Effect of Using Ethanol as the Oxygen Source on the Growth and Dielectric Behavior of Atomic Layer Deposited Hafnium Oxide

Hafnium oxide (HfO₂) is widely identified as a suitable high-k material to replace conventionally used low-k silicon oxide for gate dielectric layers in complementary metal-oxide semiconductor (CMOS) devices. High dielectric constant (~ 25) and compatibility with silicon substrate makes HfO₂ an ideal candidate for future scaling of transistors.¹

HfO₂ has been deposited using various methods. Of all, atomic layer deposition (ALD) seems to be the suitable method to deposit ultra-thin conformal layers on deep trenches and future 3D transistor structures. ALD is a vapor phase deposition technique, in which sequential exposure and purging of a surface to reactive elements in vapor phase is used to grow thin films in layer-by-layer fashion with excellent control on film thickness and composition down to Å level.²

There were numerous studies on ALD of HfO₂ using different precursor and oxygen source combinations.³ The property of the resultant HfO₂films depends on the precursor combination, deposition conditions, post deposition treatment conditions etc.

ALD of HfO₂ is traditionally performed using oxygen, ozone or water as the oxygen source. These oxidizers oxidize the underlying silicon substrates during the initial ALD cycles and form thick interfacial silicon oxide layer. This layer reduces the dielectric constant of the structure. To reduce the risk of forming such thick interfacial layer we used ethanol as the ALD oxygen source. Ethanol showed good reactivity towards the hafnium precursor, tetrakis(diethylamino)hafnium, and displayed clean ALD growth behavior with a wide ALD process temperature window of 200-280 °C (Fig. 1). In this paper, ALD growth behavior, ALD process temperature window and dielectric characterization of the ALD HfO₂films will be discussed in detail along with film compositional analysis.

References

1. J. Robertson, The European Physical Journal - Applied Physics, 28, 265 (2004).

2. S. M. George, Chem. Rev., 110, 111 (2009).

3. L. P. Riikka, J. Appl. Phys., 97, 121301 (2005).