Denuded Zone Research Articles

Effect of Rapid Thermal Process on Oxygen Precipitation in Heavily Boron-Doped Czochralski Silicon Wafer

The effect of rapid thermal process (RTP) on oxygen precipitation in heavily boron-doped (HB) Czochralski (CZ) silicon (Si) wafers has been investigated. After RTP preannealing at high temperature, it was found that, contrary to lightly boron-doped (LB) silicon, a denuded zone (DZ) was not formed in the HB silicon. The oxygen precipitates and extended defects generated in the HB Si samples were smaller than those generated in the LB Si samples. It is considered that DZ formation by means of RTP may not be suitable for HB CZ silicon.

Oxygen precipitation kinetics of Czochralski silicon preannealed under high pressure

The formation of the denuded zone (DZ) in Czochralski silicon preannealed under high pressure was systematically investigated. It was found that the DZ could not form in those specimens. It is considered that the oxygen precipitates generated during preannealing under high pressure are more stable than those grown under atmosphere, so that the oxygen precipitates in the region close to the surface area could not dissociate at the first high-temperature annealing of intrinsic gettering (IG), but grew during the subsequent IG process. The results were also confirmed by the experiments of transmission electron microscopy.

Effect of rapid thermal process on oxygen precipitation and denuded zone in nitrogen-doped silicon wafers

The effect of rapid thermal process (RTP) on the oxygen precipitation and on the denuded zone (DZ) formation in nitrogen-doped Czochralski (NCZ) silicon wafers has been investigated. The DZ can be formed at the surface of NCZ wafers subjected to RTP annealing. However, the oxygen precipitation and bulk microdefects in NCZ silicon are changed by RTP preannealing, which is a result of N–N bonds broken during RTP treatment.

Oxide precipitates in annealed nitrogen-doped 300 mm CZ-SI

The lateral distribution of oxide precipitates as well as the denuded zone were investigated in a set of 300 mm CZ silicon wafers containing different amounts of nitrogen. Two light scattering methods, infrared light scattering tomography (IR-LST) as well as scanning infrared microscopy (SIRM) were used to characterize the precipitation density and the spatial distribution. The obtained results show that under certain heat treatments a high density of oxide precipitates, more than 1×10 9 cm −3, can be achieved in the depth of 300 mm wafers. With increasing nitrogen content the radial distribution of precipitates becomes more uniform. A 10–60 μm wide precipitation-free denuded zone was observed. A comparison between IR-LST and SIRM results was performed indicating the dominance of relatively small precipitates.

Role of nitrogen related complexes in the formation of defects in silicon

Defect size and density distributions were obtained as a function of depth in nitrogen doped CZ silicon (N-CZ) following Hi–Lo–Hi and Lo–Hi annealing, using an oxygen precipitate profiler. The defects were also delineated by Wright etching and Nomarski optical microscopy on both cleaved and bevel polished samples. In addition to the enhanced precipitation and absence of voids previously reported for N-CZ Si, an unexpected mode of precipitation has been found near the annealed wafer surface, just above the traditional denuded zone. This oxynitride precipitate is discussed with regard to N-related complex interactions and point defect supersaturations/injection. High resolution transmission electron microscopy revealed that most precipitates have an octahedral shape with two distinct amorphous phases, which reflect a transition from an initial phase containing both N and O to one with primarily O, as verified with Z-contrast TEM and electron energy loss spectroscopy.

Effect of rapid thermal annealing on oxide precipitation behavior in silicon crystal

Oxide precipitation behavior after rapid thermal annealing (RTA) in Ar, N 2 or O 2 ambient was investigated. Lightly boron-, nitrogen- or carbon-doped p-CZ silicon wafers with a diameter of 200 mm ( [ O i ]=11.5–13.9×10 17 atoms/ cm 3 (old ASTM)) were prepared as samples. RTA temperature and cooling rate were changed between 1280 and 1200 °C, and between 70 and 5 °C/s, respectively. From the result of in Ar ambient, it was found that (1) M-like depth profile of precipitate density was observed in the lightly boron-doped wafer, (2) width of precipitate denuded zone (DZ) was decreased in the nitrogen-doped wafer compared with the lightly boron-doped wafer and (3) DZ width in the carbon-doped wafer was comparable to lightly boron-doped wafer. From the calculated result of the depth profile of vacancy (V) and silicon interstitial (I) concentrations, C V and C I, it was clarified that the relationships of thermal equilibrium concentration and the diffusion constant of point defects are to be C V ∗>C I ∗ and D V< D I, respectively, to appear the M-like profile in lightly boron-doped wafer. From the result of the decrease of the DZ width, it was deduced that the diffusion constant of vacancy decreased in the nitrogen-doped wafer. From the result of in lightly boron-doped wafer in N 2 or O 2 ambient, it was found that (1) the precipitate density was higher compared with that in Ar ambient and (2) the precipitate was not observed in O 2 ambient. These results due to the injection of the vacancy or the interstitial silicon during RTA in N 2 or O 2, respectively.

