Plasma etching machine is a key equipment for achieving fine pattern transfer in semiconductor manufacturing. Its working principle is based on the synergistic effect of plasma physics and chemical reactions. The following provides a detailed analysis from the aspects of core principles, key components, and process parameters:
1、 The core principle of plasma etching: the synergy between physical etching and chemical etching
1. Generation and characteristics of plasma
Generation mechanism: Through energy sources such as radio frequency (RF), microwave, or inductively coupled plasma (ICP), etching gases (such as CF ₄, Cl ₂, O ₂, etc.) are ionized in a vacuum chamber, forming a plasma composed of ions, electrons, free radicals, and neutral particles.
Key characteristics: High energy ions (such as F ⁺, Cl ⁺) in the plasma are directed to bombard the surface of the material under the action of an electric field (physical etching), while active free radicals (such as CF ∝, Cl) undergo chemical reactions with the material to generate volatile products (chemical etching).
2. The synergistic effect of physical etching and chemical etching
Physical etching: Ion bombardment provides sufficient energy for material atoms to detach from the surface, characterized by strong etching directionality (vertical etching), suitable for forming high aspect ratio structures, but poor selectivity (small difference in etching rate for different materials).
Chemical etching: Free radicals undergo chemical reactions with materials, such as SiO ₂ reacting with F ⁺ to generate SiF ₄ gas, characterized by high etching selectivity but weak directionality (isotropic etching).
Collaborative advantage: By adjusting plasma parameters such as ion energy and free radical concentration, a balance can be achieved between "high aspect ratio etching" and "high selectivity etching" to meet different process requirements (such as logic chip gate etching and storage chip deep hole etching).
2、 Typical application scenarios and differences in etching technology
1. Logic chip manufacturing
Gate etching: High aspect ratio etching (such as ICP technology) is used to form vertical sidewalls (deviation<1 °) through high ion energy and precise temperature control, avoiding short channel effects.
Contact hole etching: requires high selectivity (etching rate ratio of silicon/silicon oxide>10:1) to protect the underlying devices from damage.
2.3 DNAND storage chip
Deep hole etching: It is necessary to etch to a depth of several micrometers (such as 3D NAND holes with a depth of over 1000 layers>5 μ m), and use a "etching passivation" cycle process (such as Bosch process) to alternately pass CF ₄/O ₂ and C ₄ F ₈ to form a sidewall passivation layer to prevent hole wall collapse.
3. Manufacturing of power devices
Silicon carbide (SiC) etching: Due to the high hardness of the material, high-energy ion bombardment (such as using Ar+ions) is required. Combined with Cl ₂ gas enhanced chemical etching, the etching rate can reach over 100nm/min.
summary
The working principle of plasma etching machine is essentially to achieve precise coordination between physical and chemical etching through plasma control. Its technical core lies in the precise control of power supply, gas, vacuum and other systems to balance etching rate, selectivity and directionality in different application scenarios. As semiconductor processes evolve towards nodes below 3nm, etching technology is developing towards higher precision, lower damage, and intelligence, becoming one of the key links supporting the continuation of Moore's Law.