Void-free filling

FIGURE 15.14 Void-free fill of a via using CVD copper and liner (from Ref. 110). 

Change in deposition rate along via sidewalls leads to decrease of cleft depth in the via tops and void-free filling of the vias. The dependencies of cleft depth on via aspect ratio, applied current density, seed layer thickness and wafer center-edge nonuniformity were observed by FIB etching, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 

Full fill of features was carried out on some of the wafers after ECD seed. Figure 11 compares cross sections for trenches (0.25p, 4 1 AR) with 200A PVD copper. Figure 11a was plated directly from an acid copper sulfate bath without our ECD seed and Figure lib was plated with ECD seed. As expected, bottom-voids were observed in the trenches without ECD seed and complete void-free fill was obtained after ECD seed, indicating the need for ECD seed with a very thin copper layer. 

One of the challenges in multilevel metallization of the sub-0.5 pm generation devices is the void-free filling of high aspect ratio (depth-to-width ratio) contact holes at low temperatures [73, 80]. These holes connect one level of metal with another level of metal above or below (see Fig. 3-4). It is possible to connect the first level of metal with the gate, source and drain of the transistor. Non-conformal films can cause shoulders at the top of the contact or keyhole void formation by closing the holes. 

Another important use of dielectrics is as intermetal dielectrics (IMDs), where the dielectrics insulate metal lines from each other. The dielectric material must fill small gaps with high aspect ratios (depth to width) while maintaining all other dielectric properties. It is essential that the IMDs are void-free at submicrometer dimensions for both performance and rehabiUty. 

Figure 2. Cross sectional view of void-free Cu filling of the vertical trenches with dimensions of 0.13 pm width and 8 1 aspect ratio.

Desirable properties, such as easy filling and easy release, void-free, and warp-fi molding and no staining of the molds must be assured for the molding resins to be used. 

Porous anodic alumina (PAA) is a closely packed structure, consisting of many hexagonal cells, in the center of which is a vertical pore. PAA attractiveness is in its low range of pore sizes in diameter and this size is well controlled in the course of its formation. Deposition of In, Cd and Zn in these pores is implemented by electrochemical method using pulsed deposition, which ensures a void-free PAA pore filling by metal. 

The CjHj side groups of PB-1 are long enough to create a free volume between the molecules when the melt solidifies. During the recrystallizafion phase the voids are filled and the material shrinks approximately 2%. 

Manufacturers Comments 121 C cure. 100% solids. Non-sag, aluminium filled. Deaerated. Formulated for dense, void-free bondines. 

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