Structure and method for improving low temperature copper reflow in semiconductor features

摘要

We have discovered that complete copper filling of semiconductor features such as trenches and vias, without the formation of trapped voids, can be accomplished using a copper reflow process when the unfilled portion of the feature structure prior to reflow comprises a capillary (314) within the feature (301), wherein the volume of the capillary (314) represents between about 20 % and about 90%, preferably between about 20 % and about 75 % of the original feature volume prior to filling with copper. The aspect ratio of the capillary (314) is preferably at least 1.5. The maximum opening dimension of the capillary (314) is less than about 0.8 mu m. The preferred substrate temperature during the reflow process includes either a soak at an individual temperature or a temperature ramp-up or ramp-down where the substrate (302) experiences a temperature within a range from about 300 DEG C to about 600 DEG C, more preferably between about 300 DEG C and about 450 DEG C. By controlling the percentage of the volume of the feature which is unfilled at the time of the reflow process and taking advantage of the surface tension and capillary action when the aspect ratio of the feature is at least 1.5, the copper fill material is easily pulled into the feature (301) which comprises the capillary (314) without the formation of voids along the walls (310) of the feature. The preferred method of application of the last layer of copper prior to reflow (the layer of copper which produces the unfilled capillary within the feature) is electroplating, although CVD or evaporation or other conformal layer formation techniques may be used.