Dry cleaning of CMOS imagers in the automotive industry with CO2 snow-jet technology
ABSTRACT
In the production of CMOS-based imagers for the automotive industry, particles are removed using state-of-the-art compressed air ionization jets. In principle, this technology is efficient, reliable, and easy to install.
Due to increasing resolution and the resulting reduction in pixel size, the relevant particle size at which pixel errors occur has decreased. Depending on whether viewed on the bare die or on the IR cut-off filter glass, particles larger than 5µm (bare die) or, in some cases, larger than 25µm (IR cut filter glass) are disruptive. At these particle sizes, removal with ionization emitters is no longer efficient.
In the automotive industry CO2 snow-jet cleaning technology is increasingly being used for such applications. The advantage of this process is that even significantly smaller particles, e.g. down to 1µm or even smaller, can be removed.
In contrast to wet chemical cleaning, the CO2 snow-jet cleaning technology process is dry. The cleaning medium used is liquid carbon dioxide that has been recycled and processed from e.g. chemical production processes or energy generation from biomass. It is fed through a flexibly adjustable, wear-free two-component ring nozzle and expands into fine snow crystals upon exiting. These are bundled by a separate, ring-shaped compressed air jacket jet and accelerated to supersonic speed. When the easy to focus snow-compressed air jet hits the surface to be cleaned, a combination of thermal, mechanical, solvent, and sublimation effects occurs, which is the basis of the cleaning action. The crystalline carbon dioxide sublimates completely during the process, leaving the treated surfaces dry. Removed contaminants are extracted together with the process gas, thus preventing recontamination of the parts and contamination of the environment.
Typical applications for acp CO2 snow -jet cleaning technology are in optics, electronics, mechatronics, and increasingly also Semicon back-end. The process can be used to remove both chemical and particulate contaminants. After cleaning, the affected surface is dry and can be immediately processed, for example, assembled, bonded or packaged.
As the CO2 used in this process is a waste gas from other industries, free from PFAS and other chemicals of concern, acp systems AG is the first manufacturer of a dry-cleaning process to be awarded the GreenScreen Certification for Cleaners & Degreasers, which applies to all industrial applications, but especially to electronics manufacturing. The certificate confirms that the process gas does not contain any chemical substances that are harmful to humans or the environment. The background is the IPC-1402 Standard for Green Cleaners Used in Electronics Manufacturing, jointly developed by IPC (Association Connecting Electronics Industries).
Using two application examples
1. Cleaning CMOS imagers in automotive industry
2. Cleaning wafers after dicing this presentation will demonstrate the working principle as well as advantages and limitations of the acp CO2 snow-jet cleaning technology in practice.
BIOGRAPHY
William H Mullee (Bill), Director Technology & Sales at acp systems AG is a prolific inventor, process chemist and executive with 30+ years leading innovation in semiconductor and advanced materials manufacturing. Expertise in high-purity chemicals, CMP slurry, sustainable silica technologies, and new process commercialization. Co-founder of Supercritical Systems Inc., inventor of supercritical COշ cleaning for semiconductors. Founder, managing partner at PPT Technologies. Has 20+ US & Int’l patents.