Characterization of Borosilicate Glass Step Coverage for Multilevel Interconnection Applications

Abstract

The step coverage of atmospheric pressure chemical vapor deposited borosilicate glass (BSG) has been studied in detail. The optimized deposition conditions have been obtained for an oxygen/hydride ratio of 70/1 and a 4% boron concentration. Various BSG thicknesses obtained by only changing the speed of the carrier moving belt have been deposited over different kinds of metal steps, with sloped profiles or re‐entrant angle profiles and with different step heights. The oxide thickness, the metal thickness, , and the spacing, , between two metal lines have been chosen to cover a wide range of thickness ratios and aspect ratios . The step coverage evaluation (bottom and lateral coverage) is performed by measuring thickness ratios, which are reported on (, ) diagrams. Well‐defined curves of identical coverage can be drawn on the (, ) diagrams, showing that the step coverage of the BSG films is clearly correlated with the thickness ratio and the aspect ratio , but does not simply depend on , , and values. The limit curves of void formation and of constant coverage are drawn on these diagrams for the two metal profiles. A void formation limit is determined by the vertical asymptote to the void formation curve. This limit is obtained for an aspect ratio of 0.6 when metal steps have a re‐entrant angle profile, and 0.75 when metal steps have a sloped sidewall profile. The step coverage results are then discussed in detail. Finally, the use of graphic representation of step coverage results on the (, ) diagrams is emphasized for comparison of deposition techniques, choice of methods to elaborate intermetal dielectric, and as a guide to the design of new multilevel technologies.