Intrinsic gettering of Czochralski silicon annealed in argon and nitrogen atmosphere

The intrinsic gettering of nitrogen-doped Czochralski (NCZ) and nitrogen-undoped Czochralski (CZ) silicon annealed in argon and nitrogen ambient has been investigated by three-step annealing. It is found that the threshold oxygen concentration for effective precipitation is about 4.8×10 17 cm −3 at 1150°C. No difference of the denuded zone (DZ) width between the NCZ and CZ silicon samples was found when they were annealed in argon ambient. However, a few of small etching pits occurred in the DZ region for both of NCZ and CZ silicon samples. It is suggested that nitrogen could diffuse into the DZ region and form N–O complexes as heterogeneous nuclei, which can enhance oxygen precipitates, when the samples were annealed in nitrogen ambient.

The Realization of Uniform and Reliable Intrinsic Gettering in 200mm p- and p/p- Wafers for a Low Thermal Budget 0.18μm Advanced CMOS Logic Process

Ppolished and P/Pepitaxial wafers with and without an MDZ® (Magic Denuded Zone) heat-treatment have been processed through a low thermal budget 0.18μm advanced CMOS Logic process. Measurements at key stages in the process clearly demonstrate that very little precipitation (below detection limit) occurs in the standard Por P/Pwafers. In contrast, very uniform precipitation with consistent BMD (bulk micro-defect) and PFZ (precipitate-free zones) are observed for wafers that received the prior MDZ® heat-treatment. This was demonstrated by subjecting the wafers to an additional 16 hour 1000°C anneal designed to grow precipitates to a size where they become detectable by the cleave and etch technique. In addition, nickel haze gettering tests clearly demonstrated that reliable gettering of nickel (up to 4x10 cm) could be obtained early in the device process for wafers which received the MDZ® heattreatment without the need for the additional 16 hour 1000°C anneal. However, nickel haze was observed for standard Ppolished and P/Pepitaxial wafers even at the end of the process indicating the complete lack of any intrinsic gettering. Introduction With the move to smaller device geometries and low thermal budget processing, there has been a lot of renewed interest in the intrinsic gettering (IG) capability of silicon wafer substrates. Although P/P+ wafers generally have sufficient amounts of oxygen precipitation through a device process due to the fact that high boron concentrations enhance oxygen precipitation, this is clearly not the case for lightly doped Pand P/Pwafers. For intrinsic gettering to be effective, the density and size of oxygen precipitates in the wafer bulk needs to be greater than some critical value [1]. During wafer cooling, metals such as nickel or copper, which may have been inadvertently introduced during device processing, precipitate at the oxygen precipitates in the wafer bulk since the solubility of these metals decreases with decreasing temperature. In addition to the requirement for decreasing metal solubility with temperature, there is usually sufficient time during conventional furnace ramps to allow the metal to diffuse from the surface to the bulk. This is the so called “relaxation” model of intrinsic gettering which is generally now widely accepted [2]. It is also essential to have a region close to the wafer surface that is essentially free of precipitates (a “denuded” or “precipitatefree” zone) since nearsurface precipitates can cause device leakage problems. The traditional method of achieving this IG structure in Por P/Pwafers has been to anneal the wafers at high temperatures (T>1050°C) for several hours to allow oxygen out-diffusion in the near surface region. This is usually followed by a low temperature (T~650°C) anneal to nucleate precipitates in the wafer bulk followed by growth of these precipitates at high temperatures (T>800°C). Unfortunately, it is no longer possible or cost effective to incorporate these steps into advanced processes because of the need to maintain a low thermal budget to prevent excessive dopant diffusion. For these reasons, several new approaches including nitrogen and carbon doping (with/without epi and with/without high temperature anneals) have been developed to achieve reliable intrinsic gettering in these advanced processes. Nitrogen and carbon have been found to be effective in enhancing oxygen precipitation for a given thermal cycle [3,4,]. Both nitrogen and carbon doping, however, introduce an added complexity into crystal growth since the axial and radial concentrations of both the added impurity as well as the oxygen concentration need to be controlled for reproducible IG performance. A very effective alternative method is to use MDZ® (Magic Denuded Zone) technology [5,6]. Unlike nitrogen and carbon doping, MDZ® is applied at the wafer level and has been demonstrated to produce consistent BMD densities and PFZ depths which are largely independent of initial (Oi), crystal section and of the device process. During the MDZ® process, a vacancy template is created which basically leads to the formation of an ideal IG structure with BMDs >1x10 cm and a PFZ > 50μm during a subsequent device process. Title of Publication (to be inserted by the publisher) In this paper, the BMD and PFZ characteristics of Pand P/Pepi-wafers with and without an MDZ® pre-treatment will be compared at key stages in a low thermal budget 0.18μm advanced CMOS logic process. Oxygen measurements are reported using the “New ASTM” calibration factor (4.9α0; units of ppma)

