Search

In low-dose separation by implanted oxygen (SIMOX) the concentration of implanted oxygen is less than the SiO 2 stoichiometry even at its peak depth. The fabrication process, therefore, consists of oxygen precipitation, growth, and coalescence of the precipitates during a high-temperature anneal. It has been believed that there is a process window of 4 ± 0.5 x 10 17 /cm 2 for the oxygen dose to form a continuous buried oxide in low-dose SIMOX. However, it may be possible to extend the dose window by applying the proper annealing sequence for each dose. In this study, we succeeded in extending the dose window to 2-6 x 10 17 /cm 2 by modifying the temperature ramp rate depending on the dose for the high-temperature anneal, based on thermodynamical considerations.

Nitrogen introduced into a silicon substrate by the Czochralski method brought about an increase in the density of Si-SiO2 interface traps and in the density of electrically active defects in Si by an enhanced nucleation of oxygen precipitates. Rapid thermal annealing above 800degC led to decomposition of NxOy clusters in the vicinity of the Si-SiO2 interface and to an increase of the width of the denuded zone

The effect of the V-O complexes on oxygen precipitation in neutron-irradiated silicon has been investigated at low temperature in this paper. It is found that oxygen precipitation has been enhanced in neutron-irradiated silicon by prolonged annealing at 750/spl deg/C, which is based on denser precipitate nuclei. Furthermore, by Fourier transform infrared spectrometry (FTIR) the VO complexes can transfer into VO/sub 2/ and VO/sub 3/ complexes during low temperature annealing. Based on these facts, it is reasonably deduced that in neutron irradiated silicon the VO complexes can become the pre-nuclei of oxygen precipitates at low temperature, and therefore enhance oxygen precipitation.

Stress-induced oxygen precipitation effects in silicon were investigated after annealing as-grown Cz Si samples at up to 1620 K under hydrostatic pressure up to 1.35 × 10 9 Pa. Depending on the treatment conditions, uniform stress can considerably influence oxygen precipitation. An explanation of stress-stimulated oxygen precipitation is proposed.

Gettering efficiencies and stabilities of internal gettering sites for metallic impurities in high and low carbon doped silicon have been compared with ramped and standard two-step pre-annealing conditions. This study was intended to compare two proposed techniques to shorten the long low temperature nucleation step in the standard Hi-Lo-Hi internal gettering site formation treatment. Specifically, we compare the affect of carbon and a ramped annealing sequence on oxygen precipitate formation and gettering effectiveness. Our results show both techniques accelerate oxygen precipitation, however, only the low carbon ramped materials produced efficient and stable gettering sites. The high carbon materials did not with either annealing treatment. This disparity in performance is due to a difference in the oxygen precipitate’s strain field. The precipitates in the low carbon material possessed a high strain field with strain-induced defects while in the high carbon material they were strain-free with no defects. These results indicate the strain stabilizes the gettered impurity such that the gettering rate is increased and stability is enhanced.

Using Czochralski‐grown silicon crystals with carbon concentrations from 1014 to 1016 cm−3, we studied the influence of oxygen precipitates on the mechanical strength of silicon crystals. Reducing carbon concentration from 1016 to 1014 cm−3 suppressed oxygen precipitation and thus, improved the strength. Carbon concentration reduction from 1015 to 1014 cm−3 did not, however, decrease oxygen precipitation as dramatically as reduction from 1016 to 1015 cm−3. Carbon impurities below 1014 cm−3 no longer affect oxygen precipitation. Therefore, we conclude that reducing carbon concentration below 1014 cm−3 no longer improves the mechanical strength of silicon crystals.

For IC fabrications using CZ Si, intrinsic gettering utilizing oxygen precipitation has been extensively studied in the past, with the main efforts concentrated on the engineering and scientific aspects of the creation of gettering sites. The present review, however, will focus on recent progresses on the modeling of processes and mechanisms of the gettering of metallic impurities from the device active regions to the created gettering regions, together with the electrical activity of impurity precipitates.

