Materials Science and Engineering B73 (2000) 99 – 105 Thin oxide reliability and gettering efficiency in advanced silicon substrates M.L. Polignano a, *, G. Ghidini a , F. Cazzaniga a , L. Ceresara a , F. Illuzzi a , B. Padovani b , F. Pellizzer a a ST Microelectronics, Via Olietti 2, 20041 Agrate Brianza, Milan, Italy b INFM — Laboratorio Materiali e Dispositii per la Microelettronica, Via Olietti 2, 20041 Agrate Brianza, Milan, Italy Abstract Various substrates are compared for both bulk defect formation and thin oxide reliability. Wafers were subjected to a complete device fabrication process, and the formation of the denuded zone was monitored by SPV measurements of carrier lifetime. Oxide reliability tests were carried out by exponentially ramped current stress and constant current stress measurements. Oxides with different thicknesses (70, 150 and 300 A  ) were tested, in order to detect both gettering effects (expected to be most effective in the thinnest oxides) and defectivity related to vacancy clusters (reported to be most apparent in 200 – 500 A  thick oxides). The detrimental effect of vacancy clusters and oxygen-related defects is demonstrated by comparing Czochralski grown wafers with different densities of such defects and epitaxial p/p + material. In Czochralski material, the usual denuding and precipitation thermal cycle is compared to the recently proposed method to control oxygen precipitation through the concentration of intrinsic point defects. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Thin oxide reliability; Gettering; Defect formation; Denuded zone www.elsevier.com/locate/mseb 1. Introduction The process of crystal growth may affect the reliabil- ity of oxides grown on Czochralski (CZ) silicon mainly because of two mechanisms. First, the crystal growth process determines the density and the nature of grown- in defects [1,2]. These defects, and specifically vacancy clusters, are responsible for weak points in the oxide [3], and for this reason modifications of the crystal growth processes are studied in order to reduce grown-in defect density [4]. On the other hand, grown-in oxygen precipitation nuclei strongly affect both the growth of oxygen precip- itates in the bulk and the formation of a denuded zone in the surface region of wafers [5], and, as a conse- quence, the ability of bulk defects to getter metal impurities. This fact reflects on thin oxide characteris- tics, as metal impurities in the surface region are known to be detrimental to thin oxide reliability [6], and for this reason a controlled oxygen precipitation is required in wafer processing. Recently it was also proposed to control oxygen precipitation by creating a suitable in- depth profile of intrinsic point defects [7]. As oxygen precipitation injects silicon interstitials, it is expected to occur in regions where a vacancy excess exists. Epitaxial material is recognized to be free both from vacancy clusters and from oxygen precipitation and gettering related problems. Indeed, vacancy clusters nucleate during cool-down from the solidification tem- perature in materials grown from a melt under excess vacancy conditions, so no vacancy clusters are found in epitaxial layers. In addition, epitaxial layers are free from oxygen and therefore the risk of oxygen-related defect formation in the surface region is absent. Finally, epitaxial layers are usually grown on a heavily doped substrate, and in the case of boron-doped p/p + sub- strates, the high dopant concentration provides a very effective gettering even in the absence of extended defects [8]. Ungettered metal impurities and vacancy clusters induce oxide defects through different mechanisms. Contamination-related defects are due to the segrega- * Corresponding author. Tel.: +39-39-6035593; fax: +39-39- 6035358. E-mail address: marialuisa.polignano@st.com (M.L. Polignano) 0921-5107/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0921-5107(99)00443-2