Effects of Flow Patterns on Endothelial Cell Migration into a Zone of Mechanical Denudation

Vascular endothelial cells (ECs) in vivo are subject to different flow conditions due to the variation in vessel geometry. The aim of this study is to elucidate the effects of different flow conditions on EC monolayer migration into a mechanically denuded zone and their underlying mechanisms. Both laminar and disturbed flows significantly enhanced EC migration. EC migration speed was the fastest under laminar flow, which preferentially promoted directional EC migration from the upstream side of the wounded monolayer. C3 exoenzyme (a Rho inhibitor) inhibited EC migration under static and flow conditions, and markedly reduced the effects of flow on EC migration. These results indicate that flow promotes EC migration through the Rho signaling pathway. Genistein (a tyrosine kinase inhibitor) selectively retarded EC migration under disturbed flow, suggesting that tyrosine phosphorylation may play a role in EC migration under disturbed flow. This study has demonstrated that different flow patterns differentially affect EC monolayer migration into the denuded zone involving multiple mechanisms.

Aeolian susceptibility maps: methodology and applications

AbstractIn this paper we present a new methodology for the study of drifting-snow phenomena at an Alpine site This method emphasizes the accurate determination of local wind directions and the distribution of snow denudation and accumulation zones through the observation, measurement and mapping of aeolian “snowforms” and drifts. The aim is to find out whether the local wind directions on extensive surfaces in mountain areas (of about a few km2) are independent of the main wind intensity and direction, and whether valid erosion and accumulation zones are spatially stable and can be established for dominant winds. The methodology proposed to study the spatial distribution of snow by the wind has been used in the redesign of an old ski slope at La Molina, a resort in the eastern Spanish Pyrenees. Results have been very useful for deciding the design of the slopes. Therefore, we believe that the prediction of spatial snow distribution by wind in mountain areas, without the need for expensive instruments, has a valuable part to play in the management of mountain and ski resorts and roads, and in avalanche forecasting.

Denuded zone formation by conventional and rapid thermal anneals

Oxygen outdiffusion by conventional annealing results in well defined denuded zones and the dissolution of grown-in oxide precipitate nuclei in the region near the surface. During a rapid thermal anneal (RTA) the grown-in oxide precipitate nuclei shrink and due to vacancy outdiffusion during cooling the subsequent growth of the precipitate nuclei is suppressed in the region near the surface. However, potential defects still exist in the region near the surface which can grow during ramping with 1 K min −1 starting from 500°C. A dissolution of grown-in oxide precipitate nuclei in the region near the surface seems only possible by RTA in argon/hydrogen atmosphere. The denuded zone defect density is much lower after RTA than after conventional annealing for oxygen outdiffusion, while the depth profile of the defect density is less steep. The use of the above mentioned conclusions for ‘ramp engineering’ in device processing allows the creation of excellent denuded zones during a device process itself without influencing the device characteristics.

Intramontane basin formation during oblique convergence in the Eastern Desert of Egypt: magmatically versus tectonically induced subsidence

