The difference between wet etching and wet cleaning in semiconductors

In semiconductor device manufacturing, wet etching and wet cleaning are two key wet chemical processes. Although both involve immersing the wafer in a chemical solution for processing, their process purposes and operating methods differ.

1. Wet Cleaning

Core Purpose: To remove contaminants from the wafer surface, including metallic impurities, organic residues, particles, and other dirt. The main goal is to obtain a clean surface to prepare for subsequent process steps.

Operating Method: Specific chemical cleaning solutions are usually used, such as the widely used SC1 (Standard Clean 1, ammonia/hydrogen peroxide/water mixture) and SC2 (Standard Clean 2, hydrochloric acid/hydrogen peroxide/water mixture). These solutions effectively remove various contaminants through chemical reactions or physical actions (such as oxidation, complexation, dissolution, and reduction of surface tension).

Process Ownership: Wet cleaning is usually attributed to the Diffusion Department. This is because the diffusion department is mainly responsible for high-temperature furnace processes, such as thermal oxidation to grow silicon dioxide layers or drive-in. Before these high-temperature processes, the wafer surface must be thoroughly cleaned to remove any impurities and particles that may be present. These contaminants can cause serious defects (such as crystal defects, junction leakage, gate oxide breakdown, etc.) under high-temperature conditions, affecting device performance and yield. Therefore, cleaning is an indispensable step before high-temperature processes.

2. Wet Etching

Core Purpose: Selectively remove thin films from specific areas of the wafer surface, or etch the required fine patterned structures. The core is the thinning or patterning of the material.

Operating Method: The etching process usually requires photoresist as a mask. First, photoresist is applied to the wafer surface through photolithography and exposed and developed to form a specific pattern. Then, the wafer is immersed in a chemical solution (etchant) that has a selective etching effect on specific thin film materials. The thin film material in the area not covered by the photoresist will be dissolved and removed by the chemical solution, while the area protected by the photoresist will be retained, thereby achieving pattern transfer.

Process Ownership: Wet etching belongs to the Etch Department. The core responsibility of the etching department is to accurately remove materials from specific areas according to the pattern defined by photolithography to form the physical structure required by the device. Wet etching is a key link in the patterning process.

3. Summary and Comparison

In general, wet cleaning and wet etching are indispensable wet chemical processes in semiconductor manufacturing. Wet cleaning focuses on surface purification, providing a clean substrate for subsequent processes (especially high-temperature processes), and is usually classified as a preparatory step in the front-end process and belongs to the diffusion department. Wet etching focuses on the patterned removal of materials, which is a key step in forming device structures. Its process goals and technical requirements determine that it belongs to a dedicated etching department. Although both use chemical solutions, their goals, mechanisms, and process positioning are completely different.

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