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

Abstract

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...

Peculiarity of Electric Properties of Oxygen‐Implanted Silicon at Early Precipitation Stages

“…Such kind of dependence is expected for the ratio of the surface to total atom numbers of the precipitates and might be explained by the charge accumulation within the OP shells. This assumption is in agreement with the recent finding by Kot et al about core–shell OPs composition and structure and leads to the conclusion that charge accumulation localized in the shell of the precipitate due to broken SiO x bonds, whereas the SiO 2 core remains electrically neutral.…”

“…Numerous experimental data on the investigation of the composition and the structure of OPs collected by Vanhellemont [1] show that the OP composition can vary in different samples in wide ranges from SiO 1 to SiO 2 . Recent extensive studies of Kot et al with the help of Fourier-transform infrared spectroscopy (FTIR), [2] energy-dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS), [3] jointly discussed in the previous study, [4] revealed that the composition of the OP is nonuniform: stoichiometric SiO 2 amorphous core is surrounded with the SiO x shell. Based on the core-shell structure of OPs, Vanhellemont [1] proposed a model that explains the variation of an average oxygen content for OPs of different shapes and sizes by the variation of the shell percentage.…”

(Invited) Oxygen in Silicon: End of the Story?

“…Despite the wide knowledge about oxide precipitation, the composition of oxide precipitates SiO x still remained unclear. This was due to the different x values published varying between x = 1 and x = 2 (21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31). Skiff et al investigated plate-like precipitates by electron energy loss spectroscopy (EELS) in the near-edge and ionization edge range already in 1986 (21).…”

Characterization of Nanometer‐Sized Oxygen Precipitates in Highly B‐Doped Czochralski Silicon

“…This is, however, not the case for the EELS plasmon method. [8] In this method, the composition of the precipitates is determined from the deconvolution of the low loss EEL spectra into reference spectra of Si, SiO, and SiO 2 . For more detailed information, the reader is referred to Ref.…”

“…It is also impossible to study the morphology of oxygen precipitates by FTIR which is easily possible in moderately doped wafers. [7,8] In order to overcome the problems appearing during investigation of highly doped wafers one uses advanced investigation methods and etching solutions.…”