New developer-soluble gap-fill material with fast plasma etch rate

For the via-first dual damascene process, a planarizing anti-reflective material or gap-fill material is typically used to ensure a lithography process produces the best profiles and critical dimension (CD) control. These requirements pose many challenges to material scientists, and the most difficult task is likely to be designing spin-on materials that provide zero bias between dense and isolated pattern areas. We have developed a unique solution, in the form of wet gap-fill (WGF) materials, to further reduce both iso/dense bias and the overall process time. In order to reduce iso/dense bias, dry gap-fill materials are used in combination with a plasma dry etch-back process. However, the bias reduction is less than satisfactory because the initial coating bias will transfer to the final surface through the etch process. As their name implies, our WGF materials fill surface topography and utilize a standard photoresist developer to etch back to the substrate surface. These WGF materials, by careful design, aim to minimize bias caused by the difference between the faster bulk material dissolution rate and the slower rate in small vias. After wet etch back, the isolated and dense via-patterned areas both are fully filled, and the bias is much smaller than the bias of the initial coating. In contrast to the dry etch-back process, wet etch back eliminates the need to transfer wafers between the etch and photo bays, which is definitely financially favorable. In addition, future low-k materials will most likely be porous, which raises the concerns about etch damage. Wet-etch gap-fill materials will provide an ideal solution to this problem.