Comparative Study of Titanium Nitride ALD using High Purity Hydrazine vs Ammonia

Abstract

Emerging devices (Logic and Advanced Memory) require high quality thin (5-20 Å) electrode and barrier films. Difficult thermal budget constraints are now being placed on well-known materials such as TiN and TaN. Deposition temperature limitations have reached 350°C and below while very low resistivity (<100 micro-ohm/cm) must be achieved. Novel Ti precursors are being explored.1 Our approach has focused on hydrazine (N2H4) as an alternative nitrogen source to NH3.Hydrazine is generally difficult to handle from a safety perspective due to its flammability and toxicity. We have developed a novel method to store and generate hydrazine in situ as a high purity gas which is then delivered to ALD process chambers.2 In this study, we examine the effect that hydrazine has on low deposition temperature TiN ALD processes. We experimentally evaluate TiN ALD growth and film characteristics using TiCl4/ N2H4 in comparison to that using TiCl4/NH3.Titanium Nitride films were deposited using the hot wall type tubular furnace and a sequential gas supply system. Deposition temperature was set to predetermined value in the range from 250°C to 400°C. In the case of TiCl4/NH3, GPC was 0.10-0.27 Å/cycle at 250-400°C, where a decrease is noted as the deposition temperature is reduced. With the use of hydrazine, an increase in GPC is observed at each deposition temperature vs NH3. Moreover, the temperature dependence of GPC moved in the opposite direction of TiCl4/NH3. Specifically, GPC of TiCl4/N2H4 ALD was 19% higher at 400°C while an increase of 310% was seen at 250°C versus NH3. In the case of TiCl4/N2H4, the ALD window appears in the range of 250-400°C, where TiCl4 adsorption saturation curves are observed at 250°C and 400°C. Refractive index (R.I.) of TiCl4/N2H4 ALD was about 1.68-1.73 at 250-400°C. These values were approximately equal to R.I. of typical sputtered TiN which was about 1.66. In contrast, R.I. of TiCl4/NH3 ALD was larger than 2.00 in the 250- 300°C range. Because of R.I. of typical titanium oxide is about 2.4-2.5, it is assumed that the TiCl4/NH3 ALD film is contaminated by oxygen. In the ammonia case, background contaminants in the reactor appear to compete with low reactivity NH3 for reaction sites on the ALD surface. In the TiCl4/N2H4 case, higher temperature is not required to form high quality TiN films compared to TiCl4/NH3 ALD.From the above results, the use of high purity hydrazine is beneficial to maintaining high throughput and good film quality under the new constraints for emerging devices. Film composition by XPS and Resistivity measurements consistent with this conclusion will also be presented.