CZ Silicon Wafers Research Articles

Oxygen precipitates in annealed CZ silicon wafers detected by SIRM and FTIR spectroscopy

A scanning infrared microscope, a Fourier transform infrared spectrometer, and chemical etching have been associated with detecting precipitates in annealed Czochralski (Cz) silicon wafers and with controlling their interaction with self-interstitials injected into the bulk by phosphorus diffusion or by oxidation. After nucleation (750°C) and/or growth (900°C) annealing, phosphorus diffusion at 900°C for 4 h shrinks the precipitates revealed by SIRM, owing to a marked injection of self-interstitials in the bulk. Annealing of the two-step annealed samples in oxygen produces a similar effect; however, new defects are detected by SIRM which are identified as stacking faults.

Effect of Energy and Dose on Transient-Enhanced Diffusion and Defect Microstructure in Low Energy High Dose As+ Implanted Si

Abstract(001) CZ silicon wafers were implanted with arsenic (As+) at energies of 10–50keV to doses of 2×1014 to 5×1015/cm2. All implants were amorphizing in nature. The samples were annealed at 700°C for 16hrs. The resultant defect microstructures were analyzed by XTEM and PTEM and the As profiles were analyzed by SIMS. The As profiles showed significantly enhanced diffusion in all of the annealed specimens. The diffusion enhancement was both energy and dose dependent. The lowest dose implant/annealed samples did not show As clustering which translated to a lack of defects at the projected range. At higher doses, however, projected range defects were clearly observed, presumably due to interstitials generated during As clustering. The extent of enhancement in diffusion and its relation to the defect microstructure is explained by a combination of factors including surface recombination of point defects, As precipitation, As clustering and end of range damage.

Effect of native point defects on morphology of gettering centres in CZ-silicon wafers

The influence of native point defect concentration on oxygen precipitation processes in SiOi system has been investigated. The supersaturation degree of native point defects in the bulk of the silicon wafers was varied by changing the conditions of the preliminary oxidation. It has been shown supersaturation of a certain type of native point defect can retard the oxygen precipitation process and change the picture of defect formation.

Impurity effects on oxygen precipitation induced by MeV implants in Cz silicon

The heterogeneous precipitation of oxygen in Cz silicon wafers has been investigated for the following implanted ions: Al, C, Si, P, and As, after anneal in the 800–1200 °C temperature range. The amount of precipitated oxygen, as measured by secondary ion mass spectrometry, ranges from 7 × 10 13 (As implant) to 3 × 10 14 cm −2 (Al implant) after an anneal at 1000°C for 20 min. The residual damage, as detected by transmission electron microscopy, does not show a significant dependence on the amount of precipitated oxygen as demonstrated by the analysis of Cz and epitaxial silicon wafers. The results are explained in terms of the interstitial trapping by species like C and Al, that enhances the heterogeneous formation of Si x O y clusters. The subsequent growth of precipitates has been modelled for Al and C implants and for several annealing temperatures and times.

Genration of Oxidation Induced Stacking Faults in CZ Silicon Wafers

Genration of Oxidation Induced Stacking Faults in CZ Silicon Wafers

Fabrication of large area silicon solar cells by rapid thermal processing

Large area n+pp+ solar cells have been fabricated on 10 cm×10 cm pseudo-quasi-square CZ silicon wafers (1 Ω cm, p-type) predominantly used by the photovoltaic (PV) industry. All the high-temperature steps have been performed by rapid thermal processing (RTP). Emitter formation, back surface field (BSF) formation, and surface oxidation have been performed in just two RTP steps each lasting 50 s. Solar cells of 15% efficiency have been fabricated this way, demonstrating the applicability of this low thermal budget technology to large area, modulable size, industrial quality Si wafers. Furthermore, the rapid thermal oxidation (RTO) is shown to result in good quality thin oxides with Si/SiO2 interface trap densities (Dit)<1011 cm−3 eV−1 near-midgap.

