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Top1. Introduction
Sputtering is the process whereby coating material is ejected from coating target due to bombardment of high energy particles of an inert gas. The ejected particles from the target stick on to the substrate and form a coating layer. It is a physical vapour deposition process. The sputtering operation is a very precise, prolonged and meticulous process. The downtime of sputtering machine is very costly and leads to a cascading effect on other related operations down the manufacturing process flow. The sputtering operation deals with ionization process at high vacuum pressures. Minute leakage of atmospheric air into the sputtering working chamber can lead to inconsistent results. Any small variation in the process parameters leads to a catastrophic failure of the sputtering machine. This leads to decrease in MTBF (Mean Time Between Failure) leading to ineffective utilization time of the sputtering equipment. Thus, the aim is to minimize the MTTR (Mean Time To Repair) so that the MTBF and ultimately MTTF (Mean Time To failure) is maximized in order to improve the average lifespan of the equipment (Mortazavi, Mohamadi, & Jouzdani, 2018).
The present work focuses on one such case study where the industrial engineering principles are applied for resurrection of capability of a sputtering machine. The sputtering machine under preview of this work is manufactured by VR Technologies, DC/RF sputtering unit, of Bengaluru in India, consists of a cylindrical chamber which is pumped by 250 lit / min double stage direct driven rotary vacuum pump. The chamber is fabricated from polished stainless steel. The chamber is mounted on the Mild Steel frame. The cooling water pipe line is coiled on the outer wall of the chamber to prevent overheating. There are two target guns one is for DC sputtering and another one is for RF sputtering which are controlled by independent controllers provided on the machine.
The typical base pressure in vacuum chamber is about 1×10-5 mbar. The pressure inside the chamber is created by using rotary vacuum pump and diffusion pump. Diffusion pump uses silicone oil to entrap the air molecules inside the chamber. There are no mechanical parts in diffusion pump, so it uses rotary vacuum pumps to exhaust the air molecules. Sputter gases are fed into the system through gas needle valve. Typical sputtering gas applied is argon. Sputtering gas is supplied to the vacuum chamber by adjusting the mass flow rate according to the type of target used. The line diagram of sputtering machine is depicted in Figure 1 and the pictorial view is captured in Figure 2. Table 1 tabulates the specifications of the sputtering equipment.
This paper is an application of industrial engineering principles of problem solving and troubleshooting into the domain of sputtering operation. Firstly the knowledge gap in the industrial engineering area and the PVD area is focused in the introduction section. This is succeeded by a detailed literature survey on FMEA, Ishikawa diagrams and sputtering operations. The problem identification and definition is elucidated in the subsequent session. The Critical-To-Performance (CTP) characteristic is identified and then all the potential causes are enlisted by employing the Ishikawa diagram. The Why-Why analysis is employed for tracing the root cause. The PFMEA (Process Failure Modes and Effects Analysis) is employed for prioritizing the corrective actions for the potential causes traced. In next section, the validation of the corrective actions is done through experimentation where the results confirm the resurrection of the sputtering machine capability to its optimum use. Finally the paper ends with a conclusion followed by a list of references. Figure 3 depicts this information about organization of the work in this paper.
Figure 1. Line diagram of sputtering machine
Figure 2. Pictorial view of sputtering machine set up in laboratory