High Purity Sulfur Compounds for Semiconductor Application
Publication Date: 2015-Jan-15
The IP.com Prior Art Database
The use of sulfur containing and hydrogen free compounds for etching or deposition processes emerges as etching or deposition enhancers. However the current quality of the said sulfur containing compounds is insufficient and leads to metal corrosion of integrated circuits.
Commercially available carbon disulfide or carbonyl sulfide are claimed to be more than 99% pure, up to 99.9%, but may contain significant amounts of hydrogen sulfide, resulting in copper corrosion of nearby copper-containing layers, and adverse effects in terms of product reliability, adhesion, overheating and parasitic capacitance effects. The presence of the hydrogen-containing impurities may be detrimental to the adjoining metal or metal-containing layer. Corrosion was observed on copper lines used for TSVs. The presence of H2S in the sulfur-containing compounds altered the quality of copper layers. Furthermore, the presence of such impurities is favored by the presence of other impurities according to, for example, the following reactions: CS2 + H2O à COS + H2S; COS + H2O à CO2 + H2S; or COS + H2 à CO + H2S. Additional hydrogen-containing impurities besides H2 and H2O may include hydrocarbons, such as ethane or propane. The presence of such hydrocarbons is the source of hydrogen in process conditions, which may lead to the formation of corrosive species such as HS*.
The use of ultra pure sulfur containing hydrogen-free molecules is proposed for deposition or etching processes during semiconductor manufacturing in order to prevent the corrosion-related phenomena and associated detrimental effects in terms of product reliability, adhesion, overheating and parasitic capacitance effects. Exemplary sulfur-containing hydrogen-free etching gases include, but are not limited to sulfur chlorides, nitrosyl sulfide, CS2, COS, SF2, SF4, SF6, SO2, and/or SO3. Preferably, the sulfur-containing hydrogen-free etching as is carbon disulfide, carbonyl sulfide, or sulfur dioxide. The hydrogen-containing impurities should be lower than 100 ppm. The hydrogen sulfide (H2S) concentration should be lower than 50 ppm.
Ultra pure sulfur-containing hydrogen-free molecules may be prepared through synthesis, separation and purification, or isolation and cylinder filling. For instance, it is possible to prepare carbonyl sulfide by reacting at 350°C CO in the gas phase with H2S using a nickel sulfide catalyst. COS and H2 are produced by the reaction. The COS product and unreacted reagents are separated by distillation. This method may produce hydrogen sulfide (H2S) content lower than 100 ppm, and even down to 20 ppm without extensive efforts. Alternatively it is possible prepare carbonyl sulfide by flowing carbon monoxide on sulfur hence avoiding to nominally involve hydrogen in the reaction, and allowing easier purification conditi...