(Invited) Oxygen in Silicon: End of the Story?
Authors: Kissinger Gudrun , Kot Dawid , Schubert Markus Andreas , Dabrowski Jaroslaw , Sattler Andreas , Mueller Timo 
Published: February 2020

With the introduction of the Czochralski method for growing of silicon single crystals oxygen in silicon became an issue with positive and negative impact on silicon devices. On the one hand the oxygen strengthens the wafers against slip dislocation formation, on the other hand precipitating oxygen in the device active area can degrade the device performance. However, oxygen precipitates in the bulk are beneficial because they act as gettering sinks for metallic impurities and thus can improve the device performance. Therefore, oxygen is a major issue in silicon defect engineering.

Extensive research on oxygen precipitation started in the seventies of the 20th century and it is still ongoing because new tools become available which offer new possibilities of characterization, higher resolution and lower detection limits. In the field of modeling, the tremendous advances of computer technique and software during the last decades made it possible for a much broader community to run larger models and to make predictions being much more sophisticated.

The challenges of defect engineering in silicon device technology changed over the years. In the eighties, two or three step heat treatments were applied to out-diffuse the interstitial oxygen from the device active area followed by nucleation and growth of oxygen precipitates. This procedure is very time consuming. In the nineties, a new RTA based method was discovered. Vacancy profiles, which controlled the spatial distribution of oxygen precipitation in the wafers, were generated by high temperature RTA treatment. During this method, the oxygen does not diffuse out. Because intrinsic point defects are very fast diffusors, a good adjustment to the following device process has to be made.

Today, one of the major requirements of high end silicon device technology is void-free silicon because with ongoing decreasing feature size voids became a major yield decreasing problem. There are several solutions to this issue like the growth of void-free silicon crystals and void dissolution in silicon wafers by heat treatment at very high temperature. Both methods are strongly connected with oxygen precipitation. Growth of nearly void-free silicon often leads to radial inhomogeneities of the concentrations of intrinsic point defects [1, 2]. The challenge of defect engineering is to create a radially homogeneous concentration of oxygen precipitates.

The ongoing increase of wafer diameter imposes additional problems to oxygen precipitation. If the density of oxide precipitates becomes too high, overlay problems in mask alignment occur [3]. This requires new adjustments of oxygen precipitation. The low feature size in addition to the large wafer diameter asks for low thermal budget processing. A new problem arises because the oxygen precipitates need a certain surface and density to be able to getter enough metallic impurities.

Examples from our own recently published results about ab initio calculation for understanding of the initial stages of oxygen precipitation [4], EELS investigation of the stoichiometry of oxygen precipitates [5], the gettering mechanism of Cu at oxygen precipitates [6], and N-doping for the homogeneous oxygen precipitation during high temperature annealing in wafers optimized with respect to voids [1, 2] will be presented.

In summary, it can be said that oxygen in silicon remains an ongoing issue. Control of oxygen precipitation becomes more and more demanding for high end device technologies. Oxygen precipitation is not yet fully understood but the current developments of diagnostic methods allow new insights.

[1] G. Kissinger, G. Raming, R. Wahlich, T. Müller, 300 mm Czochralski silicon wafers optimized with respect to voids with laterally homogeneous oxygen precipitation, Physica B 407, 2993 (2012).

[2] G. Kissinger, G. Raming, R. Wahlich, T. Müller, Nitrogen doped 300mm Czochralski silicon wafers optimized with respect to voids with laterally homogeneous internal getter capabilities, Mat. Sci. Forum 725, 221 (2012).

[3] K. Izunome, Advanced silicon wafers for leading-edge semiconductor devices, Proceedings of the 6th Int. Symposium on Advanced Science and Technology of Silicon Materials (JSPS Symposium), Nov. 19-23, 2012, Kona, Hawaii, USA, pp. 9-13.

[4] G. Kissinger, J. Dabrowski, T. Sinno, Y. Yang, D. Kot, A. Sattler, Ab initio calculations and rate equation simulations for vacancy and vacancy-oxygen clustering in silicon, J. Cryst. Growth 468, 424 (2017).

[5] G. Kissinger, M. A. Schubert, D. Kot, T. Grabolla, Investigation of the composition of the Si/SiO2 interface in oxide precipitates and oxide layers on silicon by STEM/EELS, ECS J. of Solid State Sci. and Technol. 6, N54 (2017).

[6] G. Kissinger, D. Kot, M. Klingsporn, M. A. Schubert, A. Sattler, T. Müller, Investigation of the copper gettering mechanism of oxide precipitates in silicon, ECS J. of Solid State Sci. and Technol. 4, N124 (2015).