Question 9. Compare the Results with Project 27 (50% Hf)

    Finally the results were compared with Project 27 (50% Hf). All the results between two groups are summarized below:

	Project 26 (70% Hf)	Project 27 (50% Hf)
Type of Substrate	P-type	P-type
Oxide Relative Permittivity	10.64	8.67
EOT (nm)	2.81	3.04
Doping Density (m-3)	4.244x1021	2.7x1021
Work Function Difference (eV)	0.065	0.08
Flatband Voltage (V)	0.932	0.53
Midgap Voltage (V)	1.367	1.21
Oxide Charge Density (cm-3)
Flatband Condition	-6.660x1016	-3.23x1016
Mdigap Condition	-7.841x1016	-6.4x1016

    It can be noticed that a higher percentage of Hf will lead to a higher oxide relative permittivity. It could be explained by the fact that the relative permittivity of Hf is higher than SiO2. Also, the equivalent oxide thickness will be decreased. Nevertheless the EOT is still too large for commercial purpose (which should be less than 2 nm). Higher percentage of Hf will also lead to a higher doping density, which will then increase the cost of manufacture.

    Another thing should be considered is that the fixed oxide charge density almost doubled in flatband condition. According to our supervisor, the charge density should be controlled less than 1x10¹⁰ in order to get a better quality of CMOS. Thus further research should be carried out to decrease the amount of fixed oxide charge density.