Specific Process Knowledge/Wafer cleaning/RCA
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RCA cleaning
RCA1 - RCA2 - HF - BHF(pre-dep wafers)
The RCA cleaning procedure was originally developed by the Radio Corporation of America (RCA) as part of manufacturing electron tube components. This process has since been adapted to silicon semiconductor processing. RCA is a two-step process (RCA1 and RCA2), and RCA1 should always be made before RCA2 because removing organic contaminants is a requirement before metal contaminants can be removed effectively.
RCA1 is a powerful oxidizer and will thus remove organic contaminants. The ammonium hydroxide in RCA1 also has good solvating power as it can complex metals such as Cu, Ag, Ni, Co and Cd into solution. RCA2 forms soluble complexes with heavy metals and also shows cleaning action similar to that of piranha solutions. Furthermore, solutions of hydrochloric acid, which is a major constituent of RCA2, has proven effective at removing alkali metal ions. It is important that the chemicals used are very clean. RCA mixtures are therefore only used for up to a few batches (boats) of wafers and once an RCA mixture has cooled down it should not be reheated/reused. A new mixture should be made instead. Since RCA1 and RCA2 can oxidize silicon to silicon dioxide, an HF dip can be used to remove the thin oxide formed during RCA clean.
The RCA clean is used for cleaning wafers before taking them into the furnaces and a few other equipments (check the cross contamination sheet). Aa mentioned above a crucial part of the RCA cleaning procedure is the oxidation by H2O2 at elevated temperatures. Therefore, the lifetime of RCA1 and RCA2 solutions after preparation is limited because H2O2 decomposes at 70oC.
- RCA1 contains: H2O, NH4OH and H2O2 (5:1:1). It is used for removal of light organics, particles and metals.
- RCA2 contains: H2O, HCl and H2O2 (5:1:1). It is used for removal of heavy metals, metal hydroxides, and residual metals including alkali metals.
You can find the APV for the RCA bench here
RCA procedure
- RCA1: 10 min
- DI water rinsing (dumping three times)
- HF: 30 sec (you may avoid this step in case of a very thin oxide (0-200 Å) as the top layer)
- DI water rinsing (bubbler)
- RCA2: 10 min
- DI water rinsing (dumping three times)
- Optional: HF: 30 sec (avoid it if you have a very thin oxide (0-200 Å) as the top layer)
- DI water rinsing (bubbler)
For procedure details please look in the user manual in LabManager.
The user manual, user APV and contact information can be found in LabManager: RCA info page in LabManager
Overview of RCA process data
| RCA1 | RCA2 | HF | |
|---|---|---|---|
| General description |
Used for removal of light organics, particles and desorption of trace metals (Au, Ag, Ni, Cd, Zn, Co, Cr, etc). |
Used for removal of alkali ions, metal hydroxides (of Al, Fe, Mg, Zn) and residual trace metals (e.g. Cu and Au). |
Used for removal of oxide generated in RCA1 and RCA2 |
| Chemical solution | H2O, NH4OH(25-29%) and H2O2(30%) (5:1:1) | H2O, HCl(37%) and H2O2(30%) (5:1:1) | 5% HF |
| Process temperature | 70-80 oC | 70-80 oC | Room temperature |
| Process time |
10 min. |
10 min. |
30 sec. |
| Life time of the chemical solutions | Can only be heated one time. When hot: it lasts for ~1h | Can only be heated one time. When hot: it lasts for ~1h | ~2 months |
| Allowed materials |
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|
|
| Batch size |
1-25 2",4" or 6" wafers at a time |
1-25 2",4" or 6" wafers at a time |
1-25 2",4" or 6" wafers at a time |
| Size of substrate |
4"-6" wafers |
4"-6" wafers |
4"-6" wafers |