Detection and Characterization of Precipitates in Annealed Cz Silicon Wafers

A Scanning InfraRed Microscope (S.I.R.M.), a Light Beam Induced Current mapping (L.B.I.C.), a Fourier Transform infrared spectroscope (F.T.I.R.)~ and a minority car- rier diffusion length measurements tool have been associated to detect precipitates in annealed Czochralski (Cz) silicon wafers and to evaluate their recombination strength with or without metallic contamination. The influence of a phosphorus diffusion was also investigated. After two step annealings (750 °C 16 h and 900 °C 24 h or 96 h) S-I-R-M- reveals the presence of precipitates, while L-B-I-C- maps display a ring-like distribution of recombination centers and minority carrier diffusion length (Ln) collapses to 2 ~tm- Copper contaInination does not signif- icantly modify the preceding observations when precipitates are formed. Phosphorus diffusion near the surface shrink the precipitates revealed by M-I-R-B- but do not suppress the ring-like patterns in the L-B-I- C. maps and Ln increases slightly. These results suggest that the recombi- nation strength of precipitates does not depend on a metallic decoration but more probably on interfacial states between the precipitates and the host crystal or on associated extended defects. Czochralski-grown (Cz) silicon waters used for electronic and microelectronic devices contain a large concentration of oxygen atoms. Generally, these atoms are dissolved as interstitials, and the solution is supersaturated at low temperature. The concentrations are close to 10~~ cm~~

Low Temperature Anneal of the Divacancy in P-Type Silicon

AbstractResults are reported of a Deep Level Transient Spectroscopy (DLTS) study of the conversion of the divacancy, with energy level at Ev+0.19eV, to a level at Ev+0.24eV after anneal at temperatures below its dissociation temperature (300°C). In literature both levels have been associated with the donor level of the divacancy.Diodes processed on p-type Float Zone (FZ) and Czochralski (Cz) silicon wafers with boron concentration between 0.2 and 3E15 cm−3 are irradiated with 2 MeV electrons. Before and after anneal (200°C and 250°C) DLTS spectra are recorded to get a full electrical characterisation of the induced defects.The observed conversion is proposed to be a gradual transformation of the divacancy to a divacancy-oxygen complex.

Rapid Thermal Oxidation of Heavily Doped Silicon for Advanced Solar Cell Processing

AbstractCrucial steps in solar cell processing such as emitter diffusion and surface oxide passivation have been carried out by rapid thermal processing (RTP). Rapid thermal diffusion (RTD) of boron into silicon from APCVD borosilicates has been studied. Rapid thermal oxidation (RTO) of the heavily B-doped surfaces of these shallow junctions (0.2 μm) has been studied in view of applicability of this technique in solar cell processing. These shallow diffusions have excellent lateral uniformity over large areas and have high surface concentrations depending on the APCVD deposition conditions and on RTP conditions. The surface passivating oxides resulting from the RTO are exceptionally thick in case of heavy boron diffused surfaces. RTO does not cause considerable drive-in of the diffused junction profiles. In the contrary, the thick RTO oxides considerably reduce the surface concentration, thereby reducing the heavy doping effects in the junctions, making them more suitable emitters for devices such as solar cells. p+nn+ solar cells have been fabricated on n-type CZ silicon wafers by RTD of boron followed by RTO. The cells result in conversion efficiencies as high as 16.2% The passivation effect of RTO oxides have been investigated by analysing RTO MOS capacitors and are compared to conventional furnace oxides.

High Performance Of Gettering In Hydrogen Annealed Wafer

AbstractThis paper reports on the study of the gettering of nickel contamination in hydrogen annealed CZ-silicon wafers by using method of wet chemical analysis. According to the wet chemical analysis, we believe that the hydrogen annealed wafer is of high quality in the region beneath the surface (DZ) and has a higher gettering ability for nickel compared with conventional CZ wafers. This observation is also in agreement with our MOS C-t measurements.

