Atomic Layer Deposition of Hafnium Oxide Thin Films from Tetrakis(dimethylamino)Hafnium (TDMAH) and Ozone
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Atomic Layer Deposition of Hafnium Oxide Thin Films from Tetrakis(dimethylamino)Hafnium (TDMAH) and Ozone Xinye Liu*, Sasangan Ramanathan, and Thomas E. Seidel Genus, Inc., 1139 Karlstad Drive, Sunnyvale, CA 94089
ABSTRACT Hafnium oxide (HfO2) thin films were synthesized from tetrakis(dimethylamino) hafnium (TDMAH) and ozone (O3) by atomic layer deposition (ALD) on 200 mm silicon wafers. Gradual saturation was observed for TDMAH exposure pulse. However O3 showed better saturation behavior for O3 exposure. Yet, 100% step coverage was achieved for ~100nm trenches with aspect ratio of 35. Temperature dependence of the deposition rate was studied at susceptor temperature from 160 °C to 420 °C. The lowest deposition rate was observed at 320 °C. Mercury probe measurements indicated the dielectric constant increased from 16 to 20 as susceptor temperature increased from 200 °C to 320 °C. Selected comparisons with tetrakis (ethylmethylamino) hafnium (TEMAH) were also made.
INTRODUCTION As feature sizes of SiO2 based microelectronic devices scale down to near or below100 nm, poorer performance of SiO2 is anticipated. The need for alternative materials motivated study of atomic layer deposition (ALD) of hafnium oxide (HfO2) due to its high dielectric constant and moderately high thermal stability with respect to silicon surface [1, 2]. Although H2O has been used as the oxygen source in most of research [3~5], O3 has been used as early as 1994 for cerium oxide formation [6] and O3 has been investigated recently as the alternative oxygen source [7, 8]. One motivation of using O3 is that it is much easier to remove O3 than H2O from the reactor. The shortened cycle time provides great practical advantages in mass production. H2O tends to physisorb on surface strongly and needs long purge time to be sufficiently removed from the reactor surface. Long purge time results in low throughput (wafers per hour), which results in high cost. Ozone (O3) is a strong oxidizing agent. It does not physisorb on a reactor surface that is above room temperature. TDMAH has higher vapor pressure than TEMAH, but also has a lower decomposition temperature. In this paper, we present our work on the TDMAH and O3 ALD reaction, and compare the results with their TEMAH counterpart. EXPERIMENTAL The ALD reactor used in our experiment was a Genus StrataGem ALD system, which was a single wafer –vertical inject, vertical flow purge design. The reactor was a warm wall design with wall temperature of 120 ~ 160 °C. TDMAH vapor was delivered into the reactor chamber with a Genus precursor delivery system. The ozone generator was an Ebara prototype. Ozone’s carrier oxygen gas flow rate was 0.5 SLM. Ozone concentration was 150 ~ 200 grams/m3. Stainless steel gas line for delivering TDMAH vapor and O3 was heated up to 95 °C. Argon was
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