Influence of Aluminum Bond Pad Characteristic toward Wire Bond Intermetallic Compound Growth

Abstract — Long term microelectronic device reliability is important for crucial applications. There is a high percentage of field reliability failure related to wire bond defects. This pointed out that device reliability and system reliability are significantly affected by wire bond reliability. In the scenario of gold wire bonding on aluminum metallization, Excessive intermetallic compound (IMC) growth is a major reliability concern. IMC growth is contributes by gold and aluminum diffusion process. This is an ageing process that will eventually cause high resistance and open circuit of the product. In this study, aluminum bond pads with various characteristics were carefully evaluated to understand IMC growth behavior. Physical factors such as aluminum layer thickness and grains size are the focus of the study. Gold wire material was fixed during wire bonding for all samples, as well as wire bonding parameter settings. Subsequently after wire bonding, accelerated ageing conditioning was applied to the wire bonded samples. High Temperature Storage Life (HTSL) and Temperature Cycle (TC) are two common accelerated ageing methods for device reliability  assessment. HTSL treatment exposed wire bonded samples with continuous high temperatures for a long duration. Meanwhile, TC treatment conditioned the sample between cold and hot environments. Both ageing methods will accelerate IMC growth of Au-Al bonding. Ball bond cross-sectioning was conducted at various phases of HTSL and TC. SEM images were obtained from cross-sectioned samples for close examination of IMC growth patterns. This is followed by a wire bond shear test to evaluate the integrity of Au-Al bonding. The level of IMC growth influenced by aluminum layer thickness and grain size are highly interested in this study. These two characteristics are determined  by deposition rate and temperature used in wafer fabrication process. In view of this, data obtained from this study is valuable information for bond pad structure design and improvement activity in wafer fabrication process.