Warpage and Oxide Precipitate Distributions in CZ Silicon Wafers

Several types of as‐received and complementary metal oxide semiconductor (CMOS) thermal simulated 100 mm wafers were used for warpage study under different annealing conditions. The results indicated that as‐received wafers showed little increase in warpage up to 1000°C furnace temperature and 61.0 cm/min insertion rate. For the CMOS thermal simulation processed wafers, both the prior amount of oxygen precipitation, , where is the decrease in interstitial oxygen concentration, and bulk microdefect morphology affected warpage. For less than ca. 26 ppma, wafers with predominantly octahedral precipitates without associated dislocations plus a low density of small plate‐type and dot‐like precipitates underwent much less warpage than wafers with predominantly large octahedral precipitates and precipitate‐dislocation‐complexes (PDCs). When the was higher than 26 ppma, the defects consisted of a high density of large octahedral‐shaped precipitates and PDCs and thus warpage became inevitable.

On the determination of minority carrier diffusion length in the base region of n+-p-p+ silicon solar cells using photoresponse methods

A comparative study of the measurements of the minority carrier diffusion length L in the base region of n+-p-p + silicon solar cells by the LWSR, the MWSR, and the JSK methods, all of which exploit the photoresponse of cell in one way or the other, has been made. The LWSR and the MWSR methods utilize the long wavelength (e.g., 0.90 < h < 1.05 ixm) spectral response and middle wavelength (e.g., 0.75 < h < 0.90 ixm) spectral response, respectively, when the cell is illuminated from the n +-front side. However, the JSK method utilizes the rate of increase of short-circuit current density of the cell with the intensity of a single suitable middle or long wavelength radiation when the cell is illuminated from the p+-back side. Among these, the MWSR method and the JSK method each require the surface recombination velocity S b of the minority carriers at the p +-back end of the p-base region to be known. We fabricated a few n+-p-p + structure based bifacial silicon solar cells from 250 txm and 420 i~m thick CZ silicon wafers and carried out measurements of L for them. The JSK method was applicable to both the thin and thick cells and gave accurate values of L. For thick cells the LWSR method was found to be more accurate than the MWSR method, the error in the value of L being < 4% for the former and < 6% for the latter when compared with the JSK method. On the other hand, for thin cells, the LWSR method was found to be highly erroneous; the errors being 17-31% for the LWSR method in comparison with an error of 4% for the MWSR method. The results further showed that, generally, for thin front illuminated n+-p-p + cells having a shallow n+-p front junction, L sufficiently large and d/L < 2.5, the MWSR method would give more accurate value of L than the LWSR method.

Influence of the first thermal cycles of an IC process on oxygen precipitation in CZ silicon wafers: a detailed analysis

The oxygen precipitation kinetics, the oxide precipitate density (Np) and the denuded zone width (DZ) in standard CZ silicon wafers coming from the supplier and randomly sampled were determined after annealing at temperatures from 950 to 1100 degrees C. Correlations between the precipitation kinetics factors and the precipitate densities were clearly established and interpreted using the usual precipitation models. A clear relationship between the DZ values and the precipitate densities was obtained. How a further high-temperature anneal such as a CMOS well drive-in at 1160 degrees C affects these parameters was experimentally determined. All these results can be well interpreted in terms of selective precipitate growth from a population of microprecipitates. Practical recommendations for improved internal gettering are deduced from this work.

Effect of Interstitial Oxygen on Formation of Amorphous SiOx Layerin Directly Bonded Czochralski Silicon Wafers

We have investigated the effect of interstitial oxygen in CZ silicon wafers on the formation of the amorphous SiOx layer (x=0.2-0.3 after annealing at 1100°C for 2 h) at the interface in directly bonded silicon wafers using high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray (EDX). As the annealing time became longer, the thickness and the oxygen concentration in this layer increased, depending on the concentration of interstitial oxygen in wafers. These changes are caused by the diffusion of oxygen atoms from the bulk toward the bonded interface. However, they must not play such an important role in the initial stage of the formation of this layer because the layer existed discontinuously and was not affected by rotational misorientation or the microroughness.

