Yoshiko Okui

Dry Cleaning for Fe Contaminants on Si and SiO2 Surfaces with Silicon Chlorides

While investigating the surface dependence of the dry cleaning technique using Cl radicals generated with UV irradiation (UV/Cl 2 , we found that silicon chlorides [SiCl x (x = 1 to 4)], etching products created from a reaction between Si and Cl radicals, can remove Fe contaminants. SiCl 4 gas removes Fe contaminants existing on both Si and SiO 2 surfaces without surface dependence. The surface residue due to the adsorption of SiCl 4 is insignificant. We also found that a small addition of Cl 2 to SiCl 4 is advantageous for dry cleaning Si surfaces. Surface flatness and composition are maintained after cleaning with Cl 2 + SiCl 4 (5:195 ml/min) gas mixture. Dry cleaning technology has been significantly improved by the use of an SiCl 4 -based system instead of Cl 2 alone.

Characterization of cleaning technology for silicon surfaces by hot pure water containing little dissolved oxygen

We introduce new cleaning technology using pure water containing little dissolved oxygen (LDO water). To maintain the concentration of dissolved oxygen in water, we performed experiments in a glove box, controlling the ambient between the water and the ambient gas so as to satisfy Henrys law. In the experiment using intentionally contaminated wafers and LDO water containing 1 ppb of dissolved oxygen at room temperature, the amount of residual metallic contaminants, except copper, on a Silicon surface decreased from 1014 atom/cm2 to 1011 atom/cm2 after hot LDO water treatment for 30 min at the boiling point. The cleaning ability depends on the dissolved oxygen concentration, temperature of LDO, and treatment time. The ability to eliminate aluminum during the 30 min hot LDO water treatment was lower than for the other metals. Moreover, the adsorption velocity of aluminum from hot LDO water on the wafer surface was much larger than that of the other metals. Since this hot LDO water treatment simultaneously etched silicon and silicon dioxide with the removal of metal, we also investigated the morphology and chemical structure of the wafer surface after this cleaning process.

Removal of Fe Contaminants in SiO2 Layers with Successive Processing of Poly‐Si Deposition and Cl‐Radical Etching

We have developed a method to remove Fe contaminants from SiO 2 bulk layers using a technique in which poly-Si is first deposited on a Si wafer surface and then etched off. The poly-Si layer was formed by chemical vapor deposition (CVD) on an SiO 2 surface intentionally contaminated with Fe. The poly-Si was etched with Cl radicals generated by ultraviolet irradiation, a process called UV/Cl 2 . Fe concentration in the SiO 2 that was exposed after etching decreased by two orders of magnitude from the original contamination level of 10 12 atom/cm 2 . Fe concentration in the Si substrate remained unchanged after the poly-Si CVD and UV/Cl 2 processes. The Fe removal results are independent of the thickness of poly-Si when between 50 and 400 nm and are also independent of either the presence or absence of phosphorous doping in the poly-Si. We surmised that if poly-Si deposited on an SiO 2 surface can remove the Fe in the SiO 2 completely, then Fe in the poly-Si will vaporize to form Fe chloride having a high vapor pressure while the Cl radicals etch the poly-Si.

Dry cleaning of Si and SiO/sub 2/ surfaces using SiCl/sub 4/ system

We have found an effective dry cleaning technique using SiCl/sub 4/ as a cleaning gas. Now, for the first time, surface Fe contaminants can be removed from an SiO/sub 2/ surface using SiCl/sub 4/. A Cl/sub 2/+SiCl/sub 4/ combination allows dry cleaning of a Si surface at a lower temperature than the conventional UV/Cl/sub 2/ method. Use of this Cl/sub 2/+SiCl/sub 4/ mixture gave good surface flatness and surface constitution for both Si and SiO/sub 2/ surfaces.