RCA cleaning (german RCA clean) - very rarely modified Huang- cleaning - is method for glass cleaning ( wafer cleaning ) in microelectronics.
The wet chemical cleaning process was developed in the 1960s by W. Kern and D. Puotinen on behalf of the Radio Corporation of America (RCA) and first published in 1970.
The RCA method consists of two different baths:
- "Standard Clean 1 " (SC -1 ) ammonium hydroxide, hydrogen peroxide, DI water in a ratio of 1:1:5 to 1:2:7 ( removal of particles and organic impurities)
- "Standard Clean 2" ( SC -2): hydrochloric acid, hydrogen peroxide, DI water in a ratio of 1:1:6 to 1:2:8 ( Distance metallic impurities)
Both components are normally used at 75-85 ° C, and process time 10-20 minutes.
Standard Clean 1
The particle removal in the SC-1 bath is based on two processes:
- Since hydrogen peroxide is highly oxidizing, begin wafer surface and particles to oxidize, which means that the adhesion forces between particles and wafer decrease and the particles can be solved in SC1 bath.
- The ammonium hydroxide etches the wafer surface and thus undercut the particles. As generated by the hydroxide ions, a negative charge of the wafer and the particles, resulting in a rejection of existing particles, and at the same time prevents a renewed deposition of the particles.
Standard Clean 2
SC -2 is used to remove metal ( and some organic ) impurities of the wafer. Therefore one must combine a high oxidation potential with a low pH. Adhering metals are converted into their soluble metal chloride compounds by the hydrochloric acid. Subsequently, the wafer surface is passivated by the hydrogen peroxide, owing to the formation of a metal oxide layer. Organic compounds that are inherent in the wafer readily oxidized by the hydrogen peroxide.
Changes in the RCA process
Over time, the RCA process was changed because it uses chemicals and high-purity DI water in very large quantities. Few companies apply the RCA process is still in its original form. Nowadays very dilute solutions (up to 100 times thinner ) are used, they have the same or better cleaning efficiency than the original solution. For example, the mixing ratio of 1:4:50 could be instead of 1:1:5. Moreover, thinner solutions are a big plus in occupational safety and health, and reduce chemical consumption drastically. Reason for the lasting success of the RCA cleaning is the good availability of chemicals and DI water. With new developments such as the on-site generation of process fluids very high degree of purity can be achieved.
- RCA generates a large amount of chemical vapors, which must be extracted in order to avoid that the vapors entering the clean room. In addition, slowly changing by gassing the solution concentration.
- As SC -1 etches the surface, leads to a certain surface roughness by the cleaning process.