Blog: How Does RF Matching Improve Process Control for Plasma-Based Processes?

Blog: How Does RF Matching Improve Process Control for Plasma-Based Processes?

As semiconductor manufacturing moves to 10nm and below, advancements in more than just processes and materials come into play. Current equipment subsystem technologies simply do not offer the speed or precision required for next-generation manufacturing. This piece dives into the challenges manufacturers are facing, answers some key questions about this changing landscape, and shows how Reno is meeting these increasingly stringent demands.

 

Original equipment manufacturers (OEMs) are under a lot of pressure when trying to meet customer’s ever-changing requirements. For example, taking 3D NAND and stacked finFET technology from the R&D lab to high volume manufacturing is putting unprecedented demands on tool capabilities for etch, atomic layer deposition (ALD) and atomic layer epitaxy (ALE). This is because at 10nm and below, film thickness and critical dimensions (CD) are shrinking, making deposition and etch process recipes increasingly complex. The bottom line: Current tool sets don’t accommodate the repeatable deposition and etch processes necessary to build these advanced structures.

 

What Is the Problem with Plasma?

Etch, ALD and ALE tools use plasma-based processes for manufacturing advanced devices, including 3D structures. Process times—also known as radio frequency (RF) on times—have shortened for both ALD and ALE applications. At 10nm and below, controlling the plasma throughout the process, while also shortening process times, is both challenging and necessary. Device manufacturers use very short RF on times (a few tens of milliseconds) and multilevel pulsing of plasma to deposit those thin layers.

 

As processing times become shorter, the plasma instabilities become a significant portion of the process. Detecting plasma instabilities and reacting to and eliminating them before they wreak havoc is therefore one path to success. This is why RF stability, and maybe more importantly repeatability, are top yield drivers as these processes go into production.

 

Why RF Matching Is Important

RF matching is critical for stabilizing plasma processes. Multiple power levels within the same recipe require that the match be able to respond from power level to power level and match each time. By reducing matching times, as well as variability from one match to another, uniformity across a wafer, from wafer-to-wafer and run-to-run, can be achieved. This is why more OEMs are moving to pulsed plasma recipes with both pulse-to-zero and level-to-level pulsing. Getting these new recipes to run in production calls for fast and accurate RF matching.

 

Traditional RF matching approaches are built on vacuum variable capacitor (VVC) technology and can’t react to these changes quickly enough. As a result, some OEMs started using a fixed match and frequency tuning as a workaround. However, this only works if the impedance changes are relatively small, and may require an added stabilization step in the recipe, wasting time and productivity.

 

Replacing Vacuum with Electronics

Reno Sub-Systems’ solution to this problem is its solid-state Electronically Variable Capacitor (EVC™) matching network, which relies on a digital array rather than vacuum to achieve repeatable and accurate matching in plasma processing.

 

Fast and precise power regulation gives device manufacturers a higher degree of control over the film growth or etch. By eliminating variability, each wafer is exposed to the same conditions for either etch or deposition processes. Reno’s EVC matching networks reliably match to each power level change every time. There is no need for stabilization steps to maintain steady plasma delivery. This provides the process integrity and repeatability necessary to bring advanced etch, ALD and ALE into mainstream manufacturing.

 

EVC matching networks work by continuously monitoring the plasma conditions and detecting both instabilities and micro-arcing. Fast, in-situ sensors, coupled with machine learning and AI functions, create an extremely fast reaction time, which allows a rapid match that alters the network parameters and stabilizes the plasma. Manufacturers can use these features during process development to significantly shorten the development time. In production, it keeps the process stable and repeatable.

 

A Matched Set Is Better

RF generators are also a critical part of successful advanced plasma processes. Pairing of electronic RF matching networks and RF generators provides a unique set of value propositions. First of all, a “one supplier” aspect reduces conflict when finding the root cause of a malfunction. Additionally, the algorithm and control parameters make it easier to communicate back and forth between match and generator, improving the performance of both. It also allows for proprietary data collection that provides important information about what is occurring inside the tool.

 

Written by: John Voltz, VP of Business Development