“What is wet, but dry?” might sound like a riddle, and the answer for plasma process tools are “wet cleans,” an important type of preventative maintenance. The term “wet clean” comes from the early days of the industry when preventative maintenance meant disassembling the reaction chamber, submerging the quartz parts in acids, rinsing, drying and then reassembling the chamber. In today’s high precision maintenance for process tools the only wet chemistry usually used is a lint-free wipe, moistened with deionized-water, but the name persists. So, maintenance is called “wet,” but is actually “dry.”
The goal of preventative maintenance is to keep the equipment running to specifications and to minimize any unplanned downtime, which is typically very disruptive, expensive and results in lost production. Regularly changing the engine oil, for example, is key to maximizing the life and performance of a car. Over the course of etching thousands of wafers, polymers of the removed material build up on the plasma process chamber surfaces. The polymer build-up needs to be managed for two reasons; they can be a source of contamination and they have the potential to change the chamber induction or conductance which can affect the plasma processing. Build-up is mostly managed through sophisticated plasma clean cycles but at some point, the chamber will need scheduled preventative maintenance. Preventative maintenance has seen a dramatic increase in steps and required precision. In the year 2000 there were typically around 35 steps needed for maintenance, nowadays this can exceed 150 steps and the precision required is so much higher. As a consequence, the failure rate of maintenance can often be as high as 30%, which is not only a loss of production, but a significant cost increase in wasted spare parts and test wafers.
Wet Clean Optimization
Lam’s solution is a service offering called ‘Wet Clean Optimization,’ or WCO, which helps eliminate human variability and increases the success rate of preventative maintenance. WCO has been adopted on a significant number of etch and deposition chambers worldwide solving several customer problems, such as increasing production and significantly reducing wasted spending.
This holistic solution combines specialized tooling, multi–media step-by-step instructions in local languages, data analytics, and support from an expert to diagnose problems with maintenance and to drive continuous improvement.
Specialized Tooling: Having the right tools at hand greatly increases productivity and efficiency, as well as worker safety. The WCO service cart ensures the right tools, both standard and custom, are available where and when they are needed.
Multi-media Step-by-Step Instructions: The step-by-step procedures and easy to follow documentation are invaluable to the maintenance teams who are commonly faced with the challenges associated with a high turnover of technicians performing preventative maintenance – this can be as high as 100% over 18 months.
Data Analytics: A key part of WCO is the included data analytics, which takes wet cleaning data and transforms them into information that can be used. A critical requirement to be able to drive continuous improvement is to have quality analytics to identify the areas in need of most improvement and a way to measure and quantify improvements.
Expert Support: A specialist engineer drives accountability, investigates mistakes and initiates systematic improvements.
To better understand the power of WCO, let’s take a look at a couple of scenarios.
Chipmaker A was experiencing unpredictable wet clean performance of its plasma etch tools, which was affecting tool availability. The fab manager understood it was due to the high workforce turnover, but was unable to improve the situation with in-house training or other actions. With WCO, new employees simply followed the step-by-step on-screen instructions in their local language and consistent wet clean performance was quickly achieved. Yield excursion rates decreased, and tool uptime increased – both from faster wet clean times and from fewer unscheduled tool down situations.
Chipmaker B was ramping up a new chamber type and wanted to achieve high productivity as quickly as possible. By implementing the best-known methods provided by WCO, staff were quickly trained. The new chambers rapidly achieved high, consistent uptimes and a reduction in maintenance time variability.
WCO is an approach to help customers ensure they are successful and self-sufficient with their preventative maintenance. This is enabled through the integration of Lam’s proprietary software, data analytics and certified video-based cleaning procedures. WCO is part of a larger portfolio of Equipment Intelligence® productivity solutions, all built on a foundation of Lam tool knowledge and data.