Nitrogen-doped Czochralski Research Articles

Nitrogen-Doped Silicon: Mechanical, Transport and Electrical Properties

A novel dislocation locking technique is used to study the behaviour of nitrogen in float-zone silicon (FZ-Si). Specimens containing well-defined arrays of dislocation half-loops are subjected to isothermal anneals of controlled duration, during which nitrogen diffuses to the dislocations. The stress required to bring about dislocation motion is then measured. From measuring this unlocking stress as a function of annealing time and temperature it is possible to deduce information on nitrogen transport and nitrogen-dislocation interactions. In this paper, the results obtained by using the dislocation locking technique are reviewed. Furthermore, deep-level transient spectroscopy (DLTS) and high-resolution DLTS (HR- DLTS) are applied to nitrogen-doped silicon. A deep-level with an emission enthalpy of approximately 0.50eV and a concentration of order 1011cm-3 was found in n-type nitrogen- doped FZ-Si and n-type nitrogen-doped neutron transmutation doped FZ-Si. No additional deep-levels with a concentration of greater than 6 x 1010cm-3 were found in either material. No deep-levels were found in p-type nitrogen-doped Czochralski silicon (Cz-Si), for which the detection limit was approximately 1012cm-3.

Nitrogen-doped Czochralski silicon treated in rapid thermal process

Nitrogen is one of the most important elements in Czochralski (CZ) silicon used in ultra-large scale integrity circuits (ULSI). In last decades, nitrogen-doped Czochralski (NCZ) silicon, which has been widely applied in microelectronic industry, has attracted much attention. In this presentation, the behavior of NCZ silicon treated in rapid thermal process (RTP) has been reviewed. The influence of RTP on oxygen precipitation, bulk microdefects, denuded zone and nitrogen and oxygen complexes in NCZ silicon has been investigated. The interaction of nitrogen with oxygen and vacancies in CZ silicon during RTP is also discussed.

Infrared absorption peaks in nitrogen doped CZ silicon

Dependences on annealing temperature and nitrogen concentration were examined for new local vibration mode infrared absorption peaks at 856, 973, 984 and 1002 cm −1 in nitrogen-doped CZ silicon crystal. The new absorption peaks were so weak that two sets of samples were examined for temperature and concentration dependences, respectively, to get reliable results. The peak at 1002 cm −1 behaved similarly for annealing, though much weaker, to the known peaks at 810 and 1018 cm −1 which are attributed to interstitial N pair accompanied by the two oxygen interstitials (NNO i O i ). This suggests that the origin contains 2 O i also. It was strong in low concentration regime, which is similar to the behavior of shallow thermal donors. This suggests that the structure contains one nitrogen rather than two (N–O interstitial pair). The results were compared with the electronic transition absorption by shallow thermal donors (STD). The absorptions at 1002 and 240 cm −1 behaved similarly. These suggest that the peak at 1002 cm −1 is likely due to NOO i O i which is the candidate for STD. The temperature dependence of the other new peaks was slightly different from each other. Origin of the other peaks is not clear yet.

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

not Available.

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.

Crystal growth and oxygen precipitation behavior of 300 mm nitrogen-doped Czochralski silicon

A 300 mm, p-type, 〈1 0 0〉-oriented nitrogen-doped Czochralski (NCZ) silicon crystal was grown in a Keyex MCZ 150 crystal puller equipped with cusp magnetic field. In order to dope nitrogen into the crystal, the primary protection gas of argon was mixed with high-purity nitrogen gas at a flow rate ratio of 10:1. Due to the long time growth of crystal, any perturbation due to the SiO and cristobalite particles at the crystal/melt interface would generate dislocation in the crystal. In order to avoid this ‘disaster’ during the crystal growth, a thermal shield in connection with a protection gas director was used, thereby generating a sweeping flow over the melt to drive the SiO and cristobalite particles out of the crystal/melt interface. The oxygen precipitation behavior of a near-seed-end wafer subjected to 800 °C/8 h+1000 °C/16 h was investigated. It was found that oxygen precipitation within the P-band was stronger than that in the region outside of the P-band, which is generally not the case for the conventional Czochralski (CZ) wafer with P-band. Based on this result, it is deduced that the grown-in oxygen precipitates existing in the P-band are relatively smaller in size but with higher density compared to those in the CZ crystal.

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)

Analysis of electrically active N–O complexes in nitrogen-doped CZ silicon crystals by FTIR spectroscopy

Nitrogen-doped CZ silicon crystals with different oxygen contents were studied by quantitative FTIR spectroscopy. Thermal-equilibrium annealing at 600 °C is suitable to obtain information on the chemical composition of N–O related shallow donors. All species investigated (N–O-1, N–O-2, N–O-3, and N–O-5) contain one nitrogen atom. However, different numbers of oxygen atoms are involved. N-O-5 incorporates the lowest number, probably two; N–O-3 contains one oxygen atom more, whereas N–O-1 and N–O-2 contain two more.

