A method of protecting ultral low k sidewall-NHN Challenge
Original Publication Date: 2009-Oct-20
Included in the Prior Art Database: 2009-Oct-20
This publication introduced a method of densifying sidewall after via etch. Post via etch, an implantation with carbon to the sidewall is applied. It densifies via sidewall to prevent via fill material out diffusion and doped carbon also makes film surface hydrophobic which reduces moisture absorption.
A method of protecting ultral low k sidewall -NHN Challenge
Porous ultral low k (ULK) material has been used as insulator interconnect. It has been found that via fill polymer may diffuse into ULK sidewall after via etch. This influences following trench etch process causing large etch depth variation. This results in large resistance variation.
Ion implantation method can be applied to densify via sidewall after via etch, therefore prevent out diffusion of via fill polymer into sidewall. Figure 1 shows a schematic of via structure after via RIE. Hardmask prevents ions prenetrating into top of dielectric material. Via bottom is also protected by cap material.
Ultra low k
Carbon ions are implanted isotropically on wafer. Sidewall of via trenches are doped with carbon ions. A schematic is shown as Figure 2.
Figure 1. After via etch
Isotropic implantation with carbon ions
Figure 2. Sidewall are implanted with carbon. Ultral low k top and bottom are protected by hard mask and cap.
A thin doped layer is formed at via sidewall after carbon implantation (shown as Figure3) . The thickness of this layer can be controlled by dose energy. This layer is denser than bulk of ultra low-k dielectric. However, dielectric constant of this layer will not be degraded because more carbon doped in this layer. Film becomes hydrophobic which reduces moisture absorbtion.
Ultra low k