Metal Oxide Removal Using Atmospheric Pressure Plasma Technology for Electronic Applications Daphne Pappas, Andrew Sy, Ryan Robinson, and Richard Burke Plasmatreat USA, Inc. 30695 Huntwood Avenue Hayward, CA 94544 Ph: 650-596-1606 Email: daphne.pappas@plasmatreat.com Abstract Copper is one of the most commonly used metals in the electronics industry. For example, it is extensively used as a lead frame material in integrated circuit packaging due to its superior thermal and electrical conductivity and low production cost. However, the formation of a native oxide on the surface along with the presence of organic contaminants hinder wire bond strength. The work presented here will focus on a novel approach to remove copper and other oxide layers using a nitrogen/hydrogen (95%/5%) gas plasma chemistry that does not require a vacuum environment. The processes are run at temperature conditions lower than 200°C, and at speed up to 150 mm/s which make the technology attractive for industrial upscaling. Results from the elemental analysis using scanning electron microscopy (EDS-SEM) of the plasma-treated versus as-received copper surfaces will be presented. Also, a brief analysis of the gas plasma-surface interactions, process parameters leading to oxide reduction of various metals (Cu, Sn) and equipment details will be discussed. Aside from improving wire bond strength to lead frames and pads, plasmas can be used to improve die attachment to various metal solder materials for flip chip and other electronic applications. Key words Atmospheric pressure plasmas; metal oxide reduction; copper oxide; wire bonding I. Introduction Copper is extensively used in the semiconductor and electronics manufacturing due to low resistivity, high thermal conductivity, and low cost when compared to alternatives such as gold, aluminum, and tungsten. These properties make the metal favorable to use for applications such as lead frame material in integrated circuit manufacturing. However, organic contaminants and native copper oxide layers readily form on the surface during manufacturing, leading to greatly reduced quality of metal- to-metal bonding necessary for strong wire bonds. This work will mainly focus on a novel approach of selectively removing copper oxide by using atmospheric pressure plasma (APP) ionizing forming gas (95% nitrogen and 5% hydrogen). Additional metal oxide reduction processes will also be shown to illuminate the wide applicability of this method to other common electronics manufacturing metals. This process does not need a vacuum environment, operates at applied temperatures lower than 200°C, and speeds up to 150 mm/s, making industrial upscaling easily feasible. Introduction of this technology in various industries will also decrease the usage of environmentally taxing processes which use dangerous chemicals such as concentrated strong acids (e.g. HF, H3PO4, HNO3, HCl, etc.). II. Background Atmospheric pressure plasma has been used in many industries to prepare material surfaces by cleaning and increasing the surface energy to improve adhesion of metals, plastics, and ceramics. This works through the plasma- induced degradation of organic contaminants and the addition of functional groups. By using forming gas in an oxygen-free environment, it is possible to vastly reduce the presence of metal oxide layers on commonly used metals in the semiconductor industry, such as copper, nickel, and tin. Additionally, plasma increases the reduction efficiency from thermal hydrogen reduction due to the presence of the excited species and the reduced thermodynamic cost of the reactions [1]. The overall reaction responsible for this phenomenon is the conversion of the metal oxide into pure metal and water vapor. For example, copper oxide IMAPS 2022 - 55th International Symposium on Microelectronics | October 3-6, 2022 | Boston, MA USA 000324