Local vibration modes of shallow thermal donors in nitrogen-doped CZ silicon crystals

Local vibration mode (LVM) infrared absorption from shallow thermal donors (STD) composed of nitrogen–oxygen complexes in nitrogen-doped CZ silicon crystals was examined. The samples whose STD concentration had been determined were measured. The sample dependence of the peaks at 810 and 1018 cm - 1 was similar to that of STD but the estimated concentration was slightly higher. New LVM peaks were found at 855, 973, 982, 1002 cm - 1 and so on. Their magnitude and sample dependence agreed well with those of STD. Annealing temperature dependence of other samples supported the results. Annealing time dependence of STD concentration at 650 °C was examined. STD peaks at 250, 242 and those at 240, 234 and 238 cm - 1 behaved differently, suggesting the presence of two kinds of STD origin.

Effect of nitrogen doping on denuded zone formed by rapid thermal process in Czochralski silicon wafer

Denuded zone (DZ) formed by rapid thermal process (RTP) followed with the low–high (Lo–Hi) annealing in nitrogen-doped Czochralski (NCZ) silicon wafer was studied in this paper. In comparison with the conventional CZ silicon, the DZ in NCZ silicon was a little narrower, while the bulk microdefects were much denser, as a result of nitrogen-enhanced oxygen precipitation. It was also found that DZs within CZ and NCZ silicon wafers shrunk notably when further subjected to rigorous oxygen precipitation annealing, however, a width of substantial DZ remained within either wafer. Furthermore, it is definitely proved that the nitrogen doping does not affect the formation of defect-free DZ by the RTP-based internal gettering (IG) process.

Rapid-thermal-processing-based intrinsic gettering for nitrogen-doped Czochralski silicon

In order to optimize the intrinsic gettering (IG) process based on the rapid thermal processing (RTP) for nitrogen-doped Czochralski (NCZ) silicon wafer, the effects of RTP and the following nucleation anneal on oxygen precipitation in NCZ silicon and conventional CZ silicon wafers have been comparatively investigated. It was found that, for NCZ silicon, the RTP at enough high temperature (e.g., 1250°C) was necessary for generation of high density of bulk microdefects (BMDs) in the subsequent anneals despite the nitrogen enhancement effect on oxygen precipitation. With enough high concentration of vacancies introduced by the RTP at 1250°C, for the conventional CZ silicon wafer, the vacancy enhancement effect on the nucleation of oxygen precipitates was most significant at 800°C; while for NCZ silicon wafer, the vacancies and nitrogen atoms coacted most remarkably to nucleate the oxygen precipitates during the ramping anneal from 800to1000°C. It was further found that the doped nitrogen is superior to the vacancy to enhance the nucleation of oxygen precipitates at temperatures of 900–1000°C. Moreover, in order to maximize the density of BMDs, the RTP-based IG process for NCZ silicon wafer should be different from that for the conventional CZ silicon wafer.

Investigation of Ostwald ripening in nitrogen doped Czochralski silicon

Infrared laser scattering tomography was used to investigate Ostwald ripening in nitrogen-doped Czochralski silicon. Contrary to previous assumptions about oxide precipitation in nitrogen-doped silicon, the results clearly demonstrate that Ostwald ripening takes place during annealing of N-doped silicon wafers at 1000°C and 1100°C. The higher the nitrogen doping and the higher the temperature the faster the oxide precipitates grow and the faster they split into two fractions. One fraction is growing at the expense of the other.

X-ray diffuse scattering from defects in nitrogen-doped Czochralski grown silicon wafers

Nitrogen doping during crystal growth is used to create nitrogen–vacancy(–oxygen) complexes. These complexes enhance the nucleation of silicon oxide precipitates. The precipitates and other volume defects in silicon wafers serve as gettering centres for metal impurities during the device processing. We have studied nitrogen-doped silicon wafers (001) from the origin, middle and end of the ingot, annealed at low (750°C) and high (1050°C) temperatures, using triple-axis high-resolution x-ray diffraction. The reciprocal space intensity distributions from clusters, stacking faults and dislocation loops were modelled using the Krivoglaz theory and a continuum model of the defect deformation field. Good agreement of the theory with the experimental data was achieved for the model of dislocation loops. The symmetry of measured reciprocal space maps determines the type of dislocation loops and from extracted linear scans in the ⟨111⟩ direction we can obtain the radius and concentration of the loops. These parameters were combined with the results from selective etching and infrared absorption spectroscopy. Concentration of interstitial oxygen, shape, stoichiometry and volume fraction of precipitates were obtained from absorption spectra taken at room and liquid nitrogen temperature.

Formation of a denuded zone in nitrogen-doped Czochralski silicon wafer treated by ramping anneals

The formation of a denuded zone (DZ) and the bulk-microdefects (BMDs) region within conventional and nitrogen-doped Czochralski (NCZ) silicon subjected to ramping anneals has been investigated. It was found that the terminal temperature of the ramping anneal should be high enough to create a DZ while the starting temperature should be low enough to generate desirable high density of BMDs. Comparatively speaking, with the same heat treatment, the NCZ silicon possesses higher density of BMDs and a narrower DZ than CZ silicon. Moreover, for NCZ silicon, the ramping anneal can initiate at relatively higher temperature to generate an appropriately high density of BMDs. Of importance is that the ramping anneal with a final isothermal anneal at an elevated temperature such as 1150 °C can effectively create a substantial DZ, where there were no defects generated in the subsequent heat treatment significantly enabling oxygen precipitation.

