Deposition of Smooth Thin Cu Films in Deep Submicron Trench by Plasma CVD Reactor with H Atom Source
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Deposition of Smooth Thin Cu Films in Deep Submicron Trench by Plasma CVD Reactor with H Atom Source Masaharu Shiratani, Hong Jie Jin, Yasuhiro Nakatake, Kazunori Koga, Toshio Kinoshita and Yukio Watanabe Department of Electronics, Graduate School of Information Science and Electrical Engineering, Kyushu University, Hakozaki, Fukuoka 812-8581, Japan ABSTRACT Effects of H irradiation on purifying Cu films and improving their surface roughness as well as size and orientation of Cu grains in the films have been examined using a newly developed plasma CVD reactor equipped with an H atom source, in which Cu(hfac)2 is supplied as the source material. The H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness, while it has no effect on the grain orientation. The decrease in dissociation degree of material gas leads to reduction of the surface reaction probability of Cucontaining radicals, which is important to realize conformal deposition in fine trenches. Using the control of dissociation degree of material gas independent of H irradiation, we have demonstrated conformal deposition of smooth Cu films in the trench using the developed plasma CVD reactor. INTRODUCTION Because of its lower resistivity and better electromigration properties, copper metallurgy is a desirable alternative to aluminum for ULSI interconnects. While the electroplating method is currently employed for formation of Cu interconnects in industry, it needs thin Cu seed layers deposited by other means. However, at present, there is no method to obtain such thin layers in small via and contact holes, of a width below 0.13 µm and a depth above 0.8 µm [1, 2]. For the thermal and plasma CVD, conformal deposition of such holes can be achieved when the surface reaction probability β of Cu-precursors is less than 0.02 [3]. For the thermal CVD, its processes are essentially characterized by heterogeneous decomposition of material gas on an activated substrate-surface and hence the β value is controlled by varying substrate temperature (Ts) and/or flow rate of material gas. However, such control also influences the deposition rate and film properties such as purity and resistivity. The plasma CVD has a significant advantage over the thermal CVD in β control, because β can be changed by varying the dissociation degree of material gas under a constant Ts [4, 5]. Previously, we showed the useful effects of H atoms on removing impurities in Cu thin films deposited using the plasma CVD [6, 7]. Based on this result, we have newly developed a plasma CVD reactor equipped with an H atom source (hereafter referred ot as HAPCVD reactor, namely, H assisted plasma CVD reactor). In this paper, we will show that this HAPCVD reactor is useful for improving properties of Cu films, controlling β of Cu-containing radicals and depositing smooth thin Cu films in a small trench.
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EXPERIMENTAL The source material for Cu deposition used in this study was Cu(hfac)2 , bis(hexafluoroacetylacetonato) copper (II), dissolved
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