Daan Dewulf

Atomic Layer Deposition of Gd-Doped HfO2 Thin Films

Gd x Hf 1-x O y thin films were deposited by atomic layer deposition (ALD) using tris(isopropyl-cyclopentadienyl) gadolinium [Gd( i PrCp) 3 ] and HfCl 4 in combination with H 2 0 as an oxidizer. Growth curves showed a nearly ideal ALD behavior. The growth per individual Gd( i PrCp) 3 /H 2 O or HfCl 4 /H 2 O cycle was 0.55 A, independent of the Gd/(Gd + Hf) composition x in the studied range. This indicates that the amount of HfO 2 deposited during a HfCl 4 /H 2 O cycle was essentially identical to the amount of Gd 2 O 3 deposited during a Gd( i PrCp) 3 /H 2 O cycle, assuming identical atomic densities of the films independent of composition. The crystallization of Gd x Hf 1-x O y , with Gd/(Gd + Hf) contents x between 7 and 30% was studied. Films with x ≳ 10% crystallized into a cubic/tetragonal HfO 2 -like phase during spike or laser annealing up to 1300°C, demonstrating that the cubic/tetragonal phase is thermally stable in this temperature range. A maximum dielectric constant of K ~ 36 was found for a Gd/(Gd + Hf) concentration of x ~ 11%.

Alternative high-k dielectrics for semiconductor applications

Although the next generation high-k gate dielectrics has been defined for the 45nm complementary metal oxide semiconductor technology node, threshold voltage control and equivalent oxide thickness (EOT) scaling remain concerns for future devices. Therefore, the authors explored the effect of incorporating dysprosium in the gate stack. Results suggest that improved EOT-leakage scaling is possible by adding Dy to the interfacial SiO2 layer in a 1:1 ratio or by adding 10% Dy to bulk HfO2. The deposition of a 1nm Dy2O3 cap layer lowered the threshold voltage by ∼250mV. In addition, for future dynamic random access memory capacitor applications, dielectrics with e of 50–130 are projected by the International Technology Roadmap for Semiconductors, unachievable with standard high-k dielectrics. Theoretical modeling can help direct the experimental work needed for extensive screening of alternative dielectrics. Moreover, materials such as perovskites only exhibit a sufficiently high-k value when properly crystall...