Development of a Storage Getter Test for Cu Contaminations in Silicon Wafers Based on ToF-SIMS Measurements

A model is proposed describing quantitatively the temperature dependent gettering of Cu atoms in p-type Si wafers by taking into account the densities and the binding energies of all types of occupying sites, including the gettering ones. Binding energy in this context is defined as the decrease of the formation energy from the reference energy of the Cu atom when it is located at the T-site through which Cu atoms wander through the silicon lattice. By using a statistical approach, the model allows to predict the thermal equilibrium concentration of Cu atoms in each part of a wafer structure. The calculated results show good agreement with reported experimental observations. This model can also be applied to calculate thermal equilibrium concentrations of any contaminant. Gettering techniques are becoming more important for Si based VLSI manufacturing processes as the device feature size further shrinks.1 Heavily B doped Si substrates with a low doped epitaxial Si layer are one of the most promising solutions for the multi-chipmodule. Their high gettering capacity even when the chip is reduced to a thickness of about 30 μm has been experimentally evaluated by using thinned epitaxial wafers intentionally contaminated with Cu followed by thermal anneals simulating process steps.2 Meanwhile, Cu is the most important element to develop a gettering technique for as it is widely used for interconnection inside Si device chips and at the same time it can be very harmful when it is present in the junction areas. Cu is also a very fast diffuser in Si and is mobile even at room temperature, see e.g. Ref. 3 and references therein. Among the transition metals, Cu is the only one with a strong segregation at the Si surface after a drive-in from the surface to the bulk of the wafer. This segregation at the surface starts immediately after the surface has been cleaned by hydrochloric acid 4 and occurs even at room temperature during storage of the wafer for a longer time. Due to that, the stability and diffusion behavior of Cu in Si have been investigated extensively on the atomic scale.5-7 These approaches, however, are limited to the bulk and do not explain the Cu behavior near and at the Si surface.In the present paper, a statistical method is proposed to describe quantitatively the temperature dependent behavior of Cu atoms in p-type Si on the atomistic scale. In this model, the densities and the binding energies with Cu of all types of gettering sites present in the wafer are taken into account, including also Cu gettering at the Si surface. The application of the model is illustrated with an analysis of Cu gettering by the p + or p ++ substrate in p − epitaxial wafers as a function of the substrate thickness and the temperature and comparison with results of published gettering experiments. Theoretical Background and Proposed ModelAll gettering techniques are based on atomistic phenomena since the individual metal atoms that are diffusing through metastable sites are captured by stable gettering sites in the wafer. There...

Section: Comparison With Published Experimental Datasupporting

confidence: 82%

“…Ref. 3 and references therein. Among the transition metals, Cu is the only one with a strong segregation at the Si surface after a drive-in from the surface to the bulk of the wafer.…”

mentioning

confidence: 99%

A Statistical Model Describing Temperature Dependent Gettering of Cu in p-Type Si

Kamiyama

Sueoka

Vanhellemont

2015

“…[2][3][4] It was also demonstrated that metallic impurities can be effectively trapped at oxygen precipitates in the process of gettering. [5][6][7][8][9] All these features of the oxygen precipitates require the control of precipitation in the production process of silicon devices. However, this cannot be optimally executed if the features of oxygen precipitates like their composition are not fully known.…”

mentioning

confidence: 99%

Current Stage of the Investigation of the Composition of Oxygen Precipitates in Czochralski Silicon Wafers

Kot

Kissinger

Schubert

et al. 2017

Self Cite

In this work, we look on the current stage of the investigation of the composition of oxygen precipitates obtained with the help of different techniques. Moreover, we present our recent and new investigation of the composition of oxygen precipitates carried out by means of energy dispersive X-ray spectroscopy, electron energy loss spectroscopy, and Fourier transform infrared spectroscopy. The FTIR spectra measured at liquid helium temperature are compared with the spectra simulated on the basis of experimental results obtained by scanning transmission electron microscopy. Oxygen precipitates formed in Czochralski (CZ) silicon wafers in consequence of the thermal treatment were investigated since many decades (see e.g. Ref. 1). The main reason why so much effort was directed toward these defects was the impact which they have on integrated circuits and the properties of the silicon wafer itself. Oxygen precipitates can increase the resistivity of CZ silicon, change the wafer strength and cause warpage of the wafers. [2][3][4] It was also demonstrated that metallic impurities can be effectively trapped at oxygen precipitates in the process of gettering. [5][6][7][8][9] All these features of the oxygen precipitates require the control of precipitation in the production process of silicon devices. However, this cannot be optimally executed if the features of oxygen precipitates like their composition are not fully known. In spite of the wide knowledge about oxygen precipitation, the composition of oxygen precipitates SiO x still remains under ongoing discussion. This is due to the different x values varying from x = 1 to x = 2 which can be found in the literature. [10][11][12][13][14][15][16][17][18][19][20] In 1986, Skiff et al. investigated plate-like precipitates by electron energy loss spectroscopy (EELS) in the near-edge and ionization edge range. 10 The composition which they found was SiO 0.95 . At the beginning of the 90ies, Borghesi et al. modeled Fourier transform infrared spectroscopy (FTIR) spectra by an effective medium approach and concluded that the absorption band of precipitates at 1230 cm −1 can be well reproduced if SiO 1.8 is used.11 However, in 1995 Vanhellemont investigated the growth kinetics of oxygen precipitates based on the solubility and diffusivity of oxygen in silicon using precipitate sizes determined by transmission electron microscopy (TEM). He demonstrated that the precipitated phase is closer to SiO than to SiO 2 .12 The later works, exploiting again FTIR spectroscopy and effective medium theory for the determination of the composition of the oxygen precipitates and carried out by De Gryse et al., confirmed the thesis of Vanhellemont. In the beginning the authors obtained SiO x with x = 1.1-1.2 but in their more recent work they modified the algorithm and concluded that the precipitated phase behaves optically as a mixture of amorphous silicon and amorphous SiO 2 .13,14 Meduňa et al. investigated the composition of oxygen precipitates in silicon wafers characterized by different th...

“…This ToF-SIMS 7 day storage Cu getter test is described in detail in Ref. 26. The contamination level was in the range 4 × 10 12 cm −2 to 1.5 × 10 13 cm −2 .…”

Section: Methodsmentioning

confidence: 99%

Editors’ Choice—Precipitation of Suboxides in Silicon, their Role in Gettering of Copper Impurities and Carrier Recombination

Kissinger¹,

Kot²,

Huber³

et al. 2020

Self Cite

This paper describes a theoretical investigation of the phase composition of oxide precipitates and the corresponding emission of self-interstitials at the minimum of the free energy and their evolution with increasing number of oxygen atoms in the precipitates. The results can explain the compositional evolution of oxide precipitates and the role of self-interstitials therein. The formation of suboxides at the edges of SiO2 precipitates after reaching a critical size can explain several phenomena like gettering of Cu by segregation to the suboxide region and lifetime reduction by recombination of minority carriers in the suboxide. It provides an alternative explanation, based on minimized free energy, to the theory of strained and unstrained plates. A second emphasis was payed to the evolution of the morphology of oxide precipitates. Based on the comparison with results from scanning transmission electron microscopy the sequence of morphology evolution of oxide precipitates was deduced. It turned out that it is opposite to the sequence assumed until now.