Effect of Bath Temperature and Current Density on Higher Deposition Rate for Copper-Molybdenum Alloy Plated Film with High Molybdenum Content

Abstract

Recently, miniaturizing electronic devices, such as handy phone, have been strongly requested. Number of mounted electronic components has been abruptly increased. Therefore, the high density of the component is mounted, the need for heat dissipation is increased. A heat radiation substrate is one of the most promising candidates to suppress increasing temperature of electronic devices. The heat radiation substrates need both high thermal conductivity and low coefficient of thermal expansion. A semiconductor has low coefficient of thermal expansion. A copper-molybdenum alloy has both high thermal conductivity and low coefficient of thermal expansion. An electroplated Cu-Mo alloy film has been investigated. However, deposition rate was decreased with high molybdenum content in the alloy. High molybdenum content is necessary to obtain low coefficient of thermal expansion. The low deposition rate is serious issue to put into industrial usage. The purpose of this study is to produce a film with high molybdenum content by high deposition rate. The chemicals used in bath preparation were CuSO4・5H2O 0.13 mol/L, Na2MoO4・2H2O 0.53 mol/L, C6H5Na3O7・2H2O 0.91 mol/L. The bath was adjusted to pH 9.0 and then electroplated. Nickel plate is used as the substrate and platinum plate is used as the anode. In this study, both bath temperature and current density have been investigated. Higher bath temperature makes deposition rate lower as shown in Fig.1. Higher current density makes deposition rate higher, but the current density dependence of the deposition rate is different on the bath temperature as shown in Fig.2. Lower dependence is observed in the case of higher bath temperature and effect of bath temperature on molybdenum content is different in the case of each current density. In the case of high current density, the molybdenum content increased with increasing bath temperature as shown in Fig.3. Therefore, when both bath temperature and current density are high, the films with high molybdenum content are plated by relatively high deposition rate as shown in Fig.4. The three micrometers thick copper-molybdenum alloy film with 23.9 at% molybdenum content film are plated for 1 hour under the condition of 50℃ bath temperature and 10 mA/cm2 current density. This deposition time to obtain 3 micrometers is one twentieth to obtain previously studied film with 17.9 at% molybdenum content. Figure 1