Oxygen precipitation in Czochralski silicon is still an issue in various device technologies. On the one hand it is exploited for internal gettering of metallic impurities by oxygen precipitates and on the other hand it is undesired because oxygen precipitates are known to degrade the lifetime of minority carriers. At the end, it depends on the application of the silicon material how precipitation of interstitial oxygen is controlled. The reduced thermal budgets due to continuous scaling of features sizes in high end device technologies lead to the development of faster and faster anneal processes. The earlier device technologies were dominated by conventional annealing processes. Today rapid thermal processes working on the second scale are common steps in microelectronic processing. Recent developments utilize already thermal processes on the millisecond scale as e. g. flash and laser anneals. All these different time scales influence the generation of intrinsic point defects and thus also the kinetics of oxygen precipitation in a different way. Rapid thermal annealing (RTA) is a widely used thermal pretreatment to create an internally gettering bulk defect zone and a defect denuded zone below the surface. This is possible because the precipitation of interstitial oxygen strongly depends on the supersaturation of intrinsic point defects. During RTA vacancies supersaturate facilitating the formation of VmOn complexes which are the initial stages of oxygen precipitation. However, the strength of the effect depends on the temperature and cooling rate of the RTA pre-treatment. Flash lamp annealing is used first of all for the creation of shallow dopant profiles in high end electronic device technologies. The surface of a silicon wafer can be heated with this technique to temperatures up to the melting point within a few milliseconds. With the help of a thermal model we can simulate the temperature profiles. We combined this model with a second model describing the generation and annihilation of intrinsic point defects. The results of modeling help to understand the experimental results of oxygen precipitation. After 3 ms of annealing a defect denuded zone below the front surface is generated while after 20 ms annealing oxygen precipitation is suppressed in the wafer. Flash lamp annealing leads to steep temperature profiles in the wafers causing stress. Silicon wafers with etched, ground, and sawed surfaces were subjected to flash lamp annealing for 20 ms. Such wafers contain different densities of pre-existing dislocations which propagate into the wafer during flash lamp annealing up to a certain depth which is different on the front and back sides. Plastic deformation was not observed if no pre-existing dislocations were present in the wafer before flash lamp annealing. The elastic and plastic deformation was simulated by a mechanical model. In summary, the difference between thermal processing on the second and on the millisecond scales is based on the temperature profiles generated by the different types of processing. These profiles influence the shrinking of grown-in oxide precipitate nuclei and the generation, diffusion, and annihilation of intrinsic point defects and thus the oxygen precipitation during further processing.

High-spatial resolution Fourier transform infrared spectroscopy permitted us to study the effects of incident light polarization on the absorption band related to aggregates of SiO2 disk-shaped precipitates present in annealed (100) Czochralski silicon samples. This is the first report documenting the strong dependence of such a band intensity on light polarization. Experimental results were compared with the simulation obtained using the effective medium theory. From this comparison we deduce that the precipitates only lie on the planes among {100} which are parallel to the wafer surface. This result can be related to the difference between the 〈100〉 direction and those crystallographically equivalent, introduced by the ingot growth process.

A study of the optical response in the infrared (IR) spectral region of oxygen precipitates in silicon is performed at liquid helium temperature. The measurements concern a set of samples with the same density of precipitates of different dimensions and a second set of samples with different densities of precipitates of equal dimension. Two main shapes of precipitates are detected in both sets, with different behavior in terms of volume fractions occupied by each of them in the sample as a function of the thermal treatments performed. (C) 2000 Elsevier Science S.A. All rights reserved.

A suitable choice of one sample among several silicon wafers subjected to two-step thermal treatments for oxygen precipitation permits to reveal a complete series of infrared absorption peaks related to the precipitates formed in the crystal. Structured spectra are observed at 7 K and can be interpreted as due to SiO2 precipitates with different shapes and concentrations. © 1999 American Institute of Physics.

