Rapid Isothermal Fusion of PSG Films

Abstract

This paper presents results on rapid isothermal fusion (RIF) characteristics of phosphosilicate glass (PSG) obtained using an incoherent lamp annealer in a N2 ambient. The effects of varying the temperature (10007-1200~ the cycle duration (10-60s), and the phosphorus concentration in the glass (2.5-8.0 w/o) were investigated. The out-diffusion of phosphorus from the PSG films during RIF cycles were also studied. In conjunction with these experiments, dopant redistribution induced by typical RIF cycles in a boron-implanted silicon substrate was measured to assess the practicality of the RIF technique for VLSI applications and to identify a process window. The results for the boron profile redistribution were used as a basis of comparison between RIF and conventional furnace treatments. Although restricted to VLSI applications where a relatively high phosphorus content of approximately 8 w/o is acceptable in PSG films, it is concluded that RIF in a N~ ambient is nevertheless much more effective for the fusion of PSG films than conventional furnace processing and thus much more compatible with VLSI processing.As a part of the fabrication sequence for integrated circuits, a layer of phosphosilicate glass (PSG) is deposited to provide passivation and electrical insulation between metal interconnects and underlying structures. Before the subsequent deposition of metal takes place, it is necessary to smooth the surface topography to ensure continuity of the overlying metallization. At present, this treatment is typically a furnace glass fusion cycle at 1000~ for 30 min or more (1-5) and is the last high temperature process step in the fabrication of LSIC's. This heavy thermal load will be unacceptable for processing new generations of VLSI circuits because it will induce appreciative lateral and vertical dopant redistribution in small geometry devices.Thermal processing requirements can be eased by using different materials or ambients during the fusion cycle. Although increasing the phosphorus concentration does lead to a lower fusion temperature for PSG films, excessive concentrations eventually promote the formation of phosphoric acid in the presence of moisture (2, 4), thereby causing reliability problems due to corrosion of overlying aluminum interconnect lines. As an alternative solution, rapid isothermal fusion (RIF) has been shown in limited studies to improve PSG step coverage, while causing less junction diffusion than conventional furnace processing cycles because of its lower time-temperature product (6-9).In this work, we have studied the effect of RIF on PSG films having a practical range of phosphorus concentrations, namely, 2.5, 4.0, 6.6, and 8.0 w/o. The RIF experiments were performed in a N.2 ambient using a tungsten halogen lamp system. :~ In addition, the out-diffusion of phosphorus from the PSG films during RIF was examined.The amount of dopant diffusion induced by RIF in underlying device junction areas will largely determine its range of usefulness for VLSI applications (6-12). There-* Electrochem...

A New LPCVD Technique of Producing Borophosphosilicate Glass Films by Injection of Miscible Liquid Precursors

“…E x t r a p o l a t i o n of the linear part of this curve predicts for this glass composition a planarizati0n status at a t e m p e r a t u r e of 930~ It is interesting to note that, after the 950~ flow, b u b b l e formation b e c o m e s evident at these P concentrations and for these highly fluid conditions. These bubbles are believed to be associated with sublimation of the P~Os, which occurs at temperatures as low as 300~ (15,16). For processing conditions specifically requiring a 950~ flow to meet prescribed junction depths, this problem may be resolved by proper optimization of the glass composition a s demonstrated here in Fig.…”

Low Pressure Chemical Vapor Deposition of Borophosphosilicate Glass Films Produced by Injection of Miscible DADBS‐TMB‐TMP Liquid Sources

“…It is interesting to note that, during the 900~ flow, b u b b l e formation occurs at these P concentrations and for these highly fluid conditions. These bubbles are believed to be associated with sublimation of the P20~ that is known to take place at temperatures as low as 300~ (17,18). As previously demonstrated (11)…”

Rapid Thermal Flow of PSG Films in Vacuum Using a Graphite Heater

“…This situation corres p o n d s to t h e r m a l t r e a t m e n t s of 1000~ for ~p p r o x i m a t e l y 120s, 1100~ for 10s, a n d 1200~ for a p p r o x i m a t e l y 3s (8,13,14) and ~ is the surface-free energy that is primarily dependent on the surface area on the PSG profile (12,16). The value of ~ is approximately constant considering that the initial PSG profiles are supposed to be near to a large flat plane such as the flow process is only a small pertubation on the surface (12).…”

“…Most of the authors reporting on rapid thermal flow h~ve used halogen lamp RTP systems at atmospheric pressure (7)(8)(9)(10). One exception is the work reported by Downey et al (11), which used a graphite heater RTP system in vacuum.…”