Impact of Metal Contamination of 7.0nm Gate Oxides on Various Substrate Materials
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ABSTRACT Metal contamination level will be decreased in order to maintain a device reliability according to device size reduction. Metal contamination from various processes are surveyed. The influence of metal contamination for 7-15nm thick gate oxides is discussed in order to clarify the critical concentration to gate oxides. NIG(Non Intrinsic Gettering) substrates are used in a worst case for gettering. Fe contamination with 4x 100 cm-2 strongly affects the TDDM characteristics, although there is no serious influence in the breakdown voltage even at the concentration of 5x1 Oil cm-2 . The same tendency is observed for Cu contaminant and the critical concentration for TDDB characteristics is around 3x 101 cm-2. High energy B implantation is carried out to form gettering sites near device region. Breakdown voltage and TDDB characteristics are almost the same as epitaxial substrates at Fe concentration up to lX 1012 C1-2 . Detailed examination such as SIMS,C-t and DLTS measurements is also supported the effectiveness
in high energy gettering.
INTRODUCTION In sub-quarter micron devices or below, critical metal contamination level to affect device peiformance will become lower because of thinner gate oxide films, increase of local stress, etc. In order to overcome this, not only the reduction of metal contamination fi'om processes but also the improvement of gettering must be done. In this paper, firstly, metal contamination level introduced and/or affected firom process machines, materials and chemicals will be surveyed. Metal influences to devices will be discussed using nonintrinsic gettering(NIG) substrates for the worst case. Then, metal gettering effect using high energy implantation will be presented.
81 Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
METAL CONTAMINATION LEVEL The source of metal contaminants are mainly categorized in three factors; process machines, materials and chemicals & gases. In the process machines, most possible process for metal contamination aie ion implantation, CVD and dry etching and metal contamination level exists around 2x1010 to lxl01 cm-2 for Fe, Cu and Ni. For materials, metal contamination level was examined in photoresist[lI]. Metals such as Fe, Cu, Crand Ni existed on Si surfaces at a level below 2xl10 cm-2just after ashing and ashing +cleaning. For chemicals, metal contamination in chemicals is quite low and the level is about 0.01ppb for SC-I solution. This level itself is not sot serious in chemical solutions, instead the problem is the recontamination to wafers fiom chemical solutions, because metals are piledup in the chemical solutions after wafer cleaning. This influence was examined in details[2]. When Fe existed in SC-I solutions at a level of 0.1 ppb and Ippb, Fe concentration on Si surfaces was around I x 1011 cn-2 and I x 1012 Cm"2, respectively. According to this result, metal concentration is estimated to be a level of about 0.4ppb in solutions after cleaning of 25 wafers of 8 inch in 40 liter solution, when Fe atoms with the conc
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