We have found by resistivity measurements and deep‐level transient spectroscopy that four kinds of oxygen‐related shallow donors, OD1–OD4, successively appear around 500 °C in the time region 10–106 min and carbon greatly affects their generation behavior in Czochralski silicon. The formation of OD2 and OD3 donors was enhanced by the presence of carbon, while that of OD1 and OD4 donors was retarded. The OD1 donor is identified as the so‐called thermal donor that consists of several kinds of double donors observed so far by infrared studies. The OD2 donor is a new kind of donor discovered recently by us. OD3 and OD4 donors, which were formed by very prolonged annealing around 500 °C, are suggested to have correlations with so‐called new donors normally generated above 600 °C. The origins of these oxygen‐related donors are discussed in relation to oxygen precipitation.

A critical analysis of the use of infrared spectroscopy to obtain a quantitative evaluation of precipitated oxygen in silicon is presented. Precipitates were detected and studied either indirectly or directly. It is shown that, in both cases, there are some limitations in the reliability of the results, so that a quantitative evaluation of the amount of precipitated oxygen is rarely achievable.

The influence of metallic contaminants (Ni, Mo) on the oxygen precipitation process during high temperature (HT) treatment under hydrostatic pressure (HP) was studied. No significant influence of Ni and Mo contaminants on the oxygen precipitation process at 1400 K was observed. Changes of interstitial oxygen concentrations c0 after HP-HT treatment for contaminated and for non-contaminated samples were less than 10%. The metallic contaminants (ni, Mo) cause mostly generation of large strain fields in the matrix probably related to metallic precipitates as evidenced by x-ray topography.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Oxygen precipitation after thermal annealing is generally controlled by interstitial oxygen atoms and other unknown defects. This often results in wafers with an inhomogeneous distribution of oxygen precipitates, even though they have a homogeneous distribution of interstitial oxygen atoms.

Precipitation of oxygen in Czochralski grown silicon, Cz-Si, at higher temperatures is concomitant with stress [1,2]. This follows mostly from the difference in volume between the clustered (precipitated) oxygen atoms and that of the Si atoms originally present in the same region of the lattice. Stress-related effects in Cz-Si are present even at the earliest stages of clustering, that is at the “thermal donor, TD, temperature range” (TDs exert a compressive stress on the surrounding Si lattice [3]). The same takes place in the case of new donors, NDs, and of nucleation centres for oxygen precipitation, NCs, created at about 1000K.

The demands of device producers for very low impurity content in Si, gives rise to a necessity to pay attention to the impurity concentration in the raw material. The analysis of impurity distribution in quartz of various genotypes shows that the most chemically pure quartz is the quartz from the veins formed as a result of hydrothermal processes and metamorphic treatments.

A review is presented of the recent advances in the study of oxygen precipitation and of the main properties of oxide precipitates in silicon. After a general overview of the system "oxygen in silicon,"the thermodynamics and the kinetics of the precipitate formation are treated in detail, with major emphasis on the phenomenology; subsequently, the most important techniques for the characterization of the precipitates are illustrated together with the most interesting and recent results. Finally, the possible influence of oxygen precipitation on technological applications is stressed, with particular attention to recent results regarding device yield. Actually, the essential novelty of this review rests on the attempt to give an extended picture of what has been recently clarified by means of highly sophisticated diagnostic methods and of the influence of precipitation on the properties of semiconductor devices. © 1995 American Institute of Physics.

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.

The low-energy optical response of few-nanometer-thick SiO2 films is reported and compared with theoretical predictions. The limit where the surface effects become fundamental in determining the optical properties of the film is discussed and very good agreement is found between experimental and theoretical results. © 1994 The American Physical Society.

Publisher Summary The chapter presents a study on some quantitative aspects of mechanisms of oxygen precipitation. The SiO2 precipitate formation process includes two aspects, that of nucleation and that of growth. The first systematic effort to model the SiO2 precipitate nucleation process reports that, in some Czochralski (CZ) crystals, the process may be described on a homogeneous nucleation basis. However, the complexities associated with Oi precipitation in apparently normal CZ Si materials are seemingly beyond the description of the classical nucleation theory just on a homogeneous or heterogeneous basis. A large number of complexities have been observed in association with the creation of the defect-free zone (DFZ) and the wafer bulk intrinsic gettering (IG) gettering sites, all directly related to the SiO2 precipitate nucleation and growth behaviors. A brief summary of the responsible experimental factors and the associated complexities are presented in the chapter. The chapter presents a discussion on the factors and their effects on both the SiO2 precipitate nucleation and growth aspects, thereby, explaining some of the outstanding features mentioned. In most experimental results, the role of precipitate nucleation is not distinguished from that of precipitate growth.

