Amorphous ternary diffusion barriers for silicon metallizations

Citation

Reid, Jason S. (1995) Amorphous ternary diffusion barriers for silicon metallizations. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4TFH-VM05. https://resolver.caltech.edu/CaltechETD:etd-10192007-131842

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Reactively sputtered from transition-metal silicide or boride targets in [...] discharges, thin amorphous films of TM-Si-N (TM = Mo, Ta, Ti, or W) and W-B-N are investigated. Resistivity, density, stress, and structure are given as functions of composition, and in some cases, temperature. As-deposited films typically contain 100 to 900 MPa of compressive stress, which can be fully relaxed on 'Si' substrates through annealing at 400 to 500[...]. Transmission electron microscopy shows that most of the films are marginally amorphous with the scale of local order ranging from 0.5 to 1.5 nm. Small-angle scattering experiments reveal local chemically dissimilar regions within the films. When fully nitrided, Si appears to be preferentially bonded to nitrogen in the form of Si3N4 in the TM-Si-N films, according to extended energy loss fine structure (EXELFS) measurements. According to tests on shallow junction diodes, 100-nm thick TM-Si-N barriers are able to prevent aluminum overlayers from spiking the Si substrate at temperatures above aluminum's melting point, 660[...]. The exceptional degree of stability is partly attributable to a 3 nm, self-sealing AlN layer which grows at the TM-Si-N/Al interface. By virtue of the self-sealing layer, secondary ion mass spectrometry (SIMS) measurements of [...]/[...] trilayers after a 700[...]/10 h vacuum anneal reveal no diffusivity of Al in [...] films. The performance of the TM-Si-N and W-B-N barriers with copper overlayers is equally impressive. At the proper compositions, 100-nm barriers prevent copper from diffusing into the junction at 800[...] or higher for a 30-min vacuum annealing. Diode failure typically corresponds to the crystallization temperature of the barrier, which can be reduced by the presence of copper. Once the barrier crystallizes, well-defined grain boundaries are introduced that provide fast diffusion paths for Cu. Paring the barriers' thickness down to 10 nm lowers the barriers' effectiveness to approximately 650[...]. Bias stress testing of 10-nm TM-Si-N barriers with Cu overlayers on MOS capacitors reveals no penetration of Cu into SiO2 during an 80 h treatment at 300[...] and 1 MV/cm applied field. Preliminary diffusion measurements of Cu in [...] films by SIMS yield an approximate diffusivity constant of [...]. Through a microscopic four-point probe lithographically defined on a Cu/barrier/Cu trilayer stack, the specific contact resistances of barrier/Cu interfaces are determined for TM-Si-N, TiN, and W barriers. In all instances, the contact resistance is approximately [...] for as-deposited samples. The lack of difference among the barriers may be attributable to inadequate vacuum leading to interfacial impurities.

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