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Method to Remove Residual Materials in Copper Interconnects with a Metal Cap Layer

IP.com Disclosure Number: IPCOM000178922D
Original Publication Date: 2009-Jan-29
Included in the Prior Art Database: 2009-Jan-29
Document File: 4 page(s) / 33K

Publishing Venue

IBM

Abstract

This article addresses some of the reliability concerns when implementing a metal cap process for copper (Cu) interconnects. The basic idea is to deposit a metal cap layer over the Cu metal lines, and follow this with a process that oxidizes the metal cap material. A benefit of this approach is that the metal cap deposition process does not have to be ideally selective. This allows processes such as chemical vapor deposition (CVD) to be suitable if ruthenium (Ru) is chosen as the metal cap material.

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Method to Remove Residual Materials in Copper Interconnects with a Metal Cap Layer

This article addresses some of the reliability concerns when implementing a metal cap process for copper (Cu) interconnects. The basic idea is to deposit a metal cap layer over the Cu metal lines, and follow this with a process that oxidizes the metal cap material. During the oxidation process, the metal cap material above the Cu lines will certainly oxidize, but any residual metal cap between the metal lines will oxidize as well. This is followed by removal of the oxidized metal cap layer but not the metal cap itself or the dielectric layer. The region between the metal lines should now be free of metal, which will result in improved time dependent dielectric breakdown (TDDB) reliability. Since some of the metal cap above the Cu lines is consumed during the oxidation process, a thicker metal cap layer must be initially deposited. A benefit of this approach is that the metal cap deposition process does not have to be ideally selective. That is, even if some metal cap is deposited between the metal lines, a reliable structure will result so long as more metal cap is deposited above the Cu lines. This allows processes such as chemical vapor deposition (CVD) to be suitable if ruthenium (Ru) is chosen as the metal cap material.

Figure 1 shows cross sectional views of two Cu lines at various stages of a typical metal cap process. Figure 1(a) corresponds to the situation following a chemical mechanical polishing (CMP) process step, where a clean surface exists above the Cu lines as well as the interlayer dielectric (ILD) regions. In Figure 1(b), the metal cap has been deposited, resulting in the proper metal cap thickness above the Cu lines but also some residual metal material above the dielectric regions. Figure 1(c) shows the situation following dielectric cap deposition, where the residual metal material is trapped between the ILD and the dielectric cap layer. The residual material will lead to shorts yield problems and TDDB degradation. Depending on the selectivity of the metal cap deposition process, the material between the Cu lines may not be a continuous layer. For CVD processes, the continuous residual layer shown in Figure 1 is likely to occur.

(a)

Metal Cap Residual Metal Cap Material

Cu

Cu

ILD

1

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(b)

Dielectric Cap

(c)

Figure 1. Schematic cross sections of two Cu lines at various stages of a typical metal cap process , (a) following a CMP step, (b) following metal cap deposition and (c) following dielectric cap deposition .

Figure 2 shows cross sectional views of two Cu lines at various stages of the proposed meta...