A NOTCH-FREE "VEIL" REMOVAL PROCESS
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2001-Dec-12
We routinely plasma etch a structure consisting of an AI/Cu alloy underneath a thin (ca. Zk/j) oxide hard- mask which is imaged with photoresist (see Figure 1). The etch of the hardmask and the Al/G are both done in one chamber in separate steps. Following the etch of these substrates, and after the photoresist is removed, "veils" of oxide remain on the wafer. These veils ("or rabbit ears" or "picket fences") are undesir- able and must be removed. Typically, veil removal is done by first exposing the wafers to a mixture of ethy- lene glycol and buffered oxide etchant (BOE). Next, the wafers are rinsed in pure ethylene glycol, and finally rinsed with water. The purpose of using glycol in the first two steps is to minimize the amount of water contacting the wafer so that corrosion of the AI/Cu is minimized. However, this process often gives rise to notching of the etched metal. Notches are defects in the metal features where metal is missing from the feature. Notches are located along the outer edges of features and are typically "V" shaped (see Figure 2). Notching in Al/Cu alloys is often associ- ated with theta phase (Al,Cu) which can be present in the alloy; in that case the notch is probably formed by an electrochemical corrosion mechanism, which requires the presence of water or moisture (this corro- sive notching is different than other forms of corrosion mentioned above).