RIE Etch Back

In addition, several issues arise with the use of either RIE etch back or CMP to remove the metal from on top of ILD. Dual layw inlaid metal schemes have been demonstrated for tungsten, aluminum, copper,and gold metallization systems. 

As with oxide CMP (Chapter 5), metal CMP may enhance yields by virtue of reduced defect densities. In addition to a reduction in nonplanarity induced defects (Section 5.24), CMP is a cleaner process than the relatively dirty RIE etch back processes. Figure 6.5 shows a 3X reduction in particles using CMP vs. RIE. The result is a decrease in metal-to-metal shorts on the subsequent interconnection level (Figure 6.6). As with oxide CMP, increased die yields is one of the major driving forces for acceptance of metal CMP processes for tungsten stud formation. ... 

Finally, the metallisation layer usually requires patterning, which can be done by reactive ion etching (RIE) or back-sputtering. The two processes are similar. In both techniques accelerated ions hit the substrate and forcibly detach atoms or molecules from the surface. RIE uses reactive gases such as chlorine, Cl or trichlorofluoromethane [75-69-4] CCl E. Inert gases such as argon or neon are used in back-sputtering. 

Several contending technologies are presently being used to achieve local and global planarizations that include spin on deposition (SOD), reflow of boron phosphorous silicate glass (BPSG), spin etch planarization (SEP), reactive ion etching and etch back (RIE EB), spin on deposition and etch back... 

A second method of local planarization involves spinning photoresist onto the SiOj ILD to obtain local planarity. The resist is then hard baked and etched with an RIE etch tailored to remove SiOz (or ILD) at the same rate as the photoresist. Because the etch rate of the two materials is equal, the planarity of the resist film transfers into the SiOz film. However, a precise match in SiOj and photoresist etch rates is difficult to maintain because the relative ratio of SiOj to photoresist exposed increases as the etch back proceeds. Loading effects then result in a decrease in the Si02 etch rate and increase in the photoresist etch rate. Furthermore, polymer deposits build up on the etch reactor chamber walls over time etching of this polymer depletes the chemicals used to etch the photoresist, which slows the photoresist etch rate. If the etch rates are not matched, the planarity of the photoresist layer will not transfer well to the SiOz. 

Microfabrication was effected by anisotropic reactive ion etching (RIE) using a plasma [34], Back-side structures were realized by wet-chemical etching. A transparent plate is bonded on top of the microstructures. 

Back etching of the poly-Si layer is done using RIE in SF6. 

Figure 24 Details of RIE back etching of planarized resist and SiO a) partially backetched with ERg Q slightly higher than ERres st b) same as a) but fully backetched c) partially back etched with ERres- st slightly higher than ERgi0, d) fully back etched with equal etch rates.

Figure 25 Examples of CVDg g filled trenches back etched with RIE a) shallow and deep, b)wide, c) details of b).

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