RCA Clean

Family:  Alkaline Peroxides & Acidic Peroxides

Formulation:        “SC-1”—Ammonium Hydroxide and Hydrogen Peroxide

                                “SC-2”—Hydrochloric Acid and Hydrogen Peroxide

Uses:

In the production of integrated circuits, a number of chemical wafer cleaning steps is generally necessary. They are generally carried out after removal (stripping) of a resist mask and wherever possible immediately before a coating is applied.  The semiconductor wafers are either dipped into suitable chemical baths, frequently under the action of ultrasound, or the cleaning liquid is sprayed onto the wafers in a cleaner.

A frequently used process termed “RCA cleaning” is commonly enlisted which consists of two separate cleaning steps:

SC-1:

In the first cleaning step, RCA-1 or SC-1 (Standard Clean 1), the wafer to be cleaned is immersed in an alkaline cleaning solution consisting of one part of ammonia, one part of hydrogen peroxide and five parts of water, at a temperature of about 70° C. and then rinsed with ultrapure water in order to remove particles and organic contamination from the wafer surface.

SC-2:

This is followed by the second cleaning step, RCA-2 or SC-2 (Standard Clean 2).  In this step, the wafer to be cleaned is dipped into an acidic cleaning solution consisting of one part of HCl, one part of hydrogen peroxide and six parts of water, at a temperature of about 70° C. This is again followed by rinsing with ultrapure water in order to remove the metal contamination originating from the SC-1.

In general, the wafer surfaces after the SC-1 treatment are contaminated by Fe, Al, Ca, Mg, Zn and/or Cu ions and/or other metallic ions.  The metal contamination originates from the process steps carried out immediately before the cleaning step.  Contamination arises through contact with stainless steel, leaching of metals from fittings and piping material and diverse types of metal contamination from individual processes in semiconductor manufacture, such as dry etching, ion implantation and coating with photoresists, etc.

After the SC-1 treatment, the surface of the wafer is usually contaminated by approximately 1011 to 1012 iron atoms per cm2, approximately 1011 to 1013 aluminum atoms per cm2, and approximately 1010 to 1011 copper and zinc atoms per cm2.

In order to counter this problem, diverse complexing agents are often added to the cleaning solutions.  For example, ethylenediamine tetra-acetate (EDTA) is enlisted as the complexing agent.  However, the use of EDTA has proven relatively ineffective.

European Patent Application EP 0 496 605 A, discloses a process for cleaning semiconductor substrate surfaces in which compounds containing phosphonic acid groups or salts thereof are proposed as the complexing agent. The phosphonic acid compounds prove to be very effective in practice against contamination by iron ions, which generally cause relatively severe problems.

All known wet-chemical wafer cleaning processes have the common feature that they must be carried out at a temperature of 70° C., which results in increased costs and equipment complexity.  Furthermore, all known wet-chemical cleaning processes include two cleaning steps, as originating from the above-mentioned RCA cleaning.