that the TD concentration was remarkably sensitive to the cooling rate of the sample after the TD-producing anneal steps. This effect was most evident for the RTA-treated samples annealed at 500ЊC, though it was found in as-grown samples too. The effect of annealing conditions on the TD kinetics is the subject of the present work.Experimental We used a set of wafers (0.675 mm thick) cut from the same crystal from adjacent positions and subjected to an RTA treatment at 1250ЊC for 35 s in nitrogen ambient. The crystal, 150 mm in diameter, was grown in the vacancy mode, 3 at the relatively high pull rate of 0.8 mm/min. The oxygen content was 1 ϫ 10 18 cm Ϫ3 (using the calibration factor 3.14 ϫ 10 17 cm Ϫ2 ), and the carbon content was below the detection limit of 2 ϫ 10 15 cm Ϫ3 . The crystal was boron doped to the concentration N B ϭ 1.7 ϫ 10 15 cm Ϫ3 . Rectangular samples (12 mm long and 3 mm wide) were cut from the central part of the wafers.The thermal donor generation anneals were performed in two different types of furnaces. One of these was an air ambient furnace and the other a vacuum furnace (the residual pressure was 10 Ϫ3 Torr). The anneals were performed using sequential time steps of 4 h (in most cases). A total duration of up to 80 h was accumulated in this way. In the air furnace each of the sequential anneal steps was followed by one of two different cooling procedures: either quenching (placing a sample on a thick silicon plate) or slow cooling (leaving a sample inside the furnace after switching-off the power). The fast cooling rate was about 60 K/s, the slow cooling rate was about 0.2 K/s. The cooling curves, T(t), were recorded using a thermocouple attached to a sample. After each of the annealing step the samples were slightly lapped so that the sample thickness was gradually reduced, finally down to 0.55 mm. In the vacuum tube furnace the cooling rate was fixed at about 0.8 K/s, intermediate between the slow and fast cooling conditions in the air furnace. The furnace temperature was controlled by a thermocouple, and maintained at prescribed value with the accuracy of 1ЊC for the vacuum furnace and 3ЊC for the air furnace.The TD concentration was deduced from Hall effect measurements at temperatures down to liquid helium. An example of a temperature dependence of the electron concentration n(T) in a TD containing sample is shown in Fig. 1. T...
The time dependence of thermal donor (TD) concentration, N(t), during annealing at 450oC was measured in samples cut from a single slab of silicon containing bands of grown-in microdefects of different types. An enormous impact of the microdefect type on the kinetic curve was observed. Samples from the interstitial region showed simple linear rise in N(t). The samples from an inner part of the vacancy region showed a complicated oscillating variation with an abrupt disappearance of the TDs at some moment followed by an immediate restoration of a linear rise. In samples from the marginal H-band of the vacancy region, an initial anneal does not produce TDs. However if this anneal was followed by a quench, subsequent anneals produce a linear rise in N(t). On the other hand, if the sample was slowly cooled, the subsequent production of TDs remained almost negligible. These observed peculiarities are accounted for by enhanced TD growth in the presence of self-interstitials (I) - due to IO species serving as vehicles for oxygen transport.
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