Copper film, which is expected to be used as interconnection material for 1 giga DRAM integrated circuits was deposited on hole and trench patterns by Metal Organic Chemical Vapor Deposition(MOCVD) method. After a reflow process, contact and L/S patterns were filled by copper and the characteristics of the Cu reflow process were investigated. When deposited Cu films were reflowed, grain growth and agglomeration of Cu have occurred in surfaces and inner parts of patterns as well as complete filling in patterns. Also Cu thin oxide layers were formed on the surface of Cu films reflowed in $O_2$ambient. Agglomeration and oxidation of Cu had bad influence on the electrical properties of Cu films especially, therefore, their removal and prevention were studied simultaneously. As a pattern size is decreased, preferential reflow takes place inside the patterns and this makes advantages in filling patterns of deep submicron size completely. With Cu reflow process, we could fill the patterns with the size of deep sub-micron and it is expected that Cu reflow process could meet the conditions of excellent interconnection for 1 giga DRAM device when it is combined with Cu MOCVD and CMP process.