Micro-Arcing During High-Density Plasma Chemical Vapor Deposition
By Calvin Chang, Joseph Farah and Lin Zhang
Under certain process conditions, fabs operating High-Density Plasma Chemical Vapor Deposition (HDP-CVD) equipment experience micro-arcing, a condition where the highly concentrated electric field within the process chamber induces a large discharge current, causing an arc from the plasma to the chamber wall. The result is particle contamination, wafer scrap, yield loss and tool downtime. This article discusses micro-arcing and a new service strategy to help device makers manage it.
Background – The Basic Arcing Mechanism
The plasma within the HDP process chamber is at a higher electrical potential than the chamber wall. Under some process conditions, dielectric breakdown occurs on the chamber wall, resulting in a discharge current from the highly concentrated, electric field of the plasma to the side wall of the chamber.
Metal at the chamber wall vaporizes, releasing aluminum particles into the chamber and onto the wafer. The bare aluminum surface of the chamber wall becomes exposed, potentially setting the stage for subsequent micro-arcing events. Recipes that couple low pressure with high power are especially susceptible to micro-arcing (see figure 1).
Figure 1 – Basic Arcing Mechanism
Result: Contamination and Yield Loss
The particles resulting from micro-arcing cause wafer contamination and yield loss. Figure 2 shows typical wafer maps of un-patterned wafer defect inspection results for wafers impacted by micro-arcing.
Figure 2 – Particle Contamination from Micro-Arcing
The Challenge: Detecting Micro-Arcing
One of the biggest challenges in managing micro-arcing is efficiently detecting it. During inspection of a process chamber after micro-arcing has occurred, arcing marks may be visible on the gas ring or the chamber side wall (figure 3). Visibility of the arcing marks typically increases as the arcing becomes more severe. However, micro-arcing can sometimes occur without leaving any visible arcing marks in the chamber.
Figure 3: Arcing Marks
Evidence of micro-arcing can also be identified when performing on-wafer analysis of particle contamination. Particles from micro-arcing are typically round in shape and composed of aluminum as shown in figure 4. Energy dispersive x-ray spectroscopy (EDX/EDS) shows an example of aluminum spiking (see figure 5).
Figure 4 – Top View of Particles Shows Rounded Shape
Figure 5 – Energy Dispersive X-Ray Spectroscopy (EDX/EDS) Shows Aluminum Spike
Although these methods can be effective during post-mortem diagnosis of micro-arcing, they are unsatisfactory for real-time detection of micro-arcing events. The most common method used to detect micro-arcing is to visually inspect production wafers using a sampling plan. However, a visual inspection strategy has disadvantages:
- Sampling does not capture 100% of all micro-arcing events. Some micro-arcing can occur undetected, allowing wafers contaminated with aluminum to enter the process flow. Aluminum contamination from micro-arcing events can be introduced into the HDP and downstream process chambers, with potentially far-reaching impacts on device performance.
- After one micro-arcing event occurs, the chamber becomes more susceptible to subsequent events. Typically, follow-on events become more severe, introducing greater levels of contamination and making recovery more difficult.
- Visual inspection is a non-value added activity, as inspection overhead consumes valuable equipment and labor resources.
Recovery From Micro-Arcing
The recovery process for an HDP chamber typically involves polishing the chamber wall and cathode. Consequently, frequent micro-arcing can be disruptive. Moreover, some equipment owners follow the recovery procedure with additional conditioning wafers, further displacing valuable production time.
Proactive Micro-Arcing Management
An effective micro-arcing management strategy requires early detection of micro-arcing events. This enables proactive measures to prevent further arcing, and if necessary, chamber recovery before the damage to the chamber sidewall dielectric becomes severe. Early action minimizes tool downtime and helps reduce the risk of extended downtime due to unsuccessful recovery.
In response, Applied Materials has developed and released a new micro-arcing detection capability for all Applied Centura Ultima HDP-CVD systems. This hardware and software solution is offered as part of a comprehensive Applied Materials service agreement, and provides a robust method to detect and facilitate the management of micro-arcing. It is fully integrated with proprietary software and includes hardware to monitor the plasma potential of the process chamber, and to detect and report micro-arcing events. To enable real time micro-arcing identification, the system monitors sensor readings and compares them to performance models developed by Applied’s technical experts (figure 6). The micro-arcing service solution also includes features to recover arced chambers and prevent new arcing events.
Figure 6: Data from the chamber is monitored around the clock by Applied Materials to detect and notify the customer when arcing events occur.
The micro-arcing solution provides a powerful method for capturing micro-arcing events, minimizing wafer scrap and reducing yield loss. In early customer testing, this solution demonstrated 100% capture of target micro-arcing events (see figure 7).
Figure 7. Customer tests using Applied’s HDP arcing detection solution. DC plasma potential and arcing frequency dropped dramatically after removing residue from chamber surfaces, resulting in reduction in wafer scraps.
Solutions To Increase Equipment Uptime And Factory Efficiency
The new Centura Ultima micro-arcing solution is one of a diverse array of Applied Materials flexible service offerings designed to increase equipment uptime and factory efficiency, enabling fabs to focus on chip production while lowering cost per wafer. With a wide range of available service solutions, Applied Materials is committed to providing cost-competitive support options to meet customers’ specific equipment and technology requirements.
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