Comparison of Properties of CVD Copper Films Deposited on Different Substrate Materials
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ABSTRACT The crystallite size of the chemical vapor deposited Cu film is usually so large that the Cu film does not fill contact holes or via holes in ultra large scaled integrated circuits well. Therefore it is very important to make the grain size of the Cu film small enough to fill small contact holes with high aspect ratio. Pretreatment of the substrate surface with Ar plasma has been found to be effective in making the grain size of the Cu film smaller and in enhancing the deposition rate of the Cu film. The Cu film deposited on the borophosphosilicate glass (BPSG) has the characteristics of smaller grain size, lower resistivity, and higher degree of (111) preferred orientation, but slightly lower deposition rate than that on the SiO 2 glass. The higher resistivity of the Cu film on SiO 2 may be due to the formation of the intermetallic comnpound Cu 15 Si 4 at about 4001C which is not formed at the Cu-BPSG interface at the same temperature. Also the dependence of some properties of the Cu film on the substrate material is discussed. INTRODUCTION Chemical- vapor-deposited Cu is now widely accepted as a conducting material for future interconnection and contact hole filling in the semiconductor
community. It is well known that, Cu has the advantage of lower electrical resistivity and higher electromigration -resistance over AI[R]. The resistivity of Cu film may depend upon the substrate material as well as Cu deposition process parameters. Thus it is desirable to select an underlayer material to the Cu film which do not form compounds at their interface, since the formation of the compounds would increase the electrical resistance[2]. The Cu interconnect is known to have the highest resistance to electromigration and stress -migration when the degree of (111) preferred orientation of the Cu film is the highest[3]. The grain size of the Cu film is also important from the viewpoint of contact hole filling. The size of contact holes or via holes in ULSI today is so small compared with the Cu crystallite (or grain) size that the Cu crystallites may not fill the contact holes or via holes easily. Therefore it is necessary to make the grain size as small as possible for better filling of the contact holes or via holes. In this study we investigated the dependence of the properties of the Cu film such as the grain size, the degree of the preferred orientation and the formation of intermetallic compounds on the substrate material. The materials used for the substrate to the Cu film in this investigation are Si0 2 , borophosphoslicate glass
(BPSG) and Ti.
TEOS-SiO 2
is expected to be used as an intermetal dielectric
material in the multilevel metallization scheme, TEOS-BPSG as an interlayer dielectric material, and Ti as a barrier metal, so that all these materials have a possibility to be used as the underlayer material to the Cu interconnect in real 341
mat. Res. Soc. SYMP. Proc. Vol. 355 l1995 Materials Research Society
circuits. Ti isusually heat-treated inN113 or N2 to be TiN after the Cu film is deposited o
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