Microelectronic integrated circuits (ICs) based on patterned semiconductor materials are continuing to evolve towards devices with an extremely high density of circuit elements per unit volume. The use of copper (Cu), with twice the conductivity of aluminum and three times the conductivity of tungsten, has been replaced as the interconnect material in advanced ICs manufacture using either single inlay or dual damascene processes. The conventional method of patterning trenches in a via-first dual damascene process involves filling via openings with an organic bottom anti-reflective coating (BARC), applying a photoresist layer on the via plug and then performing trench lithography. The via-first dual damascene process is considered superior in terms of reliable connection to the underlying metal, but has via proximity effect that causes difference in via CD (critical dimension).
In the semiconductor manufacturing art, the resolutions obtainable using optical lithography techniques is limited by what is known in the art as “proximity effects”, resulting in variations in feature of line width, alterations in pattern shapes, closed contacts or holes, and shortened or rounded lines among other distortions. Arising from proximity effects, the vias having difference critical dimensions, depending on their different pitches, usually occur and thereby cause defects. For example, a bird's beak is observed in a relative large via, and a blind via is observed in a relative small via. The most common technique to alleviate proximity effects is the use of optical proximity correction (OPC), which utilizes the addition of enlarged features on the mask pattern so as to anticipate and correct for the proximity effects. The OPC technique, however, is limited by the size of the added shapes. For compensating the via proximity effect, the use of OPC technique is difficult to make different-pitch vias obtain an identical via CD.
Therefore, a method of alleviating proximity effects without the use of OPC technique is desired for the via-first dual damascene process. There remains, however, a need for a novel approach that affords an increased process window for the via patterning process.