Post-etch treatment enabled electroless copper metallization of porous dielectric
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Post-etch treatment enabled electroless copper metallization of porous dielectric Yezdi N. Dordi Lam Research Corp., 4400 Cushing Parkway Fremont, CA 94538, U.S.A. ABSTRACT This paper describes an alternate two-step metallization scheme for porous dielectrics. The patterned dielectric surface is first treated in a plasma etch chamber where the dielectric surface is coated with a very thin carbon-based film. This is followed by electroless copper deposition. The plasma post-etch treatment (PET) film seals the pores of the dielectric, minimizes dielectric damage, and functionalizes the dielectric to enable electroless plating. INTRODUCTION As features scale, PVD barrier/seed metallization is facing a significant challenge in ensuring continuous sidewall copper seed coverage. Poor copper seed coverage results in voids during subsequent ECP metallization, leading to increased resistance and poor reliability. In addition, pore sealing prior to barrier/seed metallization becomes critical as well for the porous dielectrics to prevent metal from migrating into the porous dielectric during metallization, leading to poor reliability.
Figure 1: Proposed metallization scheme for porous low-k.
Figure 1 shows the proposed metallization scheme. Immediately following pattern etching of the low-k dielectric, a thin PET film is deposited on the exposed dielectric and functionalized with amine terminations. The wafer is then exposed to a series of wet treatments starting with palladium (Pd) activation. The amine terminations enable adsorption of a monolayer of Pd seed layer on the dielectric surface. The next wet treatment is electroless nickel plating (< 2 nm thick) which is enabled by the Pd seed. This is then followed by electroless copper fill and CMP. This approach is very similar to the all-wet seed approach [1] which proposes using selfassembled monolayers (SAMs) to functionalize the dielectric surface, followed by electroless plating. However, SAM depositions require additional equipment and can take significantly longer to deposit than PET films. This approach also builds on some of the early work on metalizing polymers using plasma pretreatments [2] except that in this case, the treatments are optimized for much smaller feature dimensions as well as minimizing dielectric damage and sealing porous low-k on 300mm Si wafers. EXPERIMENT The plasma post tech treatment is done in a Lam Research dielectric etch system (Lam 2300 Exelan® Flex45™), which deposits a thin carbon-based film with amine terminations that coats and seals the etched dielectric. ®
The electroless plating on the amine terminated surface is done on a Lam ELD tool, depositing a stack of palladium, nickel and copper. 40 nm half pitch SiO2 pattern IMEC wafers are used to optimize the PET and metallization processes. Blanket IMEC ALK-B wafers (50% porosity) are used to characterize pore sealing and dielectric damage. RESULTS AND DISCUSSION Optimizing PET layer thickness In order to minimize RC delay, the PET layer must be just thick enough to enable metallizati
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