Chemical-Mechanical Planarization of Aluminum-Based Alloys for Multilevel Metallization

Abstract

As recently as 1993, the prevailing presumption among the semiconductor technical community was that then-current development efforts associated with aluminum lines and tungsten damascene vias needed to shift rapidly to copper multilevel interconnect schemes. This is exemplified by the June 1993 issue of the MRS Bulletin, which featured copper metallization as its theme. In the intervening years, however, that same technical community revised the Semiconductor Industry Association (SIA) roadmap and placed renewed emphasis on the use of an all-aluminum interconnect scheme. This was done largely in deference to the costs associated with converting existing semiconductor lines to copper-compatible facilities. In addition to tooling costs, there is a learning curve for copper systems that remains to be established for device reliability, field failures, yield learning, and process maturation. On the other hand, existing fabs are already compatible with aluminum metallurgies, and there is a rich history of reliability and yield data.This change in direction creates two immediate needs: (1) the need to fill small-diameter vertical interconnects (vias) with void-free aluminum and (2) the need to remove the top surface aluminum resulting from its blanket deposition (overburden) following the metal fill. In addition, for high circuit-density applications, it may be desirable, if not necessary, to form the metal lines using the same damascene fill method as is used for the vias. This process strategy replaces metal etching and insulator gap fill with insulator (usually silicon oxide) etching and metal gap fill.

Material removal regions in chemical mechanical planarization for submicron integrated circuit fabrication: coupling effects of slurry chemicals, abrasive size distribution,and wafer-pad contact area

“…This model implies that CMP is basically a mechanical process enhanced by chemical actions, whose effects on MRR are attributed to the material and mechanical properties of a passive surface layer and its generation rate. This passivation-abrasive removal-repassivation mechanism has also been applied to explain the metal removal and planarization in copper and aluminum CMP [14], [15]. For silicon and silicon oxide CMP, a near surface change was observed [11], [16], [17].…”

“…It is noted that in (8) may be approximately equal to when is much larger than . Fol- lowing similar steps as above by substituting and into (9), a simplified relationship between and the active abrasive size can be obtained as (14b) Based on the above discussions, the MRR can be written as a function of abrasive size distribution and concentration (15) when…”

“…, which is a function of weight concentration and 16when , which is independent of weight concentration. If the slope of the linear region is , which satisfies (17) as shown in (15), the relationship between and abrasive size can be written as (18) In summary, when , the contact area is independent of the abrasive size. A linear relationship between the concentration and the material removal rate exists.…”

Effects of hydrogen peroxide and alumina on surface characteristics of copper chemical–mechanical polishing in citric acid slurries

“…Several kinds of oxidizing agents, such as H 2 O 2 [5,6,8], HNO 3 [7][8][9][10][11], Fe(NO 3 ) 3 [8,12], NaClO 3 [13] and KIO 3 [14], among others, have been used to form a passive film on a copper surface or to dissolve it into slurries. Although the oxidizing powers of these agents are known, the specific roles of these agents on Cu CMP were not as clear as that found in W CMP [1] or Al CMP [2][3][4]15].…”

Electrochemical Behavior of Aluminum during Chemical Mechanical Polishing in Phosphoric Acid Base Slurry

“…1 Although CMP for interlayer or intermetal dielectrics (ILD or IMD) has been used and studied extensively, metal CMP, especially the Al CMP process is relatively new and less understood due to the difficulties and the complicated electrochemical nature of Al. 2 Ideally, in a metal CMP process, the metal being polished should dissolve fast enough to support an acceptable removal rate. On the other hand, the passive etching rate of the metal should be slow enough in the absence of polishing action to avoid dishing defects.…”