The Neoproterozoic Kareim molasse basin in the Central Eastern Desert occupies an intramontane position and is bound by faults of the crustal-scale Najd Fault System. Basin subsidence and sediment delivery rates were linked with exhumation of adjacent core complexes. Sedimentation dynamics evolved in two steps. (1) Early basin infill was magmatically induced by extraction of magmatic material from the lower crust, which was balanced by downward movement of cold and dense material. Small subsidence rates, high heat flux and sediment delivery from rising diapirs and comagmatic volcanic rocks characterise this stage. (2) Late-stage sedimentation and modification of the basin geometry were controlled by strike-slip deformation and isostatic compensation of the orogen. Subsidence rates increased and coarse clastics were delivered. From distribution of sedimentary facies and structural studies we propose a model for the formation of intramontane basins within obliquely convergent island arc orogens. Minor crustal thickening, but with intense magmatic activity, may characterise these orogens in their early history. Erosion and deposition of sediments within intramontane denudation zones does not require high relief or significant mountain topography when basin formation is largely controlled by uprise of magmatic rocks during plate convergence. Ongoing transcurrent motion in the collisional stage may release in major strike-slip faults that trigger final exhumation of core complexes. Enhanced relief energy and high sediment delivery rates suggest formation of significant mountain topography during this evolutionary stage.

Annealing Behavior of Light Scattering Tomography Defect in the Denuded Zone of Si Wafers

Light scattering tomography defects (LSTDs) have been non-destructively detected in bulk and near the surface of a Si wafer by Brewster angle illumination of infrared light scattering tomography (IR-LST). We investigated the annealing behavior of grown-in LSTDs that exist in a layer of 0 to about 20 µm depth from the wafer surface. Grown-in LSTDs were detected before annealing. Annealing behavior of such grown-in LSTDs was studied by the three-step annealing to form the denuded zone (DZ) of about 40 µm. As a result, the LSTDs mostly remained in the DZ after the three-step annealing. However, the change in the scattering intensity of the grown-in LSTDs was detected. This change suggests that the volume and/or structure was changed by the annealing treatment.

Denuded zone and diffusion length investigation by electron beam induced current technique in intrinsically gettered Czochralski silicon

Electron beam induced current (EBIC) technique is successfully used to characterize intrinsically gettered Czochralski silicon. The impact of three different sequences of thermal treatments, typically used in ultralarge scale integration device manufacturing, on the denuded zone (DZ) formation and oxygen precipitation in the bulk is evaluated. EBIC technique is applied in a nonstandard configuration, where a Schottky diode is evaporated on the wafer cross section, for the direct observation of the DZ and oxygen related defects in the silicon bulk. The reduction of minority carrier diffusion length, due to the formation of recombination centers after oxygen precipitation, is also estimated by EBIC in planar collector geometry. The DZ determination by EBIC technique is in good agreement with surface photovoltage measurements and microscopical inspections after chemical etching.

Influence of welding on structure of Al–Mg–Si matrix composites

The present study deals with the structural characterisation of welds produced in the particulate composite 6061/Al2O3/10p by means of gas tungsten arc welding. Specimens of the composite were welded under various conditions and the structure of the welds obtained was analysed using optical microscopy, electron probe microanalysis, and scanning electron microscopy. It appears that, during welding, a thin particle free (denuded) zone is formed below the upper surface of the weld. The formation of this zone results from a combination of Marangoni flow and arc plasma drag. Furthermore, it was found that, during solidification of the weld metal, particle pushing takes place, which results in redistribution of the particles. This phenomenon is particularly apparent in the vicinity of the fusion boundary. It was also shown that, during welding, Mg2Si precipitates are formed in the interfacial zone between the particle and the matrix. Welding experiments were also carried out with filler wire addition. It was found that only limited mixing occurs in the weld pool between the filler wire material and the composite.a The degree of mixing increases with increasing travel speed and is independent of wire feed rate.

Monitoring Silicon Quality From Diffusion Furnaces Using In-Line Measurements

ABSTRACTCarrier lifetimes provide an excellent indication of the concentration of impurities and defects in semiconducting materials. This paper describes a non-contact technique for measuring generation and recombination lifetimes. This technique, which is incorporated into the KLATencor Quantox system, provides a highly sensitive method for monitoring the formation of defects or incorporation of impurities in silicon wafers during processing. Several applications of these measurements are investigated, such as monitoring the effects of various thermal cycles on the formation of a high-lifetime denuded zone near the wafer surface and monitoring diffusion furnace contamination after a quartz change.

Time-temperature profiles for optimal internal gettering of iron in silicon

It is shown that the residual iron concentration in the denuded zone (DZ) can be substantially decreased by optimizing the cooling profile used in internal gettering. Computer simulations of internal gettering were performed for different DZ and substrate specifications. Linear, exponential and optimized precipitation (OP) cooling profiles were evaluated in terms of the remaining iron concentration in the DZ. Parameters such as cooling rate, time constant and end temperature were varied. The linear profiles exhibited an optimum cooling rate and were not improved by cooling below C. The performance of the exponential cooling profiles was better than that of the linear profiles and improved as the cooling profiles more closely resembled the OP profile. It is shown that the OP profile yielded the best internal gettering results.

