WTW nonuniformity

Next is described how WIW nonuniformity and WTW nonuniformity affect WID planarity. WIW nonuniformity means the maximum CMP removal rate nonuniformity that is generated in one wafer. WTW nonuniformity means the maximum CMP removal rate nonuniformity between the multiple wafers that have been polished at the same time. As shown in (2), nonuniformity (T) is usually generated in the deposition on an in-coming wafer. Although it would be best to polish the deposition by Z nm to eliminate the nonuniformity (see (4)-l), it is difficult in practice. The nonuniform part, the thickness of which is UN nm, surely remains as illustrated in (4)-2. As shown in the example in Figure 16.4, if such nonuniformity is generated in the recess process, the nonuniform... 

The above types of planarity performance are affected by the above-mentioned WIW nonuniformity and WTW nonuniformity. 

All the examples shown in Figure 16.11 are related to the control of the CMP removal rate uniformity. The examples also lead to the improvement of the above-mentioned WIW nonuniformity and WTW nonuniformity. The following explains the mechanisms and features. 

CMP step is used to planarize and remove overburden oxide. This is also called indirect STI process. The requirements for direct-polish STI CMP processes include minimal within-die (WID) oxide and nitrite ranges, limited nitride loss, limited oxide dishing, low defectivity, and excellent nonuniformity, both within wafer (WIW) and wafer to wafer (WTW) [8]. 

To properly understand CMP film thickness control, the CMP engineer should understand the sources of thickness variation and how they impact the total film thickness uniformity. Nonuniformity can be grouped in two categories—random variation and systematic variation. Examples of random variation include wafer-to-wafer (WTW), run-to-run (RTR), and some elements of within-wafer (WIW) variations. Elements of random variation add to the total thickness variation by their root mean square [19]... 

---