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 earrmr 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, et, the metal thickness, h, and the spacing, d, between two metal lines have been chosen to cover a wide range of thickness ratios eJh and aspect ratios h/d. The step coverage evaluation (bottom and lateral coverage) is performed by measuring thickness ratios, which are reported on (e~/h, h/d) diagrams. Well-defined curves of identical coverage can be drawn on the (ejh, h/d) diagrams, showing that the step coverage of the BSG films is clearly correlated with the thickness ratio ejh and the aspect ratio h/d, but does not simply depend on e,, h, and d 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 s~dewall profile. The step coverage results are then discussed in detail. Finally, the use of graphic representation of step coverage results on the (eJh, h/d) 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.Multilevel interconnection has become an essential technology for improving the performances and packing density of very large scale integrated circuits (VLSI). As the pattern size is reduced, the metal thickness cannot bc reduced proportionally. The aspect ratio (height to space ratio of interconnection) approaches 1.0 or becomes greater. New processes or materials need to be developed to obtain interlayer insulators: (i) with good step coverage and void-free filling of steep grooves, (ii) with total or partial planarization or capable of being planarized, (iii) with a short manufacturing time and no damaging of the underlying devices.Several techniques for h)rming planar insulation layers with high aspect ratios have been developed: polyimide (1), sandwich structure with permanent spin-on-glass (SOG) (2), SiOz bias sputtering (3), multiple depositionetch process in a single tool (4), and BSG (5, 6).The polyimides or SOG, due to their organic nature, are subject to reliability problems related to electrical properties, contamination, adhesion, and moisture properties. Bias sputtering techniques or multiple deposition-etch processes may be limited because of their low deposition rate and their tendency to damage the device characteristics.BSG has been shown to be suitable for practical application as interlev...

Review—Mechanical Stress in Chemically Vapor Phase Deposited Boron- and Phosphorus-Contained Silicate Glass Thin Films: A Review

“…Borosilicate glass films.-BSG stress data in CVD thin films were published very rarely 50,68,69 that seemed to be due to the lack of its practical use in IC technology. In fact, despite some attempts to show possibility to implement BSG films in IC technology, [68][69][70] these films did not find any practical interest. Stress values for BSG films obtained for silane-based APCVD processes are presented in Table VI.…”