Publisher Summary The chapter presents a study on intrinsic/internal gettering. Contamination, particularly with transition metals, during thermal processing initiates surface microdefects, while interior microdefects in Czochralski (CZ) silicon wafers are caused exclusively by oxygen precipitation, which depends on various factors, are discussed in this chapter. The chapter presents brief reviews on the surface and interior microdefects in terms of their origin and behavior, because it might be important to learn them for the understanding of the gettering phenomenon, which is discussed in this chapter. Contamination, particularly with transitionmetals, initiates surface microdefects. On the other hand, interior microdefects are caused exclusively by oxygen precipitation, which depends on various factors as discussed in this chapter. A denuded zone (DZ) is discussed as a wafer surface zone that is free of interior defects generated by oxygen precipitation. The elimination of the effects of defects and impurities can be achieved through the following three steps: (1) suppression of the sources that may generate defects, (2) annihilation of existing defects, and (3) removal of impurities from the device regions in a silicon wafer. The process that accomplishes (1) and (2), particularly (3) in a narrow sense, is generally referred to as gettering. The purpose of gettering is primarily to create a defect-free surface region in a silicon wafer used for electronic device fabrication. The gettering process involves the following three steps: (1) impurities are removed from the surface of a wafer, (2) they then diffuse through the silicon lattice into certain gettering sinks at a position away from the device region, and (3) they are gettered or captured by the gettering sinks. The gettering technology is one of the keys in the scheme of defect engineering.

Publisher Summary The chapter presents a discussion on the effects of oxygen on mechanical properties. This chapter presents reviews of both the macroscopic and microscopic aspects of oxygen effects on the mechanical behavior of silicon (Si). Effects of other light element impurities, such as nitrogen and carbon, are also mentioned. The chapter presents discussion on some basic aspect of plastic deformation of a crystal and also presents a brief description on the nature of dislocations in Si. The influence of oxygen atoms that dispersed within a Si crystal on the dislocation motion is discussed. Segregation of oxygen on dislocations and the resulting effect on the dynamic activity of dislocations are also discussed. The chapter also discusses dislocation generation in Si as affected by oxygen. The effect of oxygen on macroscopic mechanical properties of Si is described. A description of the macroscopically observed mechanical behavior of Si crystals in terms of dislocation processes is also presented. Softening of Si caused by oxygen precipitation is described and the effects of nitrogen and carbon on the mechanical strength of Si are also discussed.

The kinetics of oxygen precipitation at 900 and 1050°C was studied in Czochralski-grown silicon single crystals doped to various levels with zirconium. It is established that zirconium, while not participating in the nucleation of oxygen precipitates, decreases the concentration of interstitial oxygen in the crystals.

In this paper we report the study of early stages of oxygen precipitation in commercial Czochralski silicon as-received wafers and in wafers treated at 1100-degrees for 80 min. The high spatial resolution infrared technique used is able to detect platelet shaped SiO2 precipitates, even in low concentrations. We detected a strong polarization dependence of the precipitate related infrared absorption band performing measurements with linearly polarized light. From these results a preferred orientation of a precipitate aggregation was deduced

The effect of vacancies introduced by rapid thermal annealing (RTA) on the oxygen precipitation in germanium-doped Czochralski (GCZ) silicon has been investigated. GCZ silicon is annealed at 650–1050 °C to facilitate the precipitation of oxygen. It is observed that the oxygen precipitation in silicon is enhanced by both the vacancies introduced during RTA pretreatment and the doping of germanium. Especially, we find that the enhancement effect of vacancies on the precipitation of oxygen is larger than that of germanium atoms. In contrast to non-RTA pretreatments, RTA pretreatments lead to less significant oxygen precipitation in GCZ silicon than in conventional Czochralski (CZ) silicon at temperatures ranging from 850 to 950 °C. The mechanism for the interaction between vacancies and germanium atoms in CZ silicon is elucidated.

