5.1 Conclusion
In this work, the concept of dynamic tuning of operating CMP process is presented and one possible operation profile is proposed via sliding-mode theory.
This strategy is verified by numerical simulations. The simulation results show 14%
reduction in dishing during over-polish stage. Future experiment needs to be designed to confirm this improvement.
However, the simulation verification of step-height reduction needs to be reinforced in future work when there are better models which describes continuous transition from step-height from bulk-polish stage to dishing during over-polish stage.
Otherwise, experiments can be designed to compare directly step height reduction between conventional CMP operation and “dynamic tuning” CMP operation.
Dynamic tuning of operation profile provides a new aspect of CMP operation and it might be a candidate for within wafer control in CMP process. This concept provokes thought for the development of within-wafer control to improve CMP performance. It is the hope of this research that dynamic tuning may be considered for improving CMP planarization in the area of step height reduction and dishing reduction.
5.2 Future Works
The requirement of planarization in semiconductor fabrication is growing
rapidly with the feature size decreasing. This reveals the importance of process control in semiconductor fabrication process is greater and greater. Advanced process control (APC) becomes a hottest subject in fab production to date. To improve the performance substantially (not only in CMP process), within-wafer control may be a critical method. Once the control subject gets into within-wafer, the system must be treated as a dynamic system. It might be more complex than before but the more improvement can be expected.
Many difficulties in within-wafer control need to be solved, like in-situ sensor and the knowledge of process in the situation of dynamic operation. Except the in-situ sensor, to further research the behavior of process in dynamic state an appropriate dynamic model may be a key point. The tighter within-wafer control will be realized based on the proper dynamic model.
Although the preliminary verification/explanation of dynamic tuning is proposed in this work, more complete simulation and experiments must be done in the future. Some future works are listed below:
1. Further grasp the knowledge of CMP process including mechanical and chemical effects.
2. Establish an appropriate dynamic model for CMP process and performance indexes.
3. Examine the ability and stability of the operation strategy of dynamic-tuning by more theoretical analysis and simulations.
4. Try to overcome the limitation in the design of current CMP equipment and design experiments to verify the concept in real production.
5. To optimize the operation profiles based on more investigations on CMP process and more sophisticated control algorithm.
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Fig.1.1 Various forms of planarization [26]
t2
Before Planarization
t1 Smoothing
(just planarize high density portion)
Local Planarization t1
t2
t1
t2
t1
t1 Global Planarization t1
t1
Fig.1.2 etchback process
Fig.1.3 Schematic of CMP benefit [40]
Wafer Metal
Oxide
Photoresist
Etch the PR and top of oxide
(Local Planarization)
Fig.1.4 Illustration of CMP fabrication process
Fig.1.5 Framework of integrated CMP model [12]
Wafer (substrate)
Growing
Oxide layer Oxide
Patterning
Depositing Metal (Cu)
Barrier layer (Ta) Planarization
Fig.2.1.1 Schematic of CMP polisher (CMP on Rotary Tool) [40]
Fig.2.1.2 Schematic of CMP polisher (CMP on Orbital Tool) [40]
Fig.2.1.3 Schematic of CMP polisher (CMP on Linear Tool) [40]
Fig.2.2 Effects of slurry flow rate on the CMP process [40]
Fig.2.3 Pad conditioning [40]
Fig.2.4 Dishing and Erosion
60μm
30μm
0.5μm
Not Conditioned Conditioned
Fig.2.5 Planarization efficiency
Fig.2.6 Copper CMP Defects [40]
ΔUP
ΔDOWN