Thickness nonuniformity

We see from the thickness nonuniformity that if the TiN thickness is fixed, the oxide thickness has a lower standard deviation, indicating a tighter distribution of the measurement results. Since the measurement is on the same wafer, the difference suggests that the effect of fixed TiN thickness to help improve the repeatability of the measurement. (Of course, the TiN film must be uniform for this to be true.) In short, if the control of the TiN... 

To understand the impact of a CMP process on a certain product with a unique integrated circuit pattern, it is desirable to measure areas with different feature sizes and shapes. Since CMP polish rate may be affected by pattern density, areas encompassing various features should be included in the measurement program. The within-die thickness nonuniformity will indicate the planarization capability of a CMP process. 

The primary purpose of using CMP in back-end interconnect processes is to planarize the surface. Hence, the depth of focus of existing photolithography tools can be extended into sub-0.35-jum technologies [1]. A question arises, however, as to how much sacrificial thickness is required for polishing away to planarize the surface. Intuitively, the more thickness polished, the better planarity achieved however, at the same time, the across-wafer final thickness nonuniformity becomes worse. This concept of the relationship between the thickness polished and the remaining step height can be understood from Fig. 11. Planarity is a local, microscopic term, which is defined as... 

The nonuniformity in CMP is sometimes confusing because there are three different thickness specifications pre- and post-thickness and thickness delta. To describe the CMP tool performance, and for the daily tool qualification, usually the nonuniformity of delta thickness is used. However, for quality control of the manufacturing of integrated circuits, the nonuniformity for the final thickness is used. The relation between the delta and the final thickness nonuniformities is explained as in the Fig. 12. 

The wafer-to-wafer thickness nonuniformity (WTWNU) in oxide CMP can be attributed primarily to variation in the CMP polish rate, and secondarily to the thickness variation in incoming wafers. 

If machine direction thickness uniformity is a problem, it can best be remedied with the use of a gauge detector (beta gauge) that is part of a control system adjusting the speed of the take-up device, to correct for thickness nonuniformities. Small period variations are very difficult to remedy in this fashion. 

The color of silicon dioxide is a function of its thickness. Color variation across the dies and the wafer indicates oxide thickness nonuniformity. Ideally, there should be no color variation over the same type of underneath structures. Global color variation across the wafer indicates a CMP uniformity problem. Local color variation at a structure level or arrays of structures within a die reveals a lack of planarization. There is a fine difference between planarization deficiency and nonuniformity. Nonuniformity is revealed in the form of a very gradual thickness variation over 10 mm or more. It is usually not pattern dependent. A rapid thickness variation across arrays of structures less than 5 mm wide is indicative of a planarization problem. This is a pattern-dependent... 

Figure 8 shows the effect of the initial seed layer conductance on the plated thickness nonuniformity. It was determined that the nonuniformity depends upon the initial sheet conductance to the -0.48 power and upon the plated film conductance to the -0.70 power ( Ni K C,f 4SG-° 70). The effect of the Wagner number is shown in Figure 9. The higher the Wagner number the better the non uniformity because the ohmic effects become less important at high Wagner numbers. It was determined that the non uniformity is proportional to the Wagner number to the -0.60 power (Nt K G 0 irG 0 70W

Geometry Mandrels and pin cores should be straight. Thickness nonuniformity will result in a part that is not true, subsequently leading to premature liner failure. 

Pickup was greater in the presence of potassium laurate than of cocoamphoglycinate. Goddard et al. [33] found a relatively thick, nonuniform... 

Mesh Tension Mesh sticking to screen Poor quality printing Low coating thickness Nonuniform coating across panel... 

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