The Engineering of Silicon Wafer Material Properties Through Vacancy Concentration Profile Control and the Achievement of Ideal Oxygen Precipitation Behavior

AbstractA new kind of silicon wafer and a new class of materials engineering techniques for silicon wafers is described. This wafer, called the “Magic Denuded Zone” or MDZ wafer, is produced through the manipulation of the vacancy concentration and, in particular, vacancy concentration depth profiles in the wafer prior to the development of oxygen precipitates in subsequent heat treatments. The result is a wafer with ideal oxygen precipitation behavior for use in all types of integrated circuit applications. The methods used to prepare such wafers combine Frenkel pair generation with injection and the use of surface sinks. Simulations of the vacancy profiles produced by these techniques are presented and discussed. It is shown that within the range of vacancy concentration accessible by these techniques (up to ca. 1013 cm−3) the rate and oxygen concentration dependence of oxygen clustering can be substantially modified. Such techniques can be used to precisely engineer unique and desirable oxygen-related defect performance in silicon wafers both in terms of distribution and rate of defect formation. One result of the application of such techniques is an ideally precipitating silicon wafer in which the resulting oxygen precipitate profile (denuded zone depth and bulk density of precipitates) is independent of the concentration of oxygen of the wafer, the details of the crystal growth process used to prepare the wafer and, to a very large extent, the details of thermal cycles used to process the wafer into an electronic device. Optimal, generic and reliable internal gettering performance is achieved in such a wafer

Correlation between the gettering efficiencies and the energies of interfaces in silicon bicrystals

A comparative study of the gettering efficiency of the twin grain boundaries Σ=25, Σ=13, and Σ=9 has been carried out by means of electron-beam-induced current measurements performed on quenched silicon bicrystals precontaminated by Cu or Ni. The extent of the denuded zone appearing on both sides of each interface type has been considered as the ‘‘rating’’ of its gettering efficiency. For both contaminants, the same scaling of the gettering efficiencies of the boundaries has been observed and was found to be in the order Σ=9≪Σ=13&amp;lt;Σ=25. To account for this ranking, we have correlated the gettering efficiency to the excess energy of the grain boundary with respect to the bulk energy, as theoretically calculated. The computational procedures have been performed by means of molecular-dynamics simulations using several potentials. On the basis of the specific disorder affecting the Σ=25 structure upon heat treatment, our calculations provided the same progression for the interfacial energies as that observed experimentally for the gettering efficiencies of the corresponding grain boundaries according to the extents of the appropriate denuded zones. Calculations of the strain fields developed by the three grain boundaries also support this view.

Effects of topical budesonide on epithelial restitution in vivo in guinea pig trachea.

Continuous epithelial shedding and restitution processes may characterise the airways in diseases such as asthma. Epithelial restitution involves several humoral and cellular mechanisms that may potentially be affected by inhaled anti-asthma drugs. The present study examines the effect of a topical steroid on epithelial restitution in vivo in the guinea pig. The airway epithelium was mechanically removed from well defined areas of guinea pig trachea without surgery and without damage to the basement membrane or bleeding. An anti-inflammatory dose of budesonide (1 mg) was administered repeatedly to the tracheal surface by local superfusion 24 hours before, at (0 hours), and 24 hours after the denudation. Migration of epithelial cells, formation of a plasma exudation-derived gel, and appearance of luminal leucocytes were recorded by scanning electron microscopy. Cell proliferation was visualised by bromodeoxyuridine immunohistochemistry and tissue neutrophils and eosinophils by enzyme histochemistry. Immediately after creation of the denuded zone ciliated and secretory cells on its border dedifferentiated, flattened out, and migrated speedily (mean (SE) 2.3 (0.3) micron/min) over the basement membrane. After 48 hours the entire denuded zone (800 microns wide) was covered by a tightly sealed epithelium; at this time increased proliferation was observed in new and old epithelium and subepithelial cells. Budesonide had no detectable effect on epithelial dedifferentiation, migration, sealing, or proliferation. Immediately after denudation and continuously during the migration phase plasma was extravasated creating a fibrinous gel rich in leucocytes, particularly neutrophils, over the denuded area. Budesonide had no effect on either the gel or the leucocyte density. These observations suggest that topical glucocorticoids may not interfere with a fast and efficient restitution of the epithelium in the airways.