In the preparation process of semiconductor devices, the surface cleanliness of wafers and components directly determines the yield and performance of chips. Traditional wet cleaning is prone to residual chemical reagents and difficult to process micro scale fine structures, while plasma cleaning machines have become important surface treatment equipment in semiconductor manufacturing due to their dry, non-destructive, and high-precision processing characteristics. They are widely used in key processes such as pre-treatment before photolithography, activation before bonding, and encapsulation and de coating.

1、 The core working principle of plasma cleaning machine

The core of a plasma cleaning machine is to excite the working gas through a radio frequency power source, causing it to ionize and form a plasma composed of electrons, ions, free radicals, etc. These active particles have high chemical activity and physical kinetic energy, and can achieve surface cleaning in two ways:

1. Physical etching effect: High energy ions in the plasma bombard the surface to be cleaned at high speed under the action of an electric field, physically peeling off attached pollutant particles, organic residues, etc., achieving a "dry sandblasting" like cleaning effect, and the etching uniformity can be controlled at the nanometer level without damaging the substrate material.

2. Chemical reaction effect: Different working gases such as oxygen, hydrogen, argon, etc. are selected according to the cleaning needs, and targeted chemical reactions can occur. For example, oxygen plasma can oxidize organic pollutants into CO ₂ and H ₂ O and extract them, hydrogen plasma can remove the oxide layer on metal surfaces, and mixed gases can balance cleaning and surface modification.

2、 Typical application scenarios in semiconductor manufacturing

1. Pre treatment of wafers before photolithography process

Before photoresist coating, the presence of trace amounts of oil, water vapor, or oxide layer on the wafer surface can cause uneven photoresist coating and distorted pattern transfer. The plasma cleaning machine can complete the hydrophobic to hydrophilic modification of the wafer surface within 30-60 seconds, while removing nanoscale pollutants, increasing the adhesion between the photoresist and the wafer substrate by more than 30%, significantly reducing the defect rate of the photolithography process.

2. Surface activation in wafer bonding and packaging processes

In wafer bonding processes such as silicon silicon bonding and heterogeneous integrated bonding, insufficient surface activity can lead to problems such as insufficient bonding strength and interface voids. By mixing argon and oxygen plasma treatment, a large number of active functional groups such as hydroxyl and carboxyl groups can be introduced on the wafer surface, achieving a bonding strength of megapascals at the bonding interface and meeting high reliability packaging requirements. In addition, plasma cleaning can replace traditional wet de gluing in the chip packaging de gluing process, avoiding chemical residues in the packaging cavity and improving packaging yield.

3. Precise cleaning of semiconductor components

If residual glue or particles adhere to the precision components of semiconductor production equipment, such as the suction cup of the glue spreader and the nozzle of the developing machine, it will directly affect the process stability. The plasma cleaning machine can clean complex structural components without disassembly, ensuring cleaning accuracy and shortening equipment maintenance cycles.

3、 Key technical indicators for equipment selection

1. Plasma uniformity: For large-sized wafers (such as 12 inches), it is necessary to ensure that the plasma density deviation inside the cavity is ≤ 5%, otherwise it will result in uneven cleaning effect and affect chip consistency.

2. RF power and frequency: Low frequency RF (27MHz) is suitable for physical etching requirements, while high-frequency RF (13.56MHz) is more suitable for chemical reaction cleaning. Some equipment is equipped with dual frequency RF, which can achieve precise control of etching and modification.

3. Vacuum degree and gas control system of the cavity: A stable vacuum degree in the range of 10-100Pa can ensure plasma stability, and a high-precision mass flow controller (MFC) can achieve precise adjustment of multi gas ratios to meet diverse process requirements.

4. Non destructive processing capability: For flexible substrates or sensitive devices that are prone to damage, a low-energy plasma mode is required to control the ion bombardment energy below 10 eV to avoid lattice damage to the substrate material.

4、 Technological development trends

With the evolution of semiconductor technology towards 3nm and below nodes, plasma cleaning machines are developing towards higher uniformity, lower damage, and more intelligent control. On the one hand, the cavity structure adopts a distributed RF electrode design, combined with plasma simulation technology, to achieve uniform cleaning of wafers over 200mm; On the other hand, the equipment integrates an AI process closed-loop system, which can automatically adjust power and gas ratio based on real-time monitoring of plasma parameters, achieving adaptive optimization of the process. At the same time, green design has become a new trend, and low-power RF power supplies and recyclable working gas systems can reduce the overall energy consumption and environmental protection costs of equipment.

As the "surface cleaning and modification expert" in semiconductor manufacturing, plasma cleaning machines have always undergone technological iterations at the same frequency as chip process upgrades. In the future, with the popularization of packaging, heterogeneous integration and other technologies, plasma cleaning equipment will play an irreplaceable role in more process scenarios, laying a solid process foundation for the high-quality development of the semiconductor industry.