Browse Prior Art Database

Middle of Line (MOL) Rework Process Compatible with Aggressively Scaled SRAM

IP.com Disclosure Number: IPCOM000115620D
Original Publication Date: 2005-Mar-30
Included in the Prior Art Database: 2005-Mar-30
Document File: 3 page(s) / 89K

Publishing Venue

IBM

Abstract

We describe a method for removing and rebuilding a failed metallization level that is compatible with aggressively scaled design rules, including SRAM. If the copper is removed first with a wet etch (preferably acetic acid in one embodiment), only the liner will remain in the existing trenches. This liner will still cause the fails associated with the metallization process limited yield (PLY). By depositing another material at this point, preferably identical to the interlevel dielectric ILD material, or a material whose removal rate by chemical mechanical polishing (CMP) is similar to the ILD, the liner is enclosed within the ILD and the deposited material, and the region requiring polishing becomes much more uniform. At this point, CMP removal of the old ILD level with the newly deposited material can be performed with significantly improved control.

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Middle of Line (MOL) Rework Process Compatible with Aggressively Scaled SRAM

Process Limited Yield (PLY) in early metallization modules is easily detectable at these early metallization steps, but very difficult to repair. As ground rules scale, these fails become more difficult to repair. In older CMOS generations, polishing off the failed metal level and rebuilding it was difficult, but potentially successful. The main difficulty in this process in the polishing of metal and the inter-layer dielectric between the metal lines at the same rate. In Copper BEOL generations, the copper polishes so quickly, that this becomes nearly impossible to perform at a controlled rate.

We describe a method for the removal of the failed early metallization. First metal failure is demonstrated in the images below

 ILD (Oxide)
Copper Copper

Contact Level

Liner Liner ILD (Oxide)
Copper Copper

Liner Liner

Contact Level

Device Layer

Device Layer

At this point, polishing off the failed metallization is impossible as the copper and ILD polish at vastly different rates. Our process begins with the removal of the copper, preferably with a wet etch. In one embodiment, the ILD is an oxide, but other suitable insulating materials may also be used.

 ILD (Oxide)

Contact Level

 ILD (Oxide)

Contact Level

 ILD (Oxide)

 ILD (Oxide)

 ILD (Oxide)

 ILD (Oxide)

Device Layer

Device Layer

1

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The liner is left. CMP at this point is still imposs...