Photoluminescence of Dislocations in Nitrogen DopedCzochralski Silicon

We investigate optical properties of dislocations in nitrogen-doped andnitrogen-free Czochralski silicon. The dislocations are formedduring crystal growth, but not formed during deformation. The resultsshow that in nitrogen-doped samples, a broad band replaced the D1 bandof dislocation, regardless of dislocation density. The replacementof D1 band is caused by the non-irradiation combination induced byoxygen precipitation. Moreover, a new emission at 0.975 eV is observedin both the nitrogen-free and doped samples when the dislocationdensity is lower than 104 cm−2.

Oxygen precipitation in nitrogen doped Czochralski silicon wafers. I. Formation mechanisms of near-surface and bulk defects

Defect size distributions in nitrogen-doped Czochralski (N-CZ) silicon wafers were obtained using an oxygen precipitate profiler and Wright-Jenkins etching. These showed unique depth dependence in low-high and high-low-high cycled N-CZ wafers. Unique phenomena observed include a high defect concentration at the subsurface that decreases within the top 2μm of the so-called denuded zone. In contrast to N-free CZ Si for which the first high step annealing dissolves the grown-in defects, these appeared to be stable in N-CZ Si. As a result, the defect size distribution in the bulk was found to be independent of the annealing cycle. It was also found that the depth dependent defect concentration correlates well with oxygen and strongly with nitrogen secondary ion mass spectroscopy profiles, suggesting that nitrogen is the leading impurity in the defect formation processes even though introduced at very low concentration. Nitrogen appeared to effectively modify the nucleation regime by a drastic increase of the nuclei density. At low temperature under external stress, nitrogen and oxygen cosegregate to the surface where the stress is applied; such a phenomenon is largely increased at high temperature.

Effect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults in nitrogen-doped Czochralski silicon

The effect of oxygen precipitates and induced dislocations on oxidation-induced stacking faults (OSFs) in nitrogen-doped Czochralski (NCZ) silicon has been investigated. Both CZ and NCZ wafers were annealed at 800°C and 1000°C for 225h with or without a post-treatment at 1200°C for 8h, and then were totally oxidized at 1150°C. It was found that after oxidization, few OSFs generated in the NCZ silicon subjected to the annealing at 800 and 1000°C, while larger numbers of OSFs in the CZ silicon. However, if the post-treatment at 1200°C was employed prior to oxidization, OSFs density in the NCZ silicon was almost similar to that in the CZ silicon. It is considered that the high density of oxygen precipitates and induced dislocations formed in NCZ silicon can absorb the self-interstitial silicon atoms so that the generation of OSFs is inhibited. After the postannealing, most dislocations shrank and dissolved with the dissolution of oxygen precipitates in the NCZ silicon so as to induce the same amount of OSFs as that in the CZ silicon.

Microstructure of high temperature–pressure treated nitrogen-doped Czochralski silicon

Microstructure of the oxygen precipitates and of the annealing induced defects in nitrogen-doped Czochralski (NCZ) and conventional (CZ) silicon subjected to two-steps treatment under high pressure (HP) up to 1.1GPa has been investigated by means of photoluminescence (PL) spectroscopy. It has been found that the creation of oxygen precipitates and defects in the CZ-Si and NCZ-Si subjected to the high pressure heat treatments (HT–HP) at up to 1130°C is dependent both on annealing temperature (HT) and HP. Nitrogen doping affects the microstructure of NCZ-Si so that PL spectra of HT–HP treated NCZ-Si are different from these of CZ-Si.

Effects of nitrogen doping on the dissolution of oxygen precipitates in Czochralski silicon during rapid thermal annealing

The thermal stability of oxygen precipitates formed by prolonged annealing at 1000 °C in conventional Czochralski silicon and nitrogen-doped Czochralski silicon has been comparatively investigated. It was found that a majority of the existing oxygen precipitates in the nitrogen-doped silicon were dissolved by both conventional furnace annealing and rapid thermal annealing at 1200 °C, while those in the conventional Czochralski silicon dissolved at 1250 °C, as a result of nitrogen enhancing denser oxygen precipitates with smaller size. Furthermore, it can be considered that the dissolution of oxygen precipitates is primarily determined by the annealing temperature.

“Umbrella”-like precipitates in nitrogen-doped Czochralski silicon wafers

Nitrogen effect on nucleation of oxygen precipitates in Czochralski Si has been investigated by transmission electron microscopy, Z-contrast imaging, and electron energy loss spectrometry (EELS). We have examined unusual “umbrella” shape oxygen precipitates in bulk of ingot in depths of more than 40 μm. Two predominant orientations of “umbrella” have been found along [110] and [−1−10] directions. We have investigated the distribution of nitrogen, oxygen, and interstitial Si by EELS profile taken simultaneously with HR Z-contrast image. The mechanism of nitrogen-enriched oxygen precipitates nucleation has been discussed.