Capacitively Coupled Plasma Etching (CCP) and Inductively Coupled Plasma Etching (ICP) are the two most widely adopted low-temperature plasma etching technologies in the semiconductor etching field. Each boasts unique advantages for different etching materials and process requirements, laying a solid foundation for the development of the semiconductor industry. A detailed introduction to the two etching methods is presented as follows.

1. Capacitively Coupled Plasma Etching (CCP)

Originating in the 1960s, CCP technology was initially applied to plasma surface treatment and gas discharge experiments. With the continuous shrinking of chip dimensions, its application in the semiconductor industry has expanded from basic surface treatment to high-precision etching of complex micro-nano structures. Optimizing plasma density, etching selectivity and machining accuracy has become the core development direction of CCP technology.

The working principle of CCP is to build a high-frequency alternating electric field between electrodes via capacitive coupling, which accelerates free electrons to collide and ionize gas molecules, thereby generating plasma. In early single-frequency CCP etching systems, radio frequency (RF) power (typically 13.56 MHz) was applied to the lower electrode of the reaction chamber. Frequent collisions between electrons and gas molecules contribute to relatively high plasma density. Nevertheless, low electron density and uneven electric field distribution in the sheath lead to poor directional acceleration of ions, which deteriorates etching anisotropy. To meet higher precision requirements, dual-frequency CCP etching has gradually replaced single-frequency solutions, as shown in Figure 1.

Figure 1 Schematic diagram of capacitively coupled plasma source: (a) Single-frequency type; (b) Dual-frequency type

In dual-frequency CCP equipment, high-frequency power and low-frequency power are separately applied to the upper and lower electrodes. The high-frequency power dominates electron excitation and gas ionization to sustain plasma generation, while the low-frequency power adjusts ion energy and regulates ion incident direction by modulating the sheath electric field. This independent control over plasma density, ion energy and incident angle effectively improves etching efficiency, precision, anisotropy and directivity.

Nevertheless, traditional CCP technology reveals inherent limitations amid escalating demands for micro-nano etching accuracy and selectivity, including insufficient plasma density, low etching rate and inaccurate ion energy regulation. Against this backdrop, inductively coupled plasma etching (ICP) has been developed to address the above drawbacks.

2. Inductively Coupled Plasma Etching (ICP)

ICP reactors are widely utilized in microelectronic device fabrication owing to their high plasma density and excellent deposition uniformity. The core superiority of ICP etching lies in plasma excitation via electromagnetic induction driven by RF power without direct electrode contact. This configuration enables the generation of high-density plasma under low-pressure conditions, avoids electrode corrosion common in conventional CCP systems, and realizes precise control over ion energy and etching procedures.

Early ICP etching devices adopted single RF source for plasma generation, which has evolved into the mainstream dual-RF source structure nowadays. Based on coil winding modes, dual-RF ICP systems are mainly classified into helical coil ICP and planar disk coil ICP, as illustrated in Figure 2. Featuring simple structure, both types can generate high-density and high-quality plasma, thus gaining extensive research and industrial application. The overall performance of ICP etching systems can be further optimized by adjusting coil position, size and geometry.

Figure 2 Schematic diagram of inductively coupled plasma source: (a) Solenoid coil ICP; (b) Planar disk coil ICP

Compared with helical coil ICP, planar disk coil ICP exhibits more prominent strengths, including compact structure, high inductive coupling efficiency and uniform plasma distribution. It is particularly suitable for high-uniformity etching of large-size wafers. With superior performance in plasma density, etching uniformity and equipment integration, it has become the mainstream design of modern ICP-RIE etching equipment.