Dual-Frequency RF Impedance Matching Circuits for Semiconductor Plasma Etch Equipment

• Main Authors: Jeongsu Lee, Sangjeen Hong
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Electronics
• Subjects: dual-frequency capacitively coupled plasma; process drift; impedance matching
• Online Access: https://www.mdpi.com/2079-9292/10/17/2074

The change in electrode impedance of semiconductor equipment due to repetitive processes is a major issue that creates process drift. In the current plasma etch chamber with a dual-frequency power system, the high-powered radio frequency (RF) source contributes to the enhancement of the plasma density, and the low-frequency bias power at the bottom electrode is adopted to enhance the injected ion energy in the plasma. The impedance control of the top electrode in dual-frequency capacity coupled plasma limits the impedance matching capability of the RF matching system because it only considers the high-frequency RF source. To control the precise impedance in dual-frequency semiconductor equipment, independent impedance control is required for each frequency. In this study, the impedance corresponding to a specific frequency was independently controlled using L (inductor) and C (capacitor). A 60 MHz stop filter and VVC were used to control 2 MHz impedance at a specific point, and a 2 MHz stop filter and VVC were used to control 60 MHz impedance. In the case of 2 MHz impedance control, the 2 MHz impedance changed from 10.9−<i>j</i>893 to 0.3−<i>j</i>62 and the 60 MHz impedance did not change. When controlling the 60 MHz impedance, the 60 MHz impedance changed from 0.33 + <i>j</i>26.53 to 0.2 + <i>j</i>190 and the 2 MHz impedance did not change. The designed LC circuits cover the impedance of 60 and 2 MHz separately and are verified by the change in the capacitance of the vacuum variable capacitors implemented in the RF impedance matching system.