In this paper we develop a two-step pretreatment method which is a simple but effective cleaning process that can be used to achieve a high deposition rate and excellent interface characteristics, as well as improve the selectivity. In the first step, we use CF4/O2 mixing gases as a plasma etching system without substrate bias. The removal of damage and contaminants by reactive ion etching (RIE) during contact hole opening can thus be obtained. We consider that the role of oxygen is first to oxidize the polymer residues (i.e. fluorocarbons like CxFy) and the RIE-damaged regions on the silicon surface, and it is then followed with CF4 to remove these oxides. In experiments, the plasma modification rate can be controlled at 120 Å/min. Results of the high deposition rate, smooth interface, low selectivity loss and the other improvements are observed. These are superior to those of cases without pretreatment. The second step is that anhydrous HF cleaning was used to remove surface oxide which was formed during the first step. Obviously, this new cleaning technology is very efficient not only for contact hole pretreatment but also for polysilicon materials. This also implies that this technology may have potential for polycide gate applications.
- Ex situ pretreatment
- Plasma modification
- Selective tungsten deposition