Generic and interaction aspects of oxygen precipitation, related defect formation and denudation in Cz-Si wafers are presented. Bulk defect profiles and homogenization control are shown to be achievable by proper design of post-growth annealing.Gettering-related phenomena are discussed including stacking fault-rich bulk defect structures and peculiarities in different epitaxy systems.

We investigated phenomena of oxygen precipitation in silicon single crystals by two kinds of thermal treatment, supposing a CMOS fabrication process. The one consisted of the first annealing at 1123K for 4 hrs and the second annealing at 1423K for 16 hrs. The other one consisted of the annealing at 1273K for 4 hrs and the second annealing at 1423K for 13 hrs. In the results, a single-step preannealing at 723K for 2 hrs was effective for the oxygen precipitation by the former process and nonuniform distribution profiles along crystal growth axis were well improved, however, insufficiently improved against the latter process. We considered a two-step preannealing process consisting of the first annealing at 723K for 2 hrs and the second annealing at 923K for 2 hrs. This new process was effective for the oxygen precipitation by the latter process. Especially, we could obtain uniform distribution profiles of oxygen precipitation along a crystal growth axis.

High spatial resolution Fourier transform absorption measurements were performed with polarized light on oxygen precipitates grown in silicon samples briefly annealed. We demonstrate that the wave-number position and intensity of the 1230-cm-1 absorption band, directly related to the precipitates, give information regarding stoichiometry of the oxide constituting such precipitates and their density. In particular, the precipitates in our samples are made of amorphous suboxides, mainly SiO1.8, with 5 ppm local concentration. Moreover, our conclusions give evidence that disk-shaped precipitates in silicon have the same optical properties of thermal oxide films with comparable thickness grown on silicon. © 1992 The American Physical Society.

Oxygen content in the bulk of Czochralski silicon was analyzed by using micro‐Fourier transform infrared spectroscopy in a transversal wafer cross‐section configuration. This technique locally distinguishes between interstitial oxygen and oxygen precipitates in wafers used as substrates for epitaxial layer growth. Systematic measurements performed in the 5000–700 cm−1 wavenumber range clearly indicate the presence of oxygen microprecipitates in the bulk of the processed silicon wafers. Quantitative determination of oxygen precipitate density is reported and compared with the measured interstitial oxygen concentration.

Effects of iron and copper impurities on the amount of precipitated oxygen and the oxide precipitate and stacking fault densities in Czochralski-grown silicon have been studied under varying thermal anneals. Silicon wafers were intentionally contaminated with iron or copper and subsequently subjected to different two-step heat treatments to induce oxygen precipitation. The iron contamination level was 2 × 10exp13cm-3 and copper contamination level 6 × 10exp13cm-3. Experiments did not show that iron contamination would have any effect on the amount of precipitated oxygen or the defect densities. Copper contamination tests showed some indication of enhanced oxygen precipitation.

Czochralski (CZ) silicon wafers were firstly subjected to a variety of ramping annealing from low temperatures to 750℃, and then subjected to a prolonged anneal at 750℃ for up to 64 h. It was revealed that the prior ramping anneal from low temperature lead to strong enhancement of oxygen precipitation in the subsequent annealing, and the lower the starting temperature the stronger the enhancement. It is considered that at low temperatures (450—650℃) the diffusion of oxygen was greatly enhanced and therefore the nucleation of oxygen precipitation was facilitated. Moreover, the slow ramping rate could also increase the stability as well as facilitate the growth of the oxygen precipitate nuclei formed at low temperature. A novel internal gettering (IG) process based on ramping anneal from low temperature has been developed, which can reduce the annealing time and therefore the thermal budget. However, the ramping anneal from low temperature is not available for the application of magic denude zone (MDZ) process.