Transition metal silicide precipitation in silicon induced by rapid thermal processing and free-surface gettering

Abstract

We have investigated the effect of nickel and copper on defect formation in silicon employing the rapid thermal processing (RTP) scheme. Treatment by RTP induces haze in the silicon wafer front side when its back side is contaminated by either nickel or copper. Transmission electron microscopy studies showed that the haze consisted of metal silicide precipitates, which negates a previous suggestion that ‘‘oxidation-induced stacking faults’’ are the main defect forming the haze. The morphology and nature of these precipitates have been analyzed. The nickel silicide precipitates were found to be NiSi2 and the copper silicide precipitates are most likely CuSi (zinc blende structure). Both kinds of precipitates exhibited an epitaxial relationship with the silicon substrate and adopted the shape of an inverted pyramid or section of a pyramid. The present CuSi precipitate morphology differs totally from that obtained using furnace annealing, and is attributed to the availability of free-silicon surface as the main silicon self-interstitial sink. Implications for low-temperature ultralarge scale integration processing are discussed.

TEM analysis of (Ni,Fe)Si2 precipitates in Si

“…The only other growth shape which could explain these observations would be a pyramid with four {111} faces and a square basal {001} face. This shape can be excluded, as it is not consistent with the symmetry of the cubic crystal system and can only be achieved for NiSi 2 precipitates when the basal {001} face is supported by Si surface orientation 12.…”

“…Ref. 9–14 for an overview). NiSi 2 has fluorite structure, with Ni atoms placed on corners and face centres of the unit cell, while all tetrahedral interstitial sites are occupied by Si atoms (space group Fm$\overline {3} $ m 15, a (NiSi 2 ) = 5.408 Å 16).…”

Impurity Precipitation, Dissolution, Gettering and Passivation in PV Silicon: Final Technical Report, 30 January 1998--29 August 2001

“…Other TEM studies [94,95] provide an alternative possibility to enhance Cu precipitate stability. These works identified the formation of CuSi rather than Cu 3 Si for Cu precipitation in silicon and at the silicon surface.…”

Defect Formation of Nickel-Incorporated Large-Diameter Czochralski-Grown Silicon and Their Effect on Gate Oxide Reliability

“…8 For the same reason, nickel can easily form a precipitate in silicon during the subsequent process, which can detrimentally affect the active device area. [9][10][11][12][13][14][15] Various aspects of nickel precipitates and their accompanying secondary defects in silicon have been reported, 11 and it was revealed that NiSi 2 , which has the calcium fluoride (CaF 2 ) structure, is the most preferred phase in crystalline silicon because it has the lowest lattice mismatch with the silicon matrix. [16][17][18] In addition, various extended defects such as stacking faults and dislocations in CZ-Si have been investigated under various experimental conditions.…”

“…[16][17][18] In addition, various extended defects such as stacking faults and dislocations in CZ-Si have been investigated under various experimental conditions. 17 However, most of these studies considered wafer samples that are contaminated from the surface and in-diffused at a certain temperature [10][11][12][13][14][15][16][17][18][19][20] or doped during float-zone (FZ) growth. 21,22 These experimental conditions are a good approximation for the surface contamination of nickel, but they cannot reflect the exact behavior of nickel that appears during the CZ-Si growth process, which is accompanied with other impurities such as dopants and the formation of secondary defects during the subsequent wafering process.…”