Tungsten (W) Plugs

Tungsten (W) Plugs

Material Name: Silicon
Record No.: 121
Primary Chemical Element in Material: Si
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: The modified BT process can provide more over-etch margin for the variation of dielectric layers during CMP step since the gas chemistries etch away both oxide and TiN layers. In order to break-through TiN completely and gentlely, lower power, higher pressure, and longer etching time are also applied during modified BT step. Figure 1 shows the cross-sections of via after W plugs deposited by using same gas chemistries in both main etching and BT steps. The taper angle of via profile is around 88.6°, CD bias that means the difference between DICD and FICD is about 0.01 ìm, the Aluminum (Al) gauging is about 58 nm.
The third approach is also investigated for TiN break-through step by using SF6 gas chemistry. Much lower power, higher pressure, shorter etching time compared to main etching are applied for the SF6 break-through step. However, this process causes too much Al gauging which increases the contact resistance. Figure 2 shows the cross-section of via profile for SF6 process after W plugs deposited. Finally, the C4F8 TiN break-through process shows the least contact resistance among the three different approaches on several split lots. Therefore, this process is fixed inline as the POR process for TiN break-through application. All of the above work is completed on the development tool.
Reference: JUAN JUAN WANG, ADVANCED PLASMA-ETCHING PROCESSES FOR DIELECTRIC MATERIALS IN VLSI TECHNOLOGY, PhD Thesis, UNIVERSITY OF FLORIDA, 2002, pp. 60-62.

Figure 1: Cross-sections of Break-through (BT) process after Tungsten (W) plugs deposited.

Figure 2: Cross-sections of Break-through (BT) process after Tungsten (W) plugs deposited