Iron and Its Detrimental Impact on the Nucleation and Growth of Oxygen Precipitates during Internal Gettering Processes

The detrimental impact of iron on the nucleation and precipitation of interstitial oxygen has recently been reported from this laboratory and interpreted in terms of the different thermodynamical behavior of iron silicides and iron silicate . By varying the nucleation time of oxygen precipitation and adjusting different initial iron concentrations in CZ silicon wafers we have found a threshold concentration of iron (about ) above which the precipitation was impeded. Estimates, based on migrating interstitial oxygen and iron gave a threshold level of iron in the range of to . Scanning electron microscope (SEM) pictures provided compelling evidences that iron is retarding oxygen precipitation.

Correlation Between DLTS and TRXFA Measurements of Copper and Iron Contaminations in FZ and CZ Silicon Wafers; Application to Gettering Efficiencies

Metals forming deep traps in Si such as Fe, Cu, and Ni, are detectable with deep level transient spectroscopy (DLTS). In the present work, we used a spin‐on technique as contamination method, which guaranteed sets of silicon wafers with authentic samples of iron‐ and, respectively, copper‐contamination, that showed impurity concentrations on the wafer surfaces in the range of 1011 and 1013 atoms/cm2. A correlation between total reflection x‐ray fluorescence analysis and DLTS has also been successful. Monitoring the iron content by DLTS in the course of gettering processes, we determined external and internal gettering efficiencies. Our compelling results showed a limited gettering efficiency at the oxygen precipitate sites, due to the level of iron contamination.

Evaluation of interstitial oxygen along striations in CZ silicon single crystals with a micro-FTIR mapping system

Growth striations in CZ and MCZ silicon wafers were studied by the striation-etching method, spreading resistance measurements and the micro-FTIR mapping method. Microvariations in oxygen concentration were successfully measured using the micro-FTIR mapping system and the results were in good agreement with other results obtained by etching and resistance measurements. Two kinds of striations were observed in CZ and MCZ wafers with high oxygen concentration: weak striations at regular intervals and strong striations at irregular intervals. It was concluded that the former were related to the microsegregation of dopant impurities caused by remelting of the crystal during growth, while the latter were related to the fluctuation of oxygen concentration in the silicon melt.

Defect Distribution across 6-Inch CZ-Silicon Wafers

Defect Distribution across 6-Inch CZ-Silicon Wafers

The Influence of Thermal Treatment on Defect Characteristics in Cz-Silicon Wafers Investigated by Positron Annihilation Spectroscopy

ABSTRACTPositron lifetime and Doppler-broadening experiments as well as Fourier-transform infrared spectroscopy (FTIR) were performed on a variety of six-inch Czochralski (CZ) silicon wafers. Measurements were done at 14 equidistant locations across the wafers which were cut from the seed-, middle-, and tail-sections of two boules grown at different pull-speeds.In the as-grown wafers, the positron response consisted of components from small oxygen-related clusters and “perfect” bulk silicon only. Possible contributions from vacancy-type defects were at or just below the detection limit. After a two-step heat treatment (750°C/ 4 hrs + 1050°C/6 hrs in N2) FTIR showed that significant amounts of oxygen (4–8 ppma) had precipitated in wafers taken from the seed-sections of the boules but not in any of the other wafers. The positron data did not reflect this distinctive difference, however, both lifetime and Doppler-broadening results strongly indicate the creation of vacancy-type defects at concentrations in the 1016cm−3-range.

Defect Distribution in Large CZ-Silicon Wafers Investigated by Positron Annihilation Spectroscopy

Defect Distribution in Large CZ-Silicon Wafers Investigated by Positron Annihilation Spectroscopy