The Role of Oxygen on Defects Formation during Advanced Silicon Process Technologies
Authors: Crozelon Jérémi , Abbadie Alexandra , Melhem Kassem , Ouzaid Yanis , Frascaroli Jacopo , Takala Adonis Steve , Bluet Jean-Marie , Bremond Georges 
Published: August 2024

Impact of oxygen in silicon substrates and the formation of oxide precipitates have been widely studied in the past because of the detrimental electrical recombination and its effect on yield [1,2]. The origin of interstitial oxygen (Oi) is not only limited to the substrate but also comes from the nature of the oxide that may be deposited on it [3]. Interstitial oxygen plays a direct role in the formation of bulk microdefects (BMDs) resulting from oxygen precipitation during low-temperature Front-End anneals at 650-800°C [4,5]. The latter are of interest for the mechanical robustness of substrates, contributing to the pinning of slip lines (SL) and for the reliability of devices thanks to an internal gettering effect, but can also be harmful by emitting dislocations when they are too numerous (> 1 x 1010 BMD.cm-3) [5, 8].

In this paper, we have reviewed the different impacts of interstitial oxygen on silicon substrates during thermal annealing through 3 phenomena: (i) the influence of Oi on the reduction of the slip lines by the pinning effect, (ii) the formation of BMDs induced by Oi and their interactions with dopants during implantation processes, (iii) the BMDs limited formation in the specific case of high resistivity (HR) silicon substrates. We focused on standard and high resistivity silicon substrates obtained by Czochralski (CZ) method, used in advanced technologies for various applications (digital, bipolar, power, photonic, etc.).

To highlight the impact of interstitial oxygen, firstly on the mechanical properties of substrates, we studied the same p-type silicon substrates with two ranges of Oi concentration (5.33 x 1017 and 7.23 x 1017 at.cm-3), both annealed by furnace oxidation below 1000°C and N2 annealing above 1000°C. Figure 1 clearly shows the effect of a minor difference in Oi concentration on the number of slip lines detected by Pattern Wafer Geometry (PWG) measurements (Figure 2). Despite extrinsic process parameters to consider in the occurrence of slip lines, these results demonstrate the enhancement of slip line pinning by interstitial oxygen.

Bulk microdefects in silicon are known to interact with dopants [6]. To investigate this point, we compared the BMD occurrence in non-implanted and antimony-implanted (2 x 1015 at.cm-2) silicon substrates using micro-photoluminescence imaging. These substrates contain relatively high Oi concentrations (up to 6.7 x 1017 at.cm-3) and have been subjected to oxidation and rapid thermal annealing (RTA) above 900°C. After adjusting for background contrast in the implanted and non-implanted regions, Figure 3 shows different trends in BMD density evolution as a function of the probed depth. We assume that a mechanism based on a mechanical stress field induced by the position of the Sb-implanted atoms in the lattice limits the nucleation of oxide precipitates [7]. However, further characterization methods are required to confirm the influence of dopants on the BMD density.

Finally, high resistivity silicon substrates are being considered to significantly improve devices performance, particularly in high frequency and photonics applications [8, 9]. However, the understanding of BMD formation is poorly documented in the literature. These CZ-Si substrates are characterized by low oxygen content (< 3 x 1017 at.cm-3) and low boron dopant concentration (< 1 x 1014 at.cm-3). At such low values, the expected oxygen precipitation is very different from that of standard p-type silicon [8, 10]. We investigated the effect of these parameters on BMD formation through precipitation thermal treatments (N2 + O2 anneal > 1000°C). Figure 4 illustrates the important difference in BMD formation depending on the substrate characteristics (standard resistivity high-Oi versus high resistivity low-Oi silicon) after the same thermal treatment. BMD defects were generated in large quantities in standard silicon (3 x 109 BMD.cm-3), whereas no BMDs were observed in HR silicon.

In summary, we have demonstrated the impact of interstitial oxygen (coming from substrates and processes) on defect generation, particularly BMD, in silicon technology. In controlled proportions, they play an important role in the proper functioning of devices and very often result from the fine tuning between substrate characteristics and process conditions.

[1] Jun Fujise et al 2018 JJAP. 57 035501

[2] Zijing Wang et al 2022 APE 15 071004

[3] G. Kissinger et al 2019 ECS J3ST. 8 N79

[4] Maria Porrini et al 2018 ECS Trans. 86 7

[5] Hirofumi Shimizu et al 1985 JJAP. 24 815

[6] Hideki Tsuya et al 1983 JJAP. 22 L1

[7] Oleksandr Oberemok et al 2014 PSS. 11 163439

[8] Isabelle Bertrand et al 2022 ECS Trans. 31 108

[9] Jarosław Judek et al 2017 JEM. 46 5589-5592

[10] Kaoru Kajiwara et al 2019 PSS. 17 216

Figure 1