Revised SEMI E135 to Enable Better Precision and Improved Throughput by Evaluating an RF Generators Transient Response
By Paul Trio, SEMI and Inna Skvortsova, SEMI Standards
Requirements placed on RF components are demanding. Power cycling and operational time often push these components to their limits. As a result, device manufacturers have reported seeing over half of RF generators used in the fab fail within the first two years of operation.
There are a number of parameters associated with RF generators and matching networks that play a factor in field performance and reliability. One such area is an RF generator’s ability to respond to different transient loads. Where wafer processing takes place in a vacuum chamber, RF generators are used to “ignite” and maintain plasmas that vary continuously which may or may not be stable. Ultimately, RF generators must be capable of reacting to the plasma’s changing characteristics, ensuring that power remains stable during operation.
It is therefore important to know what an RF generator is capable of before it is selected for a tool running a specific process application. One way to achieve this is to measure an RF generator’s transient response resulting from a requested change in output power. The method to perform this measurement has been established for more than a decade in the SEMI E135 Standard - Test Method for RF Generators to Determine Transient Response for RF Power Delivery Systems Used in Semiconductor Processing Equipment.
The limitation with the original E135 standard was that it only provided testing procedures for an RF generator operating into a nominal 50 Ω load as a function of the change in set point level. A better assessment of an RF generator’s performance would be to subject it to a series of tests that better simulate dynamic load conditions.
“There is an inherent and immediate value of establishing testing and operational standards for RF systems for device manufacturers, not only due to historic inconsistencies in design –to- operational performance issues, but as technologies continue to evolve, so will the demands on the process equipment and the boundaries of performance that will pushed. These demands will benefit greatly by performance consistency and reliability of equipment component parts, such as RF components. A common recognized and utilized standardization of testing for RF generators will undoubtedly provide a common framework of performance sensitivity and expectations across both the equipment manufacturing and end-user landscapes,” states Ed Ornelas, Sr. Components Engineer & Program Manager at Intel Corporation.
The latest version of SEMI E135 now provides considerations to determine response of an RF generator operating into a nominal, high-, and low-impedance load. The intention of testing into a high- and low-impedance load is to simulate plasma ignition conditions. Additional changes to SEMI E135 also include considerations for the limited number of required test loads, expected control system gain variation as a function of load impedance on a linear load, and nonlinear (plasma) loads.
“For suppliers of RF generators the revised SEMI E135 standard provides a standardized way of reporting the transient response of a multi-state RF generator to a user commanded change in output power. Having such a standard available eases communication between suppliers and users of RF generators. The addition of an expanded related information section explains the limitations of testing equipment designed to deliver power to highly nonlinear loads using only linear loads,” says Don van Zyl, Member of Technical Staff at Advanced Energy Industries, Inc.
These critical improvements to SEMI E135 were the result of a joint, collaborative effort between the SEMI SCIS (Semiconductor Components, Instruments, and Subsystems) Technology Community and the SEMI Standards Program. SCIS was chartered to address wafer defectivity caused by process-critical components. Its activities are structured around characterizing important parameters affecting processes and impacting yields and developing test methodologies to measure them. The SCIS RF Group considered that addressing transient response was the first step in improving RF generator performance and reliability. Comprised of device maker representatives, RF generator suppliers, and RF managers from equipment OEMs, the SCIS RF Group developed the updated testing procedures as well as the required test equipment. The RF Measurements Task Force chartered under the North America Chapter of Metrics Technical Committee within SEMI Standards Program was responsible for finalizing the technical proposal and driving it through the formal standardization process. As a result, the original standard is completely rewritten and now published as SEMI E135-0918 - Test Method for RF Generators to Determine Transient Response for RF Power Delivery Systems Used in Semiconductor Processing Equipment under the Equipment Automation Hardware volume of SEMI Standards.
By including additional real-world testing conditions, the revised Standard provides a more comprehensive test method for evaluating an RF generators response time, enabling better precision and operational results. As geometry changes from 14 nm to 7 nm in high-volume manufacturing, the industry is using more complex waveforms and pulsing for etching. If the RF generator does not provide the expected transient response, its impact on process (e.g., precision demands of etching) will inevitably influence the end product resulting in wafer defects, and ultimately disrupting yields and driving up manufacturing costs. Unstable RF generators performance may also negatively impact the deposition process resulting in wafer scrap and increased costs. Consistent performance of RF generators will enable better control of uniformity during the wafer production process thereby improving throughput and process yield.
Preventing process-critical tool downtime and unscheduled system maintenance is similarly of great importance for fab operations. Any change in process recipes while retaining existing RF componentry can cause a negative impact on performance even if the RF equipment is meeting the original operational specifications. However, it is particularly challenging and time consuming to diagnose the problem when the tool is taken out of its operational environment and is returned from the field to the RF manufacturer. All these factors ultimately impact the throughput of the fab as well as the service cost for the suppliers.
Given the perpetual strife to keep yields up and costs down, it is imperative to ensure that critical components involved in semiconductor manufacturing become enablers for good yields and less as contributors to defects and unexpected tool-downs. Test methodologies described in newly revised SEMI E135 are targeted to the engineering teams on the equipment manufacturers side during the product design and fabrication stages as well as for process engineers and technical teams responsible for evaluation of RF generators. This document is of value to the field service and customer service engineers for troubleshooting of the RF generators in the fabs. Finally, purchasers of critical components within OEM should be aware and leverage newly revised SEMI E135 and related test procedures to improve the quality of purchasing decisions, components qualification, and vendor selection processes.
About SEMI Standards Program
SEMI Standards play a critical role in the success and growth of the global microelectronics supply chain. Standards ensure interoperability of equipment and components, material conformance, and safe and sustainable manufacturing practices. SEMI Standards development activities take place throughout the year in all major manufacturing regions. To get involved, join the SEMI International Standards Program www.semi.org/standardsmembership. To access SEMI Standards please visit www.semi.org/en/Standards/SEMIViews. If you have any questions regarding the SEMI Standards Program, Metrics Technical Committee activities, or the SEMI Standard mentioned in this article, please contact Inna Skvortsova (firstname.lastname@example.org).
About SEMI SCIS
SEMI SCIS is open to all SEMI Members. There will be an SCIS face-to-face meeting in conjunction with the Advanced Semiconductor Manufacturing Conference (May 6, 2019) in Saratoga Springs, New York. After this event, SCIS will reconvene in July at SEMICON West 2019. SCIS groups meet regularly via teleconference in between face-to-face meetings. For more information or to join SCIS, please contact Paul Trio at SEMI (email@example.com).
December 5, 2018